Pulp and Paper Air Pollution Emission Control
Recently advances have been made in the control of steam pollution by using a fluid bed reactor system to recover the sulfite pulp waste black liquor.
High Efficiency Dry Cyclones and Venturi Scrubbers are an integral part of this spent liquor recovery process in both Neutral Sulfite Semi -Chemical and Magnesia based pulp mills.
Sulfite Spent Liquor
Recovery Process: In the Copeland Process for treatment of magnesia based waste effluent, entrained solids are carried from the fluid bed furnace by high temperature exhaust gases that are removed by the Ducon High Efficiency Cyclones.
The collected dust is returned to the fluidized bed to be reused in the process. The exhaust gases from the Cyclones are further cleaned by scrubbing with weak black liquor in a Ducon Venturi Scrubber.
The gas continues to a cooling chamber and adsorption towers to convert the magnesiun hydroxide to cooking liquor.
Smelt Dissolving Tank
Approximately 20 lbs. of salt cake dust are generated for each ton of pulp and much of this large particle dust is entrained in the vent gases of the dissolving tank where hot furnace smelt and liquor come in contact. The removal of this dust is a relatively simple matter for a Ducon Dynamic or Centerfugal scrubber.
The removal of fly ash from Bark Boilers is generally accomplished by High Efficiency Cyclones. Present thinking is to use a wet scrubber after the cyclones for complete dust removal. A recomended collector package is the Ducon Large Diameter Cyclone and Dynamic Scrubber.
In transfer of pulp and liquor steam from Digestor to Blow Tank, Ducon Multivane Scrubbers are installed as wet cyclone seperators at top of the Blow Tank. The Multivanes remove pulp chips and liquor carry-over from the steam vapor before discharging into heat recovery unit.
For the Digestor and Evaporator vent, Odorous 820, S02 Mercaptans can be removed by adsorption, scrubbing with caustic and bleach plant water. Efficient spray scrubbers can be designed for this problem by Ducon.
For Lime Kilns and Slakers, Ducon can provide equipment for adsorption and recovery of S02 & S02 mist. This problem requires special designs to meet the requirements of each case.
Kraft Recovery Boiler
Gas Cleaning Systems: Ducon High Efficiency Wet Electrostatic Precipitator is recommended as a primary collector following cascade or cyclone evaporators. Scrubbing with weaker liquor or water will remove submicron particles at efficiencies of 99%.
Ducon E-6 Wet Precipitator offers high dust collection availability and does not deteriorate with age. Aftercoolers can be included in the upper section of the entrainment eliminator to condense water vapor out of the gas stream, reducing the temperature to 100 degrees F or less.
Stack cooling not only reduces visible plume, it also reduces gas flow to the fan and lowers horsepower requirements.
The treatment of green Iiquor with hydrated lime to produce white Liquor for the digestors involves two sources of dust emission and air pollution- the Lime Kiln & the Lime Slaking System. The particulate matter emitted is coarse calcium oxide and submicron soda fume, ranging from 10-20 grains per scf. Generally, soda emission can be reduced by adequate washing and kept below 1% in the mud feed.
For controlling lime kiln emissions, the Ducon High Efficiency Wet approach using Venturi is recommended. Efficiency of the wetted wall Venturi can be varied between 95% & 99%, depending on pressure drop. While few pulp mills control the emission of lime dust and steam from the lime slakers, more attention is now being paid to this problem.
It is basically an in-plant nuisance and can readily be resolved with a low pressure drop scrubber, such as the Ducon UH-4 Dynamic Scrubber.
Ducon has been a leader in the Pulp and Paper industry as a solution provider in controlling air pollution emissions for 80 years. Ducon equipment has gained a strong reputation throughout the world for high collection efficiency, long service life and minimum maintenance.
We offer a wide range of cyclones and scrubbers to meet the most severe service conditions, including extreme temperatures. abrasion, corrosion, and high dust loads.