Study On Sampling Method Of Selenium In Coal Flue Gas Based On Condensation And Solution Absorption

In China,selenium resources are concentrated in the region and lack of selenium on average.The annual discharge product of coal-fired power plant contains a large amount of selenium element,so it is considered as a potential source of selenium element.The content,occurrence form and sampling method of selenium element have been studied.Therefore,the method is improved on EPA29 method.The enrichment and occurrence of selenium during combustion are reviewed.A physicalchemical method for capturing selenium in coal-fired flue gas has been established.This method is used in the study of selenium capture in flue gas in the drop tube furnace.A set of flue gas selenium capture method which can be applied in power plants is established and the distribution of selenium in drop tube furnace is clarified.First,the content of selenium in lignite and its products of static combustion in tube furnace and dynamic combustion in drop tube furnace was determined by using the Ashka method and hydride generation atomic fluorescence spectrometry(HGAFS).The results show that the average release rate of selenium in coal is 91.6%.Secondly,the capture experiment is conducted with the environment condition of absorbing the bottle device as a variable.The experimental conditions were tested using tube furnace with four-price selenium as the selenium source.The optimal experimental conditions were selected:(1)When the selenium standard solution was selenium source,the selenium source was placed in the middle of the quartz tube,and the companion zone was kept fully wrapped at 150℃,and the air flow rate was 1L/min.The heating procedure is 1h temperature rise to 800℃ and 2h maintenance.(2)When lignite was the selenium source,the selenium source was placed in the middle of the quartz tube,and the belt was kept fully wrapped at 150℃,and the air flow rate was 1L/min.The heating procedure is 1h heating to 900℃ and 2h maintenance.Then the scheme of absorbing bottle is determined.Since the boiling point of the SeO2 is 684.9℃,a condensing bottle can achieve 40～50%selenium capture.According to the chemical characteristics of SeO2,other chemical solution absorption bottles use acidified 10%v/vH2O2 solution,50%v/vH3PO4 solution,4%w/vNaOH solution,anhydrous ethanol and acidified 4%w/v KMnO4 as absorption solution,and the total capture result can be increased to 69%,65%,75%,79%,78%.The results showed that the absorption effect of selenium could be improved by oxidation,reaction and dissolution methods.However,the solvent required by oxidative and reactive absorption requires post-treatment,while the solvent required by dissolved absorption does not require post-treatment and is easy to recover and separate.Therefore,the absorption bottle configuration is 1 bottle of empty bottle+2 bottles of 10%H2O2 and 5%HNO3 mixed solution+ 2 bottles of 10%v/v ethanol solution.The absorption result of flue gas is consistent with that of the standard liquid when the standard liquid of selenium is replaced by lignite.This method is used in the test of the drop tube furnace platform to prepare the sample by whether to sample at a constant speed and combining the three absorbent fluids into variables.The products from different locations of the drop tube furnace were collected as samples,and the liquid and solid samples were tested after digestion respectively.The results show that there is no significant difference between the sampling methods of constant velocity and non-constant velocity.It is inferred that particles that are greatly affected by inertia are not the main carriers that determine selenium content.In the experiment of the drop tube furnace,it is found that the method can be improved up to nearly twice the effect of the original EPA 29 method.Finally,using the accumulation method and the difference method to calculate the mass balance of selenium in the drop tube furnace,it is found that the accumulation method has a 40%recovery rate and the difference subtraction method has a 72%recovery rate.Based on the EPA29 method,an improved method for capturing selenium in coal-fired flue gas is proposed,which provides some theoretical guidance for the subsequent study of selenium sampling in flue gas.In addition,the migration and conversion of selenium and its content distribution under two calculation methods in the drop furnace are studied,which provides a theoretical research foundation and guidance for the control and recovery of selenium in power plants.