US2920923A - Slurry pipeline transportation - Google Patents

Description

Jan. 12, 1960 E. J. wAsP ETAL SLURRY PIPELINE TRANSPORTATION Original Filed April 14, 1958 4 Sheets-Sheet 1 TYLER SCREEN DESIGNATION FIG.

X (PARTICLE SIZE) zmumum Z0 owzzhwm 200 m0 .Zw0 mum FIG-m3 FIG. TYLER SCREEN DESIGNATION INVENTORS EDWARD J. WASP BY PAUL A.O. COOK THEIR ATTORNEY Jan. 12, 1960 E. J. WASP ET AL 2,

SLURRY PIPELINE TRANSPORTATION Original Filed April 14, 1958 4 Sheets-Sheet 2 JIJ IIIHIIIIII 11' 11 INVENTORS EDWARD J. WASP PAUL A. C. COOK THEIR ATTORNEY Jam-12, 1960 E. J. WASP ET Al. 2,920,923

SLURRY PIPELINE TRANSPORTATION Original Filed April 14, 1958 4 Sheets-Sheet 5 INVENTORS EDWARD J. WASP Y PAUL COOK B FZQWQ THEIR ATTORNEY Jan. 12, 1960 Original Filed April 14. 1958 E- J. WASP ETAL 2,920,923

SLURRY PIPELINE TRANSPORTATION 4 Sheets-Sheet 4 r l E (1' L 5 c 5 a m D 2 E m 2 D O.

O E R ,E

. 5 "1 i E E a o O n g t .1 IO 3 O. E g &'E o (L 0: T n F 0d INVENTORS w EDWARD J. WASP 3 y BY PAUL A. c. COOK I 522ml.

THEIR ATTORNEY United States Patent SLURRY PIPELINE TRANSPORTATION Continuation of application Serial No. 723,241, April 14, 1958. This application February 11, 1959, Serial No. 792,514

18 Claims. 01. 302-66) The present invention relates to pipeline transportation of slurries comprising finely divided solids suspended in a liqiud. More particularly, it relates to the transportation of slurries through pipelines having a length greater than about ten miles.

This application is a continuation of our co-pending application Serial No. 728,241, filed April 14, 1958, entitled Slurry Pipeline Transportation.

Certain hydraulic principles relating to pipeline transportation of aqueous coal slurry have been set forth in U.S. Patent 2,791,471. A commercial pipeline, embodying those hydraulic principles, has been constructed in Ohio. Bituminous coal which is mined in the southern portion of Ohio is transported 108 miles through that -inch diameter pipeline for consumption along the shore of Lake Erie in northern Ohio. The coal has a nominal top size of 14 mesh Tyler Standard screen, i.e., more than 95 percent of the coal will pass through a 14 mesh Tyler Standard screen and 100 percent of the coal will pass through the next larger Tyler Standard screen, to wit, an 8 mesh screen. This coal is mixed with an equal weightof water to comprise a 50 percent aqueous coal slurry. The coal slurry is pumped through the pipeline at a velocity from 4 to 7 feet per second. There are three pumping stations along the 108 mile pipeline. The first pumping station is located at the coal preparation end of the pipeline. The second pumping station is located 30 miles north of the inlet. The third pumping station is about 30 miles beyond the second pumping station. At the delivery terminal on the shores of Lake Erie, the coal slurry is recovered from the pipeline and is dehydrated both mechanically and thermally to provide low moisture content coal for consumption.

In the operation of this commercial coal slurry transportation pipeline, a hitherto unreported phenomenon has been discovered which tends to form plugs in long distance pipelines used for conveying slurn'es. While the phenomenon can be detected in an incipient form in short lengths of pipeline, nevertheless, the adverse effects of the phenomenon are cumulative with distance. The adverse effects are not manifested in short lengths of pipeline, e.g., less than about ten miles in length. A positive plug forming tendency is manifested in longer pipelines, e.g., 30 miles and longer when size distribution and pumping velocities are so interrelated that a settling tendency exists,

The object of the present invention is to provide a method for operating long distance slurry transportation pipelines without encountering plugging difficulties. A

further object is to provide a, method for intermittent line following the. main slurry slug to prevent settling of slurry particles as a trail behind the main slurry slug. In both instances, the fluid material differs in composition from the main slurry slug and from the liquid component of the slurry.

In order to explain the present invention, certain principles of slurries in general and of pipeline slurry transportation in particular must be described. These principles will be set forth in connection with the accompanying drawings in which:

Figure 1 is an idealized graphical illustration in the form of the familiar bell-shaped Poisson distribution curve illustrating the statistical distribution of particle sizes occurring in a sample of comminuted solids.

Figure 2 is a simplified Rosin-Rammler plot on special coordinates which have been designed to represent the particle size-weight relationship of comminuted coal by means of a straight line (US. Bureau of Mines Information Circular 7346, February 1946).

Figures 3, 4, 5 and 6 are exaggerated illustrations of settling properties of slurries under static conditions.

