New classification of chemical hazardous liquid waste for the estimation of its energy recovery potential based on existing measurements
Graphical abstract
Introduction
The industrial sector worldwide is responsible for 27% of the total energy use, of which 29% is consumed by the chemical and petrochemical industry (Banerjee et al., 2012), representing about 7.8% of the global energy consumption. In Switzerland, the chemical and process industry consume approximately 3.5% of the total energy (Swiss Federal Office of Energy, 2014). About 55% of that amount of energy is devoted to process heating, and 25% to other direct energy requirements for operating the process (Swiss Federal Office of Energy, 2015a), such as electricity for pumps and compressors. Approximately 50% and 25% of the gross energy consumption in Switzerland stem from fossil and nuclear fuels, respectively (Swiss Federal Office of Energy, 2015b). Therefore, increasing pressure to decrease the dependence on non-renewable energy sources poses a non-trivial challenge to these and other energy-intensive industrial sectors. This situation results in an excellent opportunity to explore alternative energy sources that were previously considered of secondary importance. In particular, the process and chemical industrial sectors generate considerable amounts of high-calorific waste solvents that are frequently incinerated as a part of their disposal (Seyler et al., 2006), thus allowing for partial recovery of the combustion heat in the from of steam (Capón-García et al., 2014).
Recent studies have shown that an appropriate management of waste incineration is indeed an efficient tool to decrease primary energy consumption of integrated chemical sites, reducing both costs and environmental load (Abaecherli et al., 2017), especially when considering plant-wide (Chakraborty et al., 2003) or enterprise-wide aspects (Wassick, 2009). However, little to no attention has been devoted to even broader network perspectives. This is of particular interest considering that smaller enterprises have usually neither the technical nor the financial means to operate own waste incineration facilities or other treatment processes, and have to outsource the disposal of their waste to third companies. Such treatment facilities are in many cases in-house incineration plants that belong to large chemical sites, since they have the necessary waste volumes to operate in a cost-effective way, as well as the possibility to directly utilize the recovered energy in other production processes on the site. These large sites analyse the composition and heating value of the different generated waste streams. In contrast, many of the industrial waste shipments to such incinerators are often organized unsystematically based on short-term waste generation forecasts and both intermediate storage and treatment capacity at incineration sites, and information on waste quality and heating value is poor. As a consequence, there is a potential benefit for systematically optimizing the management of both waste transportation and treatment of the whole network. For instance, cost and environmental savings may be achieved by decreasing the total transportation distance, and by reducing the use of auxiliary fuels in the incineration process by using combustible waste solvents to burn non-combustible residuals, which would otherwise require additional oil or natural gas. Such measures to reduce consumption of fossil fuels and environmental load by re-utilizing waste as a resource are definitely in line with the goals of many recent political initiatives aimed at environmental protection and resource efficiency, such as the Energy Strategy 2050 in Switzerland (Swiss Federal Office of Energy, 2017) and the General Union Environment Action Programme of the European Union (European Parliament and Council, 2013).
As shown by recent research activities in the field of municipal solid waste, information about the chemical composition of the residues leads to a more accurate quantification of the environmental impact of different management strategies, helping to determine the best available options (Burnley, 2007) and assess the environmental risk of hazardous residuals (Slack et al., 2007). In this sense, a broad knowledge about the different residues is an important aspect for supporting goal-oriented decision processes in waste management networks (Allesch and Brunner, 2017), and is a necessary condition for the development of dedicated optimization tools (Levis et al., 2014). Reliable information about chemical composition and energy content of green and municipal waste is particularly important for planning design and operation of thermochemical conversion systems, for which estimations of the energy content based on empirical models are often insufficient (Hla and Roberts, 2015). As the application of similar optimization tools could potentially lead to important benefits also in the case of hazardous waste stemming from the chemical and process industry, especially considering its large volumes, it is crucial to obtain more detailed information also for such residues.
Despite the fact that transportation of industrial and hazardous waste has nowadays reached considerable amounts, the information about production and management is still extremely scarce, even in OECD countries (OECD, 2013). In general, data is restricted to authorizations of transboundary movements requested by the Basel Convention (Basel Convention, 1989), but many European states, such as EU members (European Parliament and Council, 2006) and Switzerland (Il Consiglio federale svizzero, 2005), also require notification and authorization for domestic shipments. In both cases, however, there is no information about the heating value of residuals, since the legislation only obliges to notify amounts according to classification systems based either on the type of process generating the waste or roughly on pollutant species. Whereas these systems are undoubtedly very useful for guaranteeing transportation safety, both in terms of health and environment perspectives, they do not provide enough data to estimate the energetic potential of these residuals in a specific area. Although there is a broad set of available characterization techniques, also in terms of energy content, the few research activities that tackled the composition of industrial residuals have been limited to single plants (Seyler et al., 2005) or very specific waste streams (Ghimpusan et al., 2017), presumably because of the large experimental effort required to obtain such information. For these reasons, it has not yet been possible to apply systematic optimization tools for both design and management of a treatment network aimed at maximizing the contribution of industrial waste incineration to a more sustainable energy system.
