Process and apparatus for making a solution or dispersion of a hydrosoluble powder

The invention concerns a process and an apparatus for making a stable solution or dispersion of a hydrosoluble powder. It is characterized by the simultaneous use of a system for withdrawing powder from a vessel (2) e.g. by means of a gas (4), the dilution of the powder in a carrying gas, the driving with said carrying gas, of the obtained dilution, through a transfer duct (10), the passage of the dilution across an electrostatic field (11) and the solubilization in water of a tank (12). The invention is particularly applicable to the dispersion of polyacrylamides used in the technique of enhanced oil recovery.

This invention concerns a process and an apparatus for making a stable 
solution or dispersion of a powder, for example of hydrosoluble polymers. 
Such stable solutions or dispersions are of high interest for improving the 
enhanced oil recovery, but they may also be used in other applications, 
particularly in the paper industry, water treatments and drilling 
(drilling muds), i.e. all the applications where hydrosoluble polymers are 
used as thickening flocculating agent. 
The hydrosoluble polymers are sold on the trade as powders, but must be 
used, in these applications, as aqueous solutions. Thus, as far as 
enhanced oil recovery is concerned, in view of the worldwide energy 
crisis, it is now essential to recover a maximum amount of oil contained 
in the fields. 
BACKGROUND OF THE INVENTION 
One of the most usual enhanced oil recovery methods consists of scavenging 
the oil field by injection of injection of salty water, thus forcing the 
oil to sweat and flow out from the rock where it is adsorbed. 
The efficiency of such a method is very often limited by the viscosity 
difference between oil and water, this difference being responsible for 
the tendency of water, instead of spreading itself over the whole area of 
the field, to find preferential paths, directly from the injection well to 
the production well. 
In order to compensate for this viscosity difference, it is usual to 
thicken the injected water by addition of hydrosoluble polymers, very 
often an acrylamide or a polysaccharide polymer or copolymer. 
For this purpose the polymeric material must be dissolved in water. Now, 
this dissolution is often difficult to achieve in view of the low 
solubilization rate and of the difficulty to subsequently disperse the 
solid in water. 
On the other hand, accumulations of dispersed grains are immediately sealed 
in contact with water and form gelatinous conglomerates 
(micelles-microgels). A strong and extensive stirring provides for the 
dissolution of a substantial amount of said aggregates but it is 
practically impossible to stir over a very long period with a sufficient 
power. 
In addition, the storage and handling on the field of these polymers rise 
many practical problems. 
As a matter of fact, the polymer powders have the property to absorb the 
air moistness. This absorption results thereafter in a swelling and in the 
formation of conglomerates and/or microgels. 
The conglomerates tend to stick to the walls and thus to block the 
operation of the mixing equipment, particularly the feed screw. 
The microgels are not substantially dissolved in water and, once injected 
in the fields, they tend to generate clogging phenomena by blocking the 
outlet pore openings of the oil rocks. 
On the other hand, the polymer powder, spreading on the earth and in air, 
rises security problems, making the ground thick and slippery and the 
atmosphere difficultly breathable. 
In order to cope with these various disadvantages, different techniques for 
dispersing solid particles in an aqueous medium have been proposed in the 
prior art. 
Thus it has been proposed in the prior art, for enhanced oil recovery, to 
use polymers aqueous emulsions directly prepared during the synthesis of 
the polymer, as taught, for example, in U.S. Pat. Nos. 3,637,564, 
3,734,873 and 3,763,071. The water addition required in this technique is 
however unfavorable both for the transportation of the product and the 
storage thereof on the field. 
Different techniques for dispersing these particles of hydrosoluble 
polymers in a liquid which would be non-solvent for the polymer have 
already been proposed in the prior art. Thus, it has been taught to admix 
polyacrylamide with glycerine (e.g. in U.S. Pat. No. 3,839,202), with 
polyethylene glycol (e.g. in U.S. Pat. No. 3,402,137 or British Pat. No. 
1,387,367), with ethylene glycol in the presence of an emulsifying agent 
(e.g. in U.S. Pat. No. 3,657,182) or still with an organic liquid not 
miscible with water, to which water is added so as to swell the polymer 
(e.g. in U.S. Pat. No. 3,282,874). 
