WET FLUE GAS DESULFURIZATION
Redwood technology wet air scrubber is a new generation of foam wet scrubbers which is able to use highly mineralized liquid with small impurities. The stable operation of the wet air scrubber even under harsh conditions has made it one of the best air scrubbing solutions available on the market. The wet air scrubber is able to work for extended periods of time using the recirculating cleaning liquid, therefore decreasing the liquid consumption up to 10 times compared to other foam wet scrubbers.
The cleaning liquid used in the scrubber does not have to undergo special treatments as small impurities, such as small rocks and sand, do not interfere with the wet air scrubber operation. It is possible to utilize previously used cleaning liquid thus achieving considerable savings.
The core technology behind the wet air scrubber is the self-cleaning grating made out of plastic (polypropylene) or stainless steel (for high-temperature applications >140°C). The grating doesn’t fray and prevents buildup even when highly mineralized liquid is used (up to 15.6 lb/cf).
The grating itself is composed of standard square-shaped elements. The size of the grating can be changed depending on the required system capacity. Structurally, the grating consists of divergent holes formed by vanes to provide a turbulent stabilization of the foam layer without external stabilizers. The wet air scrubber capacity varies from 600 cfm to 150,000 cfm. Several grating layers can be stacked above one another to achieve the required efficiency.
We have hands-on experience in using the wet air scrubber as a flue gas desulfurization system. We have retrofitted our wet air scrubber in place of an old WFGD foam scrubbers with a capacity of at 35,000 m3/h (20,500 cfm) an aluminum plant.
The highly mineralized liquid – up to 250 gram per liter (15.6 lb/cf) – used in the wet scrubbers caused frequent maintenance stops, as well as a drop in efficiency and the rise of the hydraulic gradient, due to the buildup that formed inside the scrubbers. We have retrofitted the old scrubbers with our wet air scrubber system.
In order to complete the task, we designed a project to replace the foam grating with the wet air scrubber grating. The design and calculation processes together took one month, and the calculated SO2 treatment quality satisfied our client.
The Scroiler system design inside the foam scrubber body (in mm)
Projected specifications
| Capacity | 35,000 m3/h | 20,500 cfm |
| Peak Capacity | 50,000 m3/h | 29,500 cfm |
| Working temperature | up to 130°C | up to 266°F |
| Inside overpressure | 4,000 Pa | 0.58 psi |
| Inside overpressure, max | 10,000 Pa | 1.45 psi |
| Reagent | Na2CO3 | |
| Treatment quality | more than 95.0% |
The manufacturing of the wet air scrubber with a polypropylene grating took 2 months. The installation process, which included cutting out the packed bed of the old foam scrubber and replacing it with a dispersive grating along with other elements, took 3 days. During the commissioning period of 2 weeks, it was shown that the measured treatment quality is higher than projected.
| Input temperature | 85°C | 185°F |
| Input pollutant concentration | 150±37 mg/m3 | |
| Normal contaminated air flow | 61,040 m3/h (N) | 35,930 cfm |
| Reagent consumption | 19.1 m3/h | 11.2 cfm |
| Output temperature | 37°C | 99°F |
| Pressure drop | 0.15 kPa | 0.02 psi |
| Output pollutant concentration | 5±1 mg/m3 | |
| SO2 treatment quality | 96.7% |
During the first year of continuous operation, the scrubber was stopped each month to check for the buildup that could have formed, however none of the checks revealed any clogging or buildup growing on the grid. The efficiency remained stable and did not decline depite the lack of grid cleaning that have become routine with the old packed bed scrubbers.
The polypropylene dispersive grating unit ready to be installed inside the retrofitted foam scrubber.
The wet air scrubber dispersive grating after one year of the continuous air treatment process. The gaps in the grating elements are clearly visible.