Selection of materials for hydrogen production equipment

2 Pipeline material selection for the main parts of the hydrogen production unit 2.1 Feeding system Commonly used raw materials for hydrogen production units include natural gas, refinery exhaust gas, liquefied petroleum gas and light oil (such as naphtha). Due to different sources of raw materials, they generally contain more or less sulfide. The pipelines of the feeding system are basically corrosion-free due to the low operating temperature and operating pressure of the medium. The main material of the pipelines is generally 20-gauge carbon steel. Due to the presence of hydrogen, post-weld heat treatment must be performed to eliminate residual stress, and the hardness value should be lower than HB200. 2.2 Desulfurization section The raw gas entering the desulfurization section is preheated to about 380°C by the raw gas preheating furnace with a pressure of about 1.85MPa. It enters the hydrogenation reactor to react, converting the organic sulfur compounds into hydrogen sulfide and then enters the zinc oxide desulfurization reactor to be removed, and then enters the conversion section. The pipes from the outlet of the raw gas preheating furnace to the entrance of the hydrogenation reactor - desulfurization reactor - reformer are in direct contact with hydrogen, so some pipes should be made of hydrogen-resistant steel based on operating temperature, hydrogen partial pressure and other conditions. Since the refined gas contains very little sulfur, the corrosion caused by high-temperature H2+ H2s can be ignored. The main material of this part of the pipeline is generally CrSMo steel. Due to the presence of hydrogen, post-weld heat treatment is also required to eliminate residual stress. 2.3 The refined raw gas in the reforming part is mixed with self-produced 3.5MPa water vapor according to a certain water-to-carbon ratio, and is preheated to 500°C in the convection section of the reformer and enters the radiant section of the reformer. Under the action of the catalyst, a complex steam conversion reaction occurs. The entire reaction process is an endothermic reaction, and the required heat is provided by the reformer. After leaving the reforming furnace, the high-temperature reformed gas at 840°C undergoes heat exchange in the reformed gas steam generator, and then the temperature drops to 360°C and enters the medium-temperature conversion part. This part of the pipeline is the part that reaches the inlet of the intermediate shift reactor after heat exchange in the reformed gas steam generator. The operating temperature is 360°C and the pressure is 1.2MPa. The main pipe material is generally Cr5Mo. Due to the presence of hydrogen, post-weld heat treatment is also required to eliminate residual stress. 2.4 Transformation part The transformation gas from the transformation gas steam generator at about 360°C enters the medium temperature shift reactor, and a transformation reaction occurs under the action of the catalyst, reducing the CO content in the transformation gas to about 3%. The temperature of the medium variable gas is reduced to about 180℃ through the second boiler feed water heat exchanger, and then enters the low variable reactor. The temperature of the boiler feed water is reduced to about 150℃ through the first heat exchanger. It then passes through the deoxygenation steam generator and the desalted water preheater for heat exchange to recover most of the waste heat. It is cooled to 40℃ by the low variable gas air cooler and the low variable gas water cooler, and enters the PSA unit after water separation. The operating temperature of the pipe from the outlet of the intermediate reactor to the inlet of the second heat exchanger of the boiler feed water is 420°C and the pressure is 1.0MPa. Cr5Mo steel can generally be used for this part of the pipe. In the pipeline from the outlet of the second heat exchanger of the boiler feed water to the acid water stripper, the liquid generated after the condensation and cooling of carbon dioxide gas and water vapor forms carbon dioxide condensate, which is highly corrosive to carbon steel, so carbon steel cannot be used. According to its corrosion mechanism, 0Crl8Ni9 stainless steel is generally used as the main material of this part of the pipeline. 2.5 PSA unit After the low-variable gas from the gas generation unit with a pressure of about 2.5MPa (G) and a temperature of 40°C enters the boundary area, it enters the adsorption tower from the bottom of the tower. Under the sequential selective adsorption of a variety of adsorbents, almost all impurities except hydrogen are removed at one time to obtain product hydrogen with a purity greater than 99.9%. After being stabilized by the pressure regulating system, it is sent out of the device. The pipeline from the outlet of the last water distribution tank to the outlet of the PSA unit has low operating temperature, very little water content in the medium, and is basically non-corrosive. The main material of the pipeline is generally carbon steel. However, since the pipeline is subject to alternating pressure, its ability to resist fatigue damage must be verified. Generally, the design pressure of the hydrogen production PSA pipeline system is 2.5MPa, the design temperature is 40°C, the nominal diameter of the pipeline is DN150 (outer diameter is 168mm), the pipeline material is No. 20 steel, and the corrosion allowance is considered to be lmm. For the PSA system of the hydrogen production device, the frequency of medium pressure increase and decrease is generally once every 5 minutes, the annual start-up time is 8,000 hours, the design life is 10 years, and the annual start-up and shutdown are calculated as once. Then there are two cycles for the PSA pipeline system, and the foreseeable number of cycles of each cycle is: Normal boost and drop cycle: N1= (60/5)×8000×10=960000(times) ； Start shutdown cycle: N2=1 x 10=10 (times). Considering the instability of operation and the influence of factors such as temporary parking or accident parking, the maximum number of calculation cycles can be taken respectively: Normal boost and drop cycle: N1`=1.2N1=1.152×l000000(times) ； Start shutdown cycle: n2` =1．2N2=l2(times). The maximum allowable stress can be calculated according to the fatigue design curve. By substituting the maximum allowable stress into the pipeline component strength calculation formula, the required wall thickness of the pipeline and its components can be obtained. 2.6 Heat recovery and steam production system The desalted water from outside the device is preheated by the desalted water preheater and mixed with the purified water from the acid water stripping tower before entering the deaerator. After the deoxygenated water is boosted by the medium-pressure boiler feed water pump, it is preheated by the first boiler feed water preheater and the second boiler feed water preheater before entering the medium-pressure steam drum. The boiler water passes through the steam production section, water protection section and reforming gas steam generator of the reformer convection section through natural circulation to generate medium-pressure steam. The generated medium-pressure steam is superheated to 440°C in the steam superheating section of the convection section of the reformer and leaves the steam drum. Part of the steam is used as process steam ； The other part enters the medium-pressure steam pipe network of the entire plant. The main material of this part of pipelines whose design temperature is less than 425 aI= can generally be carbon steel. The main material of pipelines whose design temperature is greater than or equal to 425℃ can generally be made of heat-resistant steel, such as 15CrMo. This post was last edited by percy on 2007-11-21 19:58 ]

I just saw it today, thank you! :handshake

The outlet temperature of the conversion furnace is 420 degrees and the hydrogen partial pressure is 0.45mpa. Is it safe to use No. 20 steel?