GB2134646A - Surface mine ventilation system - Google Patents

Abstract

A mine ventilation system for a mine having a ventilation requirement of a volumetric flow rate between first and second limit values and a fan pressure rise requirement between third and fourth limit values, comprises two substantially aerodynamically identical centrifugal surface mounted fans 50, 51, each driven by its own variable speed motor set, the fans, when run together in parallel, being capable of any of the duties within the said limit values, provided the motor sets are both adjusted to substantially the same appropriate speed, and each, when run by itself, with that speed adjustment, being capable of at least 65%, and preferably 70%, of the volumetric flow rate of the two fans when run in parallel, a single size of fan being capable of being interchanged between mine surface ventilation systems. <IMAGE>

Description

SPECIFICATION Surface mine ventilation system The present invention relates to surface mine ventilation systems.

The ventilation of mines is carried out in two stages. Firstly, there is a ventilation system within the mine to distribute the air which has been fed from the surface and secondly, there is a surface ventilation system which draws the necessary air from the lower level, air thus being sucked or blown down the ventilation or other mine shafts.

It has been the practice for a very long time, particularly in coal mines, to design individually for each mine a surface ventilation system. Each mine is likely to be very different from other mines and the requirements for handling the air at the surface are different and a substantial amount of engineering work has to go into the production of a suitable design for that individual mine.

However, the cost of producing a design which is suitable for each mine is very large.

It is now proposed, according to the present invention, to provide a mine ventilation system, e.g. for coal mines, having a ventilation requirement of a volumetric flow rate between first and second limit values and a fan pressure tise requirement between third and fourth limit values, said system comprising two substantially aerodynamically identical centrifugal surface mounted fans, each driven by its own variable speed motor set, the fans, when run together in parallel, being capable of any of the duties within the said limit values, provided the motor sets are both adjusted to substantially the same appropriate speed, and each, when run by itself, with that speed adjustment, being capable of at least 65%, and preferably 70%, of the volumetric flow rate of the two fans when run in parallel, a single size of fan being capable of being interchanged between mine surface ventilation systems.

The variable speed motor sets can include a constant speed motor with its own gearbox or a variable speed motor. By the expression "substantially aerodynamically identical" we mean that the aerodynamic characteristics of the two fans are within 10% of one another. The fans can rotate in the same direction, but equally they can rotate in opposite directions, and then the fan casings can be substantially mirror images of one another. Similarly the speeds of the two variable speed motor sets should be within 10% of one another.

According to a further aspect of the present invention, there is also provided a method of installing a surface ventilation system in a mine, comprising the steps of:- (i) Establishing the volumetric flow and pressure requirements of that mine at any given time; (ii) Taking a standard ventilation system comprising two like variable speed motor/fan sets, adapting the standard system with reference to the established requirement by providing the appropriate speed for both motor/fan sets such that, with the motor/fan sets installed in parallel, the system may be operated in a first, normal operating mode in which the sets operate together to provide 100% of that requirement and in a second, back-up mode, in which only one set operates providing at least 65 and preferably 70% of the established volumetric flow rate requirement.

In the past it has been the practice to have for each mine ventilation system two fans, each capable of giving the 100% volumetric flow rate necessary for full ventilation of the mine. The practice has been to run, at any given time, only one fan, the other fan being there purely and simple as a standby should the first fan fail. The fans are usually run for periods of time alternately to even the wear on the two fans.

With the construction of the present invention, on the other hand, neither of the fans when run alone is capable of 100% duty, but only 65 or preferably 70% of the full duty. When the two fans are run togther, however, so that they are operating in parallel they are capable of producing the full ventilation requirement. Should one fan fail for any reason, for example, a bearing failure, then the other fan can continue to run totally independently and is then capable of producing 65 or 70% at least of the maximum ventilation requirement.

With such an arrangement it is possible to ensure that one only has one basic design and this design can be utilized in each and every mine. It will be clear that this gives a substantial saving in the engineering work which is normally necessary to produce a ventilation system for each mine.

Further advantages arise in connection with replacements and spares. If a single fan design is used, then the spares which need to be carried will be the same for each mine, and they can be interchanged between mines in moments of extreme need.

By having two fans, each driven with its own individual motor via its own individual gearbox or by its own individual variable speed motor, should one of these items, for some reason, break down, then the other fan can always be operated by itself and be capable of at least 65% of the necessary volumetric flow rate, and preferably 70%. This is perfectly adequate for safety purposes and also is adequate for mine maintenance purposes during weekend operation.

Preferably, the two fans are arranged in backto-back relationship, which greatly faciiitates the ability of the system as a whole to operate in reverse, which is a necessity in coal mines to overcome problems of fire hazard.

With the construction of the present invention it is possible to run only one fan during the weekend and this will provide fully adequate air for maintenance work, because the coal cutting machinery, which produces a very large amount of heat is not being used. The ventilation air required to dissipate this heat represents a significant proportion of the total ventilation air. Thus, there is a significant cost advantage in having the ventilation fans running at less than full capacity during weekend periods. This was not always possible with the prior known arrangements in which one had a full 100% fan and a standby fan.

