EnergyEnergy ManagementHVAC Optimization

From Waste to Worth: Textile ‘waste heat’ can be new source of energy, which is more efficient & green

The method of capturing and using extra heat produced due to various industrial operations, power production, or other thermal systems is referred to as waste heat utilization. This heat is collected and used for valuable reasons, minimizing environmental impact and increasing energy efficiency, as opposed to being lost and released into the environment. Depending on the source, waste heat can be found in various places, including flue gases, exhaust gases, or hot water streams.

Due to the high energy consumption and large waste heat generation in the textile sector, waste heat utilization is exceptionally significant. Spinning, weaving, dyeing, and finishing are just a few of the stages involved in making textiles, all of which require a significant amount of heat for processes including drying, curing, and steam generation. Concentrating on enhancing energy efficiency is crucial due to the industry’s significant energy use.

Waste heat utilisation provides a solution by capturing and recycling the surplus heat produced during the manufacture of textiles. This helps bring down energy prices by reducing the industry’s dependency on primary energy sources. Utilizing waste heat reduces the need for additional heating systems, which saves money on fuel or electricity costs, rather than wasting the extra heat, which would require additional energy to be produced.

Moreover, the energy-intensive processes used in the textile sector add to air pollution and greenhouse gas emissions. The industry may drastically lessen its carbon footprint and environmental impact by utilizing waste heat. Waste heat utilization actively encourages sustainable practices and lessens the industry’s environmental impact by lowering the energy required from non-renewable sources. Utilizing waste heat in the textile sector enables process optimization in addition to environmental advantages. To increase the effectiveness and speed of processes like steam generation, drying, or preheating, waste heat can be caught and put to use.

This optimisation results in an increase in overall production capacity and a decrease in operational downtime, which boosts productivity and lowers costs. Furthermore, The use of waste heat assists textile industries in meeting energy efficiency rules and criteria imposed by various countries. Textile companies demonstrate their commitment to sustainable practices and align with regulatory requirements by deploying waste heat utilization technology, ensuring they satisfy the appropriate compliance criteria.

Sources of ‘waste heat’ in textile industry:

Waste heat from numerous sources can be used in the textile industry for waste heat usage. Here are a few examples of common sources of heat:

  • Boilers: Boilers are frequently used in the textile manufacturing industry to generate steam for dyeing, finishing, and fabric treatment. The exhaust gases emitted from these boilers contain waste heat that can be collected and applied to other heating applications within the facility.
  • Dryers: The drying of textiles, whether for finished clothing, finished fabric, or yarn, generates waste heat in the form of hot air or exhaust gases. This waste heat can be collected and used inside the building for other heating requirements, including space heating or heating water for various procedures.
  • Stenter machines: Stenter machines are frequently used in the stretching and drying of fabrics in the textile processing industry. The fabric goes through a series of heated chambers, allowing customized drying and heat settings. The Stenter machine produces heat to dry the fabric and improve its dimensional stability. This heat can be viewed as a possible source of waste heat that the facility could capture and use for other heating uses.

Utilizing waste heat has drawn much interest from businesses in various sectors, including the textile industry. Numerous companies are researching and adopting waste heat utilisation technology to increase energy efficiency, save operating costs, and encourage sustainable practices. These businesses invest in creative solutions to capture and use this priceless resource because they understand the potential advantages of harnessing and utilizing waste heat.
Several companies are working on this waste heat utilization including AERIS, AUTEFA, BENNINGER, BRUECKNER, POZZI, BRÜCKNER, and THIES. These companies employ a variety of heat recovery techniques.

Air/air heat recovery exchanger

An air-to-air heat recovery system is a technology that absorbs waste heat from a building’s or industrial process’s exhaust air stream and transfers it to the incoming fresh air stream. This technology recovers and reuses thermal energy that would otherwise be lost, increasing energy efficiency and lowering heating and cooling costs.

The following steps are involved in the air-to-air heat recovery process:

  • Exhaust Air Collection: The process of collecting warm or cool exhaust air that contains useful thermal energy.
  • Heat Exchange: The process of transferring collected heat from exhaust air to a separate supply air stream using a heat exchanger.
  • Supply Air Conditioning: Using the recovered heat to warm or cool the supply air in colder seasons.
  • Distribution: The process of distributing conditioned and recovered heat throughout the ventilation system of a building, giving warmed or precooled air to different locations as needed.

