Designing sustainable chains

Using Process Systems Engineering

Figure 1: Flexibility in process and supply chain designs versus data requirements for quantifying sustainability performance

The circular and biobased economy is upcoming. How can Process Systems Engineering (PSE) be used to preselect and design the most promising and sustainable chains? This article describes research at Wageningen University & Research on designing novel chains that are currently still at low technological readiness levels.

New developments

Various novel conversion technologies and feedstocks are developed. These can be currently underutilised waste streams such as paper sludge and plastic waste, green feedstocks like plant residues, micro-algae and insects, and organic waste streams with high water content. It is essential to identify processing and supply chains that use available resources sustainably, produce marketable products that society needs, while simultaneously having the lowest environmental impact possible, positive social and economic impact.

Design decisions

Ellen Slegers Wageningen University and Research — Ellen Slegers, Wageningen University & Research, Operations Research and Logistics group, ellen.slegers@wur.nl

There are many design options for novel chains, ranging from strategic to operational decisions related to technology and product selection, sizing of equipment and operating conditions, as well as sourcing of feedstocks, location-allocation decisions of facilities to name a few. Especially for biobased chains and circular practices it is essential to combine both the process engineering aspects as the supply chain design because of the interconnected decisions and the effects of location and seasonality on the performance [1] (Figure 2). In general, there is no "one-size-fits-all solution".

Early assessments

It is not realistic to evaluate all the possibilities and we should take advantage of the flexibility at earlier stages of development to pre-select the most promising options (Figure 1). Various sustainability performance assessment methods are available, for example Life Cycle Assessment (LCA). However, these methods are by nature deterministic, thereby heavily relying on data. A proposed solution is to perform prospective sustainability assessments, to give an indication of expected sustainability impact of emerging products and novel technologies.

Especially for biobased chains and circular practices it is essential to combine both the process engineering aspects as the supply chain design

Role of PSE

Simulation combined with scenario analysis is a powerful tool to support prospective sustainability assessments. PSE focusses on process design, simulation and optimisation (at various length scales like phenomena, tasks, and/or unit operations), and can thus be used to reliably project how novel processing chains will perform when being upscaled [2][3][4]. Supply Chain Management (SCM) methods based on operations research are needed to manage and optimise product flows from raw material sourcing to production, logistics and delivery to the final customer.

Figure 2: Representation of the network design problem, which includes supplier selection, logistic decisions, and plant design and operation

Essential ingredients

A major challenge for prospective sustainability assessments is to deal with the immaturity of novel systems. To make reliable simulation models for novel chains one should understand very well:

which aspects of the product chain are important to include in the model (at unit operation, plant and supply chain scale),
the interaction between these various elements, e.g. how location-allocation decisions on the supply chain scale are influenced by feedstock properties and processing design at the plant scale,
how the major technical aspects impact environmental, economic and social sustainability.

Toolbox

We are developing methods to quantify the expected performance and related system-wide sustainability trade-offs, for innovations at low technological readiness levels. These innovations typically have uncertain and limited data. Approaches from PSE, SCM and sustainability assessment are combined to determine which chains are expected to be most promising. This requires close collaboration with experts within the disciplines focussing on primary production ('feedstocks') and conversion ('biorefinery and processing') to ensure validity of the developed mathematical models and resulting early sustainability assessment.

Figure 3: Example of strategic network design case, for a biorefinery facility treating lignocellulosic biomass, green leaves and manure

Examples

PSE enabled us to evaluate the economic performance of various novel micro-algal biorefineries at industrial scale [5]. We identified optimal processing capacities, operating conditions and associated revenues, while taking into account biological differences between micro-algae species. A process systems approach integrating thermodynamics, prospective LCA and cost-benefit analysis was applied to design a hybrid solar-seaweed biorefinery for co-production of biochemicals, fuels, electricity and water [6]. Key novel elements were evaluated, which will enable further technology choices for this system development. Recently, flowsheeting was used to design a biorefinery plant which is using pig manure, wheat straw and sugar beet leaves. This included the selection of processing technology and products to derive from the feedstocks (Figure 3).

REFERENCES
[1] Slegers, P.M., Leduc, S., Wijffels, R.H., van Straten, G., van Boxtel, A.J.B., 2015. Logistic Analysis of Algae Cultivation. Bioresource Technology 179, 314–322. https://doi.org/10.1016/j.biortech.2014.12.033
[2] Garcia, D.J., You, F., 2015. Supply Chain Design and Optimization: Challenges and Opportunities. Computers & Chemical Engineering 81, 153–170. https://doi.org/10.1016/j.compchemeng.2015.03.015
[3] Pistikopoulos, E.N., Barbosa-Povoa, A., Lee, J.H., Misener, R., Mitsos, A., Reklaitis, G.V., Venkatasubramanian, V., You, F., Gani, R., 2021. Process Systems Engineering – The Generation Next? Computers & Chemical Engineering 147, 107252. https://doi.org/10.1016/j.compchemeng.2021.107252
[4] van Boxtel, A.J.B., Perez-Lopez, P., Breitmayer, E., Slegers, P.M., 2015. The Potential of Optimized Process Design to Advance LCA Performance of Algae Production Systems. Applied Energy 154 (September), 1122–1127. https://doi.org/10.1016/j.apenergy.2015.01.036
[5] Slegers, P.M., Olivieri, G., Breitmayer, E., Sijtsma, L., Eppink, M.H.M., Wijffels, R.H., Reith, J.H., 2020. Design of Value Chains for Microalgal Biorefinery at Industrial Scale: Process Integration and Techno-Economic Analysis. Frontiers in Bioengineering and Biotechnology 8. https://doi.org/10.3389/fbioe.2020.550758
[6] Golberg, A., Polikovsky, M., Epstein, M., Slegers, P.M., Drabik, D., Kribus, A., 2021. Hybrid Solar-seaweed Biorefinery for Co-production of Biochemicals, Biofuels, Electricity, and Water: Thermodynamics, Life Cycle Cssessment, and Cost-benefit Analysis. Energy Conversion and Management 246, 114679. https://doi.org/10.1016/j.enconman.2021.114679

Designing sustainable chains using Process Systems Engineering