However the main difficulty encountered during the preparation of the 
polymers suspensions, according to said latter techniques, consists in the 
instability of the suspensions during their storage, due to their settling 
or their thickening as the result of a progressive swelling of the polymer 
in the presence of one of the ingredients; this instability during time 
results in the formation of compositions which are no longer uniform and 
which may become more or less compact. Their use is accordingly more 
difficult and risky. 
Hydrosoluble polymers compositions and more particularly compositions of 
ethylene oxides polymers, which quickly dissolve in water, have been 
disclosed, for example, in the European patent application No. 0 002 368. 
When fluid compositions are obtained by dispersing the hydrosoluble 
polymer in an organic liquid insoluble in water, in the presence of a 
non-ionic emulsifying agent, a settling of the compositions is observed 
during their storage at ordinary temperature. It is for this reason that 
it has also been proposed to add to the compositions a thickening agent 
such as finely dispersed silica, asbestos or even soaps such as aluminum 
stearate. However, said compositions are not suitable for the subsequent 
preparation of polymers aqueous solutions destined to enhanced oil 
recovery techniques. As a matter of fact, it has been observed that the 
thickening agents proposed in the prior art produce secondary reactions, 
either of cross-linking or of degradation, in the presence of hydrosoluble 
polymers of the type used for enhanced oil recovery, and more particularly 
of acrylamide polymers or copolymers. These secondary reactions result in 
the formation of microgels which plug the porous media where they produce 
a viscosity decrease of the aqueous solutions and, accordingly, a loss in 
efficiency for the oil recovery. 
Another technique, disclosed in the French Pat. No. 2,486,950 consists of 
producing relatively stable anhydrous suspensions in an aliphatic or 
aromatic liquid non solvent of the considered hydrosoluble polymers which 
are kept uniform and fluid during the storage and are quickly redissolved 
when dispersed in aqueous phase, finally giving diluted aqueous solutions 
suitable for enhanced oil recovery. However the use of said techninique is 
not sufficiently satisfactory. 
SUMMARY OF THE INVENTION 
The object of this invention is to provide a method or process and the 
corresponding apparatus for making a solution or dispersion of 
hydrosoluble powders (natural or synthetic) in water. 
This process or method may be applicable to any product of fine 
granulometry and high hydrophilic property. In said method or process, the 
conveying fluid is a gas, such for example as air or an inert gas. The 
powder suspension is obtained by using hydrodynamic driving with air or 
nitrogen or carbon dioxide or any other propelling agent inert with 
respect to the conveyed product. 
This well known propulsion, by pneumatic effect, has been the object of 
many patents, with application to the conveyance of various pulverulent 
products such as fecula, flour, grains (wheat), surgery, iron materials 
and in various fields, such for example as cement manufacturing, 
production and transformation of plastic materials, food industry, paper 
making, printing, tobacco industry etc. . . This type of propulsion is 
applicable to materials in bulk, shaped as grains or powders and to 
fibrous products. 
However, for the uses contemplated in this invention, this pneumatic 
conveyance must be performed through special devices adapted to obtain 
very low flow rates of the conveyed solids (from a few kg/h to a few tens 
of kg/h and more precisely from 0.6 to 100 kg/h, preferably from 2 to 50 
kg/h) at very low concentrations in the carrying gas (typically from 0.1 
to 1 kg/m.sup.3 and more particularly from 0.1 to 0.3 kg/m.sup.3). 
As a matter of fact, it is essential, in this invention, to obtain a very 
good dispersion of the solid particles in the conveying gas at regular and 
steady flow rates without shocks or swabbing or segregation phenomena, 
without deposits in the conveying duct and without saltation phenomena. An 
essential condition of the present invention is the achievement of a very 
good previous dispersion of the powdery solids in the conveying gas so as 
to subsequently favor the dispersion and the dilution of said powder in 
the aqueous medium to which it has to be admixed.

In order to further improve the dispersion of the pneumatically conveyed 
particles, the gas flow is caused to pass through an electrostatic device. 
