Conveying of Cement and Drilling Mud Powders - Freenguyen.hong.hai.free.fr/EBOOKS/SCIENCE AND ENGINEERING/ENGIN… · Cement and Drilling Mud Powders 385 Once again a high pressure

13Conveying of Cement and DrillingMud Powders

1 INTRODUCTION

Cement is another commodity that is manufactured on a large scale and, by thenature of the material, uses pneumatic conveying systems extensively for its con-veying. Because of its use in the construction industry it is distributed internation-ally, nationally and locally. Large bulk carriers are used for international transportand a wide range of ship loading and off-loading systems have been used and de-veloped over the years. Large and small scale storage depots are used for its distri-bution nationally, with inland locations generally supplied by rail wagons, andcoastal locations, often based at existing ports, supplied by self off-loading ships.Local distribution is normally by specialized road vehicles, generally capable ofbeing pressurized for self off-loading directly into storage silos.

Most large countries around the world have at least one cement manufactur-ing plant, and there are close to thirty countries with a manufacturing capability inexcess of 10,000,000 ton/year. Economy of scale is such that individual plants arerarely built to produce less than about one million ton per year.

1.1 Material Grade

Although the problem of material grade having an influence on the conveyingcapability of the material does exist with cement, it is not the major problem that it

Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

380 Chapter 13

is with most other materials. Grade can vary with cement and it can have a secon-dary effect, but is rarely to a degree that the material cannot be conveyed in densephase. Cement is manufactured to standards and these are based on fineness. Aconvenient means of determining the degree of fineness is by measuring perme-ability, from which the specific surface of a material can be ascertained.

The most common device used is that devised by Blaine, and as a conse-quence the Blaine number is generally used as the international reference for thefineness of cement. The finished product is produced by grinding and so the finerthe cement the greater the cost. Cement is always manufactured to a fineness thatwill allow the material to be conveyed in dense phase and at low velocity in aconventional pneumatic conveying system.

The influence of Blaine number on the conveying capability of cement,however, is not known. In Chapter 10 it was shown that the conveying capabilityof fine fly ash could vary by a significant degree for just small changes in meanparticle size. It is suspected that cement will be similarly effected, but not neces-sarily in the same way, for the particle shape of cement is very different from thatof fly ash.

1.2 Materials Considered

Two types of cement are considered; ordinary Portland and oil well cement. Theoil and gas industry, in addition to using oil well cement also uses large quantitiesof barite and bentonite and so these materials are also included here. For drillingpurposes they are produced as fine powders and so these materials also have verygood air retention properties.

As a consequence these materials can also be conveyed in dense phase andat low velocity in conventional pneumatic conveying systems, provided that thepressure gradient available for conveying is sufficiently high to convey at thevalue of solids loading ratio required.

All four of these materials have been conveyed through the Figure 12.11pipeline and so their conveying characteristics are presented together for referenceand comparison in Figure 13.1. The pipeline was of two inch nominal bore, 230feet long and incorporated nine 90° bends.

The materials were fed into the pipeline by means of a high pressure topdischarge blow tank. 200 ftVmin of free air was available for conveying. The bar-ite had a mean particle size of about 12 micron, a bulk density of about 100 lb/ft3

and a particle density of approximately 265 lb/ft3. For the bentonite these figureswere 24 micron, 50 and 145 lb/ft' respectively.

It will be seen that there are only very slight differences between the ordi-nary Portland and the oil well cements, and the barite was also very similar in per-formance. Only with the bentonite is there any real difference in conveying per-formance. This material did not exhibit any pressure minimum effect, and so asthe material flow rate increased continuously with reduction in air flow rate, therewas a very significant difference in performance at low values of air flow rate.


