Comparison between AS method coal gas desulfurization and vacuum potassium carbonate method desulfurization

Thread Content

Comparison of AS method coal gas desulfurization and vacuum potassium carbonate method desulfurization Wang Taiyan 1 Background and technical analysis 1.1 Background (1) AS method desulfurization and decyanation technology is an advanced desulfurization technology introduced from Germany in the 1980s. It is widely used by major coking plants in my country and promotes the progress of my country's coal gas desulfurization technology. However, due to the large investment, this technology has not been promoted on a larger scale. (2) Compared with other related desulfurization technologies, the biggest feature of this process is that acidic gas is catalyzed and oxidized at high temperature in a Claus furnace to generate high-purity sulfur (purity >99.0%). At the same time, the accessory salts produced during the desulfurization process can be cracked into H2, N2, and S, eliminating the accumulation of accessory salts in the desulfurization liquid. (3) There are still two outstanding technical problems in the AS desulfurization and decyanization process. First, the desulfurization efficiency is low. Generally, the hydrogen sulfide content in the coal gas after desulfurization by manufacturers is above 500mg/m3, which cannot meet the requirements of energy conservation and emission reduction. ； Second, all ammonia in the gas cannot be used as an alkali source for desulfurization, and the tail gas after ammonia decomposition is severely corroded and cannot be returned to the gas pipeline and is forced to escape into the atmosphere, polluting the environment. 1.2 Technical Analysis (1) The typical AS method gas desulfurization process (full negative pressure process) is shown in Figure 1. Figure 1 Typical AS method gas desulfurization process flow (full negative pressure process) The waste gas from the coke oven enters the primary cooler after gas-liquid separation, where the gas is cooled to 22-23°C, and then enters the desulfurization tower through the electric tar collector. The desulfurized gas is sent to the ammonia washing tower and the benzene washing tower in sequence. Finally, the gas is sent to the gas user by a blower. The desulfurization liquid sprayed in the desulfurization tower is a mixture of the rich ammonia liquid at the bottom of the ammonia washing tower, the deacidification poor liquid at the bottom of the deacidification tower, and the remaining ammonia water. The acidic gas extracted from the rich desulfurization liquid in the deacidification tower is sent to the Claus furnace to produce high-purity sulfur. Most of the deacidified lean liquid is sent to the ammonia evaporation tower, and the steamed ammonia vapor is sent to the Claus furnace for ammonia decomposition. It is called the double furnace and double tower process. The exhaust from the double furnace returns to the gas line. (2) Since ammonia washing technology is used to recover ammonia, the volatile ammonia content in the rich liquid at the bottom of the ammonia washing tower cannot be increased (1~2g/L). When the ammonia partial pressure in the desulfurization liquid is greater than the ammonia partial pressure in the gas, the ammonia washing will have a negative absorption effect, making the ammonia content in the gas after the ammonia washing tower as high as 100 mg/m3. The amount of ammonia and nitrogen in the separated water increases, which increases the load of the biochemical treatment device. The desulfurization liquid is mainly ammonia-rich washing liquid. Because the volatile ammonia content in the desulfurization liquid cannot be increased (up to 2 to 3 g/L), the desulfurization efficiency is low. The hydrogen sulfide content in the gas after the desulfurization tower is 500 to 600 mg/m3. Because there is a Claus furnace for ammonia decomposition, most of the ammonia is decomposed, and the alkali source for desulfurization is lost. This also causes the volatile ammonia content in the desulfurization liquid to be unable to increase, which directly affects the desulfurization efficiency. 2. Technical transformation of the AS desulfurization process. In view of the above problems in the AS desulfurization process and the practical experience of using semi-direct method to recover ammonia, appropriate technical transformation of the AS desulfurization process should be carried out to form a new and efficient process technology to meet the requirements of environmental protection and production of high-quality sulfur products. The modified AS method gas desulfurization process (semi-negative pressure process) is shown in Figure 2. Figure 2 Main points of the transformation project of the modified AS gas desulfurization process (semi-negative pressure process): (1) Change the ammonia washing process in the AS desulfurization process to a spray saturator to recover ammonia, and all the deacidification lean liquid (containing 30 to 40 g/L of volatile ammonia) is returned to the circulating desulfurization liquid, which can maximize the volatile ammonia (9 to 10 g/L) in the desulfurization liquid, thus greatly improving the desulfurization efficiency of gas. (2) The ammonia steam evaporated from the ammonia steaming tower is mixed into the gas pipeline before desulfurization to increase the ammonia source for desulfurization and increase the volatile ammonia content in the desulfurization liquid. All ammonia in the gas is recovered in the spray saturator. (3) Retain the deacidification tower and Claus furnace desulfurization liquid treatment devices in the original process to produce high-purity sulfur. (4) The tail gas of the Claus furnace is sent to the gas pipeline before the primary cooler. The acidic substances in the tail gas can be removed during desulfurization to eliminate corrosion of the gas pipeline. After the above transformation, the desulfurization efficiency can be increased from 70% to 80% to 98% to 99%, and the hydrogen sulfide content in the clean gas after desulfurization can reach less than 20mg/m3. The purity of recovered sulfur is above 99%, and no waste liquid is generated or accumulated during the desulfurization process. The Claus furnace for ammonia decomposition can be eliminated to reduce investment costs in equipment and catalysts. The recovery rate of ammonia in the gas can reach 98% to 99%, and the ammonia content in the gas after the spray saturator can reach less than 30mg/m3. 3 Comparison between the modified AS desulfurization process and the potassium carbonate method desulfurization process (1) The process flow of vacuum potassium carbonate method desulfurization and decyanation is shown in Figure 3. Figure 3 Process flow of vacuum potassium carbonate desulfurization and decyanization process (2) By comparing the modified AS desulfurization process with the vacuum potassium carbonate desulfurization process, it is not difficult to see that the process flow, equipment structure, and equipment components are basically the same, and the investment structure is also similar. The modified AS process can replace the vacuum potassium carbonate desulfurization process and achieve the same results. (3) After the transformation, the AS method desulfurization device is located before deamination, using ammonia in the coal gas as the alkali source, while the desulfurization device of the vacuum potassium carbonate desulfurization process must be located after the benzene removal tower, and the alkali source potassium carbonate or sodium carbonate needs to be purchased outsourced. (4) The deamination unit of the modified AS desulfurization process is reasonably configured (ammonia is recovered using a semi-direct method), * * The ammonia-sulfur ratio in the desulfurization process is increased (the volatile ammonia content in the desulfurization liquid can reach 9~10g/L), and the desulfurization efficiency can be significantly improved. The hydrogen sulfide content in the coal gas after desulfurization can reach 10~20mg/m3, which is close to the standard of precision desulfurization. (5) The modified new AS method desulfurization process is my country’s independently innovative desulfurization process and can completely replace the vacuum potassium carbonate desulfurization process.