Co-combustion Characteristics Of Coal Research Articles

Three-dimensional numerical simulation of coal and papermaking trash co-combustion in a circulating fluidized bed

Circulating fluidized bed (CFB) combustion is a important method of waste treatment with the benefits of harmlessness, recycling, and energy recovery. Using the existing co-firing CFB boiler to dispose of waste can reduce investment in boilers and environmental protection equipment. However, there is currently limited research available on the co-combustion of coal and waste (especially for papermaking trash), and the mechanism of pollutant emissions during unit operation remains unclear. In this work, the co-combustion of coal and papermaking trash in a three-dimensional industrial-scale CFB are investigated by using the Dense Discrete Phase Model (DDPM) method. Both homogeneous reactions (such as fuel particle pyrolysis, combustion, and surface reaction) and non-homogeneous reactions (such as gas combustion and pollutant generation) are considered. The co-combustion characteristics are comprehensively analyzed in terms of gas distribution, chemical reaction rates, and bed temperature under various operating conditions, including fuel mixing ratio, secondary air arrangement, and excess air coefficient. The results are obtained by comparing the distribution profile along the height. By reducing the mixing ratio of papermaking trash, the excess air coefficient, and adjusting the secondary air arrangement in the lower region, an expanding, reducing atmosphere is observed in the vicinity of the fuel feeding point. This, in turn, leads to an increase in CO concentration and a decrease in NO emissions, which is attributable to the interplay of gas distribution, chemical reaction rates, and bed temperature. A reduction in NO gas emissions was achieved by adjusting the secondary air arrangement and the excess air coefficient. Overall, this work provides valuable insights into the co-combustion characteristics of coal and papermaking trash in an industrial-scale circulating fluidized bed boilers.

Study on co-slurry and co-combustion characteristics of coal and modified-coal gasification fine slag

In this study, hydrocarbon oil was used to modify coal gasification fine slag(CGFS) to improve its hydrophobic performance. The modified CGFS(MCGFS) was then mixed with coal to prepare MCGFS-coal water slurry(MCGFS-CWS), and the slurry’s flowability and combustion characteristics of MCGFS-CWS were investigated. XPS analysis and contact angle experiments revealed an increase in the non-polar groups on the surface of MCGFS, resulting in enhanced hydrophobicity with higher hydrocarbon oil content. The viscosity of MCGFS-CWS decreases as the amount of hydrocarbon oil increased, significantly improving its fluidity compared to CGFS-CWS. Under the conditions of this study, when the amount of hydrocarbon oil is 8%, the constant-viscosity concentration of MCGFS-CWS is 0.46% higher than that of CWS. Combustion characteristic studies revealed that the addition of CGFS increased the concentrations of alkali metals and alkaline earth metals in the slurry, promoting the catalytic combustion reaction. When the amount of hydrocarbon oil is large, the hydrocarbon oil in MCGFS ignites and burns at a lower temperature. The temperature released during the combustion of hydrocarbon oil is beneficial to promote the ignition of slurry and reduce the ignition temperature of MCGFS-CWS. These results demonstrate that hydrocarbon oil modification enhances the hydrophobicity of CGFS and reduces the ignition temperature of MCGFS-CWS.

A Study on the Co-Combustion Characteristics of Coal and Bio-SRF in CFBC

Bio-SRF based on livestock waste has low heating value and high moisture content. The concentration of toxic gases such as SOx, NOx, and HCl in the flue gas is changed according to the composition of fuel, and it has been reported. Therefore, the study of fuel combustion characteristics is necessary. In this study, we investigated combustion characteristics on the blended firing of coal and Bio-SRF (bio-solid refused fuel) made from livestock waste fuel in CFBC (circulating fluidized bed combustor). The raw materials for manufacturing Bio-SRF include agricultural waste, herbaceous plants, waste wood, and vegetable residues. Bio-SRF, which is formed from organic sludge, has a low heating value and a high moisture content. Bio-SRF of livestock waste fuel is blended with different ratios of coal based on heating values when coal is completely combusted in CFBC. In the result of experiment, the combustor efficiency of calculated unburned carbon concentration in the fly ash shows 98.87%, 99.04%, 99.64%, and 99.71% when the multi co-combustion ratio of livestock waste fuel increased from 100/0 (coal/livestock waste) to 70/30 (coal/livestock waste). In addition, the boiler efficiency is shown to be 86.23%, 86.30%, 87.24% and 87.27%. Through the experimental results, we have identified that co-combustion of livestock waste fuel does not affect boiler efficiency. We have systematically investigated and discussed the temperature changes of the internal combustor, compositions of flue gases, solid ash characteristics, and the efficiency of combustion and of the boiler during co-combustion of coal and Bio-SRF.

