GB/T 24041-2000 Determination of the purpose and scope of environmental management life cycle assessment and inventory analysis
Some standard content:
GB/T24041--2000
This standard is equivalent to the international standard ISO14041:1998 "Determination of the purpose and scope of environmental management life cycle assessment and inventory analysis".
This standard is one of the standards on life cycle assessment in the environmental management series of standards. Previously, the first national standard on life cycle assessment, GB/T24040-1999 "Principles and framework for environmental management life cycle assessment", has been issued. ISO standards on life cycle assessment include: ISO14042 Environmental management life cycle assessment Life cycle impact assessment ISO14043 Environmental management life cycle assessment Life cycle interpretation ISO/TR14049 Environmental management life cycle assessment ISO14041 Application examples Appendix A and Appendix B of this standard are both suggestive appendices. This standard is proposed and managed by the China Standards Research Center. The drafting units of this standard are: China Standards Research Center, Ecological and Environmental Research Center of the Chinese Academy of Sciences, China Research Institute of Environmental Sciences, China National Petroleum Corporation, Department of Environmental Science and Engineering of Tsinghua University, and Center for Environmental Sciences of Peking University. The main drafters of this standard are: Fan Yuhua, Yang Jianxin, Duan Ning, Rao Yishan, Zhang Tianzhu, Luan Shengji, Sun Qihong, Huang Jin. This standard was first published in February 2000.
GB/T24041--2000
ISO Foreword
The International Organization for Standardization (ISO) is a worldwide federation composed of national standardization bodies (ISO member bodies). The work of formulating international standards is usually completed by ISO's technical committees. Member bodies interested in the work of a technical committee have the right to participate in the technical committee. Other international organizations, whether governmental or non-governmental, can also participate in its work through liaison with ISO. In the field of electrotechnical standardization, ISO maintains a close cooperative relationship with the International Electrotechnical Commission (IEC). International standards are formulated in accordance with the rules of Part 3 of the ISO/IEC Directives. The draft international standard formally adopted by the technical committee is submitted to the member bodies for voting. The international standard must be approved by at least 75% of the member bodies participating in the vote before it can be formally adopted. The international standard ISO14041 was developed by the ISO/TC207 Environmental Management Technical Committee Life Cycle Assessment Subcommittee (SC5).
Appendix A and Appendix B are both informative appendices. 205
GB/T24041--2000
This standard describes the content of the two stages of life cycle assessment (LCA): determination of purpose and scope and life cycle inventory analysis (LCI). These two stages are defined in GB/T24040. The importance of determining the purpose and scope is that it determines why a certain life cycle assessment is to be conducted (including the application intention of its results) and expresses the system and data types to be studied. The purpose, scope and application intention of the study involve factors such as the geographical breadth, time span and quality of the required data of the study, which will affect the direction and depth of the study. LCI includes the collection of required data to achieve specific research purposes. It is basically a list of input and output data about the system being studied.
