Molecular sieve application - deep drying of natural gas
At present, the main natural gas deep drying devices are using molecular sieves to achieve deep dehydration.
Synthetic zeolite molecular sieve is a kind of alumino silicate crystal with strict skeleton structure. The inner skeleton formed by the silicon-aluminum tetrahedron has numerous micropores with three-dimensional connectivity. It is a strong polar adsorbent with uniform pore size and high The choice of adsorption separation capabilities. As the ratio of silicon to aluminum increases, the polarity of the molecular sieve gradually decreases. Therefore, the molecular sieve with a low silicon to aluminum ratio has a stronger ability to adsorb moisture, and is suitable for deep dehydration of gas.
Molecular sieves are high-efficiency dehydrators commonly used in compressed natural gas. The main advantages are as follows:
1. Molecular sieve can deeply dehydrate the gas. Under normal circumstances, its adsorption amount is higher than other adsorbents, which can reduce the size of the drying tower and save costs.
2. Molecular sieves can effectively dry gases at higher temperatures.
3. Molecular sieves can selectively adsorb moisture to avoid the co-adsorption of heavy hydrocarbons and causing the adsorbent to fail.
4. Molecular sieves are not easily damaged by liquid water, and adsorbents such as silica gel are easily brittle when exposed to water.
As the gas passes through the bed of molecular sieves, the water vapor molecules in the gas enter the pores inside the molecular sieve with the gas stream. Since water molecules are highly polar molecules, they are adsorbed on the pores and no longer flow with the gas; while hydrocarbon gases such as methane are non-polar molecules, they pass smoothly and the gas is dried.
As the moisture adsorbed by the molecular sieve in the adsorption tower increases, the adsorption capacity of the molecular sieve to the water molecules gradually decreases. When a certain value is reached, the water molecules in the gas at the outlet of the adsorption tower exceed the specified value, indicating that the molecular sieve in the tower Has been saturated. At this time, it is necessary to regenerate the molecular sieve in the adsorption tower.
The regeneration process is the process of expelling the water molecules adsorbed in the micro pores of the molecular sieve to reactivate the molecular sieve. The design of the regeneration process is critical to the continuous operation of the dryer. A reasonable regeneration process can achieve the purpose of effective regeneration with as little consumption as possible (electric heating power, gas consumption rate).