Power generation from chemically cleaned coals: do environmental benefits of firing cleaner coal outweigh environmental burden of cleaning?

Abstract

Power generation from high-ash coals is a niche technology for power generation, but coal cleaning is deemed necessary to avoid problems associated with low combustion efficiencies and to minimize environmental burdens associated with emissions of pollutants originating from ash. Here, chemical beneficiation of coals using acid and alkali-acid leaching procedures is evaluated as a potential coal cleaning technology employing life cycle assessment (LCA). Taking into account the environmental benefits from firing cleaner coal in pulverized coal power plants and the environmental burden of the cleaning itself, it is demonstrated that for a wide range of cleaning procedures and types of coal, chemical cleaning generally performs worse than combustion of the raw coals and physical cleaning using dense medium separation. These findings apply for many relevant impact categories, including climate change. Chemical cleaning can be optimized with regard to electricity, heat and methanol use for the hydrothermal washing step, and could have environmental impact comparable to that of physical cleaning if the overall resource intensiveness of chemical cleaning is reduced by a factor 5 to 10, depending on the impact category. The largest potential of the technology is observed for high-ash lignites, with initial ash content above 30%, for which the environmental benefits from firing cleaner coal can outweigh the environmental burden of cleaning for some impact categories. Overall, we recommend to policy makers that coal cleaning using acid or alkali-acid leaching procedures should not be considered for direct implementation as a coal beneficiation technology. We encourage further research on chemical cleaning and its optimization, however, as chemical cleaning has advantages that might make it attractive for cleaning of difficult to treat coals when compared to the less efficient option of physical cleaning. Broader contextThe use of fossil coal for generation of electricity is a major cause of many environmental problems globally. Pulverized coal-fired power plants currently account for 97% of total coal-based electricity generation globally, and are expected to constitute a significant proportion of the environmental burden attributable to power generation also in the future. Chemical cleaning of high-ash coals can potentially mitigate some environmental impacts from firing coal in pulverized power plants, as it allows reaching higher ash removal efficiencies as compared to physical cleaning, but virtually nothing is known about whether environmental benefits from firing cleaner coal outweigh environmental burdens of cleaning. Here, life cycle assessment (LCA) is employed to evaluate chemical beneficiation of coals using acid and alkali-acid leaching procedures. The results showed that demineralization is generally not a feasible option for mitigating environmental impacts, including impacts from climate change, except in few cases where regional and local impacts were improved for high-ash coal systems. This work highlights...

A review of chemical leaching of coal by acid and alkali solution

“…The mechanism of adsorption complex silica to the following possible reactions during leaching process as shown below. Where a, b, c and x, y, z accordingly in equations (6), (8) and (9) are the stoichiometric coefficient among different element while R is the hydrocarbon groups in coal matrix. DM-Demineralization, DS-Desulfurization, T-Temperature (°C), P-Pressure, t-Time, µm-Micrometer Figure 2.…”

“…The several literature studies revealed the great potential for chemical cleaning of coals, with better ash removal was obtained from the coal. Chemical cleaning method has not widely employed on a commercial scale due to huge cost related to the requirements of chemicals and the need for dewatering of the post-demineralization and regeneration of reagents from spent solution [8][9][10]. It can be seen from literature only a few studies about the regeneration of chemical reagents from the spent solution by adding a suitable chemical reagent.…”

Optimization of methane production from bituminous coal through biogasification

“…Different from in situ gasification where syngas is produced from controlled combustion of coal [8] or ex situ gasification which is generally performed at temperatures higher than 800 o C [9], biogasification can be conducted under mild environmental conditions. In addition, coal does not need to be cleaned before biogasification like those prepared for power generation [10]. This technology can be used for both in situ (abandoned or unmineable coal seams) and ex situ (coal wastes or mined out coal) scenarios [11].…”

Demineralization mechanism and influence of parameters on high ash Indian coal by chemical leaching of acid and alkali solution

“…Chemical leaching process usually achieved remove all types of minerals from the coal compared to physical treatment method. Although, chemical cleaning method has not been widely employed on a commercial scale due to huge cost related to the requirement of chemical and need for dewatering and regeneration of reagents from spent solution (Wu and Steel 2007;Waugh and Bowling 1984;Ryberg et al 2015;Sriramoju et al 2017).…”