DESIGN DEVELOPMENT AND IMPLEIVlENTATiON OF ANALYZER BASED
CONTROL SYSTEM AND ALGORITHM
Cross-Reference to Related Applications
This application is a continuation-in-part of US Patent Application
12/263,904 which was filed on November 3, 2008
Statement Regarding Federally Sponsored Research or Development
Not Applicable.
Background of the Invention
This invention relates generally to an analyzer based control system and
algorithm for the use in a chemical process system. As described for example in US
Patents 5,503,006, 5,425,267, 5,965,785, US 5,326,482, 4,335072, US Published Patent
Applications 2010/0108566 and 2012/0053861 Ai, UK Patent 1,198,734, and
International Patent Applications 2008/005058, 2004/044266, and 03/006581, chemical
and industrial facilities utilize a variety of complex equipment, which are often subject to
harsh chemical and physical conditions. As such, a number of technologies have bee
developed to monitor the condition, efficiency, and expected lifespan of the equipment.
Such technologies include historian systems which collect and archive data from various
sources within the chemical plant. US Patent Application 2/899,250 describes a number
of methods of utilizing historian and other data.
Monitoring equipment typically involves a system in which a variety of
process variables are measured and recorded. One such system is described in US
Published Patent Application 2009/0149981 A . Such systems however often produce
massive amounts of data of which only a small portion of which is usefully tracked to
detect abnormal conditions and the information gleaned from those systems is of limited
practical use.
In the context of corrosion prevention, three of the most useful dat sets
for a monitor to measure are pH, metal (especially iron) ion concentrations, and chloride
ion concentrations. Ideally the monitored data is as close to real time as possible so
remediation techniques for the causes of extreme concentrations can be applied before the
causes effect corrosion or otherwise damage the facility Unfortunately current
monitoring technologies pro vide a large volume of false data so rea time monitoring is
usually difficult if not impossible. Moreover the false data can lead to the wasting of
expensive remedial chemistries when their addition was not needed. As a result a truly
automated remedial chemical feed system is not feasible and a human operator is
typically required to prevent the addition of remediating chemicals in the face of a "false
alarm" thereby increasing operation costs.
Thus there is a clear need for and utility i an improved method of
monitoring the conditions within a chemical plant. The art described in this section is not
intended to constitute an admission that any patent, publication or other information
referred to herein is "prior art" with respect to this invention unless specifically
designated as such. In addition, this section should not be construed to mean that a search
has been made or that no other pertinent information as defined in 37 C.F.R. § 1.56(a)
exists.
Brief of the I ventio
At least one embodiment of the invention is directed towards a method of
correcting an error in the measurement of a process variable taken by a sensor in a
chemical process system. The system is characterized by properties which cause at least
some of th measurements to be erroneous, The method comprises the steps of: 1)
identifying the component of the error caused by dynamic state factors this component of
the eiTor being determined by at least once obtaining a senor measurement in the system
and noting how that measurement deviates from an objectively correct measurement of
the process variable by varying amounts relative to time, 2) identifying the steady state
factor component of the error, this component of the error being determined by at least
once obtaining a senor measurements and noting that the measurement deviates from the
objectively correct measurement of the process variable by a fixed amount relative to
time, 3) identifying the component of the error caused by additional factors, and 4)
altering the measurement to remove the errors caused by steady state factors, dynamic
state factors, and unknown factors.
The sensor may be in informational communication with an analyzer and the
analyzer may be in informational communication with a controller. The sensor may be
constructed and arranged to obtain a raw measurement of the process variable The
analyzer may correct the error in the sensor's measurement. The controller may take the
corrected measurement. If the corrected measurement is outside of a pre-determined
range of acceptable values, it may enact a remedial measure to change the measured
value to a value within the acceptable ra ge. The remedial measure may be enacted
before the steady state value of the measurement is detected by the sensor.
The process variable may be a measurement of one item selected from the
list consisting of; oxidation-reduction potential, H, levels of certain chemicals or ions
(e.g.. determined empirically, automatically, fluorescently, electrocheraically,
colorirnetrically, measured directly, calculated) temperature, pressure, process stream
flow rate, dissolved solids and suspended solids.
There may be a least three sensors and each of the three sensors may pass
on a raw measurement to the analyzer. The analyzer may use use the average of those
raw measurements as the input in its calculations if at least one of the raw measurements
fits within a pre-determined setpoint. expected for the specific conditions under which
measurement was taken, the analyzer a historically expected value as the input in its
calculations if none of the the raw measurements fit within a pre-determined setpoint
expected for the specific conditions under which measurement was taken,
The process variable may be iron concentration. The method may further
comprise the steps of: disregarding all sensor readings that indicate zero iron
concentration, and adjusting the measured iron concentrations using regression analysis
over a 1 week time period. The remedial measure may involve adding a chemical whose
effect is non-linear in nature. The analyzer may correct for the non-linear effects of the
remedial chemical in its corrections. The remedial measure may involve adding a
chemical subject to the constraints of deadtime and the analyzer corrects for those effects
in its measurements. The process system may be one item selected from the list
consisting of: a chemical plant, a refinery, an oil refinery, a food processing facility, a
manufacturing plant, a chemical plant, a distillation column, a water filtration plant, a
factory, a waste processing facility, a water treatment facility, and any combination
thereof.
Brief Description of the Drawings
A detailed description of the invention is hereafter described with specific
reference being made to the drawings in which:
FIG. 1 is a graph which illustrates a method of correcting a measured value of a
process variable.
FIG. 2 is a graph which illustrates a method of correcting a measured value of a
process variable.
FIG. 3 is a graph illustrating the difficulty in calculating the corrosion rate of a
process system.
FIG. 4 is a graph which illustrates a method of correcting a measured value of
corrosion rate.
FIG. 5 is an illustration of sources of data used by the analyzer.
FIG. 6 is an illustration of a dashboard containing analyzer output.
Detailed Description of the Invention
The following definitions are provided to determine how terms used i
this application, and in particular how the claims, are to be construed. The organization
of the definitions is for convenience only and is not intended to limit any of the
definitions to any particular category
Chemica process system' means one or more processes for converting raw
materials into products which includes but is not limited to industrial processes which
utilize one or more of the following pieces of equipment: chemical plant, refinery,
furnace, cracker, overhead column, stripper, filter, distiller, boiler, reaction vessel, and
heat exchanger, and the like
"Dynamic State" means a condition of a measured process variable in which the
observed measurement changes over at least a portion of a discrete period of ti e during
which the condition is measured while in fact the actual magnitude of the process
variable is not changing.
