GB2167789A

GB2167789A - Reducing ignition of mine gas during operation of a section-cutting gallery driving machine

Info

Publication number: GB2167789A
Application number: GB08528214A
Authority: GB
Inventors: Friedrich Wilhelm Paurat; Roland Paurat
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-11-28
Filing date: 1985-11-15
Publication date: 1986-06-04
Also published as: FR2573809B1; FR2573809A1; DE3443289C1; GB8528214D0; GB2167789B

Abstract

A method of reducing the ignition of mine gas during the operation of a section-cutting gallery driving machine having a universally pivotable cutting arm which carries a rotating cutting head (1) with at least 30 cutting tools (3) which move at full reach at a cutting speed of 2 to 3 m/s and which produce as rock is cut away grooves (8) on the working face into which a mixed air/water spray (6) is directed, the individual cutting tools having associated spray supply ducts (4) and spray exit nozzles (5) and the spray being formed by compressed air and water, has flow rates of the spray per minute per cutting tool of 0.25 m<3> to 1.0 m<3> of air and 0.2 to 0.5 litres of water, and the stream velocity is approximately ten times the cutting speed, the mixed steam being introduced into the angle between the cutting tool tip (7) and the cut groove (8) at an incident angle of 40 DEG to 70 DEG relative to a radius (r) of the peripheral circle of the individual cutting tool to the centre of incident of the spray on the cut groove. <IMAGE>

Description

SPECIFICATION Reducing ignition of mine gas during operation of a section-cutting gallery driving.

machine This invention relates to a method of reducing the ignition of mine gas during the operation of a section-cutting gallery driving machine having a cutting arm which can swivel up and down and about a vertical axis and which carries at least one rotating cutting head with at least 30 cutting tools which move at full reach at a cutting speed of 2 to 3 m/s and which produce as rock is cut away grooves on the working face into which a mixed air/water spray is directed, the individual cutting tools having associated therewith spray supply ducts and spray exit nozzles, and the spray being formed by compressed air and water.

Cutting heads of this type generally have a maximum diameter of about 450 to 900 mm and an axial length set with cutting tools of 500 to 1000 mm. The cutting tools are usually set at a suitable pitch along a helix. The cutting head can be mounted like a mushroom cap coaxial with the cutting arm axis or project on either side of the end of the cutting arm, at right angles to the cutting arm axis.

The mixture spray can be maintained from the spray exit nozzles throughout the entire peripheral path of the cutting tools or only emerge when the cutting tools are actually removing rock from the working face.

In the context of known methods of this type (see for example, the introduction of EP-A 00 10 534) the object is to cool the cutting tools and the surfaces of the cut grooves, and accordingly water is used primarily as a coolant. The air serves to atomise the water. The ignition of mine gas during the operation of these section-cutting machines cannot be suppressed with adequate reliability by this method, particularly when the mine gas originates from what are known as blisters, which frequently occur in geological strata carrying mine gas. The specific conditions whereby such ignition can be prevented with adequate reliability have not been specified within the scope of the known methods.The ignition of mine gas during the operation of section-cutting machines of the type described is in fact a highly complex phenomenon, and efforts have been made repeatedly and extensively without any success as regards the certain suppression of ignition when mine gas is encountered during the practical use of such machines (cf "Gluckauf-Forschungshefte", 1980, pp. 17 to 21). It is obvious that ignition will only take place when a combustible mixture is present, and the combustible mixture must absorb at least that quantity of energy that corresponds to its ignition energy before it will ignite. The ignition tendency in a mixture also depends on such thermodynamic parameters as pressure and temperature, which interact to determine the thermodynamic potentials which govern ignition.The geometrical and thermodynamic boundary conditions are also relevant, as are the aerodynamic conditions in the environment of the combustible mixture, which determine the aerodynamic behaviour of the combustible mixture.

Further factors include the surface area of the sparks which are formed during the operation of this type of section-cutting machine, and their flight paths. It is easy to understand why no technical teachings have yet been developed for the adequately reliable prevention of mine gas ignition in this process.

The object of the invention is to improve the basic method so that the ignition of mine gas can be prevented with adequate reliability under all working conditions encountered with section-cutting machines of the types described.

According to the present invention the mixed air/water spray supply rates per cutting tool per minute are 0.25 m3 to 1.0 m3 of air and 0.2 to 0.5 litres of water, the stream velocity is approximately ten times the nominal cutting speed, and the mixed stream is introduced into the angle between the cutting tool tip and the cutting groove at an incident angle of 40 to 70 relative to a radius of the peripheral circle of the individual cutting tool to the centre of the incidence of the spray on the cut groove. Preferably, 0.4 m3 of air and about 0.3 litres of water are supplied per cutting tool per minute.

The mixed stream preferably has a stream velocity of 25 to 35 m/s, more particularly 30 m/s on entering the associated cut groove, and is directed at a preferred angle of 50" relative to a radius of the peripheral circle.

The stream velocity of the mixed stream refers to the velocity of the air stream in the mixture leaving the spray exit nozzles. In this range, most of the entrained water drops have the same velocity, though individual drops may move more slowly. The water drops in the mixed stream are preferably of sufficiently large mass to reach the surface of the cutting groove under their own momentum, irrespective of the divergence of the air in the mixed stream before it reaches the cutting groove.

The specified feature of the method as described can be realised, maintained and controlled very easily when the mixed stream emerged from the spray exit nozzle with a diameter of about 5 mm. In this case, the air in the mixed stream can be taken from a compressed air main operating at 1 to 2 bar above atmospheric pressure.

