Our Technology – Blue Flame Stoker

Introducing the Blue Flame Stoker, the revolutionary solid fuel heating system. Designed and manufactured to assure the most efficient combustion of solid fuels, while maintaining low emissions.

Our system design incorporates the three components required for efficient combustion of any solid fuel. They are:

– Time
– Temperature
– Turbulence

Time is achieved in the Btu/Hr per square foot of grate area and the Btu/Hr per cubic foot of furnace volume. The chain grate stoker design has a significant advantage over other systems. The system provides a large area of the grate that is conservatively designed to assure a complete combustion of any solid fuel. For example, a 100 BHP (3,500,000 BTUs) solid fuel combustion system requires (based on 7,000 Btu/Lb of solid fuel) approximately 10 FT² of grate area for proper fuel combustion. Only chain grate stoker system design can meet these criteria.

Temperature is achieved by the amount of refractory near the fuel feed and on the walls of the combustion chamber. Our combustion chamber is lined with high temperature insulation and refractory that keeps the heat in and provides the required environment for solid fuel combustion.

Turbulence is achieved by supplying additional combustion air above the second zone from the front wall directed toward the top of the grate at the rear of the stoker. The combination of combustion air (air passing through the fuel bed) and over-fire air (OFA) provides turbulence required for rapid and complete combustion of solid fuel.

Control of both the quantity and the distribution of combustion air are apportioned by the combustion control system via the use of dampers and Variable Frequency Drive (VFD).
The following is an outline of all the system components that are required for a proper operation of the system and are part of a package sold.

Equipment Construction

Fire-tube Boiler

Boiler Type “C” Style, Three Pass, Low Pressure Boiler rated for 30 Psig water pressure (other pressures available). Three Pass design provides maximum heat transfer with low stack temperature. The boiler is designed and constructed to the A.S.M.E. low-pressure boiler code and meets all the requirements of the authorities of the Provinces of Canada.

The boiler’s extra large combustion volume assures complete combustion of solid fuels, clean firing and unrestricted gas flow. The large firebox with arched crown sheet provides and exceptionally high proportion of the primary (radiant) heating surface which is many times more efficient than secondary (indirect) heating surface. The firebox boilers are used in automatically fired Solid Fuel systems all over North America. Supplied boiler horsepower ranges from 50 – 300 BHP (other sizes available).

Special Boiler features used for Solid Fuel combustion systems:

  • ASME Boiler Code Certification
  • 3-Pass full wet back design for maximum durability and economy
  • Open furnace bottom for stoker installation
  • Hinged furnace access door; front, rear or side 16 or 20 inch diameter
  • Custom rear flue gas box outlet
  • Abundant heat transfer surface per boiler horsepower
  • Outstanding inspection access as well as quick and easy maintenance
  • Flushout and inspection openings are 3×4 inch hand-hole type.
  • Covered with mineral insulation and steel jacket

Stoker Base

The stoker base is constructed of 0.250″ (or thicker) mild steel. The stoker walls are lined with two layers of High Temperature insulation.

The stoker consists of steel base with factory installed:

  • Hi temperature insulation and refractory
  • Combustion and over-fire air system
  • Automated ash removal
  • and Chain-grate

The Chain-grate stoker uses endless chain, which is constructed to form a support for the fuel bed.

The chain travels over the sprockets mounted at the front of the stoker. The stoker chain links are cast from a special high heat resistant cast iron. Chain links are designed to transport most of the Solid Fuels during the combustion process.

The stoker base is constructed of 0.250″ (or thicker) mild steel. The stoker walls are lined with two layers of High Temperature insulation (for a total thickness of 4″). The use of multi-layer insulation assures low stoker surface temperature. The primary part of the combustion chamber is lined with 9″ firebrick. The remaining part of the combustion chamber is lined with 9″ refractory. The use of firebrick and refractory combined with high temperature insulation guarantees good heat radiation, which enhances fuel combustion.

The back of the stoker base is equipped with hinged, large access door c/w sight glass. The door (lined with refractory) provides an easy access to the combustion chamber for periodic inspections. Large (4″ diameter) sight glass enables to view Solid Fuel combustion without opening the back door.

The chain grate is driven by a hydraulic motor, which enables it to move at a very low speed. The main advantage of the moving chain grate is that the fuel falls on the chain grate, and combustion is completed as it moves slowly through the base. The ash remains on the grate and falls onto the main ash removal auger as the grate turns around.

Combustion Air

In order to achieve a complete combustion of all combustible components of Solid Fuel with all the Oxygen, sufficient space, Time, Turbulence and Temperature high enough to ignite the components must be provided.

Combustion Air control is one of the most critical elements for proper Solid Fuel combustion. Efficient solid fuel combustion depends on both, primary (combustion) and secondary (over fire) air. Combustion Air provides the basic oxygen supply for solid fuel burning. Secondary Air is injected into the upper section of the combustion chamber to combust the unburned gases.

The stoker base is divided into zones (under grate wind boxes) from front to back. The purpose of the wind boxes is to deliver the primary (combustion) air for solid fuel burning. The combustion air is delivered through attached plenum by a direct drive combustion air fan driven by Variable Speed Drive (VSD). The main plenum branches off to the individual wind boxes and is equipped with hand-operated dampers. Hand-operated dampers are provided to regulate the flow of air to the zones to compensate for irregularity in the fuel bed depth. The total supply of combustion air delivered is modulated using VSD and is directly proportional to the amount of fuel delivered to the Combustion Chamber.

