The Gasifier gives the Customer possibilities to select the synthesis gas calorific value to meet the demands of the processes downstream. The main benefits of Outotec Gasifier are:
- Air or Steam & Oxygen blown depending on the synthesis gas calorific value requirement
- High carbon burn out in the bed
- Maximized modularity with the other fluidized bed units for spare part and services availability
Additionally the following benefits are unique to the Gasifier and Advanced Staged Gasifier:
- Reduced bed area for lower parasitic electrical load consumption
- Lower in bed reaction temperature further reducing the NOx formation
- Increased bed reliability due to higher margin between bed temperature and fuel related contaminants melting point
In a fluidized bed gasifier, the bed material can either be sand or char, or some combination. The fluidizing medium is usually air; however oxygen and/or steam are also used. The fuel is fed into the system either above-bed or directly into the bed, depending upon the size and density of the fuel and how it is affected by the bed velocities. During normal operation, the bed media is maintained at a temperature between 1000ºF and 1800ºF. When a fuel particle is introduced into this environment, its drying and pyrolizing reactions proceed rapidly, driving off all gaseous portions of the fuel at relatively low temperatures. The remaining char is oxidized within the bed to provide the heat source for the drying and de-volatilizing reactions to continue. In those systems using inert bed material, the fuel particles are subjected to an intense abrasion action from fluidized sand. This etching action tends to remove any surface deposits (ash, char, etc.) from the particle and expose a clean reaction surface to the surrounding gases. As a result, the residence time of a particle in this system is only a few minutes, as opposed to hours in other types of gasifiers.
The large thermal capacity of inert bed material plus the intense mixing associated with the fluidized bed enable this system to handle a much greater quantity and, normally, a much lower quality of fuel. Experience with Outotec’s fluidized bed gasifier has indicated the ability to utilize fuels with up to 55 percent moisture and high ash contents, in excess of 25 percent. Because the operating temperatures are lower in a fluidized bed than other gasifiers, the potential for slagging and ash fusion at high temperatures is reduced, thereby increasing the ability to utilize high slagging fuels.
Energy densities in a fluidized bed gasifier are dependent on the fuel characteristics and have been reported as high as four million Btu/hour/ft2. Normally, the dryer the fuel the higher the energy density and the better the quality of low Btu gas produced.
In general, gasification systems can be used in nearly every application in which natural gas, oil or pulverized coal are being used. Low Btu gases can be used to fire cement or lime kilns, rotary dryers, wood veneer dryers or dry kilns, air heaters, steam boilers, and turbine or diesel generator sets. The simplest application for a fluidized bed gasifier is to fire or co-fire an existing steam boiler.