Predictability, guaranteed drying in a shorter period and fewer losses in difficult seasons. Agrovent is specialised in storage systems for agrarian products, and they have seen demand for their VaccTek technique for drying onions increase year after year.
Onions can be dried in two different ways. Firstly, by sucking outdoor air into storage and heating it so that more moisture can be absorbed. The air is subsequently taken out via the hatches after the onions have dried, this includes the energy put into it. A different manner is to circulate the air in storage through the crates with onions and condensing the moisture out of it on a cold surface, all without outside air. “Much heat is released when condensing moisture, the opposite of evaporating moisture, which costs energy. This heat is used by the cooling machine to heat up the circulating air. The energy is therefore not expelled out. This way we create a very dry air that also becomes warmer and warmer. The importance of drying onions well is becoming more clear every season. A wetter and warmer climate and the reduction of chemical means make it increasingly more difficult to store onions with the least amount of decay and loss possible,” says Huub Kasius of Agrovent.
Fewer losses and better quality
A major advantage of condensation drying compared to drying using heaters, is not being dependent on outside air, according to Huub. “The product always dries at the same speed, regardless of outdoor temperature or conditions of the outdoor air. Because of this, a well-designed condensation drying system dries twice as fast as an installation with large gas heaters. Additionally, the energy usage is 50 to 70 per cent lower, when drying up to 30 degrees, than drying with gas. Moreover, condensation drying results in a better quality product. Sharper onions with a better colour. The bad onions that are decaying shrivel up without contaminating the good ones. These can then be easily sorted out, resulting in fewer losses. For packers, who often only dry for a few days, there’s therefore also a productivity gain.” The installation was initially developed for organic onions, for which drying is even more important. The losses in storage have been reduced by dozens of percentages to amounts that are also common in conventional production. It has now been shown that condensation drying can be used cost-effectively for most box storages with mechanical cooling.
Although interest in condensation drying is increasing, the investment remains an obstacle in some cases. “The costs are twice as high compared to traditional installations,” Huub mentions. “But it can also be profitable. If only 20 per cent of onions in storage appear to be suitable for export, this could be the difference between being allowed and not being allowed to supply. However, it is not a one-to-one replacement of the heating technology with less energy costs. Fewer losses on average and better quality should be the most important reasons to invest.” Uncertainty also plays a major part. Particularly now that there are multiple suppliers. “Customers don’t know the technology well enough to estimate the value of the often very technical offers. There are many differences in the offered capacities and options.”
What is characteristic of Agrovent’s installation? Condensation drying is not a new technology, but Agrovent was the frontrunner in making it broadly applicable in the storage of potatoes and onions. Because of the VaccTek technology it becomes possible to dry onions regardless of the weather. Agrovent has much experience, not just with the technology, but also with the method. More than 30 installations have now been supplied, and this number will double in the coming year. “We’re the only system that works well in systems with a pallet blowing wall. VaccTek produces drying air in the pressure chamber instead of in the room, and is therefore independent of the fill rate and organisation of the room. Our capacity is higher than average, and with VaccTek’s concept you won’t need evaporators and liquid lines in the storage cell. Everything is happening cleanly and drily behind the pressure wall.”
Onion sorting and packing station Ajuin from Moerkapelle, the Netherlands, expanded its location with a new warehouse, good for the crate storage of 2,000 tonnes of onions, in the past year. The brothers Johan, Paul and Jan van der Spek chose the installation of three VaccTeks from Agrovent. Jan says they’re very pleased with the technology. “Our onions have never been this dry.” The VaccTek technology makes it possible for them to dry the onions regardless of the weather. “It’s definitely given us more certainty, and that’s resulted in quality preservation. Onions can now be dried quicker particularly during the harvest. In other years, planting onions sometimes came from the field when temperatures were 20 to 25 degrees Celsius and atmospheric humidity was 90 per cent. We can now dry much quicker and without gas,” Jan says. “We’re also doing more and more organic onions, so storage becomes even more important. We’ve already seen this technology limiting losses.” He says it’s an advantage that this is a completely integrated system. “We use very few coolants, and have maximum control of the product. Besides, we can use the heat of the condensation in its entirety. All released energy is used to heat the onions.”