mitigation of post blast fume generation in soft ground ... · mitigation of post blast fume...
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Mitigation of post blast fume generation in soft ground and wet conditions
Lee Julian, Anand Musunuri, Ewan Sellers, Sarma Kanchibotla
Is it important for industry to manage?
Value: • Fines for infringement • Lost production from late re-entry • Mines closed • Projects stopped due to potential
for fume
ACARP C23016 Approach
- Known issues – soft ground, wet/deep holes - Review - Develop measurement techniques - Lab experimentation - Field observations - Risk management framework Challenges - Declining coal price - Withdrawal of partner sites
Measurement techniques
mobile laboratory • Water content in ammonium nitrate emulsion
• ANE viscosity
• ANE ammonium nitrate proportion
• Water content in ammonium nitrate prill
• Ammonium nitrate prill purity
• Ammonium nitrate prill size distribution
• Water content of blends
• Prill to emulsion ratio of blends.
Water Ingress tester Index test - Beakers
Detonation of mining explosive
• AN, fuel & Sensitiser • Pressure • Self propagating shock wave • Rapid, exothermic reaction • Expansion of confinement • Post detonation reactions
ideal detonation when explosive reacts instantaneously and completely. In a non ideal detonation not all the chemicals react fully. Deflagration is when the chemical burns
Rock Diameter Product
Good &
Large &
Good
Poor or
Small or
Poor
component
Fume and “Detonation” Oxygen balanced:
3𝑁𝐻4𝑁𝑂3 + 𝐶𝐻2→3𝑁2 + 7𝐻2𝑂 + 𝐶𝑂2 (1) Fuel lean:
5𝑁𝐻4𝑁𝑂3 + 𝐶𝐻2→4𝑁2 + 2𝑁𝑂 + 11𝐻2𝑂 + 𝐶𝑂2 (2) Fuel rich:
2𝑁𝐻4𝑁𝑂3 + 𝐶𝐻2→2𝑁2 + 5𝐻2𝑂 + 𝐶𝑂 (3) Deflagration:
3𝑁𝐻4𝑁𝑂3 + 𝑁𝐻4𝑁𝑂3→2𝑁𝑂2 + 3𝑁2 + 8𝐻2𝑂 (4) Post detonation nitrogen reactions:
2𝑁𝑂 + 𝑂2→2𝑁𝑂2 (5)
2𝑁𝑂2⇔𝑁2𝑂4 (6)
No fume Invisible fume No fume Visible fume Visible fume
Wet holes
What is the source of the water? How long must the water be in contact with the explosives? Was there a single rain event, or continuously flowing ground water? The Queensland Fume Steering Group provided their fume database of over 5000 blasts for review; 1.46 million tonnes of explosives blasted at 42 mine sites reporting 48 categories per blast for 3.25 years.
Wet holes: The data
52% 51% 41%
74% 74%
44%
19% 15% 21%
9% 11%
25%
22%
13% 16%
6% 5%
13%
4%
9% 11% 6% 6%
13%
4% 10% 8%
6% 5% 0%
0% 2% 3% 0% 0% 6%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
30% EP 40% EP 50% EP 30% EP 40% EP 50% EP
Wet Dry
Fume frequency, Wet vs Dry: HANFO
5
4
3
2
1
0
Wet Dry
Wet holes
Queensland database: Was the blast loaded to design?
