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Autho: admin от 8-02-2016, 19:05
The article describes the properties of waterless molten emulsions of ammonium, calcium and sodium nitrate mixtures in industrial oils including their physical properties, thermal resistance, combustion and detonation. There presented the ap-plication technology to be used in mining and the corresponding equipment characteristics.
The problem and its connection with research and practical tasks. In the first US patent for the emulsion explosive “water-in-oil” [1] the water content in the explosive makes up 15 – 35%. The water does not undergo any reactions ensuring the heat emission in blasting and is a ballast decreasing the blasting efficiency. The evident way of increasing specific blast energy is to decrease the water content in the emulsion explosive. For instance, some patents offer the water content of 14 – 17% [2] or 10 – 12% [3].
Research and publication analysis. The aim of increasing the specific energy can be achieved by introducing high-energy oxidizing agents like chlorates and perchlorates, individual explosives like hexogen, ten (pentaerythrite tetranitrate), monomethylamine nitrate or high-energy combustibles – aluminum and magnesium. The examples of such compounds can be found in the patent [4]. Here the water content makes up 5-12%. The compound also consists of monomethylamine nitrate and sodium perchlorate. It is offered to incorporate perchlorates, the water content making 14-20% [5].
The water content decrease causes the accelerated crystallization of the emulsion on cooling accompanied by the change in properties of explosives and the water resistance decrease. Thus, such solidifying emulsions are also of some interest and, as the authors think, are able to replace TNT and pentolite blocks [6]. These emulsions crystallize a short time after cooling. The water content in the offered compounds is up to 5%. In [7] some similar compounds of the crystallized emulsions with the water content of 5% are described, but with a special addition of crystallizing nuclei for solidification acceleration.
The problem of obtaining the emulsion with low water content and no crystallization can be solved by incorporating some substances preventing the crystal growth in the nitrate solution [8]. The water content is 8-18%.
Waterless emulsions are described in [9]. They can be called “melt-in-oil emulsion”. In some cases of the test-pieces carbamide, ammonium formate, sodium formate or ammonium acetate are used as water substitutes for decreasing the melting temperature. All these compounds contain oxygen, which is part of the organic substance and does not take part in blasting reactions accompanied by heat emission. The compound based on the mixture of ammonium nitrate and silver nitrate (19%) is the only compound of the suggested waterless compounds on the molten nitric acid salts without additional low-melt components.
Problem statement. The research aims at obtaining resistant waterless “melt-in-oil” emulsions on the basis of ammoniac, sodium and calcium nitrates and investigating their properties with possible application in blasting.
Material presentation and results. The enterprise LLC “Ukrspetsoliva” developed an emulsifier, which enables to produce emulsions for emulsion explosives without water. The emulsions include an emulsifier, combustible components such as industrial oils as well as ammoniac, sodium and calcium nitrates. Strictly speaking, the emulsions described below, contain water. The water quantity depends on its content in the primary components. Thus, for example, a prilled ammonium nitrate defined in the standard GOST 2-85 contains 0.3% of water. Therefore, the water content in emulsion is on the same level, but such quantity is not usually taken into account in engineering designs.
The properties of such emulsions differ from the properties of emulsions applied for producing wet emulsion explosives. On the basis of such waterless emulsions with the indicated components one can obtain explosives with the blasting heat of more than 3800 kilojoule/kg and the amount of gaseous explosion products of about 850 l/kg. The density of emulsion test-pieces under˚ the temperature of +20˚ degrees made up 1470 – 1480 kg/m3.
As for the indicated characteristics, the given emulsions can be compared to trotyl [10]. This fact makes it possible to produce boosters or priming cartridges according to the principle that a primer should have more considerable explosive characteristics (blasting heat, density, detonation velocity) than the initiated charge.
Speaking about physical properties, we can mention hygroscopicity of waterless emulsions. If kept outside with the relative air humidity of 30%, the emulsion has a film containing water. It has quite different properties from those of the primary emulsion. Emulsions are characterized by certain water-resistance conditioned by the formation of the mentioned film insoluble in water.
Thermal stability of emulsions
Thermal stability tests were conducted for the emulsion test-pieces of 100ml. The compounds were incubated in oil baths under the temperature of +160˚ Celsius over a period of up to 6 hours. The visual appearance change of the emulsions was observed.
Two hours later the compounds with carbamide additions under the temperature of +130˚ expand due to the gas emission. We should admit that the emulsion expansion does not occur at once, but with two-hour delay. Under the temperature of 140˚, the expansion begins in 1.5 hours.
It is observed [11] that carbamide decelerates the ammoniac nitrate decomposition. However, the tests of the emulsions containing no carbamide revealed their greater thermal stability. They can withstand thermostating with the temperature of +160˚ during 6 hours without any changes in appearance. We suggest these compounds being introduced in blasting.
