ES_FlueGas User Manual

1. Introduction

2. Formulae

  2.1 Mole Weight

  2.2 Enthalpy

  2.3 Sulfuric Acid Dew Point

  2.4 Water Dew Point

3. Screen


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1.  Introduction

 ES_FlueGas is the software to calculate the mole weight, enthalpy, sulfuric dew point, moisture dew point of flue gas.

The flue gas composition of N2, Ar, O2, CO2, CO, SO2 and H2O can be input in either of Weight% or Volume%, and for enthalpy calculation the reference temperature should be input.

Flue gas enthalpy is calculated by either of "NASA Glenn Coefficients for Calculating Thermodynamic Properties of Individual Species"(NASA/TP-2002-211556, September 2002), ASME PTC 4.4, 1981 or Babcock & Wilcox "STEAM its generation and use, 40'th Edition".

The SO3 conversion rate for sulfuric dew point calculation can be estimated by the software automatically or input by the user.  Sulfuric dew point is calculated by the method of A.G. Okkes(Hydrocarbon Processing Journal, July 1997) and the method of Verhoff F. H./Banchero J. T(Chemical Engineering Process Journal, Aug. 1974).

The moisture dew point is calculated by the partial pressure law of Dalton.

 

2. Formulae   (TOC)

2.1 Mole Weight

The following is a sample calculation of mole weight for voluem% input.

Component

Mole Weight

Volume % (Example)

Mole Weight Component

N2

28.013

72

20.169 (= 28.013 x 72 / 100)

Ar

39.948

0.09

0.036 (= 39.948 x 0.09 / 100)

O2

31.999

13

4.160 (= 31.999 x 13 / 100)

CO2

44.010

5

2.201 (= 44.010 x 5 / 100)

CO

28.010

0.91

0.255 (= 28.010 x 0.91 / 100)

SO2

64.065

1

0.641 (= 64.065 x 1 / 100)

H2O

18.015

8

1.441 (= 18.015 x 8 / 100)

Total

-

100

28.902

 

The following is a sample calculation of mole weight for weight% input.  It is noted that the mole% is equatl to volume%.

Component

Mole Weight

Weight % (Example)

Mole Quantity

Volume %

Mole Weight Component

N2

28.013

69

2.463

70.758

19.821

Ar

39.948

0.124

0.003

0.089

0.036

O2

31.999

14

0.438

12.568

4.022

CO2

44.010

8

0.182

5.222

2.298

CO

28.010

0.876

0.031

0.898

0.252

SO2

64.065

2

0.031

0.897

0.575

H2O

18.015

6

0.333

9.568

1.724

Total

-

100

3.481

100

28.727

Mole quantity is calculated by dividing the weight% by the mole weight of each component.  For N2 case, 69 / 28.013 = 2.463.

The volume% of each component is calculated by dividing the mole quantity by the mole quantity total.  For N2 case, 2.463 / 3.481 x 100 = 70.758(%).   

The mole weight component of each component is calculated by multiplying the volume% by the mole weight.  For N2 case, 28.013 x 70.758 / 100 = 19.821.  And then the mole weight of flue gas is the total of mole weight components.

 

2.2 Enthalpy (TOC)

In original definition of enthalpy, the enthalpy is the total heat added to a material from the absolute zero temperature.  That is, the enthalpy is originally referencing on the absolute zero temperature.

However, in engineering calculation, the interest is the difference of enthalpy at two different conditions, not the absolute enthalpy itself.   Therefore, the enthalpy value based on a reference temperature is normally used in engineering calculation.

For example, the enthalpy difference between steam turbine inlet and outlet is used for calculation of steam turbine output, and the absolute enthalpy value at the inlet or outlet is out of concern.

Boiler efficiency is calculated based on a reference temperature and the reference temperature selected does not affect on the boiler efficiency calculated.   That is, the boiler efficiency calculated based on 15 oC reference temperature is same with that calculated based on 0 oC reference temperature.

Engineers normally use the same enthalpy value of steam and water because ASME steam table is normally used among engineers.   Therefore, same are the enthalpy values in the heat balance diagrams prepared by different steam turbine manufacturers.   

However, the enthalpy values of the components other than steam/water are different depending on the sources, because the reference temperatures are different.   Even though the enthalpy values are different, it is OK if the enthalpy difference between two conditions is same.

In case of gases, the effect of pressure on enthalpy is negligible so that the enthalpy of gases is normally calculated by temperature input only.

