ERRORS IN BOILER EFFICIENCY STANDARDS

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Laureen Francis
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1 ASME POWER ERRORS IN BOILER EFFICIENCY STANDARDS by Fred D. Lang, P.E., Inc For delivered paper (Rev. 27) visit:

2 The Old: Topics to be Discussed Where do we go? Why Absolute Standards? Review of PTC and European The New: Mechanics Fuel Flow Criticism Applicability Examples Recommendations

3 Where do we go is Boiler Efficiency arbitrary?

4 What one Vendor stated I am well aware that the codes as they stand are arbitrary and can be manipulated, so it is certainly a case of Buyer Beware when it comes to bid evaluations by our Clients.

5 Why Absolute Standards? To Prove we understand the system or not! Do we understand basic conversion and Q WF? Do we understand the quantity of fuel required? If standards only provide a consistent basis for comparison then now can we freeze the reference temperature at 77F, then determine HHV at 95F, use combustion air at -10F, blow for soot, use constant pressure conversion, and hope to understand. 1% in boiler efficiency is worth» $20 million for a Steam Generator supplying a 400 MWe unit.

6 ASME PTC 4 and EN ASME PTC 4 has replaced PTC 4.1 EN has replaced the British and the German DIN-1942 with - BSI EN :2003 DIN EN :2004. Heat Loss = Indirect = Energy Balance Input-Output = Direct = Gross Method

7 ASME PTC 4 and EN Reference temperature = 25C. Corrections can be made to HHVs (EN). Gross or net (PTC is weak, parallel in EN). APH is included within boundary. Heat Credits are set to zero (PTC), or in error (EN). PTC: Energy Bal. 0 B-HHV = 1.0-3Losses / HHVP EN EB: 0 B-HHV = 1.0-3Losses / (m AF HHVP + Q G-Z ) EN I-O: 0 B-HHV = Q WF / (m AF HHVP + Q G-Z ) Corrections allowed to guarantee conditions. Variance procedures.

8 Mechanics of the New Š MQ T-Cal = - HHV T Cal serves as the reference for all thermodynamics Gaseous Fuels: HHV are computed at T Cal Solid & Liquid: HHV are measured at T Cal The Steam Generator boundary derives from the principle that thermal efficiency must only address how the as-fired fuel interacts with gas / air / working fluid.

9 Mechanics of the New Š MQ T-Cal = - HHV HHV = - HPR Ideal-HHV + HRX Cal-HHV - )H v/p HHVP = - HPR Ideal-HHV + HRX Cal-HHV HHVP + HBC = - HPR Ideal-HHV + HRX Cal-HHV + HBC HHVP + HBC = - HPR Ideal-HHV + HRX Act-HHV 0 B (HHVP + HBC) = - HPR Ideal-HHV + HRX Act-HHV - 3Losses 0 B (HHVP + HBC) = - HPR Ideal-HHV + HRX Act-HHV - 3Stack Losses - HNSL 0 B (HHVP + HBC) = - HPR Act-HHV + HRX Act-HHV - HNSL 0 B = ( - HPR Act-HHV + HRX Act-HHV - HNSL ) / (HHVP + HBC) 0 B = ( - HPR Act-HHV + HRX Act-HHV ) 0 A / (HHVP + HBC) 0 B = 0 C 0 A

10 Firing Correction (HBC) HBC = C P (T AF - T Cal ) Fuel Fuel + Q SAH / m AF SAH + W FD / m AF FD Fan + [ (h Amb - h Cal ) Air a (1.0 + ß)(1.0 + R Ref ) N Air Comb. Air + (h g-amb - h g-cal ) H2O b A (1.0 + ß) N H2O Moisture + (h Steam - h f-cal ) H2O b Z N H2O In-Leakage + C P (T Amb - T Cal ) PLS b PLS (1.0 + () N CaCO3 ] / (xn AF ) Limestone

11 Energy of Reactants (HRX) Start with an ultimate analysis and a calorimetric determination of the fuel (HHV), record T Cal HPR Ideal-HHV = Ideal Products at T Cal HRX Cal-HHV = (HHV + )H V/P ) + HPR Ideal-HHV Firing Correction (HBC) converts from T Cal to the actual As-Fired: HRX Act-HHV = HRX Cal-HHV + HBC

