Dry Scrubbing and Powder Dosing Units for VOCs and Hot Wax Filtration

What are dry scrubbing systems?

Dry scrubbing is a technique used for removing the vapour components of raw gas flow, using ‘absorption’ onto an inert dry powder (sorbent). It works especially well with vapours which have a dew point close to the operating, or in-duct temperature, in a dust or fume extraction system. For instance VOC’s and acid gases from various plastic extrusion processes, foundry hot wax casting processes, oven and furnace processes producing large amounts of VOC / acid gases etc.

image002The powder is usually injected into the ductwork upstream of a bag-house or cartridge filter dust collector, to allow thorough mixing with the gas stream, prior to hitting the filtration media / system. The unwanted ‘volatile/pollutant’ fume reacts and combines with the injected powder, enabling resultant product / powder to be successfully removed by the dust extraction system. It is important to allow sufficient ‘resident time’ for the VOC to combine and react with the dry powder / sorbent, prior to the filter media.

Without dry powder absorption the volatile components of the gas stream can quickly blind the filter media, even with efficient reverse pulse jet or compressed air cleaning wing, filter cleaning systems.

Common sorbents are limestone Ca(OH)2 / calcium carbonate the formula CaCO3/, sodium bicarbonate NaHCO3. Hot gas processes can also use dry-scrubbing, with the fume / dust laden air captured with high temperature ceramic elements.

R&B Industrial have designed, manufactured, supplied and installed various types of dry powder injection and metering systems, for a range of volatile fumes and gas streams.

We can carry out design and feasibility studies to determine the most appropriate powder sorbent, flow rates, molecular absorption rates and residence times required for most efficient extraction and filtration efficiencies.

We can also design manufacture most appropriate filtration system; bag or cartridge filters with particular finish or temperature range or high temperature ceramic filters, for process gas streams > 250 deg C.

pdfPowder Dosing Units.pdf


Calcium Carbonate Dosing Unit.

  • Tank unit with feed hose, valve and automatic control for pre-coat dosing into filter unit/dust collector
  • Delivered with 1m feed hose
  • Timer: Setting from 1 sec. - 99 hours per dosing shot as well as interval time
  • Height: 1050mm
  • Outside measurement: 480 x 400mm (LxW)
  • Filled through hinged top lid
  • Can in many cases increase filter element life or be used to inert explosive dusts or condition aggressive or sticky dusts.

22-11-2012 10-23-25


Electric ovens/furnaces will often need additional afterburners (or dry scrubbers) as there is more VOC in the airstream which will blind filters. If filtering below 200 C activated carbons will be required to adsorb VOC’s from air stream. Hoods over oven / furness outlets allow ambient air to be drawn in which can help; reduces process / duct temperatures / aid dry scrubbing and filtration etc.

Note wet scrubbers are less efficient than dry filtration for fine particulate < 20 – 40 micron.