System for comprehensive recycling of waste gas of pressure swing adsorption nitrogen making device

Abstract

The application discloses a kind of comprehensive recycling system for waste gas of pressure swing adsorption nitrogen making device, including air compressor, refrigeration dryer, first filter, drying tower unit, second filter, air storage tank, adsorption tower unit and nitrogen storage tank connected in sequence by pipeline;The drying tower unit includes the drying tower of parallel arrangement, and the inlet end is connected with the first filter, and the outlet end is connected with the second filter;Adsorption tower unit includes the adsorption tower of parallel arrangement, and the inlet end is connected with the air storage tank, and the outlet end is connected with the nitrogen storage tank, and the nitrogen storage tank is connected with nitrogen backflush pipe of adsorption tower;Recycling pipe connected with waste gas storage tank is arranged on adsorption tower inlet switching pipeline, and the outlet of waste gas storage tank is respectively provided with waste gas backflush pipe connected with drying tower and oxygen-enriched waste gas pipe connected with boiler air inlet pipe.The present application has the advantages of simple structure, easy implementation, low cost when modifying existing nitrogen making device, and can effectively reduce system energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nitrogen production, in particular to a comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen production device. BACKGROUND

[0002] Nitrogen accounts for more than 70% of the volume of air, and its chemical properties are relatively stable. In the industrial field, nitrogen is used in large quantities. The molecular sieve pressure swing adsorption method uses compressed air as raw material, carbon molecular sieve as adsorbent, uses the principle of pressure swing adsorption, and uses the selective adsorption of carbon molecular sieve on oxygen and nitrogen to separate oxygen and nitrogen, thereby producing nitrogen. The device using this method has the characteristics of simple process flow, high automation degree and high purity of obtained nitrogen, and is widely used. However, the regeneration of the drying agent in the air drying tower requires a large amount of compressed air, and at the same time, a large amount of waste gas is discharged during the back blowing and pressure relief of the molecular sieve adsorption tower, which wastes a lot of excess pressure and oxygen-enriched air. SUMMARY

[0003] In view of the above problems, the present application provides a comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen production device, which can specifically adopt the following technical scheme:

[0004] The comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen production device provided by the present application comprises an air compressor, a refrigeration dryer, a first filter, a drying tower unit, a second filter, an air storage tank, an adsorption tower unit and a nitrogen storage tank connected in sequence through pipelines; the drying tower unit comprises a plurality of drying towers connected in parallel, the inlet end of the drying tower is connected with the outlet pipe of the first filter through a first inlet switching pipeline, an air vent pipe is arranged on the first inlet switching pipeline, and the outlet end of the drying tower is connected with the inlet pipe of the second filter through a first outlet switching pipeline; the adsorption tower unit comprises a plurality of adsorption towers connected in parallel, the inlet end of the adsorption tower is connected with the outlet pipe of the air storage tank through a second inlet switching pipeline, the outlet end of the adsorption tower is connected with the inlet pipe of the nitrogen storage tank through a second outlet switching pipeline, and the outlet pipe of the nitrogen storage tank is connected with the second outlet switching pipeline through a nitrogen back blowing pipe; a recovery pipe is arranged on the second inlet switching pipeline, the recovery pipe is connected with the inlet of a waste gas storage tank, and the outlet of the waste gas storage tank is respectively provided with a waste gas back blowing pipe connected with the first outlet switching pipeline and an oxygen-enriched waste gas pipe connected with a boiler air inlet pipe.

