What Is Waste Heat Recovery and What Are Its Benefits?

The waste heat recovery process will vary depending on the type of waste heat source, temperature levels, and the intended application, but generally follows this sequence:

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• Source Identification and Characterization 

The first step is to identify and thoroughly characterize the sources of waste heat within the facility or process. This includes determining the temperature, flow rate, composition, and any potential contaminants present in the waste heat stream.

• Heat Recovery Equipment Selection 

Based on the characteristics of the waste heat source, suitable heat recovery equipment is selected. Common options include heat exchangers (shell-and-tube, plate, etc.), heat pipes, thermoelectric generators, or organic Rankine cycle systems.

• Heat Transfer 

The selected equipment is used to extract the waste heat from the source stream, typically by facilitating heat transfer between the hot waste stream and a cooler working fluid or medium. This heat transfer can occur through direct contact, an intervening surface, or thermoelectric conversion.

• Working Fluid Loop

In many cases, the recovered heat is transferred to a working fluid (e.g., water, thermal oil, refrigerant) that circulates through the waste heat recovery equipment. This working fluid loop transports the captured heat to the point of utilization.

• Heat Utilization

The recovered waste heat can then be utilized in various ways. For example, generating steam for power production, preheating combustion air or process streams, providing space heating or cooling (via absorption chillers), or driving other thermal cycles like organic Rankine cycles.

• Control and Optimization 

The waste heat recovery process is monitored and controlled to ensure optimal performance, efficiency, and safety. Key parameters like temperatures, pressures, and flow rates are regulated to match the waste heat recovery equipment&#;s design conditions and the demand for the recovered heat.

• Maintenance and Monitoring

Regular maintenance, inspection, and monitoring of the waste heat recovery system are essential to ensure continued efficient operation, identify potential issues, and extend the equipment&#;s lifespan.

Benefits of Waste Heat Recovery

What is industrial waste heat recovery?

Industrial waste heat recovery (WHR) involves capturing the exhaust heat normally discharged into the atmosphere or going unused in industrial processes and repurposing it for power generation or heating uses. All industrial processes, including manufacturing, refining, and power generation, produce substantial quantities of heat as a byproduct. It is possible through waste heat recovery (or Waste Heat to Power) systems to capture and repurpose it for:

• Electricity Generation: Waste heat can be harnessed to produce electricity using diverse methods like steam Rankine Cycle, Organic Rankine Cycle (ORC) and thermoelectric generators.
• Heating: Waste heat can serve for space heating, preheating combustion air, or supplying process heat for various industrial operations.
• Cooling: Waste heat can additionally be utilised for cooling needs, as seen in absorption chillers that employ waste heat to facilitate the cooling process.

By deploying waste heat recovery systems, industries can reduce energy consumption, lower operating costs, and decrease their environmental footprint, leveraging useful heat energy that would otherwise be wasted.

What are the applications of waste heat recovery?

Industrial waste heat recovery applications exploit available waste heat potential and convert it via a waste heat recovery system into carbon-free electricity. Here are some sectors where this technology can be efficiently employed:

• Energy intensive industries such as cement, steel and glass sectors which account for nearly 40% of the total global energy consumption. 
• Oil and gas processing industry such as gas network operators, oil companies, refineries, petrochemical industries 
• Other chemical industries
• Food and beverage
• Others

Industrial waste heat recovery

Cement, glass and steel manufacturing are among the most energy intensive industries and the hardest to abate as they need to face the challenge to cut energy intensity while copying with an increasing demand. These sectors have already started to acknowledge the advantages of Waste Heat Recovery and to deploy WHR systems. But there are also other sectors that can take advantage of this technology to enhance the energy efficiency of their process and reduce carbon footprint such as the pulp, paper, food and beverages, chemical and petrochemical industries.

According to the data presented by KcORC &#;The knowledge Centre on ORC technology&#;, in their &#;Thermal Energy harvesting&#; report, 75% of the thermal energy obtained by primary fuels used in energy-intensive industries&#; processes in the EU is currently wasted.

• Chemical industry accounts for 11.7% waste heat potential,
• iron and steel 16.4%,
• refineries 34.4%,
• paper and printing 9.9%,
• non-metallic minerals (including cement) 27.3%.

All of these make an estimated potential of more than 50 MWth. Just considering wasted thermal energy sources at temperatures > 250°C, for reasons of higher economic viability, a total of 6.6 GW of electricity could be produced in Europe by leveraging it with an ORC waste heat recovery system. Of this 447 MWel in the cement sector, 152 MW from glass sector, 207 MW in steel, 129 MW in refineries, MW food & beverage, MW in chemical.

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Waste heat recovery in chemical industries

Waste heat recovery for chemical plants presents an opportunity to optimise energy utilisation and enhance the overall sustainability of chemical manufacturing operations. By capturing and repurposing waste heat, chemical plants can reduce their reliance on conventional energy sources, lower greenhouse gas emissions, and improve their competitiveness in a resource-constrained world.