When interpreting the LCI results (see Chapter ? of this standard), the data should be evaluated based on the purpose and scope, further data to be collected, or both. Through the interpretation of the LCI results, a more correct understanding of the data can generally be obtained for the preparation of reports. Since LCI collects and analyzes input and output data rather than evaluating the environmental impacts corresponding to these data, the interpretation of LCI results alone is not sufficient to draw conclusions about environmental impacts. This standard can be used to:
help organizations to comprehensively understand the interrelated product systems; determine the purpose and scope of the study, define the system to be analyzed and establish a system model, collect data and prepare reports on LCI results; - establish a baseline for the environmental performance (behavior) of the system by quantifying the energy flow, raw materials and emissions to air, water and land (environmental input and output data) of the product system to be analyzed (the entire system decomposed into unit processes); identify the unit processes in the product system that consume the most energy and raw materials and have the most prominent emissions, so as to make targeted improvements; - provide data to help determine the eco-label criteria; help formulate alternative policy options (such as policies on procurement). In addition to the main uses described above, this standard may also be used in other areas. Follow-up standards ISO14042 and ISO14043 for the other two stages of LCA, as well as a technical report related to this standard that provides LCI examples (see "References") are also under development. 1) In this standard, the term "product" when used alone is equivalent to a synonym for "product or service". 206
1 Scope
National Standard of the People's Republic of China
Environmental management
Life cycle assessment
Three Goal and scope definition and inventory analysis
Environmental management---Life cycle assessmentGoal and scope definition and inventory analysisGB/T24041--2000
idtISO14041:1998 (1st Edition)
Based on GB/T24040, this standard specifies the requirements and procedures for determining the purpose and scope of life cycle assessment (LCA) and the two stages of implementation, interpretation and reporting of life cycle inventory analysis (LCI). 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard was published, the versions shown were valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. IEC and ISO members hold currently valid international standards. GB/T24040-1999 Principles and Framework for Life Cycle Assessment of Environmental Management (idtISO14040:1997) 3 Definitions
The definitions in GB/T24040 and the following definitions apply to this standard: 3.1 Auxiliary input anicillary Input Material input used in the unit process to produce the relevant product but does not constitute a part of the product. Example: catalyst.
3.2 Coproduct
Two or more products produced by the same unit process. 3.3 Data qualitydataquality
The ability of data to meet the stated requirements. 3.4 Energy flowenergy flow
Input or output measured in energy units of a unit process or product system. Note: The input energy flow can be called energy input, and the output energy flow can be called energy output. 3.5 Feedstock energy
The heat of combustion contained in the raw materials input into the product system that is not used as energy. Note: It is expressed by the high or low calorific value. 3.6 Final productfinalproduct
Product that does not require further conversion before being put into use. 3.7 Fugitive emissions emission Uncontrolled emission to air, water or land. Example: Leakage at pipeline interface.
Approved by the State Administration of Quality and Technical Supervision on February 1, 2000, implemented on October 1, 2000
3.8 Intermediate product GB/T24041—2000
Input or output in a unit process that needs further transformation. 3.9 Process energy
Energy input required to operate the process or the equipment in the unit process, excluding energy used to produce or transport this part of energy.
3.10 Reference flow
In a given product system, the process output required to achieve the function of a functional unit. 3.11 Sensitivity analysis A systematic procedure used to estimate the impact of selected methods and data on research results. 3.12 Uncertainty analysis A systematic procedure used to determine and quantify the uncertainty brought to the LCI results due to the accumulation of input uncertainty and data changes.
Note: Either intervals or probability distributions can be used to determine the uncertainty in the results. 4 Basic Contents of LCI
4.1 Overview
This chapter explains the key terms and basic contents of life cycle inventory analysis. 4.2 Product system
A product system is a collection of unit processes linked by flows of intermediate products that provide one or more defined functions. Figure 1 shows an example of a product system. The representation of a product system includes unit processes, elementary flows and product flows across the system boundary (either input or output), and flows of intermediate products within the system. The fundamental nature of a product system depends on its function and cannot be described solely in terms of the final product. Environment of the system
Access to raw materials
Other systemsbzxZ.net
Elementary flows
4.3 Unit processes
Product flows
Energy supply
Recycling
Reuse
Waste disposal
Example of a product system for life cycle inventory analysisSystem boundary
Elementary flows
Other systems
Product flows
A product system can be further divided into a set of unit processes (see Figure 2). Unit processes are connected to each other through intermediate product flows and/or wastes to be treated, to other product systems through product flows, and to the environment through basic flows. 208
Basic flow input
Basic flow input
Basic flow input
GB/T 24041—2000
Unit process
Intermediate product flow input
Unit process
Intermediate product flow output
Unit process
Figure 2 An example of a group of unit processes in a product systemBasic flow output
Basic flow output
Basic flow output
For example, crude oil and solar radiation in the ground belong to the basic flow input of a unit process. Emissions to air, emissions to water bodies, and radiation belong to the basic flow output of a unit process. Basic materials, assembly components, etc. belong to intermediate product flows. Dividing a product system into unit processes helps to identify the inputs and outputs of the product system. In many cases, some inputs participate in the formation of output products, while some inputs (auxiliary inputs) are only used within the unit process and do not participate in the formation of output products. As a result of the unit process activities, other outputs (elementary flows and/or products) are also generated. The determination of the unit process boundaries depends on the level of detail of the model established to meet the research purpose.
