POWER PLANT ENGINEERING REVIEWER (LECTURE) Revision 0 2012
Prepared By: Agerico U. Llovido – PME
CONTENTS A. VARIABLE LOAD B. FUELS AND COMBUSTION C. INTERNAL COMBUSTION ENGINE POWER PLANT D. GAS TURBINE POWER PLANT E. STEAM POWER PLANT F. CHIMNEYS AND STACKS G. GEOTHERMAL POWER PLANT H. HYDRO-ELECTRIC POWER PLANT I. NUCLEAR POWER PLANT J. NONE-CONVENTIONAL ENERGY SOURCES
A. VARIABLE LOAD - LECTURE 1. Terms and Factors Reserve over peak – is the plant capacity less the peak load. Average load – is the ratio of the kilowatt-hours of energy to the period covered. Diversity factor – is the ratio of the sum of the individual maximum demands of the various subdivisions of a system, or part of a system, to the maximum demand of the whole system, or part, under consideration. Demand factor – is the ratio of the maximum demand of a system, or part of a system, to the total connected load of the system, or part of the system, under consideration. Load factor – is the ratio of the average load over a designated period of time to the peak load occurring in that period. The average load may be determined for any specified length of time such as day, month, or year. Capacity factor – is the ratio of the average load on a machine or equipment, for the period of time considered, to the rating of the machine or equipment. When applied to a plant, this factor is called plant factor or plant-capacity factor. Output factor, or use factor – is the ratio of the actual energy output, in the period of time considered, to the energy output which would have occurred if the machine or equipment had been operating at its full rating throughout its actual hours of service during the period. Load curve – is a curve of power versus time, showing the value of a specific load for each unit of the period covered. The abscissa is usually time in hours, days, weeks, months, or years, and the ordinate is kilowatts generated. Monthly load curve – is the average of the daily load curves over a one-month period that is used in establishing rates. Annual load curve – is the average of the daily load curves over a period of one year that is used in determining the annual load factor. Load duration curve – is a curve showing the total time, within a specified period, during which the load equaled or exceeded the power values shown. Kilowatts are used as the ordinate, and normally, the 8760 hr of the year is the abscissa. Peak load - is the maximum load consumed or produced by a unit or group of units in a stated period of time. It may be the maximum instantaneous load or the maximum average load over a designated interval of time. Utilization factor - is the ratio of the maximum demand of a system, or part of a system, to the rated capacity of the system, or part of the system, under consideration. 1
A. VARIABLE LOAD - LECTURE
Connected load on a system, or part of a system – is the sum of the continuous ratings of the load-consuming apparatus connected to the system, or part of the system, under consideration. Operation factor – is the ratio of the duration of the actual service of a machine or equipment to the total duration of the actual service of a machine or equipment to the total duration of the period of time considered. Dump power – is hydro power in excess of load requirements that is made available by surplus water. Firm power – is the power intended to be always available even under emergency conditions. Prime power – is the maximum potential power (chemical, mechanical, or hydraulic) constantly available for transformation into electric power. Cold reserve – is that reserve generating capacity available for service but not in operation. Hot reserve – is that reserve generating capacity in operation but not in service. Reserve equipment – is the installed equipment in excess of that required to carry peak load. Reserve equipment not in operation is sometimes referred to as standby equipment. Spinning reserve – is that reserve generating capacity connected to the bus and ready to take load. System reserve is the capacity, in equipment and conductors, installed on the system in excess of that required to carry the peak load. Run-of-river station – is a hydroelectric generating station which utilizes the stream flow without storage. Spare equipment – is equipment complete or in parts, on hand for repair or replacement. Generating station auxiliary power – is the power required for operation. House turbine – is a turbine installed to provide a source of auxiliary power. Base-load power plants – include steam, hydroelectric, and geothermal power plants. Peak-load power plants – include diesel-electric and gas turbine power plants. 2. Equations Reserve over peak = plant capacity − peak load
Average load = Load factor =
kw − hrs energy no. of hours
average load peak load 2
A. VARIABLE LOAD - LECTURE Capacity factor =
actual energy produced maximum possible energy
Annual capacity factor = Use factor =
annual kw − hrs kw plant capacity × 8760
annual kw − hrs kw plant capacity × no. of hrs operation
Demand factor =
actual maximum demand connected load
Diversity factor =
sum of individual maximum demands maximum simultaneous demand
Plant factor =
average load rating of equipment supplying the load
Utilization factor =
maximum demand of system rated capacity of system
Operation factor =
duration of actual service total duration of the period of time considered
3. Elements of an Electric Power System 3.1 Power Plant 3.2 Substations 3.3 Feeders 3.4 Distribution transformers 3.5 Customers – domestic, industrial, business, etc. -
End -
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B. FUELS AND COMBUSTION - LECTURE 1. Definitions Fuel – is composed of chemical elements which, in rapid chemical union with oxygen, produce combustion. Combustion – is that rapid chemical union with oxygen of an element whose exothermic heat of reaction is sufficiently great and whose rate of reaction is sufficiently fast that useful quantities of heat are liberated at elevated temperatures. 2. Classification of Fuels 2.1 Solid – including coal, coke, peat, briquettes, wood, charcoal, and waste products 2.2 Liquid – including petroleum and its derivatives, synthetic liquid fuels manufactured from natural gas and coal, shale oil, coal by-products (including tars and light oil), and alcohols. 2.3 Gaseous – including natural gas, manufactured and industrial by-product gases, and the propane and butane or, liquefied petroleum (LP) gases that are stored and delivered as liquids under pressure but used in gaseous form. 3. Coal Classification 3.1 Classification by rank – degree of metamorphism, or progressive alteration, in the natural series from lignite to anthracite (lignite, subbituminous, semibituminous, bituminous, semianthracite, anthracite, superanthracite). Probably the most universally applicable method of classification in which coals are arranged according to fixed carbon content and calorific value, in Btu, calculated on the mineral-matter-free basis. 3.2 Classification by grade – quality determined by size designation, calorific value, ash, ash-softening temperature, and sulfur. The size designation is given first in accordance with the standard screen analysis method followed by calorific value, and symbols representing ash, ash-softening temperature, and sulfur. 3.3 Classification by type or variety – determined by nature of the original plant material and subsequent thereof. 4. Burners for Pulverized Coal 4.1 Vertical firing – with all the secondary air admitted around the burner nozzle so that it mixes quickly with coal primary air mixture from the burner nozzle. 4.2 Impact firing – a form of vertical firing, consists of burners located in an arch low in the furnace or in the side walls and directed toward the furnace door, with high velocities of both primary and secondary air. This type of firing is used exclusively in wet-bottom or slagging type. 4.3 Horizontal firing – employs a turbulent burner, which consists of a circular nozzle within a housing provided with adjustable valves, the unit being located in the front or rear wall. 4.4 Corner or tangential firing – is characterized by burners located in each corner of the furnace and directed tangent to a horizontal, imaginary circle in the middle of the furnace, thereby making the furnace the burner in effect, since turbulence and intensive mixing occur where the streams met. 5. Coke Coke – is the solid, infusible, cellular residue left after fusible bituminous coals are heated, in the absence of air, above temperatures at which active thermal decomposition of the coal occurs. Pitch coke or petroleum coke – are obtained by similar heating of coal-tar pitch and petroleum residues. High temperature coke – is made from coal at temperature ranging from 815 C to 1093 C. Low temperature coke – is formed at temperatures below 704 C. The residue, if made from a non-cooking coal, is known as char.
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B. FUELS AND COMBUSTION - LECTURE 6. Charcoal Charcoal – is produced by partial combustion of wood at about 400 C and with limited air. 7. Liquid Fuels Fuel Oil – is defined as any liquid or liquefiable petroleum products burned for the generation of heat in a furnace of firebox, of the generation of power in an engine, exclusive of oils with a flash point below 37.7 C. Four Classes of Fuel Oils in common uses a. Residual oils – which are topped crude petroleum’s or viscous residuum obtained in refinery operations. b. Distillate fuel oils – which are distillates derived directly or indirectly from crude petroleum. c. Crude petroleum’s and weathered crude petroleum’s of relatively low commercial value. d. Blended fuels – which are mixture of two or more of the preceding classes. Commercial Fuel Oil Specifications a. Grade no. 1 – a distillate oil intended for vaporizing pot-type burners and other burners requiring this grade of fuel. b. Grade no. 2 – a distillate oil for general purpose domestic heating in burners not requiring no. 1 fuel oil. c. Grade no. 4 – an oil for burner installation not equipped with pre-heating facilities. d. Grade no. 5 – a residual type oil for burner installation equipped with pre-heating facilities. e. Grade no. 6 – an oil for burners equipped with pre-heaters permitting a high-viscosity fuel. 8. Gasoline Gasoline – is defined as a refined petroleum naphtha which by its composition is suitable for use as a carburetant in internal combustion engines. Motor Gasoline – is a mixture of hydrocarbons distilling in the range of 37.7 C to 204.4 C by the standard method of test. 9. Kerosene Kerosene – is defined as a petroleum distillate having a flash point not below 22.8 C as determined by the Abel tester and suitable as an illuminant when burned in a wick lamp. 10. Coal Tar Coal Tar – is a product of the destructive distillation of bituminous coal carried out at high temperature. 11. Liquefied Petroleum Gases (LPG) Liquefied Petroleum Gases (LPG) – are mixtures of hydrocarbons liquefied under pressure for efficient transportation, storage, and use. They are generally composed of ethylene, propane, propylene, butane, isobutene, and butylenes. Commercially, they are classed as propane, propane-butane mixtures, and butane. They are odorless, colorless, and non-toxic. 12. Diesel Fuel Oils Refiners grade fuels classified according to methods of production. a. Distillate fuels – are produced by distillation of crudes. b. Residual fuels – are those left after the distillation process. c. Blended fuels – are mixtures of straight distillate fuels with cracked fuel stocks.
