Method of inverting, mixing, and activating polymers

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BACKGROUND

This invention relates to means for and methods of mixing and activating or inverting polymers, at a high speed, and in either batch or continuous loads, while being able to control, select and maintain polymer concentration and activation.

The term "activation" is widely used to describe the chemical transition of polymer to a usable form. Recently, the terminology has tended to focus on how much activation has occurred with some arguing that there must be 100% activation before the word can be used. Since nothing is ever perfect, it is seen that if this argument is carried to the extreme, very little polymer would ever be 100% activated. As used herein, no such fine level of distinction is made. The word "activated", in its many forms, is intended to encompass the start of the process and everything occurring thereafter. Perhaps the word "inversion" might be more appropriate since it applies regardless of the degree of completion of the activating process.

Liquid or emulsion polymers are ionic-charged organic molecules which are soluble in water or another electrolytic fluid, which are herinafter simply called "water". Unactivated or neat polymers are encased by an oil carrier. In this phase, the molecule is coiled upon itself in a microgel form suspended in the oil carrier. Due to its charge, it tries to uncoil, but the oil carrier overcomes the charge and keeps it coiled.

Liquid polymers are used by various industries to simplify their industrial processes and make them more economical. For example, liquid polymers may be used for water purification and flocculation; may be used in automotive paint spray booths; may be used in the chemical industry to separate inorganics and solids from plant effluent; may be used in the coal industry to promote solids settling and to float coal fines; may be used in the petro-chemical industry to enhance oil recovery; may be used in the phosphate industry to improve recovery; may be used in the pulp and paper industry as dewatering aids and retention aids; or may be used in the steel industry to settle wastes. Those familiar with this art will readily perceive many other uses in many other industries.

Usually polymers are manufactured and shipped in a deactivated form to a location where they will be used. At that location, it is necessary to activate or invert the polymers before they can be used. Usually, that means that a polymer must be mixed with water or other electrolyte (solvent), or with a chemical, to provide an electrolyte which can change the polymer from an inactive state into an active state which can be so mixed. The process for so converting the polymer into an active state is one of imparting a sufficient amount of energy to the polymer. Reference may be made to U.S. Pat. Nos. 4,057,223, 4,218,147 and 4,217,145 for examples of prior art polymer activating systems.

The polymer encased in the oil phase is inactive. Therefore, its hydrocarbon surroundings must be emulsified or broken to allow the ionic molecule to uncoil or hydrate. This process of hydration is called activation or inversion. The way in which emulsion polymers are activated are to dilute them with water and to add enough mixing energy to emulsify the oil carrier and thus to enable the ionic charged molecule to uncoil. More particularly, the energy imparted to the inactive polymer includes a mechanical agitation which breaks down the hydrocarbon carrier phase, and thus enables water to reach and react with the long coiled molecule. Once that molecule is in water, like charges on the molecule repel each ocher and the molecule straightens and changes from the coil into a long and more or less straight "conformation". Until this conformational rearrangement occurs, the molecule is useless for most purposes.

The exact amount of energy required for an emulsion polymer activation is not known. However, there is an increase in the viscosity of the polymer, which is proportional to its stage of activation. This increase in viscosity is due to the uncoiled molecules intertwining with each other. The uncoiling of the molecules provide active sites for the attachment of foreign material in a medium. Then, the increased weight on these molecules settles them, carrying with them the settled material.

In the utilization of emulsion polymers, care must be taken to properly prepare the polymer. Different polymers require different amounts of energy for activation, tougher polymers require more force, while others need less force. Further, care must be taken not to overshear the molecules. Overshearing tends to break the uncoiled molecules, thus lowering their viscosity and making them less effective. Undershearing also is deleterious in that the polymer is then inefficient and uneconomical.

