Mechanism And Model Study On High Efficiency Desulfurization And Dedust Based On Ultra-low Emission Technology

Atmosphere is one of the components of the natural environment on which mankind depends.With the increase of total energy consumption in our country and the increasingly stringent air quality standards,there is an urgent need to develop highly effective synergistic removal technologies for pollutants such as sulfur dioxide?SO₂?and particulate matter?PM?.The Wet flue gas desulfurization?WFGD?technology is the most widely used sulfur dioxide removal technology in our country.However,under the increasingly strict requirements of environmental protection and economic operation,the further improvement of sulfur dioxide removal efficiency and the synergistic control ability of various pollutants was the key to realize economic ultra-low emission technology in thermal power plants.In this paper,the removal mechanism of SO₂ in WFGD tower was studied.The SO₂ emission model of spray tower,bubbling area and pH zone in WFGD tower were coupled by experimental and numerical simulation.Then the mechanism of particle capture in the desulfurization tower were studied.The law of enhanced removal of sulfur dioxide and particulate matter in the WFGD tower was obtained,and industrial verification was made on the thermal power/thermal power unit.The advantage of mechanism modeling lies in that the trend reflects the influence of the main factors on the removal efficiency and the advantages of the data model Based on the high accuracy brought by strong fitting,a new hybrid forecasting model which uses the data model to correct the mechanism model error is proposed to improve the prediction accuracy of SO₂ emission concentration.The particle swarm optimization?PSO?algorithm is finally applied to the operation optimization of WFGD system.Firstly,the SO₂ ultra-low emission model including spray zone,bubbling zone and pH zone module was established.Based on the Computational Fluid Dynamics?CFD?method,the effect of efficiency components on gas-liquid mass transfer area was studied,and the gas-liquid mass transfer area under bubbling area under different working conditions was obtained.Then the effects of spray zone,bubbling area and pH zone on SO₂ Removal effeciency.The predicted results are in good agreement with the test results.The method of removing sulfur dioxide in bubbling area is proposed,which provides a theoretical basis for the design of new high-efficiency SO₂ emission technology.Secondly,the particulate matter is trapped in the desulfurization tower by slurry droplets mainly by inertia,interception,Brownian diffusion,thermophoretic force mechanism.For the micron-sized particles,Brownian diffusion is weak even can be ignored compared to inertial mechanism.For submicron-sized particles,thermophoresis trapping efficiency is higher than the Brownian diffusion of 2 to 3 orders of magnitude.The effects of spray intensity,slurry spray conditions,flue gas velocity and aerosol scale on the removal of aerosol particles were studied by experiments and general kinetic equation models.It shows that with the increase of the vertical height of the desulfurization tower?with the increase of the flue gas desulfurization time?,the PSD curve becomes more and more low and flat,indicating that the number and concentration of particles at various scales are getting smaller and smaller.The PSD curve is increasingly offset to the left,indicating that larger particles are more likely to be trapped by WFGD.Under typical working conditions,the removal efficiencies were 75.01%,82.57%,85.95%and 87.92%respectively when the vertical height of desulfurization tower was 5 m,10 m,15 m and 20 m.The particulate matter is quickly removed after entering the desulfurization tower.It shows that the removal efficiency of fine particles in sieve plate tower first decreases and then increases with the increase of particle size.The grading efficiency curve shows "V" shape distribution,and the removal efficiency is the lowest within the transition interval between micron and submicron particle size of 0.2-1.0 ?m.The sieve tray has a stronger particle removal efficiency compared with the spray tower,the removal efficiency of which can be increased by about 5%,and even can be increased by about 11%for 0.2?1.0 ?m interval.Thirdly,aiming at the problem of high energy consumption and high cost of wet flue gas desulphurization system,a hybrid predictive model of SO₂ concentration at the outlet of desulphurization system based on mechanism and data was studied,which achieved prediction accuracy of 73%,92%and 98%respectively under the actual condition of power plant operation data verification.The particle swarm optimization algorithm is applied to optimize the operation of the desulfurization system combined with the operation cost model of desulfurization system.The low cost WFGD can be realized by using the process modeling and optimization method.Finally,a nationwide inventory of SO₂ emissions including unit capacity,control technology and coal sulfur content of 1966 coal-fired power plants/thermal power plants was established.A cost-optimized national desulfurization upgrade Strategy coupled with the SO₂ cost-effective cost model and the ILP algorithm is realized.In the current situation,the average national desulfurization efficiency is 92.14%.If it can achieve the total emission reduction target of 10%,20%and 40%,the average desulfurization efficiency can reach 92.55%,93.22%and 94.56%respectively.The corresponding optimal operation costs are 53.081 billion yuan,53.384 billion yuan and 53.384 billion yuan,up 0.98%,2.16%and 5.21%respectively over the current situation.Under different emission reduction targets,both 3 00MW and 600MW units account for more than 55%of emission reduction and large units make up a larger proportion.In achieving the goal of the total pollutant emission reduction,it must consider the local conditions to implement the unit differentiation,regional differentiation,technological differentiation in policy guidance.