MERCIA 

          ENERGY 

                Ltd

Supplier of automatic wood heating systems


 

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    (useful data)

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Local sustainable solutions for:

  • Public buildings

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  • Large households

 

 

Wood Energy


  Why biomass    How it works     Key features    Useful data 

Key Features

1  Control box 

2  Heat exchanger tubes 

3  Drive for tube cleaning augers 

4  Flue gas outlet 

5  Ash container 

6  Automatic de-ashing 

7  Burner head 

8  Combustion chamber 

9  Fire box door 

10  Combustion air blowers 

11/12  Rotary valve & feed motor 

13  Feed auger cover 

14  Discharge auger motor 

15  Safety valve 

16  Flue gas temperature controller

17  Fire box door

 

Safety: Most burners are fitted with multiple safety features to prevent burn back which could otherwise result in fuel store ignition. Drop cell and rotary value. This feature gives a break in the fuel feed system such that there is always a gap between the incoming fuel and the fuel feeding directly into the boiler. It prevents the spread of fire back into the fuel store. Temperature cut outs. The boiler is programmed to shut down in the event of over heating in the feed handling system Water dosing system. In the unlikely event of the other two safety features failing, water will be released from a dosing tank into the fuel feed auger to extinguish any fire.

Power modes: Automatic wood-fuel boilers can operate between 20% and 100% of their maximum continuous rating (MCR) without a serious loss of efficiency. This enables a single boiler to be operated over a range of outputs. In power mode the boiler output is controlled by the rate at which material is fed on to the burning grate. This feed rate is determined by consecutive pauses and short pulses of the feed auger. At high power for example, the length of pulse will be much greater than at low power.

Sleep mode: When heating or hot water is not required wood-fuel boilers switch to pause mode. This feature is similar to the pilot light on a gas or oil boiler. During pause mode fuel is automatically fed very gradually to the burner to maintain a small fire, for example the length of pause would be very long. At night and when the heating is turned off most wood-fuel boilers would be in pause mode.

Automatic ignition: Most boilers can be fitted with automatic ignition. Wood-chip boilers typically use a system that blows very hot air into the fuel bed (similar to a paint stripper) until the fuel on the grate ignites. Wood-pellet boilers often use an electric coil to heat up pellets until they ignite. The top of the range models use automatic ignition to restart the boiler at the end of the sleep mode.

Automatic heater exchanger cleaning: High efficiency boilers like the Heizomat for example incorporate fire tubes in the water jacket. These tubes increase the surface area and improve the efficiency of heat transfer. The fire tubes either positioned horizontally or vertically tend to collect fly ash and become coated with residues which condense out of the exhaust gases as they pass through the boiler. Modern boilers incorporate automatic cleaning devices that periodically remove any deposits. These systems keep the boilers operating at peak performance through out the year.

Automatic de-ashing systems: Traditionally wood burning devices have always required the ash to be removed manually on a regular basis. Although ash from heartwood is less than 0.5% if left to accumulate over several days it can eventually block the grate and seriously effect the performance of the fire.