CN110080764B - Liquid nitrogen supercharging device, anti-reflection experiment system using same and experiment method - Google Patents
Liquid nitrogen supercharging device, anti-reflection experiment system using same and experiment method Download PDFInfo
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- CN110080764B CN110080764B CN201910454219.1A CN201910454219A CN110080764B CN 110080764 B CN110080764 B CN 110080764B CN 201910454219 A CN201910454219 A CN 201910454219A CN 110080764 B CN110080764 B CN 110080764B
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 825
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 414
- 239000007788 liquid Substances 0.000 title claims abstract description 319
- 238000002474 experimental method Methods 0.000 title claims abstract description 34
- 238000000034 method Methods 0.000 title claims description 32
- 238000004321 preservation Methods 0.000 claims abstract description 126
- 239000003245 coal Substances 0.000 claims abstract description 61
- 230000035699 permeability Effects 0.000 claims abstract description 8
- 210000004907 gland Anatomy 0.000 claims description 24
- 230000008569 process Effects 0.000 claims description 19
- 239000002131 composite material Substances 0.000 claims description 14
- 238000007789 sealing Methods 0.000 claims description 13
- 239000010720 hydraulic oil Substances 0.000 claims description 12
- 230000009471 action Effects 0.000 claims description 10
- 239000000463 material Substances 0.000 claims description 10
- 238000005381 potential energy Methods 0.000 claims description 8
- 238000003780 insertion Methods 0.000 claims description 6
- 230000037431 insertion Effects 0.000 claims description 6
- 238000009835 boiling Methods 0.000 claims description 5
- 239000007789 gas Substances 0.000 claims description 4
- 238000003825 pressing Methods 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 3
- 239000013013 elastic material Substances 0.000 claims description 3
- 238000007689 inspection Methods 0.000 claims description 3
- 238000009413 insulation Methods 0.000 claims description 3
- 239000000696 magnetic material Substances 0.000 claims description 3
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims description 3
- 150000001875 compounds Chemical class 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 7
- 238000001704 evaporation Methods 0.000 abstract description 5
- 230000008020 evaporation Effects 0.000 abstract description 5
- 230000002411 adverse Effects 0.000 abstract description 3
- 239000010410 layer Substances 0.000 description 28
- 238000005516 engineering process Methods 0.000 description 3
- 238000002309 gasification Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000005422 blasting Methods 0.000 description 1
- 210000005056 cell body Anatomy 0.000 description 1
- 210000002421 cell wall Anatomy 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
Classifications
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21C—MINING OR QUARRYING
- E21C37/00—Other methods or devices for dislodging with or without loading
- E21C37/06—Other methods or devices for dislodging with or without loading by making use of hydraulic or pneumatic pressure in a borehole
- E21C37/14—Other methods or devices for dislodging with or without loading by making use of hydraulic or pneumatic pressure in a borehole by compressed air; by gas blast; by gasifying liquids
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
- E21F17/00—Methods or devices for use in mines or tunnels, not covered elsewhere
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
- E21F17/00—Methods or devices for use in mines or tunnels, not covered elsewhere
- E21F17/18—Special adaptations of signalling or alarm devices
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- Engineering & Computer Science (AREA)
- Mining & Mineral Resources (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
- Sampling And Sample Adjustment (AREA)
Abstract
The invention discloses a liquid nitrogen pressurizing device which comprises a liquid nitrogen container, an electric control device, a top cover and a liquid nitrogen tank for pressurizing liquid nitrogen, wherein the electric control device is connected with a display screen. The invention also discloses an anti-reflection experiment system using the liquid nitrogen pressurizing device, which comprises the liquid nitrogen pressurizing device and a confining pressure system; the invention also discloses an experimental method using the anti-reflection experimental system, wherein the first step is a system checking step; the second step is to put in the coal sample; thirdly, applying preset circumferential pressure and axial pressure to the coal sample; fourth, vacuumize the nitrogen supply inner tube; fifthly, injecting liquid nitrogen into the liquid nitrogen heat preservation cavity; and sixthly, injecting high-pressure liquid nitrogen into the coal sample for fracturing and permeability increasing experiments. The invention greatly relieves the adverse effect caused by liquid nitrogen evaporation in the nitrogen supply pipeline, reduces the technical cost, and ensures that the liquid nitrogen fracturing anti-reflection experiment is carried out on the coal sample stably and smoothly.
Description
Technical Field
The invention relates to the technical field of coalbed methane exploitation, in particular to a liquid nitrogen pressurizing fracturing anti-reflection technology.
Background
The coal seam in China has low permeability coefficient and high gas extraction difficulty, and a pressure relief and permeability improvement method is needed, and mainly comprises loosening blasting, dense drilling, deep hole presplitting, protective layer exploitation, hydraulic punching and the like. At present, the liquid nitrogen fracturing permeability increasing technology is to be developed, liquid nitrogen fracturing is an environment-friendly and relatively low-cost fracturing means, and a plurality of liquid nitrogen rapid fracturing methods are disclosed, such as pressurizing by using a booster pump. The existing liquid nitrogen rapid fracturing technology has the defect of slow liquid nitrogen pressure rise, and is difficult to avoid the phenomenon that a large amount of liquid nitrogen is gasified in a fracturing conveying pipeline, so that adverse effects are brought to liquid nitrogen fracturing, and the technical cost is increased, so that development of a method for greatly reducing the gasification of liquid nitrogen in the conveying process is needed.
Disclosure of Invention
The invention aims to provide a liquid nitrogen pressurizing device which has the advantages of high pressure increasing speed and good heat preservation effect and greatly reduces the gasification phenomenon in the liquid nitrogen conveying process for fracturing.