Figures 7, 8 and 9 are exaggerated illustrations of settling phenomena which occur at the forward end of a slug of slurry moving through a pipeline.

Figures 10 and 11 are exaggerated illustrations of the forward end of a slug of slurry moving through a pipeline when the present invention is employed.

Figures 12, 13 and 14 are exaggerated illustrations of the settling properties of the tail end of a slug of slurry moving through a pipeline.

Figures 15 and 16 are exaggerated illustrations of the tail end of a slug of slurry moving through a pipeline when a further embodiment of the present invention is employed.

Figure 17 is a schematic illustration of apparatus at the inlet terminal of a slurry transportation pipeline adapted to the practice of the present invention.

Figure 18 is a schematic illustration of the principal elements in a commercial coal slurry transportation pipeline.

The term slurry is customarily applied to describe a uniformly dispersed mixture of finely divided solid particles in a liquid.

It is Well known that a comminuted solid material will contain particles whose sizes follow a statistical distribution by weight according to the familiar bell-shaped distribution curve as illustrated in Figure 1. In Figure 1, the function is plotted against x where W is the weight of solids and x is the particle sizes of solids. The function follows the Poisson distribution curve represented in an idealized form as the cure A. The actual distribution curve may be somewhat skewed as in the dotted line curve B. Rosin and Rammler The Laws Governing the Fineness of Powder Coal, Journal Institute of Fuel, October 1933, 2936. The actual shape of the curve may vary from the idealized curve A according to the friability of the particular material, the method of comminution, the screen analysis techniques, et cetera. The actual shape of the distribution curve need not concern us at the moment. Once the shape of the curve has been determined we can calculate the percentage of a sample of the comminuted material within designated particle size limits. For example, in Figure 1, the ratio of the crosshatched area under the curve A to the total area under the curve A is that fraction of the finely divided solids (whose distribution is represented by the curve A) which will pass through a 28 mesh screen and be retained on a 48 mesh screen. The same mathematical manipulation techniques can be applied to the skewed relationship curve, for example, the curve B, as to the idealized relationship curve A.

An ad hoc coordinate system has been devised for representing comminuted coal particle size distribution. US. Bureau of Mines Information Circular 7346, February 1946. When these coordinates are employed, a normal particle size distribution can be represented by a straight line. The oversize screen fractions may be read directly without requiring integration of areas beneath a curve, as required when the familiar bell-shaped distribution curve of Figure 1 is employed.

A portion of a chart prepared according to this ad hoc coordinate system has been copied in Figure 2. The straight line C in Figure 2 illustrates the particle size distribution of a sample of comminuted coal having about 1.5 percent of material which is retained on a 14 mesh Tyler Standard screen and having about 33 percent of material which would pass through a 100 mesh Tyler Standard screen. The actual size distribution might depart from the straight line C where additional fines are added to the starting coal as shown at D. Where fines are selectively stripped from the coal, the actual size distribution might depart from the straight line C as shown by the dotted line E.

The principle to be obtained from the discussion to this point is that any sample of comminuted solid particles contains a whole spectrum of particle sizes ranging from the coarsest individual particles down through sub-micron and colloidal size particles. The relative distribution of particle sizes between the extremes will vary in accordance with well-known statistical principles.

Thus when comminuted solid particles are mixed with a liquid to form a slurry, the slurry will contain the entire spectrum of particle sizes.

Referring now to Figure 3, we have there illustrated in an exaggerated fashion a freshly prepared slurry of finely divided solids and liquids. If allowed to stand without disturbance, the particles will tend to settle downwardly in the liquid under the influence of gravity, provided that the solids have a greater density than the liquid.

If only particles of a relatively large size were admixed with the liquid to form a slurry, these particles would settle very quickly to the bottom of the container leaving behind a supernatant clear liquid layer as shown in Figure 4.

On the other hand, if the relatively coarser particles were eliminated from the slurry, the settling tendency of the remaining fine particles under the influence of gravity would be very slight. The sub-micron and colloidal particle sizes would have virtually no tendency to settle-a principle well known in colloidal phenomena. While settling of the particles ultimately would occur, a settling period of significant duration would be required. This is illustrated in an exaggerated manner in Figure 5. The very fine particles actually coact with the liquid to form what is in elfect a different fluid which possesses the properties of a Newtonian fluid having a greater density and viscosity than the liquid component of the slurry. Hereinafter this material will be designated a pseudo fluid for distinguishing purposes.

