L factor method for determining heat rate and emission rates of a fossil-fired system

Abstract

The operation of a fossil-fueled thermal system is quantified by obtaining effluent flow, the L Factor and other operating parameters to determine and monitor the unit's heat rate and to determine the emission rates of its pollutants.

Description

[0002] This invention relates to a fossil-fired power plant or steam generation thermal system, and, more particularly, to a method for determining its heat rate from the total effluents flow, the L Factor and other operating parameters. It also teaches how the EPA's F Factor may be properly used to monitor heat rate with certain precautions. It further teaches how the L Factor may be used to determine the system's emission rates of pollutants from fossil combustion with higher accuracy than afforded from the EPA's F Factor method.

BACKGROUND OF THE INCEPTION

[0003] The importance of determining a system's thermal efficiency (also termed unit heat rate) of a fossil-fired power plant or steam generation system is critical if practical day-to-day improvements in thermal efficiency or heat rate are to be made, and/or problems in thermally degraded equipment are to be found and corrected. Although elaborate analytical tools are sometimes needed, simpler and less expensive methods are also applicable which do not require high maintenance nor the input of complex operational system data, and, also, whose accuracy is not greatly compromised. The L Factor method addresses this need.

[0004] General background of this invention is discussed at length in application Ser. No. 09/273,711 (hereinafter denoted as '711), and in application Ser. No. 09/047,198 (hereinafter denoted as '198). In '711 the L Factor is termed the “fuel factor”.

[0005] As discussed in '711, related art to the present invention was developed by Roughton in 1980; see J. E. Roughton, “A Proposed On-Line Efficiency Method for Pulverized-Coal-Fired Boilers”, Journal of the Institute of Energy, Vol.20, March 1980, pages 20-24. His approach using the L Factor (termed Md/Id in his work) in developing boiler efficiency was to compute system losses such that ηBoiler=1.0 −Σ(System Losses). This is a version of the Heat Loss Method discussed in '711. The principle losses he considered were associated with dry total effluents (termed stack losses), effluent moisture loss and unburned carbon loss. Roughton's method produces boiler efficiency independent of any measured fuel flow and independent of any measured total effluents flow.

[0006] The only related art known to the inventor since '711 and '198 were filed has been the technical paper: S. S. Munukutla, “Heat Rate Monitoring Options for Coal-Fired Power Plants”, Proceedings of Heat Rate Improvement Conference, Baltimore, Md., sponsored by Electric Power Research Institute, September 1998. In this paper Munukutla explains 40 CFR Part 60, Appendix A, Method 19, and the use of its F Factor to determine heat rate. Munukutla makes no mention of correction factors, neither conceptual nor those associated with measurement error. He concludes “. . . that the heat rate, as determined by the F-factor method, is in error by at least 10-20%.” In his “Conclusions” section, Munukutla states that: “The F Factor method may give accurate results, provided the stack gas flow rate and CO2 concentration can be measured accurately.” He makes no mention of the molecular weight, or assumed composition, of the total effluents from combustion. Further, Munukutla explicitly states in his writing and by equation that system heat rate is inversely proportional to the concentration of effluent CO2.

[0007] Related art to the present invention is the EPA's F Factor method, discussed in '711, and whose procedures are specified in Chapter 40 of the Code of Federal Regulations (40 CFR), Part 60, Appendix A, Method 19. Assumed by Method 19 is that an Fc Factor is the ratio of a gas volume found in the products of combustion (i.e., CO2) to the heat content of the fuel.

SUMMARY OF THE INVENTION

[0008] The monitoring of a fossil-fired system may involve detailed and complete descriptive understanding of the fuel being burned, analyses of all major components, and accurate determination of its fuel flow. Such monitoring is possible by applying the Input/Loss Method discussed in '711 and '198. However, for many fossil-fired systems simpler methods are needed which allow the installation of analytical tools which provide an inexpensive, but consistent, indication of a system's thermal performance. From such indication, the system's efficiency may be monitored, deviations found, and corrections implemented.

[0009] This invention discloses such a tool. Its accuracy is not at the level of the Input/Loss Method, but has been found to be within 1% to 2% when monitoring on-line, and, as importantly, has been demonstrate to be consistent.

[0010] This invention employs an L Factor to determine unit heat rate. A heat rate may also be computed using the EPA's F Factor, but with additional error relative to the L Factor, but which may be tolerable. The L Factor and the F Factor may be used to determine heat rate only if certain correction factors are applied as taught by this invention. These correction factors are both conceptual and for routine measurement error.

[0011] The present invention, termed the L Factor Method, determines total fuel energy flow of a fossil-fired system resulting, when the total fuel energy flow is divided by the measured system electrical output, the heat rate of the system results. Acceptable heat rate accuracy is achievable through the demonstrated high consistency found in the L Factor, to which this invention makes unique advantage.

[0012] The L Factor method does not use any part of the Heat Loss Method, it does not compute nor need any thermal loss term as used by Roughton. Unlike Roughton's method, the L Factor method employs certain major flows associated with a fossil-fired system, and principally the total effluents flow.

[0013] This invention is unlike Munukutla's work in several key areas. First, as taught by this invention, system heat rate using the F Factor is directly proportional to the concentration of effluent CO2, not inversely proportional as Munukutla believes. Further, it has occurred during the development of this invention that certain conceptual correction factors must be applied to the L Factor to adequately monitor a fossil-fired system. No corrections of any kind are mentioned by Munukutla. This is significant to this invention for the F Factor affords one method of computing the L Factor (there is another which is preferred), however the sensitivities of the conceptual corrections which have been found to apply to the L Factor, also fundamentally apply to the F Factor. And lastly, Munukutla makes no mention of the molecular weight, or assumed composition, of the total effluents being produced which this invention teaches must be addressed as different fossil fuels produce different mixes of combustion products comprising the total effluents.

