Multi-stage expansion machine differential pressure power generation system

Abstract

The embodiment of the invention provides a multi-stage expansion machine differential pressure power generation system which comprises N stages of expansion units and a power generation unit. Each stage of expansion unit comprises a free plunger expansion machine, a pressure relay and a three-position three-way electromagnetic valve, and the expansion units are used for outputting mechanical energy to the generator set in the process of performing expansion and pressure reduction on high-pressure gas; the gas inlet end of the first-stage free plunger expansion machine is connected with a high-pressure gas input end, the gas outlet end of the ith-stage free plunger expansion machine is connected with the ith pressure relay and the gas inlet end of the ith three-position three-way electromagnetic valve, and the gas inlet end of the (i + 1) th-stage free plunger expansion machine is connected with the first working end of the ith three-position three-way electromagnetic valve; second working ends of the N three-position three-way electromagnetic valves are connected with a low-pressure gas output end; the pressure relay is used for monitoring the gas pressure of the gas outlet end of each stage of free plunger expansion machine; the generator set is connected with the energy output end of each stage of free plunger expansion machine and used for converting mechanical energy output by the expansion set into electric energy.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure difference power generation, and in particular to a multi-stage expander pressure difference power generation system. Background Art

[0002] In the process of natural gas extraction, processing and transportation, there are many pressure reduction links. The pressure of natural gas extracted from the wellhead is 10-20Mpa, the pressure of natural gas input into the pipeline during pipeline transportation is 10Mpa, and the pressure of natural gas delivered to the city gate station is about 4-6Mpa. Then the city gate station reduces the pressure to below 0.8Mpa and delivers it to the natural gas terminal users. A large amount of pressure energy loss is generated in these processes. In the natural gas industry, expanders are usually used to recover the pressure energy lost in the pressure regulation process of high-pressure natural gas. However, since the pressure drop generated in each link is different and the operating conditions of each expander are different. In order to efficiently recover the pressure energy, it is necessary to match expanders of different forms and sizes according to different pressure regulation conditions, and even the expander needs to be redesigned under specific conditions to fully recover the pressure energy lost in the natural gas pressure regulation. This not only leads to an increase in the cost of pressure energy recovery, but also increases the complexity of the selection of expanders in the pressure energy recovery process. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0004] To this end, an embodiment of the present invention proposes a multi-stage expander pressure difference power generation system, which adopts a combination of a multi-stage free piston expander and a pressure relay, so that the hydraulic energy output by each stage of the expansion unit is connected in parallel and enters the same pipeline to flow to the hydraulic motor, avoiding the installation of a generator at each stage, saving costs, and the gas pressure can be fully utilized, thereby increasing the pressure energy recovery efficiency.

[0005] To achieve the above-mentioned purpose, an embodiment of the present invention proposes a multi-stage expander pressure difference power generation system, comprising: N-stage expander groups and generator groups; wherein each stage of the expander groups comprises a free plunger expander, a pressure relay and a three-position three-way solenoid valve, and the expander group is used to output mechanical energy to the generator group during the process of expanding and reducing the pressure of high-pressure gas; wherein the air inlet end of the first-stage free plunger expander is connected to the high-pressure gas input end, the air outlet end of the i-th stage free plunger expander is connected to the i-th pressure relay and the air inlet end of the i-th three-position three-way solenoid valve, the air inlet end of the (i+1)-th stage free plunger expander is connected to the first working end of the i-th three-position three-way solenoid valve, and the second working ends of the N three-position three-way solenoid valves are all connected to the low-pressure gas output end; the N pressure relays are used to monitor the gas pressure at the air outlet end of each stage of the free plunger expander; wherein, if the i-th pressure relay detects that the i-th stage If the gas pressure at the outlet end of the free-piston expander is higher than the corresponding preset pressure threshold, the first working end of the i-th three-position three-way solenoid valve is controlled to be connected to the air inlet end of the i-th free-piston expander, so that the gas discharged from the outlet end of the i-th free-piston expander enters the (i+1)-th free-piston expander; if the i-th pressure relay detects that the gas pressure at the outlet end of the i-th free-piston expander is not higher than the corresponding preset pressure threshold, the second working end of the i-th three-position three-way solenoid valve is controlled to be connected to the outlet end of the i-th free-piston expander, so that the gas expanded and depressurized by the i-th free-piston expander is discharged through the low-pressure gas output end; a generator set, the generator set is connected to the energy output end of each stage of the free-piston expander, and is used to convert the mechanical energy output by the expander set into electrical energy; wherein N is a positive integer greater than or equal to 2, i is a positive integer greater than or equal to 1, and N>i.