Since the system is a physical system, each unit process obeys the laws of conservation of matter and energy. Material and energy balances can be used to verify the validity of the unit process description.
4.4 Data types
The collected data, whether measured, calculated or estimated, are used to quantify the inputs and outputs of the unit process. The data can be classified into the following topics:
Energy input, raw material input, auxiliary input, other physical input; products;
Emissions to air, emissions to water, emissions to land, other environmental factors. Within these topics, individual data types must be further refined to meet the needs of the research. For example, emissions to air can be expressed separately for specific data types, such as carbon monoxide, carbon dioxide, sulfur oxides, nitrogen oxides, etc. These data types will be further described in 5.3.4.
4.5 Establish product system model
LCA studies are conducted by establishing models that represent the key elements of the physical system. It is often difficult to study all the relationships between all unit processes in a product system, or all the relationships between a product system and the system environment. The choice of elements in the physical system to be modeled depends on the purpose and scope of the study. The model used should be described and the assumptions supporting these choices should be identified. This will be further explained in 5.3.3 and 5.3.5. 5 Determination of purpose and scope
5.1 General
The purpose and scope of the LCA study must be clearly defined and consistent with the intended application. The requirements of 5.1 of GB/T24040--1999 apply here.
5.2 Study Objectives
The LCA study objectives must clearly state the intended application, the reason for conducting the study and the intended users of the study, i.e. the intended communication of the study results.
5.3 Study Scope
5.3.1 General
GB/T24041---2000
The study scope must consider all relevant items in accordance with 5.1.2 of GB/T24040-1999. It should be recognized that LCA studies are an iterative process. As data and information are collected, various aspects of the study scope may need to be modified to meet the original study objectives. In some cases, the study objectives themselves may need to be modified due to unforeseen limitations, restrictions, or new information. These modifications and their justification should be documented in a timely manner. 5.3.2 Functions, Functional Units and Reference Flows
When determining the scope of the LCA study, the functional (performance characteristics) requirements of the product must be clearly stated. Functional units define the basis for quantifying these selected functions. Functional units must be consistent with the purpose and scope of the study. One of the main purposes of functional units is to provide a standard (in a mathematical sense) for the measurement of inputs and outputs. Therefore, functional units must be clearly defined and measurable. Once the functional units are determined, the quantity of product required to achieve the corresponding function must be determined. This quantification is the reference flow. The reference flow is used to calculate the inputs and outputs of the system. Comparisons between systems must be based on the same function, quantified in the form of reference flows corresponding to the same functional unit.
