(29e) Gas-Liquid Flow Characteristics On Large-Scale Float Valve Trays Operating At Low Loads

Abstract:this paper has established a model for calculating the total energy of gas-liquid layer on the float valve trays operating at low loads. In the model the fractions of bubbling area and weeping area are defined, through the analysis of liquid flow characteristics of the different areas, the expressions of kinetic energy, potential energy and surface energy are obtained, which are related with the fractions of bubbling area and weeping area. If bubbling and weeping coexists, this definition will eliminate the inconvenient of dealing with singular point mathematically, which comes from the model. When the energy of system is at minimum, the system is at the most stable state, in this condition the fractions of bubbling area and weeping area change with the time being according to the optimized model. And because of the change of the weeping holes, the liquid heights on the trays vary and the gas pressures under the trays fluctuate. With the restriction of the model, the wave equations of liquid and gas cannot be obtained, and this unstable flow pattern will cause the pressures of the liquid on the trays and under the trays fluctuating, thus induce the gas-liquid layers on the trays to vibrate. Such vibration may cause a series of safety issues when valve trays are operated at low loads(start-up or shut-down).

The system of air-water in two-phase flow conditions are studied on the 6400×800 mm² two-pass rectangle Glisch-V1 trays which are near-industrial scale, and the valve weight is 32g, the fractional hole area is from 5% to 14%, the weir height is from 25mm to 65mm, the liquid flow rate is from 5.6 m3/h to 32 m3/h, and the superficial gas velocity is from 0.1 to 0.65m/s. Through the experiments, in the range of gas velocity at or below the seal point, all the trays bubble and weep intermittently (the fraction of bubbling area and the fraction of weeping area changes in the range of 0 to 1 alternately), meanwhile the gas-liquid layers vibrate up and down periodically, and the whole tower also shakes, which are in accordance with the flow pattern theoretically predicted in this paper. In addition, the clear liquid heights of different positions on the trays are very uniform, and the weeping rates of every valve hole are almost equal. The uniformity of these hydraulics parameters can prove the hypothesis made in the setup procedure of physical model to be reasonable.