Excerpt from Samuel Keith Ghormley's University of Nebraska Graduate Thesis from December 2017.
Foundries represent a significant part of the base of the world’s economy and as a sector are one of the largest consumers of energy and producers of solid waste in the United States. Sand casting foundries use approximately 5-10% of their total energy on sand handling processes. By adding a secondary sand reclamation process, foundries can expect to become more energy efficient as well as reducing solid waste from the foundry. To measure the broader environmental impacts, life cycle assessment (LCA) can be used. The goal of the current research was to examine a medium-sized foundry in the United States that sources its sand from a long distance away by using LCA techniques.
A comparison was made between a sand reclamation train model without any secondary sand reclamation, secondary reclamation using a mechanical process, a thermal process, and a microwave process. An economic, energy balance, and full LCA analysis was conducted for each of these processes. It was found that in addition to being economically beneficial, the life cycle environmental impacts were also less for processes that included secondary reclamation.
In eight of ten measured categories adding a secondary reclamation process reduced the environmental impact of the foundry. When comparing mechanical and thermal mechanisms for secondary reclamation it was found that thermal processes were more energy intensive at the foundry, but due to their lower sand requirements their overall life cycle impacts are less than the mechanical reclamation model. It was determined that varying the transportation distance in the model created the largest change in the associated outputs for all processes.
Chapter 1. Introduction
Foundries represent a significant part of the base of the world’s economy. Metal parts made in foundries are vital to the automotive industry, construction projects, as end products, and as parts for larger equipment. Without foundries, industry as we know it would not function. Because foundries play such an integral role, it is imperative that they operate as efficiently as possible. In the past, efficiency goals focused almost entirely on economic and production metrics, but a shift toward sustainability means foundries need to reassess the way they view efficient operations.
The foundry industry is one of the largest consumers of energy in the United States. In 2010, ferrous foundries accounted for 5.5% of all energy use in the manufacturing sector (US EIA 2013). Foundries also are responsible for 4% of all municipal solid waste produced in the United States (US EPA 2016). The goal of becoming more energy efficient and reducing foundry waste will decrease the environmental impact caused by foundries. One area where improvements can be made is the sand handling train of processes.
Sand casting foundries use sand to form molds for their end products. Their sand handling processes cover all processes from the time virgin sand arrives at the foundry to when it leaves as spent foundry sand (SFS). The specific individual processes vary by foundry and can include core and mold mixing, curing, shakeout, and any subsequent reclamation processes. The sand handling processes account for 5-10% of the total energy use in a steel foundry (Keramida 2004) but contribute nearly all of the solid waste generated. Reducing solid waste at the foundry can be accomplished by modifying the sand handling process train to include one or more sand reclamation processes. These processes can be viewed as a tradeoff where there is an additional process requiring energy offset by a reduction in virgin sand purchase and SFS disposal. When looking at the impacts from a broader environmental viewpoint, the simple tradeoff seen at the
foundry may not be wholly accurate because of transportation as well as other upstream and downstream impacts. To measure the broader impacts, life cycle assessment (LCA) can be used.
The goal of the current research was to perform an LCA on a medium-sized foundry in the United States that sources its sand from a long distance away and analyze those results. The specific objectives set were:
1) develop a model of the foundry using appropriate system boundaries,
2) analyze the environmental impacts of the model and compare those impacts when the process is modified by a secondary sand reclamation system, and
3) perform a sensitivity analysis on the model to determine important trends if important variables are altered.
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