2.2.1 NASA Glenn Coefficients

The enthalpy by NASA Glenn Coefficients is calculated according to "NASA Glenn Coefficients for Calculating Thermodynamic Properties of Individual Species"(NASA/TP-2002-211556, September 2002).

NASA Glenn Coefficients for gases cover normally up to 20,000 oK.   However, since engineering calculation does not need normally the enthalpy over 6,000 oK, ES_FlueGas calculates the flue gas enthalpy between 200 oK and 6,000 oK.

NASA Glenn Coefficients are the coefficients that express the specific heat, enthalpy and entropy by least-square method in a seven-term functional form.   The coefficients represents the thermodynamic properties of individual species covering from 200 oK through maximum 20,000 oK at 1 bar absolute pressure.

Below is the definition of enthalpy expressed by the NASA Glenn Coefficients that is described in NASA/TP-2001-210959/REV 1 "CAP: A Computer Code for Generating Tabular Thermodynamic Functions from NASA Lewis Coefficients, February 2002".   Please note that the NASA Lewis Research Center is the previous name of NASA Glenn Research Center and the Lewis Coefficients is the Glenn Coefficients.

"For NASA Glenn database, the reference state for every element has been chosen to be the stable phase of the pure element at 298.15 oK and 10^5 Pa(1 bar).   The enthalpy of each element is assigned to be zero at this temperature and pressure.   The enthalpy at 298.15 oK and 10^5 Pa of any general compound of stoichiometry AxBy...Cz is defined to be the negative of the energy released when the compound forms from the elements in their reference state;

xA + yB + ... + zC = AxBy...Cz;Ho(298.15) = delta(f) Ho(298.15) = (-)delta Hrxn

This relationship defines the contribution of each element to the compound's enthlapy at 298.15 oK.   For temperatures other than 298.15 oK, the enthalpy equals the sum of the heat of formation and any sensible heat."

The NASA documents described above can be downloaded in the NASA web site.

2.2.2 ASME PTC 4.4 - 1981

ASME PTC 4.4 - 1981 includes the computer source code for calculating the flue gas enthalpy that is used for gas turbine heat balance.

The enthalpy of ES_FlueGas is the enthalpy calculated in the same method with the source code in the ASME PTC 4.4 - 1981.   The enthalpy calculated by ASME PTC 4.4 - 1981 is based on the absolute zero temperature.   Therefore, there is no limit in temperature input.

2.2.3 Babcock & Wilcox, STEAM its generation and use, 40'th Edition

The book, STEAM its generation and use, 40'th Edition, published by Babcock & Wilcox, USA includes a equation to calculate the enthalpy to be used in boiler performance calculation.

ES_FlueGas includes an option to calculate the enthalpy by the equation presented in the book.   The enthalpy reference temperature for the equation is 0 oF.   Therefore, the temperature for the option should be higher than 0 oF.

 

2.3 Sulfuric Acid Dew Point (TOC)

Sulfuric acid dew point calculation is required for selection of boiler exit flue gas temperature when firing sulfur bearing fuel.  In case of air preheater, the average temperature of flue gas and combustion air should be higher than the sulfuric acid dew point, and in case of economizer the boiler water temperature inside of economizer should be higher than sulfuric acid dew point, in order to prevent the air preheater and economizer from sulfuric acid corrosion.

2.3.1 SO3 Conversion Rate

A part of SO2 in flue gas is converted into SO3 and then the SO3 is reacted with moisture to become sulfuric acid(H2SO4).  Therefore, sulfuric acid dew point depends on the SO3 conversion rate and the rate should be selected carefully.   The conversion rate can be determined by the experiments, not by theoretical analysis.

In ES_FlueGas the SO3 conversion rate can be input by the user or be calculated automatically by the software.

The software uses the following experimental equation for calculating SO3 conversion rate.

   T = 1.273

    KP = Exp(12.12 / T * (1 - 0.942 * T + 0.0702 * T ^ 2 - 0.0108 * T * Ln(1000 * T) - 0.0013 / T))

   pSO3 = KP * PSO2VW / 100 * (PO2VW / 100) ^ 0.5

   pSO2 = PSO2VW / 100

   PConv = pSO3 / pSO2 * 100

where,

T

: Equilibrium temperature, oK/1000

 

pSO3, pSO2

: Partial pressure of SO3 and SO2, atm

 

PSO2VW, PO2VW

: SO2 and O2 volume percent in wet flue gas, %

 

PConv

: SO3 Conversion rate, %

 

