Desulfurization and decarburization method for pyrolysis gas

Abstract

The invention belongs to the field of gas purification, and particularly relates to a method for desulfurizing and decarburizing pyrolysis gas. The cracking gas is a mixture of hydrogen, alkane, olefin, alkyne and other gases sent from a cracking unit, wherein the alkane is C1-C5. In addition, the pyrolysis gas contains carbon dioxide, hydrogen sulfide and the like, and the carbon dioxide, hydrogen sulfide and the like must be removed. After alcohol amine washing and alkali washing treatment, the content of hydrogen sulfide in the pyrolysis gas is less than 6mg / m < 3 >, and the content of carbon dioxide is less than 50ppm.

Description

Technical Field

[0001] The present invention belongs to the field of gas purification, and specifically relates to a method for desulfurization and decarbonization of cracked gas. Cracking gas is a gas mixture of hydrogen, alkanes, alkenes and alkynes sent from a cracking unit, wherein the alkanes are C1-C5. Purification of cracked gas refers to removing harmful impurities in the cracked gas. In addition, the cracked gas also contains carbon dioxide and hydrogen sulfide, which affect the quality standard of the product after being brought into the product, and must be removed. Background Art

[0002] The purification of cracking gas refers to the removal of harmful impurities in the cracking gas. Although the content of these impurities is not large, they are harmful to the cryogenic separation process, and the product does not meet the required standards.

[0003] At present, the methods for treating sulfide and carbon dioxide in cracking gas include alcohol amine method and alkaline washing method. The alcohol amine method is a cyclic process, and the lean liquid after regeneration is recycled. The absorption temperature of the alkaline washing method is 30~40 degrees, and it is necessary to drain the liquid regularly. Generally, when the cracking gas also contains sulfide, it is not economical to use the alkaline washing method. When only the alcohol amine method is used, there is a phenomenon of excessive purification, which affects the subsequent process.

[0004] Application number 201320626816.6, patent name "A light hydrocarbon alkaline washing desulfurization device" proposes a light hydrocarbon alkaline washing desulfurization device, which uses an alkaline washing method to effectively remove hydrogen sulfide while also separating some of the mercaptans contained therein.

[0005] Application number 201710006765.X, patent name "Separation process of reaction products of methane oxidative coupling to produce ethylene" proposes a method of removing CO2 from the reaction product by using an amine method. The solvent uses MEA or MDEA plus piperazine to remove CO2 to 1~100ppm in an absorption tower.

[0006] The above methods are used to treat sulfur-containing gas or carbon-containing gas. In case that the cracked gas contains both hydrogen sulfide and carbon dioxide, a new process is needed to operate the alcohol amine method and the alkaline washing method in series, and improve the equipment to improve efficiency and reduce the floor space. Summary of the invention

[0007] The object of the present invention is to provide a method for desulfurization and decarbonization of cracked gas in view of the deficiencies in the prior art.

[0008] The cracked gas described in the present invention is a gas mixture of hydrogen, alkanes, alkenes and alkynes sent from the cracking unit, wherein the alkanes are C1-C5. The purification of the cracked gas refers to the removal of harmful impurities in the cracked gas. In addition, the cracked gas also contains carbon dioxide and hydrogen sulfide, which affect the quality standard of the product after being brought into the product and must be removed.

[0009] The main technical scheme of the present invention is a method for desulfurizing and decarbonizing cracking gas. The cracking gas is firstly desulfurized and decarbonized by alcohol amine washing, and the equipment for alcohol amine washing adopts a super gravity machine; the gas after alcohol amine washing enters alkali washing for fine desulfurization, and the equipment for alkali washing adopts a tower equipment.

[0010] Generally, in the above-mentioned method for desulfurization and decarbonization of cracked gas, the concentration of the main alcohol amine is 10-60% (wt), the concentration of the alkali in the alkali washing is 10%-30%, and the balance is water.

[0011] The alcoholamines include but are not limited to one or more of diglycolamine, monoethanolamine, and diisopropanolamine. The alcoholamines are primary amines or secondary amines, and contain -NH2 and / or -NH groups in their molecular structures.

[0012] The alkali used in the alkali washing unit is one or more of sodium hydroxide or sodium carbonate, and the sodium hydroxide or sodium carbonate is dissolved in water to form an aqueous solution.

[0013] The rotation speed of the ultra-gravity machine is 500r / min-1500r / min.

[0014] The alkali washing tower equipment is a packed tower or a plate tower, and the tower bottom is provided with a liquid discharge port. Unsaturated hydrocarbons in the cracked gas may polymerize in the tower bottom to form liquids such as butter, which need to be removed regularly.

[0015] The solution after washing with the alcohol amine is recycled.

[0016] The gas regenerated by the alcohol amine washing is treated by sulfur recovery.

[0017] The temperature of the alkali washing is between 20°C and 40°C, and the alkali washing needs to be drained regularly.

