1. Combustion Control for Boilers
September 23, 2004

2. Contents Introduction Basic type of boilers. Why need boiler controls?
Combustion control for boilers.
Fuji’s oxygen gas analyzer.
September 23, 2004

3. 1. Introduction How does a boiler works?
A boiler is a water containing vessel which transfers heat from a fuel
source (oil, gas or coal) into steam which is piped to a point where
it can be used to run production equipment, to sterilize, to provide
heat, to steam-clean, etc.
The energy given up by the steam is sufficient to convert it back
into the form of water. When 100% of the steam produced is
returned to be reused, the system is called a closed system.
Since some processes can contaminate the steam, so it is not
always desirable to feed the condensate back into the boiler. A
system that does not return the condensate is called an open
system.
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4. 1. Introduction
Closed system
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5. 1. Introduction
Open system
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6. 2. Basic type of boilers. The two main types of boilers are: Firetube
Watertube
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7. 2. Basic type of boilers. Firetube
Fire or hot gases are directed through the inside of tubes within the boiler shell which are surrounded by water. The tubes are arranged in banks so that the gases can be passed through the boiler up to 4 times before passing out the stack. This system exposes the maximum heat transfer surface to the water. Firetube boilers are also known as shell boilers and can produce up to approximately 750 hp or 25,000 lbs of steam per hour. 80% of boilers in use are of this configuration.
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8. 2. Basic type of boilers.
Firetube
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9. 2. Basic type of boilers.
Firetube
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10. 2. Basic type of boilers. Watertube
Fire or hot gases are directed to and around the outside of tubes containing water, arranged in a vertical position. Watertube boilers are usually rectangular in shape and have two or more drums. The separation of steam and water takes place in the top drum, while the bottom drum serves as a collection point for sludge. This system is usually used when more than 750 hp or several hundred thousand lbs of steam per hour, are needed.
There are other designs with special configurations, adapting them to particular applications
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11. 2. Basic type of boilers.
Watertube
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12. 2. Basic type of boilers.
Watertube
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13. 3. Why need boiler controls?
Boiler efficiency relates the boilers energy output to
the boilers energy input and can be expressed as:-
Boiler efficiency (%) = Heat exported by fluid/Heat provided by fuel
An accurate control of the amount of air is essential to the boiler
efficiency.  Too much air will cool the furnace and carried away
useful heat. And too little air and the combustion will be
incomplete. Unburned fuel will be carried over and smoke may be
produced.
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14. 3. Why need boiler controls?
Increase uptime and availability
Reduce flue gas emissions
Maintain boiler safety
Control operating costs
September 23, 2004

15. 3. Why need boiler controls?
Increase uptime and availability
The primary objective of most boilers operation is maintaining the uptime and availability. It is essential to maintain and upgrade the boiler control systems to assure steam availability.
Modern controls are more reliable and can be readily adjusts to load swings caused by varying plant operations.
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16. 3. Why need boiler controls?
Reduce flue gas emissions
Failure to comply with the current emissions regulations can be as costly as loss of utilities. Government mandates are enforced by fines, threat of closure, or imprisonment will provide sufficient incentives for plants to comply with the regulations; thus, modernize controls are necessary.
Improved in combustion efficiency means reduction in waste disposal problems. And by accurately controlling the oxygen, fuel flow and stack temperature, you will see reductions in plant emissions.
September 23, 2004

