Petram FAQ

 

Why the name “Petram”?

Petram is latin for “rock”.

 

How do I use your service?

The services can be used for mining and quarry secondary blasting. It can also be used for urban construction/demolition projects. We sell the services through value-added resellers or licensed franchisees. If you are interested in ordering or providing services pleas contact us.

 

Can I be a reseller of this technology?

We are looking for Value Added Resellers. Please contact us for new information.

 

Has any vibration/air over pressure testing been performed?  If so, what are the readings at various distances?

No vibration or air over pressure formal tests have been performed. However, while the tests were performed( 46 tests)  the technicians were ~ 20 feet from the “blast”. They reported the sound to be equivalent to dropping a boulder on concrete from a height of ten feet.

 

Can you detonate multiple holes at one time or at timed intervals?

While this has not been done, it can be done.

 

What is the breakage radius?

The average breakage was ~ 2 -3 feet in each axis. Therefore the total fracture was 8-27 cu ft per shot.

 

Can you use a larger diameter hole?

All holes tested were 1-inch diameter but you could drill a larger hole.

 

Can you drill a deeper hole?  

Hole depths of 6, 12, and 18 inches were tested

 

What’s the recharge time?

The recharge time was 15 seconds in the lab. It may take 1 minute in the field.

 

Do you have to chain down the probe so it doesn’t fly away?

The probe weighed about 5 pounds and without constraint, it would recoil. In the field, however, it may be attached to a truck or machine weighing 1000 x as much.

 

Is the solution considered a hazardous material?

No. It is either plain water or water /cornstarch mixture. Only 1 oz per shot is needed or a “shot glass” 😉

 

How does your technology perform in hard rock (110 – 250MPA)?

The technology as described below performs better in hard rock than in soft rock producing cleaner fractures, higher volumes of fracture and requiring less energy. While no tests have been performed on iron ore or nickel, at least half the experimentation was performed on granite and gneiss. Pressure waves up to 1 GPa are produced so the range you prescribe should be readily achievable.

 

Has the technology been demonstrated in hard rock?

Yes, we have performed approximately 50 blasts in a laboratory environment (approximately 25 in concrete and 25 in hard rock).  The rock boulders were from the Notasulga quarry operated currently by Vulcan Materials. The rock samples we used in testing were likely Farmville Metagranite and Auburn Gneiss. According to literature, those granite rocks had tensile strength between 10-20MPa and compressive strength up to 130MPa. The concrete used was 7MPa tensile and 40MPa compressive strength

 

How does the technology perform when working with fractured rock?

Although not a purposeful part of the experimentation to date, results indicate that pre-fractured rock was easier to fracture. However if the fracture volume or cavities are too great, pressures can be dissipated causing a decrease in efficiency. So, unfortunately, the answer is it depends. It can enhance or degrade the result and optimization based on material type and pre-fractured geometry is necessary. Simulations will need to be done followed by actual field demonstrations. Some workarounds include the use of some non-Newtonian fluids or injecting some extra fluid. How this occurs in free unconstrained rock vs. large solid rock walls may differ. A thought occurs regarding the latter. If shot 1 does not seem to relieve enough, it may be followed by shot 2 and 3, depending on probe condition and constraint, and ability to continue to add new blasting fluid media.    With respect to the above, there may also exist a subtle optimum with respect to the tensile vs. compression strengths/pressure of the rock media as a function of the rock media the blasting probe is in. For the initial quarter-wave current rise-time, dI/dt, if the rise time is too quick and intense, compressive bore wall material collapse may occur and may absorb too much energy making yield less effective.

 

What is the power supply required for this technology?

The power supplied to the rock is through a capacitor bank discharge. The total energy is on the order of 1GW for 30 microseconds or approximately 0.01 kW-hr. If we assume that 100 shots are needed per 8-hour shift the energy supplied is on the order of 1 kW-hr. The size of the power supply will be dependent on how fast you want to recharge the capacitor bank. For practical purposes, it will be somewhere between the size of a car battery and perhaps ¼ the size of the back of a pick-up truck.

 

Does it work for both vertical and horizontal holes?  