[0018] The method of the present invention adopts a new process, operates the alcoholamine method and alkali washing in series, and replaces the tower equipment commonly used in the alcoholamine method with a supergravity machine, thereby strengthening the mass transfer of gas and alcoholamine solution in the equipment, improving efficiency and reducing the floor space. After the alcoholamine washing and alkali washing treatment of the present invention, the hydrogen sulfide in the cracked gas is less than 6mg / m 3 , carbon dioxide is less than 50ppm. Implementation

[0019] The method of the present invention is described in detail below with reference to the embodiments. Example

[0020] The cracking gas first enters the super gravity machine, and gas-liquid mass transfer is carried out at the interface of the high-speed rotating bed inside the super gravity machine. The gas leaving the super gravity machine enters the alkali washing tower and contacts the alkali solution sprayed from the top of the alkali washing tower in countercurrent. The purified gas goes to the subsequent process from the top of the alkali washing tower. The liquid coming out of the super gravity machine enters the regeneration tower for regeneration after heat exchange, and is heated by the reboiler at the bottom of the regeneration tower to regenerate into lean liquid. The lean liquid is pressurized by the lean liquid pump and sent to the water cooler to cool to 40~70℃, and then enters the super gravity machine to reabsorb the acidic gas. The solution of the alkali washing tower is circulated, and the liquid is discharged and replenished according to the pH change.

[0021] Operating conditions: cracking gas volume 1Nm 3 / h, pressure 1.0MPa, amine flow rate 3L / h, alkali solution flow rate 1L / h.

[0022] The present invention is further described in detail below through specific embodiments to help understand the content of the present invention.

[0023] Table 1 Selection of amines and bases .

[0024] Table 2 Purification effect .

[0025] Comparative Example 1: Using monoethanolamine as the absorbent, only the alcoholamine method is used, and the equipment is a tower equipment. The H2S content in the cracked gas is 0.0328%, the carbon dioxide content in the cracked gas is 0.0513%, and the hydrogen sulfide content in the gas after purification by the alcoholamine method is 10mg / m 3 , carbon dioxide content 75ppm.

[0026] Comparative Example 2: Using monoethanolamine as the absorbent, the alcoholamine method and alkaline washing are connected in series. The alcoholamine method uses a tower device, and the alkaline washing also uses a tower device. The H2S content in the cracked gas is 0.0328%, the carbon dioxide content in the cracked gas is 0.0513%, and the hydrogen sulfide content in the gas after purification is 7mg / m 3 , carbon dioxide content 45ppm.

[0027] Comparative Example 3: Using triethanolamine as the absorbent, the alcoholamine method and alkaline washing process are used in series. The alcoholamine method uses a supergravity machine, and the alkaline washing process uses a tower equipment. The H2S content in the cracked gas is 0.0328%, the carbon dioxide content in the cracked gas is 0.0513%, and the hydrogen sulfide content in the gas after purification is 8mg / m 3 , carbon dioxide content 63ppm.

[0028] The present invention provides a method for desulfurization and decarbonization of cracked gas. Compared with a single alcohol amine washing method, the process of alcohol amine washing and alkali washing in series ensures the index of the cracked gas after purification. The alcohol amine used in the present invention is one or more of diglycolamine, monoethanolamine and diisopropanolamine. Compared with the use of other types of alcohol amines, the removal efficiency of hydrogen sulfide and carbon dioxide in the gas is significantly improved. The use of a supergravity machine also improves the efficiency compared with the use of tower equipment, and also reduces the floor space.

Claims

1. A method for desulfurization and decarbonization of cracked gas, characterized in that The cracking gas is first washed with alcohol amines for preliminary removal of acidic substances, and the equipment for alcohol amine washing adopts a super gravity machine; the gas after alcohol amine washing enters the alkaline washing for fine removal, and the alkaline washing adopts a tower equipment.

2. The method according to claim 1, characterized in that The concentration of the main alcohol amine is 10-60% (wt), the concentration of the alkali washing unit alkali is 10-30%, and the balance is water.

3. The method according to claim 1 or 2, characterized in that The alcoholamine is selected from one or more of diglycolamine, monoethanolamine and diisopropanolamine. The alcoholamine is a primary amine or a secondary amine, and contains -NH2 and / or -NH groups in its molecular structure.

4. The method according to claim 1 or 2, characterized in that The alkali used in the alkali washing unit is one or more of sodium hydroxide and sodium carbonate, which are dissolved in water to form an aqueous solution.

5. The method according to claim 1, characterized in that The rotation speed of the ultra-gravity machine is 500r / min~1500r / min.

6. The method according to claim 1, characterized in that The tower equipment used in the alkali washing unit is a packed tower or a plate tower, and a drain port is provided at the bottom of the tower kettle.

7. The method according to claim 1, characterized in that The alcoholamine solution after alcoholamine washing is recycled.

8. The method according to claim 1 or 7, characterized in that The gas regenerated from the amine wash is treated by sulfur recovery.

9. The method according to claim 1, characterized in that The temperature of alkaline washing is 20~40℃, and the liquid should be drained regularly.