Cement and Drilling Mud Powders 381

40

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I20

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$10a

Conveying Line.Pressure Drop

- lbf/in2 Solids LoadingRatio/

100 80 60 /40

Conveying Line_ Pressure Drop

- lbf/in2

10080

120160,

Solids LoadingRatio /

60

(a)Free Air Flow Rate - ft /min

40

oo230

20

o

io

Conveying LinePressure Drop

i - Ibf7in2

120

Solids LoadingRatio

30

- 20

(b)

40

oo230

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o

40 80 120 160 200Free Air Flow Rate - ftVmin

Conveying Line.Pressure Drop_ \ -!bf/in2120100

160^ / /80 60

15 10 a\

10

Solids Loading/ Ratio

50

(c)

0 40 80 120 160 200

Free Air Flow Rate - ft3 / min

0 40 80 120 160 200

(d)Free Air Flow Rate - ft / min

Figure 13.1 Conveying characteristics for (a) ordinary portland cement, (b) oil wellcement, (c) barite, and (d) bentonite conveyed through the pipeline shown in figure 12.11.


382 Chapter 13

2 CEMENT

Conveying data for both ordinary portland and oil well cement, conveyed throughthe Figure 12.11 pipeline were presented above in Figure 13.1. Data on ordinaryPortland cement was presented earlier in Chapter 4 where the material was used toillustrate the conveying capability of materials capable of being convey in densephase in a sliding bed mode of flow. For this purpose data obtained with the mate-rial conveyed through the Figure 4.2 pipeline of two inch bore and 165 ft long wasused.

This same data was analyzed further in Chapter 7 to illustrate the influenceof conveying line inlet air velocity. Ordinary portland cement was also used inChapter 9 to illustrate the influence of conveying air velocities on pipeline purgingwith Figure 9.10. In this case the Figure 7.13 pipeline of four inch nominal boreand 310 ft long was used.

Data for oil well cement conveyed through the Figure 10.20 pipeline of twoinch bore and 140 ft long was presented earlier in Chapter 8. The oil well cementwas used to illustrate the influence of pipeline material on conveying performance.Identical pipelines of steel pipe and rubber hose were tested and the data was pre-sented in Figure 8.21 and 8.22. Barite was similarly conveyed through these pipe-lines and this data is presented in a section on rubber hose later in this chapter.

2.1 Ordinary Portland Cement

Conveying characteristics for ordinary portland cement conveyed through the rela-tively short Figure 10.20 pipeline of two inch nominal bore are presented in Figure13.2.

Since the pipeline was only 140 feet long and included six bends, conveyingat solids loading ratios in excess of 200 was possible with conveying air pressuresof 25 psig. Even with a conveying line pressure drop of 10 lbf/in2 the cementcould be conveyed at a solids loading ratio of 100 and with a conveying line inletair velocity down to about 600 ft/min.

With air supply pressures less than about 10 psig the pressure gradient wasnot sufficiently high to maintain such high solids loading ratios and so the mini-mum value of conveying line inlet air velocity had to increase as a consequence.Hence the increase in the volumetric flow rate of free air required at lower pres-sures, as shown on Figure 13.2.

The conveying limit for the material is dictated by the relationship betweenthe solids loading ratio and the minimum conveying air velocity. This was dis-cussed in Chapter 4, where the cement was used for illustrating purposes for mate-rials capable of dense phase conveying in a sliding bed mode of flow. The rela-tionship for ordinary portland cement is presented again in Figure 13.3 for refer-ence. From this it will be seen that if the cement is conveyed in dilute phase sus-pension flow a minimum conveying air velocity of about 2000 ft/min will have tobe maintained.



60

o50

J:40

SlO

Pressure Drop- Ibf/irv Solids Loading

Ratio

20

50 100Free Air Flow Rate - ftVmin

150 200

Figure 13.2 Conveying characteristics for ordinary portland cement conveyed throughthe pipeline shown in figure 10.20.

2400

20 40 60

Solids loading ratio

80 100

Figure 13.3 Influence of solids loading ratio on minimum conveying air velocity forordinary portland cement.


