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.