Design Features of Flue Gas Sulfuric Acid Generator in Lead-zinc Sintering Machine

1 Keywords 2 copper zinc sintering machine flue gas sulfuric acid plant design features 1 literature identification code 2 B 1 Author brief introduction 2 Huang Weihua, male, Nanchang Nonferrous Metallurgy Design and Research Institute senior engineer, engaged in metallurgical design.

1 Foreword A system of Shaoguan smelter was built in the 1970s. It uses British ISP technology and uses mixed lead-zinc concentrate as raw material. Sintering machine flue gas is used in the acid production system. It was designed since 1988 and it was completed in February 1996. Completed and successfully fired once. At present, the production technologies and capacities of the first and second systems are roughly the same. The lead and zinc production scale is 85 kt/a, and the sulfuric acid production scale is 150 kt/a. The second system is designed by China, and the acid plant is closed to dilute acid cleaning. Inhalation of glycine tail gas absorption process. After more than 4 years of production operation inspection, the device has reached the design requirements for its production capacity and various indicators. Most of the indicators such as conversion rate and absorption rate are higher than a system and are at the advanced level of similar domestic devices. Practice has proved that the design of the second-system sulphuric acid plant is successful and needs to be carefully summarized.

2 Characteristics of sintering flue gas The sintering process mainly removes the sulfur in lead sulfide and zinc sulfide concentrates, and at the same time sinters the finely-sized ore concentrate into blocks to meet the technological requirements of lead blast and zinc smelting in closed blast furnaces.

The main chemical reaction in the sintering process is oxidation reaction: The flue gas produced by the lead-zinc sintering machine has the following characteristics: a1 Flue gas U under normal operating conditions (SO 515, gas volume, gas concentration fluctuates little, b1 Sintering machine starts and stops frequently, average After 12 times a day, the concentration of SO gradually increased from zero to normal at the beginning of driving, and the duration was 30 60 min. During this period, the gas volume and concentration fluctuate greatly. c1 The dust component is mainly lead, w (Pb) is more than 60, and the dust particle size Fine, hydrophobic, difficult to wet, but the moisture U(SO) is lower than the viscous d1 in the purification process. Only the e1 flue gas contains a certain amount of Hg, F and a small amount of organic substances. The specific amount is affected by the ore source. Larger.

3 Designed targeted measures Purification process 31 Dilute acid deposition system design From a system operation point of view, due to the dilute acid in the thinner and more viscous, difficult to settle, the purification process used in the original foam tower sieve often blocked. Caused the resistance to rise, after using the packing tower, the situation is still the same. About half a year, the packing must be cleaned or replaced. In addition, the empty tower nozzle is often blocked, resulting in uneven acid distribution and poor results. Therefore, dilute acid dust has always been a difficult problem that plagues the normal operation of a system purification process. In response to this problem, the secondary system was designed with the following considerations for the settling system of the purification process: Huang Weihua Design features of the flue gas sulphuric acid plant for lead-zinc sintering machines a1 Properly increasing the area of ​​the settlement trough Area of ​​the settlement trough According to the formula: C) )) Constant velocity settlement, m/h))) Calculated area of ​​the settlement tank, m can be seen from the above formula, the settlement tank area is inversely proportional to the sedimentation velocity of the particles. Since the device has small dilute acid dust particles and large viscosity, the settling velocity is small, so the area of ​​the settlement tank for treating the same amount of acid is large. In view of Party A's failure to provide accurate dust deposition experimental data, the design is based on the original data of Guixi Smelter (hereinafter referred to as Guiye) for initial calculation, and then the calculation result is enlarged.

B1 Improvement of the settlement tank structure We borrowed from the successful experience of Guiye. The settlement tank was not replaced by a system of direct current and overflow weir.

As can be seen from Figure 1, the dilute acid in the second system into the sedimentation tank first enters the bottom of the sedimentation tank through the insertion tube, and then flows back to the liquid surface and overflows around the overflow weir, providing more abundance of dust particles in the dilute acid. Settling time.

The design of the parallel configuration of the c1 empty tower settling tank takes into account the configuration of the empty tower using two conical settling tanks in parallel. At the same time, the diameter of the inserting tube is selected to keep the acid flow rate in the tube at 012 013 m/s, so as to avoid acid influx to the settlement area. Perturbation returns the settled dust particles back into the liquid.

D1 Appropriate insertion tube depth According to Guiye operation practice, the insertion depth of the acid inlet tube has a great influence on the sedimentation effect: if the insertion is too deep, it will impact the settled dust particles to be inserted too shallowly and cause a liquid short circuit. Considering trade-offs, the insertion tube depth is set to 1 250 e1 to increase the settlement tank taper. Dust particles in the dilute acid are more viscous. To make the dust particles on the tank wall fall into the cone bottom as quickly as possible, properly increase the cone angle of the cone part of the settlement tank. (around 80b).