[0014] In the process leading to the present invention, several problems existing with the F Factor concept, which is used by Munukutla, have been both clarified and solutions found. These problems include the following: 1) large conventionally fired power plants have air in-leakage which alters the total effluents concentration's average molecular weight from base assumptions; 2) different Ranks of coal will produce different effluent concentrations thus different average molecular weights from base assumptions; 3) circulating fluidized bed boilers are injected with limestone to control SO2, limestone produces CO2 not addressed by the Fc Factor; 4) many poor quality coals found in eastern Europe and from the Powder River Basin in the United States may have significant natural limestone in its fuel's mineral matter, thus producing effluent CO2 not addressed by the Fc Factor; 5) the EPA requires the reporting of emission rates based on measured wet volumetric flow reduced to standard conditions, but the quantity of effluent moisture is not independently measured, whose specific volume varies greatly as a function of its molar fraction thus introducing a major source of error in using volumetric flow; and 6) ideal gas behavior is assumed.

BRIEF DESCRIPTION OF THE DRAWING

[0015] FIG. 1 is a block diagram illustrating the procedures involved in determining unit heat rate using the L Factor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The L Factor

[0017] This invention expands '711 by using its L′Fuel quantity (or its equivalence the LFuel quantity), herein termed the L Factor, also known in '711 as the “fuel factor”, to compute a thermal system's unit heat rate. L′Fuel is defined by Eq.(72) of '711, repeated here with one change:

L′ Fuel =[x Dry-theor N Dry-Fuel +a Dry-theor (1+φRef)NDry-Air−JtheorNH2O−xMAF-theorαMAF-10NAsh]/(xDry-theorNDryFuelHHVDry)  (72A)

[0018] The difference is the term (Ref which was changed from φAct. This invention teaches that φRef must be employed since changes in combustion air's oxygen content should not effect L Factor. The preferred embodiment is to set φRef=3.773725, with a range given as: 3.76≦φRef≦3.79 [i.e., 0.2088≧ARef≧0.2100, where φRef=(1−ARef)/ARef] as effects the determination of the L Factor. The equivalence of L′Fuel is LFuel, and is defined in words between Eqs.(75) and (76) in '711. When the quantities x, a and J of '711 are in per cent, the calculational base is therefore 100 moles of dry gas, thus:

L Fuel =100 xDry-theor NDryGas/theor/(xDry-theor NDry-Fuel HHVDry)   (75A)

[0019] As fully explained in '711, the numerators of the right sides of these two equations are developed from the same mass balance equation involving dry fuel and stoichiometrics associated with theoretical combustion (also called stoichiometric combustion):

[xDry-theor NDry-Fuel+aDry-theor (1+φRef)NDry-Air−Jtheor NH2O−xMAF-theor αMAF-10 NAsh]=100 xDry-theor NDryGas/theor   (80)

[0020] Eq.(80) states that dry fuel, plus theoretical combustion air, less effluent water, less effluent ash results in dry gaseous total effluents associated with theoretical combustion. Eq.(80) is the bases for the L Factor; i.e., when each side of Eq.(80) is divided by xDry-theorNDry-Fuel. This is fundamentally different than EPA's F Factor method. Although Eqs.(72A) & (75A) employ molar quantities, use of molecular weights results in a mass-base for the L Factor, and for Eq.(80). The molecular weight of the dry gas total effluents associated with theoretical combustion is the term NDryGas/theor (the identical quantity is denoted as NDry-Gas in '711), its associated mass-base, or mass flow rate, is denoted as mDryGas/theor. Units for the L Factor are poundsDry-effluent/million-BtuFuel, or its equivalence. The L Factor expresses the “emission rate” for dry gaseous total effluents from theoretical combustion of dried fuel.

[0021] For a coal fuel, having a unique Rank or uniquely mined, the L Factor has been shown to have a remarkable consistency to which this invention makes unique advantage when applied in determining heat rate. Standard deviations for coals range from 0.02% (for semi-anthracite), to 0.05% (for medium volatile bituminous), to 0.28% (for lignite B). Table 1 illustrates this, obtained from F. D. Lang, “Monitoring and Improving Coal-Fired Power Plants Using the Input/Loss Method—Part II”, ASME, 1999-IJPGC-Pwr-34, pp.373-382. Listed in the third and fourth columns are standard deviations, in engineering units. Table 1 also presents moisture-ash-free higher heating values and computed Fc Factors.

TABLE 1
L Factors and FC Factors for Various Coal Ranks
(LFuel and FC in units of lbm/million-Btu, HHV in Btu/lbm)
		Heating Value	L Factor
	No. of	HHVMAF ±	LFuel ±	Computed
Coal Rank	Samples	ΔHHVMAF	ΔLFuel	FC Factor
Athracite	29	14780.52 ±	827.55 ±	2035
(an)		262.65	1.62
Semi-Anthracite	16	15193.19 ±	804.10 ±	1916
(sa)		227.41	0.19
Low Vol. Bituminous	89	15394.59 ±	792.82 ±	1838
(lvb)		435.54	0.39
Med. Vol. Bituminous	84	15409.96 ±	786.60 ±	1593
(mvb)		491.21	0.41
High Vol. A Bit.	317	15022.19 ±	781.93 ±	1774
(hvAb)		293.35	0.98
High Vol. B Bit.	152	14356.54 ±	783.08 ±	1773
(hvBb)		304.65	1.58
High Vol. C Bit.	189	13779.54 ±	784.58 ±	1797
(hvCb)		437.67	1.55
Sub-Bituminous A	35	13121.83 ±	788.25 ±	1867
(subA)		355.55	1.07
Sub-Bituminous B	56	12760.63 ±	787.07 ±	1862
(subB)		628.26	1.13
Sub-Bituminous C	53	12463.84 ±	788.67 ±	1858
(subC)		628.26	3.07
Lignite A	76	12052.33 ±	796.52 ±	1905
(ligA)		414.79	1.53
Lignite B	25	10085.02 ±	765.97 ±	1796
(ligB)		180.09	2.11

