In 2008, Safeway has converted all its trucks to bio-diesel B20 which is a mixture of 20% of bio-diesel produced from soybean and 80% of diesel in volume. It claimed that 34,000 tons of CO₂ emissions were saved per year.

EPA recently characterized the CO₂ emission reduction for biofuel . B100 Biodiesel from soybean represents a reduction of 57% of CO₂ emissions compared to traditional Diesel (from 100 kg CO2/mmBtu for diesel to 43 kg CO2/mmBtu).

The energy contained in bio-diesel is 126kBtu/Gal, and in diesel 139kBtu/Gal.

a. What are the emissions in kg CO₂/Gal of Diesel and Bio-diesel (in kg CO₂/Gal)?

CO₂/Gal of Diesel = 100.0.139 = 13.9 kg CO₂/Gal of Diesel

CO₂/Gal of Bio-diesel = 43.0.126 = 5.4 kg CO₂/Gal of Bio-diesel

b. What are the emissions of B₂0 (in kg CO₂/Gal)?

Each gallon of B20 contains 0.8 gallon of Diesel and 0.2 gallon of Bio-diesel therefore the emissions of B20 are CO₂/Gal of B₂0 = 0.8.13.9 + 0.2.5.4 = 12.2 kg CO₂/Gal of B20

c. What is the energy contained per gallon of B20 (in kBtu/Gal)?

Similarly:

Energy/Gal of B20 = 0.8.139 + 0.2.126 = 136.4kBtu/Gal of B20

d. What are the emissions of B20 (in kg CO2/mmBtu)?

CO₂/mmBtu of B20 = 12.2/136.1000 = 89 kg CO₂/mmBtuof B20

e. The energy required by the trucks being the same with B20 and Diesel, what was the energy required by Safeway's trucks annually (in mmBtu/y)?

Safeway's trucks saved 34,000 tons of CO2 annually by switching to B20, the energy required by the Safeway trucks is therefore:

Energy/year = 34,000/(100-89).1000 = 3.2 106mmBtu/year

f. What was the annual Diesel consumption by Safeway's trucks (in Gal/year)?

Consumption/year of Diesel = 3.2 106/0.139 = 23 106 Gal/y

g. What is the annual Bio-Diesel consumption by Safeway's trucks (in Gal/year)?

Consumption/year of B20 = 3.2 106/0.136 = 24 106 Gal/y

Consumption/year of Bio-Diesel = 0.2.24 106 = 4.7 106 Gal/y

h. Knowing that the yield of Soybean is 53 Gal/acre per year, what soybean acreage is required to run all Safeway's trucks on Biodiesel (in Acre)?

Soybean acreage = 89,300 Acres = 361 km²