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%.