Heat Recovery Technologies

Principles of heat recovery

Heat exchangers

Heat exchangers are one of the most common heat recovery methods in industry. They operate by transferring heat from one medium (e.g., exhaust gases, cooling water) to another (e.g., utility water, air) to utilize this heat in other processes. Different types of heat exchangers are used depending on the medium and required parameters:

• shell-and-tube exchangers – used where large heat exchange surfaces are required, such as at high exhaust gas temperatures. Air or water flows through the tubes, and heat is transferred to the surrounding medium;
• plate heat exchangers – applied in smaller systems requiring heat recovery. The exchanger plates are arranged to maximize contact with the medium releasing heat.

Heat pumps

Heat pumps transfer heat from a lower-temperature medium (e.g., waste heat from industrial processes) to a higher-temperature medium, such as a heating system, using a small amount of electricity. This allows for significant heat recovery from low-temperature waste sources. Various types of heat pumps are used:

• air-to-water heat pumps – recover heat from air or exhaust gases and transfer it to water, which can then be used in a heating system;
• water-to-water heat pumps – utilize water as a heat source, making them ideal for recovering heat from groundwater, reservoirs, sewage, or industrial processes;
• air-to-air heat pumps – commonly used to recover heat from outdoor air and transfer it indoors as warm air.

Cogeneration

Cogeneration is the simultaneous production of electricity and heat. It is widely used in industrial plants that require both electricity and heat in the form of steam or hot water. Cogeneration captures waste heat generated during electricity production, such as in an internal combustion engine, and redirects it to industrial processes, including building heating, steam production, or water heating.

Heat recovery from waste gases

Heat recovery from waste gases involves reusing heat lost in exhaust or other industrial gases. This process employs specialized heat exchangers that extract energy from hot gases and transfer it to other applications, such as heating water, air, or raw materials. By reducing fuel consumption, this technology lowers production costs and emissions. Depending on the specific technology, different devices can be used, such as recuperators – for air heating, economizers – for water heating and other specialized installations tailored to technological requirements.

What are the benefits of heat recovery?

Heat recovery, particularly in large and energy-intensive companies, offers significant economic and environmental benefits. The most notable advantage is cost reduction. By reusing waste heat, companies can decrease their energy demand from external sources, leading to lower energy bills. Additionally, reducing fossil fuel consumption helps decrease the company's carbon footprint and supports sustainable development.

Moreover, heat recovery enhances the energy efficiency of industrial processes by maximizing the use of generated energy. Repurposing waste heat for space heating, steam production, or other technological processes reduces the need for additional energy investments.

From an environmental perspective, heat recovery significantly lowers CO₂ emissions by reducing reliance on fossil fuels. This, in turn, helps companies comply with environmental regulations and improve their ESG (Environmental, Social, and Governance) performance.

If you are unsure whether heat recovery is feasible in your facility, consider conducting a Walk-Through Audit (WTA) to quickly assess savings potential and identify areas requiring further analysis. If your processes generate recoverable heat, it is essential to find an effective way to utilize it. Since energy system modernization can be costly, conducting a feasibility study is advisable to maximize benefits and optimize investment costs.

What do you have to take into account when recovering heat?

Despite its many benefits, heat recovery in industry also has some disadvantages and limitations that can affect its profitability and efficiency under certain conditions. One of the main challenges associated with implementing heat recovery systems is the investment cost. Installing heat exchangers, heat pumps, or cogeneration systems requires significant financial outlays for equipment, installation, and potential modifications to the existing infrastructure. Although these costs can be recouped within a few years, they may pose a significant barrier for some companies.

Secondly, heat recovery is not always suitable for every industry. These technologies work best in plants that generate large amounts of waste heat as a result of processes such as combustion, drying, metal melting, or steam production. In industries where processes generate little waste heat or where there is an excess of low-temperature heat, heat recovery may be inefficient and not very profitable.

In some cases, heat recovery may be less flexible than other heating systems. For example, heat pumps are most efficient within a specific temperature range, but their efficiency decreases when the temperature difference between the heat source and the heating medium is too large. Additionally, heat recovery from certain industrial processes may be limited when production processes have variable energy loads, leading to instability in the recovery system.

Ultimately, the decision to implement a heat recovery system should be carefully considered, taking into account the specifics of the processes, initial costs, and long-term benefits. In some cases, despite the potential for savings, heat recovery technologies may not be suitable or may be too expensive to implement.

In which industries will heat recovery work?

Heat recovery can be used in many industrial sectors, especially those where processes require high temperatures for product processing, including:

• chemical industry – production of chemicals, oil refining, and fertilizer production, where large amounts of waste heat are generated, as well as in processes involving exothermic chemical reactions;
• metallurgical industry – in processes such as melting, hardening, or steel production, where high-temperature waste heat is generated;
• food industry – in cooking, drying, and pasteurization processes, where heat recovery is also possible;
• paper industry – in paper production, where heat is lost to the environment during drying and pre-treatment processes;
• energy sector – in power plants, where heat can be recovered from turbine cooling or boiler exhaust gases.

Heat recovery case study in the automotive industry

Investment cost: approx. PLN 6.7 million

Savings: approx. PLN 3.4 million

Payback period: approx. 2 years

Emission reduction: approx. 2,300 tons of CO₂ per year

Amount of energy saved: approx. 7,600 MWh per year

In an automotive industry company producing components for passenger cars, we conducted an energy audit, during which we identified 19 measures that could cost-effectively improve the plant’s energy efficiency. One of the solutions analyzed was the utilization of waste heat from the cooling process of cast iron components after casting, which need to be cooled to ambient temperature.

Previously, the castings were cooled automatically. To assess the potential of wasted heat, our engineers conducted a test showing that a single workstation with castings could boil 1 m³ of water in just 40 minutes! By using this heat to power an absorption cooling unit, the production of chilled water used in the technological process has become more efficient and requires less electricity.

Annual thermal energy savings amount to over 7,600 MWh, equivalent to the annual energy consumption of more than 4,200 Polish households. Previously, cooling was produced using electricity, but thanks to this investment, the plant no longer draws this energy from the National Power System. As a result, the need for its production is eliminated, reducing greenhouse gas emissions from coal-fired power plants – in this case, CO₂ emissions are reduced by approximately 2,300 tons per year.

To sum up, heat recovery is an innovative method that allows industries not only to reduce energy costs but also to achieve better energy efficiency and lower CO₂ emissions. The success of the investment depends on selecting the right technology, integrating it with industrial processes, and optimizing costs. While initial installation expenses can be high, long-term benefits, such as a relatively short payback period and reduced energy costs, make heat recovery a cost-effective solution for many industries.