Bob Lucas/RTP/ USEPA/US@EPA

02/06/2009 09:06 AM To: Vicente.Martinez@bp.com

cc Subject: SO2 Emissions to 0%

Vicente,

I've attached a response to your email th at addresses your questions on calculations.

Bob Lucas USEPA/OAQPS Sector Policies and Programs Division

(See attached file: SO2 Emissions to 0% O2 Compensation_jbc comments.doc)

"Martinez, Vicente" <Vicente.Martinez @bp.com>

02/02/2009 09:00 AM To: Bob Lucas/RTP/USEPA/US@EPA

cc Subject: SO2 Emissions to 0% O2 Compensation.doc

Bob,

Attached are our assumptions for the an accurate re presentation of the SO2 concentration from our CAT units.

Let me know if you concur or recommend another ap proved EPA method.

Best Regards,

Vicente Martinez 219-473-2175

(See attached file: SO2 Emission s to 0% O2 Compensation.doc)SO2 Emissions to 0% O2 Compensation.doc

January 29, 2009

Methodology for Calculating SO2 Emissions to 0% O2 Compensation During Periods of Pure Oxygen Injection

To: Vicente Martinez Keith Hammer

In the Code of Federal Regulat ions 266.105, there is a calculati on for calculating particulate matter emissions. This calculation includes a variable for the concentration of oxygen. For devices that feed oxygen-enriched air (such as pure O2 from Praxair), the value is the concentration of oxygen in the enri ched air. This equation was utilized for calculating the SO2 emissions during periods of pure oxygen usage.

This equation is stated as follows:

) stack in 2 O measured air combustion in conc (O2 20.9 * Pollutant = Pollutant

drybasis basis dry measured corrected

−

In this scenario, the pollutant in the equation would be SO2. Th e measured pollutant is the raw values for SO2 from the CEMS analyzer. The measured O2 in the stack on a dry basis is the value for O2 from the CEMS analyzer. The only va riable that needs to be calculated is the O2 concentration in combustion air on a dry basis. The following information describes the methodology used for calculating the O2 concentra tion in combustion air to account for the use of pure oxygen.

Calculating Combustion Air on a Dry Basis The first step is to calculate the total air on a wet basis based upon the flow meters in our system and then convert that flow to a dry basis. To calculate the wet basis flow, the flows from all sources of combustion ai r should be summed.

Using the absolute humidity, the total air on a we t basis was converted to a total air on a dry basis.

) * ( Humidity Absolute Air Total Air Total Air Total wetbasis wetbasis drybasis − =

In order to calculate absolute humidity, there ha s to be a reference to ambient temperature, relative humidity, and barometric pressure. Rece ntly, these weather variables have been added to the PI system. For the period in question however, this data is not available via PI. Rather, historical data for these variables were sought from http://www.weatherunderground.com

.
To calculate the absolute humidity, the following equation was utilized:

100

Humidity lative Re
* Humidity Saturated Humidity Absolute =SO2 Emissions to 0% O2 Compensation.doc

Absolute humidity is expressed as pounds of water per pound of air.

To calculate the saturated humidity, the following equation was utilized: 

## ( )
S amb S
air water P P / P * MW MW Humidity Saturated

− =

Saturated humidity is expressed as pounds of water per pound of air. Values and assumptions for each variable in the above equation are as follows.

• Molecular Weight of Water (MW water ) – 18.02

• Molecular Weight of Air (MW air ) – 28.85

• Vapor Pressure of Water at Ambient Temperature (P S ) – determined from steam tables based upon the ambient temperature for each day (expressed in psia).

• Ambient Pressure (P amb ) – daily barometric pressu re (expressed in psia).

Calculating Purchase O2 Usage Utilizing a PI, there is a tag fo r the amount of pure O2 (tons/d ay) that is used at FCU600.

Calculating O2 Concentration in Combustion Air While Using Pure O2 Utilizing the calculations above, the calculation for O2 concentration in combustion air while using pure O2 is stated as:

100 * 2 O Purchased Total Air Total 1 * 2 O Purchased Total 209

. 0 * Air Total Air Combustion in Conc 2 O

drybasis drybasis drybasis + +

=

This equation assumes 0.209 as the concentration of O2 in air and 1 as the concentration of O2 in the O2 from Praxair.SO2 Emissions to 0% O2 Compensation_jbc comments.doc

January 29, 2009

Methodology for Calculating SO2 Emissions to 0% O2 Compensation During Periods of Pure Oxygen Injection

To: Vicente Martinez Keith Hammer

In the Code of Federal Regulat ions 266.105, there is a calculati on for calculating particulate matter emissions. This calculation includes a variable for the concentration of oxygen. For devices that feed oxygen-enriched air (such as pure O2 from Praxair), the value is the concentration of oxygen in the enri ched air. This equation was utilized for calculating the SO2 emissions during periods of pure oxygen usage.

This equation is stated as follows:

) stack in 2 O measured air combustion in conc (O2 20.9 * Pollutant = Pollutant

drybasis basis dry measured corrected

−

In this scenario, the pollutant in the equation would be SO2. Th e measured pollutant is the raw values for SO2 from the CEMS analyzer. The measured O2 in the stack on a dry basis is the value for O2 from the CEMS analyzer. The only va riable that needs to be calculated is the O2 concentration in combustion air on a dry basis. The following information describes the methodology used for calculating the O2 concentra tion in combustion air to account for the use of pure oxygen.

