What Is a Coker Unit?

Coking generally refers to the process of carbonization zooming of organic substances. In the carbonization of coal, it refers to high-temperature carbonization. In petroleum processing, coking is the abbreviation of residual coke, which means that heavy oils (such as heavy oil, vacuum residue, cracked residue, and even asphalt, etc.) undergo deep cracking and condensation under high temperature around 500 ° C The process of producing gas, gasoline, diesel, wax oil, and petcoke. Coking mainly includes five processes including delayed coking, kettle coking, open hearth coking, fluid coking and flexible coking.

Coking generally refers to the process of carbonization zooming of organic substances. In the carbonization of coal, it refers to high-temperature carbonization. In petroleum processing, coking is the abbreviation of residual coke, which means that heavy oils (such as heavy oil, vacuum residue, cracked residue, and even asphalt, etc.) undergo deep cracking and condensation under high temperature around 500 ° C. The process of producing gas, gasoline, diesel, wax oil, and petcoke. Coking mainly includes five processes including delayed coking, kettle coking, open hearth coking, fluid coking and flexible coking.

Coking chemical industry

The coking chemical industry is an important part of the coal chemical industry. The main coal processing methods include high temperature coking (950--1050 degrees Celsius), medium temperature

Coking, low temperature coking and other three methods. The metallurgical industry generally uses high temperature coking to obtain coke and recycle chemical products. The product coke can be used as fuel for blast furnace smelting, and can also be used for foundry, non-ferrous metal smelting, and water gas production; it can be used to produce generator gas for the production of synthetic ammonia; The chemical products produced during the coking process can be recovered and processed to extract tar, ammonia, naphthalene, hydrogen sulfide, crude benzene and other products, and obtain net coke oven gas, coal tar, crude benzene refining and deep processing to produce benzene. , Toluene, xylene, carbon disulfide, etc. These products are widely used in chemical industry, pharmaceutical industry, refractory industry and national defense industry. Net coke oven gas is available for civilian use and as an industrial fuel. Ammonia in coal gas can be used to make ammonium sulfate, concentrated ammonia water, anhydrous ammonia, etc. There are hundreds of products in the coking chemical industry. China's coking chemical industry has been able to make more than a hundred chemical products from coke oven gas, tar and crude benzene, which is of great significance to China's national economic development.

China is a major producer, consumer and exporter of coking products. Coking products are widely used in the chemical, pharmaceutical, refractory and defense industries. In recent years, the coking industry has developed rapidly. Shanxi Province is the largest coke-producing province in China. It produced 92 million tons of coke in 2006, accounting for about one-third of the country's total. The export supply of coke resources accounted for about 80% of the country's total. The market share is more than 50%.

Coking production process

The coking plant is generally composed of a coal preparation workshop, a coking workshop, a recycling workshop, and a tar processing plant.

It consists of workshop, benzene processing workshop, desulfurization workshop and wastewater treatment workshop.

According to the flow chart of the coke oven body and the drum cooling system, the raw gas from the coke oven has been condensed into a large amount of liquid before entering the primary cooler. At the same time, the coal dust and coke powder entrained in the gas are also captured. The water-soluble ingredients are also dissolved in ammonia water. The tar, ammonia water, and dust and tar residues flow together into the mechanized tar ammonia water separation tank. After separation, the ammonia water is recycled and the tar is sent for centralized processing, and the tar residue can be returned to the coal. The coking gas enters the primary cooler and is cooled directly or indirectly to normal temperature. At this time, the moisture and tar remaining in the gas are further removed. The gas after leaving the primary cooler is mechanically captured by tar to remove the tar mist suspended in the gas through mechanical methods, and then enters the blower to be boosted to about 19600 Pa (2000 mm water column). In order not to affect the operation of the subsequent gas purification, such as the coloration of ammonium sulfate, aging of the desulfurization liquid, etc., the gas is passed through an electric tar trap to remove residual tar mist. In order to prevent naphthalene from crystallizing out of the gas when the temperature is low, a naphthalene washing tower is set up before the gas enters the desulfurization tower for washing oil to absorb naphthalene. In the desulfurization tower, the desulfurizing agent is used to absorb hydrogen sulfide in the gas, and at the same time, the hydrogen cyanide in the gas is also absorbed. The ammonia in the gas is absorbed by water or aqueous solution in the ammonia absorption tower to produce liquid ammonia or ammonium sulfate. When the gas passes through the ammonia absorption tower, the reaction of sulfuric acid to absorb ammonia is an exothermic reaction, and the temperature of the gas increases. In order not to affect the operation of crude benzene recovery, the gas enters the benzene washing tower after cooling down in the final cooling tower and is absorbed by the washing oil. Low-boiling hydrocarbons such as benzene, toluene, xylene, and cyclopentadiene in gas, and high-boiling substances such as styrene and naphthyl coumarone, meanwhile, organic sulfides are also removed.

Problems with coking

There are a large number of enterprises, small scale, scattered layout, low industrial concentration, backward technological equipment as a whole, heavy emissions pollution, insufficient recycling and comprehensive utilization and centralized processing of chemical products, backward deep processing technology, few product varieties, low quality levels, and excess capacity 2. Economic benefits are not high.

