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MEMORANDUM TO THE DOCKET: Regarding the Application of the Work 

Allocation Methodology to the Dakota Spirit Ag 

Energy Proposed Ethanol Plant

DATE: August 31, 2012

Dakota Spirit AgEnergy (“Dakota”) petitioned the Agency on October 15, 2011 to approve their 

generation of renewable fuel RINs (D-code 6), pursuant to 40 CFR § 80.1416. Through the 

petition process described under 40 CFR § 80.1416, Dakota submitted data to EPA to perform a 

lifecycle greenhouse gas emissions analysis of their production of ethanol. EPA has issued a 

technical notice in response to the petition submitted by Dakota. This memo supplements the 

notice and provides the steps and equations used in the lifecycle analysis.

Based on the information submitted by Dakota, EPA assumed that the associated upstream 

emissions, fuel transport, and co-product credits are the same as those modeled for the RFS2 

final rule for corn ethanol production. Dakota will import steam from the adjacent Spiritwood 

Station power plant for its fuel production process. As a result, Dakota’s emission analysis 

differs only in its fuel production emissions methodology.

Fuel Production Emissions

Fuel production emissions can be calculated (in terms of grams CO2e per gallon of ethanol 

produced) from the plant energy use and the GHG emission factor associated with energy use as 

follows:

Emissions (

 

 ) = Energy Use 



  × GHG Emission Factor 

 

 

Dakota’s fuel production emissions consist of four major components:

1) Process steam from Spiritwood power plant main boiler operating in CHP mode

2) Process steam from Spiritwood power plant backup boiler operating in steam mode

3) Electricity purchased from grid

4) Natural gas to operate emission controls

Process steam is the largest component, consisting of close to 90% of Dakota’s plant energy

use, while electricity accounts for most of the remainder, and emission controls use an almost 

negligible amount of energy. The emissions associated with purchased electricity use and onsite 

emission controls were derived from the energy use data from Dakota’s petition and the GHG 

emission factors promulgated as part of the RFS2 final rule. The GHG emissions associated with 

process steam are described in the next section.
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Process Steam Emissions

In the proposed Dakota plant process, thermal energy (steam in this case) for the process will be 

supplied from the Spiritwood Station power plant, located adjacent to Dakota. The Spiritwood 

plant maintains two boilers capable of providing steam to Dakota: a main boiler that operates on 

coal and a backup boiler that operates on natural gas. When the main boiler at Spiritwood is out 

of service (either due to planned or unplanned outages), the backup boiler at Spiritwood will

provide steam to Dakota. Since the backup boiler operates in steam-only mode, its emissions will 

be comparable to an onsite boiler. Therefore, the backup boiler emissions were calculated using

the backup boiler energy use provided in the Dakota petition and the natural gas GHG emission 

factor from the RFS2 final rule.

The main boiler will operate in a CHP configuration to provide electricity for the grid and steam 

for Dakota’s production process. In this configuration, a portion of the steam driving the steam 

turbine generator will be extracted to meet Dakota’s thermal energy needs. In CHP mode, for 

each unit of fuel consumed in the boiler, there is a net reduction in the amount of electricity 

generated by the power plant. Although the amount of electricity generated is reduced, the total 

fuel consumed and the resulting GHG emissions of the power plant remain unchanged. 

Work Potential Allocation Method

To determine the emissions associated with the extracted steam, the total emissions of the 

Spiritwood power plant need to be allocated to the power plant’s power production and to the 

steam extracted for use at the biorefinery. EPA’s proposed allocation approach for this CHP 

configuration is the “work potential” method. The process for determining the steam GHG 

emission factor using the work potential allocation approach is summarized by the following 

steps:

1. Calculate the GHG emission factor for the Spiritwood power plant without any steam 

extracted;

2. Determine the amount of electricity that is not generated due to the extraction of steam for 

the Dakota plant; and

3. Apply the Spiritwood GHG emission factor from Step One to the amount of electricity not 

generated due to steam extraction and calculate the emission factor associated with the 

extracted steam.
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Step One – Calculate the GHG emission factor for the Spiritwood power plant without any steam 

extracted

The power-only emission factor for the power plant was calculated based on the steam flow and 

energy value data provided in Dakota’s petition. The CO2 emission factor was based on the 

carbon content of the coal given by Dakota, and the combustion CH4, combustion N2O, and 

upstream coal emission factors were the same as those used in the 2010 RFS rule. For 

consistency, all values were represented on a lower heating value (LHV) basis. 

Based on the Dakota petition, the coal combusted in the boiler has a carbon content of 44%, a 

higher heating value (HHV) of 7450 Btu/lb, and a LHV of 6844 Btu/lb. The Spiritwood power 

plant in power-only mode has an efficiency for electricity production of 28.7% on a HHV basis, 

which converts to an efficiency of 31.3% on a LHV basis. Each emission factor was calculated 

taking the following steps:

CO2 emission factor from coal combustion (g CO2/Btu)

.  

 

×

  

  

×

 

 

×

.  

 

= 0.106927  2/

CH4 emission factor from coal combustion (from 2010 RFS2 rule) (g CO2/Btu)

4.0

 



× 21  

 

×

 

 × 

= 0.000084  2/

N2O emission factor from coal combustion (from 2010 RFS2 rule) (g CO2/Btu)

1.0

 



× 310  

 

×

 

 × 

= 0.000310  2/

Upstream GHG emission factor (from 2010 RFS2 rule) = 0.004171 2/

The GHG fuel emission factor was first determined on an input basis as follows:

GHG Emission Factor on input basis (g CO2e/Btu input)

=      +   

= 0.106927 + 0.000084 + 0.000310 + 0.004171 = 0.1115

g CO2e

Btu input

The GHG fuel emission factor on output basis can be determined from the factor developed on 

an input basis by using the efficiency of electricity production at the Spiritwood plant.
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GHG Emission Factor on output basis (g CO2e/MWh output)

= 0.1115  

 

× 3412 



× 1000 



÷ 31.3%

= 1,215,961 g CO2e/MWh
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Step Two – Determine the amount of electricity that is not generated due to the extraction of 

steam for the Dakota plant.

The amount of electricity not generated due to steam extraction is determined with the mass flow

rate of steam extracted from the process prior to the steam entering the low-pressure steam 

turbine (LPST) and the enthalpy drop over the LPST. The mass flow rates and enthalpy drop 

were based on data provided in the Dakota petition. The amount of electricity not generated was 

determined to be 9.987 MW:

Displaced Power (MW)

=

(     )× × 

⁄ 

=

(. . /)×,⁄×.%

 ⁄

×

 

 

= 9.987 
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Step Three – Apply the Spiritwood GHG emission factor from Step 1 to the amount of electricity

not generated due to steam extraction and calculate the emission factor associated with the 

extracted steam.

The GHG emission factor of the emissions associated with the extracted steam was then 

calculated with the Spiritwood “No CHP” emission factor calculated in Step One above and the 

amount of electricity not generated due to steam extraction calculated in Step Two above. We 

determined the emission factor for the imported process steam to be 53,175 g CO2e/mmbtu 

steam:

Steam emission factor (g CO2e/mmbtu steam)

=

   × 

  ∗(     )

=

,,  



×.

, / ∗(. /)

×

 × 

 

= 53,175 

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