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Weekly UpdatesABSTRACT
It is a current practice that refrigerators and freezers in many countries are shredded after the end of useful lives. The shredder residue is deposited in landfills. During the shredding process a significant fraction of blowing agent (BA) in the insulation foam may be released into the atmosphere. The objective of this study is to determine the fraction of BA released from foam during shredding, by comparing the BA content in insulation foam of refrigerator units before shredding with the BA content of shredded foam. All foam samples analyzed were manufactured with trichlorofluoromethane [CFC-11 (C[Cl.sub.3]F)] as BA. The average content of BA in the insulation foam from eight U.S. refrigerator units manufactured before 1993 was found to be 14.9% [+ or -] 3.3% w/w. Several refrigerator units also identified as being manufactured before 1993 were stockpiled and shredded at three shredder facilities, of which one was operated in both wet and dry modes. The selected shredder facilities represent typical American facilities for shredding automobiles, refrigerators, freezers, and other iron containing waste products. Shredded material was collected and separated on location into four particle size categories: more than 32 mm, 16-32 mm, 8-16 mm, and 0-8 mm. Adjusting for sample purity, it was found that the majority (>81%) of the foam mass was shredded into particles larger than 16 mm. The smallest size fraction of foam (0-8 mm) was found to contain significantly less BA than the larger size categories, showing that up to 68% [+ or -] 4% of the BA is released from these fine particles during the shredding process. Because only a minor fraction of the foam is shredded into particles smaller than 8 mm, this has a minor impact on the end result when calculating the total BA release from the shredding process. Comparing BA content in shredded samples from the three shredder facilities with the measured average BA content of the eight refrigerator units, it was found that on average 24.2% [+ or -] 7.5% of the initial BA content is released during the shredding process.
INTRODUCTION
The blowing agent (BA) for insulating foam used in appliances (e.g., refrigerators and freezers) and many building materials is frequently a fluorocarbon. Before 1993, the BA used was mostly trichlorofluoromethane (CFC-11), which has been phased out because of this chemical's depleting effect on the ozone layer after release into the atmosphere. (1) Hydrochlorofluorocarbons (HCFCs) such as HCFC-141b (C[Cl.sub.2]FC[H.sub.3]) was used widely as a substitute for CFC-11, but by 2005 use of HCFC-141b was also banned in most developed countries because of recognition of its ozone depletion potential. Hydrofluorocarbons (HFCs) such as HFC-134a (C[H.sub.2]FC[F.sub.3]) or HFC-245fa (C[F.sub.3]C[H.sub.2]CH[F.sub.2]) are expected to be used extensively in the future as foam BAs. HFCs released to the atmosphere are, however, potential greenhouse gases that may contribute significantly to global warming. (2) In 1990s, the combined carbon dioxide (C[O.sub.2])-equivalent emissions of CFCs, HCFCs and HFCs was estimated to be 7.5 GtC[O.sub.2]-eq/yr. This was equivalent to approximately 30% of the annual contribution due to global fossil fuel burning. (2) Previous studies have documented that during the life of an appliance, very little BA is released to the atmosphere. (3,4) This is primarily because the foam is encapsulated by the appliance walls and there is minimal air movement through the foam. However, in the United States, as in many other parts of the world, whenever appliances are taken out of service the current practice is that the majority end up in the scrap metal recovery industry. (5) The majority of discarded appliances are shredded along with scrap automobiles. The waste produced, commonly referred to as shredder residue, can contain the polyurethane (PUR) foam insulation from the shredded appliances. The violent action of the shredder in fragmenting the scrap items rips the foam into small pieces, opening gas cells in the polymer matrix, and releasing BA into the atmosphere. A recent laboratory study showed that the proportion of BA content of foams, which is released from foams instantaneously during shredding, is on the order of 9-40% depending on particle size (valid for a particle size range of 2-32 mm). (3) The BA remaining in the shredded material may be released very slowly if the integrity of the foam particles is maintained with respect to diffusional properties. Currently there are no treatment technologies available for recovery/recycling of shredder residues. Following the shredding operation of appliances, the waste residue is therefore typically stockpiled until it is shipped to a landfill for disposal. Both the shredding operation and the stockpiling of the shredder residue are activities that could increase the potential for the release of BAs. A recent study showed that there is a high potential of microbial anaerobic degradation of fluorocarbons such as CFC-11 and HCFC-141b released from foams in landfills, suggesting that landfills could be important sinks of fluorocarbons disposed of in foam. (6) However, the input of fluorocarbons in insulation foams to landfills remains unknown, as losses during decommissioning are unknown.
