Hydrovac excavation is a non-destructive, precise, non-mechanical process that uses pressurised water and an industrial strength vacuum to simultaneously excavate and evacuate soil. GN Solids designs and manufactures hydrovac slurry processing systems, known as a Slurry Dewatering System.

The slurry processing solution is to use liquid and solids separation equipment to treat soil, soup or slurry generated from hydrovac, excavation or horizontal directional drilling (HDD) projects, and produces reusable material for construction and discharge clean water. 

Normally, the slurry is contaminant-free and comes from physical utility location in public right of ways, and directional drilling for placement of underground pipes, utilities, or other private property construction. The slurry is of different particle sizes, and is processed by a classifying vibrating screen, dewatering fine shaker, and a dewatering decanter centrifuge.

For various applications on solid liquid separation, the concept is the same. Separate the mixed fluid to different class, with the easiest practical way is by particle size. The most commonly used method for separating particles based on particle size is screening.

Probability of separation is the process of particles reporting to the screen apertures or openings, and passing through if the particle size is less than the aperture.

Screen selection is based on the overall screen area required to achieve efficient screening at a given mass throughput capacity. Length of screen is important for ensuring the number of trials needed to achieve the desired mass throughput capacity and to provide sufficient screen underflow capacity.

Width is important for ensuring proper bed depth so as to provide sufficient stratification.

The length of the screen should be at least two times the width for good practical design.

In GN Solids’ hydrovac slurry dewatering system, the very first step is through a steel plate wire mesh, which is holding unexpected big stones. 

It will then drop to a classification vibrating screen. With different purposes, the screen wiring dimension can be very different, and the experience from the customer themselves matters as well. With intention to make a good benchmark, GN Solids’ classification vibrating screen comes with a huck revit wallboard. Through finite element analysis, the structure has been well optimised. 

The plane design of the whole screen surface is more conducive to screening and grading materials and maximises the effective screening area of the screen surface.

With design of a positive inclination angle, and the installation angle being 4 degrees adjustable, it is suitable for the requirements of different process materials.

Following the first step screening, the mixture will then be transferred to the next step – GN Solids linear motion shale shaker. It is a product more popular in oil gas application, or HDD mud recyclers, yet it fits this step very well.

GN recommends the double deck shaker, as it eventually separates the particles step-by-step, and will save money on less consumable parts.

The last step is hydrocyclones. This where a dewatering screen will be put underneath to dewater the discharge from cones, and to improve the cyclone efficiency.

The hyodrovac slurry treatment system has four types of screens. The first is big mesh bars to hold large stones. The second includes coarse classifying screen. Third screen is having double deck shaker screen, and the fourth is a cyclone discharge dewatering screen.

For more information visit GN Solids. 

This article featured in the June edition of Trenchless Australasia. 

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