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Cooling towers use a rather energy-intensive approach: Process water heated during production is atomized in order to release the excess heat into the atmosphere – a process that positively devours electricity. There are over 20 of these systems at Industriepark Höchst alone. Unfortunately, there is still no industrial-scale technology that can harness the thermal energy of hot production water. In their quest to make this organically grown infrastructure more sustainable to operate, Infraserv Höchst’s experts started looking around for alternatives. They found them in digitalization.
The little things add up – especially when reducing energy consumption and CO2 emissions. However, it seems a bit of a stretch to call it a “little thing” to save 173 metric tons of CO2 or 411 MWh a year for a single cooling tower. Especially since it entailed very little investment – no modifications required. All it took for optimization was to create a digital twin of the pump control unit. Everything is now in place for this technology to be rolled out to other cooling towers.
So where can you save on electricity? Let’s take a look at the pilot project run by Frank Mollard’s team from Infraserv Höchst’s Data Science & Data Engineering department: Cooling Tower H 211. This unit uses five pumps to supply water that needs to be cooled. Four of them are “binary pumps”, each with a nominal capacity of 1,000 m3. These pumps can only be switched on or off. The fifth pump is a high-performance inverter pump with a variable capacity of up to 1,500 m3.
The binary pumps are not all running constantly. In fact, these four pumps can be switched on or off in 16 different combinations to provide the required amount of water. The calculations get even more complicated when the inverter pump is added to the mix. Here’s an example. If you need a flow rate of 3,500 m3, you would run three of the four binary pumps and have the inverter pump provide the rest. At least in theory.
The reality is a bit more complicated. For one thing, the binary pumps do not simply provide their nameplate capacity. Their actual output depends on a number of factors such as pipe routes, location, condition and age. This increases the variety of possible combinations, which in turn places different demands on the inverter pump. Also, running the inverter pump at full capacity fails to optimize energy use – as does running it at an overly low flow rate. In addition, the relationship between energy consumption and flow rate is not linear.
The challenge, then, is to determine how to pump a given amount of water while consuming as little energy as possible. At the same time, you want to wear the individual pumps at the same rate. That means all pumps have to be utilized approximately evenly. So the math problem is this: Which combination of pumps consumes the least amount of energy with the least amount of wear? And how long will each combination run while maintaining a constant flow rate?
With previous methods, any change in water volume would have required a bewildering number of calculations. Frank Mollard and his team, working closely with people in the Refrigeration, Cooling, Water department, found an elegant solution: Over a period of one year, they analyzed all the relevant parameters of the pumps and then used the data to create a “digital twin” of Cooling Tower H 211. Now, if the actual performance of a pump changes, whether due to wear or maintenance, it is measured again separately. This is done relatively quickly – within a few days. The new data is then uploaded to the digital twin, which can immediately provide the updated ideal combinations.