Energy Seminar
Emerson Process Management
June 22/23, 2010
Process Control Fundamentals
Kurt Schmelzer & Tom Marsh
Novaspect, Inc.
Process Control Applies…
Process
Steam
Drives
Purchased
Steam
Purchased
Fuel
Central
Steam / Water
Production
Export
Steam
Process
Heating/
Cooling
Water
Process
Steam
Generated
Process
Fired
Equipment
Raw Material
as Fuel
Export
Fuel
Central
Power / Air
Production
Utility Plant
Purchased
Power
Process
Direct Fuel
Usage
Process
Misc. Electric /
Air Usage
Export
Power
Process
Electric
Drives
Site Processes
Causes of Variability
Loops
Loops
Increases
Increases
Variability
Variability
As Many As 80% of
Loops Actually
Increase Variability
20%
Design
Design
Design
30%
Tuning
Tuning
30%
20%
Source: Entech---Results
from audits of over 5000
loops in Pulp & Paper Mills
The Cause
The Cause
Control
ControlValve
Valve
Performance
Performance
SUPERHEAT TEMP.
Main Steam Temperature Control
Decreased Variability = Increased Profit
Upper Limit
NPHR
= 0.75%
Reduction
Set Point
Increased Temp. Set Point
Reduced Process Variability
Provides the Opportunity for
Setpoint Change
= ( NPHR) X Fuel cost X KW-HR generated/year = Savings
= .75% x 11,000 BTU/KW-HR X $2.22/MM BTU X 320,000 KW X 8760 hours / year =
$516,517 per operating year !!
The Energy Improvement Process
Begin
Survey and
Measure
Implement Site
Management
Optimize Unit
Processes
Fix Devices
and Loops
Address
Equipment
Practical Process Control

Basics of Process Control

Keys for Boiler Control

Keys for Chiller Control
Basics




Measurements
Final Control Elements
Controller
Control Strategy




Correct for application
Correct for application
Set-up and Tuning
Designed to the system
Basic Controls Can Save Energy
Upper Limit
Set Point
Increased Set Point
Lower Limit

What is the key to capturing the performance of
measurements and final control elements
STRATEGY
&
TUNING
Boiler Control
Boiler Control Measurements Keys

Drum Level
– Accuracy, and Reliability

Fuel Flow
– Repeatability, and Reliability

Air Flow
– Repeatability, and Reliability

Flue Gas Oxygen
– Accuracy, and Reliability

Steam Flow
– Accuracy, and Reliability

Feedwater Flow
– Accuracy, and Reliability
Boiler Control Controller Keys

Controller/s capable of handling the highly
interactive boiler process
– Fast enough to unlock the performance for the
measurements and final control elements.
Typical 0.5 Sec.
– Digital Resolution equal to the field instrumentation
32 Bit floating point required
Energy Saving Control Strategies
Stack O2 Trim
Ensures you maximize
energy savings
Tuning
Tuning – Coordinated Lambda
Tuning – Cross Limit Effect
Boiler Control Tuning

Open Loop Bump Testing
– Air & Fuel are Self Regulating Processes
• Maximize Speed of Response
• Improve performance by coordinating response to maintain
fuel/air ratio through load changes
• Optimize to lower O2 as control improves.
– Understand what your O2 reading Represents.
– Determine CO Limits
– Feedwater Flow is a Self-regulating Process
• Maximize Response as this is the inner loop
– Drum Level is an Integrating Process
• Average of Several Slopes to get best response.
Chiller Plant Overview
Chiller Overview
Cooling Towers
Sequencing
Chiller Control Measurement Keys

Temperature
– Accuracy, and Reliability

Temperature
– Accuracy, and
Reliability

Temperature
–Accuracy, and
Reliability

Water Flow
– Accuracy, and Reliability
Key Final Control Elements



Compressor Guide Vane
Actuator
Child Water Flow
Refrigerant Level
Temperature Control Tuning

Open Loop Bump Testing
– Self Regulating Process or Near Integrating Process
• Ensure self regulating process has reached final temperature
• Improve performance by treating as integrating process

Dead Time
– Chiller on-board loops should have relative short
dead-time
– System loops may have significant dead-time
• Dead time approach – PID, Model Predictive, Smith Predictor

Sequencing
– Control of the Various Redundant Systems
Optimization is a Building Process
Sustainable Business Results Are at Risk
if a Holistic Approach is Not Utilized
Optimize Unit
Process
SOP
Tuning
Math and Model
Adjustment
Control Platform and
Single-Knob Automatic Regulatory
Process
Measurement
Address
Equipment
Process
Actuation
Process Issue
Resolution / Mitigation
Fix Devices
and Loops
Single Knob - Control

Attention to fundamental are the keys.

Robust fundamental controls are the foundation
to energy management solutions.
The Takeaway
Ineffective controller tuning is the
biggest single contributor to poor
control loop performance and energy
waste …stay focused on Loop Tuning!