Example: A study of two systems that provide the "hand drying" function, paper towels and air dryers. The same number of hands dried can be used as a common functional unit for both systems, and the respective reference flows can be determined. In both cases, the corresponding reference flows are the average mass of paper towels and the average volume of hot air required for one wipe (dry). A list of inputs and outputs can then be compiled based on the reference flows. In the simplest case, it can be considered that it is related to the consumption of paper towels when using paper towels, and mainly to the energy input to the air dryer when using air dryers. If additional functions of the systems are not considered when comparing based on functional units, these omissions must be documented. For example, systems A and B have functions x and y, respectively, both expressed in selected functional units. However, system A also has function z, which is not expressed in functional units, and this must be documented. Another option is to include the system that provides function z within the boundary of system B to make the two systems more comparable. In both cases, the selected processes must be documented and justified. 5.3.3 Initial System Boundary
Determine the system boundary, that is, determine the unit processes to be included in the system to be modeled. Ideally, when modeling a product system, the inputs and outputs on its boundary should be elementary flows. However, in many cases, there is insufficient time, data or resources to conduct such a comprehensive study, and decisions must be made about which unit processes to model in the study and how detailed these unit processes should be studied. Resources should not be spent on quantifying inputs and outputs that have little impact on the overall conclusions. Decisions must be made about the types of environmental emissions to be evaluated and how detailed the evaluation should be. In many cases, as the research progresses, the system boundaries initially determined above will need to be modified based on the results of previous work (see 6.4.5). The criteria for selecting inputs and outputs should be clearly stated so that they are easy to understand. 5.3.5 will provide further guidance on this process. Any decision to ignore a phase, process or input and/or output within the life cycle must be clearly stated and justified. The criteria used to determine the system boundaries are decisive for ensuring the reliability of the research results and achieving the research objectives. The following are some examples of life cycle phases, unit processes and material and energy flows that should be considered: - Inputs and outputs in major manufacturing and processing processes; distribution and transportation;
production and use of fuel, electricity and heat; use and maintenance of products;
disposal of process waste and products;
recovery of post-use products (including reuse, recycling and energy recovery); 1) The mass in ISO14041 is expressed as "mass [material]" in this standard, indicating that it is a physical quantity to distinguish it from quality. 210
Manufacturing of auxiliary materials;
Manufacturing, maintenance and decommissioning of basic equipment;--auxiliary operations, such as lighting and heating; GB/T 24041-2000
-Other considerations relevant to impact assessment (if any). The use of process flow diagrams showing unit processes and their interrelationships can help to describe the system. Each unit process should be described initially to determine:
-Where the unit process begins in terms of obtaining raw materials or intermediate products;-The nature of the various transformations and operations that are part of the unit process;-Where the unit process ends in terms of the fate of intermediate or final products. The inputs and outputs that need to be traced back to other product systems should be determined, including decisions on allocation. The system should be described in sufficient detail and clarity to enable other practitioners to make the same inventory analysis. 5.3.4 Description of data types
What data are needed for IL.CA studies depends on the purpose of the study. These data can be collected from the production site related to the unit process within the system boundary, or they can be obtained directly from public literature or calculated. In practice, all data types may contain a mixture of data obtained through measurements, calculations, and estimates. 4.4 lists the topics of input and output data that should be quantified in each unit process within the system boundary. These data types should be considered when determining the data types to be used in the study. Individual data types should be further refined to meet the needs of the study objectives.
In conducting LCA studies, energy inputs and outputs must be treated equally with other inputs and outputs. Among the various types of energy inputs and outputs, those related to the production and transportation of fuels, raw material energy, and process energy used in the modeled system must be included. Emissions to air, water, and land are usually controlled point or non-point source emissions. In addition, more important fugitive emissions should also be included. Emissions can also be expressed as indicator parameters, such as biochemical oxygen demand (BOD). Other data types for which input and output data can be collected include noise and vibration, land use, radiation, odor, and waste heat. 5.3.5 Criteria for preliminary selection of inputs and outputs
When determining the scope, a preliminary set of inputs and outputs for the inventory is selected. It is not practical to include all inputs and outputs in the product system for simulation analysis during this process. Identification of inputs and outputs that should be traced back to the environment, that is, identification of unit processes that produce the above inputs or receive the above outputs that should be included in the product system under study, is an iterative process. Generally, a preliminary identification is made using existing data, and as data accumulates during the research process, the inputs and outputs are more fully identified, and finally verified through sensitivity analysis (6.4.5).
The criteria for selecting inputs and outputs and the assumptions on which they are based must be clearly stated, and the potential impact of the selected criteria on the research results must be evaluated and stated in the final report.
For the analysis of material inputs, the first step is to make a preliminary selection of the inputs to be studied. This selection should be based on the inputs of each unit process to be modeled. Data collected from specific sites or public literature can be used. The purpose of this selection is to determine the important inputs related to each unit process.
