Elsevier

Journal of Cleaner Production

Volume 124, 15 June 2016, Pages 132-141
Journal of Cleaner Production

New composite sustainability indices for the assessment of a chemical process in the conceptual design stage: case study on hydrogenation plant

https://doi.org/10.1016/j.jclepro.2016.02.107Get rights and content

Highlights

  • A new methodology was introduced which uses new sustainability quantification indices.

  • The indices were used to design upgrading plants & found cleaner sustainable process.

  • The above methodology ascertains sustainable processes without compromising economy.

  • The methodology can be extended to biofuels/energy, product & process at design stage.

  • The new methodology ranks processes based on safety, environmental & energy impacts.

Abstract

Sustainability indices are increasingly recognized as a powerful tool for assessing the performance of chemical process designs considering energy, environment, safety and technological improvement aspects and above all, economy. Sustainability indicators enable decision makers to simplify, quantify and analyze complex information. Generally, it is challenging to evaluate the performance of process designs on the basis of a large number of indicators. The integration of a set of key sustainability indicators in the form of a composite index is essential for simplifying the evaluation of sustainability performance. Currently available methodologies for sustainability assessment of process designs require detailed process data, which are typically unavailable at the conceptual design phase. This paper introduces a new composite sustainability index (CSI) that addresses the sustainability performance of chemical processes and which can be applied for early design phases where minimum amount of data are available. The three pillars of sustainability are considered in the development of the new composite index, which are energy, environmental and safety aspects. A conceptual decision model based on the analytical hierarchy process can be employed to compare and determine weights for the different sustainability indicators, which are then aggregated to obtain the CSI, when the indicators conflict. The capability of the proposed model is investigated by applying it to a hydrogenation case study to choose the more sustainable design among different alternatives.

Introduction

The path to continuous development of the products and services used by society without huge negative impact upon the Earth is called sustainability (Cobb et al., 2007).

Composite sustainability indicators are an innovative approach to evaluating the sustainability of process designs whose main feature is their effective utilization to summarize and condense dynamically complex sustainability data into manageable and simplified amount of information that can be easily analyzed (Chen and Shonnard, 2002).

Today, the concept of sustainability is widely employed in a variety of researches from molecular level (Manley et al., 2008) to teaching purposes (Carew and Mitchell, 2008) and designing sustainable products such as sustainable vehicles (van Lante and van Til, 2008). Corporations may use sustainability to integrate their following areas of concerns (Amimi and Bienstock, 2014): (a) corporate's strategy and stakeholders external communications; (b) organization's supply chain; (c) strategic decisions and design processes based on economic, eco-environmental, and equity-social concerns, to name a few.

Examples include: (a) Dow Jones Sustainability Indices (2013), which lead to high levels of skills in different areas such as strategy, financial, customer and product, governance & shareholders, and human resources; (b) FTSE4Good Environmental Leaders Europe 40 Index (2015), which delivers a tool for investors who are looking for European partnership in practical environmental management; (c) AIChE Sustainability Index (SI) based on a set of features that form a consolidated Sustainability Index or SI (Cobb et al., 2007). The required information is gathered from company's annual sustainability report, industrial performance rankings, government's pamphlet and newsletters. The metrics are scaled from 0 to 7 and depicted on a spider chart.

These sustainability indices have a number of pros that escalate company's profits. However, the society approach of above mentioned sustainability indices deal with customer satisfactions and after sales services. Besides, the sustainability indices have business nature and therefore, they are based on individual company's performance and cannot be used at primary stage of a process design. The AIChE's SI has tried to overcome this shortcoming; however, in order to resolve this issue successfully, they need a large number of data, which vary from company to company based on business performance. Above all, none of the existing indices can be used for prototype chemical products.

Having said this constructive perspective of sustainability, Ordouei et al. (2015) have introduced new sustainability indices for product design employing environmental and energy impacts and risk reduction associated with the new products.

The implementation of quantitative energy, environmental and safety risk assessment measures in early design stages allows engineers to easily determine an adequate evaluation of the environmental burden of process design.

As the highest impact of decisions lies at conceptual design stage (Lewin, 2004), sustainable design development has become a leading goal of policy makers and researchers that takes into account environmental, societal and economic aspects, and which can be easily monitored using sustainability indicators. The use of indicators allows the translation of sustainability issues into quantifiable amounts that facilitate achieving more sustainable design of chemical processes. Several reported frameworks propose sustainability indicators that are generally measured in different units.

Process design and optimization is conducted for the establishment of new facilities, the integration of new technologies, or the retrofitting of existing processes. It typically involves standard procedures that are sequentially performed, from data gathering and process synthesis in the early design stages, to detailed design. The typical process design is based on economic objectives, such as net present value, capital investment costs, and operations and maintenance costs (Zhang et al., 2008). The environmental impacts associated with a process are typically given low priority in the design stages, and are incorporated just as end-of-pipe treatment, such as waste treatment facilities, incinerators, etc. Such design approaches overlook the environmental impacts of materials and energy used in a process plant, which causes the generation of large quantities of waste materials and pollutants (EPA, 2012). This results in significant environmental control costs to be incurred, especially with increasingly stringent environmental regulations (Chen et al., 2002). Therefore, there has been a growing interest by industries in the incorporation of more performance measures in the process design stages, such as safety, energy, environment, reliability and flexibility (Chen and Shonnard, 2002).

