Introduction to the BEST System

Constant Fuel Feeding

~ General Description

The BEST Heating Unit is an updraft, atmospheric pressure gasification system. We will custom build the gasifier system to meet individual energy requirements utilizing biomass as fuel.

~ Main System Components

~ Design Features

~ Fuel Storage

Baled wheat straw can be stored outdoors or indoors. Indoor storage protects the fuel from precipitation (and often from freezing) and can eliminate varying moisture content and decay in the fuel supply.

Received fuel is moved onto the bale magazine by either a front-end loader or a specially designed automated crane system. The bale magazine can be designed to handle any amount of fuel desired. The magazine automatically feeds baled straw into the disintegration machine as fuel is required for processing.

~ Fuel Disintegration

The fuel processing begins in the shredder where the straw is disintegrated into smaller, manageable particles. Interruptions or delays in reclaiming fuel can occur because of undesireable fuel properties (i.e. poor flow, compaction, frozen chunks, oversize material or contaminants), so fuel preparation is critical to the operation of the entire system.

~ Fuel Transfer

~ Primary Combustion Chamber

The primary combustion chamber is an enclosed area where drying, pyrolysing and oxidizing occurs. The fixed rotating grate supports the fire bed and allows for underfire air to be blown up through the fuel. Effective oxygen supply and control is critical to ensure complete gasification without complete combustion.

Ash collects below the grate and is removed automatically by an auger. In general, ash from biofuel burning is not considered a hazardous waste and can be placed in local landfills. However, most ash is an excellent soil additive and will be of interest to local gardeners and farmers. Proper ash management is critical, as non-combustible inorganic (mineral) content of biomass can become significant, depending on the type of fuel utilized. Inherent ash is generally low in clean wood (0.5%), higher in bark (3.5%) and significant in annual crops such as straw (6.2%), but usually consistent within a fuel type. Ash content is usually expressed on a dry basis, i.e. the weight of ash as a percentage of the total moisture-free fuel weight.

~ Secondary Combustion Chamber

The hot exhaust gases exit at the top of the primary combustion chamber and pass through a refractory duct into the secondary combustion chamber. Oxygen is added in the refractory duct. As the gases flow from the primary to the secondary chambers, the injection of oxygen ignites the gases, allowing gas combustion to take place in the secondary chamber. The quantity of heat released during the biofuel gas combustion is dramatically increased to approximately 2,500 degrees Fahrenheit. Extremely high temperatures are maintained in the combustion chambers by lining the chambers with refractory, which radiates and reflects heat back into the fuel layer. The refractory also protects the walls and base of the chambers from the high temperatures in the combustion zone.

Where agricultural-based straw is the primary biofuel, silica and potassium debris settles in the removable tray at the bottom of the secondary combustion chamber. This requires periodic manual clean out.

~ Heat Exchanger

The extremely hot gases from the secondary chamber flow to the heat exchanger which is a fire-tube boiler. A hydronic system delivers this heat to desired locations and supply precise heat for any public, commercial, residential or agricultural building. Fly ash can be moved by combustion gas flow and can deposit on the heat exchange surfaces in the boiler. This ash is removed regularly to maintain good heat transfer performance. Tube cleaners are in place to automatically clean the boiler tubes and collect the fly ash in the particulate collection system.

~ Exhaust System

An induced-draft exhaust system completes the combustion process. The induced-draft system uses a large blower located in front of the stack which sucks the exhaust gases out of the boiler and forces them up the stack. The draft of this fan is regulated in relation to the combustion air to maintain a very slight negative pressure in the combustion chambers so that gas flow is continuous and that no combustion gas leaks occur.

~ Instrumentation

Instrumentation is important for efficient operation in response to energy demand and safety. The complete feed and gasification process requires a complex control system using computers and micro-processors to match heat delivery with demand. A key task of the control system is determining the rate at which fuel and air are fed to the primary combustion chamber to ensure gasification, and the rate at which air is fed into the secondary chamber of ensure efficient combustion. Control is achieved when fuel and air are automatically modulated simultaneously to maintain the correct ratio under high or low demand. Start-up and shutdown sequences are programmed, and alarms will sound in upset conditions.

~ System Requirements

• Electrical power (3 phase system preferred, single phase possible)
• Air requirement (compressor 100-120 PSI, 7-10 CSF)
• Cold water source (50-70 PSI, 2-4 gallons/minute)
• Concrete floor and building structure (brick or metal)
• Shelter (or building structure) to cover the disintegration and conveyor system
• Ash bin (to contain ashes being removed from the gasifier primary chamber)

~ System Maintenance

The BEST heating system requires little maintenance and management. Tasks such as ash disposal, general cleanup (usually in the fuel storage and handling area), checking heat exchanger water levels, checking the fuel delivery system for oversize material build-up, plus monitoring primary and secondary combustion chamber temperatures, along with stack temperature are done daily. The computer system will signal the operator in upset conditions or for out-of-range readings.

In addition, there are regular maintenance tasks that need to be carried outperiodically. These include:

• replenish depleted fuel supply
• lubricate mechanical components
• inspect and adjust chains, gearboxes, blowers, etc.
• remove silica from secondary chamber
• remove debris from heat exchange
• inspect refractory and repair as necessary
• test safety devices

Most of the routine maintenance can be carried out by the system operator or by the general on-site maintenance staff. It is recommended that the system be inspected by a BEST service technician annually.

~ System Life Expectancy

Theoretically the Biomass Energy System Technologies Heating System can last indefinitely, since the components will be replaced as they wear out or deteriorate. In the forest industry, wood combustion systems have been in operation for over 50 years. In practice, 15 to 20 years is used as a reasonable life expectancy for a biomass combustion system in life-cycle costing.