Effective waste heat recovery can help decarbonise ‘hard-to-abate’ industrial plants in energy intensive industries such as cement, glass, steel-making, pulp and paper, which currently dissipate 30–60% of the overall energy consumed to the atmosphere.

According to a European Union study in Applied Thermal Engineering, the potential for waste heat recovery from Europe’s key industries is estimated to be around 300 TWh/y (equivalent to 26mn t/y). Recovered waste heat can be used for both heat and power, to be consumed on site or distributed via local district heating and electricity networks.

There are currently over 10,000 district heating networks in Europe covering 13% of the heat market and supplying more than 60 million people. It is estimated that district heating could supply 30–50% of EU heat demand by 2050. However, the percentage of district heating is only 2% of market share in UK homes (about 12.9 TWh) due to the mass utilisation of natural gas for heat on the National Grid. By 2050, the UK government has set a target to connect 20% of buildings to district heat (about 95 TWh).

New Energy World was invited by heat pump manufacturer Turboden to visit one of the leading operators of waste heat recovery and power generation at steelmaker ORI Martin in Brescia, northern Italy.

In a move to boost energy efficiency and reduce greenhouse gas emissions, the ORI Martin plant was equipped in 2015 with a Consteel electric arc furnace (EAF) to convert recycled metal scrap to specialty steels, mostly for the automotive, construction and rail sector. Subsequently, ORI Martin installed an iRecovery evaporative cooling heat recovery system to recover the remaining thermal energy in the off-gas – from scrap melting and the super-heating process in the electrical furnace – to generate steam for Brescia’s district heating grid.

The energy from the ‘waste’ fumes converts the recirculation water of the cooling circuit into steam. During winter, the steam produced is sent to a heat exchanger unit dedicated to district heating for Brescia. During summer, the steam produced is used to feed an organic Rankine cycle (ORC) turbo-generator supplied by Turboden for the production of electricity for internal use.

About 81% of Italian steel plants use EAFs rather than blast furnaces which are reliant on conventional fossil fuels. The Italian steel industry achieved 60% CO₂ emissions reduction from 1990 to 2020 and is considered to be the industry leader when it comes to energy efficiency, with specific energy consumption 38% lower than the EU average.

An ambitious sustainability programme 
The operators of the ORI Martin plant are committed to building sustainability and circularity into their operations. The plant currently emits about 400 kg of CO₂ emissions per tonne of crude steel. The use of EAF permits about 90% natural resource saving and 80% CO₂ reduction, compared to blast furnace operations, according to the firm’s latest Sustainability Report (2022).

Carolina De Miranda, Sustainability Manager at ORI Martin, emphasises: ‘The plant is located in an urban context with a respect for the quality of life in the surrounding area, stimulating us to constantly invest in mitigating environmental impacts and any potential spill-over effect on the city.’

Indeed, she adds: ‘The decision to re-style the plant towards an innovative EAF capable of preheating scrap was the first step towards a circular economy integrated into the production process. Today our goal is to reduce our carbon footprint even further. This is why we decided to invest and test a large industrial heat pump with the objective of recovering most of the thermal waste from steelmaking which would otherwise be lost to the environment.’

Turboden’s ORC-CHP large heat pump at ORI Martin steelmaker plant in Brescia, Italy
Photo: Turboden

In 2020 ORI Martin became a member of the European Steel Technology Platform, a joint industry, universities and research initiative primarily focused on creating a sustainable EU steel industry.

In 2021, the plant integrated sustainable development goals with life-cycle assessment of emissions in its electricity system operator (ESO) strategy.

In 2022, the plant embarked on the Coralis project with environmental product declarations (EPDs) for several products, including steel billets, hot rolled wire rods and bars.

That same year, the steelmaker began the Heatleap Project in partnership with large heat pump (LHP) manufacturer Turboden, part of Mitsubishi Heavy Industries Group, under the EU-funded LIFE programme which co-finances climate and environment projects.

Further renewable energy initiatives are underway at the steel plant. ORI Martin installed 4 MW of photovoltaic panels in its Ospitaletto plant, while a further 4 MW of PV panels are being installed in the Brescia plant.

‘Sustainability is at the heart of the ORI Martin steelworks operation. The plant is located in an urban context with respect for the quality of life in the surrounding area, stimulating us to constantly invest in mitigating environmental impacts and any potential spill-over effect on the city.’ – Carolina De Miranda, Sustainability Manager at ORI Martin

CHP-ORC technology explained 
Combined heat and power (CHP) cogeneration is a key technology for optimising energy efficiency and heat capture that would otherwise be wasted. In cogeneration mode, CHP-ORC technology can produce both electricity and capture the waste heat, whenever there is heat demand nearby, that is, to meet seasonal heating demand or for hot water. In addition to direct use for district heating, waste heat recovery is suited for both power and heat production.