384 Chapter 13

2. /. / Dilute to Dense Phase Transition

Situations in which it may only be possible to convey cement in dilute phase willoccur if the pressure available for conveying is very low or if the pipeline is verylong. The critical parameter is the pressure gradient available, and for cement thisneeds to be above about 2'/2 Ibf/in2 per 100 ft of horizontal pipeline. This is an'equivalent' length and so an allowance must be made for bends and any verticallift in the pipeline. To convey at a solids loading ratio of about 100 typically re-quires a pressure gradient of about 10 Ibf/in2 per 100 ft.

The full transition from dense phase conveying capability, with a conveyingline inlet air velocity of 600 ft/min, to dilute phase suspension flow, with a mini-mum inlet air velocity of 2000 ft/min for the cement, does not occur in Figure13.2. This is because the pipeline was too short. The effect, however, will be high-lighted with data for a longer pipeline, and this is presented below.

2.1.2 High Pressure Conveying

A sketch of a very much longer pipeline through which the ordinary portland ce-ment has been conveyed is shown in Figure 13.4. This pipeline was 535 ft longand incorporated seventeen 90° bends. The pipeline was two inch nominal boreand so the air only pressure drop was consequently very high. One would notnormally build a pipeline of such a geometry, being of a relatively small bore forthe length, and incorporating so many bends, but it is very useful for illustratingthe influence of the various parameters.

Pipeline:length = 535ftbore = 2 inbends = 17x90°D/d = 24

Figure 13.4 Details of pipeline used for the high pressure conveying of ordinary port-land cement.



Once again a high pressure top discharge blow tank was used to feed thematerial into the Figure 13.4 pipeline. 200 fVYmin of free air at a pressure of 100lbf/in2 was available for conveying. Since the pipeline was long and high pressureair was available the opportunity was taken to carry out test work on the cementwith conveying line inlet air pressures of up to 75 lbf/in2 gauge.

The maximum discharge capability of the blow tank used was about 55,000Ib/h, but as the pipeline was very long, and hence of high resistance, it would bepossible to carry out tests with very much higher air supply pressures. Air flowrate and control was made possible at these pressures by using convergent-divergent choked flow nozzles, as discussed in Chapter 6.

Conveying data for the cement in this pipeline is shown in Figure 13.5.Lines of constant conveying line inlet air velocity have been superimposed in ad-dition, in order to illustrate the nature of the dilute to dense phase conveying tran-sition. Conveying line exit air velocity has also been added as an additional axis.As this is a constant bore pipeline, the magnitude of the air expansion through thepipeline, with such high air supply pressures, can be clearly seen. With a convey-ing line inlet air pressure of 75 lbf/in~, for example, the expansion in conveying airvelocity is approximately 6:1.

For materials that can be conveyed at low velocity, high pressure air can beutilized quite conveniently, for the slope of the constant conveying line inlet airvelocity curves is very steep. From Figure 13.5 it will be seen that a very signifi-cant increase in material flow rate can be obtained through a pipeline by using ahigher air supply pressure, and the corresponding increase in air flow rate requiredis not proportionately large.

For dilute phase flow, however, where the conveying line inlet air velocitymay be 2000 or 3000 ft/min, the slope of the constant inlet velocity curves is notas steep and so considerably more air must be used if a higher air supply pressureis to be utilized. The conveying facility had 200 ftVmin of free air available and soif the conveying line inlet air velocity had to be 3000 ft/min the maximum pres-sure that could be utilized would only be about 25 psig. With an inlet air velocityof 600 ft/min only 90 ft3/min of air was required at 75 psig.

Since the pipeline was of small bore and relatively long it will be seen fromFigure 13.5 that a pressure drop of about 30 lbf/in2 was required before the cementcould be conveyed in dense phase. As a consequence a marked transition is shownbetween the minimum conveying limits for the dense and dilute phase areas on theconveying characteristics in this region. The transition from dilute to dense phaseconveying is very smooth. Indeed, with such high air supply pressures, for manyoperating points on Figure 13.5 the material is quite likely to be in dense phase atthe start of the pipeline and in dilute phase at the end of the pipeline.

