Watch out when going vertical
FARMS relying on vertical aeration systems for drying should take care, warns ADAS.
An HGCA-funded project suggests they are more suited to simple cooling, says senior consultant David Bartlett.
"From an engineering point of view I have always been very sceptical about the ability of these systems to dry grain."
Air distribution from vertical columns varies, with high flows near the ventilator and fairly low movement further away.
"It is very difficult to predict their performance and growers should be careful if they are planning to dry with them," says Dr Bartlett.
"These systems have become increasingly popular. They are less expensive than alternatives and can be used in buildings not originally designed for grain storage.
"There have been reports of growers using columns too far apart and running into problems. Our aim is to produce a user guide based on science rather than hear-say."
During harvest 2000, farm stores across the country were monitored. Ventilators and temperature probes were installed, and a range of bulk sizes, storage periods and moisture contents in wheat and barley were assessed.
Temperature, airflow, static pressure and moisture were all recorded.
"On one site where air was sucked down into the heap we recorded a maximum 0.8% reduction in moisture in the top layer of grain and 0.5% in the bottom. But in general, grain got wetter at the bottom and drier at the top, suggesting moisture was being moved about.
"If you do not have a substantial airflow, you cant transfer moisture out of the heap. Airflows are quite low when drying in bulk on-floor. These systems can only be effective for drying if the number of pedestals is increased quite considerably."
Cooling results were more encouraging, and Dr Bartlett hopes to have suitable guidelines available by the end of August.
"Our next stage is to take this information, construct a computer model and test the spacings to see how far apart you can go while still achieving suitable cooling."
"It is perfectly feasible to dry using our equipment, but it takes careful management," says Martin Lishman, supplier of some of the systems used in the project.
"We have been able to dry from 20% down to 15%." But factors such as depth of grain, size of building and the use of heaters all need taking into account, he explains. *
• One-year £79,000 HGCA project.
• ADAS, CSL, SRI joint venture.
• Good cooling but drying queries.
• End August guidelines target.