| The fixed-valve tray overcomes not only the disadvantages of the sieve tray as large amount of entrainment, serious leakage and low mass transfer efficiency, but also the the disadvantages of the floated-vavle tray like expensive manufacturing cost and easily blocked. The fixed-valve tray has advantages as cheap manufacturing cost, large elasticity of operation, high mass transfer efficiency and no need of maintenance,etc. So it meets the industrial demands in lasting, full load and excellent operation, contributing to energy saving and emission reduction. Therefore, researchs on the fixed-valve tray and its industrial applications will benefit the economic construction and the harmonious development of the sociaty with far-reaching and significant significance.At present, the fixed-valve tray mainly focused on the development of new valve types, valve structures and the optimization of the trays. In this paper, a new type of fixed-valve tray was provided, called round fixed-valve tray. The projection of a round fixed-valve on the tray is a Φ40mm round area, and a valve composed of a cover and three legs, with edgefold downward from bonnet fringes of the valve cover and the legs showed a120°layout.In a Φ600mm plexiglass tower, at different air and water flow rate, the hydrodynamics performance of the fixed-valve trays were studied with the air-water system, including dry pressure drop, wet pressure drop, leakage and entrainment of the trays, etc. And still, the influence of valve types (the bubbling unites on trays were respectively round fixed-valve and elongated fixed-valve), valve rising height (the rising height of the round fixed-valve were respectively5.5mm and9.0mm) and valve numbers (24and38valves in the height of5.5mm were arranged on the round fixed-valve trays) on hydrodynamic properties were studied. Meanwhile, by the fluent6.2software, the flow field in the inside space and the surrounding of the round fixed-valve on the trays were simulated and visually inspected, which round fixed-valves were those during the hydrodynamics experiments.The hydrodynamic experimental results showed that the dry pressure drop△Pd of the fixed-valve trays increased slowly as F0increased, between which were linear in the double logarithmic coordinate system. Associated by (?), the hole flow coefficients C0of1#tray,2#tray,3#tray and4#tray were0.5887,0.5881,0.4457and0.5833respectively, which meant#3tray had the highest dry pressure drop under a same valve hole kinetic energy factor F0, while the other three trays had the similar dry pressure drop. At a spray density, the wet pressure drops△Pw of the fixed-valve trays increased as F0increased. And in a certain air flow, the wet pressure drops△Pw of the round fixed-valve trays increased as the spray density rised up, among the trays3#tray had the highest△Pw. Because of the limited capacity of the downcomers to the liquid, when the spray density was higher than60(m3·h-1)m-2, the downcomers would flood when the air capcity reached a certain level. For each of the round fixed-valve trays, under the spray density of10,20and40(m3·h-1)m-2,η decreased rapidly with increasing F0, while η decreased slowly with the increasing F0under the spray density of60and80(m3·h-1])m-2, with the higher F0when η=10%at the lower spray density. However, at every spray density, the leakage rate η of the elongated fixed-valve tray decreased gradually with the increasing Fo. But under the same F0, the absolute leakage m of the all fixed-valve trays increased with the increasing spray density, while the similar decreasing rate with increasing F0, and the absolute leakage m at60and80(m3·h-1)m-2were much higher than those of10,20and40(m3·h-1)m-2. At each spray density L, the entrainment ev of the round fixed-valve trays increased with increasing F0, and the increasing rates under the lower spray density L were relatively higher than those of the larger L, while at60and80(m3·h-1)m-2the trays had occurred downcomer flooding when the entrainment ev were less than10%. Descending operational flexibility of four fixed trays was1#tray-3#tray-2#tray-4#tray.The results of gas flow field simulation by CFD software showed that air went through the valve openings on the tray into inside space of the valves by the sudden contraction, changed directions when touched the valve covers, then got out along the edgefolds from the valve sides with sudden expansion, and the air flow rate reached the maximum at the valve seams near the value covers. Air outflew from the adjacent four-valve collided between their regional, and a part of the air flow blown downward the side seams onto the tray, while vortexes formated on the near tray and at the edges of the valve covers. Out from the9.0mm rising height vavles, air flew obliquely to the upper tray after got through the valve seams at high speed, while the air out of the5.5mm rising valves blew more horizontally onto the tray and occurred strong collision between the valves, then flew to the upper tray. The higher inlet velocity or the lower rising height was, the larger vortexes were near the edges of valve covers and on the tray. The smaller distance between the valves was, the more air flow collided and at higher velocity. |
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