An open cycle hydrogen recovery process

Abstract

The application discloses a kind of open loop hydrogen recovery methods, comprising the following steps: workpiece is placed on tool fixture, valve 1 is opened, workpiece inside is evacuated;Valve 4 is opened, and workpiece is filled with nitrogen hydrogen mixed gas;Workpiece is subjected to vacuum hydrogen leak detection;Valve 2 is opened, and nitrogen hydrogen mixed gas in workpiece is recovered to recovery cylinder;Valve 3 is opened, and workpiece pressure is released to atmospheric pressure;Workpiece is taken out, and put into next workpiece to be detected, and steps one to five are repeated, wherein gas in recovery cylinder is filled first in step two.The application better reduces the consumption of nitrogen hydrogen mixed gas in leak detection process during workpiece leak detection, greatly reduces economic cost, and has good economic effect and environmental protection and energy saving effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen leak detection, and particularly relates to an open-loop hydrogen recovery method. BACKGROUND

[0002] Hydrogen is a non-toxic and odorless fuel that is easy to store and transport, and can be widely used in petrochemical, pharmaceutical, chemical, metallurgical and other fields. Hydrogen recovery technology refers to a series of processes of treating, separating and recovering hydrogen-containing compounds in industrial waste gas to obtain high-purity hydrogen and reduce the emission of gas pollutants. Hydrogen recovery is an important measure to promote environmental protection and energy transformation in China. However, due to the uncontrollable concentration of hydrogen, safety problems are easily caused, and it is not suitable for closed-loop recovery. Helium is generally recovered in a closed loop, but the price of 5% hydrogen mixed with helium is only 1 / 20 of the price of helium. With the expansion of user capacity, the consumption of hydrogen increases dramatically, and the use cost of hydrogen detection equipment also increases exponentially. In order to reduce the use cost, it is necessary to recover part of the hydrogen to achieve cost reduction and efficiency improvement.

[0003] At present, common hydrogen recovery and utilization technologies include: hydrogen reuse, which adds discharged hydrogen into the hydrogenation system for utilization, thereby reducing the energy consumption and cost of the hydrogenation system; hydrogen storage, which stores discharged hydrogen for subsequent utilization. Storage methods include compressed hydrogen storage, liquid hydrogen storage, etc.; fuel cell power generation, which uses hydrogen as fuel to generate electricity through fuel cells. This method not only realizes the recovery and utilization of hydrogen, but also generates electricity and heat, which is efficient and clean; hydrogen recovery device, which recovers and utilizes discharged hydrogen through a hydrogen recovery device. Common hydrogen recovery devices include hydrogen recovery membrane technology, adsorption method, compressed adsorption method, etc.

[0004] The advantage of hydrogen recovery technology is that it can recover hydrogen, reduce gas emission and reduce environmental pollution. However, it also faces some challenges in the implementation process, such as the stability of the catalyst, the hydrogen recovery rate, hydrogen storage and transportation, etc. In addition, the hydrogen recovery technology generally has the problems of high cost and low efficiency in the application process.

[0005] The explosion limit of hydrogen is 4.0% to 75.6% (volume concentration), and the vacuum leak detection industry generally uses 5% hydrogen + 95% nitrogen mixed gas as tracer gas, also known as safety gas. During the hydrogen recovery process, air is mixed, the hydrogen concentration gradually decreases, which will affect the leak detection accuracy or product leak detection, and the air concentration in the system will increase. If it exceeds the safe concentration range, an explosion accident will occur. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide an open-loop hydrogen recovery method. In order to achieve the above purpose, the present application adopts the following technical solutions:

[0007] A method for recovering hydrogen in an open loop, comprising the following steps:

[0008] Step 1: placing a workpiece on a fixture, opening valve 1, and evacuating the interior of the workpiece;

[0009] Step 2: opening valve 4, and filling the workpiece with a nitrogen-hydrogen mixed gas;

[0010] Step 3: performing a vacuum hydrogen leak detection on the workpiece;

[0011] Step 4: opening valve 2, and recovering the nitrogen-hydrogen mixed gas in the workpiece to a recovery cylinder;

[0012] Step 5: opening valve 3, and releasing the pressure of the workpiece to atmospheric pressure;

[0013] Step 6: removing the workpiece, and placing a next workpiece to be detected, and repeating steps 1-5, wherein the gas in the recovery cylinder is first filled in step 2.

[0014] As a preferred mode, the interior of the workpiece is evacuated to 1000 Pa in step 1.

[0015] As a preferred mode, the nitrogen-hydrogen mixed gas filled in step 2 has a concentration of 5%, and the pressure of the workpiece is filled to 0.9 MPa.

