Research On Characteristics Of Pipe Swirl Flow For Enhancing Gas-solid Separating And Heating Transfer

Huge amounts of smoke dust that boilers and industrial furnaces generated have been released into the atmosphere. The main energy in China still depends on coal providing. With increase of requirements for environment protection standards on emissions is enacting. Now dust emission must not exceed 30mg/m3 in some sectors. The bag type dust remover has high efficiency for dust remover which applies to power, coal burning boiler, metallurgy and chemical engineering. The bag dust remover becomes the important decontaminating equipment in china. However, the bag dust is not very thorough in domestic such as bag chocking up or bag burned through. Filter bag’s technology as the key technical of the bag type dust cleaning need to be further studied. It is pointed out that not only the high flue gas temperature or much volatility temperature fluctuant destroys the filter bag, but the particles of the high temperature is more importantly part of destroying the filter dust bag. The pretreatment of dusty gas is put forward.The pretreatment of dusty gas includes gas-solid separation and cooling. Now the dusty gas is conveyed straightly by duct and cooled by air extending transportation distance with snake-pipe. The change of straight flow to swirl flow is put forward. The tangential velocity of dusty gas is produced. The movement of dusty gas changes to spiral flow and the delivery distance of dusty gas increases. There is centrifugal force field for gas-solid separating. The movement has flushing function to wall surface to enhancing heat transfer in tangential direction.The new swirl generators of single helical inlet and double helical inlets are given. Swirl flow moves towards downstream. The devices mating bag filter are helpful to protect the bag and reduce the run cost。The operation mechanism and effect of the devices are carried out by using experimental, theoretical and simulated by using CFD method.Firstly, on the basis of reviewing the recent study in separation and heating transfer by swirl flow, new generating swirl devices by helices are presented which use the XCY-3.0’s inlet configuration. Swirl flow generating models include single inlet by 180 degree helix without guide-core (Model SO) and with guide-core (Model S1), double inlets compositing of 90 and 270 degree helix without guide-core (Model DO) and with guide-core (Model D1).Secondly, the characteristics of swirl flow and pressure field are studied by theoretical analysis. Mathematical models of velocity profile, pressure drop and separation for four models are developed. According to the Newton motion law, the traces of particles in axial swirl are analyzed. The unsteady heat transfer between particles and gas is discussed. A model of particle’s heat transfer was developed by using Lumped Para meter Method (LPM). It shows that the smaller particle will get to steady heating transfer between particles and gas more quickly and have smaller temperature difference. The heating enhancement of swirl flow is analyzed under the guidance of field coordination between velocity and heat flow fields.Thirdly, experiments of swirl flow by four kinds of swirl generators are carried on. It indicated the tangential velocity reaches a peak near the wall which divides the profile into central semi forced vortex and annular semi free vortex. Axial component differs from the developing or developed smooth pipe flow; flow is accelerated near the wall, despite being decelerated in the central region, and back flow appears in the core. Model S1 and D1 with guide-core can hold up more swirl intensity during axial initial sector, so better for gas-solid separation than SO and DO respectively. The flow resistance model with swirl generators is developed and the swirl flow intensity is described by swirl number S. The decaying swirl number decreases approximately in exponential with the axial distance. The experimental setup with a concentric tube heat exchanger has been demonstrated for studying the enhanced heat transfer performance of swirling flow. By comparing the smooth tube heating transfer test, it is proved that the experimental method is feasible. The relationship of Nusselt number, Reynolds number and swirl number is analyzed. The assessment index of enhancement efficiency and friction factor is used to evaluate heat transfer enhancement techniques. The results show that D1 model is better than other models for enhancing heat transfer.Fourth, numerical simulation is an effective approach of investigating swirl flow. The swirl flow field and temperature field were simulated by means of Reynolds Stress Model (RSM). The SIMPLEC algorithm is used to handle the pressure-velocity coupling. The flow fields of gas-solid separation are simulated with Discrete Phase Model (DPM). Comparing with the experimental results, it shows that the data determined by numerical simulation is reasonable. Results show that the enhancements in Nu number are higher in compare with smooth pipe flow based on generating swirl flow and increase with Re number.After all, based on the theoretical analysis, experimental research and numerical simulation, the pre-processing device working with bag type collector is devised to cooling and cleaning gas discharged by Mashan steel’s dry coke quenching (DCQ) furnaces. It has shell-tube construction, gas by swirl generator flows through the tube side, and cooled fluid flows through shell side with counter flow type cooling. It is provided clearly to avoiding to chocking up and burning through the filter bag. The design method and energy-economic analysis is provided.In general, the new type swirl structure with helices designs for gas-solid separating while simultaneously enhancing heat transfer. The pretreatment technology protects the filter bag and makes protection of bag filter and stable operation. The separation efficiency models are established by researching and analyzing on enhancing gas-solid separation and heating transfer by pipe swirl flow. It need go on with further study about the applications of pretreatment technology and the performances with the cooperation of bag filter.