Comprehensive assessment of cement kiln co-processing under MSW sustainable management requirements

Highlights

• Established a comprehensive evaluation method for cement kiln co-processing.

• Cement kiln co-processing provides ultra-low environmental emissions.

• Recommended subsidy for MSW treatment fees based on NPV evaluation is provided.

• Effective improvement of project economics by reasonable subsidy policies.

Abstract

Although cement kiln co-processing (CKC) has been considered an important municipal solid waste (MSW) treatment method in recent years, there however still exist obstacles such as unclear technical feasibility and ambiguous legislation that impede its further development. Addressing these barriers remains difficult as a comprehensive understanding of CKC from an MSW management perspective (which is a major challenge for policy makers) is lacking in existing studies.

Therefore, this study adopted Material Flow Analysis, Life Cycle Assessment and Net Present Value evaluation methods to quantitatively analyze the waste reduction effect, energy efficiency, environmental impact and economic performance of CKC in order to provide an important basis for determining its feasibility and policy direction in comparison to existing MSW treatment technologies.

The results showed that CKC had a waste reduction rate of up to 99.5%, and 90% lower environmental emissions than incineration. However, from a life cycle perspective, the net environmental impact of CKC was not as significant as incineration and mechanical biological treatment because its coal saving effect has a relatively lower environmental impact mitigation potential compared to the potential from electricity generation brought by incineration. Furthermore, the proposed MSW treatment fee subsidy for CKC was 59 CNY/tonne, reflecting a 34% reduction from current incineration subsidy fee.

These findings are important for many countries since the main barriers to CKC development are similar. Improving the comprehensive understanding of CKC could help policymakers formulate precise promotion planning and reasonable incentive policies.

Introduction

Sustainable management of MSW is receiving increasing attention as economies improve and environmental awareness increases across the globe (Fernández-González et al., 2017). Several countries are actively seeking sustainable management approaches for MSW, such as Brazil (Bezama et al., 2007), Malaysia (Tan et al., 2015), and China (Song et al., 2017), where reducing environmental impact and enhancing energy recovery are important goals. Therefore, the reliance on landfill with significant negative environmental impacts should be reduced (Lee et al., 2017; Mishra et al., 2019; Nabavi-Pelesaraei et al., 2017). On the otherhand, incineration, which is considered a sustainable waste-to-energy option (Khan and Kabir, 2020), has strong Not-In-My-Back-Yard (NIMBY) effects (Lu et al., 2019; Mukherjee et al., 2020; Xu and Lin, 2020), and often requires high investments (Dong et al., 2014), leading to limited promotion in developing countries (Lu et al., 2017).

In this context, the introduction of CKC as a complementary technology is an effective option for improving integrated solid waste management. It was first introduced by the cement industry to reduce costs and emissions (Mokrzycki and Uliasz- Bocheńczyk, 2003), contributing to the sustainable development of the cement industry. Refuse derived fuel (RDF) and alternative raw material (ARM) obtained from MSW and co-incinerated in high-temperature cement kilns are also considered to be an energy efficient, environmentally friendly and economical waste treatment technology (Usón et al., 2013), and has been widely explored around the world (Genon and Brizio, 2008; Nidheesh and Kumar, 2019). In addition, small-scale incineration facilities are inefficient (Chen et al., 2012), while CKC, with its low investment cost and no need for re-location (Cao et al., 2018), is more suitable for promotion in cities with low MSW production. Hence, CKC seems to be a promising solution to improve MSW in small-sized cities.

So far, numerous existing studies have confirmed that CKC is a very viable energy saving and emission reduction technology for the cement industry (Asma et al., 2021; Clavier et al., 2019; Georgiopoulou and Lyberatos, 2018; Güereca et al., 2015; Kara, 2012; Nidheesh and Kumar, 2019; Reza et al., 2013), and Life Cycle Assessment (LCA) as the main environmental impact assessment method in this field has been reviewed (Galvez-Martos and Schoenberger, 2014). Some previous studies have discussed the feasibility of using CKC to enhance the sustainability of MSW management (MSWM) system, but mainly focused on its environmental performance (Lima et al., 2018; Longo et al., 2020; Panahandeh et al., 2017; Sapuay, 2016), except for a simple calculation of the cost-effectiveness of CKC projects by Anasstasia et al. (Anasstasia et al., 2020).

However, as of 2018, a decade after the first cement kiln co-processing production line was established, the capacity of MSW co-processing in cement kiln was only about 5 million tons in China (Tian et al., 2019), while the cement production in the same year was as high as 2.24 billion tons (NBS, 2018). Due to the synergistic nature of CKC technology, it is imperative to discuss its feasibility in MSWM system, which significantly affects its local application and popularization.

Despite previous works, a comprehensive understanding of CKC from the perspective of MSWM is still lacking. Therefore, it is worth exploring whether the low-investment CKC projects really have better project economics in a situation where incineration is highly subsidized and other treatment technologies are mostly unsubsidized (Song et al., 2017). Also, when cement kilns are converted from industrial facilities to urban infrastructures, the costs and subsidies of CKC projects should be evaluated. Futhermore, some of the existing studies previously mentioned were narrow in scope, generally considering only a single perspective of CKC compared with incineration and landfill. Technical selection decision and promotion making for MSWM systems is a complex task (Tan et al., 2015), with many factors to consider and significant variation from country to country. Since there is limited theoretical support, the treatment facility planning and economic incentives related to CKC are difficult to develop.

To partially fill the research gap, this paper sought to explore the feasibility of CKC in China from the MSWM perspective, through quantitative analysis of environmental, energy and economic aspects. To reveal the performance of CKC in the MSW treatment system, the evaluation results were compared with the mainstream and complementary MSW treatment technologies such as incineration and Mechanical Biological Treatment (MBT). The main conclusions of this study could help policy makers and the cement industry to formulate and improve the refined planning of CKC projects so as to economically stabilize thier operation.

The remainder of this article is structured as follows: Section 2 is dedicated to the methodological framework, including system boundary, scenario setting, data sources, and evaluation methods for each indicator. Section 3 shows the numerical results of the evaluation. Section 4 discusses the feasibility of CKC in the MSWM system, analyzes the price subsidy policy, and then provides some perspectives and observations on its development. Section 5 is the conclusion and possible future directions for improving our study.