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Desalting Interface Measurement

Application Overview

Crude oil salts present considerable operational and financial challenges to refiners throughout all of the refining plants and processes. The salts primarily present in crude include calcium, magnesium chlorides, and sodium. These salts pose significant risks of damage to refinery infrastructure, instrumentation, and environmental compliance policies. Examples of damage due to salts present in crude oil feedstocks include fouled heat exchangers, compromised catalysts, hydrochloric acid corrosion, and the plugging of valves, strainers, and burners. With crude oil feedstock ultimately reaching all refining processes, proper desalting is critical in preventing operational upsets and costly process downtime.

Desalting Application

Crude oil and water are mixed together prior to injection in the desalting vessel. After injection into the vessel, at an elevated temperature the water extracts salts from the oil before settling to the bottom vessel portion. An electrical grid aids the separation of water and oil. Cleaner desalted crude is pumped out of the top of vessel and process water out of the bottom. The oil and water interface is maintained to prevent water from compromising the electrical grid or crude oil from contaminating the bottom process water. The interface is also critical to ensure the vessel is in optimal operating conditions.

Delta Controls IPT Features

Measurement of the water/oil interface position in refinery desalters has commonly been attempted with analog type capacitance level transmitters. Unfortunately, the measuring probe of this type device becomes coated with carbon, water emulsions, and other material. This coating and buildup creates interface position errors and eventually renders the output signal meaningless. Cleaning the probe and recalibrating normally restores the signal accuracy. Unfortunately, this mandatory frequent probe cleaning has not been practical because a pressurized desalter has to be shut down before this type of continuous transmitter can be removed.

Cleaning the Delta Controls IPT interface transmitter does not require shutdown of the desalter unit. The sensing probe can be extracted, cleaned, and reinserted without disturbing operation of the desalter unit. The IPT design allows this infrequent cleaning to be completed safely and easily.

The IPT assembly is mounted on top of an isolation valve which permits its removal without depressurizing the desalter. The sensing probe, inserted down in the process fluid, is withdrawn into a chamber above the valve whenever access to the probe is required. The block valve is then closed beneath, permitting depressurization of only the withdrawal chamber. The sensing probe can then be cleaned or completely removed.

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