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Preliminary techno-economic assessment of biomass upgrading by washing and torrefaction

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Author: Abelha, P.M.R.
Source:27th European Biomass Conference and Exhibition, 27-30 May 2019, Lisbon, Portugal, 1-12
Identifier: 868453
Keywords: Torrefaction · Biomass · Residues · Upgrading · Pretreatment · Alkali · Economics. · Energy Efficiency · Energy / Geological Survey Netherlands


Three feedstocks — road side grass, wheat straw and miscanthus — were studied in a preliminary techno-economie analysis to evaluate the feasibility of the biomass upgrading routes. Depending on the moisture content of the origirial materials two lines were explored. Washing followed by torrefaction (pkwash) was chosen when the moisture content of the available raw biomass stream was higher than 30 wt%. This was the case of road side grass, which has about 75 wt% of moisture content. When the moisture content was lower than 30 wt.%, torrefaction followed by washing (postwash) was also explored as an option. This was the case for the straw and miscanthus (both with about 15 wt% moisture). To support the decision criteria and to validate the best route to follow, the prewash option was compared with the postwash option for the case of straw. Mass and energy balances were performed and are presented in flowcharts for each material, supported by the lab and pilot scale test results. Based on this, a preliminary economic analysis was performed to generate decision criteria, based on calculated internal rates of return (IRR), total annuities and payback times (P13) and sensitivity analysis based on the most critical input parameters for profitability. All the tested materials could be technically upgraded on large scale to commodity fuels, with some limitations on the quality, due to still significant alkali content in case of the road side grass. However, since a gate fee of about 20 E can be charged, the price at which the upgraded road side grass can be offered (4.7 E/GJ) is very attractive leading to IRR in the range of 14%, which can be further increased to 18% if sludge disposal costs could be reduced from 60 to 40 E/t. Apart from the fuel costs, capital costs, consumables and sludge disposal were the most critical parameters for the economics profitability. Postwash was the most profitable option in the case of dried biomasses upgrading (straw and miscanthus). Wheat straw upgrading is not profitable unless, a gate fee can be charged as well. This can be the case of residual straws from rice and sugar cane crops, upgrading the material locally and exporting it. A competitive price of 6.2 E/GJ can be applied for the upgraded straw giving a IRR of 7%.