Case Study – CDU-2
DECONTAMINATION OF THE CDU-2 PLANT INCLUDING EXCHANGERS, COLUMNS,
PIPING & FURNACES
The Job
Spanchem Technologies was awarded a job at a major refinery in the South of India to decontaminate a 3.7 mmtpa CDU-2 Unit.
The scope of work included all the major equipment including the Crude Desalters, the Atmospheric Distillation Column, the Vacuum Distillation Column, the Naptha Stabilizers, the Strippers and the Furnaces.
In addition to this the Pre-Heat Train Exchangers, the Atmospheric Column Overhead Condensers, Hot Wells and Fin-Fan Coolers were also to be decontaminated.
The shutdown was a major one and the Decontamination was to be followed by man-entry for change outs of the Tower Packings & other hot work.
e. It's easy.
Challenges
The unit shutdown was planned for a period of 48 hrs with zero time beginning after oil out to achieving the KPIs. Continuous operation of the unit over the last 2 -3 years meant that the unit contained appreciable amounts of pyrophoric iron sulfides(FeS), hydrogen sulfide (H2S), LEL’s and benzenes that needed to be eliminated completely.
The refinery also had issues with the supply of water and so the decontamination processes had to be optimized to use as little water as possible. Another concern was the layout of the exchanger networks these were spread out and at different levels.
This meant that multiple loops had to be planned by splitting the exchangers into groups that would be treated separately.
Pre-Engineering
This was the most critical part of the decontamination process and involved not only planning the equipment deployed and defining the loops but also providing the refinery, drawings for the temporary steam piping, the chemical injection points to be readied and the reject lines to the slop.
The Pre-Heat train exchangers were cleaned using a liquid phase circulation process as these exchangers were suspected of having a large amount of heavy crude deposits.
The Atmospheric columns, Strippers and the Vacuum columns were vapor phased along with the column overheads and the hot wells. The Furnaces were also taken into the vapor path through a separate set of injection points that ensured that the chemical contacted every path.
The Desalters were cleaned using a combination of liquid circulation and vapor phasing.
Neutralization of Pyrophoric Iron Sulfide was carried out by using OXONIA® to convert the iron sulfide into a nascent non-flammable form.
Execution I
The total work volume was almost 6000 m3 , there were 5 x Pre-Heat Exchanger Trains totaling to 700 m3 and these were tackled using multiple pumping rigs circulating HYDROSOL ®HD through these exchangers and associated piping as shown in the schematic below –
LIQUID PHASE DECONTAMINATION OF THE PRE-HEAT TRAIN EXCHANGERS
Execution II
HYDROSOL®VP was injected into the columns and strippers with the Atmospheric Column @ 700 m3 and the Vacuum Distillation Column @ 1200 m3, through multiple injection points targeting entries below and above the packed beds in the columns to ensure uniform distribution of the chemistry throughout the system and allow carry-over into the overhead systems.
LIQUID PHASE DECONTAMINATION OF THE PRE-HEAT TRAIN EXCHANGERS
Results
Spanchem Technologies pre-engineered the job so that the equipment could be set up in just 48 hrs before the actual shutdown. The combination of liquid and vapor phase deliveries of HYDROSOL ® to the equipment to be decontaminated ensured that all areas within the equipment and the piping came in contact with the chemistries.
Reflux pumps and temporary pumping/vaping systems were successful in delivering OXONIA® to the various columns, desalters and hot wells.
Within the required time contaminant levels reached 0 and the columns and vessels were ready to be opened. Entry was almost immediate after cooling down and inspection revealed only minimal water-wet hydrocarbon free sludge at the bottom of towers and vessels. Exchanger bundles were pulled out smoothly and were found to be relatively clean with little or no sludge.
The wastewater from the process that was sent to the wastewater treatment plants through the slop lines and the OWS added no load to the existing WWTP and part of the oil was recovered through API separators and in the settling basins.
All in all the required KPIs were met in the planned time schedule.
H2S – 0 LEL’s – 0
FeS – 0 Volatiles – 0
Zero Effluent Issues
Schedule Achieved – 48 hrs
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