Sealing Performance Research Of Primary Sealing Structure Of Metal Ball Valve In Coal Chemical Industry

Clean coal utilization is the key means to adjust energy imbalance in our country. It wasexpected to alleviate China’s growing energy crisis. Coal gasification has an importantfunction on high efficient and clean utilization of coal resource. Lock hopper valve is one of thekey equipment for coal gasification system, feathered with high pressure, high temperature andhigh solid content, used for collection mixed slag water from the bottom of the gasifier quenchchamber. So it requires high sealing performance with the strong penetration ability toxic gas.Furthermore, the sealing surface suffers friction and wear severely in the condition of frequentadjustment and high torque. The relationship between sealing performance, preloaded pressure,and torque of the metal seated ball valve is the major factor to valve design and operate.Currently, harding the sealing surface, chosing the reasonable the difference hardness, improvingthe machining accuracy are the main technical means to improve the sealing performance andprolong life of ball valve. In fact, it is lack of analysis of the seal mechanism and structure. Thispaper analyzes the sealing structure, calculates the sealing pressure, establishes the leakagemodel of valve seat, and obtains the relation between sealing pressure and leakage rate, realizesthe preloaded pressure accurately selected, and guides the valve design.This thesis focused on the lock hopper valve (including the structure, pressure drop andmaterial properties) in coal gasification system as the research object. Firstly, the sealingpressure formula in the ideal smooth, actual rough surfaces of the seat was acquired based on thesingle asperity contact model and the mechanical characteristic of seat. Then, the finite elementmodel of primary structure was developed by finite element analysis method. Combined with theaverage flow model, leakage model of the seat, equivalent contact equation of rough surface, therelationship between the leakage and sealing pressure was acquired on the different surfacemachining accuracy and texture feature. In this paper, the main research contents andconclusions were as follows:1）The sealing performance evaluation model was used to determine the design parameter ofseat(including the sealing width and pressure angle). The distribution regulation of the sealingpressure on the sealing surface was obtained in different parameters. Then the finite elementaverage pressure of the sealing surface with the required pressure and the allowable pressure were compared to judge the reliability of the seat sealing performance in different designparameters.2）With the average flow model, leakage model of the seat, equivalent contact equation ofrough surface, the leakage of the seat was computed in different surface machining accuracy andtexture feature. The results showed that the pressure flow factor had a great influence on thevalve seat leakage. When in the condition of the surface texture parameters was less than one, thepressure flow factors was less than one, the valve was easy to seal, but not vice versa.3）The finite element analysis results under different design parameters of sealing pressurewere compared with the equivalent equation calculation of contact stress and the relationshipbetween the actual pressure and valve seat leakage level can guide to valve design andmanufacture optimize the torque and improve the service life of the valve.The innovation in this paper is that:1）The average pressure within the effective seal widthas evaluation index of the sealing performance was putted forward;2）The finite element contactmodel of ball valve seat was developed, and the distribution regulation of the sealing pressure indifferent design parameter was also obtained;3）the leakage model of ball valve seat consideringthe influence of surface properties was established, and leakage in the real sealing pressure waspredicted.