|Title of Invention||
"A DEVICE USEFUL FOR UNINTERRUPTED FLUSHING OF CRYOGENIC INERT FLUID TO CONTROL FIRE IN UNDERGROUND MINES"
|Abstract||The device of the present invention essentially consists of two coaxially placed tubes separated by a filling of insulating material in pre-vacuumed space. The ends of the said tubes being sealed by annular hollow plates. The said tubes and the said annular hollow plates being joined by known welding methods. Further, the inner tube is corrugated to enable low temperature contractional adjustment. The device so obtained is suitable for passing cryogenic inert fluid. A plurality of such device when connected together is useful for uninterrupted flushing of cryogenic inert fluid to control fire in underground mines.|
|Full Text||The present invention relates to a deviee useful for uninterrupted flushing of cryogenic inert fluid to control fire in underground mines. The device of the present invention particularly relates to super insulated tubes that can be used for flushing cryogenic inert lluids such as liquid nitrogcn(LN2) /LN2 & solid CO2 slurry or any other inert cryogenic fluid or slurry from surface into a mine opening through boreholes so thai it can reach the bottom of the borehole without change of state or gain of heat thereby enable control fire by incrtisation and cooling. The device of the present invention arc to be laid along the length of the borehole from surface up to bottom of the borehole and arc made in segments of convenient length having coupling arrangements at both ends so that they can easily be joined at the spot and lowered into a borehole and also raised after flushing is over. They are retrievable and may be used a number of times.
To the best of our knowledge, the existence of such super insulated lubes as of the device of the present invention for infusion of LN2 through boreholes in underground for control of fire in mines is unknown.
Presently the following prnclices lire being ndoplcil for controlling ol'fuv in underground mines by nitrogen infusion.
LN2 and other cryogenic inert liquid or slurry can be flushed from surface directly through boreholes close to the seat of lire in underground coal mines or it can be evaporated in an evaporator at surface and then sent through borehole. When I-Nj is Unshed through borehole, water percolating from strata to the borehole comes in contact with LN2 and freezes leading to blockage of the borehole, interrupting infusion of LN2 Once a bore hole gets blocked by free/ing of water, experience shows that its clearing is very difficult and time consuming, often calling for rcdrilling. The interruption of LN2 infusion is considered detrimental for control of lire in mine. Further evaporation of LN2 inside the borehole may gcnerale buck pressure which
is dangerous. These difficulties may be overcome by using an evaporator at surface and converting the liquid into gas before infusion. With this method of nitrogen infusion cooling capacity of the liquid is losl to a great extent. Further the rate of infusion of nitrogen is limited by the capacity of the evaporator.
Mines having gaseous nitrogen generator (Pressure Swing Absorption or oilier type) can Hush nitrogen in fire area through boreholes or through pipe ranges laid below ground Nitrogen gas generators are however costly, quality of nitrogen is always not satisfactory as it contains some percentage of oxygen and rate of infusion is always limited by the capacity of the gas generator. Further, very few mines have such facilities. These problems seriously restrict the effectiveness of the above methods in controlling fire and hence there is a ddiuilc nml for a device as of this invention.
The main object of the present invention is to provide a device useful for uninterrupted Hushing of cryogenic inert Huid to control fire in underground mines without change of stale or gain of heat so that the area is inerti/ed and simultaneously cooled for quick control of lire.
Another object is to provide a device having segments of convenient length with i oiipling arrangement at both ends to enable lengthwise joining of a plurality of such devices.
Yet another object is to provide a device which is retrievable and reusable.
In figure I of the drawings accompanying this spccificalion a sectional elevation of an
embodiment of two coupled devices of the present invention are shown.
Accordingly, the present invention provides a device useful for uninterrupted flushing of cryogenic inert fluid to control fire in underground mines, which comprises two coaxially placed tubes (1, 2) the inner tube (1) and the outer tube (2) having between them a gap (4) evacuated of air and filled with high thermal insulating material such as fiberglass, powdered cork, aluminum foil, copper foil , the said tubes (1,2) being joined to each
other at both ends with annular hollow plates (3) by welding, the inner tube (1) being provided with corrugation (9) at both ends in such a manner so as to enable adjustment due to contraction in length during passage of cryogenic fluid through the said tube, the ends of the said joined tubes being provided with coupling arrangement means comprising of nut and bolt system (5,6,7,8) to enable lengthwise joining of a plurality of such devices.
Prevention/reduction of transfer of heat from strata into the liquid Hushed through a borehole is achieved by providing high thermal resistance between the borehole surface and the (lowing liquid. High quality insulating material of suitable thickness in between two coaxial lubes is used to achieve the desired thermal insulation to reduce flow of heat from strata to the liquid. To reduce heat transfer due to convection, air in between the two eoaxinl lubes is removed by creating vacuum through a hole provided on the outer tube which in Ihi'ii phi^i'd. Thus, except for initial moments at the start of flushing, liquid entering the system al ihe surliice would leave the tube at the bottom of the borehole in liquid state. Some transfer of heat would, however, prevail through the joints between the two lengths of the system where no insulation is provided. However, after a short period of flushing a thick coal of ire will In1 formed nl Ihe outer surface of joints which will restrict flow of heat through the joints.
