1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7871 : Part 1 : 1996 I
2、CS 01.040.53; 53.040.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Pneumatic conveying Part 1. Glossary of termsThis British Standard, having been prepared under the direction of the Engineering Sector Board, was published under the authority of the Standards Board and co
3、mes into effect on 15 November 1996 BSI 1996 The following BSI references relate to the work on this standard: Committee reference MHE/9 Draft for comment 96/79332 DC ISBN 0 580 26260 X BS 7871 : Part 1 : 1996 Amendments issued since publication Amd. No. Date Text affected Committees responsible for
4、 this British Standard The preparation of this British Standard was entrusted to Technical Committee MHE/9, Continuous mechanical handling equipment, upon which the following bodies were represented: Agricultural Engineers Association Association of Consulting Engineers Automated Material Handling S
5、ystems Association British Aggregate Construction Materials Industries British Coal Corporation British Rubber Manufacturers Association Ltd. Coke Oven Managers Association Cranfield University Electrical, Electronic, Telecommunications and Plumbing Union Electricity Association Mechanical Handling
6、Engineers Association Solids Handling and Processing Association Ltd.BS 7871 : Part 1 : 1996 BSI 1996 i Contents Page Committees responsible Inside front cover Foreword ii Glossary Introduction 1 Section 1. Air 2 1.1 Free air terms 2 1.2 Air flow terms 2 Section 2. Solids/gas terms 4 Section 3. Mate
7、rial characterization terms 6 Section 4. Systems 8 Annex A (informative) Main types of flow 15 Index Figures 1 Phase diagram for a particulate solid conveyed at a constant flow rate 1 2 Simple pressure system 9 3 Multi-discharge system 10 4 Simple vacuum system 11 5 Multi-pick up system 12 6 Combine
8、d vacuum/pressure system 13 7 Closed loop system 14 A.1 Idealized phase diagram for a coarse powder on horizontal co-current flow 16ii BSI 1996 BS 7871 : Part 1 : 1996 Foreword This British Standard has been prepared by Technical Committee MHE/9 in order to set out standard terms for use in the pneu
9、matic conveying industry and in a series of standards being prepared on the subject of pneumatic conveying. Compliance with a British Standard does not of itself confer immunity from legal obligations.BS 7871 : Part 1 : 1996 BSI 1996 1 Introduction Pneumatic conveying is the term used to describe th
10、e transport of particulate solids in gas, usually air, through pipes and ducts. The relative concentrations by weight of the solids phase and the gas phase can vary widely. The term solids loading ratio is used to describe the ratio of the mass flow rate of the solids conveyed to the mass flow rate
11、of the gas used for conveying. A solidsgas phase diagram is a wide ranging graph of pressure gradient versus gas velocity in a pipe containing flowing gas and solids. Because of the difficulty of finding a suitable scale to show all the detail on the same graph it tends to be used only qualitatively
12、 as an aid to communication. Figure 1 shows the relationship between pressure gradient, gas velocity and solids flow rate for a coarse powder. Different modes of flow can be related to specific locations on the diagram. A more complete example of a phase diagram covering a number of flow rates for a
13、 coarse powder, showing more detail, is given in figure A.1. Dense phase Dilute phase Gas velocity Pressure gradient Figure 1. Phase diagram for a particulate solid conveyed at a constant flow rateBS 7871 : Part 1 : 1996 2 BSI 1996 Section 1. Air No. Term Definition 1.1 Free air terms 1101 free air
14、conditions Those conditions at which p = 101.3 kN/m 2 absolute (standard atmospheric pressure) and t = 15 C (standard atmospheric temperature). NOTE. Free air conditions are generally used as the reference conditions for the specification of positive pressure air movers. 1.2 Air flow terms 1201 free
15、 air velocity The velocity of the air at free air conditions. 1202 superficial gas velocity The velocity of the gas, disregarding the volume of solid particles or porous media, at the temperature and pressure conditions under consideration within the pipeline. NOTE. In a pipeline it is the velocity
16、based upon the cross-sectional area; the space occupied by the conveyed product is neglected. For flow through a membrane or across a filter, it is the open duct velocity normal to the surface. Gas velocity is dependent upon both pressure and temperature, and so when conveying gas velocities are eva
17、luated at any point in a system, the local values of pressure and temperature at that point are used. 1203 minimum conveying air velocity The lowest superficial air velocity which can be used to convey a material. 1204 conveying line inlet gas velocity pick-up velocity entrainment velocity The super