[0005] Preferably, the drying tower unit comprises drying tower A and drying tower B arranged in parallel; the first inlet switching pipeline comprises first inlet branch pipe A and first inlet branch pipe B connected with the first filter outlet pipe, the first inlet branch pipe A is connected with the inlet of the drying tower A, and the first inlet branch pipe A is provided with first inlet valve A and emptying branch pipe A behind the valve; the first inlet branch pipe B is connected with the inlet of the drying tower B, and the first inlet branch pipe B is provided with first inlet valve B and emptying branch pipe B behind the valve; the emptying branch pipe A is provided with emptying valve A, the emptying branch pipe B is provided with emptying valve B, the emptying branch pipe A and the emptying branch pipe B are connected, and the emptying pipe is arranged between the emptying valve A and the emptying valve B; the first outlet switching pipeline comprises first outlet branch pipe A connected with the outlet of the drying tower A and first outlet branch pipe B connected with the outlet of the drying tower B, the first outlet branch pipe A is provided with first outlet valve A and waste gas backflushing branch pipe A in front of the valve, the first outlet branch pipe B is provided with first outlet valve B and waste gas backflushing branch pipe B in front of the valve, the first outlet branch pipe A and the first outlet branch pipe B are connected, the inlet pipe of the second filter is arranged between the first outlet valve A and the first outlet valve B, the waste gas backflushing branch pipe A is provided with waste gas backflushing valve A, the waste gas backflushing branch pipe B is provided with waste gas backflushing valve B, the waste gas backflushing branch pipe A and the waste gas backflushing branch pipe B are connected, and the waste gas backflushing pipe is arranged between the waste gas backflushing valve A and the waste gas backflushing valve B.

[0006] Further, the first outlet switching pipeline further comprises waste gas backflushing switching pipe connecting the drying tower A and the drying tower B, and the waste gas backflushing switching pipe is provided with waste gas backflushing switching valve.

[0007] Preferably, the adsorption tower unit comprises adsorption tower A and adsorption tower B arranged in parallel; the second inlet switching pipeline comprises second air inlet branch pipe A connected with the air tank outlet pipe and second air inlet branch pipe B, the second air inlet branch pipe A is connected with the inlet of the adsorption tower A, the second air inlet branch pipe A is provided with second air inlet valve A and recovery branch pipe A behind the valve, the second air inlet branch pipe B is connected with the inlet of the adsorption tower B, the second air inlet branch pipe B is provided with second air inlet valve B and recovery branch pipe B behind the valve, the recovery branch pipe A is provided with recovery valve A, the recovery branch pipe B is provided with recovery valve B, the recovery branch pipe A and the recovery branch pipe B are connected, and the recovery pipe is arranged between the recovery valve A and the recovery valve B; the second outlet switching pipeline comprises second air outlet branch pipe A connected with the outlet of the adsorption tower A and second air outlet branch pipe B connected with the outlet of the adsorption tower B, the second air outlet branch pipe A is provided with second air outlet valve A and nitrogen back flushing branch pipe A in front of the valve, the second air outlet branch pipe B is provided with second air outlet valve B and nitrogen back flushing branch pipe B in front of the valve, the second air outlet branch pipe A and the second air outlet branch pipe B are connected, the inlet pipe of the nitrogen tank is arranged between the second air outlet valve A and the second air outlet valve B, the nitrogen back flushing branch pipe A is provided with nitrogen back flushing valve A, the nitrogen back flushing branch pipe B is provided with nitrogen back flushing valve B, the nitrogen back flushing branch pipe A and the nitrogen back flushing branch pipe B are connected, and the nitrogen back flushing pipe is arranged between the nitrogen back flushing valve A and the nitrogen back flushing valve B.

[0008] Further, the second outlet switching pipeline further comprises nitrogen back flushing switching pipe which is connected with the adsorption tower A and the adsorption tower B, and the nitrogen back flushing switching pipe is provided with nitrogen back flushing switching valve.

[0009] Preferably, the gas pressure in the waste gas tank is 0.6-0.7 MPa, and the oxygen content is 35-40%.

[0010] Preferably, the air inlet pipe of the boiler is provided with a blower, and the oxygen-rich waste gas pipe is provided with a first pressure reducing valve.

[0011] Preferably, the waste gas back flushing pipe is provided with a second pressure reducing valve, the gas pressure after the second pressure reducing valve is 0.1 MPa, and the oxygen content of the waste gas is 35-40%.

[0012] The comprehensive recycling system for waste gas of the pressure swing adsorption nitrogen making device provided by the application recycles the waste gas when the molecular sieve adsorption tower is back flushed and depressurized, and utilizes the waste gas in two ways, first, the waste gas is collected and sent to the adsorption dryer for regeneration and back flushing of the drying agent in the drying tower, instead of the dried compressed air used in the conventional process; second, the collected waste gas is depressurized and sent to the outlet of the boiler blower, mixed with the air blown by the blower, and then sent into the boiler for combustion with fuel, thereby reducing the overall energy consumption of the device.