Coking delay process

Delayed coking is similar to thermal cracking, except that it is heated to the temperature required for the coking reaction in a short period of time, and the raw materials are basically prevented from cracking in the furnace tube, and the cracking reaction is delayed to the special coke tower, which is "delayed coking" That's why it got its name.

The delayed coking unit is mainly composed of 8 parts:

The main equipment of coking unit is heating furnace and coke tower. There are one furnace and two towers, two furnaces and four towers, and some are directly combined with other devices. Fractionation section, the main equipment is a fractionation column.

(3) The main equipments for coking gas recovery and desulfurization are absorption and desorption towers, stabilization towers, and re-absorption towers.

Hydraulic decoking section.

Dehydration, storage and transportation of coke.

Blow air vent system.

Steam generation part.

Coke roasting part. Domestic selected furnace outlet temperature is 495 500 , coke tower top pressure is 0.15 0.2 Mpa.

Coking coking raw materials

The delayed coking feedstock can be heavy oil, residual oil, or even asphalt. Delayed coking products are divided into gas, gasoline, diesel, wax oil and coke. For domestic residues, the gas yield is 7.0 to 10%, the crude gasoline yield is 8.2 to 16.0%, the diesel yield is 22.0 to 28.66%, the wax oil yield is 23.0 to 33.0%, and the coke yield is 15.0 to 24.6%, the external oil is 1 to 3.0%. Coking gasoline and coking diesel are the main products of delayed coking, but their quality is poor. Coking gasoline has a low octane number, typically 51 to 64 (MON), and diesel has a higher cetane number, generally 50 to 58. However, the two oil products have high olefin content, high sulfur, nitrogen, oxygen and other impurities and poor stability. They can only be used as semi-finished products or intermediate products. After refining, they can be used as blending components for gasoline and diesel. Coking wax oil is a low-quality wax oil for secondary processing due to its high content of sulfur, nitrogen compounds, gums, and residual carbon. At present, it is usually blended into catalytic or hydrocracking as a raw material. Petroleum coke is one of the important products that delay the coking process. It can be used as electrodes, metallurgy and fuel according to different quality. The coking gas can be used as a raw material for hydrogen production or as a fuel pipe network after desulfurization.

Coking coking development

Because of the above advantages of delayed coking, delayed coking has developed rapidly in China, mainly because:

Delayed coking is an effective way to resolve the contradiction between supply and demand of diesel-gas ratio. This is because China's crude oil is generally heavy, with high wax content and low yield of diesel oil. The diesel oil fraction of domestic crude oil is 5-7 percentage points lower than foreign crude oil on average. Therefore, China currently imports about 80 × 10t diesel each year, and at the same time has to export 30 × 10t gasoline in order to balance domestic supply and demand. Secondly, because the secondary processing of Chinese oil refining companies is mainly catalytic cracking, and the diesel-steam ratio is low (delayed coking is 1.94 and catalytic cracking is 0.56), the development of delayed coking is an effective way to resolve the contradiction between the supply and demand of diesel-gas ratio and increase diesel production. Compared with hydrocracking, delayed coking has the disadvantage of lower stability of light oil products, but its lower operating cost (the processing cost is about 1/2 to 1/3 of the hydrocracking operation cost). It has strong competitiveness.

Because delayed coking has the advantages of less investment, low operating costs, and high conversion depth, delayed coking has developed into one of the most important processing methods for residue weight reduction. Therefore, under the current situation of capital shortage in China and the contradiction between supply and demand for light oil products, especially diesel-gasoline, the delayed coking is one of the more ideal ways to resolve this contradiction.

Coking safety technology

1 ) Production characteristics

Coking plants generally consist of coal preparation, coking, recycling, refined benzene, tar, other chemical refining, laboratory and repair workshops. The test and repair workshop is an auxiliary production workshop.

The task of the coal preparation workshop is to supply the coking workshop with quality-matched coal in a timely manner. Coking workshop is the main workshop of coking plant. The production process of the coking workshop is: after the coal loading truck takes the coal from the coal storage tower, it is transported to the upper part of the pushed carbonization chamber and the coal is loaded into the carbonization chamber. Recycling workshop; push the coke from the carbonization chamber with a coke pusher, fall into the coke quenching car after passing the coke blocking car and send it to the coke quenching tower; then, unload the coke from the coke quenching car into the cold coke table and evaporate the excess water And further cool down, and then sent to the screen coke oven through the conveyor belt and divided into various levels of coke. The recycling workshop is responsible for sucking, cooling and absorbing various primary products in the waste gas from the coke oven.

2 ) Coking safety production technology and accident prevention measures

Fireproof and explosion-proof. All fire and explosion protection measures are to prevent the production of combustible (explosive) mixtures or to prevent the generation and isolation of activation energy of sufficient strength to avoid igniting combustible mixtures to explode or explode. To this end, it is necessary to understand how combustible (explosive) mixtures and activation energy are generated, and measures to prevent their generation and proximity to each other.