"Steady state" means a condition of a measured process variable in which the
observed measurement remains unchanging over a discrete period of time during which
the condition is measured while in fact the actual magnitude of the process variable is notchanging.
n the event that the above definitions or a description stated elsewhere in
this application is inconsistent with a meaning (explicit or implicit) which is commonlyused,
in a dictionary, or stated in a source incorporated by reference into this application,
the application and the claim tenns n particular are understood to be constraed according
to the definition or description in this application, and not according to the common
definition, dictionary definition, or the definition that was incorporated by reference. In
light of the above, in the event that a term ca only be understood if it is constraed by a
dictionary, if the term is defined by the Kirk-Othmer Encyclopedia of Chemical
Technology, 5th Edition, (2005), (Published by Wiley, John & Sons, Inc.) this definition
shall control how the term is to be defined in the claims.
Automation technology plays a significant role in improving and
maintaining efficient process operation. t influences the strategic and operational goals
of enterprises, their economic results, the development and quality of products, continuity
of production, and competitiveness in the marketplace. These strategies should include
(1) Improvements of unit operation and (2) Optimizing proper selected chemicals. The
key to controlling the corrosion rate is to analyze the corrosion performance and drive the
decisive knowledge based on operating data and analyzer measurements. Crude Unit
Automation (CUA) system is designed to monitor and analyze the system corrosion and
feedback control the chemicals using automation technologies. The implementation of
these strategies resulted in lower corrosion risk and continued improvement of the run
length of the overhead heat exchangers.
In at least one embodiment of the invention the control system in use in
the process system comprises two elements: (1) at least one sensor and (2) at least one
analyzer. In at least one embodiment of the invention, the control system comprises three
elements: (1) at least one sensor, (2) at least one analyzer, and (3) at least one controller.
The sensor(s) is constructed and arranged to measure at least one process variable within
at least one portion of the system. The analyzer receives the measurement taken by the
sensor and converts it into information which can be output. The controller receives the
output and can cause some operation to occur in response to the output.
In at least one embodiment the response includes adding a chemical.
Added chemicals may include neutralizer filmer, caustic, and inhibitors and so on and
are used to control corrosion process vari ables The analyzer provides on-line
measurements of process variables (especial ly pH, [C ] and [Fe]). The analyzer provides
output which is used to monitor, analyze and manage the whole system.
In a least one embodiment some or all of the information is displayed on a
dashboard. The dashboard ears also display how the system manages historian database
data, reports, alarms, and make readily available the user's selected strategy for real time
control and optimization of the crude unit system.
n at least one embodiment the system is a closed loop which utilizes
preliminary analysis of historian and archived data, updates from the analyzer and other
diagnostics (such as personal observations and discussions with operating staff) to then
generate responses and further analysis of the crude unit's operations
n at least one embodiment the use of inhibitors is to prevent or to reduce
general corrosion, and it plays an important role in the control of corrosion for those areas
in which general corrosion is the problem. The objective of the control system is ho to
prevent/reduce corrosion in crude unit overhead by controlling the inhibitors. As one of
the main components of a crude unit process, corrosion control plays a vital role in
maintaining system integrity. This invention provides a way to optimize the corrosion
control component of the crude unit through optimizing one or more system parameters
in a process stream of the crude unit. This optimization includes measuring properties
associated with those parameters in the process stream.
n at least one embodiment the analyzer is designed to reduce corrosion
of refinery processing equipment and subsequent fouling due to deposition of corrosion
byproducts. A typical corrosion control program includes components such as a
neutralizing amine a filming inhibitor, a caustic solution, etc. Such corrosion control
chemicals are traditionally injected into the system based upon measurements derived
from grab samples and analyzed in the lab or some flow indication on the unit This
invention provides an automated method of adjusting chemical injection into the system.
In at least one embodiment, the method of the invention includes a
controller operable to receive and process information and provide instructions to various
components (e.g., chemical injection pumps) The term "controller" refers to a manual
operator or an electronic device having components such as a processor, memory device,
digital storage medium, cathode ray tube, liquid crystal display, plasma display, touch
screen, or other monitor, and/or other components. Th controller is preferably operable
for integration with one or more application-specific integrated circuits, programs,
computer-executable instructions or algorithms, one or more hard-wired devices, wireless
devices, and/or one or more mechanical devices. Moreover, the controller is operable to
integrate the feedback, feed-forward, or predictive loop(s) of the invention. Some or all
of the controller system functions may be at a central location, such as a network server,
for communication over a local area network, wide area network, wireless network,
internet connection, microwave link, infrared link, and the like n addition, other
components such as a signal conditioner or system monitor may be included to facilitate
signal transmission and signal-processing algorithms.
The controller may include hierarchy logic to prioritize any measured or
predicted properties associated with system parameters. For example, the controller may
be programmed to prioritize system pH over chloride ion concentration or vice versa. It
should be appreciated that the object of such hierarchy logic is to allow improved control
over the system parameters and to avoid circular control loops.
n at least one embodiment, the method includes an automated
controller. In another embodiment, the controller is manual or serai-manual. For
example, where the crude refining process includes one or more datasets received from a
various sensors in the system, the controller may either automatically determine which
data points/datasets to further process or an operator may partially or fully make such a
determination. A dataset may include process variables or system parameters such as
oxidation-reduction potential, pH, levels of certain chemicals or ions (e.g., determined
empirically, automatically, fluorescent! y, electrochemically, colorimetrically, measured
directly, calculated), temperature, pressure, process stream flow rate, dissolved or
suspended solids, etc. Such system parameters or process variables are typically
measured with any type of suitable data capturing equipment, such as pH sensors, ion
analyzers, temperature sensors, thermocouples, pressure sensors, corrosion probes, and/or
any other suitable device or method. Data capturing equipment is preferably in
communication with the controller and, according to alternative embodiments, may have
advanced functions (including any part of the control algorithms described herein)
imparted by the controller.