[0006] The multi-stage expander pressure difference power generation system of the embodiment of the present invention comprises: comprising: N-stage expansion machine groups and generator groups; wherein each stage of the expansion machine groups comprises a free plunger expander, a pressure relay and a three-position three-way solenoid valve, and the expansion machine groups are used to output mechanical energy to the generator group during the process of expanding and reducing the pressure of high-pressure gas; wherein the air inlet end of the first-stage free plunger expander is connected to the high-pressure gas input end, the air outlet end of the i-th stage free plunger expander is connected to the i-th pressure relay and the air inlet end of the i-th three-position three-way solenoid valve, the air inlet end of the (i+1)-th stage free plunger expander is connected to the first working end of the i-th three-position three-way solenoid valve, and the second working ends of the N three-position three-way solenoid valves are all connected to the low-pressure gas output end; the N pressure relays are used to monitor the gas pressure at the air outlet end of each stage of the free plunger expander; wherein, if the i-th pressure If the relay detects that the gas pressure at the outlet end of the i-th free-plunger expander is higher than the corresponding preset pressure threshold, the first working end of the i-th three-position three-way solenoid valve is controlled to be connected to the air inlet end of the i-th free-plunger expander, so that the gas discharged from the outlet end of the i-th free-plunger expander enters the (i+1)-th free-plunger expander; if the i-th pressure relay detects that the gas pressure at the outlet end of the i-th free-plunger expander is not higher than the corresponding preset pressure threshold, the second working end of the i-th three-position three-way solenoid valve is controlled to be connected to the outlet end of the i-th free-plunger expander, so that the gas expanded and depressurized by the i-th free-plunger expander is discharged through the low-pressure gas output end; a generator set is connected to the energy output end of each level of free-plunger expanders, and is used to convert the mechanical energy output by the expansion unit into electrical energy. Therefore, the system adopts a combination of a multi-stage free piston expander and a pressure relay, so that the hydraulic energy output by each stage is connected in parallel and enters the same pipeline to flow to the hydraulic motor, avoiding the installation of a generator at each stage, saving costs, fully utilizing the gas pressure, and increasing the pressure energy recovery efficiency.

[0007] In addition, the multi-stage expander pressure difference power generation system proposed in the embodiment of the present invention may also have the following additional technical features:

[0008] According to one embodiment of the present invention, each stage of the expansion unit further includes:

[0009] N first units, the i-th first unit correspondingly controls the free plunger in the i-th free plunger expander, so that the free plunger of the i-th free plunger expander performs a return motion according to a predetermined stroke during operation;

[0010] There are N second units, and the i-th second unit corresponds to controlling the oil flow direction in the energy recovery chamber of the i-th free piston expander, so that the oil in the i-th free piston expander flows in a predetermined direction during the energy recovery process.

[0011] According to one embodiment of the present invention, the i-th first unit includes:

[0012] a first accumulator, the first accumulator being used to store and release energy;

[0013] a pressure gauge, the pressure gauge being connected to the first accumulator and being used to monitor the pressure in the first accumulator;

[0014] A hydraulic pump, one end of which is connected to the first accumulator via a first one-way valve, and the other end of which is connected to the first oil tank, and the hydraulic pump is used to provide and adjust pressure;

[0015] a first relief valve, the first relief valve being disposed between the first accumulator and the other end of the hydraulic pump and being used to limit the pressure of the liquid flowing out of the first accumulator;

[0016] a first two-position two-way solenoid valve, one end of which is connected to the first accumulator, and the other end of which is connected to the high-pressure liquid inlet end of the i-th stage free plunger expander, for controlling the supply of hydraulic fluid to the i-th stage free plunger expander;

[0017] a second one-way valve connected between the first accumulator and the first energy recovery end of the i-th stage free plunger expander to prevent fluid backflow;

[0018] A first oil tank, serving as an oil storage and recovery device, receiving return oil from the hydraulic pump and the first relief valve;

[0019] Among them, the first unit realizes the regulation of system pressure by controlling the output pressure and flow of the hydraulic pump in combination with the energy storage and release function of the first accumulator, and controls the direction and flow of the hydraulic fluid supplied to the i-th stage free-piston expander through the coordinated use of the first two-position two-way solenoid valve and the second one-way valve, thereby realizing the control of the return stroke of the free piston in the i-th stage free-piston expander.

