2018-05-07   -   Article Turbo-Hybrid symbiosis: The chemistry is right here

Cellulose is an important construction material of nature and stabilises plants and trees. It is the main component of plant cell walls and is made of wood or cotton. DOW uses the basic properties of cellulose in the Industrial Park Walsrode (Heath area) and produces derivatives which can develop a wide variety of properties depending on their composition and processing. Some gel at high or low temperatures, others form films or stick, some make liquids differently viscous. Due to their water-binding, thickening and adhesive properties, these derivatives are in demand for a large number of products. In the food and pharmaceutical industries, for example, they replace gluten in baked goods, help to reduce the fat content in food and enable the delayed release of active ingredients in medicines. In the construction sector, methyl cellulose provides the right properties in tile adhesives, wall plasters or mortar.

The waste water arising from production is treated in the wastewater treatment plant 1.5 kilometers away from the factory. DOW operates the 350,000 EWG (population equivalent) plant as a communal wastewater treatment plant, thus also taking in the municipal wastewater of the city of Bomlitz and the surrounding villages.
In the course of continuous modernisation, the company replaced three turbo blowers equipped with magnetic bearings and causing more and more expenses in 2017. Today, a combination of two AERZEN turbo blowers with air foil bearings and one Delta Hybrid package supplies the aeration tanks of biology. With a rated motor output of 150 kW each, the two AT200 turbo blowers deliver an intake volume of 5340 cubic metres per hour at a maximum differential pressure of one bar.
Both assemblies cover the base load in the communal wastewater treatment plant and run with an average differential pressure of 0.8 to 0.9 bar, according to Sebastian Göritz, assistant foreman. Both turbo machines are operated via an integrated frequency converter so that the volume flow conveyed can be adjusted according to the load operation with a regulating range of 40 to 100%. Decreasing oxygen demand leads to the gradual shutdown of both base load devices, as the efficiency of turbo machines decreases drastically with low speeds. “In this case, the Delta Hybrid takes over the air supply”, explains Sebastian Göritz. In contrast to the flow principle of the turbo compressors, in partial load operation the displacement principle makes the rotary lobe compressor accordingly more efficient due to its high regulating range of 25 to 100% in low volume flow requirement. With the installed Delta Hybrid type D 98 S, the volume flow conveyed amounts to 5800 cubic metres per hour with a motor power rate of 200 kW.

AERZEN combines the operating principles of positive displacement blowers and screw compressors in the Delta Hybrid, providing an energy-efficient solution. The machine uses the Roots principle of full pressure compression in low pressure ranges and the screw compressor principle with internal compression in higher pressure ranges. Compared to conventional compressors, this type of machine reduces energy consumption by approx. 15 percent.
However, the communal wastewater treatment plant in Bomlitz goes a big step further in terms of energy efficiency, and combines turbo blowers and rotary lobe compressors into an overall system that is independently optimised thanks to the AERsmart AERZEN global control system. “That‘s an innovative thing”, says Sebastian Göritz. AERsmart is designed to optimally distribute the air volume requested by the control room to the connected assemblies. This distribution is based on the available technologies and the associated characteristics and efficiencies. “The controller decides which machines from the pool are operated with which performance data to achieve the best overall efficiency”, says the wastewater master at DOW. AERsmart thus goes far beyond cascading with speed control and always runs the machine pool at the energetic overall optimum. The AERsmart control is equipped as a remote terminal with a visualisation on a touch display. The operational staff can immediately see the operational state on site and can read the current key figures of the connected assemblies or transfer them into the control room. Sebastian Göritz is confident that plant modernisations in this intelligent form will continue to increase. “Machines that have an ideal speed range should also be operated there”. Savings in energy consumption of at least 15 percent speak for themselves, especially as most electricity is consumed in biology.

In view of the new efficiency improvements offered by Industry 4.0 for wastewater treatment, in future, DOW intends to monitor the partial streams more continuously in Bomlitz. Online analytics in particular offers very good development potential. “In the case of carbon suppliers, we have to carry out the measurements where the carbon is produced and not only in the wastewater treatment plant. We are in a position to act instead of just reacting”, explains Sebastian Göritz. The connection of the AERsmart control to the control level is just as much the right way in this context as the control of freight quantities on the basis of actual values.