Combustion Improve

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2 Optimization of air ratio

3 The air ratio is calculated from the O2 content (O2%) in the exhaust gas.

4 Larger air ratio leads to larger heat loss with the exhaust gas.

5 Fuel saving by air ratio improvement

6 Effect of air ratio reduction

7 Criteria for air ratio (standard values)

8 Criteria for air ratio (target value)

9 Energy conservation by air preheating

10 Utilization of waste heat of exhaust gas air preheating

11 Criteria for exhaust gas temperature

12 Criteria for factories

Energy Conservation of Combustion air ratio and air preheating

Energy Conservation of Combustion air ratio and air preheating

Content

2/12

Optimization of air ratio? The excess air for combustion such as that in a boiler contributes only to an increase in heat loss with

the exhaust gas.? The degree of excess air is expressed by air ratio. The air ratio at 1 (one) represents the theoretical

combustion.? The air ratio is expressed by 21/(21-O2%) where O2 is oxygen content in the exhaust gas.? The Criteria of the Law for Rational Use of Energy set both standard and target values of air ratios

for boilers and industrial furnaces.

Required heat

Exhaust gas heat loss

Combustion air

Fuel

Boiler / furnace

Required heat

Exhaust gas heat loss

Combustion air

Fuel

Boiler / furnace

Before adjust

After adjust

3/12

The air ratio is calculated from the O2% of the exhaust gas.

? The simplified equation for obtaining the air ratio is:Air ratio = 21/(21 O2% value)where O2 is the oxygen content obtained by analysis (dray base value).

? Normally, the air ratio may be calculated by this equation. The criteria of the Law Concerning Rational Use of Energy specify this equation.

? As the air ratio becomes large, the difference between the result obtained by the simplified equation and the real value becomes large. (See the graph.)

? The air ratio is defined as real air value/theoretical air volume.

? The air ratio of 1 (one) represents an ideal state in which no more than required air is used for combustion (theoretical combustion).

? The air in excess of air ratio at 1 (one) is called excess air which causes heat loss by carrying out air from the stack at heated state.

? The air ratio short of 1 (one) causes incomplete combustion, associated with the incomplete combustion heat loss.

Air ratio and oxygen in the exhaust gas

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1.0 1.2 1.4 1.6 1.8 2.0Air ratio

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13A gas

Fuel oil A

Simplified equation

4/12

Larger air ratio leads to larger heat loss with the exhaust gas.

(13A)

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Rate of heat loss of the exhaust gas (13A gas) Rate of heat loss of the exhaust gas (fuel oil A)

Exhaust gas volume Exhaust gas volume

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Air ratio Air ratio

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Fuel saving by air ratio improvement with graph

? Reduction of the air ratio (reduction of O2% in the exhaust gas) reduces heat loss with the exhaust gas.

? This in turn leads to fuel saving.? The graph illustrates result of air ratio

reduction.? In fuel saving rate, 13A gas and fuel oil

A differ only very little.? At lower exhaust gas temperatures, the

effect is small.? (Example)

If air ratio can be reduced from the present 1.6 (O2 = 8.4%) to 1.2 (O2= 3%), a fuel saving of 2.8% is realizable.

(13A)(=200)

0.0%

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1.0 1.2 1.4 1.6 1.8 2.0

(AR1AR2)

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2.8% 8.4%

3.8

1.6

AR=1.6

Effect of air ratio reduction (13A gas)(Exhaust gas temperature = 200C)

Exhaust gas O2

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Air ratio before and after reduction (AR1AR2)

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Effect of air ratio reduction

(13A)

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1.0 1.2 1.4 1.6 1.8 2.0

(AR1AR2)

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200300400O2

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? The graphs are developed on the assumption that a change in air ratio does not affect the exhaust gas temperature.

Effect of air ratio reduction (13A gas)

Exhaust gas O2

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Exhaust gas O2

Effect of air ratio reduction (fuel oil A)

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Criteria for air ratio (standard values)(the Law Concerning Rational Use of Energy)

Standard air ratio for boilerType Load

factor, %Solid fuel Liquid

fuelGaseous

fuelBlast furnace

gas, etc.

Fixed bed Fluidized bed Byproduct gas

Electric utility service

75100 1.051.2 1.051.1 1.2

Other service(Quantity of evaporation, tons/h)

30 50100 1.31.45 1.21.45 1.11.25 1.11.2 1.21.3

1030 50100 1.31.45 1.21.45 1.151.3 1.151.3

510 50100 1.21.3 1.21.3

5 50100 1.21.3 1.21.3

Summary of note

After periodical inspection / stable operation state / air ratio at the boiler outlet Additional notes on pulverized coal combustion on fixed beds Use the fuel of higher mixing ratio in case of mixed fuel combustion. Exemption:

Small boilers specified by the Labour Safety and Health Law, boilers for which the fuel has been changed after installation, boilers burning an industrial waste with fuel Boilers burning either black liquor or waste tires, byproduct gas of a heating value of 3,800kj or lower, or burning a poisonous gas for treatment purpose Boilers for the purpose of using waste heat, using a heating medium, operating unsteadily, or for the purpose of development, research and test manufacturing

8/12

Criteria for air ratio (target value)(the Law Concerning Rational Use of Energy)

Target air ratio for boilerType Load

factor, %Solid fuel Liquid

fuelGaseous

fuelBlast furnace

gas, etc.


