IL32183A - Apparatus and method for mixing and pumping fluid explosive compositions - Google Patents

Description

APPARATUS AHi) -METHOD FOR MIXING AND .PUMPING FLUID EXPLOSIVE 'COMPOSITIONS APPARATUS AND METHOD FOR MIXING AND PUMPING FLUID EXPLOSIVE COMPOSITIONS , The present invention relates to improvements in a method and apparatus for mixing ingredients together to form an explosive slurry blasting composition. Such a blasting agent can be prepared by blending liquid and solid ingredients together to form a viscous gel or slurry. Such ■gel or slurry can be pumped into a borehole, or other blasting site, or into a receptacle for later use, through a delivery hose or tube. Compositions which are of low viscosity when pumped can thicken further when or immediately after they are . umped. This further thickening prevents gravitation segregation of the suspended solid ingredients from the liquid menstruum or their elution by ground water, etc. , e.g. when the composition sets or becomes quiescent in a borehole. In the past facilities for storing, feeding, mixing and pumping have been combined on a large mobile vehicle which carries a large supply of a liquid ingredient, such as an aqueous solution of ammonium nitrate or similar oxidizer salt. The vehicle also carries supplies of one or more dry ingredients which are to be mixed with and suspended (or sometimes partly dissolved) in said liquid, to form the explosive slurry. Means are known whereby the composition of the explosive being prepared may be varied by changing proportions from time to tLme of one or more of the ingredients. The mix may be changed during a single and continuous operation of loading or filling a single borehole/ if desired.

The apparatus and method used hitherto have been successful commercially but in some cases the apparatus is large and cumbersome. The prior system also includes complex mechanical units and electrical controls.

One object of the present invention is to extend to smaller and simpler operations benefits of the large automatic on-site mixing-pumper type operation and equipment described above.

By use of simple mechanical and/or fluid operated controls, and · by a convenient arrangement of the essential operating elements, storage bins, tanks with dispensing and blending means for the various ingredients, a highly versatile, economical and convenient .system now is made available.

In lieu of complex mechanical controls and drives, the present invention also includes use of fluid operated controls and/or drive means for the various functions, including means for driving all the- essential elements from a single central fluid power unit. Such controls and/or the drives may be operated by either pneumatic or hydraulic means.

Thus the new system appears to have several advantages over prior equipment. It is adaptable for more types of use and suitable to replace the former equipment even in large scale operations, in many cases.

Fig. 1 is a side view of a system typical of the present invention.

■ .Fig. 2 is a larger side view, partly in section and with certain parts broken away, showing the mechanical drive means and controls by which the ingredients are combined to form a slurry and then pumped to a point of use .

Fig. 3- is an end view at the rear of a mounting vehicle, which may be considered the front of the mixer-pumper unit, including a modified mixer. - .. some of the controls, ■ etc.

Fig. 5 is an elevational view at the rear of the mixer-pumper unit, i.e. looking to'the rear from the vehicle cab from approximately line 5 — 5 of Fig. 1.

Fig. 6 is a diagrammatic plan view showing approximate relative location of some of the major components of the system.

Fig. 7 is a larger and fragmentary plan view, with some parts in section and some broken away to show the drive and feed mechanism for particulate solid ingredients.

Fig. 8 is a fragmentary vertical section taken approximately on line' 8—8 of Fig. 7.

Fig. 9 is a diagrammatic view of an alternative system wherein the various operating components are operated by fluid power.

Fig. 10 is a partial elevational view, with some parts in section, showing a modified mixing system for combining a liquid and dry particulate ingredients.

Fig. 11 is a front view of the apparatus of Fig; 10.

The apparatus and method of the present invention, like the larger and more complex equipment already mentioned, eliminates need for a separate mixing plant. It reduces cost and decreases danger of transporting blasting materials to places where they are to be used.

The need of packaging the explosive for handling is obviated, although packaging still may be done with the apparatus of this invention for special situations. There are significant reductions in manpower requirements, which would otherwise be necessary to load the explosive into boreholes ^and other points of use.

In its method aspects, the invention contemplates the use of as ammonium nitrate, sodium nitrate, or the like. These may include various particulate solid sensitizers of known types, such as particulate aluminum or other heat producing metals which are essentially non- explosive per se. Other fuels are often added, such- as carbonaceous materials, sulfur, and other ingredients as is now well understood in the art. Thickening agents to control the viscosity of the blasting agents are normally added in small proportions, suitable for their purpose. In general, the materials, liquid and solid, are mixed together to form a fluid or slurry mass, at first relatively non-viscous, which can be .pumped through a delivery hose or pipe without excessive pressure or 'power requirements. The thickening ingredients, or some of them preferably are so chosen and their addition to the mixture is so timed that while the blasting agent can still readily be pumped or flowed into place, approximately by the time it reaches there it solidifies or stiffens up sufficiently that there is no substantial segregation of solids from the liquid menstruum in which they are suspended.

