Activated Carbon Equipment - slip
Activation Furnace in the thousands of years from 3000 BC to the 19th century, from ancient Egypt to China and then to Europe, charcoal has been widely used in the fields of medical treatment and purification of drinking water. The lack of adsorption capacity in the field of sugar decolorization has become an obstacle to all-round application in industrial production and life. With the continuous efforts of scientists, the birth of activated carbon has become possible. The early research results show that coke with strong adsorption can be produced in the process of coal carbonization; The adsorption capacity of coke has an upper limit, which can not meet the needs of industrial production such as sugar decolorization; In the process of dry distillation, too high temperature will reduce the porosity and specific surface area, so as to reduce the adsorption.
In the early 19th century, the reaction of activated carbon prepared by steam and carbon dioxide was found, and the large adsorption activated carbon was finally born. At the beginning, activated carbon was monopolized by the army and was completely used for gas masks and water purification. Until the end of World War I, the expanded production of activated carbon made it possible for civil activated carbon.
In 1966, Taiyuan started the SLP activation process plant, and then hundreds of SLP activation furnace plants were opened in China. This furnace is an activated carbon production furnace invented by the Soviet Union. It is used to further drill holes for carbonized coke particles by using steam and a small amount of carbon dioxide to increase porosity, so as to greatly improve the specific surface area and become activated carbon with extremely excellent adsorption performance.
Process principle:
1.1. Reaction involved
Main heating reaction: ⑴ C (s) + O2 (g) CO2 (g); Δ H＜0
Main cooling reaction: ⑵ C (s) + H2O (g) CO (g) + H2 (g); Δ H＞0
⑶ C(s) +CO2(g)2CO (g) ; Δ H＞0
Side heating reaction: ⑷ CO (g) + 1 / 2O2 (g) CO2 (g); Δ H＜0
⑸ H2(g) + 1/2O2(g)H2O(g) ; Δ H＜0
⑹ CH4(g) + 2O2(g)CO2(g) + 2H2O(g); Δ H＜0
1.2. Activation principle
The process involved in any high-temperature chemical production will be more complex, so it is necessary to carry out targeted step-by-step process analysis and overall process comprehensive analysis.
Coal is a kind of natural organic polymer compound. Its porous and multi slit characteristics make it have the characteristics of large specific surface area and strong adsorption. With the gradual transformation of coal quality from bituminous coal to anthracite, the porosity and specific surface area increase gradually. Using these characteristics, the volatile matter of coal can be removed by dry distillation, the hydrogen and oxygen groups fall off, the carbon content increases and the porosity increases, so as to obtain coke (or fired charcoal) with large specific surface area. Charcoal or coke has high adsorption, and the iodine value can reach 200-400. The main purpose of activation is to further remove volatiles from carbonized coke particles and improve carbon content. At the same time, artificial pores are made through water gas reaction, so as to prepare activated carbon with real high adsorption rate.
Various physical activation processes are carried out alternately in two stages: dry distillation and pore forming. The main principles are as follows:
1.2.1. Dry distillation process:
Heat the coal to a high temperature above 800 ℃: 1. Conduct supplementary carbonization, completely drive out and ignite the residual adsorbed volatile in the pores of carbonized material, and assist in temperature rise; 2. Non carbon groups such as hydrogen and oxygen of coke continue to oxidize and fall off, so that the carbon content continues to increase; 3. The carbon in the outer layer of Coke will also participate in combustion and be oxidized to carbon dioxide, so as to release heat to assist temperature rise. At the same time, excess oxygen will be consumed to prevent the inner carbon from being reacted by excess oxygen.
At the same time, a large amount of water gas will be produced in each reaction process, which can be burned to assist temperature rise.
Bath found that if the dry distillation temperature is too high, it may reduce the porosity and reduce the adsorption of coke particles.
1.2.2. Hole making process:
In the early 20th century, when the activated carbon equipment was officially used to produce activated carbon, the one-time pore forming method was carbon dioxide, that is, when the carbonized material was fully heated to above 600 ℃, high-pressure carbon dioxide was introduced to produce C (s) + CO2 (g) 2CO (g); Δ H > 0 reaction, so as to "breakdown" coke particles, greatly increase porosity and specific surface area.
After the activation process is mature, we generally adopt the steam pore forming method, that is, when the carbonized material is fully heated to above 800 ℃, high-pressure steam is introduced to produce C (s) + H2O (g) CO (g) + H2 (g); Δ H > 0 reaction, so as to "breakdown" coke particles, greatly increase porosity and specific surface area.
At the same time, a large amount of carbon dioxide will be produced in the process of dry distillation and pore forming, which can react with carbonized material to assist pore forming.
1.3. Tail gas
1.3.1. Main products
The activation furnace mainly includes two processes: high temperature dry distillation and steam cooling. The main reactions are the six reactions in 1.1. According to le Chatelier's principle, the reaction product should be a mixture of all reactants and products. Changing external conditions such as temperature or pressure can only change the proportion of mixture components, and can not completely remove any components. Therefore, the tail gas includes combustible gases such as CO, H2 and CH4, complete reaction products such as CO2 and H2O, as well as a small amount of combustion supporting gases such as O2 and a large amount of N2.
