1. Preferred Utilities Manufacturing Corp
Combustion Theory Boiler
Efficiency And Control
Preferred Utilities Manufacturing Corporation
31-35 South St. • Danbury • CT
T: (203) F: (203)

2. Overview Introduction Combustion Basics Efficiency Calculations
Control Strategy Advantages and Disadvantages
Summary

3. Preferred Utilities Manufacturing Corp.
Over 80 Years of Combustion Experience
Custom Engineered Combustion Solutions
Package Burners for Residual Oil, Distillate Oil and Natural Gas
Fuel Handling Systems for Residual Oil Burners
Fuel Handling Systems for Distillate Oil Burners
Diesel Engine Fuel Management Systems
Combustion Control Systems
Burner Management Systems
Data Acquisition Systems

4. Instrumentation & Control Products
DCS-III
Programmable Controller
Plant Wide Controller
PCC-III
Multiple Loop Controller
Draft Control

5. Distributed Control Station
Operator Interface
JC-10D Process
Bargraph Display
PCC-III
Faceplate Display
SCADA/Flex
Distributed Control Station
LCD
Message Display
OIT10 Operator
Interface Terminal

6. Sensors HD-A1 Tank Gauge Leak Detector Pressure Sensor Outdoor Air
Temperature Sensor
Tank Gauge
Level Sensor
ZP Oxygen Probe
PCC-300 EPA
Opacity Monitor
JC-30D
Opacity Monitor

7. Boiler Room Fire Safety

8. PCC-III Combustion Experience
Boiler Specific...
Operator Friendly
F(x) Characterizers with “Learn” Mode
Built In Boiler Efficiency
Constructed For Boiler Front Mounting
120 Vac Inputs for Direct BMS Interface
Triac Outputs to Drive Electric Actuators
Free Standard Combustion Blockware
Preferred has over 30 years experience in design, manufacturing, and field service for digital combustion control.
There are many digital controller manufacturers, but NONE have Preferred’s in-depth and ongoing combustion control experience.

9. UtilitySaverTM Burner Control
Fuel and Electrical Savings…
The UtilitySaver includes firing rate control with both oxygen trim and variable speed fan combustion air flow control.
UtilitySaver fuel and electrical savings can pay for the installed system in two years or less.

10. BurnerMate Touch Screen
Fully Integrated Touch Screen…

11. BurnerMate Touch Screen
DCS-III Controller…

12. BurnerMate TS
Advanced
Communication…

13. BurnerMate Touch Screen
Easy Operation…

14. BurnerMate Touch Screen
Easy Setup…

15. Combustion Basics What is fuel made of? What is air made of?
What happens when fuel is burned?
Where does the energy go?
What comes out the smoke stack?

16. Most Fuels are Hydrocarbons
Common fuels have “typical” analysis
can be used for most combustion calculations
especially for natural gas
also number 2 fuel oil
Residual oil can be approximated with a typical fuel oil analysis
Wood, coal, waste require a case by case chemical analysis for combustion calculations

17. Typical Ultimate Analysis of Common Fuels
Common Fuels Analysis
Typical Ultimate Analysis of Common Fuels
Percent by Weight

18. Composition of (Dry) Air
By Volume
20.95% Oxygen, O2
79.05% Nitrogen, N2
By Weight
23.14% Oxygen
76.86% Nitrogen
Can be up to 9% H2O by volume in Summer
Traces of Argon and CO2

19. Common Combustion Reactions
Neglecting H2O in Air
Neglecting NOx, Other minor reactions
Simplifying percentages:
4N2 + O H2 Þ 2H2O + 4N2 + Heat
4N2 + O C Þ CO2 + 4N2 + Heat
4N2 + O S Þ SO2 + 4N2 + Heat

20. Common Combustion Reactions
For Methane
CH4 + 2O2 Þ CO2 + 2H2O + Heat Þ
Therefore:
#O2 Required = 64
# Fuel = 16
Therefore #O2/#Fuel =4/1 or 4

21. Boiler Efficiency and Control
Boiler efficiency is computed “by losses”
Understanding of efficiency calculations helps in choosing the proper control strategy
Energy “traps” such as economizers can provide a payback
Preferred Instruments has over 75 years of combustion experience to help optimize boiler efficiency

