A high-temperature pipeline network natural gas pressure difference energy power generation system

Abstract

The present invention discloses a high-temperature pipeline network natural gas pressure difference energy power generation system, which utilizes the waste heat of the exhaust gas at the tail end of the boiler to heat the high-pressure natural gas, and then introduces it into a turbine / screw expander after increasing its enthalpy value, so that the external work capacity of the turbine / screw expander is greatly improved. In addition, based on the characteristic that the natural gas pressure of the high-pressure pipeline network and the low-pressure urban pipeline network remains basically unchanged, the corresponding relationship between the inlet temperature of the turbine / screw expander and the exhaust temperature is utilized, and by adjusting the inlet natural gas temperature of the turbine / screw expander, the natural gas discharge temperature of the turbine / screw expander can be accurately controlled. Further, through the circulating water system arranged on the exhaust side, heating in winter and cooling in summer are provided for nearby office buildings. The advantage of this system is that it improves the efficiency of natural gas pressure difference power generation, and at the same time can be used as a cold / heat source for air-conditioning systems, which can provide both heating and cooling. The present invention is particularly suitable for northern regions.

Description

Technical Field

[0001] The patent of this invention relates to the field of energy conservation and comprehensive utilization, and is particularly suitable for the recovery and utilization of huge pressure energy released during the pressure regulation process of natural gas transported by high-pressure long-distance natural gas pipelines. Background Art

[0002] my country's trunk natural gas is transported at high pressure, with a transmission pressure of 10MPa; while the natural gas transmission pressure of the urban pipeline network is 0.4MPa. For this reason, it is necessary to set up a natural gas receiving gate station or a pressure regulating station, and adjust the pressure according to the gas supply pressure requirements of downstream users before entering the downstream gas pipeline network for users to use. In order to utilize the pressure energy lost during the pressure regulation process between the trunk line and the low-pressure gas pipeline network, a turbine / screw expander generator set can be set between the high-pressure pipeline network and the low-pressure urban gas pipeline network to replace the traditional receiving gate station or pressure regulating station, and the pressure difference can be used to generate electricity. At the same time, the high-pressure natural gas enters the downstream low-pressure pipeline network for users to use after expansion and pressure reduction. According to the theory of engineering thermodynamics, after the high-pressure natural gas enters the expander to expand and do work, the discharged natural gas will be much lower in temperature due to the release of energy, generating a large amount of cold energy. Therefore, the low-temperature characteristics of natural gas after expansion and work can be used to recover cold energy. Chinese patent CN 102563958A proposes a method and device for generating electricity and making ice using natural gas pressure energy in a pipeline network. In addition to generating electricity using pressure difference, the cold energy of natural gas can also be fully utilized to produce a large amount of ice for industrial or food use; Chinese patent CN 101245956A discloses a universal method for refrigeration using natural gas pressure energy. The invention converts pressure energy into cold energy at a relatively low operating cost, and provides it to users such as cold storage, cold water air conditioners, and deep cold crushing of waste rubber around the pressure regulating station for use or to make ice cubes, dry ice products for export and sales, etc., but the invention does not involve power generation. The above disclosed process technology is suitable for the southern region with long summer and high temperature. The humid and hot southern region has a large demand for cold energy, but for the northern region with short summer, long winter and low temperature, the market demand for cold energy is not large, but the demand for heat energy is very large. Summary of the invention

[0003] In order to solve the deficiencies in the above-mentioned prior art solutions, the present invention proposes a solution of first using the waste heat of boiler flue gas to heat the high-pressure natural gas, raising its temperature, and then entering the turbine / screw expander to expand and generate power. Since the enthalpy value of natural gas is increased, the maximum power generation can be increased by more than 70%. At the same time, by changing the natural gas inlet temperature, the exhaust temperature of the turbine / screw expander can be controlled, which can provide cooling energy for air conditioning in nearby office buildings in summer and heat energy for heating in winter.

