Experimental Study On The Reduction Mechanism Of Ash Deposition During Co-combustion Of Coal And Biomass And Ammonium Bisulfate Fouling

Power station boilers is one of the three main equipments of thermal power stations.It is important to ensure its safe and stable operation.The ash deposition seriously affects the boiler operation and the economic benefits of the boiler.With the application of co-firing of coal and biomass,the ash deposition becomes more serious.The coating technology has its unique advantages over other technologies that control ash deposition.It can take into account both anti-corrosion and ash deposition control,and has high economics.In addition,the ammonium bisulfate fouling seriously affects the stable operation of the heat exchanger and the heat transfer efficiency.In order to investigate the effect of coatings on the ash deposition characteristics of co-firing of coal and biomass,the in-situ measurement technology,the pilot-scale combustion system,X-ray diffraction?XRD?,the scanning electron microscopy?SEM?and the energy dispersive X-ray spectrometry?EDX?were applied to study the reduction mechanism of ash deposition.The effects of coatings on ash deposit thickness,initial layer formation rate,and heat flux were analyzed.In addition,a bench scale experimental facility was designed to investigate the characteristics of ammonium bisulfate fouling.The growth process of ammonium bisulfate fouling on the low-temperature heat transfer surface was simulated,and the reduction mechanism of ammonium bisulfate fouling was studied.The research contents are as follows.Firstly,the pilot-scale combustion system was used to study the effect of ceramic coatings on the fouling characteristics of pure bituminous coal.The results show that the ceramic coating effectively reduces the fouling and enhanced the heat transfer efficiency of the probe.The ceramic coating can affect the content of alkali compounds and affect the adhesion behavior.Secondly,the pilot-scale combustion system was used to study the effect of Ni coating on the slagging characteristics of Shenhua coal.The results show that Ni coating has a inhibitory effect on the formation of the initial layer.The Ni coating can affect the deposition of alkali compounds and control the diffusion of Fe from the deposition probe to the slag deposit.Thirdly,the pilot-scale combustion system was used to study the effect of Cr coating on the fouling characteristics of co-firing of coal and wood.The results show that Cr can inhibit the fouling of co-firing of coal and wood.The Cr coating can effectively reduce the adhesion force between the fouling deposit and the probe surface,so that the shedding frequency of the fouling deposit in coating case is greater than that in uncoated case.Fourthly,the pilot-scale combustion system was used to study the effect of Ni coating on the slagging characteristics of Shenhua coal and corn straw.The results show that the Ni coating can effectively reduce the adhesion force between the slag deposit and the probe,thereby causing regular shedding in the coating case.Ni coating can effectively reduce the formation rate of initial layer.The Ni coating can affect the deposition of alkali compounds and control the diffusion of Fe from the deposition probe to the slag deposit.Fifthly,the characteristics of ammonium bisulfate?ABS?fouling were studied in the vertical furnace with online measurement technology.The thickness of fouling deposit,the heat flux through the probe surface,and the effective thermal conductivity of the ABS fouling deposit were obtained.The results show that the increase of flue gas temperature can effectively inhibit the growth of ABS fouling,and the increase of ABS blending ratio can promote the growth of ABS fouling.ABS can agglomerate ash particles to form a dense microstructure,thereby promoting the growth of ABS fouling,increasing the effective thermal conductivity of ABS fouling deposits,and enhancing the strength of ABS fouling deposits.Sixth,the influence of the heat transfer surface temperature on the ABS fouling characteristics was studied in the vertical furnace with online measurement technology.The results show that the temperature of the probe surface has a negative correlation with the stable thickness.Increasing the temperature of the probe surface can effectively inhibit the growth of ABS fouling.ABS as a liquid substance can strongly affect the microstructure of ABS fouling deposit.ABS affects the growth behavior of ABS fouling by constructing liquid bridges and aggregates in the deposit.Seventh,the effects of two additives?Na₂CO₃/NaHCO₃?on the ABS fouling characteristics were studied in the vertical furnace with online measurement technology.The results show that both additives can reduce the growth rate of ABS fouling.With an increasing flow rate of the additive,the inhibitory effect on the ABS fouling become more significant,and the Na₂CO₃ shows a better inhibitory effect on the ABS fouling under the same molar ratio.The effective thermal conductivity of ABS fouling deposit decreases with the addition of additives,and decreases with the increasing flow rate of the additive.Finally,The effects of two additives?Na₂SO₃/NaHSO₃?on the ABS fouling characteristics were studied in the vertical furnace with online measurement technology.The results show that both Na₂SO₃ and NaHSO₃ can inhibit the growth of ABS fouling.The addition of additives can reduce the ABS content in the ABS fouling deposit,thereby alleviating the agglomeration of the ash particles,making the ash deposit structure loose,and ultimately inhibiting the growth of the ABS fouling deposit.