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Efficient utilization of waste heat from industrial processes can be a significant source of energy savings for production plants as well as the driver of sustainable operation and emissions abatement. Industrial waste heat usually is contained in liquid or gaseous outlet streams. Alt-hough the possible ways to utilize waste heat are discussed by a wide variety of papers, these either provide only a general overview of utilization options and opportunities or focus on a narrow range of industrial processes. The aim of the present paper is to discuss practical aspects of waste heat utilization in the European Union so that the reader gains perspective on (i) thermal classification of waste heat, (ii) liquid and gaseous waste streams and their temperatures typical for industrial use cases, (iii) technical, economic, physical, and environmental aspects barring full utilization of the contained heat, (iv) waste heat sources in various industries, and (v) standard-ized equipment and technologies applicable to industrial waste heat utilization, including their advantages, disadvantages and weak points.

Heat regenerators are simple devices for heat transfer, but their proper design is rather difficult. Their design is based on differential equations that need to be solved. This is one of the reasons why these devices are not widely used. There are several methods for solving them that were developed. However, due to the time demands of calculation, these models did not spread too much. With the development of computer technology, the situation changed, and these methods are now relatively easy to apply, as the calculation does not take a lot of time. Another problem arises when selecting a suitable method for calculating the heat transfer coefficient and pressure drop. Their choice depends on the type of packed bed material, and not all available computational equations also provide adequate accuracy. This paper describes the so-called open Willmott methods and provides a basic overview of equations for calculating the regenerative heat exchanger with a fixed bed. Based on the mentioned computational equations, it is possible to create a tailor-made calculation procedure of regenerative heat exchangers. Since no software was found on the market to design regenerative heat exchangers, it had to be created. An example of software implementation is described at the end of the article. The impulse to create this article was also to broaden the awareness of regenerative heat exchangers, to provide designers with an overview of suitable calculation methods and, thus, to extend the interest and use of this type of heat exchanger.