Bohuslav Kilkovský

The efficient use of waste heat (WH) from gas streams is one of the key aspects in reducing the energy intensity, operating costs, and environmental impact of production processes and in the transition to sustainable energy. However, in many practical cases, the use of WH remained challenging due to the specific limiting conditions of the stream and critical issues such as fouling and the corresponding low heat transfer efficiencies. In particular, particle fouling hinders the operation of heat transfer equipment (HTE) and introduces several design considerations. To tackle this issue at the design stage, this study proposed a systematic framework intended for the design of fouling-resistant HTE. For a given usable stream, the major elements of the HTE design framework include (i) the Environmental assessment that enables the user to select the optimal way of WH utilization; (ii) a mobile testing device (MTD) for fouling parameters measurement, and (iii) an improved mathematical model for determining the critical fouling rate for the design of THE suited to particle-laden streams. The framework, especially the mobile testing device and the mathematical model, is tested under laboratory and/or industrial conditions, and illustrated with a case study of the WH stream with cement powder. Results show that the environmental assessment module can guide the selection of optimal usage with minimum environmental impact, and the mobile testing device and the mathematical model are able to determine the critical fouling velocity to support HTE design with higher resistance to fouling and higher operational reliability.

The efficient utilization of waste heat from industrial processes can provide a significant source of energy savings for production plants, as well as be a driver of sustainable operations and the abatement of emissions. Industrial waste heat usually is contained in liquid or gaseous outlet streams. Although the possible ways to utilize waste heat are discussed in 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 the practical aspects of waste heat utilization in the European Union so that the reader can gain perspective on (i) the thermal classification of waste heat, (ii) liquid and gaseous waste streams and their typical temperatures for industrial use cases, (iii) the technical, economic, physical, and environmental aspects barring full utilization of the available waste heat, (iv) waste heat sources in various industries, and (v) standardized 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.

A long-term experience and know-how from waste processing and especially from waste- and biomass-to-energy systems as well as continuing research and development brings new insights into manufacturing of equipment and their operation. Polluted flue gas (off-gas) causes high propensity to fouling and necessitates of subsequent cleaning. In some cases, it is not possible to utilize conventional approach. Novel designs of air pre-heaters, heat recovery steam generators and special heat exchangers therefore always respect primary importance of processes themselves as well as analyses aimed at selection and design of heat exchangers including specific features and fouling problems. However, the problems in operation cannot be avoided and therefore it is often necessary to use tailor-made solutions making provisions especially for fouling. We have been utilizing very efficient approach combining intuitive design and sophisticated tools based on Computational Fluid Dynamics (CFD). It is used for both troubleshooting and virtual prototyping and illustrated through industrial applications. Based on solving concrete industrial examples, a useful methodology which generalizes several particular features and takes into account economic aspects of different cases has been developed.

Fouling of heat exchangers' heat transfer areas is one of the serious problems of certain process plants. A waste incinerating plant is a typical example of such a process plant. The main process stream in a waste incinerating plant (i.e., produced stream of flue gas) and its thermophysical characteristics and properties significantly influence operating, maintenance, and investment costs of installed equipment and its service life. Moreover, properties of flue gas can vary over a wide range. This contribution deals with the issue of the fouling mechanism at the heat transfer area of tubular heat transfer equipment installed in plants for thermal processing of wastes and presents a mathematical model developed for fouling tendency prediction and for prevention in design and operating of tubular heat transfer equipment designed for applications in waste incinerating plants. Obtained results were compared with experimental data published in worldwide available literature and a very good agreement was found.