Discussion on the issues with alkali scrubbers in the coal-to-olefins industry
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In the olefin industry, the issue of alkali scrubbers is an important system that affects the stable, safe, and long-term operation of the plants. Some units encountered many tricky problems during their initial commissioning, which even affected the load of the entire unit. It has to operate under difficult conditions, or even stop for maintenance. Everyone can discuss any issues related to the alkali scrubber, whether they pertain to process operations or problems with the equipment itself. Over the years of my career, I have encountered many various problems related to alkali scrubbers. 1. The alkali scrubber becomes clogged during operation. 2. Freezing blockage of the alkali scrubber at startup. 3. The liquid level in the circulating alkali section of the alkali scrubber is full at startup. 4. The operating load cannot be increased at startup, and raising the load results in an excessively high pressure difference. 5. Blockage due to issues with additives after operating for a while, etc. There are other related questions as well; I hope everyone will engage in more discussions. Improve together.
How is the wastewater from the alkali scrubber treated, and what are its components?
Do you mean the spent alkali or the butter side?
Waste alkali solution contains a certain concentration of sodium hydroxide, sodium carbonate, and hydrocarbons. Depending on the additives used, it may also contain phosphorus compounds that are difficult to handle. In both the traditional ethylene industry and the current coal-based olefins industry, the treatment of waste alkaline solutions represents a major problem, and to date there is no effective solution for it. For example, after separating oil, water, and alkali, some of the waste alkaline solutions can be neutralized, while others are sent to wastewater treatment plants or used in boilers, among other options.
There are some issues we can discuss in more detail privately.
Can the alkali scrubber tower experience freezing blockages? ? ? If butter gets clogged, it indicates a problem with the operation, as too much butter is being produced. Imported and domestically produced butter inhibitors actually contribute very little to actual operating conditions. Moreover, the composition of butter is quite complex; it depends on the specific color and state it achieves. For example, MTO olefin separation typically results in red-colored butter, which is a type of aldehyde condensation product. It is essential to control the depth of the MTO reaction carefully, keeping the amount of aldehydes within the designated range at the inlet of the reaction gas, and to operate the water scrubber before the alkali scrubber properly. As long as the amount of aldehyde at the inlet of the alkali scrubber is not high, there are no problems with the scrubber; otherwise, it will lead to serious consequences. The components in the ethylene cracking process vary greatly, and butter-like substances are produced as a result, primarily due to the polymerization of heavy hydrocarbons and aromatics.
The freezing blockage in the caustic scrubber is not caused by butter, but rather by the low operating temperature of the caustic scrubber. Butter inhibitors have little impact on either side; what matters is the deoxidizer, which reduces the polymerization of oxides. The so-called red oil produced through olefin separation in MTO is merely the final apparent product; what is produced initially is a light yellow oily substance. The red oil that is seen is the result of further oxidation. To verify this, you can use bottles to hold butter – one bottle sealed and the other open – and then check for color changes after some time has passed. The butter formation from ethylene cracking is greatly influenced by dienes such as butadiene.
What is low-temperature freezing blockage in the alkali scrubber tower? Is the liquid level full in the alkali solution circulation section here? Seeking guidance, thank you.
Freezing blockage at low operating temperatures? What is the temperature, and what are the components of the reaction gas? And where is the alkali scrubbing tower process located? In terms of the caustic scrubber, we have been stopping the use of butter inhibitors and deoxidizers for over a year now; with no such additives used, the water scrubber operates well. Even under conditions of high aldehydes and ethers in MTOg, the operation remains very stable, with low and consistent pressure differences, and the amount of butter generated is ideal. The components of the red oil are to some extent related to the aldehyde-oxygen ratio. However, oxygen is also a factor in complex polymerization. For operational purposes, what is desired from the alkali scrubber is long-term stable operation; the focus remains on aldehydes, with the aim of optimizing operating conditions, reducing the use of chemicals, and achieving energy efficiency. After long-term testing of the unit, it appears that both the butter inhibitor and the deoxidizer can be discontinued under optimal operating conditions. Due to the low butadiene content, the reboilers in the high and low pressure sections as well as those in the butadiene removal column can also stop using the polymerization inhibitor. To ensure that the reboiler for starting up steam during the insurance period can be properly put into use.