Combustion of Solid Waste from Wood-Based Ethanol Production

The solid residue from wood-based ethanol production has a low ash content and high heating value, making it interesting for combustion applications, e.g. small-scale appliances and gas turbines. Combustion and gasification properties have been studied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Char combustion rate data obtained could be used in combustion simulations. TGA and DTA data are useful for comparison with other fuels where data are available for similar heating rates. One possible use is direct-firing of gas turbines for Combined Heat and Power (CHP) at the site of the ethanol plant. Another possible use of the material is for the production of fuel pellets. A combustion test with a 150 kW powder burner has been done. Fuel feeding and combustion were stable. The average concentration of CO in the stack gas was 8 mg/MJ, the averag concentration of NOx was 59 mg/MJ and the average total hydrocarbon concentration was below 1 ppm, at an average O2 concentration of 4.6 per cent. Process parameters, investments, costs and revenues for these two production options have been estimated. The conclusion is that CHP is the most profitable use, although the uncertainties in estimated costs are considerable. Reductions of greenhouse gas emissions are decidedly larger for the CHP option. It has been concluded that CHP production is an option worth pursuing further. The technical feasibility of using the material for direct-firing of a gas turbine remains to be established however.