Assessment of quality test methods for solid recovered fuel in South Korea

Highlights

• Solid recovered fuel has a poor public perception and its use is declining.

• To improve its quality, use, and perception, better quality test methods are needed.

• There were no significant differences in sample transportation temperature.

• 5 g samples were found to be more appropriate for ash content analysis.

• Minimum acid digestion conditions were 600 W, 10 min of reaction time at 180 °C.

Abstract

Management of solid recovered fuel (SRF) in South Korea is unique from most other countries in that it is based on a single standard. All SRFs are distributed at the same price irrespective of their performance, resulting in utilization problems and a low degree of acceptance among consumers. Moreover, the difficulty of temperature maintenance during transportation, excessive ash content, and the use of inappropriate microwave acid digestion methods pose challenges to SRF reliability. To address these issues, we compared the relevant management statuses in South Korea with those of the international community and reviewed the effects of the transportation temperature, ash content, and microwave acid digestion technique. The moisture, ash, sulfur, and chlorine contents as well as the lower heating values (LHVs) of all the samples from South Korea were found to be below the standard [international] thresholds, and they were barely influenced by the transportation temperature. In addition, 5 g samples were found to be more appropriate for ash content analysis than the 20 g samples used in South Korea, with the former producing smaller standard deviations. The optimal microwave acid digestion conditions were also determined to be a reaction time with nitric acid of >10 min, temperature of 180 °C, and microwave power of 600 W. The results of this study highlight the need for revising the SRF test methods used in South Korea, to boost the market and enhance quality reliability.

Introduction

Global waste generation is rapidly increasing in response to industrial development, improving standard of living, and population growth (Islam et al., 2019). Meanwhile, the development of renewable energy has become indispensable to achieving sustainable development in the face of depleting reserves of fossil fuel, which remains a major source of global energy (Park et al., 2017b). Interest in renewable energies has been further boosted by their low environmental load. Active research is thus underway toward improving the production efficiency of renewable energy sources such as waste energy, bioenergy, solar power, and hydropower. According to the Korea Energy Agency, renewable energy sources in South Korea in 2016 included waste to energy (62%), bioenergy (20%), solar power (8%), hydropower (4%), and others (7%) (Korea Energy Agency, 2016, Korea Environment Corporation, 2011). The “Renewable Energy 2030 Action Plan” of the Korean government is targeted at gradually increasing the proportion of renewable energy usage in the country through to 2030 (Kim et al., 2018a). The proportion of renewable energy supply to the total energy supply is expected to increase to 20% by 2030, exceeding the goal of existing plans. However, the supply of waste to energy is currently on the decrease in the country (Kim and Jhang, 2018).

Among the available methods for converting waste into fuel and energy is the production of solid refuse fuel (SRF) from combustible waste via physical separation of the combustible and non-combustible materials through mechanical crushing, shredding, and sorting. SRF is mainly used in incineration and power generation facilities and is of two types; fluff (crushed and shredded waste) and pellet (crushed, shredded, and molded waste) (Kim et al., 2017). South Korea has limited natural resources and is energy-dependent, importing 90% of its utilized mineral resources and 97% of its energy requirements (Thanos et al., 2019). SRF production thus promises a stable alternative to energy importation, especially considering that as much as 56% of its waste, currently incinerated or used for landfilling, is recoverable as energy (Lee and Mogi, 2018). Furthermore, SRF production promotes sustainable development and reduces the burden of traditional waste management and recycling (Hernandez-Atonal et al., 2007). However, one disadvantage is the generation of harmful materials during SRF production (Lim et al., 2015). This has nurtured a negative perception of SRF in South Korea (Park et al., 2017a). To address this issue, stringent quality standards, conformance tests, and public enlightenment are required, including the prevention of small poorly planned SRF facilities and improvement of the relevant institutional systems (Ryu et al., 2010).

General SRF quality standards are based on 10 parameters of shape & size, moisture, ash, sulfur, chlorine contents, LHV, and metal contents (Hg, Cd, Pb, and As). In the specific case of bio-SRFs, the biomass and Cr contents are also considered (Ministry of Environment, the Republic of Korea, 2014) in accordance with Article 20–2 of the Enforcement Rule of the Act on the Promotion of Saving and Recycling of Resources (PSRR) (Ministry of Environment, the Republic of Korea, 2018). The test methods for assessing compliance with quality standards include the SRF Quality Test and Analysis Methods (Ministry of Environment Notification No. 2014–135). However, three major problems associated are with the existing methods. First, the utilized samples must be stored at 0–4 °C during transportation and preservation, which can be difficult to achieve owing to the high operational costs of refrigerated vehicles and associated equipment. Second, at least 20 g of sample must be used for ash content analysis; however, the large volume of domestic fluff SRFs makes them difficult to load into test crucibles and errors are highly likely to occur through sample loss during the loading process. Third, the microwave-assisted acid digestion process, which is used to pretreat the heavy metals contained in the waste, requires at least 600 W microwave power, the use of a nitric acid/hydrochloric acid mixture, and a reaction time of 10 min; and these conditions still do not guarantee complete sample decomposition (Yang et al., 2018).

In view of the foregoing, in the present study, we explored measures for improving SRF quality test methods. First, we analytically compared the current trends of SRF management in Korea with international practices with the purpose of developing improvement initiatives from an institutional perspective. Second, we undertook a similar comparison regarding SRF quality standards with the aim of discovering improvement measures such modification of the atmospheric emission criteria and grading system. Third, experiments were performed to identify weaknesses in current SRF quality test and analysis methods. In this case, we examined factors such as the sample transportation temperature (ranges of 0–4 and 15–20 °C were considered); sample quantity for ash analysis (a range of 1–20 g was considered); and the required power, reaction time, and acid conditions for microwave-assisted acid digestion. The findings of this study could help improve SRF test methods and the eventual quality of the fuel, as well as promote public acceptance of its use.