| Volatile organic compounds are called VOCs for short and they are a kind of air pollutants.The use of organic solvents in pharmaceutical industry is quite common.With the rapid development of China's pharmaceutical industry,emissions of organic waste gas are increasing,which result in increasingly serious haze pollution and great harm on human health and natural environment.However,VOCs recycling started late in China and technology is relatively less mature.Especially,the selection of adsorbent as well as the design of and research on adsorption device are relatively scarce.At present,fixed bed adsorption process is used for organic solvent recovery at home and abroad.When this process is in the face of high-concentration or high-activity organic waste gas,its adsorption heat dissipate slowly,which leads too high local temperature of the bed,causing fire or adsorption efficiency decrease.In order to solve this problem,researches on the absorption and mobility of waste gas recovery of several typical organic solvents in pharmaceutical industry with cold multilayer fluidized bed are conducted in this thesis.Multistage fluidized bed not only has high efficiency of mass transfer and heat transfer,but also controls the back-mixing of solid adsorbent and improves the driving force of absorption.The main research contents and results are summarized as follows:1)First of all,selecting of irregular activated carbon ranging from 0.3 to 0.8mm in particle size from availably different manufacturers and raw materials is conducted.The widely used butanone,toluene,ethyl acetate and carbon tetrachloride in pharmaceutical companies are selected as adsorbent and analysis of relevance between adsorbent,adsorption properties and adsorption capacity.The results show that adsorption rate and the specific surface area of activated carbon main into the positive linear relationship;while there is no obvious linear relationship between adsorption rate and aperture and entrance,the linearly dependent coefficients of molecular weight,density,melting point and adsorption quantity are all above 0.92,but it has a poor correlation with the boiling point,the saturated vapor pressure,the diameter of molecular dynamics,.Under the same temperature,among the three kinds of activated carbons,the regeneration performance of AC-1 is best,AC-2 is second and AC-3 is the worst.With the same sorbent,the regeneration performance is best at 170?,better at 130?and worst at 210?.It shows that the relationship between regeneration performance and adsorbate is not obvious,and it is related with desorption conditions outside.Finally AC-1 is used in pilot experiment because of its large amount of adsorption,high abrasion resistance and good fluidization.2)The structure of cold model multilayer fluidized bed is designed,which is divided into three layers with each one being 1200 mm.based on this,the influence of different forms of distribution board and overflow pipe for the fluidization of AC-1 adsorbent is studied.The results show that:the angle hole structure and triangle arrangement are used in distributor with hole spacing of 59 mm,Angle size of 20 mm×20 mm,the height of angle the outlet of 14 mm and opening rate of 0.424%.The overflow pipe is external and pneumatically-controlled,which permits the control of overflow rate.When superficial gas flow rate is 0.13m/s-0.15m/s,the components designed and developed runs in good condition.With multilayer fluidized bed device,continuous and stable operation can be realized.The design and optimization of these artifacts lies a good foundation for further design and operation of adsorption experiment.3)Through the discuss of the basic performance of the layers of fluidized bed designed in this paper,it can be found the relations between various factors in the fluidized bed with the feeding rate and gas speed,the influence of fluidized state on porosity and the influence of the depth of cone bucket in layer and the height of material bed of the overflow tube,which has established a good data base for the design of practical multi-layer fluidized bed.By the mathematical model of residence time distribution of solid materials,the average residence time is calculated and ensures the availability of activated carbon in adsorption tower.It is concluded that ?_?~2 is 0.038.As a result,it is inferred that the flow pattern of the material in this device is near plug flow which can overcome the back-mixing and improve the adsorption efficiency.4)On the basis of the previous experimental data,a new set of process of multilayer fluidized bed for organic solvent absorption in practical production is designed in this paper.Pilot tests show that the overall countercurrent operation of adsorbent and adsorbate can be realized in this process.The adsorption efficiency of the whole tower is more than96%.The gas concentration of air inlet not only causes the distribution change of concentration of adsorbate the along the bed,but causes temperature change of bed material.Experimental results show that the multilayer fluidized bed designed in this paper solved the problem of the low efficiency of mass transfer and heat transfer in fixed bed and the expected goals have been reached. |
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