An operating problem that does arise with this dilute to dense phase transi-tion relates to proximity to minimum conveying conditions. It is essential to avoidoperating a conveying system in dense phase in the region where the air supplypressure is marginal for dense phase conveying, as illustrated in Figure 13.5 [1].


386 Chapter 13

40

30

utaoioE"2

20

10

Conveying Line Inlet AirVelocity - ft/min

Solids LoadingRatio

75080 / 70

1000

60 / 501250

40

J500

.30


- Ibf7in2

3000

40 80 120 160 200

Free Air Flow Rate - ft /min

2500 5000Conveying Line Exit Air Velocity - ft/min

7500

Figure 13.5 Conveying data for ordinary portland cement conveyed through the pipe-line shown in figure 13.4.



2.1.3 Influence of Pipeline Bore

The data reported so far has been for two inch nominal bore pipelines. Despitethis, material flow rates have been typically up to about 40,000 Ib/h in the datapresented. Higher flow rates can be achieved by utilizing higher air supply pres-sures, as illustrated with Figure 13.5 but there is a limit to this. An increase inpipeline bore will allow a significant increase in material flow rate, being ap-proximately in proportion to the increase in pipe section area. Air flow rates alsohave to increase in proportion to the increase in cross sectional area, in order tomaintain the necessary conveying air velocities, and so this means that the convey-ing characteristics are almost geometrically similar.

To illustrate the influence of pipeline bore, three sets of conveying data arepresented for ordinary portland cement conveyed through the Figure 7.13 pipeline.This pipeline was 310 feet long and included nine 90° bends. Data for the cementconveyed through the Figure 7.13 pipeline of two inch nominal bore is presentedin Figure 13.6.

The maximum value of material flow rate here was just over 50,000 Ib/h be-cause the pressure gradient available (air supply pressure divided by equivalentlength of pipeline) was higher than that in the previous two inch bore pipelinesthat have been used to present data for the cement. Data for this same cement con-veyed through the same pipeline, but of three inch nominal bore, is presented inFigure 13.7.

60oo250.cjB740

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CS

'£20

10

Solids LoadingRatio

" Conveying Linepressure Drop

- Ibt7in2

100 150

Free Air Flow Rate - frYmin

200

Figure 13.6 Conveying data for ordinary portland cement conveyed through the pipe-line shown in figure 7.13 of two inch nominal bore.


388 Chapter 13

120

_g

I 40

Solids LoadingRatio


- Ibt7in2

20

I I I I I L_

40 80 120 160

Free Air Flow Rate - ftj/min

200

Figure 13.7 Conveying data for ordinary portland cement conveyed through the pipe-line shown in figure 7.13 of three inch nominal bore.

It will be noted that the same range of air supply pressures was used in con-veying the cement through the three inch bore pipeline and so a direct comparisonwith the two inch bore pipeline data is possible. The material flow rate axis hasbeen doubled and it will be seen that the flow rate of cement has more than dou-bled, as would be expected, for the increase in cross sectional area from two tothree inch bore pipe is more than double.

It will be seen that the two sets of conveying characteristics are approxi-mately geometrically similar, as mentioned above. This is because the air flow rateaxis has been scaled in proportion to pipe section area and the resulting increase incement flow rate is approximately in proportion to this ratio also.

Solids loading ratios achieved are slightly higher with the three inch borepipeline and this is partly due to the fact that the air only pressure drop for thethree inch bore pipeline is much lower than that for the two inch bore pipeline.With a lower air only pressure drop, more of the pressure is available for convey-ing material.

