Effective utilization of heat in waste and biomass processing

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.Effective utilization of heat in thermal processing of waste and biomass plays an important role since it contributes to environmental and economic optimization of the processes and equipment. In case of utilizing energy released during thermal oxidization (incineration) of municipal solid waste (MSW) or of hazardous waste for generation of process steam or for cogeneration (combined heat and power systems - CHP) we can consider the thermal processing as a certain kind of recycling. Since waste has sufficient heating value, it belongs to renewable energy sources which enable to save fossil fuel as a primary energy source. Then we speak about waste to energy systems (WTE). In addition to environmental benefit, effective utilization of released energy has a positive impact on economics of the process including reduced operating costs. WTE can partially or completely compensate costs of waste treatment (costs of auxiliary fuel for incineration of low calorific industrial and/or hazardous waste) and it can even bring profit to the operator in case of waste with high calorific value. Typical examples of units for the thermal processing of both MSW and hazardous waste are shown with the objective to evaluate main factors influencing energy balance of the processes, while taking into account various regimes of operation. Basic rules of selection of the systems for efficient heat utilization including CHP are summarized and illustrated on concrete industrial examples. Conventional methods of energy availability are discussed and analyzed. Heat flows in the incineration plant are evaluated as well as factors like plant efficiency and/or energy utilization rate. A novel and original technology for combustion of various types of biomass and fytomass consisting of a feeding system, boiler, heat recovery system and flue gas cleaning system (in case of contaminated biomass) is presented. Moreover, it is necessary to take into account specific features of flue gas (and/or off-gas) as a process fluid. For an optimum design of heat exchangers as equipment and integrated items it is necessary to follow a top-down approach “process – heat recovery system – heat exchanger” while respecting specific features of the concerned process. A combination of intuitive design, know how and sophisticated approach based on up-to-date computational tools with emphasis on computational fluid dynamics (CFD) is shown in the paper. After selecting a convenient process for the given type of waste and/or biomass, the available energy for heat recovery is evaluated and a heat recovery system is designed. Novel design of air pre-heaters, heat recovery steam generators and special heat exchangers (e.g. those for sludge pre-heating) is shown. This approach always respects the primary role of the process, while stressing also the importance of analysis aimed at selection of heat exchangers and their design including specific features and fouling problems.vk201

Aspects of fouling in case of heat exchangers with polluted gas

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.This paper presents and discusses various aspects of fouling in case of heavily polluted flue gas (and/or off-gas) coming especially from incinerators/waste-to-energy systems. A long-term experience and know-how from this area as well as continuing research and development brings new insights into manufacturing of equipment and their operating. Polluted off-gas causes high propensity to fouling and necessity of consequent cleaning. In some cases, it is not possible to utilize a conventional approach. Introductory part of the paper provides a description of various types of units for thermal processing of wastes (including sludge and contaminated biomass). Fouling is classified according to various cases of industrial applications connected with easy/difficult cleaning. It is shown how fouling can influence geometry of heat exchangers and their selection. In the following part, several industrial cases are shown taking into account aspects like: • solid particles (ash and flying ash) in the gas, and adapting design according to their concentration; • species contained in flue gas which can chemically react and create fouling deposits on heat transfer surfaces; • potential corrosion between the fouling layer and heat transfer surface caused by local temperature decrease. The above aspects are clearly illustrated through industrial applications as follows: • heat recovery system of unit for the thermal treatment of sludge coming from pulp and paper production; • boiler systems in incineration plants and chemical industry plants. There are various methods to reduce fouling. We have utilized very efficient approach combining intuitive design and sophisticated tools based on CFD (Computational Fluid Dynamics). However, fouling cannot be eliminated completely therefore various efficient methods (mostly tailor-made ones) are utilized (like common mechanical cleaning, air guns, controlled local explosion) for cleaning of surfaces. There is also an effort to develop a mathematical model for fouling prediction, and selection of the most economically acceptable systems connected with current research and development in the field. However, it is difficult to validate the models. Fouling in the field described in the paper is in fact a “never ending story”.pm201

Traveling waves and pattern formation for spatially discrete bistable reaction-diffusion equations (survey)

Analysis and Stochastic

Editorial to special issue V WCDANM 2018

The special issue Advances in Computational Data Analysis of the Journal of Applied Statistics (JAS), Taylor & Francis, contains mainly papers that were presented in the fifth Annual Workshop of Computational Data Analysis and Numerical Methods (V WCDANM), which took place on 11–12 May 2018, at the Polytechnic Institute of Porto, Portugal. The organizing committee of V WCDANM – 2018, with the support of the Polytechnic Institute of Tomar and the University of Évora, developed a program that includes prominent keynote speakers and a high scientific level of oral and poster sessions, with participants from Portugal and abroad. Theoretical and applied works in different research fields were presented, namely in health and social sciences, environmental science, economics and engineering (some involving data science, data mining, big data and machine learning). A considerable number of manuscripts were submitted to this special issue and more than 30 papers, after carefully reviewed by referees, were accepted and are distributed in three issues of JAS Volume 47. The selected papers offer readers the opportunity to access different statistical approaches, as well as to view a wide range of application areas. These research works provide the appropriate framework and background for real-life problems and also they reflect a comprehensive view of different statistical fields, promoting links with a variety of related disciplines, exploring computational issues and presenting some future research trends.This work was also supported by the Bulgarian National Science Funds under the bilateral projects Bulgaria – Austria, 2016–2019, Feasible statistical modeling for extremes in ecology and finance, Contract number 01/8, 23/08/2017 and WTZ Project BG 09/2017.info:eu-repo/semantics/publishedVersio