Techno-economic analysis of energy efficiency measures in a pulp mill converted to an ethanol production plant

A conceptual ethanol production plant, based on conversion of a kraft pulp mill, has been studied. The process uses softwood as raw material, alkaline pre-treatment combined with delignification, and biochemical conversion of sugars to ethanol (i.e. hydrolysis and fermentation). The plant has been analysed by pinch methods in order to find steam-saving possibilities. It is shown in the study that a large amount of steam surplus can be found if energy efficiency measures are implemented. In order to study the possible effect on the profitability of the plant when introducing steam-saving measures, the process has been analysed from a techno-economic point of view. It is shown that implementing energy efficiency measures could have a substantial effect on profitability if the by-product (in this case lignin biofuel or power) is high-valued. It is also shown that lignin as by-product might be more profitable than power, mainly because the demand for CO(2) in lignin extraction might be supplied by CO(2) produced in fermentation of sugars to ethanol. If investments are made to convert a pulp mill to ethanol production, energy efficiency measures should be included in the discussion since they might play an important role in minimising ethanol production cost.