BSH 1: Prime Movers for Bulk Solids
     Part 1: Metering and Feeding Bulk Solids
         1. INTRODUCTION
             1.1 How to use this manual part
             1.2 Definitions
         2. FEEDER TYPES
             2.1 Mass flow rate metering devices
                 2.1.1 Belt weigh feeder
                 2.1.2 Loss in weight bins
                 2.1.3 Apron feeder
                 2.1.4 Impact flowmeters
             2.2 Volumetric flow metering devices
                 2.2.1 Screw feeder
                 2.2.2 Drag chain/En-masse conveyor
                 2.2.3 Vibratory feeder
                 2.2.4 Hydraulic high pressure piston pump
                 2.2.5 Rotary feeders
                 2.2.6 Saxlund push floor feeder
                 2.2.7 Bucket elevators
                 2.2.8 Miscellaneous volumetric flow measurement systems
             2.3 Miscellaneous feeders
                 2.3.1 Stacker/reclaimer devices
                 2.3.2 Gravity transfer
                 2.3.3 Hopper discharge aids
         3. RELEVANT SOLIDS PROPERTIES: INFLUENCE ON EQUIPMENT SELECTION AND PERFORMANCE
             3.1 Abrasiveness
                 3.1.1 Screw feeder
                 3.1.2 Vibratory Feeder
                 3.1.3 Belt feeder
                 3.1.4 Apron feeder
                 3.1.5 En-masse/Drag chain feeder
                 3.1.6 Bucket elevator
                 3.1.7 Miscellaneous
             3.2 Hardness
             3.3 Particle size and shape
                 3.3.1 Screw feeder
                 3.3.2 Vibratory feeder
                 3.3.3 Belt feeders
                 3.3.4 Apron feeder
                 3.3.5 En-masse/Drag chain feeder
                 3.3.6 Bucket elevator
                 3.3.7 Miscellaneous
             3.4 Friability
                 3.4.1 Screw feeder
                 3.4.2 Vibratory feeder
                 3.4.3 Belt feeder
                 3.4.4 Apron feeder
                 3.4.5 Drag chain/En-masse feeder
                 3.4.6 Bucket elevators
                 3.4.7 Miscellaneous
             3.5 Density
             3.6 Moisture content
             3.7 Flow properties: Cohesiveness and Adhesiveness
                 3.7.1 Screw feeder
                 3.7.2 Vibratory feeder
                 3.7.3 Belt feeder
                 3.7.4 Apron feeder
                 3.7.5 Drag chain/En-masse feeder
                 3.7.6 Bucket elevator
                 3.7.7 Miscellaneous
             3.8 Property heterogeneity
         4. DESIGN CONSIDERATIONS
             4.1 What is the installation for?
             4.2 Size
             4.3 Metering
                 4.3.1 Accuracy and repeatability
                 4.3.2 Control strategy
                 4.3.3 Sensitivity to variations in material properties
             4.4 Maintenance
         5. SELECTION OF FEEDERS
             5.1 By consideration of flowability
                 5.1.1 Screw Feeder
                 5.1.2 Vibratory Feeder
                 5.1.3 Belt Feeder
                 5.1.4 Apron Feeder
                 5.1.5 Drag chain Feeder
                 5.1.6 Bucket Elevator
             5.2 By consideration of particle size and size distribution
                 5.2.1 Screw Feeder
                 5.2.2 Vibratory Feeder
                 5.2.3 Belt Feeder
                 5.2.4 Apron Feeder
                 5.2.5 Drag chain Feeder
                 5.2.6 Bucket Elevator
                 5.2.7 Summary
             5.3 By consideration of flowrate
                 5.3.1 Screw Feeder
                 5.3.2 Vibratory Feeder
                 5.3.3 Belt Feeder
                 5.3.4 Apron Feeder
                 5.3.5 Drag chain Feeder
                 5.3.6 Bucket Elevator
             5.4 By consideration of accuracy and repeatability
                 5.4.1 Screw Feeder
                 5.4.2 Vibratory Feeder
                 5.4.3 Belt Feeder
                 5.4.4 Apron Feeder
                 5.4.5 Drag chain Feeder
                 5.4.6 Bucket Elevator
             5.5 By consideration of abrasiveness
                 5.5.1 Screw Feeder
                 5.5.2 Vibratory Feeder
                 5.5.3 Belt Feeder
                 5.5.4 Apron Feeder
                 5.5.5 Drag chain Feeder
