Exploitation of waste heat could achieve economic and environmental benefits, while at the same time increase energy efficiency in process sites. Diverse commercialised technologies exist to recover useful energy from waste heat. In addition, there are multiple on-site and offsite end-uses of recovered energy. The challenge is to find the optimal mix of technologies and end-uses of recovered energy taking into account the quantity and quality of waste heat sources, interactions with interconnected systems and constraints on capital investment. Explicit models for waste heat recovery technologies that are easily embedded within appropriate process synthesis frameworks are proposed in this work. A novel screening tool is also proposed to guide selection of technology options. The screening tool considers the deviation of the actual performance from the ideal performance of technologies, where the actual performance takes into account irreversibilities due to finite temperature heat transfer. Results from applying the screening tool show that better temperature matching between heat sources and technologies reduces the energy quality degradation during the conversion process. A ranking criterion is also proposed to evaluate end-uses of recovered energy. Applying the ranking criterion shows the use to which energy recovered from waste heat is put determines the economics and potential to reduce CO2 emissions when waste heat recovery is integrated in process sites. This thesis also proposes a novel methodological framework based on graphical and optimization techniques to integrate waste heat recovery into existing process sites. The graphical techniques are shown to provide useful insights into the features of a good solution and assess the potential in industrial waste heat prior to detailed design. The optimization model allows systematic selection and combination of waste heat source streams, selection of technology options, technology working fluids, and exploitation of interactions with interconnected systems. The optimization problem is formulated as a Mixed Integer Linear Program, solved using the branch-and-bound algorithm. The objective is to maximize the economic potential considering capital investment, maintenance costs and operating costs of the selected waste heat recovery technologies. The methodology is applied to industrial case studies. Results indicate that combining waste heat recovery options yield additional increases in efficiency, reductions in CO2 emissions and costs. The case study also demonstrates that significant benefits from waste heat utilization can be achieved when interactions with interconnected systems are considered simultaneously. The thesis shows that the methodology has potential to identify, screen, select and combine waste heat recovery options for process sites. Results suggest that recovery of waste heat can improve the energy security of process sites and global energy security through the conservation of fuel and reduction in CO2 emissions and costs. The methodological framework can inform integration of waste heat recovery in the process industries and formulation of public policies on industrial waste heat utilization.

This diploma thesis investigates the combined production of power and heat from biomass. The main aim is to compare suggested energy circles in the light of their electric, general and economic efficiency. Introduction describes the basic terms and principles of energy utilization of biomass, combustion and gasification technology are described thoroughly. The main part contains suggestions and thermal calculations of energy circles. The thermal cycle with gasification chamber, combustion chamber and hot air turbine is proposed, than thermal cycle with gasification generator and cogeneration unit and finally Rankine-Clausius circle. In conclusion calculated results are recapitulated and the usability of proposed thermal cycles is assessed.

In the last decade there is a rising interest in thermoelectric applications. Thermoelectric generators enabling the direct conversion of the heat into the electricity become attractive. This fact is caused by the demands of environmental operation and saving primary resources. Scientists intensively investigate and develop new materials and structures suitable for these applications. The efficiency of the thermoelectric conversion progressively increases. Unfortunately we have no available materials with sufficient thermoelectric properties which could provide cost-competitive price. Thermoelectric generators seem to be useable devices. For example, in case of the unused waste heat using of the thermoelectric generator can increase the overall effectiveness of the unit despite the low efficiency of the generator. This master thesis deals with the issue of the Peltier modules representing the main part of the thermoelectric generators. The physical principles and structures of the thermoelectric modules and the possibility of thermoelectric power production are described here. In the practical part of this thesis the design of the low power generator utilizing waste heat from biomass boiler Verner A 251.1 is proposed.