Reducing the discharge temperatures of industrial wastewater treatment plants – utilisation concepts for excess heat

In industrial production, products are typically manufactured from raw materials using water and external energy. In addition to residual and waste materials, used water and not inconsiderable amounts of surplus energy in the form of waste heat are usually generated.

In addition to immediate reutilisation of the heat energy within the production process and/or direct discharge from the system via separate cooling systems such as cooling towers, larger amounts of heat are also discharged via the wastewater.

Particularly in the case of industrial plants with direct discharge into small to medium-sized receiving waters, the discharge quality requirements are gradually being tightened under the influence of the requirements of the EU Water Framework Directive. This currently very often affects the limit values for phosphate, but increasingly also the discharge temperatures.

A distinction is often even made between summer and winter discharges in order to take account of the natural temperature fluctuations of surface waters. This poses major challenges for industrial dischargers, particularly in the winter months, as the wastewater has high temperatures throughout the year due to production processes.

Ideally, the necessary cooling of wastewater is carried out in such a way that the extracted thermal energy can be recovered profitably and is not lost. Unfortunately, however, direct utilisation from the wastewater is rarely possible because

1. the wastewater is rarely clean
2. the temperature level is comparatively low

With project-specific combinations of HUBER Heat Exchanger RoWin and a suitably designed heat pump, HUBER offers a wide range of possibilities to combine the reduction of discharge temperatures required for environmental protection with regenerative heat reuse. Each application is individually tested and conceptualised.

The centrepiece of every plant is the HUBER Heat Exchanger RoWin, which can be operated continuously with wastewater containing solids and grease without any problems due to its automated cleaning system. This also makes it possible to transfer the energy discharge to the inlet area of the internal wastewater treatment plant, where more favourable / higher temperature conditions usually prevail. HUBER Heat Exchangers can be used as single or group units in parallel or series connection.

Depending on the existing temperatures in the wastewater, its volume and the target temperatures for discharge and internal reuse, different energy utilisation concepts can be realised. For example, in the future and already today, plant buildings can be heated (especially in winter), rinsing and washing water can be preheated, production processes can be heated, fermenters or the fermenter inlets can be preheated.

In each case, the primary energy input for these processes is reduced. In this way, a valuable contribution can be made to conserving resources while at the same time protecting natural surface waters.