Understanding the reactions in slurry bed hydrogenation reactors
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At 340°C, the slurry-phase mixed feed (containing the catalyst precursor molybdenum octoate and the recycled catalyst molybdenum sulfide, as well as hydrogen supplied before mixing in the mixer) enters from the bottom of the reactor. There it first comes into contact with hot hydrogen at 500°C and 25% of the total hydrogen flow rate, resulting in slight hydrolysis reactions and pyrolysis-sulfidation reactions of the catalyst precursor. The easily cracked components in the slurry are instantly cracked, absorbing heat; this heat is then utilized by the secondary hydrogen to raise the temperature (to the minimum pressure point). During this upward movement, the mixture encounters hot hydrogen flowing downward at 500°C and 75% of the total hydrogen flow rate, reaching an apparent reaction temperature of around 418°C (as measured between the primary and secondary hydrogen distributors). This leads to thermal cracking of the slurry and hydrogen saturation via the coordinating active hydrogen ions of MoS. The unconverted oil and MoS are carried upward by the high-flow-rate gas phase, becoming dispersed and suspended. Within the flow field, where the temperature is higher in the center and lower at the edges, with mixing from the edges toward the center, further cracking and hydrogenation reactions occur, until the outer layer of asphaltenes is gradually stripped away, leaving behind asphalt nuclei suspended in the slurry (these nuclei tend to aggregate and form coke, but are stabilized and dispersed by the gums present). During the upward process, the bubbling changes from tiny hydrogen bubbles at the bottom to larger bubbles of reaction product gases mixed with hydrogen, thereby forming a bubbling zone in the upper part of the reactor. The reaction takes place in an isothermal fluidized bed within the reactor, with a temperature increase of 5°C plus the natural temperature loss of 2°C due to the reactor itself; this setup enables efficient utilization of thermal energy, high stability of the slurry, and precise control over the quality of the conversion.
Oil at 340°C is heated to 418°C, how much hydrogen per hour?
Circulating hydrogen 120,000 Nm3/h + fresh hydrogen 100,000 Nm3
At the same temperature, with the same volume of gas and feed mixture, and without any liquid catalyst, the temperature inside the reactor is only 380°C; however, the temperature increase is only 5°C. I don’t understand how it can reach 418°C
The mixed feed temperature is 340°C; injection begins at 370°C, and the reaction progresses gradually (more noticeably at 390°C). Heat hydrogen acts as a mass variable – as its molecular weight increases, its contribution of latent heat also increases. The temperature at the bottom of the reactor is sustained by both circulating hydrogen and reaction heat, rising slowly in a spiral pattern. The temperature rise refers to the difference between the average temperature of the first layer above the hydrogen at the reactor bottom and the highest temperature there.