Techno-economic assessment of biomass upgrading by washing and torrefaction

A techno-economic assessment on upgrading routes involving washing and torrefaction is presented for roadside grass, straw and miscanthus. Washing followed by torrefaction (prewash) and torrefaction followed by washing (postwash) is compared for straw. Mass and energy balances were calculated, based on previous experimental test results. Calculated internal rates of return, total annuities and payback times and a sensitivity analysis identified the most critical input parameters for profitability as being the cost of biomass, CAPEX, consumables and sludge disposal. Application of upgraded roadside grass in small-scale installations has technical limitations, but large-scale industrial applications seem feasible in the Netherlands. For the roadside grass, a negative gate fee of 25 (sic)/t and a biocoal market price of 4.8 (sic)/GJ lead to an IRR of 15.6% at an optimum plant size of 100-150 kt/a dry input. Postwash appears the most profitable option in the case of predried biomass (straw and miscanthus). However, straw upgrading is not profitable unless a gate fee can be charged as well. This could be the case for residual straws from rice and sugar cane crops in countries like Brazil, Thailand and Indonesia, upgrading the material locally and exporting it. For rice straw, a gate fee of 15 (sic)/t and a price of 6.2 (sic)/GJ for the produced biocoal lead to an IRR of 11.6% for large-scale industrial applications. The upgraded miscanthus with production costs of 7.7 (sic)/GJ, can compete with wood pellets in terms of fuel properties and prices only for smaller-scale installations.