[0016] As a preferred mode, the pressure in the workpiece is 0.15 Pa after the recovery of the nitrogen-hydrogen mixed gas in the workpiece is completed in step 4.

[0017] As a preferred mode, there are 6 workpieces in each cycle in step 6.

[0018] Further preferably, the maximum amount of air mixed in each cycle is 6000 PaL.

[0019] The present application has the following advantages:

[0020] In the case of direct discharge, the average gas consumption per workpiece detected is 0.9 MPa x 1 L = 0.9 MPaL = 9 atmL, and the number of workpieces that can be detected per bottle (40 L, 10 MPa) of nitrogen-hydrogen mixed gas is 5000 atmL / 9 = 555 pieces; while using the present application, the average gas consumption per workpiece detected is (5 x 0.15 x 1 L + 0.9 x 1 L) / 6 = 0.275 MPaL = 2.75 atmL, and the number of workpieces that can be detected per bottle of nitrogen-hydrogen mixed gas is 5000 atmL / 2.75 = 1818 pieces. It can be seen that the present application better reduces the consumption of nitrogen-hydrogen mixed gas during the leak detection process, greatly reduces the economic cost, and has good economic and environmental and energy-saving effects. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The present application is illustrated by the following figures.

[0022] The present application is described in detail below with reference to the accompanying drawings.

[0023] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. Embodiment:

[0024] A method for recovering hydrogen in an open loop, comprising the following steps:

[0025] Step one: place the workpiece on the fixture, open valve 1, and evacuate the inside of the workpiece to 1000 Pa;

[0026] Step two: open valve 4, fill the workpiece with 5% nitrogen-hydrogen mixed gas, and the pressure of the workpiece is filled to 0.9 MPa.

[0027] Step three: vacuum hydrogen leak detection is performed on the workpiece.

[0028] Step four: open valve 2, recover the nitrogen-hydrogen mixed gas in the workpiece to the recovery cylinder, and after the recovery is completed, the pressure in the workpiece is 0.15 Pa.

[0029] Step five: open valve 3, and release the pressure of the workpiece 1 to atmospheric pressure.

[0030] Step six: take out the workpiece and put in the next workpiece to be detected, and repeat steps one to five, wherein the gas in the recovery cylinder is filled first in step two.

[0031] After the inside of the workpiece is evacuated and then filled with gas, the concentration change can be calculated according to the ratio of the residual air pressure in the workpiece after each evacuation to the gas pressure filled into the workpiece. When the gas in the recovery cylinder is filled, the gas concentration can be controlled.

[0032] In the above steps, every 6 workpieces is a cycle, and in the cycle of every 6 workpieces, the maximum air volume mixed under the condition that the workpiece is pre-evacuated to 1000 Pa and the internal volume of the workpiece is 1 L is 1 L x 1000 Pa x 6 = 6000 PaL.

[0033] When the 6th workpiece is leak tested, the air in the mixed gas in the workpiece accounts for 6000 PaL / 900000 PaL = 0.67% < 4%, and at this time the mixed gas in the 6th workpiece is a safe gas.

[0034] According to the mixed amount of air each time, the hydrogen concentration reduction value and whether the air proportion in the mixed gas exceeds the safety value can be calculated. For safety, all of them are discharged after 6 cycles of recovery, and a new round of recovery is carried out.

[0035] The application is not limited to the foregoing specific embodiments. The application extends to any novel one, or any new combination, of the characteristics disclosed in this specification, and to any novel method or process disclosed, or any new combination of steps of any disclosed method or process.

Claims

1. An open-loop hydrogen recovery method, characterized in that, Includes the following steps: Step 1: Place the workpiece on the tooling fixture, open valve 1, and evacuate the inside of the workpiece to 1000Pa; Step 2: Open valve 4 to fill the workpiece with a nitrogen-hydrogen mixed gas with a concentration of 5%, and pressurize the workpiece to 0.9 MPa; Step 3: Perform vacuum hydrogen leak detection on the workpiece; Step 4: Open valve 2 to recover the nitrogen-hydrogen mixed gas in the workpiece to the recovery cylinder. After the recovery is completed, the pressure inside the workpiece is 0.15 Pa. Step 5: Open valve 3 to release the workpiece pressure to atmospheric pressure; Step 6: Remove the workpiece, place the next workpiece to be tested, and repeat steps 1 to 5. In step 2, the gas in the recovery cylinder is first filled. Every 6 workpieces constitute one cycle, and the maximum amount of air mixed in during each cycle is 6000 PaL.

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