Integrated adsorption and absorption process for post-combustion CO_(2) capture

This study explored the feasibility of integrating an adsorption and solvent scrubbing process for postcombustion CO_(2) capture from a coal-fired power plant.This integrated process has two stages:the first is a vacuum swing adsorption(VSA)process using activated carbon as the adsorbent,and the second stage is a solvent scrubber/stripper system using monoethanolamine (30 wt-%) as the solvent.The results showed that the adsorption process could enrich CO_(2) in the flue gas from 12 to 50 mol-% with a CO_(2) recovery of >90%,and the concentrated CO_(2) stream fed to the solvent scrubber had a significantly lower volumetric flowrate.The increased CO_(2) concentration and reduced feed flow to the absorption section resulted in significant reduction in the diameter of the solvent absorber,bringing the size of the absorber from uneconomically large to readily achievable domain.In addition,the VSA process could also remove most of the oxygen initially existed in the feed gas,alleviating the downstream corrosion and degradation problems in the absorption section.The findings in this work will reduce the technical risks associated with the state-of-the art solvent absorption technology for CO_(2) capture and thus accelerate the deployment of such technologies to reduce carbon emissions.

A critical review of ash slagging mechanisms and viscosity measurement for low-rank coal and bio-slags

Gasification or combustion of coal and biomass is the most important form of power generation today.However,the use of coal/biomass at high temperatures has an inherent problem related to the ash generated.The formation of ash leads to a problematic phenomenon called slagging.Slagging is the accumulation of molten ash on the walls of the furnace,gasifier,or boiler and is detrimental as it reduces the heat transfer rate,and the combustion/gasification rate of unburnt carbon,causes mechanical failure,high-temperature corrosion and on occasions,superheater explosions.To improve the gasifier/combustor facility,it is very important to understand the key ash properties,slag characteristics,viscosity and critical viscosity temperature.This paper reviews the content,compositions,and melting characteristics of ashes in differently ranked coal and biomass,and discusses the formation mechanism,characteristics,and structure of slag.In particular,this paper focuses on low-rank coal and biomass that have been receiving increased attention recently.Besides,it reviews the available methodologies and formulae for slag viscosity measurement/prediction and summarizes the current limitations and potential applications.Moreover,it discusses the slagging behavior of different ranks of coal and biomass by examining the applicability of the current viscosity measurement methods to these fuels,and the viscosity prediction models and factors that affect the slag viscosity.This review shows that the existing viscosity models and slagging indices can only satisfactorily predict the viscosity and slagging propensity of high-rank coals but cannot predict the slagging propensity and slag viscosity of low-rank coal,and especially biomass ashes,even if they are limited to a particular composition only.Thus,there is a critical need for the development of an index,or a model or even a measurement method,which can predict/measure the slagging propensity and slag viscosity correctly for all low-rank coal and biomass ashes.