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What is the best way to maintain a steam purge on the Delta Valve? We installed our Delta Valves last month and have experienced a problem maintaining the Delta Valve steam pressure 20 psig above the feed line pressure. The problem is that we had steam purge pressure taps installed on our feed line. We found that we had to turn off the purge steam to these taps during the quench cycle due to the hammer knock so we are not able to maintain the steam pressure differential during this phase of operation. There is also the potential of someone forgetting to turn the steam purge on the taps back on before the next coking cycle.
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AnonymousNeed to re-design your feed line steam tap / pressure reading.
Use the same tap as used for blocking steam pressure reading when feeding the sister drum. Tap should have steam purge with restriction orifice. -
AnonymousClarification to steam purge – use restriction orifice, location is on the drum side of feed isolation and utility isolation valve. Pressure gauge is reading pressure on feed line regardless of cycle time step. Steam purge to keep tap clear is very small, same setup as blocking steam. THANKS
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AnonymousI understand what you are saying. It would have worked better if we had installed the taps upstream of the switch valve so that we could use the common indication for the Drum pair. For now, we are simply going with a straight 80 psig steam purge to the Delta Valve.
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You seem to have two different issues here:
(i) Typically, we maintain the delta valve bonnet steam pressure at a differential of 25 psid above the bottom feed line pressure. We do this by measuring the feedline pressure and then adding 25psig to it using a DCS controller/algorithm block and then sending the resulting output signal to the control valve on the steam line to the DV bonnet.
(ii) For the steam purge to the pressure transmitters on the top & bottom outlet and feed lines we feel that the best design is using a Kates automatic flow rate controller to maintain a flow rate such that the flow velocity at the tapping point is always 6 ft/sec or more as this is a solids application. For a 3/4″ tapping point, this would result in a typical steam flow of only 6 lbs/hr into a feed line at 40psig, and 10 lbs/hr into a top line at 80 psig. Almost always, if you use fixed restriction orifices, the steam flow is way in excess of what you need for meeting the traditionally accepted solids purge velocity, and cannot be controlled as downstream pressure varies unless you are always in choked flow conditions. Hammering is almost inevitable due to the high steam flow through an RO – mainly because you cannot size one less than say an 1/8″ and not worry about blockage. With the adjustable controllers you can leave the steam purge on all the time and the issue of turning them on & off doesn’t arise. A caveat here – we are looking for long term reliability data on this type of purge design/equipment.
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We are doing the same, holding a straight 80 psig purge. You are right, the pressure tap should have been ahead of the switch valve.
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