Current status of methanation technology for natural gas from coke oven gas

As the world's largest coke-producing country, China's coking enterprises annually produce about 100 billion m3 of coke oven gas. In addition to the self-heating and gas generation, there are nearly 30 billion m3 remaining, which is a waste of resources and has also caused the environment Greatly polluted. Correspondingly, China's natural gas resources are scarce and there is a big gap. From this point of view, the coke oven gas methanation technology to make coke oven gas into clean natural gas energy is a key strategic layout in the national plan.

        1 Analysis of current status of domestic coke oven gas and natural gas

        1.1 Main components of coke oven gas

















        Coke oven gas as a by-product in the coke production process, with the rapid development of the coking industry, its production also shows a gradual growth trend. The main components of coke oven gas are shown in Table 1.

        1.2 Feasibility analysis of coke oven gas methanation

        Coke oven gas contains a large amount of hydrogen, methane and carbon monoxide. Through the methanation reaction, the calorific value is increased, and most of the hydrogen, carbon monoxide and carbon dioxide are converted into methane. After separation and purification, the volume fraction of methane can be obtained as a percentage More than 90% of SNG (synthetic natural gas), SNG will become CNG (compressed natural gas) after compression, and SNG will become LNG (liquefied natural gas) after liquefaction. Liquefied natural gas is a new type of clean energy, which not only has the advantages of high performance and large calorific value, but also can save long-distance transportation costs and storage space to a large extent. It is favored by more and more. At present, there are Many countries have adopted LNG as their preferred fuel.

        2.Coke oven gas methanation technology

        Coke oven gas is purified to remove benzene, naphthalene, heavy hydrocarbons, and sulfides, compressed, and heat exchanged, and then under the action of a catalyst, a methanation reaction is performed to react carbon monoxide, carbon dioxide, and hydrogen in the COG to produce methane. Methane-based mixed gas; then use PSA (pressure swing adsorption) method, membrane separation method or low temperature rectification method to separate methane in the mixed gas to produce SNG (synthetic natural gas), CNG (compressed natural gas) or LNG ( liquified natural gas).

        2.1 High temperature methanation process

        This process is mainly completed by three to four methanation furnaces. Under the theory of temperature chemical equilibrium limitation, heat is recovered through heat exchangers in multiple methanation furnaces. When the methanation reaction reaches equilibrium, it is superheated steam. The centrifugal compressor is driven. The process equipment is simple, the investment is low, the heat utilization rate is high, and the process operation has greater flexibility.

        2.2 Low temperature methanation process

        This process is mainly divided into two kinds of sulfur-resistant and non-sulfur-resistant processes. The difference between the two processes is mainly the difference in desulfurization accuracy. The total sulfur use in the sulfur-resistant process is about 10 × 10-6, while the non-sulfur-resistant process requires desulfurization to 0.1 × 10-6 or less. In the low-temperature methanation process, a large amount of raw material gas is used for circulation. In each process, the temperature of the reactor must be kept below 450 ° C to ensure that the content of CO and CO2 in the methanation furnace is less than 3%, so as to better control the methanation Furnace temperature.

        2.3 Methanation of coke oven gas

        Coke oven gas methanation is the most important process in the natural gas preparation process. In this process, methanation mainly occurs as follows:

        CO + 3H2 CH4 + H2O (1)

        CO2 + 4H2 CH4 + 2H2O (2)

        In the methanation reaction, selective catalysis of this reaction is the most typical. Using different catalysts and catalytic processes will produce different products. Currently, microcrystalline nickel is used as a methanation catalyst.

        2.4 Technical comparison

        Because the physical properties of CH4 are similar to CO and CO2, it is difficult to remove CO and CO2 in coke oven gas in one step by traditional pressure swing adsorption, membrane separation, and low-temperature rectification. The methane yield is lower. The advantage of the methanation technology is that by carrying out the methanation reaction, the useless CO and CO2 are converted to methane, which not only achieves the purpose of removing impurity gases, but also increases the output of natural gas. . However, due to the greater heat release of the methanation reaction, the operating temperature is higher, so the equipment requirements of the methanation reactor are also higher. In addition, part of the product gas needs to be recycled or a multi-stage methanation reactor is used, which increases the process. Complexity. The methane yield of non-methanization technology is lower than that of methanation technology. Its advantages are simple process, mature technology, and low investment and operating costs.

        3 Progress of Coke Oven Gas Methanation Utilization Technology

        At present, the main domestic masters of relevant technologies are: Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Southwest Research and Design Institute of Chemical Industry, Wuhan Colin Fine Chemical Co., Ltd., Xinao Group, etc., and have successively built multiple sets of coke oven gas synthesis natural gas plants. Most of the earlier built devices used foreign technology, such as the LNG project of Inner Mongolia Hengkun Chemical Co., Ltd., which was put into operation in 2012, using the British DAVY-CRG technology, and the natural gas output was 120 million m '/ a; The company's LNG project uses the Danish TopsoeTREMPTM technology, and the natural gas output is 330 million m '/ ao. Due to the high cost of foreign technology patents, most of the devices built since 2013 use domestically developed coke oven gas methanation technology. Xinao Group specializes in technology research and development in the field of coal clean energy. It completed a small-scale methane synthesis test in 2006. In 2010, it passed the Hebei provincial project achievement appraisal. The project has been tested successfully for one time and has been running smoothly till now.

        In summary, China's coke oven gas production is large, but natural gas resources are seriously in short supply. Coke oven gas to natural gas is suitable for China's current energy situation and is also an energy conversion technology that must be vigorously promoted. This technology is in line with the national energy policy , Can make full use of industrial waste gas, energy saving and emission reduction, huge economic benefits. However, the current development of coke oven gas methanation technology is still immature in China, and the process stability and reliability need to be further verified. In the future, we should focus on more efficient and stable catalysts, improve the coke oven gas methanation process, and keep its technological level constant Improve, and strive to maximize the benefits on the basis of ensuring the reliability and stability of the process.

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