[0020] According to one embodiment of the present invention, the i-th second unit comprises:

[0021] a third one-way valve and a second oil tank, wherein the third one-way valve is arranged between the second energy recovery end of the i-th stage free plunger expander and the second oil tank;

[0022] The second unit controls the third one-way valve so that the oil in the energy recovery chamber of the i-th-stage free-piston expander flows in a predetermined direction, thereby realizing energy recovery and conversion.

[0023] According to one embodiment of the present invention, the i-th second unit further includes:

[0024] A fourth one-way valve is arranged between the generator set and the energy output end of the i-th stage free piston expander.

[0025] According to one embodiment of the present invention, the first-stage expansion unit further includes:

[0026] A second two-position two-way solenoid valve, one end of the second two-position two-way solenoid valve is connected to the air inlet end of the first-stage free piston expander, and the other end of the second two-position two-way solenoid valve is connected to the high-pressure gas input end, and the second two-position two-way solenoid valve is used to control the flow rate of the high-pressure gas entering the first-stage free piston expander from the high-pressure gas input end.

[0027] According to one embodiment of the present invention, the generator set comprises:

[0028] Flow meter, which is used to monitor the flow of fluid entering the generator set;

[0029] a second accumulator, the second accumulator being used to store and release energy;

[0030] A pressure sensor, wherein the pressure sensor is used to monitor the pressure in the second accumulator in real time;

[0031] a second relief valve, the second relief valve being arranged between the second accumulator and the third oil tank and being used for limiting the pressure flowing out of the second accumulator;

[0032] A hydraulic motor, the hydraulic motor is used to receive hydraulic energy from the free piston expander and regulated by the second accumulator, and convert the hydraulic energy into mechanical energy;

[0033] A torque sensor, which is arranged on the output shaft of the hydraulic motor and is used to measure and transmit torque information of the hydraulic motor;

[0034] A generator connected to an output end of the hydraulic motor for converting mechanical energy into electrical energy;

[0035] The third oil tank is used as an oil storage and recovery device to receive the return oil from the second relief valve and the hydraulic motor.

[0036] According to one embodiment of the present invention, the gas is natural gas.

[0037] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0039] Figure 1 is a schematic diagram of a multi-stage expander pressure difference power generation system according to an embodiment of the present invention;

[0040] The reference numerals are as follows:

[0041] First-stage expansion unit 1, first-stage free-piston expander 1.1, first accumulator 1.2, pressure gauge 1.3, first two-position two-way solenoid valve 1.4, first non-return valve 1.5, hydraulic pump 1.6, second non-return valve 1.7, first overflow valve 1.8, first oil tank 1.9, third non-return valve 1.10, second oil tank 1.11, fourth non-return valve 1.12, pressure relay 1.13, three-position three-way solenoid valve 1.14, second two-position two-way solenoid valve 1.15;

[0042] Second stage expansion unit 2, second stage free piston expander 2.1, first accumulator 2.2, pressure gauge 2.3, first two-position two-way solenoid valve 2.4, first non-return valve 2.5, hydraulic pump 2.6, second non-return valve 2.7, first overflow valve 2.8, first oil tank 2.9, third non-return valve 2.10, second oil tank 2.11, fourth non-return valve 2.12, pressure relay 2.13, three-position three-way solenoid valve 2.14;

[0043] The third-stage expansion unit 3, the third-stage free-piston expander 3.1, the first accumulator 3.2, the pressure gauge 3.3, the first two-position two-way solenoid valve 3.4, the first non-return valve 3.5, the hydraulic pump 3.6, the second non-return valve 3.7, the first overflow valve 3.8, the first oil tank 3.9, the third non-return valve 3.10, the second oil tank 3.11, the fourth non-return valve 3.12, the pressure relay 3.13, the three-position three-way solenoid valve 3.14;

[0044] Flow meter 4 , accumulator 5 , pressure sensor 6 , relief valve 7 , hydraulic motor 8 , torque sensor 9 , generator 10 , and third oil tank 11 . DETAILED DESCRIPTION

[0045] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0046] The multi-stage expander pressure difference power generation system according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

[0047] Figure 1Schematic diagram of a multi-stage expander pressure difference power generation system according to an embodiment of the present invention.

