How Does a Closed Loop (LCNGS) Split Stream Dryer Work?

This type of dryer is used primarily for drying hydrogen, oxygen, natural gas and other valuable and/or explosive gases.

It does not require a blower. Instead, it uses a proportioning valve to recirculate the regeneration purge gas, typically 10 – 20% of the incoming gas. A heater is provided to heat purge gas to about 375oF/191oC. The warmed gas flows through the regenerating tower to regenerate it. The wet and warm gas then flows through a gas cooler and a separator to remove the entrained moisture.

A typical dryer has an 8 hour cycle time: 4 hours of drying, 2.5 hours of heating and 1.5 hours of desiccant cooling.

In addition, the design includes monitoring controls of the temperature of the purge gas exiting the regenerating tower. An exit gas temperature of in excess of 250oF/121oC signals completion of heating mode and switches the heater off to save energy.

A typical drying system includes, at the minimum, a coalescing pre-filter and a particulate after-filter. The pre-filter prevents condensed fluids – oils and moisture – from entering the desiccant tower and prematurely damaging the desiccant. The after-filter prevents desiccant fines from flowing downstream into the clean and dry piping system.

How Does a Hybrid Dryer Work?

A Hybrid Dryer includes a refrigeration dryer followed by a regenerative dryer, usually a heatless dryer or with a heat reactivated dryer.

In a typical installation, the refrigeration dryer dries air/gas to 40oF/4.4oC, removing approximately 80% of the moisture in the air/gas. The air/gas is dried to -40oF/-40 oC or lower by the heatless or heat regenerative dryer removing the bulk of the remaining 20% of the moisture.

Since the regenerative dryer system removes only 20% of the remaining moisture in the air/gas, the regeneration purge air/gas requirement is reduced to about 4% of volume.

This system also saves on the size and cost of compression required.
For example:
Dry air required – 800 scfm
Recommended Pioneer Model PHL1000
Required compressor capacity with heatless dryer – 950 scfm
With a hybrid dryer, the required compressor capacity is about 850 scfm

Also, there is an inherent redundancy as one dryer package serves to back up the other dryer package.

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