Erleichterungen bei der Planung und Auslegung von Schüttgut-Aufbereitungsanlagen am Beispiel der pneumatischen Förderung

Facilitating the planning and design of plant for working of bulk solids, as illustrated by pneumatic conveying . Taking the case of pneumatic conveying as an example, the article shows how plant construction companies can achieve considerable simplifications and time saving in the planning and building of plant for working of bulk solids by adopting a systematic approach utilizing card indexes of bulk materials and working diagrams. Companies operating such plant are made aware of the thorough preparation invested in new projects and of the approach adopted and problems encountered in the preparation of tenders. A simple general view of the present state of knowledge can possibly provide impulses for new considerations.     

Die Grundlagen der pneumatischen Förderung

Principles of pneumatic conveying . The design of pneumatic conveying systems is critically dependent upon a knowledge of the pressure drop and the minimum necessary velocity of the conveying gas. Starting from the areas of application of pneumatic conveying systems, the conveying states occurring are discussed and appropriately assigned to the diagram of state. The pressure loss equation is reported for conveying in form of a fully suspended flow and strand-type conveying and the theoretically predicted pressure losses are compared with experimental values for the conveying of coarse and finegrained materials. After mentioning the calculation of the pressure drops due to acceleration and to pipe bends, the article discusses the problem of pipe enlargement for long conveying distances. Equations are also given for the calculation of the so-called blocking limit and of the conveying gas velocity at which the minimum pressure drop occurs. The influence of the compressor on the choice of the operating point is also discussed. New calculation equations are then given for horizontal and vertical conveying in form of a fully suspended flow conveying and for horizontal strandtype conveying which permit reliable scale-up. Moreover, a new equation is reported for the blocking limit in horizontal conveying.     

Dichtstromförderung

High density pneumatic conveying . In distinguishing between high density pneumatic conveying and low density conveying it is insufficient to merely use the solids loading to characterize the various flow states. Less ambiguous classification is possible only on the basis of the diagram of state of pneumatic conveying. Most flowable bulk solids can be transported through normal smooth-walled piping in the high density mode with normal conveying equipment. In contrast, fine-grained products in particular tend to adhere to the wall and form blockages. Paying due attention to the differing flow properties of various bulk solids and to the mechanisms of blockage formation and clearance, various new conveying techniques and piping types have been developed in recent years, permitting in some cases the transport of adhering, abrasive, and attrition-sensitive materials. Since conveying pressures up to about 6 bar are usual in the high-density regime, various combinations of pressure vessels are primarily used for feeding the bulk solids into the conveying pipes. The advantages of conventional, and also special high-density conveying systems are discussed with the aid of examples.