The production of waste heat is inevitable within industrial processes but it also represents a future path for heating networks, as the energy transition bill towards sustainable development and green energy pushes companies to turn towards the recovery of energy.

What is waste heat?

Waste heat energy is the result of a production site whose primary purpose is not connected with heat production. This energy is, therefore, not necessarily recovered, in fact it is more often lost in the atmosphere.

According to a survey by INSEE, the energy consumption from operations of manufacturing and food industries amounted to 34.2 million TOE (tonnes of oil equivalent). This shows the potential of waste heat! This energy can be used for transportation and processing of flows of materials and energy needed for different industrial processes, maintenance or lighting. The heat produced is then in the form of effluent, either gaseous or liquid.

Many sites can be sources of waste heat, including:

– Nuclear power plants ;

– Industrial production sites (in the steel, chemical, cement, food processing or glass sectors);

– Commercial buildings which emit heat by their consumption, such as hospitals or transportation networks;

– Heat treatment and waste disposal sites…

According to ADEME (Agency for Environment and Energy Management), the heat lost by industry in France represents a pool of over 100 TWh, of which 60% is at a temperature of over 100 ° C. Making use of this heat is therefore a strategic issue for the industry.

A mandatory cost-benefit study

Without recovery, waste heat is, as its name suggests, a waste of potential resources, and one that the EU has decided to put a stop to. Thus, the European Directive 2012/27 / EU on energy efficiency mandates a cost-benefit analysis for the valuation of the waste heat through a heat network project, a key partner of such a recovery operation.

This requirement concerns:

– Installations with a total thermal input exceeding 20 MW;

– Those subject to authorization under the regulation of facilities classified for environmental protection (ICPE).

Some electricity production facilities are excluded, such as those which emit heat at temperatures below 80 ° C and those sites which are too remote from heating network compared to the amount of heat that can be recovered from the site. The analysis must be incorporated into the impact assessment, and include a description of the installation and the waste heat recovery solution.

If the solution is considered to be profitable, it must be implemented. Similarly, while heating network project must evaluate the various potential recovery of this energy source hitherto untapped.

Waste heat, part of the energy transition law project

In France, the industrial sector accounts for over 20% of energy consumption in the country. If the law on the energy transition to green growth, which should be adopted definitively by the end of 2015, wants to be successful, it must support companies in their efforts to reduce their energy consumption. And even more when we know that, according to ADEME, at equal production, energy efficiency potential of the reachable industry by 2030 is 20%.

Where waste heat can be involved in the improvement of energy performance, it is the obligation under the law on the energy transition to green growth to achieve by local authorities in charge of a heating network a master plan by December 31, 2018. This document must in particular assess the potential for intensification, expansion and interconnection of networks in the territory, and to quantify the possible development of the share of renewable energy and recovery ( RE & R).

How can waste heat be recovered in a heating network?

There are several techniques to recover waste heat in a heating network, including:

– The transfer of heat through a heat exchanger;

– Heat pumps;

– Via an absorption machine (in a process such trigeneration);

– By transforming the waste heat into another form of energy;

– For storage or for later on-site use.

Industrial sites are not the only ones affected by using waste heat in a heating network as data centres also produce a lot of heat, which can be exploited.

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