How waste heat recovery systems work in chemical plants?

Heat recovery phases in chemical industries
Waste heat in a chemical plant is generated throughout various stages of chemical processing:

1. Distillation Processes: during distillation processes, substantial amounts of heat are applied to vaporise the components. Exhaust heat can be recovered from both the hot distillate and the cooling water used in the condenser. 
2. Reaction Processes: In reaction processes waste heat available in the cooling of reaction vessels or from the product streams leaving the reactor can be efficiently repurposed for other uses.
3. Heat Exchange Systems: Waste heat can be recovered from the hot streams exiting reactors, heaters, or furnaces by transferring it to incoming feed streams or other processes requiring heat.
4. Steam Generation and Boiler Systems: Waste heat from boiler exhaust gases can be recovered through heat exchangers or used to preheat boiler feedwater, thus improving overall energy efficiency.
5. Cooling Systems:  Waste heat can be extracted from the hot cooling water employed as a cooling system in chemical processes, before it is discharged, and reused for heating purposes.
6. Ventilation and Exhaust Systems: Waste heat generated from the exhaust gases of various equipment, such as pumps, compressors, and reactors can be recovered using heat exchangers or utilised for space heating or preheating of incoming air.
7. Flue Gas and Combustion Processes: waste heat is often present in the flue gases discharged from furnaces and can be recovered through heat recovery steam generators (HRSG) or Organic Rankine cycles (ORC) for power generation or process heating.

ORC for Waste Heat Recovery

Organic Rankine cycle can be efficiently employed for waste heat recovery from distillation processes harvesting the available heat from the overhead process steam and non-condensable gases (NCG) flow from stripping columns in chemical plants. The ORC system here replaces the function of conventional column overhead condensers (fig. 1) with the key advantage of simultaneously generating electrical power. The flow of process steam and NCG is directed to the ORC heat exchangers (fi.2) transferring their heat to the organic working fluid of the ORC power cycle. The organic fluid vaporizes and is then conveyed to Exergy&#;s high efficiency ROT expander to produce electricity.

Process steam, NCG flow and organic working fluid are never in contact, hence there is no possibility of contamination of the process steam and steam condensate.

Fig 1 &#; Traditional process scheme chemical plant



Fig 2 &#; Process scheme chemical plant with ORC waste heat recovery

Exergy has recently installed an ORC WHR system for the customer Sanfame, recovering the overhead process steam and non-condensable gases (NCG) flow from the stripping column of a PET manufacturing facility in China.

Heat recovery from food and beverage Industry

Most food and beverage manufacturing processes involve a heat supply, which often comes from burning natural gas. A substantial proportion of this heat is discharged with the exhaust gases. This waste heat is available at temperatures ranging from 100 to 250°C, and can be tapped to produce heat, power or a combination of both using cogeneration, also known as combined heat and power systems (CHP).

The KcORC &#;The knowledge Centre on ORC technology&#;, in their &#;Thermal Energy harvesting&#; study, has estimated that around MWe of electrical capacity could be recovered from the waste available from food and beverage processes in the EU countries using Organic Rankine Cycle technology.

Waste heat recovery in the food & beverage processing industry can occur in various stages of the production and manufacturing process:

• Cooking and Baking Processes
• Brewing and Fermentation
• Pasteurization and Sterilization
• Carbonation and Bottling

From brewing and pasteurization to refrigeration and bottling, integrating waste heat recovery technologies can enhance the overall efficiency and sustainability of food and beverage production operations.

What are the benefits of Industrial Waste Heat Recovery Technologies?

Industrial Waste heat recovery systems allow to reduce fossil fuel energy consumption and the connected costs and environmental impact thus increasing energy efficiency, profitability and sustainability of the business

Discover the advantages of industrial waste heat recovery technologies:

1. Energy Efficiency
By harnessing waste heat, the heavy industry, the chemical, food and beverage industries can significantly improve their energy efficiency and reduce reliance on conventional fossil fuel energy sources.

2. Cost Savings
Implementing waste heat recovery systems enables the industrial sector to reduce energy expenditures associated with processing operations. Over time, these cost savings can translate into increased profitability and competitiveness within the industry.

3. Sustainability
By repurposing thermal energy that would otherwise be lost, industrial manufacturers contribute to a more sustainable and environmentally conscious approach to industrial production.

Waste heat recovery with Organic Rankine Cycle

Organic Rankine Cycle systems, which allow for the conversion of low- to medium-grade waste heat into usable electricity, are the perfect match for waste heat recovery in the industrial sector. Thanks to their flexibility of application and low cost of operation and maintenance ORC systems are expected to play a significant role in optimising resource utilisation and driving the transition towards greener industrial practices.

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