PROCESS AND MECHANISM FOR IN SITU SENSITIZATION OF AQUEOUS EXPLOSIVES

Abstract: The process for sensitizing in situ aqueous explosives before charging the mine holes comprises the formation of an emulsion or dispersion gas-in-liquid from a low sensitivity or non explosive matrix product which consists of a liquid mixture in solution, emulsion or suspension of oxidant in fuel, and a gas. The density of the final explosive product can be varied as a function of the gas flow rate and can be controlled before introducing it into the hole. The installation comprises a tank (1) with the matrix product, a gas reserve (10), a mixture (5), a pump (3) and a gas flow rate regulating device (8) and optionally a tank (2) with a gas bubble stabilizing agent, a dosing pump (4) and a flow meter (7).

Description: FIELD OF THE INVENTION The present invention relates to a procedure and an installation for "in situ" sensitization of water based explosives by means of the incorporation of air or gas in a non explosive or low sensitivity mixture of oxidants and fuels with the formation of an emulsion or dispersion of gas in liquid. BACKGROUND OF THE INVENTION The mechanism of initiation of explosives by means of the generation of hot points due to the adiabatic compression of gas bubbles is the base of the modern industrial explosives formulated without components intrinsically explosive. The introduction of gas bubbles can be made by the trapping during the mixture or by its formation through a chemical reaction. In the US patent 3,400,026 a formulation which uses protein in solution (albumin, collagen, soy protein, etc.) in order to favour the formation of bubbles and their stabilization is described. The US patent 3,582,411 describes a watergel explosive formulation which contains a foaming agent of the guar gum type modified by hydroxy groups. In the US patent 3,678,140 a process for the incorporation of air by means of the use of protein solution is described, passing the composition through a series of openings at pressures from 40 to 160 psi (274 to 1103.2 KPa) and simultaneously introducing air through eductors. The gas bubbles incorporation by means of its generation as a result of a chemical reaction is described in the US patents numbers 3,706,607, 3,711,345, 3,713,919, 3,770,522, 3,790,415 and 3,886,010. CA 2,136,572 discloses a method of making a sensitized flowable explosive of the emulsion type comprising the formation of voids for explosive sensitization within the emulsion by adding a gassing agent, such as a solution comprising a solvent which comprises water and a solute which comprises nitrite ions. EP 0 322 097 and US 4,287,010 disclose the sensitization of emulsion-type explosives by incorporating sensitising voids into the emulsion as a result of direct intensive mixing of a gas into said emulsion, although said documents do not disclose the possibility of controlling the density of the explosive by regulating the gas flow. In relation to the manufacturing of the explosive in situ , that is, in the same truck used for the pumping of the explosive to the bores, the first patents are due to IRECO, such as it is described in the US patents 3,303,738 and 3,338,033. These patents are characterized by the manufacturing in the truck of a watergel explosive by means of the dosification and mixture of oxidant salts liquid solution with a solid material which contains oxidant salts and thickeners. In US Patent 3,610,088 (IRECO) the same procedure of the previous patents are used for the formation of the watergel in situ and incorporate the simultaneous addition of air either by means of mechanically trapping or its generation through a chemical reaction. The EP patent 0 203 230 (IRECO) describes a mixer form by mobile and fixed blades which allows the manufacturing in situ of a blasting agent of water in oil emulsion type. The sensitizing of this emulsion is carried out by the addition of low density particles (oxidant or hollow microspheres). The manufacturing of the explosive in situ has as main advantage the decreasing of the risk during the transport. In contrast it cannot be guaranteed the same levels of quality in the products as in the case of being manufactured in a manufacturing plant. Another alternative is the transport of the finished product without sufficiently sensitizing, that is, at a density such that it has no capacity of propagating an stable detonation. In this context it has been generalized in the last years the transport of the base product and its sensitizing in mine either by mixing it with particulated nitrates of low density or mixtures of ammonium nitrates with hydrocarbons (ANFO) or through the generation of bubbles by means of a chemical reaction. The US patent 4,555,278 describes an explosive of this type manufactured by mixing emulsion and ANFO. The European patent EP 0 194 775 describes an explosive of the type previously mentioned, formed starting from a base watergel. The sensitizing of the base emulsion by generating bubbles of gas through chemical reaction is the widest used method at present. However in order to avoid the coalescence of the gas bubbles, such as it is described in the US patent 4,008,108, the pumping and the handling of the emulsion should be carried out before the gasification reaction takes place. In this way, this method has the great disadvantage of having to wait a certain time from the filling of the holes until the final density is achieved, not having capacity of manoeuvre if the obtained density does not coincide with the expected one, being able to produce sensitizing failures or an incorrect distribution of the explosive in the bore hole column. