Evaluating Steam Explosion as Pre-treatmentof Hemp Fibres for Use in High Value

Products

Bachelor Integration Project

Industrial Engineering and Management

Product and Process Technology

Author:Dirk van de Riets2992299(+31)617340393d.van.de.riet@student.rug.nl

First supervisor:prof. dr. ir. H.J. Heeres

Second supervisor:dr. ing. H. Kloosterman

External supervisor:dr. A. Heeres

June 19, 2019

This report has been produced in the framework of an educational program at the University of Groningen,Netherlands, Faculty of Science and Engineering, Industrial Engineering and Management (IEM) Curriculum.No rights may be claimed based on this report. Citations are only allowed with explicit reference to the statusof the report as a product of a student project.

Abstract

Because of an Economic backlog in the east of Groningen, the Netherlands’ most northern province, companiesare looking for new applications for their products to penetrate different markets. Whereas many companiescurrently produce their products in bulk, a lot of these products could be processed further to makethem suitable for other, high value, niche markets. One of the raw materials, grown in Groningen by acompany called HemFlax, is industrial hemp. HempFlax produces their hemp for usage in mainly industrialapplications while an extra ’pre-treatment’ step could make the fibres of this hemp suitable for higher valuemarkets. Steam explosion is a pre-treatment technique that proved to be very promising due to its simplicityin machinery and efficiency in resource and energy use.

During this study, the pre-treatment technique of steam explosion was evaluated based on technological andeconomical feasibility of implementation. A steam explosion process design was constructed and the operatingcosts were estimated. Design choices were made based on the requirements and production capacity ofHempFlax. Findings in this report could also be valuable for start-up companies interested in pre-treatmentof hemp. Previous research concluded that the textile and composite markets have the highest added valueand growth potential for hemp fibres. Therefore, this research was focused on the treatment of hemp forusage in these markets. The proposed design included a 2.5 m3 batch reactor, processing 1000 tonnes ofretted hemp fibres per year. It was concluded that the composite market value for cellulose fibres is not highenough for steam explosion to be profitable. However, pre-treating hemp fibres for use as textiles proved tobe highly profitable. Due to the efficiency, simplicity and low cost, implementation of steam explosion washighly recommended.

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Contents

Abstract i

List of Figures iv

List of Tables v

1 Introduction 1

2 Context 22.1 Problem analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1.1 Problem statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.1.2 Problem owner/Stakeholder analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.3 Design (research) goal and questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.4 Cycle choice/design steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.5 Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Literature review 73.1 Hemp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.1.1 Mechanical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1.2 Chemical composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2 Steam explosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2.1 Basic method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2.2 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.2.3 Chemical impregnation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2.4 Batch process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2.5 Continuous process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2.6 Severity factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.2.7 Loss of biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.3 Processed fibres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.3.1 Textiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.3.2 Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4 Design/Techno-economic evaluation 164.1 Batch set-up versus continuous set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.2 Supply chain analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.3 Process design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.3.1 Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.3.2 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.3.3 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.3.4 Feed material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.4 Cost estimations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.4.1 Capital expenditures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.4.2 Operational expenditures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.5 Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.5.1 Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.5.2 Technological readiness level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.5.3 Scalability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.5.4 Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.5.5 Costs/economic feasibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.6 Advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.6.1 Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.6.2 Opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5 Discussion 24

6 Conclusion 25

References 26

A HempFlax data sheet 31

B Dryer cost estimation graph 32

C Boiler cost estimation graph 33

List of Figures

1 Flowchart of HempFlax hemp production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Stakeholder analysis diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Visual representation of system description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Cycles of Hevner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Different applications of Cannabis Sativa L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Cross section of Hemp stem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Schematic representation of lignocellulosic biomass . . . . . . . . . . . . . . . . . . . . . . . . 88 Schematic illustration of the effect of pre-treating lignocellulosic biomass . . . . . . . . . . . . 109 Scheme of steam explosion batch plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1210 Scheme of continuous steam explosion reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . 1311 Supply chain of steam explosion hemp treatment . . . . . . . . . . . . . . . . . . . . . . . . . 1612 Schematic process diagram for steam explosion treatment unit design . . . . . . . . . . . . . . 1713 Overview of cost inputs for the steam explosion process . . . . . . . . . . . . . . . . . . . . . 22