Yes, the blasting works for both vertical and horizontal holes. For each “blast” approximately one ounce of water or non-Newtonian fluid (assume a cornstarch-water slurry) is required. In the case of horizontal holes or pre-fractured rock with cavities, more care is needed to keep the fluid in place. The cornstarch mixture or probe rubber plugs may be needed for horizontal applications. In addition, a slurry, like the one used in the oil industry could be used to fill cracks before blasting, if this proves necessary.

 

Have you investigated the application of this technology in addressing oversize in block cave mining?

We have not addressed block cave mining. However, the technology’s first applications have been targeted at the secondary blasting market to blast oversized rocks that were previously blasted but are too large for rock crushers at quarries or major excavations.

 

How does the blast wave propagate, how does the blast work?  

Pulsed power is supplied to a probe with two electrodes submerged in approximately one ounce of a fluid (water or a non-Newtonian cornstarch slurry ) causing an electrical arc. The high voltage pulsed power ( ~ 1 gigawatt for 30 microseconds)  discharged in the borehole creates a plasma channel of high energy density within the rock. The electric energy is transformed into internal thermodynamic energy with plasma channel temperatures above 100 K and pressures of the order of 1X10^9 Pa, which subsequently expands and produces the pressure wave into surrounding rock material. Like in any other high-velocity impact phenomena, the deformation of the material with the corresponding mechanical compressive, tensile and shear stresses in the range of hundreds of Mpa, goes beyond the elastoplastic limit, which at the end, fractures the rock. Some researchers indicate that this pressure depends on the spatiotemporal distribution of the electrical power deposition (energy release rate), and on shock wave propagation through the media (here the material dependency mentioned above). Then, we should be able to control the amplitude and profile of generated pressure wave causing the rock fracture, but we need a good amount of experimentation in order to match the energy release rate conditions during the discharge and the generated pressure wave characteristics for the specific material being fractured.

 

What about safety? What are the key concerns in this area?  

We will break this down into various safety issues.

  • Chemical- there are no hazardous chemicals
  • Acoustic- the sound and overpressure from the blast is relatively small compared to an explosive blast
  • Mechanical Fly rock; Fly rock is minimized and controlled especially in hard rock.

Two key safety areas of importance and risk mitigation:

  • Mechanical Probe recoil- The probe will recoil and must be tied to a heavier structure ( truck e.g.)
  • Electrical- The system is designed with electrical safety interconnects and proper lockouts to make sure the capacitor bank is fully discharged before the next shot is fired. Proper electrical cabling is also necessary. High Voltage without proper procedures can be dangerous but can be designed to work safely (dumps, metering, interlocks, etc.).  System continuity checks pre- & post-shot can improve identification of problems preemptively…but does add to design complexity.

 

Are there fumes?

The fumes are extremely minimal as we are not dealing with a chemical explosive here. There is water vapor, maybe some fumes from non-Newtonian fluid additive, minimal smells from vaporized rock, and of course, that natural smell from that of rock-face breakage.

 

 

What if there are water connections between the blast site and location of the blast operator, does this impact?

Electrical safety is of utmost importance. Proper cabling, system design, and redundant safety interlocks have yielded a very safe design. The water connections must be analyzed electrically for grounding or stray currents. They also must be analyzed physically. If they block access, longer cabling may be necessary.

 

Can I reduce oversize chunks of rock to sizes compatible with the transport equipment in use?

This is an extremely good match for the technology. Please note that all answers given are based on current configuration/design of the equipment. In any solution, tradeoffs of cost vs size vs time vs performance can be made to optimize the key factor desired. So if there an answer that alarms you please discuss with us to see what tradeoffs can be made.

 

How long would it take to reduce a refrigerator-sized rock to a manageable pile of smaller rocks, in a mine development heading?  Assume that the equipment and supplies need to be brought in from a storage area about 200m away.  Please include all components of the work, including the return to the storage area.  

