To make ice cream you need electricity ... and heat. For the last 12 years, a Rolls-Royce mtu combined heat-and-power plant has been supplying both at ice cream maker Unilever with its brands Langnese, Eskimo, Algida, Good Humor or Frido. A new engine is now making this set-up even more attractive, boosting efficiency from 87.1 to 88.0% and saving Langnese over € 30,000 per year as well as 'greening up' the way electricity and heat are generated for production purposes. All in the interests of making tasty ice cream a sustainable treat.
Ice cream, anyone? Summertime is when ice cream tastes best, which is why production at the Langnese plant in Heppenheim is currently running at full speed, producing up to five million ice creams per day and an incredible 150 million liters per year. The ice cream is exported to many European countries as well as to the US and Australia.
A 1% efficiency gain saves € 30,000 p.a.
Depending on the type of ice cream, its ingredients are milk, sugar, fat, chocolate, fruit preparations, flavors, water and air. These are mixed in weighing tanks, and then pasteurized with hot air and homogenized. The hot air is produced in the mtu combined heat-and-power plant. Until recently, this featured a 16-cylinder Series 4000 L62 engine with a 1,719 kW power rating. Early this year, service technicians from Rolls-Royce Power Systems replaced it with a fully overhauled L33 Reman engine. The new model not only has around 1% more efficiency, Rolls-Royce Power Systems also supplied the customer with a new control cabinet featuring the latest-generation software. Another benefit is that the new engine's maintenance intervals are significantly longer, requiring it to be serviced every 3,000 hours instead of 1,000 hours hitherto, thereby really improving the CHP's uptime.
“With this upgrade, not only are we saving money in operations, we've also made our production more future-proof into the bargain,” said Jan Lerch, Environmental Officer at the Langnese's facility in Heppenheim. He also praised the speed at which the engine swap went. “The CHP was up and running in just 3½ weeks, quicker than planned,” he continued.
The CHP plant feeds the thermal energy directly into the Langnese plant's 105 °C heating circuit. “The heating circuit is a bit like your central heating system at home,” explained Lerch. “When we need heat somewhere, we simply feed the hot water through heat exchangers, like radiators.” The CHP can heat up to 45 cubic meters of water per hour. The heat is used during production to keep ingredients in the tanks – such as fats and chocolate – at the right temperature for smooth processing.
How ice cream is made
Back to the ice cream mixture, which has been pasteurized and homogenized with the hot air from the CHP plant. It still has a few steps to go through before being packaged. First, it is left in maturing vats for between two and seven hours at +4 °C. The liquid mass is then pumped into freezing machines whose ammonia-filled jackets chill it to -40 °C. The next stage is portioning. With premium ice creams like the Magnum, this involves shaping the mass in a stainless steel pipe and extruding it, inserting the stick and cutting off the finished bar which is then placed onto a moving stainless steel plate. The ice cream on the plates is frozen solid in a tunnel with air circulating at -40 °C. Once through the tunnel, the frozen bars are lifted by grippers, dipped in a chocolate bath and fed into the packing machine. After that, the ice creams are ready to be enjoyed.
CHP generates electricity for the works gridThe ice cream production facilities at Langnese operate at full stretch during the hot summer months. “During this period we need more hot water than the CHP can deliver. So to heat the water to the required temperature, we hooked our existing boiler up to the CHP. Any superfluous heat is stored in buffer tanks. And we can shut the CHP down completely when demand is low”, explained Lerch.
However, the CHP generates not just heat, but electricity. A transformer converts the 400 volts supplied by the unit to the 20 kV used by the factory power grid. “That's five to six cents cheaper per kilowatt-hour than if we were to buy it from the public grid,” said Lerch.
Over 5,000 operating hours per year
In total, the CHP at Langnese in Heppenheim runs for 5,000 to 5,500 hours per year – more frequently in hot summers than in winter, when ice cream demand is lower. The CHP managed 65,000 hours on its first mtu engine. “Always reliable with no unscheduled repairs,” said Lerch. Now with the new engine, he's looking forward to the next 65,000 hours. To avoid unscheduled downtime, Langnese has signed a maintenance agreement with Rolls-Royce. “This way we'll ensure there's always enough heat and power, so the ice creams just keep on coming,” he concluded.