The important problem arising at operation of technological installations at the enterprises of energy, chemical, oil-processing and food industries is ensuring their reliability in conditions of high dynamic loadings of pipelines. The unsteady hydrodynamic processes occurring in pipeline highways at fast opening and closing of valves often lead to loss of sealing of pipelines' joints, breakage of fittings and can become the reason of emergencies. Such processes are especially dangerous to the pipelines made of polymeric materials being widely applied today, for example, in power plants. About 90 tanks-filters of chemical water purification with a capacity of 30 m3 with hundred meters of the pipeline 150 mm diameter in which unsteady flow is occurred are operated in by product recovery departments of large combined heat and power plants. Plastic pipes have high corrosion resistance, but smaller durability in comparison with steel pipes. Therefore research of dynamic processes in pipelines and development of approaches and devices which allow reducing intensity of dynamic loads of pipelines and fittings of technological installations is actual one. In the paper, mathematical model of typical pipe system of processing plant, method and software for calculation of parameters of unsteady flow and dynamic loadings on pipe work structure is developed. Methods and devices for reducing dynamic loadings are proposed. The simulation results of the model and efficiency of the devices proposed are experimentally verified. The pipeline bends fluid reaction forces decrease with the valve opening time increase. Thus, at the second bend with the discharge pipe being air filled and the valve opening time being increased from 0.1 to 4 s the fluid reaction force drops from 2.0 to 0.5 kN. If the pipe downstream the valve is fluid-filled the fluid reaction force reduces about 4 times as compared to air-filled case. For the preliminary fluid-filled pipe, the speed of the valve opening has little effect on the pipe bend fluid reaction forces. Thus, to avoid high reaction forces the pipe system should be carefully filled with fluid. Valve opening-closing time should be at least 5 seconds. The pipe bend fluid reaction forces increase with the ullage pressure. Thus, when the ullage pressure increases from 0.2 to 0.6 MPa and the pipe downstream the valve is air-filled, the second bending fluid reaction force increases from 0.2 to 1.1 kN. Therefore, the technological cycle should be completed so that the vessel residual pressure is minimal. The fluid reaction force decreases with the pipeline outlet section diameter, but at the same time the pipe bending stresses increase in third order. In addition, decreasing pipe diameter reduces flow rate, which can affect the process cycle. The use of local resistance in the form of an orifice mounted upstream of the valve can significantly reduce the fluid reaction forces. For example, using an orifice with 80 mm diameter before the valve can reduce the second bend fluid flow reaction force from 2.0 to 0.5 kN when pipeline outlet section is air-filled. It is reasonable to install two orifices: one upstream of the valve and the second - at the outlet. However, as in the case of reducing the pipe diameters, it decreases the pipeline flow rate. Therefore the orifice diameter should be taken with respect to the process flow rate requirements. The program calculates pipe flow rate characteristics with orifices providing sufficient flow rate and acceptable reaction forces.
Simulation and Experimental Results of Unsteady Flow in Pipe System of Processing Plant
2014
10 Seiten, Bilder, 6 Quellen
Conference paper
English
Heat transfer analysis for unsteady high velocity pipe flow
Tema Archive | 1977
|Unsteady flow simulation and its visualization
AIAA | 1999
|Simulation Of Unsteady, Viscous, Incompressible Flow
NTRS | 1990
|Unsteady Flow Simulation of Supersonic Impinging Jet
AIAA | 2003
|