HEAT RECOVERY UNIT
An industrial heat recovery unit is a heat exchanger designed to recover residual thermal energy from hot gases generated in an industrial process and reuse it within the same production process, directly, measurably and sustainably reducing fuel consumption, operating costs and CO₂ emissions.
It is one of the most effective solutions within industrial energy efficiency and the decarbonisation of thermal processes.
At BOIXAC, we design and engineer custom industrial heat recovery units tailored to the real operating conditions of each industrial process. Our approach ensures sustained energy performance, high operational reliability and a real return on investment in demanding industrial environments.
If you want to know whether your process is suitable for heat recovery, we can analyse your case and define the optimal solution.
Why heat recovery is critical in industry
In industrial environments, a very significant portion of consumed energy is inevitably lost through exhaust gases. This energy loss, usually discharged through the stack, represents a direct operating cost and a source of unnecessary emissions.
Waste heat recovery makes it possible to convert this lost energy into useful energy, improving the overall energy efficiency of the process without affecting its stability or production capacity. For this reason, it is one of the strategies with the best cost–benefit ratio in industrial energy optimisation.
Based on BOIXAC’s experience in real industrial projects, properly designed heat recovery units enable significant reductions in energy consumption, with typical payback periods ranging between 3 and 12 months, depending on the process and operating conditions.
What is an industrial heat recovery unit
An industrial heat recovery unit is a heat exchanger that captures the energy contained in residual hot gases and transfers it to a useful system fluid, without fluid mixing and with full control of the thermal process.
Its application allows to:
increase the overall energy efficiency of the installation
reduce primary fuel consumption
decrease CO₂ emissions and other pollutants
improve the competitiveness and sustainability of the production process
In simple terms: it recovers energy that would otherwise be lost and converts it into useful process energy.
How a heat recovery unit works
The operation of a heat recovery unit is based on the transfer of thermal energy between two fluids at different temperatures, without mixing, through a heat exchange surface specifically designed for each application.
Hot combustion or process gases flow on one side of the heat exchange bundle.
The receiving fluid flows on the other side.
Heat is transferred through the exchange surface.
Depending on the application, the heated fluid may be:
water
superheated water
thermal oil
steam, in specific configurations
This recovery of waste heat reduces primary energy demand and improves the overall energy balance of the system without negatively affecting process stability.
Economiser vs Heat Recovery Unit: Key differences
An industrial economiser is a specific type of heat recovery unit, mainly used in industrial boilers to preheat the feedwater and increase boiler efficiency.
In an economiser:
combustion gases enter at high temperature
pass through the heat exchange bundle
transfer energy to the service fluid
exit at a lower temperature before being discharged
The concept of a heat recovery unit is broader and includes applications in furnaces, engines, turbines, continuous processes and industrial drying systems, with the objective of maximising the overall energy recovery of the process.
1- Inspection opening. 2- Extraction system. 3- Condensate collection tray. 4- Transition (rectangular to circular)
Operating conditions of heat recovery units and economisers
Heat recovery units designed by BOIXAC are engineered to operate reliably in demanding industrial environments, such as:
gases containing solid particles, dust or residues
environments with high fouling levels
high temperatures, up to 850 °C
fuels such as biomass, natural gas, fuel oil or diesel
In continuous operation, adapting the design to these conditions is essential to ensure stable performance and prevent efficiency losses over time.
Design, accessibility and maintenance
One of the most common mistakes in heat recovery projects is focusing solely on heat exchange surface area without considering fouling behaviour and long-term maintenance, which can compromise the real performance of the system.
For this reason, BOIXAC heat recovery units incorporate:
structures resistant to extreme temperatures
accessible openings for inspection
heat exchange bundle extraction systems
adaptation to existing stacks and ducts
thermal insulation with refractory materials
flow control through by-pass systems, dampers and regulation
This approach ensures high operational availability and sustained performance throughout the entire service life of the equipment.
Heat exchanger bundle configurations
The configuration of the heat exchange bundle is defined according to the fluid, temperature, humidity, pressure and fouling level, using engineering criteria focused on real operating conditions.
Typical configurations include:
continuous finned tubes
helical finned tubes
plain tubes
pillow plate systems
In dirty gas applications, ease of cleaning and operational stability are often more important than maximum theoretical heat exchange surface in order to guarantee long-term performance.
Typical ROI
Efficiency
Temperature
Welds
FAQs
What us a heat recovery unit?
