Experimental And Numerical Study On Structure Of Square Cyclone And Its Improvement

The separation of gas-solid suspension as important equipment is necessary in many fields, e.g., energy and power engineering, chemical and metallurgy engineering, etc. Cyclone separator is one of the key components of circulating fluidized bed (CFB) boiler and has been investigated extensively and intensively in the past 2 decades. However, the traditional circular cyclone separator could not adapt the increasing augmentation of the CFB boiler's capacity due to its large volume and thermal inertia caused by the thick firebrick lining. The square cross-section separator takes its advantage to improve the total thermal efficiency and decrease the thermal inertia by installing water or steam-cooled tubes along the inner walls besides its smaller pressure drop.4 types of square cross-section cyclone separator with different inlets including the single normal inlet, the double normal inlets, the single slanting inlet, the double slanting inlets were developed and studied both experimentally and numerically in this thesis. The separation efficiency and pressure drop were tested by a lab-scale test rig using the ash from a thermal power plant. Then a CFD simulation based on RSM turbulent model was carried out to calculate the flow field, pressure distribution, the turbulent energy and its dissipation, the grade separation efficiency, friction factor and the particle trajectory inside the separation. Finally, numerical improvement of the structure of suspension inlet and exhaust outlet was conducted.From the results, the following conclusions could be drawn.1) The experimental results showed that the inlet arrangement has an obvious effect on the performance of the separator. Under the same condition, the pressure drop of the slanting inlet separator is less than that of the normal inlet separator, while the separation efficiency of the slanting inlet separator is a little lower than that of the normal inlet separator. The separation efficiency of the double slanting inlets separator is higher than that of the single slanting inlet separator, while the pressure drop is on the contrary. The friction factors for the single and double slanting inlets separator are 2.01 and 1.80 respectively. However, the single normal inlet separator has higher separation efficiency and higher pressure drop than the double normal inlets separator. The friction factors for the single and double normal inlets separator are 2.50 and 2.24 respectively.2) The RSM CFD simulation was first demonstrated to be good by the comparison of the velocity distribution between the calculated results and the experimental results by particle dynamic analyzer. Then it was applied to carry out the simulation of the flow field, pressure field, turbulent energy and its dissipation, separation efficiency, particle trajectory inside the separation, respectively. The results showed clearly the vector flow field, local vortex, recirculation and other useful information.3) Based on the single normal inlet separator, a CFD simulation was conducted to improve the suspension inlet and exhaust outlet. The results showed that separation efficiency was improved significantly when a normal or an arc baffle plate was installed at the inlet at a penalty of increasing pressure drop. The friction factor increased to be 6.79 and 3.13 from 2.33 for the normal and arc baffle plate respectively. When the exhaust outlet was changed to be a vertical and slanting square duct from the original circular tube, the separation efficiency increased a little and the friction factor decreased from 2.33 to be 2.00 and 1.95 respectively.As a conclusion, the structure of the inlet and exhaust outlet can influence the performance of the separator.