. Some of the improvements in method aspects of the present invention over those in the prior art relate to use of simple unitary mechanical or fluid drives and controls, improvements in effective mixing and greater facility for production of individual or sequential batches. In some cases batches may be started or stopped, or even their composition changed at will during filling of a particular borehole. Also, the degree of aeration which can be incorporated into the explosive, when such is desired, may be varied widely and by very simple control manipulations. * - ■ Referring now in detail to the drawings,' Fig. 1 shows a mixing and pumping system of the present invention, mounted on a small or intermediate sized automotive truck 11 or the like. The vehicle 11 may be mounted bodily. Unit 15 normally is not secured permanently - to the truck, although it can be, but it is ordinarily independent and can be readily unfastened so that it may be lifted out bodily and placed on the ground or on some other- mobile supporting apparatus such as a mine car, for use in mine tunnels where overhead clearance would not be sufficient for a vehicle of larger dimensions. This unit 15 comprises a generally rectangular framework 17 of conventional type which has a main base or floor 21, supported on rails 23. See Fig. 2. The system of Figs. 1 and 2 comprises a drive motor, e.g. a gasoline engine 25, mounted in the front right corner of the cargo compartment of the vehicle. Obviously, for some situations, an electric motor may- be used.

The rear end of the truck or vehicle may be considered the "front" of the slurry mixing and pumping unit, since that is the place where it is controlled primarily. In this sense, the motor 25 is located at the rear right corner as- one faces the unit. Motor 25 has fuel tank 27 and on its power output shaft 28 is mounted a triple drive pulley 29; An air compressor 37 is located near the rear left corner. The front sheave 30 of pulley 29.is connected by a belt 31 to a pulley 33 on the drive shaft 35 of the air compressor. See Fig, 5. The compressor is mounted on a base 39 and is provided with an intake air'filter 41, a main outlet line 43, and a pressure control line 45. Line 45 operates in known manner to open a by-pass valve in the compressor and stop air delivery. When pressure reaches a predetermined level, the compressor is rendered inoperative and when pressure in tank 49 drops, the compressor will be reactivated.

Motor 25 normally operates more or less continuously. The two inner sheaves of ulle 29 drive a main transmission shaft 51 throu h bearings 57,, 59 and 61, and extends towards the front of the unit,, that is, towards the back of the truck; its front end is seen at the left of Fig. 2. Shaft 51 carries a clutch mechanism 71 on which is supported a do.uble belt pulley 73. Clutch operating control lever 75, pivoted on a stationary member 77, is operable by a pull rod 79, equipped with a handle 81, which. -projects through the cover plate 83. See also Figs. 3 and 4. When the clutch is engaged, the double pulley 73, through drive belts 87, Fig. 2, drives a pulley 89 mounted on the drive shaft 91 of a slurry pump 93. Pump 93 preferably is of positive displacement type, receiving slurry through a hose or line 95 equipped with a quick release coupling 97 from a slurry mixing unit 99.

The slurry pump shaft 91 is provided also with an additional pulley or sheave .103 which through belt 105 drives a variable split pulley 107 fixed on a jack shaft 109 to which also is secured another pulley 111. Pulley 111, through a drive belt 113, drives a floating pulley 115 mounted for free rotation on operating shaft 117 for. a solution pump Pulley 115 has a second sheave 116 which through a twisted belt 118, Fig. 4, drives a pulley 120 fixed to the upper end of a mixer shaft 122 mounted in the mixer unit 99. The mixing operation will be described more fully presently.

The shaft 117 hich drives the solution pump 119 is driven through a clutch 133 operated by a lever 134 pivoted at 135 and equipped with a' pull rod 136. An operating knob of handle 137 extends through the front plate 83. See Figs. 1 and 2. When clutch 133 is engaged, a dual drive pulley 140 is operatively connected to shaft 117. This pulley is driven-by a pair of belts 141 which engage a dual drive pulley 142 on the main shaft 51, to operate the pump. An oxidizer solution suction line 121 which occupies a major central area of the lower part of unit 15. It normally contains a heated and substantially saturated aqueous solution of a strong inorganic oxidizer salt, preferably ammonium nitrate or ammonium nitrate mixed with sodium nitrate. Other oxidizers, such as calcium nitrate, barium nitrate, etc. , or one or more of the various ammonium and alkali metal chlorates and/or perchlorates may be added or substituted in part or in full. A preferred practice is to use a strong aqueous solution, usually heated, containing from about 60 to 85% by weight of ammonium nitrate, which may include sodium nitrate.

The pump 119 delivers the solution through outlet line 147 to mixing chamber 99. The outlet 260 is shown in Fig. 4 between the outlets of two augers, described hereinafter, which deliver particulate solid materials to the same mixing chamber.

The main drive shaft 51 operates the slurry delivery pump 93.

Through the pulley 103 and drive belt 105 power Ls transmitted also to pulley 107, which is connected directly with pulley 111 to drive the floating pulley 115 whenever the slurry pump is operating. The latter, through pulley 116, belt 118, and pulley 120 drives the mixer shaft 122, whether the pump shaft 117 is rotating or not. The double pulley 142, also mounted on shaft 51 and fixed thereto, drives pulley 140 and the latter drives pump shaft 117. Thus the solution pump does not operate unless its clutch is engaged. In this manner, means are provided for drawing the liquid solution, which preferably is heated as mentioned above, but may be cold in some cases, from its tank 123, forcing it into the mixing chamber. The liquid in the mixing chamber is blended with other ingredients, usually including at least some solid, dry insoluble particles which are to be suspended in the liquid to form a smooth, homogeneous point of use, as will be described more fully. Pump 93 does not operate unless clutch 71 is engaged. However, when it does operate, the mixer ■ shaft 122 is rotated too, to prevent building up of deposits in the mixer which might clog the slurry punip or cause other difficulties.