In order to achieve the purpose, the liquid nitrogen pressurizing device comprises a liquid nitrogen container, an electric control device, a top cover and a liquid nitrogen tank for pressurizing liquid nitrogen, wherein the electric control device is connected with a display screen;
the notch of the liquid nitrogen tank faces upwards, the top cover is buckled on the liquid nitrogen tank, the inner wall of the left side of the liquid nitrogen tank is connected with an electromagnet, and a connecting line of the electromagnet passes through the tank wall of the liquid nitrogen tank in a sealing way and is connected with the electric control device;
a sliding plate made of soft magnetic materials is arranged in parallel with the electromagnet in the liquid nitrogen tank, and the top end of the sliding plate is in sliding sealing fit with the top cover; the top cover and the liquid nitrogen tank enclose a cavity, and the sliding plate divides the cavity into a liquid nitrogen cavity positioned on the right side of the sliding plate and a spring cavity positioned on the left side of the sliding plate;
a high-strength spring is connected between the sliding plate and the electromagnet; the high-strength spring is positioned in the spring cavity; the top cover at the right part of the liquid nitrogen tank is connected with the liquid nitrogen container through a nitrogen inlet pipeline, and an upper one-way valve and an upper manual valve are arranged on the nitrogen inlet pipeline; the opening direction of the upper one-way valve is from the liquid nitrogen container to the liquid nitrogen cavity;
the bottom wall of the liquid nitrogen tank right below the joint of the nitrogen inlet pipeline and the top cover is connected with a compound pipeline,
the composite pipeline comprises a nitrogen supply inner pipe, a liquid nitrogen heat preservation pipe sleeved outside the nitrogen supply inner pipe and a vacuum heat preservation pipe sleeved outside the liquid nitrogen heat preservation pipe; a connecting rib plate is arranged between the nitrogen supply inner pipe and the liquid nitrogen heat-preserving pipe, and a connecting rib plate is arranged between the liquid nitrogen heat-preserving pipe and the vacuum heat-preserving pipe; a liquid nitrogen heat preservation cavity is formed between the liquid nitrogen heat preservation pipe and the nitrogen supply inner pipe, and a vacuum heat preservation cavity is formed between the vacuum heat preservation pipe and the liquid nitrogen heat preservation pipe; both ends of the vacuum heat preservation cavity are sealed, and the liquid nitrogen heat preservation cavity and the nitrogen supply inner pipe are communicated with the liquid nitrogen cavity;
a solenoid valve for heat preservation is arranged at the liquid nitrogen heat preservation cavity, and a lower one-way valve is arranged at the position of the nitrogen supply inner pipe adjacent to the liquid nitrogen tank; the electromagnetic valve for heat preservation is connected with the electric control device;
the limiting position of the sliding plate sliding leftwards in the liquid nitrogen cavity is adjacent to the electromagnet, and the limiting position of the sliding plate sliding rightwards in the liquid nitrogen cavity is positioned at the left side of the joint of the nitrogen inlet pipeline and the top cover and adjacent to the joint of the nitrogen inlet pipeline and the top cover.
The buckling structure between the top cover and the liquid nitrogen tank is specifically as follows:
the top of the left side groove wall of the liquid nitrogen groove is horizontally bent to form a left buckle plate, and the top of the right side groove wall of the liquid nitrogen groove is horizontally bent to form a right buckle plate; the left side of the top cover is bent to form a left hook-shaped buckling part matched with the left buckling plate, and the right side of the top cover is bent to form a right hook-shaped buckling part matched with the right buckling plate; the left buckle plate stretches into the left hook-shaped buckle part, and the right buckle plate stretches into the right hook-shaped buckle part.
The top cover comprises a top cover heat insulation layer positioned on the outer layer and a sliding connection layer positioned on the inner layer, and the sliding connection layer is made of rigid materials; the cell wall of liquid nitrogen groove is including being located the outer cell body heat preservation and being located the rigid material layer of inlayer, and the top surface and the sliding connection layer sliding seal cooperation of sliding plate, the bottom surface and the rigid material layer sliding seal cooperation of sliding plate.
And a temperature sensor is arranged in the liquid nitrogen heat preservation cavity and is connected with an electric control device through a circuit.
Comprises a liquid nitrogen pressurizing device and a confining pressure system;
the nitrogen supply inner pipe in the composite pipeline is connected with a vacuum pipeline which is connected with a vacuum pump; the vacuumizing pipe is provided with a first valve; the liquid nitrogen heat preservation pipe in the composite pipeline is connected with a safety valve which is communicated with the liquid nitrogen heat preservation cavity; the vacuum pump is connected with the electric control device; a first pressure sensor is arranged on the vacuumizing pipe between the vacuum pump and the first valve;
the confining pressure system comprises a box body, the top of the box body is open, the top of the box body is connected with a horizontal plate, and the horizontal plate is connected with a gland for closing the box body through bolts; an elastic cylinder made of elastic materials is arranged in the box body and is used for storing coal samples, and an opening at the upper end of the elastic cylinder is connected with the gland; a shaft pressing cavity for applying upward pressure to the elastic cylinder is arranged on a bottom plate of the box body below the elastic cylinder, and the shaft pressing cavity is connected with an axial pressure applying pipeline; an annular cavity is formed between the elastic cylinder and the side wall of the box body, the side wall of the box body is connected with a radial pressure applying pipeline for applying radial pressure to the elastic cylinder, and the radial pressure applying pipeline is communicated with the annular cavity; the axial pressure applying pipeline and the radial pressure applying pipeline are communicated with a hydraulic pump station; the center of the gland is provided with a through hole which is penetrated up and down and is matched with the nitrogen supply inner pipe in a sealing way; the opening direction of the lower one-way valve is from the liquid nitrogen cavity to the elastic cylinder;
the axial pressure applying pipeline is provided with a first electromagnetic valve and a third pressure sensor, and the radial pressure applying pipeline is provided with a second electromagnetic valve and a second pressure sensor; the first pressure sensor, the first electromagnetic valve, the third pressure sensor, the second electromagnetic valve and the second pressure sensor are all connected with the electric control device.
The invention also discloses an experimental method using the anti-reflection experimental system, which comprises the following steps:
the first step is a system inspection step;
the second step is to put in the coal sample;
the third step is to apply preset circumferential pressure and axial pressure to the coal sample;
the fourth step is to vacuumize the nitrogen supply inner tube;
the fifth step is to inject liquid nitrogen into the liquid nitrogen heat preservation cavity;
and the sixth step is to inject high-pressure liquid nitrogen into the coal sample for fracture permeability increasing experiment.
