Grain storage: Insulating main air duct slashes fuel bill

Better insulation of grain store air tunnels can help counter rocketing drying costs, says a Wiltshire farmer.

Alastair Fitzgerald is convinced that spraying urethane foam on the inside of the central air tunnel of his 2000t floor store at Red House Farm, Swallowcliffe has cut his harvest fuel bill.

The move stops his gas burner heat being wasted when the store, divided in two by a Harvest Installations tunnel, is only part-full.

“It’s quite hard to calculate, but in our previous wet harvest four years ago we spent £12,000 on gas. This year taking out an average of 6% moisture from our barley and 11% in the wheat we dried 2000t using 20,000 litres of gas.”

Even allowing for the fact that his gas was bought well, at 40p/litre, this season’s £8000 outlay represents a significant saving. He attributes this mainly to ensuring that heat from the drying fan was used more efficiently because of the newly-insulated steel tunnel.

The 400ha (1000-acre) mainly sandland farm grows winter wheat and oilseed rape plus spring malting barley.

Last year, when drying the rape, which occupied only part of one half of the store, Mr Fitzgerald and his sole staff member, James Preistner, realised the system was shedding heat, partly through leaks, but mainly by radiation.

“The tunnel is 120ft long, 9ft high and 3ft wide, but it was three-quarters exposed. With the fan running it was acting like the biggest radiator in the world. We did some experiments with thermometers and found the temperature of the walls was 50-60C.”

This harvest, after a 30mm (1.2in) layer of urethane foam was sprayed on its inside surfaces – apart from where the lateral ducts exit – the outside remained quite cool, says Mr Fitzgerald. “We had 800-900t of barley on one side, and the other uncovered side felt just the same temperature as the ambient air.”

The foam treatment by Renotherm, cost about £4000 and should last indefinitely.

Alastair-Fitzgerld-2

A urethane coat on the inside of Alastair Fitzgerald’s drying tunnel stops it acting as a radiator and wastefully heating store air instead of grain.

The insulation is the latest step in Mr Fitzgerald’s quest for a drying system that fully accommodates his harvesting equipment, a Case IH 8010 Axial-Flow 30ft cut combine.

“I want something that allows me to harvest as I like, when I like, at what moisture I like and with minimal staff.”

His aim is to avoid having heaps of wet grain lying outside vulnerable to the weather and risking quality loss. “That’s something that occurred all too often this summer on many farms.”

An early adopter of grain stirrers he has since modified and improved the way they are managed.

First he raised their drive system to allow grain to be stored more deeply and maximise the building’s capacity.

More recently, after many stirrers broke when they couldn’t cope with the strain of moving through extra wet grain in the harvest of four years ago, he installed a speed controller.

“We’ve fitted an electrical inverter, which can be adjusted to run the main motor at anything from the normal 50 cycles/sec down to 30.”

This, via gearing, allows the speed of the gantry carrying the stirrers to be set to avoid damaging drag, he says.

Given the rapid hike in diesel prices, gas remains relatively cheap and the farm’s drying costs are now comparable with the largest continuous flow driers, Mr Fitzgerald maintains.

“The calorific value of gas is slightly less than diesel’s, but that’s pretty well offset because the burners are more efficient.

“With our barley I estimate we used 1.5 litres/t for each 1% moisture, which I’m told is about the same as for a 150t/hr continuous flow machine. With the wetter wheat it was probably nearer 2.25 litres/t for each 1%.

“One thing people often forget is that if you have grain at 20% moisture you can easily take out 2% just by blowing with cold air.”

Provided even the wettest grain is blown and stirred continuously it will not deteriorate, he maintains.