Therm-Liner is a heat exchanger that is installed into the existing sewer flows, along the pipe invert, so that the effluent flows directly over the heat exchanger elements.

By connecting the Therm-Liner to a heat pump on the surface, which circulates heat extraction fluid through the Therm-Liner elements, the heat energy from the wastewater or effluent is transferred to a local power station, recycled and reutilised.

The heat from the effluent can also be used to warm water that is used as part of centralised local area heating system for local buildings such as council offices, schools or industrial sites and factories, normally within 300 m of the heat source (in this case the sewer pipes) and heat pump circulation system.

By utilising the wastewater in existing sewers this way it is possible to reduce the need for the buildings on the system to use new additional fossil fuel energy to maintain good working environments or to heat water for production process, ultimately reducing the need for carbon-loaded energy use.

The heat recovery system does not produce new electricity but simply transfers what would be waste heat back into the system for reuse.

Therm-Liner

The Therm-Liner heat recovery elements are designed and shaped to fit the most commonly used pipeline formats including circular, egg-shaped and other shapes as necessary, ideally starting at a nominal diameter of 800 mm, but there are also solutions for smaller diameter pipes.

The installation can be carried out through most, if not all, existing manhole structures and designs, normally eliminating any need to excavate or to remove the ‘biscuit’ for access to the sewer pipe.

The stainless steel units are usually 1 m long and can be interconnected during installation. This allows a flexible approach to the various projects and ensures the possibility of an extension or removal of Therm-Liner Elements.

As the Therm-Liner unit is installed in the sewer flow, heat extraction fluid is passed through pipes which form part of the Therm-Liner system. These pipes have very high heat transfer properties which allow the heat from the effluent to pass into the circulating heat recovery fluid, raising its temperature.

This fluid is circulated around the heat exchanger by low-power pumps in the ‘transfer station’ on the surface. In the transfer station, a heat exchanger uses this recovered heat to warm water which is passed into a local centralised heating system and is passed to buildings on the system where it is fed directly into their normal central heating systems.

Because the Therm-Liner elements are installed in the sewer pipe invert, they are always immersed in the sewer flows and recover heat even when flows are low. Specific heat recovery figures will depend on the sewer into which the system is placed and its flow characteristics. Tests have shown, for example, that in a 1,200/1,800 mm diameter egg-shaped sewer with an average flow of 8.3 litres per second with just 39 m of Therm-Liner heat exchange units in place, the local area heating system effectively saved around 43 per cent of its new energy usage which in turn lead to a 60 per cent carbon dioxide reduction from the fuels normally used.

Uhrig International Sales Manager Brian Hickland said “Having used this system in Europe for some time now, the data feedback from the various installed and functional projects confirm that the heat energy recovery from sewer flows is not only possible, but is also a very cost-effective method.

“The system is very quick and easy to install in existing sewer pipes, once personnel have been trained correctly, which means minimal lead time and early results on reducing energy consumption from more conventional means. Taking into account we have hundreds of miles of sewers running under our cities a future low cost energy source is literally running under our feet and is already at our door step. So, let’s not waste time but utilise this low cost source of future energy.”

German Environmental Minister Tanja Gönner said “It is the intention of the German Government that this sort of technology will be increasingly used across the country to take heat energy from wastewater in the future for the heating and supply of warm water to buildings to save on oil and gas usage. The first projects are starting in Konstany, Leonberg and Bretten.”