Overall, air-to-air heat recovery systems offer a cost-effective and long-term option for recovering waste heat and lowering energy consumption in buildings and industrial processes.

Air/water heat recovery exchanger: The technique known as an air-to-water heat recovery system extracts waste heat from the exhaust air of a structure or industrial process and transfers it to a water-based system for use in heating or other purposes. This method increases energy efficiency while lowering heating costs by allowing thermal energy that would otherwise be lost to be recovered and used again.

The following steps are involved in the air-to-water heat recovery process:

  • Exhaust Air Collection: Collecting warm or cool exhaust air containing valuable thermal energy.
  • Heat Exchange: The transfer of heat captured from exhaust air to a water system.
  • Water heating or other applications: The recovered heat can warm water for various uses, including space heating, residential hot water delivery, and boiler water preheating.

Heat is distributed throughout the structure or process to deliver hot water for the desired applications.

Figure: Heat recovery from stenter machine depreciation calculation-20.000 air water

Counter-flow tubular heat exchanger

A counter-flow tubular heat exchanger is a form of heat exchanger with parallel tubes that allow two fluid streams to flow through them in opposition to one another. “Counter-flow” describes the configuration in which the hot and cold fluids enter the heat exchanger at opposing ends and proceed in opposite directions. The cold fluid flows outside the tubes while the hot fluid flows inside them in a counter-flow tubular heat exchanger.

The walls of the tube conduct heat from the hot fluid to the cold fluid as they pass each other. Proper design factors, such as tube size, tube material, flow rates, and thermal insulation, are essential to maximise the performance of a counter-flow tubular heat exchanger and guarantee effective heat transfer between the two fluid streams.

Figure: counter-flow tubular heat exchanger

Some companies have built their waste heat utilization system, as shown in ITMA 2023, like Pozzi Leopoldo RCR EOP – heat recovery system. Over the past 25 years, Pozzi Leopoldo has created a highly effective self-cleaning heat exchanger that has received widespread recognition in the textile sector. This heat exchanger has a continuously revolving central element driven by a tiny motor and made entirely of stainless steel. A hollow axle connecting two hollow discs with baffle plates allows clean water to flow through the element. The effluent flows the other way from the pure water inside a trough with baffles. The novel design has a number of noteworthy benefits, mainly when applied to contaminated effluents. Heat transfer is considerably enhanced by the rotating core element’s turbulence in the primary and secondary flows.

Additionally, the continual rotation avoids the build-up of deposits from the impure effluent, and the centrifugal separation action brought on by rotational turbulence prevents contaminants from coming into contact with the exchanger surfaces. As a result, the system continually maintains high heat exchange efficiency and virtually no maintenance or cleaning is required. Pozzi Leopoldo’s self-cleaning heat exchanger has shown to be a dependable and effective solution, especially for textile applications with dirty effluents.

The first installation of the RCR was performed on a Benninger continuous bleaching machine and has been operating for about two months.
The following data have been collected in a typical working week of the machine:

  • Flowrate: 15.2 m3/h (for both hot effluent and freshwater)
  • Temperature of fresh water (tap water): 17°C
  • The temperature of effluents: 86°C
  • Temperature of cooled effluents: 33°C
  • The temperature of heated water: 66°C
  • Recovered energy: 860kW (approx. 738000 kilocalories/hour) 
  • Heat recovery efficiency: 70%
Figure: Pozzi Leopoldo RCR EOP – heat recovery system

Utilizing waste heat is essential for advancing sustainability and circularity in the textile sector. Utilizing waste heat lessens the need for primary energy sources like fossil fuels, which lowers greenhouse gas emissions and helps combat climate change. Utilizing waste heat is consistent with circularity because it turns waste into a useful resource.

Waste heat is used as an input for other processes rather than being considered a byproduct that needs to be disposed of. This strategy advances the circular economy by reducing waste production, increasing resource efficiency, and closing the resource loop.

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