Co-Combustion Characteristics of Typical Biomass and Coal Blends by Thermogravimetric Analysis

In this study, the co-combustion characteristics of coal and biomass blends (20, 40, 60, 80, and 100 wt%) were investigated by thermogravimetric analysis. All the samples were operated under an oxidative atmosphere, with a heating rate of 20 C/min. The reaction stages, ignition and burnout temperature, maximum weight loss rate, and different combustion indices were determined. When the percentage of biomass in the blends was increased, the maximum mass loss rate was enhanced in the second region, and the ignition and burnout temperature was lowered, indicating the higher reactivity and better combustion performance of the samples. The comprehensive performance index presented an N shape with the increasing biomass blending ratio. Based on various combustion indices, 20% was an optimum percentage for the co-utilization of coal-biomass blends. A significant promoting interaction was observed between corn straw and rice straw blends, while inhibiting effects occurred between rice husk and coal. The kinetic parameters of the blends were evaluated by the Coats and Redfern method using the nth-order reaction model. The value of activation energy and the pre-exponential factor increased with the decreasing biomass percentage in the blends.

Co-combustion of coal and carbonaceous wastes: thermogravimetric analysis

ABSTRACT The co-combustion characteristics of coal, two types of carbonaceous wastes (HDPE and scrap tire) and their blends were investigated in this study via a non-isothermal thermogravimetric method. The temperature indices and burnout index were used to evaluate the combustion performance of fuel. Strong synergistic effect emerged between carbonaceous wastes and coal, which showed the enhancement effect on devolatilization and the inhibition effect on char oxidation for the mixtures of coal and scrap tire while the opposite result for the mixtures of coal and HDPE. However, the addition of HDPE into coals can promote the release of volatile in advance. Moreover, the shape of TGA curves and the strength of the synergistic effect was different when carbonaceous wastes blending with different ranks of coal, which related to the combustion temperature zone and volatile content of coal.

파일럿 규모의 기포 유동층 반응기를 이용한 석탄과 하수 슬러지 고형 연료의 혼소에 대한 실험적 연구

In this study, the co-combustion characteristics of coal and sewage sludge were investigated using 100 kWSUBth/SUB bubbling fluidized bed (BFB) combustion system. Sub-bituminous coal (Coal), dried sewage sludge solid fuel (DSS), and hydrothermal carbonization sewage sludge solid fuel (HTCSS) were considered as fuel blends. The higher heating value of HTCSS was about 1,500 kcal/kg higher than that of DSS since the fuel ratio, H/C and O/C ratio were improved by the hydrothermal carbonization. The hardgrove grindability index (HGI) was performed to understand the feasibility of industrial applications. In the pilot-scale BFB experiment, the heat input, as 72 kWSUBth/SUB, was fixed in all cases. The mixing ratios of HTCSS and DSS were 2, 5 and 10% respectively based on the higher heating value. Under the co-combustion conditions, the temperature in the reactor was increased in the freeboard zone due to the higher volatile matter of HTCSS and DSS than Coal. The trend of CO and NOSUBx/SUB emissions was similar in all cases as mixing ratio was increased. However, SO₂ emission was decreased in HTCSS co-combustion case due to the lower sulfur content compared to than that of DSS. Ash acquired after BFB combustion was analyzed by XRF to evaluate the slagging/fouling tendency. The variation of slagging/fouling tendency was minor in all cases.

Co-combustion characteristics of coal with invasive alien plant chars prepared by torrefaction or slow pyrolysis

Lignocellulosic samples of Lantana camara (LC) and Mimosa pigra (MP) were pre-treated by torrefaction (300 °C) or pyrolysis (>500 °C) in order to study their potential use as co-fuels with coal. Combustion of the resultant chars, three coals and some blends was investigated by thermogravimetric analysis (10 °C min−1). The effects of biomass composition, pre-treatment temperature of char and blending ratio, on combustibility parameters of ignition, burnout and combustion indices were determined. The addition of reactive char in the fuel mixture consistently resulted in the reduction of ignition temperature, while lowered burnout temperatures of the blends indicated interactions between char and coal during co-combustion. Blends up to 15% showed similar combustion characteristics as those of the parent coals, with co-combustion occurring within the coal combustion zone. Most of the lowest combustion indices were obtained at 30% blends, mainly due to combustion occurring over a wider temperature range, while for blends ≥60%, co-combustion took place in the char combustion zone, with better co-combustion efficiencies, by up to 244% for 90% blend when compared with parent coal. Comparatively, pyrolysed char blends recorded higher combustion indices than torrefied sample blends. The results also showed that lignocellulosic composition of the precursor influenced the combustion mechanisms.