Award as “Low Carbon Model Company of the Year”
For more than 50 years Steinmüller Babcock Environment has relied on the proven technology of grate firing, one of the world’s oldest forms of firing. Here, the fuel is laid out and burned on a grate surface; the space between the grate bars is used to supply combustion air and to remove ash. Our combustion system is based on forward moving grates. The grate bars form rows with shallow steps, every second row moves continuously and pushes the fuel forward. In addition, the waste is stoked to favour a good burn-out. Moving grates are ideally suited to the thermal recovery of household
and commercial waste,as well as for other bulky, ash-rich fuels. Grate firing reaches a combustion temperature of at least 850° C. We use modular air-cooled or water-cooled grate systems. The spectrum of fuels ranges from household waste with high humidity to highly calorific fuels (substitute fuels, plastics). The maximum throughput capacity per line is approx. 400,000 tons per year. The moving grate guarantees high availability and a long life-cycle, as well as operational security and economic efficiency.
The waste hopper collects the waste dropped by the waste grab via the hopper cover flap to the fuel shaft. It seals the waste bunker against the boiler house. We build all of the necessary parts of the hopper from wear-resistant materials, in accordance with the specific requirements.
The water-cooled hopper cover flap, which is operated by hydraulic cylinders, separates the fuel shaft from the waste bunker. During the start-up and shutdown process of the boiler and in cases where the fuel shaft is insufficiently filled, it guarantees an airlock towards the combustion chamber. During inspection work in the grate area, the flap is closed and sealed mechanically for safety reasons by means of a pin lock. Microwave device is provided beneath the damper to measure the fuel level.
The fuel shaft feeds the fuel to the fuel feeder. To prevent blockages, the width of the shaft increases downwards. The walls are water-cooled, the shaft is fitted additionally with a water injection system in case of back- fire. At a defined height, sensors measure the height of the fuel bed.
The fuel feeder conveys the fuel to the forward moving grate. Each grate track has its own hydraulically-driven feeder. The ’Automatic Combustion Control’ system (ACC) determines how much fuel is fed. The feeder ram, table surface and sides are protected by means of wear plates; in the relevant areas the walls of the feeder are water-cooled or built as water chambers with additional protection by means of refractory.
The modular structure of our grate system allows individually adapted grate sizes ranging from small, one-track grates to large, multiple-track systems. The individual grate zones can be controlled separately in terms of primary air feed and grate moving speed. This allows a high degree of flexibility when integrating it into the firing output control.
The following grate parameters are variable:
Five grate zones per track are customary. In most European plants with average calorific values, element lengths of 1.8 m, 2.4 m and 3.0 m lead to a grate length of between 9.6 m and 12 m. In countries with a high organic portion in household waste, the grate is extended to max. 13.2 m, for a better burn-out.
Discreet steps of between 2.25 m and 3.55 m and individual widths are possible.
Most grates have one to four tracks. The overall surface of the grate system influences the specific thermal load [KW/m²] or the specific mechanical spread load [kg/m h].
Two grate steps are usually sufficient for a very good reallocation of the fuel and good burn-out behaviour. For fuels with a high organic portion, a third step increases the burn-out.
In European incineration plants, tubed combustion chambers are used as standard, in which pre-installed brickwork or added cladding guarantees optimum heat distribution and heat extraction. In cases of moist waste with a high organic portion, which is not readily ignitable, an adiabatic combustion chamber is used. This consists of a steel frame and accordingly strong brickwork. The heat is maintained in the firing chamber to support the combustion process.