For sub-zero pressure dew point requirements, the industry standard dictates using an adsorption dryer. However, a foreign vendor now offers a different, simpler proposition: directly select an adsorption dryer, which minimizes system complexity and lowers initial investment.
1.Preliminary conclusions
In a combined dryer, the pre-cooled refrigerated section handles 82.89% of the total water vapor load, leaving 17.11% for the post-desiccation stage. Higher intake temperatures increase the refrigerated section’s share. For broader inlet temperature ranges, industry practice generally allocates 85–90% of the load to the refrigerated dryer and 10–15% to the desiccation dryer. A standalone desiccation dryer, by contrast, bears 100% of the total load.
2.How to choose model
When selecting a combined refrigerated + desiccant dryer, pay special attention to the refrigerated unit. Its sizing requires not only inlet airflow, but also ambient temperature, inlet air temperature, and inlet air pressure. Use these three values to look up the corresponding correction factors from a table, then apply them to choose a refrigerated dryer that meets normal performance specs (pressure dew point 2–10°C). Selecting the desiccant dryer is simpler: only inlet air pressure matters. For standard 7 kg pressure, pick the model directly from the product catalog based on flow rate; for non-standard pressure, apply pressure correction to size it accordingly.
3.Advantages
For the same compressed air capacity, a desiccant dryer sees only 10–15% of the moisture load when preceded by a refrigerated dryer, versus 100% when standing alone. The combined unit’s optimized layout also lowers the desiccant inlet temperature, improving its drying performance. A standalone desiccant dryer lacks these benefits, and its sizing requires both inlet pressure and temperature corrections—above 50°C inlet temperature, it fails to operate properly. Additionally, the combined system offers seasonal flexibility: in cool, dry autumn/winter conditions, you can shut off the refrigerated section and run the desiccant dryer independently.
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