Case Study – PACKINOX
CHEMICAL CLEANING OF PACKINOX EXCHANGER IN MS UNIT
The Job
In June 2021 Spanchem Technologies was awarded a job at a major refinery in the Central India to chemically clean a PACKINOX exchanger in their MS Unit.
The exchanger was badly fouled and was being removed from service and was to be replaced with a new exchanger.
The job was to be carried out in the minimum possible period after which it was to be preserved under nitrogen & moved to a secure storage location
Challenges
The exchanger was being cleaned after a service of almost 3 years and there was no clear idea of the type of scale that would be found and for that reason it was necessary to develop a procedure that would take care of all the various types of deposits.
Provision had to be made for the removal of ammonium carbonate deposits, iron oxide and any residual hydrocarbon deposits that might be present.
Since the exchanger might have been exposed to various feeds it was necessary to ensure that it was protected from polythionic stress cracking by using alkaline salts with very low chloride levels.
A decision had to be made on whether the exchanger would be cleaned by circulation or soaking and the process had to ensure that the operating temperature & pressure conditions of the exchanger were not exceeded.
Process Development
The chemical cleaning process was developed based on a previous experiences of cleaning the PACKINOX exchangers on 2 previous occasions at a refinery in Western India and a HELITOWER exchanger with pressure/ temperature / operating conditions similar to the PACKINOX.
References were taken from the equipment manufacturer “Alfa Laval” to develop this procedure.
Procedure
The developed procedure for this work was based on the past experience that the main foulant was ammonium salts and the need to prevent polythionic stress cracking.
Reference was made from NACE Standard RP0170-2004 for the “Protection of Austenitic Steel & other Austenitic Alloys from Polythionic Stress Corrosion Cracking during Shutdown of Refinery Equipment”
Process Flow
- Rig-up Effluent & Feed Sides for Circulation/ Fill & Drain
- Prepare a solution of 2% Soda Ash (LR Grade) + 0.2% Sodium Nitrate (LR Grade) + 0.01% Wetting Agent in DM water with a chloride concentration of < 10 ppm
- Fill the solution in the feed side keeping all vents on feed side open, bubble nitrogen, drain the solution if it changes color, turning dark, Repeat till Chlorides < 25 ppm
- Fill the solution in the effluent side in parallel , bubble nitrogen, drain the solution if it changes color, turns dark, Repeat till Chlorides < 25 ppm
- Rinse the exchanger on the feed & effluent sides till the chloride content is < 10 ppm
Process Checkpoint
- Feed (Shell) Side Pressure > Effluent Side Pressure
- Always fill Feed (Shell) Side first & then Effluent Side
- Always drain Effluent Side first & then Feed (Shell Side)
- If only Effluent Side is to be cleaned, even then Feed (Shell) side must be kept filled with DM water + Ammonia
- Always dry the Packinox exchanger with Nitrogen after the cleaning before opening
The above graph shows the trends during the cleaning of the exchanger, initially chloride levels were at 480 ppm and declined with each fresh chemical wash till levels of as low as 27 ppm were reached on both feed & effluent sides, as per mfg. recommendations the difference in Chloride levels were around 20 ppm and a final rinse of the system was carried out with DM water and chloride levels fell to 5 ppm, the exchanger was then blown through with Nitrogen for 12 hrs. and handed over to client.
During the cleaning inlet chloride levels of the chemical mix were < 10 ppm and temperature was maintained between 60 – 70 deg C. On reaching peak chloride levels Nitrogen bubbling was carried out to increase turbulence & dislodge loose contamination. The entire process took 72 hrs. to complete and the Fill & Drain Technique was used.
Results
Spanchem Technologies pre-engineered the job so that the equipment could be set up just 48 hrs before the actual shutdown. The combination of low chloride lab grade chemicals ensured that residual chloride levels were kept at the lowest and ensured complete removal of the deposits.
Correctly sized pumping equipment, level tubes and clear procedures ensured that the
pressure balance in the PACKINOX exchanger was always maintained.
The resulting wastewater was neutralized and then sent to the plant drains, there was zero load on the ETP
All in all the required KPIs were met in the planned time schedule.
