What Is Waste Heat Recovery and What Are Its Benefits?

What Is Waste Heat Recovery and What Are Its Benefits?

The process of waste heat recovery can differ based on the type of waste heat source, temperature levels, and intended application. However, the general sequence is as follows:

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• Source Identification and Characterization

The initial step involves identifying and thoroughly characterizing the sources of waste heat within a facility or process. Key aspects include 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, appropriate heat recovery equipment is selected. Common choices include heat exchangers (shell-and-tube, plate, etc.), heat pipes, thermoelectric generators, or organic Rankine cycle systems.

• Heat Transfer

The chosen equipment is employed to extract waste heat from the source stream 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 be utilized in various ways. Notable applications include generating steam for power production, preheating combustion air, providing space heating or cooling (via absorption chillers), or driving other thermal cycles such as organic Rankine cycles.

• Control and Optimization

The waste heat recovery process is closely monitored and controlled to ensure optimal performance, efficiency, and safety. Key parameters, such as temperatures, pressures, and flow rates, are regulated to match the design conditions of the waste heat recovery equipment and the demand for recovered heat.

• Maintenance and Monitoring

Regular maintenance, inspection, and monitoring of the waste heat recovery system are essential for ensuring continuous efficient operation, identifying potential issues, and extending the equipment's lifespan.

Benefits of Waste Heat Recovery

Industrial Waste Heat Recovery: What Are Its Applications?

What is Industrial Waste Heat Recovery?

Industrial waste heat recovery (WHR) involves capturing exhaust heat that would otherwise be released into the atmosphere or remain unused in industrial processes. This heat can be repurposed for power generation or heating applications. All industrial processes, including manufacturing, refining, and power generation, produce significant heat as a byproduct. Waste heat recovery (or Waste Heat to Power) systems allows for this heat to be captured and reused for:

• Electricity Generation: Waste heat can be used to generate electricity using methods like steam Rankine Cycle, Organic Rankine Cycle (ORC), and thermoelectric generators.
• Heating: Waste heat can be utilized for space heating, preheating combustion air, or supplying process heat for various industrial operations.
• Cooling: Waste heat can additionally meet cooling needs, as seen in absorption chillers, which utilize waste heat for the cooling process.

By implementing waste heat recovery systems, industries can decrease energy consumption, lower operating costs, and reduce their environmental footprint, effectively harnessing useful heat energy that would otherwise be squandered.

What Are the Applications of Waste Heat Recovery?

Industrial waste heat recovery applications tap into the available waste heat potential and convert it into carbon-free electricity via a waste heat recovery system. The following sectors can efficiently employ this technology:

• Energy-Intensive Industries: Sectors like cement, steel, and glass account for nearly 40% of total global energy consumption.
• Oil and Gas Processing Industry: This includes gas network operators, oil companies, refineries, and petrochemical industries.
• Other Chemical Industries
• Food and Beverage
• Others

Industrial Waste Heat Recovery

Cement, glass, and steel manufacturing are some of the most energy-intensive industries that face the challenge of reducing energy intensity while meeting increasing demand. These sectors have already started recognizing the benefits of Waste Heat Recovery and deploying WHR systems. Other sectors, such as pulp, paper, food and beverages, and chemical and petrochemical industries, can also leverage this technology to enhance energy efficiency and lower their carbon footprint.

According to data from the KcORC - The Knowledge Centre on ORC Technology, as presented in their Thermal Energy Harvesting report, more than 75% of thermal energy obtained from primary fuels in energy-intensive industries in the EU is currently wasted.

• The 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%.

This equates to an estimated waste heat potential exceeding 50 MWth. Focusing solely on wasted thermal energy sources at temperatures greater than 250°C, due to higher economic viability, a total of 6.6 GW of electricity could be produced in Europe by positioning it with an ORC waste heat recovery system. This includes 447 MWel in the cement sector, 152 MW from the glass sector, 207 MW in steel, and additional potential in refineries and food & beverage industries.