Now referring back to Figure 3, the slurry which comprises the entire spectrum of particle sizes will exhibit settling tendencies of the type shown in both Figure 4 and Figure 5. The composite settling tendencies are illustrated in an exaggerated manner in Figure 6. As shown in Figure 6, the very fine particles of comminuted solids tend to form a higher viscosity and higher density pseudo fluid in combination with the liquid components of the slurry. The settling tendency of the very fine particles in the pseudo fluid is about the same as that illustrated in Figure 5. The relatively coarse particles, however, must now settle out downwardly under the influenceof gravity through the pseudo fluid. Since this '4 pseudo fluid has a greater density and a greater viscosity than the liquid alone, a significantly greater static settling time is required for. the relatively coarse particles as shown in Figure 6. In other words, the pseudo fluid exerts a suspending influence on the relatively coarse particles of solids which is substantially greater than the suspending force exerted by the liquid alone. Contrast Figure 4 and Figure 6.

The principle to be obtained from this discussion is that a slurry containing comminuted solids from an entire particle size spectrum can be considered as a suspension of the relatively coarser particles in a pseudo fluid :hich comprises the liquid and the relatively finer particles, This pseudo fluid has a much greater suspending property for the relatively coarse particles than does the liquid alone. It is this interaction of solid particles throughout the entire spectrum which makes possible the transportation of slurries comprising comminuted solids in a liquid. The interaction prevents particle settling resulting from gravity. Thenominal top size of the comminuted solid particles determines a minimum pipeline velocity for each particular type of solids which is required to prevent settling of the moving solids to the bottom of the pipeline under the influence of gravity. This determined velocity is referred to as the minimum non-settling velocity.

Expressed in different language, the transportation of slurries is made possible by the existence of turbulent eddy currents which continually resuspend the coarser particles of the slurry. A high viscosity and density fluid requires a lower quantity of force to be imparted by the turbulent eddy currents. Thus, with higher density and viscosity of the pseudo fluid, the minimum nonsettling velocity is lowered. Hence, the interaction of solid particles throughout the entire spectrum of particle sizes depends upon a turbulent flow condition.

The nominal top size for comminuted solids is that screen size through which substantially all of the solids will pass. Conveniently it corresponds to the top intercept on the coordinate plot shown in Figure 2.

Where the finely divided solids are coal having a nominal top size in the range of 28 mesh to 6 mesh Tyler Standard screen, the minimum non-settling velocity for aqueous slurries (35 to 55 percent coal) is in the range from about 3 /2 to 7 feet per second. The coarser slurries have higher minimum settling velocities.

The phenomenon with which the present invention is concerned will now be explained by reference to Figures 7, 8 and 9 which are exaggerated illustrations of a slurry moving through a slurry transportation pipeline. To simplify the discussion, the slurry will be assumed to be comminuted coal suspended in water at a concentration of 35 to 55 percent by weight of coal.

Once the slurry pipeline is constructed, it is initially filled with water from one end to the other. The slug of clear water is indicated by the numeral 10. Thereupon the coal slurry, indicated by the numeral 11, is introduced into the pipeline. As shown in Figure 7, the boundary between the slug of clear water 10 and the slug of slurry 11 is sharply defined. This condition exists immediately following the introduction of the slurry slug 11. I

However, as the slurry moves through the pipeline, the boundary between the slurry slug 11 and the clear water slug 10 becomes less sharply defined as intermixing of the two fluids occurs. The zone of intermixing is indicated in Figure 8 by the numeral 12. The solid particles within the coal slurry do not move forwardly through the pipeline at exactly the same velocity as the water which comprises the slurry. Instead, the solid particles experience a certain slip and consequently lag behind the water portion. This slip factor combined with the turbulence of the moving fluids causes the zone of intermixing 12 to increase in length as the slurry slug 11 moves for greater distances through the pipeline. The zone of intermixing 12 may be several thousand feet long when the coal slurry has moved coal slurry (i.e., the pseudo fluid as illustrated in Fig ure 6), but instead are supported almost entirely by water alone (similar to the condition illustrated in Figure 4). Accordingly, the solid particles in the zone of intermixing 12 have a positive tendency to settle downwardly against the bottom of the pipe under the influence of gravity. Since the zone of intermixing 12 may extend for distances of several thousand feet along the pipeline, a substantial quantity of solid particles which have infiltrated into the zone of intermixing 12 will settle to the bottom of the pipeline. Settling occurs when the particle slippage relative to the liquid increases.

As the slurry slug 11 continues in its passage through the pipeline, it is continuously following the zone of intermixing 12. The slurry slug 11 contains the pseudo fluid (as shown in Figure 6) which has a substantial suspending power. The slurry slug 11 accordingly will suspend the particles of settled coal which have already been deposited on the bottom of the pipeline from the zone of intermixing 12. The settled solids which thus are resuspended by the slurry slug 11 increase the concentration at the head of the slurry slug 11. A zone of increased concentration 13 is formed at the head of the slurry slug 11 as shown in Figure 9.

Coal slurries in concentrations of 57 to 58 percent by weight of coal are too concentrated to move in a turbulent manner. Instead the highly concentrated slurries exhibit almost no relative motion between the particles. These highly concentrated slurries move through a pipeline in what has been called plug flow. Plug flow results in an extremely high pressure drop per unit length of travel. Moreover, the factors which promote plug formation, if allowed to continue, will eventually form a highly concentrated solids bridge across the pipeline and prevent further movement of the slurry therethrough.