The Swiss chemical and pharmaceutical industry is strongly based on high-revenue specialty chemicals, which represent nowadays more than 90% of its portfolio, and is extremely differentiated, with more than 30,000 different products ranging from fragrances to dyes (Papadokonstantakis et al., 2013). In this country, thermal treatment is compulsory whenever material recycle or regeneration are not technically feasible, economically viable or make no sense from an environmental perspective, i.e. when recycling leads to higher environmental load than ex novo production (Il Consiglio federale svizzero, 2015). Hence, many liquid hazardous residuals undergo thermal treatment in one of the five incineration (waste-to-energy) plants located in five large chemical sites (VBSA, 2017), while a smaller and less polluted fraction is used as substitution fuel in cement plants (Cemsuisse, 2015) or other industrial furnaces (DATEC, 2005). Furthermore, since the Swiss chemical industrial sector is composed of many small-medium enterprises (Swiss Federal Statistical Office, 2017b) spreading across all regions of the country (Swiss Federal Statistical Office, 2017a), waste shipments to treatment sites are required (Fig. 1). Shipments of all kinds of hazardous waste have to be notified (Il Consiglio federale svizzero, 2005) under a specific classification (DATEC, 2005), which is substantially equivalent to the one used in the European Union (European Parliament and Council, 2006). As previously discussed, the related information focuses on safe transport conditions and does not involve specific data about the energy content of the transported residuals. In contrast, most Swiss incineration plants keep records of the heating value and other properties of their waste streams, but they often refer to own classification systems for waste streams treated internally. Therefore, Switzerland represents an ideal case study for investigating the potential of a more systematic management of industrial waste incineration, with many sparse industries producing a highly differentiated set of waste streams and centralized treatment sites. Consequently, a rigorous estimation of the energy content of liquid hazardous residuals is a crucial first step for the design of sustainable industrial waste incineration networks, as well as for their proactive management.
The aims of this work are i) to define a general classification system for chemical hazardous liquid waste; ii) to create a methodology linking such new classification to inconsistent information from waste incinerators and compulsory transport notification, characterizing several physicochemical properties for all the newly defined waste classes; and, iii) to show possible applications of such methodology for assessing the energetic potential of hazardous waste incineration with an illustrative case study. This investigates the evolution of the chemical hazardous liquid waste generated in Switzerland for the period from 2010 to 2014, based on historical data, and estimates the total energy content of such residues in the different regions of the country. Since it only relies on existing information sources, the methodology can be constantly updated with the latest information concerning waste composition and amounts, without requiring additional time-consuming experimental measurements. The generated knowledge can be used by the incinerators to better exploit the energy content of the waste, thus reducing the total consumption of primary energy for the different production processes on the site.
Section snippets
Sources of information
This work focuses on the analysis of liquid hazardous waste stemming from chemical, pharmaceutical and process industries, without considering used oils. The overall analysis relies on different data sources for the system description. Specifically, information is given about: (i) waste generation in chemical sites that possess an incineration plant; (ii) measurements of lower heating value and other physicochemical properties of incinerated streams; and, (iii) waste generation in
Characterization of the chemical hazardous liquid waste
The representative properties of the twelve categories of the proposed classification system have been obtained by averaging experimental measurements provided by the incineration companies as explained in the previous section. The representative figures have been determined for each waste class with a weighted mean of all waste streams with available analytic measurements. Concerning industrial waste incineration, the following properties are particularly relevant for modelling purposes:
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Conclusion
This work proposes a new waste classification system based on lower heating value and on both water and pollutant content of the residues. For every waste category, average energy content and other physicochemical properties can be obtained from measurements provided by the enterprises managing the Swiss facilities for industrial waste incineration. Such information has also been used to establish a link between the proposed classification and the system used for the notification of hazardous
Acknowledgements
The authors thank the companies Cimo Compagnie industrielle de Monthey SA, Dottikon Exclusive Synthesis AG, Holcim Schweiz AG, Infrapark Baselland AG, Lonza AG, Valorec Services AG and the Swiss Federal Office for the Environment for supplying data and their support in technical questions. Sincere gratitude is also dedicated to Marta Roca Puigròs and Aline Gazzola for their precious help concerning data processing. This research project is part of the National Research Programme ”Energy
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