Discussion on the adsorption efficiency of molecular sieves
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A 60x20,000-ton methanol plant produces LNG as a by-product, with molecular sieves installed in front of the cryogenic tank to absorb methanol and carbon dioxide. Due to poor adsorption, the cold box became clogged after 2 months, forcing a re-warming process. The reason was analyzed to be the high adsorption temperature (30°C); therefore, technical modifications were carried out to reduce the adsorption temperature to 11–15°C, with the cold box being warmed up every 4–5 months. The data below show the analysis results before and after adsorption. Column A: Inlet carbon dioxide 5.92 ppm, methanol 38.5 ppm; Outlet carbon dioxide 4.73 ppm, methanol 1.0 ppm. Column B: Inlet carbon dioxide 7.00 ppm, methanol 65.8 ppm; Outlet carbon dioxide 5.07 ppm, methanol 1.0 ppm
The manufacturing of molecular sieves should involve certain intellectual property rights. It seems from your question that you are not from a production or development unit, but rather from a user unit. It is recommended to select an appropriate molecular sieve and strictly adhere to the requirements regarding its operating conditions. The operating conditions for molecular sieves are within certain limits; they are not universal.
I have used molecular sieves from several companies, but they did not achieve the desired results.
I have used molecular sieves from several companies, but they did not achieve the desired results.
It is recommended to keep the carbon dioxide inlet concentration at 2-3 ppm; give it a try
It is relatively difficult to control the methanol and carbon dioxide contents at the molecular sieve inlet, as the process gas comes from low-temperature methanol washing.
In fact, the adsorption efficiency is determined by various factors. Firstly, it depends on the properties of the adsorbent itself (molecular sieve) as well as its manufacturing quality; secondly, it is influenced by the processing methods, such as the adsorption time and the desorption process (vacuum desorption or purge desorption).
Send a flowchart – the gas coming out of the methanol wash is at minus 50 degrees or so. What does 11-15°C refer to? The CO2 level entering the cold box should be kept below 1 ppm.
The gas coming out of the methanol wash tower is at -50°C; after heat exchange, its temperature rises to 30-40°C. After entering the methane plant, the gas is cooled to 20°C, but this does not yield good results; after technical modifications, it was cooled to 11–15°C.
Methanol is washed out, adsorption is carried out, and then heat exchange and temperature increase take place; the lower the temperature, the better the adsorption effect.
The methanol level at the molecular sieve inlet is on the high side, and the blockage in the cold box is mainly caused by high levels of CO2 at the outlet; the CO2 level at the outlet should be less than 1 ppm. The performance of the molecular sieve and whether regeneration has been effective are the key factors to consider here.