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CN-119574828-B - Distributed measurement method and device for hydrocarbon fuel cracking component content

CN119574828BCN 119574828 BCN119574828 BCN 119574828BCN-119574828-B

Abstract

The invention discloses a distributed measurement method for the pyrolysis component content of hydrocarbon fuel, which comprises the steps of pumping target substances into a reaction tube and heating the target substances to a target temperature required by pyrolysis, monitoring relevant parameters in real time, cooling and collecting gas-phase and liquid-phase substances of the target substances after pyrolysis in real time, analyzing the component distribution of the target substances after pyrolysis in online to obtain the component distribution of the target substances after pyrolysis at different temperatures, changing the pressure, continuing the steps to obtain the component distribution of the target substances after pyrolysis at different pressures, and respectively obtaining the conversion rate of the target substances and the distribution of the component content along the reaction tube based on the different temperatures and the component distribution of the target substances after pyrolysis at different pressures. The invention also discloses a device adopting the method. The method and the device realize the accurate measurement of the conversion rate of the distributed fuel and the content of each component.

Inventors

  • Shao Chongkun
  • WANG PEILUN
  • MI JI
  • JIANG PENGFEI
  • GUO YONGSHENG
  • FANG WENJUN

Assignees

  • 浙江大学

Dates

Publication Date
20260508
Application Date
20241118

Claims (8)

  1. 1. A distributed measurement method for hydrocarbon fuel cracking component content, characterized in that the distributed measurement method comprises: (1) Pumping a target substance into a reaction tube, and applying stable heat flux density to the reaction tube by using a direct current power supply to heat the target substance to a target temperature required by thermal cracking, wherein the flow rate of the target substance pumped into the reaction tube is 0.1-10 g/s or 1-1000 ml/s; (2) Monitoring the temperature change of the inlet and outlet of the target substance in real time the temperature of the wall surface of the reaction tube the system pressure at two ends of the reaction tube; (3) Cooling and collecting gas-phase and liquid-phase substances of target substances after thermal cracking in real time; (4) Analyzing the composition distribution of the target substance after thermal cracking by gas chromatography and gas chromatography-mass spectrometry on line to obtain the composition distribution of the target substance after thermal cracking at different temperatures; (5) When the reaction tube is cooled to room temperature, changing the pressure, and continuing the steps (1) - (4) to obtain the component distribution of the target substance after thermal cracking under different pressures; (6) Based on the component distribution of target substances under different temperatures and different pressures after thermal cracking, respectively obtaining functions of the conversion rate of the target substances and the component content along with the temperature change, and further respectively obtaining the distribution conditions of the conversion rate of the target substances and the component content along the reaction tube; In the step (6), the function of the conversion rate of the target substance along the reaction tube is alpha (T), the function of the content of each component along the reaction tube is M i (T), the reaction tube is divided into n micro-elements in advance, the temperature distribution of the target substance along the reaction tube is calibrated according to the temperature-heat sink function, the distribution condition of the conversion rate of the target substance along the reaction tube is alpha -1 (T) assuming that the target substance is isothermal inside each micro-element and the correlation between the thermal cracking and the reaction time is negligible, and the distribution condition of the content of each component along the reaction tube is M i -1 (T).
  2. 2. The distributed measurement method for hydrocarbon fuel cracking component content according to claim 1, wherein in step (1), the target substance is selected from one or a combination of at least two of alkane, alkene, cycloalkane, cycloalkene or aromatic hydrocarbon.
  3. 3. The distributed measurement method for hydrocarbon fuel cracking component content according to claim 1, wherein in step (1), the inside diameter of the reaction tube is 1-6 mm, the length of the reaction tube is 0.5-1.0 m, the heat flux density of the direct current stabilized power supply applied to the target substance is 0-1×10 6 W/m 2 , the temperature rising rate is 5-25K/min, and the target temperature required for thermal cracking is 773-1073K.
  4. 4. The method for measuring the cracking component content of hydrocarbon-oriented fuel according to claim 1, wherein in the step (3), the gaseous phase of the target material after thermal cracking contains hydrogen, an alkane compound, an alkene compound, and an alkyne compound, and the liquid phase of the target material after thermal cracking contains an alkane compound, an alkene compound, a cycloalkane compound, a cycloalkene compound, and an aromatic compound.
  5. 5. The method for distributed measurement of hydrocarbon fuel cracking component content according to claim 1, characterized in that said method comprises: (7) And (3) carrying out an accuracy verification experiment of the conversion rate of the target substance and the component content in the along-path distribution condition of the reaction tube, namely changing the length of the reaction tube, maintaining the same flow heat exchange characteristics of each group, and continuing the steps (1) - (5) to obtain the fuel conversion rate and the component distribution of the target substance after thermal cracking under the condition of different tube lengths.
  6. 6. The distributed measurement method for the cracking component content of hydrocarbon fuel according to claim 5, wherein the same flow heat exchange characteristic of the target substance is that the heat flux density of the direct current stabilized power supply applied to each reaction tube is the same, and under the same heat flux density condition, the error between the wall surface temperature distribution of x m reaction tubes and the wall surface temperature distribution of 1m reaction tubes at 0-x m is less than 1.0%.
  7. 7. The method for measuring the cracking component content of hydrocarbon fuel according to claim 5, wherein the principle of accuracy verification is that under the same heat flux density condition, the gas and liquid phase substance temperature and content distribution at the outlet end of the x m reaction tube is regarded as the gas and liquid phase substance temperature and content distribution reference value of the 1m reaction tube at x m.
  8. 8. A distributed measurement device employing the method of any one of claims 5-7, wherein the measurement device comprises: The high-pressure constant flow pump is used for stably pumping target substances to the reaction tube, the liquid flowmeter is used for monitoring the mass flow of the target substances and the mass flow of liquid substances in real time, the gas flowmeter is used for monitoring the mass flow of the gas substances in real time, the direct-current constant-voltage power supply is used for inputting stable heat flow density into the reaction tube, the reaction tube is used for thermal cracking of the target substances, the thermocouple is used for monitoring the temperature of a fluid outlet in real time, the infrared thermal imager is used for monitoring the temperature of the wall surface of the reaction tube in real time, the pressure sensor is used for monitoring the pressure of a system in real time, the back pressure valve is used for providing stable system pressure, the condensing tube is used for rapidly cooling the gas-liquid substances of the target substances after thermal cracking, the gas-liquid separation storage tank is used for separating the gas-liquid substances of the target substances after thermal cracking, the gas chromatograph and the gas-liquid mass spectrometer is used for analyzing the composition of the gas-liquid substances of the target substances after thermal cracking, and the waste gas-liquid recovery device is used for recovering the cracked gas and the cracked liquid of the target substances; and the industrial personal computer is used for executing the step (6) and the step (7).

