Wet Process Phosphoric Acid Containing Fluorine Gas Absorption System In The Process Of Production

This subject mainly studies the engineering transformation of fluorine-containing tail gas produced in wet phosphoric acid production process by improving the existing treatment unit.The wet phosphoric acid used phosphoric rock and sulfuric acid as the main raw materials to extract phosphate rock from strong acid sulfuric acid through extraction reaction to obtain medium and strong acid phosphoric acid suitable for downstream use condition.In the process of extraction,about 7%of fluorine is released in the form of gas?the main form of fluorine is SiF₄,HF?,because this fluorine-containing gas has great damage to the natural environment and will cause great harm to human body.Osteoporosis and so on,serious may be poisoning death,so the process usually use tail gas washing,absorbent device,water or lye washing,absorb the fluorine in the tail gas,so that it can form fluorosilicate or fluorosilicate added Based on the recovery treatment,the main reaction equations are as follows:3SiF₄+?n+2?H₂O?2H₂SiF₆+SiO₂·nH₂O?The resulting silica gel precipitates are mostly gelatinous or soft fibrous,and the deposits encapsulated with fluorosilicic acid will cause blockage in the system.The higher the SiO₂,F^-content in the ore,the higher the reaction temperature,and the larger the SiF₄ emission.The more silica gel deposits are formed,the more serious the blockage will be,and in general,the fluoride released from the extraction tanks will be more or less entrained with the slurry and foam inside the tanks,so the silica gel precipitates that block the pipes contain fluorine,calcium,and iron.Aluminum and a variety of other ionic compounds,the main part of the system plugging gas pipes and circulating liquid pipes,resulting in a decrease in circulation,absorption,production,Operation brings a lot of difficulties,but also causes the exhaust gas can not meet the standards of emission,need frequent parking cleaning,can not guarantee the continuity of driving,and ultimately bring greater environmental risk and reduce economic benefits.Our company has three fluorine absorption systems,starting from cleaning up for120 hours,the fluorine emission will exceed the national air pollution emission standard?total fluoride?9mg/m³?.Day shift cleaning a set of system operation every day,and fluoride absorption system cleaning mode is manual cleaning,time-consuming and laborious,at the same time affect the start-up rate,reduce economic benefits.Through demonstration and analysis,the following modifications have been carried out:?1?By calculating the spray density,the circulating pump is reselected to improve the liquid-gas ratio.?2?replace the spray head,except Venturi keep the spiral nozzle,each tower is replaced by the swirl nozzle,so as to reduce the production of water mist and bring out as far as possible;?3?by hardware controlling the head of the pump,the high head pump can easily blow the water into a water mist;?4?adjusting the arrangement and quantity of sprinkler head to ensure the effect of washing;?5?increase the washing series,add four layers of swirl sprinkler on the vertical pipe from one tower to the fan,use one pump for washing water circulation in the lower three layer sprinkler head,water supply on the upper layer sprinkler head from the external sewage pool pump,add circulation pool under the pipe wash,Continuously replenish water from the sewage pond and continuously overflow through the ditch to return to the sewage pond;?6?optimizing water balance,without increasing the total water supply of phosphoric acid system and without affecting water balance,the fluorine absorption terminal tower will be replenished in other places first.Because of the large amount of water,the fluorine content after washing is not high?0.005⁰.05%?.It also has little effect on water equipment.It also reduces the temperature of tail gas and the concentration of circulating liquid.?7?Venturi is separated from a washing tower circulation tank,and the Venturi circulation tank is added separately.The circulating fluid in the Venturi circulating tank and the first washing tower circulating tank are continuously pumped out and filtered into the fluorine water plate and frame,and the silica gel precipitate in the system is discharged as the filter slag.Reduce the frequency of sedimentation and clogging.It is not difficult to see Venturi,a washing tower is more place of silica gel formation,basically washing enough,silica gel all in these two places to form,so the two places of silica gel filtration,the system significantly reduced the phenomenon of blockage;After the approval of the scheme,the technical transformation was carried out on the industrial plant of the company,and the related data after the modification were monitored and the expected goal of"continuous operation for 15 days under the premise of meeting the emission standard"was achieved.After half a year trial run,the project is accepted and accepted in the company,which solves the hidden trouble of environmental protection,improves the working environment and reduces the labor intensity.