Life cycle assessment of bio-ethanol from forest resources (hemicelluloses)
A technical analysis is performed for a new process to produce bio-ethanol from the forest resources. The new process, termed the “near neutral” hemicellulose extraction process, involves the extraction of chemical feedstock (mainly hemicellulose) using green liquor and white liquor in addition to the production of bleached hardwood Kraft pulp. The extracted chemical feedstock is used for the production of bio-fuel (ethanol) and others co-products. The goal and scope of this study is to evaluate cradle-to-gate potential human health and ecological impacts associated with the bio-ethanol product’s system. The unit processes in the defined product system are analyzed per functional unit, particularly focusing on environmental emissions as well as ancillary substances, material and energy consumptions.
The study results show the bio-ethanol contributes significantly to human toxicity (air, water and soil), global warming, ozone depletion and bulk waste potential environmental impacts categories. The raw material stage contributes significantly to human health and ecological impact categories. Collection of specific site data on raw material stage is needed to strengthen the robustness of the results. The recovery boiler, extraction and lime burning processes in the production stage have a strong contribution to human toxicity via air, water and soil, global warming and radioactive waste. Anthraquinone (AQ) material in the extraction process and fuel oil consumption in lime burning process are the significant contributors in the production stage. Landfilled gypsum material contributes strongly to bulk waste. Anthraquinone material used in the extraction is an optional input to the process and may be avoided. Fuel oil consumption in the lime burning process can be reduced by improving the percentage of smelt conversion into green liquor and white liquor.