Global cooling demand is expected to grow significantly in the future, especially in developing countries, such as India, China, and Indonesia, and there are concerns that electricity consumption and its global warming impact will increase by about three times between 2016 and 2050 [1]. The life-cycle global warming impact of air conditioners and refrigeration equipment can be divided into two main categories: indirect impacts due to carbon dioxide emissions from energy consumption during equipment use, and direct impacts when refrigerants are emitted into the atmosphere. Comparative evaluation results have been reported for various types of refrigerants and equipment (Wan et al. 2021 [2]; Troch 2016 [3]; Hill and Papasavva 2005 [4]; Banks and Sharatt 1996 [5]; Chen, 2008 [6]; Spatz and Motta, 2004 [7]; Aprea et al. 2016 [8]; Bovea et al., 2007 [9]; Cao and Hwang 2022 [10]; Jovell et al. 2022 [11]; Wang et al. 2021 [12]). For example, using a simulation, Jovell et al. 2022 [11] showed that the R32 recovery from wasted R407F has considerably lower environmental impacts than the production of fresh R32, with a global warming potential (GWP) reduction of 86% (10.9 vs. 2.13 kgCO2eq). Wang et al. 2021 [12] reported that the refrigerant-manufacturing CO2 emissions were about 15.9 kgCO2eq per kg for the R134a production process. Troch 2016 [3] found that an advanced cycle heat pump with low GWP refrigerants (10) can reduce the total lifetime carbon dioxide emissions by 13.7%, 16.3%, and 18.6% compared to a conventional cycle heat pump with R410A.
On the other hand, F-gases (fluorinated gases: Hydrofluorocarbons (HFCs), Perfluorochemicals (PFCs), Sulfur Hexafluoride (SF6), Nitrogen trifluoride (NF3)) account for about 2% of global GHG emissions [13]. About 20,000 tons of HFCs are produced every year in Europe and Japan, representing about 35–45 MT of CO2 [14,15]; China is the largest producer (60% of the global production), with more than 300,000 tons produced annually (based on 2013 figures) [16,17]. R410A, R32, and R134a are widely used refrigerants; R22 is still used in developing countries, but it is no longer mainstream in developed countries. R22 is a refrigerant with excellent characteristics in terms of performance, safety, and economy, but it is an HCFC refrigerant with production as a refrigerant that was discontinued in developed countries in 2019 due to its ozone-depleting effects. There is still a lot of equipment on the global market that uses R22, as there is demand for service refrigerants. R410A is an HFC refrigerant that has no ozone-depleting effect and was developed as an alternative refrigerant to R22. It is widely used in residential and commercial air conditioners and refrigeration. R32 is positioned as a low-level GWP refrigerant and as one of the technological innovations necessary to reduce environmental and safety risks associated with refrigerants [18], so conversion from R410A to R32 is being promoted worldwide. R134a is widely used in car air conditioners, refrigerators, and turbo chillers, though conversion to lower GWP values is underway.
Under the Kigali Amendment [19], which added greenhouse gases as target substances to the protocol framework, it was agreed to gradually reduce the production and consumption of HFCs in terms of GWP values. HFCs, the main constituents of F-gas, account for about 86% of F-gas production [20] and are mostly used as refrigerants for refrigeration and air-conditioning equipment. Although countries are switching to refrigerants with lower GWP values, for example, from R410A to R32, there is a growing demand for cooling in developing countries. Even in developed countries, practical refrigerants with sufficiently low GWP values have not yet been found for all applications. Therefore, there are concerns that the refrigerant supply might not be enough in the near future, meaning prices would skyrocket [21,22]. Against this background, there is a movement to position refrigerant reclamation as a key part of the HFC emissions reduction strategy and to mandate the use of a certain amount of reclaimed refrigerant in new equipment [23,24].
It will take a considerable amount of time to complete the conversion of refrigerants, and service refrigerants are needed to continue to keep the pre-transition existing units in use for a period equivalent to the equipment’s life. Thus, during the transition period, there will still be a demand for pre-transition refrigerants, and it is desirable to actively utilize reclaimed refrigerants rather than producing new refrigerants. The use of reclaimed refrigerants can replace the production of new refrigerants and reduce GHG emissions and energy consumption during production. Furthermore, the amount of fluorite mined, which is the raw material for HFC refrigerants, can be reduced, which is desirable from the perspective of resource recycling and the circular economy.