At its rear end, in addition to the double pulley 56 driven directly by belts 53 and 55, main drive shaft 51 carries an additional pulley 151, shown at the extreme right in Fig, 2 and at the upper left in. Fig. 5.

Through belt 153, pulley 151 drives the input shaft 155 of a gear reducer 157 through pulley 159. ThLs gear reducer may be of a fixed ratio type or it may contain or comprise a variable ratio drive. Its purpose is to provide reduced rotational speed for driving augers which are used to feed dry particulate materials. In some cases alternative particle feeders such as vibrators or shakers may be used. Through its output shaft 192 pulleys .161 and belts 163, see Fig. 7, the gear reducer drives an auger operating pulley 165, Fig. 7, provided its operating clutch 196, on shaft 192, is engaged. The pulley 165 is mounted on the operating shaft 167 of an auger 169 which is mounted in and extends transversely of the bottom of a hopper or bin 170 adapted to hold a particulate solid, e.g. a supply of auxiliary oxidizer in dry or granular form, such as ammonium nitrate, sodium nitrate, or other particulate oxidizer material.

.A bin 171, usually but not necessarily larger than 170, is mounted beside the latter and is designed to hold a so-called "pre-mix" of dry particulate non-oxidizing ingredients to be added to the liquid in making the slurry. This pre-mix contains fuels and/or sensitizers, such as finely divided coal, sulfur, aluminum granules or powder, sugar, etc. It may mixer 99. Auger 180 feeds its ingredients from bin 170 through housing 181 into the mixing chamber or funnel 99.

It is preferable for safety reasons not to pre-mix dry oxidizer materials with dry combustibles such as fuel, carbon, solid hydrocarbons, metallic aluminum, self-explosives, -and other fuel materials; hence, separate bins and augers are used. The dry pre-mix ingredients may and commonly do include a thickening agent, such as guar gum, starch or equivalent, for increasing the viscosity of the' slurry and causing it to thicken or set up, at least in the borehole where it is to be detonated, so that the suspended solid particles in the slurry will not settle out and cause a detonation failure. However, the thickener, or part of it, may be pre -incorporated in the oxidizer solution or may be added thereto as the solution flows to the mixer and before the liquid is mixed with the dry or solid ingredients.

Fig. 8, at the top shows an auger 180 on shaft 182 which passes through bin 170, preferably inside a. housing 183. The shaft can be left exposed in bin 170, if desired. A sprocket 187 fixed to shaft 182 is driven by a chain 188 passing over a sprocket 189 on shaft 167. Thus the two augers 169 and 180 are driven simultaneously, but not necessarily at the same rates, to discharge simultaneously the pre-mix from hopper 171 and the so-called "drys", which are commonly supplemental oxidizer materials, from hopper 170. The relative discharge rates of the two augers depends on their diameters, pitches, and rates of rotation. These elements are' selected or varied, as desired, to feed appropriate proportions of- ingredients. Also, the feed rate of both augers may be changed by changing the drive ratio in the speed reducer 157. Relative rates of either auger may be varied independently also, as by changing one or both sprockets Ingredients maybe fed, as will be obvious. The effective drive ratios may be changed between batches or even during a' single batch or borehole filling operation, if desired. For example, a more powerful charge may be needed at the bottom of a borehole than higher up and a suitable shift in feed ratios of the respective ingredients will accomplish this objective. When this is desired, a change gear or variable speed drive for one or more feeders may be used, rather than changing sprockets, as is obvious.

.As shown in Figs. 5 and 7, speed reducer 157 is mounted on shaft 192 which may be its output shaft, appropriately supported for rotation in bearings 190 and 191, mounted on a suitable frame member 195. Power input,' as already noted, is from pulley 151 through belt 153, Fig. 5.

The output shaft 192 of the gear reducer 157 has affixed thereto 'drive clutch element 196, designed for engagement and disengagement by fluid pressure, i.e. an air piston and cylinder assembly inside a housing 197. The latter is operated by compressed air under control of manually operable valve 200, from tank 49. The air connection is indicated in Fig. 7 at 198. The pivoted control lever 199 of a valve operating control unit 200 is mounted in the upper left side of the control panel, as shown in Fig. 3. By this means the clutch may be engaged and disengaged with respect to the double output pulley 161. The latter drives belts 163 which engage driven auger pulley 165, as already described.' As best shown in Fig. 4, the mixing unit 99 comprises a tank or funnel member 215, cylindrical in shape at the upper part, but having a tapered or conical bottom portion-216 which connects to an outlet line 217. The tatter connects to slurry pump connection 95, previously described.

