Analysis of Wear Mechanisms in Pneumatic Conveying Pipelines of Fly Ash

Abstract

Pneumatic conveying is a frequently used method of material transport particularly for in-plant transport over relatively short distances. This is primarily to exploit the degree of flexibility it offers in terms of pipeline routing as well as dust minimization. Approximately 80 % of industrial systems are traditionally dilute phase system which uses relatively large amount of air to achieve high particle velocities to stay away from trouble, such as blocking the pipeline. However, for many applications higher velocities lead to excessive levels wear of pipelines, bends, and fittings. To combat these problems, many innovative bends have been designed. These designs have solved the problem of wear in the bends, but often introduce the wear problem in the area immediately after the bend due to the changed flow conditions. Wear in pneumatic conveying is a very complex problem and at present there is limited understanding of the wear mechanisms responsible for the severe wear in certain areas of a pneumatic conveying pipeline. The ability to determine the wear mechanisms in these areas holds the key for determining the service life of pneumatic conveying pipelines in industry. Even though the fly can be conveyed at low velocity dense phase mode, wear of pipeline conveying fly ash remained a critical issue for many power plant operators. In this paper the wear mechanisms in a fly ash conveying pipeline has been analyzed. Wear samples from fly ash conveying pipeline have been collected and analyzed for dominant wear mechanisms in the critical wear areas. Analysis of the worn pipeline showed continuous wear channels along the bottom of the pipeline consistent with the abrasive wear by larger particles. The other severe wear areas are the sections after the special bends used to reduce bend wear. Scanning electron microscope (SEM) analysis of the surfaces revealed that both erosive wear and abrasive wear mechanisms are present in these areas. Formation of a surface layer similar to transfer film in alumina conveying pipelines have been recognized in this analysis. These layers seem to be removed through brittle manners such as cracking and spalling. The wear mechanisms and the wear debris seen on the surface are consistent with wear by larger particles.