A heat recovery unit is an industrial heat exchanger that allows residual thermal energy from hot gases to be recovered and reused within the production process.
In industrial environments, large amounts of energy are lost through exhaust gases. According to BOIXAC’s experience, this energy can be recovered to heat water, thermal oil or generate steam, reducing fuel consumption and improving the overall efficiency of the installation.
What is the difference between a heat recovery unit and an economiser?
An economiser is a specific type of heat recovery unit mainly used in industrial boilers to preheat the feedwater.
The concept of a heat recovery unit is broader and includes applications in furnaces, engines, turbines, continuous processes and industrial drying systems.
What is the maximum temperature an industrial heat recovery unit can withstand?
An industrial heat recovery unit can typically operate at temperatures of up to 850 °C, depending on its design and the materials used.
In high-temperature applications, BOIXAC considers thermal expansion, material selection and mechanical stability to ensure long-term safety and reliability.
Can heat recovery units be used with dirty or particle-laden gases?
Yes, heat recovery units can operate with dirty gases provided that the design is adapted to the fouling level of the gas.
In processes with dust, ash or solid residues, BOIXAC prioritises robust solutions, plain tubes or pillow plate systems, and designs that facilitate periodic cleaning.
What is the most important design criterion for a heat recovery unit?
The most common mistake is failing to consider the long-term behaviour of the system.
According to BOIXAC’s technical expertise, designs take fouling, maintenance and real operating conditions into account to avoid significant performance losses over time.
What pressure drop is acceptable in a heat recovery unit?
The acceptable pressure drop depends on the process and the existing ventilation system.
When designing a heat recovery unit, it is essential to balance energy gains with the impact on fan power consumption, ensuring that increased pressure losses do not offset the energy benefits achieved.
Can a heat recovery unit be installed in an existing plant?
Yes. Most industrial heat recovery units are designed to be integrated into existing installations.
Through adaptations to stacks, ducts and control systems, energy recovery can be implemented without major structural modifications to the process.
Can condensation occur in a heat recovery unit?
Yes, when gases are cooled below their dew point.
In such cases, it is essential to select corrosion-resistant materials and provide condensate collection and drainage systems to prevent operational issues. In addition, BOIXAC has a construction system that allows operation even with condensing economisers.
How often should a heat recovery unit be cleaned?
Cleaning frequency depends on the level of gas fouling and the type of process.
In processes involving biomass or solid residues, periodic cleaning and designs that allow quick access to the heat exchange bundle are commonly required. With BOIXAC, maintenance can be relatively straightforward thanks to accessible designs, extraction systems and solutions developed for day-to-day operation.
Is it better to use finned tubes or plain tubes?
There is no universal solution; it depends on the application.
Finned tubes provide higher performance with clean gases, while plain tubes are more robust and better suited for dirty gases or applications with a high risk of fouling.
What is the most common mistake in heat recovery projects?
The most frequent mistake is not considering the long-term behaviour of the system.
According to BOIXAC’s expertise, the proposed designs consider fouling, maintenance and real operating conditions to avoid significant performance losses within a few months.
What impact does a heat recovery unit have on CO₂ emissions?
Heat recovery reduces primary fuel consumption and therefore the CO₂ emissions associated with the process.
This reduction is direct, measurable and effectively contributes to industrial sustainability objectives.
What materials are commonly used in the construction of a heat recovery unit?
Industrial heat recovery units can be designed using different materials depending on operating temperature, media corrosivity and process type.
Common materials include carbon steel, stainless steels AISI 304, AISI 316, AISI 309 and AISI 310, as well as aluminium alloys such as AL5754, AlMg3, Al5052 or AlMg2.5. Proper material selection is essential to ensure safety, durability and optimal thermal performance.
In which industrial processes is it recommended to install a heat recovery unit?
It is particularly recommended in processes that generate residual hot gases, such as boilers, furnaces, engines, turbines or industrial drying processes.
Industrial heat recovery units are used in sectors such as energy, oil and gas, food and beverage, shipbuilding, marine installations, industrial thermal processes, material drying, industrial boilers and wastewater treatment plants.
What is the typical return on investment?
In real industrial projects, the return on investment of a heat recovery unit typically ranges between 3 and 12 months.
This return depends on the process, the level of energy recovery and the adaptation of the design to operating conditions.
Finned tubes heat exchanger
Smooth tubes heat exchanger
Dimple plate heat exchanger