| A large number of desulfurization wastewater will be produced in the process of wet oxidation desulfurization of coke oven gas by ammonia HPF,and in China,about 4.4 million tons of desulfurization wastewater will be produced every year.Desulfurization wastewater contains COD（>100000 mg/L）,sulfide（>2000 mg/L）,ammonia nitrogen（>20000 mg/L）and salt（～200 g/L）,which is a pollutant with great harm.Thus the efficient,clean and low-cost treatment technology of desulfurization wastewater is urgently needed in the coking industry at home and abroad.In view of the problems existing in the current technology of treating desulfurization wastewater,such as large equipment investment,high operation cost and easy secondary pollution,a new method of"pyrolysis treating desulfurization wastewater by waste heat of high temperature coke-oven raw gas in riser"was proposed in this study.However,it was found that the composition and properties of desulfurization wastewater were not systematically and completely understood,there was no report on evaporation of saline waste liquid at high temperature,and the mechanism of pyrolysis of desulfurization wastewater in riser raw gas was unclear.Besides,the process parameters of desulfurization wastewater treatment by riser waste heat needed to be determined and optimized,and the core equipment needed to be developed in the test operation of large coke oven.Aiming at the above-mentioned existing problems,in this study,HPF desulfurization wastewater produced by coke oven gas purification was used as the research object,and five research works were mainly carried out:（1）Research on the composition and properties of desulfurization wastewater;（2）Study on the characteristics and kinetics of co-pyrolysis of desulphurization wastewater and coal;（3）Research on high temperature evaporation model of desulfurization wastewater and optimization of model parameters;（4）Study on pyrolysis characteristics of desulphurization wastewater in single riser and optimization of spraying parameters;（5）Development of core equipment for pyrolysis desulphurization wastewater process of large industrial coke oven.On this basis,an engineering demonstration device for treating the 12000 tons of desulfurization wastewater per year by waste heat pyrolysis was established in Yixing Coking Plant of Shanxi Coke Group Corporation Co.,LTD.（a scale of 1million tons of coke per year）,and the influence of this process on coking related products or operations was systematically evaluated.The main results and conclusions are as follows:1.In the mixed salt of desulfurization wastewater,S was the main element,accounting for 95.97%of the total atomic number less than Na elements.The XRD phase analysis curve corresponded well with the standard spectrum of NH4SCN（25-0044）,（NH4）2SO4（41-0621）and（NH4）2S2O3（31-0068）.The infrared vibration peaks of NH4SCN and（NH4）2SO4corresponding to the absorption peaks of FT-IR analysis curves were stronger.SEM analysis showed that the crystallization was better and the slender columnar crystal structure was obvious.The desulfurization wastewater was weakly alkaline solution with p H value of about 8-9,of which the main inorganic components were ammonium thiocyanate and ammonium thiosulfate,with average values of 158.84 g/L and85.04 g/L respectively.The main organic components were phenol and p-cresol,accounting for 29.01%and 16.84%of the total organic components respectively.The relation between salt concentration and boiling point of desulfurization wastewater satisfied the formulaTb（28）0.0053c2（10）0.0664c（10）100.The weight loss of mixed salt of desulfurization wastewater in argon environment could be divided into five stages.The pyrolysis started at 95.26℃,and the cumulative weight loss of pyrolysis reached 99.00%when the temperature reached 436.55℃,at which the mixed salt was basically completely decomposed.2.The copyrolysis of desulfurization wastewater and coal started to decompose and produce a large amount of gas after heating from room temperature to 500℃,of which the maximum hydrogen content could reach about 65%-70%.The content of COD in the absorption liquid increased greatly from 9.54 mg/L to 142.06 mg/L.The summit of g-C3N4in the pyrolysis residue at 27.4°increased slightly,while the summit at 13.0°decreased with the increase of temperature.The accelerated heating rate was conducive to the formation of CO2,CH4and CO,and the range of change would also increase.At12℃/min,there was the largest amount of emission of CO2,CH4and CO.The content of COD and ammonia nitrogen in the absorption solution increased with the acceleration of the heating rate,while the content of SCN-decreased slightly.Increasing the content of desulfurization wastewater in coal blending would inhibit the formation of CO2and CH4,sharply increase the contents of COD,SCN-and ammonia nitrogen in the absorption liquid,and raise the contents of Na and S elements in pyrolysis residues,thus reducing the quality of coke.The production of H2S would increase rapidly after 540℃and reach the peak of2.061 g/L at 600℃.The release of H2S would increase rapidly with the increase of desulfurization wastewater content.The S content in pyrolysis residue would decrease with the increase of final temperature,but with the increase of desulfurization wastewater content from 0%to 15%,the S content in residue would increase from 0.16%to 0.95%.Based on DAEM model of distributed activation energy,the kinetic model of coal blending pyrolysis with desulfurization wastewater was established,and the relationship equation between the concentration of desulfurization wastewater,final pyrolysis temperature,heating rate and volatilization analysis yield was obtained by the equation mj（7）T（8）（28）m j??.3.When the evaporation model of desulfurization wastewater sprayed in high temperature raw gas in riser was 800℃,the maximum distance of droplet movement was calculated to be 0.051 m by the formulaWe（28）f（7）T（8）.The average distance between nozzle and coke surface could be obtained to be 0.075 m according to the height of 300 times of coal loading,with the confidence interval（CI）of the average distance of 95%（0.047-0.103）,which was more in line with the evaporation of droplets