The tail gas can be oxidized into carbon dioxide and water vapor through the incinerator or converter tower, and then discharged into the atmosphere from the chimney. The heat generated by combustion can be recycled by waste heat boiler. After a large amount of hydrogen and air are reacted, the remaining nitrogen can be proportioned in theory for the production of synthetic ammonia, chemical fertilizer and synthetic ammonium nitrate explosive. In theory, a large amount of water gas can be proportioned for methanol production.
1.3.2. Toxic products
1.3.2.1. Organic by-products
The carbonization material still contains about 3% volatile matter, including phenols, aromatic hydrocarbons and other toxic and combustible gases produced during carbonization, dry distillation and water gas reaction, which will enter the tail gas during activation and temperature rise. This part of tail gas needs to be completely removed by combustion in the incinerator, and the product carbon dioxide and water vapor can be directly discharged into the atmosphere.
1.3.2.2. Sulfur containing substances
① "S-R" (organic sulfur) H2S
② "S" (inorganic sulfur or elemental sulfur produced by reaction) + o2so2
③H2S + 3/2O2H2O +SO2
The above three reactions are the main sources of sulfur in tail gas. Because coal comes from plant corpses, a large number of sulfur-containing elements in protein enter into coal molecules, which cannot be completely removed by scientific and technological means at present. Therefore, a large number of sulfur elemental substances (yellow smoke) and sulfur-containing tail gas (sulfur dioxide and hydrogen sulfide) will still be produced in the process of high-temperature dry distillation. If they are directly discharged into the atmosphere, It will directly lead to acid rain and haze, so it needs to be removed.
(among them, I can't draw an accurate conclusion based on the knowledge I have learned. Therefore, I explained my guess on the hydrogen shedding mechanism of organic sulfur with a postgraduate friend of China University of mining and technology, which was supported by him, so I wrote it here for reference only.)
At present, the desulfurization technology is to spray and absorb sodium hydroxide solution, add hydrated lime to the desulfurization waste liquid in the sewage treatment plant to make up oxygen to produce gypsum, filter and purify the waste liquid, and reuse the fresh water.
1.3.2.3. Nitrogenous substances
① "N-R" (organic nitrogen) NOx (main)
② N2 + o22no (small amount); NO + O2NOx
③ N2 + 3h22nh3 (trace); NH3 + O2NOx
The above three reaction processes are the main sources of nitrogen in tail gas. Because coal comes from plant corpses, a large number of nitrogen elements contained in protein enter into coal molecules, which cannot be completely removed by scientific and technological means at present. Therefore, a large number of nitrogen oxides (such as highly toxic nitrogen dioxide and nitrogen tetroxide) will still be produced in the process of high-temperature dry distillation. If they are directly discharged into the atmosphere, It will directly lead to acid rain and haze, so it needs to be removed.
(② the process is found in recent years. Under local high temperature and high pressure, nitrogen in the air will combine with oxygen to form nitric oxide and then oxidize into toxic nitrogen oxides. It is the main source of nitrogen oxides in motor vehicle exhaust. In the slep activation furnace, it meets the conditions of high temperature and high pressure caused by local gas vortex, so it will occur in a small amount.
③ The process should be the main reaction of synthetic ammonia industry and requires catalyst, but in the production process, there is a strong ammonia smell in the furnace body and the reused desulfurization liquid, so it is speculated that the synthetic ammonia reaction may occur in a small amount in the furnace body. The reason for the absorption of ammonia and ammonia in the coke washing process in coking production is not ruled out, which is only for reference.)
At present, the spray absorption method of concentrated sodium hydroxide solution is also adopted for denitrification, which does not affect the pH of mother liquor. Except for the deep purification of water in the waterworks, no waste liquid treatment is carried out.
Process principle of SLP activation furnace
1.4.1 oven drying
The production process of SLP activation furnace is divided into oven drying and formal production. The main task of the oven drying stage is to raise the temperature of the activation furnace to a suitable high temperature for production. In this process, the furnace wall and furnace body are baked at high temperature and fully dried, and have adapted to the high-temperature environment to prevent the risk of furnace collapse caused by subsequent non adaptation to high temperature and uneven temperature.
In the understanding of high-temperature production-oriented chemical industry, blast furnace drying is the top priority. It is necessary to raise the temperature successfully and officially put into operation in the shortest possible time, but at the same time, it is necessary to ensure that the temperature rises steadily from bottom to top, because if there is large fluctuation and uneven temperature, the furnace body may be damaged, thus reducing its service life.
In this process, factors such as season, wind force, auxiliary equipment and steam need to be comprehensively considered. Various appropriate measures shall be taken reasonably to deal with different abnormal conditions, so as to ensure that the SLP activation furnace can be put into operation safely and without abnormalities in a short time. It can be said that the drying process is short and no normal product output, but it is an important step in the production process of the whole activation furnace.