[0004] The object of the present invention can be achieved through the following technical solutions: a high-temperature pipeline network natural gas pressure difference energy power generation system, which includes a high-pressure pipeline network, a generator, a turbine / screw expander and a low-pressure pipeline network, which also includes a high-pressure heat exchanger and a low-pressure heat exchanger, the outlet end of the high-pressure pipeline network is connected to the first inlet of the high-pressure heat exchanger, the first outlet of the high-pressure heat exchanger is connected to the air inlet of the expander, the second inlet of the high-pressure heat exchanger is connected to the outlet of the temperature regulator, the inlet of the temperature regulator is connected to the outlet of the flue gas induced draft fan, and the inlet of the flue gas induced draft fan is connected to the high-temperature flue gas; the air outlet of the expander is connected to the first inlet of the low-pressure heat exchanger, and the first outlet of the low-pressure heat exchanger is connected to the inlet end of the low-pressure pipeline network; the second inlet of the low-pressure heat exchanger is connected to the outlet of the water pump, the inlet of the water pump is connected to the outlet of the user's circulating water system, the second outlet of the low-pressure heat exchanger is connected to the inlet of the water storage tank, and the outlet of the water storage tank is connected to the inlet of the user's circulating water system.

[0005] Furthermore, the temperature regulator is a flue gas-air mixer, the first air inlet of the flue gas-air mixer is connected to the outlet of the flue gas induced draft fan, the second air inlet of the flue gas-air mixer is connected to the outlet of the air induced draft fan, and the mixed air outlet of the flue gas-air mixer is connected to the second inlet of the high-pressure heat exchanger.

[0006] Furthermore, the flue gas-air mixer includes a mixing tube, one end of which is a first air inlet, the other end of which is a mixing air outlet, and an air inlet pipe is connected to the side wall of the mixing tube; a spiral air distribution pipe arranged axially is fixed inside the mixing tube, and a plurality of air holes are opened on the air distribution pipe; an end of the air distribution pipe adjacent to the mixing air outlet is a closed end, the other end of the air distribution pipe is connected to the outlet end of the air inlet pipe, and the inlet end of the air inlet pipe is a second air inlet; a control valve and a check valve are installed on the air inlet pipe.

[0007] Furthermore, the air distribution pipe is coaxially designed with the mixing pipe, and a bending diameter of the air distribution pipe gradually decreases along a direction from the first air inlet to the mixing air outlet.

[0008] Furthermore, the maximum bending radius of the air distribution pipe is less than 1 / 2 of the radius of the mixing pipe.

[0009] Furthermore, a multi-layer metal wire mesh disk having a diameter equal to the diameter of the mixing tube is provided in the mixing tube between the air distribution tube and the air outlet, and the metal wire mesh is a 5-18 mesh wire mesh.

[0010] Furthermore, a water storage tank is installed between the second outlet of the low-pressure heat exchanger and the inlet of the user circulating water system.

[0011] Furthermore, it also includes a pressure regulating station, in which a high-pressure three-way valve and a low-pressure three-way valve are respectively installed at the outlet end of the high-pressure pipeline network and the inlet end of the low-pressure pipeline network, the first outlet of the high-pressure three-way valve is connected to the first inlet of the high-pressure heat exchanger, and the second outlet of the high-pressure three-way valve is connected to the air inlet of the pressure regulating station; the first inlet of the low-pressure three-way valve is connected to the first outlet of the low-pressure heat exchanger, and the second inlet of the low-pressure three-way valve is connected to the air outlet of the pressure regulating station.

[0012] The specific process and operation steps are as follows:

[0013] Step 1: High-temperature flue gas is introduced into the mixer, and low-temperature ambient air enters the mixer through the air distribution pipe. The flue gas and air are fully mixed to form a mixed gas, and the temperature of the mixed gas is controlled by changing the flow ratio of the two. After reaching the design temperature, it enters the high-pressure heat exchanger as a hot fluid.

[0014] Step 2: The high-pressure pipeline network is connected to the high-pressure heat exchanger. The natural gas in the pipeline network enters the cold fluid side of the high-pressure heat exchanger as the cold fluid and exchanges heat with the mixed gas on the hot fluid side of the high-pressure heat exchanger.