It is within the scope of the invention to supply the compressed air and the water respectively through separate exit nozzles, to unite subsequently as a mixed stream. However, mixing can conveniently be effected within the spray supply ducts, and the com pressed air and the water are preferably mixed in the spray supply duct at least nearly the spray exit nozzle, the water being atomised into drops on an atomising edge or edges in the spray supply duct upstream of the mouth of the spray exit nozzle. A wetting agent can be added to the water, and the air can be mixed with an inert gas such as nitrogen for example.

The accruing advantages are to be seen in that when the method of the invention is applied to a section-cutting gallery driving machine of the type described, the ignition of mine gas is suppressed with adequate reliability. The invention thus arises from the realisation that the prevention of ignition requires certain measures which are separate in themselves but nevertheless interact functionally when combined, viz., on the one hand the introduction of a sufficiently large volume of air into spaces where a combustible mixture of air and mine gas might form, and on the other hand the introduction of this volume at an adequately high kinetic energy level, which depends on the cutting speed and corresponds to a velocity about ten times the cutting speed. The volume of water must be sufficient to wet the surface of the cut groove adequately.However, the water volume must not be too great, since the effect of the air stream would otherwise be impaired. The drops should be sufficiently large for their momentum to carry them on to the surface of the cut groove as described; this is achieved easily and with certainty when the drop size is regulated and in addition the mixed stream is directed at the specified angle of incidence into the angle between the cutting tool tip and the cutting groove. Nevertheless, this angle is also a significant factor in ensuring that the incoming air assists in preventing ignition of the mine gas.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side elevation of a cutting tool set up in a mount in a section-cutting machine; and Figure 2 shows in section and on a larger scale the area A in Fig. 1.

Fig. 1 shows part of the cutting head 1 of a section-cutting machine for driving galeries, having a cutting arm (not shown) which can swivel up and down and about a vertical axis; the part shown includes a single so-called mount 2 which carries a cutting tool 3. With the cutting tool 3 there is associated a spray supply duct 4 which terminates in a spray exit nozzle 5. The spraying agent consists of compressed air and water, and the mixed stream 6 emerges as shown from the spray exit nozzle 5 to enter the angle between the cutting tool tip 7 and the groove 8 cut by it in the indicated direction of rotation. The supply rates per cutting tool 3 per minute are 0.25 m3 to 1.0 m3 of air and 0.2 to 0.5 litres of water. The arrangement is such that the mixed stream 6 emerges from the spray exit nozzle 5 at a stream velocity approximately ten times the cutting speed. Its incident angle relative to the radius r of the peripheral circle of the individual cutting tool 3 is in the range between 40 and 70" and is more or less 50 in the embodiment shown.

The compressed air and the water are mixed in the spray supply duct 4 at least near the spray exit nozzle 5, and Fig. 2 shows an atomising edge 9, the effect of which is that the water is atomised into drops of not too large a size in the spray supply duct 4 upstream of the spray exit nozzle mouth 10. As a result, the mixed stream 6 contain water drops of sufficient size to reach the surface of the cutting groove 8 under their own momentum, irrespective of the divergence of the air in the mixed stream 6 before it reaches the cutting groove 8.

Claims

1. A method of reducing the ignition of mine gas during the operation of a sectioncutting gallery driving machine having a cutting arm which can swivel up and down and about a vertical axis and which carries at least one rotating cutting head with at least 30 cutting tools which move at full reach at a cutting speed of 2 to 3 m/s and which produce as rock is cut away grooves on the working face into which a mixed air/water spray is directed, the individual cutting tools having associated therewith spray supply ducts and spray exit nozzles, and the spray being formed by compressed air and water supplied at rates per cutting tool per minute of 0.25 m3 to 1.0 m3 of air and 0.2 to 0.5 litres of water, the stream velocity being approximately ten times the nominal cutting speed, and the mixed stream being introduced into the angle between the cutting tool tip and the cut groove at an incident angle of 40 to 70" relative to a radius of the peripheral circle of the individual cutting tool to the centre of incidence of the spray on the cut groove.

2. A method as in Claim 1, wherein 0.4 m3 of air and 0.3 litres of water are supplied per cutting tool per minute.

3. A method as in either of Claims 1 or 2, wherein the mixed stream has a stream velocity of 25 to 35 m/s, preferably about 30 m/s, on entering the cut groove.

4. A method as in any one of Claims 1 to 3, wherein the mixed stream is introduced into the cutting groove at an angle of 50 relative to the radius of the peripheral circle.

5. A method as in any one of Claims 1 to 4, wherein the water drops in the mixed stream are of sufficiently large mass to reach the surface of the cut groove under their own momentum, irrespective of the divergence of the air in the mixed stream before it reaches the cut groove.

6. A method as in any one of Claims 1 to 5, wherein the mixed stream emerges from the spray exit nozzle with a diameter of about 5 mm.

7. A method as in any one of Claims 1 to 6, wherein the air in the mixed stream is taken from a compressed air main operating at 1 to 2 bar above atmospheric pressure.

8. A method as in any one of Claims 1 to 7, wherein the compressed air and the water are mixed in the spray supply duct at least near the spray exit nozzle, the water being atomised into drops in the spray supply duct on an atomising edge or edges upstream of the mouth of the spray exit nozzle.

9. A method as in any one of Claims 1 to 8, wherein a wetting agent is added to the water.

10. A method as in any one of Claims 1 to 9, wherein an inert gas is mixed with the air.

11. A method of reducing the ignition of mine gas during the operation of a sectioncutting gallery driving machine substantially as hereinbefore described with reference to the accompanying drawings.