(Chemical Engineering and Process
Abstract: In late July 2003, I took advantage of the summer in a regional sulfuric acid plant for a period of five days of observation practice internship. In the course of the internship, I *** examined two sulfuric acid chemical plants, in-depth investigation and understanding of several workshops, and learned a lot of theoretical and practical knowledge. This report is the insights and experiences of this practical internship and a summary of what I have learned.
Keywords: sulfuric acid, sulfurous iron ore, flotation, tailings
In late July 2003, I contacted two chemical plants in Qionglai City: Qionglai Chemical Plant in Ranyi Township and GaoYu Group Chemical Plant in YangAn Township, and carried out a five-day observation of practical internship in the two factories.
Practice report
Object of study: sulfuric acid chemical plant
Examination project: the process of sulfuric acid production
Examination content: to understand the production process of sulfuric acid, sulfuric acid production of waste gas and waste liquid and waste residue treatment and sulfuric acid use
For the sake of simplicity of narration, I will be DENGXIA chemical plant set up as the A plant, and the GaoYu Group chemical plant set up as the B plant.
I. Production
(a) production of raw materials
The production of raw materials for plant A is divided into sulfurous iron ore, and the production of raw materials for plant B, in addition to sulfurous iron ore, there are flotation sulfurous iron ore and tailing sand. The sulfur grade of flotation sulfurous iron ore and tailing sand is higher than that of sulfurous iron ore, but the transportation cost of flotation sulfurous iron ore and tailing sand is higher than that of sulfurous iron ore. Comprehensive comparison of the utilization rate of the flotation of sulfurous iron ore and tailings seems to be very considerable, the economic strength of the use of flotation of sulfurous iron ore and tailings better than the use of sulfurous iron ore.
The main component of sulfurous iron ore is FeS2, according to its different sources are divided into: ordinary sulfurous iron ore, flotation sulfurous iron ore and tailings and coal sulfurous iron ore.
Sulfurous iron ore is generally massive. Flotation sulfurous iron ore and tailing sand is powdery and contains a lot of water, and will also be caked in the storage and transportation process. They must be properly treated before being sent to the roasting process. Crushing and screening of lumpy or agglomerated flotation ores, drying of flotation ores and tailings, and mixing of raw materials of different compositions.
The crushing of sulfurous iron ore usually passes through two processes of coarse crushing and fine crushing, coarse crushing with jaw crusher, fine crushing with 锟锟絪 type crusher or impact crusher, squirrel cage crusher is mainly used to break up the tailing sand agglomerates.
(B) Sulfurous iron ore roasting
Sulfurous iron ore roasting, mainly the FeS2 in the ore and the reaction of oxygen in the air. With different conditions and get different products. Industry in order to ensure that the components of the raw material as far as possible to transform into sulfur dioxide, must be roasted at a temperature of 600 ℃ or more.
The roasting of sulfurous iron ore is carried out in a boiling furnace.There are two systems in Plant A, one with a production capacity of 20T/year and the other with a production capacity of 40T/year. I went to the workshop of plant A and saw that the finely crushed ore is fed evenly by conveyor belts directly into the furnace. plant B has a larger workshop, with a 60T/year system and a 40T/year system, so it has a unified stockpile of raw materials, and the processed raw materials are delivered to each of the workshops by conveyor belts.
During the roasting process, it is generally necessary to remove heat from the boiling layer to avoid high temperatures in the charge pavilion, using the heat transfer element of the waste heat boiler to remove the heat, which is used to generate steam. plant B built a system to use the steam generated by the waste heat boiler to generate electricity, and the electricity generated by this system meets the electricity consumption of the entire plant. This system saves money and creates efficiency. It cleverly utilizes the energy that the system needs to transfer to produce new energy and is a method that modern manufacturers should promote. The slag produced after ore roasting is sent to the waste slag collection pond.
(2) furnace gas dust removal and purification
l. Dust removal
From the boiling furnace out of the roasting furnace gas, all contain mineral dust. The amount of dust with the grade of raw materials, particle size, roasting method, roasting intensity and other factors.
The method of removing the furnace dust, usually according to the different sizes of the mineral dust particles, from large to small, step by step to separate the mineral dust. Roasters out of the return gas temperature is high, the production of dust and gas cooling at the same time.
Just out of the furnace gas with water washing method of dust removal. Another role of this method is to reduce the temperature of the furnace gas, so that the furnace gas can basically meet the temperature requirements of the process behind. The raw material removed after water washing is sent to the slag collection place.
After washing the furnace gas into the cyclone separator dust. The cyclone dust collector can remove 65.75% of the total mineral dust.
2. Purification
At this time, the SO2 body also contains many gases that are toxic to the catalyst in the later process.
Then the furnace gas successively into the two venturi, further dust removal, purification and cooling.
Generally, a foam tower is used for dust removal and purification. The structure of the foam tower has a partition and sieve holes, the gas enters from the lower part of the foam tower, and the water is showered from the upper part.
