Recirculation can be defined as any portion of mine airflow that travels through the same location more than once.
Users of Ventsim™ Advanced can use new recirculation simulation routines, to test and calculate recirculation through every single airway in the mine simulation model. This function provides essential information on portions of the mine that may have controlled or uncontrolled recirculation, and allows users to gauge the potential impact and consequences of such recirculation.
In addition, while it does not necessarily indicate how much of the air has already recirculated in other portions of the mine, there is a secondary option called ‘Recirculation Stream’ which shows the maximum amount of recirculated air present in all downstream headings.
To activate the recirculation function, as before simply press the recirculation button to instantly show the results. For large models with significant recirculation, a warning may show indicating the process may take a little time to calculate.
The colours will automatically change to display recirculation percentage. The alternative data display for downstream recirculation (“Recirculation Stream”) can be selected from the colour or data ‘Contaminant Menu’ group.
In some cases, minor recirculation of air (for example, air leaking under the seal of a closed door) may be unavoidable, particular where high pressures are present. If this contributes to a relatively low total recirculation percentage, this can generally be ignored, although the permissible amount may need to be risk assessed for hazards such as heat, fumes and gas buildup. In addition, there is an option in the Tools > Settings > Airflow Simulation menu to restrict reporting of lower recirculation flows.
Chasm Consulting suggests a permissible figure of no more than 5% recirculation due to leakage, however this figure is highly dependent on the situation and type of mine. A coal mine for example, with potential buildup of methane may find this unacceptable, whereas an ‘over’-ventilated metalliferous mine may feel comfortable exceeding this level.
It should be noted that regulations in some countries do not permit any recirculation. While regulatory authorities are normally sympathetic to minor recirculation from leakage, each mine should check its own regulatory requirements before ‘designing’ recirculation (whether controlled or uncontrolled) in to their mine model.