In LCA practice, there are some criteria for identifying inputs that should be included in the study, including a) material, b) energy, c) environmental relevance, etc. If the initial identification of inputs focuses only on the material aspect, important inputs may be missed in the study. Therefore, the energy and environmental relevance criteria should also be considered in this process: a) Material: When the material criterion is applied, when the cumulative total amount of material input exceeds a certain percentage of the total material input of the product system, it should be included in the system input.
b) Energy: When the energy criterion is applied, when the cumulative total amount of energy input exceeds a certain percentage of the total energy input of the product system, it should be included in the system input.
c) Environmental relevance: When the environmental relevance criterion is applied, when a data type in the product system exceeds a certain percentage of the estimated amount of that type, it should be included in the system input. For example, taking sulfur dioxide as a data type, a percentage is first specified for the sulfur dioxide emission of the product system. When the input is greater than this percentage, it is included in the system input. 211
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These criteria can also be used to identify which outputs should be traced back to the environment by taking into account the final waste treatment process. When the results are used to support comparative claims for the public, the final sensitivity analysis of the input and output data must include the above-mentioned material, energy and environmental relevance criteria. The inputs identified by this process should be modeled as basic flows. 5.3.6 Data Quality Requirements
The statement of data quality requirements is important for correctly understanding the reliability of the study results and for the appropriate interpretation of the study results. Data quality requirements must be specified to meet the purpose and scope of the study. Data quality should be characterized by qualitative, quantitative and data collection and consolidation methods. The following data quality requirements should be included: - Time span: the required data years (e.g. within the last 5 years) and the shortest period from which data are collected (e.g. 1 year); - Geographical breadth: the geographical scope from which unit process data are collected to meet the research objectives (e.g. local, regional, national, continental, global);
- Technology coverage: technology portfolio (e.g. actual process portfolio, best available technology, weighted average of worst operating units); In addition, other factors that determine the nature of the data must be considered, such as whether they are collected from a specific site or from publications, whether they should be measured, calculated or estimated, etc.
System unit processes that contribute most of the material and energy flows, as confirmed by sensitivity analysis (5.3.5), should use data obtained from a specific site, or representative average data. Unit processes that produce emissions that affect the environment should also use data obtained from a specific site. In all studies, the following further data quality requirements must be considered, the degree of detail of which depends on the purpose and scope of the study. Accuracy: a measure of the variability of data values in each data type (e.g. variance); Coverage: the percentage of sites that report basic data for each data type in a unit process to the total number of sites that actually exist; Representativeness: a qualitative assessment of the extent to which the data set reflects the actual group of interest (i.e., geographic breadth, time span, and technical coverage); Consistency: a qualitative assessment of the degree to which the research methodology is applied to different analytical contents. Reproducibility: a qualitative assessment of the likelihood that other practitioners will obtain the same research results using the same methodology and data value information. When the research is used to support comparative assertions for the public, all data quality requirements for the above aspects must be specified in the research. 5.3.7 Critical Review The type of critical review (see 7.3 of GB/T24040-1999) must be determined. When the purpose of the research is to provide comparative assertions for the public, the critical review specified in 7.3.3 of GB/T24040-1999 must be conducted.
6 Inventory Analysis
6.1 Overview
The determination of the purpose and scope of the study provides a preliminary plan for conducting LCA research. Life cycle inventory analysis (LCI) involves data collection and calculation procedures. This activity should be carried out according to the steps shown in Figure 3. 6.2. Preparation for Data Collection
After the scope of the LCA study is determined, the unit processes and related data types are initially determined. Since the data collection may cover several reporting sites and multiple publications, the following steps will help ensure a unified and consistent understanding of the modeled product system. These steps should include:
---Draw a detailed process flow chart to depict all unit processes that need to be modeled and their interrelationships;--Detail each unit process and list the data types associated with it and compile a list of measurement units;
For each data type, describe the data collection techniques and calculation techniques so that the personnel at the reporting site understand what information is needed for the LCA study;
~---Issue instructions to the reporting site to clarify the special circumstances, anomalies and other issues related to the reported data.
