BioFuels

Biomass Farming

The bio-masses used for the bio-fuels pathways are:

• Soybean Farming
• Palm FFB Farming
• Rapeseed Farming
• Jatropha Farming
• Camelina Farming

All those farming processes are implemented in GREET. They are using regular US averages fertilizer production and Diesel for non road engine to power the farming tractors and other stationary engines used (pumps, conveyors...)

The products are assumed to be transported dried so there is no need to specify the moisture content of those materials in the transportation processes after those farming processes.

Fuel Production

General Biofuel Production Process Level ModelFile:Biofuels.dia

Bio-fuels production generates a lot of valuable co-products such as SBM, Fuel Gas or Glycerine. In the Excel spreadsheet options are offered on the main page to switch between system level allocation or process level allocation/displacement.

For the process level allocation/displacement method we create two distinct processes Oil Extraction and Transesterification. Each of them have their set of inputs and a definition of the co-products. It is therefore allowed to perform an displacement on the first process and a market allocation on the transeterification process, the co-products treatment method chosen for each process is independent.

For system level allocations, the extraction and transesterification processes are modeled as a single process with two co-products. They are aggregated in a single process to make abstraction of the vegetable oil link between the extraction and trans. processes, thus making them a single system.

Renewable Diesel II Production from Soybeans(Process Level Model)

Here are the assumptions used for this pathway :

• Yield for oil extraction : 4.7lb of dry soybeans for 1 lb of oil
• Coproducts for oil extraction : 3.7lb of SBM for 1 lb of oil
• Yield for transesterification : 1.17lb of Vegetable Oil for 1lb or Renewable Gasoline II
• Coproducts for transesterification : 0.059lb of Propane fuel gas per 1 lb of Renewable Gasoline II

The structure of the pathway is exactly the same as shown above, the pathway can be found under : LDV Fuels -> Diesel -> Renewable Diesel II -> From Soy Oil

The results of this pathway have been evaluated against the GREET1_2011 Excel spreadsheet for all available types of allocation both for Extraction and Transesterification, however the displacement options have not been validated yet. The results obtained with GREET.net are showing an error between 0.1% and 1.06% compared to the excel spreadsheet. We are still investigating those errors.

Total Energy Calculations

Naming Convention:

• OH(FaTr), OH(OlEx), OH(Trest) : Overhead energy ( former process fuel energy ) used for FArming and TRansportation of soybean, OiL EXtraction of vegetable oil, and TRansESTerification process.
• HV(SyBn), HV(SyOl), HV(D2) : Heating value Soybean, Soyoil, Diesel II
• E(CoProd2) : Energy content for coproduct 2 (the transesterification process coproducts)
• y1, y2 yield one and two, respectively extraction and transesterification
• af1, af2 allocation factors one and two, respectively extraction and transesterification

The total energy is calculated in GREET1_2011 as this :

${\color {green}{\Bigg (}}{\color {magenta}{\bigg [}}{\color {red}{\Big (}}{\color {blue}{\big [}}OH(FaTr)+HV(SyBn){\color {blue}{\big ]}\cdot y_{1}}+OH(OlEx)-HV(SyOl){\color {red}{\Big )}\cdot af_{1}}+OH(OlTr)+HV(SyOl){\color {magenta}{\bigg ]}\cdot y_{2}}+OH(Trest)-HV(D2)-E(CoProd2){\color {green}{\Bigg )}\cdot af_{2}}$

For the Oil Extraction process, the overhead is calculated using :

$(E_{in}-E(mainOut))\cdot af_{1}$

The energy content of the co-products are not accounted there. However for the Transesterification process, the overhead is calculated like this :

$(E_{in}-E(mainOut)-E(CoProd2))\cdot af_{1}$

In this one, the energy content of the co-products is accounted, here the co-product is propane fuel

In order to do that in .net we are defining a matrix which details the link between the inputs and the outputs of the process. That way we can trace what is the Basic Resource ( or the share of basic resources) which leads to this product, and when we allocate the energy content of CoProd2 is removed from the basic resources in the total energy vector. In that case Soybean.

Total Emissions Calculations

For the emissions there is no specific calculations as we are only talking here about some kind of overhead, we do not have emissions in and out to balance as for the materials in and out. Therefore the emissions calculations using allocations :

${\color {green}{\Bigg (}}{\color {magenta}{\bigg [}}{\color {red}{\Big (}}{\color {blue}{\big [}}Em(FaTr){\color {blue}{\big ]}\cdot y_{1}}+Em(OlEx){\color {red}{\Big )}\cdot af_{1}}+Em(OlTr){\color {magenta}{\bigg ]}\cdot y_{2}}+Em(Trest){\color {green}{\Bigg )}\cdot af_{2}}$

BioDiesel production from Soybeans

For bio diesel production these are the basic assumptions used :

• Yields and co-products for Oil Extraction don't change
• Yield for transesterification is 1.04lb of Vegetable Oil for 1 lb of Biodiesel
• Co-products for transesterification : 0.214 lb of Glycerine per 1 lb of Biodiesel

Glycerine can be allocated using Mass, Energy or Market value, the Heating Value (low and higher) for Glycerine is 7979 Btus/lb

The structure of the pathway is the same as presented in the Fuel Production chapter, the pathway can be found in GREET.net under : LDV Fuels -> Diesel -> Biodiesel -> From Soy Oil -> Biodiesel Production

When comparing the results from .net against the excel spreadsheet, emissions are very good, arround 0.1% of error, but some energy values are way off. Total energy was 10% off as Natural Gas and Petroleum. However there is a solution for that explained in the Total Energy Calculations below

Total Energy Calculations

The total energy is calculated in GREET1_2011 as this :

${\color {green}{\Bigg (}}{\color {magenta}{\bigg [}}{\color {red}{\Big (}}{\color {blue}{\big [}}OH(FaTr)+HV(SyBn){\color {blue}{\big ]}\cdot y_{1}}+OH(OlEx){\color {red}{\Big )}\cdot af_{1}}+OH(OlTr)+HV(SyOl){\color {magenta}{\bigg ]}\cdot y_{2}}+OH(Trest)-HV(BioDiesel){\color {green}{\Bigg )}\cdot af_{2}}$

Now comparing to the formula used for Soybean to Renewable Diesel II, this equation is missing some terms : The energy content of Vegetable Oil is not removed from the Oil Extraction process ( usually we remove the energy content of the main output ) and the energy content of the co-product is not removed from the transesterification process:

• $-HV(SyOl)$
• $-E(CoProd2)$

If those two missing terms are put back into Excel like it is done for the Soybean to Renewable Diesel II, we obtains results which are only 0.38% off for the total energy. We have discussed this phenomena with an Excel developer and it would seem that the formula used in the Renewable Diesel II pathway shown above is correct and that this one is missing necessary terms. This discrepancy must be corrected in the Excel model. A similar error occurs when analyzing the Renewable Diesel I pathway. That formula also needs to be adjusted to match the way Renewable Diesel II calculates its total energy.

=Total Emissions Calculations

Nothing spectacular, the emissions are calculated as follow :

${\color {green}{\Bigg (}}{\color {magenta}{\bigg [}}{\color {red}{\Big (}}{\color {blue}{\big [}}Em(FaTr){\color {blue}{\big ]}\cdot y_{1}}+Em(OlEx){\color {red}{\Big )}\cdot af_{1}}+Em(OlTr){\color {magenta}{\bigg ]}\cdot y_{2}}+Em(Trest){\color {green}{\Bigg )}\cdot af_{2}}$