1. Controlled Recirculation of Air
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2. Ventilation
Ventilation is the control of air movement, its amount, and direction.
The goal of ventilation system is to provide work environment that contains minimal safety and health risks and is conducive to hard work.
It’s a non-productive job.
It is a cost function so the goal of ventilation should be met as inexpensively as possible.

3. Basic ventilation system in underground
Source : Kissell, F.N. (2006).

4. Recirculation of air
If a particular amount of air, passes through a single point, more than once, then air is said to be recirculated.
Recirculation causes:
Spontaneous heating
Methane accumulation
May reduce oxygen concentration

5. A Single District Recirculation Circuit
Source : Kissell, F.N. (2006).

6. Recirculation in a heading
Source : Kissell, F.N. (2006).

7. Controlled partial recirculation of air
The definition of a system of controlled partial recirculation is one in which a controlled fraction of the air returning from a work area is passed back into the intake while, at the same time, the volume flow of air passing through the region is monitored to ensure that it remains greater than a predetermined minimum value.

8. Advantages of controlled recirculation of air
It improves environmental conditions and allows mining to proceed in areas of a mine that are too distant from surface connections to be ventilated economically by conventional means.
It reduces the tendency to methane layering and diminishes the probability of accumulations of explosive methane-air mixtures

9. Principle of controlled re-circulation of air
source : McPherson, M.J. (1991).

10. The general body gas concentration, C, is given by
The fractional gas concentration, Cg, at position D must be

11. Continued…..
Gas flow, G = Gas concentration*airflow
The gas flow in the duct, ,must then be

12. Hence, the gas concentration in the duct, Also,

13. Comparison Between Conventional Ventilation and Controlled Recirculation
Source :Stachulak, J.S. (1992)

14. Case study COLD CLIMATE MINES – CANADA
Controlled recirculation of mine exhaust air has potential for reducing the cost of heating cold fresh air in winter.
The controlled recirculation objective in Canadian mines is to reduce heating costs of cold air.
This can be accomplished through a decrease in intake air volume, which then is replaced by an equal amount of recirculated air.

15. The application of recirculation for Canadian mines is actually entirely different from the application in UK coal mines and South African gold mines.
In both these countries, recirculation is stimulated by the necessity to control two major environmental parameters, heat and dust.
The recirculation models presented for U.K. and South African mines are still valid, but they cannot be interpreted in the same way.

16. ln Canadian mines, the diesel pollutants are the principal concern and major aspect of health and environmental engineering.
The cost of heating intake air in Canadian mines considerably outweighs the ventilation airflow distribution costs
Since intake airways and shafts need to be heated, recirculation then should take place as close to the surface main fresh airway as practical.

17. Recirculation Ventilation System with Underground Main Fans
Source : Stachulak, J.S. (1992).

18. References :
McPherson, M.J. (1991). Subsurface Ventilation and Environmental engineering, chapter-4, pp
Stachulak, J.S. (1992). Controlled air recirculation for Canadian hard rock mining, ISBN Publishers, Montreal, Canada, pp
Kissell, F.N. (2006). Handbook for Methane Control in Mining, Information Circular 9486, Pittsburgh, pp 15.
Morgan, L (SEP,2009). Recirculating air from dust collectors, Plant Engineering, pp 1-4.