ADDITIONAL INFORMATION FOR REFERENCE EMISSIONS
I.

Conservative setting of burner efficiencies

According to the results of the interviews to manufacturers, when holding aluminum melt at thetemperature of 600-800 degrees Celsius, furnace atmospheric temperature commonly ranges
750-950 degrees Celsius (see Table 1).
In a furnace with a conventional burner, the exhaust gas temperature is the same as the furnace
atmospheric temperature because there is no equipment between the furnace and the exhaustduct. Since the furnace atmospheric temperature commonly ranges 750-950 degrees Celsius, thereference exhaust gas temperature is set at the lowest value (750 degrees Celsius) of that range.
In a furnace with a regenerative burner, the exhaust gas temperature becomes lower than thefurnace atmospheric temperature due to the heat absorber. From the measured test data forregenerative burners, the exhaust gas temperature is below 300 degrees Celsius even when thefurnace atmospheric temperature is at 750-950 degrees Celsius (see Table 2). In order to beconservative, the project exhaust gas temperature is set at 300 degrees Celsius which is higherthan the possible temperature of the project exhaust gas.
Assuming constant furnace atmospheric temperature, energy efficiency of burner increases asthe exhaust gas temperature falls since low exhaust gas temperature means recovery of energy
contained in the exhaust gas. This methodology results in a conservative calculation of emission
reductions by assuming a low exhaust gas temperature for reference furnace and a high exhaustgas temperature for project burner when calculating the default burner efficiency.
Table 1: Interview results on holding and furnace atmospheric temperatureInterviewee
Association ACompany B

Summary of comments
Holding temperature for ADC12 aluminum alloy* typically ranges
660-710 degrees Celsius.
Holding temperature in the semi-solid aluminum casting ranges
610-630 degrees Celsius.
Aluminum holding furnace atmospheric temperature typically

Association Cranges 850-950 degrees Celsius.
Aluminum holding furnace atmospheric temperature is commonly
150-degrees higher than holding temperature.

Source: Interviews conducted by the methodology proponents.
Note: * ADC12 aluminum alloy accounts for over-90% share of the entire alloy die casting.

1Table 2: Interview results on regenerative burner’s exhaust gas temperature
Interviewee

Summary of comments
In a common aluminum holding furnace with regenerative burner,

Company D (A burnermanufacture)

the exhaust gas temperature is controlled to maintain at all times
below 300 degrees Celsius (usually around 200 degrees Celsius) inorder to prevent damage caused by high temperature on switch
valves, the apparatus unique to regenerative burners.
Regenerative burner’s exhaust gas temperature is commonly

Association C

designed to be around 200 degrees Celsius.

Source: Interviews conducted by the methodology proponents.

Following the above assumption, the default vales of reference furnace energy efficiency is
calculated to be 0.682 assuming a value of 1.05 for the air ratio. It is observed that this value isconservative since 0.682 is higher than the measured data reported by one of the manufacturers
for the range of furnace atmospheric temperature during normal operating conditions (750-950
degrees Celsius) as shown in Figure 1.

■Exhaust gas temperature

Energy efficiency (%)

Exhaust gas temperature (degrees Celsius)<Conventional burner>＊Energy efficiency

Furnace atmospheric temperature (degrees Celsius)

Figure 1: Energy efficiencies with the furnace atmospheric temperature(Source: Company D)

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II.

Other parameters for energy efficiency of furnaces

1) Theoretical amount of air necessary for the combustion of fossil fuels
The theoretical amount of air necessary for the combustion of fossil fuels is calculated based on
the type and composition of fossil fuel.
Where the combustion reaction formula is:
CmHn+(m+n/4)O2→mCO2+(n/2)H2O
The theoretical amount of air necessary for the combustion of fossil fuels is calculated by thefollowing formula. “0.21” is the composition of O2 in the air.
A0,ff =(m+n/4)/0.212) Theoretical volume of wet exhaust gas from the combustion of fossil fuels
The theoretical volume of wet exhaust gas from the combustion of fossil fuels is calculated
based on the theoretical amount of air and the theoretical volume of dry exhaust gas.
Under the aforementioned combustion reaction formula, the theoretical volume of dry exhaustgas is calculated by the following formula:
Theoretical volume of dry exhaust gas = Theoretical amount of air*(1-0.21)+mThen, the theoretical volume of wet exhaust gas is calculated by the following formula:
Theoretical volume of wet exhaust gas = Theoretical volume of dry exhaust gas+(n/2)
By the formulas explained above, actual parameter values of theoretical amount of air andtheoretical volume of gasses for the specific fossil fuel components are calculated as follows:3

Table 3: Calculation of the parameters regarding combustion of major fuel components
Unit: Nm3/ Nm3

Fuelcomponent

Combustion reaction formula

Theoreticalamount of air

Theoretical

Theoreticalvolume ofvolume ofdry exhaust gas

wet exhaust gasMethane

CH4+2O2→CO2+2H2O

9.5

8.5

10.5

Ethane2 C2H6+7O2→4CO2+6H2O

16.7

15.2

18.2

Propane

C3H8+5O2→3CO2+4H2O

23.8

21.8

25.8

Butane2 C4H10+13O2→8CO2+10H2O

31.0

28.5

33.5

Source: The methodology proponents.