Data transmission of measured parameters or signals to chemical pumps,
alarms, or other system components is accomplished using any suitable device, such as a
wired or wireless network, cable, digital subscriber line, internet, etc. Any suitable
interface standard(s), such as an ethemet interface, wireless interface (e.g., IEEE
802.1 a b/g x 802.16, Bluetooth, optical, infrared, radiofrequency, etc.), universal serial
bus, telephone network, the like, and combinations of such interfaces/connections may be
used. As used herein, the term "network" encompasses all of these data transmission
methods. Any of the described devices (e.g., plant archiving system, data analysis
station, data capture device, process station, etc.) may be connected to one another using
the above-described or other suitable interface or connection.
n at least one embodiment, system parameter information is received
from the system and archived n another embodiment, system parameter information is
processed according to a timetable or schedule. In a further embodiment, system
parameter information is immediately processed in real-rime/substarilially real-time.
Such real-time reception may include, for example, "streaming data" over a computer
network.
n at least one embodiment two or more samples are taken a t different
locations in the system. For example one could be at the dew point and one at the boot
accumulator. The measurement differences at these two sample points require a
corresponding algorithm to adjust chemical injection. The term "dew point" refers to the
point of initial condensation of steam to water or the temperature at which a phase of
liquid water separates from the water vapors and liquid hydrocarbons and begins to form
liquid water as the vapors cool. Though possible to use the accumulator water boot to
measure pH and chloride ion level, a level of accuracy is usually sacrificed because data
is diluted or masked by the full volume of steam and weak acids and bases that have
condensed downstream of the water dew point.
Likewise, it is possible to measure iron (or other metals, such as copper,
molybdenum, nickel, zinc) ion concentration from the dew point water n at least one
embodiment the metal ion concentration is measured at the accumulator water boot
because these ions indicate eorrosion has taken place and metal has been removed from
an internal component in the system upstream of the sample point.
t should be appreciated that any suitable method may be used for
obtaining the dew point water sample. For example, devices for obtaining the dew point
water sample are disclosed in U.S. Patent Nos. 4,335,072, titled "Overhead Corrosion
Simulator' and 5,425,267, titled "Corrosion Simulator and Method for Simulating
Corrosion Activity of a Process Stream," each of which is incorporated herein by
reference in its entirety.
In at least one embodiment different fluid or system parameters or process
variables or other constituents present in the system could be measured and/or analyzed
including but not limited to pH; chloride ion; other strong a d weak acids, such as
sulfuric, sulfurous, thiosulfurous, carbon dioxide hydrogen sulfide; organic acids;
ammonia; various amines; and liquid or solid deposits and the like. Various methods of
taking measurements are contemplated and the invention is not limited to one particular
method. Representative methods include, but are not limited to those disclosed in US
Patent Numbers 5,326,482, 5,324,665, and 5,302,253.
In response to the measurements taken at various locations in the system
remedial chemistry can be added to the system to respond to the measured readings
Such remedial chemistries include but are not limited to neutralizes, filming inhibitors
(sometimes referred to herein as "filmers"), and caustic agents. These points are labeled
"Neutralizer based on acid or pH," "Filmer based on iron," and "Caustic based on
chloride." t should be appreciated that such chemicals may be added at any suitable
location in the system. In at least one embodiment, introduction of such chemicals into
the system are adjusted continuously. In other embodiments, chemical introduction is
adjusted intermittently or in relation to a schedule as determined for each individual
system.
Neutralizes), caustic agent(s), and filming inhibitors) may be introduced
to the system using any suitable type of chemical feed pump. Most commonly, positive
displacement injection pumps are used powered either electrically or pneumat al .
Continuous flow injection pumps are sometimes used to ensure specialty chemicals are
adequately and accurately injected into the rapidly moving process stream. Though any
suitable pump or delivery system may be used, exemplary pumps and pumping methods
include those disclosed in U.S. Patent Nos. 5,066,199, titled "Method for Injecting
Treatment Chemicals Using a Constant Flow Positive Displacement Pumping Apparatus"
and 5,195,879, titled "Improved Method for Injecting Treatment Chemicals Using a
Constant Flow Positive Displacement Pumping Apparatus," each incorporated herein by
reference in its entirety.
Representative neutralizers include but are not limited to 3-
methoxypropylamine MO ) (CAS # 5332-73-0), monoethanolamine (MEA) (CAS #
141-43-5), N N-dimemylaminoethanol (DMEA) (CAS # 108-01-0), and
methoxyisopropylamine (M O ) (CAS # 37143-54-7).
As a caustic agent, a dilute solution of sodium hydroxide is typically
prepared in a 5 to 0 % concentration (7.5 to 14° Baunie) for ease of handling and to
enhance distribution once injected into the crude oi , or desalter wash water, for example.
Concentration may be adjusted according to ambient conditions, such as for freeze point
in co d climates.
Filming inhibitors or fdmers used in conjunction with this invention in a
crude u it corrosion control program are typically oil soluble blends of amides and
imidazolines. These compounds offer good corrosion control with minimal effects on the
ability of the hydrocarbons in the system to carry water.
It should be appreciated that a suitable pH control or optimal range should
be determined for each individual system. The optimum range for one system may vary
considerably from that for another system. It is within the concept of the invention to
cover any possible optimum pH range.
n different embodiments, changes in the neutrahzer pump are limited in
frequency. Preferably, adjustment limits are set at a maximum of per 5 min and
sequential adjustments in the same direction should not exceed 8. For example, after 8
total adjustments or a change of 50 % or 100 the pump could be suspended for an
amount of time (e.g., 2 or 4 hours) and alarm could be triggered. If such a situation is
encountered, it is advantageous to trigger an alarm to alert an operator. Other limits, such
as maximum pump output may also be implemented. It should be appreciated that it is
within the scope of the invention to cause any number of adjustments in any direction
without limitation. Such limits are applied as determined by the operator.
It should he appreciated that a suitable or optimal chloride ion
concentration range should be determined for each individual system. The optimum
range for one system may vary considerably from that for another system It is within the
concept of the invention to cover any possible optimum chloride ion concentration range.
In at least one embodiment other metallurgy is used so such as mone
titanium, brass etc. may be used in some systems. In these eases, rather than an iron ion
concentration signal, the appropriate metal on (e.g.. copper, nickel, zinc, etc.)
concentration signal would be detected and analyzed.
