Issues with catalytic or ethylene cracking gas alkaline scrubbing

1. For the acid removal of pyrolysis gas, a process design using three-stage alkali scrubber towers is commonly employed. How is the circulation volume of the alkali solution determined? The magnitude of the circulation volume depends on whether the levels of hydrogen sulfide and carbon dioxide in your pyrolysis gas meet the required specifications. 2. A washing gasoline system is often installed for waste alkali solution. What is generally the relationship between the amount of washing gasoline used and the amount of feed material or waste alkali solution? The process of using spent alkaline solution to wash gasoline seems to be largely obsolete these days; its main purpose was to remove certain thiol compounds from gasoline, with the amount of these compounds being proportional to the amount of gasoline. However, an oxidizing gas stream also needs to be introduced in order to achieve sulfur and thiol removal. 3. To what extent are H2S and CO2 present in the pyrolysis gas, that an amine scrubbing step needs to be added before the alkaline scrubbing? Do you know about this issue...

Thank you for your response. Ethylene cracking gas generally contains low levels of H2S and CO2 (with concentrations of 0.23 mol%, of which 0.09 mol% is H2S and 0.14 mol% is CO2). It is required that these concentrations be reduced to 1 ppm (vt) each. What is the approximate range for the circulation rate of the alkaline solution? The washing gasoline system is installed in the alkali washing tower mainly because the waste alkaline solution contains butter, which causes this butter to dissolve in the pyrolysis gasoline; it has little to do with desulfurization of alcohols. I want to know the quantitative relationship between the amount of pyrolyzed gasoline injected and the amount of pyrolysis gas feedstock (or spent alkali solution). For example, the volume ratio of spent alkaline solution to pyrolysis gasoline might be 100:1 or something like that (these numbers are given only as examples and are not accurate).

With limited time and energy, you might want to take a look at the chapters on absorption and desorption in \"Principles of Chemical Engineering\"; it might be helpful to you!

There is no need for amine washing anymore; two alkali washing towers can be used, with the second one designed with a three-stage alkali washing cycle. The volume of the three alkali washing cycles mainly controls the alkali concentration. What we have set is hydrogenated gasoline washing.

This post was last edited by longziyun on 2020-7-13 at 12:34. The original poster’s first question is a bit nonsensical. Based on my limited knowledge of ethylene, here are my thoughts. 1. The circulation rate of the alkali solution in the ethylene caustic scrubber is generally specified in the process package; in other words, it is determined through calculations. There are various factors that affect this circulation rate, including the flow rate of the pyrolysis gas, the molecular weight of the pyrolysis gas, as well as the desired concentrations of strong, medium, and weak alkalis. The type of tray used in the caustic scrubber also plays a role, along with the efficiency of separating the alkali solution from the pyrolysis gas within the scrubber (the presence of alkali residues can affect the subsequent dryer). Lastly, the content of acidic gases in the pyrolysis gas – primarily CO2 – is another factor that influences the circulation rate. The specific situation needs to be analyzed on a case-by-case basis; different devices use different process flows and different patented technologies, so the volume of alkaline solution circulation cannot be the same across all of them. What relevance does the alkaline solution circulation volume of other devices have for you? Give up the idea of trying to uncover these technical secrets; it’s not very interesting to know them anyway. Is it bad to delve deeper into pyrolysis furnaces? 2. The initial idea of using gasoline to clean butter had some merits based on a certain design concept, but in practice it didn’t work as well as expected; the effectiveness of using gasoline for this purpose wasn’t very good, and oil contamination in the alkaline solution became a common problem. Just like the appendix in the human body, such designs existed, but they were mostly abandoned. It is more important to choose a butter inhibitor that suits one’s own equipment. 3. Perhaps in an effort to reduce the amount of alkali solution used in the caustic scrubbing tower system, it was tried as a novel approach to use renewable amine solutions to wash away the acidic gases in the pyrolysis gas. Although water washing was employed, amine solutions are organic bases that tend to form bubbles; when carried by the pyrolysis gas, they can have an adverse effect on the subsequent processes in the impurity removal unit. This approach has also been abandoned.

Thank you for your answer; I’ve learned new knowledge.