Slurry handling and transportation developments

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The Institution of Engineers, Australia

Slurry Handling and Transportation Developments

G.R. RIGBY

and

A.D. THOMAS

AUSTR

INCORPORATED ROYAL CHARTER

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Austalia Cal Mic Materials Storage, Handling and International Conterence on Bulk

Mael 1984,p/6. Transportation, 1983, Newcastle, 22-24 August

Slurry Handling and Transportation Developments

G.R. RIGBY

BHP Central Research Laboratories, Shortland, NSW

and

A.D. THOMAS

Consultant, Newcastle

The expanding role of slurries in providing means for the utilisation, handling and transportation of a wide range of bulk solids will continue to be an important factor in the future development of mineral resources. Recent developments in slurry technology with particular reference to conventional long distance transportation, coarse solids pumping and energy slurries are reviewed. 1 INTRODUCTION by rail, truck and conveyor is cumbersome. A large proportion of all bulk materials are The transportation of these materials by pipeline currently being handled and transported throughout is now feasible and such operations have now become the world in the form of slurries. New developa standard part of the overall system for moving ments in slurry technology offer the potential to bulk materials in many parts of the world increase the range of these materials and (Rigby, 1982). applications. Typical examples of present and potential applications include the following: Typical examples include the following: - long distance transportation of coal and other (1) the Black Mesa pipeline which has been minerals conveying 5 million tonnes per year of coal

over a distance of 439 km from a mine in

- slurries for utilisation in combustion and Arizona to the 1500 MW Mohave power station energy conversion applications, for example in Nevada since 1970 (Montfort 1982) coal-oil-mixtures, coal-water slurries, coalmethanol slurries etc. (11) the 396 km Samarco iron ore pipeline in

Brazil which has a capacity to transport

- relatively short distance conveying and in-plant 12 million tonnes per year of hematite slurries, for example hydraulic hoisting of coal, concentrate from a beneficiation plant in-plant transportation such as in coal 300 km north of Rio de Janeiro to a pellet washeries and beneficiation operations plant at Point Ubu (Stetler, 1982) - utilisation of slurry system for loading and (iii) the 24 km Gladstone limestone pipeline in unloading ships Queensland which was commissioned in 1982

and transports a limestone-clay slurry from

- tailings and fly ash disposal systems a new quarry and grinding plant at East End

to a new cement clinker plant at Fishermans

- sand mining and beneficiation operations Landing (Venton, 1982). - chemical reactor and processing slurries, for One of the areas where significant advancement and example alumina processing, hydroliquefaction expansion in slurry pipeline technology and of coal operations is likely to occur is in the movement

of coal. The Black Mesa operation, having

- concrete pumping applications transported some 50 million tonnes of coal, has

- sewerage and other waste disposal systems. demonstrated the technical and economic of this mode of transportation. viability The size range of materials handled in slurries can In the U.S.A. additional pipelines to convey in vary from 100 to 150 mm down to a few microns. An excess of 100 million tonnes per year of coal over understanding of the properties of the various a total distance in excess of 10,000 km have been slurries and their effects on operating parameters proposed (Rigby, 1982): The most advanced of is essential in ensuring the reliability of the these is the 2300 km long ETSI pipeline from This paper reviews some of these features Northern Wyoming to various energy utilities in with particular reference to recent developments Arkansas, Louisiana and Mississippi (Wasp, 1982). in the areas of transportation and energy This pipeline will have an internal diameter of

conversion applications. the order of 1 m and an annual capacity of approx-

imately 30 million tonnes. Whilst this system will

LONG DISTANCE TRANSPORTATION use a similar pipeline slurry to that used in the One of the attractions of oil and gas is the ease Black Mesa operation, the ETSI organisation has introduced some novel additions to the dewatering with which they can be transported over long circuit to yield a product having a surface distances by pipeline, a clean and economically moisture between 7 and 11% (compared to the Black attractive transport medium. By comparison, Mesa product surface moisture of approximately 16%). traditional means of transporting many bulk solids The lower level of product moisture is achieved

