POWER PLANT ENGINEERING
REVIEWER
(LECTURE)
Revision 0 2012 Prepared By:
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
1 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.
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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 load peak capacity plant peak over serve Re = − hours of no energy hrs kw load Average . − = load peak load average factor Load =
3 energy possible imum max produced energy actual factor Capacity = 8760 × − = capacity plant kw hrs kw annual factor capacity Annual operation hrs of no capacity plant kw hrs kw annual factor Use . × − = load connected demand imum max actual factor Demand = demand eous tan simul imum max demands imum max individual of sum factor Diversity = load the plying sup equipment of rating load average factor Plant = system of capacity rated system of demand imum max factor n Utilizatio = considered time of period the of duration total service actual of duration factor Operation =
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.
1 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.
2 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.
3
Cracked stocks – are residual of fuels which have been treated thermally or catalytically to obtain yields of lighter-grade 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.
water of density fuel liquid of density SG= air of density fuel gaseous of density SG=
4
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,
(
)
[
1 00007 156]
6 15. − . − . =SG t SG C t o in SI units(
)
[
1 00004 60]
60 − − =SG t SG F t o . in English unitsAmerican 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.
5 131 6 15 5 141 . . . − = C at SG API o o
Baume Gravity Unit, oBaume’ or oBe’
- Another standard commonly associated with brine. 130 6 15 140 − = C at SG Baume o o . 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) Or centistokes SSU SSU 180 22 . 0 − = ν
SSF (Saybolt Second Furol) – unit used for very viscous liquids using a relatively large orifice. 62 SSF = 600 SSU
5 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.
6
d. Fixed Carbon – is the difference between 100 % and the sum of the percentages of moisture, ash, and volatile matter.
19.2 Ultimate analysis – analysis of composition of fuel which gives, on mass basis, the relative amounts of carbon, hydrogen, oxygen, nitrogen, sulfur, ash, and moisture.
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. kg kJ S O H HHV 9,304 8 212 , 144 820 , 33 + − + = lb Btu S O H HHV 4050 8 000 , 62 600 , 14 + − + =
22.2.2 ASME Formula for petroleum products
(
API)
kJ kg HHV=41,130+139.6 o(
API)
Btu lb HHV=17,680+60 o22.2.3 Bureau of Standard formula
(
SG)
kJ kg HHV=51,716−8,793.8 2(
SG)
Btu lb HHV=22,230−3780 2Difference 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
7
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.
S O H C Wta 432 8 36 34 53 11 2 2 . . . + − + = 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
8
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.
(
)
ta aa eW W = 1+ ta ta aa W W W e= −where e is the excess air in decimal. 27. Typical Combustion Reaction
Fuel + Air = Product of Combustion
(
n 025m)
O2 376(
n 025m)
N2 nCO2 05mH2O 376(
n 025m)
N2 H Cn m+ + . + . + . → + . + . + .(
)(
)
(
)
m n m n m n m n Wta + + = + × + + = 12 25 0 28 137 12 28 76 3 32 25 0. . . .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.
aa ta W W = φ 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
(
)
ab dg C CO CO O CO W + + + = 2 2 2 3 700 4Boiler test code formula corrected to account for the SO2.
(
)
(
CO CO)
C S S N CO O CO Wdg ab 8 5 8 3 3 7 8 11 2 2 2 2 + + + + + + = 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
r r C A W − = 1
9 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
A W C Cab= − r+ Or 600 14, r r ab HV W C C = − 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.
ab i C CO CO CO C × + = 2
where Ci is the pounds of carbon the CO per pound of fuel burned. 35. Air Actually Used During Combustion
2 2 2 8 8 H O C S N W Waa dg − ab− − − + =
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.
(
)
f w W h h W Q 2 1 1 − = in whichWw = 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
10 b. Energy loss due to dry flue gas.
This loss is the greatest of any of the boiler losses for a properly operated unit.
(
g a)
dg t t W Q2=0.24 − 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.
(
t t)
whent F M Q3= f 1089+0.46 g− f , g <575(
t t)
whent F M Q3= f 1066+0.5 g− f , g >575 whereMf = 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 low-hydrogen coal.
(
h hff)
H Q4=9 2 − 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
(
t t)
whent F H Q4=9 21089+0.46g− f , g<575(
t t)
whent F H Q4=9 21066+0.5g − f , g>575The 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. lb Btu CO CO CO C C Q i ab + = = 2 5 10,160 10,160
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.