Electric utility service

75100 1.051.1 1.051.1 1.151.2


30 50100 1.21.3 1.21.25 1.051.15 1.051.15 1.21.3

1030 50100 1.21.3 1.21.25 1.151.25 1.151.25

510 50100 1.151.3 1.151.25

5 50100 1.151.3 1.151.25

Summary of note: almost the same as those of the table of standard values

9/12

Energy conservation by air preheating? Air preheating preheats the

combustion air using the heat of the combustion gas.

? The preheated combustion air carries heat to the boiler / furnace; therefore, the required fuel is reduced.

? Consequently, heat loss attributable to the exhaust gas is reduced.

? The effect of air preheater becomes higher as the air ratio is higher.

/

Before adjust

After adjust

Exhaust gas

Combustion air

Fuel

Required heat

Boiler, furnace

Boiler, furnaceFuel

Required heat

Air preheater / recuperator

Exhaust gas

Preheated airCombustion air

10/12

Effect of air preheating

13AA,400

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13A,AR=1.0 13A,AR=1.213A,AR=1.4 13A,AR=1.6A,AR=1.0 A,AR=1.2A,AR=1.4 A,AR=1.6

13AA,200

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13A,AR=1.0 13A,AR=1.2

13A,AR=1.4 13A,AR=1.6A,AR=1.0 A,AR=1.2

A,AR=1.4 A,AR=1.6

? If the heat contained in the exhaust gas is recovered by installing an air preheater, the temperature of the exhaust gas is lowered and the required fuel is reduced.

Effect of air preheating13A gas, fuel oil A, exhaust gas temperature at 200C

Fuel oil A, AR = 1.4

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Effect of air preheating13A gas, fuel oil A, exhaust gas temperature at 400C

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Air preheating temperature (C) Air preheating temperature (C)

13A gas, AR = 1.0

13A gas, AR = 1.4



13A gas, AR = 1.2

13A gas, AR = 1.6



13A gas, AR = 1.0

13A gas, AR = 1.4



13A gas, AR = 1.2

13A gas, AR = 1.6


11/12

Criteria for exhaust gas temperature(the Law Concerning Rational Use of Energy)

Criteria for boilers, standard / target exhaust gas temperatureType Solid fuel Liquid

fuelGaseous

fuelBlast furnace

gas, etc.


Electric utility service 145/135 110/110 200/190


30 200/180 200/170 200/160 170/140 200/190

1030 200/180 200/170 200/160 170/140

510 /300 220/180 200/160

5 /320 250/200 220/180

Summary of note

After periodical inspection / 20C at air feeder inlet, load factor at 100%, boiler outlet (heat recovery, flue gas treatment facility outlet) Additional notes on pulverized coal combustion on fixed beds, use the fuel of higher mixing ratio in case of mixed fuel combustion, the target temperature for black liquor combustion being 180C Exemption:

Small boilers specified by the Labour and Health Law, boilers for which the fuel has been changed after installation, boilers burning an industrial waste with fuel Boilers burning either black liquor or a poisonous gas for treatment purpose Boilers for the purpose of using waste heat, using a heating medium, operating unsteadily, or for the purpose of development, research and test manufacturing

12/12

The criterion should be observed to the extent economically and technically possible.The target is the objective to pursue to achieve a reduction of energy unit consumption of 1 (one) percent per year (average).

Subjects of criteria (matters concerning standards)

1. Rationalization of fuel combustion.2. Rationalization of heating, cooling and heat transfer.3. Prevention of heat loss by radiation, conduction, etc.4. Recovery of waste heat.5. Rationalization of heat conversion into power, etc.6. Prevention of electricity loss by resistance, etc.7. Rationalization of conversion of electricity into power, heat, etc.

Quantitatively specified item of criteria (standard value, target value)1. Air ratio for boilers2. Air ratio for industrial furnaces3. Outer wall temperature of industrial furnaces4. Exhaust gas temperature for boilers5. Waste heat recovery rate of industrial furnaces6. Facility for which power factor should be improved7. Target efficiency of high-efficient totally-enclosed electric motors (02 to 37kw)

Criteria for factories (the Law Concerning Rational Use of Energy)

Energy Conservation of Combustion air ratio and air preheating Optimization of air ratio The air ratio is calculated from the O2% of the exhaust gas. Larger air ratio leads to larger heat loss with the exhaust gas. Fuel saving by air ratio improvement with graph Effect of air ratio reduction Criteria for air ratio (standard values) (the Law Concerning Rational Use of Energy) Criteria for air ratio (target value) (the Law Concerning Rational Use of Energy) Energy conservation by air preheating Effect of air preheating Criteria for exhaust gas temperature (the Law Concerning Rational Use of Energy) Criteria for factories (the Law Concerning Rational Use of Energy)

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Combustion Improve