17. 3. Why need boiler controls?
Maintain boiler safety
Modernize control system will have tight integration with flame safety or burner management system to improve safety.
Accessing field data, diagnostics functions and alarms can be achieved by coupling modern electronic controls. Password security of the configuration software also assures no unintended changes can be done which can endanger your personnel and equipment.
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18. 3. Why need boiler controls?
Control operating costs
Reduction in fuel consumption
Reduction in engineering, installation and startup costs
Reduction maintenance costs associated with older
equipment
Reduction manpower with automatic responds
Provide a flexible control strategy to reduce process upsets
Readily data available for remote monitoring to determine process optimization, boiler efficiency and load allocations
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19. 4. Combustion control for boilers.
Burner combustion control generally includes one or a
combination of the following methods:-
Excess air regulation
Oxygen trim
Burner modulation
Air/Fuel cross-limiting
Total heat control
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20. 4. Combustion control for boilers.
Excess air regulation
In actual practice, gas , oil, coal burning and other systems do not do a a perfect job of mixing the fuel and air even under the best achievable conditions. Additionally, complete mixing may be a lengthy process. To ensure complete combustion and reduce heat loss, excess air has to be kept within suitable range.
The regulation of excess air provides:-
A better boilers hear transfer rate
An advance warming of flue gas problems
Excess air coming out of the zone of maximum efficiently
Substantial savings on fuel
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21. 4. Combustion control for boilers.
Excess air regulation
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22. 4. Combustion control for boilers.
Oxygen trim
When a measurement of oxygen in the flue gas is available, the combustion control mechanism can be vastly improved (since the percentage of oxygen in flue is closely related to the amount of excess air) by adding an oxygen trim control module, allowing
Tighter control of excess air to oxygen setpoint for better efficiency
Faster return to setpoint following disturbances
Tighter control over flue emissions
Compliance with emission standards
Easy incorporation of carbon monoxide or capacity override
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23. 4. Combustion control for boilers.
Oxygen trim
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24. 4. Combustion control for boilers.
Burner modulation
Modulating control is a basic improvement in controlling combustion. A continuous control signal is generated by a controller monitoring the steam or hot water line. Reductions in steam pressure or hot water temperature lead to an increase in firing rate. The advantages of introducing burner modulation in combustion control include.
Fuel and air requirements are continuously matched to the combustion demand
Steam pressure or hot water temperature is maintained within closer tolerances
Greater boiler efficiency
Weighted average flue gas temperature is lower
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25. 4. Combustion control for boilers.
Air/Fuel cross-limiting
A cross limiting combustion control strategy ensures that there can never be a dangerous ration of air and fuel within a combustion process. This is implemented by always raising the air flow before allowing the fuel flow to increase or by lowering the fuel flow before allowing the air flow to drop.
Cross-limiting combustion control is highly effective and can easily provide the followings
Optimization of fuel consumption
Safer operating condition by reducing risk of explosion
Fast adaptation to variation in fuel and air supplies
Satisfaction of the plant demand fore steam
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26. 4. Combustion control for boilers.
Air/Fuel cross-limiting
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27. 4. Combustion control for boilers.
Total heat control
A cross limiting combustion control strategy ensures that there can never be a dangerous ration of air and fuel within a combustion process. This is implemented by always raising the air flow before allowing the fuel flow to increase or by lowering the fuel flow before allowing the air flow to drop.
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28. 4. Combustion control for boilers.
Total heat control
September 23, 2004

29. 4. Fuji’s oxygen gas analyzer.
Top class performance zirconia oxygen analyzer
September 23, 2004

30. 4. Fuji’s oxygen gas analyzer.
Accurate O2 Measurement is Essential for Energy Saving! 
The oxygen analyzer consists of a compact zirconia detector that
can be inserted directly in wall of the flowing sample gas. The
detector measures the oxygen content in the flowing sample gas
and transmits the signal to the converter. The converter will then
trigger the ON-OFF alarm based on the preset oxygen
concentration and give control signal to other devices.
Fuji Electric’s oxygen analyzer has a unique construction that
eliminates the necessity of aspirating sampling gas or injecting air.
And make it extremely suitable for monitoring and controlling
combustion system like, heater boiler, kiln, melting furnace, low
oxygen warehouse and food packing machine.
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31. 4. Fuji’s oxygen gas analyzer.
Excess air coefficient and energy loss ratio
Excess Air Coefficient
Exhaust Oxygen, O2 (%)
Energy Loss Ratio,
Exhaust Gas (%)
1.1
1.9
9.4
1.2
3.5
10.3
1.3
4.8
11.1
1.4
6.0
12.0
1.6
7.9
13.7
(In the case of heavy oil combustion at exhaust gas temperature of 250 °C and atmospheric temperature of 20 °C)
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32. 4. Fuji’s oxygen gas analyzer.
Calculation of cost saving with improved combustion efficiency
(The data may varies based on the construction and performance of the boilers)
Item
Case 1
Case 2
Evaporation rate from boiler
5ton/hr
1ton/hr
Annual operating hours
2,000hrs
Evaporation multiplier factor for boiler 12
Improved value of excessive air coefficient
1.6 -> 1.2
(O2 gas from 7.9% -> 3.5%)
Kerosene price
USD 1.05/kg (USD 0.82/ℓ, SG 0.78)
Kerosene consumption rate
5,000kg/hr ÷ 12 = 420kg/hr
2,000kg/hr ÷ 12 = 85kg/hr
Annual saving through the improved combustion efficiency
420kg/hr x USD 1.05/kg x (13.7 – 10.3) % x 2,000hrs
= USD 29,988.00
85kg/hr x USD 1.05/kg x (13.7 – 10.3) % x 2,000hrs = USD 6,069.00
Note: The data shown in the above table are calculated on an assumption of improvement of energy loss = full reduction ratio, therefore the combustion efficiency of the boiler must be taken into account for calculating fuel reduction rate accurately. Fuel reduction ratio will therefore be least several percent higher in actuality.
September 23, 2004