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a schematic drawing of a particular embodiment of an installation for "in situ" sensitization of water based explosive according to this invention which includes a stabilizing tank, a doser and a flowmeter. DETAILED DESCRIPTION OF THE INVENTION The invention provides a procedure for "in situ" sensitization of water based explosives, comprising (i) the transport to the borers loading place of a non explosive or low sensitivity base product composed by an aqueous liquid mixture which comprises oxidants and fuels, in solution, in emulsion or in suspension, optionally together with sensitizing and thickening agents, and (ii) the sensitization of said base product before its loading in the borers, characterized in that: such sensitization is performed by mixing said base product with a gas towards a mixer, by the formation of a suspension or an emulsion of gas in liquid; the density of the sensitized explosive is adjusted by the regulation of the gas flow; and a stabilizing solution of the gas bubbles is added to the mixer wherein said base product is mixed with the gas. In this description "in situ sensitization" means the sensitization of the explosive before the loading of the holes. The base product is formed by a water based liquid mixture that comprises oxidants and fuels in solution, in emulsion or in suspension, and optionally, sensitizing and thickening agents. As oxidant salts, nitrates, chlorates and perchlorates of ammonium, alkaline and alkaline-earth metals may be used as well as mixtures thereof. Precisely, these salts can be among others, the nitrates, chlorates and perchlorates of ammonium, sodium, potassium, lithium, magnesium, calcium, or mixtures thereof. The total concentration of oxidant salts present in the base product may vary between 30% and 90% by weight of the formulation, preferably between 40 and 75%. Organic compounds belonging to the group formed by aromatic hydrocarbons, saturated or unsaturated aliphatic hydrocarbons, oils, petrol derivatives, vegetable occurring derivatives such as starches, flours, sawdust, molasses and sugars, or metallic fuels finely divided such as aluminum or ferro-silica may be used as fuels. In general, the total fuel concentration in the base product may vary betweeen 1% and 20% by weight of the formulation, preferably between 3 and 7%. The alkylamine nitrates, alkanolamine nitrates, and mixtures thereof, such as methylamine nitrate, ethanolamine nitrate, diethanolamine nitrate, triethanolamine nitrate, dimethyl-amine nitrate, as well as the nitrates from other hydrosoluble amines such as hexamine, diethylenetriamine, ethylenediamine, laurylamine and mixtures thereof, may be used as sensitizing agents. The total concentration of sensitizing agents in the base product (if present) may vary betweeen 0.5% and 40% by weight of the formulation, preferably between 2 and 30%. As thickening agents, products derived from seeds such as guar gum, galactomananes, biosynthetic products such as xanthane gum, starch, cellulose and their derivatives such as carboxymethylcellulose or synthetic polymers such as polyacrylamide, may be used. The concentration of thickening agents in the base product (if present) may vary between 0.1% and 5% by weight of the formulation, preferably between 0.5 and 2%. The formation of the emulsion or gas dispersion in the base product is carried out in an inline mixer preferably of the dynamic type such as a stirrer. The base product, the gas and the bubbles stabilizing agent are sent to the mixer through their respective doser. In a preferred embodiment, the feeding of the components is carried out through the bottom of the mixer, with the product coming out spilling over by the upper part. As gases it may be employed those commonly used for the sensitizing of the explosives such as nitrogen, oxygen, air or carbon dioxide. The volumetric ratio between the gas and the base product may vary between 0.05 and 5, preferably between 0.1 and 1. Among the stabilizing agents of the gas bubbles which can be added, there are surface-active agents solutions or dispersions of the type derived from amines of fatty acids such as for example laurylamine acetate or proteins of the type egg albumin, lactalbumin, collagen, soy protein, guar protein or modified guar gum of the guar hydroxypropyl type. The stabilizing agent may be added to the base product in a concentration comprised between 0.01% and 5% by weight of the formulation, preferably between 0.1% and 2%. By means of this procedure an explosive may be manufactured with a suitable density before charging it into the hole, in this way allowing to control the quality of the explosive which is being