[0022] This paragraph discusses several definitions which are useful in understanding this invention. First, As-Fired fuel energy flow is numerically is the same as dry fuel energy flow if based on either actual combustion or theoretical combustion: mAs-FiredHHV=mDryFuel/ActHHVDry, or mAs-Fired/theorHHV=mDryFuel/theorHHVDry. However, the dry fuel energy flow based on actual combustion is not the same as dry fuel energy flow based on theoretical combustion implied in Eqs.(72A) & (75A): mDryFuel/Act HHVDry≠mDryFuel/theor HHVDry. Second, the US Environmental Protection Agency (EPA) requires the measurement of the actual total effluents flow from most thermal systems, discussed in '711. Although reported for the EPA as a volumetric flow at standard conditions, this invention teaches to convert to a mass-base using the hot densities (not cold), involving both gas and moisture. This is not the same total effluents mass flow associated with theoretical combustion, termed mDryGas/theor. This invention also teaches the elimination of the total effluents. Third, the conversion from any efficiency (η)) to a heat rate (HR) is common art, for example: HRturbine-cycle=3412.1416/ηturbine-cycle where the constant converts units from Btu/hr to kilowatts, thus HR carries the units of Btu/kW-hr. Fourth, the following equality is important when determining the L Factor: xDry-theor NDryFuel HHVDry=xWet-theor NWet-Fuel HHV.

[0023] This invention teaches that first correcting LFuel from conditions associated with theoretical combustion to actual conditions, and then dividing the corrected LFuel into the measured total effluents mass flow rate, the total (i.e., “As-Fired”) fuel energy flow, mAs-Fired (HHVP+HBC), is derived:

m As-Fired (HHVP+HBC)=106 ΞGas mDryGas/Act[LFuel ΞAF]  (81)

[0024] where the units of mass flow (m) are lbm/hr, corrected heating value (HHVP) and Firing Correction (BBC) in Btu/lbm, and the L Factor in lbm/million-Btu. ΞGas and ΞAF are discussed below.

[0025] From Eq.(8 1) As-Fired fuel mass flow may then be determined if heating value and the Firing Correction have been determined:

m As-Fired =106 ΞGas mDryGas/Act/[LFueI ΞAF (HHVP+HBC)]  (82)

[0026] As is common art for an electric power plant, dividing mAs-Fired (HHVP+HBC) by the total useful output, denoted as P in kilowatts, see '711 Eq.(1), unit heat rate is then determined.

HR unit =106 ΞGas mDryGas/Act[LFuel ΞAF P]  (83)

[0027] '711 teaches the determination and use of HHVP and HBC. Alternatively, for situations where heating value may be reasonably estimated the methods of '711 developing HHVP need not apply. Further, the HBC term could be assumed to have negligible effect and thus taken as zero, computed using '711 procedures, or estimated and/or held constant. HBC and HHVP are included here to illustrate consistency with '711 and '198. The LFuel parameter is typically based on an uncorrected heating value, HHV, thus requiring the HHV/(HHVP+HBC) correction within the ΞAF term, see Eq.(84). The corrected heating value, HHVP, could be used to develop LFuel, but is not preferred.

[0028] In Eqs.(81), (82) & (83), ΞGas is a correction factor for measurement error in the total effluents flow. As a defined thermodynamic factor addressing conceptual corrections, ΞAF of Eq.(84) principally converts conditions associated with theoretical combustion to those associated with the actual (As-Fired) conditions, thus allowing the use of the L Factor. The combined LFuelΞAF expression is termed the corrected L Factor, that is, producing actual total effluents flow divided by the actual As-Fired fuel energy flow, and as normalized to the bases of efficiency used at a given facility. For example, if the power plant uses HHV, then the term HHV/(HHVP+HBC) would not appear in Eq.(84); if only HHVP is used then the term HHV/HHVP would appear. This is termed the correction for the system heating value base. Use of (HHVP+HBC) as a bases, thus Eq.(84) as presented, is preferred.

ΞAF=[mDryGas/Act mWetFuel/theor/(mDryGas/theor mAs-Fired)]HHV/(HHVP+HBC)  (84)

[0029] Although LFuel is based on dry fuel energy flow associated with theoretical combustion, the ratio mDryFuel/theor/mDryFuel/Act is equivalent to the ratio mWetFuel/theor /mAs-Fired, allowing ΞAF of Eq.(84) to correct the denominator of LFuel such that its bases is the As-Fired (actual, wet) fuel conditions.

[0030] When the total effluents flow is measured on a wet-base, mWetGas/Act, LFuel is further corrected with the term (1−WFH2O), where WFH2O is the weight fraction of moisture determined to be in the wet total effluents. The factor (1−WFH2O) converts the LFuel's numerator from a dry-base to a wet-base expression of the total effluents mass. The preferred embodiment is to use a dry-base total effluents which involves less uncertainty given possible inaccuracies in determining WFH2O. However, FH2O may be determined by measurement of the volume (molar) concentration of effluent moisture and converting to a mass-base, or through computer simulation of the system, estimated, or other means. As applied: ΞAF/Wet=ΞAF/(1−WFH2O), the corrected L Factor then being the quantity LFuel ΞAF/Wet. This correction is termed conversion to a wet-base L Factor.

[0031] '711 teaches that turbine cycle energy flow (BBTC in Btu/hr) may be used to compute As-Fired fuel flow, via its Eq.(2 1). However, this may also be used to overcheck Eq.(82)'s fuel flow, or Eq.(81)'s fuel energy flow, given a determined boiler efficiency.

m′ As-Fired =BBTC TC /[ηBoiler (HHVP+HBC)]  (85A)

m′ As-Fired (HHVP+HBC)=BBTC ΞTC/[ηBoiler]  (85B)

[0032] Boiler efficiency may be determined by: 1) estimation by the power plant engineer; 2) methods of '711; 3) held constant; 4) determined using the methods of the American Society of Mechanical Engineers (ASME), Performance Test Codes 4.1 or 4; 5) the methods described in the technical paper: F. D. Lang, “Monitoring and Improving Coal-Fired Power Plants Using the Input/Loss Method—Part III”, ASME, 2000-IJPGC-15079(CD), July 2000; and/or 6) the methods described in the technical paper: E. Levy, et al., “Output/Loss: A New Method for Measuring Unit Heat Rate”, ASME, 87-JPGC-PWR-39, October 1987.