Metal ions commonly exist in two or more oxidation stales. For example,
iron exists in Fe and Fe as well being present in soluble states (ionic and fine
particulate), insoluble states (i.e., filterable), etc Analysis and control of metal ions
includes measurement or prediction of any combination (or all) of such pe tations
present in the system.
Although the corrosion probes (e.g., electrical resistance corrosion probes,
linear polarization probes, and/or any other suitable method for detennining metal loss)
may be placed at any convenient location in the system, preferably they are placed in
historically reliable locations in the system in addition, f, for example, 2 overrides are
activated over a 12 hr period, a reliability check is typically initiated to ensure that the
corrosion probes are operating properly. If such a situation is encountered, it is
advantageous to trigger an alarm to alert an operator. Other limits, such as maximum
pump output may also be implemented. It should be appreciated tha it. is within the
scope of the invention to cause any number of adjustments in any direction without
limitation. Such limits are applied as determined by the operator.
n at least one embodiment, if the communication link between the
analyzer and the controller is severed or impaired, the controller continues with whatever
action it was undertaking prior to losing communication. In at least one embodiment, if
the communication link between the analyzer and the sensor is severed or impaired the
controller continues with whatever action it was undertaking prior to losing
com unication in at least one embodiment, if the analyzer output induces the controller
to enact a response beyond the physical limitations of the equipment the controller the
best response possible (such as turning on/off one or more pumps, vents, drains lifts,
stators, conveyers, furnaces, heat exchangers . .. etc.) and the controller keeps that
imderperforrning responding equipment running at its maximum capacity until the
analyzer output warrants a reduction in at least one embodiment at least one piece of
responding equipment is constructed and arranged to respond to analyzer output only
gradually. In at least one embodiment while the equipment can respond only gradually, it
is constructed and arranged to return to its pre-response setting as soon as physically
possible. This allows for the negation of an incorrect response before the response has
caused a significant effect An example of gradual response is a pump that increases the
flow of chemical from 0% of a maximum flow rate to 100% of maximum flow ate over
the course of up to 10 minutes even though it can reach 100% within a few seconds.
In at least one embodiment the analyzer utilizes a model method of data
analysis to correct for inaccuracies that occur in the measurements of process variables.
Because corrosion is by definition the result of a finite amount of mass from the plant
equipment detaching fro those pieces of equipment, the amount of corrosion measured
should be easy to correlate with physical damage to components of the system. However
due to large amounts of noise inherent in such facilities the measured rates, fluctuate
widely and are often not accurate. Significantly the noise often leads to measured
corrosion rates greater than the actual mass that has been removed from the equipment.
In addition different forms of crude oil (especially opportunity crude) and inconsistencies
in their composition cause equipment to often function differently during different
production runs. This leads to varying and hard to predict rates of corrosion. Moreover
as corrosion changes the very environment being analyzed each production run may
make further ambiguous future analyses.
In at least one embodiment the analysis takes into account the known
difference between the steady state measurement and the dynamic state measurement
taken by the sensor to correct for inaccuracies that occur in the measurements of process
variables. As illustrated in FiG. 1, in many situations a disturbance in the system (such
as turning on or off a pump, adding or ceasing addition of a chemical, changing pH, [Fe],
temperature, pressure etc. . ) causes a short term dynamic state change in the sensor
measurement as well as a longer term steady state change in the sensor measurement.
The analyzer learns to associate the specific dynamic state changes that occur in response
to specific disturbances with specific sensors and when under those conditions it detects a
similar dynamic measurement, instead of outputting the detected measurement the
analyzer outputs the corrected value that it has learned is associated with the properties of
the detected dynamic state.
As a result, in at least one embodiment the output of at least one sensor
measurement of a process variable obtained by the analyzer undergoes a conversion.
That output can be represented by the function;
u f (ef A , d)
in which u is output of the analyzer measuring a process variable, e is the error detected
in the dynamic state, d is the magnitude of the disturbance that caused the error, and Ae is
the change in the error over time. The error itself can be calculated using the equation:
e = SP-PV
in which PV s a process variable, or the actual value that the analyzer measured for the
variable and SP is the setpoint or what the value should have bee but for the disturbance
based noise.
In at least one embodiment the specific parameters of any predictive
function used to correct for a measured process variable can be calculated through direct
observation of the system.
Utilizing the above equations, one of ordinary skill in the art would
recognize that based on a Taylor series expansion,
— f Ae, )
where ί denotes steady state controller output; e ? ,and *are e, and d. The
controller consists of two parts: steady state, =/(e° , D έ , if) and dynamics /(e), ,
fid). The steady state can be obtained from direct measurements of the system steady
state n at least one embodiment at steady state at least one of e , d are e, A
and d is 0.
The dynamic part is approximated by the following nonlinear dynamic
model:
D . represents lumped uncertainties and other unmodeled terms, n at least
one embodiment it can be attenuated by control technology because it is bounded.
At steady state, ·' is known by human experience, or it is easy to know
by test or simple analysis and modeling. One useful meaning of -< is the result of the
ideal pump output when the controlled variable is at it's target Each dynamic part ./ is a
tunable function based on specific process, the function is also knowledge based and
S
within a control limits ' . In at least one embodiment the function is
designed according to a proportional format. In at least one embodiment the function is
designed according to a sigmoid format.
n at least one embodiment the system comprises output limits and the
variable limits ί to designate the boundaries permissible by system
control. In practice, mi — — l ' c U — +
where ' is a output scale factor which is
a constant tuned on-line, P s the variable scale factor which is a constant tuned on¬
line.
In addition, the resulting changes in the system due to feeding chemicals
needs to be predictable. Precise control of pH and corrosion is quite difficult due to large
variations in process dynamics. One difficulty arises from the static nonlinear
relationship in results of chemical additions such as titration. Titration is the relationship
between pH of a medium and the concentration of acids and bases in that medium. The
nonlinearity in titration depends on the substances in the solution and their
concentrations. For example the presence of some weak acids or weak bases causes a
buffering effect (a resistance to proportional changes in pH despite proportional changes
in the concentrations of acids and bases).
