| Abstract [eng] |
The final work of the Master's project includes a literature analysis, which looks into the current situation of the energy sector in Lithuania. The planned strategies, the overall consumption of renewable energy resources as fuel in the district heating sector, the potential of waste heat and its recovery in thermal power plants through the application of condensing economizers and absorption heat pump technologies are reviewed. Technological cases of water spraying in biofuel combustion plants are discussed, two cases are selected as test cases, water droplet spraying into the high temperature flue gas stream and into the flue gas stream upstream of the condensing economiser for the efficient use of biofuel combustion technology. For both cases, cycles of phase transformation modes of water droplets in a medium humidity flue gas stream were simulated by spraying the recovered and cleaned 40℃ condensate from the flue gas. The first phase consists of spraying two water droplets of different diameters 2R0= 100 µm and 2R0= 400 µm into the high temperature flue gas stream of 800℃ after the introduction of liquid catalysts to clean them, and the second phase consists of spraying the same water droplets of the same diameters into the 150℃ removed flue gas before the condensation economiser to cool and humidify the flue gas. A mathematical model based on the heat flow balance equation was developed for the calculations, which, due to the unknowns of the external convection and Spolding heat transfer parameters, was calculated by an iterative approach. The KTU EK program "LAŠAS" numerically simulated the phase transformation modes for different spraying cases with different dispersed droplet diameters 2R0= 100 µm and 2R0= 400 µm. The most important parameters and their variations are graphically represented by the analysis of the obtained output data. The analysis of the thermal and energetic state of the droplets, the variation of the dynamic parameters, the variation of the phase transformations in the phase transformation cycle regimes and the analysis of the parameters defining the heat and mass transfer of the droplets have been performed. For the convenience of numerical modelling, the use of the Fourier Fo universal timescale was chosen, which is useful to define the time step in the numerical scheme to represent the droplet coarsening sensitive phase transformation regimes cycle. The analysis confirmed that the cycle of the phase transformation modes remained consistent under the set input data. The results confirmed that the temperature of 150℃ in the flue gas stream is not significant for the thermal state of the radiant water droplets. It was confirmed that the Stefan hydrodynamic flow enhances the convective heat and mass transfer processes in the condensation regime and weakens them in the evaporation regime. In parallel with this thesis, more research was carried out and the results were submitted to the editors in the form of articles. The paper "Influence of Flue Gas Flow Temperature and Humidity on Heating and Evaporation of Injected Water Droplets", which investigates the droplet HMT in high temperature flue gas at different flue gas humidity, was presented at the Industrial Engineering 2023 CIRCULAR ECONOMY: PRODUCTION AND CONSUMPTION conference. The second paper "Numerical Modelling of Phase Transformations of Water Droplets for Efficient Heat Recovery From Biofuel Flue Gas" has been submitted to the Mechanics Journal. It includes a study to determine the effect of radiation on HMT at different flue gas temperatures and the spraying of a heated 80℃ condensate against a condensation economiser. And the third paper "Modelling Of The Composite Heat Transfer Of a Sprayed Water In The Gas Flow From An Applied Technological Aspect" has been submitted and accepted for publication in INDUSTRIAL ENGINEERING 2024 from Zero to Hero. The paper presents the use of different droplet diameters in low-temperature flue gas and the convenience of the Fourier scale in the analysis of phase transformation mode cycles. |
