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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: closed (30 November 2018) | Viewed by 15808

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Prof. Dr. Lin Ma

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Energy 2050, Department of Mechanical Engineering, Faculty of Engineering, University of Sheffield, Sheffield S3 7RD, UK
Interests: clean and sustainable energy; industrial decarbonization and energy efficiency technology with a focus on multi-scale energy process computational and CFD modelling
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Dear Colleagues,

Clean coal combustion technology aims to reduce carbon and other pollutant emissions from coal fired combustion systems in particular for applications in power generation and heavy industry sectors. Although fewer coal power plants are being built in Europe and North America, a significant percentage of electricity generation worldwide still relies on coal combustion and this will remain the case for the foreseeable future. Therefore reducing emissions from coal combustion for both existing and new systems will contribute significantly to the global emissions reductions. This special issue on clean coal combustion will cover topics of all aspects of new advances on the clean coal technology research and development, including such as low NOx and high-efficiency combustion, particulates and mercury emissions, supercritical and ultra-supercritical coal-fired technologies, carbon capture technology, gasification, combustion of low rank coals, co-firing with biomass, ash deposition, slagging and fouling. Topics on fuel (coal or biomass) preparations are also welcome.

Prof. Lin Ma
Guest Editor

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Published Papers (5 papers)

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Research

13 pages, 2980 KiB

Open AccessArticle

Cycle-to-Cycle Variation of a Diesel Engine Fueled with Fischer–Tropsch Fuel Synthesized from Coal

by Jinhong Shi, Tie Wang, Zhen Zhao, Zhifei Wu and Zhengwu Zhang

Appl. Sci. 2019, 9(10), 2032; https://doi.org/10.3390/app9102032 - 17 May 2019

Cited by 17 | Viewed by 2417

Abstract

Cycle-to-cycle variations during the combustion phase should be comprehensively investigated because these variations are among the most serious causes of higher emissions and lower efficiency. The main objective of this study was to evaluate the relationship between cyclic variations and combustion parameters. The combustion and cyclic variation characteristics were investigated using a diesel engine operating on Fischer–Tropsch (F–T) fuel synthesized from coal. Experiments were conducted under full load conditions at three engine speeds of 1200, 2000, and 2800 rpm. The results revealed that cyclic variations of F–T diesel were lower than those of 0# diesel, acquired the minimum value at the speed of 2000 rpm, and reached the maximum at the speed of 2800 rpm. The mean fluctuation intensity of F–T diesel was 0.185, 0.189, and 0.205 at speeds of 1200, 2000, and 2800 rpm, respectively, smaller than that of 0# diesel under the corresponding conditions. The relationships between cyclic variations and combustion parameters were analyzed by correlation methods. Maximum in-cylinder pressure (P_max) increased linearly with increased ignition delay, while it decreased linearly with increased combustion duration. The Pearson’s correlations between P_max and ignition delay were 0.75, 0.78, and 0.73; however, the corresponding values between P_max and combustion duration were 0.61, 067, and 0.65 when fueled with F–T diesel at speeds of 1200, 2000, and 2800 rpm, respectively. Moreover, the Pearson’s correlations of 0# diesel were higher than those of F–T diesel at the same operating loads. Compared with combustion duration, the ignition delay had more important effects on cyclic variations with a higher Pearson’s correlation. Furthermore, the ignition delay significantly influenced cyclic variation under a high speed load, while the combustion duration had a marked effect under low speed conditions. Overall, the results revealed the importance of combustion parameters on cyclic variation, which has great significance for controlled cyclic variation in diesel engines. Full article

(This article belongs to the Special Issue Clean Coal Combustion)

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16 pages, 9847 KiB

Open AccessArticle

Numerical Investigation on Co-firing Characteristics of Semi-Coke and Lean Coal in a 600 MW Supercritical Wall-Fired Boiler

by Chang’an Wang, Qinqin Feng, Qiang Lv, Lin Zhao, Yongbo Du, Pengqian Wang, Jingwen Zhang and Defu Che

