Cold Plasma: High-tech answer to odor

by World Grain Staff
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by Håvard Vetrhus

The need for feed manufacturers to address the issue of odor and other emissions into the surrounding area has become pressing.

There are no universally applied standards for odor or volatile organic compound (VOC) emissions. Finding solutions that fit specific factory needs can be complex, but the answer needs to include: compact design that minimizes space requirements; end-of-pipe solutions; low running costs; minimal maintenance; an ability to operate at normal feed manufacturing temperatures in order to avoid cooling costs; high odor removal efficiency; no chemical additions; no liquid effluent waste; instant on/off – no warm up time; modular construction, ease of relocation in the event of a change of production location and the ability to add on modules according to required capacity, and of course, competitive capital cost.

This is a tall order, but a new technology has been developed that can answer most of these needs: cold plasma.

In 2003, a major petfood manufacturer tested new technology for odor removal on drier and extruder flash-off exhausts. The technology had obvious advantages compared with more conventional solutions and as a result, the manufacturer looked for a suitable technology partner with whom to collaborate in developing its "cold plasma" technology application.

In 2003, an agreement was formed with APP (Applied Plasma Physics ASA), a research and development and equipment supply company, specializing in the application of high voltage technology for industrial processes. APP has over 50 reference plants, most running on difficult applications, a record of experience on ultra high odor applications — where odor levels can be more than 100,000 odor units per m³ — and has achieved odor removal efficiencies of up to 96%.

During 2002 and 2003, extensive testing with a pilot system on extrusion Here, five reaction chambers are installed in parallel, to handle up to 100,000 m³/hr. Untreated emission enters the reaction chambers from the lower duct and escapes vertically through the upper duct. Closing valves on the inlet- and outlet duct can isolate each reaction chamber. flash-off, driers and coolers was carried out. All possible variables were reviewed to determine the optimum operating conditions for the cold plasma system:

Residence time;

Effects of water scrubber at inlet or outlet of cold plasma;

Cold plasma unit operating alone;

Adding water to humidify inlet or outlet gas;

Air infiltration volume (ion enrichment);

Intensity of cold plasma generation;

Geometry and arrangement of reaction cells.

The pilot plant (test unit) is designed to handle 1,600 cubic meters per hour (m³/hr) and tests were repeated to check validity. Independent olfactometry testing was used as a means of determining odor reduction efficiency.

Test results indicate that odor removal efficiencies of up to 90% are achievable within the food and feed industry and that the standard cold plasma module will handle around 20,000 actual cubic meters per hour (Am³/hr). Higher efficiencies may be achieved by using a final polishing module. During testing, both high and low odor concentrations were experienced; nonetheless cold plasma achieved real odor reductions even on very low inlet conditions.

Overall the tests indicated that the cold plasma unit operated most effectively without a scrubber either at the inlet or outlet. Dust removal was very effective.

As a result of these tests, several sites have now selected and ordered cold plasma technology for their processes. WG

Håvard Vetrhus is director of sales and marketing for Applied Plasma Physics ASA. He may be contacted at: Havard @ appliedplasma . com