Method for monitoring and controlling salt content of desalted crude oil in gas-oil separation process

A method for controlling a salt content of desalted crude oil, comprising:

• feeding a dehydrator feed stream comprising a wet crude stream and a first water recirculation stream to a dehydrator;
• separating the dehydrator feed stream into a dehydrator crude effluent stream and a dehydrator water effluent stream;
• feeding a first desalter feed stream comprising the dehydrator crude effluent stream and a second water recirculation stream to a first desalter unit;
• mixing the first desalter feed stream in the first desalter unit;
• separating the first desalter feed stream into a first desalter crude effluent stream and a first desalter water effluent stream;
• recirculating at least a portion of the first desalter water effluent stream to the dehydrator as the first water recirculation stream;
• feeding a second desalter feed stream comprising the first desalter crude effluent stream and a wash water stream to a second desalter unit;
• mixing the second desalter feed stream in the second desalter unit;
• separating the second desalter feed stream into a second desalter crude effluent stream and a second desalter water effluent stream;
• recirculating at least a portion of the second desalter water effluent stream to the first desalter unit as the second water recirculation stream;
• periodically measuring:
• a flowrate of the wet crude feed stream, the wash water stream, the first water recirculation stream, and the second water recirculation stream;
• a water content of the wet crude feed stream;
• and
• a salt content of the wet crude feed stream and the wash water stream;
• obtaining target parameters comprising a target basic sediment and water (BS&W) of the dehydrator crude effluent stream, the first desalter crude effluent stream and the second desalter crude effluent stream;
• iteratively calculating a salt content of the second desalter crude effluent stream according to salt mass balances around the dehydrator, the first desalter and the second desalter, based on input process parameters, the target parameters and a trial salt content value of the second desalter crude effluent stream;
• comparing the salt content of the second desalter crude effluent stream and a target salt content of the second desalter crude effluent stream;
• and
• when the salt content of the second desalter crude effluent is equal or greater than the target salt content of the second desalter crude effluent stream:
• adjusting at least one of the input process parameter or the target parameter;
• and
• repeating the iteratively calculating, the comparing, and the adjusting until the salt content of the second desalter crude effluent stream is less than the target salt content,
• wherein the input process parameters comprise:
• the flowrate of:
• the wet crude feed stream,
• the wash water stream,
• the first water recirculation stream, and
• the second water recirculation stream;
• the water content of the wet crude feed stream;
• and
• the salt content of the wet crude feed stream and the wash water stream.