[0033] The term ΞTC of Eq.(85A) is a factor chosen such that the computed fuel flow from Eq.(85A), m′As-Fired, and that of Eq.(82) have reasonable agreement. An alternative approach is to choose ΞTC of Eq.(85B) such that the computed fuel energy flow, m′As-Fired (HHVP+HBC), and that of Eq.(81) have reasonable agreement. For the typical power plant situation, the greatest uncertainty in determining fuel flow (or fuel energy flow) using Eq.(85), or Eq.(21) of '711, lies with the turbine cycle energy flow, BBTC; provided HHVP (or HHV) is known. Thus the factor ΞTC is used to adjust and correct the BBTC quality until fuel flow, and/or fuel energy flow, from the two methods have reasonable agreement. Broadly, ΞTC is a general correction to the turbine cycle energy flow; however errors in boiler efficiency and/or heating value are also addressed. The advantage of this technique lies in its foundation with the demonstrated consistency of the L Factor. With adjustments through ΞTC, the turbine cycle heat rate may be determined:

HR turbine-cycle =BBTC ΞTC/P   (86)

[0034] The L Factor method may be further extended to eliminate the requirement to measure total effluents flow, replaced with a fuel flow measurement. This may be accomplished by simplification of ΞAF to the following given cancellation of the mDryGas/Act term; see Eqs.(83) & (84):

ΞFG=[mWetFuel/theor/ mDryGas/theor]HHV/(HHVP+HBC)  (87)

[0035] Thus:

m As-Fired (HHVP+HBC)=106 ΞFuel mAF/On-L/[LFuel ΞFG]  (88)

m As-Fired =106 ΞFuel mAF/On-L/[LFuel ΞFG(HHVP+HBC)]  (89)

HR unit =106 ΞFuel mAF/On-L/[LFuel ΞFG P]  (90)

[0036] where the quantity ΞFG may be computed explicitly knowing only the fuel chemistry and assuming theoretical combustion. In Eqs.(88), (89) & (90), ΞFuel is a correction factor for measurement error in the unit's indicated As-Fired fuel flow measurement, termed mAF/On-L. The advantage of using ΞFG, and Eqs.(88), (89) & (90), lies when the fuel flow measurement, although typically not accurate in coal-fired plants, is a consistent measurement, thus correctable through ΞFuel. Further, the ΞFG quantity is constant for a given fuel, and easily calculated. Although Eq.(90) reduces to [mAs-Fired/Act (HHVP+HBC)/P], the classical definition of HRunit, it is composed of quantities which could be measured on-line if having the necessary consistently (in the mAF/on-L and P terms). It also has usefulness to check the measured total effluents flow by equating Eqs.(81) and (88) and solving for mDryGas/Act, Eq.(90) has applicability for fuels with highly variable water and ash contents, but where LFuel is constant (as has been demonstrated in Table 1, e.g., lignite fuels). Eq.(89) may also be used for checking the indicated fuel flow, or fuel energy flow via Eq.(88), with the tested or observed quantity.

[0037] Additionally, this invention is not limited by the above presentation. Heating value could be computed using Eqs.(81) and (85A), or Eq.(88), provided fuel flow is independently determined. The preferred embodiment of this invention is to use the L Factor, and when off-line, Eqs.(81), (82) & (83).

[0038] The F Factor

[0039] The following discusses the EPA's F Factor in light of its use in determining the L Factor. Using the Fc Factor, if effluent CO2 is measured on a dry base, the emission rate for the dry gaseous total effluents is given by Eq.(91), which is an alternative method for computing the L Factor. A validity test for use of the Fc Factor lies in whether Eq.(91) produces constant values; at least as consistent as observed with actual data, and especially for coal data (see Table 1). The L Factor as computed from the Fc Factor is herein termed LFuelEPA. It is corrected with the ΞAF term defined by Eq.(84). The corrected L Factor is given as LFueI/EPA ΞAF.

L Fuel/EPA =100 NDryGas/Act Fc/(385.321 dAct ΞAF)  (91)

[0040] NDryGas/Act is the molecular weight of the actual dry gaseous total effluents (with system air in-leakage), and dAct is the measured concentration of CO2 at the system's boundary on a dry base (in per cent). Reference should be made to '198 and '711 for encompassing stoichiometrics. Fc may be determined: 1) by computation based on fuel chemistry using EPA procedures; 2) by using constant values as suggested by the EPA for certain fuels; or 3) by using values from Table 1. The bases for Eq.(91) is fully discussed in the technical paper: F. D. Lang and M. A. Bushey, “The Role of Valid Emission Rate Methods in Enforcement of the Clean Air Act”, Proceedings of Heat Rate Improvement Conference, Baltimore, Md., sponsored by Electric Power Research Institute, May 1994 (also published in: FLOWERS '94: Proceedings of the Florence World Energy Research Symposium, editor E. Carnevale, Servizi Grafici Editoriali, Padova, Italy 1994). Lang and Bushey used the symbol βCO2-dry for dAct (as used here and in '711), and E for emission rate whereas ER is used here and in '711. Also note that Lang and Bushey correct for the molecular weight of the gas actually being computed using the gas constant, assuming ideal gas behavior, leading to the conversion factor of 385.321 ft3/lb-mole at standard EPA conditions of 68F and 14.6959 psiA. Fc carries units of ft3-CO2 /million-Btu, thus needed conversion from the volumetric.

[0041] It has been found that Eq.(91) may produce reasonable L Factors. However, when assuming a constant fuel chemistry, LFuel/EPA is not found dead constant (as with LFuel) when varying operational parameters (e.g., total effluents flow, excess O2, etc.). EPA regulations rely on Eq.(91) and its underlying technology to describe the dry pounds of the total effluents per million-Btu of fuel burned, for actual conditions found at any stationary source of fossil combustion. This may be adequate for some situations, it is not preferred over the LFuel method and use of Eqs.(72A) or (75A).

