SU1477454A1 - Method of removing carbon dioxide from gas - Google Patents

Abstract

The invention relates to methods for cleaning gas from acid components, in particular from carbon dioxide, and can be used in the chemical industry, for example, in the production of ammonia, methanol and hydrogen, the raw materials for which are natural and coke oven gas or coal subjected to gasification. The invention allows to reduce the energy and material costs for the process of gas purification from carbon dioxide and to reduce the rate of structural destruction of the equipment material. According to the proposed method, carbon absorption is carried out with a solution containing aliphatic alcohol, at a temperature of 15-40 ° C, the separated purified gas stream is subjected to an additional water wash, and the resulting water-alcohol mixture is sent for rectification in return of distillate to absorption. 2 hp f-ly, 1 tab.

Description

one

The invention relates to methods for purifying gas from acid components, in particular carbon dioxide, and can be used in the chemical industry, for example, in the production of ammonia, methane and hydrogen, the raw materials for which are natural and coke oven gas or coal subjected to gasification.

The purpose of the invention is to reduce the energy and material costs of gas purification and reduce the rate of structural destruction of equipment material. o The method is carried out as follows.

in a way.

The converted gas in the large-capacity ammonia production unit enters the cleaning section from

carbon dioxide in the amount of 218300 nm / h under a pressure of 3.3 MPa and at 55 ° C. The initial content of carbon dioxide in the gas is 19.74% by volume. The gas flow, having passed the heat exchanger, is cooled to a temperature of 40 ° C, then the gas flow is fed to two parallel-working absorbers, where it is cleaned from carbon dioxide OA (organic absorbent) containing 95% by weight of organic components and 5% by weight of water, to a residual carbon dioxide content in the gas of 6 vol.%.

OA is fed to the upper part of the absorbers with a pump in the amount of 2,700 m3 / h at 25 ° C, while it passes mass transfer plates and is saturated with carbon dioxide up to 1

СП SP

4i

314

holding 16 nm3 / me, then when it enters the turbine. After the turbine, the pressure is reduced to 0.8 MPa. OA temperature after desorber 728.3PC. By reducing the pressure in the apparatus, hydrogen, nitrogen and carbon dioxide are desorbed from the OA. The outgoing gas stream containing up to 29% by volume of hydrogen and 13% by volume of nitrogen is returned by means of a compressor with absorbers, and OA goes to the turbine, after which the pressure drops to 0.45 MPa. Tempeterur OA after desorber 2,1 ° C,

Next OA passes desorber. The pressure in the stripper is maintained at 0.3 MPa at a temperature of 26.5 ° C. The desorbers from gases containing up to 4% by volume of hydrogen, carbon dioxide and OA vapors are sent for incineration. OA enters the last stage of desorption in the apparatus, where a pressure of 0.15 MPa and a temperature of 25 ° C are maintained. The 11385 nm / h effluent of carbon dioxide from the stripper undergoes a water wash and is supplied to the consumer at the urea plant.

Purified from carbon dioxide, OA is mixed with the stream coming from the rectification stage. Then OA pump at a temperature of 25 ° C is served in the upper part of the parallel absorbing cleaning absorbers.

The purified gas stream from the absorbers enters the washer, where the OA vapors are removed. Then the heat exchanger passes, the gas stream enters the chemisorption purification. A 20% aqueous solution of monoethanolamine is used as the adsorbent, which is regenerated in the regenerator-heat exchanger using heat from the bottom of the regenerated solution. The chemisorption cleaning allows the gas to be cleaned to a carbon dioxide content of 100.

Converted gas enters the wet process. The main part of this moisture is absorbed by OA simultaneously with the purification of gas from carbon dioxide, and the concentration of water in OA in the lower part of the absorber increases and increases with time. To remove water from the system part of the absorber5

bent (in this case 10 m / h)

0

0

is removed for rectification and then returned to the system with a concentration of 98% by weight of the organic component. This allows the water concentration in the absorbent to be maintained at a level of 5% by weight. Water-organic streams from washers are also sent for rectification. Rectification of water-organic mixtures due to the high partial pressure of organic substances does not require significant energy costs. To reduce the heat consumption for rectification, it is advisable to supply mixtures with a higher concentration of organic components, i.e. with a water concentration of no more than 12 May, 7 ,.

The table shows the comparative performance of the proposed and known cleaning methods.

As can be seen from the table, the energy costs in the process of gas purification by the proposed method in the range of 5–4 ° C absorption temperature (examples 1-3) are much higher than by a known method at a temperature of 51 ° C.

The process of absorption 0 at temperatures above 40 ° C (example 5) is associated with a significant absorption of the absorbent by the flow of purified gas and, consequently, an increase in heat consumption for the rectification of the water-alcohol solution, an increase in the consumption of absorbent and, consequently, the cost of pumping it.

Carrying out the absorption process at temperatures below leads to

five

a significant decrease in the driving force of the process in the upper part of the absorber, which leads to a sharp increase in the size of the apparatus and an increase in capital costs. Carrying out the process at these temperatures will require additional costs of cold.

Therefore, carrying out the absorption process at temperatures above 40 s and below is practically impractical.

In addition, when implementing the proposed cleaning method, a sharp decrease in the rate of structural destruction of the equipment material is achieved. The equipment used in the Rektizol process is made of alloyed steels. In the implementation of the proposed method, an apparatus made of

five

carbon steels, so the cost of mass transfer equipment in this case is about 3 times less compared to the process by a known method. The table shows that the rate of structural destruction of the material of the apparatus using the proposed method is 10 times lower than with the known.

Claims (3)

1. A method for purifying carbon dioxide gas, including the absorption of carbon dioxide by an aqueous solution containing aliphatic alcohol, the recovery of a saturated solution by a decrease in pressure, the rectification of a portion of the solution with the distillate being returned to absorption, differing 774546 By the fact that, in order to reduce the energy and material costs for gas purification and reduce the rate of structural destruction of the equipment material, absorption is carried out at 15–40 ° C, and the purified gas stream is subjected to additional water washing, the resulting water-alcohol mixture are rectified with the return of distillate for absorption. 2. The method according to claim 1, characterized in that the concentration of water in the saturated solution fed to the regeneration is maintained at 2-12 wt.%. 3. Method according to claims 1 and 2, characterized in that the stream of purified gas after the water washing is directed to chemisorption purification with an aqueous solution of alkanolamines. Famous 51 Editor N. Tupitsa Compiled by E. Kornienko Tehred M. Didyk Order 2188/10 Circulation 600 VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, Raushsk nab. 4/5 1,839-2,312 1,0 Proofreader N.Korol Subscription