Methodological issues 3921 Choice of method

The emissions from petrochemical and carbon black production vary both with the process used and the feedstock used. The choice of method should thus be repeated for each product, process and feedstock used. Three methodological tiers are provided depending on the availability of data. The choice of method depends on national circumstances and is given by the decision trees in Figure 3.8 and Figure 3.9.

Figure 3.8 Decision tree for estimation of CO2 emissions from petrochemical industry and carbon black industry

Figure 3.8 Decision tree for estimation of CO2 emissions from petrochemical industry and carbon black industry

Petrochemicals Tree

Note:

1. See Volume 1 Chapter 4,"Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Note:

1. See Volume 1 Chapter 4,"Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Figure 3.9 Decision tree for estimation of CH4 emissions from petrochemical industry and carbon black industry

Figure 3.9 Decision tree for estimation of CH4 emissions from petrochemical industry and carbon black industry

Note:

1. See Volume 1 Chapter 4,"Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

2. Note that there is no Tier 2 method for estimating CH4 emissions. The Tier 2 method is a total feedstock carbon mass balance method that is applicable to estimating total carbon (CO2) emissions but not applicable to estimating CH4 emissions.

Note:

1. See Volume 1 Chapter 4,"Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

2. Note that there is no Tier 2 method for estimating CH4 emissions. The Tier 2 method is a total feedstock carbon mass balance method that is applicable to estimating total carbon (CO2) emissions but not applicable to estimating CH4 emissions.

The Tier 3 methodology can be used to estimate plant-level CO2 emissions and CH4 emissions. The Tier 3 method depends upon the availability of plant-specific data for the petrochemical process. The Tier 2 methodology is a mass balance approach that is applicable to estimating CO2 emissions but is not applicable to estimating CH4 emissions. When using the Tier 2 methodology, both carbon flows of primary and secondary feedstocks to the process are included in the mass balance calculation. Carbon flows of primary fuels to the process may involve combustion of part of the hydrocarbon content for heat raising and the production of secondary fuels (e.g., off gases). In order to apply the Tier 2 methodology the flows of primary and secondary feedstocks to the process and the flows of primary and secondary products must be characterised, and the flows of by-products burned for energy recovery within the process and flows of by-products transferred out of the process must be characterised.

CARBON DIOXIDE

The decision tree for choice of method for CO2 emissions is shown in Figure 3.8. The Tier 1, Tier 2, and Tier 3 methods are described in this section.

Tier 1 product-based emission factor method

The Tier 1 emission factor methodology is applied to estimate CO2 emissions from the petrochemical process in cases where neither plant specific data nor activity data for carbon flows are available for the petrochemical process. The Tier 1 emission factor method does not require activity data for the consumption of each carbon-containing feedstock to the petrochemical production process. It requires only activity data for the amount of product produced. The Tier 1 methodology does not consider the carbon content of emissions of carbon monoxide or NMVOC that may be generated by the petrochemical processes. The equations in this section for petrochemical production processes also apply to carbon black production.

The Tier 1 method calculates emissions from petrochemical processes on the basis of activity data for production of each petrochemical and the process-specific emission factor for each petrochemical, as shown in the Equation 3.15 for production of each primary petrochemical product (e.g., methanol, ethylene, ethylene dichloride, ethylene oxide, acrylonitrile) and carbon black.

Equation 3.15 Tier 1 CO2 emission calculation

Where:

ECO2i = CO2 emissions from production of petrochemical i, tonnes PPi = annual production of petrochemical i, tonnes

EFi = CO2 emission factor for petrochemical i, tonnes CO2/tonne product produced

GAF = Geographic Adjustment Factor (for Tier 1 CO2 emission factors for ethylene production, See Table 3.15), percent

Tier 1 CO2 emission factors for ethylene production (discussed in Section 3.9.2.2) have been developed based on data for ethylene steam crackers operating in Western Europe. Geographic Adjustment Factors are applied to the Tier 1 emission factor to account for regional variability in steam cracker operating efficiency. Geographic Adjustment Factors are only applicable to ethylene production.