[0042] This invention teaches by the very nature of the Fc formulation used by the EPA, errors must be realized when Fc is employed for actual systems. As found in the course of developing this invention, the definition of the L Factor must intrinsically involve effluent water and effluent ash, see Eq.(72A); Fc does not, it is a simple conversion of fuel to effluents using ideal assumptions, without consideration of basic combustion. Different fuels have different water and ash contents, and are subtracted from the fuel and combustion air terms of Eq.(72A), their presents and consideration is conceptually important. Although Eq.(91) uses the ΞAF term to correct, use of a constant Fc, derived without consideration of basic combustion, results in a slightly variable L Factor as demonstrated in Table 2.

[0043] In Table 2 the RAct term is the air pre-heater “leakage factor” discussed in '711; the AAct term is also defined and used throughout '711, yielding φAct=3.82195 for the example; by “boiler” is meant that the excess O2 measurement is taken at the combustion gas inlet to the air pre-heater, before dilution by air pre-heater leakage. The last case studied varied the AAct term, thus φAct, which would affect the mass of the dry total effluents although not the fuel per se. Table 2 clearly illustrates in its fourth column that LFuel/EPA varies for different combustion conditions, Fc being constant for the same fuel. The standard deviation in LFuel for hvAb coal, studying 317 samples is 0.13%. The range of LFuel/EPA implies, for the averaged hvAb coal (a constant fuel chemistry), a 100 ΔBtu/kW-hr heat rate change (or 1.2% error). This is a conceptual error, and although may not be serious for all situations, it may be significant for some fossil fueled systems whose fuel's heating value does not vary significantly.

TABLE 2
Typical Sensitivities of LFuel and LFuel/EPA
for High Volatile A Bituminous (hvAb) Coal
			Correction	LFuel/EPA
		LFuel,	ΞAF,	(FC = 1774),
	hvAb Case	Eq.(75A)	Eqs.(84)	Eq.(91)
	Theoretical	781.93	1.00000	773.81
	Combustion
	1.0% excess O2,	781.93	1.04664	776.39
	RAct = 1.00.
	2.0% excess O2,	781.93	1.09820	778.99
	RAct = 1.00.
	3.0% excess O2,	781.93	1.15551	781.61
	RAct = 1.00.
	3.0% excess	781.93	1.26410	781.89
	O2 (boiler),
	and RAct = 1.10
	3.0% excess	781.93	1.27821	782.62
	O2 (boiler),
	RAct = 1.10, and
	AAct, = 0.207385.

[0044] If Fc Factors are to be used to produce the L Factor, this invention teaches that Eq.(91) must be used with caution, and that applying numerical bias or a contrived correlation to the resulting heat rate must be considered.

[0045] The following equations apply for determining fuel flow and unit heat rate based on the Fc Factor, employing mass or volumetric flows.

m As-Fired =385.321×106 ΞGas mDryGas/Act dAct/ [100NDryGas/ActFc (HHVP+HBC)]  (92A)

m As-Fired =385.321×106 ΞGas mWetGas/Act DAct/Wet/[100NWetGas/ActFc (HHVP+HBC)]  (92B)

m As-Fired =1.0×106 ΞGas qDryGas/Act dAct/ [100 Fc (HHVP+HBC)]  (92C)

m As-Fired =1.0×106 qWetGas/Act dAct/Wet/ [100 Fc (HHVP+HBC)]  (92D)

HR unit =385.321×106 ΞGas mDryGas/Act dAct/ [100 NDryGas/Act Fc P]  (93A)

HR unit =385.321×106 ΞGas mWetGas/Act dAct/Wet/ [100 NWetGas/Act Fc P]  (93B)

HR unit =1.0×106 ΞGas qDryGas/Act dAct/ [100 Fc P]  (93C)

HR unit =1.0×106 ΞGas qWetGas/Act dAct/Wet/ [100 Fc P]  (93D)

[0046] where mDryGas/Act or mWetGas/Act are the dry-base or wet-base mass flow rates (lbm/hour) of total effluents, and qDryGas/Act or qWetGas/Act are the volumetric flow rates (ft3/hour). Multiplying both sides of Eq.(92) by (HHVP+HBC) produces total fuel energy flow as in Eq.(81). Eq.(93) states that heat rate is directly proportional to the total effluents flow and the CO2 concentration, and inversely proportional to Fc and electrical power (kilowatts). These equations may be repeated using the Fw and FD Factors, also described and allowed by 40 CFR Part 60, Appendix A, Method 19.

[0047] Although the correction MAF cancels from Eqs.(92) & (93), as discussed above the concept of Fc results in a lack the accuracy when compared to the L Factor; see typical results in Table 2. Without sensitivity to the terms comprising ΞAF, or ΞAF/wet, Eqs.(92) & (93) must rely on the single sensitivity of the concentration of CO2, dAct or dAct/Wet, to account for the effects of changing total effluents and As-Fired fuel flow. This observation has lead to corrections associated with on-line monitoring using the Fc Factor.

[0048] On-Line Monitoring

[0049] The following presents a similar factor to ΞAF, termed ΞOn-L, which is applied for on-line monitoring and may be determined from routine system operational data. Thus ΞOn-L may be substituted for ΞAF to achieve on-line monitoring of heat rate. By on-line monitoring is meant the analysis of plant data using the methods of this invention in essentially real time, and/or simply the acquisition of plant data.

[0050] As taught, the L Factor requires corrections to the actual, from total effluents and fuel flows associated with theoretical combustion. The total effluents flow correction is developed by first dividing all terms of Eq.(80) by xDry-theorNDry-Fuel, thus developing an Air/Fuel ratio (termed AFDry-theor), and then substituting LFuel from Eq.(75A):

1.0+AFDry-theor−(JtheorNH2O+xMAF-theor αMAF-10 NAsh) / (xDry-theor NDry-Fuel)=LFuel HHVDry   (94)

[0051] The terms in Eq.(94) involving effluent moisture and ash may be expressed as fuel weight fractions given theoretical combustion. However, since only the influence of dry total effluents on LFuel is desired it has been found that only the As-Fired weight fraction of ash needs to be considered in practice:

1.0+AFDry-theor−WFAsh≈LFuel HHVDry   (95)

[0052] or simplifying using a constant K1 (=1.0−WFAsh), descriptive of a given fuel:

−K3AFWet-theor+K1=LFuel HHVDry   (96)

[0053] where K3 is a conversion from dry-base to wet-base for theoretical combustion. LFuelHHVDry is approximately constant for any operation burning the same fuel; noting that the fuel's water content may vary as it commonly does with poorer quality coals. Thus the ratio of indicated system wet Air/Fuel ratio to the wet Air/Fuel ratio associated with theoretical combustion, addresses the correction for total effluents flow. The correction for fuel flow is addressed as the ratio of the system's indication of As-Fired fuel flow (mAF/On-L) to the fuel flow associated with theoretical combustion (mWetFuel/theor).

