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In my refinery we have Diesel Hydrotreater unit which has undergone an emergency shutdown, following the tripping of recycle gas compressor. The compressor was tripped off due to the false ESD activation of high level switch on the suction K.O drum. Recycle compressor started up and started increasing the reactor inlet temperature . During the DHT unit start up, higher hydrogen consumption of 1.5 vs normal 1.0 MMSCFH and lower system pressure of 620 vs normal of 670 PSIG was observed.
My question is where is go the higher hydrogen consumption?
 
Answers
08/12/2011 A: Ali Saud, operation, fairy00love@hotmail.com
We isolate the relief valve and check it find ok. In addition we Stabilize the unit capacity at turndown with only fresh feed and without recirculation. also we Adjust the operating temperature to get on-specification product (250wtppm – 300wtppm) at turndown capacity.Previously observed temperature at 100% capacity was between 610-615°F. On-specification product should normally be met at 50% capacity with an operating WABT close to 580-585°F and we left the system to stabilize .
still the problem not solved ...???!!! Maybe the leak on the second cold separator liquid preheater or First cold separator liquid preheater.
08/12/2011 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
Perhaps a strange thought.
Was the high level switch alarm truly a false alarm?
Do you happen to have an amine absorber upstream of the compressor?
Possibly the absorber foamed and filled the KO drum with foam.
Recycling hydrogen + amine to your reactor can create both an increase in reactor temperature and an increase in hydrogen consumption.
07/12/2011 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
If it is not consumed, additional or excess hydrogen should come back with recycle Hydrogen via HP separator.
One thing you may want to consider also is if you have onl a KO drum on the suction of your H2 recycle gas compressor, you may want to also install a high efficiency Seprasol LG coalescer after the KO pot / mesh pad which I assume you have. KO pot / mesh pad is not very efficient for aerosol sized droplets and due to condensation (cooling) there can be a considerable amount of aerosol sized droplets in the recycle H2 stream which KO drum / mesh pad cannot remove. This is usually bad news for the reliability of recycle H2 compressor valves when this is a reciprocating compressor which it usually is for a DHTU.
06/12/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
There are only two places the 'extra' hydrogen can go---either into higher conversion i.e. more hydrogenation of the feed, or, loss out the reactor loop via leaks, purge gas or light ends.
To resolve the quandary, first establish the validity of hydrogen make-up quantity for certain. Then conduct a good material balance around the reactor loop. It is important to ensure pressure relief and de-pressuring valves have re-seated leak-tight. Also verify losses past the compressor shaft seals are normal and did not increase --due to damage during the 'trip.'