The thermal residue treatment and energy utilisation plant (TREA) of Stadtwerke Gießen AG (SWG) is in trial operation as planned. Following the successful cold commissioning in April, the municipal utilities were able to start the hot commissioning of the plant. As the TREA is to run in regular operation without supervision, maximum precision and reliability are required when starting up the plant. Numerous measurement and control systems must monitor the smooth operation of the plant. "Only if a system has been thoroughly tested during commissioning, i.e. where failures of individual components have also been simulated, can you be sure that the system will fulfil all functions correctly in automatic mode," explained Reinhard Paul (Technical Director of SWG).
Experience with comparable systems shows that it is nothing unusual for the test phase to take up to a year.
Measures for optimisation
The trial run of the first few weeks has shown the experts at SWG which areas and processes and which technical details require improvement. SWG's first priority is to strengthen the induced draught fan. The system's previous blower was too small and could not maintain the vacuum in the boiler under unfavourable conditions. The blower with a drive power of 55 kilowatts will be replaced by a new induced draught blower with a 160 kW electric motor.
The fuel transport also needs to be optimised. The fuel is transported on an apron conveyor from the feed hopper in the fuel bunker to the feed chute of the feed stamps. Because the apron conveyor used transported the fuel too quickly, it had to be stopped repeatedly. In order to achieve the best possible control range for the transport of the fuel, SWG is now installing a motor with a larger reduction ratio so that the frequency converter can work within the permissible control range without stopping the motor.
It is not only the optimal transport of the fuel that is decisive, but also the quantities that reach the boiler grate. So-called feed plungers push the fuel through the grate mouth onto the grate. During the test phase, too much fuel entered the feed mouth of the boiler at once, causing a jam that led to a standstill in this area. A total of 14 feed stamps are part of the feed system and must be finely tuned to each other. Here too, SWG is working on the ideal solution. The fuel should be pushed onto the grate with as little pressure as possible. In order to reduce the pressure of the plungers from 200 bar to 80 bar, various valves have to be moved.
Outlook
The experts at Stadtwerke Gießen AG are very positive about the commissioning of the TREA. Even during the trial phase, in which the plant was operated with natural gas, an optimal combustion process was observed. SWG plans to complete the trial operation of the thermal residue treatment and energy utilisation plant (TREA) this year. "We are doing everything we can to be able to start automatic operation this year following successful TÜV approval," says Reinhard Paul.