11
(
C C)
Btu lb Q =14600 − ab 6 , or r rHV W Q6=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. 6 5 4 3 2 1 7 HHV Q Q Q Q Q Q Q = − − − − − − h. Boiler Heat Balance Tabulation
Item Energy, Btu per lb fuel Percentage
Q1 Q2 Q3 Q4 Q5 Q6 Q7 HHV 100% - End -
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1 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
2 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
3 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 intake stroke
1-2 isentropic compression 2-3 isometric heat intake 3-4 isentropic expansion 4-1 isometric heat release 1-0 exhaust stroke
Heat Added, QA=mcv
(
T3−T2)
Heat Rejected, QR=mcv(
T4−T1)
Net Work, Wnet=QA−QR Net Work, k V p V p k V p V p pdV Wnet − − + − − = =∫
1 1 3 3 4 4 1 1 2 2 Cycle Efficiency = A R A A net Q Q Q Q W e= = − Cycle Efficiency = 1 1 1 − − = k k r eSpecific heat ratio, k = 1.4 for air standard. Clearance volume, Vc = V3 = V2 Compression ratio, c c V V V V rk= = =1+ 3 4 2 1 Clearance ratio, 2 1 2 2 V V V V V c D − = =
where VD = piston volume displacement Other relationship, V3 = V2 and V4 = V1 1 3 1 4 3 3 4 − − = = k k k r T V V T T
4 1 2 1 1 2 2 1 − − = = k k k r T V V T T
Mean effective pressure, Cut-off ratio,
D net m V W p =
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 intake stroke
1-2 isentropic compression 2-3 isobaric heat intake 3-4 isentropic expansion 4-1 isometric heat release
Heat Added, QA=mcp
(
T3−T2)
Heat Rejected, QR=mcv(
T4−T1)
Net Work, Wnet=QA−QR Cycle Efficiency = A R A A net Q Q Q Q W e= = −5 Cycle Efficiency =
(
)
− − − = − 1 1 1 1 1 c k c k k kr r r e Compression ratio, c c V V rk= =1+ 2 1 Cut-off ratio, 2 3 2 3 T T V V rc = =Specific heat ratio, k = 1.4 for air standard. Clearance ratio, 2 1 2 2 V V V V V c D − = = Other relationship, 1 1 1 2 1 1 2 − − = = kk k r T V V T T c k k k r r T V V T T 1 1 1 2 3 2 3 − − = = k c r T T4= 1
Mean effective pressure, Cut-off ratio,
D net m V W p =
Cycle Analysis of 2-stroke Diesel Engine
6 0-1 intake heat stroke
1-2 isentropic compression 2-3 isobaric heat intake 3-4 isentropic expansion 4-1 isometric heat release
Cycle Efficiency =
(
)
− + − − − = − − 1 1 1 1 1 1 1 c p p k c p k k r rkr r r r ePressure ratio during constant volume process 2-3, 2 3 p p rp = Cut-off ratio, 3 4 V V rc =
Mean effective pressure, Cut-off ratio,
D net m V W p = 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
7 6.1.6 Starting system
Air compressor, air storage tank 6.1.7 Governing system
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.
Otto Cycle Spark Ignition Diesel Cycle Compression Engine
a. Useful work 25 34
b. Cooling 30 30
c. Exhaust 37 26
d. Friction, radiation, and unaccounted
8 10
Input; heating value of fuel 100 100
9. Performance of Diesel Generating Set 9.1 Heat generated (fuel)
HV m
QA= f kw where:
mf = fuel consumption, kg/s HV = heating value of fuel, kJ/kg 9.2 Volume displacement c p D D LN N V 2 4 π = m3/sec 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
8 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 D
miV p
IP = kw where:
pmi = indicated mean effective pressure
c c c mi L S A p =
VD = piston volume displacement, m3/sec. Ac = area of indicator card diagram. Sc = spring scale.
Lc = length of indicator card diagram. or c p miLAN N p IP = kw
where A = is the area of bore or net piston area.
If working cylinder (wc) and crankcase (cc) are to be considered
cc cc cc wc wc wc mi L S A L S A p = −
Note: crankcase compression is used for scavenging.
9.5 Brake power (BP) c p mbLAN N p BP = Where:
pmb = brake mean effective pressure.
Calculating brake power using either prony brake or dynamometer Tn
BP=2π
where:
T = brake torque, measured by dynamometer. n = engine rotative speed
Also Fr T = where:
F = brake force or brake load. r = brake arm or torque arm.
9 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 mi mb m p p IP power indicated BP power brake = = , , η
9.7.2 Electrical or generator efficiency, he BP power brake EP output electrical o , , = η 9.7.3 Over-all efficiency, ηo e m o IP power indicated EP output electrical η η η = = , , 9.8 Thermal efficiencies
9.8.1 Indicated thermal efficiency, ei, HV m IP fuel by plied sup heat power indicated e f i = =
10 9.8.2 Brake thermal efficiency, eb.
