plant control - iea · 2009-04-10 · control of biological wwt 2002-03 gustaf olsson, iea, lund...
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Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Content
• Nitrate recirculation control
• Carbon dosage control• Chemical precipitation control
• Phase length control• Plant wide control
• Sampling – measurements• Control computers
• Plant information systems
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Nitrate recirculation control
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Pre-denitrification plant
Aerobic reactor
Sludge outtakeSludge recirculation
Influent
Internal recirculation
Effluent
Anoxic reactor
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Nitrate recirculation control
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Flow rate (lines 3 and 4)
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Effluent total nitrogen
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Total N concentration (lines 3 and 4
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Comparison of ratio and NO3setpoint control
Recirculation rate
Total N
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
The Nitrifier concentration as function of DO and NO3
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Carbon dosage control
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Influence of C addition
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Carbon Dosage Control
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Chemical Precipitation Control
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Chemical dosage based on hydraulic load
Effluent PO4-P conc.
Ingildsen
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Chemical dosage based on P load
Effluent PO4-P conc.
Ingildsen
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Chemical dosage based on P sensor feedback
Effluent PO4-P conc.
Ingildsen
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Detailed Look into the Control
Standard deviation is typically 0.03 mg/l PO4-P
Ful
l-Sca
le C
ontr
ol E
xper
imen
ts
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Chemicals Consumption
Strategy Average dosing
(l/min)
Relative consump. (compared to in situ
controller)
Insitu 0.42 100%
Constant 0.66 167%
Flow proportional 0.62 156%
Load proportional 0.54 136%
Källby WWTP: 130 % of the insitu control was used in parallel line using load proportional control
Ful
l-Sca
le C
ontr
ol E
xper
imen
ts
(in compliance during 90 % of time)
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Phase length control
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
One day in an alternating plant (Avedore, Denmark)
NH4-N
DO
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Content
• Nitrate recirculation control
• Carbon dosage control• Chemical precipitation control
• Phase length control• Plant wide control
• Sampling – measurements• Control computers
• Plant information systems
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Plant Wide Control
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Plant Wide Control
• Prepare the plant for large disturbances• Coordinate sludge treatment and WW
treatment• How to return to “normal” operation?• Implementations are gaining momentum
but at a low speed
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Uncertainty at the Plant Level
• External disturbances– storms, concentration variations
• Compromise sewer capacity -plant capacity
• New regulations
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Plant Wide Control (1)
Key interactions:
• hydraulics• use of resources• recycles within the plant• the operator
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Plant Wide Control (2)
• System definition– control handles
– setpoints of concentrations (C, N, P)– disturbances
• Degrees of freedom• Constraints• Objective function
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Ex: Plant wide BNR control
• Highly variable load
• Automatic adjustments of setpoints using N and P sensors
• Phase control
• DO setpoint control• Pure oxygen
addition• Chemical dosage• Return sludge flow
rate
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Ex: Stormwater Control
Required settler volume:
Vclarifier =
= k * Q * SSto clar* SVI
Aeration tank settling (Krüger A/S)
During high loads:increase the settler volume
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Operational Aspects (1)
• Almost universal acceptance of ICA –still a great amount of opportunity to further apply ICA
• Surveys show approximately 50% of control loops are currently run in manual mode
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Operational Aspects (2)
• On-line sensors no longer the main limitation for on-line control
• The lack of process flexibility is more troublesome and limiting
• “Software sensors” can be used to further enhance the benefits of ICA
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Conclusions
• We have to assume that all the local controllers are working
• Good DO control is crucial for the rest!• Use NH4 sensor to determine DOref
• Nitrate recirculation vs. DO setpoint• Plant wide control: take couplings into
consideration!