According to the present invention as illustrated in Figures and 11, plug formation conditions can be avoided during the introduction of coal slurry into a transportation pipeline. As illustrated in Figure 10, the slug of clear water 10 is maintained initially in the pipeline as before. Thereafter a slug of pseudo fluid having a greater suspending power than water is introduced into the pipelline. This slug of pseudo fluid is designated by the numeral 14. Preferably the pseudo fluid slug 14 should have a suspending power for the comminuted solids which is about equal to that of the pseudo fluid formed by the water and the very fine coal particles (as illustrated in Figure 5). Immediately following the pseudo fluid slug 14, the slurry is introduced into the pipeline. The slurry slug is designated by the numeral 11.

The length of the slug of pseudo fluid 14 should be sufficient to accommodate all intermixing between the clear water slug 10 and the slurry slug 11. As the pseudo fluid slug 14 progresses through the pipeline, it will intermix at its forward end with the clear water slug 10 to form a zone of intermixing 15. As the slurry slug 11 is introduced into the pipeline, there will be initially a sharp dividing boundary between the pseudo fluid slug 14 and the slurry slug 11 as shown in Figure 10.

However, as the slurry slug 11 proceeds through the pipeline, a zone of intermixing 16 will develop and extend between the slurry slug 11 and the pseudo fluid slug 14. Within the zone of intermixing 16, the solid particles, which are separated from the main slurry slug 11 have entered into the pseudo fluid slug 14 which hasthe same suspending power which the solid particles encountered within the slurry slug 11 itself As a result there is no loss of suspending force. Alternatively expressed, there is no increase in the tendency of the separated slurry particles in the zone of intermixing 16 to settle to the bottom of the pipline. As a consequence, the separated slurry particles in the zone of intermixing 16 continue to advance through the pipeline while suspended in the pseudo fluid slug 14. As the slurry slug 11 continues its travel through the pipeline it does not encounter settled solid particles which it can resuspend to form highly concentrated plugs (as shown in Figure 9). Hence the phenomenon of increasing concentration at the head of the slurry slug is avoided by the present invention.

For the purposes of convenience, this pseudo fluid slug 14 is termed a cap preceding the main slurry slug 11. The inherent properties of the cap are as follows:

(1) It should possess a greater suspending power for comminuted solids than does the liquid comprising the clear liquid slug 10.

. (2) It should possess a suspending power for comminuted solids which is about equivalent to that confronting the solids in the slurry slug 11.

(3) Preferably it should not leave any deposit within the pipeline.

(4) It should not introduce any major complications into the dewatering treatment at the discharge end of the pipeline.

(5) It should be relatively inexpensive and readily available in substantial quantities.

The preferred composition of. the cap in the present invention is a slurry comprising a selective fine fraction of the same solids which make up the main slurry slug 11. This selected fine fraction of solids preferably is suspended in the same liquid which comprises the main slurry slug 11. The concentration of the selected fine fraction of solids in the liquid should be somewhat higher than the concentration of this same selected fine fraction in the main slurry slug.

For example, a typical nominal 14 mesh top size coal slurry containing about 1.5 percent by weight of particles which will be retained on a 14 mesh Tyler Standard screen will contain about 30 to 35 percent by weight of particles capable of passing through a mesh Tyler Standard screen (see Figure 2). A preferred cap" for use with a slurry containing such a nominal 14 mesh top size coal would be a 30 to 45 percent by weight aqueous suspension of particles having a nominal top size in the range of 48 mesh to 100 mesh Tyler Standard screen and containing less than about 10 percent by weight of coal which can be retained on a 100 mesh Tyler Standard screen.

The length of the cap will vary with the length of the pipeline. Since the plug formation tendency is a cumulative phenomenon (with distance), the problem of plug formation as herein described is not manifested in pipelines having a length of less than about ten miles. Accordingly, such pipelines do not require the use of cap for satisfactory operation. For longer distance pipelines with which the present invention is concerned, the cap length should be sufficient that no intermixing occurs between the clear liquid slug 10 and the slurry slug 11.

In general, the cap length can be related to the pipeline transportation distance as follows:

C=(300 to 500) D- where C=cap length (in feet) and D=pipeline distance (in miles).

For a 30-mile pipeline, a cap of 2300 to 3850 feet is suitable. A cap about 3200 feet in length provides a 30 percentsafety margin. For a IOO-mile pipeline, a cap of 4750 to 7900 feet is suitable.

As alternative compositions which may be used for the cap, virtually any liquid having a greater (density times viscosity) product than that of the clear liquid slug is considered suitable. For example, aqueous sols containing up to about percent by weight of carboxymethylcellulose are suitable for use as caps. Aqueous sols of gelatin, soluble starch or bone glue similarly are suitable provided that these materials do not present a disposal problem at the slurry dewatering terminal. Heavy liquids such as carbon tetrachloride would be suitable.

