Liquid ammonia is produced using the off-gases from the methanol production process and nitrogen from the air separation system as raw materials.

On March 17, the Southwest Chemical Research and Design Institute, which is part of Sinochem Group, won the bid for three pressure swing adsorption (PSA) units for Hebei Fengmei Coking Company, a subsidiary of Jizhong Energy Group. These three sets of pressure swing adsorption units will be used in conjunction with the project for the comprehensive utilization of methanol off-gases to produce 80,000 tons per year of synthetic ammonia. Hebei Fengmei Coking’s annual 80,000-ton synthetic ammonia production project utilizes the off-gases generated during the methanol production from coke oven gas, as well as the nitrogen produced in the air separation process for oxygen production, to manufacture synthetic ammonia and thereby achieve rational use of resources. It is understood that the pressure swing adsorption section, which consists of three sets of high-pressure pressure swing adsorption and temperature swing adsorption units, plays a crucial role as an important part of this project. This section includes one set of pressure swing adsorption hydrogen production unit with an adsorption pressure of 3.9 MPa and a capacity of 28,000 Nm³/h for methanol off-gas treatment, one set of nitrogen deoxidation unit with an operating pressure of 4.0 MPa and a capacity of 7,200 Nm³/h, and one set of hydrogen and nitrogen dehydration unit with an operating pressure of 3.85 MPa and a capacity of 26,000 Nm³/h.

On March 17, the Southwest Chemical Research and Design Institute, which is part of Sinochem Group, won the bid for three pressure swing adsorption (PSA) units for Hebei Fengmei Coking Company, a subsidiary of Jizhong Energy Group. These three sets of pressure swing adsorption units will be used in conjunction with the project for the comprehensive utilization of methanol off-gases to produce 80,000 tons per year of synthetic ammonia. Hebei Fengmei Coking’s annual 80,000-ton synthetic ammonia production project utilizes the off-gases generated during the methanol production from coke oven gas, as well as the nitrogen produced in the air separation process for oxygen production, to manufacture synthetic ammonia and thereby achieve rational use of resources. It is understood that the pressure swing adsorption section, which consists of three sets of high-pressure pressure swing adsorption and temperature swing adsorption units, plays a crucial role as an important part of this project. This section includes one set of pressure swing adsorption hydrogen production unit with an adsorption pressure of 3.9 MPa and a capacity of 28,000 Nm³/h for methanol off-gas treatment, one set of nitrogen deoxidation unit with an operating pressure of 4.0 MPa and a capacity of 7,200 Nm³/h, and one set of hydrogen and nitrogen dehydration unit with an operating pressure of 3.85 MPa and a capacity of 26,000 Nm³/h.

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Due to the numerous side reactions that occur during methanol synthesis, these reactions generate large amounts of inert gases which accumulate within the system, affecting the normal operation of the methanol synthesis process. It is necessary to continuously remove these gases, and such discharged gases are known as purge gases. The main components of the methanol synthesis off-gas are inert gases such as H2, CO, H2O, and CH4, among which H2 and CH4 account for approximately 90% by volume. Using gas membrane separation technology to recover H2 from the methanol synthesis off-gases can achieve both the goal of increasing methanol production and that of saving energy and reducing emissions. Prison membrane separation technology is used in the hydrogen recovery process. Prison films are made from a type of polymer material, with polyimide or polysulfone being the main components. The material of the membrane determines the performance and efficiency of the membrane separation system. Basic principle of membrane separation technology: By taking advantage of the differences in the transport rates of various components in a mixed gas as they pass through a polymer membrane, as well as the membrane’s preference for allowing certain components to pass through more easily, the mixed gas is subjected to a pressure difference that drives it through the membrane. This process enables one of the components in the mixture to be selectively removed and recovered through the membrane, while other components are retained. The order of selective permeation rates of various gas components through the membrane is: H2 > H2O > He > NH3 > H2S > CH3OH > Ar > CO2 > CO > N2 > CH4 > C2H6

] Producing methanol from coke oven gas, a by-product of coking, can help alleviate China’s increasingly severe energy situation to some extent； On the other hand, it opens up a new, effective, economical, and environmentally friendly approach for the comprehensive utilization of waste gases from numerous coking enterprises. The existing technology for producing methanol from coke oven gas involves converting the desulfurized coke oven gas to obtain a feed gas whose main components are CO, CO2, and H2; this feed gas is then fed into a methanol synthesis tower where methanol is synthesized under the action of a catalyst. After the gas exiting the synthesis tower is cooled and methanol is separated from it, most of this gas is sent back to the synthesis tower as recycled gas together with the fresh feed gas. To maintain system balance, the remaining gas is discharged as methanol off-gas; currently, companies that produce methanol from coke oven gas typically burn this methanol off-gas.