GB/T 24041--2000
Appendix A (Suggested Appendix) gives an example of a data collection form. Determination of purpose and scope
Preparation of data collection
Revised data collection form
Data collection
Confirmation of data
Data collection form
Collected data
Confirmed data
Relationship between data and unit processes
Confirmed data of each unit process
Relationship between data and functional units
Confirmed data of each functional unit
Merge of data
(6. 4. 4)
Requirement for additional data
or unit processes
6.3 Data collection
Modification of system boundaries
Calculated inventory
Completed inventory
Figure 3 Outline of inventory analysis procedures
(Some iterative processes are not shown)
Allocation and recycling
In LCA studies, data collection procedures will vary for each unit process in different system models, and may also vary depending on the composition and qualifications of the researchers involved, and the need to meet property and confidentiality requirements. Such procedures and the reasons for adopting them should be documented.
Data collection requires a thorough understanding of each unit process. In order to avoid double counting or gaps, the description of each unit process must be recorded. This includes a quantitative and qualitative description of the inputs and outputs used to identify the start and end points of the process, as well as a quantitative and qualitative description of the unit process functions. If the unit process has multiple inputs (such as multiple water flows entering a sewage treatment system) or multiple outputs, the data related to the allocation procedures must be documented and reported. Energy inputs and outputs must be quantified in energy units. The mass [mass or volume] of fuel should also be recorded when feasible.
If data are collected from public publications, the source must be indicated. For data collected from literary sources that are significant to the conclusions of the study, the public source must be cited to detail the data collection process, collection time and other data quality parameters. If the data do not meet the initial quality requirements, this must be stated. 6.4 Calculation procedures
6.4.1 General
After the data are collected, the calculation procedures are used to obtain inventory results for each unit process and functional unit in the production system. When determining the basic flows related to the production of electricity, the production combination used and the efficiency of combustion, conversion, transmission and distribution must be considered. The assumptions made must be clearly stated and justified. Whenever possible, the actual production mix should be stated to reflect the type of fuel consumed.
The energy input and output can be converted to energy input and output by multiplying the input and output combustible materials, such as oil, natural gas or coal, by the corresponding heat of combustion. In this case, it should be stated in the report whether the higher or lower heating value is used. The same calculation procedure should be used throughout the study. 6.4.2 to 6.4.5 and 6.5 describe some of the calculation steps required in the data calculation process. All calculation procedures must be clearly documented.
6.4.2 Validation of data
The validity of the data must be checked during the data collection process. Validation may include the establishment of material and energy balances and/or comparative analysis of emission factors. If data are found to be obviously unreasonable during this process, they must be replaced. The data used for replacement must meet the data quality requirements specified in 5.3.6. For each data type or reporting location, if missing data are found, the missing data and gaps should be handled and replaced by: - a reasonable "non-zero" data;
- a reasonable "zero" data;
- a value calculated based on data reported from unit processes using similar technology. The handling of missing data must be documented. 6.4.3 Association of data with unit processes
An appropriate reference flow (such as 1 dry gram of material or 1 megajoule of energy) must be determined for each unit process, and quantitative input and output data for the unit process must be calculated based on this.