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B. FUELS AND COMBUSTION - LECTURE Cracked stocks – are residual of fuels which have been treated thermally or catalytically to obtain yields of lightergrade fuels or gasoline. Lightest grade distillates – classed as kerosene or No. 1 fuel oil, may have an initial boiling point of 176.6 C and end point of 260 C. Heaviest grades of distillates – classed as No. 3 or 4 fuel oil, may have an initial boiling point of 232 C to 260 C and end point of 343 C to 371 C. Residual fuels, No. 4 or No. 5 – are suitable only for the slower-speed diesel. 13. Gaseous Fuels Gaseous fuels – are commonly used in industry, whether distributed by public utilities or produced in isolated plants, are composed of one or more simple gases in varying proportions. 14. Diesel Lubricating Oils Crude oils – are frequently described as “paraffinic”, “napththenic”, or “mixed based” according to the physical characteristics of the crude. Two broad types of oil a. “Straight” oils – are produced entirely from the crudes chosen through elimination of undesired constituents by suitable refining processes. b. “Additive” oils – are produced by adding to straight mineral oils certain oil-soluble compounds that enhance the lubricating oil properties for use in a diesel engine. Additives – are used principally to inhibit or slow down oxidation, to increase film strength, to keep solids in finely divided state and to hold them in suspension, to improve the viscosity index, to lower the pour point, to decrease friction and wear under extreme pressure conditions, to reduce foaming, and as rust or corrosion inhibitors. SAE Three Types of Lubricating Oils a. Regular type – suitable for moderate operating conditions. b. Premium type – having oxidation stability and bearing corrosion preventive properties making it generally suitable for more severe service than regular duty type. c. Heavy duty type – has oxidation stability, being corrosion-preventive properties, and detergent-dispersant characteristics for use under heavy-duty service conditions. SAE Numbers – are a means of coordinating and standardizing the products of oil companies and the recommendations by the oil companies. The system of SAE motor classification is a system based entirely on viscosity and is totally unrelated the other qualities of a lubricating oil. 15. Specific Gravity Specific Gravity – a dimensionless parameter, it is the ratio of the mass of a unit volume of fuel to the mass of the same volume of a standard substance at a specified temperature. density of liquid fuel SG = density of water density of gaseous fuel SG = density of air 3
B. FUELS AND COMBUSTION - LECTURE In reporting SG data the 15.6 C or 60 F standard is common, that is, the oil is at 15.6 C or 60 F and is referred to the density of water taken at 15.6 C or 60 F. Specific gravity at other temperature with correction factor, SGt = SG15 .6o C [1 − 0.0007(t − 15.6 )] in SI units SGt = SG60 o F [1 − 0.0004(t − 60)] in English units
American Petroleum Institute Gravity Unit, oAPI - Is the accepted standard by the petroleum and oil industry, it was drawn up to correct vales measured by incorrectly calibrated hydrometers. 141.5 o − 131.5 API = SG at 15.6o C
Baume Gravity Unit, oBaume’ or oBe’ - Another standard commonly associated with brine. 140 o Baume = − 130 SG at 15.6 o C 16. Viscosity Viscosity – is measure of resistance to flow. Absolute Viscosity – is defined as that unit force required to move one layer of a fluid at unit relative velocity to another layer of the fluid which is at unit distance from the first. Kinematic Viscosity – is defined as the ratio of absolute viscosity divided by density. Units of viscosity: Absolute viscosity, µ 1 reyn = 1 kb-sec / in2 1 poise – 1 dyne-se/cm2 = 0.1 Pa-sec Kinematic Viscosity, ν 1 stoke = 1 cm2/sec = 0.0001 m2/sec Centipoises and centistokes are more commonly used. Saybolt viscosimeter – measures the time required for a given quantity of oil at standard temperature to flow through a specified tube. SSU (Saybolt Second Universal) – is obtained by timing the interval required for 60 cc of oil to flow through tube or pass through a standard orifice. For 30 to 45 SSU at 37.8 C, Centistokes = 0.308(SSU – 26) 180 Or ν = 0.22SSU − centistokes SSU SSF (Saybolt Second Furol) – unit used for very viscous liquids using a relatively large orifice. 62 SSF = 600 SSU
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B. FUELS AND COMBUSTION - LECTURE 17. Other Properties Flash point – is the temperature at which oil gives off vapor that burns temporarily when ignited. Flash point – is the temperature to which oil must be heated to give off sufficient vapor to form an inflammable mixture with air. Flash point – is the temperature at which ignition of the fuel vapors rising above the heated oil will occur when exposed to an open flame. Fire point – is the temperature at which oil gives off vapor that burns continuously when ignited. Pour point – is the temperature at which oil will no longer pour freely or the temperature at which oil will solidify. Dropping point – is the temperature at which grease melts. Cloud point – is the temperature at which the paraffin elements separate from oil. Conradson number (carbon residue) – is the carbonaceous residue remaining after destructive distillation, expressed in percentage by weight of the original sample. Viscosity index – indicates the relative change in viscosity of an oil for a given temperature change. Octane number – the ignition quality rating of gasoline, which is the percentage by volume of iso-octane in a mixture of iso-octane and heptanes that matches the gasoline in anti-knock quality. Cetane number – the ignition quality rating of diesel, which is the percent of cetane in the standard fuel. Aniline point – is that temperature where equal parts if oil and aniline will dissolve in each other. Volatility – is the ability of a liquid fuel to change into vapor which is manifested in the temperature range at which various portions of the fuel are vaporized. 18. Composition of Fuels a. Paraffins, CnH2n+2 – saturated hydrocarbons, very stable in characters b. Olefins, CnH2n – unsaturated hydrocarbons, characterized by the presence of a double bond between carbon atoms. c. Diiolefins, CnH2n-2 – less saturated than olefins, characterized by the presence of two double bonds. 19. Analysis of Composition 19.1 Proximate analysis – is made by heating the coal until it decomposes successively into three of the four complex items of proximate analysis. The fourth is found by the difference. A typical proximate analysis of coal determines the percentage of moisture, volatile matter, fixed carbon, and ash. a. Moisture – is determined by subjecting a 1-g sample of the coal to a temperature of 220 F to 230 F for a period of exactly 1 hr. b. Volatile matter – consists of hydrogen and certain hydrogen-carbon compounds that can be removed from the coal merely by heating it. c. Ash – is performed by heating the sample of coal used in the moisture determination to a temperature of 1290 F to 1380 F in an uncovered crucible, with good air circulation, until the coal is completely burned. 5
B. FUELS AND COMBUSTION - LECTURE Fixed Carbon – is the difference between 100 % and the sum of the percentages of moisture, ash, and volatile matter. Ultimate analysis – analysis of composition of fuel which gives, on mass basis, the relative amounts of carbon, hydrogen, oxygen, nitrogen, sulfur, ash, and moisture. d.
19.2
20. Basis of Reporting Analysis a. As received or as fired b. Dry or moisture free c. Moisture and ash free or combustible d. Moisture, ash, and sulfur free 21. Heating Values of Fuels or Calorific Value a. Higher heating value (gross calorific value), HHV – is the heating value obtained when the water in the products of combustion is in the liquid state. b. Lower heating value (net calorific value), LHV – is the heating value obtained when the water in the products of combustion is in the vapor state. 22. Methods of Determining Heating Values 22.1 Laboratory experiment 22.1.1 Bomb calorimeter for solid and liquid fuels 22.1.2 Gas calorimeter for gaseous fuels 22.2 Empirical formulas 22.2.1 Dulong’s formula for solid fuels of known ultimate analysis. O HHV = 33,820 + 144,212 H − + 9,304 S kJ kg 8 O HHV = 14,600 + 62,000 H − + 4050S Btu lb 8 22.2.2 ASME Formula for petroleum products HHV = 41,130 + 139.6 o API kJ kg
(
(
o
)
)
HHV = 17,680 + 60 API Btu lb 22.2.3 Bureau of Standard formula HHV = 51,716 − 8 ,793.8(SG )2 kJ kg HHV = 22,230 − 3780(SG )2 Btu lb
Difference between higher and lower heating values HHV – LHV = 9H2(2442) in SI units HHV - LHV = 9H2(1050) in English units Where: 9H2 = lbs or kg of water formed per lb or kg of fuel burned. 2442 kJ/kg or 1050 Btu/lb – latent heat of vaporization of water. Also H2 = 26-15(SG), percent by weight. 23. Fuel Production Process a. Fractional distillation – the primary method of crude oil refining. 6
B. FUELS AND COMBUSTION - LECTURE b. Thermal cracking – changing heavy oil into gasoline by means of high pressure, high temperature and longer exposure time. c. Catalytic cracking – subjects oil to high pressure and high temperature in the presence of a catalyst; permit accurate control of the compounds formed and produces a gasoline of higher octane number than the one produced in thermal cracking. d. Hydrogenation – process of catalytic cracking in a hydrogen atmosphere; obtained are more saturated products than those from cracking process alone. e. Isomerization – process by which the atoms of carbon and hydrogen in normal hydrocarbons are rearranged to produce a more complex structure of higher anti-knock value. f. Polymerization – makes use of high pressure, high temperature and a catalyst to combine light and volatile gases into gasoline. g. Alkylation – process of combining an isoparaffin usually iso-butane, with an olefin, usually butane or propane, to form a large isoparaffin molecule, usually iso-octane or iso-heptane, having a very high octane number. h. Reforming –used to obtain fuels with substantially higher than 100 octane number; currently used to process about forty percent of motor gasoline. i. Hydrodesulfurization – process of adding hydrogen to unsaturated hydrocarbons and reducing the sulfur content of the resulting fuel oil. 24. Combustion Combustion – a chemical reaction between fuel and oxygen (air) which is accompanied by heat and light. 25. Composition of Air and Molecular Weights a. Composition by weight 76.8 % nitrogen, 23.2 % oxygen Or 76.8 / 23.2 = 3.3 lb of nitrogen per lb of oxygen. b. Composition by volume 79.0 % nitrogen, 21.0 % oxygen Or 79.0/21.0 = 3.76 moles of nitrogen per moles of oxygen c. Molecular weights Air = 28.97 kg/kgmole C = 12 kg/kgmole H2 = 2 kg/kgmole O2 = 32 kg/kgmole N2 = 28 kg/kgmole S = 32 kg/kgmole 26. Air Fuel Ratio Theoretical air-fuel ratio, Wta – is the exact theoretical amount, as determined from the combustion reaction, of air needed to burn a unit amount of fuel, kg air per kg fuel or lb air per lb fuel. O Wta = 11.53C + 34.36 H2 − 2 + 4.32 S 8 where: Wta = theoretical air, lb per lb fuel C = carbon, lb per lb fuel H2 = hydrogen, lb per lb fuel O2 = oxygen, lb per lb fuel S = sulfur, lb per lb fuel 7
B. FUELS AND COMBUSTION - LECTURE Actual air-fuel ratio, Waa – is determined by the presence of excess air which is defined as the amount of air supplied over and above the theoretical air. Waa = (1+ e)Wta W − Wta e = aa Wta where e is the excess air in decimal. 27. Typical Combustion Reaction Fuel + Air = Product of Combustion C nHm + (n + 0.25m)O2 + 3.76(n + 0.25m)N2 → nCO2 + 0.5mH2O + 3.76(n + 0.25m)N2 Wta =
(n + 0.25m)(32 + 3.76 × 28) 12n + m
=
137.28(n + 0.25m ) 12n + m
28. Classification of combustion reaction a. Combustion reaction with chemically-correct or stoichiometric condition general chemical formula of the fuel is CnHm. b. Combustion reaction with greater amount of theoretical air, or having a fuel-lean mixture. c. Combustion reaction with lesser amount of theoretical air, or having a fuel-rich mixture. 29. Equivalence ratio for a given mass of air, φ. W φ = ta Waa Note: φ = 1, for stoichiometric mixture. φ < 1, for fuel-lean mixture. φ > 1, for fuel-rich mixture. 30. Orsat Analyzer Orsat analyzer – is a convenient portable apparatus for determining the volumetric percentage of CO2, O2, and CO in the dry flue gas. 31. Dry Flue Gases from Actual Combustion 4CO2 + O2 + 700 Wdg = C ab 3(CO2 + CO ) Boiler test code formula corrected to account for the SO2. 11CO2 + 8O2 + 7(CO + N2 ) 3 5 Wdg = C ab + S + S 3(CO2 + CO ) 8 8 where: CO2, O2, CO, and N2 are volumetric Orsat analysis Cab and S are decimal fractions by weight. 32. Weight of dry refuse from the coal analysis A Wr = 1− Cr 8
B. FUELS AND COMBUSTION - LECTURE where: Wr = dry refuse per lb coal as fired, lb A = ash in coal, lb Cr = combustible In 1 lb of refuse. 33. Carbon Actually Burned Cab = C − Wr + A Or HVr C ab = C − Wr 14,600 where: Cab = carbon actually burned per lb of fuel, lb C = carbon in 1 lb of fuel, lb HVr = heating value of the dry refuse, Btu per lb.
34. Carbon burned to CO due to incomplete combustion. CO Ci = × C ab CO2 + CO where Ci is the pounds of carbon the CO per pound of fuel burned. 35. Air Actually Used During Combustion O Waa = Wdg + 8 H2 − 2 − C ab − S − N2 8 Values of H2, O2, S, and N2 are obtained from the ultimate analysis of the fuel and all values are expressed as decimals. 36. Boiler Heat Balance Consist of percentage energy absorbed by boiler fluid, energy loss due to dry flue gases, energy loss due to moisture in fuel, energy loss due to evaporating and superheating moisture formed by combustion of hydrogen, energy loss due to incomplete combustion of carbon to CO, energy loss due to combustible in the refuse, and energy loss due to radiation and unaccounted for totaling to higher heating value as 100%. a. Energy absorbed by boiler fluid. The useful output of the steam generator is the heat transferred to the fluid. W (h − h ) Q1 = w 2 1 Wf in which Ww = weight of fluid flowing through the boiler during the test, lb h1 and h2 = fluid enthalpies entering and leaving the boiler, respectively, Btu per lb Wf = weight of fuel burned during test, lb Q1 expressed as a percentage of the higher heating value of the fuel is the boiler efficiency.
