Ethylene removal Background
Ethylene removal by UV might seem like a strange title, but Ultra Violet Light is an effective method of controlling ethylene in fresh produce storage and processing facilities. Like other more traditional technologies like dry chemical scrubbing, the UV installation needs to be properly engineered and set up, but once in use the big benefit of using UV is its very low running costs.
The storage and processing of fruit and vegetables is a finely orchestrated battle against time. Most products do not linger in storage for long and in many processing facilities the time spent from ‘goods in’ to ‘goods out’ is measured in minutes, rather than hours. The investment in machinery to make this slick process so effective can not be jeopardized by anything that can have an adverse effect on the self life of the finished product. Competitive advantage is defined by freshness, speed from field to shop and shelf life.
Ethylene produced by the decomposition process in fruit and vegetables in turn stimulates decomposition in fresh produce, and it is vital that where unprocessed produce is held in storage ethylene is controlled, to ensure that the freshness is preserved and that waste from the process is minimised.
Ethylene removal the old way
Traditional ethylene removal often uses dry chemical scrubbers. These machines generally have a prefilter, a chemisorption bed and an after filter. These stages make for quite a high pressure drop for the onboard fan to overcome in order to move sufficient air through the machine. With any system using a fan, pressure drop has a direct effect on running cost related to electricity consumption. The power costs, replacement dry chemical media costs and the down time cost of changing the filters and media, make the overall running cost of the traditional scrubbers relatively high.
Ethylene removal the UV way
UV ethylene removal is totally different, and is ideally suited to the cool, humid environments typical of fresh produce storage. UV light at 187nm wave length is very effective at oxidising airborne chemical contaminants such as ethylene. The key is to ensure that there is the correct balance between the intensity and exposure of this wavelength UV and the volume flow of air being treated. 187nm is known as UVV light, and it has the characteristic of making oxygen react with chemical contaminants and in treating ethylene, it oxidises to produce carbon dioxide and water vapor.
C2H4 + O* CO2 +H2O
Using UVV for ethylene removal is easy and there are generally two methods.
Firstly the UV lamps can be incorporated into existing chillers or air handling units serving the room. In this method the spliced lamps are
arranged to bask the cooling coils in UV light, which not only ensures that ethylene that passes through the coils is oxidised, but also ensures that the UVC light which is germicidal, prevents any biomass slime forming on the coils.
The second method is to use a UV lamp array such as a Sanuvox Quattro or Biowall in a purpose-built scrubber. Unlike the dry chemical scrubber these units are quite lightweight and are usually assembled from standard ducting components and ancillaries. The UV lamps in this case will also be ‘spliced’ thereby combining the germicidal merits of UVC light and the ethylene oxidising property of UVV light. The scrubber complete with its own axial fan and inlet filter is usually suspended from the ceiling or can be mounted above the ceiling with just inlet and outlet grilles showing inside the room.
Because the upsizing of UV based ethylene removal systems is relatively cheap there is every reason to provide sufficient sizing for these systems for any given application from the start. In Contrast dry chemical scrubber systems are heavier and more expensive which creates the temptation to cut corners in design and sizing.
Ethylene removal by UV also has much lower associated pressure drop through the scrubber so that even when the power of the fan is combined with that of the lamp ballast the power consumption will typically be only 1/5th or 1/6th of that used by a chemical scrubber handling the same airflow.
Maintenance is an important consideration and although lamps will periodically require changing, it is a very easy, quick and clean procedure. UV based systems ensure that it is not just an ethylene removal system. The germicidal UVC part of the lamps will ensure that airborne spores bacteria and viruses are controlled as well – something that dry chemical scrubbers just don’t do.
Ethylene Removal with UV – Summary
UV based ethylene removal uses both UVV and UVC, which means that it not only removes ethylene but also controls airborne fungi mould and spores. This means that as well as the stimulant for ripening being controlled but also the biological contaminants associated with rotting are controlled. Ethylene removal with UV is;
- Very effective
- Clean – does not cause dust
- Low running cost
- Easily scalable
- Easily maintained
- Can be controlled by gas monitors
- Can be linked to BMS
- Is suited to humid environments
- Also controls biological contaminants
- Can be fitted within evaporator housings, or free hanging
For further help on ethylene control, call us – 01729 824108