BULK EMULSION EXPLOSIVES


Modern bulk emulsion systems require careful attention to detail from start to finish. Raw material selection and formulation are of utmost importance. The selection and design of production and handling equipment is of equal importance. The success of bulk emulsion systems are reliant upon every choice that is made beginning with selection of raw materials and ending only upon the completion of a successful detonation achieving the expected blasting results.


Raw Materials

Raw material quality and consistency is extremely important for the success of bulk emulsions. It is imperative that materials be purchased from trusted suppliers. Our experience tells us that all raw materials should be “pre-qualified” before being introduced to manufacturing. This includes routine materials purchased from alternate manufacturers. 

The preferred aqueous phase for high quality bulk emulsions is a “virgin” ammonium nitrate solution (AN-SOL).  These virgin materials come directly from the AN production facility and contain no additive materials. This virtually eliminates the introduction of destabilizing contaminants that are introduced when melting AN prill. The melting of AN prill will always introduce contaminants that are detrimental to emulsion quality. In cases where dual salt solutions are required, unwanted contaminants may also be introduced when melting CN

(calcium nitrate) or SN (sodium nitrate) materials.

Virgin AN solutions are the best choice when longer emulsion shelf-life and re-pump conditions are required. Elimination of the AN dissolving process should also provide an economic benefit. The melting of AN prill is most common in remote areas or plants with low production volumes.

Globally, AN SOL is routinely delivered by insulated tanker trailers or insulated rail cars. In some cases, AN SOL is delivered by pipeline directly to the emulsion plant from the AN SOL source.

Chemical gassing sensitization will most often requires that further chemicals be added to the aqueous phase prior to emulsification. These may include acids or bases for pH modification, buffers for pH stabilization and/or catalysts or accelerants to enhance the gassing reaction. Gassing additives will also have some effect on emulsion quality and must always be thoroughly tested.


The choice of diluent oil used for the fuel phase is also very important. Diesel fuels are the most common diluent material due to low cost and common availability. Diesel fuels are distributed for use in automobiles and heavy equipment and therefore will often contain contaminants harmful to emulsions. In some cases it is possible to purchase diesel fuels prior to the addition of harmful additives.

The better choice of diluent material is a refined mineral oil. Refined mineral oils do not introduce unwanted contaminants and thus provide emulsions with superior shelf life and re-pump characteristics. Mineral oils often allow for better control of emulsion viscosity.

The choice of emulsifier is perhaps the most important choice contributing to the success or failure of modern bulk emulsion programs.

A poor emulsifier (such as SMO) will always provide inferior results. A high quality emulsifier will most often provide a vast improvement if utilized with the same raw materials. The best emulsifier is no guarantee for emulsion success. However, we can confidently state that PIBSA-based emulsifiers are the modern industry standard and are vastly superior to SMO-based emulsions.

Modern distributed bulk emulsion systems are reliant on all of the things discussed above. Each emulsion formulation is unique to the blasting requirement and must be systematically and consistently applied.


Production

The stir pot/static mixer emulsification process is the superior choice to manufacture emulsions. The stir pot/static mixer systems deliver a high level of safety while also providing extreme flexibility. Experience tells us that stir pot/static mixer systems are capable of producing quality emulsions across a wide range of production flow rates (250 kg/min – 900 kg/min). Stir pot systems are capable of producing bulk or packaged product of high or low viscosity. Stir pot systems are also very adaptable and can be enhanced with secondary refinement systems where further emulsion processing may be required.

The US bulk market commonly utilizes emulsion “super plants” that produce emulsions at rates >450 kg/min with only one emulsion line. These plants require minimal space while being fully capable of emulsion production levels > 600 MT/day.

The magnitude of these numbers clearly demonstrates that successful production of modern distributed bulk emulsions is about more than just making emulsion. Rather, success is heavily reliant upon the plant inputs and outputs. The raw material and finished goods infrastructure and logistics are much more complex, costly and labor-intensive than production. Plant inputs require precise and exhaustive management of raw materials as well as the necessary road and rail infrastructure.