                 5.5.6 Bucket Elevator
             5.6 By consideration of cleaning/spillage
                 5.6.1 Screw Feeder
                 5.6.2 Vibratory Feeder
                 5.6.3 Belt Feeder.
                 5.6.4 Apron Feeder
                 5.6.5 Drag chain Feeder
                 5.6.6 Bucket Elevator
             5.7 By consideration of costs (maintenance and capital)
                 5.7.1 Screw Feeder
                 5.7.2 Vibratory Feeder
                 5.7.3 Belt Feeder
                 5.7.4 Apron Feeder
                 5.7.5 Drag chain Feeder
                 5.7.6 Bucket Elevator
         6. REFERENCES
     Part 2: Pumps for Wet Bulk Solids
         1. INTRODUCTION
             1.1 Summary of Contents
             1.2 Background
             1.3 Description of materials pumped
             1.4 Bulk solids pump development
             1.5 Advantages of using pumps for wet bulk solids
         2. TYPES OF PUMP FEEDERS EMPLOYED
             2.1 Single augers
                 2.1.1 Use of trough rider bars
             2.2 Double augers
                 2.2.1 Use of modified augers to include a mixing action
             2.3 Bridge breakers
             2.4 Agitator-equipped hoppers
         3. ROTARY POSITIVE DISPLACEMENT PUMPS (PROGRESSIVE CAVITY)
             3.1 Allweiler AG
             3.2 Bornemann Pumps
             3.3 Mono Pumps
             3.4 Moyno Pumps
             3.5 Netzsch/Nemo
             3.6 Orbit Pumps
             3.7 PCM Pompes
             3.8 Pumpenfabrik Wangen
             3.9 Roto Pumps
             3.10 Seepex
         4. RECIPROCATING POSITIVE DISPLACEMENT PUMPS
             4.1 Abel Pumps
                 4.1.1 Abel SH Solids Handling Pump
             4.2 Geho
                 4.2.1 Geho SHC/DHC Pump
                 4.2.2 Geho DHT Pump
             4.3 Putzmeister
                 4.3.1 HSP seat valve pumps for fine-grained high density solids
                 4.3.2 KOS pumps for coarse-grained high density solids with high solids content
                 4.3.3 KOV ball valve pump for fine-grained, lower viscosity/concentrated slurries
                 4.3.4 Putzmeister single-cylinder EKO pump for very dry solids
                 4.3.5 Putzmeister calotte pump
             4.4 Saxlund
                 4.4.1 Saxlund solids pump maintenance
             4.5 F W Schwing GmbH
                 4.5.1 Schwing sludge pump
                 4.5.2 Schwing single cylinder sludge pumps (EKSP10 and EKSP17)
             4.6 Wirth
             4.7 Comparison of Operating Ranges of Commercial Reciprocating PD "Solids Handling" Pumps
         5. TYPES OF SPECIALIST VALVES USED IN RECIPROCATING PD PUMPS
             5.1 Putzmeister Pumps Valving
                 5.1.1 S Transfer Tube
                 5.1.2 Calotte valve
             5.2 Schwing Poppet Valves
             5.3 Schwing Transfer Tube Valve
         6. METHODS TO PREDICT FRICTIONAL PRESSURE LOSS IN PIPEFLOW
             6.1 Commercial pump suppliers' methods
         7. COMMERCIAL PIPELINE LUBRICATION SYSTEMS
             7.1 Introduction
             7.2 PCM Pompes
             7.3 Putzmeister
             7.4 Saxlund
             7.5 Schwing
         8. PUMP APPLICATION AREAS
             8.1 Introduction
             8.2 Sewage sludge filter cake
                 8.2.1 Progressive cavity pumps
                 8.2.2 Piston pumps
             8.3 Wet fine coal
                 8.3.1 Piston pumps
             8.4 Pulverised fuel ash (PFA)
                 8.4.1 Piston pumps
             8.5 Cement Industry
                 8.5.1 Piston pumps
             8.6 Food Industry
                 8.6.1 Progressive cavity pumps
                 8.6.2 Piston pumps
         9. CONCLUDING REMARKS
         10. REFERENCES
             10.1 Progressive cavity pumps
                 10.1.1 Allweiler Pumps
                 10.1.2 Seepex Pumps
                 10.1.3 Moyno Pumps
                 10.1.4 Wangen Pumps
             10.2 Piston pumps
                 10.2.1 Putzmeister Pumps
                 10.2.2 Schwing Pumps
                 10.2.3 Wirth Pumps
         11. APPENDIX A : DETAILS OF COMMERCIAL SUPPLIERS
             11.1 A1 : EUROPEAN SUPPLIERS AND AGENTS
             11.2 A2 : NORTH AMERICAN SUPPLIERS AND AGENTS

