Adsorption Dryer Purge Consumption Worksheet

Route: /engineering-tools/adsorption-dryer-purge-consumption-worksheet/ (proposed until route reconciliation). It does not apply a universal purge percentage across all adsorption-dryer designs.

1. Purpose and Engineering Decision

Adsorption dryers can consume compressed air during regeneration, electrical power for heaters and blowers, or a combination of both. The energy and capacity consequence depends on the dryer technology, cycle sequence, operating pressure, inlet conditions, dew-point duty and the exact way the supplier states purge consumption.

The worksheet also shows the effect of purge on net useful dry-air delivery.

2. Purge Basis Must Be Explicit

A purge figure is incomplete unless its basis is known. It may be stated as a percentage of dryer rated inlet flow, a fixed reference flow, an actual volumetric flow at regeneration pressure, or a time-averaged value over a complete cycle.

3. Reference-Flow Purge from a Documented Percentage

Q_purge,ref = Q_basis,ref x f_purge

This equation is valid only when the supplier explicitly defines purge fraction f_purge against the same Q_basis,ref.

4. Convert Actual Regeneration Flow to Reference Flow

When purge is measured or stated as actual volumetric flow at a regeneration pressure and temperature, it must be converted to the common reference condition before capacity or energy comparison.

Q_ref = Q_actual x (P_actual,dry / P_ref,dry) x (T_ref / T_actual) x (Z_ref / Z_actual)

Gauge pressures are converted to absolute before use.

5. Regeneration Duty Fraction

f_active = Purge-Active Time / Total Cycle Time

Q_purge,avg,ref = Q_purge,instant,ref x f_active

Do not apply the duty fraction when the supplier has already provided a cycle-average purge value.

6. Purge Volume and Energy Worksheet - Required Asset

7. Annual Purge Volume

Annual Purge Volume_ref = Q_purge,avg,ref x Operating Hours x 60

If Q is entered in m3/min, multiplying by hours and 60 gives m3 of reference air per year. For a shift or project study, replace annual hours with the relevant operating period.

8. Net Useful Dry-Air Delivery

Q_net,dry = Q_inlet,ref - Q_purge,avg,ref - Other Verified Dryer Losses

Purge Fraction of Inlet (%) = Q_purge,avg,ref / Q_inlet,ref x 100

It must not assume valve leakage, depressurization losses or cooling purge unless they are documented or measured.

9. Compressed-Air Energy Equivalent

P_purge,equiv (kW) = Q_purge,avg,ref x Specific Power

E_purge,equiv (kWh) = P_purge,equiv x Operating Hours

This is an energy-equivalent screening calculation using the stated compressor or fleet specific power. It is not automatically equal to the plant's incremental electrical saving if purge is eliminated, because compressor controls, unload time and fleet dispatch may change.

10. Heater and Blower Electrical Energy

E_heater = P_heater x Heater Active Hours

E_blower = P_blower x Blower Active Hours

E_regeneration,total = E_purge,equiv + E_heater + E_blower + Other Verified Auxiliary Energy

The worksheet keeps compressed-air energy equivalent and directly metered auxiliary electricity visible as separate rows before presenting a combined project-energy view.

11. Reference Test Case A - Heatless Dryer with Documented Purge Fraction

Synthetic validation case: a dryer data sheet states purge at 15% of a 20.0 m3/min reference-flow basis and identifies that number as cycle-average purge. The dryer operates 6,000 h/y. Use 6.0 kW per m3/min as the matched fleet specific-power input.

Because the supplier statement is already cycle-average, no additional purge duty factor is applied.

12. Reference Test Case B - Instantaneous Purge with Active Fraction

Synthetic validation case: instantaneous purge is 4.0 m3/min on the selected reference basis. Purge is active for 2 minutes in each 10-minute cycle.

Average Purge = 4.0 x (2 / 10) = 0.80 m3/min

If a developer incorrectly treats 4.0 m3/min as a cycle-average value, annual purge is overstated by a factor of five.

13. Reference Test Case C - Actual Purge Flow at Regeneration Pressure

Synthetic validation case: measured purge is 0.50 m3/min actual at 2.0 bar(g), 30 C. Atmospheric/reference pressure is 1.01325 bar(a), reference temperature 20 C, Z = 1, humidity correction omitted.

Q_ref = 0.50 x (3.01325/1.01325) x (293.15/303.15) = 1.438 m3/min

The example shows why an actual regeneration-line flow cannot be compared directly with FAD or another reference-flow number.

14. Reference Test Case D - Heated / Blower Regeneration Energy

Synthetic validation case: average compressed-air purge is 0.60 m3/min for 5,000 h/y at 6.0 kW/(m3/min). A 12 kW heater runs 1,500 h/y and a 4 kW blower runs 2,000 h/y.

15. Depressurization and Repressurization Losses

Some adsorption-dryer cycles vent vessel pressure during switching and consume air during repressurization.

The tool must not roll an assumed switching loss into purge percentage without evidence.

16. Dew-Point Demand and Purge Control

Demand-controlled regeneration may reduce purge or heater/blower runtime when the desiccant bed does not require a full fixed cycle.

17. Purge Cost

Purge Energy Cost = E_purge,equiv x Electricity Tariff

Auxiliary Electrical Cost = (E_heater + E_blower + other kWh) x Tariff

A flat tariff can be used for screening. Demand charges, time-of-use tariffs and compressor-control interactions belong in the broader lifecycle model when material.

18. Capacity Check

Dryer Inlet Requirement = Useful Dry-Air Demand + Average Purge + Other Verified Internal Losses

For some designs the upstream compressor must supply useful plant demand and regeneration consumption simultaneously.

19. Confidence Model

20. Validation and Guardrails

21. Output Specification