The first step specifically comprises the steps of connecting all parts in the anti-reflection experiment system, starting an electric control device, controlling a vacuum pump, an electromagnet, a solenoid valve for heat preservation, a first solenoid valve and a second solenoid valve to act, and ensuring that all the parts are in a normal state;
the second step is to drill down an insertion hole on the upper surface of the coal sample, wherein the insertion hole is matched with the nitrogen supply inner pipe; opening the gland, putting the coal sample into the elastic cylinder, inserting the coal sample after passing through the through hole on the gland from top to bottom at the outlet end part of the nitrogen supply inner pipe, and arranging an outlet one-way valve at the outlet end part of the nitrogen supply inner pipe, wherein the conduction direction of the outlet one-way valve is that the nitrogen supply inner pipe leads to the coal sample;
then a gland is covered, and bolts are screwed to connect the gland with the box body and the horizontal plate thereof; the free ends of the liquid nitrogen heat preservation pipes and the vacuum heat preservation pipes are respectively and closely arranged and respectively connected with the upper surface of the gland;
the third step is that the first electromagnetic valve and the second electromagnetic valve are opened through the electric control device, the hydraulic pump station is controlled to inject hydraulic oil into the annular cavity between the elastic cylinder and the side wall of the box body through the radial pressure pipeline, and the hydraulic oil in the annular cavity tightly presses the elastic cylinder along the circumferential direction of the elastic cylinder so as to generate confining pressure on the coal sample;
simultaneously controlling the hydraulic pump station to inject hydraulic oil into the shaft pressure cavity through the axial pressure pipeline, and enabling the hydraulic oil in the shaft pressure cavity to upwards press the elastic cylinder so as to generate axial pressure; the electric control device displays the pressure values detected by the third pressure sensor and the second pressure sensor on a display screen; the confining pressure and the axial pressure are controlled to be a preset value by controlling the output pressure of the hydraulic pump station, and the fine adjustment of the confining pressure and the axial pressure is realized by controlling the opening degree of the first electromagnetic valve and the second electromagnetic valve;
the fourth step is to open the first valve on the vacuumizing pipe, open the electromagnetic valve for heat preservation, close the upper manual valve, then open the vacuum pump to vacuumize the system; under the action of negative pressure, the lower one-way valve is opened, and the liquid nitrogen heat preservation cavity, the liquid nitrogen cavity and the nitrogen supply inner pipe are communicated; the vacuum pump pumps out the gas in the nitrogen inlet pipeline below the manual valve above the liquid nitrogen heat preservation cavity, the liquid nitrogen cavity and the nitrogen supply inner pipe; observing a pressure signal detected by a first sensor through a display screen, and closing the vacuum pump and the first valve after the pressure detected by the first sensor is reduced to a preset value, so as to keep the electromagnetic valve for heat preservation in an open state;
the third step and the fourth step are not sequential;
the fifth step is to open an upper manual valve on the nitrogen inlet pipeline, and the liquid nitrogen in the liquid nitrogen container enters the liquid nitrogen cavity through the upper one-way valve and the nitrogen inlet pipeline under the action of negative pressure and then enters the liquid nitrogen heat preservation cavity through the heat preservation electromagnetic valve; in the process, under the action of negative pressure, the lower one-way valve is opened, and liquid nitrogen is filled in the nitrogen supply inner pipe between the outlet one-way valve and the liquid nitrogen cavity; after filling liquid nitrogen into the liquid nitrogen heat preservation cavity, closing the electromagnetic valve for heat preservation;
the sixth step is that the electromagnet is started through the electric control device, the electromagnet generates a magnetic field to adsorb the sliding plate, the sliding plate compresses the high-strength spring in the process of approaching the electromagnet, and the high-strength spring stores elastic potential energy; the sliding plate generates negative pressure in the liquid nitrogen cavity in the process of moving to the left limit position, and the negative pressure in the liquid nitrogen cavity can only be conducted into the liquid nitrogen container due to the existence of the lower one-way valve and the outlet one-way valve, so that liquid nitrogen in the liquid nitrogen container is sucked into the liquid nitrogen cavity;
the electric control device turns off the electromagnet, the magnetic attraction force between the sliding plate and the electromagnet disappears, the elastic potential energy accumulated by the high-strength spring is released instantaneously, the sliding plate is pushed to rapidly move to the right limit position, the volume of the liquid nitrogen cavity is reduced, liquid nitrogen is extruded, and the pressure of the liquid nitrogen is rapidly increased to become high-pressure liquid nitrogen; because the upper one-way valve exists, high-pressure liquid nitrogen cannot flow to the liquid nitrogen container, and finally enters the coal sample after passing through the lower one-way valve, the nitrogen supply inner pipe and the outlet one-way valve, and liquid nitrogen fracturing anti-reflection experiments are carried out on the coal sample.
The method also comprises a seventh step, namely a continuous fracturing step;
the seventh step is that when the coal sample is large, after the electromagnet is closed for 0.5 plus or minus 0.1 seconds, the electromagnet is started for 1-2 seconds, the sliding plate is attracted to the left limit position again, and the liquid nitrogen in the liquid nitrogen container is sucked into the liquid nitrogen cavity; then the electromagnet is closed for 1+/-0.3 seconds, and high-pressure liquid nitrogen is sent into the coal sample; and repeatedly operating the switch electromagnet in the step until a preset amount of liquid nitrogen is injected into the coal sample, then performing system pressure maintaining, and performing liquid nitrogen fracturing anti-reflection experiment on the coal sample.
In the process of the sixth step and the seventh step, the vacuum heat-preserving cavity plays a role in preserving heat of the first layer, and the cooling capacity of the nitrogen supply inner pipe and the liquid nitrogen heat-preserving cavity which are dissipated outwards is reduced; the liquid nitrogen heat preservation cavity plays a role in second-layer heat preservation, and the temperature of the outer wall of the nitrogen supply inner pipe is maintained below the boiling point of liquid nitrogen;
when the liquid nitrogen in the liquid nitrogen heat preservation cavity is heated and evaporated, and the pressure in the liquid nitrogen heat preservation cavity is higher than the opening pressure of the safety valve, the safety valve is opened, high-pressure nitrogen is released into the environment, the pressure in the liquid nitrogen heat preservation cavity is reduced, and the safety valve is automatically closed until the pressure in the liquid nitrogen heat preservation cavity is lower than the opening pressure of the safety valve.
The liquid nitrogen pressurizing device disclosed by the invention has a simple structure, can store elastic potential energy by using the high-strength spring, and can rapidly improve the pressure of liquid nitrogen by instantly releasing the elastic potential energy, wherein the pressurizing speed of the liquid nitrogen is more than 3 times that of a traditional liquid nitrogen pump, so that the time required for injecting the liquid nitrogen into a coal sample is reduced compared with the time required by injecting the liquid nitrogen into the coal sample, and the cooling capacity emitted by the liquid nitrogen for cracking in the process of injecting the liquid nitrogen into the coal sample is reduced. Especially, the liquid nitrogen cavity is large enough, and when the liquid nitrogen injected once is the liquid nitrogen amount for injecting the coal sample required by the experiment, the time for injecting the liquid nitrogen is shortened more obviously.
The vacuum heat preservation cavity plays a role in heat preservation of the first layer, and reduces the outwards-scattered cold energy of the nitrogen supply inner pipe and the liquid nitrogen heat preservation cavity; the liquid nitrogen heat preservation cavity plays a role in heat preservation of the second layer, and the temperature of the nitrogen supply inner pipe is maintained below the boiling point of liquid nitrogen. Before the evaporation of the liquid nitrogen in the liquid nitrogen heat preservation cavity is completed, the temperature of the outer wall of the nitrogen supply inner pipe is always below the boiling point of the liquid nitrogen, so that the evaporation phenomenon of the liquid nitrogen in the nitrogen supply pipeline is greatly reduced compared with the traditional heat preservation means.