The known activating systems have required relatively long periods of time (such as an hour or so) in order to, for example, complete the inversion of the polymer. This long period of time increases the requirements for holding tanks during activation. Therefore, the relatively long period of activation time is relatively expensive. Also, the requirement for such a long term for activation greatly increases the capital requirements for the purchase of machinery when a system is operating continuously, as opposed to a batch system. Thus a faster polymer activating system is highly desired.

Primarily, the prior art used the batch method to invert liquid polymers. Polymer and water are delivered to a common mixing tank. Once in the tank, the solution is beat or mixed for a specific length of time in order to impart energy thereto. After mixing, the resulting solution must age to allow enough time for the molecules to unwind.

There are many different kinds of polymers which leads to a plethora of application requirements. It might be easy to build an entirely new custom designed system or machine for each and every different polymer activation job; however, the cost would then become prohibitive. This highlights the need for a great flexibility for a polymer activation system or machine, which in turn leads to the need for alternative mechanisms which may be added to or removed from the activating hydraulic circuits according to the then current needs.

One way to satisfy both the greater flexibility and a reduced system cost is to adjust the system to process a greater concentration of polymer. For example, instead of producing an output fluid which is 1% polymer, the system may be adjusted to produce a more concentrated fluid which is 2% polymer. Then, the concentrated 2% outflow may be diluted downstream to become 1% polymer, which would double the volume produced by a relatively small machine, to become the volume of a machine of twice the size, if it was originally designed to process a polymer as a 1% fluid. The activation process continues long after the discharge of the inverted polymer from the system outlet.

Merely adding more water in the primary dilution of a polymer might very likely wash away necessary inverting agents, called "activators" or surfactants which are useful in emulsifying the hydrocarbon carrier. For example, a particular use of a particular polymer might require a tenth percent (0.1) polymer solution, but the polymer would lose necessary chemical components if an effort is made to dilute the polymer this much in a single pass through the system. Once a polymer is inverted, there is little, if any, need for retaining these chemical activators. Therefore, the invention presents the opportunity to invert a polymer solution to, say, one percent. (1.0) Once the polymer is inverted, the solution may be diluted downstream to reduce the one percent solution to become a tenth percent solution. Hence, in this example, with the invention, it is possible to produce a tenth percent solution that could not have been produced heretofore.

Two examples of dilution systems which have been designed with these thoughts in mind are found in Rosenberger's and Brazelton's U.S. Pat. Nos. 4,128,147 and 4,642,222. Each of these patents shows a method of adding dilution water to an inverted polymer as it exits a system, thereby theoretically enabling the system to deliver higher concentrations of polymer which are then diluted to give a greater volume of total output. However, it is thought that each of these patents contain basic design flaws since each subjects activated polymers to abrupt pressure changes or additional mixing once the polymer has reached its extended state. That is the output lines of these patents include pressure regulators and/or mixing devices which will create a higher upstream pressure as compared to a lower downstream pressure. Once a polymer is activated, such a pressure change or additional mixing may cause shear and break the now linear polymer molecule, thereby damaging or destroying the polymer.

According to FIG. 1 of the Rosenberger patent the polymer solution is subject to a pressure drop as it passes through the second fixed flow rate regulator. Brazelton teaches the reduction or increase in the input of polymer flow to his mixing system instead of varying the water flow.

SUMMARY

Accordingly, an object of the invention is to provide new and improved means for and methods of activating polymers.

Another object of the invention is to provide flexible polymer activating systems or machines, which may be adapted to fit the needs of particular polymers which are being processed. In particular, an object is to provide means for activating concentrated polymer solutions and for thereafter introducing downstream a secondary dilution to bring the concentrate into a useful range before the molecules become fully hydrated.

Yet another object of the invention is to provide an efficient system and method for activating liquid polymers. Here an object is to provide an automatic, continuous system which is able to vary the output rate of inverted polymer, while automatically maintaining the amount of energy imparted thereto and while maintaining a desired concentration of the polymer.

In particular, an object is to monitor the level of active solids in an outflow from the system and to provide system control functions in response to the level detected during the monitoring in order to maintain greater stability.