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using a combination of screen bowl centrifuges and respectively. For these slurries the pressure vibrating bed dryers. It has been claimed that gradient is low and pipe wear is almost negligible. this product can be handled with conventional However there are numerous cases when it is either equipment and stockpiled successfully under adverse not economic to reduce the particle size or when climatic conditions (Derammalaere et al. 1982). the end product is required to be large. Typical

examples are tailings disposal from mineral

Like the Black Mesa system the ETSI pipeline will processing plants, pumping material in chemical use a fine coal slurry (coal top size approxand mineral processes, sand mining, coarse coal imately 1 mm) to give optimum pumping charactertransportation, dredging and concrete pumping. istics and pressure gradients. The two main problems caused by the coarser

particle size are high pressure gradients, often

This technology is basically limited to energy coal 5 to 10 times that of a fine particle slurry, and being supplied to local power generation stations high pipe wear rates. Current developments aim to or other pulverised fuel users. The product is minimise these two problems. not generally suitable for the export market or for coking coal applications, primarily due to the The centrifugal pump is the most common the coal (Rigby and Callcott, 1972). these slurries and pump developments

and the extension of

In Australia, a joint venture between the Broken Hill Proprietary Company Ltd. (BHP) and British station pressures by multiple staging of limits to permit higher pump Petroleum Australia (BPA) is developing an Numerous wear resistant materials have been tried alternative fine coal transportation/beneficiation for pump liners and impellers. system (Elkes et al. 1982). development particles the most successful appears to be rubber (IPTACCS - Integrated Pipeline Transportation and System) uses oil agglomeration (10 to 20 times the life of large sharp cornered particles nickel steel techniques to allow the fine coal. to be recovered (Ni-hard) and high chrome iron have proved from the slurry in the form of agglomerates which popular with lives some four times steel Want, suitable for local or export use as Pump casing pressures have been rising or coking coals. A 30 tonne/hour steadily and a number of projects are currently demonstration plant, near Newcastle is being six centrifugal pumps in series to achieve operated to develop this technology on a commercial pressures of around 4.5 MPa. basis (Rigby et al, 1982). The demonstration plant appears to be around 5.2 MPa (Ghandi et al, 1980). has facilities for recovery and recycle to the process to yield a product containing less than 0.5% (by weight of coal) residual oil. are necessary. For very high pressures positive displacement pumps In this case the emphasis has been some applications, for example in the preparation on reducing wear rates of wetted parts by better of coal-oil mixtures or in hydroliquefaction design of valves (e.g. Patton, 1981) and by use of operations it is not necessary to recover the oil. water flushed plunger pumps (Null, 1982). However As well as providing a means transport, the normal piston and plunger pumps are limited to a process provides for beneficiation of the coal, maximum particle size of around 6 mm due to valve A number of means of overcoming thus avoiding the necessity closure problems. washing plant. Other potential advantages include this have been developed such as the Hitachi yields of coal compared to conventional hydrohoist (Sakamoto, 1974) and other pipe feeder systems and product containing o1l or 2% for de-oiled product). lower product moistures (6 to 10% for (Kocsanyi, 1972) and lockhopper types (Thompson et al., 1972). The main disadvantage of these

are the relatively sophisticated control systems

The IPTACCS process is also being developed in which are needed to open and close the slurry conjunction with the Electricity Commission of New valves. South Wales for the combined beneficiation, transportation and production of dry pulverised An alternative approach is to use rotary feeders coal for direct firing in a power station boiler. whereby valve operation is achieved by fast rotary A 30 tonne per hour plant is currently being Any coarse particles impeding valve commissioned to test the process on a 60 MW boiler closure are smashed. Examples are the Kamyr (Rigby et al. 1983). rotary injector (Funk et al., 1978) and the Boyle

rotary pump (Stewart, 1972).

The economics of these fine coal systems compared industry the peristaltic pump has proven popular to conventional transportation systems (e.g. road, for medium pressure applications. rail, conveyor) are dependent on the particular case. However many studies have shown that for a Pipe wear is also a serious problem with coarse new system, the capital costs of a slurry pipeline particle slurries, not only because of the coarse system can be of the order of 50% of that for the particles but because of the high velocities alternative systems. Operating costs for the involved. To try and reduce pipe wear rates many pipeline operation are also generally lower, different lining materialshave been tried, among particularly when the lower costs associated with them wood, basalt, rubber, cast iron, polyurethane inflation effects are taken into account (Rigby and asbestos. Probably the most successful has et al., 1983, Kennett, 1981, Rigby, 1982, been polyurethane for which reported wear lives Pike, 1982, Dawson and Sargent, 1975, Dawson et have been 8 to 20 times steel (Sambells, 1974, al., 1980). Rouse, 1982). 3 DEVELOPMENTS IN COARSE SOLIDS PUMPING Much of the above discussion has been concerned

with hardware developments to improve pump and

Optimum pumping properties for slurries pipe performance of coarse particle, settling achieved when the particle size is small. slurries. Despite these improvements, the Typically median particle sizes ranging from transportation of coarse particle heterogeneous about 150 um for coal to 30 um for iron ore are slurries is still essentially limited to necessary. Such materials have a wide particle relatively short distance applications. Neverthesize distribution with top sizes about an order less there is still a place for this mode of of magnitude higher, i.e. 1.5 mm and 0.3 mm operation and several installations have