·": The drive shaft of the mixer has mounted on it near the top. of c lindrical art 215 a fan or blower 218 which is ada ted to draw off provided in a transverse partition 220. This is needed particularly when the mix contains very finely divided particles, such as paint grade aluminum, powder, very fine ground gilsonite or coal, etc. An outlet line 221 leads the dust out of the unit and away from the operating mechanism, as shown best in Fig. 3. By this means the mixing chamber is kept fairly clear so that the operator can observe visually what is going on, e.g. through the open door 263, also in order that accumulations of dusty explosive materials or other dusts within the mechanism may be prevented. The full amount of dust so drawn off is quite small, usually inconsequential. Augers 169 and 180 preferably are arranged to deliver the dry particles into the mixing chamber. During a major part of the operation, both liquid and dry particles are delivered simultaneously to the mixer. However, it ■is often desirable to start feeding one ingredient, such as the liquid, before the dry particulate materials are fed to the mixer. ■ Shaft 122 of the mixer is mounted in bearings 227, 228, secured to partition 220, and on its lower portions this shaft supports mixing elements 220 and 230 which are of conventional type, e.g. of propeller shape. The lower blade 230 is located in the conical part of the mixing chamber and is somewhat smaller than the upper one. By these means the liquid and suspendable particles are thoroughly mixed together so that a homogeneous slurry is produced before leaving the mixing chamber. It flows by gravity through the outlet 217, through the quick detachable hose 95, and into the slurry pump 93. Some particulate solids,, such as oxidizer salt or gum, may dissolve in the liquid during mixing but at 'least some of them, such as aluminum particles, carbonaceous particles, sulfur, etc. , do not dissolve but are suspended.

Supplemental mixing may be desirable to increase slurry sensitivity shows a "pug mill" type mixer extension. Here the mixer 99 has a cylindrical lower end 231 provided with inwardly directed fingers 232, •arranged in staggered relationship with respect to mixing bars 233 on shaft 122. With this arrangement the slurry is mixed longer and more vigorously, and fine air bubbles may be incorporated to reduce slurry density as much as 25% or more by aeration. With some formulations also, the supplemental mixing gives time for the thickener to become more effective. A shorter hose 95A replaces the hose of the structure described above.

The slurry pump 93 driven as previously described is designed to propel the slurry to its destination at an adequate rate, say 50 to 500 pounds per minute. The product is delivered through a hose or conduit 238 connected to outlet 236 by means of a three-way valve 235 provided in outlet line 236 from the slurry pump. 'Valve 235 has a control handle 237 and is arranged so that when the delivery valve is wide open the whole pumped stream may pass to the -borehole through the outlet 238. .Alternatively, a part of the stream, or all of it, for that matter, may be recycled to the mixer or pump inlet, through a bypass or recycle line 239, depending on the valve setting. In Ueu of the three-way' valve shown, two separate valves of ordinary design may be used. Such valves, of course, may be interconnected to a single control. By either arrangement, some or all of the mixed slurry can be recycled through line 239 to the pump, or by proper connection to the mixing chamber above it, if desired, to control the slurry level therein by merely pushing the lever 237, Fig. A, to the appropriate control position. In this way, although ' the pump is operating at capacity and the slurry is flowing through it, the valve ma be set for full rec cle so that no slurr flows to the thus can control slurry level and continued mixing in the mixer. This level .can be observed by the operator, either by watching sight glass 240 which contains a visible fluid to indicate slurry level by manometer pres-' sure, or by observing the slurry level directly through open door 263, Fig. 4.. When slurry pump 93 is not operating, the valve 235 can be closed so that air pressure can be admitted through blow-down line 241, under control of a valve 282 to clear residual slurry from the delivery hose.

The slurry pressure is indicated by a gauge 243.

It will be understood, of course, that a hose, or a pipe, 'if desired, of suitable length and diameter, is used to conduct the slurry from the pump to a borehole or to packaging, or to some other place of use or delivery. The hose or pipe should be large enough to. deliver, without undesirable high pressure, a stream produced as fast as ingredients fed to the mixer require. It should not be so large, however, as to allow significant separation or stratification of solid particles from suspension in the mix. The machin-e may be used either to fill boreholes, etc. , or to package slurry in suitable receptacles; in the latter case the hose is simply led to an appropriate receptacle filling point. ■ A water tank 250 Is included in the system so that a supply of clean water may be available for flushing out valves and flow lines, rinsing out the mixer, and cleaning hoses and other internal or external parts, as desired. 'One arrangement is to fit the water tank under one of the sloping sides of the solids hoppers or bins.170, 171. See Fig. 8.

.Another arrangement is to mount the water tank 250A, as in Fig. 6, inside the solution tank 123. With the latter arrangement the hot solution, which is customarily used, will keep the water hot. See Figs. 2 and 8, as well as Fig. 6. A water outlet line 251 extends to or near the hose 255. The latter can be used to rinse the mixer, wash off the apparatus, etc. Water is forced out by maintaining air pressure in the ■tank 250A, supplied through a line 356 to the top of the tank from air pressure tank 49. This pressure may be of any suitable magnitude, say 100- lbs. per sq. inch, or more or less, to force the water at effective ■ pressure through outlet line 251 when valve 252 is opened. A control valve 254 is provided for draining the solution tank.

