Separating process and system of low-energy-consumption MTO product gas

Abstract

The invention discloses a separating process and system of low-energy-consumption MTO product gas. Valuable hydrocarbon such as ethylene in the methanol to olefin (MTO) product gas (demethanizer tailgas) is recovered through a powerless copious cooling technology, the operation pressure of a first carbon and second carbon separation system is reduced, the grade of a product gas centrifugal compression machine is reduced, and process energy consumption is reduced; by means of the powerless copious cooling technology, the temperature of first carbon tail gas can be reduced, mixed propane or even pure propylene is used as the first carbon and second carbon separation washing absorber, and the loss of propylene carried in the first carbon tail gas is quite low; the washing absorption materialfor first carbon and second carbon separation is sent into the system from the upstream of a first carbon removal tower, the circulation of lots of materials returning from the downstream of the device to the upstream in an existing process is avoided, and energy loss is caused. The product gas is dried behind the outlet of a three-section compression unit, and water in the product gas can be effectively removed.

Description

technical field [0001] The invention belongs to the field of methanol-to-olefins in the coal chemical industry, and relates to a low-energy-consumption MTO product gas separation process and system, which purifies the methanol-to-olefins product gas to obtain main products such as polymer-grade ethylene and polymer-grade propylene. Background technique [0002] The methanol-to-olefins technology is a powerful supplement to the petroleum product cracking technology to produce olefins. Although it is not as large-scale and complete as the petroleum product cracking technology, with the popularization of industrial production of the methanol-to-olefins technology in the past ten years, its products are low in my country. Olefin products hold a significant share in the market. Moreover, it also has a major impact on international crude oil prices. Since my country's methanol-to-olefins industrialization, international crude oil prices have remained low. Therefore, methanol-to-ole...

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Problems solved by technology

[0006] No matter which olefin separation technology is used in the methanol-to-olefins plant that has been put into operation or is under construction in China, the product gas is compressed using a four-stage centrifugal compressor, and the final pressure of the product gas is controlled above 3.0 MPa; the value of the use of supercooling is relatively low Materials are used to wash and recover ethylene in methane tail gas; high and low pressure double-tower depropanization system; high-pressure depropanization tower is in the product gas compression system; only propylene refrigerant is provided, and the refrigerant with the lowest cooling level is -41°C, resulting in carbon dioxide It cannot be effectively separated from the carbon-1 tail gas. In order to recover the ethylene component entrained by the carbon-1 tail gas, most manufacturers adopt the method of increasing the pressure of the separation system of carbon 1 and carbon 2, and use liquid supercooled materials that are cheaper than propylene (such as propane, mixed carbon Fourth, etc.) The method of washing and absorbing reduces the loss of ethylene, and the materials used for washing and absorbing all return to the upstream from the downstream of the olefin separation unit, which will inevitably cause a large amount of materials to circulate in the system. However, due to the limitation of the lowest temperature, there is still a A certain amount of ethylene and some scrubbing materials are entrained in the carbon-tail gas, and finally burned as fuel gas. Compared with ethylene and propylene, the value of these scrubbing and absorption materials is much lower, but its price is much higher than that of fuel gas. An MTO plant that processes 1.8 million tons of methanol per year loses ethylene, propylene and washing and absorbing materials worth more than 30 million yuan from carbon-1 tail gas

However, this stock used for washing and absorbing materials must be circulated in multiple systems of the olefin separation unit, resulting in increased investment and operating costs.

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