Ancillary Equipment

Hot gas filters are often used in conjunction with other items of equipment to create a complete gas treatment system. If the gas is a waste gas it frequently needs to be treated for a range of potential pollutants which may include VOCs, particulates and acid gases.

VOCs are removed by burning the gas, which is normally done in an afterburner. If the gas is to be filtered in a ceramic filter then it probably needs to be cooled and if acid gases are to be removed then a sorbent needs to be added to the gas stream. Caldo can supply equipment for each of these purposes.

Caldo Afterburner

Caldo has designed and supplied oil-fired afterburners to expose the process gas to 850 degC or above in the presence of at least 6% oxygen for at least 2 seconds.

The photo shows an afterburner treating gas from a plasma furnace that is being used for melting automotive catalysts to recover the precious metals. The afterburner vessel is vertical with the gas inlet being at the bottom on the side away from the camera and the outlet being at the top.

Gas Cooling

400 degC is a very good temperature at which to operate a ceramic filter. This is because:

• lime reacts well with the main acid gases at 400degC but the reaction with CO2 is very slow
• the ceramic filters can be constructed in carbon steel, stainless steel is not required
• there is every chance of avoiding 'de novo' dioxin formation

However, very often the gas will need cooling from 850 to 400 degC. This can be done with air dilution, but the gas volume increases substantially. Using a heat exchanger reduces the gas volume but the equipment is complicated, expensive and subject to fouling.

An alternative solution is evaporative cooling, where water is sprayed into the gas stream and evaporates. The latent heat of water is quite high so a relatively small water addition can generate a lot of cooling. However, the design is very important - it is very undesirable to have liquid water running down the inside walls of the cooler.

The photo shows the afterburner exit duct in black where it feeds ito the spray cooler. The cooler has 3 water sprays and these cool the gas from 1200 degC.

Powder Feeder

See the dry scrubbing page and download the datasheets from the download page.