Mines, rail and road tunnels, dams – the number of major construction sites that need significant explosive work has increased considerably over recent years. At the same time, the requirements for explosives have been changing. Higher performance and increased safety are the overriding objectives that are demonstrated above all in the greater use of emulsion explosives.
The Benefits Of Emulsion Explosives
The benefits are huge: the components are not mixed until they are on site, thus increasing the overall safety of the blasting operation. Certainly, high-performance, customised pumps that meet the special challenges of the emulsion matrix or of the explosive are a significant addition to the operational safety.
Additional Flow Control
Netzsch Pumps & Systems has developed its own progressing cavity pumps for this purpose, which enable flow control while in operation and that are resistant to corrosion from the media. Additionally, the operating principle ensures stable pressure conditions with very little pulsation and extremely low levels of shear.
Mobile Mixing Units
This type of explosive material certainly requires special conveyance conditions. Netzsch therefore developed special equipment for mobile mixing units to convey emulsified explosives.
The proven Nemo progressing cavity pump has therefore been extensively reworked to implement the necessary testing possibilities and safety measures. The two inspection openings that have been incorporated into the pump housing above the joints of the coupling rod are the most visible difference with respect to conventional designs. These mean that it is possible to easily check whether the joint seals are still intact during regular inspections.
Gear Joints (K-Joints)
Gear joints, known as K-joints are fitted for the connection parts themselves, which transmit the torque from the motor to the pump’s rotor. These gear joints have a double seal system and therefore provide increased security. In addition, the coupling rod is drilled through, so that the joints can undergo a pressure test if necessary. If there is leakage of the pressure applied, this means there is a fault. The mechanical seals are external, specifically for pressure equalisation, so that possible overpressure can be avoided. There is also the option of the pump being fitted with a safety stator. With this, grooves reduce the strength of the walls, so that it can open if the pressure increases too much.
Chambers For Transportation
With this pumping principle, the stator and rotor together form chambers in which the medium is transported.
- Firstly, this means pressure-stable conveyance with very low pulsation and shear forces.
- Secondly, the technology also allows the pumping of emulsions containing prill as the passage of solid particles is not impaired through the stator chambers.
The pump is driven via a hydraulic drive using the truck’s own hydraulic system. This avoids the inconvenience of requiring a connection to an electrical supply and additionally the need for hazardous area certification for electric motors is removed.
Customised Pump Versions
Moreover, Netzsch also offers customised pump versions for transporting and combining the explosive elements. These were initially developed at the request of an ANFO producer. In this process, a wax-oil mixture is added to an ammonium nitrate solution at high temperatures through an emulsifier. The high heat in combination with the salt solution encourages corrosion and attacks the elastomers in the pump.
Therefore highly resistant Viton was chosen for the seals and stators, so as to achieve the longest possible service life. Stainless steel is used for the metal components. In addition, the pump housing has been equipped with a heating jacket, in order to maintain the required heat during conveyance as well. At the same time, a measuring system monitors the friction heat in the pump with a temperature sensor and therefore protects against dry running.
Roger Willis is with Netzsch