GRP Scrubber: The Optimal Choice For Waste Gas Treatment

As industrial waste gas emission standards continue to tighten, the use of wet scrubbing technology to control acidic gases (such as HCl, SO₂, HF) and soluble organic matter is rapidly increasing. GRP scrubbers (fiberglass reinforced plastic scrubbing towers), with their integrally molded corrosion-resistant shells and flexible internal configurations, are gradually replacing rubber-lined carbon steel or stainless steel towers in the field of small to medium volume exhaust gas purification.

The key to the suitability of GRP (glass fiber reinforced plastic) for scrubbing towers lies in the fact that its resin matrix can be adjusted according to the gas phase composition. For example, when treating exhaust gases containing hydrogen fluoride, phenolic vinyl ester resin should be selected; while for alkaline scrubbing conditions, isophthalic unsaturated polyester provides sufficient alkali resistance. Unlike metal towers, the GRP scrubber's cylinder is manufactured using a winding process, where continuous glass fibers and resin are cross-laid at calculated helix and circumferential angles-this process produces an axial to circumferential strength ratio that precisely matches the negative or positive pressure load inside the tower.

The internal structure of the tower is generally divided into three sections: the lower air inlet scrubbing zone, the middle packing mass transfer zone, and the upper demisting and emission zone. Among these, the material selection for the packing support plate and spray pipe bracket is most easily overlooked: if 304 stainless steel bolts are used to fix the PP support grid, "galvanically accelerated corrosion" will occur at the gaps when the Cl⁻ concentration is higher than 200ppm and the pH fluctuates. A more prudent approach is to use the same grade of GRP pultruded profiles or CPVC material for all internal components (including pressure grids and liquid redistributors).

Acid effluent systems in the semiconductor industry are a frequent application scenario for GRP scrubbers. The mixed exhaust gas (HF + HNO₃ + acetic acid) emitted from etching and cleaning processes is almost ineffective against metals-even Hastelloy alloys struggle to withstand the coexistence of 65% nitric acid and hydrofluoric acid. However, a GRP tower body made of bisphenol A epoxy vinyl ester resin, combined with a two-stage process of pre-washing + packing absorption, can stably control total fluoride emissions below 5mg/m³.

Another typical application is in wastewater treatment plant deodorization systems: malodorous substances such as H₂S and methanethiol are absorbed through alkaline washing followed by sodium hypochlorite oxidation. GRP towers can last 12-15 years in such high-humidity and salt-spray environments, far exceeding the 5-8 years of coated carbon steel towers.

During long-term operation, three indicators need to be monitored: tower pressure drop, spray nozzle flow rate, and circulating liquid pH trend. A pressure drop increasing from the initial 600 Pa to 1200 Pa usually indicates packing blockage-for dusty exhaust gases (such as incinerator tail gas), a dry pre-filter or cyclone plate tower can be added upstream of the GRP scrubber. Nozzle blockage is mostly caused by crystallization salt precipitation: the solution is to add a scale inhibitor (concentration 50-100 ppm) to the circulating liquid or periodically backflushing with low-pressure steam.

In terms of economics, although the initial purchase price of a GRP scrubber is about 20% to 30% higher than that of a PP scrubber (due to mold amortization and resin costs), considering that PP softens above 60°C and is sensitive to ultraviolet light, while GRP can withstand 80°C (up to 120°C with special resins) and does not require an additional steel frame anti-corrosion coating, its total life cycle cost is usually more advantageous. For applications requiring the handling of halogenated or strongly oxidizing gases (such as ozone and chlorine), GRP is almost the only reasonable choice.