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B. FUELS AND COMBUSTION - LECTURE b. Energy loss due to dry flue gas. This loss is the greatest of any of the boiler losses for a properly operated unit. Q2 = 0.24Wdg (t g − t a ) in which 0.24 = specific heat of the flue gas at constant pressure, Btu per lb per deg F. tg = temperature of the gas leaving the boiler, F ta = temperature of the air entering the boiler, F c. Energy loss due to evaporating and superheating moisture in fuel. Moisture entering the boiler with the fuel leaves as a superheated vapor in the same way as does moisture from the combustion of hydrogen. Q3 = M f (1089 + 0.46t g − t f ), when t g < 575 F Q3 = M f (1066 + 0.5t g − t f ), when t g > 575 F
where Mf = moisture in fuel, lb per lb of fuel tf = temperature of fuel, F d. Energy loss due to evaporating and superheating moisture formed by combustion of hydrogen. This loss is higher for gaseous fuels containing relatively large percentages of hydrogen than for the average lowhydrogen coal. Q4 = 9H 2 (h − h ff ) where: h2 = weight of hydrogen in the fuel, lb per lb fuel h = enthalpy of superheated vapor, Btu per lb hff = enthalpy of liquid at the incoming fuel temperature or Q4 = 9H 2 (1089 + 0.46t g − t f ), when t g < 575 F Q4 = 9H 2 (1066 + 0.5t g − t f ), when t g > 575 F
The proper value of H2 to be used in the equation is the amount of hydrogen in the fuel that is available for combustion. To obtain the value of H2, deduct from the value of H2 in ultimate analysis one ninth of the weight of moisture from the proximate analysis. e. Energy loss due to incomplete combustion. Products formed by incomplete combustion may be mixed with oxygen and burned again with a further release of energy. CO Q5 = 10,160C i = 10,160C ab Btu lb CO2 + CO f.
Energy loss due to unconsumed carbon. All combustible in the refuse may be assumed to be carbon, since the other combustible parts of coal would probably be distilled out of the fuel before live embers would drop into ash pit. 10
B. FUELS AND COMBUSTION - LECTURE Q6 = 14,600(C − C ab ) Btu lb
or Q6 = Wr HVr g. Unaccounted-for and radiation loss. This loss is due to radiation, incomplete combustion resulting in hydrogen and hydrocarbons in the flue gas, and unaccounted-for losses. Q7 = HHV − Q1 − Q2 − Q3 − Q4 − Q5 − Q6 h. Boiler Heat Balance Tabulation Item Q1 Q2 Q3 Q4 Q5 Q6 Q7 HHV
Energy, Btu per lb fuel
Percentage
100%
-
End -
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B. FUELS AND COMBUSTION - LECTURE
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C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 1. Definitions Propulsion system – is a system which changes the momentum of a driven body; it covers system that drives vehicles and major pieces of industrial equipment. Heat engines – are machines that convert heat into work or mechanical energy; heat supplied comes from the combustion of a certain amount of fuel in oxygen (air); a working fluid absorbs the heat supplied in order to drive the linkages that produce the mechanical energy. 2. Classification of Heat Engines External combustion engine (ECE) – an engine where the generation of heat is effected outside the work-producing unit; combustor is distinct and separate from the work-producing unit; typical example includes steam engine. Internal-combustion engine (ICE) – an engine where the generation of heat is effected inside the work-producing unit; combustor and work-producing unit are the same; products of combustion eventually become the working fluid. 3. Comparison of Heat Engine Types External combustion engine (ECE) a. Less vibration b. High starting torque c. Cheaper fuel d. In large units, advantage in space requirement and weight dimension Internal combustion engine (ICE) a. Higher over-all efficiency b. Lower combustion energy lost to cooling system c. Less weight and bulk per unit maximum output d. Mechanical simplicity 4. Classification of Internal Combustion Engines according to: 4.1 Manner of ignition 4.1.1 Spark-ignition engine (SI engine) - Accepts air-fuel mixture upon intake; fuel used is gasoline; ignition energy supplied by spark plug. 4.1.2 Compression-ignition engine (CI engine) - Accepts only air upon intake; fuel is sprayed through a nozzle inside engine cylinder upon reaching its auto-ignition temperature; fuel used is diesel; ignition energy supplied by heat of compression. 4.2 Work-producing motion 4.2.1 Reciprocating as in the case of piston engines 4.2.2 Rotary as in the case of the Wanker rotor 4.3 Intake pressure or manner of aspiration 4.3.1 Naturally-aspired 4.3.2 Supercharged 1
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 4.3.3 Turbo-charged 4.4 Number of strokes per cycle 4.4.1 Four-stroke cycle 4.4.2 Two-stroke cycle 4.5 Location of the cam(s) 4.5.1 Overhead 4.5.2 In-block 4.6 Method of cooling 4.6.1 Water-cooled 4.6.2 Air-cooled 4.7 Number of cylinders 4.7.1 Single-cylinder 4.7.2 Two-cylinder 4.7.3 Three-cylinder, etc. 4.8 Position of cylinders 4.8.1 Vertical 4.8.2 Horizontal 4.8.3 Incline 4.9 Arrangement of cylinders 4.9.1 In-line 4.9.2 Radial 4.9.3 Opposed cylinder 4.9.4 Opposed piston 4.9.5 V-type 4.10 Number of piston sides working 4.10.1 Single-acting 4.10.2 Double-acting 4.11 Method of starting 4.11.1 Manual: crank, rope, kick 4.11.2 Electric: battery 4.11.3 Compressed air 4.11.4 Using other engines 4.12 Application 4.12.1 Automotive 4.12.2 Marine 4.12.3 Industrial 4.12.4 Stationary power 4.12.5 Locomotive 4.12.6 Aircraft
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C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 5. Ideal or Air Standard Cycles 5.1 Otto Cycle – is the ideal prototype of spark-ignition (SI) engines commonly known as gasoline engine. Cycle Analysis of 4-stroke Gasoline Engine
0-1 1-2 2-3 3-4 4-1 1-0
intake stroke isentropic compression isometric heat intake isentropic expansion isometric heat release exhaust stroke
Heat Added, QA = mcv (T3 − T2 ) Heat Rejected, QR = mcv (T4 − T1 ) Net Work, Wnet = QA − QR
p2V2 − p1V1 p4V4 − p3V3 + 1− k 1− k W Q − QR Cycle Efficiency = e = net = A QA QA
∫
Net Work, Wnet = pdV =
Cycle Efficiency = e = 1 −
1 rkk −1
Specific heat ratio, k = 1.4 for air standard. Clearance volume, Vc = V3 = V2 V V 1+ c Compression ratio, rk = 1 = 4 = V2 V3 c Clearance ratio, c =
V2 V2 = VD V1 − V2
where VD = piston volume displacement Other relationship, V3 = V2 and V4 = V1
V T4 = T3 3 V4
k −1
=
T3 rkk −1
3
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE V T1 = T2 2 V1
k −1
=
T2 rkk −1
Mean effective pressure, Cut-off ratio, pm =
Wnet VD
Cycle Analysis of 2-stroke Gasoline Engine
5.2 Diesel Cycle – is the ideal prototype of compression-ignition (CI) engines. Cycle Analysis of 4-stroke Diesel Engine
0-1 1-2 2-3 3-4 4-1
intake stroke isentropic compression isobaric heat intake isentropic expansion isometric heat release
Heat Added, QA = mc p (T3 − T2 ) Heat Rejected, QR = mcv (T4 − T1 ) Net Work, Wnet = QA − QR Cycle Efficiency = e =
Wnet QA − QR = QA QA
4
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 1 rck − 1 rkk −1 k (rc − 1) V 1+ c Compression ratio, rk = 1 = V2 c
Cycle Efficiency = e = 1 −
Cut-off ratio, rc =
V3 T3 = V2 T2
Specific heat ratio, k = 1.4 for air standard. V V2 Clearance ratio, c = 2 = VD V1 − V2 Other relationship,
V T2 = T1 1 V2
k −1
V T3 = T2 3 V2
= T1rkk −1 k −1
= T1rkk −1rc
T4 = T1rck
Mean effective pressure, Cut-off ratio, pm =
Wnet VD
Cycle Analysis of 2-stroke Diesel Engine
5.3 Dual Combustion Cycle (Limited Pressure Cycle or Mixed Cycle)
5
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 0-1 1-2 2-3 3-4 4-1
intake heat stroke isentropic compression isobaric heat intake isentropic expansion isometric heat release
rp rck −1 − 1 1 Cycle Efficiency = e = 1 − k −1 rk rp − 1 + rp k (rc − 1) Pressure ratio during constant volume process 2-3, rp = Cut-off ratio, rc =
p3 p2
V4 V3
Mean effective pressure, Cut-off ratio, pm =
Wnet VD
6. Diesel Power Plant
6.1 Basic Elements in Plant Design 6.1.1 Stationary diesel engine 6.1.1.1 Structural parts: bed plate, frame, liners, heads 6.1.1.2 Major moving parts: piston,, connecting rods, crankshaft, and their bearings 6.1.1.3 Arrangements for getting air in and exhaust out: valves, valve mechanisms, manifold, scavenging and supercharging systems, and 6.1.1.4 Fuel-injection system: pumps, nozzles, control devices. 6.1.2 Fuel system Fuel storage tank, fuel filter, fuel pump, transfer pump, day tank 6.1.3 Lubrication system Lube oil tank, lube oil pump, oil filter, oil cooler, lubricators 6.1.4 Cooling system Cooling water pump, heat exchanger, cooling tower, surge tank 6.1.5 Intake and exhaust systems Air filter, supercharger, intake pipe, exhaust pipe, exhaust silencer (to minimize exhaust noise) 6
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 6.1.6
Starting system Air compressor, air storage tank Governing system
6.1.7
7. The Diesel Engine Diesel engine – is an excellent prime mover for electric power generation in capacities of 101 hp to 5070 hp which makes it widely-used in hotels, utility companies, municipalities, and private industries. Advantages of the Diesel engine: a. Low fuel cost. b. No long warming-up period. c. No standby losses. d. Uniformly high efficiency of all sizes. e. Simple plant layout. f. Needs no large water supply. 8. Typical Full-Load Heat Balances (%) based on heating value of fuel.
a. b. c. d.
Useful work Cooling Exhaust Friction, radiation, and unaccounted Input; heating value of fuel
Otto Cycle Spark Ignition 25 30 37 8 100
9. Performance of Diesel Generating Set 9.1 Heat generated (fuel) QA = m f HV kw where: mf = fuel consumption, kg/s HV = heating value of fuel, kJ/kg 9.2 Volume displacement
π
D 2 LN pNc m3/sec 4 where: D = bore, m L = length of stroke, m Np = speed, rev/sec (for 2-stroke) Np = speed/2, rev/sec (for 4-stroke) Nc = number of cylinders VD =
7
Diesel Cycle Compression Engine 34 30 26 10 100
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 9.3 Piston Speed Piston Speed = 2LN, m/s where 2L = distance travelled by piston in one revolution 9.4 Indicated power (IP) Indicated power – power developed inside the cylinder IP = pmiVD kw where: pmi = indicated mean effective pressure AS pmi = c c Lc
VD = piston volume displacement, m3/sec. Ac = area of indicator card diagram. Sc = spring scale. Lc = length of indicator card diagram. or IP = pmi LAN pNc kw where A = is the area of bore or net piston area. If working cylinder (wc) and crankcase (cc) are to be considered A S A S pmi = wc wc − cc cc Lwc Lcc Note: crankcase compression is used for scavenging. 9.5 Brake power (BP) BP = pmbLAN p Nc Where: pmb = brake mean effective pressure. Calculating brake power using either prony brake or dynamometer BP = 2πTn where: T = brake torque, measured by dynamometer. n = engine rotative speed Also
T = Fr where: F = brake force or brake load. r = brake arm or torque arm.
