Booster fan applications for sections in longwall and room-and-pillar mining

1. Booster fan applications for sections in longwall and room-and-pillar mining Christopher Pritchard MS PE Acting Team Lead Ventilation Group Fires and Explosions Branch Spokane, WA

2. Acknowledgement • Thanks to Co-Authors • Anu Martikainen PhD • Andrew Wala PhD • Garrett Frey • Gerrit Goodman PhD

3. Introduction • Background • Short development modeling • Long development modeling • Small mine field testing • Large mine field testing • Discussion and Conclusions

4. Background Booster fan use in US coal mines 30 CFR 75.302: Each coal mine shall be ventilated by one or more main mine fans. Booster fans shall not be installed underground to assist main mine fans except in anthracite mines. In anthracite mines, booster fans installed in the main air current or a split of the main air current may be used provided their use is approved in the ventilation plan. 2006 Technical Study Panel recommendation: that booster fans be examined as one of the potential available tools to assist main surface fans, reduce leakage, and provide more air to ventilate working areas

5. Proposed Study NIOSH Project in response to Technical Stugy Panel: Modeling of booster fan installations in: Short panel development systems < 1000m Long panel development systems ~3000m Perform field studies in: Small mine – Bruceton research coal mine Large mine – Wyoming trona mine with longwall and development panels MNM Class III Gassy Mine Similar layout and equipment to coal mining

6. Short development model scenarios • No. of EntriesDescription • 2 Intake / Return • 3 Intake central, belt, and return outside • 4 Belt and intake central, outside return entries (fishtail) • 5 Dual return left, belt/track central, intake outside right • Utilized Ventgraph to simulate a single booster fan operation • Booster locations (a) first Xcut inby portal or (b) Mid-way to face • Installed in: (a) belt, (b) travelway or (c) return

7. Illustration: Small Mine Development Model #4“Fishtail” VentilationBooster Mid-Panel Travelway Main Fan

8. Small development results • Outby locations generally minimize recirculation • Inby locations recirculate more air with increasing pressure, necessitating increased vigilance • Belt installations are not practical (as expected) and were eliminated from further modeling • Boosters increase airflow, but not always system efficiency • Even small networks require effort to correctly locate booster fans due to system sensitivity from small pressure changes • Small developments are good place to start modeling to understand booster fans

9. Extended 3,000m development model scenarios • 1. base case model—main fan only • 2. four boosters, two intake and two return (shown) • 3. single outby intake booster • 4. single inby intake booster • 5. two offset boosters—outby intake and inby return • 6. two boosters—outby intake and outby return Main Fan

10. Discussion - modeling • 3,000-m longwall extended developments show that booster fans operating at lower pressures, around 125 Pa, can improve system efficiency with minimal recirculation. • In some applications, multiple booster fan systems show improved results, although benefits must be balanced with the associated issues of ventilation system complication and management. • Recirculation was less than 2.5% of booster fan airflow in all extended development system models, except for the inby intake booster fan which, at 18%, is consistent with results from the small mine development system models. • A well-designed system minimizes pressure differentials, stopping leakage, and recirculation through appropriate booster fan location and pressure management. • Extended development system models showed that booster fans can increase face airflow and, through careful placement and pressure management, can control pressure differentials to minimize recirculation.

11. Booster Fan Testing at the Bruceton Experimental (small) Mine Booster Inby Booster fan with VFD Booster Outby

12. Bruceton small mine results • Confirmed small mine modeling results • Inby booster systems are more prone to recirculation • In both cases, airflow in neutral entries ultimately reversed as booster fan pressure increased • With increasing pressure, the booster fan caused recirculation outby the fan and reversal of neutral airflow • Airflow at the face increases with higher inby booster fan pressure, often containing a recirculated air component

13. Field Work at large room and pillar longwall mine

14. Booster fan test area Booster Fan – 125 HP w/VFD in Belt Drift Airflow / Pressure Differentials

15. Test results – large room and pillar longwall mine • Ventilation airflow efficiency and panel/submain recirculation percentages rose with booster fan airflow • Booster fan test panel circuit recirculation was high outby the fan, with most of additional panel airflow leaking back into the intake • Recirculation caused by return airway restriction outby • Test and model airflows and pressures showed good correlation, but existing mine model needs updated • Modeling of leakage during normal and booster fan operation was not equivalent. Stopping resistance value is different depending on return or intake direction.

16. Discussion – field work • Booster pressures over 500 Pa greatly increased test panel airflows (2.6 to 4.3 times), caused high localized recirculation with minimal effects on nearby panel airflows, and produced good correlation with pretest modeling. • As booster fan pressures increase, efficiency can decrease due to overriding of main fan or localized ventilation capacity. • Balancing is easier during modeling when the mine is in a static condition, and much more complicated in the dynamic conditions of day-to-day operation.

17. Conclusions • Booster fans have yielded favorable results in US metal and non-metal mines and international coal mines over many years and under different conditions. • When installed and operated correctly to minimize recirculation, and by utilizing the improved technology of network modeling, ventilation system monitoring and control, booster fans can be an effective tool to increase airflow in underground coal mines. • Studies of short and extended coal mine development systems in conjunction with small and large in-mine tests show that booster fans can be used to increase face airflow.

18. Conclusions continued • Outby locations minimize recirculation, and multiple booster fan installations may be used to balance leakage and recirculation effects. • In coal mine applications, safety is enhanced by pressurizing the intake entry with an outby booster fan to prevent the potential influx of belt entry contaminants and to minimize recirculation. • Multiple booster fans installations may add safety and efficiency benefits, but also complicate the ventilation system. • Mine environments continually change, requiring constant vigilance should booster fans be installed.

19. Where are we? Remember? – 2006 Technical Study Panel recommendation: That booster fans be examined as one of the potential available tools to assist main surface fans, reduce leakage, and provide more air to ventilate working areas Answer: Yes - with appropriate precautions, booster fans can be used to accomplish the above goals.

20. Thank you! Questions?May 2nd, 40th Anniversary of Sunshine Fire Questions or Comments? CPritchard@cdc.gov 509-354-8021