12 Energy of Products (HPR) HPR Act-HHV-k = [ Heat of Formation at T Cal plus sensible heat (T Stack - T Cal ) ] k Water is the key: Can not form water from combustion, referenced to )H f Cal, mix it with fuel water at T Cal and then think its OK to apply HHV at any other temperature. Water s energy and MAF s energy levels must be the same. The key is the HRX Cal-HHV term. HPR Act-HHV-H2O = [ Heat of Formation at T Cal plus sensible heat (h Stack - h Cal ); Fuel Water; Air Moisture; Leakage ] H2O

13 Non-Chemistry & Non-Stack Losses HNSL losses are only included if they affect computed fuel flow (i.e., affect the combustion process) + Radiation & Convention + Ash Pit and Fly and Bottom Ash terms + Miscellaneous sensible heats - ID Fan 0 A = 1.0 HNSL / [- HPR Act-HHV + HRX Act-HHV ] 0 B = 0 C 0 A m AF = Q WF / [ 0 B (HHVP + HBC) ]

14 ) ) Criticism T H 0 f - T = H 0 f I dh Compounds - 3 I dh Elements Contribution to HHV from Ash and MAF: )HHV = ( Fuel-Ash h T-Ash + ( Fuel-MAF ( HPR Ideal + HRX Cal ) MAF T Contribution to HHV from Water: )HHV = ( Fuel-H2 ()H o Vap T )h fg T ) H2O + ( Fuel-H2O h T-H2O EN (DIN 1942): HHV T = HHV 25 + [ (:C P ) MAF-Fuel + ((C P ) Fuel-H2O + (:C P ) dry-air (:C P ) Stack-Gas (:C P ) Stack-H2O ] (T 25)

15 Applicability of the New Energy Balance is only allowed if: Fuel Water + Hydrogen > 10%. If Energy Balance, base tolerance on: Fuel sampling of ultimate analyses and HHVs Useful Energy Flow (Q WF ) If Energy Balance, calculation of fuel flow is required. If Input-Output, base tolerance on: Fuel sampling of ultimate analyses and HHVs Useful Energy Flow (Q WF ) Use an agreed T Ref with an assigned range, leading to a Firing Correction tolerance.

16 Example Say we are firing PRB in identical units in the Sahara and in the Antarctic: both HHVs were determined at 77F, adjustments made to produce the same losses, with different Firing Corrections, units will have the same efficiencies PTC 4 agrees & EN disagrees. Now, same fuel, but HHV determined at 34F & 120F: with no further adjustments, different HHVs will again produce the same efficiencies PTC 4 disagrees & EN disagrees.

17 Fuel Flow, 640 MWe Coal-Fired Fuel Flows, lbm/hr Input/Loss Fuel Flow Plant Indicated Fuel Flow Input/Loss Heating Value Heating Value, Btu/lbm :00 18:00 0:00 6:

18 Soot Blowing Flow Emulating a Tube Leak 30 Soot Blowing Flow (K-lb/hr) Input/Loss Computed Soot Blowing Flow Measured Soot Blowing 0 18:00 20:00 22:00 0:00 2:00 4:00 6:00

19 H = f (C) for Powder River Basin POWDER RIVER BASIN MAF Molar Diatomic Hydrogen Hyd = (Car) R 2 = MAF Molar Carbon

20 OHC Approach for Interrogating Data 0.96 MAF Molar Carbon + Diatomic Hydrogen PRB Generic: Car+Hyd = (Oxy) R 2 = POWDER RIVER BASIN (generic) Systems Effects Test MAF Molar Oxygen

21 Recommendations for the New Proposal are 16 recommendations (review paper). Reference temperature = Calorimetric temperature. No corrections allowed to measured HHVs. Gross or net efficiencies produce identical fuel flows. APH is included within boundary. Firing Corrections only affect Reactant streams. Energy Balance allowed: fuel water + hydrogen > 10% 0 B-HHV = (HPR Act HRX Act ) 0 A / (HHVP + HBC) m AF = Q WF / [0 B-HHV (HHVP + HBC)] Input-Output required: fuel water + hydrogen < 10% 0 B-HHV = Q WF / [m AF (HHVP + HBC)] Simple treatment of variances.

22 From the 1890 Edition of Steam: Most of the abuses connected with steam engineering have arisen from two causes avarice and ignorance: avarice on the part of men who are imbued with the idea that cheap boilers and engines are economical, and ignorance on the part of those who claim to be engineers, but who at the best are mere starters and stoppers.

23 To those who are not mere starters and stoppers, Thank You.

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