Could someone explain me the procedure to calculate the diameter of distallation column reflux accumulator?
Answers
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05/10/2016
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Leonardo Leite Garcia de Souza, Petrobras SA / Duque de Caxias Refinery, llgs394041@yahoo.com.br
This procedure has to be done iteratively. First of all you have to guess the drum internal diameter. I personally like to use as a initial guess the average height of a human being, like 1.7 or 1.8 m (remember that your vessel will have to be serviced internally, so it can't have a small diameter). Then, the cross-sectional area of the drum is divided into three zones: 1) below the LLL (low liquid level) - typically, this zone have a height of 6 to 8 in; 2) above the HLL (high liquid level) - the height of this zone should be such that you have enough free area above the HLL so the vapor will not flow at critical velocity (given by the Souders & Brown correlation, google it!), entraining liquid to the vapor outlet, and, finally, 3) the zone between the LLL and HLL - this zone should provide enough residence time for the separations, as well as damping upsets and instabilities from the upstream processes, and this residence time depends on a number of factors, but for a reflux accumulator with up-to-date instrumentation 5 min is a good value. Now, use your liquid volumetric flowrate and the residence time to estimate the liquid volume between the LLL and HLL. The length of the drum is given by the ratio between this volume and the cross sectional area between the LLL and HLL. If the ratio between the length and the internal diameter remains between 3 to 5 you are fine. If not, guess another appropriate diameter and repeat the procedure untill it converges. Best regards.
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03/10/2016
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Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
The quick and dirty way is to assume a residence time for the hydrocarbon liquid in the drum, typically 5 to 10 minutes. Assume the drum is half full and assume an L/D ratio for the drum. Typical vessels like that have a length to diameter ratio in the range of 3-4 to 1. With those assumptions it is quite easy to estimate the size required for the drum. Separate calculations are then done to size the water draw boot attached to the drum.
You can use more sophisticated sizing techniques and look at stokes law settling calculations for vapor/hydrcarbon liquid and hydrocarbon liquid/water separation in the drum but because you don't really have a good way to estimate the droplet sizes you are trying separate, it can be difficult to do a meaningful calculation.
Proper design of internal baffles and nozzles can also help improve the separation in this vessel so that water, hydrocarbon liquid and vapor all goes where it should.
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03/10/2016
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Krishna Rao Pulugurti, Retired/Consultant, pkrao2012@yahoo.com
After the carbon on the catalyst is burnt away, and after oxychlorination, the catalyst becomes highly active and decomposes the feed naph tha and gets coked fast. In order to reduce the catalyst activity, any sulfur compound is dozed, DMDS is one of them. Sulfur is adsorbed on the catalyst and reduces its activity because it is temporary poison to the catalyst and released afterwards as hydrogen sulfide in the gas.
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