Sustainable Process Design by Hybrid Techno-Economic Models

Transcription

1 Sustainable Process Design by Hybrid Techno-Economic Models Rebecca J. Hanes and Bhavik R. Bakshi William G. Lowrie Department of Chemical and Biomolecular Engineering The Ohio State University, Columbus OH 43210, USA China-US NSF Workshop on Sustainable Manufacturing Wuhan, China, March 13-15, 2014 Hanes & Bakshi (PSE Sustainable Process Design 1 / 12

2 Motivation Current vs. proposed approaches Sustainable Process Design: Current Approach Expand system boundary to include selected processes in life cycle (value chain) Accomplished by means of life cycle emissions factors for inputs to process being designed Analogous to process model-based LCA Apply multi-objective optimization techniques, find and interpret the Pareto curve(s) Hanes & Bakshi (PSE Sustainable Process Design 2 / 12

3 Motivation Current vs. proposed approaches Sustainable Process Design: Current Approach Expand system boundary to include selected processes in life cycle (value chain) Accomplished by means of life cycle emissions factors for inputs to process being designed Analogous to process model-based LCA Apply multi-objective optimization techniques, find and interpret the Pareto curve(s) maximize NPV ( x Eq) minimize V ( x Eq, c VC ) subject to g Eq ( x Eq) 0 Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 2 / 12

4 Motivation Current vs. proposed approaches Shortcomings of Current Approach Current approach is very sophisticated in its use of PSE techniques However, it is lagging in its use of latest thinking and methods from Sustainability Science and Engineering Hanes & Bakshi (PSE Sustainable Process Design 3 / 12

5 Motivation Current vs. proposed approaches Shortcomings of Current Approach Current approach is very sophisticated in its use of PSE techniques However, it is lagging in its use of latest thinking and methods from Sustainability Science and Engineering Two major shortcomings 1. Inadequate system boundary Reliance on Process LCA databases captures only 20-50% of life cycle Resulting designs are likely to be suboptimal or even perverse Consider larger life cycle boundary by utilizing data at multiple scales - equipment, value chain, economy Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 3 / 12

6 Motivation Current vs. proposed approaches Shortcomings of Current Approach Two major shortcomings 2. Ignoring the basis of sustainability Sustainability of all activities relies on ecosystem goods and services Ignored by most methods, including those meant to enhance sustainability Include the role of ecosystems in engineering design This presentation focuses on addressing the first shortcoming Hanes & Bakshi (PSE Sustainable Process Design 4 / 12

7 Approach Hybrid Models Proposed Approach Accounting for all processes in a life cycle is computationally intractable Use coarser models to account for ignored processes Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 5 / 12

8 Approach Hybrid Models Proposed Approach S 1 S 2 S 3 S 4 S 5 Accounting for all processes in life cycle is computationally intractable Use coarser models to account for ignored processes Such models are available in the form of environmentally-extended input-output models at regional, national and global scales Hybrid LCA combines process LCA and EEIO models, but not used for design Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 6 / 12

9 Approach Hybrid Techno-Economic Models Hybrid Models Flowsheet and Process LCA x 14' x25' x 5'2 v 4' S 4' f 5' S 5' Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 7 / 12

10 Approach Hybrid Techno-Economic Models Hybrid Models Flowsheet and Process LCA v 4' x 5'2 S 4' f 5' S 5' EEIO model n 3 S 3 v 1 f 1 n 1 S 1 x 13 x 12 v 3 v 2 S 2 n 2 f 3 f 2 x 23 Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 7 / 12

11 Approach Hybrid Models Hybrid Techno-Economic Models Flowsheet and Process LCA v 4' x 14' x25' x 5'2 S 4' f 5' S 5' EEIO model n 3 S 3 v 1 f 1 n 1 S 1 x 13 x 12 v 3 v 2 S 2 n 2 f 3 f 2 x 23 = Hybrid model v 1 n 1 x S 1 13 x12 n 3 v S 3' S 2 2 S v 3 3 S f 5' v 4' 4' S 5' x 14' x 25' x 5'2 Flowsheet models are usually based on fundamental knowledge and can be nonlinear Process LCA and EEIO models are usually empirical and linear Hybrid techno-economic model combines diverse models and data across multiple scales Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 7 / 12

12 Optimization Formulation Current Approach x 14' x25' x 5'2 Approach Hybrid Models v 4' S 4' f 5' S 5' maximize minimize (x Eq) NPV V (x ) Eq, c VC subject to g Eq ( x Eq) 0 Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 8 / 12

13 Optimization Formulation Current Approach x 14' x25' x 5'2 Approach Hybrid Models Proposed approach v 1 n 1 x S 1 13 x12 n 3 v 4' S 4' f 5' S 5' v 3 S 3' S 3 S 2 v 2 x 14' x 25' x 5'2 maximize minimize (x Eq) NPV V (x ) Eq, c VC subject to g Eq ( x Eq) 0 maximize minimize S f 5' v4' 4' S 5' (x Eq) NPV V (x Eq, x VC, x Ec) subject to g Eq ( x Eq) 0 g VC ( x Eq, x VC ) 0 g Ec ( x Eq, x VC, x Ec) 0 Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 8 / 12

14 Case study Problem statement Case Study: Superstructure Design a supply chain by optimizing a superstructure containing options for each of three supplier processes Coal Electricity New Steel Production Expanded Plastic Production Widget Production Natural Gas Electricity Steel Recycling Expanded and Thermoformed Plastic Production Linear process models except for ETPP process ETPP: Non-linear model with two design variables Also produces one unused by-product Objective Minimize life cycle CO 2 emissions Hanes & Bakshi (PSE Group@OSU) Sustainable Process Design 9 / 12

15 Case study Case Study: Hybrid Model Problem statement The economy scale was modeled as an eight-sector EEIO model Four sectors were disaggregated: Water and sewage Coal mining Oil and gas extraction Iron ore extraction Power generation Iron and steel mills Plastics manufacturing General appliance manufacturing Hanes & Bakshi (PSE Sustainable Process Design 10 / 12

16 Case study Results Optimal designs Conventional approach misses large fraction of the impact (gray area in first bar) Solution from proposed approach results in lower emissions Hanes & Bakshi (PSE Sustainable Process Design 11 / 12

17 Summary Summary Existing methods for sustainable process design are prone to errors Incomplete system boundary Ignorance of ecosystem services Proposed framework for hybrid techno-ecological modeling Combines models at equipment, value chain, economy scales Considers effect of design on life cycle and vice versa Can consider local, regional, national and global supply chains Hybrid techno-economic modeling also advances LCA by incorporating nonlinear models and better improvement analysis Hanes & Bakshi (PSE Sustainable Process Design 12 / 12