• Part 1 Metering and Feeding Wet Bulk Solids
• Part 2 Pumps for Wet Cakes

Volume BSH 1: Part 1 Metering and Feeding Wet Bulk Solids

The bulk properties of wet solids determine the handling characteristics of such materials as damp powders, pastes, cakes and slurries in various storage and conveying operations. In addition, the bulk properties determine the behaviour of these materials when fed to, or discharged from, a wide range of chemical/process engineering operations including filtration, drying, crystallisation, centrifugation, etc.

Design methods for the storage and conveying of liquids (including many types of pseudohomogeneous slurry) and nominally dry powders are comparatively well-developed for many pieces of equipment. Pipelines can be designed with a reasonable degree of confidence for pumpable materials using tube and rotational viscometers, and procedures exist for the specification of many types of dry powder handling equipment, such as hoppers using shear and wall friction tests .

For liquids and low or medium concentration slurries with no elastic or time-dependent flow properties, shear stress developed during flow depends only on shear strain rate, and the relationship between the two gives the flow curve which is the basis of the subject of rheology. Flow curve information then facilitates the design and specification of pumps and pipelines. On the other hand, the shear strength of dry powders depends on normal stress and bulk density but not appreciably on strain rate. This relatively simple dependence has permitted the development of design procedures for equipment such as hoppers.

Thus in general, the shear strength of wet, granular solids depends on strain rate, the level of normal stress either imposed or developed by the flow and on bulk density. Wet solids have flow properties which are characteristic of both liquids and dry powders , as a consequence, this granulo-viscous behaviour cannot easily be analysed and hence design procedures have not been developed. The presence of moisture in granular materials also causes other material bulk properties to be pronounced, such as cohesion between solid particles and adhesion between the material and equipment surfaces. Cohesion and adhesion properties of dry powders are often sufficient to cause severe handling problems , the presence of moisture aggravates these problems . Cohesion between particles causes lumping or balling. Coupled with an increased tendency to stick to equipment surfaces, this can cause clogging of any transfer equipment which relies on the free movement (i.e. low friction) over its internal surfaces, e.g. chutes and pipes.

In fact, 37 major handling problems for wet solids have been identified in a recent survey of 26 of ICI solids handling plants. The findings from the survey indicated that many problems could be attributed to high adhesion forces between wet solids and equipment surfaces causing excessive stickiness. This high adhesion was often a direct result of the presence of moisture in what might otherwise be a relatively easy-to-handle, dry, non-cohesive powder. Other important bulk properties include:

• Cohesion and tensile strength;
• rheological properties, including shear strength under various normal
• stress and bulk density conditions;
• wall friction forces on equipment surfaces

But it is not just in the chemical industry where wet solids handling problems arise. The economic importance of wet solids is vast. Industries known to handle wet solids include:

• cement, concrete and other building products
• coal
• food
• fertilizers
• animal feed
• chemicals
• pharmaceuticals
• iron and steel
• mining
• sewage treatment
• ceramics
• mastics
• sealants
• paints
• soap and detergents

These industries handle wet solids over a very wide range of tonnages but all will be concerned to a greater or lesser extent with such areas of difficulty in handling wet solids as:

• flow down chutes
• discharge from hoppers
• emptying of drums and cans
• cleaning of conveyor belts
• flow on vibratory feeders/conveyors
• build-up and caking in drag-link conveyors, screw conveyors and bucket elevators
• cake discharge from filter cloths and centrifuges
• balling and wall deposits in dryers poor paste extruder performance
• difficulty in deaerating pastes
• reliable and uniform metering and feeding.

In a survey of 51 companies carried out by Warren Spring Laboratory in 1984, most interest was shown in metering and feeding problems. Those companies covered most of the industries listed above. Companies were asked to fill in a questionnaire (See Appendix A for its format) which asked for preferences for research topics and state-of-the-art reviews as a prelude to the recently launched multi-client co-operative venture between the Department of Trade and Industry and industrial companies, entitled "The Wet Solids Handling Project".

