Edition 03/13

At its site in Frechen, near Cologne, RWE Power AG processes 5.15 million tons of crude lignite every year into about 900,000 tons of pulverised lignite and 1.1 million tons of briquettes. In a second operational area the company’s own power plant produces 0.983 terawatt hours of electrical energy every year using briquetting carbon. For the 24-hour-production of both areas a fail- safe compressed air supply is a must. This is generated in a central station by three oil-free compressing, speed-controlled Aerzen screw compressors: two units for base and peak load, the third for redundancy. Afterwards the compressed air is dried in three water-cooled adsorption dryers to a pressure dew point of -80 °C, kept available separately as working and instrument air in two compressed air reservoirs and then fed into two separate operating networks. The station works with a pressure of 6.5 bar as only then can the flawless functioning of all the consumers connected within the entire system be guaranteed.

Double dilemma

In 2012/2013 this concept was systematically reviewed. Leakage was detected in the cooling water system of the three adsorption dryers which could only be removed during standstill of all three dryers. But, as the compressed air could not be fed into the systems in an undried condition, the stand- still of the dryers also meant a standstill of the compressors, the compressed air supply and consequently of the entire production.

Furthermore, the inspection showed that upgrades were also needed in fire protection and asset value protection, which could only be achieved during a two day complete shutdown of the electrical distribution station. Consequently, the electrical supply of the company’s compressed air station was not available during the repair period. For the repair period an external emergency supply had to be found.

The Wachtberg briquette factory has been co-operating with Aerzener Maschinenfabrik for many years now, as Aerzen compressors are not only working in the central compressed air station, but also in the ash-handling plant. So, together with Aerzener they were looking for potential solutions.

Meticulous planning

Besides the Aerzen sales office West in Velbert, the Aerzen subsidiary company Aerzen International Rental (AIR) played an important role in the detailed planning and realisation of the entire project. The company, which has its head office in Duiven, Netherlands, specialises in the emergency supply of industrial enterprises with compressed air with extensive machinery. They can be reached around the clock, issue emergency plans, supply and install the required units with their own staff, take care of the cabling, the electrical connection to the piping and put every- thing into operation.

Also at Wachtberg: The scope of supply included six speed-controlled, oil-free compressing, air-cooled Aerzen screw compressors. In addition, AIR provided for the period of the repair an external electrical supply with five diesel driven generators: Four generators each directly supplied the four large compressors, while a fifth generator supplied electrical energy for two smaller units via a sub-distributor. Furthermore, AIR installed five filled fuel containers for energy supply of the diesel engines. For safety reasons a tanker truck was available at the factory’s premises for quick refilling of the fuel tanks. Half of the produced compressed air was dried with two adsorption dryers provided by AIR - a compromise, which was sufficient for the short repair phase.

AIR supplied all the required Aerzen bypassing components on low-loaders, put these on the courtyard and connected them in readiness for operation. Within two days all the components had been installed, test runs and inspections were completed and the compressed air supply was changed smoothly, by shutting down the Wachtberg factory compressors one after the other and simultaneously starting the Aerzen rental compressors one after the other. After the repair had been completed the Wachtberg station was reactivated step-by-step and since then has once again been supplying all the locations on the network independently.