Calculation method for space velocity in suspended-bed hydrocracking
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In our newly installed suspended-bed hydrocracking process, the catalyst and feed oil are mixed in the required proportions in advance and then fed into the reactor as the temperature rises. Could you please advise on how to calculate the space velocity under such operating conditions? Can the space velocity for this process not be calculated in the same way as in a fixed-bed reactor, where the catalyst is loaded in advance? :handshake
As a supplementary note, it is continuous production, with both the catalyst and raw materials being fed continuously.
Space velocity, abbreviated as SV, refers to the volume of fluid that passes through a unit volume of catalyst per unit of time. In a slurry bed reactor, you only need to know the feeding ratio of the feedstock to the catalyst in order to calculate the space velocity; for example, if 20 tons of feedstock are fed per hour along with 20 tons of catalyst, then the space velocity is 1. Also, since numerically the space velocity and contact time are inverses of each other, it is possible to first calculate the total contact time between the feedstock and the catalyst; the inverse of this time value is the space velocity. However, calculating this contact time is quite complicated, as many parameters need to be taken into account. The space velocity in suspended-bed reactors is relatively high, at least above 0.5 (for fresh feed), with a space velocity of 1 being quite common.
@Hello ardance1977, thank you for your answer. If we calculate based on proportions alone, the space velocity would be too high. The amount of catalyst used is very small – we use 500 ppm of catalyst, while the feed rate of crude oil is 72.5 kg/h. There is also a hydrogen gas flow rate of 300 Nm/h at the bottom of the suspension bed. How should we calculate the space velocity in this situation?
The 500ppm you mentioned is likely the amount you added; the ratio when the material was first introduced was probably not this one.
No, it’s a pilot-scale plant that processes 500 tons per year; the catalyst consumption is 250 kg per year. The catalyst remains mixed with the feed materials, and it also circulates back together with the residue oil coming from the vacuum distillation tower to be mixed again with fresh feed materials. Occasionally, some heavy residue oil containing catalyst is removed.
Is the catalyst you use oil-soluble or in the form of solid particles?
Well, this might be the key point: it is oil-soluble, with a diameter of less than 30nm
In your case, if you want to know the empty space velocity, I think the only option is to measure the concentration of catalyst in the material inside the reactor; it’s likely difficult to obtain accurate results using calculation methods.