[0054] The following functionality has been found to yield good results while monitoring a system on-line, when the total effluents flow is being measured:

ΞOn-L=[K2 (AFWet/On-L+K1)mAF/On-L]HHV/(HHVP+HBC)  (97)

[0055] It has been found in practice that the system engineer may determine K1 and K2 quickly by adjustments to his/her on-line monitoring routines, on-line monitoring software, or to the plant's data acquisition computer, or by estimation. To determine reasonable initial estimates: K1 may be computed as taught above; K2=1.0/[(K3 AFWet-theor+K1) mWetFuel/theor] as based on theoretical combustion, and requiring adjustment for the type of flow being monitored either mass-base or volume-base (e.g., the conversion factor 385.321 ft3/lb-mole at standard conditions); and where K3=1.0. Eq.(97) employs the system's on-line measurements of Air/Fuel ratio (AFWet/On-L), and the As-Fired fuel flow (mAF/On-L). Eq.(97) could also be expressed in terms of the actual combustion air flow measurement, mAir-On-L:

ΞOn-L=[K2 (mAF/On-L+K1 mAF/On-L)]HHV/ (HHVP+HBC)  (98)

[0056] Finally, the methods of this invention may be applied on-line using the following equation. In Eq.(99) qDryGas/Act is the measured dry total effluents volumetric flow, typically reported by system instruments in units of ft3/hour. If the total effluents flow is reported as a mass flow then Eqs.(81), (82) and (83), would apply replacing ΞAF with ΞOn-L. The effluent density, termed p, must be consistent with the measurement base of the volumetric flow. The preferred embodiment, if using Eqs.(99) or (100), is the use of hot flows with hot densities.

HR unit =106 ΞGas qDryGas/Act ρDryGas/ [LFuel ΞOn-L P]  (99)

[0057] The combined LFuelΞOn-L expression is termed the corrected L Factor. For a total effluents volumetric flow measured on a wet-base, the following applies:

HR unit =106 ΞGas qWetGas/Act ρWetGas (1−WFH2O)/[LFuel ΞOn-L P]  (100)

[0058] Thus the L Factor may be corrected to a dry-base or wet-base, reflecting the nature of the total effluents considered.

[0059] To illustrate the accuracy of the L Factor method the following table presents results of using several of the procedures discussed. Its accuracy is considered exceptional.

TABLE 3
Typical Heat Rate Results for
High Volatile A Bituminous (hvAb) Coal
(using ΞAF from Table 2, and ΞOn-L via Eq.(97))
		Measured	L Factor	L Factor
		Unit	Heat Rate,	Heat Rate,
		Heat Rate	Off-Line	On-Line
	hvAb Case	(Btu/kW-hr)	Eq.(83)	Eq.(99)
	Theoretical	8436	8436	8436
	Combustion
	1.0% excess O2,	8452	8452	8455
	RAct = 1.00.
	2.0% excess O2,	8471	8469	8474
	RAct = 1.00.
	3.0% excess O2,	8491	8488	8483
	RAct = 1.00.
	3.0% excess	8530	8526	8526
	O2 (boiler),
	and RAct = 1.10
	3.0% excess	8535	8530	8529
	O2 (boiler),
	RAct = 1.10, and
	AAct = 0.207385.

[0060] To apply the Fc Factor to the on-line monitoring of a power plant the following equations apply:

HR unit =ΞOn-L/F mDryGas/Act dAct/ [100 NDryGas/Act Fc P]  (101A)

HR unit =ΞOn-L/F qDryGas/Act dAct/ [100 Fc P]  (101B)

[0061] or, for wet-base quantities:

HR unit =ΞOn-L/F mWetGas/Act dAct/Wet/ [100 NWetGas/Act Fc P]  (102A)

HR unit =ΞOn-L/F qWetGas/Act dAct/Wet/ [100 Fc P]  (102B)

[0062] When on-line, the molecular weight of the total effluents, NWetGas/Act or NDryGas/Act, may be held constant or computed knowing the fuel's chemistry and operating parameters as was well discussed in '711 and '198; see Eq.(29) of '711. It has been found that the factor ΞOn-L/F, suggested by the factor ΞOn-L discussed above, may be resolved as follows:

ΞOn-L/F=[K2F (AFWet/On-L+K1F) mAF/On-L]HHV/ (HHVP+HBC)  (103)

[0063] where the factors K2F and K1F are adjusted such that the system operator's observations and those produced from Eq.(101) or (102) have reasonable 10 agreement. The factor K1F may be computed as taught for K1, or otherwise determined; it generally may be held constant. The factor K2F is typically estimated or otherwise determined, and may include functionalities related to moisture in the total effluents, As-Fired fuel moisture, addresses different flow measurements (volumetric- or mass-base), and/or a correlation which adjusts the Air/Fuel ratio using operational parameters. In practice, for a given thermal system, the factor K2F is developed as a variable, having at least functionality with a measured moisture in the total effluents. The preferred embodiment of this invention is to use the L Factor, and when on-line, Eqs. (99) & (100).