After passage in an electric field of 10 to 40 kV and preferably 30 to 40 
kV, all the individual particles carry electro-static charges of the same 
sign. The presence of said charges makes the particles to repel each other 
and the conglomerates, if any, to dissociate. 
At the output of the electrostatic field, the gas flow is directed, through 
an insulating pipe or tube, to a dilution tank. The liquid (water) used 
for the dilution is stirred by means, for example, of a helix or an anchor 
or any equivalent device, preferably driven from the tank bottom (system 
of the Vortex type) so that the mechanical parts be preferably completely 
immersed; deposits on the one or more shafts of the stirrer are thus 
avoided. 
When the stirring is of the Vortex type, the stirring speed is so adjusted 
as to obtain a Vortex developing a Reynolds number ranging from 1,000 to 
10,000, preferably from 1,000 to 3,000 and, for example, of about 2,000, 
so as to provide for a quick renewing of the liquid surface. 
The value of the Reynolds number is given by the formula: 
##EQU1## 
.rho.=liquid/density (kg/m.sup.3) .rho.=dynamic viscosity in Pascal-second 
(1 Pascal-second=10 poises) 
D=diameter of the stirrer (meters) 
n=rotating speed of the stirrer in number of turns per second. 
The Reynolds number determines the flow conditions corresponding to the 
fluid stirring speed. 
For N.sub.Re &gt;2,000, the flow is considered as eddy; the present invention 
has precisely the advantage of a N.sub.Re value of about 2,000. 
In particular, the method according to the invention is advantageously 
applied to the dispersion of hydrosoluble polymers (natural or synthetic) 
and more particularly to the preparation of polyacrylamides or 
polysaccharides solutions, used mainly for enhanced oil recovery. This 
mode of introduction makes dissolution in water very easy and further 
provides for a very quick dissolution of the polymers in water. 
The total duration of the injection and maturation is generally from 
fifteen to thirty minutes, for example. 
The quality of the solution, i.e. its excellent homogeneity and absence of 
aggregates or of microgels, may be ascertained from viscosity measurements 
versus time (these measurements are performed, for example, by means of a 
viscosimeter of the type with coaxial cylinders). 
The invention contemplates the manufacture of solutions at concentrations 
varying from 100 ppm to 5-10% by weight and more particularly from 100 to 
10,000 ppm when the process is used for enhanced oil recovery. 
EXAMPLES 
The following examples illustrate the invention. 
By the used techniques it is possible, in particular, to obtain very 
viscous solutions, for example of about 1,000 cP (1,000 mPa.s) for a 
solution at 5,000 ppm, which, surprisingly, remain filterable. The 
filterability tests, at constant pressure (0.1 bar) with solutions at 
1,000 ppm, effected with millipore membranes of 8 .mu.m openings and 47 mm 
diameter, do not show any increase of differential pressure about these 
membranes during time. Hence no clogging phenomenon, as usually produced 
by aggregates or microgels, occurs. This filterability property thus makes 
the viscous solutions prepared according to the invention particularly 
adapted for use in enhanced oil recovery where they are injected in the 
porous medium formed by the field reservoir rock. 
The invention thus concerns a process for obtaining a stable solution or 
dispersion of a hydrosoluble powder (pulverulent solid) and more 
particularly a powder of hydrosoluble polymers. 
It is characterized in that: 
(a) the powder to be treated, placed in an enclosure, is discharged 
therefrom at a rate from 0.6 kg/h to 100 kg/h and preferably from 2 kg/h 
to 50 kg/h, either by ejection by means of a gas, preferably anhydrous, 
for example an inert gas or air (FIG. 1) or by mechanical driving (FIG. 
