Innovative recuperator technology in the low-grade heat recovery from industrial processes
Author: Daniel Zając, Marcin Czupala, Marcin Karaś
Due Date: 16.11.2023
Recently, worldwide interest in waste heat recovery has increased significantly. For example, in EU, utilization of waste heat is a key priority for energy transition from a fossil-fuel based production and consumption system, towards a sustainably produced energy supply. 17% of waste heat sources in the EU is related to various industrial processes (Fig.1).
Source: International energy Agency iea.org
While most industries successfully recover high- and medium-grade waste heat, valorising low-grade waste heat still remains challenging technologically and economically. Increased energy costs and limits imposed on CO2 emissions require companies to seek out more effective methods of energy consumption in their processes. These days, effective energy management in industrial processes is important from both, an economic and ecological, point of view. The general energy efficiency of an industrial or the manufacturing process is influenced by, among other factors, the minimisation of waste heat emitted to the environment, strictly related to temperature levels (Fig.2).
In the literature, one can find many industrial waste heat potential examinations among EU countries (1), as well as in USA (2), focusing on the amount that can be recovered and exploited, referred to as technical potential of waste heat.
Fig 2. Examples of low, medium, and high-grade heat sources across industry
The main result of such analysis is the estimation of the total waste heat potential, where one third is corresponding to temperature level below 200 °C, which is often referred to as low-temperature (or low grade) waste heat, another 25% in the range 200–500 °C and the rest above 500 °C (mostly in the range 500–1000 °C).
For medium and high temperature applications, fully welded heat exchangers are in most cases the only viable technological solution, while low-grade waste heat generating processes, quite often are working with less challenging process parameters – hot air as the medium under atmospheric pressure. As the world leader in heat exchanger technology, KTS is constantly working on improving its products by researching new materials and welding technologies to ensure even better efficiency and durability of heat recovery systems.
But not only welding technologies are being developed in KTS – to cover low-grade waste heat recovery demands, KTS did introduced in the product portfolio air-to-air recuperator, where, instead of welding tube-to-tube sheet technology, gluing process had been applied. This bonded recuperator in a light, compact heat exchanger which, thanks to its reduced weight, can be installed where the competition’s products cannot.
The design involved a full range of tests (strength, thermal and flow tests, influence of corrosion on the bonds and numerical simulations to optimise the recuperator's geometry), the results of which enabled the design and manufacturing of prototype recuperators for operation in specific conditions.
The proper selection of materials, such as the bonding agent (glue) or appropriate steel grade and the correct manufacturing technology, make it possible to use the recuperator in a broad range of low-grade waste heat recovery applications. The significant weight reduction of the heat exchanger allows one to install it in previously inaccessible locations. The reduced need for welding and use of thin-walled components makes the new construction cost effective and less complicated to manufacture, while also maintaining its full functionality.
Table 1. Glue characteristics
In this innovative construction, the tubes are glued to the tube sheets and not welded. This enables the use of thinner wall of the tubes while maintaining the process parameters and the strength of the entire construction. These modifications made reduction of the tube weight possible, which in turn decreases the weight of the entire heat exchanger, as the weight of the tubes can exceed 70 % of its total weight, depending on the size of the recuperator. Thanks to thin-walled tubes and the lack of welding, it is also possible to use support tube sheets manufactured from thinner materials. The reduced weight of the internal components allows one to use a much lighter supporting construction for the exchanger. Optimised reinforcement walls ribs enable the use of smaller and thinner structural elements. Fig. 3 shows the comparison of heat exchanger tubes welded and bonded to the tube sheet.
Fig. 3 Tube-to-tube sheet: a) bonded (glued), b) welded
Fig. 4 Main components of the heat exchanger (tube bundle, support plates, casing)
The total weight of the heat exchanger is reduced by 40 %. The weight reduction of particular components is also significant and can be as high as 50 % in the case of tubes.
Fig. 5. Reduction of weight of heat exchanger with glued joints
Since this recuperator allows one to increase the energy efficiency of the process, its integration with the process line, reduces both the energy consumption of the entire process and any negative impact on the environment. Its unique properties, such as low weight to power ratio and lower price (in comparison with welded heat exchangers) makes this product highly competitive on the market. The advantages which make KTS innovative recuperator perfectly suited for operation in specific conditions include:
wide range of industries: wood, plywood, paper, food and others,
environmental advantages: reduced fuel consumption, less welding materials, less harmful pickling and passivation agents,
cost efficient solution,
thin tube wall can be used: low weight, less steel material used
Fig. 6 shows one of the exchangers constructed according to the new technology.
Fig. 6. Example of a bonded recuperator and the tubesheet
KTS continues to develop its products, which are manufactured to the highest standards of quality and sold all over the world. Our portfolio of heat exchangers is one of the most comprehensive, available for covering equipment suitable for a wide range of applications. As an international company heavily focused on green tech solutions, which contains heat recovery, we operate in the global markets for power generation, chemistry, food and beverages and many heavy&light industries. Our products are efficient, safe, and environmentally friendly.
Currently, those companies that want to become leaders or maintain their position on the market must constantly improve their technical and technological solutions. No less important are rational energy management and reduction of the negative impact on the environment. As mentioned above, one of the methods of complying with these requirements is to use waste heat recovery systems. Waste energy recovery is an excellent means of decreasing manufacturing and operating costs, which translates to increased competitiveness and overall sustainability of the business. The use of our innovative recuperator designed for operation in specific industrial conditions significantly broadens the possibilities of low-grade waste heat recovery.
For one of our partners from pulp and paper industry we had delivered an air-to-air recuperator which is working 24/7 and during full year can recover almost 1 MWh of the energy, significantly reducing consumption of natural gas fuel.
Fig. 7. Example of heat recovery installation in paper industry
Table 2. Process parameters
1. Michael Papapetroua, George Kosmadakis, Andrea Cipollina, Umberto La Commare, Giorgio Micale: Industrial waste heat: Estimation of the technically available resource in the EU per industrial sector, temperature level and country. Applied Thermal Engineering, 138 (218) pp. 207-216
2. Waste Heat Recovery: Technology and Opportunities in U.S. Industry, US Department of Energy, 2008