| In order to control the emission of conventional flue gas pollutants from coal-fired boilers in thermal power units,the country has formulated ultra-low emission standards,that is,under the condition of 6%baseline oxygen content,the emission concentrations of soot,SO2 and NOx are not higher than 5,35 and 50mg/m3,respectively.The ultra-low emission standards reduce the emission concentration of soot,SO2 and NOx,and moderate the atmospheric pressure.But some problems have appeared,such as the decrease of boiler efficiency caused by low nitrogen combustion,the uneven distribution of ammonia injection concentration field of flue gas SCR denitrification,the poor operation effect of ammonia injection automatic control mode,the unreasonable operation mode of wet desulphurization slurry circulating pump,high power consumption and large limestone consumption.The study uses Zouxian Power Plant No.3 unit as the researche object in order to solve the above problems.The efficient and economic operation of low nitrogen combustion,denitration and desulphurization facilities of boiler is optimized based on safety and environmental protection.Through orthogonal experiment and range analysis,the influence of coal quality,boiler oxygen set value,unit load,the second layer SOFA opening,and the 3/4 layer SOFA opening on boiler efficiency and furnace outlet NOx concentration has been studied.The economic operation mode which takes into account both the boiler efficiency and the furnace outlet NOx concentration is determined.When the boiler evaporation is in 950 t/h～994t/h and feed water flow is in 877 t/h～992 t/h,the boiler operation oxygen value is set at around 3.2%,low sulfur content coal is burned,the 3/4 layer SOFA opening degree is maintained to be 100%,and the second layer SOFA opening degree is maintained to be 60%.Compared with the non-optimal operation condition burning the same coal,the boiler efficiency is 0.4%higher and the power supply coal consumption is reduced by 1.4 g/（kW·h）.The furnace outlet nitrogen oxides concentration is reduced by 16 mg/m3.The NOx concentration distribution at SCR reactor outlet is improved after field test optimization,and the relative standard deviation of the outlet NOx concentration distribution of reactor A and B is decreased from 48.6%and 34.7%to 12.7%and 14.7%,respectively.The automatic control technology of SCR ammonia injection based on the cooperation of main steam flow rate and NOx emission concentration has been proposed.The theoretical ammonia injection amount is calculated through the main steam flow rate,which improves the calculation accuracy of theoretical ammonia injection amount.During CEMS purging,NOx emission concentration is taken as a variable to participate in the regulation,so as to avoid the large range of fluctuations of NOx emission concentration and ammonia injection amount.The response speed and control quality of automatic control of ammonia spraying are improved.After SCR optmization,the liquid ammonia consumption of SCR denitration facility is reduced by 0.13kg/（104 kW·h）.The operation optimization of the slurry recirculation pumps and the pH value of the slurry in the absorber have been conducted according to unit load and SO2 inlet concentration.The operating current of the slurry circulating pump is decreased by 33.25A,and the power consumption rate of the desulfurization facility is decreased by 0.1 percentage point.An automatic control technology of desulphurization slurry supply based on the synergism of pH value of absorber slurry and SO2 emission concentration has been proposed.SO2 emission concentration is used as the input variable to control limestone slurry supply,and the automatic control logic of slurry supply is optimized under pH labeling flushing and CEMS purge.The problem that the widely used slurry supply can not be put in automatically based only on the pH value of the absorber slurry is solved,and the stable control of the limestone slurry supply,pH value of the absorber slurry and SO2 emission concentration is realized,and the consumption of the limestone slurry is reduced by 18.7 kg/（104 kW·h）.The study has analysized the economic benefit,environmental benefit and social benefit.Generally speaking,it reduces the power supply coal consumption of the unit,the liquid ammonia consumption of SCR denitration facilities,the operation power consumption and limestone powder consumption of wet desulfurization facilities,realizes the year-on-year improvement of energy and material consumption indicators,and reduces the emissions of CO2,SO2 and NOx of the unit,It has important environmental and social benefits.The research results after operation optimization have been put into use.After the application of unit 3 of Zouxian Power Plant in February 2018,operation cost of 2.195 million yuan is saved and the emissions of CO2,NOx and SO2 are reduced,which has important environmental and social benefits. |
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