Process and apparatus for separating valuable or harmful liquids from slurries

Abstract

This invention relates generally to a filtration process and apparatus for separating valuable or harmful process liquids from mixtures or slurries that contain such liquids and solid particles. In particular, the invention relates to a filtration process for separating Process Liquid from a feed slurry that comprises a mixture of the Process Liquid and solid particles, the process employing a Sweep Liquid that is less dense than the Process Liquid.

Description

FIELD OF THE INVENTION[0001]This invention relates generally to a filtration process and apparatus for separating valuable or harmful process liquids from mixtures or slurries that contain such liquids and solid particles.BACKGROUND[0002]Many industrial and commercial processes utilise a valuable and / or potentially harmful process liquid that becomes mixed with finely divided waste solid matter. For commercial and environmental reasons it is desirable to recover this liquid before disposing of the waste matter. Many types of devices including gravity separators, cyclone separators, filters, clarifiers, centrifuges, and combinations thereof, are used for this purpose.[0003]The simpler gravity separators typically yield a waste sludge or sediment that contains a significant amount of the original process liquid. This can lead to high loss of the process liquid in the waste sediment unless further steps are added to the process to recover process liquid from the sediment. Furthermore g...

AI Technical Summary

Benefits of technology

This patent describes a device that removes solid particles from a liquid feed by using a filter medium, an agitation means, and a housing. The device also prevents overmixing of different liquids by using mechanical components. In another embodiment, the filter medium is designed to rotate at high speeds to keep the slurry moving and prevent the buildup of solid particles on its surface. The technical effects of this device include improved quality of liquid feed by removing solid particles and prevention of clogging and fouling.

Problems solved by technology

Many industrial and commercial processes utilise a valuable and / or potentially harmful process liquid that becomes mixed with finely divided waste solid matter.

This can lead to high loss of the process liquid in the waste sediment unless further steps are added to the process to recover process liquid from the sediment.

Furthermore gravity is not always an effective driving force for separation if the particles are very fine and remain suspended without settling in a timely manner.

A major drawback of filtration systems in which a filter cake is formed is the reduction in flow as the filter cake builds in thickness.

The pressure must then be increased (or the filtration area increased) to maintain a high flow rate, however increasing the pressure in a filter increases costs and potential hazards, and may not be desirable or feasible.

In the absence of further refinements the liquid in the resultant thickened slurry that is produced in these cross flow filtration systems is still the original process liquid, hence disposal of this slurry without further treatment can result in significant loss of process liquid.

The commonly known drawbacks to displacement washing include uneven distribution and flow of wash water through the filter cake.

However dilution washing is also not ideal because of the higher consumption of wash water and greater dilution of the process liquid that is recovered in the filtrate.

Furthermore when a back wash is used to unclog filter media or when washing liquid is used to sluice out the solid matter or to clean critical surfaces before moving to the next step in the separation process then some of the valuable or harmful process liquid may be swept into highly diluted waste streams from which it is often overly expensive to recover the residual valuable or harmful liquid.

Overall, although a large fraction of the original liquid is recovered by modern filtration systems, the waste matter still typically contains a significant quantity of the original liquid.

If the original liquid is valuable or potentially harmful then costs increase and there may be greater health, safety and environmental (HSE) risks.

Hence there is more solid waste to dispose of and greater loss, or at least a risk of greater loss, of valuable or harmful process liquid that is trapped in this waste.

The associated costs and environmental risks arising from this increase in solid waste volume can be significant.

Added costs are also incurred to purchase and store the filter aid and to operate and maintain the added equipment.

This approach adds complexity, adds cost to comply with air emission regulations, potentially increases safety and environmental hazards, and results in total loss of the residual process liquid.

Another commonly encountered problem with filtration processes that produce a filter cake is that there can be a limit to the pressure differential that can be applied across the filter to maintain high filtrate flow rates.

In these circumstances the increase in pressure, which typically requires greater expenditure to supply and operate the means of applying the higher pressure, may achieve limited or no benefit.

The term “overmixing” as used herein in connection with Process Liquid mixing with Sweep Liquid means an excessive degree of mixing of Process Liquid with Sweep Liquid that results in an excessive loss of Process Liquid into the Sweep Liquid.

If the Process Liquid is at least partially miscible with the Sweep Liquid this excessive loss can occur if there is excessive turbulence in the Interface Zone resulting in an excessive amount of Process Liquid dissolving into the Sweep Liquid layer.

If the Process Liquid is substantially non-miscible with the Sweep Liquid excessive loss is still possible if the two liquids are prone to form stable emulsions and there is high enough turbulence near the interface between the Process Liquid and Sweep Liquid to cause long lasting emulsions of Process Liquid and Sweep Liquid.

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