If the reclamation is difficult, the recovered refrigerant has to be destroyed. Liquid injection incineration provides fluorite from the destruction products, which can be used as a raw material for chemical recycling to produce refrigerant again. This is considered desirable from the perspective of resource recycling, but there is a trade-off with energy consumption, GHGs, and the amount of sludge generated. Gaseous/fume oxidation in Europe can recover hydrochloric acid and hydrofluoric acid water instead of fluorite and is considered the preferred treatment method if those applications are available. Future research is required on desirable resource recovery methods from the perspective of promoting resource recycling.
Reclaimed Refrigerant as a Product: Setting the Functional Unit as the Production of 1 kg of Reclaimed Refrigerants
In Section 3, a comparison was made between destruction treatment and reclamation treatment as treatment methods for the recovered refrigerant. Alternatively, the treatment of refrigerant can be seen in another way, which focuses on the reclaimed refrigerant as a product. In this case, the reclamation process can be regarded as a production method. Figure 5 shows the situation where the standardized flow that generates 1 ton of reclaimed refrigerant is set as the functional unit and compared with its equivalent by the destruction of used refrigerant and the creation of new refrigerant. From the perspective of disposing of air-conditioning equipment and recovering refrigerant, it is appropriate to set the functional unit per recovered refrigerant, as this study wants to compare the environmental impacts of destruction treatment and reclamation treatment as a method for treating recovered refrigerant. On the other hand, from the perspective of manufacturing, installing, or purchasing equipment, it is appropriate to use the functional unit per produced refrigerant, as it is also desirable for comparing the environmental impacts of newly produced refrigerant and reclaimed refrigerant. The difference between the two is whether the reclamation process is regarded as a process that replaces the production of a new refrigerant or whether the production of a new refrigerant is necessary after the destruction treatment within the same system boundary. The LCIA results are also uniformly affected by the yield of the reclamation process. Therefore, in this section, we also evaluated and compared the destruction and reclamation treatment per 1 kg of reclaimed refrigerant, using R410A as a reference in accordance with the general LCA approach. R410A was selected as it has the highest recovery volume for the time being in Japan.
Figure 6 shows the results of a comparison of the environmental impact of the reclamation process and the destruction process, using R410A, the most recovered refrigerant in Japan, as an example, based on 1 ton of available reclaimed refrigerant. In this graph, each of the three processes is shown: reclamation treatment, destruction treatment, and refrigerant production.
It can be seen that, for all the indicators, GHG emissions, energy consumption, and LIME3 results, the reclaimed treatment is smaller than the destruction treatment. This trend was similar regardless of refrigerant and region (14.1 vs. 2 tonCO2eq; 161 vs. 7.2 GJ; 810 vs. 40 USD, respectively). The results were in the same range as Jovell et al. 2021 [11], who showed that refrigerant reclamation had considerably lower environmental impacts than the production of fresh R32, with a GHG emissions reduction of 86% (10.9 vs. 1.5 kgCO2eq/kg, respectively, for produced and reclaimed refrigerants).
Novelty and Critical Comparison with the Previous Studies
At first, before comparing the results with the previous studies, as explained in the introduction, it has to be highlighted that most of the previous studies only reported on refrigerant production emissions and did not focus on the destruction/reclamation of refrigerant because they assessed the life cycle of air conditioners and refrigeration equipment, not the life cycle of refrigerants. Therefore, only a little information is available in the literature.
According to the authors’ knowledge, recently, only two research articles (Jovell et al. andWang et al.) focused on the refrigerant disposal treatment. Jovell et al. tried to assess the environmental impact of refrigerant reclamation for R32 using the commercial blend R407F. Wang et al. [12] compared CO2 emissions between new refrigerant production and reclaimed refrigerant for R134a. Indeed, R32 was only introduced to the market recently; knowing that the total life-cycle of an air-conditioner is more than 10 years on average, it is necessary to consider the refrigerants that could be reclaimed soon, i.e., the ones used in the oldest machines. For example, in Japan, even if residential and commercial split systems have already shifted to R32, packaged units will shift from R410A by 2025. In accordance with the actual situation of refrigerant transition, we evaluated R410A, which currently has the highest refrigerant-recovery amount [34]; R22 and R134a, which have a large refrigerant-recovery amount. Since R32 [34] has only recently been introduced to the market, the amount of refrigerant recovery is not yet large, and R407F, as presented by Jovell et al., has not been adopted for residential air conditioners or general commercial air conditioners.
