Driving down the cost of grain drying

A new ‘closed loop’ grain drying system, using Bowman heat exchangers has significantly reduced energy costs and improved efficiency in Finland.

In what is believed to be a world first, a Bowman exhaust gas heat exchanger has helped a new ‘closed loop’ heat recovery system dramatically reduce the amount of energy used and emissions produced, during the grain drying process at a farm in Finland.

Drying is an essential part of the grain production process in Finland as it must be dried after harvesting to reduce its moisture content prior to storage. Large dryers blow hot air through the grain, usually via an oil or gas burner and the energy costs involved are significant and directly impact on food production costs.

During the drying process, warm air, which has passed through the grain, is exhausted to outside atmosphere, in a ‘total loss’ cycle. Typically this exhaust air still has a temperature of 35 °C, so a valuable energy source is lost. It takes up to 24 hours to achieve the required moisture level in a 30 ton batch of grain and as typical drying season can last for up to 2 months, the process can consume between 25,000 and 40,000 litres of oil, which is a significant part of the farms operating costs.

The new system works by recovering a large proportion of the warm exhaust air that is traditionally expelled from the farm’s grain dryer. Any contaminants and grain debris are removed prior to the ‘cleaned’ air being recirculated through the Bowman exhaust gas heat exchanger, where it is heated back up to 65 °C.

The CHP system has been set up to recover heat energy from half of the exhaust air that would normally go to atmosphere. In the first year of operation, it has reduced the farm’s fuel oil consumption by half, saving around 18,000 litres of fuel and halving its CO2 emissions!

The system is designed to operate with outside air temperatures between -5 °C to +30 °C – the typical outside air temperatures in the Nordic drying season – and can be easily retrofitted to existing grain drying systems, as well as new installations.