A second problem manifested in pipeline transportation of slurries of comminuted solids is associated with the trailing end of the slurry slugs. Ideally, of course, a slurry transportation pipeline system is operated continuously, i.e., 24 hours daily at constant velocity. There are occasions nevertheless where it is desirable or necessary to interrupt the flow of slurry through the pipeline. In order to purge the pipeline of finely divided solids, it is desirable to introduce a slug of clear liquid behind the slurry in order to maintain the pipeline filled at all times. Where the pipeline is constructed of ordinary carbon steel, for example, the entry of air pockets into the pipeline would create an objectionable corrision-inducing environment.

As shown in Figures 12, 13 and 14, a tailing-out phenomenon occurs at the boundary between a slug of moving slurry and a following slug of clear liquid. Referring to Figure 12, the slurry slug 17 has entered the pipeline and a slug of clear liquid 18 has been introduced behind the slurry. Initially a sharply defined boundary exists between the two slugs.

Referr ng to Figure 13, as the slurry slug 17 advances through the pipeline, a zone of intermixing 19 develops between the slug of slurry 17 and the slug of clear liquid 18. Comminuted solids in the tail portion of the slurry slug 17 slip backwardly into the zone of intermixing 19 where they are no longer exposed to the same suspending force which exists in the main body of the slurry slug 17. Accordingly, there is a tendency for the comminuted solids in the zone of intermixing 19 to settle downwardly into the bottom of the pipeline. The particles which settle out form a zone 20 and remain undisturbed on the bottom of the pipeline. The slug of clear water 18 passes over the settled particles since it has insuflicient suspending power to raise them from the bottom of the pipeline. This is shown in an exaggerated manner in Figure 14 where the zone 20 containing settled particles ultimately would extend over a substantial length of the pipeline. It would be possible to remove the settled particles from the pipeline after the preceding slurry slug has been completely transported through the pipeline. This can be accomplished by purging the entire line with a subsequent clear liquid slug moving at an increased velocity, for example, 6 to 10 feet per second (where the minimum non-settling velocity is 3.5 to 7 feet per second). This purging technique requires pump operation and clear liquid movement without accompanying slurry transportation. Thus, while effective, it is not considered economically feasible.

While the deposited bed of particles in the zone 20 does not disturb or interfere with the movement of the slurry slug 17 out of the pipeline, nevertheless, the bed of particles in the zone 20 presents a formidable problem when a subsequent slug of slurry is introduced into the pipeline.

It would be possible to compensate for the settled particles by providing a cap of substantially increased length preceding the subsequent introduction of a slurry slug. The substantially longer cap of pseudo fluid would have sufficient suspending power and capacity to pick up and convey out from the pipeline all of the settled particles in the zone 20. The zone 20, of course, extends over a substantial length of the pipeline after the preceding slurry slug has been pumped out.

According to the present invention, the tailing-out phenomenon just described in connection with Figures 12, 13 and 14 can be overcome successfully by providing a slug of pseudo fluid immediately behind the slurry slug.

, Referring to Figure 15, the slurry slug 17 is followed immediately by a pseudo fluid slug 21 which in turn is followed by a clear liquid slug 13. Initially a rather sharp boundary is defined between the pseudo fluid slug 21 and the slurry slug 17. boundary exists between the clear water slug 18 and the pseudo fluid slug 21.

the pipeline slurry transportation proceeds, a zone of intermixing 22 develops (as shown in Figure 16) between the slurry slug 17 and the pseudo fluid slug 21. Similarly a zone of intermixing 23 develops between the pseudo fluid slug 21 and the clear liquid slug 18. The length of the pseudo fluid slug 21'should be sufficient to avoid intermingling of the two zones of intermixing 22 and 23.

The suspending power of the pseudo fluid slug 21 is equivalent to that which exists within the slurry slug 17 itself. Accordingly, there is substantially no tendency for the particles in the zone of intermixing 22 to settle downwardly in the pipeline. Thus, the solid components of the slurry can be eliminated from the pipeline without substantial settling.

For the purpose of convenience, the term chaser" is applied to the pseudo fluid slug 21 which is introduced into the slurry transportation pipeline following a slurry slug. In general, the chaser should have the same properties as the cap. These properties already have been set forth.

Chasers find particular utility where it is desirable or necessary to terminate flow operations in a slurry transportation pipeline intermittently. For example, where difiiculties arise in the slurry preparation or dewatering terminal, it may be necessary that the flow of slurry through the pipeline be discontinued. Thus it may be necessary to cease operations while the pipeline is, for the most part, filled with slurry. These temporary shutdowns with the line filled with slurry can be conducted without difliculty where the slurry slug is preceded by a,

cap and followed by a chaser.

Apparatus for carrying out pipeline slurry transportation according to this invention is schematically illustrated in Figure 18.

