FREQUENTLY ASKED QUESTIONS
Click on topic to see questions:
Q. Will this system upset operations while I am home enjoying my weekend?
A. The system only makes suggestions. The board operator can override any suggestion. The system will not suggest anything it determines could cause your operating parameters to be violated.
Numerous checks and balances (see next question) have been utilized to ensure accuracy of decisions. A demonstrator has been provided to give the engineer the opportunity to manipulate process variables and operating parameters
so that you can verify for yourself that
the system will always make the correct decision as conditions change. For specific algorithm refer to the
demonstrator file, “Introduction” worksheet, under the heading “Details Of System Algorithm” or use the “Algorithm Details” button provided on the “12D2” worksheet.
safeguards are utilized to ensure accuracy of decisions?
A. The following safeguards have been implemented to protect against disruption of plant operations and to protect your product quality:
• Operating Parameters Entered By Engineer Faithfully Obeyed: The system will not ask the operator to
do anything that might take a variable outside of established limits (e.g., It will not decrease reflux if the
heavy component in the distillate is approaching the maximum limit or if tower loading parameters are
approaching minimum). For more information on system "permissives" please see row 24 of the
sheet "T. S." worksheet, accessible by pressing the "Technical Support" button on most
pages in the demonstrator file.
• Test for Stability of Operations Before Making Suggestions: The system will not make
recommendations unless it has determined operations to be at steady-state when prior
compositions/temperatures are compared to current (N/A if using lab data). When instability is detected
a warning is activated. The engineer can set the limits on this test. For more information please refer to
rows 47 and 48 of Technical Support ("T. S." worksheet found in the
• Protection Against Making Suggestions Based on Analyzer "Spikes": The aforementioned test for
stability of operations protects against bad recommendations based on analyzer spikes.
• Trending/Forecasting Minimizes Recommendations Based on Current Conditions Alone:
Forecasting avoids response to current conditions alone (e.g., It is much more beneficial to respond to
where the process has been and where it is going as opposed to where it is at the moment).
• Test For Current Lab Data: A timer is used to determine whether lab results are current. If system
determines time limit has been exceeded, operations is requested to verify lab results before making
recommendations (for more information see row 49 of "T. S."
worksheet found in the demonstrator file).
• Test for Current Update: Upon opening, the system checks for current update and a red message alerts
the operator that date and time may not be current, with a request to press the "Update" button.
• Messages Become More Aggressive When Product Specifications are Threatened: If the system
determines heavy components (or temperature) in the distillate to be greater than 120% of the distance
between the minimum and maximum limits (or if measuring purity, the purity is less than -20% of the
distance) it goes into a more aggressive position, adding reflux as opposed to the slower, but more energy-efficient approach of decreasing reboil. The same applies to the base composition. If the light components
in the base are more than 120% (or if measuring purity or temperature, the purity/temperature is less than
-20%) it will ask for an increase in reboil rather than a decrease in reflux. When this occurs a message is
activated to alert the operator that energy conservation messages have been deferred to address high
concentrations of heavies in the distillate (or lights in the base). More Info: See row 58
(Algorithm Details) of the "Instructions" worksheet found
in the demonstrator file.
• Test for Discrepancies Between Tower Delta Pressure, Feed and Reflux Rates: The system
compares the feed flow, feed plus reflux flows and the tower Delta pressure with the relationship to the
minimum/maximum limits for each. When a discrepancy it observed, a yellow warning is activated
and all suggestions for pressure changes are suspended. More information: See rows 42-45 of "T.
S" worksheet found in the demonstrator file.
• Test for Bad Instrumentation, Abnormal Feed Composition or Incorrect Operating Parameters: The system compares tower liquid loading to tower vapor loading to test for conflicting information. If a conflict is observed, a yellow warning is activated. For more information see row 46 of the "T. S."
worksheet found in the demonstrator file.
• Protection of Product Specifications When Automatically Adjusting Parameters: An absolute
maximum and/or minimum can be entered into the feature that automatically adjusts operating limits. The
system will not violate this maximum or minimum regardless of any other adjustment criteria.
• Links to Data Historian Are Checked Each Time System is Updated: The system checks for errors in
the data from the data historian and for changes in the data each time the update button is pressed. If errors
are detected or if the system does not detect a change in the data from one update to the next it attempts to
repair the links. If unsuccessful, a red warning is activated. For more information see row 20 of
the "T. S." worksheet found in the demonstrator file.
• Protection Against Discrepancies on Questionnaires: The system checks for discrepancies on the
questionnaire for each tower that could negatively impact decisions and alerts the user with a red message.
