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The Research on the Cavitation-erosion Failure Prediction of the High-temperature Hydraulic Control Valve in Coal Liquefaction System

Author: ZhengZhiJian
Tutor: OuGuoFu
School: Zhejiang University of Technology
Course: Fluid Machinery and Engineering
Keywords: Coal liquefaction hydraulic control valve cavitation erosion mechanism numerical simulation cavitation erosion prediction
CLC: TH137.52
Type: Master's thesis
Year: 2011
Downloads: 41
Quote: 1
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Abstract


The high-temperature hydraulic valve in the coal liquefaction equipment has the characteristics such as large pressure drop, high velocity, frequent operation and various operating conditions, so its current life is less than one month for its serious cavitation erosion damage. The current research which mainly focused on material upgrading and surface hardening is useless to improve its anti-cavitation performance. In this paper, the mathematical model and numerical analysis is carried out according to the actual operating conditions, fluid properties and structural parameters. Then the quantitative prediction for cavitation erosion is finished that provide a basis for the structural and operational optimization of the hydraulic valve.In this paper, a mathematical model for calculating a single bubble deformation and collapse near the wall is constructed based on the mechanical mechanism of cavitation erosion. The bubble surface movement during its deformation process and the high speed micro-jet and shock pressure formed in its collapse is calculated. Then, the numerical simulation of bubble collapse in other environmental features, such as the bubble on the wall, in the infinite field, near another bubble, is completed. Meanwhile, the influence of the distance between the cavity and the wall, bubble inside and outside pressure difference, surface tension, liquid viscosity and outside flow on the bubble collapse is analyzed. On the basis of cavitation-erosion mechanism research, the computational model for calculating the cavitating flow in the high-temperature hydraulic control valve is constructed. The fluid physical parameters are calculated via Aspen software. The distribution of key hydrodynamics parameters in the two typical valves with different structures, such as velocity, pressure and vapor phase fraction, is obtained. Then the quantitative calculation of the cavitation-erosion failure regions in the valve is completed. Combining with typical valve failure cases, the reliability of numerical simulation is verified. Meanwhile, the influence of the import and export pressure, operating temperature, valve opening, solid particles and valve angle on the cavitation region and intensity are analyzed. The method can also be extended to the cavitation failure prediction, structural optimization, service detection, life prediction and risk assessment of other control valves, pumps and pressure pipelines in the coal liquefaction plant, providing the technical support for its safety, stable and long-term operation.The innovative research in this paper is: (1) the features of bubble collapse in different environments is analyzed by numerical simulation. The bubble morphology in the collapse process is captured and the quantitative calculation of the cavitation mechanical mechanism is completed. Meanwhile, the factors affecting the bubble collapse is also precisely analyzed; (2) the inside and outside pressure of the bubble and the impact of the liquid flow is analyzed simultaneously, and the characteristics of double bubble collapse is studied preliminarily; (3) the cavitation erosion failure prediction of the hydraulic valve is finished by using the actual operating parameters and fluid properties, which makes the calculated results much closer to the engineering. Besides, the influence of the presence of solid particles on the cavitating flow is analyzed by considering the interaction between the discrete phase and continuous phase.

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CLC: > Industrial Technology > Machinery and Instrument Industry > Mechanical parts and gear > Hydraulic transmission > Hydraulic components > Hydraulic control valves
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