3p04_tutorial_1 sensorflow 2008.pdf
TRANSCRIPT
![Page 1: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/1.jpg)
Chemical Engineering 3P04
Process Control
Tutorial # 1
Learning goals
1. Sensor Principles with the flow sensor example
2. The typical manipulated variable: flow through a conduit
![Page 2: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/2.jpg)
Sensors: We need them to know the process conditions(for safety, product quality, ….)
Where are the sensors?- Located at the process equipment
- Some displays near the equipment for use by people working on the equipment
- Some displays transmitted to a centralized location for use by computers and people to control, monitor, and store in history
![Page 3: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/3.jpg)
Sensors, local indicators, and valves in the process
Central control room
Sensors: We need them to know the process conditions(for safety, product quality, ….)
The control system does a lot!
Displays of variables, calculations, commands to valves and historical data are in the centralized control center.
Valve opening determined by the signal from computer
![Page 4: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/4.jpg)
Sensors: What are important features for process control?
• Accuracy• Repeatability• Reproducibility• Span (Range)• Reliability• Linearity• Maintenance• Consistency with process
environment• Dynamics• Safety• Cost
These are explained in the “pc-education” site.
Most engineers select sensors, do not design
them.
![Page 5: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/5.jpg)
Sensors: What are important features for process control?
Sensors - We must “see” key variables to apply control
Please define the following terms
Accuracy =
Reproducibility =
![Page 6: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/6.jpg)
Sensors - We must “see” key variables to apply control
Please define the following terms
Accuracy = Degree of conformity to a standard (or true) value when a sensor is operated under specified conditions.
Reproducibility = Closeness of agreement among repeated sensor outputs for the same process variable under the same conditions, when approaching from various directions.
Sensors: What are important features for process control?
![Page 7: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/7.jpg)
A B
C D
Discuss the accuracy and reproducibility in these cases
Sensors: What are important features for process control?
![Page 8: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/8.jpg)
Sensors: Is accuracy in flow measurement important?
Petroleum refinery processing 100,000 barrels/day of crude oil: A +0.50% errorin flow measurement represents about
15 million $ /year extra cost to purchaser!
Petro-Canada Refinery
Add a strong base to neutralize (pH=7) a strong acid: a +0.50% error in the base flow represents
A pH of about 10-11 !
Strong Acid-Base Titration Curve
0
2
4
6
8
10
12
14
0 0.5 1 1.5 2
Flow of Base (fraction of neutralization)
pH
![Page 9: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/9.jpg)
McMaster University pH Control Laboratory
Titration: Do you believe in automation?
http://www.mpcfaculty.net/mark_bishop/titration.htm
Manual Automated
http://www.fhs.mcmaster.ca/oehl/main.html
pH control
![Page 10: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/10.jpg)
FC
cooling
Sensors: How do we measure fluid flow?
This control system requires a flow measurement. Let’s consider a situation in which the liquid is a “clean fluid” with turbulent flow through the pipe.
liquid
![Page 11: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/11.jpg)
Sensors: How do we measure fluid flow?
The most frequently used flow sensor is the orifice meter. What is the basic principle for this sensor?
Velocity increases; Bernoulli says that pressure decreases
FC
cooling How can we use this behavior to measure flow?
liquid
![Page 12: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/12.jpg)
Porifice=P1 – P3
Distance
pres
sure
Sensors: Principles of the orifice meter
PorificeMeasure pressure drop
![Page 13: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/13.jpg)
From: Superior Products, Inc. http://www.orificeplates.com/
Sensors: Principles of the orifice meter
Nice visual display of concept.
In practice, pressure difference is measured by a reliable and electronic sensor = Porifice
![Page 14: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/14.jpg)
Bernoulli’s eqn.
General meter eqn.
Installed orifice meter(requires density measurement)
0 = aver. density
C0 = constant for specific meter
Installed orifice meter(assuming constant density)
31 PPKF Most common flow calculation, does not require density measurement
v = velocity
F = volumetric flow rate
f = frictional losses
= density
A = cross sectional area
Relate the pressure drop
to the flow rate
![Page 15: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/15.jpg)
P
cooling
K
Take square root of measurement
Multiply signal by meter constant K FC
Measure pressure difference
“Measured value” to flow controller
When an orifice meter is used, the calculations in yellow are performed.
Typically, they are not shown on a process drawing.
Sensors: Principles of the orifice meter
liquid
![Page 16: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/16.jpg)
General meter eqn.
v = velocity
F = volumetric flow rate
f = frictional losses
= density
A = cross sectional area
Relate the pressure drop
to the flow rate
Cmeter
Reynolds number
We assume that the meter coefficient is constant. The flow accuracy is acceptable only for higher values of flow, typically 25-100% of the maximum for an orifice
Sensors: Are there limitations to orifices?