Through circularly executing the seventh step, the invention can be suitable for larger coal samples, and even can be directly used for fracturing and permeability improvement of an actual coal bed. Of course, when manufacturing the liquid nitrogen pressurizing device of the invention, the size of the electromagnet and the liquid nitrogen cavity should be selected according to the planned experiment.
The liquid nitrogen cavity volume is the biggest when the sliding plate is located left extreme position, and the liquid nitrogen cavity volume is the minimum when the sliding plate is located right extreme position, and the difference of the biggest volume and the minimum volume in liquid nitrogen cavity is the volume of once carrying liquid nitrogen.
The stronger the magnetic force of the electromagnet is, the larger the volume of liquid nitrogen conveyed at one time is, and the larger the corresponding experimental coal sample is. According to the size of the experimental coal sample, a liquid nitrogen pressurizing device which can convey enough experimental liquid nitrogen by one-time action of an electromagnet can be manufactured.
The composite pipeline has simple structure, and has better heat preservation effect compared with the prior art by utilizing the double heat preservation effects of vacuum heat preservation and liquid nitrogen heat preservation. The concrete buckling structure between the top cover and the liquid nitrogen tank is convenient for manufacturing and buckling or separating the top cover and the liquid nitrogen tank in use.
The anti-reflection experiment system provided by the invention can simulate the pressure of a coal bed by using the liquid nitrogen pressurizing device, create experiment conditions, and monitor experiment parameters (such as confining pressure and axial pressure) in the experiment process.
The experimental method is carried out by utilizing the anti-reflection experimental system, the simulated confining pressure and the axial pressure are transmitted to the coal sample through the elastic cylinder, the third step and the fourth step can be carried out simultaneously without sequence, the step arrangement is simple and efficient, the experimental efficiency is improved, the gasification phenomenon in the liquid nitrogen conveying process for fracturing is greatly reduced, the adverse effect caused by liquid nitrogen evaporation in a nitrogen supply pipeline is greatly relieved by shortening the nitrogen injection time and adopting better heat preservation measures, the technical cost is reduced, and the stable and smooth liquid nitrogen fracturing anti-reflection experiment on the coal sample is ensured.
Drawings
FIG. 1 is a schematic diagram of a liquid nitrogen pressurizing device;
FIG. 2 is a cross-sectional view of a composite conduit;
FIG. 3 is a schematic diagram of the structure of an anti-reflection experiment system;
fig. 4 is an electrical schematic of the present invention.
Detailed Description
As shown in fig. 1 to 4, a liquid nitrogen pressurizing device 29 in the invention comprises a liquid nitrogen container 1, an electric control device 2, a top cover and a liquid nitrogen tank for pressurizing liquid nitrogen, wherein the electric control device 2 is connected with a display screen 3; the top cover comprises a top cover heat insulation layer 4 positioned on the outer layer and a sliding connection layer 5 positioned on the inner layer, wherein the sliding connection layer 5 is made of rigid materials; the groove wall of the liquid nitrogen groove comprises a groove body heat preservation layer 6 positioned on the outer layer and a rigid material layer 7 positioned on the inner layer,
the notch of the liquid nitrogen tank faces upwards, the top cover is buckled on the liquid nitrogen tank, the inner wall of the left side of the liquid nitrogen tank (namely the rigid material layer 7) is connected with an electromagnet 8, and a connecting line of the electromagnet 8 passes through the tank wall of the liquid nitrogen tank in a sealing way and is connected with the electric control device 2;
a sliding plate 9 made of soft magnetic materials is arranged in parallel with the electromagnet 8 in the liquid nitrogen tank, and the top end of the sliding plate 9 is in sliding sealing fit with the top cover; specifically, the top surface of the sliding plate 9 is in sliding sealing engagement with the sliding connection layer 5, and the bottom surface of the sliding plate 9 is in sliding sealing engagement with the rigid material layer 7. The top cover and the liquid nitrogen tank enclose a cavity, and the sliding plate 9 divides the cavity into a liquid nitrogen cavity 10 positioned on the right side of the sliding plate 9 and a spring cavity 11 positioned on the left side of the sliding plate 9;
a high-strength spring 12 is connected between the sliding plate 9 and the electromagnet 8; the high-strength spring 12 is positioned in the spring cavity 11; the top cover at the right part of the liquid nitrogen tank is connected with the liquid nitrogen container 1 through a nitrogen inlet pipeline 13, and an upper one-way valve 14 and an upper manual valve 15 are arranged on the nitrogen inlet pipeline 13; the opening direction of the upper one-way valve 14 is from the liquid nitrogen container 1 to the liquid nitrogen cavity 10; the upper manual valve 15 is used for preventing the vacuum pumping, and the negative pressure in the liquid nitrogen cavity 10 enables the upper one-way valve 14 to be automatically opened to suck out the liquid nitrogen in the liquid nitrogen container 1.
The bottom wall of the liquid nitrogen tank right below the joint of the nitrogen inlet pipeline 13 and the top cover is connected with a composite pipeline 30, and the composite pipeline 30 comprises a nitrogen supply inner pipe 16, a liquid nitrogen heat preservation pipe 17 sleeved outside the nitrogen supply inner pipe 16 and a vacuum heat preservation pipe 18 sleeved outside the liquid nitrogen heat preservation pipe 17; a connecting rib plate 19 is arranged between the nitrogen supply inner pipe 16 and the liquid nitrogen heat preservation pipe 17, and a connecting rib plate 19 is arranged between the liquid nitrogen heat preservation pipe 17 and the vacuum heat preservation pipe 18; a liquid nitrogen heat preservation cavity 20 is formed between the liquid nitrogen heat preservation pipe 17 and the nitrogen supply inner pipe 16, and a vacuum heat preservation cavity 21 is formed between the vacuum heat preservation pipe 18 and the liquid nitrogen heat preservation pipe 17; both ends of the vacuum heat preservation cavity 21 are closed, and the liquid nitrogen heat preservation cavity 20 and the nitrogen supply inner pipe 16 are communicated with the liquid nitrogen cavity 10; the vacuum (negative pressure) in the vacuum heat-preserving chamber 21 is pre-pumped when the composite pipeline 30 is manufactured, and the vacuum heat-preserving chamber 21 is not required to be additionally pumped when the experimental method of the invention is carried out.