In a typical operation, the oxidizer solution temperature may be kept in insulated tank 123 at a temperature of up to about 185°F. In this case, hot water of about the same temperature is normally available with the arrangement of Figs. 2 and 6. With the arrangement of Fig. 8, more capacity for liquid solution is available in tank 123 but the triangular cross-sectioned tank is not as suitable for elevated pressures. Water may be drawn by gravity into a small unpre'ssured tank, not shown, which then can be pressurized with air and used for flushing, etc. When it is desired to refill the water tank in either case, the air pressure is relieved by closing an air supply valve and opening a suitable vent, not shown. Then water can then be run in from a suitable water supply by reverse flow, e.g. through the hose 255 and valve 252, etc.

As shown in Figs. 4 and 7, the solution normally is fed into the mixer 99 through line 147 (see. also Fig. 8), outlet 260, which is placed between the outlets of the augers 169 and 180; see Fig. 4, in dotted lines behind shaft 122. The outlet 260 can be in the form of a simple pipe end or a spray nozzle. The latter can discharge a flow of sufficient width to cover the falling dry particles as they emerge from the augers and facilitates mixing. In either case the dry particles are w tted and washed down the walls of the mixin tank 215, The shown in Fig, 4.

The system normally will be calibrated so that a counting device 280 records the revolutions of auger 180 in the pre-mix bin 171. The connections are shown from a pulley 2.73, on shaft 182, through a belt 274, pulley 275 on jack shaft 276, which has a flexible shaft 277a on its front end to drive the counters. Each revolution of shaft 182 will deliver a certain specific quantity of pre-mix solids; the other ingredients will be fed in appropriate proportions for each mix. The slurry so produced is caught, weighed and the counting device calibrated to determine quantity of slurry delivered per unit count. Counter 280 is of the resettable type. A counter 281 of the totalizer type, Fig. 3, shows the total quantity of explosive delivered over an'extended period of time. For each different mix a new calibration is made, if necessary.

This system has advantages over the prior systems in addition to compactness, simplicity and portability. It is versatile and readily controllable and adjustable in all its functions. For example, the density of the mix produced may be varied and controlled in several ways with or without change in proportions of ingredients: (a) by choice of dry ingredients which promote or control foaming or gas entrapment in the slurry, (b) by forming bubbles or froth in the solution, e.g. at the pump 119 (by cavitation or drawing air into the liquid solution before solids are added, 'and/or by including a foam stabilizer in the liquid), (c) by introducing gas-forming ingredients, such as carbonates, etc., with the dry ingredients ("pre-mix") or by permitting cavitation or air injection (or injection of. other gases) at the main slurry pump. The latter, however, must be done with care so as not to introduce large bubbles which might produce discontinuities in a column of explosive or promote slurry instability. as guar gum, etc., which will stabilize at least the fine gas bubbles, as introduced in any of these ways. Finely divided gas bubbles may be incorporated in the liquid before solids are added, i.e. before it reaches the mixing zone. They may be added in said zone, too, or at the slurry delivery pump, or at both.

Thus the density and sensitivity characteristics of the delivered explosive slurry may be controlled as desired. This can be done without use of detergents or surfactants, or by use of very -small quantities of such. This makes it possible, in the filling of a single borehole, to start at the bottom with a dense and relatively gas free slurry having a substantially incompressible and continuous liquid phase. Such slurry has advantages as is known. Later, as filling proceeds, slurry density may be reduced progressively or in one or more steps so as to place less weight of explosive per unit volume of borehole. This is often advantageous and economical since the blasting force may not need to be as great towards the top of the charge.- In a sense, these aerated slurries may be considered to have a substantially continuous liquid phase.

Drive of all units for the systems of Figs. 1 to 8 is primarily thropgh the single main drive shaft 51 which operates the solution pump 119, the augers 169, 180, the fan or blower 218, the main slurry dispenser pump 93 and the mixer 229, 230, from the latter. The slurry pump operates at all times so that slurry need not accumulate in the mixer, an-important safety feature. Since the mixer must operate whenever the. slurry pump operates, there are no unmixed accumulations in the mixing chamber, another safety feature. The dust removing blower is still .

- The air compressor 37 is driven directly from the engine and supplies air pressure to operate the various pneumatic controls and to pressurize the water tank for auxiliary liquid supply and/or cleaning.

Water from this tank can be added to the mix if desired. The pressurized water supply is a safety feature and, of course, the separation of fuels and oxidizer until mixing and immediate delivery is the most important safety feature of all.

The several controls may all be pneumatic, for convenience, such as the controls 197 for clutch 196 which drives the augers for feeding the particulate solids.

The air compressor stores compressed air in tank 49 which, as shown in Fig. 5, may be mounted in any suitable place. The compressor output line 43 leads to the top of tank 49. A filter 352 is shown in the outlet line, followed by a regulator. and pressure gauge 353, followed in turn by a lubricator 354. From the lubricator, the air flows through line 356 and appropriate branches to the various valves and controls already mentioned. ' · An air pressure chamber is- rovided in the water tank so that .water for rinsing, etc. , is available at good pressure. A main air line 358 leads to valve 282, Fig. 4. Upon opening valve 282 and cbsing valve 235 the air is admitted into line 241 to blow out the slurry in the delivery line without blowing back into the slurry pump or mixing unit, etc. Line 241 contains a check valve to prevent slurry entering the valve 282.

