Q & A

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This face to face interactive event, features experts from leading European refineries and technology providers; engineers will have the chance to hear unparalleled knowledge through interactive discussions such as fishbowl panels, Q&A Panels and Poster Sessions. Learn more here: asktheexperts.wraconferences.com  


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Recent Questions
Date  Replies
19/07/2020 Q: We are facing a problem in crude/condensate decanting which is received from local fields. Settling time for the oil tankers is one hour; after this a dip is taken, water observed in the dip is nil. Then we decant the tankers into our crude oil tanks. After settling time for the tanks we are observing raised water level. What can be the potential causes?  
19/07/2020 Q: Our recycle gas compressor is giving higher flow than it is designed for at the same loading. What can be the reasons?  
19/07/2020 Q: How effective is hydrogen in stripping H2S from hydrotreated naphtha?  
09/07/2020 Q: Pumparound flows through a preheat exchanger and after that passes through a control valve and back into the column. While deciding how much pump should be used, what should we consider?
Condition #1: Reduce the control valve opening, provide the pumparound more residence time inside the exchanger which will cool it down more and then it will return at a lower temperature but with a lower flow rate.
Condition #2: Increase the control valve opening which will allow more flow to be fed back into the column but with a relatively higher temperature.
Which one should we choose?
 
06/07/2020 Q: Our catalytic reforming unit is running at 500°C . A short length flame and smoke was seen at the heater outlet flange; we have a steam ring which we have used to extinguish the fire. Now my query about hot bolting: is it safe to tighten the bolt at 500°C to stop the leak? If not then what should be the maximum temperature and safe procedure for hot bolting?  
Recently Answered Questions
Date  Replies
28/06/2020 Q: The refinery I work in has a 40 year old hydrotreating reactor with a very high design minimum pressurization temperature (MPT) of 120degC. it always takes ages to clear the MPT before we can proceed to the next step in the unit startup. We run our 2x recycle gas compressors which are fixed volume reciprocating compressors, loaded to 200%. The question I would like to ask is: is it better to have higher purity H2 for heating up? Higher H2 purity would mean less mass flow at constant volume. However, H2 thermal conductivity is way higher than other gases such as N2 or CH4, C2H6. The other school of thought is to bring in less pure H2 source to boost the mass circulation.
This is probably a heat transfer question also. Would like to hear if anyone has done any research on this.
(2)
27/06/2020 Q: We have been facing issues in one of our sour water stripping units wherein we observe continuous plugging of the feed control valve to the stripper column with greenish black hard deposits. The temperature of sour water passing through this control valve is in the range 146-152 deg C. Could anyone suggest the testing we should carry out to understand this heavy deposit? Does anyone have experience with hard greenish black deposits in their sour water stripping units? (2)
25/06/2020 Q: I am currently working on designing a flue gas system for a Fluid Catalytic Cracking unit on the regenerator side. The typical set-up is regen effluent flue gas comes out of the regenerator at 1300F. It passes through the Waste Heat Boiler, generating 600 psig (high pressure steam) by recovering heat from the effluent flue gas. The flue gas then passes through a series of pressure let down devices (double disc slide valve, followed by an orifice chamber (bunch of orifice plates lined in a duct)), before going through the wet gas scrubber (caustic wash for any catalyst carryover) into the stack and vent to the atmosphere.

Normally the slide valve (one of the pressure let down devices) is used to control regenerator pressure. This valve is also designed with a minimum cut out and/or a mechanical stop, that prevents the slide valve from going completely closed, the reason being this serves as a path of relief in case the slide valve goes slam shut, causing a source of overpressure on the regenerator. In this case the regenerator is designed for 38 psig.



One of the scenarios to be considered, credible under the current setup, is if the tube in the WHB ruptures, high pressure BFW on the shell side of the WHB can pass through the tube (process gas side), which is open to the regenerator and creates an overpressure. As mentioned above the minimum opening in the slide valve, through the orifice chamber, through the wet gas scrubber, will be a relieving path for this fluid.



Question: I am trying to calculate the amount of relief that will be generated through the tube. Since BFW on the shell side is at saturated conditions, there will be flashing (two-phase flow) passing through the tube. As the relieving flow exits the tube, it should be under sonic conditions (choked flow).

I need to determine how much flashing will occur across the tube as it exits the tube, and secondly the amount of flow that will exit the end of the tube (probably a two-phase restriction orifice calculation needs to be performed) to determine the flow.



I would greatly appreciate if someone can guide me as to how to perform this calculation as I have not done much two-phase through tube (at sonic conditions) and two-phase RO calculation.



(1)
04/06/2013 Q: If the tail gas of SRU contains more SO2 , is there any chance of smoke formation in stack after incinerator. If H2S slip smoke formation happens and increasing air ratio to control the stack some free. But sometimes in low throughput smoke is coming. is it because of more SOx and NOx...? (1)
26/06/2020 Q: In a multi-bed filter why is the larger particle size bed placed over the smaller particle size bed? (1)
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