If activity data for annual primary product production are not available, primary product production may be estimated from feedstock consumption, as shown in the Equation 3.16:

Equation 3.16 Primary product production estimate calculation

Where:

PP! = annual production of petrochemical i, tonnes

FAlk = annual consumption of feedstock k consumed for production of petrochemical (i), tonnes

SPPj,k = specific primary product production factor for petrochemical i and feedstock k ,tonnes primary product/tonne feedstock consumed

Either Equation 3.15 or both Equation 3.15 and Equation 3.16 would be applied separately to each of the known feedstocks for each petrochemical process. The Tier 1 emissions estimate shown in Box 1 of Figure 3.8 would utilise Equation 3.15, while the Tier 1 emissions estimate shown in Box 2 of Figure 3.8 would use either

Equation 3.15 or both Equation 3.16 and Equation 3.15. Equation 3.15 would be utilised alone in cases where annual primary product production data are available for the petrochemical process. In cases where annual primary product production data are not available but feedstock consumption data are available for the petrochemical process, Equation 3.16 would be utilised to estimate the annual production of primary products, and the annual primary product production estimated using Equation 3.16 would then be applied in Equation 3.15 to estimate the emissions.

Tier 2 total feedstock carbon balance method

The Tier 2 method is a feedstock-specific and process-specific carbon balance approach. This approach is applicable in cases where activity data are available for both feedstock consumption and primary and secondary product production and disposition. Activity data for all carbon flows are required to implement the Tier 2 methodology. Examples of process flow diagrams that illustrate feedstock and product flows for the methanol, ethylene dichloride, ethylene oxide, acrylonitrile, and carbon black production processes are included in an Annex to Section 3.9. The number of potential feedstocks and products for ethylene production from the steam cracking process is such that the process is better illustrated by a feedstock-product matrix rather than by a process flow diagram. The feedstock-product matrix for ethylene production is included in Table 3.25 in Section 3.9.2.3. A flow diagram of the Tier 2 method is shown in Figure 3.10.

Figure 3.10 Tier 2 carbon mass balance flow diagram

Figure 3.10 Tier 2 carbon mass balance flow diagram

The Tier 2 method calculates the difference between the total amount of carbon entering into the production process as primary and secondary feedstock and the amount of carbon leaving the production process as petrochemical products. The difference in carbon content of the primary and secondary feedstocks and the carbon content of the primary and secondary products produced by and recovered from the process is calculated as CO2. The Tier 2 mass balance methodology is based on the assumption that all of the carbon input to the process is converted either into primary and secondary products or into CO2. This means that any of the carbon input to the process that is converted into CO, CH4, or NMVOC are assumed to be CO2 emissions for the purposes of the mass balance calculation.

The overall mass balance equation for the Tier 2 methodology is Equation 3.17.

Equation 3.17

Overall Tier 2 mass balance equation

ECO2i =\z(FAhk * FCk )-

PPt * PCi + * SCj )

I * 44/12

[k

_ j _

ECO2i = CO2 emissions from production of petrochemical i, tonnes

FAik = annual consumption of feedstock k for production of petrochemical i, tonnes

FCk = carbon content of feedstock k, tonnes C/tonne feedstock

PPi = annual production of primary petrochemical product i, tonnes

PCi = carbon content of primary petrochemical product i, tonnes C/tonne product

SPy = annual amount of secondary product j produced from production process for petrochemical i, tonnes

[The value of SPy is zero for the methanol, ethylene dichloride, ethylene oxide, and carbon black processes because there are no secondary products produced from these processes. For ethylene production and acrylonitrile production, see secondary product production Equations 3.18 and 3.19 below to calculate values for SPy.]