A solenoid valve 22 for heat preservation is arranged at the liquid nitrogen heat preservation cavity 20, and a lower one-way valve 23 is arranged at the position of the nitrogen supply inner pipe 16 adjacent to the liquid nitrogen tank; the electromagnetic valve 22 for heat preservation is connected with the electric control device 2;
the limiting position of the sliding plate 9 sliding leftwards in the liquid nitrogen cavity 10 is adjacent to the electromagnet 8, and the limiting position of the sliding plate 9 sliding rightwards in the liquid nitrogen cavity 10 is positioned at the left side of the joint of the nitrogen inlet pipeline 13 and the top cover and adjacent to the joint of the nitrogen inlet pipeline 13 and the top cover. Therefore, the sliding plate 9 is ensured not to cross the joint of the nitrogen inlet pipeline 13 and the top cover when moving left and right, and meanwhile, the joint of the composite pipeline 30 positioned right below the joint and the bottom wall of the liquid nitrogen tank is not crossed, so that the liquid nitrogen is prevented from entering the spring cavity 11, the pressurizing effect is reduced, and the liquid nitrogen is prevented from being wasted.
The electric control device 2 is an X86 computer, a singlechip or an integrated circuit. The high-strength springs 12 are equally arranged in three groups between the sliding plate 9 and the electromagnet 8.
The buckling structure between the top cover and the liquid nitrogen tank is specifically as follows:
the left buckling plate 24 is formed after the top of the left side tank wall of the liquid nitrogen tank is horizontally bent, and the right buckling plate 25 is formed after the top of the right side tank wall of the liquid nitrogen tank is horizontally bent; the left side of the top cover is bent to form a left hook-shaped buckling part 26 matched with the left buckling plate 24, and the right side of the top cover is bent to form a right hook-shaped buckling part 27 matched with the right buckling plate 25; the left latch plate 24 extends into the left hook latch portion 26, and the right latch plate 25 extends into the right hook latch portion 27.
The arrangement of the top cover heat preservation layer 4 and the tank body heat preservation layer 6 avoids excessive outward loss of cold energy in the liquid nitrogen tank in the experimental process.
A temperature sensor 28 is arranged in the liquid nitrogen heat preservation cavity 20, and the temperature sensor 28 is connected with the electric control device 2 through a circuit.
The invention also discloses an anti-reflection experiment system using the liquid nitrogen pressurizing device 29, which comprises the liquid nitrogen pressurizing device 29 and a confining pressure system;
the nitrogen supply inner pipe 16 in the composite pipeline 30 is connected with a vacuumizing pipeline 31, and the vacuumizing pipeline 31 is connected with a vacuum pump 32; the vacuumizing pipeline 31 is provided with a first valve 33; the liquid nitrogen heat preservation pipe 17 in the composite pipeline 30 is connected with a safety valve 34, and the safety valve 34 is communicated with the liquid nitrogen heat preservation cavity 20; the vacuum pump 32 is connected with the electric control device 2; a first pressure sensor 35 is arranged on the vacuumizing pipeline 31 between the vacuum pump 32 and the first valve 33;
the confining pressure system comprises a box body 36, wherein the top of the box body 36 is open, the top of the box body 36 is connected with a horizontal plate 37, and the horizontal plate 37 is connected with a gland 39 for closing the box body 36 through a bolt 38; an elastic cylinder 40 made of elastic material is arranged in the box body 36, the elastic cylinder 40 is used for storing coal samples, and the upper end opening of the elastic cylinder 40 is connected with a gland 39; an axial pressure cavity 41 for applying upward pressure to the elastic cylinder 40 is arranged on the bottom plate of the box body 36 below the elastic cylinder 40, and the axial pressure cavity 41 is connected with an axial pressure pipeline 42; an annular cavity 43 is defined between the elastic cylinder 40 and the side wall of the box body 36, a radial pressure applying pipeline 44 for applying radial pressure to the elastic cylinder 40 is connected to the side wall of the box body 36, and the radial pressure applying pipeline 44 is communicated with the annular cavity 43; the axial pressure applying pipeline 42 and the radial pressure applying pipeline 44 are communicated with a hydraulic pump station 45; the center of the gland 39 is provided with a through hole which is penetrated up and down and is matched with the nitrogen supply inner pipe 16 in a sealing way; the opening direction of the lower one-way valve 23 is from the liquid nitrogen cavity 10 to the elastic cylinder 40;
the axial pressure-applying pipeline 42 is provided with a first electromagnetic valve 46 and a third pressure sensor 47, and the radial pressure-applying pipeline 44 is provided with a second electromagnetic valve 48 and a second pressure sensor 49; the first pressure sensor 35, the first solenoid valve 46, the third pressure sensor 47, the second solenoid valve 48 and the second pressure sensor 49 are all connected to the electronic control device 2.
The invention also discloses an experimental method using the anti-reflection experimental system, which comprises the following steps:
the first step is a system inspection step;
the second step is to put in the coal sample;
the third step is to apply preset circumferential pressure and axial pressure to the coal sample;
the fourth step is to vacuumize the nitrogen supply inner tube 16;
the fifth step is to inject liquid nitrogen into the liquid nitrogen heat preservation chamber 20;
and the sixth step is to inject high-pressure liquid nitrogen into the coal sample for fracture permeability increasing experiment.