[0013] The present application has simple structure and is easy to implement. When the existing nitrogen making device is modified, the cost is lower. Compared with the prior art, the present application has the following advantages:

[0014] 1) The waste gas is used to replace the dried compressed air for the regeneration backflush of the drying agent in the drying tower, which saves the drying compressed air, improves the nitrogen making efficiency and reduces the operation cost;

[0015] 2) The waste gas is introduced into the boiler as oxygen-rich air to improve the fuel combustion temperature in the boiler and improve the heat utilization efficiency;

[0016] 3) The waste gas has a certain residual pressure, and after pressure reduction, it is sent into the air pipe at the rear end of the air blower, which can reduce the power consumption of the air blower;

[0017] 4) The boiler adopts oxygen-rich combustion to reduce the emission of NOx in the flue gas, which brings environmental benefits;

[0018] 5) The boiler adopts oxygen-rich combustion to reduce the flue gas volume and reduce the heat loss taken away by the flue gas, thereby improving the thermal efficiency of the boiler. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a structural schematic diagram of the present application. DETAILED DESCRIPTION

[0020] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. The present application is implemented on the premise of the technical scheme, and detailed implementation modes and specific working processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0021] As shown in Figure 1 , the comprehensive recycling system for waste gas of pressure swing adsorption nitrogen making device comprises

[0022] The comprehensive recycling system for waste gas of the pressure swing adsorption nitrogen making device, comprising air compressor 1, refrigeration dryer 2, first filter 3, drying tower unit, second filter 4, air storage tank 5, adsorption tower unit and nitrogen storage tank 6 connected by pipeline in sequence, wherein the drying tower unit comprises several drying towers (two in the embodiment, drying tower A 701 and drying tower B 702) arranged in parallel, the inlet end of the drying tower is connected with the outlet pipe of the first filter 3 through the first inlet switching pipeline, the first inlet switching pipeline is provided with a vent pipe 703, the outlet end of the drying tower is connected with the inlet pipe of the second filter 4 through the first outlet switching pipeline; the adsorption tower unit comprises several adsorption towers (two in the embodiment, adsorption tower A 801 and adsorption tower B 802) arranged in parallel, the inlet end of the adsorption tower is connected with the outlet pipe of the air storage tank 5 through the second inlet switching pipeline, the outlet end of the adsorption tower is connected with the inlet pipe of the nitrogen storage tank 6 through the second outlet switching pipeline, and the outlet pipe of the nitrogen storage tank 6 is connected with the second outlet switching pipeline through the nitrogen back flushing pipe 601; the second inlet switching pipeline is provided with a recovery pipe 803 connected with the inlet of the waste gas storage tank 9, and the outlet of the waste gas storage tank 9 is respectively provided with a waste gas back flushing pipe 901 connected with the first outlet switching pipeline and an oxygen-enriched waste gas pipe 902 connected with the boiler 10 air inlet pipe.

[0023] Specifically, the drying tower unit comprises drying tower A 701 and drying tower B 702 arranged in parallel; the first inlet switching pipeline comprises first inlet branch pipe A and first inlet branch pipe B connected with the outlet pipe of the first filter 3, the first inlet branch pipe A is connected with the inlet of the drying tower A 701, the first inlet branch pipe A is provided with first inlet valve A 704 and emptying branch pipe A behind the valve, the first inlet branch pipe B is connected with the inlet of the drying tower B 702, the first inlet branch pipe B is provided with first inlet valve B 705 and emptying branch pipe B behind the valve, the emptying branch pipe A is provided with emptying valve A 706, the emptying branch pipe B is provided with emptying valve B 707, the emptying branch pipe A and the emptying branch pipe B are connected, and the emptying pipe 703 is arranged between the emptying valve A 706 and the emptying valve B 707; the first outlet switching pipeline comprises first outlet branch pipe A connected with the outlet of the drying tower A 701 and first outlet branch pipe B connected with the outlet of the drying tower B 702, the first outlet branch pipe A is provided with first outlet valve A 708 and waste gas back flushing branch pipe A in front of the valve, the first outlet branch pipe B is provided with first outlet valve B 709 and waste gas back flushing branch pipe B in front of the valve, the first outlet branch pipe A and the first outlet branch pipe B are connected, the inlet pipe of the second filter 4 is arranged between the first outlet valve A 708 and the first outlet valve B 709, the waste gas back flushing branch pipe A is provided with waste gas back flushing valve A 710, the waste gas back flushing branch pipe B is provided with waste gas back flushing valve B 711, the waste gas back flushing branch pipe A and the waste gas back flushing branch pipe B are connected, and the waste gas back flushing pipe 901 is arranged between the waste gas back flushing valve A 710 and the waste gas back flushing valve B 711. Further, the first outlet switching pipeline further comprises waste gas back flushing switching pipe connecting the drying tower A 701 and the drying tower B 702, and the waste gas back flushing switching pipe is provided with waste gas back flushing switching valve 712.