Yes No N/A 4876 116 43 97% 2% 1%
Correlation: Low % 70% blend correlates to fume Causality Rain causes ad hoc changes on bench and the products already charged are damaged Proactive Design for rain. Expand patterns
higher PF
Field observations
Wet holes
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0
20
40
60
80
100
120
140
160
180
200
Janu
ary
2011
Febr
uary
201
1
Mar
ch 2
011
April
201
1
May
201
1
June
201
1
July
201
1
Augu
st 2
011
Sept
embe
r 201
1
Oct
ober
201
1
Nov
embe
r 201
1
Dece
mbe
r 201
1
Janu
ary
2012
Febr
uary
201
2
Mar
ch 2
012
April
201
2
May
201
2
June
201
2
July
201
2
Augu
st 2
012
Sept
embe
r 201
2
Oct
ober
201
2
Nov
embe
r 201
2
Dece
mbe
r 201
2
Janu
ary
2013
Febr
uary
201
3
Mar
ch 2
013
April
201
3
May
201
3
June
201
3
July
201
3
Augu
st 2
013
Sept
embe
r 201
3
Oct
ober
201
3
Nov
embe
r 201
3
Dece
mbe
r 201
3
Janu
ary
2014
Febr
uary
201
4
Mar
ch 2
014
April
201
4
May
June
Fum
e ra
ting
Mon
thly
rain
fall
(mm
)
Rainfall and fume
Wet holes Evidence of groundwater could be observed readily through the pit
Borehole camera observed dynamic water down hole
Water ingress tester
Testing issues and solutions overnight
Separation and Deflagration:
3𝑁𝐻4𝑁𝑂3 + 𝑁𝐻4𝑁𝑂3→2𝑁𝑂2 + 3𝑁2 + 8𝐻2𝑂
Wet holes: Detonation performance ANFO rinsed with 4 litres ANFO rinsed with 6 litres
70 000 fps Critical amount of water creates fume
Wet holes: Detonation performance ANFO rinsed with 4 litres ANFO rinsed with 6 litres
3168 2905
Similar Max VoD
Wet holes: Detonation performance
From left to right: ANFO rinsed with 2 litres of water, ANFO rinsed with 6 litres of water, ANFO rinsed with 2 litres of acid, ANFO rinsed with 5 litres of acid, ANFO saturated with water
VOD not strong indicator of fume potential
Soft ground: Modelling the detonation
Two explosives were modelled, ANFO and a 40% ANE HANFO using Vixen2009 code.
Blend
ANFO
Hard rock
weak rock
hot
cool
Sellers; Furtney et al. FRAGBLAST10
Soft ground: Modelling NOx
The rate at which NO converts to NO2 was identified to be a very strong function of temperature. Conversion happens at low temperature.
Soft ground: Modelling NOx in soft ground Bringing the modelled relationships from detonation and NO2 synthesis:
strong
weak ANFO Blend
weak
ANFO Blend
weak
Soft ground: Detonation testing
• Wedge tests to simulate cavity • below critical diamater • Non ideal detonation • Cools more rapidly • DRY ANFO = fume
Methodology to minimise fume
1. Characterise long term influences well ahead of blast design seasonal rain variation, ground water flow, rock mass strength and structure as well as the presence of catalysts , such as carbon, acid or organics
2. Regular explosive testing to track quality variations Quality vital. Affected by small components eg surfactants. Mobile laboratory for constituent tests, Beaker tests, Viscosity
3. Design blasts ahead of time for expected conditions possible rain and long term ground water seepage
4. Implement to design Systems in place to manage necessary variations to the plan. Minimise last minute changes on a blast pattern to add water resistant product during rain by planning ahead and charging blasts with suitable products proactively.
5. Measure during blast Pressure, VoD, temperature.
6. Reactive systems as back up Risk assessment, wind direction simulation, gas detectors and emergency evacuation plans.
Conclusions
• Water flow routes obvious, but unexpected on site. • Post detonation reactions cause visible fume. Many
small factors contribute. • Product selection, downhole quality, testing vital. • In soft ground rapid expansion and cooling leads to
conditions for NO2 • Fume mitigation requires proactive approach and
testing, which will reduce fume, improve efficiency on the mine and also offers cost advantages.
http://hfacs.com/hfacs-framework.html
Acknowledgements
• Australian Coal Industry’s Research Program (ACARP) C23016.
• Steve Simmons, Vishwa Bhushan, Lindsay Ford and Keith Smith are thanked for their support and assistance.
• Gary Cavanough and Miguel Araos for testing. • Site teams