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Digital Re-print - September | October 2011 Direct Cold Plasma: The innovative answer to odour control in the food and feed industry

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Increasingly, feed manufacturers are being required to address the issue of release of odour and harmful contaminants

into the surrounding community.

Local communities, special interest groups and government legislation all bring pressure to bear on factories to minimise real or perceived risks of contamination.

There are no universally applied standards for odour or Volatile Organic Compounds (VOC) emissions, and to provide solutions that fit specific factory needs can be com-plex. There is no single solution but under-standing the feed manufacturers problems certainly helps a great deal.

In recent years, there have been numer-ous changes regarding where production facilities are situated. Factory closures and relocation of manufacturing units has become commonplace.

At the same time urban sprawl has resulted in residential areas being built closer to previously remote industrial areas.

Another pressure companies face is meeting local environmental needs.

So what does the industry need from its odour abatement equipment? This is a complex question and the answer needs to include:• A compact design minimising space

requirements

• End of pipe solution• Low running cost• Minimal maintenance• Ability to operate at normal feed

manufacturing temperatures, to avoid cooling costs

• High odour removal efficiency• No chemical additions and need to

maintain chemistry• No liquid effluent waste• Instant on/off – no warm up time• Modular construction, ease of relocation

if change of production location and ease the ability to add on modules according to required capacity

• Competitive capital cost

This is a tall order but there is a technol-ogy can answer most of these needs: Cold Plasma.

A high tech, high voltage solution

In 2003 a global petfood manufacturer tested a new technology for odour removal, referred to as Direct Cold Plasma, on drier and extruder flash-off exhausts.

The technology had obvious advantages over more conventional solutions. As a result the petfood manufacturer looked for a suit-able technology partner for collaboration on the application of cold plasma on petfood applications.

In 2003 they formed such an agreement

with APP (Applied Plasma Physics AS). APP is both an R&D and equipment sup-

ply company, specialising in the application of high voltage technology and non-thermal plasma systems for industrial processes. APP has now delivered more than 200 systems, most running on difficult applications.

APP has experience on ultra high odour applications – where odour levels can be over 200,000 odour units per m³ - and the company achieved odour removal efficien-cies of up to 97 percent. Another advantage that is unique for this specific technology is that both odour and dust are removed from the production emissions.

Cold plasma technology – Nature in a box

Odour bearing gases enter the cold plasma module, where care is taken to dis-tribute gases evenly as it enters the reaction chamber. The reaction chamber comprises a cluster of hexagonal cells. Running centrally through each cell is a corona wire, which is isolated from the rest of the chamber.

The high voltage generator distributes a modulating high voltage supply to each corona wire, and this process results in a discharge between the corona wire and the cell wall.

The discharge promotes the emission with high-speed electrons, which collide with background gas molecules creating chemically active species known as radicals

Direct Cold Plasma: The innovative answer to odour control in the food and feed industry

by Havard vetrhus, Director Sales & Marketing, Applied Plasma Physics AS, Norway Tel: + 47 5160 2220, Email: havard.vetrhus@app.no

Grain&feed millinG technoloGy26 | September - october 2011

FEATURE

GFMT11.05.indd 26 04/10/2011 15:15

and charge carriers. This is actually identi-cal to what happens with pollution in the atmosphere. Reactions occur with the odour bearing compounds in the gas to be treated. Ambient air may be injected just prior to the reaction chamber to optimise humidity and temperature as well as adding ions to the gas stream.

In essence the cold plasma process encourages ‘oxidation’ of the odour bearing compounds at low temperature by creating discharge (cold plasma).

A closed-loop cooling unit ensures that operating conditions within the high voltage generator are maintained within controlled limits. A proprietary control system moni-tors the high voltage passed to each of the corona wires in the reaction chamber, and controls the voltage modulation that gener-ates the cold plasma.

The system also detects arcs between the corona wire and the cell wall, automatically shutting down electrical supply for a fraction of a second before power is reinstated.

The reaction chamber may be oper-ated with the gas flow passing upwards or downwards depending on site layout. The unit is capable of operating on emissions with relative humidity close to 100%, although the closer to 100% RH the unit operates, the higher the possibility of arcs and conse-quently risks of reduced efficiency.

The unit can be operated with emission temperatures up to 70°C.

In most cases in the feed industry, the emission tem-perature from dryers will be less than this temperature limi-tation.

Maintenance is minimal, if the unit is used as a dust collector as well as odour abatement system, then the unit would have a ‘wash-down’ maybe once per week and an internal inspection once a month would be recom-mended. Operating costs are very low and mostly associated with the cost of electricity; 10-20kW for a standard 20,000m³/h cold plasma unit.

A costing exercise produced by one of APP’s customers, is shown below. This is based on a 10-year period, including both investment and operating cost for a volume of 20,000m³/h. The operating costs for the scrubber alone or scrubber biofilter do not include cost of water.

Testing in the petfood and fish feed industries

Since 2003, extensive testing with a pilot system both on extrusion flash-off, driers and coolers has been carried out. All possible variables have been reviewed to determine the optimum operating conditions for the cold plasma system.

Variables tested:• Residence time (determines volume to

be handled by a standard module)• 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 1600m³/h and tests were repeated to check validity. Independent Olfactometry testing was used as a means of determining odour reduction efficiency.

Test results indicate that odour removal efficiencies of up to 90 percent are achiev-able within the food and feed industry and that the standard colds plasma module will handle around 20.000Am³/h.

Higher efficiencies may be achieved by using a final polishing module. During testing, both high and low odour concentrations were experienced; nonetheless cold plasma achieved real odour reductions even on very low inlet concentrations, something that is not always the case on alternative technologies.

Overall the tests indicated that the cold plasma unit operated most effectively with-out a scrubber either at the inlet or outlet. Dust removal was very effective (99% reduc-tion).

As a result of these tests, several petfood sites have now installed cold plasma technol-ogy for their processes. As per today, 50 units are in operation in the petfood industry, a figure that will increase substantially in the years to come.

The experience of the environmen-tal needs of the feed industry, and APP’s approach to innovative design is combined to offer a competitive alternative solution to a problem that is of increasing significance to the food and feed industry.

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Grain&feed millinG technoloGy September - october 2011 | 27

FEATURE

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GFMT11.05.indd 2 04/10/2011 15:14

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A subscription magazine for the global flour & feed milling industries - first published in 1891

In this issue:

• Sample preparation of feeds and forage for NIR analysis

• 15-Year Celebration: Fortifying with folic acid prevents 22,000 birth defects annually

• Global Feed Markets:Wheat supply grows and grows as corn crop shrinks

October 2011

• Producing Flaked breakfast Cereals

• Direct Cold Plasma: The innovative answer to odour control in the food and feed industry

• Milling Technology Redefined

GFMT11.05.indd 1 04/10/2011 15:14

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