charged. Once the explosive is sensitized this can be either directly delivered to the bore holes or it may be added to it a crosslinking agent to improve its water resistance. Among the crosslinking agents the antimmonium compounds such as potassium pyroantimoniate, antimmonium and potassium tartrate, chromium compounds such as chromic acid, sodium or potassium dichromate, zirconium compounds such as zirconium sulphate or zirconium diisopropylamine lactate, titanium compounds such as titanium triethanolamine chelate or aluminum compounds such as aluminum sulphate, can be used. The concentration of the crosslinking agent may vary between 0.01% and 5% by weight of the formulation, preferably between 0.01% and 2%. In an specific and preferred embodiment, the procedure for "in situ" sensitization of water based explosives provided for this invention is carried out in a truck for loading the holes which has available a tank containing the base product, a doser pump of the base product and a device for the dosification of gas to the base product in the mixer. The procedure for "in situ" sensitization of water based explosives provided by this invention has the advantage of allowing the instant change of the density of the explosive, as well as the size of the air bubbles through the adjustment of the energy applied in the mixer. In this way for a final density value of the explosive, it can be acted upon its sensibility and speed of detonation. Additionally, with the procedure of the invention it can only be manufactured the explosive which must be charged in the hole. The high precision of the method allows to vary the explosive density either between different holes or in the same hole. Optionally the addition of particulated oxidants or ANFO type explosives, that is a mixture of a particulated oxidant and a hydrocarbon, is contemplated. The invention also relates to an installation for "in situ" sensitization of water based explosives according to the previously described procedure, as the one shown in Figure 1, which comprises: a mixer (5); a first tank (1) for the storage of the base product; a first pump (3) which connects said first tank (1) to the mixer (5); a gas reserve (10) operatively connected to the mixer (5) ; a gas flow regulating device (6); a second tank (2) for the storage of a stabilizing solution of the gas bubbles; and a second pump (4) which connects said second tank to the mixer (5). The installation also contains two flowmeters (7, 8). The mixer (5) can operate continuously and may be of the dynamic type such as for example a stirrer or a static mixer. At the outlet of the mixer (5) a pump provided with hopper (9) can be installed which is used for charging the explosive already sensitized in the holes. In a particular and preferred embodiment, the installation is located on a truck for loading the holes or a pumping truck, which has available a tank that contains the base product, a loading pump and a device in order to dose the gas to the base product. The invention is illustrated by means of the following example which in any case limits the scope of the invention. EXAMPLE In this example a typical installation and the explosive manufactured thereof, is described. This installation is located on a truck which allows the transport of the base mixture and its sensitizing in the mine. It has the following elements (Figure 2): a tank (1) of 10,000 1 where the base mixture is stored; a tank (2) of 200 l for the storing of the stabilizer; two pumps (3 and 4) for the transfer of the base mixture and the stabilizer to a mixer (5) of stirrer type; a valve (6) connected to an air line, for the dosification of air to the mixer (5); two flowmeters (7 and 8) interpolated among the pump (4), the valve (6) and the mixer (5) for the control of the respectively stabilizing and air flows; and a pump provided of a hooper (9) located at the outlet of the mixer (5) used to load the explosive already sensitized in the holes. The tank (1) was filled with the base formulation described in Table 1. Composition of the base product Component % Water 11.5 Ammonium Nitrate 75.6 Monomethylamine Nitrate 9.2 Guar Gum 0.6 Mineral oil 3.1 The density of this base product before its sensitizing in the previously described device was 1.49 g/cm 3 . In the tank (2) a solution of a stabilizer composed by 90 parts of water and 10 parts of powdered milk serum with a protein content of 30%, was prepared. After the dosers have been calibrated, the operation started connecting the stirrer and the different pumps in the conditions described in Table 2. Operating conditions and properties of the obtained explosive Mixer r.p.m. Base Material kg/min Stabilizer kg/min Air l/min Density g/cm 3 VOD m/s 520 150 0.5 23 1.21 3850 750 150 1 35 1.11 4050 1,300 200 1.5 40 1.15 4500 1,000 100 1 35 0.98 4400 1,200 80 1 50 0.77 3200 The explosive already sensitized came out spilling over the mixer (5) falling over the hopper (9) from which it was pumped to the holes injecting in the hose a crosslinking solution of 6% chromic acid in water. The VOD values correspond to samples tested in iron pipes of 50 mm of inner diameter and primed with a 15 g pentrite (PETN) booster.