In keeping with an aspect of the invention, the activation of a polymer occurs in four stages, which are: pre-mixing, blending, recycling, and a final sudden pressure reduction. The pre-mixing occurs in a manifold containing a static mixer. The blending occurs within a centrifugal pump where water is blended with the polymer. The outflowing stream from the centrifugal pump divides with part of the outflow feeding back through the static mixer and centrifugal pump. The other divided part of the outflow is delivered to a mixing pressure regulator where the pressure imparted by the centrifugal pump is suddenly reduced to, or near, atmospheric pressure. This suddenly relaxes the coiled, long polymer molecule to hasten its straightening. This system provides three different kinds of shear which are imparted during the inversion of the polymer fluid. First, there is a boundary layer shear occurring in the centrifugal pump. Second, there is a visco-elastic shear at an orifice where the polymer fluid flows faster at the center of the orifice than at the periphery of the orifice. Third, there is a structuring shear when the pressure suddenly reduces as the polymer solution passes through the mixing pressure regulator. In one exemplary inventive system, the entire inversion requires only about one second.

The invention enables an adjustment which controls the amount of energy introduced into the polymer for inversion. Once the relationship between the amount of introduced energy and the output rate is established, the inventive system automatically compensates for variations therein.

The system also provides controls for varying the concentration of the polymer. A secondary fluid delivery system may dilute the concentrated polymer after it is inverted.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the invention are shown in the attached drawings, wherein:

FIG. 1 schematically shows the principles of an inventive system having two inputs, which are for water and for the polymer that is to activated;

FIG. 2 is a perspective view of a pre-mixing manifold;

FIGS. 3A and B are two plan views (rotated by 90.degree. from each other) a static mixer which is used inside the manifold of FIG. 2;

FIG. 4 is an end view of the static mixer, taken along line 4--4 in FIG. 3A; and

FIG. 5 is a schematic showing of a more sophisticated version of the system of FIG. 1 with provisions for introducing one or more chemicals which may be used in the electrolyte for activating the polymer;

FIG. 6 is a front plan view of a system incorporating the invention;

FIG. 7 is a plan view of the inventive system taken along lines 7--7 of FIG. 6;

FIG. 8 is a schematic disclosure of a prior at system for introducing secondary delivery;

FIG. 9 is a schematic diagram of an inventive system for introducing a diluent via primary and secondary legs;

FIG. 9A is a cross-section of a pilot valve used in FIG. 9;

FIG. 9B is part of FIG. 9 with an automatic control for maintaining a ratio of flows in primary and secondary legs of an electrolyte delivery system;

FIG. 10 is a front elevation of the inventive machine having secondary dilution capabilities;

FIG. 10A shows an alternative wet polymer sensor for use in FIG. 10; and

FIG. 11 is a top plan view of the machine of FIG. 10.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, the polymer inverting and activating system 18 components are an input throttling valve 20 for controlling the ratio of water to polymer, a centrifugal pump 22 for introducing the water, a closed mixing loop 24, a pre-mixing manifold 26, and a centrifugal pump 28 for introducing the polymer. The water and polymer first meet in the pre-mixing manifold 26, the water flow being indicated in FIG. 1 by solid lines and the polymer flow being indicated by dashed lines. Valve 20 may be set to provide a ratio of water to about 1% polymer, in one example, with a useful ranger of ratios being in the order of 0.25 to 15% polymer. Associated with valve 20 may be a meter (not shown) which is calibrated in gallons per minute. By an adjustment of the valve 20, one can also select the desired output of the system, or a more highly concentration of inverted polymer solution.

The mixing pressure regulator 30 is critical in three areas. It is used to maintain a constant net positive discharge head on the booster module or centrifugal pump 22, which is an important consideration in the hydraulics of the system. It controls the amount of recycling which occurs in the recycle stage. It provides a variable pressure drop zone in the final stage and enables the operator to select a proper amount of mixing energy, based on the type and concentration of polymer being processed. The higher solids polymers and higher solution concentrations require more mixing energy than usual.

