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BP’s manufacturing facility for acetic acid in Hull found its integrity threatened when the water treatment plant began to corrode. This endangered the availability of the continuous supply of water to the site’s steam generators. Elga Process Water’s engineers were able to design and install replacement internals without compromising production.
Acetic acid is one of the world's most important chemicals, andis a key raw material for the production of a wide number of productswe simply couldn’t do without in our everyday lives, including washingpowder, drink bottles and food packaging. Other chemicals from the BPsite are equally important: acetic anhydride is used in the synthesisof a number of pharmaceuticals such as aspirin and paracetamol, ethylacetate is a solvent for high-resolution printing inks and laminatingadhesives, and vinyl acetate monomer (VAM) is used in the paint on our walls, the adhesive in our furniture, in the manufacture of our clothes, the soles of our shoes and in the paper this is printed on.
The water treatment plant, which consists of three 140m3/h streamseach with weak and strong acid cation exchangers, a common degasser and weak and strong base anion exchangers, was installed in 1997 to provide feed water to the factory’s 64barg and 45barg steam boilers. Without steam, production stops therefore the reliability of the water treatment plant is critical to the site.
The problem occurred in the 2.4m diameter strong acid cation exchangers. The units are co-counter current flow regenerated using a technique in which 25% of the sulphuric acid regenerant flows simultaneously downwards through the top part of the resin bed with the remaining 75% flowing upwards through the bottom section and is collected in a central header and lateral system. The forces on this collector system during the occasional backwashand possibly during regeneration can be very high and, if it is not properly designed and supported, it can move leading to eventual mechanical failure. Within a few years of installation the units were suffering from loss of resin and inefficient regeneration.
BP stated“The strong acid cation exchange units were backwashed on an infrequent basis, however the collector systems were not adequately supportedand there was enough movement to damage the protective rubber coating.This allowed the regenerant acid to attack the carbon steel underneath resulting in corrosion and failure of the collector header to vesselmanifold joint with a resultant escape of resin, ineffective regeneration and eventually leading to total failure of the units .”
BPWorks Engineering planned to retrofit new collectors. They were ableto design and install the necessary supports inside the pressure vessels and fitted new stainless steel nozzles on the SAC shell for connection to the collector system. The design of the collector system itselfwas a job for specialists with BP selecting ELGA Process Water, whoseexperience in the engineering design of ion exchange units goes backover eighty years. ELGA Process Water designed and fabricated a complete new stainless steel header with laterals fabricated from stainlesssteel wedge wire.
The modifications were carried out in three stages over a period of four months. BP stated “The modified internalshave performed well, with good distribution of the regenerant acid, greatly improved reliability, with no further problems.”
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