The procedure for the development of a sustainable design of a chemical process should incorporate the improvement of its environmental and safety performances in order to meet environmental and safety regulations, and it should be assessed using various impact categories in order to provide a more extensive evaluation of environmental effects and process hazards. The evaluation of the environmental performance of a chemical process should start from the early design stages using simplified screening procedures to more accurate assessments during detailed design (Adu et al., 2008).

Multiple production routes incorporating different configurations of various equipment can be used for the production of a certain chemical product. Screening methods can be applied in early design stages to eliminate unpromising alternatives, which plays a significant role in reaching sustainable design objectives. Attempts for improving environmental performance at later design stages holds a significantly lower potential in reducing wastes and emissions (Chen and Shonnard, 2002). Various performance evaluation methods involve the calculation of indices based on mass of pollutant emissions and waste streams, as well as toxicity-weighted mass indices for risk assessment applications.

Sugiyama et al. (2009) have investigated the role of economic and environmental assessment results to changes in the ranking of design alternatives (e.g. reaction routes, recycling configurations, operating conditions, etc.) and evaluation settings (e.g. indicator methods). Other methodologies include material balance environmental index that evaluates the environmental impact of toxicities emitted (Torres et al., 2011), and the development of a rigorous simulation model of the process in hand for which economic and environmental objectives are generated. The environmental objective is geared towards minimizing: (a) the use of natural resources and environmental impact potential (Li et al., 2009), (b) estimation of the probability of an incident such as explosion, toxic release, etc. and risk reduction (Rathnayaka et al., 2014), (c) environmental performance index calculation based on potential environmental impact, energy consumption, resource conservation and fugitive emissions (Ramzan et al., 2008), (d) cradle-to-gate life cycle assessment by providing weightings for the individual indices using process simulation tool (Aspen HYSYS) to obtain the data required for its calculation (Hossain et al., 2011), (e) life cycle indexing system (LInX) by incorporating four index categories, which are environment, health and safety, economic, technical feasibility, and socio-political factors (Khan et al., 2004), (f) a simple quantitative safety risk index, which combines four elements; frequency of accidents, hazards associated with chemical exposure, chemical inventory and plant size (Al-Sharrah et al., 2007).

The above mentioned frameworks imply that the aggregation of a set of different indices into a composite index that would enable the comprehensive assessment of the sustainability of a process design is well investigated. However, the existing methodologies are dependent on the quality of training the data collectors may receive; require detailed process data, which are unavailable at the early stage of process design; in addition to their afore-mentioned disadvantages. Therefore, the development of new simple indices that account for various sustainability factors are still demanded by researchers and industries. The application of such indices during early design phases when various process and retrofitting alternatives are proposed is of significant importance for reaching sustainability design objectives. The evaluation of new process designs and retrofitting alternatives in the conceptual design stages is typically based on proposals that provide minimum process data (e.g. block flow diagrams, typical stream data, etc.). New simple indices can be derived based only on this type of data to be employed in the comparative analyses and screening of design proposals.

The objective of this paper is to extend the application of already introduced new composite sustainability indices (Ordouei et al., 2015) for the evaluation of alternatives at the early design stages of chemical processes. The new methodology is based on three indicator categories, which are environment (process streams and emissions), risks to process safety associated with process streams, and energy (utility consumptions within process and emissions).

In case of facing with conflicts within metrics, the analytical hierarchical process (AHP) is utilized to assign appropriate weighting for the metrics (Saaty, 2008), which are used to aggregate them in order to obtain the value of the composite sustainability indices associated with each design alternative. The proposed methodology is applied to a hydrogenation case study to illustrate its applicability in the selection of an environmentally friendlier and inherently safer hydrogenation process. Alternatives process designs of the hydrogenation process are generated using Aspen HYSYS. In the first section of the paper, the procedure of evaluating the proposed composite index will be presented. In the second section of the paper, a case study will be presented to illustrate the applicability of the proposed index.

The new Composite Sustainability Index (CSI) is based on the minimum process data from energy and material balance available at the design stage of a chemical process; therefore, it can be used in a wide variety of chemical process industries. The CSI has been wisely created as a strong tool for designing of sustainable chemical processes and products ranging from inorganic and organic chemicals to energy, bio fuel, fossil fuel, and synthetic gas (syngas) process plants. Recently, the CSI methodology with an application to the sustainable gasoline blends (fossil fuels) has been introduced by Ordouei et al. (2015).

Section snippets

Sustainability indices

The indices introduced in this paper that will be incorporated in the construction of the CSI are the following:

  • The Waste Reduction algorithm (WAR) and its amendment Potential Environmental Impacts (PEI) theory for the waste reduction and estimation of the impacts of materials on the environment (Young and Cabezas, 1999, Young et al., 2000).

  • A new simple and quantitative methodology for the estimation of energy impacts of process and non-process designs on the environment in terms of the

Illustrative case study

The new sustainability indices have been already applied to product design (Ordouei et al., 2015). The aim of this case study is to evaluate the applicability of the proposed composite sustainability indices to process design alternatives. Hydrogenation process is, by its nature, profitable, reduces the corrosion risks to downstream process units, and protects the environment from pollution by manufacturing environmentally friendly products for end users. However, the availability of

Conclusions

This paper provides a methodology for the simple and the quantitative evaluation of sustainability performance of chemical process designs that is particularly useful at the early design stages. However, the CSI may also be applied in a targeted context to reflect the status of an already established chemical process regarding its sustainability performance, which facilitates obtaining important information for critical decision making processes.

The paper presents a new composite sustainability

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