Previous studies on the environmental assessment of the refrigerant life cycle, focusing on refrigerant recovery and its treatment, are limited [11,12,25]. Currently, there is no information available in the literature based on actual plant survey data that evaluates R410A and R134a, which have relatively large refrigerant-recovery volumes. Assuming that refrigerant recovery at the time of equipment disposal will be promoted worldwide to achieve carbon neutrality in the future, using indicators such as GHG emissions (kgCO2-eq), energy consumption (MJ), and LIME3 (USD), this study investigated the actual performance data of reclamation, destruction, and manufacturing facilities for R410A, R32, R134a, and R22. The system boundary was set up from the equipment disposal to the supply of other equipment.
In this study, we evaluated the desirable treatment methods for recovered refrigerants, not only from the perspective of global warming mitigation but also from the perspective of resource recycling and the circular economy. Compared to previous studies, this study considered not only the refrigerant production process but also the treatment process of recovered refrigerants and compared the environmental impact assessments of the two treatment methods: destruction and reclamation. The study also considered two aspects of the reclamation process: the treatment of recovered refrigerants and the refrigerant production method. Additionally, according to the authors’ knowledge, for the first time, different treatment methods after refrigerant recovery in different locations and for different refrigerants using real facility data were evaluated and compared. We believe that this led to more general findings.
Materials and Methods
Goal and Scope
The goal of this study was to evaluate and compare the environmental impact of two treatment methods: reclamation and destruction after refrigerant recovery. An evaluation was made based on the data obtained from a survey conducted on the actual status of reclamation, destruction, and manufacturing facilities for general air-conditioning refrigerants. R410A and R22 were targeted in Japan, while R410A and R134a were targeted in Europe. Japan has the highest refrigerant-recovery rate in the world at about 40% [22], and Europe is a regionwhere heat pump installations are rapidly increasing under the re-Power EUprogram[18]; additionally, demand for refrigerants is rising. These two locationswere chosen as itwas possible to collect the data for production/destruction/reclamation for various plants using different treatment methods. For R32, which is becoming mainstream as a low-GWP refrigerant, the amount recovered was still small, and data on reclamation and destruction were not available; therefore, the evaluation for R32 was based on estimated results using survey data for R410A, with the exception of one plant for batch distillation. As formanufacturing, some refrigerants are imported from China, so in addition to Japan and Europe, manufacturing facilities in China (Figures A6 and A7) were also surveyed. The treatmentmethods of the reclamation and destruction facilities surveyed are shown in Table 1. As for the refrigerant-recovery method, segregated gas recovery is common in Japan, while batch recovery of gas types is common in Europe. The simplified systemboundary for this study is provided in Figure 1.
In this study, a cut-off was applied when data collection was presumed to be difficult or when the contribution of the load was considered small. The cut-off items are listed below:
Manufacturing, transportation, and post-use treatment processes of packaging materials for raw materials and auxiliary materials;
Sub-materials used for general purposes in factories that are not directly related to the production of products, such as gloves, masks, uniforms, products for cleaning, etc.;
Construction of the facilities or transportation services not related to refrigerants, such as cars, ships, trains, and capital goods used for multiple years (however, capital goods included in secondary data are covered, and land use occupied by the factories is included in the calculation).
Additional information related to the life-cycle flowcharts for the different detailed production, destruction, and reclamation treatment processes is provided in Appendix A. Several observations can be made concerning Figures A1–A5.
In Figure A1, the destruction process “superheated-steam incineration” is presented: The refrigerant is destroyed in a vapor phase under very high temperatures. When mixed with F-gas, water vapor and air are preheated up to approximately 500C and fed into a tubular reactor with walls that are electrically heated up to 800–10000C [26]. The resulting exhaust gas is fed into a scrubber to be quenched with a calcium hydroxide solution (also called slaked lime) to neutralize the acid gases.
In Figure A2, the destruction process “liquid-injection incineration” is presented. A typical liquid-injection incinerator consists of a waste-burner feed system, an auxiliary fuel system, an air supply system, and a combustion chamber [27]. F-gas is sped into the furnace with a combustion improver, waste oil, and a waste-melting agent [28]. A typical combustion temperature in the chamber is in the range of 700–17000C. Fluorite can be recovered from the destruction process to produce hydrofluoric acid later.
In Figure A3, the destruction process “gaseous/fume oxidation” is presented. Waste refrigerants andwater vapors are thermally destroyed in fire-resistant combustion chambers [26]. Hydrofluoric and hydrochloric acids can be recovered from the destruction process.