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Content
• Nitrate recirculation control
• Carbon dosage control• Chemical precipitation control
• Phase length control• Plant wide control
• Sampling – measurements• Control computers
• Plant information systems
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Sampling
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Sampling (1)
0 1 2 3 4 5 6 7 8 9 10 110
10
20
30
40
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Sampling - alias (2)
0 1 2 3 4 5 6 7 8
-1
-0.5
0
0.5
1
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Sampling - alias (3)
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40
0.5
1
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40
0.5
1
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Sampling -alias (4)
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40
0.5
1
1.5
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Loop sampling interval (1)
• In commercial process control software: 1 – 10 times per second
• Using larger sampling intervals – reduces the load on the computer– reduces wear and tear on the actuator
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Loop sampling interval (2)
• Sampling rate 6-10 times the bandwidth• Sample 6-10 times within the rise time
of the step response• Take notice if the instrument analysis
time is long
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Measurements
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Signal transmissionMeasurement
principle
Level
Conc
Instru-ment
SampleTrans-mission
Scree-ning
Sto-rage
Valuedisplayed
App-lica-tion
Sen-sor
Trans-mission
Scree-ning
Sto-rage
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Visualisation
• What you measure is considered important => Work will be focused to improve what is measured
• To measure is to know• You can control what you measure• Without information you can not take
responsibility • With information you will take the
responsibility
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
1. Know the demand2. Measurement principle3. Transmission4. Validation5. Maintenance 6. The application7. Self diagnosis
Measurement Quality
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Common errors
• The sensor– Is the measurement
representative?– Is the sensor
mounted properly?– The sensor is never
better than the measurement principle
• Presentation– Do not show
unreasonable accuracy (DO conc = 2,54675 mg/l)
– Show the inaccuracy (DO conc = 2,5 +/-0,1 mg/l)
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Content
• Nitrate recirculation control
• Carbon dosage control• Chemical precipitation control
• Phase length control• Plant wide control
• Sampling – measurements• Control computers
• Plant information systems
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Control computers
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
The State Concept
Sequencing circuits
– one state at a time– state transfer
– conditions for each state transfer
1 2
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Grafcet 11
2
3
4
Close outlet valve
Pump on
Tank empty
Pump off
Heat on
Heat off
Wait_time = tim1
Open outlet valve
5
Empty ∗ start " True if the lower level sensor Empty = 1 and when a start order is given
" Starts the filling
Full " The level has reached the upper limit
" Stop filling and start heating
Temp " The desired temperature is reached
" Define waiting time = tim 1
Wait_time " The tim1 has expired
Empty " Tank is empty
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Grafcet 2• Developed in France 1977• Graf + AFCET (Association Francaise
pour la Cybernetique Economique et Technique)
• French standard 1982• IEC standard 1988 - IEC 848
(=SFC, Sequential Function Chart)• Essential part of IEC 61131-3
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
PLC programming
New standard 61131-3 implies:• definition of sequential function chart
(SFC), and 4 language options– instruction list– function block– ladder diagram
– structured text
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
PLC open
• PLC open is an organisation to support the standard IEC 61131-3
• Manufacturer and product independent• Members of the PLC open group are
expected to deliver products that follow the 61131-3 standard
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Plant information systems
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
The Operator
• Makes critical decisions in real time
• Well educated
•Demands improvement
Use the human resources to improve the process
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
OEE - Overall Equipment Efficiency
• Availability• Plant efficiency• Quality
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
Process-industri
Plastindustrin Skärandebearbetning
Elektronik,övriga
Elelektronik-industrin
Plåtindustrin Elektronik,ytmontage
OEE in some industries
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Functional View
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Supervisory Level
• Time minutes to hours• Plant-Wide Control:
– model-based control– optimisation
– scheduling– decision support systems
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Management Level
Time - hours to days• Information Systems:
– production reporting– financial reporting
– production planning– decision support systems
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Reporting
• Key to successful management• Format reports CAREFULLY:
– apply KISS (Keep It Short & Simple) principle
– keep a high signal-to-noise ratio
– tailor reports by reader, time and place– organise information hierarchically (easy
lookup for custom reporting)
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Quality Information System
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Quality information
• Confidence limits for measurements• Check that a variable is not constant too
long• Compare measurements at the same
time• Compare measurements with models• Alarm for deviations from expected
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Decision Support
• Supervisory:– operational advice (encapsulating process
knowledge)– problem detection & diagnosis
• Management:– production planning constraints
(encapsulating process knowledge)
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Implementation
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Implementation Issues
• Accessibility - data flows and rights of access
• Reliability - architecture, redundancy, time to repair
• Flexibility - “standard” & common open architecture
• Equipment Constraints - avoid proprietary systems
• Cost - yes always, but compare to the benefits
Control of Biological WWT 2002-03
Gustaf Olsson, IEA, Lund University
Summary
• Many different time scales – sampling• Measurement quality• Who needs the information?• Quality in information• Information for decision support