Claims: A procedure for "in situ" sensitization of water based explosives, comprising (i) the transport to the borers loading place of a non explosive or low sensitivity base product composed by an aqueous liquid mixture which comprises oxidants and fuels, in solution, in emulsion or in suspension, optionally together with sensitizing and thickening agents, and (ii) the sensitization of said base product before its loading in the borers, characterized in that : such sensitization is performed by mixing said base product with a gas towards a mixer, by the formation of a suspension or an emulsion of gas in liquid; the density of the sensitized explosive is adjusted by the regulation of the gas flow; and a stabilizing solution of the gas bubbles is added to the mixer wherein said base product is mixed with the gas. A procedure according to claim 1, characterized in that such base product comprises between 30% and 90% by weight of oxidants. A procedure according to claim 1, characterized in that such base product comprises an oxidant selected from the group formed by nitrates, chlorates and perchlorates of ammonium, alkaline and alkaline-earth metals as well as mixtures thereof. A procedure according to claim 1, characterized in that such base product comprises between 1% and 20% by weight of fuels. A procedure according to claim 1, characterized in that such base product comprises a fuel selected from the group formed by aromatic hydrocarbons, aliphatic hydrocarbons, oils, petrol derivatives, vegetable occurring derivatives, finely divided metallic fuels, and their mixtures. A procedure according to claim 1, characterized in that such base product comprises between 0.5% and 40% by weight of sensitizing agents. A procedure according to claim 1, characterized in that such base product comprises a sensitizing agent selected from the group formed by alkylamine nitrates, alkanolamine nitrates, and their mixtures. A procedure according to claim 1, characterized in that such base product comprises between 0.1% and 5% by weight of thickening agents. A procedure according to claim 1, characterized in that such base product comprises a thickening agent selected from the group formed by products derived from seeds, biosynthetic products and their derivatives and synthetic polymers. A procedure according to claim 1, characterized in that such gas is selected from the group formed by air, nitrogen, oxygen and carbon dioxide. A procedure according to claim 1, characterized in that the volumetric ratio between the gas and the base product is comprised between 0.05 and 5. A procedure according to claim 1, characterized in that such stabilizing solution of the gas bubbles is selected from the group formed by surface-active solutions or dispersions of the type derived from amines of fatty acids, proteins and modified guar gum. An installation for "in situ" sensitization of water based explosives, according to claim 1, which it is located in a loading truck, comprising: a mixer; a first tank for the storage of the base product; a first pump which connects said first tank to the mixer; a gas reserve operatively connected to the mixer; a gas flow regulating device; a second tank for the storage of a stabilizing solution of the gas bubbles; and a second pump which connects said second tank to the mixer. An installation according to claim 13, characterized in that the mixer is of the dynamic type.

Inventors: BEITIA GOMEZ DE SEGURA FERNAND, LANZA RIVAS RAFAEL, QUINTANA ANGULA JOSE RAM N, BEITIA GOMEZ DE SEGURA, FERNANDO, LANZA RIVAS, RAFAEL, QUINTANA ANGULA, JOSE RAM N, Quintana Angula, José Ram n
Applicants: ESPANOLA EXPLOSIVOS, UNION ESPANOLA DE EXPLOSIVOS S.A.
Application year: 1997
Main classification: C06B21
IPC codes: C06B47, C06B23, C06B21, B01F3