R. Marcus

Fluid and particle dynamics

In pneumatic conveying, particles are generally in suspension in a turbulent gas stream. The question of drag on a single particle, and the effects of Reynolds number, particle shape and roughness, voidage, turbulence intensity and scale of turbulence, acceleration, etc. on drag are relevant to pneumatic conveying. These factors will be discussed in this chapter. Equations for calculating important properties such as drag coefficient, terminal velocity, minimum fluidization velocity, and the equation for flow through a packed bed are presented. The characteristics of a powder in terms of its fluidization behaviour are relevant to pneumatic conveying, and will also be discussed.

Principles of Pneumatic Conveying

Chapter 6 gets down to the basic principles, analysis and design on pneumatic conveying systems. The system is broken down into its major components and energy requirements and relates the physics of gas–solid transport to the practical pressure loss for design purposes. The various components of the system are considered in details with diagrams showing the behavior of the system as well as provided basic design equations for the student and practitioner.

Feeding of Pneumatic Conveying Systems

Essential to the effective operation of a pneumatic conveying system is the efficient feeding of the solids into the pipeline. Feeding devices perform a variety of functions, including a sealing function, in which the conveying gas is essentially sealed from a storage hopper holding the product to be conveyed. Further, these devices might be required to accurately control the solids feed rate into the pipeline for process control features as in chemical plants or in dosing operations.

An overview of pneumatic conveying systems and performance

This chapter sets the scene for understanding and design of pneumatic conveying systems. Pneumatic conveying is broken down into its component parts indicating the further details will be given in the following chapters. The basic state diagram is presented and the various flow conditions are related to this diagram. Some of the recent comprehensive discussions on pneumatic conveying are cited.

Flow in standpipes and gravity conveyors

This chapter is concerned with the flow of solids under gravity. Two types of flow will be considered. In one, solids flow downwards in a vertical or inclined tube generally known as a ‘standpipe’. Standpipe flow is often encountered in the outlet of hoppers, in cyclone diplegs and particularly in transferring solids out of a fluidized bed. The other type of gravity flow considered here is analogous to open channel flow of a liquid. This is known as flow in a gravity conveyor or an air-slide. Solids flow down a channel tilted a few degrees to the horizontal (often between 1° and 8°). The solids are fluidized by an upflow of gas close to the minimum fluidization velocity and flow down the channel like a liquid. In this chapter, the two types of gravity flow will be considered separately.

Some Comments on: The Flow Behaviour of Solids from Silos; Wear in Pneumatic Conveying Systems; Ancillary Equipment

There are a number of additional facets in the design of pneumatic conveying systems which in their own right could form the basis of a separate handbook. An awareness of the intricacies of silo and hopper design, wear in pneumatic conveying systems and the type and characteristics of a number of essential hardware components are deemed to be important information for the system designer.

An Overview of High-Pressure Systems Including Long-Distance and Dense Phase Pneumatic Conveying Systems

The recent surge in interest in dense phase and long distance pneumatic conveying has stimulated vendors to develop a number of new systems specially directed towards increasing their market share in bulk materials handling. The proliferation of such systems has met with varied success and in many situations a basic lack in understanding of the flow phenomena has resulted in inappropriate solutions being offered for a particular handling problem.

Single Phase Flow in Pneumatic Conveying Systems

The design of any pneumatic conveying system requires a basic understanding of air flow in pipes and ducts as well as an appreciation of the various prime movers used to supply air.

System design and worked examples

In an attempt to illustrate the various concepts discussed in the preceding chapters, a number of worked examples relating to pneumatic conveying systems will be presented in this chapter. Where possible each example has been structured so as to illustrate a number of facets of the theory, whilst an attempt has also been made to design each problem so that it relates to practical pneumatic conveying problems.

Control of Pneumatic Transport

For pneumatic transport the basic principle of analysis is the material balance of the solids transported. A number of different situations could arise for the control of the solids flow. The macro approach to the control analysis will be considered first; then more detailed distributed models of the actual solids flow will be explored.