It has to be also noted that Jovell et al. [11] used computer simulation values, while Wang et al. [12] adopted equipment-rating catalog values as the values for reclamation treatment, whereas the evaluation in our study is more in line with the actual plant operation. Wang et al. [12] did not consider destruction. While looking closely at the results reported by Jovell et al., the results for the production of R32 were reported to be 10.9 kgCO2eq for the GHG emissions (vs. 7.77 kgCO2 eq for R32 in our study results per 1kg of produced refrigerant are provided in Table A6) and 115 MJ for the energy use (vs. 147 MJ for R32 in our study). For the reclamation, the results were 1.5 kgCO2eq (vs. 1.6 kgCO2 eq for R32; batch distillation in our study) and 2.13 MJ (vs. 15.7 MJ for R32 in our study). The results are close to ours, even though the impact of the reclamation was lower in Jovell et al. ((results for destruction were not provided). One possible reason is that in Jovell et al., the fugitive emissions during the production process of fluorinated ionic liquids and in the process of recovering R32 and regenerating fluorinated ionic liquids were mostly considered: representing 90% of the GWP vs. 30% in our study. Waste treatment after R32 separation (a mixture of R32, R125, and R134a) was also not considered, though it accounted for about 50% of the GHG emissions in our study. Those observations could lead to the conclusion that it was worth collecting the information related to the actual plants’ energy use and waste treatment processes in our study. It is difficult to compare our results with Wang et al. 2021, as their results were not provided per functional unit (i.e., kg), and a breakdown of the results was also not provided.
Finally, in other documents [11,12], only one type of refrigerant and one type of treatment method were evaluated; however, in this study, multiple plants/regions and multiple refrigerants were consistently evaluated and compared using the same method. We believe that this led to more general findings. In addition, this study provided the first detailed analysis on refrigerant reclamation from both a global warming control and circular economy perspective, using three indicators: GHG emissions, energy consumption, and LIME3.
Limitations
From the viewpoint of LCA, AIST IDEA v2.3 (AIST, Tokyo, Japan) was used as the background data, including the main raw materials for refrigerant production; however, Japanese background data were applied to the production process in China. Although some adaptations were made to suit each country’s circumstances, such as the use of coal for electricity and energy, the challenge is to examine these background processes more closely in order to improve the accuracy of the refrigerant production data.
Further Research
Further research issues for the future include scrutiny of the background processes of refrigerant production, understanding the material flow of sludge generated during destruction treatment for each disposal method, understanding and improving the tradeoff in the chemical-recycling process, and understanding the environmental impact of promoting recovery and reclamation on a global scale.
Conclusions
As the GWP value of refrigerants used in refrigeration and air-conditioning equipment is large, the GHG emission-reduction effect of refrigerant recovery is very large, so refrigerant recovery is an effective and essential measure from the perspective of combating global warming, alongside switching to practical refrigerants with low GWP values. On the other hand, the recovered refrigerant must be treated, either by destruction or reclamation. The objective of this study was to evaluate and compare the environmental impact of reclamation and destruction treatment methods for recovered refrigerants from refrigeration/air-conditioning equipment. Primary data consistent with the system boundary were collected, and the environmental impact of each treatment method could be quantified.
The GHG emissions from reclaimed treatment per kg of used refrigerant were approximately 5.7 to 15.9 kg CO2eq less than those from destructive treatment, confirming that the promotion of reclaimed treatment together with refrigerant recovery can contribute to global warming mitigation. The trend was also confirmed for energy consumption (82.5 to 250.6 MJ per kg of used refrigerant) and LIME3 (0.40 to 0.97 USD). This trend was similar for different refrigerant types and different treatment regions (Japan and Europe). This is thought to be due to the fact that reclamation treatment has a significant effect in terms of replacing the production of new refrigerants. A comprehensive environmental impact analysis using LIME3 considered the dominant impact of waste treatment in destruction treatment and the dominant effect of credits in reclamation treatment; the results of this analysis indicate that reclamation treatment, which avoids the need for new mining of fluorite, the raw material of refrigerants, is desirable from the perspective of resource recycling and the circular economy. It is expected that the recovery and reclamation of refrigerants will be promoted globally from the viewpoints of global warming mitigation, Kigali Amendment compliance, and resource recycling.
…Concluded
This article was first published in the MDPI journal, MDPI, Basel, Switzerland. Authors retain the copyright. Copyright: © 2022 by
the authors.
Yoshihito Yasaka, Selim Karkour and Koichi Shobatake belong to TCO2 Co., Ltd., Tokyo 102-0082, Japan. Norihiro Itsubo is a Faculty of Environmental Studies, Tokyo City University, Tokyo 158-8557, Japan. Fumiaki Yakushiji is from Daikin Industries, Ltd., Osaka 530-8323, Japan.