[0015] Step 3: The outlet of the cold fluid side of the high-pressure heat exchanger is connected to the air inlet of the expander. The heated high-pressure natural gas enters the turbine / screw expander to expand and work. The turbine / screw expander drives the generator set to generate electricity. The exhaust port of the turbine / screw expander is connected to the low-pressure heat exchanger. The natural gas after work enters the circulating water on the hot fluid side of the low-pressure heat exchanger and exchanges heat with the cold fluid side.

[0016] Step 4: The hot fluid inlet of the low-pressure heat exchanger is connected to the exhaust port of the turbine / screw expander, and the hot fluid outlet is connected to the medium and low pressure natural gas pipeline network. After the natural gas exchanges heat with the circulating water, it enters the medium and low pressure natural gas pipeline network for users. The air conditioning circulating water on the cold fluid side obtains heat and cold energy to provide heating and cooling for nearby office buildings. A water storage tank is installed in the circulation pipeline to stabilize the pressure and flow.

[0017] Theoretical explanation of the present invention: According to the theory of engineering thermodynamics, the working fluid in the turbine / screw expander converts heat enthalpy into power generation. Under the condition of keeping the working fluid pressure at the inlet and outlet of the expander unchanged, increasing the temperature of the inlet working fluid can improve the heat-to-work conversion efficiency of the expander and increase the power generation. At the same time, the inlet temperature of the working fluid determines the outlet temperature of the expander working fluid. Table 1 is the result of theoretical calculation (the inlet pressure of the expander is 1.6MPa, the exhaust pressure of the expander is 0.4MPa, and the mechanical efficiency is 0.85)

[0018] Table 1. Parameter changes and expansion work per kilogram of natural gas before and after passing through the expander

[0019]

[0020]

[0021] The advantages and beneficial effects of the present invention over the prior art are as follows: Generally, the temperature of natural gas in the pipeline network is about 5-30°C, while the temperature of flue gas from the boiler is about 160-350°C. The flue gas can be used to heat the natural gas to above 200°C. The heated high-temperature natural gas is introduced into the expander for pressure difference power generation, which can increase the efficiency by more than 70%, and the economic benefits are obvious. Another function of this system is that in the blender, by mixing flue gas of different qualities with air, the outlet temperature of the mixed gas in the blender can be adjusted and controlled and introduced into the natural gas heater. The temperature of the mixed gas as a hot fluid determines the outlet temperature of the natural gas in the natural gas heater. Subsequently, the high-temperature natural gas is introduced into the expander; different natural gas inlet temperatures correspond to different natural gas temperatures at the expander outlet (as shown in Table 1). In summary, this technical route can be adjusted according to the needs of different seasons by adjusting the outlet temperature of the mixed gas in the blender. The outlet of the natural gas heater can obtain natural gas with different design temperature requirements of the system. After natural gas of different temperatures enters the turbine / screw expander for power generation, the temperature of the natural gas after expansion can also be determined. This part of natural gas then enters the air conditioning water heat exchanger, transferring heat / cold energy to the air conditioning circulating water, providing heat for heating in winter and cold energy for cooling in summer. This solution is particularly suitable for northern regions.