SCj = carbon content of secondary product j, tonnes C/tonne product

For ethylene production and acrylonitrile production there are both primary and secondary products produced by the process. If activity data are not available for the amount of secondary products produced by these processes, the amount of secondary products produced may be estimated by applying default values to the primary feedstock consumption, as shown in Equations 3.18 and 3.19:

Equation 3.18

Estimate secondary product production from primary product [ethylene]

production

Where:

SPEthyiene j = annual production of secondary product j from ethylene production, tonnes

FAEthyiene k = annual consumption of feedstock k consumed for ethylene production, tonnes

SSPj,k = specific secondary product production factor for secondary product j and feedstock k, tonnes secondary product/tonne feedstock consumed

Equation 3.19

Estimate secondary product production from primary product [acrylonitrile]

production

SPAcrylonitrile, j Z (FPAcrylonitrile,k * SSPj,k ) k

Where:

SP Aoybmtniej = annual production of secondary product j from acrylonitrile production, tonnes FP Acrylonitrile,k = annual production of acrylonitrile from feedstock k, tonnes

SSPj,k = specific secondary product production factor for secondary product j and feedstock k, tonnes secondary product/tonne acrylonitrile produced

Note: It is anticipated that in most cases only a single feedstock (propylene) would be used for acrylonitrile production.

Feedstock and product carbon contents

Carbon contents of feedstocks and products of petrochemical production processes are listed in Table 3.10, in units of tonnes of carbon per tonne of feedstock or product. Carbon contents of pure substances (e.g., methanol) are calculated from the chemical formula. Carbon contents of other feedstocks and products (e.g., carbon black feedstock, carbon black) are estimated from literature sources. Representative carbon contents of fossil fuels (e.g., natural gas, naphtha) can be found in Table 1.3 in Chapter 1 of Volume 2: Energy; however, carbon contents for fossil fuels will vary by country and region and are best obtained from national energy statistics or fossil fuel product specifications or national standards.

Tier 3 direct estimate of plant-specific emissions

The most rigorous good practice method is to use plant specific data to calculate CO2 emissions from the petrochemical production process. In order to apply the Tier 3 method, plant-specific data and/or plant-specific measurements are required. The emissions from the petrochemical production process include CO2 emitted from fuel or process by-products combusted to provide heat or thermal energy to the production process, CO2 emitted from process vents, and CO2 emitted from flared waste gases. These emissions are calculated using Equations 3.20 through 3.22.

Overall CO2 emissions from the petrochemical production process are calculated using Equation 3.20

Equation 3.20 Tier 3 CO2 emissions calculation equation

ECO2i — ECombustion,i + EProcessVent ,i + EFlare,i

Where:

ECO2i = CO2 emissions from production of petrochemical i, tonnes

E Combustion,i = CO2 emitted from fuel or process by-products combusted to provide heat or thermal energy to the production process for petrochemical i, tonnes

E Process Vent,i = CO2 emitted from process vents during production of petrochemical i, tonnes

E Flare,i = CO2 emitted from flared waste gases during production of petrochemical i, tonnes

E combustion and E flare are given by Equations 3.21 and 3.22 where plant specific or national net calorific value data should be used. The emission factor is given by the carbon content of the fuel, the combustion oxidation factor and a constant (44/12) converting the result from carbon to CO2. If the emission factor is not known a default value may be found in Table 1.4 in Chapter 1 of Volume 2: Energy. Net calorific values are included in Table 1.2 in Chapter 1 of Volume 2: Energy. Carbon contents are included in Table 1.3 in Chapter 1 of Volume 2: Energy. For the process vents, inventory compilers should measure/estimate emissions of CO2 directly and thus no further equation is provided.

Equation 3.21 Fuel combustion Tier 3 CO2 emissions calculation

Where:

FAlk = amount of fuel k consumed for production of petrochemical i, tonnes

NCVk = net calorific value of fuel k, TJ/tonne

(Note: In Table 1.2 in Chapter 1 of Volume 2, net calorific values are expressed in TJ/kg)

EFk = CO2 emission factor of fuel k, tonnes CO2/TJ

(Note: In Table 1.4 in Chapter 1 of Volume 2, CO2 emission factors are expressed in kg/TJ)

Equation 3.22 Flare gas Tier 3 CO2 emissions calculation

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