In Figure A4, the reclamation process “simple distillation” is presented. Simple distillation, used for separating components with boiling points that are different by a significant degree, can be used to remove non-refrigerant contaminants (e.g., oil)
by evaporating components and then condensing them in separation [29].
In Figure A5, in batch rectification, solvent vapors pass through a fractionating column, where they contact condensed solvent (reflux) entering at the top of the column. Solvent not returned as reflux is drawn off as overhead product [30].
In this study, cutoffs were made for processes for which data collection was presumed to be difficult or for which the contribution of the load was considered small, such as the manufacturing, transportation, and post-use treatment processes of packaging materials or the leakage during recovery of processed refrigerant from waste equipment.
Life-Cycle Inventory (LCI) Data
The evaluation was conducted using a functional unit: 1 kg of used 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 to compare the environmental impacts of newly produced refrigerant and reclaimed refrigerant; this latter aspect is evaluated in Section 4.2. In this LCA, the following data were collected to evaluate the environmental impact of used refrigerant, from receipt to treatment to final disposal of waste, avoiding production of new refrigerants through reclamation of used refrigerant. Additional information is provided in Table 2 to indicate the source of the data for this LCA.
The life-cycle database AIST IDEA v2.3 (English version) contained inside the LCA software Simapro (version) 9.3 (PRé Sustainability, Amersfoort, Netherlands) was used as a background LCA database. Concerning secondary data in the background databases, other than heat sources for electricity and steam, the same processes were used whether in Japan, China, or Europe. For Japan, the source of the power supply was selected based on the factory’s address. Additionally, as primary data, the recovery ratios calculated for the different reclamation technologies through a survey in the different facilities are provided in Table A1.
Life-Cycle Impact Assessment (LCIA)
GHG emissions (kgCO2-eq), energy consumption (MJ), and LIME3 (USD) were used as indicators to evaluate the environmental impacts in this study. The GHG emissions were calculated using the GWP AR5 (IPCC 2013 GWP 100a) developed by the Intergovernmental Panel on Climate Change, which contains the climate change factors of IPCC with a timeframe of 100 years. The GWP AR5 values shown below (Table 3) were used to calculate GHG emissions. The GWP value for R410A is 1920 kgCO2-eq/kg in AR5, but, in this calculation, R410A was treated as a mixture of R32 and R125; therefore, a GWP value of 1924 kgCO2-eq/kg was used. Energy consumption was evaluated based on the resource consumption of coal, oil, and natural gas. LIME3 is an indicator developed by Inaba and Itsubo [31] as part of the outcome of a national project in Japan. It is an index that comprehensively identifies and calculates multiple environmental impacts, weights them, and evaluates them in an integrated manner as the calculated amount of damage expressed in USD [31,32]. The consumption-based integration factors for Japan, Germany, and China were used with the G20 population weighting average and a discount rate of 5%.
refers to direct CO2 emissions. Direct refrigerant refers to direct refrigerant emissions. Waste treatment refers to the waste treatment of the manufacturing plant.
Results
GHG Emissions
Production Process
The average GHG emissions per 1 kg of produced refrigerant are shown in Figure 2 (values are shown in Table A2). This calculation was necessary to evaluate the avoided emissions for the reclaimed refrigerant.
Results were found in the range of 4.26 (R22 Japan) to 10.5 (R134a Europe) kgCO2-eq per kg of refrigerant produced. For the main material, most of the impacts occur due to the production of chemicals (37–69%) required for refrigerant production: methylene chloride (R32, R410A), tetrachloroethylene (R125, R410A), and methane derivatives (R22). The remaining impacts occur due to heat and electricity (0–44%).
Several observations can be added: R410A was produced by mixing R32 and R125. Therefore, very little electricity or energy was used, and almost all of the production GHGemission load is for R32 and R125 refrigerants; the contribution of R32 and R125 to the total GHG emission was about 50% each (for R125, the main material and energy accounted together for 80% of the refrigerant production impact). For R134A, distillation water is fed into the system, which accounts for an important source of CO2 emissions (“other”).
The results obtained were similar to the values of 10.9 CO2eq/kg for R32 and 14 CO2eq/kg for R410A reported elsewhere (Jovell et al. 2022 [11]; Dieckmann 1999 [33]). It has to be noted that the data from Jovell et al. are simulated values, not actual data, for the purpose of developing new reclamation methods using ionic liquids.
