Introduction to pneumatic conveying and the guide
The Pneumatic Conveying Design Guide is intended to be of use to both designers and users of pneumatic conveying systems. It has been written on the basis that the reader knows little or nothing about pneumatic conveying or pneumatic conveyors, hence each aspect of the subject is discussed from basic principles and many of the chapters are of an introductory nature. The Guide, however, also includes detailed data and infor- mation on the conveying characteristics of a number of materials embracing a wide range of properties.
The data can be used to design pneumatic conveying systems for the particular mater- ials, using logic diagrams for design procedures, and scaling parameters for the con- veying line configuration. Where pneumatic conveyors already exist, the improvement of their performance is considered, based on strategies for optimizing and up-rating, and the extending of systems or adapting them for a change of material is also considered.
In this introductory chapter a brief introduction to pneumatic conveying is given to introduce the common terms and concepts. First among these are dilute and dense phase conveying and the specific problem of compressibility of air and other gases that might be used. The capability of pneumatic conveying systems in terms of distance, tonnage and orientation are addressed, together with a brief history of developments. A very brief review of the chapters is given, along with some of the basic definitions, and the nomenclature adopted in the book is presented here for reference.
Pneumatic conveying systems are basically quite simple and are eminently suitable for the transport of powdered and granular materials in factory, site and plant situations. The system requirements are a source of compressed gas, usually air, a feed device, a conveying pipeline and a receiver to disengage the conveyed material and carrier gas.
The system is totally enclosed, and if it is required, the system can operate entirely without moving parts coming into contact with the conveyed material. High, low or negative pressures can be used to convey materials. For hygroscopic materials dry air can be used, and for potentially explosive materials an inert gas such as nitrogen can be employed. A particular advantage is that materials can be fed into reception vessels maintained at a high pressure if required.
With a suitable choice and arrangement of equipment, materials can be conveyed from a hopper or silo in one location to another location some distance away. Considerable flexibility in both plant layout and operation are possible, such that multiple point feed- ing can be made into a common line, and a single line can be discharged into a number of receiving hoppers. With vacuum systems, materials can be picked up from open stor- age or stockpiles, and they are ideal for clearing dust accumulations and spillages.
Pipelines can run horizontally, as well as vertically up and down, and with bends in the pipeline any combination of orientations can be accommodated in a single pipeline run. Conveying materials vertically up or vertically down presents no more of a problem than conveying horizontally. Material flow rates can be controlled easily and monitored to continuously check input and output, and most systems can be arranged for completely automatic operation.
Pneumatic conveying systems are particularly versatile. A very wide range of mater- ials can be handled and they are totally enclosed by the system and pipeline. This means that potentially hazardous materials can be conveyed quite safely. There is minimal risk of dust generation and so these systems generally meet the requirements of any local Health and Safety Legislation with little or no difficulty.
Pneumatic conveying plants take up little floor space and the pipeline can be easily routed up walls, across roofs or even underground to avoid existing equipment or structures. Pipe bends in the conveying line provide this flexibility, but they will add to the overall resistance of the pipeline. Bends can also add to problems of particle degradation if the conveyed material is friable, and suffer from erosive wear if the material is abrasive.