2.3.2 A.G. Okkes Method

The sulfuric acid dew point by A. G. Okkes method is calculated using the following equations.

   pSO3 = PSO2VW / 100 * PConv / 100

   pH2O = PH2OVW / 100

   SADbyOkkes = 203.25 + 27.6 * Log10(pH2O) + 10.83 * Log10(pSO3) + 1.06 * (Log10(pSO3) + 8) ^ 2.19

where,

pSO3, pH2O

: Partial pressure of SO3 and H2O, atm

 

PSO2VW, PH2OVW

: SO2 and H2O volume percent in wet flue gas, %

 

SADbyOkkes

: Acid dew point by A.G. Okkes method, oC

 

2.3.3 Verhoff F. H. and Banchero J. T method

The sulfuric acid dew point by Verhoff F. H. and Banchero J. T method is calculated using the following equations.

   pSO3 = PSO2VW / 100 * PConv / 100 * 760

   pH2O = PH2OVW / 100 * 760

   SADbyVerhoff = 1 / (0.002276 - 0.00002943 * Ln(pH2O) - 0.0000858 * Ln(pSO3) + 0.0000062 * Ln(pH2O) * Ln(pSO3))

where,

pSO3, pH2O

: Partial pressure of SO3 and H2O, mmHg

 

PSO2VW, PH2OVW

: SO2 and H2O volume percent in wet flue gas, %

 

SADbyVerhoff

: Acid dew point by Verhoff F. H. and Banchero J. T method, oK

 

2.4 Water Dew Point

Water dew point calculation is also required for selection of boiler exit flue gas temperature.  Water dew point should be considered when firing hydrogen bearing fuel or air with moisture.  This means that water dew point should be always considered because pure dry air does not exist in normal atmosphere and almost all fuels have hydrogen components.

Normally water dew point is lower than sulfuric acid dew point.   Therefore, when firing sulfur bearing fuel, sulfuric acid dew point should be considered for selection of boiler exit flue gas temperature, while water dew point should be considered when firing no sulfur fuel.

Water dew point is calculated using the following equations.

   pH2O = PH2OVW / 100

   WDP = Steam saturation temperature at pH2O pressure

 

3.0 Screen (TOC)

The green color boxes are for user input.   After inputting the flue gas composition, gas temperature and enthalpy reference temperature in green color boxes, then press [Calculate] button for calculation.

The screen shot above is for automatic calculation of SO3 Conversion Rate.   If the user wants to input the SO3 Conversion Rate for himself, then select the [User input] in the menu [Option] - [SO3 conversion rate].  If the [User input] is selected, then the value box of SO3 conversion rate is automatically changed into green color.

Menu :

Main Menu

Sub Menu

Description

[File]

[Exit]

exits the program.

 

 

 

[Option]

[Unit]

[Set calculation units...]: sets the units in the current calculation.

 

 

[Set the current units as default] : sets the current units as default units.

 

 

 

 

[Gas component unit]

selects the gas component unit in either of [Volume %] or [Weight %].

 

 

 

 

[Enthalpy calculation formula]

selects the enthalpy calculation method among the following formulae.

 

 

[NASA Glenn Coefficients], [ASME PTC 4.4 - 1981], [B&W STEAM its generation and use]

 

 

 

 

[SO3 conversion rate]

selects SO3 conversion rate input method in either of [Automatic calculation] or [User input]

 

 

 

[Info]

[End User License Agreement...]

shows the End User License Agreement for using the Free Execution Software of ENGSoft Inc.

 

Buttons :

Button

Description

[Calculate]

performs calculation.

 

 

[Make 100% by H2O]

calculates the percent value of H2O components subtracting the sum of other component's percent values from 100%.

 

 

[Component total]

calculate the total of component percent values.

 

References :  (TOC)

1. NASA/TP-2002-211556, September 2002 - NASA Glenn Coefficients for Calculating Thermodynamic Properties of Individual Species

2. NASA/TP-2001-210959/REV 1, February 2002 - CAP: A Computer Code for Generating Tabular Thermodynamic Functions from NASA Lewis Coefficients

3. ASME PTC 4.4 - 1981, Performance Test Code for Gas Turbine Heat Recovery Steam Generator

4. B&W STEAM its generation and use, edited by S.C. Stultz and J.B. Kitto of Babcock & Wilcox, a McDermott company

5. Hydrocarbon Processing Journal, July 1997

6. Chemical Engineering Process Journal, Aug. 1974


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