Harnessing Waste Heat: A Gateway to the Energy Transition for Hard-to-Abate Industries

Decarbonising the global energy system will be a massive undertaking, requiring a broad range of new technologies, industries and processes to be developed.

Much of the attention in this energy transition is given to largescale newly built projects and new technologies which will generate electricity on a commercial scale in several years. However equally important to the low-carbon transition are technologies that can have a direct impact in the shorter term by improving the efficiency performance of existing energy-related processes and industrial activities.

The opportunity of thermal energy harvesting

Virtually every industrial sector relies on thermal energy for manufacturing or processing materials and products. However, due to inefficiencies in power conversion processes, a significant portion, ranging from 20% to 50%, of this heat is ultimately discharged as exhaust energy into the atmosphere. This waste heat holds the potential to be transformed into clean electricity with zero carbon emissions through Waste Heat Recovery systems, also known as Waste Heat to Power systems.

In the EU28 countries alone, the thermal energy discharged by the industrial sector was estimated to be around 980 TWhth/yr in 2015. The Knowledge Center for Organic Rankine Cycle (kCORC) has assessed that harnessing this untapped thermal energy potential through Waste Heat Recovery systems could generate at least 150 TWhel/yr of electricity, equivalent to the combined annual electricity consumption of the Netherlands and Denmark (source: KcORC, “Thermal Energy Harvesting”).

Two main technologies can be employed for Waste Heat Recovery in the industrial sector: the steam Rankine cycle and the Organic Rankine Cycle (ORC). While both cycles operate similarly from a thermodynamic standpoint, they differ in the working fluid used. The steam Rankine cycle utilises water, whereas the ORC employs an organic fluid, typically a hydrocarbon or refrigerant. The organic working fluid, with its lower boiling point and higher vapor pressure compared to water, enables ORCs to produce electricity more efficiently from low-medium temperature heat sources. Consequently, ORCs are particularly suitable for waste heat recovery from low to medium-high temperature sources and for small power sizes.

Various sectors stand to benefit from waste heat recovery and the conversion of this potential into carbon-free electricity, including:

• Energy-intensive industries like cement, steel, and glass production.
• The oil and gas processing industry, including gas network operators, oil companies, refineries, and petrochemical industries.
• Other chemical industries.
• Food and beverage production.
• And more.

Industries such as cement, glass, and steel manufacturing have already begun to recognise the advantages of Waste Heat Recovery systems. However, numerous other sectors, including chemical, and petrochemical industries, food and beverage, pulp and paper can enhance their energy efficiency and reduce their carbon footprint through the adoption of this technology.

According to data from KcORC's "Thermal Energy Harvesting" report, approximately 75% of the thermal energy obtained from primary fuels used in energy-intensive industrial processes in the EU is currently wasted. The chemical industry accounts for 11.7% of waste heat potential, iron and steel for 16.4%, refineries for 34.4%, non-metallic minerals (including cement) for 27.3%, presenting an estimated potential of more than 50 MWth. When considering only wasted thermal energy sources at temperatures > 250°C (for reasons of higher economic viability) approximately 6.6 GW of electricity could be produced in Europe by leveraging ORC waste heat recovery systems.  Of this, 447 MW in the cement sector, 152 MW from the glass sector, 207 MW in steel, 129 MW in refineries, 1813 MW in food & beverage, and 3562 MW in the chemical sector.

In cement production, waste heat is available from waste gases and exhaust air produced in the preheater and clinker cooler. A part of this heat can then be transferred to an ORC system and converted into power, with no impact on the normal operation and production capability of the cement plant. It can be estimated that up to 30% of the internal manufacturing process's electricity demand can be covered by self-production from an ORC-WHR system.

Similarly, in the glass industry, high-temperature waste heat from furnace exhaust gases can be converted into electricity using ORC systems. According to a report by Global Market Insights, this application is projected to grow at a CAGR of 11.7%, increasing the installed capacity to 2400 MWe by 2032.

Steel manufacturing also offers significant opportunities for waste heat recovery, with large amounts of waste heat generated from Electric Arc Furnace (EAF) and Basic Oxygen Furnace (BOF) operations. Other waste heat sources can be found in at Sinter Coolers or at Reheating furnaces. In steelmaking, waste heat can be recovered at various temperatures, ranging from very high temperatures in blast furnaces (over 1300 °C) to medium-low temperatures from various cooling processes with exhaust gases from 100°C to 500°C. These lower temperature sources can be harnessed using Organic Rankine Cycle (ORC) systems to generate electricity.

In chemical industries, waste heat is generated throughout various stages of chemical processing, including distillation processes, reaction processes, heat exchange systems, steam generation and boiler systems, cooling systems and flue gas and combustion processes. ORC systems can efficiently recover waste heat from flue gases and from distillation processes, providing a sustainable alternative to conventional energy sources. A recent application from Exergy International for a PET manufacturing facility in China harness the overhead process steam and non-condensable gases (NCG) flow from the stripping column to produce electricity. The ORC system here replaces the function of conventional column overhead condensers with the key advantage of simultaneously generating electrical power.

Advantages

The benefits of industrial waste heat recovery technologies are manifold:

1. Energy Efficiency: By harnessing waste heat, industries can significantly improve their energy efficiency and reduce reliance on conventional energy sources.
2. Cost Savings: Waste heat recovery systems can help reduce energy expenditures associated with processing operations, leading to increased profitability and competitiveness.
3. Sustainability: Repurposing thermal energy that would otherwise be lost contributes to a more sustainable and environmentally conscious approach to industrial production and helps to avoid indirect CO2 emission associated with electricity consumption

In conclusion, the urgency to decarbonise industrial activities to meet medium-term climate change targets by 2030 highlights the importance of increasing energy efficiency. Waste heat recovery systems, particularly Organic Rankine Cycle systems, offer proven, deployable, and cost-effective solutions to curb carbon emissions and energy intensity in industries. By optimising resource utilisation and driving the transition towards greener industrial practices, ORC systems are poised to play a significant role in sustainable industrial development.

Learn more at: https://www.exergy-orc.com/