[0048] like Figure 1 As shown, the multi-stage expander pressure difference power generation system of the embodiment of the present invention comprises: N-stage expander units and generator units; wherein each stage of the expander unit i comprises a free plunger expander i.1, a pressure relay i.13 and a three-position three-way solenoid valve i.14, and the expander unit i is used to output mechanical energy to the generator unit during the process of expanding and reducing the pressure of high-pressure gas (such as natural gas); wherein the air inlet end of the first-stage free plunger expander 1.1 is connected to the high-pressure gas input end, and the air outlet end of the i-th stage free plunger expander i.1 is connected to the high-pressure gas input end. The i-th pressure relay i.13 is connected to the air inlet of the i-th three-position three-way solenoid valve i.14, the air inlet of the i+1-th free plunger expander (i+1).14 is connected to the first working end of the i-th three-position three-way solenoid valve i.14, and the second working ends of the N three-position three-way solenoid valves i.14 are all connected to the low-pressure gas output end; the N pressure relays i.13 are used to monitor the gas pressure at the outlet end of each level of the free plunger expander i.1; wherein, if the i-th pressure relay i.13 detects that the i-th If the gas pressure at the outlet of the i-th free plunger expander i.1 is higher than the corresponding preset pressure threshold, the first working end of the i-th three-position three-way solenoid valve i.14 is controlled to be connected to the air inlet end of the i-th free plunger expander i.1, so that the gas discharged from the outlet of the i-th free plunger expander i.1 enters the i+1-th free plunger expander (i+1).14; if the i-th pressure relay i.13 detects that the gas pressure at the outlet of the i-th free plunger expander i.1 is not ... force threshold, then the second working end of the i-th three-position three-way solenoid valve i.14 is controlled to be connected to the gas outlet end of the i-th free plunger expander i.1, so that the gas expanded and depressurized by the i-th free plunger expander i.1 is discharged through the low-pressure gas output end; a generator set is connected to the energy output ends of the free plunger expanders i.1 at each level, and is used to convert the mechanical energy output by the expander set i into electrical energy; wherein N is a positive integer greater than or equal to 2, i is a positive integer greater than or equal to 1, and N>i.

[0049] For example, Figure 1As shown, the first-stage expansion unit 1 includes a first-stage free-piston expander 1.1, a first accumulator 1.2, a pressure gauge 1.3, a first two-position two-way solenoid valve 1.4, a first non-return valve 1.5, a hydraulic pump 1.6, a second non-return valve 1.7, a first overflow valve 1.8, a first oil tank 1.9, a third non-return valve 1.10, a second oil tank 1.11, a fourth non-return valve 1.12, a pressure relay 1.13, a three-position three-way solenoid valve 1.14, and a second two-position two-way solenoid valve 1.15. The second-stage expansion unit 2 includes a second-stage free-piston expander 2.1, a first accumulator 2.2, a pressure gauge 2.3, a first two-position two-way solenoid valve 2.4, a first non-return valve 2.5, a hydraulic pump 2.6, a second non-return valve 2.7, a first overflow valve 2.8, a first oil tank 2.9, a third non-return valve 2.10, a second oil tank 2.11, a fourth non-return valve 2.12, a pressure relay 2.13, and a three-position three-way solenoid valve 2.14. The third-stage expansion unit 3 includes a third-stage free-piston expander 3.1, a first accumulator 3.2, a pressure gauge 3.3, a first two-position two-way solenoid valve 3.4, a first non-return valve 3.5, a hydraulic pump 3.6, a second non-return valve 3.7, a first overflow valve 3.8, a first oil tank 3.9, a third non-return valve 3.10, a second oil tank 3.11, a fourth non-return valve 3.12, a pressure relay 3.13, and a three-position three-way solenoid valve 3.14.