Whole Scope
The GHG emissions related to the treatment of 1 kg of used refrigerant are shown in Figure 3 (values shown in Table A3). When considering only the environmental burden without any credits, the results for the destruction of the refrigerant were, on average, more than twice as high as the reclamation of refrigerant. When including the credits due to the refrigerant reclamation that replaced the production of new refrigerant in the case of the reclamation process, as well as the credits due to the recycled acids and regenerated fluorite in the case of the destruction process, the GHG emissions in the reclamation processes were 5.7 to 15.9 kgCO2eq less than those from destructive treatment in Japan and approximately 7.8 to 9.9 kgCO2eq less than those from destructive treatment in Europe.
The effect of the reclamation process in obtaining reclaimed refrigerant and replacing the production of new refrigerant, as well as the benefits induced by the recycled acids and regenerated fluorite in the case of the destruction process, are expressed on the lower part of the X-axis. When considering the recovery and substitution effect of fluorite and hydrofluoric acid for the destruction of refrigerant, gaseous/fume oxidation achieved the best performance, with an average value of 0.95 kgCO2-eq/kg of used refrigerant, compared with 3.8 for superheated-steam incineration and 6.6 for liquid-injection incineration. The GHG emissions value for the gaseous/fume oxidation in Europe was lower than the other destruction methods because gaseous/fume oxidation outputs hydrochloric acid and hydrofluoric acid water as (valuable) by-products, thus eliminating the need for sludge treatment.
Liquid-injection incineration has higher GHG emissions than superheated-steam incineration. This is because the investigated liquid-injection-incineration plant is dedicated to destroying recovered refrigerants and is used to destroy a wide range of other chemical substances that are by-product outputs when producing other fluorinated compounds. This operational condition forces the plant to operate at higher temperatures than those required for refrigerant destruction only, resulting in excessive energy consumption. Furthermore, the additional drying process, after precipitation and dehydration to recover fluorite, increases energy consumption.
For the reclamation processes, no significant differences were found with regard to the method. The reclamation process can further reduce GHG emissions, as it can substitute for new refrigerant production.
Energy Consumption
The results of energy consumption per 1 kg of used refrigerant are shown in Table A4. The energy consumption was shown to be, on average, 155 MJ higher for the destruction results than the reclamation. Overall, the results were found to have a similar trend to the results obtained for the GHG emissions with the importance of credits for the reclaimed refrigerant (reclamation in Japan and Europe).
LIME3 (Integrated Weighted Evaluation Index)
The results of LCIA per 1 kg of used refrigerant are shown in Figure 4 (values shown in Table A5). The weighting results (external costs) were shown to be, on average, USD 0.65 higher for the destruction results than the reclamation. Similar to the GHG emissions and energy consumption, in this section, the effect of the reclamation process on obtaining reclaimed refrigerant and replacing the production of new refrigerant, as well as the benefits induced by the recycled acids and regenerated fluorite, in the case of the destruction process, are also considered (reported as “credits”).
For the destruction processes, when looking at the breakdown per process in Japan, the waste treatment (waste_SA) showed a significant contribution to the destruction processes in Japan, USD 0.37 on average; this is mainly due to the wastewater amount generated by the treatment process, about 2 kg per kg of used refrigerant for the destruction processes in Japan. The other impact categories were almost negligible except for climate change for R410A and R32 (about 0.15 USD/kg of used refrigerant). For the European refrigerant, no particular process could be highlighted as a main contributor to the burden. It should be noted that no waste is generated in Europe, as the plants investigated this time recovered hydrofluoric acid through gaseous/fume oxidation; therefore, the environmental impact is rather small.
For the reclamation process, no particular impact could be highlighted. No trade-off could be observed between the impact categories, whether for reclamation or destruction. Indeed, when looking at the results for each impact category, reclamation was shown to have lower impacts than destruction, and the trend observed for climate change was also valid for the other impact categories, including resource consumption. The impacts from waste treatment on destruction treatment and the dominant effect of credits on reclamation treatment indicate that reclamation treatment is desirable from the perspective of resource recycling and the circular economy.
Discussion
Comments on Section 3
Most GHG emissions during reclamation in Japan are attributable to sampling gases during refrigerant inspections. These emissions can be reduced by ensuring separate recovery of each refrigerant type, reducing the number of inspections, and destroying the sampling gases.
…To be continued
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.
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