18、ficial gas velocity at the point where the product is fed into the pipeline. NOTE. In a single bore pipeline this will be the lowest gas velocity in the conveying line and so it will be greater than the minimum conveying gas velocity required to ensure successful conveying of a product. 1205 conveyi
19、ng line exit gas velocity The superficial gas velocity at the end of a conveying line where the product is discharged into the receiving hopper. NOTE. In a single bore pipeline this will be the highest gas velocity in the conveying line. 1206 saltation The process of deposition of solid particles al
20、ong the bottom of a horizontal pipeline. 1207 saltation velocity The superficial gas velocity at which solid particles begin to fall from suspension in horizontal flow. NOTE 1. Saltation occurs in dilute phase flow when the gas velocity falls below the minimum conveying gas velocity. NOTE 2. The dep
21、osited particles may move slowly along the bottom of the pipe but are not generally re-entrained. 1208 choking A process which occurs in vertically upward flow and commences when solid particles near the pipe wall begin to flow downwards. NOTE. Choking in vertical transport is somewhat analogous to
22、saltation in horizontal transport, for both phenomena represent saturation conditions in dilute phase conveying. BSI 1996 3 BS 7871 : Part 1 : 1996 No. Term Definition 1209 choking velocity The superficial gas velocity at which choking occurs. NOTE 1. For mixed size particles the velocity at which c
23、hoking occurs is usually lower than the saltation velocity. NOTE 2. An alternative definition for choking velocity takes the superficial velocity at which the entire suspension collapses into slug flow as the choking velocity. However not all powders can be made to collapse into slug flow and the gi
24、ven definition is preferred. 1210 null point The position in a system where the pressure is equal to the ambient pressure. NOTE. This is often used in relation to closed loop systems and can identify a natural point of access to the system for monitoring or conditioning. 1211 specific humidity The r
25、atio of the mass of water vapour to the mass of air in a given volume of the mixture. NOTE. Specific humidity gives an indication of the amount of water vapour that is actually contained in the gas. 1212 relative humidity The ratio of the partial pressure of the gas, at a given temperature, to the p
26、artial pressure of the gas when saturated, at the same temperature. NOTE 1. Relative humidity gives an indication of how much water vapour the gas is capable of supporting before it becomes fully saturated. Its value is usually expressed as a percentage. NOTE 2. The relative humidity may change thro
27、ughout a pneumatic conveying system as relative humidity increases with rise in pressure and decreases with rise in temperature.BS 7871 : Part 1 : 1996 4 BSI 1996 Section 2. Solids/gas terms No. Term Definition 2001 solids loading ratio phase density The ratio of the mass flow rate of the solids con
28、veyed, to the mass flow rate of the gas used for conveying. NOTE 1. Solids loading ratio is used by pneumatic conveying engineers to describe the nature of the solid/gas flow in a pipeline. Other terms used include phase density, mass ratio, solids to air loading and mass flow ratio. It is a useful
29、dimensionless quantity since its value does not vary with the conveying gas pressure and so it remains constant throughout the pipeline. NOTE 2. Some references may define phase density as a mass volume ratio which should not be confused with the above definition. 2002 aeration The process by which
30、a particulate solid is conditioned by the introduction of gas locally within its mass. NOTE. The objective of aeration is usually to assist movement by reducing interparticle friction or to prevent compaction. 2003 fluidization A mode of contacting solids with gas such that the particulate solids ar
31、e given fluid-like properties. NOTE. A common example of fluidization occurs where a gas is passed upwards through contained particulate solids with a velocity which just lifts and suspends the particles without carrying them away. If this condition can be achieved, the particles will disengage from
32、 each other and the bulk may be stirred or caused to flow like a liquid with relatively little energy expenditure. 2004 fluidized flow The movement of fluidized solids, by pouring or other means, under the influence of gravity or a pressure gradient. 2005 dilute phase conveying lean phase suspension
33、 flow The conveying of a material in suspension in a flowing gas. NOTE. It is necessary to exceed a minimum value of conveying line inlet gas velocity to produce sufficient drag force on the solid particles to ensure dilute phase conveying. The vast majority of material can be conveyed in this mode.
