Tray Towers

Tray tower gas scrubber systems for industrial air pollution control

Tray towers are used for cleaning gas flows contaminated with both particulate and soluble noxious gases, providing combined particulate and gas‑phase scrubbing in a single vessel. Their unique design enables them to capture particulate larger than 2 microns as well as soluble gases at high removal efficiencies, and ERG designs each tray scrubber to meet the specific application and detailed process requirements.

Key advantages of tray scrubbing

Key advantages of tray scrubbing are:

Multiple tray stages of scrubbing give excellent efficiencies of removal.
Highly effective at treating large gas flows at comparatively low capital cost.
Running costs are relatively low due to the low gas‑side pressure drop and the low liquor rates required.
Trays are self‑cleaning, reliable and robust in continuous industrial service.
Tray types such as fixed‑valve designs can be matched to suit the application.
Tray weir height can be adjusted to give enhanced capture of contamination and greater turndown if this is required.

Tray towers are therefore well suited to industrial air pollution control systems where both particulate and soluble contaminants need to be removed in a compact, high‑throughput gas cleaning system.

Design parameters

Typical design parameters for ERG tray tower scrubbers are:

Flowrates from 2,000 to 100,000 m³/hr per tower; multiple cylindrical towers in parallel or rectangular cross‑section vessels can be used for higher flowrates.
Removal of any soluble gaseous contaminant and soluble or insoluble particulate larger than 2 microns.
Gaseous contaminant loadings typically from 100 to 10,000 mg/m³; particulate loadings typically up to 5,000 mg/m³.
Removal efficiencies typically 90–95% and up to 99% as required.
Vessel diameters from 600 to 3,800 mm; vessel heights typically up to 12 m.

These design ranges allow tray towers to be integrated into a wide variety of industrial emissions control and gas cleaning applications.

Key features and system integration

ERG supplies complete tray tower systems including recirculation pumps, pipework, fans, ductwork, access platforms, instrumentation and control system. They can also be integrated with other ERG mass and heat transfer equipment (e.g. quench, venturi scrubber, packed tower scrubber, carbon filter, etc.) into a single air pollution control solution.

Key features include:

Tray options including simple perforated plates and impaction valve designs.
Adjustable weirs providing variable pressure drop and stage efficiency; under‑tray sprays to improve resistance to fouling.
Recirculated liquor flowrate selected to minimise pump flow and energy consumption at optimal scrubbing performance.
Droplet elimination using chevron, impaction blade or woven mesh designs to suit the application – clean‑in‑place sprays available to assist with on‑line maintenance.
Scrubber sump tank integrated into the vessel – cone and sloping‑base designs available to improve maintainability in solid‑laden applications.
Chemical dosing, water make‑up and blowdown control matched to the performance requirements.
Side‑stream settler and dewatering of captured solids available if required.
Instrumentation selection to give robust operation, high reliability and tight performance control.
System control by stand‑alone MCC/C&I panel or integrated DCS, with HART or Profibus protocols available as standard.

Vessels are designed as standard to PD 5500 (metal) and BS EN 13121 or BS 4994 (plastic/GRP), with CE marking to the Pressure Equipment Directive as appropriate. Other design codes are available as required. Materials selection is made to suit contaminants and reaction chemistry; common materials include uPVC, PP, cPVC, Derakane GRP, Crystic GRP, 304SS and 316SS.

Principle of operation

The gas to be treated flows upwards through each tray stage, passing through the orifices on each tray plate and then as bubbles through the scrubbing liquor on top of each tray. The scrubbing liquid flows across each tray, over the weir and down the downcomer to the tray stage below.

For high‑efficiency scrubbing, additional tray stages are added to increase gas–liquid contact and mass transfer. Access for maintenance and cleaning is provided between each tray stage. An indicative diagram of a tray scrubber can be retained on the page, and further information is available in the product brochure.

Tray selection and materials

The materials of construction and tray design are matched to each application, taking into account gas composition, scrubbing chemistry and solids loading. It is typical, for example, to use stainless steel trays with plastic or GRP vessels to give additional robustness and maintainability in demanding air pollution control duties.