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demonstrated the advantages of these slurry return pipeline to recycle the vehicle. It is handling applications over more conventional means being actively studied in Australia by Slurry of handling the material. Systems Pty. Ltd. of Sydney. include the hydromining and hydraulic hoisting of coal from a mine to the surface or coal preparation 4 ENERGY SLURRIES plant, for example in West Virginia (George, 1982); the transport of coal from a storage stockpile to a 4.1 Coal Oil Mixtures (COM) ship loading facility as proposed for the Staten Island coal export terminal (Orr and Thompson, The rapid rise in the cost of oil in the 1982) and the slurry loading of coal from a port decade has spurred interest in the use of coal storage facility to a large ship via a submarine slurries as fuels. Although in Australia most pipeline and single point mooring (Faddick, 1982, electricity is generated by burning coal, Rigby et al. not the case overseas especially in the USA and

In these countries a large proportion of

An alternative approach for handling coarse the electricity is generated in oil fired stations. has been to try and modify the behaviour These boilers cannot easily be modified to burn slurry itself. The aim is to reduce the coal as a solid fuel, hence the interest in settling tendency of the coarse particles. substituting oil with a coal slurry. novel approach has been to use specially shaped possible areas of application include injection of pipes (Sauermann, 1982). Another approach which COM into blast furnaces, open hearth furnaces and has created a lot of interest has been the solime and brick kilns. Initial interest centred on called stabilized slurry. coal-oil mixtures typically in the ratio 50% coal particular interest in regard to the pumping of to 50% oil. To achieve a stable mixture the coal coarse coal. It involves mixing the coarse must either be ground extremely fine or else a particles with a proportion of finely ground chemical stabilizer employed. A number of

form a viscous vehicle which demonstration projects have proven the technical

reduces the settling tendency of the coarse feasibility of COM technology (e.g. Gilbert &

is that this will result in Jackson, 1981), however to date commercial

lower pressure gradients and pumping velocities. applications have been limited to relatively small It should also allow simpler dewatering than Although it was first suggested in 1970 (Elliot & Gliddon, 1970) it has yet to be The utilisation of coal-oil mixtures containing proven that it is commercially viable. finely ground coal (so called little doubt that provided the fine particle "micronised" coal, with a particle size below vehicle portion is made sufficiently viscous a 10 microns) has been suggested for use in diesel stable slurry can be achieved (e.g. Duckworth et engines (George, 1982). al., 1982, Rigby et al., 1982). together with the removal of impurities in the

coal offers the potential for a clean fuel.

The question marks surround the resulting pressure Whilst it has been demonstrated that this type of

gradients at economically viable coarse/fine ratios slurry can be burnt in diesel and gas turbine and the scale-up to large diameter pipes. At this engines, micronised coal slurry requires further stage it appears that roughly 50% of the coal needs investigations to optimise grinding and to be less than 0.5 mm. Dewatering of this preparation costs and to evaluate the commercial fraction presents the same problems as with viability of the process. conventional fine coal slurries. Given this fact, unless the pressure gradients can be reduced to 4.2 Coal Water Mixtures (CWM) near that of the fine coal slurries (which at present seems unlikely) the economics of the Because of the apparently debatable economics of approach seem doubtful for other than some COM, research has recently switched to direct specialised relatively short distance applications. firing of coal water mixtures. In this case all Technical problems may also exist concerning of the oil is substituted by coal so the savings scale-up to large diameter pipes (Thomas, 1979, in fuel costs are roughly twice the savings al., 1982). These slurries are currently resulting from use of COM. It is easier to undergoing study in Australia both by the CSIRO and achieve a stable CWM than is case with COM and the BHP/BPA IPTACCS group. The CSIRO, in generally no stabilizer additive is necessary. co-operation with the R.W. Miller Coal Company, is Indeed the reverse is the case in that much currently constructing a 300mm diameter test 100p research has centred on viscosity reducing at Minmi near Newcastle. additives so that the solids concentration operation the future of the stabilized slurry Without any additives viscosity approach may become clearer. considerations generally limit the coal

concentration to about 60% by weight. With

This approach of using mixtures of coarse and fine additives the concentration of coal can be solids could have a potential application in the increased to around 75%. disposal of overburden material mixed with fine thermal energy of the coal is used in vaporizing tailings slurries from mineral processing the water. Henderson & Schaffee (1981) claim that operations. In this the cost of converting coal to CWM is between $25 distances would be involved. to $30 per tonne. The resulting price per unit of

thermal energy is about one half that of oil.