2), 
(b) the solid thus discharged outside from said enclosure, in an elongate 
zone of tubular shape, is admixed with a carrying gas or conveying fluid 
whose feed rate to the elongate zone is so adjusted that the concentration 
of powder or pulverulent solid in the carrying fluid be in the range from 
0.1 to 1 kg/m.sup.3 and preferably from 0.1 to 0.3 kg/m.sup.3, 
(c) the mixture powder-carrying gas or gas flow passes across the whole 
zone of elongate shape, 
(d) said gas-flow then circulates, preferably downwardly, through a zone 
subjected to an electrostatic field whose voltage (or potential) ranges 
from 10 kV to 40 kV and preferably from 20 kV to 35 kV, with respect to 
the earth, 
(e) said gas-flow is then introduced in a zone of dilution with water, said 
zone being subjected to stirring, preferably of the Vortex type, said 
stirring being so adjusted as to develop a Reynolds number ranging from 
1,000 to 10,000, preferably from 1,000 to 3,000 and, more particularly, of 
about 2,000, so as to provide for a quick renewing of the liquid surface. 
The two FIGS. 1 and 2 of the accompanying drawings illustrate two possible 
preferred embodiments of the invention relating to a pneumatic conveying 
system providing for low flow rates of the conveyed solids, with very 
small concentrations in the conveying gas, with regular and steady flow 
rates and with a good dispersion of the particles in the gas flow. 
The apparatus shown in FIG. 1 comprises: 
a tank (2) containing a powdery solid (1) 
a sucker (3) (or device for sucking-up solid) plunging into the solid mass 
(1) and which is fed with gas from duct(4), said gas generating a 
over-pressure in tube (5) of the sucker, said over-pressure producing the 
sucking-up of powder into said tube (5), 
an elongate tube (10) (made of an electrically insulating material) 
connected to tube (5) and wherein, at the vicinity of the sucker (3), 
opens a tube (6) for injecting a carrying gas adapted to carry the powder 
therewith into the elongate tube (10), 
an electrostatic field (11) fed with an electrostatic generator, the 
potential or voltage of this field ranging from 10 kV to 40 kV (preferably 
from 20 to 35 kV) with respect to the earth, 
a metal tank (12) placed below the electrostatic field, said tank being 
filled with water (13), electrically connected to earth (14) and provided 
with a stirring system (15). 
Thus, in FIG. (1), the powdery solid (1), conditioned in an enclosure or 
tank, which here may be a vessel, a barrel or even a bag (2), is directly 
sucked by means of a sucker (3) of adjustable sucking power, with a 
minimum amount of carrying gas (4) just necessary to suck small amounts of 
solids. The gas injected in (4) produces an over-pressure in tube (5), 
thus driving through tube (10) the solid particles thus ejected from zone 
(2). When the solid to be conveyed is very hydrophilic, the conveying gas 
(4), in view of the small flow rates required for driving along the solid, 
may advantageously consist of completely dehydrated air or inert gas, thus 
not affecting the conditioning of the powdery material. 
The so-achieved suspension (5) is then diluted and brought to the desired 
concentration and then conveyed towards an electrostatic field, by 
injection of a carrying gas, or conveying fluid, consisting of air and/or 
additional gas, directly at the output of the sucker (3). The air or 
additional gases injected at this level in tube (6) need not to be 
dehydrated since they are only in contact with already suspended powder. 
The selection of the gas feed through line (6) makes possible to act on the 
solids suction by generating a more or less intense depression in tube 
(10), thereby regulating the flow of solids towards zone (12). 
In order to achieve the regular and steady driving of the pulverulent 
solid, it is preferable not to modify, during operation, the position of 
the sucker (3), initially deeply plunged into the product. 
In the embodiment of FIG. (1), tubes (5) and (10) have been so selected as 
to form therebetween a substantially right angle. 
The regular feeding with solids (1) at the bottom of the sucker (3) is 
advantageously achieved by a device generating vibrations (7), pneumatic 
or not, at the level of vessel (2) containing the powdery solid (1). The 
weight of material so engaged in pneumatic conveyance is periodically 
controlled, up to the injection of the desired amount of powder, by means 
of the balance (8), automatic or not, on which lies the vessel(2). 
The so-obtained suspension (9) is conveyed, very diluted, in the pneumatic 
conveying duct (10), made of an electrically insulating material (e.g. 