The general operation will now be described. When the unit is started up, the slurry pump is started first by engaging clutch 71, i.e. pulling the. handle 81, Fig, 4. Shaft 51 then drives the slurry shaft 109, pulley 111, and belt 113. The latter drives floating pulley 115 secured to its companion to drive the twisted belt 118.

The mixer is driven whenever the slurry pump operates. Normally, both are in operation before any ingredients are fed into the mixing chamber 99. This prevents building up deposits of unmixed materials, either in the mixer or in its outlet line to the slurry pump 93.

The next step, normally/ is to start the oxidizer solution which is fed by pump 119 from the supply tank, the solution being drawn into the tank through line 121 and fed to mixing chamber 99 through line 147 and its outlet 260. Activation of clutch 133 through lever 135 and handle 13? initiates this operation.

Next, the augers are started to dispense the dry materials into the mixing chamber. It is usually preferable to start the liquid flow before solids are fed and stop it after flow of the' solids is stopped to prevent building up deposits of granular materials on the wet surfaces of the mixer elements and tank. However, this may not always be necessary. Activation of the pneumatically controlled clutch 196, Fig. 7, starts and stops the augers and this may be done manually.. Preferably, however, this control is operated automatically from the liquid supply line, so that the' clutch 196 is engaged after liquid starts to flow, as by a pressure build-up in line 147 sensed by element 361, Fig. 2, which transmits a clutch closing signal through line 362, shown only fragmentar , to clutch control element 197, Fig, 7. · Normally, the slurry valve 235 will not be opened until a small amount of slurry accumulates above it in slurry pump inlet line 95, Fig. 4 or 95A, Fig. 3. A small accumulation usually is permitted in the bottom recycles a small proportion of the pumped slurry to the mixer, or to the pump, this proportion being determined by the setting of valve 235 (by control handle 237, Figs. 3 or 4). The by-pass can be connected into the line 95 or 95A, instead of into the mixer by a connection 363, Fig. 3. (The recycle line is not shown In Fig. 3). It is usually desirable to keep enough slurry in the mixer to cover the mixer blades, or at least the lower ones, to avoid poorly mixed slurry product. In fact, the degree of mixing can be increased considerably by increasing the recycled proportion and setting valve 235 appropriately.

The height of slurry in the mixer is indicated by the sight tube or manometer.240. Some operators prefer to watch the slurry level and the quality of mixing in the mixer itself by leaving door 263 open. In this case, a small inward draft caused by blower 218 tends to keep dust from fine dry carbonaceous materials, powdered aluminum, etc., from billowing out to obscure the view and deposit dust on the equipment. Use of the auxiliary mixer elements 231, 232, 233, Fig, 3, makes it unnecessary to do this. However, the solids should be well washed with the liquid, to insure a homogeneous mix, even though some of them may be lyophobic and resist actual wetting.

In pumping the explosive slurry into a borehole, there should not be excessive aeration, although some aeration may be desirable to improve sensitivity. The degree of aeration can be largely controlled by controlling the extent of slurry recycle and controlling slurry level in the mixer. The dry particulate solids bring some, air in with them. By performing ¾ folding sort of mixing, holding the slurry level in the mixing ■ chamber at the right level with respect to the mixing blades, more aeration can be obtained. Aeration can be reduced b addin more li uid to et into a partly prepared slurry.

·■ The delivery hose may contain considerable slurry, especially if it is a long one. It is desirable, usually,' for economic reasons, to empty the hose by "blow-down", using the compressed air connection and valve 282, as described above, before moving to the next hole or filling operation.

The system described above has the advantages of simplicity, using a single main drive shaft from which motive power is taken off for pumping, dispensing and mixing. It depends on individual controls for the several clutches, etc., to jet the desired timing and proportions of ingredients, dispensing, recycling, control of delivery and blow-down. For some purposes, it is desirable to program-all these controls and. the system shown dlagrammatically in Fig. 9 is well suited to such programming or automation.

Referring back to Fig. 3 above, an interleaved blade or finger type mixer 34 of the "pug-mill" type was shown at the bottom of the mixing unit. For some purposes a mixer, as shown in Fig..10, is preferred, omitting the propeller or puddle type stirrers 229,, 230, Fig. 4. Such a unit consists of a mixing chamber or vessel 501, having its longitudinal axis inclined from about 5° to 90° with respect to a horizontal plane. A mixer shaft 502 is mounted axially within the mixing vessel, being driven, for example, by a pulley or equivalent 503 operated by any suitable mechanism, not shown. Inwardly extending from the walls of the vessel towards Its center are a series of projecting radial fingers 505, 506, etc. The shaft itself is provided also with radial fingers or blades 509, 510 which move between blades 505, 506, in pug mill fashion. The outlet end of the mixing vessel may be closed either by a builds up, or it may be closed by rotatably adjustable end plate 511, Fig. 10, held in place by a retaining ring or flange 512, and having outlet opening 513 through which the slurry product flows. The amount of slurry inventory kept with in-' the mixing chamber, Fig. 10, and the degree of mixing, aerating, etc. ,- depends on the position of outlet 513. By rotating the plate 511 to the position shown in dotted lines, Fig. 11, a larger inventory may be maintained. When the rubber flap 501, Fig. 11, is used, a spiral impeller or "slinger" 516, fixed to shaft 512 propels the ingredients towards the outlet end. This prevents wet material from backing up into the inlet 517 through which the dry particulate solids are fed. .. .

