Study On The Performance Of Desulfurized Slag Oxygen Carrier In Chemical Looping Combustion Of Coal

Coal combustion will produce a lot of pollutants such as NOx,SOx and a lot of greenhouse gases CO₂.Among them,NO_x and SO_x are the main air pollutants,and CO₂ is the main cause of the greenhouse effect and global warming.Therefore,it is urgent to achieve the reduction of CO₂ and other gases during the coal combustion process.Chemical looping combustion technology,as a new type of combustion technology,has the characteristics of efficient and clean combustion,suppression of NO_x generation and efficient and low-cost capture of CO2,and has become a key research object.Low-cost,highly reactive oxygen carriers are the prerequisite and basis for the industrialization and application of coal chemical looping combustion technology.The desulfurization slag is used as industrial solid waste generated by desulfurization and purification of flue gas generated by fuel combustion in thermal power plants.Its main component is CaSO4,which is used as an oxygen carrier in the coal chemical looping combustion process.It has many advantages such as large oxygen capacity,extensive resources,as well as low price.Therefore,exploring the purification technology of desulfurization slag and realizing the resource utilization and efficient utilization of desulfurization slag in the coal chemical looping combustion has significant development potential and application value.This article first collected the wet flue gas desulfurization slag of the power plant and purified it as the oxygen carrier of the desulfurization slag.A high-performance desulfurization slag mixed oxygen carrier was prepared using the purified desulfurization slag as a template matrix and a template-sol-gel combustion composite synthesis method.Further,the combustion characteristics of the desulfurization slag oxygen carrier and the modified desulfurization slag mixed oxygen carrier as well as the evolution characteristics of the side reaction sulfur were carried out in detail on a fixed bed.In this way,CO2 reduction in coal combustion process,directional in-situ capture of gas-phase sulfur,and resource utilization of desulfurization slag were realized.The main research contents and results are as follows:Power plant flue gas desulfurization slag has many impurities,variable components,as well as complex formation causes.This paper first analyzed and described the basic physical and chemical characteristics of flue gas desulfurization slag collected in power plants,and determined reasonable purification steps as well as optimized process parameters.It was found that the desulfurization slag purified by the H₂SO₄+NaOH/KOH acid-base combined method as well as the H2SO4+HF acid method has a purity of more than 95%;XRD characterization showed that the purified desulfurization slag was mainly composed of CaSO4,with a pure phase and high diffraction intensity;SEM-EDX microscopic morphological characteristics and apparent composition analysis showed that the purified desulfurization slag was a porous medium with a stripe and fine particle structure at the microscopic level,which was very conducive to its reaction with fuel as an oxygen carrier.The purified flue gas desulfurization slag oxygen carrier was used to experimentally evaluate the reaction characteristics of coal and reference CaSO₄ oxygen carrier samples with coal on a fixed bed.Comparing the reaction performance of the desulfurization slag as it was,the purified CaSO₄ of Sinopharm analysis and the purified desulfurization slag as oxygen carriers.It was found that purified oxygen carrier of flue gas desulfurization slag had the highest reactivity.Further,the effects of many factors such as reduction reaction temperature,oxygen carrier excess coefficient,oxidation reaction temperature,and multiple reduction as well as oxidation cycles on the reaction between purified oxygen carrier and coal were studied on a fixed bed.The optimal reaction conditions were determined.And revealed the potential mechanism of the reaction process.When CaSO₄ is used as an oxygen carrier,various sulfur release side reactions are unavoidable.Not only will it impairs the reactivity of the CaSO₄ oxygen carrier,but also the stability of the reaction during repeated cycling reactions,and the release of sulfur in the gas phase will cause great harm.Therefore,in this paper,the evolution and distribution of various types of gas phase sulfur during the combustion of the desulfurization slag oxygen carrier and the chemical looping of coal are tested in detail on a fixed bed.It was found that the higher the temperature of the reduction reaction,the higher the concentration of sulfur-containing gas in the side reaction,especially when the SO₂ is above 900?;The larger the oxygen carrier coefficient,the higher the concentration of sulfur-containing gas.When the oxygen carrier coefficient is greater than 1,the release of sulfur-containing gas tends to be saturated;The greater the concentration of CO₂ in the reducing atmosphere,the higher the concentration of sulfur-containing gas.A more suitable reducing atmosphere is 40%CO₂;With the increase of the number of cycles,the concentration of sulfur-containing gas showed a downward trend;meanwhile the process and mechanism of the evolution of the side reaction sulfur were analyzed.Finally,in order to make full use of the large amount of lattice oxygen contained in CaSO₄,to achieve the cooperative removal of carbon and sulfur when the CaSO₄ oxygen carrier reacts with coal,A template-sol-gel combustion composite synthesis method was used to prepare CaSO₄-CuO,CaSO₄-Fe₂O₃,CaSO₄-CuFe₂O₄,and CaSO₄-CaO desulfurization slag mixed oxygen carriers.The synergistic decarburization and sulfur fixation characteristics of the oxygen carrier were experimentally studied on a fixed bed.Studies have shown that:compared with desulfurization slag oxygen carrier,desulfurization slag mixed oxygen carrier improved the reactivity of calcium-based oxygen carrier and inhibited sulfur release from side reactions.The carbon conversion rate of CaSO₄-CuFe₂O₄ was 82%between the two kinds of desulfurization slag mixed oxygen carriers,CaSO4-CuO and CaSO4-Fe2O3.However,the sulfur-fixing characteristics of CaSO₄-CuFe₂O₄ were the best among them,and especially the effect of suppressing the release of side reactions SO2 was ideal.