The amount of theoretical combustion air required is carefully calculated for each individual Solid Fuel used. Since the majority of the combustion occurs directly above the stoker grate, the injection of secondary air assures proper oxygen mixing and complete combustion of carbon monoxide and volatile gases. The secondary air is injected to the combustion chamber (above the grate) using a high-pressure blower.

Fuel Handling

The Fuel Handling system is designed to convey coal and other fuels, such as wood chips and agricultural waste.

The Fuel Handling system is designed to convey coal and other fuels, such as wood chips and agricultural waste. Included is a twin-screw fuel-metering conveyor that is designed to transfer fuel from customer supplied hopper bottom bin to the fuel injector fan.
The system consists of:

  • Twin-screw auger
  • Gearbox motor
  • Fuel injector fan

The feeder-and-distribution system utilizes a high-pressure blower to inject the fuel into the combustion chamber. This type of system has a wide application with respect to both, the fuel that can be handled and the boiler sizes to which they can be applied. This fuel handling system functions to vary the supply of solid fuel to the furnace and to provide even distribution on the chain grate. Variations in performance of the fuel injection fan, due to changes in fuel size are corrected by means of an external damper adjustment. The fuel feed ratio is directly related to the power demanded by the boiler control system. The use of a Variable Speed Drive (that powers the gear box) enables modulation the feed rate from a few pounds of fuel per minute to a few hundred pounds.

Automated Ash handling

The system shall incorporate automated ash removal as follows. Each of the combustion air duct is equipped with ash removal auger that drops off the ashes onto the transfer-auger and further onto the cross auger. The cross auger shall be factory installed into the stoker base. Ash will drop off the end of the moving chain grate onto the cross auger. This auger will then transport ashes out of the base automatically. In some cases an additional ash transfer box is used to transfer the ashes to the outdoor ash container.

The ash augering system is powered by the hydraulic system and is controlled automatically from the supplied electrical control panel. An outdoor ash storage container is not included in the equipment quote but could be provided to the customer as optional equipment.

Automated Soot Blowers

The soot blowers are factory installed into the boiler (in some cases on site installation is required). The function of the soot blowers is to eliminate any soot build-up within the boiler tubes, thus increasing its heat recovery efficiency. Included is an automatic soot blower control system. PLC controlled soot blowers are programmed to blow the tubes at predetermined intervals, guaranteeing a maximum boiler heat recovery 24 hrs a day. Compressed air (min. 40SCFM at 100PSIG) is required for proper operation of the soot blower system.

Control Panel

The Electrical Control Panel consists of a CSA approved steel enclosure, with lock, approximate dimensions (36″x 36″x 8″), complete with:

  • One (1) PLC
  • One 8″ Color Touch Screen panel
  • All motor controls (including VSDs), indicator lights
  • Audible alarm
  • All necessary terminal blocks to make inter connections.

All of the above are completely internally wired prior to shipment. The Control Panel is designed to operate the Chain Grate Stoker, Twin-Screw Fuel Feed Conveyor, Automated Ash Removal Augers, Combustion Air Fan, Exhaust Air Fan and Automated Soot Blower.

System Function – All motors will have Hand/Off/Auto selectable switches. During a normal system operation all the switches will be in the “Auto” position. The “Hand” (manual) mode will operate all the motors at a pre-set speed. The “Hand” option will also be used during equipment testing and troubleshooting. On the start-up, the system will automatically start all the functions (fuel feed rate, combustion air fan speed, exhaust air fan speed) at a pre-set values.

On/Off time and cycle times for Chain Grate and Ash Removal Augers will be pre-set by the user and stored in the PLC. The set-up will be performed via the Touch Screen Panel directly interfaced with the PLC. The Touch Screen will display all the functions of the system (including alarm status). The set-up screen will be password protected (for authorized personnel only).

Control Functions – A type J thermocouple will be used in combination with the temperature controller, mounted directly on the Control Panel. Temperature controller will have a PID function with 4-20 mA output to control the fuel feed rate and combustion air volume (in order to maintain a proper fuel combustion).

Hold Fire – Used only during the periods of low heat demand. If the system reaches the set point temperature the system will shut down. If the temperature remains at the set point for a long period of time the system will start up at a pre-set time intervals in order to maintain fire. The time interval between start-ups is selectable by the user.

Dust Collector

The dust collector is designed to eliminate most of the fly ash, generated during Solid Fuel combustion, that otherwise would be discharged from the chimney.

The dust collector is designed to eliminate most of the fly ash, generated during Solid Fuel combustion, that otherwise would be discharged from the chimney. The heart of the system is a multi-cyclone design complete with exhaust blower and fly ash removal auger. The speed of the exhaust fan is controlled by a Variable Speed Drive coupled with Photohelic® gauge in order to maintain a constant negative pressure inside the combustion chamber.

The dust collector system is sized and specifically designed for the supplied stoker. The fly ash is collected in the bottom hopper of the dust collector system and discharged into ash removal system. The use of the air-loc valve between the bottom of the hopper and transfer auger prevents any air leakage outside the dust collector.