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(1) Scope of application: This technology is applicable to pressurized gasification gases with high impurity contents, such as coke oven gas, Lurgi gasification gas, and Texaco gasification gas. Low-temperature methanol washing is an effective gas purification process that was jointly developed by Linde and Lurgi in the early 1950s. It was first used in 1954 for the purification of gas produced by coal pressure gasification, and subsequently applied to the purification of city gas as well. After the 1960s, with the emergence of large-scale ammonia plants using residue oil and coal as raw materials, the low-temperature methanol washing purification technology came to be widely used. It is recognized both domestically and internationally as a method with high purification efficiency, inexpensive and readily available solvents, and low operating costs. Given the weak domestic equipment manufacturing capabilities and the incomplete availability of data on the properties of the purification products from low-temperature methanol washing, all the low-temperature methanol washing purification technologies used in China are imported from abroad. Through joint research and development of the low-temperature methanol washing purification technology by Shandong Hualu Hengsheng Chemical Co., Ltd. and China Global Engineering Corporation, the development of a software package for the low-temperature methanol washing process as part of a large-scale fertilizer production facility was completed. This technology was put into practice in Shandong Hualu Hengsheng Chemical Co., Ltd.’s project to localize the production of large-scale nitrogen fertilizers, thereby enabling its practical application and localization. (II) Performance characteristics of technical products: Ammonia synthesis requires the simultaneous removal of impurities such as H2S, COS, and CO2 from syngas. There are many methods for removing these impurities from gases, and from a process perspective, they can be classified into chemical absorption, physical absorption, and physico-chemical dual absorption methods. Industrial production practices for these three methods exist both domestically and internationally. The main advantage of the chemical absorption method is its fast absorption rate; it proceeds according to a stoichiometric reaction, and the absorption pressure has little effect on the absorption capacity. But its biggest drawback is high regenerative heat loss. The main advantages of physical absorption are exactly the opposite of those of chemical absorption. Its absorption mechanism relies on the different affinities of the functional groups in solvent molecules for various molecules, thereby enabling selective gas absorption. Solvents generally follow Henry’s law when absorbing gases; their absorption capacity is not subject to stoichiometric limitations and is only proportional to the partial pressure of the gas being dissolved. Therefore, physical absorption is the preferred method when the partial pressure of acidic gases is high. Moreover, it is easier to regenerate the solvent, with low energy requirements for regeneration. The characteristic of the physico-chemical absorption method is the mixing of two solvents with different properties, enabling the solvent to possess both physical and chemical absorption capabilities; it represents a method that lies between chemical absorption and physical absorption. Based on the comparison of these three methods, and taking into account the specific conditions of vaporization pressure and acidic gas partial pressure, ammonia synthesis plants generally choose the physically absorption method, which is less energy-intensive. In physical absorption methods, they are generally divided into hot and cold methods based on the absorption temperature. The hot method is represented by the Selexol (NHD) process, while the cold method is represented by the low-temperature methanol washing process. Through a comparison of the raw material consumption, operational costs, capital investment, solvent loading costs, equipment manufacturing expenses, and intellectual property aspects of the two purification technologies—low-temperature methanol washing and NHD—it is evident that although low-temperature methanol washing requires higher investment, it offers significant energy savings and reduced consumption, delivers excellent purification results, allows for the complete recovery of sulfur from the feed gas, and provides notable environmental benefits. For the gas purification in the domestic technology upgrade project of the large-scale nitrogen fertilizer plant at Shandong Hualu Hengsheng Chemical Co., Ltd., low-temperature methanol washing technology is employed. Low-temperature methanol washing can remove various impurities from gases. At temperatures ranging from -30°C to -70°C, methanol is capable of removing impurities such as H2S, COS, CS2, RSR, C4H4S, CO2, HCN, NH3, aromatic hydrocarbons, and crude gasoline from the gas. It can also remove water, thereby drying the gas. The useful components that are absorbed can be recovered during the regeneration of the methanol. The low-temperature methanol washing purification technology achieves a high level of gas purification; the total sulfur content in the