22. Boiler Efficiency “by Losses”
Conservation of Energy
Fuel energy in equals heat energy out
Energy leaves in steam or in losses
Efficiency = 100% minus all losses
Typical boiler efficiency is 80% to 85%
The remaining 15% to 20% is lost
Largest loss is a typical 15% “stack loss”
Radiation loss may be 3% at full input
Miscellaneous losses might be 1 to 2%

23. Boiler Energy Balance

24. Stack Losses Latent heat of water vapor in stack
Fixed amount depending on hydrogen in fuel
About 5% of fuel input for fuel oil
About 9% of fuel input for natural gas
Assumes a non-condensing boiler (typical)
Sensible heat of stack gasses
Typically around 10% of fuel input
Increased mass flow and stack temperature increase the loss

25. Radiation Loss Generally a fixed BTU / hour heat loss
As a percentage, is greater at low fire
Depends on the boiler construction
Is generally about a 3% loss at high fire
Would be 12% loss at 25% of fuel input

26. Miscellaneous Losses Consist of: Generally on the order of one percent
blow down losses
unburned fuel losses (carbon in ash or CO)
Generally on the order of one percent

27. Excess Air Required for Burners

28. Excess Air Required for Burners

29. Excess Versus Deficient Air

30. Effects of Stack Temperature
Generally, stack temperature is:
Steam temperature plus 100 to 200 degrees F
Rule of thumb – watertube-150, firetube-100F
Higher for dirty boilers, higher loads and increased excess air levels
A 100 degree increase in stack temperature
Costs about 2.5% in energy losses
May mean the boiler needs serious maintenance
Economizers are useful on medium and high pressure boilers as an energy “trap”

31. Efficiency Calculation Charts

32. Oxygen and Air Required for Gas
To release 1 million BTU with gas
42 lbs. of gas are burned
168 lbs. of oxygen are required no excess air
725 lbs. of combustion air
767 lbs. of stack gasses are produced
5% to 20% excess air is required by burner
Each additional 10% increase in excess air:
Adds 73 lbs. of stack gasses
Reduces efficiency by 1% to 1.5%

33. Cost of Inefficiency
The combined effects of extra excess air and the resulting increase in stack temperature:
Could mean a 2% to 10% efficiency drop
Reducing this “extra” excess air saves fuel
Savings = (Fuel Cost)*[(1/old eff)-(1/new eff)]
For a facility with a 30,000 pph steam load
10% to 60% Extra Excess Air Represents From $6,000 to $35,000 in potential savings per year
Running 20 hours, 300 days, $4.65 per MM Btu

34. Combustion Control Objectives
Maintain proper fuel to air ratio at all times
Too little air causes unburned fuel losses
Too much air causes excessive stack losses
Improper fuel air ratio can be DANGEROUS
Always keep fuel to air ratio SAFE
Interface with burner management for:
Purge
Low fire light off
Modulate fuel and air when safe to do so

35. Related and Interactive Loops
Feedwater Flow
feedwater is usually cooler than water in boiler
adding large amounts of water cools the boiler
cooling the boiler causes the firing rate to increase
Furnace Draft
changing pressure in furnace changes air flow
changed air flow upsets fuel to air ratio

36. Variations in Air Composition
“Standard” air has LB. O2 per FT3
Hot, humid air has less O2 per cubic ft
20% less at 95% RH, 120OF, and 29.9 mm Hg
Dry, cold air has more O2 per cubic ft
10% more at 0% RH, 32OF, and 30.5 mm Hg
Combustion controls must:
Adapt to changing air composition (O2 trim), or
Allow at least 20% extra excess air at “standard” conditions

37. Control System Errors
Combustion control system can not perfectly regulate fuel and oxygen flows. Therefore, extra excess air must be supplied to the burner to account for control system errors…
Hysteresis
Flow transmitter can not measure fuel Btu flow rate (Btu / hr)
Oxygen content per cubic foot of air changes with humidity, temperature and pressure
Fuel flow for a given valve position varies with temperature and pressure

38. Control System Errors

39. Control System Errors

40. Combustion Control Strategies
Single Point Positioning (Jackshaft)
Fuel and air are tied mechanically
Simple, low cost, safe, requires extra excess air
Parallel Positioning
Fuel valve and air damper are positioned separately
Allows oxygen trim of air flow
Fully Metered
Fuel and air FLOW (not valve position) are controlled

41. Jackshaft Strategy
One actuator controls fuel and air via linkage. It is assumed that a given position will always provide a particular fuel flow and air flow.
All control errors affect this system. Typically, % extra excess air must be supplied to the burner to account for control inaccuracies.
Oxygen trim systems can reduce the extra excess air to 10%
Suitable for firetube boilers and small watertube boilers. Used when annual fuel expense is too small to justify a more elaborate system.

