How do we assess if a supply chain is becoming greener?
Duflou et al. (2012) provide a systematic analysis of the many scales involved in greening a supply chain. These scales of production are:
Device/Unit Process => Line/Cell/Multi-Machine System => Facility Level => Multi-Factory System => Global Supply Chain
In the Duflou et al. (2012) paper, you will find applications of many of the system analysis methods that have been introduced as part of this course.
These scales represent physical units or sets of physical units of production that result in the creation of individual (discrete) items. This selection simplifies some of our choices in system boundaries. However, this simplification progressively loses usefulness as we move to the larger scale analysis.
We are already familiar with some of the analytical methods used at the Device/Unit Process level, namely the life cycle inventory (LCI) introduced in Module 4.2 and described in detail in ISO 14040 and ISO 14044. In the Duflou et al. (2012), the scope of analysis is wider, not only including material and energy flows, but also potential gains in efficiency and effectiveness that can be made based on technological improvements. Duflou et al. (2012) provide application of this methodology to specific case studies. This exercise is very helpful, and I recommend you to take a close look at these examples and use them to shape the analysis that you will be doing as part of your second term paper.
We are also familiar with the input/out analysis that is introduced for studying Multi-Machine ecosystems. We discussed how to create flowcharts to follow the flow of materials and energy in section 3.4 of Module 3 (Sustainability Science and Engineering, Volume 1: Defining Principles. pp. 91-112). In addition to this method, exergy analysis is introduced. Exergy is defined as the useful energy that can be harvested down the energy cascade, generated by processes in a multi-machine ecosystem. This cascade is most evident if the processes are linked by series architectures, in other words, if the output from process A acts as the input for process B.
Figure 3.3 shows an example of materials and energy flows at a Facility level. When it comes to the gains in efficiency and effectiveness at the facility/plant level, Duflou et al. (2012) turn their focus from the processes taking place in manufacturing to the actual physical plant where these processes take place. Analysis here is linked with the materials and choices made in construction processes. While not the focus of this course, it is important to note that the area of applications of sustainability to civil engineering is a very fertile field of research in which great gains continue to be made.
In this module, we are most interested in the analysis at the Multi-Factory and Global Supply Chain levels.
At the Multi-Factory level, the concept of Industrial Symbiosis is introduced and supported on three types of gains:
- Conversion or collection of energy/material waste from an industrial partner that can be effectively used by another;
- Substitution of inputs from internally generated feedstocks, and
- Avoidance of waste production.
These gains are in line with the principles for greening the supply chain discussed in the previous sections.
After discussing both the Fiksel (2013) chapter and the Duflou et al. (2013) paper, it is very clear that assessing to what degree a supply chain is environmentally friendly is a complex operation!
When we talked about thermodynamics many moons ago, we discussed the difficulties in choosing appropriate system boundaries. We discussed why choosing too small of a system was, in some ways, as limiting of an assumption as choosing too large of a system. Here is where we run into the challenges of choosing too large of a system! Clearly, if LCA analysis of a supply chain is to be meaningful, all the energy and material inputs and outputs need to be taken into account. Yet, this type of first-principle analysis can prove very intractable. Given the growing complexity of supply chains, the study footprint indicators have become a popular way to group and simplify life cycle analysis. However, there is an extreme lack of consistency when it comes to how footprints are calculated. In the Fiksel (2013) chapter, you can find a brief discussion of the weaknesses of using footprint indicators.
Duflou et al. (2013) present two alternative methods for tackling the large number of feedback loops in supply chains. One is the implementation of an "environmentally enhanced" statistical input/output model and the second is to use a hybrid LCA. Both of these methods rely on fragmentary and incomplete databases. However, they highlight the need for formalization and quantification of energy and material flow across the scales. Significant progress is underway. Numerical modeling have been successfully applied to distribution, utilization, and disposition stages in the supply chain. Yet, quantification of the input/outputs and LCA of manufacturing process remain elusive.