The first step is to connect all parts in the anti-reflection experiment system, start the electric control device 2, control the vacuum pump 32, electromagnet 8, heat preservation electromagnetic valve 22, first electromagnetic valve 46 and second electromagnetic valve 48 to act, ensure all parts are in normal state;
the second step is to drill down an insertion hole on the upper surface of the coal sample, wherein the insertion hole is matched with the nitrogen supply inner pipe 16; opening the gland 39, putting the coal sample into the elastic cylinder 40, inserting the coal sample after passing through the through hole on the gland 39 from top to bottom at the outlet end of the nitrogen supply inner tube 16, and arranging an outlet one-way valve 50 at the outlet end of the nitrogen supply inner tube 16, wherein the conduction direction of the outlet one-way valve 50 is that the nitrogen supply inner tube 16 leads to the coal sample;
then the gland 39 is covered, and the bolt 38 is screwed to connect the gland 39 with the box 36 and the horizontal plate 37 thereof; the free end of the liquid nitrogen heat preservation pipe 17 and the free end of the vacuum heat preservation pipe 18 are all arranged in a closed way and are respectively connected with the upper surface of the gland 39;
the third step is to open the first electromagnetic valve 46 and the second electromagnetic valve 48 through the electric control device 2, control the hydraulic pump station 45 to inject hydraulic oil into the annular cavity 43 between the elastic cylinder 40 and the side wall of the box body 36 through the radial pressure pipeline 44, and the hydraulic oil in the annular cavity 43 tightly presses the elastic cylinder 40 along the circumferential direction of the elastic cylinder 40 so as to generate confining pressure on the coal sample;
simultaneously, the hydraulic pump station 45 is controlled to inject hydraulic oil into the shaft pressure cavity 41 through the axial pressure pipeline 42, and the hydraulic oil in the shaft pressure cavity 41 is pressed upwards to the elastic cylinder 40 so as to generate axial pressure; the electronic control device 2 displays the pressure values detected by the third pressure sensor 47 and the second pressure sensor 49 on the display screen 3; the confining pressure and the axial pressure are controlled to be preset values by controlling the output pressure of the control hydraulic pump station 45, and fine adjustment of the confining pressure and the axial pressure is realized by controlling the opening degree of the first electromagnetic valve 46 and the second electromagnetic valve 48;
the fourth step is to open a first valve 33 on the vacuumizing pipeline 31, open the electromagnetic valve 22 for heat preservation through the electric control device 2, close the upper manual valve 15, and then open the vacuum pump 32 through the electric control device 2 to vacuumize the system; under the action of negative pressure, the lower one-way valve 23 is opened, and the liquid nitrogen heat preservation cavity 20, the liquid nitrogen cavity 10 and the nitrogen supply inner pipe 16 are communicated; because the upper manual valve 15 is closed, the negative pressure can not suck out the liquid nitrogen in the liquid nitrogen container 1 through the nitrogen inlet pipeline 13; the vacuum pump 32 pumps out the gas in the nitrogen inlet pipeline 13 below the manual valve 15 above the nitrogen supply inner pipe 16, the liquid nitrogen heat preservation cavity 20 and the liquid nitrogen cavity 10; observing the pressure signal detected by the first sensor through the display screen 3, and closing the vacuum pump 32 and the first valve 33 after the pressure detected by the first sensor is reduced to a preset value, so as to keep the electromagnetic valve 22 for heat preservation in an open state;
the third step and the fourth step are not sequential;
the fifth step is to open an upper manual valve 15 on a nitrogen inlet pipeline 13, and the liquid nitrogen in the liquid nitrogen container 1 enters a liquid nitrogen cavity 10 through an upper one-way valve 14 and the nitrogen inlet pipeline 13 under the action of negative pressure, and then enters a liquid nitrogen heat preservation cavity 20 through a heat preservation electromagnetic valve 22; in the process, the lower one-way valve 23 is opened under the action of negative pressure, and liquid nitrogen is filled in the nitrogen supply inner pipe 16 between the outlet one-way valve 50 and the liquid nitrogen cavity 10; after the liquid nitrogen is filled into the liquid nitrogen heat preservation cavity 20 (the work of filling the liquid nitrogen into the liquid nitrogen heat preservation cavity 20 is completed after the upper manual valve 15 is opened for 1 minute), the electromagnetic valve 22 for heat preservation is closed, so that the safety valve 34 is opened and the liquid nitrogen is lost due to the fact that the pressure of the liquid nitrogen in the liquid nitrogen heat preservation cavity 20 is too high in the sixth step is prevented;
the sixth step is that the electromagnet 8 is started by the electric control device 2 (even if the electromagnet 8 is electrified), the electromagnet 8 generates a magnetic field to adsorb the sliding plate 9, the sliding plate 9 compresses the high-strength spring 12 in the process of approaching the electromagnet 8, and the high-strength spring 12 stores elastic potential energy; the sliding plate 9 generates negative pressure in the liquid nitrogen cavity 10 in the process of moving to the left limit position, and the negative pressure in the liquid nitrogen cavity 10 can only be conducted into the liquid nitrogen container 1 due to the existence of the lower one-way valve 23 and the outlet one-way valve 50, so that liquid nitrogen in the liquid nitrogen container 1 is sucked into the liquid nitrogen cavity 10;
the electric control device 2 turns off the electromagnet 8 (even if the electromagnet 8 is powered off), the magnetic attraction force between the sliding plate 9 and the electromagnet 8 disappears, the elastic potential energy accumulated by the high-strength spring 12 is released instantaneously, the sliding plate 9 is pushed to rapidly move to the right limit position, the volume of the liquid nitrogen cavity 10 is reduced, liquid nitrogen is extruded, and the pressure of the liquid nitrogen is rapidly increased to become high-pressure liquid nitrogen; the specific pressure of the high-pressure liquid nitrogen can be controlled by selecting the magnetic force of the electromagnet and the elastic force of the high-strength spring.
Because the upper one-way valve 14 exists, high-pressure liquid nitrogen cannot flow to the liquid nitrogen container 1, and finally enters the coal sample after passing through the lower one-way valve 23, the nitrogen supply inner pipe 16 and the outlet one-way valve 50, and liquid nitrogen fracturing anti-reflection experiments are carried out on the coal sample.
The method also comprises a seventh step, namely a continuous fracturing step;
the seventh step is that when the coal sample is large, after the electromagnet is closed for 0.5 plus or minus 0.1 seconds, the electromagnet is started for 1-2 seconds (including two end values), the sliding plate 9 is attracted to the left limit position again, and the liquid nitrogen in the liquid nitrogen container 1 is sucked into the liquid nitrogen cavity 10; then the electromagnet is closed for 1+/-0.3 seconds, and high-pressure liquid nitrogen is sent into the coal sample; the operation of the switch electromagnet 8 in the step is repeatedly carried out until a preset amount of liquid nitrogen is injected into the coal sample, then the system pressure maintaining is carried out, and the liquid nitrogen fracturing anti-reflection experiment is carried out on the coal sample.
In the sixth step and the seventh step, the vacuum heat-preserving chamber 21 plays a role of heat preservation of the first layer, and reduces the cold energy dissipated outwards by the nitrogen supply inner tube 16 and the liquid nitrogen heat-preserving chamber 20; the liquid nitrogen heat preservation cavity 20 plays a role in second-layer heat preservation, and maintains the temperature of the outer wall of the nitrogen supply inner pipe 16 below the boiling point of liquid nitrogen;
when the liquid nitrogen in the liquid nitrogen heat preservation cavity 20 is heated and evaporated, and the pressure in the liquid nitrogen heat preservation cavity 20 is higher than the opening pressure of the safety valve 34, the safety valve 34 is opened, high-pressure nitrogen is released into the environment, the pressure in the liquid nitrogen heat preservation cavity 20 is reduced, and the safety valve 34 is automatically closed until the pressure in the liquid nitrogen heat preservation cavity 20 is lower than the opening pressure of the safety valve 34.
The safety valve 34 avoids potential safety hazards caused by heated evaporation and overhigh pressure of nitrogen.
During the experimental process, the electronic control device 2 displays the detection data of the temperature sensor 28, the first to third pressure sensors 35, 49 and 47 on the display screen 3 for the experimenter to monitor the experimental process.
The above embodiments are only for illustrating the technical solution of the present invention, and it should be understood by those skilled in the art that although the present invention has been described in detail with reference to the above embodiments: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention, which is intended to be encompassed by the claims.