Emulsion production facilities are often co-located within range of AN SOL or heavy mining areas. There is a fast moving trend globally to locate ‘transportable’ emulsion production facilities on the ultra-large or remote mining operations, and to provide full service plant operations to the mine.

Plant output and efficiency are heavily reliant upon storage limitations and regulation, truck logistics/availability and the design of the distribution system between the plant and the customer site.



Emulsion Quality

Distributed bulk emulsion systems require care and attention from all personnel 
involved in manufacturing, logistics, distribution and blasting. These bulk emulsions remain as fluid systems throughout their useful life (as opposed to waxed packaged emulsions). Factors such as multiple re-pump events (as the emulsion cools), ambient temperatures (winter and summer), long transport distances, storage conditions, duration of storage, equipment conditions, etc., will have a direct effect on the emulsion products. All systems must be designed around the product in order to ensure that a high quality product reaches the customer and performs as it was designed.


Quality in the manufacturing environment relies on the factors previously discussed 
in this document. An additional requirement is that the emulsion should be routinely tested by plant personnel as well as automated testing equipment. Emulsion density and viscosity are quick, simple and inexpensive tests that should be performed manually by operations personnel. In our experience, it is common for these

parameters to be monitored in real-time by automated sensors while also being verified manually in 15 – 30 minute intervals. Emulsions are inherently safe explosives but remain explosives and must be treated in that manner.


Emulsion droplet size (or “particle size”) is an important quality parameter. This, of course, measures the size of the aqueous oxidizer droplets dispersed throughout the fuel phase. Measurement is best performed with modern laser diffraction instruments. Laser diffraction provides a wealth of information and much more resolution than the older microscope analysis methods. Droplet size analysis is much more important when starting a new plant or modifying existing equipment or formulations. Droplet size analysis can be performed less frequently on a well-known and more mature manufacturing process and product. In general, larger droplets are considered to be less desirable than smaller droplets. However, this is a basic understanding and the significance of droplet size data must be considered in conjunction with the choice of emulsifier system, required emulsion shelf-life, re-pump requirements and other factors.

Finally, the most important emulsion parameter is shelf-life/stability. Emulsion density, viscosity, droplet size and formulation mean nothing if the emulsion cannot remain stable throughout its useful life. This brings us back around to where we started: raw materials must be properly selected and the emulsion product must be thoroughly tested before it is introduced to manufacturing and the customer site. In our experience, the only true test for emulsion stability is real-time shelf-life testing. Accelerated shelf-life/stability tests have been devised throughout the industry: resistivity or conductivity, oven testing, thin film testing, etc. These tests can be useful but results are generally only applicable to a specific emulsion product manufactured under a single set of known conditions. Accelerated tests are much less accurate when comparing different products or new formulations and should not be relied upon when making product or process modifications. The ultimate shelf-life test is time itself.

Further emulsion testing is also required where more demanding conditions exist downstream of manufacturing. This usually requires that emulsion must be sensitized with chemical gassing or addition of microspheres. Sensitized emulsion is often mixed with ANFO to make a Heavy ANFO blend. Each addition of further chemicals or materials creates a potentially new problem for the emulsion. Therefore, each addition or manufacturing step requires further shelf life testing.

This comprehensive quality program is quite simple, time consuming and vitally important. These deliberate steps are necessary to 
ensure that each tonne of emulsion is of high quality and the same as the tonne made one day or one month or one year before. Our target for distributed bulk emulsions is such that poor emulsion quality can never be the reason for a blast delay or failure. 

This is a very achievable goal.


