Study On Performance And Lifetime Of Denitration Catalystat Abnormal Operating Temperature

The deteriorating global human environment has forced China to focus on the emission control of air pollutants in coal-fired power plants.The newly proposed ultra-low emission standards have also posed a great challenge to coal-fired power plants.Selective catalytic reduction denitration technology is currently the world's major flue gas denitration technology.The main reaction mechanism is the catalytic effect of the denitration catalyst,the reductant NH₃ and NOx react to generate harmless N₂ and H₂O.Because of its technology has good selectivity,stability,economy,and high denitrification efficiency can be achieved,it will become the mainstream of China's flue gas denitration technology for a long time.At present,the reaction temperature of the high-temperature catalyst mostly used in the SCR denitration system at home and abroad is in the range of 300-420?.However,in some practical operation,it is found that in actual project operation,over-temperature operation or low-load starting-up situation often occurs.Therefore,this article will study the performance of denitration catalyst under abnormal temperature,mainly for the engineering practice of the thermal power plant when the unit is started,the flue gas temperature is low during low load operation,the temperature of the exhaust of some units is high,and the over-temperature operation is performed.The experimental samples in this paper are all from a domestic thermal power plant with an installed capacity of 660MW.The denitration catalyst activity testing device is used to complete the main experiment.The flue gas analysis system was used to test the reactor inlet and outlet NOx and NH₃ concentration.SO₂ and SO₃were collected using isopropanol absorption method and their content was determined by titration with thorium reagent.The specific surface area and pore size analyzer were used to analyze pore specific surface area of catalyst.X-ray fluorescence spectrometer was used to detect and analyze the types and contents of some trace elements in the catalyst.The results show:?1?The fresh catalyst has a higher V₂O₅content than the catalyst already in operation,due to the gradual loss of the active component with increasing operating time.?2?Some of the internal channels have become clogged due to long-term operation of the catalyst in flue gas containing toxic substances and fly ash,resulting in a slightly lower specific surface area than fresh catalyst.?3?The denitration efficiency of denitration catalyst increases with the normal operating temperature at low temperature and normal temperature,while the denitrification efficiency decreases with increasing temperature at high temperature.This phenomenon is due to the increase of temperature leading to the oxidation of NH3 to NO and other side reactions occurred.?4?The conversion rate of SO₂/SO₃gradually increases with the increase of temperature,because the higher the combustion temperature,the more free oxygen in the furnace,the easier the conversion of SO₂to SO₃ occurs,and the catalyst that has been running at each temperature SO₂/SO₃ conversion rate is lower than the fresh catalyst,which is caused by the loss of active components,it should be replaced regularly catalyst.?5?The volume fraction of NH₃ at the exit of the reactor generally decreases with the increase of the reaction temperature,which is due to the extra ammonia not participating in the reaction when the reaction temperature is low,resulting in large ammonia slip.Therefore,the operating temperature should not be too low,should ensure the efficiency of denitration under the premise of reducing ammonia escape.?6?Below400?,with the increase of airspeed,the denitration efficiency of different temperature showed a downward trend to some extent.When the temperature was higher than 400?,the effect of airspeed on denitration efficiency was not obvious.?7?When the oxygen content increases from 0%to 2%,the denitration efficiency increases greatly.After that,the oxygen content continues to increase with little effect on the denitration efficiency.Therefore,good denitration can be achieved when oxygen is controlled at about 2-3%effect.?8?When n?NH₃?/n?NOx?is 0 to 1,the higher the NH₃ volume fraction in flue gas,the higher the denitration efficiency.When n?NH₃?/n?NOx?is greater than 1,the denitration efficiency tends to be stable.Through this experiment,we have studied the performance of the catalyst running at very warm temperatures,which is instructive for the operation mode and energy saving of the boiler.