[0050] like Figure 1 As shown, each stage of the expansion unit i also includes: N first units, the i-th first unit corresponds to controlling the free plunger in the i-th free plunger expander i.1, so that the free plunger of the i-th free plunger expander i.1 performs a return motion according to a predetermined stroke during operation; N second units, the i-th second unit corresponds to controlling the flow direction of the oil in the energy recovery chamber of the i-th free plunger expander i.1, so that the oil in the i-th free plunger expander i.1 flows according to a predetermined direction during the energy recovery process.

[0051] like Figure 1As shown, the i-th first unit includes: a first accumulator i.2, the first accumulator i.2 is used to store and release energy; a pressure gauge i.3, the pressure gauge i.3 is connected to the first accumulator i.2, and the pressure gauge is used to monitor the pressure in the first accumulator i.2; a hydraulic pump i.6, one end of the hydraulic pump i.6 is connected to the first accumulator i.2 through a first one-way valve i.5, and the other end of the hydraulic pump i.6 is connected to the first oil tank i.9, and the hydraulic pump i.6 is used to provide and adjust the pressure; a first overflow valve i.8, the first overflow valve i.8 is arranged between the first accumulator i.2 and the other end of the hydraulic pump i.6, and is used to limit the pressure of the liquid flowing out of the first accumulator i.2; a first two-position two-way solenoid valve i.4, one end of the first two-position two-way solenoid valve i.4 is connected to the first accumulator i.2, and the other end of the first two-position two-way solenoid valve i.4 is connected to the i-th free The high-pressure liquid inlet end of the plunger expander i.1 is used to control the supply of hydraulic fluid to the i-th stage free plunger expander i.1; the second one-way valve i.7, the second one-way valve i.7 is connected to the first accumulator i.2 and the first energy recovery end of the i-th stage free plunger expander i.1 to prevent fluid backflow; the first oil tank i.9, as an oil storage and recovery device, receives the return oil from the hydraulic pump i.6 and the first overflow valve i.8; wherein, the first unit controls the output pressure and flow of the hydraulic pump i.6, combined with the energy storage and release function of the first accumulator i.2, to achieve regulation of the system pressure, and controls the direction and flow of the hydraulic fluid supplied to the i-th stage free plunger expander i.1 through the coordinated use of the first two-position two-way solenoid valve i.4 and the second one-way valve i.7, thereby achieving control of the return stroke of the free plunger in the i-th stage free plunger expander i.1.

[0052] like Figure 1 As shown, the i-th second unit includes: a third one-way valve i.10 and a second oil tank i.11, and the third one-way valve i.10 is arranged between the second energy recovery end of the i-th free piston expander i.1 and the second oil tank i.11; wherein, the second unit controls the third one-way valve i.10 so that the oil in the energy recovery chamber of the i-th free piston expander i.1 flows in a predetermined direction, thereby realizing energy recovery and conversion.

[0053] like Figure 1 As shown, the i-th second unit further includes: a fourth one-way valve i.12, and the fourth one-way valve i.12 is arranged between the generator set and the energy output end of the i-th free piston expander i.1.

[0054] like Figure 1As shown, the first-stage expansion machine unit 1 also includes: a second two-position two-way solenoid valve 1.15, one end of the second two-position two-way solenoid valve 1.15 is connected to the air inlet end of the first-stage free piston expander 1.1, and the other end of the second two-position two-way solenoid valve 1.15 is connected to the high-pressure gas input end, and the second two-position two-way solenoid valve 1.15 is used to control the flow rate of the high-pressure gas entering the first-stage free piston expander 1.1 from the high-pressure gas input end.