Data for this same cement conveyed through the same Figure 7.13 pipelineof four inch nominal bore is presented in Figure 13.8. A further increase in airflow rate is required, as will be seen, but the same axis for material flow rate hasbeen maintained. As a consequence a lower maximum value of conveying linepressure drop has been employed. It will be seen, however, that for a given valueof conveying line pressure drop, the material flow rate achieved in the four inchbore pipeline is significantly greater than that achieved in the three inch bore line.



ooo

a

80

oE 40

U"S

Solids LoadingRatio


20

0 100 200 300 400

Free Air Flow Rate - ftVmin

Figure 13.8 Conveying data for ordinary portland cement conveyed through the pipe-line shown in figure 7.13 of four inch nominal bore.

2.1.4 Industrial Installations

Because of the empirical nature of pneumatic conveying, little practical informa-tion on industrial plant finds its way into the literature. System design is generallybased on the scaling of data for the particular material to be conveyed. If previousexperience with a material is not available, the material will be conveyed througha test facility in order to generate the necessary data. The building, maintainingand operating of test facilities is an expensive support item for a company, and soany data that they obtain on materials has too much commercial value to publish.

Most reputable companies that manufacture pneumatic conveying systemshave such test facilities. Companies will request a representative sample of thematerial to be conveyed and undertake tests, even if they have previous experi-ence, simply because of the problems of different grades of the same material be-having very differently. Sometimes data does get published, particularly for adver-tising purposes, but very often it is incomplete so that it is not possible to extractuseful design information. Some interesting examples for cement are presentedbelow.

2.1.4.1 Positive Pressure ConveyingSchaberg and Mehring [2] reported on a pneumatic conveying facility for cementin England that was commissioned in 1986. The distance to the furthest mill wasabout 2800 feet and a material flow rate of 264,000 Ib/h was required. The con-veying route included twelve bends and incorporated five diverters. A single blow


390 Chapter 13

tank with a 66,000 Ib batch capability was used. The total cycle time was fifteenminutes, giving the 264,000 Ib/h. The conveying time was twelve minutes, whichis equivalent to 330,000 Ib/h during the conveying phase of the cycle.

The pipeline bore was 10 inch (257 mm) and conveying line inlet and exitair velocities were quoted as being 732 ft/min (3-72 m/s) and 4468 ft/min (22-7m/s), with a conveying line pressure drop of 75 lbf/in2 (5-1 bar). The cement wasconveyed at a solids loading ratio of 32 and the compressor delivered 3425 ftVmin(97 nrVmin) of free air at a pressure of 100 lbf/in2 gauge (7 bar gauge), giving aspecific power consumption of 5-6 hp-h/ton (4-6 kWh/tonne).

From the above conveying air velocity data it wi l l be seen that a single borepipeline was used; for 732 x [(75 + !4-7)/14-7] = 4468 ft/min. Using the outletvelocity at atmospheric pressure, the free air flow rate used for conveying will beapproximately 4467 x n x 102/576 = 2436 frYmin which means that only about70% of the air available is used for conveying. Using this lower air flow rate andan air density of 0-0765 lb/ft3, a check on the solids loading ratio gives330,000/(2436 x 0-0765 x 60) = 30, which is close enough for a check. From Fig-ure 13.3 it will be seen that at a solids loading ratio of 32 the minimum conveyingair velocity suggested is approximately 850 ft/min and so for the cement in ques-tion this is obviously a conservative value.

2.1.4.2 Ship Off-loadingLigthart [3] reported in 1991 on a pneumatic conveying system for off-loadingcement from bulk carriers at 1,764,000 Ib/h (800 tonne/h), and its onward convey-ing to silos 1640 feet (500 m) distant through twin pipelines. The company had aneed to import up to one million tonne/yr of cement at a terminal 15 miles east ofLondon on the River Thames. Because the river is tidal (23 feet) it was necessaryto build a jetty in the river against which the ships could berth, and hence the longconveying distance.

A single vacuum nozzle was employed to off-load at 800 tonne/h, but it wasdecided to use two pipelines at 400 tonne/h each for the transfer to silos over 1640feet, as it was considered that a single bore pipeline would be more expensive tobuild. Four concrete silos of 10,000 tonne capacity were available for storage.