The dry solid particles may be supplied by one or more augers, through line 518, as explained above; see Fig. 11. Liquid is brought in through line 519. This liquid may be water, water mixed with other liquid, or an oxidizer solution, as desired. All of the oxidizer salt may be supplied in dry form. The slurry thus may be prepared from water, salt and the various insoluble particles required, all fed separately into the mixer. It is generally prefe red, to use pre-dissolved oxidizer. Thickeners, which preferably are usually prehydrated, may be mixed in by holding the ingredients for adequate hydration time.

In the system of Fig. 9 the moving parts are driven by fluid motors which obtain their operating power from a stream of circulating fluid driven by a master pump system. In this case two master pumps and M2 are driven respectively by prime movers and P2. Each draws a supply of motive liquid through an inlet line 300 from a vessel 301 to which the fluid is supplied by recirculation through a filter 302..

When the master pump is in operation, all of the fluid is recycled through line 305 unless one or more fluid motors described hereinafter are being driven.

A pressure gauge 307 is attached to line 308 which continues from the relief valve 304 to a manifold 309. From the latter, the driving fluid is led by lines 310, 311 and 312 to solenoid operated valves 313, 314, and 315 respectively. The outlet of the latter is provided, with a variable orifice valve 316 in line 310. A similar adjustable valve 317 is provided in line 311 and valve 318 in line 312. These lead respectively to fluid motors MF^ and MF2 and MFg. The effluent from these motors passes into a manifold 320 from which it returns through line 321 to recycle line 306.

Each of the motors MF^, F^, and MF^ drives an auger, the three augers being indicated at 323, 324 and 325. Each of these is used to feed a dry particulate ingredient to the funnel or mixing vessel 330. These materials pass respectively through lines indicated diagram-matically at 327, 328"and 329. '■ · '.'' '' ' ■■■ [ ' . ..

;'' Another line 331, connected to manifold 309, conveys the driving fluid to a solenoid operated cut-off valve 335 which is followed by a variable orifice valve 336. The latter controls the flow of fluid to a fluid motor 337 which, through linkage 338, drives a fluid pump 339 which preferably is of positive displacement type. The latter is used to pump a solution of oxidizer, preferably an aqueous solution of ammonium nitrate, sodium nitrate, etc, , from a tank 341 which sup'pltes the solution to a three-way valve 340. ', " - ·. "·-/''''·' \ . ' ·' ,' ' -: .Thus the pump 339 supplies this liquid solution to the funnel 330 to be mixed with the dry ingredients fed by the respective augers latter may be used. at times. By adjustment of the variable orifice valves 316, 317, etc. , the driving'"speed of any of the motors Fj and Μί?2' etc" ' may ^e adjusted to feed the ingredients at the appropriate rate to obtain the desired composition in the mixing vessel 330.

The other master pump M2 supplies fluid in- the same manner as the first master pump to a relief valve 344 from which it may be recycled, when required, through line 345 to line 306. Thus the fluid re-enters the filter 302 through a tube on which a line 347 returns it to both supply tanks 301. A screen 348 is provided in each of the vessels 301 to prevent recirculation of foreign matter through the system. Master pump M2 is used to supply driving fluid for fluid motor MF^ which drives •the operating shaft 350 in the mixing chamber 330. This shaft is provided with suitable mixing blades 351.' · The master pump also supplies driving fluid through a cutoff solenoid-operated valve 381 and a variable flow valve 382 in a line 383 which connects to the relief valve 344. Thus a variably controllable stream of driving fluid is supplied to fluid motor MF which drives the operating shaft 385 of the slurry pump 386. In this way the velocity of the pump can be controlled. The pump 386 draws slurry from the mixing chamber 330 through a line 387 and delivers it to a manually operated slurry valve 388 in outlet line 389. A pressure gauge 390 is connected to this line to show delivery pressure. Line 389 terminates in a connection for a flexible delivery hose 391.

Driving energy for the mixer shaft 350' is supplied through line driven at high speed, if desired, to beat air into the slurry and "reduce its density.

An air compressor 410 supplies compressed air through line 411 to an air tank 412 from which it may be withdrawn through line 413. Any suitable motive power may be used for the compressor, such as its own motor or a power take-off. ■ One branch line 414 from the tank outlet leaves the air tank at full pressure to a cut-off valve 415 and thence through a line 416, to connect with slurry output line 389. Since this line is at full tank pressure, by opening valve 415 manually and closing valve 388 adequate pressure is available to "blow-down" or clean out the hose 391. The check valve 417 prevents blowing slurry back into the pump 386.

Another branch 421 of line 413 goes through a pressure reducing valve 420 in line 421 to a multi-purpose valve 422. Through the latter air may be vented through a line 424 or it may be passed at the desired reduced pressures through a line 423 into 'a water tank 425. In this way pressure is applied to the water so' that it may be forced on through a line 427, under control of a manually operated valve 428, to connect with a hose 429, for washing down the apparatus, flushing the mixer, etc. · . . ' , ■ .