8
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 9.6 Frictional power (FP) FP = IP – BP Morse test as a method of determining friction power. Applicability of test is for multi-cylinder engines. Consider a six-cylinder engine, IP6 = BP6 + FP, all six cylinders are firing IP5 = BP5 + FP, only five cylinder firing =========== IP1 = BP6 – BP5, for one cylinder cut-out Friction power, FP, is constant no matter how many cylinders are firing. Total engine indicated power, IP, for equal cylinder IP1, IP2, IP3 . . . IP = IP6 = 6(IP1) = 6(BP6 – BP5) For not equal cylinder IP’s IP = IP1 + IP2 + IP3 + IP4 + IP5 + IP6 where: IP1 = BP6 – BP5,1, for cylinder no. 1 cut-out IP2 = BP6 – BP5,2, for cylinder no. 2 cut-out IP3 = BP6 – BP5,3, for cylinder no. 3 cut-out IP4 = BP6 – BP5,4, for cylinder no. 4 cut-out IP5 = BP6 – BP5,5, for cylinder no. 5 cut-out IP5 = BP6 – BP5,6, for cylinder no. 6 cut-out
FP = IP – BP = IP – BP6 9.7 Engine efficiencies based on power developed 9.7.1 Mechanical efficiency, ηm brake power , BP p = mb ηm = indicated power , IP pmi 9.7.2
Electrical or generator efficiency, he electrical output , EP ηo = brake power , BP
9.7.3
Over-all efficiency, ηo electrical output , EP ηo = = η mη e indicated power , IP
9.8 Thermal efficiencies 9.8.1 Indicated thermal efficiency, ei, indicated power IP ei = = heat supplied by fuel m f HV
9
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 9.8.2
Brake thermal efficiency, eb. brake power BP eb = = heat supplied by fuel m f HV
9.8.3
Combined thermal efficiency, ek, electrical power Wk ek = = heat supplied by fuel m f HV where: mf = mass of fuel burned HV = heating value of fuel Wk = combined work
9.9 Engine efficiencies 9.9.1 Indicated engine efficiency, ηi e ηi = i e 9.9.2 Brake engine efficiency, ηb e ηb = b e 9.9.3 Combined engine efficiency, ηk e ηk = k e where: e = ideal thermal efficiency = net work/heat added = Wnet / QA 9.10
Specific fuel consumption, kg/kW-hr 9.10.1 Indicated specific fuel consumption, mi. 3600m f mi = IP 9.10.2 Brake specific fuel consumption, mb. 3600m f mb = BP 9.10.3 Combined or over-all specific fuel consumption, mk. 3600m f mk = EP Note: mass of fuel burned mf is expressed in kg/s. For other units change 3600 kJ/kW-hr to 2544 Btu/hp-hr or 3412 Btu/kW-hr
9.11
Heat rate, kJ/kW-hr 9.11.1 Indicated heat rate, HRi. HRi = mi HV
10
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 9.11.2 Brake heat rate, HRb HRb = mbHV 9.11.3 Combined heat rate, HRk HRk = mk HV 9.12
Volumetric efficiency, hv Actual volume of air entering VA ηv = = Piston displacement VD m RT VA = A p VD = LAN p Nc
9.13
Speed Data 9.13.1 Piston speed, PS PS = 2Ln. m/s 9.13.2 Generator speed, N 120 f N= rpm n where: f = frequency, usually 60 Hz p = number of even poles
10. Power developed at an altitude, P B T P = Ps 29.92 520 where: Ps = standard power or power at sea level. B = barometric pressure at a given altitude, in. Hg. (decrease in pressure, approx. 1 in. Hg per 1000 ft) T = absolute temperature at a given altitude, R. (decrease in temperature, approx. 3.6 F per 1000 ft). 29.92 in. Hg = standard atmospheric pressure. 520 R = temperature at sea level. 11. Supercharging Supercharging – an admittance into the cylinder of an air charge with density higher than that of the surrounding air. Reason for supercharging: a. To reduce the weight-to-power ratio. b. To compensate for power loss due to high altitude. Types of superchargers: a. Engine-driven compressor. b. Exhaust-driven compressor (turbo-charger). c. Separately-driven compressor.
11
C. INTERNAL COMBUSTION ENGINE POWER PLANT - LECTURE 12. Waste heat recovery boiler utilizing diesel engine exhaust.
By Heat Balance in Boiler: mg c pg (t1 − t 2 ) = ms (hs − h f ) where: cpg = specific heat of exhaust gas. -
12
End -
D. GAS TURBINE POWER PLANT - LECTURE 1. Definition Gas Turbine – is a type of prime mover that derives its energy from heat, commonly supplied by combustion. The products of combustion form the working medium, but the combustion region is external to the prime mover. 2. Basic Elements in Plant Design Schematic diagram – open cycle gas turbine power plant (direct mixing of air and fuel).
a. Air compressor, ac Axial-type or centrifugal b. Combustor or combustor chamber, cc c. Gas turbine, gt Reaction-type d. Electric generator, eg e. Gas turbine auxiliaries 1. Starting motor or engine, sm 2. Fuel system 3. Lubrication system 4. Speed control or governing system
3. Classes of application of Gas Turbine 3.1 As a means of increasing the capacity and decreasing the heat rate of steam generating plant. 3.2 As an independent source of electrical energy in direct competition with other prime movers. 3.3 As a peak-load or back-up unit.
4. Applications of the Gas Turbine to utility electric generation 4.1 Peaking power 4.2 Mechanical drives for auxiliaries 4.3 Supercharged boilers 4.4 Exhaust heat recovery
1
D. GAS TURBINE POWER PLANT - LECTURE 5. Gas-Turbine Cycle Brayton cycle – is the theoretical cycle for the gas turbine which is composed of isentropic compression, constantpressure heat addition, isentropic expansion, and constant-pressure heat rejection. This is known as the simple cycle gas turbine. Air Standard Ideal Brayton Cycle
1-2 2-3 3-4 4-1
isentropic compression isobaric heat addition isentropic expansion isobaric heat rejection
Isentropic compression Process 1-2 s1 = s2 , p1V1k = p2V2k k −1
k −1
T2 p 2 k V1 = = T1 p1 V2 Compressor Work Wc = m(h2 − h1 ) = mc p (T2 − T1 )
where cp = 1.0 kJ/kg-K for air
p 2 p3 = p1 p4 V Compression ratio = rk = 1 V2 Heat addition isobaric process 2- 3 in the combustor QA = mc p (T3 − T2 ) = m(h3 − h2 ) Pressure ratio = rp =
Turbine isentropic expansion Process 3-4 s3 = s4 , p3V3k = p4V4k k −1
k −1
T3 p 3 k V4 = = T4 p4 V3 Turbine work Wt = m(h3 − h4 ) = mc p (T3 − T4 )
2
D. GAS TURBINE POWER PLANT - LECTURE Net Work Wnet = Wt − Wc Heat rejection isobaric process 4-1 QR = mc p (T4 − T1 ) = m(h4 − h1 ) Note: 1. If mass of fuel, mf is considered For process 1-2, m = mass of air, ma For process 2-3, 3-4 and 4-1, m = ma + mf 2. If basis is air-standard cycle For all processes, m = ma 3. For closed cycle, m = ma Thermal efficiency W W − Wc QA − QR e = net = t = QA QA QA In terms of enthalpy h −h e =1− 4 1 h3 − h2 In terms of temperature T −T e =1− 4 1 T3 − T2 In terms of compression ratio, rk 1 e = 1 − k −1 = 1 − rk1−k rk In terms of pressure ratio, rp
e =1−
1− k
1 k −1
= 1 − rp k
rp k Closed Cycle Gas Turbine
Intermediate temperature for maximum work 1
T2 = (T1T3 )2
3
D. GAS TURBINE POWER PLANT - LECTURE Considering irreversibilities
Isentropic or adiabatic compressor efficiency (compressor internal efficiency), ηc. ideal compressor work ,Wc h − h T −T ηc = = 2 1 = 2 1 actual compressor work ,Wc′ h2′ − h1 T2′ − T1 Isentropic turbine efficiency (turbine internal efficiency) ideal turbine work ,Wt′ h3 − h4′ T3 − T4′ ηt = = = actual turbine work ,Wt h3 − h4 T3 − T4 Actual heat added in the combustor Q′A = m(h3 − h2′ ) = mc p (T3 − T2′ )
Actual thermal efficiency h −h T −T e = 1 − 4′ 1 = 1 − 4′ 1 h3 − h2′ T3 − T2′
e=
k −1 p4 k T1 ηtT3 1 − − p3 ηc
k −1 p2 k − 1 p1
k −1 p 2 k − 1 p T3 − T1 1 + 1 ηc k −1 T1rp k ηt T3 − η 1 c e= 1 − k −1 k −1 rp k − 1 rp k T − T − T 3 1 1 η c Combustor efficiency heat absorbed by air ecc = heat supplied by fuel
4
D. GAS TURBINE POWER PLANT - LECTURE 6. Performance of Actual Cycle
Ideal compressor work Wc = ma c pa (T2 − T1 ) Actual compressor work Ideal compressor work Wc = Wc′ = Compressor efficiency η c m c (T − T ) Wc′ = ma c pa (T2′ − T1 ) = a pa 2 1
ηc
where cpa = specific heat of air = 1.0 kJ/kg-K Ideal turbine work Wt = (ma + m f )c pg (T3 − T4 ) Wt = ma (+ r f )c pg (T3 − T4 )
Wt′ = actual turbinework = ideal turbinework × turbine efficiency Wt′ = ma (1 + r f )c pg (T3 − T4′ ) = ma (1 + rf )c pg (T3 − T4 )ηt where cpg = specific heat of gas rf = fuel to air ratio
5
D. GAS TURBINE POWER PLANT - LECTURE Heat generated by fuel QA = (ma rf )HV = m f HV where: HV = heating value of fuel Actual net work ′ = Wt′ − Wc′ − Waux Wnet
Wt′ − Wc′ − Waux QA Generator output Overall thermal efficiency = QA Heat absorbed by air Combustion Efficiency = Heat supplied byfuel Thermal efficiency =
7. Ideal Gas Turbine Cycle with Regenerator Regenerator – is a heat exchange used to provide heat transfer between the exhaust gases and the air prior to its entrance to the combustion chamber the purpose of which is to increase thermal efficiency.
Head added in combustor QA = mc p (T3 − Tx ) Heat balance in regenerator mc p (Tx − T2 ) = mc p (T4 − Ty ) Tx − T2 = T4 − Ty
6
D. GAS TURBINE POWER PLANT - LECTURE Effectiveness of the regenerator – is defined as the ratio of actual amount of heat transferred to the amount of that could be transferred reversibly. actual amount of heat transferred εr = amount that could be transferred reversibly T −T εr = x 2 T4 −T 2 For 100% regenerator efficiency, Tx = T4 k −1
e = 1−
T2 − T1 T = 1 − 1 rp k T3 − T4 T3
8. Thermal refinement of the Gas Turbine Cycle 8.1 Regeneration – is the transfer of heat energy from exhaust gases to compressed air flowing between the compressor and combustion chamber. A surface heater called the “regenerator” is required. 8.2 Intercooling – is the removal of heat from compressed air between stages of compression. 8.3 Reheating – is the increase in temperature of partially expanded gas by burning more fuel in it. -
End -
7
E. STEAM POWER PLANT - LECTURE 1. Basic Elements of Plant Design 1.1 Steam Generator – is a combination of apparatus for producing, furnishing, or recovering heat, together with apparatus for transferring to a working fluid the heat thus made available. It indicates the furnace, boiler, waterwalls, water floor, water screen, superheater, reheater, economizer, air preheater, and fuel-burning equipment. The term boiler has been used for such a long period of time that the two terms are used interchangeably. 1.2 Steam Turbine – is the most versatile prime mover capable of an almost endless variety of application. It is a practical power source when built in as small as 5 hp or as large as 100,000. It is relatively quiet and smooth in operation. 1.3 Condenser – a heat exchanger where steam enters the top and the condensate is collected in the hot well at the bottom while cooling water flows through the tubes. 1.4 Boiler Feed Pump or Feedwater Pumps – its function is to increase the pressure existing on a liquid an increment sufficient to the required service. 2. Rankine Cycle Rankine cycle – is the ideal steam power cycle. This ideal plant consist of a steam generator which receives feedwater under pressure from a pump, a prime mover in which to obtain the working expansion, and a condenser to reduce the exhaust steam to liquid, ready for pumping.
