Photo 1: Heat treatment with electrical heaters
HEAT TREATMENT: precision fumigation with benefits by Vasilis Sotiroudas, Food Scientist, Heat Treatment specialist, Agrospecom, Greece
Use of Methyl Bromide (MeBr) has been banned in most developed countries since 2007. From January 1, 2015, it is not available anywhere as a fumigant for flourmills and other industries. Several fumigation alternatives have been tried around the world with
heat treatment being one of them. But how good are these compared to good old MeBr? Can such alternatives be used for precise fumigation, i.e. a tightly controlled and monitored fumigation process?
ethyl Bromide has been a good fumigant, but not excellent since the main disadvantage of gas fumigants is that they need airtight buildings. And in the real world, very few buildings are made airtight or can become airtight with proper sealing work. The majority of buildings will never hold the gas, especially on a windy day or when there are significant temperature differences between day and night.
The heat advantage
Heat treatment has been practiced worldwide for a few years and is by now deemed a very effective replacement of MeBr for structural fumigation. Insects die at temperatures above 50oC because the proteins in their bodies coagulate, their salt equilibrium becomes damaged and they dry out. All insect stages
46 | Milling and Grain
are affected and no resistance to heat has been observed in the lab or in the field. Electricity, gas, petrol and steam can be used to generate heat for insect extermination. In our work, we have found out that each type of heater has its plusses and minuses. Electrical heaters (Photo one) are easy to use, easy to handle and efficient; but they cannot be used to treat an empty concrete silo (you need a gas heater for that, with a long ductwork). Gas heaters (Photo two) need to be placed outside the building, so for high buildings you may need to lift heaters by crane to the top floor. In most of the cases, the use of special air ducts through available shafts enables us to treat several floors and sections of a mill at the same time (Photo three). In comparing recycling of air (electrical heaters placed inside the building) with introduction of new air (gas heaters placed outside), we found out that the increase of pressure in the latter case helps the hot air to enter cracks and crevices. In practice, the merits of electrical and gas heaters can be combined, using both types to treat large mills with speed and efficiency.
No sealing required
A main operational advantage of heat is that it does not need any sealing at all. In fact, when new hot air is introduced in a building we need to leave a top floor window partly open to avoid the increase of internal pressure.
Heat treatment is fast
Proper cleaning of the mill area to be treated is needed, but since no sealing is required preparation time is minimal. With the right equipment, an experienced team will need slightly more than 24 hours to treat a building. In Diagram one, temperatures are plotted from various sensors inside a mill during a heat treatment; as can be seen, lethal temperature levels are reached in