KT Consortium. Foto: Thorkild Christensen

Modelling, synthesis and analysis of biorefinery networks

Abstract

The production of fuels and chemicals is primarily based on crude oil. The use of biomass as raw material represents a sustainable alternative. In order to establish a new industrial system on the basis of biomass, a systematic approach to generating, evaluating and selecting biorefinery processing networks is needed. In this PhD study, a generic computer-aided methodology for synthesis and design of different processing networks, including biorefinery networks, is developed, along with the associated methods and tools

Introduction

Innovation in process synthesis-design is motivated by the current and projected increase in commodities, water and energy demand caused by the growing world population. The use of the present technologies and processes to satisfy the stated demands is causing an undesired raise in greenhouse gas emissions (especially carbon dioxide). Therefore, new process synthesisdesign methods are needed towards finding more sustainable processes in terms of using alternative raw materials (from renewable sources, such as biomass), incorporating new process technologies and satisfying new design objectives and constraints, including sustainability. In this project, a computer-aided framework has been developed for biorefinery processes, which includes specific tools, i.e. a database and a software interface. The framework is based on a superstructure optimization approach, including four key elements: (i) a superstructure representation named Process StepInterval Network (PSIN); (ii) a generic process model; (iii) a solver from an optimization environment; and (iv) a database for data management. Two special tools have been created: a database and a software implementation of the framework. The biorefinery database contains 10 types of biomass, over 100 processing alternatives and 9 products, which generate over 7∙1014 theoretical alternative routes. The software implementation named Super-O integrates the necessary in-house and commercial tools.

Synthesis framework

The framework for synthesis of biorefinery networks consists of a workflow and methods, algorithms and tools that are used in different steps. They key elements of the framework are shown in Figure 1.Figure 1: Three key elements of the framwork (superstructure, model, and solution strategy) and database as the fourth key element, which enables storage and retrieval of data for its use in new problems.
The synthesis workflow consists of three main steps: (1) problem formulation; (2) superstructure generation; and (3) solution of the optimization problem. Step 1: Problem formulation The objective of this step is to define the synthesis problem that needs to be solved by specifying raw materials, products, locations, processing steps, and available technologies in each of the considered steps. Step 2: Data collection and superstructure generation The objective is to collect all the necessary data for the problem that has been defined and to generate a superstructure of alternatives. Step 3: Solution of the optimization problem. The optimization problem is solved by employing solvers from an external optimization environment (GAMS) through Super-O.

Computer-aided tools

Biorefinery database.
The purpose of the database is to provide a common platform for different users to store, search and retrieve data for the formulation and solution of biorefinery synthesis problems. Table 1 lists some of the statistics related to the data available in the biorefinery database. The database is built on a specifically designed data structure that consists of three main data sections, namely a basic data section, a section for data related to the material, and a section containing process data.

Super-O: Software implementation
The software implementation of the framework, named Super-O, guides the user through the steps for formulating and solving synthesis problems of different processing networks. It allows for the reduction of the time needed for the formulation and solution of network optimization problems. A schematic representation of the workflow implemented in Super-O including the data flow and tools integration is shown in Figure 2.

Application example: Ethanol biorefinery

Ethanol is an attractive biofuel that can be used in blends with gasoline. It is therefore a good solution for reducing emissions and many countries have policieswhere it is required to use a percentage of ethanol from renewable sources in blends with gasoline [1]. The type, characteristics and availability of biomassbased feedstocks in different geographic locations is not homogeneous, which makes the problem of planning and designing production processes for this biofuel a location-dependent problem. Step 1: Problem formulation. The desired product is specified as fuel grade ethanol. Various alternatives in terms of biomass-based feedstocks and locations should be considered. The objective is to determine the most suitable locationfeedstock-process combination. Step 2: Data collection and superstructure generation. Six feedstocks and seven geographic locations are considered; the superstructure is shown in Figure 3.

Conclusions

A framework for synthesis of biorefinery networks has been developed, which can handle various types of problems efficiently and considers location-dependency of data and solution. Its software implementation guides users through the workflow, thus reducing time and minimizing errors.

Supervisors

Prof. Rafiqul Gani
Prof. John Woodley
Prof. Anker D. Jensen

PhD Study started: September 2014 to be completed: August 2017

To see figures and references for this text, please find the original in the Graduate Schools Yearbook 2016

To see figures and references for this PhD study, please download the Graduate School Yearbook.

The yearbook provides an overview of most of the PhD theses currently being written at DTU Chemical Engineering and is updated every year in February.