Evaluation of Catalytic Effects in Gasification of Biomass at Intermediate Temperature and Pressure

Abstract

This paper proposes and examines an alternative thermo-chemical process for biomethane production from lignocellulosic biomass, termed self-gasification. Self-gasification of biomass is envisaged to utilize a high-pressure steam gasifier (30−80 bar) at temperatures of 600−900 °C and to use the alkali metals in biomass as gasification and methanation catalysts. The concept was studied by performing preliminary process simulations and by several screening experiments with wood. The simulations gave insight into the effect of gasifier operating conditions on methane yield. After screening tests of different alkali metals, KOH was chosen as a model compound for biomass-derived ash for further experimentation. It improves char reactivity by more than an order of magnitude, and thermogravimetric data interpreted by a first-order reaction model showed that it accelerates the pyrolysis reaction reducing the activation energy from E a = 143 kJ/mol to E a = 65 kJ/mol. Methane amounts higher than dictated by equilibrium are produced with and without impregnated KOH.

Simulated Process Evaluation of Synthetic Natural Gas Production Based on Biomass Gasification and Potential of CO₂ Capture Using Membrane Separation Technology

“…In our simulation, the gasifier was operated at 60 bar and 600 . These conditions are within those investigated in the previous study 1) . To increase the methane yield of the biomass-to-SNG process, an additional methanation reactor can also be introduced, as illustrated in Fig.…”

“…The operation conditions in the reactor are highly sensitive to the composition of the outlet raw SNG gas. The reaction temperature of fluidized bed methanation is reported to vary between 200 and 500 6) , to be 350-500 at a pressure of 35 bar 2) , and to be 270 at 10 bar 7) . In the present study, to evaluate the performance of the additional methanation reactor, two criteria were introduced: unreacted hydrogen molar fraction in the outlet raw gases after water removal, and methane yield of the autothermal SNG production process shown in Fig.…”

“…To use the heat released in exothermic methanation effectively, autothermal gasification of biomass has recently been studied 1), 2) . The block diagram of the process modeling is illustrated in Fig.…”

“…However, the CO2 absorption process is generally energy-intensive and a highly efficient technology is very desirable 2) . The membrane separation unit could be an alternative approach to achieving drastically lower energy consumption.…”

Fast pyrolysis of biomass

“…Other research groups [37][38][39][40]46 who carried experiments in a wire-mesh reactor observed low char yields as well; their minimum reported char yield varies from 5-10 wt%. The vapor residence time and also vapor temperature in the wire-mesh reactor can to a certain extent be increased by increasing the total pressure inside the reactor and by removal of the liquid nitrogen cooling (section 2.4.2, Table 2.4).…”