WELLONS is the only company manufacturing wood-fired boilers with a furnace grate and a unit output of up to 120 MTH of high-pressure steam. These boilers require no auxiliary fuel (fuel oil or fuel gas) for operation. For this reason, our technology is constantly compared with the method of wood waste combustion in fluidized bed boilers. In the article "OPERATION PRINCIPLE AND DESIGN FEATURES OF WELLONS BOILERS" we focused on the description of technological features and advantages of our systems where a patented technology of wood fuel combustion on rotary grates in vortex/cyclone-type furnaces is used. (WELLONS, INC. know-how).

In this review, we want to draw your attention to a number of disadvantages inherent in the technology of wood fuel combustion in a fluidized bed. These are as follows:

  • Fluidized bed plant is more complex and metal consuming.
  • Investment and operational costs are significantly higher by at least 25-30%;
  • The competitive cost-effectiveness of these systems manifests itself at a boiler unit heat output over 150-200 MW;
  • Low operating range within 60-100% of the rated capacity;
  • These systems are designed primarily for low-calorie fossil fuels (coal, lignite, peat, etc.) and solid waste disposal. Since the wood fuel ash is highly alkaline and contains large amounts of alkali oxides R2O, which reduce the melting point of the inert layer (sand) up to 750-800°C, the fluidized bed technology of wood fuel combustion has the following disadvantages:
    • slagging of space between the nozzles and the nozzles themselves;
    • the formation of large inert layer (sand) cakes, sharply reducing the efficiency of the boiler;
    • the need for additional complex systems to control the combustion temperature and, accordingly, the temperature of the inert layer.
  • The large amount of inert material necessitates the use of a high-pressure fan with high power consumption;
  • The intensive carry-over of unburned carbon particles (20-30%), that makes necessary the use of additional equipment (cyclones) to capture and return them back into the furnace for re-incineration;
  • The inevitable loss of inert material (sand) due to wear. Additional equipment required for feeding sand into the boiler, large operating costs for the purchase of sand that should meet the stringent requirements for the chemical composition and fraction, as well as its refractoriness. Deviation from the set parameters in the course of operation will inevitably lead to reduced efficiency of the boiler.
  • Increased abrasion of the boiler water tubes, due to the increased carry-over of ash and inert layer of particles (sand).
  • Increased nozzle abrasion requiring regular replacement during operation of the boiler.
  • Need to use a startup/auxiliary burner in fluidized bed systems. The use of such burners is dictated by technological necessity in these systems. Based on the experience of operation of these boilers, equipped with burners fed with alternative fuels (gas, oil) , it is their concurrent use for burning wood fuel with high humidity that allows the fluidized bed boiler to remain in operation. Analysis of the "auxiliary" fuel consumption shows an increase in gas/fuel oil flow rate proportional to moisture content in bark and wood fuel fed to the boiler. In other words, when using fuel with a moisture content above 55%, gas/fuel oil becomes the main fuel instead of auxiliary. This is also one of the factors of high operating costs, which negatively affects both the cost of steam, and the cost of the plant end-products, reducing the payback period of your project. 

The use of auxiliary burners on Wellons boilers is not necessary. For example, such burners for gaseous fuels were installed at JSC "Solikamskbumprom", however after the boiler commissioning these burners have never been used, even when a fuel mixture of BW/sludge in a ratio of 1:1 (50:50) was utilized. On request, we install auxiliary burners, which ensure the maintenance of boiler parameters (characteristics, performance) and put our system on an equal footing with the fluidized bed plant when choosing the boiler running on wood waste/fuel.

   We are always pleased to introduce your staff to Wellons boilers operation. All the professionals that operate our boilers, point out to the simplicity of design, reliability, possibility of incinerating/recycling sludge deposits with high humidity content (up to 70%), extremely low operation cost, excellent technical solutions from the design of furnaces to ash handling systems, low metal intensity of its structure, workmanship etc. Example of "Solikamskbumprom" shows a lack of large expenditures on the operational needs of the boiler itself – after 15 years of heavy operation no replacement of grate rolls is required; the original lining of furnaces and boilers, installed at the boiler commissioning still remains intact.

   We hope this brief information will allow you to better understand the technology of burning all kinds of waste wood on our systems compared to fluidized bed technology and use a more balanced approach to choosing a boiler systems for your projects. By choosing Wellons boiler you insure yourself against the disadvantages of other systems.