[0064] Emission Rates of Pollutants

[0065] The ability to compute As-Fired fuel flow based on the L Factor, as taught by this invention, allows the determination of pollutant emission rates (ER) typically required for regulatory reporting. As taught in '711, and its Eq.(70B) and associated discussion, the emission rate of any effluent species may be determined by knowing its molar fraction (i.e., its concentration) within the total effluents, molecular weight of the species and the As-Fired fuel, the fuels' heating value and the moles of fuel per mole of effluent. The procedure for calculating emission rates may be greatly simplified using the L Factor, which also results in increased accuracy.

[0066] By solving for Fc in Eq.(91) and then substituting into the conventional emission rate equation, see Lang & Bushey's Eq.(2-2), the following is developed:

ER 1 =L Fuel ΞAF φDry-1 N1/ [100 NDryGas]  (104)

[0067] where φDry-1 is the dry-base molar concentration of species i (in per cent), N1 is the species' molecular weight, and NDryGas is the molecular weight of the dry total effluents. As an example, for SO2 effluent using the nomenclature of '711, see Eq.(29) of '711: φDry-SO2=k.

[0068] For any effluent measured on a wet-base (φWet-1):

ER 1 =L Fuel ΞAF φWet-1 N1/ [100 NWetGas (1−WFH2O)]  (105)

[0069] The preferred embodiment is to use Eq.(104) which involves less uncertainty given possible inaccuracies in determining WFH2O, discussed above. The factor ΞAF is defined by Eq.(84). The factor ΞOn-L may be substituted for ΞAF in Eqs.(104) and (105) as taught in Eqs.(97) and (98).

[0070] The accuracy of using the L Factor for computing emission rates is demonstrated by the L Factor's ability to match measured unit heat rates (see above table). The L Factor may track operational changes, whereas the F Factor requires numerical bias or contrived correlations. As reported by Lang & Bushey, errors in emission rates based on the F Factor may exceed 10% for certain fuels, with common errors of 3%. The preferred embodiment of this invention when determining emission rates is to use the L Factor as taught by Eqs. (104) & (105), replacing EPA methods.

THE DRAWINGS

[0071] FIG. 1 illustrates an important portion of this invention, the determination of unit heat rate associated with a fossil fueled power plant. Box 301 depicts the measurement of electrical generation produced by the thermal system. Box 303 depicts the calculation of the L Factor defined by Eqs.(72A) or (75A), or otherwise determined as discussed herein, including the use of Eq.(91) if applicable. Box 305 depicts the calculation of the factors ΞAF or ΞOn-L defined by Eqs.(84), (97) or (98), or otherwise determined as discussed herein, including ΞAF/Wet. Box 307 depicts the multiplication of the L Factor by the correction to the L Factor. Box 309 depicts the measurement of the total effluents flow from fossil combustion. Box 311 depicts the determination of a correction factor to the measured total effluents flow, termed φGas, and its consistent use with either a mass or volume total effluents flow measurement. Box 313 depicts the multiplication of the measured total effluents flow by its correction factor. Box 315 depicts the calculation of the system's total fuel energy flow as taught, for example, through Eqs.(81), (88), and as discussed following (92A), (92B) & (92C). Box 317 depicts the calculation of the heat rate of the system as taught, for example, thought Eqs.(83), (90), (99) and (100).

[0072] For FIG. 1 and elsewhere herein, if used, the words “obtained”, “obtaining”, “determined”, “determining” or “determination” are defined as measuring, calculating, assuming, estimating or gathering from a data base. The word “total effluents” is used to mean all products resultant from the combustion of fossil fuel as found at the point where the flow rate of these combustion products is obtained, for example all effluents exiting from the smoke stack, the smoke stack being the point of flow measurement. The word “effluent” refers to a single, unique, combustion product at the point where the flow rate of all combustion products is obtained, for example CO2 found in the smoke stack. Further, the words “theoretical combustion” refers to the combustion of fossil fuel with just enough oxygen that none is found in the products of combustion, and such that no pollutants are found in the products of combustion (e.g., CO, NO, SO3), and, essentially only CO2, H2O, SO2 and N2 are found in the combustion products, and that the combustion air has no moisture. The words “theoretical combustion” and “stoichiometric combustion” mean the same. The words “adjust” or adjusting” means to correct to a determined value. The words “reasonable agreement” mean that two parameters which are being compared, agree in their numerical values within a determined range or per cent.

Claims

1. A method for quantifying the operation of a fossil-fired system, the method comprising the steps of: obtaining an L Factor; determining a correction to the L Factor which converts its applicability from theoretical combustion to combustion associated with the fossil-fired system, and if applicable the correction for the system heating value base, and if applicable conversion to a wet-base L Factor; combining the L Factor and the correction to the L Factor, resulting in a corrected L Factor; obtaining a total effluents mass flow rate from the fossil-fired; obtaining a correction factor for the total effluents mass flow rate, resulting in a corrected total effluents mass flow rate; and dividing the corrected total effluents mass flow rate by the corrected L Factor, resulting in a total fuel energy flow of the system.

2. The method of claim 1, wherein the step of obtaining the total effluents mass flow rate includes the steps of: obtaining a total effluents volumetric flow rate from the fossil-fired system; obtaining a density of the total effluents; and obtaining the total effluents mass flow rate by multiplying the total effluents volumetric flow rate by the density of the total effluents.

3. The method of claim 1, including additional steps, after the step of dividing, of: obtaining a produced electrical power from the fossil-fired system; and dividing the total fuel energy flow of the system by the produced electrical power, resulting in a heat rate of the fossil-fired system.

4. The method of claim 1, including additional steps, after the step of dividing, of: obtaining a fuel heating value of the fuel consumed by the fossil-fired system; and dividing the total fuel energy flow of the system by the fuel heating value, resulting in a fuel flow rate of the fossil-fired system.

5. The method of claim 4, including additional steps, after the step of dividing, of: obtaining a turbine cycle energy flow; obtaining a boiler efficiency; obtaining a turbine cycle based fuel flow rate by dividing the turbine cycle energy flow by the product of the boiler efficiency and the fuel heating value; and adjusting the turbine cycle energy flow until the turbine cycle based fuel flow rate and the fuel flow rate are in reasonable agreement.