Claims (4)
1. The experimental method is carried out by using an anti-reflection experimental system, wherein the anti-reflection experimental system comprises a liquid nitrogen pressurizing device and a confining pressure system; the method is characterized in that:
the liquid nitrogen pressurizing device comprises a liquid nitrogen container, an electric control device, a top cover and a liquid nitrogen tank for pressurizing liquid nitrogen, and the electric control device is connected with a display screen;
the notch of the liquid nitrogen tank faces upwards, the top cover is buckled on the liquid nitrogen tank, the inner wall of the left side of the liquid nitrogen tank is connected with an electromagnet, and a connecting line of the electromagnet passes through the tank wall of the liquid nitrogen tank in a sealing way and is connected with the electric control device;
a sliding plate made of soft magnetic materials is arranged in parallel with the electromagnet in the liquid nitrogen tank, and the top end of the sliding plate is in sliding sealing fit with the top cover; the top cover and the liquid nitrogen tank enclose a cavity, and the sliding plate divides the cavity into a liquid nitrogen cavity positioned on the right side of the sliding plate and a spring cavity positioned on the left side of the sliding plate;
a high-strength spring is connected between the sliding plate and the electromagnet; the high-strength spring is positioned in the spring cavity; the top cover at the right part of the liquid nitrogen tank is connected with the liquid nitrogen container through a nitrogen inlet pipeline, and an upper one-way valve and an upper manual valve are arranged on the nitrogen inlet pipeline; the opening direction of the upper one-way valve is from the liquid nitrogen container to the liquid nitrogen cavity;
the bottom wall of the liquid nitrogen tank right below the joint of the nitrogen inlet pipeline and the top cover is connected with a compound pipeline,
the composite pipeline comprises a nitrogen supply inner pipe, a liquid nitrogen heat preservation pipe sleeved outside the nitrogen supply inner pipe and a vacuum heat preservation pipe sleeved outside the liquid nitrogen heat preservation pipe; a connecting rib plate is arranged between the nitrogen supply inner pipe and the liquid nitrogen heat-preserving pipe, and a connecting rib plate is arranged between the liquid nitrogen heat-preserving pipe and the vacuum heat-preserving pipe; a liquid nitrogen heat preservation cavity is formed between the liquid nitrogen heat preservation pipe and the nitrogen supply inner pipe, and a vacuum heat preservation cavity is formed between the vacuum heat preservation pipe and the liquid nitrogen heat preservation pipe; both ends of the vacuum heat preservation cavity are sealed, and the liquid nitrogen heat preservation cavity and the nitrogen supply inner pipe are communicated with the liquid nitrogen cavity;
a solenoid valve for heat preservation is arranged at the liquid nitrogen heat preservation cavity, and a lower one-way valve is arranged at the position of the nitrogen supply inner pipe adjacent to the liquid nitrogen tank; the electromagnetic valve for heat preservation is connected with the electric control device;
the limiting position of the sliding plate sliding leftwards in the liquid nitrogen cavity is adjacent to the electromagnet, and the limiting position of the sliding plate sliding rightwards in the liquid nitrogen cavity is positioned at the left side of the joint of the nitrogen inlet pipeline and the top cover and adjacent to the joint of the nitrogen inlet pipeline and the top cover;
the buckling structure between the top cover and the liquid nitrogen tank is specifically as follows:
the top of the left side groove wall of the liquid nitrogen groove is horizontally bent to form a left buckle plate, and the top of the right side groove wall of the liquid nitrogen groove is horizontally bent to form a right buckle plate; the left side of the top cover is bent to form a left hook-shaped buckling part matched with the left buckling plate, and the right side of the top cover is bent to form a right hook-shaped buckling part matched with the right buckling plate; the left buckle plate stretches into the left hook-shaped buckle part, and the right buckle plate stretches into the right hook-shaped buckle part;
the top cover comprises a top cover heat insulation layer positioned on the outer layer and a sliding connection layer positioned on the inner layer, and the sliding connection layer is made of rigid materials; the groove wall of the liquid nitrogen groove comprises a groove body heat-insulating layer positioned on the outer layer and a rigid material layer positioned on the inner layer, the top surface of the sliding plate is in sliding sealing fit with the sliding connection layer, and the bottom surface of the sliding plate is in sliding sealing fit with the rigid material layer;
a temperature sensor is arranged in the liquid nitrogen heat preservation cavity and is connected with an electric control device through a circuit;
the nitrogen supply inner pipe in the composite pipeline is connected with a vacuum pipeline which is connected with a vacuum pump; the vacuumizing pipe is provided with a first valve; the liquid nitrogen heat preservation pipe in the composite pipeline is connected with a safety valve which is communicated with the liquid nitrogen heat preservation cavity; the vacuum pump is connected with the electric control device; a first pressure sensor is arranged on the vacuumizing pipe between the vacuum pump and the first valve;
the confining pressure system comprises a box body, the top of the box body is open, the top of the box body is connected with a horizontal plate, and the horizontal plate is connected with a gland for closing the box body through bolts; an elastic cylinder made of elastic materials is arranged in the box body and is used for storing coal samples, and an opening at the upper end of the elastic cylinder is connected with the gland; a shaft pressing cavity for applying upward pressure to the elastic cylinder is arranged on a bottom plate of the box body below the elastic cylinder, and the shaft pressing cavity is connected with an axial pressure applying pipeline; an annular cavity is formed between the elastic cylinder and the side wall of the box body, the side wall of the box body is connected with a radial pressure applying pipeline for applying radial pressure to the elastic cylinder, and the radial pressure applying pipeline is communicated with the annular cavity; the axial pressure applying pipeline and the radial pressure applying pipeline are communicated with a hydraulic pump station; the center of the gland is provided with a through hole which is penetrated up and down and is matched with the nitrogen supply inner pipe in a sealing way; the opening direction of the lower one-way valve is from the liquid nitrogen cavity to the elastic cylinder;
the axial pressure applying pipeline is provided with a first electromagnetic valve and a third pressure sensor, and the radial pressure applying pipeline is provided with a second electromagnetic valve and a second pressure sensor; the first pressure sensor, the first electromagnetic valve, the third pressure sensor, the second electromagnetic valve and the second pressure sensor are all connected with the electric control device;
the method comprises the following steps:
the first step is a system inspection step;
the second step is to put in the coal sample;
the third step is to apply preset circumferential pressure and axial pressure to the coal sample;
the fourth step is to vacuumize the nitrogen supply inner tube;
the fifth step is to inject liquid nitrogen into the liquid nitrogen heat preservation cavity;
and the sixth step is to inject high-pressure liquid nitrogen into the coal sample for fracture permeability increasing experiment.
