【JST-102】Gas Fractionation (Including Double Removal) One-on-one Mutual Assistance and Exchange Office

Hello: Coking liquefied gas sweetening: process: The liquefied gas is first desulfurized (after desulfurization, the hydrogen sulfide is less than 5) - pre-alkali washing - demercaptan - water washing - sand filtration - adsorption refining - out of the device. At present, our liquefied gas processing capacity is 3 tons/hour, and the catalyst alkali solution (sulfonated titanium cobalt cyanocobalt) circulation capacity is 2 tons/hour. The alkali solution The concentration is 20, the catalyst concentration is 200ppm, the alkali heater outlet (regeneration temperature) is 60 degrees, the regeneration tower pressure is 0.25mpa, the total sulfur before removal is 4000, but the total sulfur after removal is always high, around 1000 (the indicator is not greater than 343), I hope you can analyze the reason.

Hello: Coking liquefied gas sweetening: process: The liquefied gas is first desulfurized (after desulfurization, the hydrogen sulfide is less than 5) - pre-alkali washing - demercaptan - water washing - sand filtration - adsorption refining - out of the device. At present, our liquefied gas processing capacity is 3 tons/hour, and the catalyst alkali solution (sulfonated titanium cobalt cyanocobalt) circulation capacity is 2 tons/hour. The alkali solution The concentration is 20, the catalyst concentration is 200ppm, the alkali heater outlet (regeneration temperature) is 60 degrees, the regeneration tower pressure is 0.25mpa, the total sulfur before removal is 4000, but the total sulfur after removal is always high, around 1000 (the indicator is not greater than 343), I hope you can analyze the reason.

This post was last edited by Raining Wutong on 2015-3-27 11:56. What is the oxidation air volume of the alkali solution regeneration part? Are there any measures to back-extract the solvent oil from the regenerated alkali solution? There may be two reasons: 1. The oxidation air volume is insufficient, resulting in the sodium mercaptide in the alkali solution not being effectively regenerated, and the alkali solution concentration being low. Have you analyzed the alkali solution concentration? If there is, you can look at the changes in the concentration of the alkali solution, or you can analyze the exhaust gas. Generally, the oxygen content in the exhaust gas should be kept above 5 to 6%, and should be kept as high as possible to ensure that all mercaptans are oxidized into disulfide. 2. The separation effect of the regenerated alkali liquid in the disulfide separation tank is not good. It is necessary to add back-extraction measures of low-sulfur solvent oil to control the amount of disulfide in the regenerated alkali liquid. In the past, our catalytic liquefied gas desulfurization used traditional liquid-liquid extraction desulfurization, but with a solvent oil back-extraction system, the quality of the liquefied gas is only slightly higher than that using fiber membrane desulfurization, which can ensure product quality. By the way, have your installations always been high or did they just become high recently? Have you ever analyzed the changes in coked liquefied gas? Is it because there are more sulfur components in the raw material and the content of inactive sulfur in the liquefied gas has increased? Can’t handle the thiol removal part?

The injection volume of oxidizing air is 35-45 standard cubic meters/hour, and the design value is 35 standard cubic meters. We are only extracting towers for liquefied gas and alkali liquid, and there is no back-extraction of the alkali liquid. The disulfide and alkali liquid you mentioned are not completely separated in the separation tank, resulting in disulfide being carried in the liquefied gas. This possibility is very high, but how can we confirm that the disulfide carried in the liquefied gas is not mercaptan? The composition of the exhaust gas can be tested and analyzed to see the oxygen content in it. Determine whether the oxidation tower is too small, thank you

May I ask how much the flash temperature and pressure are controlled at your place? The operation of our amine liquid regeneration tower is not stable.

It is impossible to separate disulfides in general liquid-liquid extraction demercaptanization. The main reason is that the amount is relatively small and generally cannot be observed in the liquid level gauge. The fiber membrane system has been running for about half a year before there is a disulfide liquid column of about 5 to 10 cm, which is stratified with the alkali solution and can be seen. Normally, if the amount of reacted alkali solution and the amount of catalyst are sufficient, general mercaptans will be converted into sodium mercaptide and enter the regeneration step. If the separation of the regeneration alkali solution and disulfide is not complete enough, it will cause disulfide to enter the liquefied gas, seriously affecting the product quality of the liquefied gas. If you want to analyze the reason. It is recommended to analyze the components and forms of sulfur in the liquefied gas to see if it is caused by incomplete separation. If there is mercaptan in the liquefied gas, it means that the circulation volume of the alkali solution may be too small, or the contact between the alkali solution and the liquefied gas is not good enough. There may be problems with the operation of your extraction tower, or there may be gaps in the packing. For the oxidation tower, you can first try to increase the air volume and check the product quality. Generally, the sulfur content in the exhaust gas we analyze here can reach about 2000mg/m3, and most of it should be converted into SO2. If you have photos of previous maintenance, you can see if there is sulfur deposited in the disulfide separation tank, and you can also judge whether the air volume is sufficient.

Our amine liquid regeneration part is now at the solvent regeneration device. When I get back to work, I will show you the latest operating parameters...

The current flash evaporation temperature of amine liquid is 60℃, and the pressure is about 0.05Mpa. This operation generally maintains high temperature and low pressure is conducive to flash evaporation. Check the cause of your fluctuations to see if it is a temperature change or unstable pressure operation, and then analyze the reason.

If it can be confirmed that the sodium mercaptide cannot be completely converted into sodium hydroxide due to poor oxidation effect, and the demercaptanization is incomplete, what are the adjustment methods without technical modification of the device?

If the demercaptanization reaction is sufficient and the mercaptans in the liquefied gas can be completely absorbed by the alkali solution, you can consider increasing the amount of oxidizing air and observe the changes in the product quality of the liquefied gas.； If it is true that the contact and reaction between the alkali liquid and the oxidizing air cannot be guaranteed due to the limited volume of the equipment, you can consider changing the existing alkali oxidation regeneration system to a semi-regeneration process to reduce the alkali flow rate inside the alkali liquid tower and increase the reaction intensity between the oxidizing air and the alkali liquid. You can consider and analyze whether the process flow is suitable. By the way, does the processing capacity of your sweetening system match the existing processing capacity of coking liquefied gas?