Description

Distributed measurement method and device for hydrocarbon fuel cracking component content Technical Field The invention relates to the fields of thermodynamics, thermochemistry and supercritical fluid of hydrocarbon fuels, in particular to a distributed measurement method and device for the cracking component content of hydrocarbon fuels. Background The scramjet engine is the main power component of hypersonic aircraft. Under the combined action of fuel combustion and heat release and pneumatic heating in the flight process, the surface temperature of the engine is increased sharply, and great risks are brought to safe and stable operation of the aircraft. The active regeneration cooling technology adopting the endothermic hydrocarbon fuel as the combustible coolant is a key for effectively cooling and thermally protecting the key parts of the engine so as to ensure the safe operation of the aircraft. As hypersonic aircraft mach numbers increase further, the cooling requirements of the engines continue to increase, requiring further cracking of the hydrocarbon fuel to release more chemical heat sinks. However, a great amount of coking precursors are generated by the secondary reaction of hydrocarbon fuel cracking products, and the coking precursors accumulate on the wall surfaces of the cooling channels to generate coking, so that the heat exchange performance of the regenerative cooling system is affected, and the cooling channels are blocked when serious, so that the regenerative cooling system is disabled. Therefore, the cracking degree and the fuel composition change of the hydrocarbon fuel in the pipeline are clarified, and the method has important significance for researching the flow state, the convective heat transfer mechanism, the mass transfer characteristic and the thermochemical reaction mechanism of the hydrocarbon fuel. Since the fuel thermal cracking process can be deconstructed into an infinite number of continuous micro-reactions under different fuel conversion rates, jiang Peixue and the like establish an integral differential reaction (DGR) model with variable stoichiometric coefficients by means of fluid dynamics simulation means and successfully predict the flow heat transfer process and thermal cracking reaction of n-decane. The DGR model determines the stoichiometry of each component based on the mass/mole fraction of each component in the n-decane thermal cracking experiment and accounts for the secondary reaction of the partially cracked product. For the n-decane thermal cracking experiments with fuel conversion lower than 24.2%, the prediction error of the model on the mass fraction of cracked products is lower than that of the model 4.2%（Jiang P, Wang Y, Zhu Y. Differential Global Reaction Model with Variable Stoichiometric Coefficients for Thermal Cracking of n-Decane at Supercritical Pressures[J]. Energy & Fuels, 2019, 33, 7244-7256.）. Zhang Dingrui, et al, developed a thermal cracking experiment of n-dodecane under supercritical pressure, and divided the thermal cracking of n-dodecane into three stages according to the cracking depth, namely primary cracking, secondary cracking and deep cracking. For the primary cracking stage with fuel conversion below 13%, the pen builds one-step global reaction kinetics to establish the primary cracking product mass fraction as a function of fuel conversion. For the secondary cracking stage, the pen further considers thermal decomposition of paraffins, olefins and formation of monocyclic aromatics and cycloolefins. The three-dimensional numerical model covering fuel flow heat exchange and thermal cracking reaction is established based on the component content of each cracking product in the primary cracking and secondary cracking stages. The predicted values of the fuel outlet temperature, the conversion rate and the pyrolysis product distribution are well matched with the experimental results, and the reliability of the three-dimensional numerical model of primary and secondary thermal cracking of n-dodecane is verified （Zhang D, Hou L, Gao M. Experiment and Modeling on Thermal Cracking of n-Dodecane at Supercritical Pressure[J]. Energy & Fuels, 2018, 32, 12426-12434.）. Zhang Limei and the like are based on the n-decane pyrolysis mechanism, a high-precision n-decane pyrolysis reaction model of 16 substances and 26 reaction mechanisms is established, the secondary reaction of n-decane under high conversion rate is further examined, and in Computational Fluid Dynamics (CFD) simulation, compared with a global one-step n-decane reaction model, the model is more accurate in the aspects of fuel conversion rate, temperature and product distribution prediction. The model can better reflect the change trend of the isobaric specific heat and the convective heat transfer coefficient of the fluid （Zhang L, Yin R, Wang J. Numerical Investigations on the Molecular Reaction Model for Thermal Cracking of n-Decane at Supercritical Pressures[J]. ACS Omega,