The VenturiPak scrubber is a result of re-examining and optimizing the venturi concept to achieve high collection efficiency at modest energy consumption (i.e. low to medium pressure drop).
The fine particulate fraction in furnace stack off-gases is comprised of fine solid particles (< 1 micron), and condensed solid and liquid aerosols resulting from the cooling and sub-cooling in the scrubber. These fine particles are problematic in that:
The EnviroCare VenturiPak places the scrubber components in proper sequence rather than the traditional practice of placing a high energy venturi directly following the quench section. The VenturiPak scrubber incorporates the latest technological advances in wet scrubbing and atomization technologies. Features of the system include:
Each component is designed for durability and is integrated into a state-of-the-art air pollution control system.
The VenturiPak scrubber performance has been verified through test results on small (±1000 ACFM), medium (±10,000 ACFM) and large (65,000 ACFM) installations. The system, with a local controller, is designed to provide high removal efficiencies over a wide range of gas volumes. It is also designed to remove pollutants not included in the 503 regulations, such as condensables, acid gases, soot, and hydrocarbons.
The design places each scrubbing stage in a logical sequence much like arranging screens for a sieve analysis where the screens are stacked with the coarsest first, then grading down to the finest screen. The design concept places a low energy venturi quench section first. The quench section captures more than 90% of the ash, sand and other particulate. Velocity in the quench section remains low, eliminating the need for wear plates or special wear resistant material.
The gases then enter the bottom of the scrubber and continue upward, passing through impingement trays for sub-cooling and further particulate removal. Sub-cooling serves to convert condensables to particulate and to "grow" the heavy metals, most of which will be sub-micron, for subsequent capture in the venturi stage. SO2 also becomes more soluble in the cooler water and is further reduced.
The gases pass upward and into a zone of atomized water at the entrance of each of several "near true" venturi tubes. The direct contact of the sub-micron particles with the small water droplets accomplishes removal of virtually all the remaining particulate including aerosols and soot. Table I shows that the gases leaving the venturi stage contain very little particulate or SO2 thus meeting stringent emission levels.
Following table shows an example of gas volumes, temperature, pressure drop and pollutants exiting each stage in the scrubber system.
|Gas Quantities and Pollutants through Successive VenturiPak Scrubber Stages|
|Gases exiting scub stage||Inlet Gas||Quench Section||Tray Sub-Cooling||Venturi Stage|
|∆p inches w.c.||-||3||5||20|
Note: Total ∆p for scrubber system is 29" w.c.
Particulate removals are based on EnviroCare operating data and established calculations.
Recent tests conducted on municipal sludge burning (either fluid bed or multiple hearth incinerator) with a VenturiPak scrubber showed heavy metal removals for As, Cd, Cr, Ni. and Pb of 99.8% or greater. Mercury removal was 93.2%, which indicated that very little elemental mercury was present. NOTICE: The scrubber will capture a high percentage of bound mercury, but will have little, if any affect on elemental mercury.