1-2 2-3 3-4 4-5
isentropic (or reversible adiabatic) expansion isobaric (or reversible constant-pressure) heat rejection isentropic (or reversible adiabatic) compression isobaric (or reversible constant-pressure) heat addition
Turbine Work Wt = m(h1 − h2 ) 1
E. STEAM POWER PLANT - LECTURE Actual turbine work Wt′ = m(h1 − h2′ ) = m(h1 − h2 )ηt Heat rejected in condenser QR = m(h2 − h3 ) Actual heat rejected in condenser QR = m(h2′ − h3 ) Pump work Wp = m(h4 − h3 ) Wp ≈ mv3 (p4 − p3 )
Actual pump work m(h4 − h3 ) Wp′ =
ηp
Wp′ ≈
mv 3 (p4 − p3 )
ηp
Head added to boiler QA = m(h1 − h4 ) Actual heat added to boiler m(h1 − h4 ) QA =
ηb
where: ηt = turbine efficiency ηp = pump efficiency ηb = boiler efficiency Boiler efficiency – is meant the measure of ability of a boiler or steam generator to transfer the heat given it by the furnace to the water and steam. Thermal Cycle Efficiency For Rankine Cycle Wt − Wp (h1 − h2 ) − Wp (h1 − h2 ) − (h4 − h3 ) = ecycle = = (h1 − h3 ) − Wp Qb h1 − h4 For Rankine engine or turbine (combination with condenser) h −h eengine = 1 2 h1 − h3 For plant thermal efficiency electrical power output EP ep = = heat supplied by fuel m f HV 3. Methods used in increasing the thermal efficiency of a Rankine cycle a. For the same throttle pressure and condenser pressure, increase the throttle temperature. b. For the same throttle temperature and condenser pressure, increase the throttle pressure. c. For the same throttle temperature and pressure, decrease the condenser pressure. d. Using reheat cycle e. Using regenerative cycle f. Using reheat-regenerative cycle 2
E. STEAM POWER PLANT - LECTURE 4. Reheat Cycle Reheat cycle- to increase turbine power, increase thermal efficiency
Turbine work Wt = m(h1 − h2 ) + m(h3 −h 4 ) Heat added in the boiler QAb = m(h1 − h6 ) Heat added in the reheater QArh = m(h3 − h2 ) Pump work Wp = m(h6 − h5 ) ≈ mv 5 (p6 − p5 ) Heat rejected in the condenser QR = m(h4 − h5 ) Thermal efficiency of reheat cycle W − Wp W − Wp ecycle = t = t QA QAb + QArh 5. Regenerative Cycle Regenerative cycle – to improve the cycle efficiency, decrease turbine power, decrease heat addition.
Turbine work Wt = m(h1 − h2 ) + (m − m1 )(h2 −h 3 ) 3
E. STEAM POWER PLANT - LECTURE Heat added in the boiler QA = m(h1 − h7 ) Pump work 1 Wp1 = (m − m1 )(h5 − h4 ) ≈ (m − m1 )v 4 (p5 − p4 ) Pump work 2 Wp 2 = m(h7 − h6 ) ≈ mv 6 (p7 − p6 ) Heat rejected in the condenser QR = (m − m1 )(h3 − h4 ) Heat balance in regenerative heater (feedwater heater or deaerator) m1h2 + (m − m1 )h5 = mh6 Thermal efficiency of reheat cycle W − (Wp1 + Wp 2 ) Wt − (Wp1 + Wp2 ) = ecycle = t QA QA 6. Reheat-Regenerative Cycle
7. Steam Generators (Boilers) Steam generators – commonly referred to as boiler – is an integrated assembly of several essential components the function of which is to produce steam at a predetermined pressure and temperature.
8. Boiler Types 8.1 Classification according to the contents of the tubular heating surface. 8.1.1 Fire-tube boilers Fire-tube boilers – are those in which the products of combustion pass through the tubes and the water lies around the outside of them. a. Horizontal or vertical axes b. External or internal furnaces c. Fully cylindrical or partially cylindrical shells 4
E. STEAM POWER PLANT - LECTURE 8.1.2
Water-tube boilers Water-tube boilers – are those in which the water is inside the tubes while the products of combustion surrounds the tubes. Classification according to: a. Shape of the tubes 1. Straight tube - have a parallel group of straight equal-length tubes, arranged in a uniform pattern and joined at either end to headers. Classification of headers a. Box headers b. Sectional headers 2. Bent-tube - are header less. The drum serve the same function as the headers. b. Drum position 1. Longitudinal 2. Cross c. Method of Water Circulation 1. Forced 2. Natural d. Number of Drums 1. Drum –and-a-half – a long upper drum is paralleled by a shorted drum. 2. Two-Drum – two parallel horizontal drums of equal length but not necessarily equal diameter are set on one above the other and joined by multiple rows of bent tubes. 3. Three-Drum – two upper drums and one lower drums are arranged so that one upper drum carries the water level and the other, being lower, really acts as a header. e. Service 1. Marine 2. Stationary f. Capacity g. Thermal Conditions
9. Parts of Steam Generator 9.1 Pressure parts 9.1.1 Boiler heating surface – tubes with attached drums or shells for storage of water and steam. 9.1.2 Superheated surface – provides more heating surface through which the steam must pass after leaving the boiler if a final superheated state is desired. 9.1.3 Economizer – is a feedwater pre-heating device which utilizes steam mixed with the feedwater. 9.2 Enclosure or setting 9.2.1 Water walls – water tubes installed in the furnace to protect furnace against high temperature. 9.2.2 Furnace – encloses the combustion equipment to utilize effectively the heat generated. 9.2.2.1 Factors to be considered in furnace design a. Air supply b. Character of fuel used c. Degree of pre-heating d. Draft equipment available 9.2.2.2 Types of furnace walls a. Air-cooled masonry walls b. Partially water-cooled walls c. Solid masonry d. Water-jacketed furnace 5
E. STEAM POWER PLANT - LECTURE 9.2.3
9.2.4
Combustion equipment a. Burner – used in fire-tube boilers for firing liquid and gaseous fuels. b. Stoker – used in water-tube boilers for firing solid fuels Auxiliaries and accessories a. Air preheater – a heat exchanger utilizing the heat of the flue gases to pre-heat the air needed for combustion. b. Forced-draft fan – forces air inside to support fuel combustion c. Induced-draft fan – usually situated at the bottom of the chimney or smokestack, it is responsible in extracting flue gases out. d. Soot blower – removes soot around steam pipes developed as a result of combustion, employs the use of extracted steam from the main steam line. e. Blowdown valve – valve through which the impurities that settle in the mud drum are removed; also called blow-off valve. f. Breeching – duct connecting boiler to chimney. g. Baffles – direct the flow of the hot gases to effect efficient heat transfer between the hot gases and the heated water. h. Fusible plug – a metal plug with a definite melting point through which the steam is released in case of excessive temperature which is usually caused by low water level. i. Safety valve – a safety device which automatically releases the steam in case of over-pressure.
10. Definitions from PSME Code 2008 Boiler or Steam Generator – a closed vessel intended for use in heating water or for application of heat to generate steam or other vapor to be used externally to itself. Coal-Fired Boiler – used stoketed water temperature coal or pulverized coal for water-tube. Condemned Boiler Unfired Pressure Vessel – a boiler or unfired pressure vessel that has been inspected and declared unsafe to operate or disqualified, stamped and marked indicating its rejection by qualified inspecting authority. Existing Installations – any boiler or unfired pressure vessel constructed, installed, placed in operation but subject to periodic inspection. External Inspection – an inspection made on the external parts, accessories and/or component even when a boiler or unfired pressure vessel is in operation. Fire Tube Boiler – a boiler where heat is applied inside the tube. Fusion Welding – a process of welding metals in a molten and vaporous state, without the application of mechanical pressure or blows. Gas-Fired Boiler – uses natural gas or liquefied petroleum gas (LPG) for heating boiler, fire tube or water-tube. Heat-Recovery Steam Generator – unfired pressure vessel that uses flue gas heat. Internal Inspection – an inspection made when a boiler or unfired pressure vessel is shut-down and handholes, manholes, or other inspection openings are opened or removed for inspection of the interior. 6
E. STEAM POWER PLANT - LECTURE Locomotive Boiler – a boiler mounted on a self-propelled track locomotive and used to furnish motivating power for traveling on rails. Low Pressure Heating Boiler – a boiler operated at a pressure not exceeding 1.055 kg/cm2 gage steam water temperature not exceeding 121 C. Medium Pressure Heating Boiler – a boiler operated at a pressure not exceeding 103.5 MPa gage steam, or water temperature not exceeding 130 C. Miniature Boiler – as used in this Code herein mean any boiler which does not exceed any of the following limits: 405 mm inside diameter, 1065 mm overall length of outside of heads at center, 1.85 m2 of water heating surface, 7.03 kg/cm2 maximum allowable working pressure. New Boiler or Unfired Pressure Vessel Installation – include all boilers and unfired pressure vessels constructed, installed, placed in operation or constructed for. Oil-fired Boiler – uses Bunker C as fuel for heating boiler and power boiler. Portable Boiler – an internally fired boiler which is self-contained and primarily intended for temporary location and the construction and usage is obviously portable. Power Boiler – a closed vessel in which steam or other vapor (to be used externally to itself) is generated at a pressure of more than 1.055 kg/cm2 gage by the direct application of heat. ASME Boiler Construction Code – the term, ASME Boiler Construction Code of the American Society of Mechanical Engineers with amendments and interpretations thereto made and approved by the Council of the Society. Reinstalled Boiler or Unfired Pressure Vessel – a boiler or unfired pressure vessel removed from its original setting and re-erected at the same location or erected at a location without change of ownership. Second Hand Boiler or Unfired Pressure Vessel – as used herein shall mean a boiler or unfired pressure vessel of which both the location and ownership have been changed after primary use. Unfired Pressure Vessel – a vessel in which pressure is obtained from an external source, or from an indirect application of heat. Waste-Heat Boiler – unfired pressure vessel that uses flue gas heat from waste incinerator. Waste Tube Boiler – a boiler where heat is applied outside the tube.
7
E. STEAM POWER PLANT - LECTURE 11. Performance of Boilers
11.1
Factor of Evaporation, FE h s − h fw FE = h fg where: hfg = latent heat of vaporization or evaporation at standard atmospheric conditions. hfg = 970.3 Btu/lb or hfg = 2257 Btu/lb or hfg = 539 kcal/kg
11.2
Equivalent Evaporation, EE EE = ms FE where: ms = amount of steam generated.
11.3
Equivalent Specific Evaporation, ESE m EE ESE = s FE = mf mf where: mf = amount of fuel burned in the furnace.
11.4
ASME Evaporation unit, ASME EU ASME EU = ms (hs − h fw )
11.5
Rated Boiler Horsepower (Rated Bo Hp) Rated Bo Hp = Total Heating Surface / k where: k = 12 sq ft = 1.1 sq m for fire-tube boilers k = 10 sq ft = 0.91 sq m for water-tube boilers Also Package Fire-Tube Boiler have a heating surface of 5 sq ft per boiler horsepower.