Emulsion combustion
The combustion rate measurement was carried out on the test-pieces of emulsions of a cylindrical form 20mm in diameter in a paper case.
Emulsions are ignited and burn steadily at atmospheric pressure at the rate of 4-6mm/min (0,1 – 0,15 kg/m2sec). To start combustion a cylindrical test-piece butt of the emulsion is placed into the flame of an alcohol lamp. After being ignited the cylinders are mounted vertically to change the combustion rate.
The compounds containing a sodium nitrate burn with a steady hissing flame accompanied with a colourless smoke. The compounds with a calcium nitrate burn with a steady noiseless flame without any smoke, but some drops of molten combustion products appear on the burning surface. Being accumulated the drops roll down beyond the burning cylinder.
We should admit that emulsions containing more than 15% of water in the above mentioned diameter are not able to burn steadily at atmospheric pressure.
Emulsion sensitization was performed by microspheres. The storage time of the emulsion is up to 30 days. The density of the test-pieces made 900-1250kg/m3. The testing conditions corresponded to the detonation adequacy tests as to the standard GOST 14839.19-69 (an open charge in a paper case). As a result, it is defined that the charges with the optimum content of microspheres detonate in the diameter of 8mm and in the diameter of 5mm they don’t. It should be noted that this result is valid for the given density, for certain type of microspheres and the emulsion with the indicated storage time.
Such detonation diameter enabled us to determine the brisance of the compounds according to the testing similar to Hess testing. On the basis of the brisance results the compound with the optimum correlation of ammoniac, calcium and sodium nitrates was developed. Besides the optimum content of microspheres was determined using this method. The crucial criterion is the maximum brisance.
Application technology
The technology includes emulsion production, packing in storage tanks (from 10 l), natural cooling and storage; emulsion delivery to the blasting sites and production of emulsion explosives (sensitization with microspheres). The sensitization device has been developed and produced. After sensitization the obtained explosive should be recorded in the approved control forms of explosives. It also includes production of priming cartridges or filling the charge cases with the explosives and\or charging a bore-hole with non-cartriged explosives.
It should be noted that the consistence of the emulsion sensitized with microspheres resembles paste and can be pumped over using conventional emulsion pumps.
We have worked out a device for bore-hole charging and sensitized emulsion cartridging. The device characteristics include:
- the mass of two units is 40kg each,
- the drive is an electric motor of 2.2kWt, 380V (a compressed air drive is possible);
- the gopher hole is 10m long and 32mm in diameter. The charging capacity (the feed velocity of explosives into bore-holes of 50mm in diameter) into horizontal bore-holes is 5kg/min, into the vertical bore-holes from the bottom up (ascending) is 1kg/min. The testing bore-hole length is 3-4m. The mentioned high viscosity of the emulsion explosive ensures the conservation of the charge in ascending bore-holes.
The device also makes it possible to cartridge the sensitized emulsion. The cartridging capacity is 18kg/hour. Two people can maintain the device.
The advantages of the above mentioned technology include:
1. No need to store, purchase and deliver the explosives. One has to purchase and keep only electrical detonators or nonelectrical detonation systems. To manufacture explosives and cartridges one should purchase ammoniac, calcium or sodium nitrates, mineral oil and emulsifier.
2. Zero oxygen balance and minimum poisonous gas emission.
3. No dust emission during bore-hole charging.
4. Water resistance
5. The possibility to change the explosive properties taking into account the rock type and the bore-hole diameter.
6. Blasting cost reduction due to lower cost of raw materials necessary for emulsion explosive production compared to the cost of factory-made cartridges.
7. The possibility to apply the device to produce emulsions in unheated premises with sub zero temperatures. The device can be mounted on vehicles.
The peculiarity of the technology is the limited storage time of the emulsion. The storage time of the emulsion and the corresponding ready explosive depends on the formulation and makes about a month. In case of longer storage time the emulsions lose transparency, become dull in shear, the sensitization emulsions have a greater critical diameter. That is why the inappropriate application of this emulsion explosive due to the mentioned reasons is very problematic. We consider this technology to be safer compared to the existing ones in view of the cases of misappropriation, withdrawal, failure application of explosives, etc.
It is known that conventional blasting technologies are based on factory-made cartridged explosives or blasting cartridges with considerable storage time, often almost unlimited. This very fact enables to use factory-made explosives for non-production related purposes.
Conclusions and further research directions. In order to introduce the suggested technology it is necessary to obtain the approval for testing the explosive, the devices for its production, charging or for cartridge production.
The suggested technology improvement can concern the rheological properties of waterless emulsions (viscosity reduction), sensitization simplification and development of the emulsifier enabling to obtain an emulsion from molten ammoniac nitrate.