The Studies On Slurrv Ability, Combustion Characteristics And Application Of Low-quality CWS

As a clean alternative fuel to oil, CWS (coal water slurry) has been used broadly in China. And the effect of the alternative to oil, energy conservation and environmental protection is approving. With the rapid growth of economy in China, coal resource used as primary energy will face the shortage condition, especially the high-quality bituminous coal. CWS is prepared by high-quality washing coal currently, which restricts the material source and increases the produce cost. That makes the application of CWS confined. So people pay more and more attention to the use of raw or low-quality coal as the material to prepare CWS.The differences of fuel properties affect the CWS’slurry ability and combustion characteristics directly. Based on the program of retrofitting an oil-designed220t/h boilers to fire CWS in the Wanfeng thermal plant, detailed investigation, theoretical analysis and numerical simulation about low-quality fuel are conducted in the paper. CWS properties examined in the study include slurry ability, rheological behavior, combustion characteristics and slagging characteristics.Primarily investigation is conducted about the slurry ability, rheological behavior of the low volatile coal. Using four kinds of sold additives, the viscosity of the low volatile CWS is below1000mPa.s when the concentration is between65%-66%. In the study, the MF additive has the best effect with which the maximum solid concentration is up to66.49%. The rheological characteristics of low volatile slurry show obvious shear-thinning appearance, namely, pseudoplastic fluid.TGA and horizontal furnace test indicates that the several kinds of low-quality coal have similar combustion process and temperature. The ignition temperature of low volatile slurry and Lu’an coal slime slurry is higher than Datong bituminous slurry, and comprehensive combustion characteristics and beginning combustion performance are worse than latter. The combustion characteristics of slurry prepared by Datong bituminous coal and petroleum coke (50%to50%) are similar to the Datong bituminous CWS. The slagging of the low volatile coal is light, but it’s relatively serious to the Lu’an coal slime slurry and slurry prepared by Datong bituminous coal and petroleum coke (50%to50%).During the design of retrofitting an oil-designed220t/h boilers to fire CWS, some existent problems and the combustion characteristics of low-quality slurry have been analysed and relevant technical measures have been raised. In the paper, it innovatively proposes a kind of asymmetric CWS burner with a pre-combustion chamber. The combustion experiment indicates that the alteration is successful. The combustion of low volatile slurry in the furnace is stable, and the boiler parameters can achieve the design requirement and meet the safe and economic operating conditions of the facilities. In the anoxic condition, combustion efficiency and boiler efficiency are97%and89%respectively. The SO2emission concentration has decreased substantially compared with burning oil, and the NOx emission is also in low level.The slagging process of the combustion area in the furnace has been investigated by using silicon carbide rod. And the ash sediment on the rod is studied by means of XRD patterns and SEM analysis. Predicted by the single slagging indicator of coal ash components, the fuzzy comprehension evaluation model and the integrated mathematical model of slagging characteristics based on attribute and contact mathematics, it concludes that the low volatile CWS belongs to moderate or light slagging, which is consistent with experimental result.Coal-water slurry combustion process and pollutant emission rules of the220t/h boiler are simulated using the CFD software. In different load condition and with high, medium and low-volatile concentration, it gets the rules of the furnace flowing distribution, the temperature distribution and the atmosphere distribution. The calculated results are consistent with the real operating conditions. That has great significance to the combustion adjustment and optimization design of the CWS boiler.Investigation indicates that low-quality CWS including low volatile CWS, coal slime CWS. slurry prepared by bituminous and petroleum coke have approving slurry ability. Appropriate technical measures can make the ignition and combustion stable and meet the safe and economic operating conditions of the facilities. So the investigation and application of CWS in the oil-fired boiler is feasible and has good social and economic benefits.