6. The method of claim 1, including additional steps, after the step of dividing, of: obtaining a fuel flow rate of the fossil-fired system; and dividing the total fuel energy flow of the system, by the fuel flow rate, resulting in the fuel heating value of the fuel consumed by the fossil-fired system.

7. The method of claim 6, including additional steps, after the step of dividing, of: obtaining a turbine cycle energy flow; obtaining a boiler efficiency; obtaining a turbine cycle based fuel heating value by dividing the turbine cycle energy flow by the product of the boiler efficiency and the fuel flow rate; and adjusting the turbine cycle energy flow until the turbine cycle based fuel heating value and the fuel heating value are in reasonable agreement.

8. A method for quantifying the operation of a fossil-fired system, the method comprising the steps of: obtaining a L Factor; determining a correction to the L Factor which converts its applicability from theoretical combustion to combustion associated with the fossil-fired system, and if applicable the correction for the system heating value base, and if applicable conversion to a wet-base L Factor; combining the L Factor and the correction to the L Factor, resulting in a corrected L Factor; obtaining a concentration and molecular weight of an effluent from fossil combustion associated with the fossil-fired system; obtaining an average molecular weight of the total effluents; dividing the product of the corrected L Factor, the effluent concentration and the effluent molecular weight, by the average molecular weight of the total effluents, resulting in an emission rate of the effluent.

9. A method for quantifying the operation of a fossil-fired system, the method comprising the steps of: obtaining a concentration of the effluent CO2 found in combustion products from the fossil-fired system; obtaining a total effluents volumetric flow rate from the fossil-fired system; obtaining a correction factor for the total effluents volumetric flow rate, resulting in a corrected total effluents flow rate; obtaining an Fc Factor; and dividing the product of the corrected total effluents flow rate and the concentration of effluent CO2 by the Fc Factor, resulting in a total fuel energy flow of the system.

10. The method of claim 9, wherein the steps of obtaining the total effluents volumetric flow rate and obtaining the correction factor for the total effluents volumetric flow rate, includes the steps of: obtaining a total effluents mass flow rate from the fossil-fired system; obtaining a correction factor for the total effluents mass flow rate; obtaining a density of the total effluents; and obtaining the corrected total effluents flow rate by combining the correction factor for the total effluents mass flow rate with the total effluents mass flow rate, and dividing by the density of the total effluents.

11. The method of claim 9, wherein the steps of obtaining the total effluents volumetric flow rate and obtaining the correction factor for the total effluents volumetric flow rate, includes the steps of: obtaining a total effluents mass flow rate from the fossil-fired system; obtaining a correction factor for the total effluents mass flow rate; obtaining a conversion from volume to moles; obtaining an average molecular weight of the total effluents; and obtaining the corrected total effluents flow rate by combining the total effluents mass flow rate, the correction factor for the total effluents mass flow rate, and the conversion from volume to moles, and then dividing by the average molecular weight of the total effluents.

12. The method of claim 9, including additional steps, after the step of dividing, of: obtaining a produced electrical power from the fossil-fired system; and dividing the total fuel energy flow of the system by the produced electrical power, resulting in a heat rate of the fossil-fired system.

13. The method of claim 9, including additional steps, after the step of dividing, of: obtaining a fuel heating value of the fuel consumed by the fossil-fired system; and dividing the total fuel energy flow of the system by the fuel heating value, resulting in a fuel flow rate of the fossil-fired system.

14. The method of claim 13, including additional steps, after the step of dividing, of: obtaining a turbine cycle energy flow; obtaining a boiler efficiency; obtaining a turbine cycle based fuel flow rate by dividing the turbine cycle energy flow by the product of the boiler efficiency and the fuel heating value; and adjusting the turbine cycle energy flow until the turbine cycle based fuel flow rate and the fuel flow rate are in reasonable agreement.

15. The method of claim 9, including additional steps, after the step of dividing, of: obtaining a fuel flow rate of the fossil-fired system; and dividing the total fuel energy flow of the system by the fuel flow rate, resulting in the fuel heating value of the fuel consumed by the fossil-fired system.

16. The method of claim 15, including additional steps, after the step of dividing, of: obtaining a turbine cycle energy flow; obtaining a boiler efficiency; obtaining a turbine cycle based fuel heating value by dividing the turbine cycle energy flow by the product of the boiler efficiency and the fuel flow rate; and adjusting the turbine cycle energy flow until the turbine cycle based fuel heating value and the fuel heating value are in reasonable agreement.

17. The method of claim 1, wherein the step of determining the correction to the L Factor is replaced with the steps of: obtaining a combustion air flow rate of the fossil-fired system by on-line monitoring; obtaining a fuel flow rate of the fossil-fired system by on-line monitoring; determining a correction for the system heating value base used by the fossil-fired system; determining an on-line correction to the L Factor by combining the combustion air flow rate, the fuel flow rate and, if applicable, the correction for the system heating value base; and combining the L Factor and the on-line correction to the L Factor, resulting in the corrected L Factor.

18. The method of claim 8, wherein the step of determining the correction to the L Factor is replaced with the steps of: obtaining a combustion air flow rate of the fossil-fired system by on-line monitoring; obtaining a fuel flow rate of the fossil-fired system by on-line monitoring; determining a correction for the system heating value base used by the fossil-fired system; determining an on-line correction to the L Factor by combining the combustion air flow rate, the fuel flow rate and, if applicable, the correction for the system heating value base; and combining the L Factor and the on-line correction to the L Factor, resulting in the corrected L Factor.

19. The method of claim 1, wherein the step of obtaining the L Factor, includes the step of: obtaining a concentration of the effluent CO2 found in combustion products from the fossil-fired system; determining the correction to the L Factor which converts its applicability from theoretical combustion to combustion associated with the fossil-fired system, and if applicable the correction for the system heating value base, and if applicable conversion to a wet-base L Factor; obtaining an average molecular weight of the total effluents; obtaining a conversion from volume to moles; obtaining an Fc Factor; and dividing the product of the average molecular weight of the total effluents and the Fc Factor by the product of concentration of the effluent CO2, the conversion from volume to moles and the correction to the L Factor, resulting in the L Factor.