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Bought for their easy installation, relatively low cost and ease of use, portable batch driers can provide a quick-fix for a shortfall in drying capacity.

They come on wheels but are rarely moved about. But portable batch driers save a packet on installation and support equipment costs compared with the needs of a fully installed continuous flow drier, and have other advantages to boot.

One of which is the seemingly simplistic principle that loading is performed from ground level while discharge comes from on high - the opposite to a continuous flow system. As a result, trailers can tip directly on the intake auger - or a loading bucket can be used to fill from the top - and, when dried, grain can be discharged by gravity to a trailer or into storage alongside.

The key is performance matching - to ensure that any handling equipment to get the machine quickly emptied and filled again, and drying of the next batch under way with the minimum of delay. It is the only way to extract the full performance potential of such a machine.

The lack of a supporting cast of augers, elevators and bins is a feature that goes down well with Graham Fenton of J Fenton & Sons.

"We don't have any conveyors or bins - we just put the grain into the hopper with a tractor bucket, then it is loaded into the lorries and everything goes back into the shed again", he says.

The farm has been a committed batch drier user since the wet harvest of 1985. The OPICO automatic 5000, now in its sixth season, has a holding capacity of 12t and a maximum throughput of 150t in 24 hours.

Work rate obviously varies according to how much moisture is being extracted and , in a very wet season it can struggle to cope.

"Last year some crops were going into the drier at 20% to 30% moisture and sometimes we fall a bit behind with the wheat," says Mr Fenton. "But it doesn't matter because wheat can sit in the shed for a week, it doesn't go off. We just keep drying away and eventually get through it without any bother."

Economics are also favourable, he maintains.

"The capital cost of the machine was written off in the first three years, repairs and maintenance have been minimal, and last year we put through 2,800t at a cost of £2.66/t for gas to fuel the burner." Mr Fenton explains. "It 's been a good investment and it's simple to run."

Management of the drying process is straightforward - particularly with an automatic control system fitted. OPICO's GT driers, for example, are calibrated by drying, say, wheat to the required moisture content, noting the grain temperature reached at the point that has been achieved, and using this as the reference for future batches of the same crop.

Wet grain brought off a headland will take longer to reach the reference temperature while that from within the field will reach it more quickly. Either way, grain is simply circulated through the drier, perhaps once every six or seven minutes, until the required grain temperature ( and therefore moisture content) has been reached.

This continuous recirculation of grain has the added benefit - assuming a cleaning screen is fitted - of improving the quality of the sample. Chaff and other light material tends to be blown off the top as, on an upright type drier, grain is discharged from the central high capacity auger into the drying chamber that surrounds it.

"It can turn a mediocre sample into a saleable one," says Robin Jibson of Mile Farm, Pocklington, York. "It polishes the grain very nicely."

Mr Jibson purchased an OPICO 580S drier in 1988 mainly as back-up for a 400t in-bin drying system.

"We stopped combining because of bad weather and realised that we weren't making very good progress with the drying either," he recalls. "If it's not a good combining day it's not a good drying day either for our in-bin system."

The batch drier, with a holding capacity of 12t and maximum throughput of 6t/hour, is loaded by forklift from a heap on the floor, and unloads dry grain into a trailer positioned alongside.

Production last year amounted to about 1,500t of grain and the drier is worked for typically between 150 and 350 hours depending on the season.

With strong demand for second hand machines Mr Jibson's drier was sold earlier this year and an OPICO 600QF, of slightly higher capacity, automatic operation (including loading and discharge) and quieter in operation, now sits ready for harvest 2001.

"We are just on the edge of a village and noise has always been an issue, so we're hoping the quieter fan on this new model will help us keep the peace." says Mr Jibson.

In weighing up the seemingly modest capacities of these batch drying machines, bear on mind that the drier does not have to match combine capacity tonne for tonne. Even the most versatile combine can rarely work around the clock and catchy seasons prevent seven days a week operation. But a drier can do both; and, besides, for most growers, not all grain needs drying.

OPICO says the capacity calculation should be based on the total tonnage harvested divided by the typical number of days involved in the harvest campaign.

On this basis a 4 to 6t/hour drier should happily partner a 20t/hour combine simply because it can be used all day, every day when necessary.

Crops 7 July 2001