8
E. STEAM POWER PLANT - LECTURE 11.6
Developed Boiler Horsepower (Dev Bo Hp) ms (hs − h fw ) ASME EU Dev Bo Hp = = c c where: c = 33,475 Btu/hr = 35,316 kJ/hr = 8,433 kcal/hr
11.7
Percent Rating Developed (% Rating Dev) Dev Bo Hp % Rating Dev = ×100 Rated Bo Hp
11.8
Over-all Boiler Efficiency or Steam Generator Efficiency, eo. ms (hs − h fw ) + mrs (hro − hri ) + mbo (hbo − h fw ) eo = m f HHV where: mrs = amount of steam reheated hro = enthalpy of steam leaving reheater hri = enthalpy of steam entering reheater mbo = amount of water blowdown at boiler pressure hbo = enthalpy of saturated liquid at boiler pressure if there is no reheater and no boiler blowdown. ms (hs − h fw ) eo = m f HHV
11.9
Boiler and Furnace Efficiency, ebf ms (hs − h fw ) ebf = m f HHV − mr HVr where: mf = amount of ash refired HVr = heating value of ash
11.10 Net Efficiency of Steam Generating Unit, enet (ms − maux )(hs − hfw ) enet = m f HHV where: maux = amount of steam used for SGU auxiliaries. 11.11 Gross Station (Power Plant) Heat Rate, GSHR - Defined as the amount of heat required per unit power developed . Gross heat supplied by fuel GSHR = Gross work output 11.12 Net Station (Power Plant) Heat Rate, NSHR Heat supplied by fuel , m f HHV NSHR = (kW − hr generated) − (kW − hr used by auxiliaries ) 9
E. STEAM POWER PLANT - LECTURE 11.13 Over-all (Gross) Station Efficiency, ηo kW − output at generator terminals ηo = Heat supplied by fuel 11.14 Grate Efficiency, egr m HV egr = 1 − c r m f HHV where: mc = amount of carbon in refuse or ash HVc = heating value of combustible in refuse or ash 12. Steam Turbines The operation of the steam turbine generator involves the expansion of steam through numerous stages in the turbine, causing the turbine rotor to turn the generator rotor. The generator rotor is magnetized, and its rotation generates the electrical power in the generator stator. 12.1 Principal Parts a. Rotor – is the main moving element of a turbine. b. Casing – is the principal stationary element, often called the cylinder. It surrounds the rotor and holds, internally, any nozzles, blades, and diaphragms that may be necessary to control the path and physical state of the expanding steam. c. Bearings – this the main bearings of a single-cylinder turbine which are two in number and are placed outboard of the shaft seal. d. Shaft seals – to prevent outflow at the high-pressure end and air inflow at the vacuum end. e. Steam control – regulate the flow of steam through a stationary turbine to produce constant rotative speed in the presence of variable power demand. f. Oil system – is required for lubricating the bearings. 12.2 Classification of Steam Turbine 12.2.1 Types of Blades a. Impulse Stages - consists of a stationary nozzle with rotating buckets or blades. The steam expands through the nozzle, increasing in velocity as a result of the decrease in pressure. The steam then strikes the rotating buckets and performs work on the rotating buckets, which in turn decreases the steam velocity. 1. Velocity compound stage – involves a stationary nozzle followed by several rotating and stationary buckets. The nozzle has a large pressure drop with a resulting increase in velocity. The velocity compound stage is also called a Curtis stage. 2. Pressure compound stages – involve several sets of nozzles with small pressure drops through each set of nozzles and complete velocity dissipation in each row of rotating buckets. The pressure compound stages are also called Rateau impulse stages. b. Reaction Stages – are composed of one stationary row of blades and one rotating row of blades with a pressure drop occurring in each stationary and rotating row. 12.2.2 Cylinder Arrangement a. Single cylinder - With all rotating blades attached to one shaft and the steam flow all in one direction. b. Double flow units - Single cylinder units with steam entering in the center and flowing in two equal quantities, but in opposite directions along the shaft. c. Tandem-compound units 10
E. STEAM POWER PLANT - LECTURE
12.2.3 12.2.4
12.2.5
12.2.6
d. Cross-compound units - Differ from tandem-compound units only in that the high- and low-pressure ends are not on the same shaft. e. Steeple- or vertical-compound units Back Pressure Initial Temperature and Pressure High Pressure – 1800 to 2400 psig range. Supercritical Pressure – Above 3206 psig. Low Pressure – 200 to 400 psig range. High Temperature – Inlet temperature above 900 F. Reheat Reheat turbine – when steam is extracted from the turbine and its temperature increased (usually in the steam generator) before being returned to the turbine. Other Methods a. Single-stage or multistage units b. Mixed-pressure units c. High or low speed turbines d. Nonextraction or extraction turbines e. Uses – stationary, marine, or mechanical-drive turbines.
13. Power Rating Mechanical drive turbines are rated in horsepower; turbine-generator units, in kilowatts. Internal power – is the product of torque and rotor speed. Nominal rating – is a declared power capacity expected to be the maximum load. Capability – is the manufacturer’s guaranteed maximum continuous output for a clean turbine, operating under specific throttle and exhaust conditions, with full extraction at any openings, if provided. Overload capacity – is the difference between capability and rating. 14. Willan’s Line Willan’s line – is a straighlt line which shows the relation between the steam consumption in lb per hr and the load in kW of a steam turbine generator unit.
11
E. STEAM POWER PLANT - LECTURE Note that the Willans line for throttle governing and for an infinite number of governor valves is a straight line and will conform to the general equation y = a + bx Where
y = throttle steam flow, lb per hr a = no-load steam consumption, lb per hr b = slope of the curve, lb per kwhr x = load, kw
15. Performance of Steam Turbines
15.1
Ideal Turbine Work Wt = ms (h1 − h2 ) where:
h1 = enthalpy of steam entering h2 = enthalpy of steam after ideal (isentropic) expansion 15.2
Actual Turbine Work Wt = ms (h1 − h2a ) = ms (h1 − h2 )ηst where: h2a = enthalpy of steam after actual expansion hst = stage efficiency
15.3
Turbine Power Output Wt = ms (h1 − h2 )ηt = ms (h1 − h2 )ηstηm where: ηt = turbine efficiency = ηst x ηm ηm = mechanical efficiency
15.4
15.4
Electrical or Generator Efficiency Generator output ηe = Turbine output Generator output = Turbine Output x ηe = ms(h1 – h2)ηtηe 12
E. STEAM POWER PLANT - LECTURE 15.5
Thermal Efficiency 15.5.1 Brake thermal efficiency Turbine output eb = ms (h1 − h f 2 ) 15.5.2 Combined or overall thermal efficiency Generator output ec = ms (h1 − h f 2 ) 15.5.3 Ideal Rankine thermal efficiency h −h er = 1 2 h1 − h f 2
15.6
Engine Efficiency of Turbine 15.6.1 Brake engine efficiency Brake power η eb = ms (h1 − h2 ) 15.6.2 Combined or Overall engine efficiency Generator output η ec = ms (h1 − h2 )
16. Steam Condensers Steam condenser – a heat exchanger where steam enters at the top and the condensate is collected in the hot well at the bottom while cooling water flows through the tubes. 17. Functions of Steam Condenser a. To convert steam to liquid before entering the steam-generating unit. b. To create a vacuum at turbine exhaust thereby increasing turbine power. 18. Classification of steam condensers a. Surface condenser – where steam and cooling water are not allowed to mix; commonly shell and tube design.
13
E. STEAM POWER PLANT - LECTURE b. Direct-contact condenser (mixing) – also called jet condensers , where steam and cooling water are allowed to mix.
19. Heat Balance in Condenser
mw c p (t 2 − t1 ) = ms (hs − h f )E
where: cp = 4.187 kJ/kg-C or 1.0 Btu/lb-F E = heat extraction factor
20. Vacuum Efficiency, hvac p −p ηvac = atm cond patm − psat where: patm – atmospheric pressure pcond – absolute condenser pressure psat – saturation pressure 21. Feedwater Heater Terminal difference – is the difference between the saturation temperature of the steam in the heater and the temperature of the water leaving the heater. Subcooling – the reduction below saturation temperature. 14
E. STEAM POWER PLANT - LECTURE Open heaters or Contact heaters – are feedwater heaters that function by mixing steam with the feedwater. Deaerator – a contact heater especially designed to remove the noncondensable gases. 22. Feedwater Pumps and Boiler Feed Pump Boiler feed pump – whose function is to increase the pressure existing on a liquid an increment sufficient to the required service.
Pump Work = m(h2 − h1 ) Pump Work ≈ mv1 (p2 − p1 ) Pump Work = mgH where: m = mass flow rate, kg/s v1 = specific volume, m3/kg p1 = entrance pressure, kPa p2 = exit pressure, kPa H = head, m
Pump input power (Brake power of the pump) =
Pump Work Pump Efficiency
23. Steam Engines Steam engines – where steam is admitted to the engine cylinder at throttle pressure during the first part of the working stroke, then cut off by closure of the steam valve. The steam so trapped in the cylinder expands adiabatically to the release pressure, then is exhausted from the cylinder during part of the return stroke. Steam engines are double-acting and the process is isentropic.
15
E. STEAM POWER PLANT - LECTURE 23.1
Ideal p-V Diagram
23.2
Piston Volume Displacement Piston rod neglected: π VD = 2 D 2 LN 4 Piston rod considered: π π VD = D 2 LN + D 2 − d 2 LN 4 4 Indicated Power IP = pmiVD pmi = indicated mean effective pressure Area of Diagram pmi = × Spring Scale Length of Diagram
(
23.3
23.4
)
Brake Power BP = 2πTN where: T = torque, kN-m N = speed, rev/s Using brake mean effective pressure, pmb BP = pmbVD
23.5
Friction Power Friction Power = Indicated Power – Brake Power FP = IP – BP
23.6
Mechanical Efficiency Brake Power ηm = Indicated Power
16
E. STEAM POWER PLANT - LECTURE 23.7
Thermal Efficiency a. Indicated thermal efficiency Indicated Power ei = ms (h1 − h f 2 ) b. Brake thermal efficiency Brake Power eb = ms (h1 − hf 2 )
23.8
Engine Efficiency a. Indicated engine efficiency Indicated Power ηi = ms (h1 − h2 ) b. Brake engine efficiency Brake Power ηb = ms (h1 − h2 )
23.9
Efficiency of Equivalent Rankine Cycle h −h er = 1 2 h1 − h f 2
24. Combined Cycle Power Plant Combined gas turbine-steam cycle – is employed to transfer heat carried by the flue gas in the gas turbine cycle to the feedwater in the steam cycle; the heat exchanger performs the function of a boiler.
Schematic Diagram
17
E. STEAM POWER PLANT - LECTURE
Gas Turbine Cycle: Net Work of the Cycle, Wnet = ma [(hc − hd ) − (hb − ha )] = ma c p [(Tc − Td ) − (Tb − Ta )] Heat Added in the Combustion Chamber, QA = ma (hc − hb ) = ma c p (Tc − Tb ) Heat Loss in the Heat Exchanger, QL = ma (hd − hc ) = ma c p (Td − Tc ) Steam Cycle: Net Work of the Cycle, Wnet = ms [(h1 − h2 ) − v 3 (p4 − p3 )] Heat Gained in the Heat Exchanger, QG = m fw (h1 − h4 ) = ms (h1 − h4 )
Thermal Efficiency of the Combined Cycle, W W + WnetS ek = net = netG QA QA Energy balance in the heat exchanger, Heat lost by exhaust gases = heat gained by feedwater ma c p (Td − Tc ) = ms (h1 − h4 )
ms =
ma c p (Td − Tc ) h1 − h4
where: ms = steam mass flow rate ma = air mass flow rate
25. Binary Mercury-Steam Cycle Power Plant Binary mercury-steam cycle - is employed to transfer heat carried by the mercury in the mercury vapor cycle to the feedwater in the steam cycle; the heat exchanger performs the function of a boiler.