42. Jackshaft Strategy

43. Jackshaft Strategy Disadvantages Advantages
Fuel valves and fan damper must be physically close together
Changes in fuel or air pressure, temperature, viscosity, density, humidity affect fuel-air ratio.
Only one fuel may be burned at a time.
Not applicable to multiple burners.
Not applicable to variable speed fan drives.
Oxygen Trim is difficult to apply, trim limit prevents adequate correction
Advantages
Simplicity
Provides large turndown
Inexpensive

44. Parallel Positioning Strategy
Separate actuators are used to position fuel and air final devices, flows are unknown. Fuel to air ratio can be varied automatically
Cross Limiting is employed for safety and to prevent combustibles or smoke during load changes. Cross Limiting requires and accurate position feedback signal from each actuator. A failure of either actuator or feedback pot will force the air damper open and the fuel valve to minimum position.
Many of the same applications, limitations and improvements described in the Single Point Positioning section also apply to Parallel Positioning

45. Parallel Positioning Strategy

46. Parallel Positioning Strategy
Advantages
Allows electronic characterization of fuel-air ratio
Adapts to boilers with remote F.D. fans and / or variable speed drives
Provides large turndown
Allows low fire changeover between fuels
Oxygen trim is easy to accomplish
Disadvantages
Changes in fuel or air pressure, temperature, viscosity, density, humidity affect fuel-air ratio.
Only one fuel may be burned at a time.
Not applicable to multiple burners.
Position feed back is expensive for pneumatic actuators
Oxygen Trim limit prevents adequate correction

47. Fully Metered Strategy
Both the fuel flow and the combustion air flow are measured. Separate PID controllers are used for both fuel and air flow control. Demand from a Boiler Sub-master is used to develop both a fuel flow and air flow setpoint.
Fuel and Air Flow setpoints are Cross Limited using fuel and air flows.
Oxygen trim control logic is easily added as an option. Flue gas oxygen is measured and compared against setpoint to continuously adjust (trim) the fuel / air ratio. The excess air adjustment allows the boiler to operate safely and reliably at reduced levels of excess air throughout the operating range of the boiler. This reduction in excess air can result in fuel savings of 2% to 4%. The flue gas excess oxygen setpoint is based on boiler firing rate or an operator set value.

48. Fully Metered Strategy

49. Fully Metered Strategy
Advantages
Corrects for control valve, damper drive and pressure regulator Hysteresis
Compensates for flow variations.
Applicable to multiple burners.
Allows simultaneous firing of oil and gas.
Disadvantages
Installation is more costly.
With no oxygen trim….For all types of flow meters, the fuel Btu value and air oxygen content must be assumed.
By summing the air requirements for each
Fuel to air ratios near “ideal” can be maintained
Actual flows can be cross limited for safety

50. Comparison

51. Other Control Loops that Impact Control of Fuel and
Draft Control
Feedwater Control

52. Draft Control Changing furnace draft can change air flow
Changed air flow effects efficiency
Changed air flow effects emissions
Draft Control keeps furnace pressure constant
Draft Control becomes extremely important:
When multiple boilers share a stack
Stack is very high
Induced FGR is used for NOx control

53. Draft Control Schematic

54. Types of Draft Control Self contained units such as Preferred JC-20
“Sequencing” closes damper when boiler is off
Saves energy
Draft sensing diaphragm and logic in one unit
Micro-processor controllers for tighter control
Feedforward based on firing rate
True PID control of furnace draft

55. Feedwater Control Benefits of stable water level control
high and low water trips are avoided
water carryover in steam is minimized
steam pressure stays more nearly constant
Swinging feedwater flow can:
cause pressure swings
cause firing rate to hunt
create extra wear and tear on valves and linkage
waste fuel

