Maximising the resource

For years industries around the world have been encouraged to use less fossil fuels in a bid to cut down on carbon emissions. But the Therm-Liner system is showing how better use can be made of the energy already produced.

For more than a decade now world governments have been pressing industry, utilities and the general public to be more aware of energy usage, and to play their part in the reduction of carbon emissions that are deemed crucial in the fight against global currently afflicting the planet.

To date, much of the effort towards carbon reduction has been to reduce the use of fossil fuels and increase the application of renewable carbon-free energy sources such as wind and wave. Less emphasis has been placed on maximising the use of the energy already available having been created by mainly fossil fuel power production sources. Much of this energy produced is being allowed to go to waste after only one, yet not always efficient, use.

With the help of a new product, Therm-Liner, from Uhrig Kanaltechnik this could be changing. A large percentage of the fossil fuel energy used in homes, office buildings, schools, factories goes into the heating of water and the environment in general. This means that much of the wastewater, which has been used for heating or been warmed by the local environment, is flushed into the local sewer network.

This wastewater is at a higher temperature than local ambient conditions, often running at between 12 and 15ºC. The fossil fuel energy used to create this heat is, at present increasing the carbon emissions and generally lost to the environment as the effluent travels through the sewer network, which is energy literally wasted.

This can be up to as much as 25% of the energy used to heat the buildings from which the wastewater and effluents carry the bulk of the energy loss into the underground sewer pipes.

Under the right circumstances the recycling of the heat energy recovered from this process can lead to up to 75% reduction of existing fossil fuel energy consumption.

Power station

Because the wastewater sewer flows run at a higher temperature than the pipeline and surrounding ground through which the effluent runs, any heat in the effluent is generally lost through the sewer pipe wall into the local soil or dissipates into the atmosphere at the sewerage plants.

The Therm-Liner V4A heat exchanger unit is designed to minimise this loss by recovering this heat before it is lost to the environment. It is installed into the existing sewer flows, along the pipe invert, so that 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. Here the heat from the effluent can also be used to warm water which 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 300m of the heat source and heat pump circulation system.

The wastewater / effluent in the sewer flows undisturbed onward on its normal path.

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 for their workforces, students or to heat water for production process, so ultimately reducing the need for carbon-loaded energy use.

It should perhaps be pointed out that the heat recovery system does not produced new electricity but simply transfers what would be waste heat back into the system for reuse.

It can be termed heat recycling due to maximisation of and increase in the effectiveness of the power or fossil fuel energy which was initially used to heat the water which was then introduced into the sewer system with a higher temperature. 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 800mm, but there are solutions for smaller diameter pipes also.

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 normally 1m long and can be interconnected during installation. This allows a flexible approach to the projects and insures the possibility of an extension or removal of Therm Liner Elements. It is possible at any time to adopt and to suit changing client needs or a later dynamic increase in client energy demands.

As the Therm-Liner unit is installed in the sewer flow, heat extraction fluid is passed through pipes that form part of the Therm-Liner system. These pipes have very high heat transfer properties that 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 surface. In the transfer station, a heat exchanger uses this recovered heat to warm water that is passed into a local centralised heating system at temperatures of between 40 and 60ºC. This now hot water 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.

Energy usage

Specific heat recovery figures will depend on the sewer into which the system is placed and its flow characteristics but tests on the system have shown that in a 1,200/1,800 egg-shaped sewer with an average flow of 8.3l/s with just 39m of Therm-Liner heat exchange units in place, the local area heating system saved around effective 43% of its new energy usage which in turn lead to a 60% CO2 reduction from the fuels normally used.

Brian Hickland, Uhrig international sales manager, said: “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.”

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