Experimental study of electrostatic precipitator of a coal based power plant to improve performance by capturing finer particles
thesisposted on 29.10.2020, 00:00 by Abu SayemAbu Sayem
Electrostatic Precipitators (ESPs) are widely used to capture particulate matter from flue gas. In coal-based power stations, they are used for capturing fly ash before the flue gas is released to the environment. Coal-based power plants are still one of the major suppliers of energy because they are more reliable and have lower unit cost of power generation. Under the current environmental protection regulation controlled by the Environment Protection Agency (EPA), only the finer particles can be released to the environment. However, this is likely to change and coal-based power plants will then have to face stricter rules about permissible size limits for particulate matter (PM) discharged in flue gas, namely the particle size of PM 2.5 (micron) or less. It is therefore required that the capabilities of ESPs are enhanced so that they will be able to capture these finer particles. The main aim of the research is to investigate the micro-size particulate matter capture ability of existing ESPs and determine the operational parameter relationships to improve the collection efficiency of ESPs. In particular, this research focuses specifically on the flow phenomena of the finer fly ash particles inside the ESP model and how they are impacted by the changed geometries and varied electric fields. This involves studying the flow velocity and forces associated with the flow and the electric field and the relevant parameters affecting the dust collection and thus establishing and validating a relationship between the interaction of two phase flow and electric field to reveal the underlying physics for collecting finer particles. To achieve the aim, a laboratory scale ESP was constructed for undertaking various tests and measurements using a novel method. This method involved flow measurement in the ESP chamber using a pitot tube and a cobra tube, whilst employing different shaped baffles in the chamber, varying production of electrostatic field in the ESP model and testing its capturing capacity. This research investigated the influence of internal geometry of the ESP on the flow in the ESP chamber. Two different shaped baffles – semicircular and arrow shaped - were designed, fabricated and inserted in the ESP chamber to effect changes to the flue gas pathway to enhance collection efficiency and collection capability of submicron particles. The flow measurements and experimental results were compared and validated with the 2D ii simulation results. Results using baffles indicate that internal geometry of the ESP has an influence on collection efficiency and changing the internal shape produces swirling flow inside ESP, which, in turn, improves collection efficiency. In addition, baffles increase residence time, which allows capture of sub-micron particles. A high voltage transformer and associated electrode plates and rods were designed, constructed and fitted into the model ESP for measuring and investigating particle collection efficiency under various velocities and electric/voltage characteristics. Production of electric field in a lab model ESP of this type and its testing constitutes a novel approach as such work is not found in the public domain. The experimental results show that ESP collection efficiency is higher at high voltages and at low fly ash velocity and the collection efficiency rapidly decreases when voltage reduces. A mathematical model was developed and validated with the experimental measurements to confirm the collection efficiency. By analysing the various conditions and scenarios, an optimum operational condition within an operational range were developed and recommended for future ESP operation. By implementing a TR (Transformer–Rectifier) in different collection chambers, power consumption of the ESP can be reduced. The research also revealed new information on the particulate matter size distribution and the collection of submicron particles from flue gas of coal-fired power plants. Particle size distribution analysis was conducted using a Mastersizer and the morphology of the particles was analysed using a Scanning Electron Microscope (SEM). Size distribution analysis suggested that higher voltage and lower flue gas velocity will be more suitable to capture submicron particles. The morphology study indicated that smaller particles have a tendency to agglomerate with bigger particles. Overall, this thesis provides new knowledge about Electrostatic Precipitator operation with new geometries and under various electric field conditions at a laboratory scale, whilst achieving operational efficiency improvement and improving the capture of sub-micron particulate matter. The knowledge obtained from this research would be a good basis to operate industrial ESPs for future sustainable coal-fired power generation.