The objective of this study was to determine the amount of BA released to the atmosphere following decommissioning of appliances, focusing on the shredding process. The objective was met by comparing the BA content in insulation foam of refrigerator units before shredding with the BA content of shredded foam residues (foam fluff). All foam samples analyzed were manufactured with CFC-11 as BA. Eight appliances were selected before shredding. Representative foam samples were cut out of the appliances from four manufacturers, and the BA content of the foam samples was determined. An important step was to determine how appliances are currently decommissioned. Landfill and shredder operators were interviewed to determine if their operations are "typical" for the industry and, therefore, good candidates for inclusion in this study. Three shredder facilities, which are all located in the United States in the state of Tennessee, were part of this study. One shredder was operated in both wet and dry modes. The operation of the selected shredders is typical of the industry and all have the capability of running the shredder setup for appliance in-feed only.
The driving concept utilized during the study was to quantify the size distribution of refrigerator/freezer insulation particles generated as a result of the mechanical shredding process. The sorted foam samples from the shredding operation were then analyzed for BA content. The difference in BA content between the preshredded foam taken from the appliances and the postshredded samples should represent the amount of BA that is released in the shredding process.
EXPERIMENTAL SECTION
Foam Samples--Preshredded
For each of four home appliance manufacturers, foam panels from two old refrigerator units containing PUR foam blown with CFC-11 were supplied for laboratory analysis of BA content. From each unit, foam samples were taken from the top, left side, right side, rear, and bottom using a reciprocating saw, leaving the plastic casing and metal exterior of the refrigerator units attached to the foam. Each sample measuring approximately 10 x 10 cm was sealed with gas-tight metallic tape and kept in sealed Tedlar bags before shipment. Shipping of samples was done by air in a pressurized cabin. At the laboratory, the samples were stored at low temperature (10 [degrees]C) before analysis. The eight refrigerator units are referred to as A1, A2, B1, B2, C1, C2, D1, and D2 throughout this paper.
Sampling of Shredded Foam Materials
Appliances, or "white goods," are a normal component of the in-feed mix at metal recycling facilities, which operate shredders. Scrap recycling in the United States has used shredders for processing automobiles and light iron (appliances) for about 40 yr. Automobile shredders are very specialized units. There are a small number of manufacturers of shredders in the United States. Although there are some differences in equipment design, the similarities from one manufacturer to another are more prevalent than the differences. Refrigerator units identified as manufactured before 1993 were collected and shredded at three shredder facilities in Tennessee, which in this paper are identified by their location as Harriman, Nashville, and Pulaski. At the Harriman facility, the shredder was operated in two modes: a dry and a wet mode. First, sample materials were collected for analysis after running the shredder in dry mode. Then, new sample materials were collected after running the shredder in a wet mode. At each shredder facility several refrigerator units (17-40) were stockpiled and shredded, providing a sufficient amount of sample material, which contained shredded foam particles from several appliances. For the selected refrigerators it took less than 15 min to shred the entire collected pile. The shredded sample material from each facility was collected and sieved to separate the material in four size fractions: retained on 32-mm screen, retained on 16-mm screen, retained on 8-mm screen, and passed 8-mm screen. The shredded foam fractions were stored in 15-L Tedlar gas bags and shipped in plastic coolers for BA content analysis. These size fractions are referred to as 32R, 16R, 8R, and 8P respectively. Table 1 lists abbreviations that are used to identify samples of shredded material. Shipping of samples was done by air in a pressurized cabin. All samples were stored at low temperature (10 [degrees]C) before laboratory analysis.
Measurement of BA Content in Preshredded Foam Panels
To quantify the total content of BA in the insulation foam of the eight refrigerator units from four manufacturers, core foam samples (diameter = 1 cm) were cut out from the center of the panels with a sharp cork bore after removing the plastic casing. To protect the surface of the foam panels from damage and to avoid further loss of BA by diffusion from the foam panels after sampling, the panels were sealed with metallic vapor-tight tape and stored in sealed Tedlar bags (SK Inc.). One sample from each of the five foam panels from each refrigerator unit was cut out, weighed, and placed in a 1123 mL glass bottle, which was sealed with Teflon coated septa and aluminum caps to be measured for BA content.
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