Other chemistries present in the process system may also have non-linear
responses to added chemicals n addition because of the ebb and flow rate of operations
in a process system, there are very long periods of deadtime. As previously mentioned
' can he represented by the result of the ideal pump output when the controlled
variable is at it's target h practice however due to sizes, distances that the chemicals
must traverse, and other physical constraints, the pump is in fact no ideal and there is a
significant lag between when the instruction is given to feed a chemical, and when the
chemical appears in the system in a dosage significant enough to appropriately affect the
system. For purposes of this application the time lag between activating a pump and the
pump causing the proper effect is known as "deadtime." During deadtime a number of
changing dynamics occur which ead to wildly inaccurate measurements of process
variables.
In at least one embodiment the analyzer utilizes a combination of human
knowledge and experience to adjust feed rates to take into account the nonlinear
properties the controller must address. This makes the controller more intelligent and
feasible.
The presence of other materials in the process system often affects the
nature of various acids further complicating any attempt to predict resulting pH from
changing the concentrations. As a result, if graphed, the shape of the expected titration
curve becomes quite irregular. In at least one embodiment, by disregarding noise and
error, the analyzer can accurately model an predict the correct titration curves is
required for effective pH control.
As a result, a method of signal processing may need to be utilized to
correctly measure a process variable. Suitable forms of signal processing include but are
not limited to DSP algorithms, filtering (including low pass, high pass, adaptive, and
moving average filters), smoothing, ARX, Fourier transform, S-plane analysis, Z-plane
analysis, Laplace transforms, DWT wavelet transforms bilinear transforms, and
Goertzel algorithms. In at least one embodiment analysis using dynamic state error is
2.0
done prior to the signal processing. n at least one embodiment analysis using dynamic
state error is subsequent to the signal processing.
Signal processing is of particular benefit with regards to detecting Fe.
One particular error involves the trend of iron detection to drop to zero. This reading is
obviously erroneous. As a result, if the signal processing does not correct for zero
concentration of Fe in a system that obviously contains Fe due to ongoing or previous
corrosion, the analyzer will correct the iron reading to what its learned experience
indicates it should be and/or to what the reading was immediately before it began its drop
to zero. In at least one embodiment, if the sensor detects zero iron the analzyer does not
pass on the detected iron value to the controller but instead passes on a value based on
what the iron level should be based on previous performance under similar conditions.
In at least one embodiment the control system compr es one or more
methods, compositions, and/or apparatuses described in Published US Patent Application
2012/0053861 A .
n at least one embodiment the control system compr es one or more
redundant sensors detecting the same process variable at substantially the same location
in the process system. Because much of the noise causing inaccuracies is random in
nature, the errors do not always affect all the sensors at. the same time. As a result under
certain circumstances a minority of sensors may be erroneous and a majority may be
correct n at least one embodiment if all of the sensors provide readings consistent with
pre-determined setpoints based on the specific conditions present, the analyzer returns the
average measurement to the controller. In at least one embodiment if at least one of the
sensors provides measurements consistent with the setpoints, the analyzer returns the
average measurement of the consistent measurements to the controller. In at least one
embodiment if all of the sensors provide measurements inconsistent with the setpoints,
the analyzer rejects all of the measurements and instead passes on to the controller
measurements based on historical data until at least one sensor again provides consistent
measurements. In at least one embodiment the historical data will be the average of some
or all previous measurements consistent with the setpoints.
In at least one embodiment, the analyzer's variable sampling period is
much longer than that of normal transmitters, (in some ases as high as 60 minutes). I
addition, the controlled variable expectations (setpoints) are normally in a range instead
of a single point.
In at least one embodiment remedial chemistry or process chemistry fed
by the controller is added according to a feedforward model. Feedforward can best be
understood by contrasting it to a feedback approach. In feedback the receipt of
information about a past event or condition influences the same event or condition in the
present or future. As a result the chain of cause and effect forms a circuit loop that feeds
back into itself.
In a feedforward model d e reaction to the information occurs before the
actual information is received. This allows for faster reaction to system problems,
reducing the duration, severity, and consequences of unwanted conditions. Feedforward
can be achieved using the same observations that are used to dete ne the analyzer
output function. Specifically because the analyzer changes the output to the correct value
before the correct value is detected by the sensor (in some cases while it is still receiving
dynamic state changing information.) Moreover feedforward allows for the elimination of
conditions that would otherwise persist during the dead time between the actual existence
of an unwanted condition and the delays caused by inaccurate measurements and
imperfect pump flow properties. In at least one embodiment the feedforward strategy
addresses an unwanted system condition faster than a feedback system can
n at least one embodiment the feedforward model is used to analyze the
variable relationship and eliminate the interactions. For example, in a crude oil refinery
logic used to determine if corrosion control measures needs to be enacted in response to
Fe concentration would be governed by a feedforward model reacting to analyzer output
according to a function of (Caustic, Neutralizer). This control algorithm provides whole
functionalities and capabilities to implement feedforward model. In at least one
embodiment the properties of the feedforward strategy is included in the controller
algorithm. The format of the controller algorithm its data analysis can be designed based
on specific properties of the system it is used within
As previously mentioned because corrosion is due to loss of mass in
process equipment, by definition the detected amounts of corrosion should equal the lost
mass. Because that however is not what the sensors often detect special measures need
to be taken by the analyzer to correct the detected levels of corrosion. In at least one
embodiment the corrosion rate (CR) is corrected by the analyzer by taking into account
both on-line detected levels and an analysis of the corrosion rate.
n at least one embodiment this analysis makes use of two definitions of
CR, instant CR and period CR. Both of the two rates reflect different aspects of
corrosion speed. Instant CR is defined as the rate of metal loss change at a specific fixed
period of time, e.g. one day or week. In at least one embodiment a corrosion probe (the
sensor) is used to detect a raw value. Due to the noisy signal inherent in such detections,
a linear regression or other form of signal processing may be used to correct the detected
value of Instant CR. Instant CR provides insight into instantaneous causes of corrosion
which is extremely helpful in determining the effect of changes in the process system
conditions.
n at least one embodiment Period CR requires several days or weeks to
determine the general corrosion rate. Period CR is determined by identifying which
linear function best represents the metal loss in such noisy environment. A simple linear
calculation is based on two points of beginning and end, this calculation assumes the
metal loss is monopoly increased function, does not consider the data between the two
points Obviously, this calculation does not. reflect real situation under noisy signals, most
likely, this calculation is far away from reality. A proper linear curve is generated by least
squares regression, which minimize the total distances between each point to the linear
curve.
m å ( —Y .)
where 7 represents the linear curve we design; Yi denotes real probe reading at i point.
