22.06.2009
Exhaust Gas Heat Recovery Units with Automatic Cleaning
Depending on the customer specifications, largely pre-assembled heat recovery systems can be individually adapted to the requirements of the CHP
A project in Russia involved the use of exhaust gas heat recovery units with integrated automatic cleaning of the heating surfaces, which are installed downstream of the engines operated with heavy fuel oil (HFO).
The thermal output of the exhaust gas heat exchanger is adjusted to the heat requirement of the plant and is 1 MW with an inlet temperature of 155°C and a max. positive operating pressure of 16 bar gauge.
With fluctuating thermal energy requirements an exhaust gas butterfly valve is also used to adapt the thermal output of the exhaust gas heat exchanger to the current energy demand without affecting the electrical output of the engine. This ensures that the plant can efficiently cover a wide range of loading conditions.
As the fuel HFO contains a relatively high level of sulphur, it must be ensured that as little aggressive condensate as possible is produced in operation. This might not only damage the exhaust gas heat exchanger but also the downstream pipework. In this case the likelihood of condensate being produced is minimised by a mixed circuit. In the mixed circuit not just the return temperature to the exhaust gas heat exchanger is increased: there is also the option of adjusting the inlet temperature to the consumer.
A switch cabinet is used for complete control of the heat recovery unit including the necessary safety equipment as well as the bypass dampers with the help of the APROVIS Controlling System (ACS), which communicates with the engine control system.
Given the type of fuel used (HFO), relatively high levels of contamination must be expected for the heat transfer surface. The customer therefore opted for in-situ cleaning of the heating surfaces. These surfaces are cleaned during engine operation, so reducing the effect of the contamination on the transfer of heat.
The use of an in-situ cleaning system extends the cleaning intervals for the exhaust gas heat exchangers while reducing the operating costs and downtimes for the entire plant.
Complete assembly of the heat recovery unit at the factory minimises the amount of installation work required on site as well as any error sources during mounting on the plant, so ultimately maximising reliability in terms of project handling.