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.

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 Development

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”

References were taken from the equipment manufacturer “Alfa Laval” to develop this procedure.

Process Flow

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

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.