[0055] like Figure 1 As shown, the generator set includes: a flow meter 4, which is used to monitor the fluid flow entering the generator set; a second accumulator 5, which is used to store and release energy; a pressure sensor 6, which is used to monitor the pressure in the second accumulator 5 in real time; a second overflow valve 7, which is arranged between the second accumulator 5 and the third oil tank 11, and is used to limit the pressure flowing out of the second accumulator 5; a hydraulic motor 8, which is used to receive hydraulic energy from a free piston expander and regulated by the second accumulator 5, and convert the hydraulic energy into mechanical energy; a torque sensor 9, which is arranged on the output shaft of the hydraulic motor 8, and is used to measure and transmit the torque information of the hydraulic motor 8; a generator 10, which is connected to the output end of the hydraulic motor 8, and is used to convert mechanical energy into electrical energy; a third oil tank 11, which is used as an oil storage and recovery device to receive return oil from the second overflow valve 7 and the hydraulic motor 8.

[0056] In the first-stage expansion of the present invention, the second two-position two-way solenoid valve 1.15 is opened, and the high-pressure natural gas enters the first-stage free-piston expander 1.1. The first-stage free-piston expander 1.1 converts the gas pressure energy of the high-pressure natural gas into hydraulic energy, passes through the fourth one-way valve 1.12, the flow meter 4, and the hydraulic motor 8, and finally returns to the third oil tank 11. The hydraulic motor 8 converts the hydraulic energy into mechanical energy to drive the generator 10 to rotate and generate electrical energy.

[0057] The pressure of the natural gas after the first-stage expansion is measured by the pressure relay 1.13. If the pressure after the first-stage expansion is lower than the preset pressure threshold set by the pressure sensor 1.13, the second working end (left position) of the three-position three-way solenoid valve 1.14 is energized, and the gas enters the low-pressure pipeline for discharge. If the pressure after the first-stage expansion is higher than the preset pressure threshold set by the pressure sensor 1.13, the first working end (right position) of the three-position three-way solenoid valve 1.14 is energized, and the gas enters the second-stage expansion unit 2.

[0058] In the second-stage expansion unit 2, similarly to the first-stage expansion unit 1, the gas after secondary expansion enters the low-pressure exhaust pipeline or the third-stage expansion unit 3, and the high-pressure natural gas undergoes multi-stage expansion until the pressure is reduced to meet the requirements, and finally enters the low-pressure pipeline and is discharged through the low-pressure gas output end.

[0059] Therefore, the system of the present invention can make full use of the natural gas pressure and increase the pressure energy recovery efficiency; the free plunger expander has the characteristics of resistance to two-phase flow, pollution resistance and wide operating conditions, which broadens the application scenarios of the multi-stage expander pressure difference power generation system; the free plunger type is used in combination with the hydraulic system for energy recovery, and the hydraulic energy output of each stage is connected in parallel and enters the same pipeline to flow to the hydraulic motor, avoiding the installation of generators at each stage and saving costs.

[0060] In summary, the multi-stage expander pressure difference power generation system of the embodiment of the present invention includes: including: N-stage expansion machine groups and generator groups; wherein each stage of the expansion machine groups includes a free plunger expander, a pressure relay and a three-position three-way solenoid valve, and the expansion machine group is used to output mechanical energy to the generator group during the process of expanding and reducing the pressure of the high-pressure gas; wherein the air inlet end of the first-stage free plunger expander is connected to the high-pressure gas input end, the air outlet end of the i-th stage free plunger expander is connected to the i-th pressure relay and the air inlet end of the i-th three-position three-way solenoid valve, the air inlet end of the (i+1)-th stage free plunger expander is connected to the first working end of the i-th three-position three-way solenoid valve, and the second working ends of the N three-position three-way solenoid valves are all connected to the low-pressure gas output end; N pressure relays are used to monitor the gas pressure at the air outlet end of each stage of the free plunger expander; wherein, if the i-th If the pressure relay detects that the gas pressure at the outlet end of the i-th free-plunger expander is higher than the corresponding preset pressure threshold, the first working end of the i-th three-position three-way solenoid valve is controlled to be connected to the air inlet end of the i-th free-plunger expander, so that the gas discharged from the outlet end of the i-th free-plunger expander enters the (i+1)-th free-plunger expander; if the i-th pressure relay detects that the gas pressure at the outlet end of the i-th free-plunger expander is not higher than the corresponding preset pressure threshold, the second working end of the i-th three-position three-way solenoid valve is controlled to be connected to the outlet end of the i-th free-plunger expander, so that the gas expanded and depressurized by the i-th free-plunger expander is discharged through the low-pressure gas output end; a generator set is connected to the energy output end of each level of free-plunger expanders, and is used to convert the mechanical energy output by the expansion unit into electrical energy. Therefore, the system adopts a combination of a multi-stage free plunger expander and a pressure relay, so that the hydraulic energy output by each stage is connected in parallel and enters the same pipeline to flow to the hydraulic motor, avoiding the installation of a generator at each stage, saving costs, and making full use of the gas pressure energy, thereby increasing the pressure energy recovery efficiency; the pressure energy of natural gas is converted into easily usable hydraulic energy, so that the energy that was originally wasted can be recycled, which has a beneficial effect on the comprehensive utilization of natural gas and energy conservation and emission reduction; the device adopts a multi-stage pressure reduction system, which makes the pressure energy recovery efficiency higher and more suitable for the pressure energy recovery of high-pressure natural gas; the hydraulic system is used to realize energy recovery and resetting, and the high-pressure gas enters the expansion chamber and expands rapidly, releasing a large amount of energy in a short time. The hydraulic system can play the role of a spring, making the plunger run smoothly, and the hydraulic system has high power transmission efficiency, and can realize functions such as buffering and safety protection; the hydraulic components in the hydraulic circuit are small in size and fast in response speed, which can make the layout of the entire mechanism more compact.