32 Anti-blockage design of the washing tower packing In order to prevent the plugging of the washing tower packing, the corresponding countermeasures have been adopted: a1 Improving the dust collection efficiency of the empty tower. The empty tower nozzle adopts a spiral type, and it is not easy to block under a certain acid pressure, and at the same time, the impact type dust removal efficiency of the noble metallurgy is higher, so that the amount of smoke that is moved to the packed tower can be reduced.

The b1 packed tower uses Haier ring plastic packing with large voidage and strong self-cleaning ability.

For the c1 production operation, the sedimentation tank and the circulation tank of the packed tower are required to be discharged twice a day.

The two systems have been put into operation so far, and no phenomenon of clogging of the nozzles and the washing tower has been found, and the problems that the system has not solved for many years have been avoided.

33 intercooler water supply pipeline improvement According to the project's flue gas conditions and local climate calculations, production 93) sulfuric acid out of the purification process flue gas temperature must be reduced to 36 e below. The local summer circulating water temperature is as high as 33 e, which brings certain difficulties to the cooling of the flue gas. For example, in the summer of a system, it is often impossible to produce w (H 93 sulfuric acid) due to lack of cooling capacity, and it is necessary to adjust the acid concentration by adding w(H) 98 sulfuric acid. Therefore, how to avoid excessively large cooling equipment to save equipment investment, and to ensure that the summer output of qualified H (H 93 sulfuric acid) is a problem that must be carefully considered in the design of the two-system decontamination.

In fact, under certain flue gas and equipment conditions, simply increasing the heat transfer coefficient of the chiller to strengthen the equipment capacity is limited. If the average temperature difference between the tube and the shell can be appropriately increased in some way, it can be obtained. More direct and effective results.

In view of this, the design considers the intercooler and the purifying circulating water cooling system as a comprehensive consideration, and configures the water supply line of the flue gas cooler in the manner as shown in Fig. 2, so that it can supply water in series or in parallel. In winter, series water supply is adopted to reduce water consumption and parallel water supply is used in summer to increase the average heat transfer temperature difference between the intercoolers (from 10138 e to 18 e ) to increase the cooling effect. In this way, the water supply capacity of the purification and circulating water system can be fully tapped. The design capacity of the purification system cooling water pump is 3 000 m sulfuric acid industry h, and the design water consumption is 2 360 m / h. The above improvements reduce the area of ​​the flue gas cooler and thus reduce the The number of equipments reduces the floor space and avoids the production and installation difficulties and risks caused by the oversized equipment.

34 intercooler and electric defogger interphase configuration with reference to a system equipment configuration, one, two intercooler and one or two electric defogger interphase configuration, and the intercooler at the top to adopt a cyclic spray mode, so that the dust particles It is not easy to adhere to the inner wall of the graphite tube, so that the fine mist particles that are not removed by the primary demister can have more chance of condensation growth, thereby increasing the overall efficiency of the electric demister.

35 increase the size of inter-stage cooler graphite tube diameter given the adhesion of graphite tube inner wall of lead dust is hard and strong adhesion, and graphite tube material is brittle, easy to break, will be an interstage cooler graphite tube The conventional a32 mm/a22 mm is changed to a50 mm/a36 mm for manual manual cleaning.

36 Electro-mist eliminator adopts anti-mercury erosion measures through the air tower.) After the scrubber cools down, the mercury vapor in the flue gas is saturated, 45 of which enters the subsequent equipment, and condenses in the various equipment as the temperature decreases. In order to prevent the corrosion caused by the amalgam 0 reaction, isolation measures are taken on the surface of the lead plate of the lead, which is easily condensed by mercury vapor in the electric demister.

37 Dilute Acid and Sludge Treatment Process The flue gas containing SO is very low in the purification process. According to the calculation, dilute) 015, and the components mainly composed of lead and zinc are difficult to filter, so the design will dilute acid and acid mud. Two for one, sent to the sulfuric acid plant sewage treatment station processing. After the secondary lime milk is neutralized to a pH of 67, it is finally sent to the sintering plant for treatment in a 500 m thick pool.

38 Fluoride-prevention measures A systematic purification process The condition of fluoride erosion in the lining tiles of packed towers is relatively serious. Some tiles can be seen during the overhaul period. 3. For this reason, the second system purification process design uses a lot of fluorine-resistant FRP equipment and pipelines. As well as plastic packing and lined plastic valves. Among them, the scrubbers, the upper and lower heads of the graphite intercooler, the circulation tank, and the settling tank are all made of glass steel.

39 Eliminating electric defogger gas distribution plate fillers due to the soot is more viscous, open and stop more times, the gas distribution plate filled with fumes inside the continuous accumulation of plugging, but the electric defogger inlet uneven distribution, so the gas will be commonly used The filler on the distribution plate is removed.

