Ortho-para hydrogen conversion process in liquid hydrogen production
Technical Field
The invention relates to a liquid hydrogen production process, in particular to an ortho-para hydrogen conversion process in the process of producing liquid hydrogen.
Background
The liquid hydrogen is a colorless and odorless transparent liquid liquefied from hydrogen, and is a mixture of parahydrogen (p-H2) and orthohydrogen (o-H2). Orthohydrogen and parahydrogen are two spin isomers of molecular hydrogen, and parahydrogen and orthohydrogen have the same chemical properties but different physical properties. At or above room temperature, the equilibrium composition ratio of normal to para-hydrogen is 75:25, referred to as normal hydrogen (n-H2) or normal hydrogen. At a temperature lower than the normal temperature, the equilibrium composition ratio of para-hydrogen to para-hydrogen changes, and the percentage of para-hydrogen increases. The normal-to-secondary conversion of gaseous hydrogen occurs in the presence of a catalyst, while liquid hydrogen spontaneously undergoes normal-to-secondary conversion in the absence of a catalyst, but at a slower rate. The positive and secondary hydrogen conversion is an exothermic reaction, and the heat evolved during the conversion is related to the temperature at which the conversion takes place. In order to reduce the evaporative loss of liquid hydrogen due to the exothermic heat of conversion of ortho-para-hydrogen, it is desirable that the para-hydrogen content of all liquid hydrogen products be at least 95% or greater, i.e., that essentially all ortho-hydrogen be catalytically converted to para-hydrogen upon liquefaction. However, the existing ortho-para hydrogen conversion process for producing liquid hydrogen cannot basically convert ortho-hydrogen in the liquid hydrogen into para-hydrogen, so that the concentration of para-hydrogen in the liquid hydrogen does not exceed 90%.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: it would be desirable to provide an ortho-para hydrogen conversion process for producing liquid hydrogen that increases the concentration of para-hydrogen in the liquid hydrogen.
In order to solve the problems, the technical scheme adopted by the invention is as follows: an ortho-para hydrogen conversion process for producing liquid hydrogen, characterized by: the process comprises the following steps: firstly, raw material hydrogen for preparing liquid hydrogen sequentially enters a heat exchange pipeline in a first heat exchanger and a heat exchange pipeline in a first reactor for heat exchange and cooling, the first heat exchanger and the first reactor adopt liquid nitrogen for heat exchange, then the raw material hydrogen sequentially enters a first absorber and a second absorber for adsorption cleaning of harmful gas impurities, and a catalyst for catalyzing the conversion of ortho-para hydrogen in a subsequent ortho-para hydrogen conversion pipeline is prevented from being poisoned by the harmful gas impurities; then the raw material hydrogen enters an ortho-para hydrogen conversion pipeline in the first reactor for heat exchange cooling and primary conversion of gaseous hydrogen ortho-para hydrogen; then the raw material hydrogen enters a heat exchange pipeline in the first reactor for heat exchange and cooling; then the raw material hydrogen sequentially enters heat exchange pipelines in a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger, a sixth heat exchanger and a second reactor for heat exchange, cooling and liquefaction, liquid hydrogen obtained through cooling and liquefaction enters an ortho-para hydrogen conversion pipeline in the second reactor for liquid hydrogen ortho-para hydrogen secondary conversion through a catalyst, and the second reactor also adopts liquid nitrogen for heat exchange.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the process steps further comprise: circulating hydrogen enters a first heat exchanger and a heat exchange pipeline in a first reactor for heat exchange and cooling after being pressurized by a pressurization pipeline, and then enters a third adsorber for adsorption cleaning of impurities; then the circulating hydrogen enters a second heat exchanger for heat exchange and cooling, and then the circulating hydrogen is divided into two parts, namely: the first part of circulating hydrogen enters a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger and a sixth heat exchanger in sequence for heat exchange and cooling, and then the first part of circulating hydrogen enters a second reactor to provide cold energy for the second reactor; the first part of circulating hydrogen is discharged from the second reactor and then sequentially enters a sixth heat exchanger, a fifth heat exchanger, a fourth heat exchanger, a third heat exchanger, a second heat