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Decommissioning Vapour Recovery Plant
CASESTUDY
DALMENY TERMINAL
DECONTAMINATION SOLUTION After much discussion with site personnel it was agreed that the best means of decontamination was to split it into four separate sections and implement a Vapour Phase process through each section individually. This was considered to be the best option given that steam was supplied from a temporary steam boiler with a maximum output of approximately 5000lbs/hour and was operating at a reduced pressure due to plant restrictions. The decontamination was carried out over a four- day window with a Supervisor, Technician and Boiler Operator all working a 12 hour shift only. Testing was carried out to determine the reduction in levels of contaminants during the Vapour Phase and to ensure good distribution of RESULTS All four systems were each decontaminated within the 12-hour tie frame. An issue with poor temperature distribution was quickly rectified by using a 2" steam hose at all injection points to achieve correct temperatures throughout the systems (usually 1" are suitable to supplement the main 2" steam out connection but due to the reduced operating pressure of the boiler this proved insufficient). Test results showed that H2S and LEL levels were reduced to zero and on opening the vessels post Vapour Phase the levels of residual solids were deemed to be insignificant.
OVERVIEW The Vapour Recovery Plant had been out of use for several years and was due to be decommissioned. Site personnel were unsure of levels of contamination but were expecting LEL and possible H2S. It was also expected that there would be some residual solids but little heavy fouling. Vessels to be decontaminted included Absorber and Stripper columns plus overheads, lines and vessels. Also included was the ground flare package comprising flare drums and closed drain drum. CHALLENGES There was no previous history information to indicate the likely levels of contamination and fouling. The planned decon duration presented a challenge as it was all single shift day working. There were no site services available other than fire water so all supporting equipment had to be hired in. Also, there were pressure restrictions on the plant which meant that the boiler and relief valves had to be set at 6bar operating pressure. This is lower than normal pressure for a vapour phase application unless there is a main hard steam out feed line to the vessels which was note the case in this instance. PAST PROCEDURE There was no previous experience at this site for the client to draw on in planning and implementing this decontamination as this was the first time the plant had been decontaminated.
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