18
E. STEAM POWER PLANT - LECTURE
Schematic Diagram
Overall Turbine Work, Wt = Whgt + Wst = mhg (ha − hb ) + ms (h1 − h2 ) Overall Pump Work, Wp = Whgp + Wsp = mhg (hd − hc ) + ms (h4 − h3 ) Wp = mhg v c (pd − pc ) + ms v 3 (p4 − p3 )
Heat Added in the Mercury Boiler, QA = mhg (ha − hd ) Thermal Efficiency of Binary Cycle, W − Wp W eb = net = t QA QA
Energy Balance in the Heat Exchanger, Heat lost by the mercury – heat gained by water mhg (hb − hc ) = m fw (h1 − h4 ) m fw = ms
Thus,
mhg =
m fw (h1 − h4 ) hb − hc
where: ms = steam mass flow rate mfw = feedwater flow rate mhg = mercury flow rate
19
E. STEAM POWER PLANT - LECTURE 26. Cogeneration Steam Power Plant The terms cogeneration and CHP are used interchangeably paper and are defined as the combined simultaneous generation of heat and electrical energy with a common source of fuel. Common examples of cogeneration applications include pulp and paper mills, steel mills, food and chemical processing plants, and District Heating (DH) applications. Schematic Diagram
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20
F. CHIMNEYS AND STACKS - LECTURE 1. Definition Chimneys and stacks – are used to dispose the exhaust gases at a considerable height and produce the necessary draft for the flow of the gases. Chimneys indicating brick or concrete construction and stacks designating steel construction. 2. Functions of Chimney a. To dispose the exhaust gases at suitable height so that no pollution will occur in the vicinity. b. To produce the necessary draft required for the flow of the gases. 3. Calculation of Chimney Diameter and Height
Let D = internal diameter of chimney, meters (for tapered chimney, D is the internal diameter at the top). H = height of chimney, meters. Ta = temperature of air, K . Tg = average temperature of flue gases, K. Ra = gas constant of air = 0.287 kJ/kg-K Rg = gas constant of flue gas = 8.3143/MWfluegas ( same as for air if MW not given) P = barometric pressure, kPa = 101.325 kPa Height: pt = draft pressure = H (ρ a − ρ g )g , Pa p , kg/m3 RaTa p ρ g = density of flue gases = , kg/m3 RgTg
ρ a = density of air =
Tg = average temperature flue gases =
H=
T1 + T2 ,K 2
pt (ρa − ρg )g , meters
For purposes of stack design it is customary to assume that the barometric pressure decreases 0.1 in. Hg for each one hundred-foot rise in elevation. 1
F. CHIMNEYS AND STACKS - LECTURE
Diameter: Volume flow of flue gases Qg = AV = Qg =
π
4 mg RgTg
D 2V
, m3/s
p Theoretical Velocity of flue gas in chimney p Vt = 2 t , m/s
ρg
Actual velocity of flue gases in chimney is only 30% to 50% of theoretical velocity, thus to get the actual velocity, multiple the theoretical velocity by a velocity coefficient of 0.30 to 0.50. Usual assumption is 0.40 for Cv. V = C vVt Then, 4Qg D= πV
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2
G. GEOTHERMAL POWER PLANT - LECTURE 1. Definitions: Magma – molten metal within the earth which is basically nickel-iron in composition whose stored energy heats the surrounding water thereby producing steam or hot water. Well-bore product – the effluent coming out from the geothermal well as produced after drilling. This can be purely steam or hot water, or a mixture of both. Steam-dominated geothermal field (Vapor dominated) – refers to a geothermal plant with its well producing all steam as the well-bore product. Liquid-dominated geothermal field (Hot Water dominated) – the well-bore product for this type of field is practically all hot water, pressurized. Sources of Geothermal Energy a. Hot spring b. Steam vent c. Geyser Fumarole – a crack in the earth through which the geothermal substances passes. 2. Geothermal Sources 2.1 Hydrothermal fluids Hydrothermal fluids – basically made up of hot water, steam and minerals. It is the only form of energy currently being tapped for significant commercial heat and electric energy supply. 2.2 Geopressurized brines Geopressurized brines – represents a special subject of hydrothermal fluids typically found in depths exceeding 3 km and is characterized as hot water existing at pressures above the normal hydrostatic gradient and containing dissolved methane. 2.3 Hot dry rock Hot dry rock – is a water-free, impermeable rock at high temperature and practically drilling depth to extract energy, high-pressure water may be injected through one or more wells to create new or to enhance existing natural fracture system with limited access to ground water flow. 2.4 Magma Magma – is characterized by motion or partially molten rock with temperature reaching as high 1200 C. 3. Applications of Geothermal Energy 3.1 Electric power generation Geothermal energy available at temperature above 150 C is most suitable for electricity production. 3.2 Space heating and cooling 3.3 Industrial applications – includes preheating, washing, cooking, blanching, peeling, evaporating, drying and refrigeration. 3.4 Agricultural applications – includes greenhousing, aquaculture, soil warming and biogas generation. 3.5 By-products – certain compounds such as boron and calcium chloride can be recovered from geothermal fluids as by-products.
1
G. GEOTHERMAL POWER PLANT - LECTURE 4. Types of Geothermal Power Plants 4.1 Dry or superheated steam Dry or superheated steam – geothermal source is vapor-dominated (characterized by dry or superheated steam); steam directly runs the turbine.
4.2 Separated steam or single-flashed Separated steam or single-flashed – geothermal source is hot water-dominated (characterized by mixture of steam and hotwater); employs the use of steam separator; re-injects hot water, steam goes to turbine.
4.3 Separated steam/hot water-flashed or double flashed Separated steam/hot water-flashed or double flashed – where flasher is employed and located at the hot waterend of the steam separator; purpose is to further extract the steam which were not extracted in the separator; such steam is then directed to the turbine’s low-pressure side.
2
G. GEOTHERMAL POWER PLANT - LECTURE 4.4 Single-flashed with pumped well Single-flashed with pumped well – employs down-hole pump in production wells for better steam recovery.
4.5 Binary geothermal plant Binary geothermal plant – like the binary mercury-steam cycle, it uses two working fluids, one is the steam from the production well, the other is feedwater; the heat exchanger serves the function of the boiler.
5. Performance of Flashed-Steam Geothermal Plant
T-s Diagram
3
G. GEOTHERMAL POWER PLANT - LECTURE Mass flow rate of steam entering the turbine, ms: Throttling process 1-2 h1 = h2 = h f 2 + x 2 h fg 2 ms = x 2 mg
where: x2 = quality of steam after throttling mg = mass flow rate of ground water from wells Turbine Work, Wt: Wt = ms (h3 − h4 )ηt where: ηt = turbine isentropic efficiency Generator power output, EP EP = Wtη e where: ηe = generator efficiency Heat rejected in condenser, QR QR = ms (h4 − h5 ) Overall plant efficiency, eo W eo = t mg h1 6. Installed and fully operational geothermal power plants in the Philippines a. Tiwi Geothermal Power Plant, 330 MW. Location: Albay. b. Makiling-Banahaw (Mak-Ban) Geothermal Power Plant, 3309 MW. Location: Los Banos, Laguna. c. Tongonan Geothermal Power Plant, 112.5 MW. Location: Leyte. d. Palimpinon-Dauin Geothermal Power Plant, 112.5 MW. Location: Negros Oriental -
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4
H. HYDRO-ELECTRIC POWER PLANT - LECTURE 1. Basic Elements in Hydro-Electric Power Plant.
1.1 Storage Reservoir or Reservoir Reservoir – used to store water during rainy days and supply the same during the dry season. Also stores the water coming from the upper river or water falls. 1.2 Spillway Spillway – a weir in the reservoir which discharges excess water so that the head of the plant will be maintained. 1.3 Dam Dam - the concrete structure that encloses the reservoir used for impounding the water for storage and for creating head for the power plant. 1.4 Intake Structure or Equipment Intake structure – consists of racks or screens to prevent trash or entry of debris into the turbine runners. 1.4.1 Silt Sluice – a chamber used to collect and discharge mud. 1.4.2 Trash rack – a screen which prevents leaves, twigs, branches and other water contaminants to enter the penstock. 1.5 Water way 1.5.1 Open channel 1.5.2 Penstock – a pressure conduit which leads water from reservoir to turbine. 1.5.3 Tailrace – a channel which leads water from turbine to tailwater. 1.6 Surge Tank or Chamber 1.6.1 Surge Tank - is used to reduce the water hammer during decrease in turbine load. 1.6.2 Surge Chamber – a standpipe connected to the atmosphere and attached to the penstock so that the water will be at atmospheric.
1
H. HYDRO-ELECTRIC POWER PLANT - LECTURE 1.7 Powerhouse Powerhouse – consists of building structure of hydraulic and electrical equipment which includes the following: a. Hydraulic turbines b. Speed governors c. Generators d. Switchgears e. Pressure relief valves f. Isolation valves g. Transformers 1.8 Draft Tube Draft tube – an integral part of reaction turbine used to recover energy head. It connects the turbine outlet to the tailwater so that the turbine can be set above the tailwater level. 1.9 Forebay 1.10 Turbine – converts the energy of the water into mechanical energy. 1.11 Generator – converts the mechanical energy of the turbine into electric energy output. 1.12 Tailwater – the water that is discharged from the turbine. 2. Types of Hydraulic Turbines 2.1 Impulse (Pelton) Turbine – is also known as tangential wheel or Pelton wheel, it utilizes kinetic energy of high velocity jet which acts upon a small part of the circumference at an instant.
2.2 Reaction turbine – develops power from the combined action of pressure and velocity of the water that completely fills the runner and water passages. 2.2.1 Francis Turbine – low head and high efficiency.
2.2.2
Propeller-Type(Axial Flow) – very low head and efficiency is lower than Francis a. Fixed Blade b. Adjustable blade or Kaplan 2
H. HYDRO-ELECTRIC POWER PLANT - LECTURE
3. Classification of Hydro-Electric Power Plants according to the: 3.1 Available head for power generation. a. Low head – 6 m to 30 m b. Medium head – 30 m to 150 m c. High head – 150 m and above 3.2 Nature of load or function. a. Base-load plant b. Peak-load plant 3.3 Quantity of water available for power generation. a. Run-of-river plant without pondage b. Run-of-river plant with pondage c. Storage reservoir hydro plant (most common in RP) d. Pumped storage hydro plant
4. Run-of-the River (Low Head) Hydro-Electric Power Plant
Pondage – the water behind the dam of a run-of-the-river hydro-electric plant. 5. Pumped Storage Hydro-Electric Plant or Hydraulic Accumulator Pumped storage plant – is a hydro-electric plant which involves the use of off-peak energy to store water and to use the stored water to generate extra energy to cope with the peak load.
3
H. HYDRO-ELECTRIC POWER PLANT - LECTURE
6. Performance of Hydro-Electric Power Plant. 6.1 Gross head, hg Gross head, hg – is the difference between the head water and tailwater elevation. 6.2 Friction head loss, hf hf = f
L V2 - Darcy Equation D 2g
where: f = coefficient of friction. L = total length of pipe, in meters V = velocity, m/s g =9.81 m/s2 D = inside diameter, meters (Friction head loss is usually expressed as a percentage of the gross head). 6.3 Net head or effective head, h h = hg − h f 6.4 Penstock efficiency or pipeline efficiency, ep effective head on impulse turbine ep = gross head on impulse turbine ep =
h hg
6.5 General flow equation Q = AV where: Q = volume flow rate, m3/s A = cross-sectional area, m2 V = velocity, m/s 4
H. HYDRO-ELECTRIC POWER PLANT - LECTURE 6.6 Water power, WP WP = γQh = ρgQh kW Where: γ = specific weight of water = 9.81 kN/m3 ρ = density of water = 1000 kg/m3 6.7 Turbine output, Wt Wt = γQhηt = ρgQhηt kW Where: ηt = turbine efficiency 6.8 Generator output, EP EP = γQhηtη e = ρgQhηtηe kW Where: ηe = electrical or generator efficiency 6.9 Generator speed, N 120 f N= p where: N = speed, rpm f = frequency (usually 60 Hz) p = number of poles (even number) 6.10
Utilized head hw = hηh where: ηh = hydraulic efficiency
6.11
Head of Pelton (impulse) turbine
h=
p V2 + γ 2g
where: V = velocity of jet p = inlet gage pressure g = 9.81 m/s2 6.12
Head of Reaction (Francis and Kaplan) turbine
h=
p
γ
+Z+
VA2 − VB2 2g 5
H. HYDRO-ELECTRIC POWER PLANT - LECTURE
6.13
Peripheral coefficient (relative speed or speed ratio), θ Peripheral Velocity πDN θ= = Velocity of Jet 2gh where: D = diameter of runner, meters N = speed of runner, rev/sec g = 9.81 m/s2 h = net head, meters
6.14
Specific speed, Ns Specific speed – defined as the number of revolutions per minute at which a given runner would revolve if it were so reduced in proportions that it would develop 1 hp under one foot head; it serves to classify a hydraulic turbine and to indicate its type. N HP H5 4 where: N = turbine runner rotative speed, rpm HP = horsepower output per runner H = available head acting on turbine per stage in feet. Ns =
7. Identification of hydraulic turbine type based on available head and specific speed. Hydraulic Turbine Type Available Head, m Impulse 800 and up Reaction (Francis) 50 to 800 Reaction (Propeller – Kaplan) 15 to 100 -
End -
6
Specific Speed 5.5 to 80 22 to 80 85 to 170
I.
NUCLEAR POWER PLANT - LECTURE
1. Typical Nuclear Power Plant
2. Definitions Isotopes – are forms of an element that have the same chemical properties but different atomic weights because of different numbers of neutrons in the atom. Alpha particles – carry a positive charge and have a mass of 4. They are composed of two protons and two neutrons; thus, they are the nucleus of the helium atom. Beta particles – are electrons emitted from the nucleus of an atom. Gamma rays – are similar to X-rays in that they are electromagnetic. Fusion process – is the combination of light elements into heavier elements. Fuel core – are radioactive materials, U235 with U238, which is the source of energy. Moderator – slows down the neutrons to thermal energy, made of carbon and beryllium. Control rods – are boron coated steel rods used to control the reactor, also called neutron-absorbers. Reflector – made of lead or carbon which surrounds the core to bounce back any leakage of neutrons. Thermal shield – prevents escape of radiation from reactor vessel. Reactor drum – encloses the fuel core and components.
1
I.