A branch line 430 also leads from three-way valve 4 8 to a manually operated three-way valve 340. By appropriate setting of these valves water may be drawn from the water tank to flush out the pump' 339 and/or the mixing vessel 330. Ordinarily, however, valve 340 will be used to draw the hot concentrated solution of oxidizer salt, such as In the system described above, the master pump supplies power for feeding the various dry and wet ingredients to a mixing zone whereas master pump supplies power for mixing the ingredients and 'delivering them as a slurry to a point of use. Various other arrangements can be used, e.g. with one or more master pumps applying the necessary motive force for any or all of the various fluid motors.

Various features of the several modifications described may be lnter-changed as will readily occur to those skilled in the art.

Claims (21)

1. n WHAT WE CLAIM ISj I* A system for preparing and delivering pumpable explosive slurries of suspended solid particles in a liquid solution of oxidizer, which comprises, in combination, a mixing zone, a means for holding a supply of said particles, positively driven metering means for delivering said particles to said zone from said supply at a controlled rate,' r means for selectively varying said metering rate, a tank for liquid, -.selectively variab¾erameans for delivery liquid from said tank to said zone at a controlled rate,' mixing means in said zone to form said .. . . . _~ , · 13-- particles and said liquid into a pumpable slurry, slurr /pump means for ■ taking said slurry from said mixing zone to a point of delivery, and a recycle connection between the slurry pump and a conduit leading towards said slurry pump, said eystem including selectively controllable swans for varying the delivery rate of said slurry pump.

2. Combination according to claim 1 wherein a single drive element supplies driving power simultaneously and selectively to said particle metering means, said liquid delivering means and said slurry pump means.

3. Combination according to claim 2 wherein a prime mover drives a jack ahaft directly and said jack shaft drives the metering means, liquid delivering means and pump means directly.

4. Combination according to claim 1 wherein the mixing means and the slurry pump are interconnected to insure operation of each whenever the other is operated independently of the operation of other parts.

5. Combination according to claim 1 comprising a recycle connection at the slurry pump which is variably controllable to vary the inventory of slurry in the mixing zone, thereby to control the time and degree of slurry mixing.

6. Combination according to claim 1 wherein the mixing means comprises a plurality of rotating bars movable between fixed bars to facilitate rapid formation of smooth, homogeneous explosive slurry with safety.

7. Combination according to claim 6 wherein the mixing means provides sufficient shear of said slurry to incorporate substantial aeration therein.

8. · Combination according to claim 1 which includes an air compressor and an air storage tank.

9. Combination according to claim 8 which includes an air operated clutch for driving the particle metering means.

10. Combination according to claim 1 which includes a fluid pump as a prime mover, fluid flow lines for the pumped fluid, and separate motors operable by said pumped fluid for driving respectively the particle .metering means, the liquid delivery means and the slurry pump*

11. Combination according to claim 1 which includes means for auto-? matically timing the operation of the metering 'means and the liquid delivery means.

12. Combination according to claim 1 which comprises a means for supplying a stream of water under pressure in addition to said liquid delivery means.

13. " 13. Combination according to claim 1 which comprises a plurality of said particle metering means, and means for variably controlling the respective delivery rates of said plural metering means to vary the proportions .of different particulate materials in the slurry.

14. Combination according to claim 1 which comprises means for removing fine dust from the mixing zone.

15. The method of preparing an explosive slurry comprised of a liquid containing oxidizer in solution and containing also undissolved suspended particles which are sufficiently reactive with said oxidizer to cause the Blurry to explode powerfully when detonated, said method comprising the steps o positively metering said particles at a selectively controlled rate, and delivering said liquid also at a selec- Λ tlvely controlled rate /to a mixing station* including a delayed action thickener material for said liquid in the slurry, mixing the liquid and the particles to form a smooth slurry in said station, withdrawing Blurry in a stream from said -station and pumping it to a ^ejlveryjppintf. and controlling both the inventory in the mixing station and the slurry delivery rate by recycling a selected portion of said withdrawn slurry stream, thereby to control physical properties of. the slurry.

16. Method according to claim 15 wherein aeration of the slurry is augmented by said recycling.

17. Method according to claim 15 which also comprises the step of homogenizing the slurry by substantial shear mixing before it is finally pumped to the delivery point.

18. Method according to claim 15 which comprises forcibly pumping a circulating driving fluid through a cycle and carrying out the metering and pumping steps by the driving action of said circulating fluid*

19. Method according to claim 15 which comprises mixing the liquid and the particles together simultaneously with the slurry delivery, and separately controlling the flow of the liquid and particulate ingredients to the mixing stage so that build-up of deposits in said mixing stage is substantially prevented. τ

20. Method according to claim 15 which includes substantially simultaneous and continuous mixing and slurry delivery while the supply of Ingredients is independently controlled, and wherein the supply of particulate solids is commenced after the mixing and delivery opera ations are initiated.

21. Method according to claim 15 wherein the mixing operation is conducted with sufficient vigor and shear to incorporate a substantial number of small air bubbles in the slurry, .here toj-reduce'½its"·density to a controlled degree. '