[0024] The adsorption tower unit comprises an adsorption tower A 801 and an adsorption tower B 802 arranged in parallel. The second inlet switching pipeline comprises a second air inlet branch A and a second air inlet branch B connected to the outlet pipe of the air storage tank 5. The second air inlet branch A is connected to the inlet of the adsorption tower A 801, and the second air inlet branch A is provided with a second air inlet valve A 804 and a recovery branch A located behind the valve. The second air inlet branch B is connected to the inlet of the adsorption tower B 802, and the second air inlet branch B is provided with a second air inlet valve B 805 and a recovery branch B located behind the valve. The recovery branch A is provided with a recovery valve A 806, and the recovery branch B is provided with a recovery valve B 807. The recovery branch A and the recovery branch B are connected, and the recovery pipe 803 is arranged between the recovery valve A 806 and the recovery valve B 807. The second outlet switching pipeline comprises a second air outlet branch A connected to the outlet of the adsorption tower A 801 and a second air outlet branch B connected to the outlet of the adsorption tower B 802. The second air outlet branch A is provided with a second air outlet valve A 808 and a nitrogen backflushing branch A located in front of the valve, and the second air outlet branch B is provided with a second air outlet valve B 809 and a nitrogen backflushing branch B located in front of the valve. The second air outlet branch A and the second air outlet branch B are connected, the inlet pipe of the nitrogen storage tank 6 is arranged between the second air outlet valve A 808 and the second air outlet valve B 809, the nitrogen backflushing branch A is provided with a nitrogen backflushing valve A 810, the nitrogen backflushing branch B is provided with a nitrogen backflushing valve B 811, the nitrogen backflushing branch A and the nitrogen backflushing branch B are connected, and the nitrogen backflushing pipe is arranged between the nitrogen backflushing valve A 810 and the nitrogen backflushing valve B 811. Further, the second outlet switching pipeline further comprises a nitrogen backflushing switching pipe connecting the adsorption tower A 801 and the adsorption tower B 802, and the nitrogen backflushing switching pipe is provided with a nitrogen backflushing switching valve 812.

[0025] Generally, the gas pressure in the waste gas storage tank 9 is 0.6-0.7 MPa, and the oxygen content is 35-40%. The air inlet pipe of the boiler 10 is provided with a blower 11, and the oxygen-rich waste gas pipe 902 is provided with a first pressure reducing valve 903. The waste gas backflushing pipe 901 is provided with a second pressure reducing valve 904, and the gas pressure after the second pressure reducing valve 904 is 0.1 MPa.

