Research On Typical Trace Elements Emission Control In Ultra-low Emission Power Plant

There are many trace elements in coal.In the process of coal transformation and utilization,the emission and control of some harmful trace elements and their compounds have become the focus of coal combustion pollution.In this paper,trace elements such as mercury,arsenic,selenium and lead are taken as objects,and their transformation behavior and emission after combustion in different coal-fired power plants are systematically simulated and analyzed,and modified fly ash injection adsorption of trace elements such as arsenic,selenium and lead is studied for ultra-low emission power plant.This paper studied the distribution and removal regular of trace element arsenic under different conditions of air pollutant control devices for 9 coal-fired units,and investigated the mass balance of trace element concentration or content in flue gas,coal,fly ash,slag,limestone,gypsum and waste water.The use of ultra-low emission technology and keeping low flue gas temperatures facilitated the removal of arsenic compounds in electrostatic precipitator,and the installation of hot electrostatic precipitator before the selective catalytic reduction system prevented the chemical reaction between arsenic and the selective catalytic reduction catalyst.Electrostatic precipitator was the most important arsenic removal unit.Both the desulfurization system and the wet electrostatic precipitator system have a certain removal effect on arsenic,and a small part of arsenic is emitted into the atmosphere.A variety of trace elements,such as beryllium,cadmium,chromium and uranium,were tested on the 300MW ultra-low emission coal-fired units using selective catalytic reduction+low temperature economizer+electrostatic precipitator+wet flue gas desulphurisation+wet electrostatic precipitator technology.The results showed that most trace elements were accumulated in fly ash,but the proportion in slag was quite small.Along the flue gas process,with the decrease of temperature,the concentration of trace elements in the flue gas gradually decreases,and eventually a small part of trace elements is emitted into the atmosphere.According to the test and analysis results of trace elements,the synergism of oxidation,absorption and washing for the removal of trace elements such as arsenic,selenium and lead in ultra-low emission power plant was obtained.A fly ash brominated coupling mechanical on-line modified method for mercury removal was applied in 300 and 1000MW coal-fired units and showed good results.This paper studied the control effect of this method on arsenic,selenium,lead and other trace elements in 1000MW units.Injecting modified fly ash can not only remove mercury from flue gas,but also enhance the removal effect of other trace elements,with removal efficiency ranging from high to low in the order of mercury,arsenic,lead and selenium.Compared with raw ash,modified fly ash has better oxidation performance,finer particle size and more active parts.The results showed that the fine fly ash of mechanical grinding had the greatest effect on the mercury and selenium.The higher the calcium content,the stronger the oxidizing capacity and the more arsenic can be removed.Mercury removal from flue gas of commercial brominated activated carbon was studied in laboratory and ultra-low emission power plant.The study of fixed bed in laboratory showed that the adsorption capacity of activated carbon was strongest at 120℃ under the selected temperature.Experiments of adsorption mercury removal by activated carbon injection were carried out in the 300MW ultra-low emission coal-fired unit,which were injected at the two points after selective catalytic reduction before air preheater and after air preheater before low temperature economizer respectively.The effect of temperature on adsorption and demercurization of activated carbon was stronger than that of residence time.