Development of Pneumatic Stowing Equipment and a Study of the Principles Involved

Abstract

In certain methods of coal mining it is necessary to extract rock in order to enlarge the excavations which provide access to the coal seam. This rock must either be transported out of the mine or be deposited into space provided by the extraction of the coal.  It is desirable to mechanise the deposition of rock into this space. One means of doing this is to blow the rock through pipes by means of compressed air, feeding the rock and compressed air into the pipes through a unit known as a stowing machine. The operation is known as pneumatic stowing. The aim of the work described in this thesis is to make an assessment of existing stowing machines used for the disposal of material underground, and to carry out a study of the principles associated with the development of pneumatic stowing equipment. The faults and failures of existing stowing machines are examined and a Design Theory as a basis for a new development is given. The manufacture of a test rig and a study of the results of trials carried out with it, is used to design a prototype stowing machine. The stages of development of the prototype machine with the subsequent trials results are given, and an assessment of the performance, efficiency and economic possibilities are made. A full scale model manufactured in perspex has been used to obtain a clearer understanding of the behaviour of material passing from the stower into the conveying pipeline. The construction of the model is described. Model tests using different types of material are examined as a means of assessing the optimum air flow and rotor speed values for the stowing machine. The author holds the position of Mechanical Project Engineer at the National Coal Board Mining Research end Development Establishment. The N.C.B. MK.I Stowing Combine described in chapter 1 was already in existence, and the author's contribution to this development was to carry out design improvements, assess the results of underground trials, and formulate conclusions and recommendations for future development. The author's stower design theory is given in chapter 3, and chapter 4 describes the subsequent investigation and development of a prototype stowing machine. The author's laboratory investigations using a stower model test rig, the observations made, and the resulting conclusions, are outlined in chapters 5 and 7. The work carried out for this thesis also includes a search and examination of other investigators research to obtain any available information which could be relevant to the author's investigations. The scope and limitation of the search are outlined in chapter 2, with a more detailed reference to the work of Broadhurst16 which is given in chapter 6. The work of Broadhurst has been referred to specifically because his investigations were concerned with stowing materials and conveying pipelines in stowing installations within the National Coal Board. Throughout the thesis, British units are given, followed by the equivalent metric values rounded off to the nearest unit.