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Waste Heat Recovery in Chemical Industries

Waste heat recovery in chemical plants provides an opportunity to enhance energy utilization and overall sustainability. By capturing and repurposing waste heat, chemical plants can decrease reliance on conventional energy sources, lower greenhouse gas emissions, and increase competitiveness in a resource-constrained environment.

How Do Waste Heat Recovery Systems Work in Chemical Plants?

Heat recovery phases in chemical industries include:

1. Distillation Processes: Significant heat is applied during distillation, allowing recovery from both hot distillate and cooling water used in the condenser.
2. Reaction Processes: Waste heat can be repurposed from the cooling of reaction vessels or from product streams leaving the reactor.
3. Heat Exchange Systems: Waste heat can be recovered from hot streams exiting reactors and transferred to incoming feed streams or processes needing heat.
4. Steam Generation and Boiler Systems: Waste heat from boiler exhaust gases can be recovered via heat exchangers or used to preheat boiler feedwater, enhancing overall energy efficiency.
5. Cooling Systems: Waste heat can be extracted from hot cooling water used in chemical processes before discharge for repurposing.
6. Ventilation and Exhaust Systems: Waste heat from exhaust gases can be recovered using heat exchangers for space heating or preheating incoming air.
7. Flue Gas and Combustion Processes: Waste heat in flue gases discharged from furnaces can be recovered through heat recovery steam generators (HRSG) or Organic Rankine cycles (ORC) for process heating or power generation.

ORC for Waste Heat Recovery

The Organic Rankine Cycle can efficiently recover waste heat from distillation processes by harvesting heat from the overhead process steam and non-condensable gases (NCG) flow from stripping columns in chemical plants. The ORC system replaces conventional column overhead condensers with the advantage of simultaneously generating electrical power. In this setup, process steam and NCG flow are directed to ORC heat exchangers, transferring their heat to the organic working fluid, which vaporizes and drives Exergy's high-efficiency ROT expander to produce electricity.

Process steam, NCG flow, and organic working fluid remain separate, preventing contamination of the process steam and condensate.

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

Heat Recovery from the Food and Beverage Industry

Many food and beverage manufacturing processes rely on heat supplied through natural gas combustion. A substantial portion of this heat is expelled with exhaust gases, ranging from 100 to 250°C. This waste heat can be captured to produce heat, power, or both via cogeneration, also known as combined heat and power systems (CHP).

The KcORC - The Knowledge Centre on ORC Technology estimates that significant electrical capacity could be recovered from waste available in food and beverage processes in the EU using Organic Rankine Cycle technology.

Waste heat recovery in the food and beverage industry can occur throughout various stages of the production process, including:

• 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 improve 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 help reduce fossil fuel energy consumption, lower associated costs, and minimize environmental impact, enhancing the energy efficiency, profitability, and sustainability of businesses.

Discover the advantages of industrial waste heat recovery technologies:

1. Energy Efficiency:
By capturing waste heat, heavy industries, as well as the chemical, food, and beverage sectors, can significantly boost their energy efficiency and reduce reliance on conventional fossil fuel energy sources.

2. Cost Savings:
Implementing waste heat recovery systems allows the industrial sector to lower energy expenses related to processing operations. Over time, these savings can enhance profitability and competitiveness in the industry.

3. Sustainability:
Repurposing thermal energy that would otherwise be wasted enables industrial manufacturers to adopt a more sustainable and environmentally conscious approach to industrial production.

Waste Heat Recovery with Organic Rankine Cycle

Organic Rankine Cycle systems facilitate the conversion of low- to medium-grade waste heat into usable electricity, making them ideal for waste heat recovery in the industrial sector. Due to their versatile applications and low operational and maintenance costs, ORC systems are expected to significantly contribute to optimizing resource use and advancing greener industrial practices.

If you want to learn how to valorize the waste heat potential in your industrial process, contact us now!

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