September 29, 2012 at 7:22 am #1807
Vacuum Residue sampling is very hazardous activity in any unit. Lot’s of accident has been reported while collecting VR samples. Attached is a design of interlocked VR sampling system , which can be operated in auto/semiauto mode using a local control panel.
Appreciate your comments please.
VR SAMPLING SYSTEM
There shall be continuous flow through the recirculation line , which shall be verified using the flow indication by the FT . There shall be low flow alarm in the DCS in case of low flow.
This is to ensure that there is a continuous flow of VR and no chocking is there
When operator wants to take sample, he will inform DCS panel operator, who will check indication of all the valves in the DCS and then click SAMPLING PERMISSIVE soft button provided on the DCS. Immediately, warm up permissive light will glow on the local panel.
Field operator shall check the things physically then place the sampling bucket on the seat of EV2 and press START push button on the local panel.
Following activities shall take place.
1. Warm up: XV4 shall open first, then XV1 , then MP steam valve (XV2). Steam will start flowing through the pipe and temp will start rising( measured by TXI-1 and TXI-2). Once it achieves the required temp 260<240 degC or as decided) XV2 shall close first , then XV1( XV4 shall remain open to drain out any condensate).
2. Sampling: Once TXI-1 & 2 have achieved the required temp and XV1&2 have closed, chute will go down through EV3.
Once chute goes down and sampling bucket has been placed( confirmed by proximity sensors), EV2 will move and place the bucket just below the sampling valve XV4( confirmed by indication of EV2).
Based on placement indication of the sampling bucket below XV4 and completion of Warm up and closure of XV1 , XV2 and XV3, sampling permissive shall be issued by the DCS .
Field operator shall start SAMPLING push button on the local panel, which shall open XV1 first, then EV1 slowly( in steps).
After opening of the EV1, within some time, temp of the bucket sensed by TXI-3 should start rising. After sensing the material in the bucket( we are also looking into the possibility of weighing the sample received in the bucket and indicating the same in DCS for putting in interlock ), EV1 shall close . With sensing of EV1 closure, EV2 will operate and pull out the bucket away from the OWS pit. Sensing bucket out of OWS pit, EV3 will operate and bring the Chute up.
3. Flushing : With sensing of completion of sampling, closure of the valve EV1 , XV2 and placement of chute in UP position, Flushing oil valve XV3 shall open and flush the line for a predefined period then XV3 shall close.
Once system senses, completion of warm up, sampling , placement of chute in up position and Flushing the line by XV3, shall initiate opening of MP steam valve XV2 , which shall cleanse the left over traces of VR and FO.
XV2 shall operate for a predefined period ( as defined in DCS) then close.
Once system senses, completion of warm up, sampling ,Chute in up position ,flushing by FO(operation of XV3) and flushing by MP steam(operation of XV2), XV1 will close first then XV4 shall close.
Operator shall press the STOP PUSH BUTTON and lock it.
Now system is ready for another sampling.
NOTE : “Cooling water/air jacket shall be provided in the sampling system and can be operated as and when temp of the VR is above 260 degC or above it’s self ignition temp, for cooling the sample to bring it below the self ignition temp.”
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