For the waste disposal of urban areas and major cities at the North American market place rather large scale energy from waste (EfW) plants are needed. This implies a mechanical input of approx. 40 Mg/h [39.36 tn l./h] and thermal input by waste per unit of 110 MW [375.3 MBTU/h] and more.
There are basic design criteria that feature large scale EfW plants:
- Layout of boiler with horizontal or vertical orientation of convective part.
- Top or bottom suspension of boiler.
- Flexible design of stoker regarding large throughput figures and heating values of waste with water or air cooled grate bars.
- Design and geometry of combustion furnace in order to optimize the flow pattern.
- Optimization of boiler steel structure: integrated steel structure for boiler and boiler house enclosure.
- Optimization of corrosion protection and maintainability of large scale boilers: cladding versus refractory lining.
- Maintenance aspects of the boiler.
The paper gives information on the pros and cons regarding the design features with special focus on optimized solutions for large scale EfW plants.
For the core component of the combustion system — the grate — Fisia Babcock Environment (FBE) is using forward moving grates as well as roller grates. The moving grate in STEINMÜLLER design, which is used in the great majority of all our plants, has specific characteristics for providing uniform combustion and optimal burnout.
The automatic combustion rate control system is the key component in the combustion process in order to receive good burn out quality in slag and flue gas as well as constant steam production and oxygen content of flue gas. This paper includes a detailed report on a modern control system with focus on a simple and efficient control structure.
Besides these measures regarding the combustion process, this paper also reports about the respective aspects and concepts for the flue gas cleaning systems. In this field the FBE CIRCUSORB® process was presented in previous papers and is now compared with a multistage wet flue gas cleaning system. The latter is relevant in case of very low emission requirements.