33. 4. Fuji’s oxygen gas analyzer.
Advantages:
No sampling device is required
The instrument requires no gas aspirating pump or ejector for normal measurements; therefore it can be operated easily. It can be used very conveniently like traditional thermocouple.
Compact and light weight design
The detector and converter weigh about 1.6kg and 3.5kg respectively.
Instrument equipped with indicator and transmitting function
The converter is equipped with an indicator that permits direct readout of the oxygen concentration transmitting output function or RS485 communication.
Alarm and control functions available
Though compact it is compact and lightweight in design, the converter consists of an oxygen concentration setting mechanism as well as alarm setting and control circuits that can transmit control signals.
Lost cost
Comparing Zircomat-P with other conventional oxygen analyzers it is much more economical in cost.
Easy maintenance
Zircomat-P assures easier maintenance comparing to other conventional oxygen analyzers and can be used under severe site conditions for a long time.
September 23, 2004

34. 4. Fuji’s oxygen gas analyzer.
System Outline
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35. 4. Fuji’s oxygen gas analyzer.
Technical Specifications
Measuring range
0 to 2 ~ 50%
Repeatability
Within ± 0.5% maximum output signal
Linearity
± 2% full scale
Response time
With 7 seconds
Power Supply
100, 115, 220 or 230 Vac, 50/60Hz
Power consumption VA
Warm up time
15minutes
Detector
Type
Direct insertion type zirconia detector
Applicable gas temperature
-20~+600 °C or -20~+1,590 °C
Sample gas pressure
-3~+3kPa (-306~+306mmH2O)
Ambient temperature
-20~+60 °C or -5~100 °C
Converter
Output signal
4~20mA or 0~1Vdc
Indication oxygen concentration
3-digits LED
Indication operation/settings
16-digits LCD
Mode display
03 x LED
Mounting
Panel or Pipe Mounting
Optional function
RS-485
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36. 4. Fuji’s oxygen gas analyzer.
Standard air ratio by Energy Economy Law in Japan for conservation of energy
Based on Article 4, Clause 1 of the law regarding rational use of energy (Law No. 49 published in 1979), judging standard for enterprisers at factories (Notification No. 467 of the Ministry of Commerce and Industry, dated October 1979) has been amended on October 26, 1979 (Notification No. 559 of the Ministry of Commerce and Industry) to specify standard air ratio.
1. Boilers
Classification
Load Ratio (%)
Standard air ratio
Solid Fuel
Liquid fuel
Gaseous fuel
Blast furnace gas
For electrical enterprise
75~100
1.2~1.3
1.05~1.1
1.2
Others
Evaporation rate exceeding 30ton/hr
1.1~1.2
1.3
Evaporation rate from 10~30ton/hr -
Evaporation rate not exceeding 10ton/hr
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37. 4. Fuji’s oxygen gas analyzer.
2. Industrial Furnaces
Classification
Standard air Ratio
Metal melting furnace
1.3
Continuous steel heating furnace
1.25
Metal heating furnace not continuous steel heating type
Continuous thermal treatment furnace
Gas producer and gas heating furnace
1.4
Oil heating furnace
Pyrolytic furnace and modification furnace
Cement kiln
Alumina kiln and lime kiln
Continuous glass melting kiln
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38. The End
September 23, 2004