Appl. Sci. 2019, 9(5), 889; https://doi.org/10.3390/app9050889 - 1 Mar 2019

Cited by 19 | Viewed by 3697

Abstract

Semi-coke is one of the principal by-products of coal pyrolysis and gasification, which features the disadvantages of ignition difficulty, low burnout rate, and high nitrogen oxides (NO_x) emission during combustion process. Co-firing semi-coke with coal is a potential approach to achieve clean and efficient utilization of such low-volatile fuel. In this paper, the co-firing performance of semi-coke and lean coal in a 600 MW supercritical wall-fired boiler was numerically investigated which has been seldom done previously. The influences of semi-coke blending ratio, injection position of semi-coke, excess air ratio in the main combustion zone, the co-firing method, and over fire air (OFA) arrangement on the combustion efficiency and NO_x generation characteristics of the utility boiler were extensively analyzed. The simulation results indicated that as the blending ratio of semi-coke increased, the NO_x emission at furnace outlet decreased. The blending methods (in-furnace versus out-furnace) had certain impacts on the NO_x emission and carbon content in fly ash, while the in-furnace blending method showed more flexibility in co-firing adjustment. The injection of semi-coke from the upper burners could significantly abate NO_x emission at the furnace outlet, but also brought about the rise of carbon content in fly ash and the increase of outlet temperature. Compared with the condition that semi-coke and lean coal were injected from different burners, the burnout ratio of the blend premixed outside the furnace was higher at the same blending ratio of semi-coke. With the excess air ratio in the main combustion zone increased, NO_x concentration at the furnace outlet was increased. The excess air ratio of 0.75 in the main combustion zone was recommended for co-firing 45% semi-coke with lean coal. The operational performance of the boiler co-firing semi-coke was greatly affected by the arrangement of OFA as well. The amount of NO_x generated from the supercritical wall-fired boiler could be reduced with an increase of the OFA height. Full article

(This article belongs to the Special Issue Clean Coal Combustion)

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22 pages, 2154 KiB

Open AccessFeature PaperArticle

Simulation of Coal Gasification in a Low-Temperature, High-Pressure Entrained-Bed Reactor with a Volatiles Condensation and Re-Evaporation Model

by Ming-Hong Chen, Yau-Pin Chyou and Ting Wang

Appl. Sci. 2019, 9(3), 510; https://doi.org/10.3390/app9030510 - 1 Feb 2019

Cited by 5 | Viewed by 3353

Abstract

The objective of this study is to implement a tar condensation and re-vaporization sub-model in a previously established Computational Fluid Dynamics (CFD) model for the Entrained Slagging Transport Reactor (E-STR) gasifier, modified from the existing E-Gasifier simulation models in previous studies. The major modifications in E-STR, compared to the existing E-Gas^TM design, include higher operating pressure and lower temperature, with the aim of achieving a higher H₂/CO ratio of syngas, which is more favorable for synthetic natural gas (SNG) production. In this study, the aforementioned sub-model is described by the UDF (User-Defined Function) and incorporated in a previously developed computational model for entrained-flow gasification process, to study the syngas composition without implementing a tars-cracking catalyst in the E-STR gasifier. The results show that incorporating the tar condensation model leads to a formation of approximately 6.47% liquid volatiles and an exit temperature increase about 135 K, due to the release of latent heat. These sub-models have been successfully implemented and will be useful in the condition that the gasifier temperature is intentionally kept low, just as the E-STR gasifier. The results indicate that high pressure and less oxygen feed produce a higher H₂/CO ratio, more favorable for SNG production. Full article

(This article belongs to the Special Issue Clean Coal Combustion)

