LIFECYCLE ASSESSMENT OF SWEET SORGHUM STALK JUICE-BASED BIOETHANOL IN KENYA

Authors

  • J. Mbothu Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya
  • U. Mutwiwa Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya
  • B. Eshton Technical University of Kenya, Nairobi Kenya
  • L. Abubakar Technical University of Mombasa, Mombasa Kenya

Keywords:

Sweet sorghum stalk juice, bioethanol, energy balances, greenhouse gas emissions, life cycle assessment, Kenya

Abstract

Biofuels have been promoted in many countries for reducing greenhouse gas (GHG) emissions and fossil fuel consumption. Sweet sorghum has gained traction as a viable bioethanol feedstock due to its short maturity period as well as being drought resistance. This study evaluates greenhouse gas (GHG) emissions and energy inputs in the production of sweet sorghum stalk juice-based bioethanol in Kenya. The bioethanol production stages include cultivation, milling, bioethanol conversion and co-generation. The study estimated the GHG emissions to be 424.19 gCO2eq per litre of bioethanol produced. The total energy consumption was calculated to be 10.08 MJ per litre of bioethanol produced. For energy balances per litre of bioethanol, the study obtained; net energy value (NEV) = 11.12 MJ, net renewable energy value (NREV) = 19.68 MJ and net energy ratio (NER) = 13.6. The positive value of NEV indicates that the total energy consumption to produce a litre of bioethanol is less than its energy content. The high positive values of NREV and NER indicate low amount of fossil fuels are required to produce a litre of bioethanol. The study used mass allocation to partition GHG emissions and energy inputs at each stage/operation of the sweet sorghum lifecycle. Sensitivity analysis on the effects of stalk, juice and bioethanol yields on GHG emissions and NEV was performed. The study found GHG emissions to be sensitive to stalk yield and NER to be sensitive to bioethanol yield.

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Published

2019-07-22