In greater detail, the mixing manifold 26 (FIG. 2) is, for example, a solid block of metal having a central bore 32 extending through substantially its entire length. The bore 32 stops short of a counterbored and threaded input opening 34, to form a bulkhead 36. An orifice 38 of fixed diameter is formed in the center of the bulkhead 36 to establish communication between the water inlet hole 34 and the central bore 32, with a flow rate that is controlled by the orifice diameter. The polymer solution experiences an extrusion type of shear as it passes through the orifice 38.

TABLE I ______________________________________ AN EXEMPLARY FLOW RATE AND RECYCLE VOLUME IN ONE EXEMPLARY SYSTEM DIAMETER SOLUTION RECYCLE TYPE OF OF OUTPUT VOLUME PUMP ORIFICE 38 (GPM) GPM ______________________________________ 054 AnCAT 3/32" to 3/16" .25 to 10 gpm 1.85 @ 40 psi to 8.12 @ 60 psi L-10 AnCAT 1/8" to 1/4" 3 to 10 gpm 2.56 @ 30 psi to 14.5 @ 60 psi L-20 AnCAT 1/8" to 1/4" 3 to 20 gpm 2.56 @ 30 psi to 14.5 @ 60 psi L-30 AnCAT 1/8"to 3/8" 3 to 30 gpm 2.56 @ 30 psi to 32.5 @ 60 psi L-60 AnCAT 3/16" to 1/3" 5 to 60 gpm 5.75 @ 30 psi to 57.8 @ 60 psi L-80 AnCAT 3/16" to 5/8" 5 to 80 gpm 5.75 @ 30 psi to 90.4 @ 60 psi L-100 AnCAT 3/16" to 3/4" 5 to 100 gpm 5.75 @ 30 psi to 130.0 @ 60 psi ______________________________________

The last or recycle column indicates that the recycled or returned output from the derated pump 15 is in the order of about 5% to 70by volume. These figures are derived from a Cameron Table, which a conventional tool for hydraulic engineering. The converse statement would be that the outflow is 95% -30% by volume.

A first threaded hole 40 leads to another bulk head 42 between the entrance to the counter bored and threaded hole 40 and the central bore 32. An orifice 44 is formed in the bulkhead 42 to establish communication and to control the flow rate between the hole 40 and the central bore 32.

The output port 46 is in direct communication with the central bore 32 to give an unimpeded outflow of a mixture of polymer and water.

A static mixer 50 (FIGS. 3,4) comprises two sets of semi-elliptical baffles which are set at an angle with respect to each other so that the over all end view configuration is a circle (FIG. 4). The baffles 52 (FIG. 3A) on one side of the static mixer are a series of spaced parallel plates. The baffles 54 on the other side of the static mixer are Joined on alternate ends to give an over all zig-zag appearance. The outside diameter of the static mixer corresponds to the inside diameter of the central bore 32. Therefore, the static mixer 50 slides through an end opening 56 and into the bore 32. Thereafter a plug 58 seals off the end of the bore. In one embodiment, the static mixer 50 is a standard commercial product from TAH Industries of Inlaystown, N.J.

Water is introduced through the centrifugal pump 22 and into the mixing loop 24 (FIG. 1). The flow of water is controlled and metered by the throttling flow valve and meter at 20. The beginning stages of activation or the pre-blend stage occurs inside the centrifugal pump assembly 22.

The centrifugal pump 22 is a modified commercial item which is derated on the high end of its output flow by a factor in the order of 2 to 7, for example, for most applications. On the low end of its output flow, the derating factor may be much higher. That is the diameter (for example) of the impeller is trimmed to give a derated performance wherein there is a larger amount of stirring and mixing per volume flow, as compared to what might normally be expected from standard commercial centrifugal pump. Other techniques for derating an impeller including changing a pitch of the blades, thinning the width of blades, and the like.