While general guidelines can at present be given to aid the engineer in designing and selecting equipment for wet solids handling, a recent
articles indicated how far these guidelines are useful (particularly with respect to hopper and chute design) and what the requirements are to achieve practical design and selection guides for a wide range of handling equipment.

What is needed are, first, reliable and practical design methods for new plant and, second, improved operating and trouble shooting methods for existing plant.

The first requirement is to be able to design new plant with confidence that it will work for a particular material in the manner specified. This
in turn requires that the material to be handled can itself be adequately specified in terms of those physical properties which affect handling
performance. Thus immediately there is a need for test methods to characterise wet solids for properties, such as shear strength, adhesion, apparent viscosity, internal friction, etc, which govern handling behaviour.

If the wet solid can be so characterised, there is then the possibility that numerical values of the relevant physical properties can be inserted into design equations, which take proper account of how plant performance is affected by the various physical parameters. This in turn means that effects of changes in plant operational procedures, or modification of existing plant, can be predicted in advance. Thus the second objective can be achieved through the application of rational methods, rather than from rule-of-thumb or experience based approaches.

The existence of design equations for the various items of handling plant then leads to the possibility that the material itself can be engineered to have desirable properties for handling. Perhaps it is easiest to control moisture content of a wet solid so that the material is not too sticky, but it might also be possible to control the particle size distribution or, even more difficult, the particle shape, both of which may affect stickiness.

There is some information in the literature concerning characterisation methods, design methods and the engineering of material properties. The purpose of this report is essentially to acquaint the reader with the characterisation methods for the bulk properties of wet solids which are currently available, and to identify gaps in the range of methods which need to be filled if reliable design and selection procedures are to be developed.

Mechanisms Responsible for Bulk Property Characteristics

Bulk property characteristics are determined by what may be termed wet solids "basic" characteristics such as:

• particle size/size distribution
• particle shape(s)
• particle/liquid density difference
• particle/liquid interfacial characteristics, such as wetting behaviour
• moisture content

These basic characteristics in turn are determined by processing operations such as particle growth processes (including crystallisation,
precipitation, chemical reaction, agglomeration) and dewatering equipment such as filters, thickeners and centrifuges. Figure 1.1. demonstrates how handling and processing stages are linked to "basic" and bulk properties of wet solids, which in turn contribute to a selection of handling problems as identified by the ICI survey .

Fig 1.1 Relationship between wet solids properties and main problem areas

Adverse bulk properties of wet solids can sometimes be minimised by better control over processes which determine the more "basic" characteristics of these materials. In addition, variations in these quantities throughout a granular mass can compound handling problems and so should be minimised whenever possible.

Additional processing and conveying stages can themselves determine "basic" characteristics. For instance, particle friability will determine the extent of particle attrition which will modify particle size distribution after the particle formation stage, and further changes in moisture content can arise after dewatering stages.

It is apparent that many of the wet solids handling problems are aggravated by the failure to control particle size and moisture content at various points along the process stream, but since at present both the optimal bulk properties and the relationships between the properties of individual particles and the bulk properties are poorly understood, it is difficult to decide from available information what should be the objectives of any control over such characteristics as particle size and moisture content.

Nevertheless some progress has been made in relating what occurs on a microscopic scale to bulk property behaviour. A better understanding of how capillary forces in unsaturated moist solids contribute to increased cohesion and tensile strength is available as a result of the work of Schubert and others . Observations of the reduction in strength of filter cakes through mechanical working has led to speculation that in many cases large adhesive and cohesive forces in wet solids are the result of the creation of negative pore liquid pressures which can occur in such processes as compression filtration and when masses of pastes and cakes impact on equipment walls and surfaces such as in chutes and at screw conveyor-to-belt or belt-to-belt transfer points. It is the progressive raising of this negative pore liquid pressure to atmospheric (or ambient) pressure from mechanical working (caused, for instance, by auger discharge or extrusion) which may be responsible for often-observed corresponding progressive decreases in strength.

Volume BSH 1: Part 2 Pumps for Wet Cakes

This part will survey the increasing number of commercially-available pumps that can pump wet bulk solids in an unsaturated state using suitable feeders.