Project E-mission commenced early in 2010 and completed in September of the same year. Today, 1.6MW of electric power and 2MW of thermal power are generated by means of a Caterpillar combined heat and power (CHP) plant. The heat is used to provide the factory’s 90oC process heat supply, although there is still a need for a boiler to produce 6.5 tons of steam per hour at 12bar for many of the production processes.Three intelligently controlled air compressors were commissioned, with a total installed capacity of 500kW. Six refrigeration compressors have also been installed and the waste heat from these is recovered via a heat-pump adapted to supply the building’s central heating and hot water systems.SCADA SystemHellebrekers Technieken designed and installed a ViSpro SCADA system for the control, monitoring and operation of the boiler-house. A Profibus communication network allows the SCADA system to monitor all data within the system. As well as the usual functions provided by such a system, Hellebrekers wrote custom-designed ‘energy pages’ to monitor and log energy usage.At a glance, energy values can be compared with values from a preceding period or with the same period from the previous year. This can be actively controlled to reduce energy consumption and thus CO2 emissions.Hot water distributionHot water from the boiler room is stored in buffers and distributed to where it is needed via double or triple centrifugal pump-sets. There were three main considerations for the pump system:1) The system was designed so that the failure of a single unit did not cause total system failure.2) Energy conservation was the prime reason for the boiler-house renovation so pump efficiency had to be maximised.3) It should be possible to carry out maintenance on the system without shutting down the processes.A Danfoss VLT AQUA Drive with a VLT Extended Cascade Controller MCO 101 was selected for pump control. An external 24V supply ensures that if the 400V mains fail, control circuits will remain powered-up. Decentralised controlThe choice of a decentralised system offers numerous advantages. It permits certain sub-processes to work independently and only the data necessary for other processes are made available for import and export.Pump Cascade ControlThree pumps are arranged in parallel to ensure sufficient capacity for hot water circulation. The pumps are pressure controlled via a pressure transmitter connected directly to the cascade control system installed in one of the inverters. The Unilever installation has two and three-pump configurations but Danfoss' pump cascade control can be extended up to eight pumps, if necessary. The three pumps in this system are sized to meet 150% of the calculated capacity so that full capacity is achieved with just two pumps running. However, to ensure reliability, a 50% reserve has been provided so that should one of the three pumps fail, 100% capacity is maintained.Running hours evenly distributed With the built-in intelligence of the cascade system, the operating hours of the three pumps are evenly distributed. Based on a change in capacity, or to a built-in calendar, the controller will set individual pumps as ‘master’ or ‘follower’, thus ensuring even wear.During operation, the operator can take a pump off-line simply by switching it off. The pump control system will identify this by the pressure drop and will automatically switch to another pump.Process DataAll process data such as measured pressure, set-point, flow, operating hours, etc. is passed via Profibus to the SCADA system where it can be used for control and monitoring purposes.Flow CompensationThe Danfoss VLT AQUA Drive provides a number of internal software features to ensure that energy savings are optimised. The built-in flow compensation ensures that adjustments are made even for small pressure reductions. For example, operation at 3 bar pressure might be acceptable, but 2.8 bar might equally suffice, thus improving energy efficiency.Commissioning with VLT Software Tool MCT10Using the VLT MCT10 set-up software made it extremely easy to commission the drives with the customer’s preferred values. The installation was up and running within one hour and after a few minor adjustments during the following week, control was fully optimised.Project manager with Hellebrekers Technieken ‘Thuis in Techniek’, Ferro Koornberg concludes: “Hellebrekers Technieken were involved in this project right from the start. Unilever gave us a complete design specification and commissioned us to create the complete automation and control system for the new boiler-house. The specification was for a system that had to be transparent, reliable and easy to maintain since any failure of the boiler-house would bring the entire factory to a standstill. It was from this requirement that, together with Danfoss, we created the ideal solution.”
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