The single unloader is mounted on rails on the jetty to service the entireship. For onward conveying to the silos it is connected to the pipelines by flexiblehoses, through manifolds provided every 50 feet along the length of the ship dock-ing section. Air is blown into the pipelines at their start, at the end of the jetty, andthis dilutes the flow and transports the cement the 1640 feet to the silos. The un-loader has a single filter receiver vessel with four 20 tonne capacity blow tanksbeneath, arranged in two pairs.

It also has eight vacuum pumps, and two compressors to provide air to thestart of the two pipelines. All air movers are screw type with an 85% vacuum ca-pability for suction, and deliver oil free air, without cooling, at 44 lbf/in2 (3 bar)gauge for blowing. Although the total installed power is 4290 hp (3200 kW), only75% of this is required for conveying at 800 tonne/h over the 1640 feet.



A pneumatic system was chosen in preference to alternative mechanical sys-tems for the duty for cost, maintenance and environmental reasons. Although thecost of the actual pneumatic ship off-loading system was higher than the price fora mechanical un-loader, the cost for the overall system was lower for the pneu-matic system. This is because the pneumatic system required only two pipelines toconvey the cement the 1640 ft to the silos. A mechanical un-loader would haverequired long conveying belts, and vertical screw conveyors in addition, to bringthe cement to the top of the silos.

3 BARITE

As mentioned above, barite is a relatively dense material, having a bulk density ofabout 100 lb/ft3 and a particle density of about 265 lb/ft3. In drilling mud applica-tions, however, the material is typically ground down to a mean particle size ofabout 12 micron and at this value the material has very good air retention proper-ties.

As a consequence it is capable of being conveyed in dense phase at low ve-locity in a conventional conveying system, despite the high values of density. Thematerial will, of course, convey in dilute phase and a minimum conveying air ve-locity of about 2400 ft/min is required.

3.1 Low Pressure Conveying

Low pressure, dilute phase data for barite conveyed through the Figure 10.16 isshown in Figure 13.9. Although the conveying air pressure available was rela-tively low, the conveying distance was short, and so the start of the transition fromdilute to dense phase conveying is seen to occur with conveying line pressure dropvalues above about 6 lbf/in~.

This is the point, on Figure 13.9, where the solids loading ratio is already upto a value of 14 under minimum conveying conditions. Further increase in pres-sure results in an increase in pressure gradient to allow the material to be conveyedat a higher solids loading ratio. This, in turn means that the material can be con-veyed at a lower velocity, and hence with a slightly lower air flow rate.

It will be recalled that the influence of pressure gradient was illustrated inChapter 4 on Gas-Solid Flows with Figure 4.23 for low pressure conveying, andthis included both positive pressure and vacuum systems. It must be emphasizedthat the conveying distance on Figure 4.23 is an equivalent distance that takesaccount of vertical lift and the number of bends in the pipeline, as well as the hori-zontal conveying distance.

Although the pipeline for which the data relates was only 110 ft long, it didcontain seven 90° bends and it will be seen from Figure 8.16a that the equivalentlength of the bends, for which the conveying line inlet air velocity is 2400 ft/min,is about 40 ft each. Since the length of vertical lift in the pipeline was negligible,the equivalent length would be about 390 ft.


392 Chapter 13

10ooo

aerf

Solids LoadingRatio

24


- lbf/in2

ConveyinLimit

50Free Air Flow Rate - ftVmin

100 150

13.9 Conveying characteristics for barite conveyed through the pipeline shownin figure 10.16.

3.2 High Pressure Conveying

High pressure conveying data for barite conveyed through the 230 ft long, twoinch bore Figure 12.11 pipeline was presented earlier in Figure 13.Ic. A similartransition from dilute to dense phase conveying occurred, as shown in Figure 13.9above, but as conveying data was undertaken at pressures of up to 30 lbf/ingauge, the vast majority of the data presented related to dense phase conveying.Figure 13.9, in effect, provides a magnification of the very low pressure and mate-rial flow rate section of Figure 13.1c.

