Method of Reducing Corrosion and Corrosion Byproduct Deposition in a Crude Unit (Nalco)

Method of Reducing Corrosion and Corrosion Byproduct Deposition in a Crude Unit (Nalco)
United States Patent Application 20160024395
Scattergood; Glenn L. ;   et al.   January 28, 2016
Assignee: Nalco Company
Abstract
A method of optimizing system parameters in a crude unit to reduce corrosion and corrosion byproduct deposition in the crude unit is disclosed and claimed. The method includes measuring or predicting properties associated with the system parameters and using an automated controller to analyze the properties to cause adjustments in the chemical program to optimize the system parameters. Adjusting the system parameters effectively controls corrosion in the crude unit by reducing the corrosiveness of a fluid in the process stream and/or by protecting the system from a potentially corrosive substance. System parameter sensing probes are arranged at one or more locations in the process stream to allow accurate monitoring of the system parameters in the crude unit.
TECHNICAL FIELD
[0001] This invention relates generally to methods of reducing corrosion in a crude unit. More specifically, the invention relates to methods of optimizing system parameters in a process stream of a crude unit to reduce corrosion in the crude unit. The invention has particular relevance to sampling dew point water and accumulator boot water to measure system parameters and respond to such measurements to reduce corrosion and/or corrosion byproduct deposition in the crude unit.
BACKGROUND
[0002] In a crude oil refinery, generally the oil is pumped from a storage tank to a crude unit for processing. The crude unit cleans the oil through water washing in a desalter and then splits the oil into fractions in an atmospheric distillation tower. These fractions are pumped to various processing units downstream of the crude unit (e.g., coker, catalytic cracker, hydrotreater etc.). Though corrosion and corrosion byproduct deposition (the latter sometimes referred to herein as fouling) occur in many areas of a crude unit, the most severe corrosion and fouling typically take place in the overhead condensing system of the atmospheric distillation tower.
[0003] Refinery crude unit processing has becoming increasingly difficult in recent years and is predicted to become even more challenging and complex for several reasons. For example, significant increases in crude oil prices have caused refiners to aggressively pursue "opportunity" or "challenging" crudes that are obtainable at discounted prices. The lower price is linked to a crude property such as high acid or high solids content that makes it less desirable than the light, sweet benchmark crudes.
[0004] Refiners switch crude slates more frequently than in the past due to minimum on-hand crude oil inventory combined with increased crude oil variety. A crude slate switch typically upsets the steady state condition of a crude unit for up to several hours. Generally, about eighty percent of the corrosion and fouling occurs during these switches or disruptions, which normally last about twenty percent of the time. If fouling and corrosion issues are severe enough, the refiner will discontinue processing the crude oil or blend of crudes causing the problem. However, these challenging crudes are available to the refiner at a discount thus making them more profitable. Discontinuing such problematic crudes is accordingly not a very popular option.
[0005] In efforts to reduce corrosion, a crude unit may be serviced two or three dines per week, or in sonic cases daily. Daily service at best provides a snap shot view of a dynamic crude unit system. Crude type and/or raw crude storage tanks are switched several times per week, sometimes daily. The contents of each tank are different from the others, so each switch causes a change of feed quality to the crude unit, many times upsetting the steady state status and causing disruptions in the system. Preheating, desalting, and distilling operations shift with the new crude, sending products and/or effluent water sources off specification. Many adjustments over several hours (in some cases days) normally take place to return the crude unit to steady state operation.
[0006] The most common current industry practice to control such disruptions and optimize crude unit operation is to provide enough manpower and man-hours. For instance, each crude unit may have an operating crew from three to ten people, depending on size and complexity of the unit. This crew may spend their day gathering various samples for wet chemistry lab testing, and measuring and making adjustments for temperature and flow to keep the unit running within specification. Such practice is typically geared towards keeping the unit operating properly with respect to fractionation quality cut points and end points, with minimal attention being paid to a specialty chemical corrosion control program. If a disruption is severe, changes may be made to the process chemicals and/or changes in levels, flows, or temperatures may be recommended around the crude unit to keep the dynamic system in as optimum a condition as possible.
[0007] Attempts to compensate for periodic or sometimes prolonged lack of human involvement include installing online pH meters on atmospheric distillation towers overhead accumulator water boots; however, due to a high rate of fouling of the pH sensor only a small percentage of these meters operate correctly for any length of time. Online instrumentation, such as pH meters, requires routine maintenance and calibration. Moreover, online pH merely tracks the pH and sends an alarm to the operator when the pH is outside the control limits. Often, poorly calibrated and/or fouled pH meters cause frequent alarms. This frequency tends to minimize the effectiveness of the alarm system.