[0022] One of the key equipment in the system of the present invention is the mixer. In order to evenly mix the two gases in the mixer and keep the outlet temperature of the mixed gas stable, the present invention designs the gas distribution pipe into a spiral coil shape. The bending diameter of the spiral coil gradually decreases along the gas flow direction to form a tower shape, and is coaxial with the cylindrical shell of the mixer. The surface is densely covered with air outlet holes. According to the classical theory of fluid mechanics, the velocity distribution on any section in the circular channel is symmetrical to the axis, that is, a two-dimensional axisymmetric form. The fluid particles on the cylindrical surface equidistant from the axis have the same velocity. Conversely, the fluid particles on the cylindrical surface at different distances have different velocities. Experimental and theoretical calculations show that the flow velocity u0 at the axis is the largest, and the velocity gradually decreases with the increase of radial distance, and the velocity tends to zero at the wall. Among them, when the distance from the axis is greater than 1 / 2 of the cylinder radius, the velocity drops very quickly, while the velocity at a position less than 1 / 2 of the cylinder radius drops very slowly, equal to or greater than 0.9u 0。Therefore, the maximum bending radius of the spiral coil-shaped air distribution pipe of the present invention is less than 1 / 2 of the radius of the cylindrical shell of the mixer, so that the air distribution pipe is in a relatively large velocity field of the flue gas: in addition, the spiral coil-shaped air distribution pipe is in a tower shape, and is composed of a plurality of circular rings with different bending radii, so that its exhaust almost covers the entire cross section, increasing the mixing points of air and flue gas, so that the mixing is uniform. In addition, a plurality of layers of 5-18 mesh copper wire mesh disks are arranged along the flow direction of the mixed gas. When the flow velocity is very high, a large number of vortices will be generated in the mixed gas, which will be broken when passing through the wire mesh, and the velocity field and temperature field on the cross section will be uniform; at the same time, the thermal conductivity of the copper wire is very good. When the radial temperature is uneven, when the mixed gas passes through the wire mesh, the thermal conductivity of the wire mesh can be used to reduce the temperature of the high temperature of the mixed gas, and vice versa, the temperature of the low temperature can be increased, thereby once again uniformizing the temperature of the mixed gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall structure of the embodiment.

[0024] Figure 2 Schematic diagram of the overall structure of the temperature regulator in the embodiment.

[0025] High-pressure pipeline network 1, generator 2, expander 3, low-pressure pipeline network 4, high-pressure heat exchanger 5, low-pressure heat exchanger 6, high-temperature flue gas 7, user circulating water system 8, temperature regulator 9, first air inlet 9.1, second air inlet 9.2, mixed air outlet 9.3, mixing pipe 9.4, air inlet pipe 9.5, air distribution pipe 9.6, air hole 9.6.1, control valve 9.7, check valve 9.8, mesh disk 9.9, air induced draft fan 10, water storage tank 11, pressure regulating station 12, high-pressure three-way valve 13, low-pressure three-way valve 14, water pump 15, flue gas induced draft fan 16. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages and disadvantages of the present invention more clear, Figure 1 The present invention is further described in detail.

[0027] As shown in the structure Figure 1 As shown in the figure, the traditional pressure regulating method of throttling pressure regulating at the pressure regulating station is used as a bypass to connect the high-pressure natural gas pipeline network and the low-pressure natural gas pipeline network. The 300℃ flue gas from the chimney enters the mixer and mixes with an appropriate amount of ambient air. After reaching the design temperature, it flows into the natural gas heater through the regulating valve to heat the high-pressure natural gas.

[0028] Working condition 1: In winter, natural gas is heated to 215℃ and then enters the expander to expand and do work. Considering the flow rate of 1kg / s, it can generate 254.8kW of electricity, and the exhaust temperature is equal to 100.6℃. It passes through the air conditioning water heat exchanger to heat the circulating water, and the water temperature is heated to 80-90℃. It is used as hot water.

[0029] Working condition 2: In summer, natural gas is heated to 67℃ and then enters the expander to expand and do work. Under the condition of 1kg / s flow rate, it can generate 177.5kW of electricity, and the exhaust temperature is equal to -12.7℃. It passes through the air conditioning water heat exchanger to cool the circulating water, and the water temperature is cooled to about 7℃-12℃. It is used as air conditioning cooling water.

