Grain dryers: using biomass as a heat source

Biomass is a low-cost renewable energy source for grain dryers

Grain drying

Drying grains in agricultural grain dryers is an operation that requires huge amounts of hot air that will heat the grain and evacuate the moisture. In most of the agricultural grain dryers, the heat source is simply a huge propane burner placed in the air intake of the dryer.

The drawback of a direct-flame heating system is that all the flue gas generated from the combustion will enter the grain dryer. This means that the moisture of the fuel will reduce the efficiency of the drying process, and the grain will be contaminated by dioxins and other chemical compounds.

Using propane, a fossil-fuel, for grain drying generates also a huge carbon footprint.

Grain dryer with a Säätötuli biomass hot-air generator

Using biomass to heat the grain dryer

Biomass is a renewable energy that is in most cases produced locally. Using biomass will therefore render the grain drying process carbon neutral.

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Almost all grain dryers can be converted to use biomass instead of propane. It requires only a hot air generating biomass heating device that is plugged in the air intake of the grain dryer.

Unlike propane, using a direct biomass flame inside the grain dryer is not an option. A biomass burner requires a perfect control of the combustion airs, which will be impossible in the huge airflow of a grain dryer. Therefore, the combustion of a direct-flame biomass burner in a grain dryer would be incomplete. That would increase the risk of sending hot ashes and sparks inside the dryer with the catastrophic consequences.

Because of this constraint, biomass will always be used with a heat exchanger in a grain dryer. This will guarantee that only clean hot air will go inside the dryer and all the flue gas will be evacuated into a chimney.

There is two main ways to produce hot air from a biomass fuel: systems with air-air exchangers and hot-water boilers connected to radiators. You will find more details of these below.

Air-air exchangerHot-water boiler and radiator

Air-air exchanger

Principle of the air-air biomass system for grain dryers

The air-air exchanger is the simplest solution:

    • The biomass burner generates a flame.
    • Hot combustion gases are sent to the exchanger that transfers the heat; the flue gas is sent to a chimney.
    • Fresh air is sent into the exchanger to be heated and will then be sent to the grain dryer.

This system has a lot of advantages as it is easy to set-up and requires no water (no icing-related problems in winter).

Säätötuli’s hot air generator has an efficiency of 80%. This is lower than for hot-water boilers (usually 93 to 96%), but in the hot-water systems, you have to take into account also the efficiency of the radiator and not only the boiler.

Hot-water boiler and radiator

Principle of using a hot-water biomass boiler on a grain dryer

The hot-water boiler and radiator, a more complex system:

  • The biomass burner generates a flame.
  • Hot combustion gases are sent to the exchanger that heats water; the flue gas is sent to a chimney.
  • The hot water is sent to a radiator near the grain dryer. The radiator has a fan that will push air through the radiator, thus heating it before it enters the dryer.
  • Hot air is sent to the dryer, the cooled water is sent back to the boiler.

This system is more complex to set-up than an air-air exchanger and needs to consider the freezing conditions in wintertime.
But this system has its advantages as the same boiler can be connected to heat several buildings in addition to the grain dryer. Hot-water systems allow to create a heat-network that provides heat to the whole farm. Our pre-insulated PEX piping is a cost-effective way to build a hydronic heat network for this kind of application.

Converting a grain dryer to biomass

When converting a grain dryer to biomass, the whole energy need of the grain dryer can be covered by biomass. However, it is also possible to install a biomass heating system that will not cover the whole energy need but will work together with the existing propane heater.

In all retrofit cases, it is recommended to keep the existing heat source. It can be used for any peak energy demand that goes over the biomass system’s capacity and will also be a helpful backup system. Sometimes you might get a stone or a piece of metal with your biomass delivery and have one of the feeding augers jammed. In those cases, the backup energy system will kick in while you troubleshoot and take care of the problem.

Grain dryers can be connected to containerised biomass heating systems

Before deciding on the output of the biomass system, we recommend that you assess the heating cycle of your grain dryer. If for example there is a short peak demand during the cycle, it might be more profitable to invest in a biomass heating system that will cover the major part of the energy need, but not the peak. In some cases, that practice can cut your initial investment by a huge amount but still displace more than 90% of your propane consumption.

Säätötuli’s biomass heating systems for grain dryers

Säätötuli’s biomass heating systems are able to use a large selection of solid fuels. They can run on woodchips as well as pellets. The efficient burning technology allows the use of low-grade woodchips with up to 35% of moisture content. The sturdy feeding augers and powerful motors and gears can feed the burner even with woodchips made with a low-quality chipper with used blades.

Säätötuli’s biomass burners can also run on other solid fuels that can be mixed with woodchips if needed. In Northern Europe, many farmers use the dust collected from the grain dryer as a fuel to heat the dryer, meaning that the dryer produces a part of its own fuel.

Säätötuli has hot-air and hot-water systems that can be fitted on grain dryers.

Hot-air systemsHot-water systems

Hot-air systems for grain dryers

The biomass hot-air generator is easy to install on grain dryers

Säätötuli’s biomass hot-air generator was developed with a grain dryer manufacturer. It outputs 1.7 million BTU/hr (500kW). When comparing the output with some of our competitors, it is important to know that hot-air biomass systems do not have the same level of standardization as hot-water systems.

Säätötuli’s hot-air generator’s 500kW output is the real output you will get at the hot-air outlet of the machine. Some manufacturers will only show the burner’s theoretical output, which can be almost more than 50% superior to the real output.

To avoid any errors on the choice of your hot-air biomass system, we recommend that you compare the real amount of hot-air that the system produces and the temperature differential. For example, Säätötuli’s hot-air generator will output 17,500 CFM (about 30,000 m3/h) with an increase of temperature of +75°.

Huge grain dryer with multiple biomass hot-air generators

For huge grain dryers, the output of a single hot-air generator will not be enough. The hot-air generators are easy to combine to increase the total output.

Combining several hot-air generators can be made in parallel as on the pictures above. The hot-air generators can also be put one in front of the other if your system requires extra hot air. In that case, the first hot-air generator will be used as a pre-heater for the second. With that kind of setup, temperatures above 100°C can be obtained.

Containerised biomass hot-air generator on a grain dryer

The hot-air generator is also available as a containerised biomass hot-air plant. The containerised plant is easy to move with a roll-off truck and can be used on the grain dryer on fall and moved to heat a building for the winter. It is an ideal solution to shorten the payback on the investment.

Biomass hot-water systems for grain dryers

An ASME biomass hot-water boiler can be connected to grain dryers

Säätötuli’s hot-water boilers can be connected to radiators to provide the heat for a grain dryer.

Hot-water boilers are available for multiple outputs and can be connected to a heat network that will provide hot air for the dryer, but also heat a lot of other buildings in the area.

Containerised biomass hot-water boiler

Hot-water biomass boilers are available also as containerised biomass heating plants.