[0026] In operation, air enters the refrigerated dryer 2 from the air compressor 1 to complete the initial drying, so as to reduce the water content to reduce the erosion of the molecular sieve in the drying tower unit, and prolong the service life of the molecular sieve. Then, the compressed air enters the drying tower unit through the first filter 3. In the drying tower unit, the automatic switching of the opening and closing states of the first air inlet valve A 704, the first air inlet valve B 705, the exhaust valve A 706, the exhaust valve B 707, the first air outlet valve A 708, the first air outlet valve B 709, the waste gas back flushing valve A 710, and the waste gas back flushing valve B 711 enables the drying tower A 701 and the drying tower B 702 to keep one tower drying and the other tower back flushing, so as to realize the regeneration of the drying agent in the tower. The compressed air discharged from the drying tower unit enters the air storage tank 5 through the second filter 4, and then enters the adsorption tower unit. In the adsorption tower unit, the automatic switching of the opening and closing states of the second air inlet valve A 804, the second air inlet valve B 805, the recovery valve A 806, the recovery valve B 807, the second air outlet valve A 808, the second air outlet valve B 809, the nitrogen back flushing valve A 810, and the nitrogen back flushing valve B 811 enables the adsorption tower A 801 and the adsorption tower B 802 to keep one tower pressure swing adsorption, and the generated nitrogen enters the nitrogen storage tank 6 for storage, and the other tower performs nitrogen back flushing to realize the regeneration of the adsorbent in the tower. Each of the above-mentioned adsorption towers includes three working stages of pressure swing adsorption, pressure relief, and back flushing regeneration, and different adsorption times can be set to produce nitrogen with different purities. Most of the nitrogen in the nitrogen storage tank 6 is output as finished nitrogen, and a small part of it returns to the adsorption tower unit through the nitrogen back flushing pipe to perform nitrogen back flushing of the adsorption tower. Since the exhaust gas discharged from the adsorption tower after the completion of the nitrogen back flushing has a high pressure (about 0.6-0.7 MPa) and is rich in oxygen (oxygen content is 35-40%), the part of the exhaust gas is introduced into the waste gas storage tank 9 for two uses: first, the exhaust gas is sent to the drying tower unit for the regeneration back flushing of the drying agent in the drying tower (see the foregoing steps), instead of the conventional process of back flushing with dry compressed air, so as to avoid the consumption of nitrogen in the system and improve the nitrogen production of the system; second, the collected exhaust gas is decompressed and sent to the air inlet pipe of the boiler 10, mixed with the air blown by the air blower 11, and then sent into the boiler 10 to be burned with fuel.

[0027] It should be noted that in the description of the present application, terms indicating the orientation or positional relationship, such as "front", "back", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as limiting the present application.

Claims

1. A comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen generating device, characterized in that: it comprises an air compressor, a refrigeration dryer, a first filter, a drying tower unit, a second filter, an air storage tank, an adsorption tower unit and a nitrogen storage tank connected in sequence through pipelines; the drying tower unit comprises a plurality of drying towers connected in parallel, the inlet end of the drying tower is connected with the outlet pipe of the first filter through a first inlet switching pipeline, a vent pipe is arranged on the first inlet switching pipeline, the outlet end of the drying tower is connected with the inlet pipe of the second filter through a first outlet switching pipeline; the adsorption tower unit comprises a plurality of adsorption towers connected in parallel, the inlet end of the adsorption tower is connected with the outlet pipe of the air storage tank through a second inlet switching pipeline, the outlet end of the adsorption tower is connected with the inlet pipe of the nitrogen storage tank through a second outlet switching pipeline, and the outlet pipe of the nitrogen storage tank is connected with the second outlet switching pipeline through a nitrogen back flushing pipeline; a recovery pipe is arranged on the second inlet switching pipeline, the recovery pipe is connected with the inlet of a waste gas storage tank, the outlet of the waste gas storage tank is respectively provided with a waste gas back flushing pipe connected with the first outlet switching pipeline and an oxygen-enriched waste gas pipe connected with a boiler air inlet pipe.

