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Desalter effluent water cooling, preventing corrosion and shutdowns during the summer months

Client: Refinery

Location: Italy

Sectors: Petrochemical and refining

The Challenge

Ensure effective biological wastewater treatment of desalter effluent

Residual waste from cleaning refining products can cause problems for refineries due to the build up of unwanted products in refinery equipment. The customer on this occasion needed a best practice solution to help with crude oil desalting and Aggreko were swift to make sure they had a firm solution in hand.

Crude oil desalting is needed after the clean-up of crude oil. Often, heated crude oil is mixed with washing water to help remove the many impurities such as sand, drilling mud and salt.

To eradicate corrosion in equipment, crude oil desalting is performed. This process is generally performed at 140°C. After pre-heating the oil, water is injected into the desalter to extract salts contained from the oil, preventing introduction of chlorides in the crude distillation unit (CDU), which can lead to extensive corrosion of the top condensers.

Salt is a big problem for refineries as this washing process uncovers vast amounts, too much, will result in problems such as corrosion of distillation columns due to hydrochloric acid forming from hydrogen chloride gas – a product of decomposing salt in crude oil pre- exchangers and heaters. This can result in shutdown and simply isn’t an option for the refinery.

The desalter effluent was the major contributor in terms of biochemical oxygen demand (BOD) and thermal load. A flow rate of 200 m3/h at a variable temperature between 55°C and 73°C had to be cooled down to 34°C to allow oil flotation at the API separator, followed by biological treatment and disposal to the sea. Summer temperatures and non-availability of cooling water added to the challenge for the customer.

The customer needed a solution which would factor in the refinery’s compact design, including the need to keep internal roads open for emergency response. The only option was to cool the oily process water accumulating in a large storage tank at the site.

Leaving things as they were would have dire repercussions for the refinery as the 160,000 BPSD leaving the refinery from an effective CDU would have to be significantly reduced due to corrosive damage. Meaning, an unavoidable capacity downturn of up to 50%.

Project Fact File

Deliveries of equipment 3batch
Flow rate 200m3/h
Thermal application 9MW

The Solution

A 9MW temporary cooling solution during summertime with minimum electric power required

Aggreko engineers decided that a 9MW thermal application would be implemented, this would use basket filters and titanium plate heat exchangers resistant to corrosion. Also added were plate gaps ensuring the free flow of the water-oil mixture contaminated with dissolved and non-dissolved salts.

As the maximum air wet bulb temperature was rarely above 24°C a combination of compact mobile cooling towers in closed loop with titanium plate heat exchangers was the most logical choice.

Aggreko remote monitoring (ARM) was in place on the heat exchanger, allowing pressure and temperature to be monitored. This complied with the temporary solution as the wastewater’s effluent temperature had to be regularly monitored – ensuring it was meeting local compliance and regulation.

The operational feedback also provided alerts as to when periodic back-flushing of the exchangers became necessary. The automated solution provided control of the water make-up and blow-down, as well as the biocide injection to avoid the legionella risk, again ensuring that health and safety was paramount.

Aggreko Process Services designed the cooling system and interconnections with refinery piping to ensure safety and reliability in a swift package that was delivered in 3 batches to ensure the most affective install.

The Impact

Compliance with local regulations and avoidance of capacity turndown

For four consecutive summers the refinery complied with all local authorities’ environmental inspections. Furthermore, the solution managed to achieve compliance with internal environmental requirements as no oil spillages occurred.

The effective cooling solution and treatment saw no need for capacity downturn meaning that a very attractive 160,000 BPSD could continue flawlessly due to no reduction in the CDU operation.

The worst case of reducing by 50% was avoided and by preventing a capacity downturn we undoubtedly helped achieve financial benefits for our customer through a higher rate of refining production.