From the perspective of production and operation practices, the effectiveness of the purification system design due to the above-mentioned effective measures is quite obvious. At present, the resistance of the entire sulfuric acid system only increases by 500 800 Pa a year, and the screening process of the conversion process is expected to extend from the original 1 year to once every 23 years.

Dry suction process 31 Absorption of high temperature absorption process is the last step in the production of sulfuric acid. Absorption index will directly affect the sulfur trioxide content in the exhaust gas.

The traditional domestic absorption process is low-temperature absorption, and the absorption acid temperature is about 55 e, which is mainly based on the considerations of concentrated acid pipes and cooling pipe used in cast iron materials and concentrated acid pumps that are difficult to withstand high temperature and concentrated sulfuric acid corrosion. Since the high-temperature absorption process was successfully adopted by Guizhou Metallurgical Co., Ltd., it has gained some understanding and gradually promoted it, but it is mainly applied to two-to-two suction processes. Under the flue gas conditions of this project, a high-temperature absorption process is also adopted in consideration of the following considerations: a1 High-temperature absorption process can reduce the generation of fine-grained acid mist, thereby achieving the purpose of improving absorption efficiency.

B1 As the acid temperature increases, the average temperature difference of the concentrated sulfuric acid cooler increases, which can save the cooling area. Under the conditions of this project, the cooling area can be reduced by 35, which meets the requirements of the owners and the original color metal company to save investment.

The lower the concentration and the lower the reaction heat of the absorption process, the lower the temperature increase of the acid in the tower. If it is designed into the acid temperature of the absorption tower 70 e , the tower temperature 89 e is calculated. The effect of the cast iron pipeline is good at this temperature, and the domestic stainless steel shell anode protection acid cooler and the high temperature concentrated acid pump can also be used completely.

D1 contains a small amount of organic substances in the flue gas. When dry, it cannot completely remove the design features of the Huangweihua lead-zinc sintering machine flue gas sulphuric acid plant. It is oxidized to carbon dioxide and water vapor in the conversion process and increases the moisture content in the flue gas. necessary.

In the actual production process, when the temperature of the acid in the absorption tower is as low as 55 60 e, the amount of white fog in the exhaust stack is significantly increased, which means that the absorption process parameters selected under the above-mentioned flue gas conditions are correct. From the production indicators of 1996 and 1997, the absorption rate of the two systems has been maintained at 99,195 or more, with an average of 99,198, which has achieved significant economic and environmental benefits.

31 Improved orifice setting method The dry absorption tower adopts traditional trough-type acid distributors, and additional acid orifices have additional orifice plates. However, improvements and simplifications have been made to the traditional setting methods, details of which have been described. From the use of the situation in recent years, the drying and absorption effects have been significantly improved over the one system, which means that the above improvement measures are reasonable.

Conversion process Because the sintering system equipment is mostly stand-alone, no backup, and the entire system is interlocked and running, any failure of any equipment will cause the sintering system to stop, and most of them are short-term shutdowns (1 2 h).

Therefore, how the acid conversion system adapts to changes in the operating conditions of the sintering system has become the key to the success of this project design.

31 Blower outlet setting When the bypass pipe is started, the gas concentration is gradually increased from zero, the duration is longer, the conversion system is difficult to operate according to the normal conditions, the preheating temperature increasing system must be started, and the preheating is started for a long time or often. The warming system is economically unreasonable. According to a system's production experience, when the gas U (SO) is lower, the conversion system is more difficult to maintain the original temperature system. In view of the above situation, the second system design adds a bypass at the outlet of the fan directly to the absorption tower, bypassing the bypass to avoid the original temperature system of the conversion system, and at the same time, to ensure that the exhaust SO does not exceed the standard when operating under this condition. , tail suction process set up secondary absorption device. In the past two years, there has been very little excess of SO in the exhaust gas.

31 Preheating furnace with stainless steel jacketed preheater After a system shutdown for more than 16 hours, the conversion process must start the preheater to increase the temperature when the car is started. Therefore, the use of the preheater is more frequent than that of the normal smelting flue gas acidification system. . Because the temperature of the furnace gas at the outlet of the preheated heating furnace is up to 960 e, and it is turned on at the time of stop, the preheater is easily damaged, and it needs to be overhauled and replaced in 12 years. In view of this, during the design of the second system, a jacketed stainless steel preheater with an area of ​​80 m was installed at the outlet of the preheating furnace furnace gas to reduce the furnace gas temperature below 580 e into the carbon steel preheater, thus effectively The service life of the preheater is extended and the heat energy is fully utilized. The schematic flow of the warm-up heating system is shown in Figure 3.

