Wet Scrubber Liquid-to-Gas Ratio and Removal

The ratio is expressed in gallons per minute per thousand actual cubic feet per minute of gas, and it is the primary sizing variable -- but which mechanism it serves depends on what the scrubber is removing, and that distinction is the useful part. In a venturi removing PARTICULATE, the energy of the gas passing the throat atomizes the liquid, and removal follows the PRESSURE DROP; the liquid-to-gas ratio supplies the liquid that pressure drop works on. In a packed tower absorbing a GAS, removal follows the contact between the gas and a continuously renewed liquid surface, so the ratio and the packing height are the controls and pressure drop is a cost rather than a mechanism. Fine particulate is where the energy cost becomes severe. Removal of submicron particles in a venturi rises steeply with pressure drop, and pressure drop is fan power spent continuously for the life of the installation -- so a scrubber achieving a high efficiency on fine particulate is an expensive machine to run, and that operating cost, not the capital cost, is usually what decides against it. Two consequences sit outside the arithmetic and neither should be forgotten. Dissolved material accumulates in the recirculating liquid, so a blowdown or purge is required and its rate sets the chemistry the scrubber actually runs at. And a wet scrubber does not destroy the pollutant, it TRANSFERS it to water -- which then has to be treated, discharged under its own permit, or hauled. A scrubber's real cost includes that stream. This computes circulation and the power to move it from an ENTERED ratio; it does not predict removal efficiency, which depends on the contactor design, the chemistry, the particle size distribution and the solubility, and which is measured rather than calculated. It does not size the packing or the vessel, compute the blowdown rate or the resulting chemistry, or address mist eliminators, reheat, and the visible plume. The scrubber manufacturer's performance data, the permit, and a qualified air quality engineer govern.

liquid gpm = gas acfm / 1,000 x the L/G ratio; pump brake horsepower = gpm x head x specific gravity / (3,960 x efficiency); fan brake horsepower = acfm x in wc / (6,356 x efficiency).

The wet scrubber liquid-to-gas ratio as air pollution control practice writes it, with the customary pump and fan horsepower relations. It does not predict removal efficiency, which depends on contactor design, chemistry, particle size distribution and solubility and is MEASURED rather than calculated; it does not size the packing or vessel, compute blowdown rate or the resulting chemistry, or address mist eliminators, reheat and the visible plume.

One ratio and two horsepower relations.

Estimate. AHJ and licensed professional govern.

Field names used by the API: gas_acfm, lg_ratio_gpm_per_1000, pump_head_ft, pump_efficiency, specific_gravity, annual_hours, energy_rate_per_kwh, alternate_lg_ratio, pressure_drop_inwc, fan_efficiency, scrubber_type, liquid_gpm, pump_bhp, fan_bhp, alternate_liquid_gpm, alternate_pump_bhp

• Removal is not predicted it depends on contactor design, chemistry and particle size and is measuredthe scrubber manufacturer's performance data
• Blowdown is not computed dissolved material accumulates and the purge rate sets the chemistrythe water treatment design
• The water stream is a real cost the pollutant is transferred, not destroyedthe discharge permit