Our Cross-Flow (HRP) Scrubbers offer combined flexibility for efficient removal of gas, liquid and solid contaminants from exhaust air steams. Contaminated air moves horizontally through a packed bed and is irrigated by the scrubbing liquid, which flows vertically down through the packing. Low liquid irrigation rates, high volume airflow and low-pressure drop characterize the cross-flow scrubber design. Scrubbers assembled in our factory are available in 2,000 to 100,000 CFM capacities.
The cross-flow packed scrubber is the most versatile of all the wet packed scrubber types. The units capabilities include the removal of the following either individually or in various combinations.
1. Soluble gases
2. Liquid particulate
3. Solid particulate (up to 1.0 grains/cu. Ft)
4. Odor removal
Industries presently using cross-flow scrubbers include: metalworking, chemical processing, metals finishing, sewage treatment, pulp and paper, fertilizer, rendering and aluminum reduction.
• SCRUBBING LIQUID
Liquid flow rates of each scrubber are based on specific operating conditions. The scrubbing liquid is usually recirculated, thus reducing both fresh make-up liquid consumption and the overflow effluent from the scrubber. A small amount of fresh makeup liquid usually fed continuously to the scrubber. The fresh liquid keeps the absorbed gaseous pollutant concentration in the recycled liquid at a sufficiently low level to maintain absorption efficiency. Fresh makeup liquid is also required to balance evaporation losses. Fresh makeup liquid can be either fresh water, relatively clean process water, or chemically treated water. Water treated with chemicals such as caustic soda, lime or soda ash is used only when fresh water or process water will not achieve the desired collection efficiency, or when treated water suits the waste treatment criteria of the specific plant.
• ENTRAINMENT SEPARATION
The HRP packed scrubbers normally contain a liquid entrainment separator following the irrigated section of packing. This entrainment section may be either an integral part of a single packed bed of set apart as a separator section within the common shell. When entrainment removal is to be accomplished as part of the single bed, a section of packing is left unirrigated.
The packed entrainment separator will give 99+ % collection efficiency of the entrained liquid particles. Other entrainment separators may also be used depending on the specific application.
• PACKING SUPPORT PLATE
Packing support plate design is critical; since support plates must have a large open area to permit maximum gas or liquid flow, but have small enough openings to retain the packing.
The plugging potential of a cross-flow packed scrubber is a direct function of the net cross-sectional open area at the front packing support plate. The larger net cross-sectional open area achieved in our scrubbers greatly reduces the plugging potential.
• DESIGN CONSIDERATIONS
Regardless of the packing type or depth selected, a scrubber can only provide maximum performance if the shell is properly designed. The shell design for our HRP Scrubbers includes the following factors:
A. The wall thickness of both the sides and bottom must be adequate to take stresses caused by the static pressure developed by the fan.
B. Maximum corrosion resistance for both the interior and exterior surfaces is provided to assure long service life and low maintenance costs.
C. Access manholes, nozzles and internal supports attached to the shell are designed to withstand all expected stresses, and to assure the same corrosion resistance as the shell.
Often, the shell is designed with additional space for a future increase in packing depth. This minimize the initial investment, while permitting an increase in scrubber efficiency at the lowest possible cost if future air pollution control regulations require greater scrubbing
► Construction Materials
The shells and structural components of our cross-flow scrubbers are usually fabricated from fiberglass reinforced plastic (FRP). FRP is available in a number of different chemically resistant formulas, and can handle most Air Pollution Control environments. All FRP fabrications meet the Product Standard for Custom Contact-Molded Reinforced Polyester Chemical Resistant Process Equipment (PS 15-69) as established by the National Bureau of Standards.
Our HRP scrubber usually contains an integral sump. This reduces the floor area required for the scrubber, as well as the scrubber’s initial cost. The sump will normally provide a two or three minute supply of recirculating liquid. This assures good mixing and keeps the solution constantly agitated to hold insoluble in suspension. The suspended insoluble can then be carried out through the overflow piping. Use of the lower scrubber shell as an integral sump gives a completely unitized, corrosion-resistant scrubber at minimum cost.
► Liquid Distribution System
The liquid distribution system for Hexagon HRP Scrubbers is designed to make maximum use of the scrubbing liquid and achieve optimum scrubbing efficiency. To realize the best possible scrubbing liquid distribution, spray header assembles with low pressure, large orifice; non-plugging spray nozzles are used for most applications. Most plastic packaging requires uniform initial liquid distribution to achieve the expected scrubbing efficiency. Therefore, liquid distribution by weirs is usually not recommended. The droplets formed by the liquid distributor spray nozzles also add absorption capacity. All header piping and spray nozzles can be easily inspected, and removed for maintenance or cleaning if necessary.
► Component Parts
The design and integration of various component parts within or on the scrubber shell affect the cost of installation, operation, and maintenance for the scrubber. Component parts in a horizontal packed scrubber include access doors, piping connections, drains, overflow nozzles, lifting lugs, hold-down lugs, and internal structural supports.
While some component parts are optional accessory equipment, the engineering of each component part must be carefully evaluated for its effect on scrubber location, installation, operation, and maintenance.
Access doors are positioned and sized to allow inspection or possible removal of the packing, plus inspection and cleaning of the liquid distribution system. Access to the sump and entrainment separator sections ate also provided when necessary.
Piping connections for the liquid distribution system are sized to handle the maximum recommended flow with minimum head loss. The pump connection is sized and positioned to minimize head loss and maximize recirculation efficiency. The makeup nozzle is large enough to handle the recommended makeup rate, and to quickly fill the system when necessary.
The integral sump drain in a Hexagon Scrubber will completely empty the sump if prolonged shutdown is required.
All internal structural supports are completely corrosion-resistant and strong enough to support the scrubber at maximum operating weight. In addition, they are located to minimize turbulence, pressure drop, and channeling.
Other components, such as lifting lugs and hold down lugs, are optional. Their construction and location depend on the physical requirements of the specific system.
► Recirculating Piping
Recirculation piping for Hexagon Scrubbers is custom designed to suit each application. Piping is provided in PVC, polypropylene, FRP, or other corrosion-resistant material to fit the specific corrosive service. When beneficial for the specific application, the recirculation piping system includes line strainers, throttling valves, shutoff valves, and pressure gauges.
Hexagon’s FRP Scrubbers, containing Packing s packaging, are mush lighter than lined-steel scrubbers or those containing metal or ceramic packaging. Hexagon scrubbers can usually be installed on an existing roof, balcony, or mezzanine without added structural support. The scrubber, fan, and recirculating pump can also be mounted as a single unit, thus simplifying job site installation.
Fans for the scrubbing system can be located either before or after the scrubber, as determined by the specific application. The fan can be integrally mounted on the scrubber, separately mounted near the scrubber, or separately mounted some distance from the scrubber. Space limitation is a major factor in determining fan location.
Specially designed scrubbers are available for unusual locations that will not accept standard scrubbers.
Hexagon has qualified field installation crews available, and can therefore offer unit responsibility for a complete air pollution control system, including design, fabrication, installation, and final testing.