PVC). Then it passes through a metal section (11) brought to a high 
voltage (from 10 to 40 kV) by an external generator. The electrostatically 
charged particles repel each other and are precipitated in the metallic 
dilution tank (12), filled with water (13) and electrically connected to 
earth. The stirring system of said dilution tank comprises a stirrer, for 
example of the helix or anchor type (15), preferably actuated from the 
bottom of the tank, in order to avoid any deposit on the emerged 
mechanical parts; the tank (12) also preferably comprises counter-baffles 
(16)(or counter-deflectors) of a size defined according to the art for 
producing an adequate mixture, preferably intimate. 
The rotating speed of the stirrer is so adjusted as to produce a quick 
renewing of the liquid surface facing the opening of the pneumatic 
conveying duct, wherefrom the electrified particles of the diluted 
suspension are precipitated. 
The assembly of this device constitutes a simple apparatus, easy to adjust 
and to use in the working conditions on a worksite. The same holds true in 
respect of the second device hereinafter described with reference to FIG. 
(2). 
The apparatus of FIG. (2) comprises: 
(a) a feed hopper (18) containing the powder or powdery solid (1) to be 
treated, said hopper further comprising the following devices: 
means for introducing powder in the hopper, 
at least one endless screw system (20) or any equivalent system arranged at 
the lower part of the hopper and actuated by a motor (21) of variable 
speed, the endless screw system (20) providing for the discharge of the 
powder out of the hopper (18), 
(b) a pneumatic conveying duct (10), made of electrically insulating 
material, provided with a system for introducing a flow of carrying gas 
(arrow 28), this carrying gas being used to drive the powder therewith all 
along duct (10), 
(c) an electrostatic field (11) fed by a generator, 
(d) a metallic tank (12) placed below the electrostatic field, said tank 
being filled with water (13), electrically connected to earth (14), and 
provided with a stirring system (15), 
More precisely, in FIG. 2, the powdery solid (1) of barrel (2) is here 
poured into the feed hopper (18) of a feed regulator of the screw type. In 
order to favor the lowering of the solid, this hopper is preferably 
asymmetric (i.e. it has for example at least one oblique wall and at least 
one vertical wall). It is advantageously equipped with a stirrer of the 
vault-breaker type (19) or a similar system. The powdery solid (1) is 
extracted from said hopper (18) by means of an endless screw, spiral or 
Archimedes screw system (20) mechanically driven by a motor of variable 
speed (21). For sticky products, a double twin-screw system will be 
advantageously used to provide for a regular and steady flow of the 
product. By the judicious selection of the nature and geometry of the 
screw extraction system, in accordance with the characteristics of the 
powdery solid, it is possible to adjust the rotating speed of motor (21) 
to obtain as low as possible flow-rates of extracted solid, such for 
example as 0.6 kg/h. The amount of the soextracted solids may be 
periodically controlled, up to the total amount, for example by means of a 
balance (22), automatic or not, which may be used in turn to control the 
rotating speed of motor (21). The screw (20) here acts as solid 
distributor to duct (10). 
When the solid products are particularly hygroscopic, it is possible, just 
after the loading of the hopper (18), to purge said solids from their 
interstitial gas by means of a countercurrent scavenging with anhydrous 
gas, through the screw system (20). When products particularly sensitive 
to ambient moistness are concerned, it is possible to unload them through 
the screw system (20) under perfectly anhydrous atmosphere, by 
hermetically sealing the hopper with a cover (23). Optionally, the closing 
and opening of valves (24) and (25), for the feed (26) and exhaust (27) of 
perfectly anhydrous auxiliary gas, is performed through a servomechanism 
(PC) so as to balance the pressures between the output of the screw system 
(20) and the top of the hopper (18). 
The powdery solids extracted through the screw system (20) are poured into 
a pneumatic conveying tube or duct (10) made of electrically insulating 
material, and scavenged with a carrying gas (arrow 28) necessary to obtain 
the desired high rate of dilution. It is unnecessary that this carrying 
gas (arrow 28) be previously dehydrated since its flow rate is such, with 
respect to the amount of driven solid, that the dispersion of said 
particles in the large amount of carrying gas is easily achieved. The 
cross-sectional area of the pneumatic conveying duct (10) is so selected 
as to impart a high circulating velocity (minimum of 10 m/s) to the 
diluted suspension (9). It must be observed that these values are also 
applicable in the conveying duct (10) of FIG. 1. 
