Jakob Stiefel GmbH

A STIEFEL project Waste Incineration Plant (KVA) Trimmis case study


Courtesy of Jakob Stiefel GmbH

The waste incineration plant (KVA) Trimmis is situated in the eastern part of Switzerland and is connected to the railway network. As it is the only incineration plant in this province, it serves a large area with approximately 131’000 inhabitants. The local authorities waste disposal association named GEVAG is a public body serving 43 convention communities and 97 associated municipalities

Newly Built Combustion Line in the KVA Trimmis

Report of François Boone, Plant Manager:
The authorities responsible for the KVA Trimmis concluded that the existing incineration line no longer met the current demands. A new incineration line would ensure the future incineration requirements.

Various wide ranging criteria had to be considered for the new plant at Trimmis. For example, during a period of intensive operation, the maintenance should be minimised. The feeder chute and the grate which are exposed to extremities of heat and mechanical wear should be long lasting and extremely reliable. All maintenance work should be able to be completed quickly and at a low cost. In addition, it was of importance to minimise the wear of fire resistant material and to minimise the corrosion in the entire boiler to achieve the maximum availability output and usage.

Jakob Stiefel GmbH belongs to the select group of innovative grate suppliers for waste incineration. Hence we intended to benefit from their ideas, know-how and flexibility.

For our Trimmis project, Jakob Stiefel GmbH acted as the main contractor for the combustion, the boiler, the electro filter as well as the slagtransport and implemented their water cooled grate system from the latest technology.

The Jakob Stiefel GmbH is well versed in knowhow as well as many years of experience in project management and EPC. Highly qualified specialists and state-of-the-art planning methods ensure a smooth execution of the project and provided the customer with premium solutions.

As the main contractor for line no. 1, Jakob Stiefel GmbH coordinated the various elements, grate combustion, boiler, e-filter, ash- and slag transport, control system as well as all the integrated peripheral installations. The plant was handed over to the customer on time and met the full high specification demanded. The plant is noted for high reliability with low maintenance and outstanding emission values.

Water Cooled Forward Moving Grate
The water cooled, forward moving grate is a single track construction consisting of 24 grate steps and is underneath divided into 5 air zones. Due to the water cooling, the thermal abrasion of the parts is almost eliminated. Furthermore the water cooled construction prevents thermal expansion and distortion and the need for expansion compensators. The steps are built of a welded construction with a continuous surface allowing for an uniform air distribution. An even loading within the combustion chamber, outstanding low emissions as well as high burnout values all result from this technology. Finally an inspection under the grate reveals very low spillage levels of ash.

Movable Secondary Air Beam
The movable secondary air nozzles are water cooled and operate over the entire width of the combustion chamber through an adjustable angle of 20 degrees. The depth of penetration is adjustable to each nozzle and optimises the gas flow conditions within the boiler flue and positively effects the emission values.

Cooling System
High reliability is the most important requirement for the cooling system. It is guaranteed by high volume flows, a redundant pump station and additional security systems. Therefore the operator enjoys the security of a straightforward and robust operating system.

Due to the high flow volume, the self-contained cooling circuit responds to fluctuating loads with minimal temperature differentials. The absorbed heat is recovered efficiently by the primary combustion air system. Hence the wastage is marginal.

Grate Ash Spillage and Ash Discharger
The grate ash spillage system comprises of 2 by 5 primary air funnels which directs the ash to the base of the funnels where it is then transported by the wet ash conveyor into the ash discharger. A hydraulically driven pusher moves the ash together with the slag from the discharger onto the conveyor transport system.

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