[0061] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0062] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A multi-stage expander pressure difference power generation system, characterized in that: include: N-stage expansion units and generator sets; wherein each stage of the expansion unit (i) comprises a free plunger expander (i.1), a pressure relay (i.13) and a three-position three-way solenoid valve (i.14); the expansion unit (i) is used to output mechanical energy to the generator set during the process of expanding and reducing the pressure of high-pressure gas; wherein, The air inlet end of the first-stage free plunger expander (1.1) is connected to the high-pressure gas input end, the air outlet end of the i-th stage free plunger expander (i.1) is connected to the air inlet end of the i-th pressure relay (i.13) and the i-th three-position three-way solenoid valve (i.14), the air inlet end of the (i+1)-th stage free plunger expander ((i+1).14) is connected to the first working end of the i-th three-position three-way solenoid valve (i.14), and the second working ends of the N three-position three-way solenoid valves (i.14) are all connected to the low-pressure gas output end; N of the pressure relays (i.13) are used to monitor the gas pressure at the outlet of each level of the free plunger expander (i.1); wherein, if the i-th pressure relay (i.13) detects that the gas pressure at the outlet of the i-th free plunger expander (i.1) is higher than the corresponding preset pressure threshold, the first working end of the i-th three-position three-way solenoid valve (i.14) is controlled to be connected to the air inlet of the i-th free plunger expander (i.1) to discharge the gas discharged from the outlet of the i-th free plunger expander (i.1). The gas enters the (i+1)th free plunger expander ((i+1).14); if the i-th pressure relay (i.13) detects that the gas pressure at the outlet of the i-th free plunger expander (i.1) is not higher than the corresponding preset pressure threshold, the second working end of the i-th three-position three-way solenoid valve (i.14) is controlled to be connected to the outlet of the i-th free plunger expander (i.1), so that the gas expanded and depressurized by the i-th free plunger expander (i.1) is discharged through the low-pressure gas output end; A generator set, connected to the energy output ends of the free-piston expanders (i.1) at each level, for converting the mechanical energy output by the expander set (i) into electrical energy; Wherein, N is a positive integer greater than or equal to 2, i is a positive integer greater than or equal to 1, and N>i.

2. The system according to claim 1, characterized in that Each stage of the expansion unit (i) further comprises: N first units, the i-th first unit correspondingly controls the free plunger in the i-th free plunger expander (i.1), so that the free plunger of the i-th free plunger expander (i.1) performs a return motion according to a predetermined stroke during operation; N second units, the i-th second unit corresponds to controlling the oil flow direction in the energy recovery chamber of the i-th stage free piston expander (i.1), so that the oil in the i-th stage free piston expander (i.1) flows in a predetermined direction during the energy recovery process.