[0008] Due to the lack of industry success with online pH metering and other monitoring efforts refiners have not pursued more exotic and effective online instrumentation for process chemical programs. There thus exists an ongoing need for more sophisticated and effective online and/or automatic methods for monitoring parameters and reducing corrosion in crude units.
SUMMARY
[0009] This invention accordingly provides methods to generate reliable crude unit data in a feedback, feed-forward, or predictive loop(s) to make real-time adjustments to process stream treatments thus reducing corrosion and corrosion byproduct deposition (sometimes referred to herein as fouling). In a preferred aspect, the invention is implemented to provide continuous or intermittent feedback, feed-forward, or predictive information to process chemical injection pumps to make real-time adjustments. The invention incorporates programming logic to convert analyzer signals to pump adjustment logic and, in a preferred embodiment, controls one or each of a plurality of chemical injections with a unique basis. Examples include neutralizer injection based on pH, chloride, or acid content; caustic agent injection based on pH, chloride, or acid content; and filming inhibitor injection based on iron concentration or corrosion rate.
[0010] It is also envisioned that the invention will manage the readings from existing electrical resistance corrosion probes, linear polarization probes, and/or other techniques for measuring metal loss. These readings will be programmed through a Programming Logic Controller (PLC) to possibly override or modify the other chemical inputs and change pump rates. Moreover, because the crude unit atmospheric distillation tower overhead heat exchanger system suffers frequent and costly issues with corrosion, the invention focuses on that part of the crude unit. However, the invention has utility on many other units in the refinery.
[0011] In an aspect, the invention includes a method of optimizing a system parameter in a process stream of a crude unit to reduce corrosion in the crude unit. A property associated with the system parameter is measured and/or predicted at or more points in the crude unit and is converted into an input electrical signal capable of being transmitted to a controller. In turn, the controller is operable to receive the transmitted input electrical signal, convert the received electrical signal into an input numerical value, analyze the input numerical value, generate an output numerical value, convert the output numerical value into an output electrical signal, and transmit the output electrical signal. An optimum corrosion-reducing range for the input numerical value is determined and if the input numerical value is outside of the optimum range, the transmitted output electrical signal causes a change in an influx of a composition into the process stream. The composition is capable of adjusting the property associated with the system parameter in a manner to bring the input numerical value within the optimum range. In an embodiment, an influx of one or more different compositions into the process stream are collectively and/or individually capable of adjusting the property(ies) associated with the system parameter(s). The method is optionally repeated for a plurality of different system parameters, where each different system parameter has a unique associated property.
[0012] In another aspect, the invention includes a system for optimizing a system parameter in a process stream of a crude unit to reduce corrosion in the crude unit. The system comprises a sensing device operable to sense and/or predict a property associated with the system parameter and convert the property into an input electrical signal capable of being transmitted. A transmitter transmits the input electrical signal to a controller. The controller is operable to receive the transmitted input electrical signal, convert the received input electrical signal into an input numerical value, analyze the input numerical value to determine if the input numerical value is in an optimum range, generate an output numerical value, convert the output numerical value into an output electrical signal, and transmit the output electrical signal. A receiver receives the output electrical signal and is operable to cause a change in an influx rate of a composition into the process stream if the output numerical value is not within the optimum range, wherein the composition is capable of adjusting the property associated with the system parameter.
[0013] In an embodiment, one or more of the described controller functions may be imparted to one or more data capturing devices.
[0014] It is an advantage of the invention to provide continuous control of one or more key process corrosion control chemicals, an improvement over the current practice of manual, highly variable frequency optimization.
[0015] Another advantage of the invention is to provide a method to achieve optimum efficiency through reduced corrosion and fouling, minimizing the amount of product that does not meet specification, and reducing the amount of slop oil processing.
[0016] It is another advantage of the invention to provide an automated process to efficiently minimize disruptions and the resulting corrosion and fouling caused by a switch between various types of crude slates, including challenging crude, and minimize corrosion, disruptions, and downtime during such switching.
[0017] It is a further advantage of the invention to provide continuous data to measure the magnitude of a disruption and to more precisely identify the root cause of a disruption, including determining the concentration of corrosion byproduct(s) formed in the system due to a spike in corrosion during a disruption.
[0018] An additional advantage of the invention is to provide a method of optimizing system efficiency when crude slates are changed by quickly stabilizing system operating parameters.
[0019] It is yet another advantage of the invention to provide data leading to a level of corrosion control that will help prevent expensive metallurgy upgrades in crude refining systems in order to process acidic crudes.
[0020] Additional features and advantages are described herein, and will be apparent from, the following Detailed Description, Examples, and Figures.
Free Full Text Source:  http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=7&f=G&l=50&co1=AND&d=PG01&s1=corrosion.TTL.&s2=refinery&OS=TTL/corrosion+AND+refinery&RS=TTL/corrosion+AND+refinery