F Gs. 3 and 4 show compared corrosion rates based on two point corrosion reading, two
point filtered corrosion reading, and linear regression. Essentially, the corrosion rate is
the slope of the linear curve, it shows how big discrepancy of the three calculations and
also we can understand which calculation is more reasonable and scientific. As shown in
FIG. 3, using a linear analysis of detected corrosion rates over the period can result in
multiple rates based on which form of analysis is used.
As illustrated in FIG. 4. in at least one embodiment the use of the linear
representation of the average regression curve is used to identify the actual rate of
corrosion that occurs in the system.
In at least one embodiment the decision regarding which linear
representation to use is constantly updated to best reflect observations made of the
system.
Referring now to FIG. 5 there is shown a logical flowchart illustrating
how information from various sources is constantly fed to and used by the analyzer to
improve the logic it uses to correct for incorrect readings. The analyzer utilizes:
(1) On-line and off-line filter design to smooth noisy corrosion probe reading and exclude
outliers, (2) corrected definitions of corrosion rates (instant mnning rate, period rate) and
their relationship to each other. This gives different definitions to calculate and compare.
(3) On-line (running regression CR) and off-line corrosion rate calculation and
monitoring and alarming corrosion rate. (4) Corrosion rate evaluation and analysis, used
by the controller, and (5) automatically generated analysis reports
In at least one embodiment the control system makes use of on-line
measurements of Process changes in one or more of temperature, pressure, velocity and
concentration to detect acceleration in corrosion rate. This can he done by making use of
instant CR and period CR.
n at least one embodiment the analysis is according to the following
equations:
Instant CR= dy/dt. Therefore:
A Instant CR y
D ΐ ®0
Because Period CR can be said to be the rate of metal loss change at a fixed period of
time, such as At or Ay/At. However, because of the signal "noise" that accompanies
metal loss y, if a linear regression of > is first used and then Period CR is calculated as the
slope with time At then:
Period CR
Instant CR and Period CR reflect different aspects of corrosion speeds. In at least one
embodiment Period CR is determined over several days or weeks to determine the
general corrosion rate: Instant CR is instantaneous corrosion which is extremely
helpful in determining the effects of process changes on corrosion.
In at least one embodiment the relationship between instant CR and Period CR is
determined by an integral mean- value theorem. For example:
Period CR
In which there exist a point x in [tl, t2] where the instant CR wi l be the same as the
Period CR. This point however will not necessarily be the mean median, mode, and/or
average of Instant and Period CR.
Although the corrosion process is very complex, under certain
circumstances the corrosion rate can approximate a simple linear function of time i,
according to the equation: y = at + b
where y is the monopoly metal loss function; t is time and a and h denote the slop
and bias of the function. Both a and b are all time-invariant constants.
Under this approximation:
y Ay y —y p . Instant CR = - — = a - - Perioa OK at i
This illustrates that if and only if the slope and bias a, b are unchanged
constants in the period of time At then Period CR will be equal to instant CR.
As shown in FIG. 6, in at least one embodiment the analyzer outputs
information into a dashboard format that provides a user with a helpful and easy to
understand perspective on the operations of at least a portion of the system For example
the various detected perfomiance variables can be expressed according to a relative
evaluation indicating how well or poor the system is doing.
n at least one embodiment the evaluation will be expressed according to
at least one of the following categories;
Control Variable Stability
Variable stability is very critical for process operation m cmde unit corrosion control
system, three critical variables (pH, CI, Fe) are the key to maintain the corrosion
system stable. Daily cpk is used and compared.
Chemical Usage
Neutralize!, Caustic and Filmer are used to control the three controlled variables./?//.
CI and Fe. One of objectives of this control design is to maintain the controlled
variables while saving the chemical usages.
Evaluation on Automation System Operation
The system not only provides the key variable measurement by the analyzer but also
(1) The system provides whole information, include pumps, boot water pressures,
working temperatures, inferred chemical flow rates,corrosion... (2) Provides friendly
interface, gives us a platform to remotely monitor and operate the whole system,
modify parameters... (3) Collects analyzer alarms, generates/sets all variable
operation alarms, and provides instant cell phone and email alarms, (4) Provides a
platform of on-line and off-line data analysis and translating information into
refined knowledge..., this is the spotlight of the system, (5) The control system on
stream time is 0% except some events happened.
Corrosion Performance Analysis
On line corrosion rate must be calculated and compared with other variables FIG. 7
gives an example of a weekly period corrosion rate based on two probes FIG. 8
shows an evaluation demonstrating that the corrosion rate is strongly correlated to the
critical variables F e and pH.
In at least one embodiment the process system that the control system in
used within contains at least one of a crude unit, de-sal ter, atmospheric tower, vacuum
tower, cooling unit, heating unit, furnace, cracker, and any combination thereof. The
control system will optimize and improve the performance of some, par or all the
components of the process system. Such improvement will ( ) Improve and maintain
process stability and reliability. (2) Optimize chemical usages and reduce cost. (3)
Improve system robustness, operating flexibility, provide reliable information system and
friendly low-cost interface. (4) Define, calculate, monitor, control and optimize corrosion
rate.
n at least one embodiment, not on y does the control system determine
and predict the corrosion in the aqueous phase of a crude unit overhead system but it can
also calculate and predict the formation of salts as well as their impact of corrosion. In at
least one embodiment, the analyzer can calculate in real time the amount of additive
(amine) to inject to remedy the impact of salts on corrosion.