HV m BP fuel by plied sup heat power brake e f b = =
9.8.3 Combined thermal efficiency, ek, HV m W fuel by plied sup heat power electrical e f k k = = 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
ei i=
η
9.9.2 Brake engine efficiency, ηb e
eb b=
η
9.9.3 Combined engine efficiency, ηk e
ek k=
η
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. IP
m mi =3600 f
9.10.2 Brake specific fuel consumption, mb. BP
m
mb f
3600 =
9.10.3 Combined or over-all specific fuel consumption, mk. EP
m mk =3600 f
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. HV
m HRi = i
11 9.11.2 Brake heat rate, HRb
HV m HRb= b
9.11.3 Combined heat rate, HRk HV m HRk= k 9.12 Volumetric efficiency, hv D A v V V nt displaceme Piston entering air of volume Actual = = η p RT m V A A = c p D LAN N V = 9.13 Speed Data 9.13.1 Piston speed, PS PS = 2Ln. m/s 9.13.2 Generator speed, N rpm n f N=120 where: f = frequency, usually 60 Hz p = number of even poles 10. Power developed at an altitude, P
520 92 29 T B P P s = . 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.
12 12. Waste heat recovery boiler utilizing diesel engine exhaust.
By Heat Balance in Boiler:
(
)
s(
s f)
pggc t t m h h m 1− 2 = − where:
cpg = specific heat of exhaust gas.
1 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
2 5. Gas-Turbine Cycle
Brayton cycle – is the theoretical cycle for the gas turbine which is composed of isentropic compression, constant-pressure heat addition, isentropic expansion, and constant-constant-pressure heat rejection. This is known as the simple cycle gas turbine.
Air Standard Ideal Brayton Cycle
1-2 isentropic compression 2-3 isobaric heat addition 3-4 isentropic expansion 4-1 isobaric heat rejection Isentropic compression Process 1-2
2 1 s s = , k k V p V p1 1 = 2 2 1 2 1 1 1 2 1 2 − − = = k k k V V p p T T Compressor Work
(
h2 h1)
mc(
T2 T1)
m Wc = − = p − where cp = 1.0 kJ/kg-K for airPressure ratio = 4 3 1 2 p p p p rp= = Compression ratio = 2 1 V V rk=
Heat addition isobaric process 2- 3 in the combustor
(
T3 T2)
m(
h3 h2)
mc
QA= p − = −
Turbine isentropic expansion Process 3-4 4 3 s s = , k k V p V p3 3 = 4 4 1 3 4 1 4 3 4 3 − − = = k k k V V p p T T Turbine work
(
h3 h4)
mc(
T3 T4)
m Wt= − = p −3 Net Work c t net W W W = −
Heat rejection isobaric process 4-1
(
T4 T1)
m(
h4 h1)
mcQR= p − = − 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 A R A A c t A net Q Q Q Q W W Q W e= = − = − In terms of enthalpy 2 3 1 4 1 h h h h e − − − = In terms of temperature 2 3 1 4 1 T T T T e − − − =
In terms of compression ratio, rk k k k k r r e= − − = − 1− 1 1 1 1
In terms of pressure ratio, rp k k p k k p r r e − − = − − = 1 1 1 1 1
Closed Cycle Gas Turbine
Intermediate temperature for maximum work
(
)
2 1 3 1 2 TT T =4 Considering irreversibilities
Isentropic or adiabatic compressor efficiency (compressor internal efficiency), ηc.
