Optimization Design For Regenerated Waste Hydrochloric Acid Process By Spray Roasting

With the development of China’s economy and the adjustment of industrial structure,the demand for cold-rolled,coated and silicon steel products in automotive,household appliances,construction and power generation industries will be increasing,therefore,the output of cold-rolled sheets(including coated and silicon steel)will also be further increased.The consumption of hydrochloric acid and the generated waste acid will also be further increased.With the increasingly stringent requirements of national environmental protection,it is urgent to optimize the design of the existing spray roasting device and spray roasting technology to meet the environmental emission requirements and reduce equipment maintenance and energy consumption.This paper summarizes the problems occurred in the process of engineering design,production and use of the regeneration technology of spray roasting waste hydrochloric acid,and optimizes the design from the aspects of technological process,equipment design,piping layout and theoretical calculation.The actual use of the technology has achieved good results and has reached the requirements of national environmental protection emission.The main optimization design contents are as follows:(1)The spray roasting device easily occurs red smoke phenomenon in acid water conversion operation for 30～60 minutes.Regenerative acid is introduced into the pre-concentrator equipment.The acid regeneration unit first performs regenerative acid operation in the acid-water conversion operation to ensure that the HCl concentration in the pre-concentrator is more than 14.21%.The fine iron powder produced in the roaster is fully absorbed by the pre-concentrator and then transferred to the corresponding water operation or acid operation.The operation time of regenerated acid can be set on HMI screen,and the remaining operation time of regenerated acid can be displayed.This method thoroughly solves the problem of red smoke in acid regeneration plant and avoids excessive iron oxide powder in the plant.(2)The exhaust gas temperature of roaster is 80℃,which contains 50%-60%water vapor.At the same time,it is easy to cause HCl and dust emission exceeding the standard.The tail gas of roaster was cooled by a graphite heat exchanger with round holes.The temperature of the tail gas of roaster was reduced to below 40℃,and the content of water vapor in the tail gas of roaster was reduced to below 10%.The HCl content and dust content in the tail gas of roaster can reach 30mg/m~3 required by GB 28665-2012.The heat exchanger adopts graphite heat exchanger with circular hole,and designs and calculates the opening of heat exchanger,the area of heat exchanger,the amount of cooling water and the structure of heat exchanger.(3)The original pre-concentrator is an integral structure,which is easily blocked.The structure of the preconcentrator has been changed to split type.The material of Venturi section is made of titanium alloy,which completely avoids the blockage and caking of the preconcentrator.It also solves the problem of difficult maintenance.(4)As the most important equipment of the device,the reaction temperature of the calciner is calculated theoretically.The theoretical reaction temperature in the calciner is594℃,and the engineering value range is 560-590℃.Temperature monitoring varies with the diameter of roaster and the type of gas.The temperature of monitoring is 50-160℃higher than that of theoretical calculation.(5)As the most important part of the roaster,the flue of the original roaster is prone to collapse.In this paper,the structure of the flue of the roaster has been changed,and the structure with the same diameter before and after has been adopted.The combustion temperature in the flue of roaster is calculated.When natural gas is used as combustion,the actual combustion temperature is 1283℃.The physical and chemical data of each layer of baking furnace were confirmed and the thickness and temperature of each layer were calculated.After optimization design,the gas consumption is reduced and the failure and maintenance frequency of the equipment are reduced under the condition that the temperature of the steel shell is lower than 250℃and the temperature of the external surface of the equipment is lower than 50℃.(6)The existing titanium blowers are very susceptible to corrosion,resulting in plant shutdown.After the temperature of the tail gas of the roaster is reduced to below 40℃,the FRP fan is selected as the tail gas fan of the roaster,which can avoid the corrosion of chloride ion and negative ion to the fan.According to the optimized design of this paper,the exclusion of 85%steam will be reduced.If the optimized technology is used in the regeneration of waste water from the roasting process,the annual water saving will be approximately 6 million 670 thousand cubic meters(approximately￥20,000,000),and the natural gas consumption of 78 million500 thousand cubic meters(approximately￥274,750,000)will be saved,and the amount of HCl discharged into the ambient air will be 353 tons(Protection of the environment,Reduced purchase of hydrochloric acid,approximately$470,000).The benefits of improving the quality of iron oxide powder are approximately￥251,200,000(￥200 per ton of iron powder).At the same time,the operation stability of acid regeneration unit is increased and the maintenance quantity is reduced..