![Page 17: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/17.jpg)
Porifice=P1 – P3
Distance
pres
sure
Sensors: Is there a downside to orifices?
What is a key disadvantage of the orifice meter?
Pressure loss!
When cost of pressure increase (P1) by pumping or compression is high, we want to avoid the “non-recoverable” pressure loss.
Ploss = P1 – P2
Non-recoverable pressure drop
![Page 18: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/18.jpg)
Accuracy • Typically, 2-4% inaccuracy• Strongly affected by density changes from base case
Repeatability • Much better than accuracyReproducibility • Much better than accuracySpan • Accuracy limited to 25-100% of span
• Span achieved by selecting diameter of orifice and Porifice
Reliability • Very reliable, no moving partsLinearity • Must take square root to achieve linear relationship
between measured signal and flow rateMaintenance • Very lowProcess Environment
• Turbulent, Single liquid phase, no slurries (plugging)• Straight run of pipe needed (D= pipe diameter),
10-20D upstream, 5-8D downstreamDynamics • Nearly instantaneousSafety • Very safeCost • Low equipment (capital) cost, large number of suppliers
• High operating cost (non-recoverable pressure loss)
Sensors: Factors in selecting an orifice meter
![Page 19: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/19.jpg)
![Page 20: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/20.jpg)
Principles of flow through a closed conduit
For liquids we typically install a pump to provide the work required for flow.
What is the principle for a centrifugal pump?
What in adjusted to affect the flow in this system?
Constant speed centrifugal pump
In typical processes, we manipulate the flow to achieve desired operating conditions
liquid
![Page 21: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/21.jpg)
Inlet (suction)
Outlet
Flow principles: Let’s look at a typical centrifugal pump
Motor (work)Pump
Flow = F1 (m3/min)
Pressure = P1 (kPa)
Flow = F2 (m3/min)
Pressure = P2 (kPa)http://www.pumpworld.com/centrif1.htm
For an animation and description of the basics of a centrifugal pump, follow the hyperlink below.
![Page 22: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/22.jpg)
Inlet (suction)
Outlet
Flow principles: Let’s look at a typical centrifugal pump
Motor (work)Pump
Flow = F1 (m3/min)
Pressure = P1 (kPa)
Flow = F2 (m3/min)
Pressure = P2 (kPa)
F1 F2
P1 P2
What goes here?
=
>
<
![Page 23: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/23.jpg)
Inlet (suction)
Outlet
Motor (work)Pump
Flow = F1 (m3/min)
Pressure = P1 (kPa)
Flow = F2 (m3/min)
Pressure = P2 (kPa)
F1 = F2
P1 < P2
What goes here?
=
>
<
Flow principles: Let’s look at a typical centrifugal pump
![Page 24: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/24.jpg)
Flow rate
Hea
d at
pum
p ou
tlet
Constant speed centrifugal pump
Principles of flow through a closed conduit
liquid
P0 = constant
We turn on the pump motor and let the system reach steady state. How do we calculate the flow rate that would occur?
Hint: Use the plot at the left.
![Page 25: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/25.jpg)
Flow rate
Hea
d at
pum
p ou
tlet
Pump head curve
“system” curve, pressure drop vs flow rate
Steady-state flow rate at given conditions
Constant speed centrifugal pump
What if we want a different the flow in the system?
Principles of flow through a closed conduit
liquid
P0 = constant
![Page 26: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/26.jpg)
Flow rate
Hea
d at
out
let o
f pum
p To achieve the desired flow, we vary the system resistance by changing the pressure drop across a valve .
We adjust thevalve opening
to achieve the desired flow rate!
Constant speed centrifugal pump
Principles of flow through a closed conduit
liquid
![Page 27: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/27.jpg)
Principles of flow through a closed conduit
http://www.cheresources.com/centrifugalpumps2.shtml
liquid
For a clear and comprehensive description of centrifugal pumps and flow in pipes, follow the hyperlink below.
![Page 28: 3P04_Tutorial_1 SensorFlow 2008.pdf](https://reader030.vdocument.in/reader030/viewer/2022032522/55cf905c550346703ba52a2f/html5/thumbnails/28.jpg)
Tutorial # 1 Learning goals
1. Sensor Principles with the flow sensor example
2. The typical manipulated variable: flow through a conduit
P
K
Take square root of measurement
Multiply signal by meter constant K FC
Measure pressure difference
“Measured value” to flow controller Now, we understand the sensor and the
flow principles!
liquid