3. The system according to claim 2, characterized in that The i-th first unit comprises: a first accumulator (i.2), the first accumulator (i.2) being used to store and release energy; a pressure gauge (i.3), the pressure gauge (i.3) being connected to the first accumulator (i.2), and the pressure gauge being used to monitor the pressure in the first accumulator (i.2); a hydraulic pump (i.6), one end of the hydraulic pump (i.6) being connected to the first accumulator (i.2) via a first one-way valve (i.5), and the other end of the hydraulic pump (i.6) being connected to the first oil tank (i.9), and the hydraulic pump (i.6) being used to provide and adjust pressure; a first overflow valve (i.8), the first overflow valve (i.8) being arranged between the first accumulator (i.2) and the other end of the hydraulic pump (i.6), and being used for limiting the pressure of the liquid flowing out of the first accumulator (i.2); a first two-position two-way solenoid valve (i.4), one end of which is connected to the first accumulator (i.2), and the other end of which is connected to the high-pressure liquid inlet end of the i-th stage free plunger expander (i.1), for controlling the supply of hydraulic fluid to the i-th stage free plunger expander (i.1); a second one-way valve (i.7), the second one-way valve (i.7) being connected between the first accumulator (i.2) and the first energy recovery end of the i-th stage free piston expander (i.1) to prevent fluid backflow; A first oil tank (i.9), serving as an oil storage and recovery device, receiving return oil from the hydraulic pump (i.6) and the first overflow valve (i.8); The first unit adjusts the system pressure by controlling the output pressure and flow of the hydraulic pump (i.6) in combination with the energy storage and release function of the first accumulator (i.2); and controls the direction and flow of the hydraulic fluid supplied to the i-th free-piston expander (i.1) by using the first two-position two-way solenoid valve (i.4) and the second one-way valve (i.7) in coordination, thereby controlling the return stroke of the free piston in the i-th free-piston expander (i.1).

4. The system according to claim 2, characterized in that The i-th second unit comprises: a third one-way valve (i.10) and a second oil tank (i.11), wherein the third one-way valve (i.10) is arranged between the second energy recovery end of the i-th stage free piston expander (i.1) and the second oil tank (i.11); The second unit controls the third one-way valve (i.10) so that the oil in the energy recovery chamber of the i-th stage free piston expander (i.1) flows in a predetermined direction, thereby realizing energy recovery and conversion.

5. The system according to claim 2, characterized in that The i-th second unit also includes: A fourth one-way valve (i.12), wherein the fourth one-way valve (i.12) is arranged between the generator set and the energy output end of the i-th stage free piston expander (i.1).

6. The system according to claim 1, characterized in that The first-stage expansion unit (1) further comprises: A second two-position two-way solenoid valve (1.15), one end of the second two-position two-way solenoid valve (1.15) is connected to the air inlet end of the first-stage free piston expander (1.1), and the other end of the second two-position two-way solenoid valve (1.15) is connected to the high-pressure gas input end, and the second two-position two-way solenoid valve (1.15) is used to control the flow rate of the high-pressure gas entering the first-stage free piston expander (1.1) from the high-pressure gas input end.

7. The system according to claim 1, characterized in that The generator set comprises: A flow meter (4), the flow meter (4) is used to monitor the flow of the fluid entering the generator set; A second accumulator (5), the second accumulator (5) is used to store and release energy; A pressure sensor (6), the pressure sensor (6) being used to monitor the pressure in the second accumulator (5) in real time; a second overflow valve (7), the second overflow valve (7) being arranged between the second accumulator (5) and the third oil tank (11) and being used for limiting the pressure flowing out of the second accumulator (5); a hydraulic motor (8), the hydraulic motor (8) being used to receive hydraulic energy from the free piston expander and regulated by the second accumulator (5), and convert the hydraulic energy into mechanical energy; A torque sensor (9), the torque sensor (9) being arranged on an output shaft of the hydraulic motor (8) and being used for measuring and transmitting torque information of the hydraulic motor (8); A generator (10), connected to the output end of the hydraulic motor (8) and used for converting mechanical energy into electrical energy; A third oil tank (11), the third oil tank (11) serving as an oil storage and recovery device, receiving return oil from the second overflow valve (7) and the hydraulic motor (8).

8. The system according to claim 1, characterized in that The gas is natural gas.

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