exchanger and a first heat exchanger to provide cold energy for each heat exchanger; the second part of circulating hydrogen enters a first turbine expansion unit to be subjected to hydrogen compression and expansion throttling, so that the second part of circulating hydrogen is cooled, and then the second part of circulating hydrogen enters a fourth heat exchanger to provide cold energy for the fourth heat exchanger; then the second part of the circulating hydrogen enters a second turbine expansion unit for hydrogen compression, expansion and throttling, so that the second part of the circulating hydrogen is cooled; then the second part of circulating hydrogen sequentially enters a fifth heat exchanger, a fourth heat exchanger, a third heat exchanger, a second heat exchanger and a first heat exchanger to provide cold energy for each heat exchanger; the first part of circulating hydrogen and the second part of circulating hydrogen provide cold energy for the first heat exchanger and then flow together into a pressurization pipeline, so that one cycle is completed; then the circulating hydrogen is pressurized by a pressurization pipeline and then continuously circulated.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the first heat exchanger, the first reactor, the first absorber, the second absorber and the third absorber are integrated in a first-stage hydrogen liquefaction cold box.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the second heat exchanger, the third heat exchanger, the fourth heat exchanger, the fifth heat exchanger, the sixth heat exchanger and the second reactor are integrated in the second-stage hydrogen liquefaction cold box.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the flow rate of raw material hydrogen at the inlet of an ortho-para hydrogen conversion pipeline of the first reactor is 240-265 kg/h, the pressure is 1.95-2.15 MPa, the temperature is 97-107K, and the flow resistance is not more than 57-63 kPa; the temperature of the raw material hydrogen at the outlet of the normal-para hydrogen conversion pipeline of the first reactor is 77-85K, and the concentration of para-hydrogen in the raw material hydrogen is not lower than 46.3%.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the flow rate of raw material hydrogen at the inlet of an ortho-para hydrogen conversion pipeline of the second reactor is 240-265 kg/h, the pressure is 0.228-0.252 MPa, the temperature is 22.42-24.78K, the steam content is 12.54-13.86%, and the flow resistance is not more than 12.35-13.65 kPa; the concentration of parahydrogen in the raw material hydrogen at the outlet of the normal-parahydrogen conversion pipeline of the second reactor is not lower than 98 percent.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the flow rate of a circulating hydrogen inlet in a heat exchange pipeline of the first reactor is 1558-1722 kg/h, the pressure is 1.95-2.15 MPa, the temperature is 97-107K, and the flow resistance is not more than 57-63 kPa.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the power of a first reactor unit is 140.2-155 kW, the heat conversion of raw material hydrogen in the first reactor is not more than 10.2-11.2 kW, the average integrated temperature head difference is not less than 7.315-8.085K, the liquid nitrogen saturation pressure is 0.1235-0.1365 MPa, the liquid nitrogen pressure in a first reactor shell is 0.11875-0.13125 MPa, the boiling point of the liquid nitrogen in the shell is not more than 75.24-83.16K, the liquid nitrogen consumption is 2584-2856 kg/h, and no nitrogen steam is overheated in the reactor shell.
Further, the foregoing n-para hydrogen conversion process in producing liquid hydrogen, wherein: the power of a second reactor unit is 30.02-33.18 kW, the heat conversion of raw material hydrogen in the second reactor is not more than 24.7-27.3 kW, the average integrated temperature difference is not less than 2.02-2.23K, the pressure of liquid nitrogen in a shell of the second reactor is 0.11875-0.13125 MPa, the boiling point of the liquid nitrogen in the shell is not more than 20-22.1K, the consumption of the liquid nitrogen is 300-330 kg/h, and no nitrogen vapor is overheated in the shell of the reactor.
The invention has the advantages that: the ortho-para hydrogen conversion process for producing liquid hydrogen can ensure that the concentration of para-hydrogen in the liquid hydrogen is not less than 98 percent, and can save energy after circulating by utilizing the circulating hydrogen.
Drawings
FIG. 1 is a process flow diagram of an ortho-para hydrogen conversion process for producing liquid hydrogen in accordance with the present invention.
Detailed Description
The present invention will be described in further detail below with reference to specific embodiments and the attached drawings.
