Low-Temperature Gasification of Biomass and Lignite: Consideration of Key Thermochemical Phenomena, Rearrangement of Reactions, and Reactor Configuration

Abstract

This paper discusses gasification of solid fuels, such as biomass and lignite, at temperatures well below 1000 °C, which potentially realizes a loss of chemical energy (LCE) smaller than 10% but encounters difficulty in fast and/or complete solid-to-gas conversion in conventional reactor systems. First, key thermochemical and catalytic phenomena are extracted from complex reactions involved in the gasification. These are interactions between intermediates (i.e., volatiles and char), catalysis of inherent and extraneous metallic species, and very fast steam gasification of nascent char. Second, some ways to control the key phenomena are proposed conceptually together with those to rearrange homogeneous/heterogeneous reactions in series/ parallel. Third, implementation of the proposed concepts is discussed assuming different types of gasifiers consisting of a singlefluidized bed, dual-fluidized bed, triple-bed circulating fluidized bed, and/or fixed (moving) bed. The triple-fluidized bed can attain gasification with a LCE as small as 10% by introducing enhancement and/or elimination of the key phenomena and another way to recuperate heat from gas turbine and/or fuel cells (i.e., power generators in gasification combined cycles) into chemical energy of fuel gas. A particular type of fixed-bed gasifier is proposed, which is separated from a pyrolyzer to realize not only control of the key phenomena but also temporal/spatial rearrangement of exothermic and endothermic reactions. This type of gasifier can make a LCE smaller than 4%. Even a conventional single-fluidized bed provides simple and effective gasification, when tar-free/reactive char is used as the fuel instead of parent the one and contributes to a novel integrated gasification fuel cell combined cycles with a theoretical electrical efficiency over 80%.

Macroalgae-Derived Biofuel: A Review of Methods of Energy Extraction from Seaweed Biomass

“…The gasification of dry lignite and woody biomass can have high yields with up to 90% of the original chemical energy in the biomass being recovered as energy in syngas [87], with the net energy return, including energy inputs, for pyrolysis operation of dry land agricultural biomass waste ranging from 42%-53% [80].…”

Toward Low-Temperature Coal Gasification: Experimental and Numerical Studies of Thermochemical Coal Conversion Considering the Interactions between Volatiles and Char Particles

“…Its reforming is mandatory for power generation and liquid production (Hayashi et al, 2014). Liquid scrubbing techniques and catalytic reforming methods suffer from undesirable overall thermal efficiency loss and/or catalyst deactivation because of the deposition of chlorine/sulfur compounds and carbon (Abu El-Rub et al, 2004a;Devi, et al, 2002;Simell et al, 1997).…”

“…The volatiles-char interaction has been frequently reported for different reactor systems, and the results show that the interaction has a significant role in inhibiting char gasification and promoting nascent tar decomposition. (Hayashi et al, 2014;Li C.Z., 2013). However, those studies focused on laboratory-based experimental investigations only.…”

“…The cold gas efficiency can be raised theoretically further by decreasing O 2 consumption while increasing steam or CO 2 consumption, which would result in gasification operations at lower temperature. Low-temperature gasification with higher cold gas efficiency has received widespread attention in recent years (Hayashi et al, 2014).…”

Modeling of gas/particle flow in coal conversion with a drop tube reactor using a lumped kinetic model accounting volatiles–char interaction

“…Gasification is an efficient and environmentally attractive process for coal utilization [1,2]. A major challenge in coal gasification is dealing with the refractory aromatic compounds that constitute the tar formed during gasification.…”