Industrial waste heat recovery potential is still largely untapped due to a number of technical and non-technical barriers. Among them, the need for efficient and cost-effective technologies to recover heat losses and to re-use, upgrade or transform them for heat valorisation.

The Rankine (thermodynamic) cycle is widely used by coal-fired and nuclear power plants to produce heat within a boiler, converting water into steam which then expands through a turbine to produce useful work.

Waste heat valorisation of industrial processes can be achieved through the ORC, a variation of the Rankine cycle which uses an environmentally-friendly organic, high molecular mass fluid, such as refrigerants and hydrocarbons, which vaporises at a lower temperature than water, as the working fluid. The fluid allows heat recovery from lower temperature sources (<70°C) such as industrial waste heat, biomass combustion, geothermal heat and solar energy.

In Turboden’s ORC-CHP cogeneration configuration, electricity and heat can be used either on-site or delivered to a district heating network nearby or for industrial processes.

Under the Heatleap Project, Turboden designed and installed a customised LHP to extract heat from thermal waste, which would otherwise be lost to the atmosphere. During its scrap metal melting cycle, the EAF consumes electricity and produces heat. Much of the heat from the flue gas and the cooling water is now recovered by the iRecovery plant, using the heat from the flue gas in the heating tunnel to transform liquid water into steam (raising the temperature from 70°C to 120°C). The steam is stored and then converted to ‘electric power’ through an ORC turbogenerator; and to ‘thermal power’ that supplies the district heating system in Brescia run by A2A Calore e Servizi.

The recovery of heat is carried out in a continuous cycle where water from the degasser evaporates in the waste heat boiler (a steam generator with natural circulation water tube bundles), cools down in the heat exchangers and is then sent back in the form of condensate to the degasser, thus closing the thermal cycle.

Today the cogeneration project supplies 2,000 homes with heat during winter and 700 homes with power using the electricity generated. Previously the heat generated by the process was transferred to the cooling water and dispersed (lost) into the atmosphere.

The heat pump has a thermal output of 6 MWth and can maximise energy recovery from the steel plant, while regulating the heat transfer temperature from about 95°C up to 120°C using a heat exchanger, to meet the specific hot water needs of the local district heating network, at the same time reducing CO₂ emissions.

High flexibility is achieved using a custom-designed heat pump with two high-speed compression stages and a variable-frequency drive to maximise the thermal output under different heat source conditions. The system operates automatically and can run at partial load, according to the available thermal power. The heat pump also enables heat produced during cooling operations to be raised and re-used, instead of being dissipated through the cooling towers.

Since steel production in the furnace is a batch process, hot exhaust production is not constant. For example, heat recovery is not possible during furnace discharge. When molten steel is sent to continuous casting, the iRecovery system is inactive due to the absence of hot fumes.

However, the cooling circuit remains in operation. During this time, the heat pump receives cooling water from the furnace at 75°C ready for the next melting batch, and raises the outlet temperature from 95°C to 120°C to feed the district heating network. When the furnace restarts the process, the exhaust fumes return to the primary circuit and the heat pump returns to delivery of heat at 95°C, as shown in Fig 1.

Fig 1: Diagram of the waste heat recovery process using a large heat pump at the ORI Martin steel plant
Source: Turboden

According to Heat Roadmap Europe, about 80% of the 2,740 TWh final energy demand for the heating sector (including residential and industrial heating) is still generated by burning fossil fuels. Only 20% comes from renewable energy. Turboden claims that about half of the fossil-based heat (1,100 TWh) generated could be decarbonised using its ORC-CHP heat pump technology.

Looking forward 
‘Turboden sees its mission as playing a key role in the decarbonisation path by designing cutting-edge solutions in the field of renewables and energy efficiency,’ remarks Marketing Director Marco Baresi. And continues: ‘As a member of the board of European Heat and Power, the European association devoted to waste heat recovery, we see an enormous opportunity to change traditional district heating with a more decarbonised approach. But there are still some barriers to overcome in terms of the long-term return on investment. So, you need to be focused not only on financial factors, but consider the social and environmental perspectives.’

Looking forward, Turboden is set deliver a further innovative project next year connected to a paper pulp company in Finland, collecting waste heat from the process at 13℃ and delivering super-heated steam at 180℃, using a combination of its heat pump and mechanical vapour compression technologies. ‘This will be the first of its kind in the sector,’ claims Baresi.

• Further reading: ‘Heat pumps, refrigerants and UK district heating network’. Discover some of the advantages of the refrigerant used with heat pumps that are being installed in a London district heating system.
• Decarbonisation is one of the biggest challenges for the hard-to-abate iron and steel sector. Learn about some of the front-runners in the race to produce green steel.