In methanol production plants using coke oven gas, it is necessary to increase production capacity to meet the demands of economic development. One solution is to rebuild a set of production facilities, which requires large investment; should the demand for methanol decline, the risk of losses for the company becomes high ； Another solution is to increase the production load of existing facilities. However, taking a certain coal chemical enterprise as an example, the average load of its coke oven gas is 20,000 Nm3/h. Under reaction conditions of a pressure of 4.2–5.2 MPa and an outlet temperature of 236°C in the synthesis tower, the methanol off-gas volume is 7,000 Nm3/h, with a CO content of 2.10%, a CO2 content of 4.33%, and a total carbon content of approximately 6.43%. However, when the load reaches 34,000 Nm3/h, the methanol off-gas volume is approximately 14,000 Nm3/h; at this point, the CO content in the off-gas is 7.43%, while the CO2 content is 8.56%. The carbon content in the flare gas is very high, which means that a significant amount of carbon is lost through this flare gas. If such gas with a high carbon content is burned and released directly, it will inevitably cause severe damage to the environment and lead to considerable waste of energy.

In methanol production plants using coke oven gas, it is necessary to increase production capacity to meet the demands of economic development. One solution is to rebuild a set of production facilities, which requires large investment; should the demand for methanol decline, the risk of losses for the company becomes high ； Another solution is to increase the production load of existing facilities. However, taking a certain coal chemical enterprise as an example, the average load of its coke oven gas is 20,000 Nm3/h. Under reaction conditions of a pressure of 4.2–5.2 MPa and an outlet temperature of 236°C in the synthesis tower, the methanol off-gas volume is 7,000 Nm3/h, with a CO content of 2.10%, a CO2 content of 4.33%, and a total carbon content of approximately 6.43%. However, when the load reaches 34,000 Nm3/h, the methanol off-gas volume is approximately 14,000 Nm3/h; at this point, the CO content in the off-gas is 7.43%, while the CO2 content is 8.56%. The carbon content in the flare gas is very high, which means that a significant amount of carbon is lost through this flare gas. If such gas with a high carbon content is burned and released directly, it will inevitably cause severe damage to the environment and lead to considerable waste of energy.

Furthermore, in the production of methanol from coke oven gas, the sulfur content in this gas, which is produced during coking, is relatively high – possibly ranging from 100 ppm to 300 ppm. This high sulfur content poses a severe threat to the catalysts used in the subsequent conversion of the coke oven gas into methanol, as it causes the catalysts to lose their activity. Therefore, it is necessary to desulfurize the coke oven gas in order to meet the requirements for methanol synthesis. In production, iron-manganese desulfurizers are commonly used for desulfurization. Newly installed iron-manganese desulfurizers must first be reduced before they can be used, and when using coke oven gas for reduction, a large amount of such gas is required. As a result, the production load must be reduced to a very low level, or even the plant may have to stop operating. Meanwhile, changing the volume of coke oven gas also hinders the stable progress of production operations and increases potential risks in production.

Industrial utilization of methanol off-gas Tag: Methanol 2010/08/04 Introduction: Good news has recently come from Hancheng City, Shaanxi Province – the project for the comprehensive utilization of coke oven gas and methanol off-gas to produce synthetic ammonia, developed using the proprietary technology of Baoji Taihe Chemical Technology Co., Ltd., has been successful at Hecat Energy Utilization Co., Ltd. in Hancheng City. According to Wang Wanhe, the chief engineer at Baoji Taihe Chemical, the project involves an investment of nearly 100 million yuan. Its design capacity is to produce 100,000 tons of synthetic ammonia per year, along with 15,000 tons of methanol. It enables the full utilization of 2.4 trillion cubic meters of coke oven gas and 48 million cubic meters of methanol off-gas each year; in addition, 58 million cubic meters of nitrogen emitted from the air separation unit in the methanol production plant can be recovered. This project has been listed as a key energy-saving and emission-reduction project in Weinan City, Shaanxi Province, for 2009. It is understood that this project pioneers the use of the physical method of temperature- and pressure-variable adsorption to purify feed gas; compared with other processes, it can **reduce the loss of useful gases. In the ammonia synthesis production process, they employ the advanced domestic double-methane process, which features a short process route, low investment requirements, and a high degree of automation. Its key equipment, the large-scale compressor, features a novel design structure that is safe, reliable, and energy-efficient; it has obtained three patents for its structure, packing, and cylinder design. To date, the plant has been in trial operation for 6 months, with the total cost of producing ammonia and methanol at around 1,400 yuan per ton; this makes the cost per ton 600 yuan lower than that of similar products produced from coal. As the device operates more stably, production costs will also decrease accordingly. It is understood that Hancheng Black Cat Energy Utilization Co., Ltd. is a joint-stock company established through a partnership between Shaanxi Yellow River Mining Co., Ltd. and Jiangxi Kaimenzzi Group Co., Ltd.