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Summary: Coal is the most abundant energy source, and around 40% of the world's electricity is produced by coal combustion. The emission generated through it put a constraint on power production by coal combustion. There is a need to reduce the emissions generated through it to utilize the enormous energy of coal for power production. Detailed understanding of various aspects of coal combustion is required to reduce the emissions from coal‐fired furnaces. The aim of present paper is to review various aspects of pulverized coal combustion such as oxy‐fuel combustion, co‐combustion of coal and biomass, emissions from pulverized coal furnaces, ash formation and deposition, and carbon capture and sequestration (CCS) technologies to outline the progress made in these aspects. Both experimental and numerical aspects are included in this review. This review also discusses the thermodynamic aspects of the combustion process. Furthermore, the effect of various submodels such as devolatilization models, char combustion models, radiation models, and turbulent models on the process of pulverized coal combustion has been investigated in this paper. [ABSTRACT FROM AUTHOR]

In this paper we show the effects of expanding the system when evaluating well-to-wheel (WTW) CO2 emissions for biomass-based transportation, to include the systems surrounding the biomass conversion system. Four different cases are considered: DME via black liquor gasification (BLG), methanol via gasification of solid biomass, lignocellulosic ethanol and electricity from a biomass integrated gasification combined cycle (BIGCC) used in a battery-powered electric vehicle (BPEV). All four cases are considered with as well as without carbon capture and storage (CCS). System expansion is used consistently for all flows. The results are compared with results from a conventional WTW study that only uses system expansion for certain co-product flows. It is shown that when expanding the system, biomass-based transportation does not necessarily contribute to decreased CO2 emissions and the results from this study in general indicate considerably lower CO2 mitigation potential than do the results from the conventional study used for comparison. It is shown that of particular importance are assumptions regarding future biomass use, as by expanding the system, future competition for biomass feedstock can be taken into account by assuming an alternative biomass usage. Assumptions regarding other surrounding systems, such as the transportation and the electricity systems are also shown to be of significance. Of the four studied cases without CCS, BIGCC with the electricity used in a BPEV is the only case that consistently shows a potential for CO2 reduction when alternative use of biomass is considered. Inclusion of CCS is not a guarantee for achieving CO2 reduction, and in general the system effects are equivalent or larger than the effects of CCS. DME from BLG generally shows the highest CO2 emission reduction potential for the biofuel cases. However, neither of these options for biomass-based transportation can alone meet the needs of the transport sector. Therefore, a broader palette of solutions, including different production routes, different fuels and possibly also CCS, will be needed. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY In recent years, integrated gasification combined cycle technology has been gaining steady popularity for use in clean coal power operations with carbon capture and sequestration (CCS). This study focuses on investigating two approaches to improve efficiency and further reduce the greenhouse gas (GHG) emissions. First, replace the traditional subcritical Rankine steam cycle portion of the overall plant with a supercritical steam cycle. Second, add different amounts of biomass as feedstock to reduce emissions. Employing biomass as a feedstock has the advantage of being carbon neutral or even carbon negative if CCS is implemented. However, due to limited feedstock supply, such plants are usually small (2-50 MW), which results in lower efficiency and higher capital and production costs. Considering these challenges, it is more economically attractive and less technically challenging to co-combust or co-gasify biomass wastes with low-rank coals. Using the commercial software, Thermoflow®, this study analyzes the baseline plants around 235 MW and 267 MW for the subcritical and supercritical designs, respectively. Both post-combustion and pre-combustion CCS conditions are considered. The results clearly show that utilizing a certain type of biomass with low-rank coals up to 50% (wt.) can, in most cases, not only improve the efficiency and reduce overall emissions but may be economically advantageous, as well. Beyond a 10% Biomass Ratio, however, the efficiency begins to drop due to the rising pretreatment costs, but the system itself still remains more efficient than from using coal alone (between 0.2 and 0.3 points on average). The CO2 emissions decrease by about 7000 tons/MW-year compared to the baseline (no biomass), making the plant carbon negative with only 10% biomass in the feedstock. In addition, implementing a supercritical steam cycle raises the efficiency (1.6 percentage points) and lowers the capital costs ($300/kW), regardless of plant layout. Implementing post-combustion CCS consistently causes a drop in efficiency (at least 7-8 points) from the baseline and increases the costs by $3000-$4000/kW and $0.06-$0.07/kW-h. The SOx emissions also decrease by about 190 tons/year (7.6 × 10−6 tons/MW-year). Finally, the CCS cost is around $65-$72 per ton of CO2. For pre-combustion CCS, sour shift appears to be superior both economically and thermally to sweet shift in the current study. Sour shift is always cheaper, (by a difference of about $600/kW and $0.02-$0.03/kW-h), easier to implement, and also 2-3 percentage points more efficient. The economic difference is fairly marginal, but the trend is inversely proportional to the efficiency, with cost of electricity decreasing by 0.5 cents/kW-h from 0% to 10% biomass ratio (BMR) and rising 2.5 cents/kW-h from 10% to 50% BMR. Pre-combustion CCS plants are smaller than post-combustion ones and usually require 25% less energy for CCS due to their compact size for processing fuel flow only under higher pressure (450 psi), versus processing the combusted gases at near-atmospheric pressure. Finally, the CO2 removal cost for sour shift is around $20/ton, whereas sweet shift's cost is around $30/ton, which is much cheaper than that of post-combustion CCS: about $60-$70/ton. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]