In general the traditional method required adjustment of dampers or vanes in the fan inlet duct but one is not really saving anything on power here because of the significant reduction in overall efficiency. With the construction of the present invention, on the other hand, one will only use the power necessary to drive one fan and one is therefore saving up to half of the eiectricity costs during the weekend period.

In arriving at the design of the present invention, consideration was given to using axial flow fans rather than centrifugal fans. The reason for this is that it has been the practice to use either one type of fan or the other when arriving at an individual design for a particular mine. However, investigations carried out show that it was impractical to use axial flow fans with the arrangement of the present invention unless they were made of variable or adjustable pitch which would make them undesirable from a practical point of view. On the other hand, with the centrifugal fan arrangement of the present invention, a very high percentage of existing mine requirements are met by the provision of two centrifugal fans.

A further consideration in the design of surface mine ventilation fans is the question of noise. It has been found in the past that where one is using a relatively large fan, the fan system requires a silencer to bring the sound produced by the fan down to an acceptable level. On the other hand, the problem normally is significantly reduced with relatively small fans. With the construction of the present invention, therefore, where one is using two relatively small fans instead of one relatively large fan, the silencing requirement is much less.

The two fans running together produce a sound level which is somewhat less than the level of sound produced by a single fan designed for the same duty. This means that because the necessity for a silencer is very often only marginal, the two fan design of the present invention brings one below the threshold where silencers are likely to be necessary and this makes a very substantial saving in the overall cost of the fan system. Not only does one have a saving in the installation cost, but one also has a saving in the running cost because a silencer increases the duty requirement of the fan system and therefore causes the fan motor to draw more current.

When constant speed motors and gearboxes are used, the design of the present invention requires, for each fan of the pair of fans, an individual gearbox. Now it is preferred that the individual gearboxes should each be capable of having no less than 10 and preferably up to 20 different gear ratios readily available. By having such a large number of gear ratios, one can adapt the fan system according to the present invention to the requirements of an individual mine without having to do any other design work. The fan itself is of standard size as is the motor, so no engineering work has to be done here and all that one then does is to select the particular one of the large number of available gear ratios for that particular requirement.Furthermore, as a mine grows due to further use, one can readily change to the optimum fan speed for the increased duty as and when that arises, and indeed one has greater flexibility in giving the accurate correct adjustment at rather closer time intervals than was hitherto commercially practical.

In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a graph of a static head against the volume flow rate showing the duties of the vast majority of known British mines; Figure 2 is a graph of pressure head against flow rate of a fan system according to the present invention, showing both single and two fan operation; Figure 3 is a side elevation partly in section, of one embodiment of arrangement according to the invention; Figure 4 is an end elevation of the assembly of Figure 3; and Figure 5 is a simplified plan view thereof, to a reduced scale.

Referring first to Figure 1 of the drawings, there is plotted with crosses the static head in kilopascals as the ordinate and the volumetric flow rate in cubic metres per second as the abscissa.

Also shown on this drawing are two boundary areas. The smaller area 10 on the left shows the capabilities of a single fan with various gear ratios used. The larger area on the right indicated by the reference numeral 12 indicates the capabilities of two identical fans that run in parallel. The area 10 is made up of upper and lower fan characteristic curves, at approximately 475 and 793 R.P.M., 15 and 1 6 respectiveiy and left and right fan efficiency curves 1 7 and 18, the line 1 7 being for 88% adiabatic static fan efficiency and the line 1 8 for 80% efficiency. Similarly, the area 12 is made up of fan characteristic lines 19 and 20 and 88 at the same speeds and 80% fan efficiency curves 21 and 22. It will be seen that all but four of the British National Coal Board mines fall within the areas 10 and 12. Of these four, which have been indicated by the reference letters A, B, C and D, the present invention does not attempt to meet the requirements of A and B but the requirement of C can readily be achieved by conceding that the fan efficiency can fall slightly below 80%, say 79%, with the fan speed increased slightly. The point D is also probably acceptable and only requires a slightly higher than normal allowable pressure of about 7.5 kilopascals.

Thus, it can be seen that the vast majority of known mine ventilation requirements can be met by fan systems according to the present invention.

If one now studies Figure 2, the characteristic curve of a single fan is plotted with the same units as in Figure 1 , the single fan curve being shown at 24 and two fans in parallel being shown at 25.

Also plotted on Figure 2 is the mine system resistance, that is to say the resistance of a particular mine to the flow of air, this being indicated at 26. It can be seen that with two fans operating in parallel, the curve 25 intersects the curve 26 at the point 27 which gives, on the scale shown, a volumetric flow rate of approximately 300 cubic metres per second. If one follows the curve 26 down to the point 28 where it intersects the curve 24, to give the comparable figure for only one of the two fans operating, then the flow rate comes out to a figure of approximately 210 cubic metres per second. It will be appreciated, therefore, that a single fan operating by itself achieves a voiumetric flow rate of approximately 70% of the volumetric flow rate of the two fans running in parallel.