2. The method of claim 1, wherein:
the first step specifically comprises the steps of connecting all parts in the anti-reflection experiment system, starting an electric control device, controlling a vacuum pump, an electromagnet, a solenoid valve for heat preservation, a first solenoid valve and a second solenoid valve to act, and ensuring that all the parts are in a normal state;
the second step is to drill down an insertion hole on the upper surface of the coal sample, wherein the insertion hole is matched with the nitrogen supply inner pipe; opening the gland, putting the coal sample into the elastic cylinder, inserting the coal sample after passing through the through hole on the gland from top to bottom at the outlet end part of the nitrogen supply inner pipe, and arranging an outlet one-way valve at the outlet end part of the nitrogen supply inner pipe, wherein the conduction direction of the outlet one-way valve is that the nitrogen supply inner pipe leads to the coal sample;
then a gland is covered, and bolts are screwed to connect the gland with the box body and the horizontal plate thereof; the free ends of the liquid nitrogen heat preservation pipes and the vacuum heat preservation pipes are respectively and closely arranged and respectively connected with the upper surface of the gland;
the third step is that the first electromagnetic valve and the second electromagnetic valve are opened through the electric control device, the hydraulic pump station is controlled to inject hydraulic oil into the annular cavity between the elastic cylinder and the side wall of the box body through the radial pressure pipeline, and the hydraulic oil in the annular cavity tightly presses the elastic cylinder along the circumferential direction of the elastic cylinder so as to generate confining pressure on the coal sample;
simultaneously controlling the hydraulic pump station to inject hydraulic oil into the shaft pressure cavity through the axial pressure pipeline, and enabling the hydraulic oil in the shaft pressure cavity to upwards press the elastic cylinder so as to generate axial pressure; the electric control device displays the pressure values detected by the third pressure sensor and the second pressure sensor on a display screen; the confining pressure and the axial pressure are controlled to be preset values by controlling the output pressure of the hydraulic pump station, and fine adjustment of the confining pressure and the axial pressure is realized by controlling the opening degrees of the first electromagnetic valve and the second electromagnetic valve;
the fourth step is to open the first valve on the vacuumizing pipe, open the electromagnetic valve for heat preservation, close the upper manual valve, then open the vacuum pump to vacuumize the system; under the action of negative pressure, the lower one-way valve is opened, and the liquid nitrogen heat preservation cavity, the liquid nitrogen cavity and the nitrogen supply inner pipe are communicated; the vacuum pump pumps out the gas in the nitrogen inlet pipeline below the manual valve above the liquid nitrogen heat preservation cavity, the liquid nitrogen cavity and the nitrogen supply inner pipe; observing a pressure signal detected by a first sensor through a display screen, and closing the vacuum pump and the first valve after the pressure detected by the first sensor is reduced to a preset value, so as to keep the electromagnetic valve for heat preservation in an open state;
the third step and the fourth step are not sequential;
the fifth step is to open an upper manual valve on the nitrogen inlet pipeline, and the liquid nitrogen in the liquid nitrogen container enters the liquid nitrogen cavity through the upper one-way valve and the nitrogen inlet pipeline under the action of negative pressure and then enters the liquid nitrogen heat preservation cavity through the heat preservation electromagnetic valve; in the process, under the action of negative pressure, the lower one-way valve is opened, and liquid nitrogen is filled in the nitrogen supply inner pipe between the outlet one-way valve and the liquid nitrogen cavity; after filling liquid nitrogen into the liquid nitrogen heat preservation cavity, closing the electromagnetic valve for heat preservation;
the sixth step is that the electromagnet is started through the electric control device, the electromagnet generates a magnetic field to adsorb the sliding plate, the sliding plate compresses the high-strength spring in the process of approaching the electromagnet, and the high-strength spring stores elastic potential energy; the sliding plate generates negative pressure in the liquid nitrogen cavity in the process of moving to the left limit position, and the negative pressure in the liquid nitrogen cavity can only be conducted into the liquid nitrogen container due to the existence of the lower one-way valve and the outlet one-way valve, so that liquid nitrogen in the liquid nitrogen container is sucked into the liquid nitrogen cavity;
the electric control device turns off the electromagnet, the magnetic attraction force between the sliding plate and the electromagnet disappears, the elastic potential energy accumulated by the high-strength spring is released instantaneously, the sliding plate is pushed to rapidly move to the right limit position, the volume of the liquid nitrogen cavity is reduced, liquid nitrogen is extruded, and the pressure of the liquid nitrogen is rapidly increased to become high-pressure liquid nitrogen; because the upper one-way valve exists, high-pressure liquid nitrogen cannot flow to the liquid nitrogen container, and finally enters the coal sample after passing through the lower one-way valve, the nitrogen supply inner pipe and the outlet one-way valve, and liquid nitrogen fracturing anti-reflection experiments are carried out on the coal sample.
3. The method of claim 2, wherein: the method also comprises a seventh step, namely a continuous fracturing step;
the seventh step is that when the coal sample is large, after the electromagnet is closed for 0.5 plus or minus 0.1 seconds, the electromagnet is started for 1-2 seconds, the sliding plate is attracted to the left limit position again, and the liquid nitrogen in the liquid nitrogen container is sucked into the liquid nitrogen cavity; then the electromagnet is closed for 1+/-0.3 seconds, and high-pressure liquid nitrogen is sent into the coal sample; and repeatedly operating the switch electromagnet in the step until a preset amount of liquid nitrogen is injected into the coal sample, then performing system pressure maintaining, and performing liquid nitrogen fracturing anti-reflection experiment on the coal sample.
4. The method of claim 1, wherein: in the process of the sixth step and the seventh step, the vacuum heat-preserving cavity plays a role in preserving heat of the first layer, and the cooling capacity of the nitrogen supply inner pipe and the liquid nitrogen heat-preserving cavity which are dissipated outwards is reduced; the liquid nitrogen heat preservation cavity plays a role in second-layer heat preservation, and the temperature of the outer wall of the nitrogen supply inner pipe is maintained below the boiling point of liquid nitrogen;
when the liquid nitrogen in the liquid nitrogen heat preservation cavity is heated and evaporated, and the pressure in the liquid nitrogen heat preservation cavity is higher than the opening pressure of the safety valve, the safety valve is opened, high-pressure nitrogen is released into the environment, the pressure in the liquid nitrogen heat preservation cavity is reduced, and the safety valve is automatically closed until the pressure in the liquid nitrogen heat preservation cavity is lower than the opening pressure of the safety valve.
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| CN110823757A (en) * | 2019-11-28 | 2020-02-21 | 辽宁工程技术大学 | Low-permeability coal bed gas microwave-liquid nitrogen circulating freeze-thaw degradation-promotion permeability-increasing experimental device and method |
| CN114856678B (en) * | 2022-05-16 | 2022-11-22 | 中国矿业大学(北京) | Distributed type dragging pipe continuous nitrogen injection fire prevention and extinguishing method and system for goaf under coal mining condition |
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