A supply of coal slulry as described in the aforementioned US. Patent 2,791,471 is provided in a surge vessel 30. A source of clear water is provided, as, for example, a pump 31. A supply of pseudo fluid having a greater particle suspending property than water is provided in a surge vessel 32.

A valved conduit 33 extends from the surge vessel 30; a valved conduit 34 extends from the water pump 31; a valved conduit 35 extends from the surge vessel 32. The conduits 33, 34 and 35 communicate with a manifold conduit 36.

Alternate slurry pumps 37 are provided with valved conduit connections 38 to the manifold conduit 36. One of the pumps 37 serves as an emergency spare while the other is in actual pumping operation. The discharge flow from the pump 37 passes through valved conduit 39 into the transportation pipeline proper 40.

T o fill the pipeline 40 with water, the conduits 33 and 35 are closed. The conduit 34 is opened and water is introduced to the operating pump (of the pair 37) for- The 108 mile long commercial coal pipeline described in the introduction of this specification is illustrated schematically in Figure 18. A first pump 50 is provided at the pipeline inlet. 51 a second pump 52 is provided. Thirty miles thereafter Similarly, a sharply defined Thirty miles along the pipeline a third pump 53. is provided which movesthe coalslurry the remaining 48 miles to a dewatering terminal 54 where the coal is freed from the water.

Example of deposition and plug formation 1 Twopipeline runs were attempted without caps? or chasers. In each run the coal had the following screen analysis:

Screen size: Weight percent Retained on 8 mesh 0.2 10 Through 8 mesh on 14 mesh 10.3 Through 14 mesh on 28 mesh 37.1 Through 28 mesh on 48 mesh 30.0 Through 48 mesh on 100 mesh 13.1 Through 100 mesh on 200 mesh 3.1 15 Through 200 mesh on 325 mesh 1.0 Through 325 mesh 5.2

Run 1.The entire pipeline was filled with water. 38,700 gallons of 37 weight percent concentration coal slurry was pumped into the line. The slurry contained 20 tons of coal and extended as a slug in the pipeline for 0.54 mile. Thetransportation velocity was 4.5 feet per second. The pipeline was opened at the third pumping station (60 miles from the inlet).

Analysis of samples at the second pumping station showed that only 10 tons of coal passed beyond the second pumping station. Only 9.3 tons of coal were recovered at the third pumping station.

Thus ten tons of coal were deposited in the pipeline between the inlet and the second pumping station. Only 0.7 ton of coal was deposited in the line between the second and third pumping station.

The short slug of unusually coarse coal slurry was entirely intermixed with water in which the coal experienced little suspending force. Hence severe deposition resulted.

Run 2.-l66,000 gallons of similar coal slurry (42 weight percent concentration) was introduced into the pipeline filled with clear water. The slurry contained 375 tons of coal in a slug 8.1 miles long. The slurry slug was followed by clear water moving at 4.5 feet per second. The slurry slug plugged the pipeline when its head had traveled 27 miles, i.e. no coal reached the second pumping station.

Immediately prior to plug formation, the pressure in 45 the pipeline rose and fell erratically. At shutdown conditions, the pressure rose to a level of 1200 p.s.i.g. to open a relief valve which automatically terminated pumping.

The results of run 2 demonstrate the plug formation phenomenon which occurs in long distance slurry pipelines. Neither cap nor chaser was employed in run 2.

Examples of caps and chasers 5 Two pipeline runs were completed over the entire 108 a mile length of commercial pipeline. In each run the coal slurry slug was preceded by a cap and followed by a chaser. l

The coal slurry comprised coal having the following screen analysis:

Through 325 mesh 14.5

In one run the cap comprised an aqueous sol containing 1 to 1.5 percent of carboxymethylcellulose.

An aqueous slurry of relatively fine coal comprised the cap in the other run and also comprised the chaser-s in 10 both runs. The relatively fine coal had the following screen analysis: a

Screen size: Weight percent Retained on 14 mesh 0.0 Through 14 mesh on 28 mesh 0.5 Through 28 mesh on 48 mesh 1.2 Through 48 mesh on mesh 6.6 Through 100 mesh on 200 mesh 19.5

Through 200 mesh on 325 mesh 18.7 Through 325 mesh 53.5

Run 3.The coal pipeline was filled with clear water. 25,000 gallons of aqueous carboxymethylcellulose sol was introduced into the line behind the clear water as a cap 1.2 miles long.

Thereafter 54,500 gallons of coal slurry containing 119 tons of coal (49 weight percent concentration) was introduced into the line as a slurry slug 2.65 miles long.

Following the slurry slug, 31,500 gallons of aqueous suspension of relatively fine coal was introduced into the pipeline as a chaser 1.5 miles long. The chaser contained 43 tons of coal in a concentration of 28.8 weight percent.

Clear water was introduced into the pipeline at a velocity of 4.5 feet per second behind the chaser. The entire shipment of coal traveled the 108 mile length of the pipeline'and was recovered at the dewatering terminal.