6.4.4 Association of data with functional units and merging of data The unit processes can be related to each other based on the flow chart and system boundaries, so that calculations can be made for the entire system. This calculation is based on a unified functional unit as the material in all unit processes of the system. , and the common basis of energy flow, in order to obtain all the input and output data in the system, caution should be exercised when merging the input and output data of the product system. The degree of merging should be sufficient to achieve the purpose of the study. Data merging is allowed only when the data type involves equivalent substances and has similar environmental impacts. If more detailed merging rules are required, they should be demonstrated at the stage of determining the purpose and scope of the study, or left to the subsequent impact assessment stage for demonstration. 6.4.5 Modification of system boundaries
Iterativeness is an inherent feature of LCA. The selection of data must be determined based on the importance of the data determined by the sensitivity analysis, so as to verify the results obtained from the initial analysis described in 5.3.5. The initial product system boundaries must be appropriately modified based on the demarcation criteria specified when determining the scope. Sensitivity analysis may lead to: - Excluding data that are determined to lack importance by sensitivity analysis - exclude inputs and outputs that lack importance to the study results; - include new unit processes, inputs and outputs that are considered important through sensitivity analysis. The above modification process and the results of the sensitivity analysis must be documented. Conducting a sensitivity analysis helps to limit data processing to the range of input and output data that are judged to be important for the purpose of the LCA study. 6.5 Allocation of logistics, energy flows and emissions
6.5.1 Overview
Life cycle inventory analysis relies on linking unit processes in a product system with simple logistics or energy flows. In fact, it is extremely rare for an industrial process to produce only a single product or for which the raw material input and output only reflect a linear relationship. Most industrial processes produce multiple products. products, and intermediate and discarded products are recycled as raw materials. Therefore, the material flows, energy flows and environmental emissions must be allocated to each product according to the established procedures. 6.5.2 Allocation principles
The inventory is based on the material balance of inputs and outputs, so the allocation procedure should reflect the basic relationship and characteristics of such inputs and outputs as much as possible. The following principles apply to co-products, internal energy allocation, services (such as transportation, waste treatment), and open or closed loop recycling:
- The process common to other product systems must be identified in the study and treated according to the procedures required below; - The sum of inputs and outputs before and after allocation in the unit process must be equal; - If there are several possible allocation procedures, a sensitivity analysis must be performed to explain the difference in results between the use of other methods and the selected method.
The allocation procedure used for each unit process to be allocated inputs and outputs must be documented and justified. 6.5.3 Allocation Procedure
The following steps must be performed step by step based on the above principles\: a) Step 1: Whenever possible, allocation should be avoided by: 1) further dividing the unit process to be allocated into two or more sub-processes and collecting input and output data for these sub-processes. 2) expanding the product system to include functions related to co-products. When doing this, take into account 5.3.2.
b) Step 2: When allocation is unavoidable, the inputs and outputs of the system should be allocated to the different products or functions in it in a way that reflects the corresponding physical relationship between them, that is, how the inputs and outputs change with the quantitative changes in the products or functions provided by the system. However, the final allocation results do not have to be proportional to simple measurements (such as the mass [physical] or molar value of co-products). c) Step 3: When a simple physical relationship cannot be established or cannot be used as a basis for allocation, the inputs should be allocated between the products or functions in a way that reflects other relationships between them. For example, the input and output data can be allocated to the co-products in proportion to the economic value of the products.
Some outputs may contain both co-products and wastes. In this case, the ratio between the two must be determined, because the inputs and outputs are allocated only to the co-product part of them.
The same allocation procedure must be used for similar inputs and outputs in the system. For example, the allocation procedure for useful products (such as intermediate or separated products) output from the system must be the same as the allocation procedure for similar products input into the system. 6.5.4 Allocation procedures for reuse and recycling For reuse and recycling, the same allocation principles and procedures as described in 6.5.2 and 6.5.3 apply. Further considerations should be given to the following situations.
a) In reuse and recycling (and composting, energy recovery and other processes that may be included in reuse and recycling), the inputs and outputs of the unit processes related to the acquisition and processing of raw materials or the final disposal of products may be common to more than one product system. b) Reuse and recycling may change the inherent properties of the materials during subsequent use. c) Special attention should be paid to the determination of the system boundaries of the recovery process. Some allocation procedures are applicable to reuse and recycling, in which the changes in the inherent properties of the materials must be taken into account. Figure 4 provides a conceptual illustration of such procedures. The following is a brief description of the differences to illustrate how the above constraints can be met. 1) Strictly speaking, step 1 is not part of the allocation procedure. 215
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