Common industrial waste heat recovery systemsN. Mughees | January 27, 2023
The term "industrial waste heat" refers to the heat produced during manufacturing operations but is then abandoned and released into the environment without being put to any good use. In order to supply useful power sources and lower total energy consumption, waste heat recovery may be accomplished using a number of waste heat recovery devices, which are discussed in this article.
A power source driven by recovered heat may be utilized to produce extra heat or electricity and mechanical energy. All temperatures are valid for capturing waste heat, but traditionally, the higher the temperature, the better the quality of the waste heat and the simpler it is to optimize its recovery process. Finding the optimum or maximum quantity of high-potential recoverable heat from a process is crucial for maximizing the effectiveness of a waste heat recovery setup.
Recuperative and regenerative burners, plate heat exchangers, heat pipe heat exchangers, economizers, waste heat boilers, air preheaters and direct electrical conversion devices are only some of the prevalent types of equipment utilized in waste heat recovery systems. All of these machines are based on the same idea, which is to exchange and recover process heat that contains potential energy. The following sub-sections discuss these common waste heat recovery systems in industries.
Common waste heat recovery systems in industries
Recuperative and regenerative burners
Burners that are both regenerative and recuperative maximize energy efficiency with heat exchanger surfaces that absorb the heat from the flue gas produced during combustion. Regenerative devices are typically two burners linked to the furnace through separate control valves via which the combustion air approaching the furnace in alternating cycles is heated. The device functions by channeling the furnace's by-product gases into a housing made of refractory material like aluminum oxide. Aluminum oxide media are heated by the exhaust gas, and the wasted thermal energy is then stored and recovered.
Plate heat exchanger
When there is a requirement to transmit heat across fluids while preventing cross contamination, plate heat exchangers are employed. Thin metal plates are layered in parallel to create a hollow metal shell and form the plate heat exchanger. Fluid flow may be regulated, and turbulence created for increased heat transfer by means of the various pressed patterns that typically compose each plate and their surrounding gaskets. The gaskets are set up such that one kind of fluid can move through one hole whereas another fluid is redirected via an adjacent hole.
Heat pipe heat exchangers
These systems transfer heat by the condensation and evaporation of a working fluid between two locations. The design is based on a sealed container, wicking material, and a tiny amount of working fluid in equilibrium with its own vapor, such as methanol, water, acetone, ammonia or sodium. Three distinct parts comprise the heat pipe: the evaporator, the adiabatic transport and the condenser.
The working fluid within the pipe vaporizes when heat is provided to one end, and the heat travels via the pipe wall and the wick assembly. This causes pressure to build up in the vapor, which in turn pushes the vapor via adiabatic transport portion and out the other end of the pipe. The latent heat of vaporization is dissipated via the wick assembly and the pipe wall to the heat sink, causing the vapor to condense. The wick material subsequently soaks up the liquid that formed from the vapor flow. As the liquid travels through the wick, the menisci generate capillary force that ultimately returns it to the pipe’s hot side.
Economizers, also known as finned tube heat exchangers, are commonly used to heat liquids and recover low to medium levels of waste heat. Heat absorption and transfer efficiency are both improved by the system, composed of tubes coated with metallic fins. This system is installed in the exhaust duct and absorbs heat by directing hot gases through several portions that are enclosed by finned tubes. The thermal efficiency is maximized and enhanced by recycling the heated liquid.
Waste heat boilers
Multiple water tubes, arranged in a parallel fashion and facing the direction in which waste heat is being expelled, make up a waste heat boiler. Steam is produced as a byproduct of the system, which recovers heat from exhaust gases at medium to high temperatures. Next, the steam can be utilized to generate electricity or recycled into the system for power restoration.
When preventing process-wide contamination is critical, air preheaters take the lead. They are generally utilized for applications needing low to medium temperature conditions and exhaust-to-air heat recovery systems. Exhausts from gas turbines and heat salvaged from cooking appliances and boilers are two examples. Two distinct architectures, the plate and heat pipe, are available for use in air preheating.
Direct electrical conversion devices
There are additional setups in industries that can generate electricity straight from recovered heat energy without the necessity for first converting heat into mechanical energy. Piezoelectric, thermoelectric, thermo-photovoltaic and thermionic devices are all examples of such technologies that may be used to generate energy.
Industrial waste heat recovery techniques involve collecting and returning wasted heat energy to the system as a supplementary power source. The waste heat may be captured and reused with the help of a variety of heat recovery devices, the most common of which are energy recovery heat exchangers housed within a waste heat recovery unit in industries.