As shown in FIG. 1, the process for converting ortho-para hydrogen in the production of liquid hydrogen comprises the following steps: firstly, raw material hydrogen for preparing liquid hydrogen sequentially enters heat exchange pipelines in a first heat exchanger 1 and a first reactor 2 through a raw material hydrogen pipeline 91 for heat exchange and cooling, the first heat exchanger 1 and the first reactor 2 adopt liquid nitrogen for heat exchange, then the raw material hydrogen sequentially enters a first adsorber 21 and a second adsorber 22 for adsorption and cleaning of harmful gas impurities, and a catalyst for catalyzing normal-secondary hydrogen conversion in a subsequent normal-secondary hydrogen conversion pipeline is prevented from being poisoned by the harmful gas impurities; then the raw material hydrogen enters an ortho-para hydrogen conversion pipeline 23 in the first reactor 2 for heat exchange and cooling and primary conversion of gaseous hydrogen ortho-para hydrogen is carried out through a catalyst; then the raw material hydrogen enters a heat exchange pipeline in the first reactor 2 for heat exchange and cooling; then the raw material hydrogen sequentially enters heat exchange pipelines in a second heat exchanger 3, a third heat exchanger 4, a fourth heat exchanger 5, a fifth heat exchanger 6, a sixth heat exchanger 7 and a second reactor 8 for heat exchange, cooling and liquefaction, and liquid hydrogen obtained through cooling and liquefaction enters an ortho-para hydrogen conversion pipeline 81 in the second reactor 8 for liquid hydrogen ortho-para hydrogen secondary conversion through a catalyst.
The raw material hydrogen can be better converted into the ortho-para hydrogen after being subjected to heat exchange and cooling for many times, and the raw material hydrogen is subjected to primary conversion of the gaseous hydrogen ortho-para hydrogen in a gaseous state and secondary conversion of the liquid hydrogen ortho-para hydrogen in a liquid state, so that the ortho-hydrogen in the raw material hydrogen can be converted into the para-hydrogen to the greatest extent.
The first and second reactors 2 and 8 are all multi-airflow sinking type tube shell equipment, the normal-secondary hydrogen conversion pipelines in the first and second reactors 2 and 8 respectively comprise a section of spiral curled heat exchange tube and a section of straight heat exchange tube, the spiral curled heat exchange tube is sleeved on the outer side of the straight heat exchange tube, and a catalyst capable of catalyzing the conversion of hydrogen normal-secondary hydrogen is arranged in the straight heat exchange tube. The outlets of the normal-secondary hydrogen conversion pipelines in the first reactor 2 and the second reactor 8 are respectively provided with a metal filter element capable of filtering hydrogen and preventing a catalyst from flowing out, the filtering precision of the metal filter element in the first reactor 2 is not more than 40 micrometers, the filtering precision of the metal filter element in the second reactor 8 is not more than 10 micrometers, and the two metal filter elements can be externally heated/precooled and can also clean the surface through back flushing. The hydrogen can exchange heat with liquid nitrogen in the shell in the spiral curling heat exchange tube, so that cold energy is provided for hydrogen liquefaction, and the spiral curling heat exchange tube can increase the heat exchange area of the hydrogen and the liquid nitrogen, so that the hydrogen can be cooled more quickly; then the hydrogen gas can carry out ortho-para hydrogen conversion in the straight heat exchange tube, and simultaneously can carry out heat exchange with liquid nitrogen, so that hydrogen cooling and ortho-para hydrogen conversion are synchronously carried out, heat generated in the ortho-para hydrogen conversion process is absorbed, and the problem of temperature maintenance in the ortho-para hydrogen conversion process is solved.
In addition, the process steps further comprise: circulating hydrogen is pressurized by a pressurizing pipeline 11 and then sequentially enters heat exchange pipelines in a first heat exchanger 1 and a first reactor 2 through a circulating hydrogen pipeline 92 for heat exchange and cooling, and then enters a third adsorber 24 for adsorption cleaning of impurities; then the circulating hydrogen enters a second heat exchanger 3 for heat exchange and cooling, and then the circulating hydrogen is divided into two parts, namely: the first part of circulating hydrogen and the second part of circulating hydrogen enter a third heat exchanger 4, a fourth heat exchanger 5, a fifth heat exchanger 6 and a sixth heat exchanger 7 in sequence for heat exchange and cooling, and then the first part of circulating hydrogen enters a second reactor 8 to provide cold energy for the second reactor 8; after the first part of circulating hydrogen comes out of the second reactor 8, the first part of circulating hydrogen can sequentially enter a sixth heat exchanger 7, a fifth heat exchanger 6, a fourth heat exchanger 5, a third heat exchanger 4, a second heat exchanger 3 and a first heat exchanger 1 due to low temperature so as to provide cold energy for each heat exchanger; the second part of the circulating hydrogen enters the first turbo-expander set 12 for hydrogen compression, expansion and throttling, so that the second part of the circulating hydrogen is cooled, and then the second part of the circulating hydrogen enters the fourth heat exchanger 5 to provide cold energy for the fourth heat exchanger 5; then the second part of the circulating hydrogen enters a second turbine expansion unit 13 for hydrogen compression, expansion and throttling, so that the second part of the circulating hydrogen is cooled, and the turbine expansion unit is a device capable of cooling gas by utilizing the throttling expansion principle; then the second part of circulating hydrogen sequentially enters a fifth heat exchanger 6, a fourth heat exchanger 5, a third heat exchanger 4, a second heat exchanger 3 and a first heat exchanger 1 to provide cold energy for each heat exchanger; the first part of circulating hydrogen and the second part of circulating hydrogen provide cold energy for the first heat exchanger 1 and then converge into the booster pipeline 11, so that one cycle is completed; the circulating hydrogen is then pressurized by the pressurizing line 11 and then continuously circulated.