3.2.1 Influence of Pipeline Bore

As with the cement, reported above, barite has also been conveyed through two,three and four inch bore pipelines. In this case the pipeline was the 165 ft longFigure 4.2 pipeline. Data for the barite in the two inch nominal bore pipeline ispresented in Figure 13.10. With conveying line inlet air pressures of up to 30lbf/in2 gauge the vast majority of the data relates to dense phase conveying, withsolids loading ratios up to 200.

Similar data for the barite conveyed through the Figure 4.2 pipeline of threeinch nominal bore is presented in Figure 13.11. This shows an unusual anomaly.At low values of conveying line pressure drop, and low values of air flow rate, thematerial flow rate through the three inch bore pipeline is less than that through thetwo inch bore pipeline of identical geometry.



ooo

-O

I

60

50

40

30

20

10

0

Conveying LinePressure Drop- Ibf/in2

200 Solids LoadingRatio

20

1

'50 100Free Air Flow Rate - ft3/min

150

Figure 13.10 Conveying characteristics for barite conveyed through the pipelineshown in figure 4.2 of two inch nominal bore.

This is a rare occurrence, but is not unknown, and is yet another problemwith which to contend in pneumatic conveying.

120ooo

oi

o

80

Solids LoadingRatio

^ ,200150


- lbf/in2

40 80 120 160

Free Air Flow Rate - ft3/min

200

Figure 13.11 Conveying characteristics for barite conveyed through the pipelineshown in figure 4.2 of three inch nominal bore.


394 Chapter 13

The reason for this is not fully understood at the present time and it is doubt-ful whether any computer aided design program currently available would cor-rectly predict this reduction in performance with this particular material.

The fact that such data is recorded throws into doubt the use of small borepipelines to derive conveying data for system design purposes. In recent years,however, most companies that manufacture pneumatic conveying systems havebeen installing larger bore test facilities. A number of companies now have sixinch bore pipelines and four inch is typically the smallest bore of pipeline that iscurrently used.

Conveying data for the barite conveyed through the four inch bore pipelineis presented in Figure 13.12. Material flow rates here are significantly greater thanthose for the three inch bore pipeline, as would normally be expected.

3.2.2 Influence of Pipeline Material

Cement and drilling mud powders, as mentioned earlier, are regularly transportedby small ships to storage facilities at ports, particularly those ports that are used toservice off-shore drilling operations. Drilling mud powders are then loaded ontoservice boats to supply the off-shore drilling rigs. These vessels are generally selfoff-loading, usually by means of single or twin blow tanks, and flexible hoses arewidely used. At ports, flexibility is needed to overcome problems of tidal move-ment. For the loading of materials onto off-shore platforms flexibility is requiredto accommodate movement of the vessel on the open sea in bad weather, and thefact that the vessel must stand some distance off from the oil or gas rig.

200

x 160

1

k 120C3

ei

I 80

40

Solids Loadin;Ratio


- Min2

200 300

Free Air Flow Rate - fWmin

400

Figure 13.12 Conveying characteristics for barite conveyed through the pipelineshown in figure 4.2 of four inch nominal bore.


Cement and Drilling Mud Powders395

In these applications very long lengths of flexible hose, usually ot natural orsynthetic rubber, are used to connect the supply boat with the fixed pipeline on theplatform In these situations the hose naturally forms a catenary and so bends areof exceptionally long radius and the additional pressure drop is minimal. Pressuredrop for the hose, compared with that of a steel pipeline, however, must be taken

into consideration. . ,The influence of pipeline material on conveying performance was consid-

ered in detail in Chapter 8 with Figures 8.21 and 22. Oil well cement was the ma-terial considered and this was conveyed through identical pipelines of steel pipeand rubber hose (shown in Figure 10.20). Conveying characteristics for the ce-ment conveyed through the two pipelines were given and an analysis of the com-parative performance was presented. Barite has also been conveyed through thesesame 140 ft long Figure 10.20 pipelines and the two sets of data are presented in

xac the same axes have been used for the two sets of barite data in Fig-ure 13 13 as for the two sets of oil well cement data in Figure 8.21 so that directcomparisons can be made for both the different materials and the different pipe-

lines.

