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MPhil in Engineering for Sustainable Development

global challenges, engineering solutions

Studying at Cambridge

Bettina Schreck

Optimal Scale and Technological Options for the Sustainable Production of Biodiesel

This study analyses conventional technologies and current business schemes for the production of biodiesel derived from both waste sources and specifically grown crops. The aim is to provide judgment elements to determine which of the current technological alternatives and plant scales are sustainable. Despite of the current debate on energy crops becoming competitive with food provision, biofuels are a given in the current legal context. The study is limited to the chemical processing technological alternatives and agricultural activities are beyond the scope.

The environmental impacts of biodiesel production have been modelled using Life Cycle Analysis. Existing reports demonstrated that raw material production (agriculture) and manufacturing (physicochemical processing) are the stages that produce the highest impacts. This study focuses on the latter, the processing stage.

The objective is to calculate a set of economic indicators to evaluate if economies of scale have an influence in these kinds of projects and to determine the optimal scale for biodiesel plants. It also investigates alternative technologies which have different environmental and economic impacts. The extent to which the capital costs of using cleaner technologies have either positive or negative impacts on the project profitability is explored. The main results obtained are:

In terms of scales: the production of biodiesel can be profitable, having investment with positive net present value, at the current market conditions and for scales >10 000 ton of biodiesel per year; the use of waste cooking oil is more profitable than vegetable oil, since raw materials dominate costs - being 83 to 89% of manufacturing costs; that small and micro scale plants are non profitable and there is an influence in the capacity use rather than scale for these plants. In situ crushing makes the capital investment more costly and has lower economic benefits.

With regards to the technological routes: the purification of glycerol to crude grade is the best economic option; methanol distillation is considerably more expensive, with a 48% increase in the capital expenditure, but generates significant environmental benefits. When comparing washing, dry washing represent a 15% increases in capital expenditure compared to wet washing, but manufacturing costs only differ in 0.15%, hence, dry washing is economically feasible and consumes less of a critical resource.

Finally, the barriers and incentives for community scale plants are discussed.