If allowed we envision our products are mounted in the back of a pickup truck. Assuming a very slow speed of 5 km/hr the transportation back and forth 200m away will take approximately 5 minutes roundtrip.  The next aspect of time is to calculate the number of holes needed and the amount of time per hole. We assume the “refrigerator” sized rock is 2mx1mx1m. Based on experimentation and using the same size equipment, we believe this will take three holes/three blasts which can be done simultaneous or in series. Let’s assume the worst case and have the three holes done in series. Holes of a size approximately 25mm diameter and 25 cm deep will need to be drilled. We assume this will take approximately one minute each. The probe needs to be set up with approximately one ounce of water or cornstarch mixture. Again we assume one minute each for a subtotal of 3 Minutes. Clear hole of debris (compressed air and/or water blast. Insert blasting probe. Clear area around rock, Start Plasma Blaster unit, self-checks, ARM (charge ~ 15sec), blast, inspect, RE-blast same hole?? (optional). SAFE system, Move probe, Repeat. repeat…3 blasts ~4 mins.    

 

  • Transport  to blast and return                                  5 minutes
  • Drill holes                                                               3 minutes
  • Setting Probes                                                         3 minutes
  • Blast/ recharge/ safety check                                  4 minutes
  • Total                                                                             15 minutes
  • Total without transport  per “refrigerator”        10 minutes

OVERALL ~ 15 mins (move equip, drill, blast, store equip). If breaking more than 1 boulder per cycle, then “economy of scale” would reduce net per-unit time.  

 

How much training would an operator of this equipment need?

 We estimate a two-day training session:

—-General overall (high-level) system (principles) intro,

—-Intro HV Safety, capacitors, hearing & eye.

—-Understanding of applicable (rock blasting, concrete) applications as a function of hardness, voids, etc.

—-Pre-operation system/component condition inspection:  blasting cable, blasting probe and tip,

—-Attachment/Connections of blasting cable to blasting power source and Blast probe to cable.

—-Prime electrical power source/prep:  batteries (charging, SOC), electrical generator?

—-Hole Drilling and clearing holes of debris (appropriate depth?).

—-Preparation of blasting media (water, electrolyte, non-Newtonian, etc.); pumping system checkout.

—-Insertion of blasting probe (bottom?), pumping in fluid,

—-Determination of blasting power (voltage) to use (based on volumetrics, hardness, size?).

—-System start, self-check, arming, fire, No-Fire Aborts and Safeing,

—-Re-Blasting determination/decision.

—-Post-firing re-inspection of tips; re-conditioning ?, replacements ?, refurbs?

—-Hands-on experience, observation, competency evaluation.

—-Knowledge of First-Aid, CPR certification, Trained in use of Automated External Defibrillators (AED).

—-When to call support center; How to obtain replacement parts or get Maintenance support.

 

What would be the capital cost of the equipment?  

The estimated cost of the equipment is $50,000. In addition optional pickup truck, mounting, 10kwh battery supply, seismic test equipment, and specialty tools of $50,000. Therefore the total will be $50,000-$100,000 depending on options taken. 

 

Are talking about 10 kWh per ‘blast’(?)  Is there any materials consumed during the ‘blast’?  

We estimate it to be 500x less than   10 kWh or approximately 0.02 kWh per blast. So if you had a 10kwh energy source you could do 500 blasts in a day without recharging!!!! Example…If using 1 bank of 2 capacitors-parallel ( 206μF each, Maxwell (General Atomics) Mod. 32317, – 22 kV rated voltage), charging 16-22 kV requires 53-99 kJ …or 0.015 – 0.0275 kWh.   For each blast, one ounce of water is vaporized. In addition, the blasting probe tips are reduced in life due to erosion. We are currently exploring two types of tips in production: either a $1000 tip that lasts up to 200 blasts or a more “throw away tip” that would cost $15 and last three blasts.

 

Also, how large is the equipment? and how heavy  

We are designing the system to be transportable in a heavy-duty pickup truck like a Ford F-150 or a super-duty F-250 including optional drilling equip, generator or battery, air-compressor, blasting media fluid. The heaviest parts of the system are the capacitor banks ( 250 kg) and an optional energy storage battery system which may weigh an additional 250 kg.

 

How do capacitors work?

Here is one example:

 

Have questions of your own? Send them to info@petramtechnologies.com