NUCLEAR POWER PLANT - LECTURE
Biological shield – concrete or lead which absorbs any leakage of radiation and protects operators from exposure to radioactivity. Control crucible – contains the meters that show the operating quantities in the reactor. Containment vessel – prevents spread of radiation in case of a major explosion, made of concrete. Coolant – absorbs the heat from the fuel core and then release the heat to the water in the steam generator. Coolant pump – circulates the coolant. Turbine-generator – generates electric power. Condenser – converts steam coming from the turbine into liquid. Feedwater pump – delivers the feedwater to the steam generator. 3. Nuclear Reactors Nuclear reactors – are assemblies of fissionable and other materials so arranged and in sufficient quantities so as to be capable of supporting a chain reaction. 4. Nuclear Reactor Materials 4.1 Fissionable material or fuel Uranium 92U235, 92U233 Plutonium 94Pu239 4.2 Fertile materials Uranium 92U238 Thorium 90Th232 4.3 Coolant 4.4 Moderator 4.5 Structure (including reflectors, container, and shielding material). 5. Types of Reactors 5.1 Pressurized water reactor (PWR) – where there is primary coolant circuit containing water at high temperature and pressure, typically 270 C and 2000 psi. Attached to this is a steam-generating unit which then supplied the turbine. This type of reactor uses high pressure light or heavy water as both moderator and coolant. This is the type constructed in Morong, Bataan with a capacity of 620 MW and intended to supply power to the Luzon area. 5.2 Boiling water reactor (BWR) – this is the simplest form of nuclear reactor. The feedwater from the power turbine goes directly into the reactor and picks up the heat from the fuel core. Thus the feedwater serves as the coolant. The first experimental reactor installed in Diliman, Quezon City is of this type. It has a capacity of 1 MW. 5.3 Heavy water reactor (HWR) – This is the first alternative to the light-water types as it is still liquid-cooled and can either be pressurized-coolant or boiling-coolant type. It uses heavy water or deuterium as coolant. 2
I.
NUCLEAR POWER PLANT - LECTURE
5.4 Gas-cooled Reactors (GCR) – these were suggested as far back as 1943 but were discarded in favor of watercooled types for fear regarding the leakage of the chosen coolant, helium. 5.5 Fast reactors – a reactor containing no moderator and employ fast or high-energy neutrons. 5.6 Thermal reactor – wherein the neutrons have been slowed down. 5.7 Intermediate reactors – employ neutrons having an energy somewhere between fast and thermal reactors. 5.8 Heterogeneous reactors – where fissionable material for a reactor is in the form of a lump. 5.9 Homogeneous reactors – where the fuel may be in a liquid form. The fuel is a salt, such as uranium sulfate, and is mixed with moderator, which is water. -
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J. NON-CONVENTIONAL ENERGY SOURCES - LECTURE 1. Non-conventional Energy Sources Non-conventional Energy Sources – also referred to as renewable energy sources, these are actually energy flows which are replenished as they are used, hence, the use of the term renewable. These are characterized by a maximum theoretical rate at which energy may be extracted in a renewable mode, that is, the rate at which new energy is arriving or flowing into the reservoirs associated with many of the renewable energy flows. All forms of energy sources with the exception of geothermal energy, salinity gradient and tidal energy are indirect manifestations of solar energy. 2. Solar Energy There are many applications for the direct use of solar thermal energy, space heating and cooling, water heating, crop drying and solar cooking. Solar Constant = 1353 W/m2 Useful energy from the sun is between 10 AM – 2 PM = 1000 W/m2 3. Solar Radiation Phenomena a. Atmospheric scattering by air molecules, water vapor, dust. b. Atmospheric absorption by O3 (ozone), H2O, CO2. 4. Forms of Solar Radiation a. Beam or direct radiation – without having beam scattered by the atmosphere. b. Diffuse radiation – direction is changed by scattering. c. Total or global solar radiation – the sum of beam and diffuse radiation. 5. Pyranometer Pyranometer – is the instrument used to measure the total solar radiation. 6. Photovoltaic Cell Photovoltaic cell – is a device which converts solar energy to electrical energy. 7. Solar Collectors Solar Collectors – whose ideal characteristics are high absorptivity and low emissivity. 7.1 Flat Plate Collectors (FPC) a. Area absorbing solar radiation is the same as the area intercepting solar radiation. b. Uses both beam and diffuse radiation. c. Does not require orientation. d. Little maintenance. e. Working fluid is either air or water. f. Measure of performance is by means of collection efficiency. Collection efficiency = useful gain / incident solar radiation. 7.2 Focusing or concentrating collectors a. Utilize optical systems, either reflectors or refractors. b. Uses beam radiation only. c. Needs tracking. 1. Total or full-tracking. 2. Fixed-reflector, tracking-receiver. 3. Fixed-reflector, tracking-reflector. 1
J. NON-CONVENTIONAL ENERGY SOURCES - LECTURE d. Measure of performance is by means of concentration ratio. Concentration ratio = aperture area / receiver area e. Classifications 1. Plane receiver, plane reflectors 2. Parabolic concentrators. 3. Fresnel reflectors or refractors 4. Array or heliostat (reflectors) f. Concentrator types. The purpose of concentrator is to increase the flux of radiation n receiver. 1. Cylindrical: focus on a line. 2. Circular: photovoltaic cell. 8. Conversion and Applications of Solar Energy 8.1 Solar water heating systems (swsh). a. Flat plate collector, storage tank, auxiliary heating equipment. b. Classifications: 1. Natural circulation system – tank is located above collector, no circulation at night, auxiliary equipment may be needed. 2. Forced circulation system – requires a pump to circulate water, tank may not be located above collector, employs check valve whose purpose is to prevent reverse circulation of water and to prevent nighttime thermal losses from the collector. 8.2 Solar space heating. a. Ho t air systems b. Hot water systems 8.3 Solar space cooling. a. Continuous 1. Closed a. Absorption system b. Solar vapor-compression system. e.g. lithium bromide (LiBr) – water. 2. Open a. Liquid desiccant b. Solid desiccant b. Intermittent 1. Liquid absorbent 2. Solid absorbent 8.4 Solar power conversion a. Photovoltaic (PV) devices or solar cells 1. Single crystal silicon – most widely-used and technically-developed. 2. Cadmium-sulfide (CdS). 3. Gallium arsenide 4. Thermoelectric and thermionic b. Solar thermal electric power (STEP).
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J. NON-CONVENTIONAL ENERGY SOURCES - LECTURE 9. Wind Power Winds – are a result of air motion caused by uneven heating of the earth’s surface by the sun and rotation of the earth. 10. Typical uses of wind power. a. To drive water pumps. b. To drive rice and corn mills. c. To charge batteries. d. To generate power. 11. Types of windmills. a. Turbine type b. Rotor type c. Propeller type d. Dutch sail type e. Panemone type 12. Types of wind energy collectors a. Horizontal-axis rotors – axis of rotation is parallel to the direction of the wind; can be either lift or drag-type; yaw-active, meaning it changes position depending on wind direction. b. Vertical-axis rotors – do not have to be turned into the wind as wind stream direction changes, design is simplet. 1. Savonius rotors – employ S-shaped blades and are primarily drag devices. 2. Darrieus rotors c. Cross-wind horizontal-axis rotors 13. Conversion and Applications of Wind Energy a. Water pumping which could be used directly for irrigation. b. Used to compress air for use in a variety of applications including operating electricity during peak demand periods of a public utility system. c. Used in centralized utility applications to drive synchronous AC electrical generators. d. Used for direct heat applications. e. Used in the production of hydrogen by electrolysis of seawater (in the case of off-shore winds). 14. Wind Energy Storage Systems a. Batteries in the form of chemical energy. b. Pumped-hydro storage energy. c. Compressed air storage systems. d. Hydrogen gas produced from pyrolysis of water. e. Thermal energy storage systems. f. Flywheel 15. Site selection Wind power is proportional to the cube of the wind velocity. Factors to be considered a. Windshear. b. Turbulence, or rapid change in speed and/or direction. c. Acceleration or retardation.
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J. NON-CONVENTIONAL ENERGY SOURCES - LECTURE 16. Wind Power Performance Betz’s law – is a theory about the maximum possible energy to be derived from a wind turbine. The ideal or maximum theoretical efficiency, also called power coefficient, of a wind turbine is the ratio of maximum power from the wind to the total power available in the wind. The factor 0.593 is known as Betz’s coefficient. It is the maximum fraction of the power in a wind stream that can be extracted. Total power available from the wind 1 Ptotal = ρAV 3 2 Maximum available power from the windmill 1 Pmax = ρ AV 3η c 2 where: ρ = wind density A = swept area =
π 2 D 4
V = wind velocity D = blade diameter 17. Bio-Energy or Bio-mass Biogas is a good fuel. Have you thought how this is formed? Biomass like animal excreta, vegetable wastes and weeds undergo decomposition in the absence of oxygen in a biogas plant and form a mixture of gases. This mixture is the biogas. Its main constituent is methane. This is used as a fuel for cooking and Lighting. 18. Aerobic and anaerobic bio-conversion process a. Bioproducts: Converting biomass into chemicals for making products that typically are made from petroleum. b. Biofuels: Converting biomass into liquid fuels for transportation. c. Biopower: Burning biomass directly, or converting it into a gaseous fuel or oil, to generate electricity. 19. Bio-mass source a. Manure b. Crop residues c. Fuel wood d. Sugar crops e. Urban refuse: paper, yard and food wastes f. Municipal sewage-sewage sludge: 0.02 – 0.03% solids, above 99% water g. Aquatic plants: water hyacinth h. Energy farming: denthrothermal or energy crops 1. Fast-growing trees: ipil-ipil 2. Sugar and starch crops: cassava in ethanol production 3. Oil and hydrocarbon crops: coconut oil 4. Herbaceous crops
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J. NON-CONVENTIONAL ENERGY SOURCES - LECTURE 20. Bio-mass Conversion Processes a. Biochemical: introduction of microorganisms 1. Ethanol fermentation 2. Anaerobic digestion b. Thermochemical 1. Pyrolysis – an irreversible chemical change caused by the action of heat in the absence of oxygen. 2. Combustion/gasificiation Gasification – is the conversion of a solid fuel to a combustible gas as a means of thermochemical reaction. Complete combustion takes place with excess oxygen or at least 100% theoretical oxygen, whereas gasification takes pace with an oxygen deficit. 21. Advantages a. Inexpensive b. Low sulfur content c. Reduces environmental hazard d. Convertible to gaseous/liquid fuels e. Less CO2 build-up f. Generates additional employment g. Simple to store 22. Disadvantages a. Low thermal content, only about 20 MJ/kg b. High moisture content, approximately 50% c. Low bulk density d. Transpo uneconomical e. Rarely homogeneous f. Low concentration 23. Tidal Power Tidal power – is basically hydro-electric power utilizing the difference in elevation between high and low tide to produce energy. A basin is required to catch the sea water during high tide while the water drives the turbine. In the Philippines, commercialization is not full-scale since it is found that the average difference is only about 6 meters. 24. Ocean Thermal Energy Conversion (OTEC) This is otherwise known as low thermal head plant, it utilizes the temperature difference between the ocean surface water and the water at the sea bottom. Surface water which is at relatively high temperature is pumped to an evaporator where the water evaporates into saturated steam. This steam drives a single stage turbine thereby producing electricity, and exhaust to a jet condenser maintained at the saturation pressure of the subsurface water temperature pumped from the sea bottom. 5
J. NON-CONVENTIONAL ENERGY SOURCES - LECTURE In the Philippines, full-scale commercialization is also not economically-viable because of the small temperature difference out waters have. 25. Magneto Hydrodynamic Plant Magneto hydrodynamic generator – where combustion gases produced in a combustion chamber at high pressure and temperature and seeded with metal vapor to increase its electrical conductivity, is passed through an expansion tube lined with a strong magnetic field. This induces an electric voltage in the gas conductor and effect the flow of electrons through the electrodes along the magnetic field, thereby generating electricity. 26. Thermionic Converter Thermionic converter – is a device which converts heat energy directly to electrical energy. All metals and some oxides have free electrons which are released on heating. These electrons can travel through a space and collected on a cooled metal. These electrons can return to hot metal through an external load thereby producing electrical power. 27. Fuel Cell Fuel cell – is a device which converts chemical energy to electrical energy. Fuel cells produce electricity from an electrochemical reaction between hydrogen and oxygen. Fuel cells are efficient, environmentally benign and reliable for power production. The use of fuel cells has been demonstrated for stationary/portable power generation and other applications. -
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