2. The comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen generating device according to claim 1, characterized in that: the drying tower unit comprises drying tower A and drying tower B connected in parallel; the first inlet switching pipeline comprises first inlet branch pipe A and first inlet branch pipe B connected with the first filter outlet pipe, the first inlet branch pipe A is connected with the inlet of the drying tower A, a first inlet valve A and an emptying branch pipe A located behind the valve are arranged on the first inlet branch pipe A, the first inlet branch pipe B is connected with the inlet of the drying tower B, a first inlet valve B and an emptying branch pipe B located behind the valve are arranged on the first inlet branch pipe B, an emptying valve A is arranged on the emptying branch pipe A, an emptying valve B is arranged on the emptying branch pipe B, the emptying branch pipe A and the emptying branch pipe B are connected, and the vent pipe is arranged between the emptying valve A and the emptying valve B; the first outlet switching pipeline comprises first outlet branch pipe A connected with the outlet of the drying tower A and first outlet branch pipe B connected with the outlet of the drying tower B, a first outlet valve A and a waste gas back flushing branch pipe A located in front of the valve are arranged on the first outlet branch pipe A, a first outlet valve B and a waste gas back flushing branch pipe B located in front of the valve are arranged on the first outlet branch pipe B, the first outlet branch pipe A and the first outlet branch pipe B are connected, the inlet pipe of the second filter is arranged between the first outlet valve A and the first outlet valve B, a waste gas back flushing valve A is arranged on the waste gas back flushing branch pipe A, a waste gas back flushing valve B is arranged on the waste gas back flushing branch pipe B, the waste gas back flushing branch pipe A and the waste gas back flushing branch pipe B are connected, and the waste gas back flushing pipe is arranged between the waste gas back flushing valve A and the waste gas back flushing valve B. the first outlet switching pipeline further comprises a waste gas back flushing switching pipe connecting the drying tower A and the drying tower B, and a waste gas back flushing switching valve is arranged on the waste gas back flushing switching pipe. the adsorption tower unit comprises adsorption tower A and adsorption tower B connected in parallel; 3. The comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen generating device according to claim 2, characterized in that: ​ 4. The comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen generating device according to claim 1, characterized in that: ​ The second inlet switching pipeline comprises a second air inlet branch A connected with the air tank outlet pipe and a second air inlet branch B, the second air inlet branch A is connected with the inlet of the adsorption tower A, the second air inlet branch A is provided with a second air inlet valve A and a recovery branch A behind the valve, the second air inlet branch B is connected with the inlet of the adsorption tower B, the second air inlet branch B is provided with a second air inlet valve B and a recovery branch B behind the valve, the recovery branch A is provided with a recovery valve A, the recovery branch B is provided with a recovery valve B, the recovery branch A and the recovery branch B are connected, and the recovery pipe is arranged between the recovery valve A and the recovery valve B; The second outlet switching pipeline comprises a second air outlet branch A connected with the outlet of the adsorption tower A and a second air outlet branch B connected with the outlet of the adsorption tower B, the second air outlet branch A is provided with a second air outlet valve A and a nitrogen back flushing branch A in front of the valve, the second air outlet branch B is provided with a second air outlet valve B and a nitrogen back flushing branch B in front of the valve, the second air outlet branch A and the second air outlet branch B are connected, the inlet pipe of the nitrogen tank is arranged between the second air outlet valve A and the second air outlet valve B, the nitrogen back flushing branch A is provided with a nitrogen back flushing valve A, the nitrogen back flushing branch B is provided with a nitrogen back flushing valve B, the nitrogen back flushing branch A and the nitrogen back flushing branch B are connected, and the nitrogen back flushing pipe is arranged between the nitrogen back flushing valve A and the nitrogen back flushing valve B.

5. The comprehensive recycling system for waste gas of pressure swing adsorption nitrogen making device according to claim 4, characterized in that: The second outlet switching pipeline further comprises a nitrogen back flushing switching pipe connecting the adsorption tower A and the adsorption tower B, and the nitrogen back flushing switching pipe is provided with a nitrogen back flushing switching valve.

6. The comprehensive recycling system for waste gas of a pressure swing adsorption nitrogen generating device according to claim 1, characterized in that: The gas pressure in the waste gas tank is 0.6-0.7 MPa, and the oxygen content is 35-40%.

7. The comprehensive recycling system for waste gas of pressure swing adsorption nitrogen generating device according to claim 1, characterized in that: The air inlet pipe of the boiler is provided with a blower, and the oxygen-rich waste gas pipe is provided with a first pressure reducing valve.

8. The comprehensive recycling system for waste gas of pressure swing adsorption nitrogen generating device according to claim 1, characterized in that: The waste gas back flushing pipe is provided with a second pressure reducing valve, and the gas pressure after the second pressure reducing valve is 0.1 MPa.

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