Run 4.-23,800 gallons of relatively fine coal in aqueous suspension was introduced into the water filled pipeline as a cap 1.16 miles long. The cap contained 43.3 tons of coal in a concentration of 38.8 Weight percent.

Thereafter 66,790 gallons of coal slurry containing 156.8 tons of coal (49.1 weight percent concentration) was introduced into the line as a slurry slug 3.3 miles long.

Following the slurry slug 36,430 gallons of relatively fine coal in aqueous suspension was introduced into the line as a chaser 1.8 miles long. The chaser contained 64 tons of coal in a concentration of 38.8 weight percent.

Clear water was introduced into the pipeline at a velocity of 4.5 feet per second behind the chaser. The entire shipment of coal traveled the 108 mile length of the pipeline and was recovered at the dewatering terminal.

Example of deliberate pipeline shutdown Run 5 .22,400 gallons of relatively fine coal in aqueous suspension was introduced into the water filled pipe- 0 line as a cap 1.1 miles long. The cap contained 43.3 tons of coal at a concentration of 36.6 weight percent.

Thereafter 45,200 gallons of coal slurry containing 105.6 tons of coal (48.7 weight percent concentration) was introduced into the pipeline as a slurry slug 2.3 miles long.

Immeditely thereafter, the pumping was terminated and the contents of the pipeline were allowed to settle for eight hours.

Following the eight hour shutdown, 25,300 gallons of relatively fine coal in aqueous suspension was introduced into the pipeline as a chaser 1.2 miles long. The chaser contained 40 tons of coal in a concentration of 43.1 weight percent.

Clear water was introduced into the pipeline behind the chaser at a velocity of 4.5 feet per second. The entire coal shipment was delivered at the slurry dewatering terminal.

The run demonstrates that the presence of a cap in advance of a slurry slug will permit shutdown of a slurry transportation pipeline while slurry is in transit.

I Commercial operation Run 6.The described commercial pipeline has a volume from end to end of about 2,224,000 gallons. When slurry is introduced at the rate of 1060 gallons per min 11 u'te', the'elapsed time for transit through the entire pipeline is about 35 hours.

A cap comprising fine coal slurry is prepared to the following specifications:

Solids content 35 to 40 weight percent. Particles retained on a 48-mesh screen Less than 2 percent. Nominal top size 100 mesh.

The cap material is pumped into the water filled pipeline at about 1060 gallons per minute for at least 15 minutes, i.e., approximately 4.5 feet per second linear velocity. An average cap comprises 18 to 20 minutes of pumping time and contains from about 30 to 35 tons of coal.

Thereafter the main body of aqueous coal slurry is introduced at a rate of about 1060 gallons per minute.

One typical run encompassed a slurry pumping period of 246.1 hours duration during which 35,801 tons of coal were transported. The pipeline operated without incident.

A typical chaser has the same properties just described for the cap material. In actual operation, the chaser is pumped for at least five minutes at a rate of about 1060 gallons per minute, preferably for at least 15 minutes.

General While the examples in this specification describe transportation of aqueous coal slurries, it is evident that the newly discovered hydraulic phenomenon herein reported applies to any slurry of comminuted solids in a liquid. The principles herein set forth pertain to slurries having liquids other than water as one component.

According to the provisions of the patent statutes, we have explained the principle, preferred construction and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may bepracticed otherwise than as specifically illustrated and described. a

We claim:

1. In the method of transporting through a pipeline at least ten miles long a slurry of comminuted solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, the improvement for avoiding plug formation comprising introducing into said pipeline a slug of pseudo fluid having a solids suspending property greater than that of said liquid of said slurry, and thereafter introducing said slurry into said pipeline.

' 2. The improvement of claim 1 wherein the pseudo fluid consists essentially of a liquid containing finely divided solids suspended therein.

3. The improvement of claim 1 wherein the pseudo fluid consists essentially of a liquid having suspended therein finely divided solids of the same material which comprises the slurry.

4. The improvement of claim 1 where in the pseudo fluid comprises aqueous carboxymethylcellulose.

5. The improvement of claim 1 wherein the slurry comprises coal in water.

6. In the method of transporting through a pipeline at least ten miles long a slurry of comminuted solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, the improvement for avoiding plug formation comprising filling the pipeline with a liquid, introducing into said pipeline a slug of pseudo fluid having a solids suspending property greater than that of said liquid of said slurry, and thereafter introducing said slurry into said pipeline.

7. In the method of transporting through a pipeline at least ten miles long a slurry of comminuted solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, theimproveabsc ssa 12 ment for avoiding plug formation comprising introducing into said pipeline a slug of pseudo fluid having a solids suspending property greater than that of said liquid of said slurry, thereafter introducing said slurry into said pipeline, introducing a second slug of pseudo fluid into said pipeline immediately behind said slurry and there after introducing a liquid into said pipeline.

