Optromix Company presents the new type of wet scrubber – the Scroiler™. The Scroiler™ can be used to remove dangerous gases, particulate matter, vapors and other contaminants from the air to meet EPA and OSHA requirements. The difference of the Scroiler™ is that it uses up to 10 times less cleaning liquid than a typical wet scrubber and it has no scale up issues. This water- and reagent-saving device has found wide applications in wet flue gas desulfurization (WFGD).

The Scroiler™ - Introduction

Figure 1. The polypropylene dispersive grating unit ready to be installed inside the retrofitted foam scrubber.

The Scroiler™ is a new generation of foam wet scrubbers that has a very stable operation in harsh environments using cleaning liquid with high mineralization and high impurities content. The Scroiler™ can work for extended periods of time using the recirculating cleaning liquid. The Scroiler™ decreases liquid consumption up to 10 times compared to a typical foam wet scrubber.

The cleaning liquid does not require a special treatment and may contain solids (e.g. sand, small rocks) and other contaminants. For this reason the cleaning liquid may be used after other process cycles, thus achieving considerable savings.

The self-cleaning grating is the Scroiler™’s core patented technology. It is usually made of plastic (polypropylene) or stainless steel (for high temperature applications >140°C). This grating does not fray and does not grow scaling, even when using cleaning liquid with mineralization of up to 250 gram per liter (15.6 lb/cf)

The self-cleaning grating is assembled from the standard square-shaped elements. The grating size is determined by 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 Scroiler™ capacity may vary from 1,000 m3/h to 100,000 m3/h (600 cfm to 150,000 cfm). It is possible to place several grating layers one above another in the Scroiler™ system to achieve the required efficiency.

FGD Application in Aluminum Production

The Scroiler™ system was applied to retrofit existing WFGD foam scrubbers at the Krasnoyarsk Aluminum Plant (East Siberia, Russia) owned by the RUSAL Corporation. The foam scrubbers capacity was 35,000 m3/h (20,500 cfm) each.

The Aluminium plant uses recirculating cleaning liquid from other technological processes with the mineralization of up to 250 gram per liter (15.6 lb/cf). That mineralized liquid caused the regular rescaling of the foam scrubbers. Every month the foam scrubber had to be stopped for service due to efficiency decreasing and hydraulic gradient rising. The client did not consider to dismantle the old scrubber. Thus we decide to retrofit it with scroiler system.

Figure 2. The Scroiler system design inside the foam scrubber body (in mm)

We designed the project to replace the foam grating with the Scroiler grating. The design and calculations took 1 month. The calculated SO2 treatment quality satisfied the client.

Projected retrofit 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 Scroiler system took 2 month. The dispersive grating was made of polypropylene. The packed bed of the foam scrubber was cut out and the dispersive grating with the other Scroiler elements were installed instead. The installation was performed in 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%

The new Scroiler system was put to the test considering dispersive grating self-cleaning properties. During the testing period the Scroiler device was in process continuously. Once per month the Scroiler was stopped to measure the scaling inside the reaction chamber. The result was constant from month to month during the whole year: there were no significant scaling to rise the hydraulic gradient and to decrease the efficiency. The efficiency were remaining exactly the same during the whole period.

Figure 3. The Scroiler dispersive grating after one year of the continuous air treatment process. The gaps in the grating elements are clearly visible.

After the testing period the Scroiler system retrofitted to the old foam scrubber continues to work for half a year already without service downtimes. The Aluminium Plant retrofitted all the foam scrubbers by the Scroilers. Now RUSAL Corporation ask Optromix to retrofit foam scrubbers at the other Aluminium Plant to perform WFGD.

This example demonstrates the Scroiler self-cleaning properties that prevents scaling in heavily mineralized media. Optromix has other Scroiler WFGD installations which shows that these properties are not subjected by the reagent formula and is suitable for the gypsum production. The Scroiler can be installed to perform WFGD process at coal power plants, aluminum and iron production.