An alternative method of achieving a non-settling slurry has been proposed by Cowper et al. Whilst the economics of CWM's would appear to be This involves use of fine magnetite to achieve a favourable there are many problems to be vehicle of density equal to the coal. before they will gain widespread acceptance. settling tendency of the coarse coal is prevented, them are the extent of boiler de-rating necessary, not by the viscosity of the vehicle as in the case the long term reliability of equipment, environof stabilized slurries, but by neutral mental considerations and transportation costs of This approach has the potential advantage of very low pressure gradients, similar to fine particle slurries, but has the disadvantage of requiring a In the long term it holds promise as a viable

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replacement for oil, pumpable and transportable as ELLIOTT, D.E. and GLIDDON, B.J. (1980). a liquid fuel. In this regard a major disadvantage "Hydraulic transport of coal at high concen-

of CM's is their high viscosities even with trations", Proc. Hydrotransport 1 Conf.,

• additives. For example, Henderson & Schaffee Coventry, England, 1980, p G2. (1981) quote viscosities of between 0.60 and 3 Pas. For economic pumping over long distances the FADDICK, R.R. "Shiploading coarse-coal slurries" viscosity needs to be an order of magnitude less. (1982) - Proc. Hydrotransport 8 Conf., It can be noted here that typical No.6 fuel oil at Johannesburg, South Africa, P 37. room temperatures also has a high viscosity of around 1.2 Pa s but because its viscosity is very FUNK, E.D., BARRETT, M.D. and HUNTER, D.W. (1978). highly temperature dependent this can be reduced "Pilot experiences with run of mine coal dramatically by heating prior to pumping. For injection and pipelining" • Proc. Hydrotransport 5 example heating to 65°C will reduce its viscosity Conf., Hanover, Germany, P F3. to around 0.1 Pa s. CWM's do not exhibit this strong temperature dependence and the viscosity GEORGE, T.J. (1982). "Expanding the role of coal can only be reduced by reducing the concentration. slurries", Coal Mining & Processing, Nov., P 42. Thus the requirements of high thermal efficiency and low pumping costs are in direct conflict. GHANDI, R.L., SNOEK, P.E. and CARNEY, J.C. (1980). Combustion trials in test furnaces have shown that "An evaluation of slurry pumps", Proc. 5th Int Tech. Conf. on Slurry Transportation, Lake Tahoe, CWM can be burned stably without supplementary U.S.A., p 267. fuels. However carbon burn-out was somewhat less than that with the parent coal alone. Modifi- GILBERT, B.F. and JACKSON, G.E. (1981). cations to burner nozzle designs are required to oil mixture experience at Florida Power and Light

overcome erosion problems and to provide Company", Proc. 6th Int. Tech. Conf. on Slurry

effective atomisation (Scheffee et al., 1982). Transportation, Las Vegas, U.S.A. P 226.

4.3 Other Slurries development of coal oil slurries as a boiler feed", HENDERSON, C.B. and SCHEFFEE, R.S. (1981). "The

Coal-methanol slurries containing approximately Proc. 6th Int. Tech. Conf. on Slurry Transport- 60% coal have been proposed as an alternative to ation, Las Vegas, U.S.A., P 218. other energy slurries for combustion applications. Such a fuel could contain minimum levels of KENNETT, E.R. (1981). "The growing viability of sulphur and nitrogen and have highly favourable combustion characteristics. The scarcity and continuous systems for the Coal Trans. Conf., C.S. Publications Ltd., London, transportation of coal", high cost of methanol, however would appear to UK, Sept. 29-Oct. 1. limit such an alternative to areas where methanol could be produced at economically attractive KOCSANYI, L. (1972). "High pressure hydraulic costs (Bergman, 1982). transport for coal and other mining materials"

Proc. Hydrotransport 2, Coventry, England p H4-69.

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