8. In the method of transporting through a pipeline at least ten miles long a slurry of comminuted solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, the improvement for avoiding plug formation comprising filling the pipeline with a liquid, introducing into said pipeline a slug of pseudo fluid having a solids suspending property equivalent to that of said slurry, thereafter introducing said slurry into said pipeline, introducing a second slug of pseudo fluid into said pipeline immediately behind said slurry, and thereafter introducing a liquid into said pipeline.

9. In the method of transporting through a pipeline at least ten miles long a slurry of comminuted solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, the improvement for avoiding plug formation comprising introducing into said pipeline a slug of pseudo fluid having a solids suspending property substantially equivalent to that of said slurry, and thereafter introducing said slurry into said pipeline.

10. In the method for avoiding plug formation while transporting through a pipeline at least ten miles long a slurry of comminuted solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, the steps comprising introducing a slug of pseudo fluid into a pipeline filled with a liquid, said pseudo fluid having a solids suspending property greater than that of said liquid in said pipeline, and thereafter introducing said slurry into said pipeline.

11. In a method for avoiding plug formation while transporting through a pipeline at least ten miles long a slurry of comminuted solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, the steps comprising introducing a slug of pseudo fluid into a pipeline filled with water, said pseudo fluid having a solids suspending property greater than that of said water, and thereafter introducing said slurry into said pipeline.

12. In a method for avoiding plug formation while transporting through a pipeline at least ten miles long a slurry of cornminuated solids in a liquid in which said solids have a tendency to settle downwardly under the influence of gravity, which method comprises introducing a slug of pseudo fluid into a pipeline filled with water, said pseudo fluid having a solids suspending property greater than that of said water, thereafter introducing said slurry into said pipeline,,introducing a second slug of pseudo fluid into said pipeline immediately behind said slurry, and thereafter introducing water into said pipeline.

i 13. In the method of transportating coal through a pipeline at least ten miles long which comprises comminuting the coal to a nominal top size in the range of 6 mesh to 28 mesh Tyler Standard screen, preparing an aqueous slurry containing 35 to 55 percent by weight of the comminuted coal having less than 25 percent by weight of particles which are retained on a 14 mesh Tyler Standard screen, and conveying said slurry through said pipeline at a velocity of 4 to 7 feet per second, the improvement for avoiding plug formation comprising introducing into said pipeline a slug of pseudo fluid having a solids suspending property substantially equivalent to that of said slurry, thereafter introducing said slurry into said pipeline in a continuous slug, and recovering coal from said pipeline as a continuous slug of slurry.

14-, In the method of transporting coal through a ipeline at least tenmiles long which comprises comminuting the coal to a nominal top size in the range of 6 mesh to 28 mesh Tyler Standard screen, preparing an aqueous slurry containing 35 to 55 percent by weight of recovering coal from said pipeline as a continuous slug of slurry.

15. The improvement of claim 14 wherein the pseudo fluid is an aqueous suspension of 30 to 45 percent of coal having a nominal top size in the range of 48 mesh to 100 mesh Tyler Standard screen, and containing less than 10 percent by weight of coal which can be retained on a 100 mesh Tyler Standard screen.

16. The improvement of claim 14 wherein the slug of pseudo fluid has a length (in feet) which is from 300 to 500 times the length of the pipeline (in miles) raised to the 0.6 power.

17. In the method of transporting coal through a pipeline at least ten miles long, which comprises comminuting the coal to a nominal top size in the range of 28 mesh to 6 mesh Tyler Standard screen, preparing an aqueous slurry containing to percent by weight of the comminuted coal having less than 25 percent by weight of particles which are retained on a 14 mesh Tyler Standard screen, and conveying said slurry through said pipeline at a velocity of 4 to 7 feet per second, the improvement for avoiding plug formation comprising introducing a slug of pseudo fluid into a pipeline filled with water, said pseudo fluid having a solids suspending property greater than that of said water, thereafter introducing said slurry into said pipeline in a continuous slug, introducing a second slug of pseudo fluid having a greater solids suspending property than said water into said pipeline immediately behind said slurry, and thereafter introducing Water into said pipeline in a continuous slug.

18. The improvement of claim 17 wherein at least one slug of pseudo fluid comprises an aqueous suspension of 30 to 45 percent of coal having a nominal top size in the range of 48 mesh to mesh Tyler Standard screen and contains less than 10 percent by weight of coal particles which can be retained on a 100 mesh Tyler Standard screen.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,920,923 I January 12, 1960 Edward J. Wasp et al. It is hereby certified that error. appears in the printed specification of the above numbered patent requiring correction and that the said Letters patent should read as corrected below.

Column 1, line 17, for "liqiud" read liquid column 2, line 54, for "cure A" read curve A column 5, line 51, for pipelline read pipeline column 12, line 49, for -comminuated" read comminuted Signed and sealed this 12th day of July 1960.

(SEAL) Attest: KARL H. AXLINE ROBERT c. WATSON Attesting; Officer Cormiissioner of Patents

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