Straw Bales as Fuel to run Barley Dryer

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Barley used for malting and production of whisky must be dried before the distillery will accept it. This sometimes requires the use of a grain dryer, which is an expensive process.

In the next few sections we will examine the feasibility the use of straw bales to dry barley by combusting them in a furnace to supply heat to a grain dryer. The first section gives reasons for drying barley.

Why Dry Barley Grain

Barley grain is a living organism, and if stored wet in a storage bin it will ferment. During the fermentation cycle it takes in oxygen from the atmosphere, expelling carbon dioxide while producing a rise in temperature. Barley grain is practically inactive when dry.

The cycle for wet barley grain is as follows:

  • When it is wet, the rate of fermentation increases producing more heat.
  • Heat slowly raises the temperature that along with oxygen depletion and rising CO2 levels, provide ideal breeding conditions for molds and bacteria.
  • These multiply to produce additional molds and bacteria that lead to the grain being spoiled and unsuitable for use.

So the answer is to store only dry barley, often requiring the use of a dryer.

Three Methods of Drying Barley

1. Bin Drying

This consists of a storage silo having a perforated floor, under floor loader, a fan, and a means of providing heat. The grain is loaded in batches, remaining stationary throughout the process of drying.

2. Batch Drying

There are two designs of this process.

  • Stationary drying
  • Recirculating drying

Stationary drying is where the grain remains in place throughout the process

Recirculating drying is similar design except there is a mechanism for stirring the grain during drying.

3. Continuous flow dryers

In this process, hot air is blown into the grain that is provided in a continuous flow. It is then subjected to a cool air stream.

Problems Associated with Over Drying Barley Grain

The purpose of a grain dryer is to remove moisture from the grain, preventing the conditions cited in the previous section.

However there is a point in the drying process where “over drying” can occur, and this must be avoided as the whiskey distillers will reject the overheated grain as it is useless for malting. Precautions to avoid this include:

  • Dry the barley very slowly using a continuous drying process.
  • Never let temperature exceed 43°C.
  • Set the circulating fans to supply large quantities of air and leave them operating for some time when the heating system is shut down. This will even out the grain temperature and prevent moisture from returning to it.
  • Be careful when distributing/mixing the grain as the kernels are easily damaged. Slowing the feed conveyors and running them as full as possible will prevent this damage.

Round Straw Bale Furnaces

I have chosen to examine a round straw furnace as opposed to a square bale burner due to the fact that the majority of bales left in the barley stubble are round. However, square bales can be equally used and I believe they are cheaper to produce and purchase, due to their smaller mass.

A typical round straw bale furnace incorporating a water jacket is shown below, and may be referred to with the accompanying notes.

A basic straw bale burner consists of a furnace that combusts the bales, being enclosed by a water jacket that is in contact with the heat from combustion of the bales. The combustion chamber is lined with firebricks, and the entire component is enclosed in a steel frame that can be insulated if required.

The bales are loaded by a tractor using a hydraulically operated “spiked” steel bar, through a water cooled door operated by an overhead or side mechanism.

The door also contains an inspection hatch that is also used to light the initial fire to ignite the bales.

The ashes are removed through the open door into a container by a scraper attached to the tractor. The ashes may be suitable for use as a fertilizer, but please see my notes at the end of the article.

Combustion air is supplied by a fan. The air may be passed through a pre-heater in the path of the combustion fumes before they exit through ducting to the chimney. The chimney needs to be sized to ensure that the fumes are injected to a height that prevents low-lying smoke affecting the farmstead and immediate area.

In the type of straw burner illustrated, as the water in the jacket is heated, it passes to a hot water holding tank. The tank can be situated above the furnace framework giving better control of the temperature and supply of the hot water to the heat exchanger that is used to supply heat to the dryer. The water is circulated through the heat exchanger by a small pump before returning to the water jacket to be reheated. Anti-corrosion fluid along with anti-freeze can be added to the water.

Thermostats are located in the storage tank that controls the combustion air supply through operating dampers or decreasing the fan revolutions. This effectively controls the furnace temperature, maintaining the required water temperature and preventing overheating.

A fan circulates air around the exchanger before discharging the resultant heated air it to the barley dryer, as is examined in the next section.

The Process of Barley Drying

As we have seen, barley drying is a risky business and must be carried out with great care and attention to temperature. A basic example of a hot air dryer is shown below.

The basic dryer consists of a tank that is supplied with hot air by a centrifugal fan blowing the air over the heat exchanger.

The grain is loaded onto the conveyor by the tractor front loader, entering the dryer at the top, being distributed by a rotating distributer rotor evenly throughout the tank.

The hot air enters through a perforated pipe in the bottom of the tank being forced up through the grain as it falls from the distributer. A mesh grill over the perforated pipe prevents the grain from obstruction the hot air flow.

Temperature and moisture content probes are fitted at several locations throughout the tank, being wired back to instrument gauges and alarms on the small control panel.

The heating air is discharged upwards through the barley grain exhausting through a pipe in the tank, a screen preventing grain from the distributer from being discharged with the air. A mesh filter is located on the discharge pipe to prevent dust/grain entering the atmosphere.

When the grain has reached around 16% dryness factor, the heat exchanger can be bypassed and cool air blown up through the grain until the desired dryness fraction is achieved.

The barley grain can now be removed through a hinged door at the bottom of the dryer, being discharged into the conveyor that loads it into the grain trailer for transportation or storage in a dry are of the barn.

A modern system of grain drying is shown below.

The above sketch illustrates the use of an efficient but expensive four stage system, applicable to the high acreage cereal farm. However, we can economize on this system for the use of the crofter or smallholder farmer. These guys only need a basic drying method for their own use to achieve a moisture level of around 14% or as required by the distilleries.

First, they won’t need a wet storage silo; the barley grain can normally be stored in a dry barn after harvesting.

They can also do without the dryeration silo if the temperature and moisture levels are carefully controlled in the dryer. Cool air can be circulated through the grain dryer just before the required moisture is reached, as per the dryeration process.

The storage silo can also be replaced by using another area of the original storage barn that is completely dry, with the grain only being stored for a short time.

As well, the dried grain can be loaded directly into the tracto’rs grain carrier for immediate transportation to the distillery. (Hiring a mobile diesel driven conveyor will reduce the conveyors required for this system from three to only one.)

The sketch below shows a possible system for use by the smallholder farmer.

Authors Notes:

Scotland is world-famous for the production of quality grain and malt whisky and I am fortunate to live in Morayshire. This is one of the main regions for growing barley for the many whisky distilleries in this area of the Highlands of Scotland.

1. I was talking to a young crofter (smallholder) recently, and she told me of her plight in bringing in the barley crop due to the cold wet summer. The barley was lying flat in the fields and after eventually harvesting they had to make the decision to have it dried by a local company or feed it to the cattle. This was because the drying was so expensive due to the rocketing fuel prices. She confirmed that the bales were broken up and used as livestock bedding, but the majority was left to rot in the fields. This is what prompted me to research the burning these straw bales using the resultant heat to dry the barley.

2. Remove any plastic covering shrunk onto to the bales by the baling machine. If combusted with the bales, this will produce toxins that may fall into the ashes or emitted into the atmosphere along with the straw exhaust fumes.

3. The ash from the combustion of straw bales contains potassium (K) and calcium (Ca) that can possibly be used as fertilizer. However, it is mandatory to have a sample of ash analyzed by the local authority to ensure it contains no toxins or heavy metals.

4.. My thanks to Stacey Tames and Darrel Slingerland of The Government of Alberta Canada Agriculture and Rural Development for their help in compiling this article.