In addition, poor emulsion products are a safety hazard. Poor emulsions break down unexpectedly or experience large increases in viscosity; both of which create unsafe pumping conditions. Broken or unusually viscous emulsions do not flow properly and can create low or no-flow conditions. Poor emulsions will often liberate water and become more sensitive over time. Poor emulsions will result in the build-up of broken emulsion or AN residue within the bulk tanks, lines and pumping systems. None of the above conditions are desirable and will certainly lead to undesirable results.

Emulsion quality and downstream blasting performance is vital.


Emulsion Sensitization

Bulk emulsion is normally sensitized in one of two ways: chemical gassing or microsphere addition.

NOTE: The United States has historically designated booster-sensitive, microsphere sensitized emulsions as Class 1.5 Blasting Agents. These products may be transported in bulk on public roadways.



Each method of sensitization has its own strengths and weaknesses:

CHEMICAL GASSING:
Strengths                                                                                       
• Lower Cost (relative microspheres)

• Emulsion density is variable when loading boreholes


Weaknesses

• Emulsion sensitization and quality is greatly affected by truck operators working in adverse conditions

• ​Improperly gassed emulsions can lead to poor results or failure​

• Chemical gassing is highly temperature dependent

MICROSPHERES (GLASS OR PLASTIC):

Strengths                                                                                      
​• Emulsion sensitization takes place in the manufacturing environment

• Emulsion sensitization density is a constant

• Modern microsphere products do not destabilize emulsions

• Plastic microspheres (Expancel) do not break


Weaknesses

• Higher cost (due to logistics)***

• Glass microspheres can and will break due to re-pump conditions and shock from adjacent boreholes



** Plant site expansion of plastic microspheres will greatly reduce high logistics costs historically associated with pre-expanded and glass microspheres.

A hybrid method of sensitization can be used wherein microspheres are added initially to provide the minimum sensitivity while gassing is used to provide additional density modification. This technique has limitations but can be a good solution for some applications.

It should be noted that chemical gassing is achieved in many different ways and can have a very negative effect on overall emulsion stability in the borehole. There have been instances in the past where microspheres also caused emulsion destabilization due to “soured” coatings or surface incompatibilities. Such problems are no longer as common.


Heavy ANFO Blends

Heavy ANFO Blends are mixtures of ANFO and bulk emulsion that may contain emulsion levels of 20% to 80% (weight %). Blends most commonly used contain 40% emulsion to 75% emulsion. In general, heavy ANFO blend products can be pumped when the emulsion content is > 70%. Emulsion levels <70% generally behave more like a solid and will be conveyed by augers.

Heavy ANFO blends provide a way of controlling cost (as ANFO is often the low cost component) while also enabling a level of control over explosive column density and energy partitioning (heave vs brisance). Emulsion content > 50% will provide a high level of water proofing for the ANFO component of the blend. The exact blend ratio at which water resistance is achieved is dependent upon factors such as emulsion matrix density, ANFO density and AN prill size, porosity and “fines” content.

Heavy ANFO blends have the benefit of some inherent sensitization that is provided by the porosity of industrial grade AN prill. However, this sensitization cannot be relied upon and diminishes as blend products “sleep” in the borehole. Emulsion used in Heavy ANFO must be sensitized with chemical gassing or microspheres. 

Emulsions of high quality will provide excellent compatibility with ANFO or AN prill. AN prill surfaces can be highly destabilizing for emulsion products. This is particularly true in applications where Heavy ANFO blend products “sleep” for extended periods of time. This most often occurs during the period between loading of boreholes and the final blast. It is not unusual in the US market for bulk Heavy ANFO blends to “sleep” for a period of 6-8 weeks in large boreholes > 30m deep. These blends may be subjected to ground water as well as the hydrostatic head pressure of the explosive column.

Modern bulk emulsions have overcome these issues through the formulation, processing and quality practices discussed earlier in this document. At the same time, AN prill quality has been vastly improved due to the use of improved prilling technologies, surface coatings and crystal habit modifiers. Heavy ANFO blend products must also be thoroughly tested and monitored by the overall quality control system.


