Study On The Emission Characteristics And Control Of Pollutants With Oxy-coal Combustion In Pressurized Fluidized Bed

At present,the situation of China's CO₂ emission is more severe.In the next long period of time,coal-fired power stations are still the most important source of CO₂ emissions in China.Oxygen-enriched combustion technology has the advantages of easy scale and low CO₂ separation cost.Promising carbon capture technology for coal-fired power stations.Pressurized fluidized bed oxy-fuel combustion technology combines oxy-fuel combustion technology with a pressurized fluidized bed,reduces the energy loss of pressure switching between different units during atmospheric oxy-fuel combustion,and takes advatages in fuel compatibility,combustion efficiency and pollutant emission control.In the process of oxy-fuel combustion,emissions of nitrogen oxides and SO₂ will not only bring about a series of environmental problems,but also cause serious corrosion to the flue gas compression and purification module and the CO₂ pipeline,thus increasing the operational risk of the entire CCS system.To the present,there are few experimental studies on the emissions and control of nitrogen oxides and SO₂ in pressurized fluidized bed oxy-fuel combustion,which has good research value.The coal combustion experiments carried out on the 30kW_th pressurized fluidized bed oxy-fuel combustion test system which independently designed and constructed by Southeast University.The two main pollutants generated in the combustion process of pressurized fluidized bed oxyfuel coal:nitrogen oxides and sulfur dioxide generation/emission characteristics and control/removal methods were studied.The operating parameters such as bed temperature,pressure,reaction atmosphere and excess oxygen coefficient and the effects of desulfurization agent on the emission of nitrogen oxides in bituminous coal and anthracite were observed.The results showed that the pressurized fluidized bed was rich in oxygen.Compared with the atmospheric fluidized bed,the NO_x emission and the total amount of nitrogen oxide emissions in the oxyfuel combustion decreased significantly.Bed temperature,pressure,and oxygen concentration have opposite effects on NO_x and N₂O emissions.During the oxy-combustion process,the NO_x emission decreased significantly with the increase of pressure in the pressure range of 0.1⁰.4MPa.The influence of pressure on NO_x emissions is more pronounced than on N₂O emissions,and the total amount of NO_x emissions decreases with increasing pressure.When the reaction atmosphere was switched from the air atmosphere to the 30%O₂/70%CO₂ oxygen-rich atmosphere,the NO_x emissions of the two kinds of coals were significantly reduced,but the N₂O emissions of anthracite were significantly improved.When the oxygen concentration is in the range of 21%³0%,the NO_x emission increases with the increase of oxygen concentration,and the formation of N₂O is inhibited.The factors affecting SO₂ emission were studied.The effects of operating parameters such as bed temperature,pressure,reaction atmosphere and excess oxygen coefficient on SO₂emission after lignite and anthracite combustion were investigated.The results showed that the oxygen-enriched atmosphere has a significant inhibitory effect on SO₂ emission.The increase of oxygen concentration in the oxy-fuel combustion of pressurized fluidized bed is beneficial to enhance the sulfur-fixing capacity of coal ash and thus reduce the emission of SO₂.At the same time,XRF and SEM analysis showed that the sulfur fixation capacity of fly ash increased with the rise of bed pressure,and the SO₂ emission in 21%O₂/79%CO₂oxygen-rich atmosphere decreased about 17%with bed pressure raise from 0.1 to 0.4 MPa.The effects of operating parameters such as bed temperature,pressure and reaction atmosphere on the desulfurization efficiency of limestone in anthracite combustion were also investigated.The results show that in the pressurized oxygen-enriched?0.4MPa,30%O₂/70%CO₂?atmosphere,only the direct sulfurization reaction of limestone occurs in the operating temperature range of fluidized bed combustion,and the direct sulfurization reaction is mainly controlled by temperature.The desulfurization efficiency increases linearly with the increase of temperature.When the temperature is close to 950°C,the desulfurization efficiency can reach more than 80%.In order to achieve higher desulfurization efficiency in a pressurized fluidized bed oxy-fuel combustion,the bed temperature can be raised to a higher value.Under the conditions of 0.4 MPa,30%O₂/70%CO₂ oxygen enrichment,limestone can reach the desulfurization efficiency close to dolomite at a higher bed temperature.