13 Set up hot sub-line In order to adapt to the characteristics of frequent start and stop of sintering machine and solve the problem of heat balance of the converter when carrying out low-concentration sulphuric acid production, in addition to the normal setting of the cold sub line, in addition to The heat exchanger sub steam line is added to the SO heat exchanger to adjust the temperature, as shown in Figure 4.

With the addition of thermal sub-lines, normal continuous production, due to gas concentration, gas volume fluctuations are not large, mainly by the thermal sub-line to adjust the temperature of each catalyst layer, avoiding the cold sub line caused by the temperature fluctuations of various layers and temperature system disorders. However, when the vehicle is just driving, the adjustment of the heat secondary line is conducive to the temperature increase in the second and third stages.

14ó Heat Exchanger Pipeline Configuration In this project, the conversion system flue gas U (SO) design value = , the equilibrium conversion rate is high. In fact, when a system is in normal production, the conversion rate in the first and second stages reaches about 91, and there is little reaction in the three stages. When the SO concentration is lower, the temperature rise in the third stage is even equal to zero. According to this situation, according to the The 5 way has designed the piping of the two system ó heat exchangers.

Sulfuric acid industry can be seen from Figure 5, according to the level of smoke SO concentration, through regulation?

The outlet valve of the heat exchanger can conveniently control the temperature index of the third and fourth sections. Especially when the SO concentration is low to a certain value, the four-stage conversion process can be quickly switched to a three-stage four-layer conversion process. In addition, the smoke into the ó heat exchanger from?

Heat exchanger leads to avoid the use of high temperature valves.

15 Improvement of the converter's four-stage flue gas outlet pipeline According to a system production situation, due to condensation acid adsorption catalyst powder and other impurities, ?

Severe blockage in the heat exchanger tubes, sometimes clogged tubes up to 50. For this reason, the second system design will be?

The inlet mode of the heat exchanger SO range of flue gas is changed from bottom-in, top-up, and top-down, so as to reduce the adhesion of dust on the inner wall of the pipe. Although this extended the flue gas line, it played a role in preventing the heat exchanger from being blocked.

16 Increase the conversion system heat storage capacity According to the characteristics of sintering flue gas acidification, the design has given full attention to the insulation of the conversion system, such as the use of aluminum silicate fiber mats with better insulation properties, insulation layer thickness of 200 mm insulation coating 10 Mm thick hemp knife cement for moisture and heat insulation. After driving, the surface temperature of the converter was measured to be close to the atmospheric temperature, and the gas temperature of the conversion system was maintained at more than 180 e. Due to the good insulation effect, the preheating temperature increase system can be not started when the vehicle is parked for 24 hours and then driven again.

17 Change the trend of preheating and warming pipelines To save energy and draw on the experience of other domestic production plants, change the preheating and warming pipelines from the conventional fan outlets.

The heat exchanger is led out (as shown in Figure 5) to reduce the gas consumption by using the heat of the flue gas itself. In view of normal production?

The heat exchanger outlet temperature is only about 200 e, no need to use high-temperature valves, so consider the lead from the place.

4 Conclusion The production practice for more than four years shows that the design of the two-system sulfuric acid plant was successful due to the experience gained and lessons learned from the system and the successful experience of Guiye, which represents the advanced level of acid production from domestic smelting flue gas at the time. The measures taken according to the characteristics of the sintering flue gas are feasible.

According to the requirements of the owners and the original color metal company, no production equipment was introduced into the project. As the second-system sulphuric acid plant was the largest single-series acid plant designed and manufactured by itself at the time, it was extremely difficult, but the idea of ​​adapting to local conditions and daring to innovate was adopted in the design. At the same time, a cautious attitude towards the selection and selection of domestic equipment was taken. It laid the foundation for the successful operation of the device.

1 References 2 Huang Weihua 1 The second phase of the Sulfuric acid project design and construction of Shaoguan Smelter The annual national sulphuric acid industry technical exchange meeting will be published. The 2001 National Sulfuric Acid Industry Technical Exchange Conference will be held in September and is now collecting papers. The main topics of this conference include: the impact of WT O's participation in China's sulfuric acid industry, the institutional reform of the sulfuric acid enterprises, product structure optimization, production technology management, raw material route selection, process equipment reform, waste heat utilization, waste management, extended product development, etc. . We sincerely welcome the participation of the majority of people in the industry and actively contribute.

Application paper Please attach a brief introduction of the author's personal situation about 200 words. At that time, the General Assembly will select a number of 1 3rd prizes from the draft paper, and the prize will be sponsored by Jiangsu Xinhongda Group. The deadline for receiving the document is June 30, 2001.

The papers should be sent to: Editorial Office of No. 699, Geguan Road, Dachang District, Nanjing, China, 5 Sulphuric Acid Industry 6 Tel: (025) 7795064 Contact: Hu Xiaoyun, Huang Weihua Design Features of Flue Gas Sulfuric Acid Plant with Lead-Zinc Sintering Machine

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