Derating is also controlled by an adjustment of the water inlet flow. In greater detail, by way of example, a centrifugal pump usually has a series of flow charts which are supplied by the manufacturer. One flow chart, which may be the one normally used, may describe how the pump could provide a flow of 20 gallons per minute to the top of a 40 foot head, for example. Another flow chart may describe how the same pump could be operated at a different speed to provide five times that capacity, or at 100 gallons per minute to the same 40 foot head, in this particular example.

According to the invention, the pump is operated, for example, in the manner described by the manufacturer to deliver 100 gallons per minute, but the diameter of the impeller is reduced until the delivery returns to 20 gallons per minute, while the pump continues to be operated in the manner which the manufacturer suggests for 100 gallons per minute. Thus, in this particular example, the centrifugal pump has been derated by a factor of 5 (i.e. derated from 100 to 20 gallons per minute). After derating, the increased impeller speed, which is normally required to deliver 100 gallons per minute imparts a higher level of energy to the mixed fluid, without increasing the volume of fluid output.

The following chart illustrates a number of different centrifugal pumps which may be used for polymer injection at pump 28.

______________________________________ TYPE PUMP FLOW RATE ______________________________________ 054 AnCAT 0-864 gpd L-10 AnCAT 0-2160 gpd L-20 AnCAT 0-4320 gpd L-30 AnCAT 0-6480 gpd L-60 AnCAT 0-12,960 gpd L-80 AnCAT 0-17,280 gpd L-100 AnCAT 0-21,600 gpd ______________________________________

In pump type L-60, the impeller diameter was 5 inches; in pump type L-S0, it was 6 inches, and in pump type L-100, it was 6.25 inches.

The unactivated or neat polymer is introduced through the premix manifold 26 and into the mixing loop 24 by a variable speed, positive displacement pump 28 which delivers the polymer at a rate which achieves, a range of desired concentrations. Because the centrifugal pump 22 is derated, it causes a desirable mixing shear of the polymer. A calibration column (not shown) is provided to correlate the variable speed pump 28 to its capability to deliver the unactivated polymer at a rate which accurately obtains the desired concentration. The pump 28 is not modified and merely delivers the polymer to the mixing manifold 26.

The mixed water and polymer solution is recycled, via loop 24, back through the premix manifold 26 and the booster module (derated centrifugal pump 22) which continues to boost the level of the activation or inversion of the polymer.

The final stage of polymer inversion is controlled by the mixing pressure regulator 30. The polymer solution passing through the regulator 30 experiences a sudden and abrupt pressure drop which further inverts the solution. The pressure drop causes a third kind of shear of the polymer. This pressure drop is adjustable and represents an important factor in the development of the inversion of polymer molecules. The pressure regulator 30 is a standard commercial item.

More specifically, the mixing pressure regulator 30 is provided in the mixing loop to enable a discharge of the inverted polymer at a desired level of activation while, maintaining a net positive suction head in the centrifugal pump to prevent cavitation. Once the desired output rate and level of inversion is selected, the mixing pressure regulator 30 automatically compensates for any surging or ebbing flow which is attendant upon changes in the output flow rate. Thus pressure regulator 30 maintains the desired level of inversion in the centrifugal pump 22.

It should now be apparent that the mixing pressure regulator is critical in three areas. It is used to maintain a constant net positive discharge head on the booster module, which is an important consideration in the hydraulics of the system. It controls the amount of recycling which occurs in the recycle stage. It provides a variable pressure drop zone in the final stage and enables the operator to select a proper amount of mixing energy, based on the type and concentration of polymer being processed. The higher solids polymers and higher solution concentrations require more mixing energy than usual.

Regulator 30 is set to cause a sudden and abrupt relaxation of pressure, from the pressure in line 60 to or near atmospheric pressure. This sudden and abrupt relaxation causes an effect which is somewhat similar to th