Many industries – from huge steel factories to large power plants – are always looking for ways to use energy more efficiently. One opportunity that has been overlooked is waste heat recovery. Waste heat is the leftover heat that comes from industrial processes and is usually just released into the environment. Waste heat recovery systems cleverly capture and reuse this leftover heat instead of letting it go to waste. With this in mind, this article will explain the fundamentals of waste heat recovery, showing why waste heat recovery has become an essential part of modern industrial plans that aim to save money and be environmentally sustainable for many businesses.

What Is Waste Heat Recovery?

Waste heat recovery refers to the process of capturing and utilizing the thermal energy that is generated as a byproduct of various industrial processes or combustion systems, which would otherwise be released into the environment as waste heat. This heat, which can take the form of hot exhaust gases, steam, or cooling water, is recovered through specialized equipment and technologies. The recovered heat is then repurposed for a wide range of applications, such as generating electricity or providing process heating or cooling. Waste heat recovery systems can be designed to operate across a wide range of temperature levels, from low-grade waste heat sources like exhaust gases or cooling water to high-temperature streams from furnaces or thermal oxidizers. 

Types of Waste Heat Recovery

Waste heat recovery systems can be categorized based on the type of heat source, temperature range, and the waste heat recovery technology employed. The most common types of waste heat recovery include:

• Exhaust Gas Heat Recovery: This captures the waste heat from hot exhaust gases generated by combustion processes, such as those found in power plants. Exhaust gas heat recovery systems typically use waste heat recovery heat exchangers or recuperators to extract thermal energy from the flue gases before they are released into the atmosphere.
• Cooling Water Heat Recovery: Many industrial processes and power generation systems require significant amounts of cooling water, which carries away waste heat. Cooling water heat recovery systems use heat exchangers or plate-and-frame units to recover this low-grade waste heat. This can then be used for space heating, preheating, or other low-temperature applications.
• Process Waste Heat Recovery: Various manufacturing and chemical processes generate waste heat as a byproduct, which can be recovered and utilized within the facility. Examples include heat recovery from hot product streams, reactor jackets, distillation columns, and other process equipment.
• Jacket Cooling Heat Recovery: In certain processes, equipment like engines, compressors, and turbines require jacket cooling systems to dissipate waste heat. This waste heat can be recovered and used for various purposes, such as preheating, space heating, or driving absorption chillers.
• Organic Rankine Cycle (ORC) Systems: ORCs are specialized systems that use an organic working fluid with a low boiling point to convert low-grade waste heat (typically below 370°C) into usable power through a closed-loop cycle.
• Thermoelectric Generator (TEG) Systems: TEGs are solid-state devices that directly convert waste heat into electrical energy through the Seebeck effect. TEGs are suitable for applications where direct power generation from waste heat is desired.
• Heat Pump Systems: These systems use waste heat as the energy source to drive a refrigeration cycle. This process provides both heating and cooling capabilities from the same waste heat source.

Waste Heat Recovery Process

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:

• 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.

Waste heat recovery industrial steam boiler

• 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

Implementing a waste heat recovery system offers multiple advantages for industrial operations, making it an attractive investment for businesses seeking to optimize sustainability and profitability:

1. By capturing and utilizing heat that would otherwise be wasted, waste heat recovery technologies significantly boost the overall energy efficiency of industrial operations. It can also reduce the need for primary energy sources and associated costs.
2. Reducing energy consumption through waste heat recovery directly translates into lowered operational costs, as less fuel or electricity is required to meet the facility’s energy needs. Additionally, the recovered heat can be used for various applications, further reducing expenses.
3. By maximizing the use of generated heat and minimizing reliance on fossil fuels or other primary energy sources, waste heat recovery systems help reduce the carbon footprint and overall environmental impact of industrial activities, contributing to compliance with environmental regulations.
4. Lowering the operational load on equipment by recycling heat can lead to longer system lifespans and reduced maintenance costs, as components are subjected to less thermal stress and wear.

Examples of Waste Heat Recovery Applications

• Power Plants 

Power plants, particularly those based on fossil fuels or nuclear energy, are major beneficiaries of waste heat recovery systems. Waste heat recovery power plants capture excess heat from exhaust gases, steam, or cooling water that would normally be released into the atmosphere. This recovered heat can then be used to produce additional electricity through steam turbines or other power generation cycles.

• Manufacturing Industries 

Many manufacturing processes, such as steel production, glass manufacturing, and cement production, release substantial amounts of heat due to the high temperatures involved. Waste heat recovery systems can capture this excess heat and reuse it to preheat furnaces, generate steam for various applications, or provide space heating for the facility.

• Vehicle Exhaust Systems 

Modern vehicles, particularly those with internal combustion engines, are equipped with waste heat recovery systems that capture heat from exhaust gases. This heat can be used to improve engine efficiency by preheating the intake air or fuel, or to power auxiliary systems like climate control.

• Chemical Processing Plants

Chemical processing plants often involve high-temperature reactions and distillation processes that generate significant amounts of waste heat. Recovering this heat can be used to preheat incoming raw materials, generate steam for other processes, or even drive absorption chillers for cooling applications.

How to Choose a Waste Heat Recovery Company?

Selecting the right waste heat recovery company is important for maximizing the benefits of the implemented system. Key factors to consider are as follows:

1. Experience and Expertise: Look for companies with a proven track record in your industry and a deep understanding of the specific processes and waste heat streams involved. Experienced providers can offer tailored solutions that effectively address your unique requirements.
2. Customized Solutions: Ensure the company can design and engineer custom waste heat recovery systems that are tailored to fit your specific needs. This customization ensures optimal performance and maximizes the potential benefits.
3. Support and Maintenance: A reputable waste heat recovery company should offer comprehensive after-sales support, including installation assistance, training for your personnel, and ongoing maintenance services. This ensures the system operates at peak efficiency throughout its lifespan.
4. Sustainability Credentials: Consider companies that adhere to high environmental standards in their designs, manufacturing processes, and operations. This commitment to sustainability aligns with the core purpose of waste heat recovery and demonstrates a holistic approach to environmental stewardship.
5. Financial Stability: As waste heat recovery systems can represent a significant investment, it’s important to evaluate the financial stability and long-term viability of the company you choose. Make sure they will be able to provide ongoing support and fulfill their commitments over the lifespan of the system.