The wide dispersion of solid particles of suspension (9) is improved by the 
electrostatic dispersing system (11) of the same type as that shown in 
FIG. (1). This wide dispersion of suspension (9) during the pneumatic 
conveyance is essential to the obtainment of a good dilution of the powder 
in water (13) of tank (12). 
The remainder of the device used for making this dilution is in any respect 
similar to that described with reference to FIG. (1) (same reference 
number for the same part of apparatus). 
EXAMPLE 1-A (comparative) 
In this example, the apparatus of FIG. 1 is used, but without electrostatic 
field. 
800 liters of water at 20.degree. C. are contained in a circular tank of 
1000 liters, stirred by means of a three-stage helix rotating at 100 
turns/minute, whose rotation axis is at the top of the tank and whose wall 
is provided with four counterblades. The solvent is strongly stirred. A 
torque meter, measuring the power developed by the stirrer, is mounted on 
the motor axis. A polyacrylamide (product sold as "Pusher P 700" by the 
Dow Chemical Company, of particle size ranging from 50 to 250 .mu.m) is 
progressively added by means of a pneumatic sucker. The powder to be 
treated is discharged at a rate of 25 kg/h. The powder concentration in 
the carrying fluid (air) is 0.2 kg/m.sup.3, the water flow rate in the 
sucker being 1 m.sup.3 /hour. The obtained mixture remains stable and 
fluid during several weeks. A sample of said solution is taken for 
following the variation, during time, of the viscosity, by means of a 
viscosimeter of the coaxial cylinders type (1500.10.sup.-3 Pa.s. for the 
solution, i.e. 1500 centipoises). The dissolution of the polymer is 
completed after less than 15 minutes, the viscosity is at the maximum 
value at the end of the same period. 
The power supplied during this experience was 45 W; Reynolds 
number=1500-2000. 
The obtained viscous solution remains filterable. However, the 
filterability tests, at constant flow rates, with solutions at 1,000 ppm, 
effected with millipore membranes having openings of 8 .mu.m and a 
diameter of 47 mm, show an increase in the differential pressure about 
said membranes, during time. Various clogging phenomena are observed, 
particularly in filters during the filtration test. 
EXAMPLE 1 
Example 1-A is repeated but with the addition of an electrostatic spray gun 
fed with an electrostatic generator of 30 kV. The polymer is dissolved in 
about the same time but no polymer deposit is observed on the immersed 
parts. The electrified particles are more quickly oriented on the stirred 
liquid surface. 
The supplied power during said experiment is 45 Watts for a measured 
viscosity of 1500 10.sup.-3 Pa.s (1500 centipoises). (Reynolds number: 
1,500-2,000). Here, the obtained solutions do not produce any clogging in 
the filters during the filtration test, thus showing the complete absence 
of clots or microgels, and hence the obtainment of a very homogeneous 
solution. 
EXAMPLE 2-A (comparative) 
Example 1-A is repeated but, instead of introducing the polymer by means of 
a pneumatic sucker, the latter is added by means of the device shown in 
FIG. 2 (however without using an electrostatic field) i.e. by means of a 
feed screw. 50 grams of product are introduced simultaneously, the other 
operating conditions being those of example 1-A. On the one hand, it is 
observed that a stirring time of about 2 hours is necessary to obtain a 
stable viscosity and, on the other hand, that the solution exhibits 
apparent heterogeneities in the transparent medium with clogging of the 
filter during the filtration test. 
EXAMPLE 2 
Example 2-A is repeated but with the use of an electrostatic field device, 
as in example 1. The other operating conditions are those of example 1. 
Substantially the same results are obtained and the resultant solutions 
are successfully subjected to the filterability test. 
EXAMPLE 3 
The device of example 1 has been used to prepare 800 liters of a 3.5% by 
weight solution of a polysaccharide: zanthane gum of molecular weight 
3.10.sup.6. 
The polymer has been introduced by means of the apparatus described with 
reference to FIG. 1 and under the conditions of example 1. 
The viscosity measurements during time show that the solution is stabilized 
after 15 minutes. 
The viscosity at 20.degree. C. is 7000.10.sup.-3 Pa.s.