Abstract: Based on the circulating desulfurization with high ratio of ash and calcium( No Gap Desulphurization) of Shendong 30 t/h coalfired industrial boiler,and in order to further find the desulfurization process and mechanism,the influence of different factors on the desulfurization efficiency was studied.In this paper,the sulfur content and water content of desulfurizer in different positions were detected by drilling and sampling along the reactor firstly.The results show that the water content and sulfur content in desulfurizer decrease and increase respectively with the desulfurizing reaction,which indicate that water is very important for desulfurizing reaction.In the presence of water,the desulfurizing reaction changes from gas-solid two-phase reaction to liquid-phase reaction between ions,and the desulfurization reaction rate increases significantly.At the same time,with the desulfurization reaction,the reaction products in the desulfurizer increase,so the sulfur content increases. Secondly,the change of composition and content of flue gas along the reactor is detected. According to the change rate of desulfurization efficiency per unit distance on the reactor,the desulfurization process is divided into three stages: constant speed section,deceleration section and quasi balance section.The desulfurization reaction rate of first two stages is fast,which is the key section of desulfurization reaction.The SO_2 removed accounts for 90% of the total SO_2. Therefore,It is a effective method to improve the desulfurization efficiency by strengthening the first two desulfurization stages.Finally,the engineering test was carried out on the NGD desulfurization unit to study the influence of the humidification water quantity,initial concentration of SO_2 and the mixing ratio on the desulfurization efficiency.Finally,the results are as follows: the humidification water quantity increases,the initial concentration of SO_2 decreases,and the proportion of hydrated lime increases,which is equivalent to the increase of the initial concentration of the desulfurization reactant,and promotes the desulfurization reaction to the right,and the desulfurization reaction rate increases in the initial stage,so the final desulfurization efficiency shows an increasing trendy.However,due to the limitation of pore structure and active substance content of desulfurizer,there are optimal technological conditions for desulfurizing reaction to make full use of the effective substances in desulfurizer.According to the variation of desulfurizing efficiency,the optimal range of humidification water quantity,initial concentration of SO_2 and mixing ratio is finally determined,which are 0.14-0.27 t/h,350-550 μL/L and 3 ∶ 1-2 ∶ 1 respectively.At this time,the variation of desulfurizing efficiency is 28.81%,25.87% and 10.55% respectively.