2009 Optimisation of energy plant
Plant thermal capacity increase from 20 to 27 MW
& new instrumentation and control for Pfleiderer in Gschwend / Germany
Pfleiderer AG, a renowned particle board manufacturer has operated, for some years, a solid fuel fired hot gas generator for the energy provision to a chip dryer in their factory located at Gschwend / Germany. Production waste wood burned on a reciprocating grate and sander dust are use used as fuel for this unit, which had an initial design capacity of 24 MW. As the unit was designed, by the initial plant supplier, for the burning of bark with a high moisture content, the achieved capacity was measured at only 20 MW. Furthermore the operation was difficult as there were only analogue controls available and sometimes, the now in force environmental requirements, especially with regards to CO emissions could not be met.
Alera GmbH was commissioned to retrofit the system to achieve at least 24 MW continuous load and to fulfil the environmental requirements under all operational conditions. To enable a better operation and at the same time introduce long time monitoring, a new instrumentation and control system, utilising a Siemens PLC and WonderWare visualisation software were also delivered and installed by Alera
The key part of this retrofit was the installation of a complete new combustion air system. By introducing automatic control flaps for each of the combustion grate zones, it is now possible to adjust the air supply to the different grate areas according to the necessity of the fuel in use. Furthermore the load increase to 27 MW was possible and the plant could be run efficiently within a wide range of load conditions and with a great variety of fuels.
Additionally the secondary air system was rebuild completely to achieve optimum combustion conditions and equal furnace temperatures under all operational conditions.
The new instrumentation and control system further improved the system, so that under all operational conditions a CO value well below the environmental requirements could be achieved. After recommissioning the plant, the CO emissions were always below 5 mg/Nm3.
The new secondary system is equipped with a new, generously sized, radial fan, which is controlled by a variable speed drive.
To further increase overall plant efficiency, the air can be mixed with vapour returned from the dryer. Large secondary high velocity secondary air nozzles ensure the good mixing of the combustion gases with the secondary air.
Before the retrofit, it was not possible to stretch the fire over more than ¼ th of the length of the grate, which resulted in insufficient load and high emissions.
After the retrofit design distribution of the fire over the grate was achieved with active fire over ¾ oft eh grate and a ¼ cooling zone. With this arrangement, temperature excursions could be avoided and efficient, environmentally friendly combustion over the whole load range as well as the desired additional capacity of 27 MW could be reached.
Additionally to the renewal of the combustion air plant, the complete electrical, instrumentation and control equipment was replaced. All larger motors where equipped with variable speed drives and the remaining control flaps were equipped with automatic electric actuators.
A Siemens S7 PLC control was added and for the optimum operation of the plant, a WonderWare InTouch visualisation system was added.
The complete retrofit was executed as a turnkey project .The programming of the PLC and also the complete software for the WonderWare InTouch system was done in-house without subcontracts.
Dipl. Ing. Michael kaden was managing director of Alera GmbH during the above described developments.