Experimental study on sulfur dioxide ultra-low emission base on semi-dry NGD desulfurization technology

With the increasingly serious environmental protection situation,ultra-low emission requirements for the treatment of flue gas pollutants from medium and small coal-fired industrial boilers has been put forward by our state.It is one of the effective ways to solve SO_2 pollution in tail flue gas of medium and small coal-fired boilers and achieve ultra-low emission by using Semi-dry flue gas desulfurization( FGD) technology.As a new semi-dry flue gas desulfurization technology,the NGD desulfurization uses high calcium fly ash from boiler as desulfurizer,which effectively reduces the operation cost of desulfurizer.In order to verify the super-low SO_2 emission effect of the technology and the economic use of desulfurizer,a 40 t/h pulverized coal fired boiler NGD desulfurization unit in a Shendong boiler house was taken as the research object to carry out industrial tests,and the operation stability of the device and the influence of key factors on the desulfurization effect were investigated.The experimental results show that the average in and out of the pressure differenceof NGD reactor is about 1 100 Pa,and there is no sharp rise or decrease of curve,which indicates that the overall operation stability of the device is good.After an appropriate amount of calcium hydroxide being added,the average SO_2 emission concentration( 9% O_2) of the NGD desulfurization unit is tested to be less than 35 mg/Nm~3,which achieves ultra-low emission effect.The Ca/S molar ratio n( Ca ∶ S) of the added Ca( OH)_2 and SO_2 at the inlet of the reactor is calculated to be 0.9.As the active calcium is mainly used in the autogenous fly ash of the boiler,the consumption of added Ca( OH)_2 is lower than that of the similar semi dry flue gas desulfurization technology.It is found that the desulfurization efficiency of the plant increases with the increase of the amount of humidified water.Under the test conditions,the desulfurization rate increased from 70% to more than 90% when the sef-generated boiler fly ash mixed with a small amount of Ca( OH)_2.