Wellons FEI uses an air cooled, reciprocating grate at the heart of their combustion systems. The main advantage of this technology is that it’s able to progressively move the fuel within the combustion chamber. As the material moves forward it goes through the different stages of combustion. At first the biomass enters the combustion chamber and is immediately exposed to the heat of the combustion chamber, at this stage the biomass starts to dry. Once the biomass has finished shedding its moisture, it’s now ready to gasify and send the hot gases to the process. After the material has been completely consumed you are left with only ash. All of these stages are done in a sequence as the material is coming down the moving grate. This is a major advantage over a fixed grate system were the ash, wet fuel and material combusting is all mixed up in the same pile. The other negative point of a fixed grate system is that it does not extract ash automatically which can be very problematic especially with high ash content fuels like forestry biomass and bark. For example a 600 hp boiler operating at capacity using bark as fuel can generate up to 200 pounds of ash per hour. This is why the Wellons FEI reciprocating grate can handle these fuels.
At the end of the Wellons FEI reciprocating grate is an ash removal rake that is automatically operated by a hydraulic cylinder. The rake cycles back and forth and extracts the ash that falls off the grate, out of the combustion chamber and onto a conveyor. The rake is fabricated of special high temperature alloys in order to survive the high temperature environment. Unlike other manufacturers that might use a screw to remove ash from the combustion chamber, the Wellons FEI ash rake is much less prone to jam, even if there is and odd rock or piece of steel that makes its way into the system.
The grates used in the Wellons FEI grate system are all made of a special high grade stainless steel casting. Most manufacturers will use cast iron grates that you have to change out every few years. Wellons FEI has standardised on stainless steel grates that will last 4 to 5 times longer than their cast iron competitors. Combined with the air cooling effect of the primary air plenum, the grate does not require any water cooling circuit; thus minimizing total system maintenance.
Primary air is forced into a plenum underneath the stepped grate in order to promote drying and gasification. The primary air is zoned on the length of the grate so that you can fine tune the quantity of air through the grate by adjusting dampers outside of the unit. The secondary air nozzles are high velocity jets placed above the grates that cut across the combustion chamber in order to complete oxidation of the gases leaving the grate.
When the size of the combustion units is transportable, Wellons FEI pours the refractory inside its combustion chambers in the shop. Field installation time can be cut back considerably by having the refractory installed in the shop as Wellons FEI does. Most vendors have the refractory installed on site were quality assurance can become an issue. Most of the time vendors will supply their systems and pass the cost of the refractory as an on site installation costs. This is not the Case with Wellons FEI, all of our refractory is shop poured complete with expansion joints and anchors. Refractory service temperature is 3200 F, well above the typical 1800F seen in biomass combustion systems.