FEATURES:

As an interesting tool for determining in real-time the effectiveness of a emergency measures adopted in case of fire in underground mines, the present study was carried out to analyse the macro-scale behaviour of smoke.
Starting from a numerical simulation of the ventilation system on static conditions, the software has been developed to simulate how the creation of smoke and the increase of temperatures affect the whole ventilation system, and which effects can give the emergency measures adopted, such as closing and opening ventilation doors and stopping or inverting fan. Great attention has been paid to keep the simulation time very small.

Figure 01
This simple schema explain how the Hardi-Cross algorithm works: by adding an arbitrary flow rate additional in a defined direction, the flows relationship at each node does not change.

Figure 02
To optimize the solution algorithm, the additional flow rate is defined as a function of the pressure difference at each closed loop. This allows a quicker convergence and more precise results.

Figure 03
Using different function for defining the additional flow rate, the convergence curve on the same loop can change significantly.

Figure 04
The simulation of the static ventilation conditions give results closed to real data. Notice that the simulation time is around 5 minutes.

Figure 05
Flows results are also provided in graphical way. The chromatic scale ranges from 0 to 90m3/s.

Figure 06
Detail of the bottom levels: fresh air descends the slope, recirculates over exploitation zones and then exit from the return draft.

Figure 07
A study of how smoke behave at tunnel crossing has been carried out using FEM software. Smoke distribution is not simple proportional to flow rates but also depends on geometric and pressure conditions.

Figure 08
Fire temperature evolution is described with a curve similar to ISO-834. Flashover has been placed at fifteenth minute.

Figure 09
To approximate temperature diffusion, each tunnel is assimilated to a heat changer. Smoke and fresh air are considered immiscible fluids.

Figure 10
Changes on the ventilation system do not take effect immediately, but due to the whole mine inertia, the ventilation system needs a certain time to reach the full equilibrium after a change is done. For that reason door's friction factor decreases over time to simulate the inertia.

Figure 11
The emergency measures adopted aims to suffocate the fire: a door is opened to bypass the fire and the secondary fan is turned off. Even so, effects are so significant that the flow in the right zone of the mine inverts his direction.

Figure 12
After 45 minutes, when emergency measure are fully effective, a strong smoke recirculation occurs between levels around the fire. At the same time fresh air bypass the zone of the mine affected by the fire.

Figure 13
Flow rate evolution on the return drift, where the auxiliary fan is located.

Figure 14
Fresh air flow feeding the fire evolves over time: when the emergency measures aiming to suffocate the fire start to have effect, the flow decrease.

Figure 15
The software also determines smoke propagation and concentration in the mine.

Figure 16
Comparing simulation time with the real time, it can be appreciated how fast SIMONE can provide useful data about fire evolution. The situation after an hour can be simulated half an hour in advance.



Actually, the project SIMONE is still under development.
The activities on which we are now focusing our attention are:
  • validation of the static algorithm;
  • subroutines implementation:
    • fire behaviour in function of oxygen feed;
    • improvement of the subroutine that determine the smoke propagation (problems when the smoke recirculate till the fire point, when the flow direction changes);
    • approximation problems due to very large elements;
  • validation of the change curves that simulate inertia;
  • graphic user interface (GUI) development;
  • algorithm optimization to reduce the runtime;
  • map of the smoke behaviour at crossings.




area3 engineering    Universidad de Oviedo    RavenRoad Mining



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