Roasting produces SO2 so that a large number of O2 in contact with it, in the sulfurous iron ore roasting generated by the catalyst of iron-containing substances, there is often a small part of SO2 is oxidized into SO3, this part of the SO3 in the process of water washing will be generated H2SO4 to form an acid mist, the output of the SO2 absorption of a great deal of adverse effects, so it must be removed from this part of the acid mist. After the cyclone separator, the furnace gas, Plant A uses a plain porcelain filter to remove dust and purify. This is a method of removing acid mist. plant B adopts a more advanced method - electric mist elimination. In this process, the equipment is a diameter of about 4 meters, the height of about 3 meters of plastic drums, drums installed is dozens of barrels and barrels with the height of the diameter of tens of centimeters of steel tubes, each steel tube is installed in a very thin steel wire. It is the principle of the steel pipe and steel wire with a very high voltage, the acid mist electrolysis, so that it flows down the steel pipe. The acid that is removed is collected in a tank that contains the product acid. This method is very effective in removing acid mist. In comparison, the effect of acid mist removal in plant A is also good, but it has to be purified by several vein porcelain filters to reach a certain standard.
In this link, other methods are also used to remove those gases that have a toxic effect on the catalyst.
(3) SO3 absorption
Because SO3 absorption with water is not good, it is easy to form acid mist, so it is absorbed with 98% sulfuric acid. SO3 absorption is carried out in the absorption tower. SO3 absorption is an exothermic reaction, and SO3 can only be reacted with the water in the concentrated sulfuric acid after it reaches a certain degree of degree. the method adopted by plant A is to heat the SO3 gas with heat generated from the waste heat boiler in the boiler. The method adopted by Plant A is to use the heat generated by the waste heat boiler in the boiling furnace to heat the SO3 gas, which then enters the absorption tower to react with the concentrated sulfuric acid. The generated acid is sent to the storage tank, and after adjusting the concentration of the acid by adding water, etc., it is sent to the finished acid storage tank for sale.Plant B again utilizes the exothermic property of the system to design a more reasonable absorption system for SO3. It utilizes the exothermic property of SO3 absorption, and designs the absorption tower into three sections, each section isolated from each other, and installs heat exchange equipment outside the absorption tower. SO2 entering the absorption system is first heated to an appropriate temperature by the heat exchanger equipment, and then enters the first section, where it is absorbed with 98% sulfuric acid catalyzed by a catalyst and sent to the first storage tank. The heat generated by this reaction is used to heat the SO3 entering the absorption tower after the heat exchanger is transferred to the ratio. the insufficiently reacted SO3 of the first stage enters the second stage, as in the previous general reaction, and then enters the third stage of the reaction after passing through the second storage tank, and then the generated acid is sent to the third storage tank. In this way, the theoretical conversion of SO3 is 98%, while in practice it is only 92%. The reason for the discrepancy is a problem with the equipment as well as the production process. These varying concentrations of acid are fed into a conditioning tank, adjusted to the proper concentration and pumped into tanks at the entrance to the plant for sale.
(IV) Summary
During my internship at the two plants, I saw the differences between the two plants with different economic strengths in many ways. Factory B also considered some good methods when it needed to observe the status of some systems such as pneumatic and hydraulic pressure. For example, linking the electrics to these barometric water pressures and installing observation meters centrally will help to increase productivity.
II. Treatment of waste gas, waste residue and waste water
(I) Treatment of waste gas
The tail gas of sulphuric acid production contains a small amount of SO2 because SO2 is always not reacted completely.This gas has to be removed, and nowadays the general method is to use alkali absorption. The absorption of SO2 with ammonia is not only effective, but also produces ammonium sulfite, which is a very cost-effective method.
(ii) treatment of slag
The slag contains a large amount of iron, which can be sent to the ironworks for smelting and so on.
(iii) Treatment of waste water
The treatment of waste water is generally to keep the slag contained in the water from flowing into the rivers, so the waste water has to be settled before it flows into the rivers and then discharged into the rivers.
(D) Summary
Such a treatment method, some have the effect, but the treatment of wastewater is not very satisfactory, the impact on the environment is very large, there should be a way to improve. After all, developing the economy at the expense of the environment is not a long-term development method.
3. Summary
In this vacation, I went to the factory internship practice, so that I have grown knowledge and insight, but also let me grow a lot of practical knowledge, very rewarding and very touching. In a few days of activities, I strengthened at least one point of view - the development of the economy should have a long-term vision, knowledge and technology. This internship has also strengthened my belief that I need to work hard to learn knowledge and skills to contribute to the future development of China's economy.
I would also like to thank the technicians of the factory for their support and care, they taught me a lot of knowledge and things beyond the textbook, without their help, there is no my summer practice activities, without their explanation, I would not have learned so much and have so much to gain. Thank them very much!