Caribbean basin ethanol dehydration energy usuage and co2 emissions



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CARIBBEAN BASIN ETHANOL DEHYDRATION
ENERGY USUAGE AND CO2 EMISSIONS

Hydrous ethanol is imported from Brazil to dehydration plants in the Caribbean Basin where it is processed through molecular sieve technology into anhydrous ethanol. The dehydration process requires steam energy to heat and cool ethanol. The energy used to create steam is generated by burning fossil fuels which range from natural gas in Trinidad to heavy fuel oil at the plants in the other countries.


Industry experts have calculated that approximately 4000 BTU’s of fuel and .05kwh of electricity are used in the conversion of one gallon of hydrous to anhydrous ethanol.1 All this fossil fuel energy usage represents less than 5 gCO2MJ when calculated using the GREET model.
Additional CO2 emissions are generated from the transportation of the ethanol from Brazil to the Caribbean Basin and then onward to the United States. These emissions are no greater than from the transportation of ethanol directly from Brazil to the United States.
Also, pathways for Brazilian cane-based ethanol through CB ethanol dehydration facilities are more economically viable than the pathway for ethanol shipped via a direct route for anhydrous ethanol from Brazil to California. As noted by EPA in their proposed RFS2 rules, “the most likely route(for Brazilian cane-based ethanol is) through the Caribbean Basin Initiative”” because the ethanol would not be subject to the 54 cent per gallon and 2.5% ad valorem tariffs. Indeed, since a duty drawback loophole ended in September 2008, direct Brazil to U.S. ethanol shipments have practically ceased.
In analyzing the differences in the direct Brazil to U.S. pathway and the CB dehydration pathway to determine the lifecycle emissions, it is necessary for a fair comparison to look at such factors as the fugitive emissions from the pipelines carrying the hydrous or anhydrous ethanol as well the natural gas. Dehydration plants in the Caribbean Basin are at or near the ports so the distances traveled- and the accompanying fugitive emissions -in pipelines are negligible. This is not the case in Brazil. Fossil fuels such as natural gas may be shipped hundreds of miles and even imported from Bolivia in pipelines of various age and states of repair.
Since the same technology is used in Brazil and in CB countries to dehydrate ethanol, the same amount of energy should be generally required to power the dehydration process in Brazil and the Caribbean Basin. The dehydration plants in the Caribbean Basin are
1. Source: Swain, R.L. Bibb, “Molecular Sieve Dehdyrators. How they became the industry standard and how they work”, Chapter 19 in the Alcohol Textbook, p. 292
newer than those in Brazil and because of age and technology are more efficient. These factors as well as the greater emissions from the cyclohexane and benzene used in the azeotropic distillation of some of the dehydration plants in Brazil needs to be considered in comparing the dehydration pathways in the Caribbean Basin and Brazil.
We encourage EPA to use these factors as credits and lower the life cycle carbon footprint of Caribbean Basin dehydration.
The energy usage differs from plant to plant in the Caribbean Basin. The table below indicates the range.

CO2 EMISSIONS FROM CB ETHANOL DEHYDRATION




ENERGY USAGE Per Gallon of Anhydrous Produced
Gallons of fuel oil .031 to .044
BTU of natural gas 5,000
KWH of electricity .0458 to .0617

CO2 EMISSIONS CALCULATIONS


Natural Gas Fuel Oil Electricity

CO2 emissions per gallon of

anhydrous ethanol produced (lbs) 0.47 0.65
CO2 emissions (gCO2/MJ) 2.64 3.67
CO 2 emissions(gCO2/MJ) per gallon

of anhydrous ethanol produced 1.31
TOTAL CO2 EMISSIONS FROM

ENERGY USAGE 3.95 4.98

Caribbean Basin ethanol dehydration emits less than 5 g of CO2/MJ from fossil fuels used to produce anhydrous ethanol. Credits from factors indicated above should be applied to reduce this number. Nevertheless, this number should be within the life cycle threshold to classify CB ethanol as an advanced biofuel.


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