The formation of some flammable (explosive) mixtures is unavoidable. For example, there is a flammable (explosive) mixture in the upper space of a flammable liquid tank. Therefore, before filling the material, fill the storage tank with an inert gas (such as nitrogen) and avoid the above phenomenon after exhausting the steam. In addition, the use of floating roof storage tanks can also avoid the generation of flammable (explosive) mixtures. The causes and precautions for other abnormal formation of flammable (explosive) mixtures are as follows:

Leak. Leaks are a common cause of flammable (explosive) mixtures. Leaks of flammable gases, flammable liquids, and liquids with temperatures exceeding the flash point can create flammable (explosive) mixtures in the leaked area or on the leaked liquid surface. There are two main reasons for the leak:

The first is that there are loopholes or cracks in equipment, containers and pipes. Some are of poor manufacturing quality, and others are caused by long-term disrepair and corrosion. Therefore, all equipment, storage tanks and pipelines that process, process, produce or store flammable gas, flammable liquid or flammable liquid whose temperature exceeds the flash point must pass the acceptance test before being put into use. During use, check its tightness and corrosion regularly. Because many materials in the coking plant contain corrosive media, special attention should be paid to the anticorrosive treatment of the equipment or use of anticorrosive materials.

The second is improper operation. Relatively speaking, there are more leakage accidents caused by such causes than the defects of the equipment itself. There are many oil and gas running accidents due to negligence or operation errors. To prevent such accidents, in addition to requiring strictly standardized operations, measures must also be taken to prevent overflow. The "Coking Safety Regulations" stipulates that flammable and combustible liquid storage tank areas should be provided with fire dyke. The volume in the fire dyke shall not be less than half of the total storage capacity of the above-ground part of the storage tank and shall not be less than the above-ground part of the largest storage tank. Gates shall be provided at the sewers passing through the fire dike. This gate is only opened when the water is discharged, and it should be closed after the water is discharged.

(3) Release. Many equipment in the coking plant are equipped with diffusing pipes, which process or store flammable and combustible materials or storage tanks. Some of the gas (vapor) gas released by the diffusing pipe is a flammable (explosive) mixture, or it is released with air. Mix into a flammable (explosive) mixture. The "Coking Safety Regulations" stipulates that each discharge pipe should be separately purified and treated according to the type of gas and vapor released before being released. The outlet of the diffusing pipe for toxic and flammable gas should be more than 4m higher than the equipment and the adjacent buildings. A flame arrester shall be provided at the outlet of combustible gas.

Dust-proof and anti-virus. Coal dust is mainly generated during the loading and unloading, transportation, and crushing of coal. The main dust producing points are coal yards, dumpers, coal receiving pits, conveyor belts, transfer stations and crushing and crushing machines. Generally, coal yards use measures such as spraying covering agents or spraying water during shipping to reduce the dust concentration. Conveyor belts and transfer stations mainly rely on the installation of conveyor belt profiles, local or overall closed dust covers, etc. to isolate and capture coal dust.

Dust production points such as crushing and pulverizing equipment should strengthen the closed suction, and set up bag dust removal, wet dust removal, ventilation dust collection and other devices to reduce coal dust concentration.

In the coking plant, carbon monoxide is present in the gas, especially the carbon monoxide content in the blast furnace gas for coke oven heating is about 30%. There are many gas equipment in the basement and flue of the coke oven, and the valves are frequently opened and closed, making it easy to leak gas. Therefore, the gas equipment must be inspected regularly and maintained in a timely manner. The lean gas valve of the flue duct should ensure that it is in a negative pressure state.

In order to prevent poisoning by hydrogen sulfide and hydrogen cyanide, coking plants should set up desulfurization and decyanation process facilities. In the past, only domestic gas was used for desulfurization, and metallurgical enterprises generally did not desulfurize. As for decyanation, yellow blood salt is generally produced only by decyanation from part of the final cold water or ammonia gas. With the increasing awareness of the severity of pollution, in recent years, coking plants have begun to attach importance to the desulfurization and decyanation of coal gas. In order to prevent poisoning by hydrogen sulfide and hydrogen cyanide, the diffusing pipe of the ammonia distillation system should be located on the leeward side operated by man.

Coking risk factors

Analyze risk factors from plant process and operating conditions

Delayed coking is a secondary processing device that thermally destroys processed residual oil to obtain petroleum coke, gasoline, diesel, wax oil and gas under high temperature conditions. Coking process is a comprehensive process of thermal decomposition and condensation. The device belongs to high temperature (the highest temperature of the device can reach above 1000 , the medium temperature can reach 500 ), high pressure (the highest pressure is 3.8MPa), and it is flammable and explosive. The raw material used in the device is vacuum residue at atmospheric pressure. Its spontaneous ignition point is 230-240 ° C, and the operating temperature of the device is more than 300 ° C. Once leaked, it is very easy to cause fire. They are all very low, and they can form explosive mixed gases when mixed with air, and their explosion limits are 1.5% to 15% (V / V) and 1.4% to 7.6% (V / V). At the same time, because the spontaneous ignition points of its diesel oil and wax oil are lower than the operating temperature of the device, fires are extremely easy to occur and there is a greater danger.