purified gas can be reduced to below 0.1 ppm, while CO2 can be purified to below 20 ppm. Low-temperature methanol washing can be applied in chemical manufacturing processes with strict requirements regarding sulfur content. H2S and CO2 can be selectively removed and recovered separately for further reuse. With the low-temperature methanol washing process, regardless of the sulfur content in the feed gas, the final H2S concentration can meet the requirements for sulfur recovery in the Claus process. The solvent circulation volume in the low-temperature methanol washing purification unit is small, resulting in lower power consumption. Since the solubilities of H2S, COS, and CO2 in methanol are high at low temperatures, the absorption capacity at a pressure of 5.5 MPa (G) is approximately 220–250 m3 (standard) of CO2 per m3 of solution; as a result, the amount of methanol that needs to be circulated is small, resulting in lower energy consumption. This is particularly true when the pressure of the feed gas and the concentration of the gases to be removed are high. The solvent loss in low-temperature methanol washing purification units is low. Methanol possesses good thermal and chemical stability; it is not degraded by components such as organic sulfur or cyanides. During production, methanol does not form bubbles, and its vapor pressure is also very low, which helps to keep solvent loss at a low level. It is more reasonable to use low-temperature methanol washing to remove H2S and CO2 in combination with liquid nitrogen washing to remove CO and CH4. When the gas purified by methanol washing enters the liquid nitrogen washing unit at –63°C (5.2 MPa), the cooling capacity of the liquid nitrogen washing system can balance itself, thereby saving energy consumption during the refrigeration process. Gas purification is carried out using low-temperature methanol washing and liquid nitrogen washing, which removes all impurities from the gas in one step, including H2S, CO2, CO, Ar, CH4, etc. The inert gas content in the synthesized fresh gas is less than 10 ppm, and it is free of water. Due to the high degree of gas purification, there is no vent gas in the synthesis loop, which reduces gas losses and lowers compression power consumption as well. Technical level and source: The low-temperature methanol washing purification technology developed and applied by Shandong Hualu Hengsheng Chemical Co., Ltd. is the result of specialized research efforts under a major technical equipment development project during the 10th Five-Year Plan period; the China Petroleum and Chemical Industry Association is currently conducting an evaluation of this research project. More than a year of operational experience has shown that, in terms of technical performance and utility consumption, this purification unit has reached the level of imported units. The technical level of low-temperature methanol washing purification technology has now reached the international advanced level. Through a comprehensive analysis of the operational data from low-temperature methanol washing units in use across China, Shandong Hualu Hengsheng Chemical Co., Ltd. and China Global Engineering Corporation utilized literature reviews, as well as the property data already available to Global Engineering Corporation and the models developed by them, to calculate the necessary material and heat balance values. Based on this, they successfully constructed a low-temperature methanol washing unit for the technological upgrade project of Shandong Hualu Hengsheng Chemical Co., Ltd.’s large-scale nitrogen fertilizer production facility – a unit whose capacity is sufficient to meet the requirements for producing 1,000 tons per day of synthetic ammonia. (III) Application results: On October 16, 2004, the low-temperature methanol washing purification unit of the domestication technology renovation project for Shandong Hualu Hengsheng Chemical Co., Ltd.’s large-scale nitrogen fertilizer plant was successfully put into operation. On November 25, the entire ammonia synthesis process was operational, and the plant entered the trial operation phase; on December 6, it reached a stable operating state. In 2005, a total of 251,331 tons of ammonia were produced, accounting for 83.78% of the production capacity. By the end of 2005, new sales revenue amounted to 650 million yuan, new profits reached 70 million yuan, and new taxes amounted to 50 million yuan. After the purification unit was put into operation, the purification parameters of the syngas and the energy consumption of the unit met the design requirements, and no system shutdown has occurred to date due to issues with the purification unit. (IV) Prospects for promotion: The successful development of low-temperature methanol washing purification technology by Shandong Hualu Hengsheng Chemical Co., Ltd. will provide a new approach for medium and small nitrogen fertilizer manufacturers to expand their production capacity, carry out renovations, and reduce energy consumption. The development of domestic design and equipment manufacturing for low-temperature methanol washing purification units can promote the advancement of chemical technology in China, boost the growth of the domestic machinery manufacturing industry, and bring about significant social and economic benefits.