56. Simple Feedwater Control Strategies
On-off control
typically used on small firetube units
Single Element Feedwater Control
opening of valve is influenced by change in level
typical of older thermo-hydraulic systems
thermo-hydraulic systems are proportional only
use of PID controller can add “reset”
suitable for steady loads

57. Shrink and Swell
Momentary drum level upsets in water tube boilers when the steam load swings
Increase in load causes swell:
drops pressure in boiler
increases size of steam bubbles in watertubes
causes more water to flash to steam
causes the actual level in the drum to rise while the total amount of water actually drops
single element will close the valve, not open it

58. Shrink and Swell, cont. Drop in load causes:
pressure to rise
some steam to condense
size of remaining bubbles to shrink
water level in drum drops
actual amount of water might be rising
Controls reduce impact of shrink and swell
controls can’t compensate for poor design or condition of boiler

59. Two Element Feedwater Control
Control on water level and steam flow
drop in level increases valve opening
rise in steam flow increases valve opening
reduces impact of shrink and swell
better for swinging loads
PID control with steam flow feed-forward which can be characterized to match the valve trim
Requires a steady feedwater supply pressure

60. Two Element Feedwater Control

61. Three Element Feedwater Control
Water level, steam flow and feedwater determine controller output signal
Two PID loops in cascade configuration:
hold drum level at setpoint
hold feedwater flow to match steam flow
Very stable level control
Keeps water inventory constant during periods of shrink and swell

62. Three Element Feedwater

63. Auxiliary Controller Functions
Calculation of pressure compensated steam flow
Compensation of drum level signal for changing water density in steam drum
Totalization of steam flow
Totalization of feedwater flow
Alarms for high and low water levels

64. Data Acquisition for Combustion
Allows remote operation of controllers
Reduces manpower requirements in plant
Provides historical data
Trend data to replace strip or circular charts
Reports to document plant operation
Can compare energy usage per degree day
From year to year
From building to building
Allows energy wasting trends to be spotted

65. New Advances in Combustion Control
These features offers help firing systems meet emissions goals.
Combustrol's fully metered combustion control strategy includes differential cross limiting of fuel and air flows. This feature adds an addition level of protection to the conventional air flow and fuel flow cross limiting combustion control scheme by preventing the air fuel ratio from becoming too air rich as well as too fuel rich.
To enable improved burner turndown, Combustrol provides automatic switching to positioning control of the air control damper whenever the firing rate of the unit is below the turndown range of the air flow transmitter.
For rapid boiler load response, the air flow control output is the sum of the air flow controller output and an air flow demand feedfoward index.

66. Saving Fuel with Combustion Control
Oxygen Trim of air flow
Applicable to any control strategy
Should be applied to any large boiler
Oxygen readout is valuable even if trim is impractical
Variable speed drive of combustion air fan
Can generate considerable horsepower savings
Economic Boiler Dispatch

67. Oxygen Trim Strategies
Mechanical trim devices for single point positioning
Can vary the air damper position
Can vary the fuel pressure
Biasing the air damper actuator position for parallel positioning control
Changing the fuel to air ratio in metering systems
Changing the fan speed in systems with VFD

68. Oxygen Trim for Jackshaft System

69. Oxygen Trim Cautions Replace worn dampers and linkage FIRST!
Use only proven analyzers for the signal
Use only proven controllers and control strategies to accomplish the trim
Budget calibration and probe replacement.

70. Variable Speed Fan Drives
Applicable to parallel “positioning” or metering control strategies
Can generate considerable electricity savings
For a 40,000 pph boiler running at 50% load:
Savings could be up to $12,000 per year
R.O.I. could be as low as 1.5 years
Might be a candidate for a utility company rebate

71. Summary Combustion control is a specialty field
Each application has unique requirements
Each system should balance:
efficiency of operation
installed cost
safety and reliability
Preferred Instruments is leader in the field of special combustion control systems

72. Preferred Utilities Manufacturing Corp
For further information, contact...
Preferred Utilities Manufacturing Corporation
31-35 South Street • Danbury • CT
T: (203) • F: (203)