in high temperature.The flow velocity of raw gas increased from 0 m3/h to 700 m3/h,the dispersion degree of droplet particle trajectory increased from-0.181-0.174 m to-0.308-0.246 m on the x-axis,the time for droplet particles to reach the flow velocity of raw gas increased from0.007 s to 0.02 s,and the relationship between the vertical flow field velocity in the center of riser and the height wasu（28）f（7）h R（8）before and after spraying wastewater.The relationship between the average temperature of the riser before and after spraying desulfurization wastewater wasT（28）568.49ln（7）T 0（8）-3151.9.Within 20 hours of coking time,desulfurization wastewater was sprayed 3m away from the water seal of the riser.After evaporation,the average temperature of the riser was 620.44℃,and the average evaporation time was 0.0025 s.The increase of spraying amount would increase the spraying pressure of the spray,which was conducive to improving the evaporation rate,but would increase the heat consumed during evaporation.The optimized spraying flow rate was about55 kg/L.The smaller the aperture of the nozzle,the greater the injection pressure,the smaller the average particle size of the droplet,and the shorter the evaporation time would be.The increase of jet angle would disperse the droplets and increase the spacing,which was beneficial for the droplets to absorb more heat and reduce evaporation time.4.The pyrolysis of solid mixed salt obtained by evaporation and drying of desulfurization wastewater in simulated coke oven gas atmosphere（55%H2+6%CO+25%CH4+14%Ar）had five main stages:The crystalline transformation of ammonium thiocyanate（92.87-127.38℃,mainly from monoclinic crystal to orthogonal crystal and orthogonal crystal to square crystal）,isomerization of ammonium thiocyanate to thiourea（127.38-246.26℃）,co-pyrolysis of ammonium thiocyanate and ammonium thiosulfate（246.26-290.45℃）,decomposition of ammonium thiosulfate and ammonium sulfate（294.29-375.15℃and 375.15-543.26℃）.The cumulative weight loss was 99.00%at 384.19℃.Compared with pyrolysis in argon environment,the temperature required for starting pyrolysis and complete pyrolysis in simulated coke oven gas was lower,and the endothermic peaks corresponding to ammonium thiocyanate crystal form transformation,isomerization and thermal decomposition were more sharp.In the small-scale test of single riser,the optimal spraying conditions were:the spraying position was 3m away from the water seal cover of the riser,the spraying amount was 50-55 L/h,and the spraying time was within 10 minutes after coal loading to 20 hours during coking process.When the spraying amount of desulfurization wastewater in a single riser was 40-96 L/h,and the temperature of the riser reduced by76-287℃.the relationship between spraying amount v and temperature differenceΔT wasΔT=-2.939v,and the relationship between spraying amount v and ammonium thiocyanate concentration C at the outlet of high temperature raw gas in the riser was C（7）N H4SCN（8）（28）f（7）v（8）.The maximum waste liquid treatment capacity of 4.3 m single riser was 61.98 kg/h.5.The development of the core system of the large coke oven pyrolysis desulfurization wastewater process was mainly:（1）A fine filtration system for desulfurization wastewater was developed,which adopted a multi-level and multi-material composite structure;（2）A constant pressure and continuous conveying system was developed,and desulfurization wastewater was pressurized from the storage tank to the injection system through a pump;（3）The optimized nozzle aperture was 1mm,the injection angle was 60°,and the injector rotation protection device,nozzle self-cleaning device and pressure relief device was added.The sealing-spraying-angle integrated high temperature and high pressure drip prevention technology was developed to ensure the sealing performance of the nozzle joint of the injector,and a new injector device suitable for engineering demonstration was developed.（4）A system automatic control technology was developed to protect the safety of the carbonization chamber.When the temperature of the riser was low,the ejector was controlled to automatically switch to steam.（5）A wet drilling technology using self-made coolant to drill holes in the lining brick of the riser was developed.The tightness and installation angle of the injector positioner could be ensured through fusion welding technology and positioner;（6）The whole process of filtration,storage,pressurization and injection of desulfurization wastewater was monitored and controlled by the general control system.6.Before and after spraying desulfurization wastewater in large industrial coke ovens,the effects on coking products and process wastewater was:（1）The average contents of H2S,HCN and CS2detected in the coal gas were all at the same level,while thiocyanate was not detected at the inlet of the desulfurization tower.The components of the gas detected at the outlet of the laboratory gas were all at the same level,and the average concentrations of NH3and benzene reached the standard rate of 99%-100%;（2）The viscosity(E80)in tar reduced by17.58%,which was conducive to the improvement of tar quality.All indexes were consistent,conforming to the normal range;（3）The p H value of the desulfurizer was about 8.5,and the content of all components was basically at the same level;（4）All indexes of steam ammonia wastewater met the indexes of coking biochemical water inlet,and the contents of indexes in the coking regulating tank and biochemical water drainage were basically consistent;（5）All indexes of belt coke were kept at the same level.The method of pyrolysis of desulfurization wastewater by using waste heat of high-temperature raw gas in coke oven riser had no adverse effect on coking system,and the treatment capacity of desulfurization wastewater could be increased by 9.6%compared with coking coal blending method.Compared with the current technology,the technology of pyrolysis desulfurization wastewater by using waste heat of raw gas had the technical advantages of low investment,low energy consumption,low operation cost,low labor intensity of workers,thorough treatment and so on. |
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