Selection of Molecular Sieves for Adsorption Dryers, Filling Precautions, and Basic Operating Parameters

I. Selection of Molecular Sieves

The choice of molecular sieve depends on the type of gas to be treated and the desired dryness level. Common types of molecular sieves include 3A, 4A, 5A, and 13X, each with specific pore sizes and application ranges:

• 3A Molecular Sieve: Suitable for drying polar small molecules such as acetylene and propylene, with a pore size of approximately 3Å, effectively adsorbing these molecules.
• 4A Molecular Sieve: Widely used for drying gases like air, natural gas, and hydrogen, with a pore size of approximately 4Å, providing good adsorption performance for various gases.
• 5A Molecular Sieve: This sieve is designed for larger molecules such as liquefied petroleum gas and ethylene. Its pore size is approximately 5Å, ensuring efficient moisture removal.
• 13X Molecular Sieve: Features larger pores, suitable for drying air and other non-polar molecules, and boasts high adsorption capacity, making it a preferred choice in many industrial applications.
   

2. Consideration of Adsorption Capacity

Different molecular sieves exhibit varying adsorption capacities under different temperatures and pressures. Therefore, when selecting molecular sieves, optimization based on specific operating conditions (e.g., gas temperature, Pressure, flow rate, and moisture content) is essential to ensure the selected sieve meets production needs.

3. Durability and Regeneration Performance

Excellent durability and regeneration performance are crucial for the long-term stable operation of molecular sieves. Selection should prioritize those that undergo unique treatments, resist wear and contamination, and maintain high adsorption efficiency even after multiple regeneration cycles.

II. Precautions During Filling and Adsorption

1. Uniform Filling

When filling molecular sieves, ensure they are evenly distributed within the dryer to prevent airflow short-circuiting or local over-saturation areas. This improves adsorption efficiency and extends the sieve's lifespan.

2. Prevention of Powdering

Protect molecular sieves from severe impacts or friction during transportation and filling to prevent powdering. Powdered sieves significantly reduce adsorption efficiency and may clog equipment piping.

3. Moisture-Free Handling

Maintain molecular sieves in a dry state before filling to prevent adsorption of ambient moisture. Once sieves adsorb moisture, their adsorption capacity drops significantly, affecting drying effectiveness.

4. Good Sealing

The dryer's sealing is paramount. Ensure all connections are tightly sealed to prevent external moisture from entering the dryer interior, impacting sieve adsorption.

III. Basic Operating Parameters

1. Operating Pressure

The operating Pressure of adsorption dryers typically ranges from 0.6 to 1.0 MPa. Pressure values depend on gas type, flow rate, and process requirements.

2. Operating Temperature

Operating temperatures generally fall between -20°C and 50°C, but the exact range depends on sieve type, gas properties, and process conditions.

3. Regeneration Temperature

Regeneration temperature is crucial for restoring sieve adsorption capacity. Depending on sieve type and adsorption capacity, it typically ranges from 150°C to 250°C. Excessively high temperatures may damage sieve structures, while too low temperatures may fail to desorb adsorbed moisture effectively.

4. Adsorption Cycle

The length of the adsorption cycle depends on gas flow rate, moisture content, and sieve adsorption capacity. It can vary from several hours to days, requiring adjustments based on actual conditions.


5. Regeneration Time

Regeneration time typically ranges from 2 to 8 hours, depending on the regeneration method and equipment size. Proper regeneration time settings ensure that sieves fully recover their adsorption capacity before the next adsorption cycle.

In conclusion, proper selection and filling of molecular sieves, along with reasonable operating parameters setting, are crucial for ensuring the efficient operation of adsorption dryers. Adjustments and optimizations should be made in practical applications based on specific operating conditions.