Flue gas to Hot Water (or Steam) Exchange
The derived hot flue gas, at >850°C, travels through a number of heat exchanger flue gas to hot water (or steam) tubes. The heat exchanger section comprises a refractory wall enclosure providing a gas tight atmosphere surrounding the module banks.
The design of the non-drainable heat exchangers is crucial in terms of alkali deposit formation on tube surfaces and minimising the risk of de-novo dioxin formation. Independent tests have shown that Dioxin reformation does not take place due to the residence period and gas velocities. Heat exchanger surfaces are prone, where high alkali biomass fuels are the primary fuel, to severe fouling from ash deposits.
The BHSL heat exchange is designed to continuously remove ash and prevent it from building up. This maintains the ongoing efficiency of the process. Ash from the heat exchange area is removed by a horizontal screw conveyor.
Flue Gas to Primary Air Exchange
In order to maximise the efficiency of the process the air used for primary combustion is pre-heated using an air to air heat exchange. The flue gas temperature at the exit of the primary air heater is controlled to ensure that stack exit temperatures are well above dew point temperatures of the main gas constituents and to minimise flue gas heat losses.
Instrumentation within the flue gas path is mainly focused on flue gas temperatures; other instruments on the water path are designed to monitor flow and thermal gain.
The BHSL heat exchange uses alloys specifically selected for their performance on the flue gasses from manure combustion.
The Life Cycle of these parts has been proven over many years of operation.