The figure I of the drawing with this specification shows sectional elevation of two coupled devices of the present invention. The device essentially consists of two coaxial tubes namely an inner (1) and an outer tube (2) joined at the ends by welding to a hollow plate (3). Oulcr diameter of the hollow plate (3) should be equal to Ihe ouler diameter of oilier lube (?) and Ihe inner diameter of plale (3) should Iv equal to llir iinii'i diameter of (he inner Ink- (I) The inner tube (I) is made of a material that can withstand very low temperature of -I9()V and below. The inner tube (1) must have some corrugation (9) at both ends so thai contraction in its
length when cooled to very low temperature can he easily accommodated wilhoiil damaging the system. Before welding the end of the lube (he gap between inner (I) and outer lube (.') is Tilled up with high quality thermal insulating material (4) for prevention of heat How. 'To reduce heat transfer by convection, air in the space in between tube (1) and tube (2) is removed by creating a vacuum through a plug hole (10) provided in the outer lube (2) which is sealed after evacuation. For joining two such tube systems a coupling arrangemenls is provided which basically iw a nut (5) and bolt (6) system. If one end of tube system is provided with a mil (5), (he oilier end should be provided with a bolt (6). Both the nut (5) and boll (6) arc tighlly secured lo Ihe outer lube (2) by means of counlersunk screws (7) that fix into suitable rings (8) provided in the ouler surface of outer tube (2). Ouler surface of the coupling system has been given a suitable profile so dial il can be easily moved in and oul of Ihe borehole vvilhoul much resistance. When Ihe mil (5) and Ihe boll (6) arc tightened one tube is securely joined wilh another leaving no gap between them allowing (low of LN2 from one tube length to the other without any chance of leakage llirough Ihe joints. The coupling should be made of material that can withstand very low lemperalure, al Ihe same time it must be strong enough lo lake the load of number of lube lengths thai may be used at a lime for flushing of LN2 and some extra force needed during icliieval operation of lubes.
I'or (lushing liquid nitrogen (LN2) through a plurality of interconnected devices of the present invention laid in a borehole lo control fire by incrlizalion and cooling in below ground mines the following operations are adopted:
A borehole of diameter slightly bigger than the ouler diameler of coupling of llu: lube is essential. One length of the super insulated tube system is gradually lowered into the borehole wilh Ihe help of a winch machine. To the upper end of this tube a second segment of Ihe system
is so placed that nut & bolt ends arc placed one on the other. Now the upper tube is rotated keeping the lower tube tightly fixed so that both the lube segments are securely joined leaving no gap between them. Now the lube range is further lowered till the upper end of the second tube is slightly above the mouth til' I he borehole. At this point a third segment i,s joined and the lube range lowered further into the borehole. The process is repeated till 11 if lower end of the tube reaches the bottom of the borehole. No force except the weight of the tube would normally be needed for downward movements of tubes during lowering. The design of coupling system with countersunk screws and ring arrangements with slight play between two lube lengths would help the tube system to adjust to the layout of borehole even when it is not perlec'lly vertical. Aller all the lubes have been joined and lowered the top end of Ihe lopmosl lube may now be joined wilh I,NT tanker through a flexible hose which is normally provided with the tanker using either nut and boll system or a flange system which may be fabricated locally depending on the system and si/c available with LN.2 tanker. The tube system should be suitably anchored to Ihe ground. Now the system is ready for operation. Hushing of LN2 through borehole may now commence by opening suitable valve provided in (lie lanker. Normally I,N; (ankers arc provided wilh suitable valves, by manipulation of which rate and pressure of flow of LN2 can be controlled. Once the flushing is over and fire brought under control the tube system can be gradually raised with the help of a winch machine and individual tubes carefully detached from the system one after another. It is expected that a thick coal of ice will be formed around each joint which may net as a lighl plug in (he borehole preventing movements of lubes in borehole. Thus, aller the (flushing of LN.2 is over some lime must be given for this ice coating to melt and allow free movement of lubes before the tubes may be raised. 'Cubes may be stored and reused at some other place whenever necessary.
The main advantages of the device of the present invention are:
1. Uninterrupted llow of LN2 without change of state or much gain of heat at any desired rule ol'
How and pressure is assured by this invention.
2. Avoids blockage of borehole as I,N? is infused through super insulated lubes which prevents
entry of water into the lube. Thus re-drilling of the borehole to clear blockage is redundant
and lire can be suppressed al shortest possible time using minimum amount of I.N.>
3. Retrievable and reusable thus resulting in economy.
4. Since LNa will llow in liquid slate there is no question of back pressure of gas and therefore
the system is also quite safe.
5. Since the tube system is made of suitable length they are convenient for handling,
transportation and use.
1. A device useful for uninterrupted flushing of cryogenic inert fluid to control fire in underground mines, which comprises two coaxially placed tubes (1,2) the inner tube (1) and the outer tube (2) having between them a gap (4) evacuated of air and filled with high thermal insulating material such as fiberglass, powdered cork, aluminum foil, copper foil, the said tubes (1,2) being joined to each other at both ends with annular hollow plates (3) by welding, the inner tube (1) being provided with corrugation (9) at both ends in such a manner so as to enable adjustment due to contraction in length during passage of cryogenic fluid through the said tube, the ends of the said joined tubes being provided with coupling arrangement means comprising of nut and bolt system (5,6,7,8) to enable lengthwise joining of a plurality of such devices.
2. A device useful for uninterrupted flushing of cryogenic inert fluid to control fire in underground mines substantially as herein described with reference to the drawing accompanying this specification.
|Indian Patent Application Number||2158/DEL/1998|
|PG Journal Number||12/2008|
|Date of Filing||24-Jul-1998|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI - 100 001, INDIA.|
|PCT International Classification Number||E03D 9/00|
|PCT International Application Number||N/A|
|PCT International Filing date|