Abstract
Possibilities of more efficient use of regional lignocellulosic resources (wood, wheat straw, peat) of different origin for an environmentally friendly energy production using selectively MW pre-treated blends of commercial wood or wheat straw pellets with raw peat pellets are studied. A hypothesis is proposed and tested that selective MW pre-treatment of wood or wheat straw pellets at the frequency 2.45 GHz and blending of MW pre-treated pellets with raw peat pellets can be used to enhance and control the thermo-chemical conversion of biomass blends. To test this hypothesis, a combined experimental study and mathematical modelling of the processes were performed. The thermo-chemical conversion of selectively activated blends was experimentally studied using a batch-size pilot device, which consists of a biomass gasifier and a combustor. To evaluate the effect of selective MW pre-treatment of biomass pellets on the thermo-chemical conversion of pre-treated blends, measurements of the kinetics of weight loss, yield of combustible volatiles, flame temperature, heat output of the device, and composition of emissions were made at different MW pre-treatment regimes of wheat straw and wood pellets and different mass fractions of pre-treated pellets in biomass blends. The developed novel 2D numerical model of thermo-chemical conversion of MW pre-treated straw confirmed that the pre-treatment of wheat straw pellets increases the generated heat and significantly affects the temperature distribution in the flame/bed zones. It was confirmed that MW pre-treatment leads to a faster thermal decomposition of biomass pellets, synergistically activating the non-treated parts of blends. The overall improved yield of combustible volatiles and their complete combustion provide a surplus of heat production by limiting the formation of GHG emissions, which allows promoting MW pre-treated biomass of different origin as efficient regional bioenergy resources for energy production.
Highlights
To reduce still growing global warming, the 2030 Climate Target Plan of the EUCommission proposes to raise the EU’s ambition on reducing greenhouse gas (GHG)emissions from 40% to at least 55% below 1990 levels by 2030 to become climate-neutral by 2050 [1]
A higher content of volatile matter was found in wood (84.1%) and wheat straw biomass (74.8%), whereas the lowest contents of volatiles were found in peat biomass (67.6%) [32]
It was shown that MW pre-treatment of wood and wheat straw pellets produced a higher heat output as a result of volatiles combustion if compare with that of raw biomass pellets
Summary
Emissions from 40% to at least 55% below 1990 levels by 2030 to become climate-neutral by 2050 [1] To ensure such a reduction in GHG emissions, it is necessary to limit the use of fossil energy sources (coal, natural gas, etc.) for energy production by gradually replacing them with renewable energy sources. Unlike solar and wind energy, all used predominantly for electricity production, plant biomass is mainly used to produce biofuels available for both heat and power generation and can be stored in solid, liquid, and gaseous states [3]. This implies that biomass is a very prospective renewable resource to replace fossil fuels reducing GHG during energy production
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