in at least one embodiment this calculation is achieved by using at least
one of the following inputs: pH, chloride temperature, pressure, density, flowrate, wash
water rate, total steam, and the presence of the following compounds: Chloride, total
amine, total nitrogen, halogen, bromide, iodide, oxygen, water, and ammonia level. n at
least one embodiment this is accomplished by the addition of and observation of the
reaction of one or more of the following amines: meth amine, dimethyl amine,
trimethyl mine, ethylamine, diethylaraine, triethyi amine, n-propylamine, isopropylamine,
di-n-propylamine, di-isopropylamine, n-butylamme, sec-butylamine, l-amino-2,2-
dimethylpropane, 2-amino-2-methylbutane, 2-aminopentane, 3-aminopentane,
morpholine, monoethanolamine, ethyienediamine, propyl enediamine, N Ndimethylethanolamine,
N,N-diethylethanoiarnine, N,N-dimethylisopropanolamine,
Methoxyethylamine, Piperidine, Piperazine, Cycldhexylamine, N-methylethanolamine,
N-propylethanolamine, N-ethylethanolamine, N,N-dimeihylaminoethoxyethanol, N,Ndiethylaminoethoxyetlianoi,
N-methyldiethanolamine, N~propyldiethanolamine, N
ethyldiethanolamine, i-butylethanolamine, t-butyldiethanolamine, 2-(2-
di-n-butylaniine, tri-n-butylamine, di-iso-b ty amine ethyl-nbutylamine,
pentylamine, 2-am no-2,3-d y]b lane, 3-amino-2,2-dimethylbutane, 2-
amino- -methoxypropane, dipropylamine, monoarayl amine, n-butyiamine,
isobutylamme, 3-amino- -methoxypropane, and any combination thereof.
Using sensors to detect pH, Chloride, Fe, as well as a least one nitrogen
sensor, at leas one total nitrogen sensor or ihe combination thereof, a mathematical
model can calculate the formation of salt and or corrosive species This information and
th corresponding calculations can be made in real time from sample collected in real
time. The calculated and stored information can then be used to calculate and control the
addition of additives in real time into the overhead based on the corrosive nature and
composition of the compounds present in the overhead.
In at least one embodiment the control system can continuously
recalculate in real time the corrosive conditions; the salt formation and have the
controller add appropriate additives should any one-parameter change. These additives
include but are not. limited to: Water, Sodium Hydroxide, potassium hydroxide, lithium
hydroxide, methyl amine, dimethyl amine, trimethylamine, ethylamine, diethyl amine,
triethylamine, n-propylamine, isopropylamine, di-n-propylamine, di-isopropylamine, nbutylamme,
see-butylamine, l-amino-2,2-dimethylpropane, 2-amino-2-methylbutane, 2 ~
aminopentane, 3-aminopentane, morpholine, nionoethanoiamine, ethyl enedi mine
propylenediamine N,N-dimethylethanol amine, N.N-diethylethanolamine, N,Ndimethyiisopropanolamine,
Methoxyethylamine, Piperidine, Piperazine,
Cyclohexylamine, N-methylethanoiamine, N-propyiethanolamine. N-ethylelhanoiamine,
N,N-dimethylaminoethoxyeihanol, N.N-diethylaminoethoxyethanol, Nmethykiiemanol
amine, N-propyldiethanolamine, N-ethyidiethanolamine, tbutylethanolamine,
ί -butyldiethanolamine, 2-(2-aminoethoxy)ethanol, di-n-butylamine,
tri-n-butylamine, di-iso-butylamine, ethyl-n-butylamine, pentylamine, 2-amino-2,3-
dimethylbutane, 3~a ino~2,2 di ethylbutane, 2-amino- -methoxypropane,
dipropylamine, monoamylamine, n-butylamine, isobu y amine, 3-arnino-lmethoxypropane.
and any combination thereof.
In at least one embodiment the control system can detect through the use
of sensors the corrosion resulting from aqueous fluids or the formation of salt
compounds. These sensors are H, Chloride, Fe, Nitrogen, total nitrogen, ammonia
electrical resistance corrosion probes. In addition to measuring the corrosive
environment these sensors provide input into the analyzer facilitating the calculation of
appropriate amounts of chemical additives.
While this invention may be embodied in many different forms, there
described in detail herein specific preferred embodiments of the invention. The present
disclosure is an exemplification of the principles of the invention and is not intended to
limit the invention to the particular embodiments illustrated. All patents, patent
applications, scientific papers, and any other referenced materials mentioned herein are
incorporated by reference in their entirety. Furt hermore the invention encompasses any
possible combination of some or all of the various embodiments described herein and/or
incorporated herein. In addition the invention encompasses any possible combination
that also specifically excludes any one or some of the various embodiments described
herein and/or incorporated herein.
The above disclosure is intended to be illustrative and not exhaustive This
description will suggest many variations and alternatives to one of ordinary skill in this
art. The compositions and methods disclosed herein may comprise, consist of, or consist
essentially of the listed components, or steps. As used herein the term "comprising"
means "including, but not limited to". As used herein the term consisting essentially
of refers to a composition or method that includes the disclosed components o steps,
and any other components or steps that do not materially affect the novel and basic
characteristics of the compositions or methods. For example, compositions that consist
essentially of listed ingredients do not contain additional ingredients that would affect the
properties of those compositions. Those familiar with the art. may recognize other
equivalents to the specific embodiments described herein which equivalents are also
intended to be encompassed by the claims.
All ranges and parameters disclosed herein are understood to encompass
any and al subranges subsumed therein, and every number between the endpoints. For
example, a stated range of " 1 to 0" should be considered to include any and all
subranges between (and inclusive of) the minimum value of 1 and the maximum value of
10; that is, a subranges beginning with a minimum value of 1 or more, (e.g. 1 to 6.1),
and ending with a maximum value of 10 or less, (e.g. 2 3 to 9.4, 3 to 8, 4 to 7), and
finally to each number , 2, 3, 4, 5, 6, 7, 8, 9, and contained within the range.
All numeric values are herein assumed to be modified y the term
"about," whether or not explicitly indicated. The term "about" generally refers to a range
of numbers that one of skill in the art would consider equivalent to the recited value (i.e.,
having the same function or result) in many instances, the term "about" may include
numbers that are rounded to the nearest significant figure. Weight percent percent by
weight, % by weight, wt %, and the like are synonyms that refer to the concentration of a
substance as the weight of that substance divided by the weigh of the composition and
multiplied by 00.
As used in this specification and the appended claims, the singular forms
''a," "an," and "the" include plural referents unless the content clearly dictates otherwise.
Thus, for example, reference to a composition containing "a compound" includes a
mixture of two or more compounds. As used in this specification and the appended
claims, the term "or" is generally employed in its sense including "and/or" unless the
content clearly dictates otherwise.
