Foam Injection Technologies for Goaf Inertisation

This report consists of the summary of the research work carried out under the Australian coal association research program (ACARP) project C15020 -"Foam Injection technologies for Goaf Inertisation". The main objective of the project is to develop and demonstrate the application of foam technologies as a ventilation restriction to reduce airflow in longwall goafs during normal operation and to enhance the effects of low flow inertisation techniques.

A critical review of the several heating control operations in Australian longwall mines has revealed that the success or failure of inertisation operations depends entirely on design of inertisation strategies and control of inert gases underground. Thus the development and use of technologies that maximise the effectiveness of inertisation process is warranted. This project is envisaged to develop and demonstrate cost effective foam technology applications with the current inertisation practices. The aim is to reduce the risk of heatings in longwall panels during slow retreat periods and during final stages of panel extraction during bolting up operations. The project is carried out in three areas, firstly the products suitable for foam plugs are identified, secondly extensive CFD modelling studies to simulate the air flow in the goaf are conducted and finally field trials and tracer gas tests are carried out at the mine site to evaluate the effectiveness of the foam plugs.

Laboratory tests were conducted to identify the constituents and the additives to give consistent and long lasting foam. Foam production trials at surface were also conducted to know the effect of various foaming agents and the effect of surrounding atmosphere and air velocity on the stability of the foam.

Three dimensional CFD models were developed to simulate the oxygen ingress and methane distribution patterns in the longwall goaf. These models are validated with gas monitoring data from the mines. A number of parametric studies were conducted to investigate the use of foam plug at different locations to minimise the air ingress into the goaf with and without inert gas injection into the goaf.

Tracer gas studies were done at the trial mine sites to determine the goaf air flow patterns with and without the presence of foam plug. The results are used to calibrate the CFD models and formulate field trial strategies.

Laboratory tests indicate that the new chemical blend for foaming could last for many days. The durability or stability of the foam depends upon the surrounding wind airflow and confinement conditions. CFD studies illustrated that the introduction of foam plug into the perimeter of the longwall has limited the oxygen ingress and potentially aided the self inertisation process of the goaf. The results of the tracer gas tests and field studies revealed that introduction of foam air plug can change deep goaf gas flow patterns and therefore facilitate better goaf inertisation. The project results will be helpful for the industry in developing strategies to reduce self heating incidents while operating the longwalls in difficult geo-mining conditions.

An e-newsletter has also been published for this project, highlighting its significance for the industry.