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12 pages, 1903 KiB

Open AccessArticle

Experimental Study on NO_x Reduction in Oxy-fuel Combustion Using Synthetic Coals with Pyridinic or Pyrrolic Nitrogen

by Chang’an Wang, Pengqian Wang, Lin Zhao, Yongbo Du and Defu Che

Appl. Sci. 2018, 8(12), 2499; https://doi.org/10.3390/app8122499 - 5 Dec 2018

Cited by 6 | Viewed by 2739

Abstract

Oxy-fuel combustion technology can capture carbon dioxide (CO₂) in the large-scale and greatly lower nitrogen oxides (NO_x) emission in coal-fired power plants. However, the influence of inherent minerals on NO_x reduction still remains unclear and the impact of oxy-fuel combustion on the transformation of different nitrogen functional groups has yet to be fully understood. The present work aims to obtain a further understanding of the NO_x reduction during oxy-fuel combustion using synthetic coals with pyrrolic or pyridinic nitrogen. Compared to pyridinic nitrogen, more of the pyrrolic nitrogen in synthetic coal was converted to NO_x. The conversion ratio of nitric oxide (NO) first increased significantly with the rising oxygen content and then trended to an asymptotically constant as the oxygen (O₂) content varied between 10–50%. The nitrogen dioxide (NO₂) formation was roughly proportional to the oxygen content. The NO₂ conversion was increased with particle size but the case of NO showed a non-monotonic variation. The catalytic effects of sodium carbonate (Na₂CO₃), calcium carbonate (CaCO₃), and ferric oxide (Fe₂O₃) on the transformation of pyridinic nitrogen to NO were independent of the combustion atmosphere, while the alteration from air to the oxy-fuel combustion led to a change of mineral catalytic effect on the oxidation of pyrrolic nitrogen within the coal matrix. Full article

(This article belongs to the Special Issue Clean Coal Combustion)

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14 pages, 2309 KiB

Open AccessArticle

Emission Behaviors of Inorganic Ultrafine Particles during Zhundong Coal Oxy-Fuel Combustion with Characterized Oxygen Input Fractions Comparable to Air Combustion

by Bin Fan, Chang Wen, Xianpeng Zeng, Jianqun Wu and Xin Yu

Appl. Sci. 2018, 8(9), 1486; https://doi.org/10.3390/app8091486 - 29 Aug 2018

Cited by 10 | Viewed by 3125

Abstract

Zhundong low-rank coal is very likely to be utilized extensively in oxy-fired boilers in the near future. Its PM₁₀ (particulate matter with an aerodynamic diameter of ≤10 μm) emission behaviors during oxy-fuel combustion need to be carefully studied before its large-scale use. The present study examines the emission behaviors of inorganic ultrafine particles (PM_0.5, with an aerodynamic diameter of ≤0.5 μm), as well as PM₁₀ during the combustion of Zhundong coal in air and oxy-fuel conditions (O₂/CO₂) at three characterized O₂ input fractions, i.e., 21, 27 and 32 vol.%. The combustion experiments were carried out in a high-temperature drop-tube furnace (HDTF) at a combustion temperature of 1500 °C. The results show that PM_0.5 is composed of Na, S, Mg and Ca, with total fractions of ~90%, while PM_0.5–10 (with an aerodynamic diameter between 0.5 and 10 μm) predominantly contains Ca (~50–65%). At three characterized oxygen fractions during oxy-fuel combustion (OXY21, 27 and 32), the promoted O₂ fraction was found to increase the yields of both PM_0.5 and PM_0.5–10. A higher particle-burning temperature and a lower CO₂ fraction promote the reactions of both organically bound elements and inorganic minerals, increasing the partitioning of Mg and Ca and causing an increased yield of PM_0.5. The yield of PM_0.5 from air is high and similar to that from OXY32 while the yield of PM_0.5–10 from air is similar to that from OXY27. The high yield of PM_0.5 from air is mainly generated by the highest yields of Ca in four conditions. Full article

(This article belongs to the Special Issue Clean Coal Combustion)

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