☆ 4.7 Article

Co-firing of coal and biomass under pressurized oxy-fuel combustion mode: Experimental test in a 10 kWth fluidized bed

CHEMICAL ENGINEERING JOURNAL (2022)

Journal

CHEMICAL ENGINEERING JOURNAL

Volume 431, Issue -, Pages -

Publisher

ELSEVIER SCIENCE SA

DOI: 10.1016/j.cej.2021.133457

Keywords

Oxy-fuel combustion; Pressurized combustion; Co-firing of coal and biomass; Pressurized oxy-fuel fluidized bed; CO2 capture

Funding

Key Program of the National Natural Science Foundation of China [51736002]
Postgraduate Research & Practice Innovation Program of Jiangsu Province [KYCX20_0098]
Fundamental Research Funds for the Central Universities [3203002108D]
China Scholarship Council (CSC)
Australian Research Council

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Abstract

Successful realization of stable, pressurized, and oxy-fuel combustion mode with coal and biomass mixtures as fuels in fluidized bed. Increasing combustion pressure and biomass blending ratio not only benefits better temperature distribution, more CO2 enrichment in flue gas, and higher combustion efficiency, but also reduces NOx and SO2 emissions.

Pressurized oxy-fuel combustion (POFC) of solid fuels in fluidized beds possess the potential for CO2 capture at low cost. However, the practical experience of oxy-coal combustion in pressurized fluidized beds (PFB) is still very limited, and there is a lack of attempts on the co-firing of coal and other fuels. In this study, the co-firing of coal and biomass in a POFC mode at a 10 kWth PFB was tested. The dynamic behaviors of the start-up process and combustion mode switching were investigated. The effects of key operating parameters, including combustion pressure (P), biomass blending ratio (M-b), and excess oxygen coefficient (alpha), on the temperature distributions, CO2 enrichment and conversion, pollutant emissions (CO, NOX, SO2), and solid residues were methodically studied. The results show that the stable, pressurized, and oxy-fuel combustion mode with coal and biomass mixtures as fuels can be successfully realized in a fluidized bed. Increasing P and M-b not only conduces to better temperature distribution, more CO2 enrichment in flue gas, and higher combustion efficiency but also has the advantage of reducing NOx and SO2 emissions by over 30%. In the oxy-fuel PFB, the positive effect of alpha on the combustion performance is more significant than that under atmospheric conditions. As P increases, the fly ash surface is more cracked, and the particle size distribution of fly ash decreases, while the bottom slag surface is smoother. Besides, the increase in P results in a decreased specific surface area and cumulative pore volume but an increased average pore diameter in fly ash.

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Co-firing of coal and biomass under pressurized oxy-fuel combustion mode in a 10 kWth fluidized bed: Nitrogen and sulfur pollutants

Qinwen Liu, Wenqi Zhong, Aibing Yu, Chi-Hwa Wang

Summary: This study investigates the nitrogen and sulfur pollutants generated from co-firing coal and biomass under pressurized oxy-fuel combustion. The results show that increasing combustion pressure and biomass blending ratio can significantly reduce emissions of nitrogen oxides, sulfur dioxide, and carbon monoxide, and improve the sulfur self-retention efficiency. The study also reveals that sulfur self-retention occurs through direct sulfation under the typical operating temperature range. Additionally, the pressurized and co-firing conditions have a synergistic effect on reducing sulfur dioxide emissions.