3) Mean specific heat at constant pressure
The mean specific heat at a specific temperature is defined as the mean value between thattemperature and 0 degrees Celsius, which is referred to JIS G, Appendix Table 2.
Strictly speaking, the specific heat at constant pressure of wet exhaust gas and of air varies
depending on their pressure. On the other hand, the influence of the pressure on the specific heatis considered to be negligible in the methodology because the value increases only by 0.07%
even in the condition that the pressure inside furnaces doubles, i.e. to be at around 2 atm, while
the pressure inside furnaces commonly remains around 1 atm (101.3kPa) at actual operating
condition.
4) Air ratio for the reference burner
The air ratio for the burner is regularly given as a design variable for each equipment andcontrolled to maintain within a certain range from the perspective of the safety and theefficiency. When substantial and/or frequent deviation occurs, its causes are examined at theperiodical check or other investigating opportunities.
While the optimum air ratio is 1.00 which theoretically realizes the most appropriate condition
for combustion, in actual operation it is usually recommended to set the ratio at least as 1.05 forthe safety reason. As the ratio rises, the energy efficiency of a furnace falls as shown in Table 4.
Therefore setting 1.05 as default air-ratio for the reference burner is considered to beconservative.

4Table 4: Change of the energy efficiency in response to the air ratio for the burner
Air ratio for the reference burner

1.05

1.15

Energy efficiency of the reference furnace

0.682

0.656

Source: The methodology proponents.

5) Composition and net calorific value of natural gas
Natural gas is the assumed fossil fuel for the calculation of energy efficiencies in thismethodology. While composition and net calorific value (NCV) of natural gas may fluctuatedaily in the actual situation, in this methodology these values in calculating reference andproject burner efficiencies are set as the conservative default value referring to IPCC Special
Report on Carbon dioxide Capture and Storage, Annex I, Table AI.10.
Table 5 compares the value of default NCV derived from its composition to the actual highest
and lowest values of NCV derived from their compositions which are reported by an Indonesiannatural gas provider as the data in March 2014 as well as their effect on the burner efficiencies.
The NCV (Typical) falls between those of the actual highest and lowest values of NCV, thus it isconsidered to be appropriate to set it as the default value in the calculation of emission
reductions. In addition, it is observed that possible fluctuation of the natural gas composition
has marginal effect on the calculation of emission reductions since based on the actual reported
highest and lowest values mentioned above whose fluctuation is calculated to be 3.3%, its effecton the efficiency ratio of the project burner to the reference burner is 0.6%.
Table 5: Change of the energy efficiency in response tothe net calorific value and composition of natural gas
TypicalHighLow

36,65938,59736,133

Methane CH4

94.4

86.0

89.4

Ethane C2H6

3.1

4.4

3.7

Propane C3H8

0.5

2.5

0.9

Isobutan/N-butan C4H10

0.2

1.1

0.4

Carbon dioxide CO2

0.5

4.0

4.8

Nitrogen N2

1.1

1.2

0.6

Energy efficiency of the project furnace ηPJ [-]

0.865

0.872

0.863

Energy efficiency of the reference furnace ηRE [-]

0.682

0.698

0.678

Efficiency ratio ηPJ/ηRE [-]

1.268

1.249

1.274

3Net calorific value [kJ/Nm ]Composition [%]Source: IPCC Special Report on Carbon dioxide Capture and Storage, Annex I, Table AI.10;

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PT Perusahaan Gas Negara (Persero) Tbk.

III.

Mechanism of the regenerative burner

Fuel

Heat storage(Ceramic reservoir)

Flame

Exhaust gas

PreheatExhaustcombustion airgas

Normaltemperature
air
Switching valve

Switching in constant cycles(Regenerative combustion)

Exhaust gas
heating storage

Heat storage
preheating
combustion air
after valve switching

Figure 2: Schematic diagram of the regenerative burner(Source: Japan Industrial Furnace Manufactures Association)

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