JBC: The use of this equation is appropriate provided that the emission limit was derived primarily (or only) from systems that did not use oxygen enrichment. While some of the fluid catalytic cracking unit (FCCU) or fluid coking unit (FCU) data might have been from oxygen enriched systems, we do not know how many or to what extent oxygen enrichment was used. It is very unlikely that we have da ta for units that have very high oxygen enrichment. As such, the equation above can be used to effectively reduce the measured concentration in the oxygen enriched system to the concentration that woul d have occurred had air been used. The emission limit assumes a certain amount of N2 will dilute the measured po llutant concentration. Without the extra nitrogen, you will have less total gas flow and but hi gher concentrations even though you have the same mass emissions as a system that burns only air. The equation suggested for FCCU corrects this higher measured concentratio n downward to be comparable to concentration that would be present had the unit been air- fed (all other things being equal). All O2 concentrations used in this equa tion should be in units of % by volume, on a dry basis. [Note: the above equation is not appropriate for oxygen en riched sulfur recovery units (SRU), because the emission limits for that affect ed facility were derived specif ic for oxygen enriched systems.] [end JBC]SO2 Emissions to 0% O2 Compensation_jbc comments.doc

Calculating Combustion Air on a Dry Basis The first step is to calculate the total air on a wet basis based upon the flow meters in our system and then convert that flow to a dry basis. To calculate the wet basis flow, the flows from all sources of combustion ai r should be summed.

Using the absolute humidity, the total air on a we t basis was converted to a total air on a dry basis.

) * ( Humidity Absolute Air Total Air Total Air Total wetbasis wetbasis drybasis − =

In order to calculate absolute humidity, there ha s to be a reference to ambient temperature, relative humidity, and barometric pressure. Rece ntly, these weather variables have been added to the PI system. For the period in question howev er, this data is not available via PI. Rather, historical data for these variables were sought from http://www.weatherunderground.com

.
To calculate the absolute humidity, the following equation was utilized:

100

Humidity lative Re
* Humidity Saturated Humidity Absolute =

Absolute humidity is expressed as pounds of water per pound of air.

To calculate the saturated humidity, the following equation was utilized: 

## ( )
S amb S
air water P P / P * MW MW Humidity Saturated

− =

Saturated humidity is expressed as pounds of water per pound of air. Values and assumptions for each variable in the above equation are as follows.

• Molecular Weight of Water (MW water ) – 18.02

• Molecular Weight of Air (MW air ) – 28.85

• Vapor Pressure of Water at Ambient Temperature (P S ) – determined from steam tables based upon the ambient temperature for each day (expressed in psia).

• Ambient Pressure (P amb ) – daily barometric pressu re (expressed in psia).

JBC: I agree with the last equation. However, note the (Percent) Relative Humidity is actually defined as RH = 100 P WV /P S (where P WV is the partial pressure of water vapor). Absolute Humidity is defined as:



## ( )
WV amb WV
air water P P P MW MW Humidity Absolute

− = / *

The middle equation would only change the numerat or, but not the denominator. The correct equation for absolute humidity should be:SO2 Emissions to 0% O2 Compensation_jbc comments.doc



## ( )( ) ( ) 100 / * / 100 / * * RH P P RH P MW MW Humidity Absolute S amb S
air water

− =

Finally, absolute humidity has units pounds of wate r per pounds of DRY air. As such, the first equation in this section is not correct.

[Note: There may also be issues with the flow meter: does the flow meter measure volumetric flow (e.g., velocity, which is then translated to volu metric flow) or is it really a mass flow meter? For current purposes, I will assume the flow meter provides (or is used to estimate) the mass flow. However, to properly convert a volumetric flow rate to mass flow rate, you would have to know the average molecular with of the gas str eam, and given confusion on the water content, I am concerned that this flow rate may have errors...]

I believe the correct equation fo r mass flow of dry air is:

) 1 ( Humidity Absolute Air Mass Total Air Mass Total wetbasis drybasis + =

[end JBC]

Calculating Purchase O2 Usage Utilizing a PI, there is a tag fo r the amount of pure O2 (tons/day) that is used at FCU600.

Calculating O2 Concentration in Combustion Air While Using Pure O2 Utilizing the calculations above, the calculation for O2 concentration in combustion air while using pure O2 is stated as:

100 * 2 O Purchased Total Air Total 1 * 2 O Purchased Total 209

. 0 * Air Total Air Combustion in Conc 2 O

drybasis drybasis drybasis + +

=

This equation assumes 0.209 as the concentration of O2 in air and 1 as the concentration of O2 in the O2 from Praxair.

JBC: Again, I have issues with units in this equation. The 0.209 factor is a volumetric concentration of oxygen in air. Ex cept for this term, a ll other factors on the RHS of the equation appear to be provided on a mass basis. The oxygen concentration of air on a mass basis is approximately 0.232. However, the “O2 Conc in Combustion Air dry basis ” needs to be determined on volumetric basis (for use in the initial equation of this section). As such, all of the flow rates need to be calculated on a volumetri c basis for use in this equation. [end JBC]