Abstract
The conversion of solid fuels via gasification is a viable method to produce valuable fuels and chemicals or electricity while also offering the option of carbon capture. Fluidized bed gasifiers are most suitable for abundantly available low-rank coal. The design of these gasifiers requires well-developed kinetic models of gasification. Numerous studies deal with single aspects of char gasification, like influence of gas compositions or pre-treatment. Nevertheless, no unified theory for the gasification mechanisms exists that is able to explain the reaction rate over the full range of possible temperatures, gas compositions, carbon conversion, etc. This study aims to demonstrate a rigorous methodology to provide a complete char gasification model for all conditions in a fluidized bed gasifier for one specific fuel. The non-isothermal thermogravimetric method was applied to steam and CO2 gasification from 500 °C to 1100 °C. The inhibiting effect of product gases H2 and CO was taken into account. All measurements were evaluated for their accuracy with the Allan variance. Two reaction models (i.e., Arrhenius and Langmuir–Hinshelwood) and four conversion models (i.e., volumetric model, grain model, random pore model and Johnson model) were fitted to the measurement results and assessed depending on their coefficient of determination. The results for the chosen char show that the Langmuir–Hinshelwood reaction model together with the Johnson conversion model is most suitable to describe the char conversion for both steam and CO2 gasification of the tested lignite. The coefficient of determination is 98% and 95%, respectively.
Highlights
The electric power sector contributes to about a quarter of the total CO2 emissions worldwide.in most mitigation scenarios for climate change the share of low-carbon electricity supply increases from the current share of approximately 30% to more than 80% by 2050 [1].A power plant based on integrated gasification combined cycle (IGCC) is a very suitable addition to any future power system, because it offers the possibility to capture CO2 in a very efficient pre-combustion process
A correction term of an exponential type fits the results for every kinetic models (VM, grain model (GM), random pore model (RPM), and Johnson model (JM))
The L–H model generally leads to significantly better results than the Arrhenius model with the coefficient of determination being larger for any given conversion model except from the GM for CO2 gasification
Summary
In most mitigation scenarios for climate change the share of low-carbon electricity supply (comprising renewable energy, nuclear and carbon capture and storage) increases from the current share of approximately 30% to more than 80% by 2050 [1]. A power plant based on integrated gasification combined cycle (IGCC) is a very suitable addition to any future power system, because it offers the possibility to capture CO2 in a very efficient pre-combustion process. In a poly-generation configuration, this technology is able to accommodate the intermittent renewable power generation from wind and solar and operate the gasification island at full load by producing synthetic chemical products like hydrogen, SNG, methanol, and Fischer–Tropsch fuels. An understanding of the mechanics of char gasification for the chosen fuel is essential for the design of gasifiers. Irfan et al [3] did a comprehensive review on
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