Wastewater as a heat source

Recovering heat from wastewater

Energy efficiency is a hot topic. In light of rising energy prices and the need to reduce carbon emissions, the use of waste heat – especially from wastewater from industrial processes – is gaining in popularity. But conventional heat exchangers cannot cope with anything more than even slightly contaminated water; dirty water causes their efficiency and heat transfer to plummet rapidly. With this in mind, the company Jaske & Wolf Verfahrenstechnik, based in Lingen in northern Germany, drew up a concept for a continuously self-cleaning heat exchanger called DUPUR®. The implementation of this R&D project was sponsored by an international mechatronics funding program. Scientific support came mainly from the Steinbeis Transfer Center for Technology Marketing, the non-profit innovation center at the Steinbeis Transfer Center for Power and Environmental Engineering, and additional partners in the Netherlands.

The heat exchanger was first used in the Moskaubad outdoor swimming pool in Osnabrück. Local utility company Stadtwerke Osnabrück, the operator of the pool, wanted to use the new heat exchange system to halve its annual energy consumption for heating outdoor swimming pools. “Up to now, the Moskaubad pool has consumed 600,000 kilowatt hours a year,” explained Jürgen August, head of pool technology, “but in future, we want to reduce this to 300,000.”

The new technology will be applied in an area responsible for a large proportion of this energy consumption: heating fresh water for the pool. The filters need to be cleaned by rinsing several times a day, depending on visitor numbers, and each rinsing removes up to 35 cubic meters of warm water from the pool. Formerly, this water was disposed of directly into the sewers at 24 °C, and the fresh, cool water added to the pool was warmed to the pool temperature mainly using a gas condensing boiler. Now, the heat exchanger instead absorbs thermal energy from the 24 °C wastewater and uses it to raise the temperature of the fresh water from 12 to 22 °C. Pre-warming the water in this way means a lot less gas is needed to heat it to the pool temperature.

Contaminants and suspended matter, as commonly found in the filter backwash water of swimming pools, rapidly impair the performance of conventional commercially available heat exchangers. Particulate matter suspended in the water is deposited on the heat transfer surfaces, causing the machine’s efficiency to nosedive. In the industry, this process is known as fouling.

The new DUPUR® heat exchanger solution solves the problem of fouling on the surface of the heat exchanger by using an intelligent pig system that mechanically cleans the heat exchanger when needed. The centerpiece of the multiple tube-within-a-tube heat exchanger is a pig valve that makes it possible to simultaneously pig all pipe sections during operation. Using a dedicated control mechanism, cleaning intervals can be set as needed, thereby ensuring high efficiency and economical operation.

“Working together with the Steinbeis Transfer Centers and our partners in the Netherlands opened up a lot of new market opportunities for our company,” comments Wolfgang Jaske, summarizing the benefits of the collaboration. “Without their support, we wouldn’t have been able to make this project a reality so quickly and easily.”

The DUPUR® system is suitable for strongly discolored waste water and water containing suspended matter and process fluids. It can be used in a variety of industries:

  • Food, milk and starch processing
  • Beverages
  • Meat packing, sewage treatment plants, biogas plants
  • Petrochemicals and chemical engineering, painting/varnishing machines, galvanization
  • Swimming pools, geothermal energy
  • Parts cleaning machines

Summary of features:

  • Continuous heat transfer the whole time the machine is running
  • Cleans itself during operation, taking just a few seconds
  • Cleaning cycles can be adjusted to the level of contamination
  • Subsequent heat pumping often no longer necessary
  • No need for chemical cleaning, so operating costs are lower

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