Distributing of Finished Emulsion


The distribution of finished emulsion is an ever-changing system that is reliant upon many factors such as the number of customers, frequency and size of orders, number of distribution/storage hubs, long-haul trucking capacity, local truck capacity, driver availability/ utilization and delivery distances. Logistics and supply chain visibility is expected with many mines requiring 2-hour delivery service notice.  Logistics compliance with transportation regulations includes tank certification, vehicle standards, road routing for security, vehicle tracking and monitoring, and permits. Drivers must be properly trained and licensed to carry hazardous materials, and adhere to regulatory standards for operations including drivers hours logging, surveillance for drugs and alcohol, annual health physicals and annual training.  Compliance levels must be 100%.


Central or Regional Emulsion Plant Logistics to the End User

In the USA, it is not uncommon for over the road tankers to transport ANE or sensitized UN 1.5 D Blasting Agents 500 miles on interstate highways to regional storage bulk bins located in the end-use market. Back in the 1970’s, a hard lesson was learned that the mechanical agitation within the tankers sometimes destabilized emulsion during transit. In the worst cases, massive crystallization occurred rendering the entire cargo incapable of off loading by pumps. The broken emulsion had to be removed by hand and steam lances.  

The lessons learned prompted advanced research in to improving emulsion formulations and simulating lengthy logistics with ‘paint-shaker’ and other simulation testing over a range of temperatures and times.




Blasting Application Considerations for Bulk Emulsion 

Surface Open Pit Mining

Explosives intensive (90%) versus initiation system (10%) intensive

Key Drivers:
    • Bulk emulsion product technology and performance
    • Access to ammonium nitrate
    • Logistics
    • Down-the-hole services
    • No room for error
    • Technical services
    • Security of supply
    • Maintaining high product and service quality
    • Enhancing mining performance
    • Advanced explosives safety
    • Blast modeling
    • Controlling costs
    • Trained blasters
    • Pre-blast and post-blast services
    • Seismic and air-blast monitoring


Underground Mining

Initiation system (70%) intensive versus explosives (30%) intensive
Nonelectric systems dominate with electronics making inroads

Key Drivers:
    • Underground bulk emulsion product technology 
    • Superior performance and sleep time
    • Up-hole and horizontal loading equipment
    • No room for error
    • Logistics and underground bulk storage
    • Sequential mining process
    • Security of supply
    • Maintaining high product and service quality
    • Enhancing mining performance
    • Advanced explosives safety
    • Blast modeling
    • Controlling costs
    • Trained blasters


Blasting Technology

The mining market expects and requires suppliers of bulk emulsion explosives to deploy high quality and expertly trained field technical support. The bulk emulsion supplier who just delivers Into-The-Bin is just providing a commodity without value and no added revenue, and this scenario will eventually result in loss of the customer account to a full service suppler. Down-The-Hole and Rock-On-Ground service is expected and adds value. Blasting has no room for errors and must be conducted by well-trained professionals. Insurance and liability protection is very important.

A full service bulk emulsion explosives supplier requires the following attributes to be successful in the global market place: 
    • Quick response to all blasting demands – often on a few hours notice High performance boosters and accurate initiators
    • Laser profiling and borehole tracking
    • Blast modeling software and modeling services
    • Virtual mine blasting software to track with mine planning software 
    • Energy, mass and time management
    • Integration of explosives and initiators with mining methods
    • Mine to mill studies to reduce mining costs, increase yield and productivity
    • Management of drill, blast and muck cycles
    • Auditing explosives and detonator usage and security
    • Blaster training, blasting licenses.  Drug, alcohol and smoker free blasters
    • Seismic and air blast monitoring equipment and cloud data management
    • Bulk down-the-hole delivery
    • Rock-On-The-Ground (ROG) program
    • Integration of booster and initiator accessories into blasting services packages
    • Surface and underground drilling services
    • Underground up-hole loading services, technology and equipment
​    • Urban quarry, utility and construction blasting expertise