Screening Mechanism Study And Optimization Design On Elliptical Motion Shale Shakers

For a long time the research on shale shakers is mainly focused on the dynamics and the study for the dynamic screening mechanism is not enough, especially for elliptical motion shale shakers. In this paper the screening mechanism and optimization design method about elliptical motion shale shakers are researched.By studying the screening mechanism it was found that liquid can flow through screen smoothly only if the vertical acceleration of a horizontal screen is much larger than -9.8 m/s2 and when the screen is moving up. The penetrating velocity becomes larger with vertical acceleration increasing. There is liquid penetrating stage, particles thrown stage and transition stage in a vibrating cycle. And the upper part of acceleration ellipse corresponding to screen moving up stage is the main penetrating stage for liquid. Compared with forward vibrating cycles the backward elliptical vibrating forces with the same amplitude may produce larger penetrating velocity. Using backward cycle particles will be transported forward more slowly, but the distance thrown backward is longer than that of forward cycle. Particles being thrown backward can result in particle agglomeration. And more small particles are prevented from penetrating screen and many particles in screen opening can be hauled out. With screen self-cleaning and long residence time on screen for particles larger flow capacity and more dry cuttings can be expected. The multi-phase flow model of shale shakers was established and the affect of the vibrating souce was involved. According to assumption of the single-phase, the flow through vibrating screen was simulated for the first time. And pressure drop coefficients through the real screen were obtained under both static and dynamic conditions. It is found that the pressure-drop coefficient changes significantly according to the motion direction of the screen. When the fluid moves in the same direction with the screen the pressure-drop coefficient becomes large, as a result, it is difficult for the fluid to flow through the screen. And when the fluid moves in the opposite direction of the screen the pressure-drop coefficient becomes small, so it is easy for the fluid to flow through the screen. Based on the pressure-drop coefficient of penetrating stage for liquid, the calculation method for full flow of the shaker was put forward. And the air-liquid profile and the liquid end line were got. Using the kinetic energy law the inequation method was put forward according to the wet particles on the screen. And two agglomeration models were developed based on the inequation method including agglomeration model by work of forces and the agglomeration model by rolling and holding. And the maximum diameter of particles to agglomerate was obtained based on both models, which explained the dimension profile of particle clusters on the screen. It is pointed out that the agglomeration facilitation technology is the key to break through the bottleneck of drilling fluid screening. The shale shaker with side installation of motors was analyzed dynamically. The relationship of fatigue strength versus key shaker parameters and the effect of the spring stiffness to the stabilization of the shaker were studied. The method to evaluate the degree of stabilization was developed. And a method to design the composite spring according to the nonlinear performance of the spring came up, which is different from the traditional concept according to the linear spring performance.A new type of shale shaker with side installation of motors was developed using the backward exciting mode, the concept of high frequency and small amplitude. Field application shows that the capacity of shakers excited by backward elliptical forces is larger than that of linear ones by 30% and the dryness of drilling cuttings is 20% higher than that of linear shakers. And shakers with backward cycle excelled ones with forward cycle of the same amplitude in performance greatly, which confirms theoretical conclusions. The research result of this paper filled the theory and technology blank in drilling fluid screening.