34、 2006 dense phase conveying Conveying of materials in air at velocities lower than those required for dilute phase conveying. NOTE. The nature of dense phase flow is very varied, for it depends upon the properties of the bulk solid, the phase density of the conveyed material and the conveying air ve
35、locity. Typical flows include flow over a deposited layer, which may itself be moving slowly, and flow in discrete or separate slugs of material which may be formed quite naturally. The range of materials which can be totally conveyed in this mode is limited. 2007 transition region An unsteady part
36、of the phase diagram which occurs immediately below the value of air velocity necessary to maintain dilute phase conveying. NOTE. This is not an operating region and may be characterized by a change in type of flow, often with particles forming dunes in horizontal pipelines. The capability for relia
37、ble flow at lower velocities depends upon the properties of the product to be conveyed. Some products can only be conveyed in dilute phase and will block the pipeline in the transition region. 2008 capsule conveying Transporting bulk solids loaded into containers through a pipeline with gas as a mot
38、ive source. NOTE. For large diameters and heavy payloads wheeled capsules coupled in trains are generally employed. BSI 1996 5 BS 7871 : Part 1 : 1996 No. Term Definition 2009 air slide conveying Fluidizing a bulk solid in a channel with a porous base and causing it to flow normally under the influe
39、nce of gravity. NOTE. Large particles and unit loads can be handled in enclosed ducts with directional jets.BS 7871 : Part 1 : 1996 6 BSI 1996 Section 3. Material characterization terms The characteristics of materials to be conveyed feature prominently in the decisions made at many stages in the de
40、sign of a conveying system. This section includes some of the more common material properties. No. Term Definition 3001 cohesive material A material in which the particles tend to stick together. NOTE. Problems may be experienced with cohesive materials sticking to hopper walls and pipelines. 3002 e
41、xplosive material A material which in a finely divided state, when dispersed in air, will propagate flame if ignited. NOTE. There is a wide range of materials which can be classified as explosive including foodstuffs such as sugar, flour, custard powder and cocoa, synthetic materials such as plastic
42、s, chemical and pharmaceutical products, metal powders and fuels such as wood and coal. A safe system for handling such powders must be established at the design stage. This is likely to be obtained by adopting one or more of the following approaches. a) Use of inert gas as the conveying fluid. b) U
43、se of automatic explosion suppression equipment. c) Elimination of every possible ignition source. d) Use of explosion venting (to a safe area). e) Containment of explosion pressure within the system. 3003 damp or wet material A material containing a high level of particle surface moisture. NOTE. Mo
44、st of the handling problems with wet materials occur in feeding them or discharging them from vessels. Fine materials which are wet will tend to coat the pipeline and bends and gradually block the line. (Lump coal having a large proportion of fines can be a particular problem in this respect.) 3004
45、moisture content The mass of water contained in a material with respect to its own mass expressed as a percentage. NOTE. Particle surface moisture content will differ from total moisture content. 3005 electrostatic material A material which tends to accumulate an electrostatic charge during conveyin
46、g NOTE. All conveying systems should be suitably earthed throughout their length. 3006 abrasive (erosive) material A material which is hard enough (or of a shape) to cause significant wear on system components. NOTE. Erosive wear is likely to occur at all surfaces against which the particles impact.
47、 Velocity is one of the major parameters and so the problem may be significantly reduced in a low velocity system. 3007 friable or degradable material A material in which the particles are easily damaged. NOTE. If degradation of the conveyed product is to be minimized, a system in which the material
48、 can be conveyed at low velocity should be considered. The number and magnitude of particle impact points, particularly against bends in the pipeline, should be reduced as this is one of the major causes of the problem. 3008 hygroscopic (deliquescent) material A material which readily takes up moist
49、ure. NOTE. For products which are hygroscopic or deliquescent it may be necessary to condition the conveying medium to avoid the introduction of moisture into the conveyed material. BSI 1996 7 BS 7871 : Part 1 : 1996 No. Term Definition 3009 low melting point material A material that softens or melts at temperatures which may be encountered in a pneumatic conveying system. NOTE. The energy from the impact of particles against bends and pipe walls at high velocity in dilute phase conveying can result in high particle temperatures being generated. The effect is localized t