• System "Permissives" Adjust To Conditions: This system contains internal settings as permissives
that will not allow certain suggestions until satisfied. Generally, if the OH or base composition/temperature
is greater than 80% of the distance between the min and max limits it is considered to be approaching high
(designated as "~Hi"). However, if it is trending up or lab data, it is considered to be approaching high if it is
greater than 65% of the distance. If the OH or base composition/temperature is less than 20% of the
distance between the min and max limits it is considered to be approaching low ("~Lo"). However, if it is
trending down or lab data and is measuring the purity of the distillate, or the purity or the temperature of the
base stream, it is considered to be approaching low if less than 35%. Note: This has been a very simplistic
description. Please refer to row 24 of "T. S." worksheet
found in the demonstrator file for a complete description of all system
information on specific algorithm details refer to the Demonstrator, “Introduction” worksheet, under the heading “Details Of System Algorithm” or use the “Algorithm Details” button provided on the “12D2” worksheet.
Q. What if I have malfunctioning (or nonexistent) instrumentation?
A. Any non-existent or malfunctioning instrumentation can be taken out of the decision-making loop by entering "N/A" as the maximum parameter and “0” as the minimum. Bear in mind, however, this can have an effect on the quality of decisions the system makes.
Q. Does the system suggest magnitude of change (or only direction)?
A. The system makes suggestions for direction of move but does not suggest the magnitude of the change needed. This is left up to the discretion of the board operator.
Q. What if the board operator makes too large a move?
A. The system will not tell him he has made too large a change unless the move affects the column to the point one of the operating variables are in danger of moving outside of established parameters. If this happens, the system will suggest the most energy-efficient move to bring the column back under control. If operations become unstable, it will provide a message to that effect (error messages are fully addressed in the “Troubleshooting/Technical Support”
section of the demonstrator file).
Q. Does this system increase my risk of going off-spec?
A. Many clients have actually observed a
decrease in incidents due to the combination of increased scrutiny by operations and consistency of instructions afforded by our system.
This system is designed to eliminate over-refluxing of columns, which tends to “push the spec envelope”. Companies in the past have allowed operations to over-reflux as insurance against going off-spec. At current fuel prices this “insurance” is prohibitively expensive and worse, your customers do not pay extra for it.
Q. Does the system respond only to what it sees at the moment or does it try to determine direction?
A. The system monitors current distillate and base compositions (or temperatures) against those 40 minutes and 20 minutes prior in order to determine direction of movement before making suggestions. For specific algorithm refer to the Demonstrator, “Introduction” worksheet, under the heading “Details Of System Algorithm” or use the “Algorithm Details” button provided on the “12D2” worksheet.
Q. How does this system forecast direction of future movement?
The system looks at the values for compositions 40 minutes and 20 minutes prior to the current time as well as the current value and then by linear regression extrapolates to where the distillation tower will most likely be 40 minutes in the future. The program logic takes into account this future forecast in its decision making in order to produce advice for board operators that anticipates where the tower will be if no intervention takes place.
Q. How does the system respond to changing feed rates?
A. Very well. If operations are unstable it will notify the user that conditions are too unstable to make suggestions at the moment. If rates change it adjusts conditions accordingly, allowing the column to become a little less efficient during the initial change (to protect product quality), then optimizing over the next 12 to 24 hours after conditions stabilize. The system has proven to be very capable when providing suggestions for changing operating pressure as feed rates change.
Q. How does the system respond to changing feed compositions?
A. This system has proven to be very effective at cutting energy costs when feed compositions change on a regular basis. When compositions change it adjusts conditions accordingly, allowing the column to become a little less efficient during the initial change (to protect product quality), then optimizing over the next 12 to 24 hours after conditions stabilize. If operations are unstable it will notify the user that conditions are too unstable to make suggestions at the moment.
Q. What keeps the system from making decisions based on old lab data?
A. The system checks to ensure lab data is current before making suggestions. If lab data is not current a warning is given to the operator and no suggestions are made.
Q. Have you experienced reluctance on the part of board operators to follow system suggestions?
A. In some cases, yes. Board operators tend to over-reflux columns and the system is asking them to go against their human nature. Initially, operations may need a little prodding from management (the engineer may want to use the system to print “Daily Instructions” for operations).
An external override system is
built into the system that can be set up very easily to monitor other
towers and conditions in your process (whatever you choose) before
making changes to reflux, reboil or pressure. We have found using
this feature greatly improves the acceptance by operations
personnel. For more information on how to set up external overrides
please refer to row 54 of the "Instructions" worksheet
found in the demonstrator file. For more information on how human nature contributes to wasted
energy refer to row 8 of the same page.
Q. Can an operator make changes to the basic algorithms in the system?
A. Only employees of
EP Monitoring have access to system formulas.
Q. Can an operator make changes to minimum and maximum parameters?
Only authorized personnel can make these changes. Settings on the Questionnaire and Customize Sheets are password protected. The engineer assigned to the particular distillation column , or other person you charge with this responsibility, will make the determination as to who is assigned rights to change the settings established in the initial configuration of the software.