As has been explained earlier, therefore, a single fan can operate adequately at a weekend period, for example, or when failure occurs on one of the fans, for some technical reason or another, for example a broken bearing, and yet still produce approximately 70% of the full requirement. This wilF be perfectly adequate for a short period with the full underground mining staff working, giving them ample air to breathe during a period when they would need to be able to leave the mine.

Also, in a condition of failure of one of the fans one could readily shut down the coal cutting equipment which consumes very large quantities of power and thereby produces considerable heat at the vicinity of the mine face, and it is one of the main functions of the air which is induced by the surface fans to being about a cooling of the coal face area. Thus, it can be seen that the approximate 70% capacity of the single fan will be adequate for a considerable time. In particular, it will be quite clearly adequate during a week-end period when no coal cutting is being carried out.

Referring now to Figures 3, 4 and 5, the installation includes a pair of centrigual fans 50 and 51 (Figure 5) mounted in back-to-back relation, as can be seen in Figure 4, and each having a bearing 52, 53 for a fan shaft 54, 55 which is driven by an individual gearbox 56, 57.

The gearboxes 56 and 57 are driven by electric motors 58 and 59, the shafts 60 and 61 of which are mounted in bearings 62 and 63. The fans themselves are substantially identical as are the bearings, gearboxes and motors.

Each fan includes an impeller 64 of the conventional centrifugal type mounted within a volute 65, 66 the discharge portions of which have a common wall 67. The bearings 52, 53, 62, 63, the gearboxes 56, 57 and the motors 58, 59 are all mounted within a housing 68 having separate access doors 69, 70. A control system is indicated very schematically at 71 in Figure 5 and can be used to control the motors 58, 59 so that they run together or separately. In practice, the actual control facility will be located outside the housing 68.

The inlets to the fans 50 and 51 consist of a pair of ducts 74, 75 which are connected via a common duct 76 to a mine main shaft or ventilation shaft. Controllable vanes 77, 78 are provided in the duct 74, 75 and further air inlet doors 79, 80 are also provided in these ducts.

When one installs the system of the present invention, one does the various calculations on the particular mine orifice to determine the speed at which the fans should operate for normal working.

One then selects the correct one of the gear ratios of the two gearboxes 56, and 57 from the range of 20 available gear ratios. The suitable gear shafts are then fitted into these gearboxes 56 and 57 and the system is ready to run. In normal use, the two motors 58, 59 are operated simultaneously so that the fans 50,51 operate in parallel drawing air via their duct 74, 75 from the common duct 76 and thence from the mine shaft.

At other times, for example, if one of the fans should break down, or during a maintenance period, for example at the weekends, it is perfectly acceptable to operate with only one of the fans 50, 51 because this would be capable of producing up to 70% of the total ventilation requirement.

As will be apparent from the foregoing, instead of using constant speed motors and gearboxes, one can use a variable speed motor to drive each individual fan.

Claims (9)

1. A mine ventilation system for a mine having a ventilation requirement of a volumetric flow rate between first and second limit values and a fan pressure rise requirement between third and fourth limit values, said system comprising two substantially aerodynamically identical centrifugal surface mounted fans, each driven by its own variable speed motor set, the fans, when run together in parallel, being capable of any of the duties within the said limit values, provided the motor sets are both adjusted to substantially the same appropriate speed, and each, when run by itself, with that speed adjustment, being capable of at least 65%, and preferably 70%, of the volumetric flow rate of the two fans when run in parallel, a single size of fan being capable of being interchanged between mine surface ventilation systems.

2. A mine ventilation system according to claim 1, wherein the fans rotate in opposite directions, and wherein the fans include casings which are substantially mirror images of one another.

3. A mine ventilation system according to claim 1 or 2, wherein the speeds of the two variable speed motor sets are within 10% of one another.

4. A mine ventilation system according to claim 1,2 or 3, wherein the variable speed motor sets each include a variable speed motor.

5. A mine ventilation system according to claim 1,2 or 3, wherein the variable speed motor sets each include a constant speed motor with its own gearbox.

6. A mine ventilation system according to claim 5, wherein the gearbox has at least ten different gear ratios readily available.

7. A method of installing a surface ventilation system in a mine, comprising the steps of: (i) Establishing the volumetric flow and pressure requirements of that mine at any given time; (ii) Taking a standard ventilation system comprising two like variable speed motor/fan sets, adapting the standard system with reference to the established requirement by providing the appropriate speed for both motor/fan sets such that, with the motor/fan sets installed in parallel, the system may be operated in a first, normal operating mode in which the sets operate together to provide 100% of that requirement and in a second, back-up mode, in which only one set operates providing at least 65 and preferably 70% of the established volumetric flow rate requirement.

8. A mine ventilation system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

9. A method of installing a surface fan ventilation system for a mine, said method being substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.