This completes the description of the preferred and alternate embodiments
of the invention. Those skilled in the art may recognize other equivalents to the specific
embodiment described herein which equivalents are intended to be encompassed by the
claims attached hereto.
W at is claimed is;
. A method of correcting an error in the measurement of a process variable taken
sensor in a chemical process system characterized by properties which causes at least
some of the measurements to be erroneous, the method comprising the steps of:
identifying the component of the error caused by dynamic state factors, this
component of the error being detemiined by at least once obtaining a senor measurement
in the system and noting ow that measurement deviates from an objectively correct
measurement of the process variable by varying amounts relative to time,
identifying th steady state factor component of the error, this component of the
error being determined by at least once obtaining a senor measurements and noting thai
the measurement deviates from the objectively correct measurement of the process
variable by a fixed amount relative to time,
identifying the component of the error caused by additional factors,
and altering the measurement to remove the errors caused by steady state factors,
dynamic state factors, and unknown factors.
2, The method of claim 1 in which the sensor is in informational communication
with an analyzer and the analyzer is in informational communication with a controller,
the sensor constructed and arranged to obtain a raw measurement of the process variable
the analyzer correcting the error in the sensor's measurement, the controller taking the
corrected measurement and if the corrected measurement is outside of a pre-detennined
range of acceptable values enacting a remedial measure to change the measured value to
a value within the acceptable range.
3, The method of claim 2 in which the remedial measure is enacted before the steady
state value of the measurement is detected by the sensor.
4. The method of claim I n which the process variable is a measurement of one
item selected from the list consisting of: oxidation-reduction potential, pH, levels of
certain chemicals or ions (e.g., determined empirically, automatically, fSuorescently,
electOchem al colo etriea y, measured directly, calculated), temperature, pressure,
process stream flow rate, dissolved solids and suspended solids.
5, The method of claim 2 in which there are at leas three sensors, wherein each of
the three sensors passes on a raw measurement to the analyzer, the analyzer using the
average of those raw measurements as the input in its calculations if at least one of the
raw measurements fit within a pre~determmed setpoint expected for the specific
conditions under which measurement was taken, the analyzer a historically expected
value as the input in its calculations if none of the the raw measurements fit within a predetemiined
setpoint expected for the specific conditions under which measurement was
taken,
6. The method of claim 2 in which the process variable is iron concentration, the
method further comprising the steps of: disregarding all sensor readings that indicate zero
iron concentration, and adjusting the measured iron concentrations using regression
analysis over a 1 week time period.
7. The method of claim 2 in which the remedial measure involves adding a chemical
whose effect is non-linear in nature, the analyzer correcting for the non-linear effects of
the remedial chemical in its corrections.
8 The method of claim 2 in which the remedial measure involves adding a chemical
subject to the constraints of deadtime and the analyzer corrects for those effects in its
measurements.
9. The method of claim 2 in which the process system is one item selected from the
list consisting of: a chemical plant a refinery, an oil refinery, a food processing facility, a
manufacturing plant, a chemical plant, a distillation column, a water filtration plant, a
factory, a waste processing facility, a water treatment facility, and any combination
thereof.
10. The method of claim 2 in which the analyzer predicts the corrosion that
will result from the formation of salt compounds, the method utilizing inputs from at least
one of each of a : pH sensor, Chloride sensor, Fe sensor. Nitrogen sensor, total nitrogen
sensor, ammonia sensor, total amine sensor, and an electrical resistance corrosion probe
and in response the controller feeds into the system an appropriate amount of at least one
of: Water, Sodium Hydroxide potassium hydroxide, lithium hydroxide, methylamine,
dimethylamine, trimethyl amine, ethylamine , diethylamine, triethylamine, n-propylamine,
isopropylamine, d -n-propylamine, di-isopropyl amine, n-hutylamine, sec- butylamine, 1-
amino-2,2-dimethylpropane, 2-amino-2-methylbutane, 2-aminopentane, 3-aminopentane,
morpbo!ine, monoethanol mine, ethyl ned mine, propylenediamme, N,Ndimethylethanoiamine,
N, -diethylethanoiamine, -d methy isopropano a me,
Methoxyethylamine, Piperidine, Piperazine, Cyclohexylamine, N-methylethanolamine,
N-propylethano!amine, N-ethylethanolamine, N, -dimethylaminoethoxyethanol, N,Ndiethyiaminoethoxyefhanol,
N-methyldiethanolamine, N-propyidiethanolamine, Nethyldiethanolamine,
t-butylethanolamine, t-butyldiethanolamine, 2-(2-
aminoethoxyjeihanol, di-n-butyiarnine, tri-n-butylamme, di-iso-bulylaniine, ethyl-nbuty!
amine, pentylamine, 2-amino-2,3-dimethylbutane, 3-amino-2,2-dimethylbutane, 2-
amino- -methoxypropane, dipropylamine, on amyla nine n-butylamine,
isobutylamine, 3-amino-l -methoxypropane and any combination thereof.
11. The method of claim 2 further comprising the steps of:
(a) introducing an opportunity crude oil into a crude unit that previously
contained a different kind of crude oil, the properties of the opportunity crude
differing such from the previous crude oil that it disrupts the steady state of the
unit including causing a corrosion inducing spike in chloride concentration,
(b) the sensor measuring and/or predicting a property associated with the system
parameter at one or more points in the crude unit;
(c) determining an optimum range associated with the measured and/or predicted
property;
(d) if the measured and/or predicted property is outside of the optimum range
associated with that property, causing a change in an influx of a composition into
the process stream, the composition capable of adjusting the property associated
with the system parameter in a manner to bring the measured and/or predicted
property within said optimum range; provided that adjustments are limited to no
more than one per 30 minutes and if there are either four overall adjustments or
the adjustment results n a change of at least 50% of added composition then
further influx of composition is suspended for 4 hours; and
wherein the measuring/or predicting property comprises the steps of: collecting a sample
of fluid from a process stream to form a sample stream; adding a sulfide scavenger
obtained by reacting morpholine with iomialdehyde to the sample stream; passing the
sample stream through a membrane tha t prevents a reaction product of the sulfide
scaveiiger and sulfide from flowing therethrough; and allowing the sample stream that
flows through the memhrane to contact a chloride specific electrode of a measurement
cell to measure chloride content.