Molecular sieve drying issue in front of the cold box
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Before the near-cold box, it is necessary to remove substances in the feed gas that are prone to freezing, such as water and CO2. Normal-temperature removal and low-temperature removal are commonly used; what are the advantages and disadvantages of each? What is the basis for the selection?
It is determined by the performance and quantity of the molecular sieve. Water content is higher at room temperature than at low temperatures.
If you can find a reasonable source of cold energy, use low temperature; otherwise, use normal temperature.
The lower the temperature, the less water content in the gas. Before entering the cold box, we need to remove water and carbon dioxide from it. It’s also possible to use a low temperature along with molecular sieves, but this requires more energy and increases costs! Room temperature is sufficient.
Currently, the normal-temperature molecular sieve process is generally used
Room temperature is more commonly used; it’s difficult to find cold sources at low temperatures
If there is an existing cold source for the air separation equipment, it can be utilized; for example, the nitrogen gas released from the air separation tower can be reused, and cooling the air with molecular sieves can help reduce costs.
In most current coal slurry gasification processes, it is common to use low-temperature methanol washing before proceeding to the next cold box stage in a cooled state. The advantage of this approach is that it reduces the cooling load on the cold box (CO or liquid nitrogen washing) systems; however, it increases the cooling capacity required for low-temperature methanol washing. Which one is better specifically still requires further comparison