Claims

1. A high-temperature pipeline network natural gas pressure difference energy power generation system, which includes a high-pressure pipeline network, a generator, a turbine / screw expander and a low-pressure pipeline network, characterized in that: It also includes a high-pressure heat exchanger and a low-pressure heat exchanger, the outlet end of the high-pressure pipe network is connected to the first inlet of the high-pressure heat exchanger, the first outlet of the high-pressure heat exchanger is connected to the air inlet of the expander, the second inlet of the high-pressure heat exchanger is connected to the outlet of the temperature regulator, the inlet of the temperature regulator is connected to the outlet of the flue gas induced draft fan, and the inlet of the flue gas induced draft fan is connected to the high-temperature flue gas; the air outlet of the expander is connected to the first inlet of the low-pressure heat exchanger, and the first outlet of the low-pressure heat exchanger is connected to the inlet end of the low-pressure pipe network; the second inlet of the low-pressure heat exchanger is connected to the outlet of the water pump, the inlet of the water pump is connected to the outlet of the user's circulating water system, the second outlet of the low-pressure heat exchanger is connected to the inlet of the water storage tank, and the outlet of the water storage tank is connected to the inlet of the user's circulating water system; The temperature regulator is a flue gas-air mixer, a first air inlet of the flue gas-air mixer is connected to an outlet of a flue gas induced draft fan, a second air inlet of the flue gas-air mixer is connected to an outlet of an air induced draft fan, and a mixed air outlet of the flue gas-air mixer is connected to a second inlet of the high-pressure heat exchanger; The flue gas-air mixer comprises a mixing tube, one end of which is a first air inlet, the other end of which is a mixed air outlet, and an air inlet pipe is connected to the side wall of the mixing tube; a spiral air distribution pipe arranged along the axial direction is fixed inside the mixing tube, the spiral coil-shaped air distribution pipe is in a tower shape, and is composed of a plurality of circular rings with different bending radii stacked together, and a plurality of air holes are opened on the air distribution pipe; the end of the air distribution pipe adjacent to the mixed air outlet is a closed end, the other end of the air distribution pipe is connected to the outlet end of the air inlet pipe, and the inlet end of the air inlet pipe is a second air inlet; a control valve and a check valve are installed on the air inlet pipe; The air distribution pipe is coaxially designed with the mixing pipe, and the bending diameter of the air distribution pipe gradually decreases along the direction from the first air inlet to the mixing outlet; The maximum bending radius of the air distribution pipe is less than 1 / 2 of the radius of the mixing pipe.

2. A high-temperature pipeline network natural gas pressure difference energy power generation system according to claim 1, characterized in that: A multi-layer metal wire mesh disk having a diameter equal to that of the mixing tube is arranged in the mixing tube between the air distribution tube and the air outlet.

3. A high-temperature pipeline network natural gas pressure difference energy power generation system according to claim 2, characterized in that: A water storage tank is installed between the second outlet of the low-pressure heat exchanger and the inlet of the user circulating water system.

4. A high-temperature pipeline network natural gas pressure difference energy power generation system according to claim 1 or 3, characterized in that: It also includes a pressure regulating station, in which a high-pressure three-way valve and a low-pressure three-way valve are respectively installed at the outlet end of the high-pressure pipeline network and the inlet end of the low-pressure pipeline network, the first outlet of the high-pressure three-way valve is connected to the first inlet of the high-pressure heat exchanger, and the second outlet of the high-pressure three-way valve is connected to the air inlet of the pressure regulating station; the first inlet of the low-pressure three-way valve is connected to the first outlet of the low-pressure heat exchanger, and the second inlet of the low-pressure three-way valve is connected to the air outlet of the pressure regulating station.

5. A high-temperature pipeline network natural gas pressure difference energy power generation system according to claim 2, characterized in that: It also includes a pressure regulating station, in which a high-pressure three-way valve and a low-pressure three-way valve are respectively installed at the outlet end of the high-pressure pipeline network and the inlet end of the low-pressure pipeline network, the first outlet of the high-pressure three-way valve is connected to the first inlet of the high-pressure heat exchanger, and the second outlet of the high-pressure three-way valve is connected to the air inlet of the pressure regulating station; the first inlet of the low-pressure three-way valve is connected to the first outlet of the low-pressure heat exchanger, and the second inlet of the low-pressure three-way valve is connected to the air outlet of the pressure regulating station.

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