1 2 1 2 1 2 1 2 T T T T h h h h W work compressor actual W work compressor ideal c c c − − = − − = ′ = ′ ′ , , η
Isentropic turbine efficiency (turbine internal efficiency)
4 3 4 3 4 3 4 3 T T T T h h h h W work turbine actual W work turbine ideal t t t − − = − − = ′ = ′ ′ , , η
Actual heat added in the combustor
(
3− 2′)
=(
3− 2′)
=′ mh h mc T T
QA p
Actual thermal efficiency
2 3 1 4 2 3 1 4 1 1 ′ ′ ′ ′ − − − = − − − = T T T T h h h h e − + − − − − = − − − c k k k k c k k t p p T T p p T p p T e η η η 1 1 1 1 1 1 2 1 3 1 1 2 1 1 3 4 3 − − − − − = − − − k k p c k k p c k k p t r r T T T r T T e 1 1 1 1 3 1 1 3 1 1 1 η η η Combustor efficiency fuel by plied sup heat air by absorbed heat ecc=
5 6. Performance of Actual Cycle
Ideal compressor work
(
T2 T1)
cm
Wc = a pa −
Actual compressor work
c c c W efficiency Compressor work compressor Ideal W η = = ′
(
)
(
)
c pa a pa a c T T c m T T c m W η 1 2 1 2 − = − = ′ ′ wherecpa = specific heat of air = 1.0 kJ/kg-K Ideal turbine work
(
m m)
c(
T3 T4)
Wt = a+ f pg −( )
r c(
T3 T4)
m Wt= a + f pg − efficiency turbine work turbine ideal work turbine actual Wt′= = ×(
f)
pg(
)
a(
f)
pg(
)
t a t m r c T T m r c T T W′= 1+ 3− 4′ = 1+ 3− 4 η wherecpg = specific heat of gas rf = fuel to air ratio
6 Heat generated by fuel
(
m r)
HV m HV QA= a f = f where:HV = heating value of fuel Actual net work
aux c t net W W W W′ = ′− ′− Thermal efficiency A aux c t Q W W W′− ′− =
Overall thermal efficiency
A Q output Generator = Combustion Efficiency byfuel plied sup Heat air by absorbed Heat =
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
(
x)
p A mc T T Q = 3−
Heat balance in regenerator
(
x)
p(
y)
p T T mc T T mc − 2 = 4− y x T T T T − 2= 4−7
Effectiveness of the regenerator – is defined as the ratio of actual amount of heat transferred to the amount of that could be transferred reversibly.
reversibly d transferre be could that amount d transferre heat of amount actual r= ε 2 4 2 T T T Tx r − − = ε
For 100% regenerator efficiency, Tx = T4 k k p r T T T T T T e 1 3 1 4 3 1 2 1 1 − − = − − − =
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.
1 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 isentropic (or reversible adiabatic) expansion
2-3 isobaric (or reversible constant-pressure) heat rejection 3-4 isentropic (or reversible adiabatic) compression
4-5 isobaric (or reversible constant-pressure) heat addition
Turbine Work
(
h1 h2)
m2 Actual turbine work
(
)
(
)
t t mh h mh h W′= 1− 2′ = 1− 2 ηHeat rejected in condenser
(
h2 h3)
m QR= −
Actual heat rejected in condenser
(
h2 h3)
m QR= ′− Pump work(
h4 h3)
m Wp = −(
4 3)
3 p p mv Wp ≈ − Actual pump work(
)
p p h h m W η 3 4− = ′(
)
p p p p mv W η 3 4 3 − ≈ ′Head added to boiler
(
h1 h4)
mQA= −
Actual heat added to boiler
(
)
b A h h m Q η 4 1− = where: ηt = turbine efficiency ηp = pump efficiency ηb = boiler efficiencyBoiler 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
(
)
(
)
(
)
(
)
4 1 3 4 2 1 3 1 2 1 h h h h h h W h h W h h Q W W e p p b p t cycle − − − − = − − − − = − =For Rankine engine or turbine (combination with condenser)
3 1 2 1 h h h h eengine − − =
For plant thermal efficiency
HV m EP fuel by plied sup heat output power electrical e f p= =
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
3 4. Reheat Cycle
Reheat cycle- to increase turbine power, increase thermal efficiency
Turbine work
(
h1 h2)
m(
h3 h4)
mWt = − + − Heat added in the boiler
(
h1 h6)
mQAb= −
Heat added in the reheater
(
h3 h2)
m QArh= − Pump work(
h6 h5)
mv5(
p6 p5)
m Wp = − ≈ −Heat rejected in the condenser
(
h4 h5)
m QR= −
Thermal efficiency of reheat cycle
Arh Ab p t A p t cycle Q Q W W Q W W e + − = − = 5. Regenerative Cycle
Regenerative cycle – to improve the cycle efficiency, decrease turbine power, decrease heat addition.
Turbine work
(
h1 h2) (
m m1)(
h2 h3)
m4 Heat added in the boiler
(
h1 h7)
m QA= − Pump work 1(
1)(
5 4) (
1)
4(
5 4)
1 m m h h m m v p p Wp = − − ≈ − − Pump work 2(
7 6)
6(
7 6)
2 mh h mv p p Wp = − ≈ −Heat rejected in the condenser
(
m m1)(
h3 h4)
QR= − −
Heat balance in regenerative heater (feedwater heater or deaerator)
(
1)
5 62
1h m m h mh
m + − =
Thermal efficiency of reheat cycle
(
)
(
)
A p p t A p p t cycle Q W W W Q W W W e = − 1+ 2 = − 1+ 2 6. Reheat-Regenerative Cycle7. 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
5 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
6 9.2.3 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
9.2.4 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.
