Questions about the water washing of catalytic cracking liquefied gas?
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This post was last edited by linweihua6 on 2012-5-8 at 16:21. Recently, the liquefied gas I process – whose raw materials are catalytic cracking liquefied gas and reforming liquefied gas – continues to have unsatisfactory sulfur content even after desulfurization, dewaxing, and washing. Additionally, the washing water becomes severely emulsified (forms bubbles), which results in water being carried along with the liquefied gas. Changing the water every two days is no longer sufficient; sometimes it’s necessary to change it several times a day. I’m not sure what the problem is. The alkali solution has also become emulsified, the liquid level is normal, and the amine solution system is working fine as well. I’m not sure if other companies use this kind of process. For washing, is the water changed regularly or is fresh water added continuously? What is an optimal process flow for washing? Can the water used after washing be fed into the sulfur-containing ammonia wastewater system used in catalytic cracking?
I haven’t encountered the situation you mentioned, but we change the water regularly, usually every 2-3 days. When the sulfur content is high, the washing effect isn’t very good; it’s possible that the sulfur content in the raw oil is too high. The water from our washing process can be fed into the catalytic cracking sulfur-containing ammonia wastewater system.
Thank you for the information. Is the alkaline wastewater not neutralized before it enters the sulfur-containing ammonia wastewater system? What is your wastewater treatment system like?
The purpose of washing liquefied gas with water is to remove the trace amounts of alkaline substances remaining after deodorization; it is not intended for desulfurization. It is necessary to thoroughly check whether the preceding desulfurization and deodorization units are functioning properly, as well as to determine whether the sulfur content in the raw material is too high.
What was said on the 5th floor is correct – washing cannot remove sulfur. ““The severe emulsification of the wash water” – is this related to the amine solution mentioned earlier? After all, liquefied gas does not contain any substances that can cause emulsification, unless it contains amines or disulfides; it’s possible that some other factor led to intense mixing. In the case of unsatisfactory sulfur content, it is first necessary to ensure that the alcohols and amines-based hydrogen sulfide removal process is functioning properly (this can be determined by analyzing the hydrogen sulfide content in the liquefied gas, which should generally be less than 20 ppm). If the hydrogen sulfide level is not high but the total sulfur content in the liquefied gas is excessive, it is due to a high level of thiol compounds. Then it is necessary to consider adding desulfurization units. The processes used in the washing process mostly involve using mixers to combine water with liquefied gas, thereby separating the water-soluble substances contained in the liquefied gas from it; fiber membrane technology is also being used nowadays. Water replenishment can be done either on a regular basis or in small amounts continuously; this decision depends on the process being used and the properties of the wash water.
Bubbling occurs in liquefied gas when its impurity content is high. I’m not sure if it’s possible to prepare a liquefied gas sample after desulfurization and analyze one of its components to see if there are issues in the desulfurization process.
The desulfurization of liquefied gas in our facility uses a fiber membrane process, and the final water washing tank is fed with water continuously. Analyzing the reasons for the problems you mentioned, on one hand, the desulfurization effect is poor; a large amount of H2S enters the desulfurization system, which leads to high consumption of alkali and a decline in the quality of the alkaline solution. It is possible to replace some of this alkaline solution with fresh one. Additionally, the large volume of liquefied gas can carry along alkaline substances. It is necessary to test the pH value of the wash water to determine whether it contains alkaline substances. The wash water should be replaced promptly, otherwise the liquefied gas will cause corrosion issues that render it unsuitable
First, it is necessary to determine the composition of sulfur in the defective products; only by knowing what type of sulfur it is can appropriate countermeasures be taken. Water washing and an excessive sulfur content are two different issues
The unsatisfactory sulfur content is due to the deodorization section; if there’s no problem with that part, then the main cause is likely poor quality of the catalytic feed, which leads to an increase in sulfur content. Additionally, the LPG may contain water. Based on your situation, it’s possible that the yield of liquefied gas is too high, resulting in a large volume of material to be processed, which overloads the washing system and results in insufficient settling time
1. It is certain that the high sulfur content after desulfurization is not caused by washing; washing does not remove sulfur, but the quality of washing affects the product’s corrosion parameters. 2. High sulfur content: investigate the reasons for the hydrogen sulfide removal and desulfurization processes, including the concentration of amine/alkaline solutions, the amount of impurities, and the effectiveness of regeneration. 3. Emulsification of water after washing may be due to a large amount of alkaline solution being carried over from desulfurization, as well as the dirtiness of this alkaline solution. 4. It is recommended to change from batch washing to continuous washing, which yields better results, but requires more water.
A high sulfur content is not the cause of washing; the solution of ethanolamine and alkaline solutions need to be examined
1. The washing water does not need to be added continuously. 2. Severe emulsification of the washing water and unacceptable sulfur content in the liquefied gas indicate that there is a problem with the regeneration of the alkaline solution; the disulfides produced as a result of this regeneration are not removed in time, and they end up returning to the desulfurization unit, which leads to poor removal of mercaptans. As a result, the sulfur content in the liquefied gas exceeds the allowable levels. Additionally, the liquefied gas contains excessive amounts of alkali (due to insufficient settling time), which ultimately causes the water level in the washing tank to become too high. I guess your alkali solution regeneration process doesn’t involve the use of gasoline for back-extraction; your process needs improvement. We can discuss this, and I believe we can solve your problem.
The concentration of the amine solution should not be too high; the level boundary between the alkali washing tank and the water washing tank for liquefied gas should not be too low. A control valve should be installed for discharging water from the bottom of the water washing tank, with water being supplied from above and discharged from below, allowing for continuous flow.
Should we go over the previous desulfurization and hydrodesulfurization processes and conduct an analysis? Washing is meant to remove the trace amounts of alkaline substances present in liquefied gas, and it does not serve any purpose in desulfurization. It is recommended to check the previous process.
The purpose of washing liquefied gas with water is to remove the trace amounts of alkaline solution remaining after desulfurization; it is not intended for desulfurization itself. It is best to supply water continuously for this washing process, and it is important to regularly measure the pH value of the wastewater – the pH should be below 8, ideally
The problem was identified; a larger washing tank was installed, and the alkali solution regeneration process was changed to use fiber membranes, which improved the situation significantly. The previous two washing tanks were connected in parallel. The deviation flow is severe, causing overload, emulsification of water, and significant carrying. Thank you all for the discussion. I haven’t been here in a long time.