The circulating hydrogen is usually the evaporation gas generated by the evaporation of the liquid hydrogen in the storage tank, and the evaporation gas is used as the circulating hydrogen, so that on one hand, the evaporation gas can be recovered, the hydrogen is saved, on the other hand, the circulating hydrogen can provide cold energy for the system after circulation, particularly, the cold energy is provided for the second reactor 8, the normal operation of the second reactor 8 is ensured, and the secondary conversion of the liquid hydrogen n-para-hydrogen is better completed.
In this embodiment, the first heat exchanger 1, the first reactor 2, the first adsorber 21, the second adsorber 22, and the third adsorber 24 are integrated in the first-stage hydrogen liquefaction cold tank. The second heat exchanger 3, the third heat exchanger 4, the fourth heat exchanger 5, the fifth heat exchanger 6, the sixth heat exchanger 7 and the second reactor 8 are integrated in a secondary hydrogen liquefaction cold box.
In the embodiment, the flow rate of the raw material hydrogen at the inlet of the normal-secondary hydrogen conversion pipeline 23 of the first reactor 2 is 240-265 kg/h, the pressure is 1.95-2.15 MPa, the temperature is 97-107K, and the flow resistance is not more than 57-63 kPa; the temperature of the raw material hydrogen at the outlet of the normal-para hydrogen conversion pipeline 23 of the first reactor 2 is 77-85K, and the concentration of para-hydrogen in the raw material hydrogen is not lower than 46.3%.
The flow rate of raw material hydrogen at the inlet of an ortho-para hydrogen conversion pipeline 81 of the second reactor 8 is 240-265 kg/h, the pressure is 0.228-0.252 MPa, the temperature is 22.42-24.78K, the steam content is 12.54-13.86%, and the flow resistance is not more than 12.35-13.65 kPa; the concentration of parahydrogen in the raw material hydrogen at the outlet of the normal-parahydrogen conversion line 81 of the reactor II 8 is not less than 98%.
The flow rate of a circulating hydrogen inlet in a heat exchange pipeline of the first reactor 2 is 1558-1722 kg/h, the pressure is 1.95-2.15 MPa, the temperature is 97-107K, and the flow resistance is not more than 57-63 kPa.
The power of the unit of the first reactor 2 is 140.2-155 kW, the heat conversion of raw material hydrogen in the first reactor 2 is not more than 10.2-11.2 kW, the average integrated temperature difference is not less than 7.315-8.085K, the saturation pressure of liquid nitrogen is 0.1235-0.1365 MPa, the pressure of liquid nitrogen in the shell of the first reactor 2 is 0.11875-0.13125 MPa, the boiling point of the liquid nitrogen in the shell is not more than 75.24-83.16K, the consumption of the liquid nitrogen is 2584-2856 kg/h, and no nitrogen vapor is overheated in the shell of the reactor.
The unit power of the second reactor 8 is 30.02-33.18 kW, the heat conversion of the raw material hydrogen in the second reactor 8 is not more than 24.7-27.3 kW, the average integrated temperature difference is not less than 2.02-2.23K, the liquid nitrogen pressure in the shell of the second reactor 8 is 0.11875-0.13125 MPa, the boiling point of the liquid nitrogen in the shell is not more than 20-22.1K, the consumption of the liquid nitrogen is 300-330 kg/h, and no nitrogen vapor is overheated in the shell of the reactor.