Conveying Line PressureDrop - Ibf/in2

, Solids Loading\ 200 Ratio*

50

8o

:40

_0

I 20

I10

50

Conveying Line PressureDrop - Ibf/in2

I Solids loading/ ratio

1 200 /160 /

130100

24

(a)

0 50 100 150

Free Air Flow Rate - ftVmin (b)

50 100 150

Free Air Flow Rate - frVmin

Figure 13.13 Conveying characteristics for barite conveyed through the pipelineshown in figure 10.20 pipeline made of (a) steel pipeline and (b) rubber hose.


396 Chapter 13

The difference in conveying performance for the barite in Figures 13.13aand 13b follows a very similar pattern to that reported for the oil well cement andpresented in Figure 8.22. At very low values of conveying air velocity there islittle difference between the two sets of data and material flow rates for a givenconveying line pressure drop are very similar. As velocity increases there is a con-stant reduction in material flow rate for the barite conveyed through the rubberhose.

This is attributed to the fact that the coefficient of restitution for the materialimpacting against rubber pipe walls is much lower than that for material againststeel pipe walls. As a consequence the material, after impact with the rubber pipewall, will be at a lower velocity, compared with the steel pipe, and so additionalenergy will be lost in re-accelerating the material back to its terminal velocity.

4 BENTONITE

Both bentonite and barite have been conveyed through the 185 ft long Figure 8.2pipeline of two inch nominal bore. For comparison purposes the conveying char-acteristics for both materials are included in Figure 13.14.

60

50ooo

40

oE 20"s'Cu

I 10

(a)

SolidsLoading

Ratio ~

20


iO 120,- Ibf7in2

0 50 100 150

Free Air Flow Rate - tf/min

60

50


- Ibf'/in"

ooo

ooi

oE20.3

(b)

SolidsLoading

Ratio

50 100 150

Free Air Flow Rate - ft /min

Figure 13.14 Conveying characteristics for (a) bentonite and (b) barite conveyedthrough the pipeline shown in figure 8.2.



Figure 13.14 illustrates quite clearly the differences in conveying capabilitybetween the barite and bentonite, particularly for low velocity dense phase con-veying. While the conveying characteristics of barite are similar to those of ce-ment, the conveying characteristics of bentonite are similar to those of a fine gradeof fly ash. At low air flow rates, therefore, the differences in material flow ratesbetween these different powdered materials can be quite considerable.

Conveying data for bentonite was included in Figure 13.1 along with similardata for ordinary portland cement, barite and oil well cement, for comparison. Allfour materials were conveyed through the 230 ft long Figure 12.11 pipeline. Of thefour materials included, bentonite was the only one that showed a significant dif-ference in conveying capability in comparison with the other materials.

REFERENCES

1. D. Mills. An investigation of the unstable region for dense phase conveying in slidingbed flow. Proc 4th Int Conf for Conveying and Handling of Paniculate Solids. Budapest.May 2003.

2. F. Schaberg and B.F. Mehring. Dense phase conveying. Large outputs/long distances.Proc Pneumatech 4. pp 281-299. Jersey, UK. March 1987.

3. A. Ligthart. World's largest cement unloader. Bulk Solids Handling. Vol 11, No 3. pp671-676. August 1991.


Documents

Conveying of Cement and Drilling Mud Powders - Freenguyen.hong.hai.free.fr/EBOOKS/SCIENCE AND ENGINEERING/ENGIN… · Cement and Drilling Mud Powders 385 Once again a high pressure