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List of Tables

1 Mechanical properties of Hemp, Cotton, E-glass, and Carbon . . . . . . . . . . . . . . . . . . 92 Wt% of Cellulose, Hemicellulose, and Lignin in Hemp fibre . . . . . . . . . . . . . . . . . . . 93 Summary of steam explosion process conditions employed in various batch applications . . . . 114 Summary of steam explosion process conditions employed in various continuous applications . 115 Cellulose fibre markets volumes and market price . . . . . . . . . . . . . . . . . . . . . . . . . 146 Chosen process parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 HempFlax fibre specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Capital expenditures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 Operational expenditures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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1 Introduction

The economy in the east of Groningen, the Netherlands’ most northern province, is not what it used tobe. As of now, unemployment rates are still above the Netherlands’ average numbers [ING, 2018]. Thisis, among other factors, due to the decrease in natural gas extraction on which a substantial part of theeconomy in Groningen relies [Duijkers et al., 2018].

In order to counter this economic backlog, companies in this area could benefit from investing in newproduction techniques to penetrate different markets and expand business. Start-up companies could installthemselves in the east of Groningen, creating new applications for byproducts of other companies andexpanding market potential of the province’s locally harvested crops. This would open up a wide range of newjob opportunities, giving the Groningen economy the possibility to flourish. To realize a boost in the economyin the east of Groningen, companies want and need to communicate and collaborate. This collaborating, andfinding new market potentials, was initiated by a group of professors and scientists who created a hub in theeast of Groningen where knowledge and ideas could be shared between different companies: ‘InnovatiehubOost-Groningen’.

Currently, some of the major companies located in Goningen and interested in joining the project areproducing their products in bulk. Innovatiehub Oost-Groningen is exploring innovative possibilities ofcreating new applications for raw materials, giving them a higher value [Geijp, 2018]. For instance, minorproduct treatment steps could increase the value of products by making them suitable for use in other,more niche focused, markets. Whereas for bulk producing companies it is not always strategic to widentheir range to niche markets, start-up companies are more likely to take on this challenge and focus on thesmaller, higher value, markets.

One of these Groningen based companies, actively involved in the innovation hub, is called HempFlax.HempFlax is one of the largest Hemp producers in the Netherlands, producing Hemp in bulk for different,more industrial focused, applications. Hemp (Cannabis Sativa L.) is a promising, multi-purpose, crop withprofitable potential in multiple applications [Ranalli and Venturi, 2004]. The growing need for bio-basedalternatives to chemical, plastic and textile resources is making multi-purpose fibre crops increasinglyinteresting [Mekonnen et al., 2013]. In addition to that, interest in fibre crops is increasing, to find alternativesto crops that require a higher input such as cotton, or to relieve pressure on natural forests by the paperindustry [Ranalli and Venturi, 2004]. Examples of possible applications for hemp are in bio-composites in,for instance, the automotive industry [Wibowo et al., 2004], and in the textile industry [van der Werf andTurunen, 2008].

Previous research by Hemmes investigated possible processing techniques for hemp fibres in order to makethem suitable for use in higher value markets [Hemmes, 2019]. One of Hemmes’ conclusions was that usingsteam explosion as pre-treatment for hemp fibres was most promising as it provides a high quality fibresuitable for use in the textile and composite markets. Textiles and composites proved to be the mostpromising markets with a high added value and growth potential [Keijsers et al., 2013].

This study will focus on the pre-treatment technique of steam explosion, treating hemp fibres for use in thetextile and composite markets. Due to its simplicity in machinery, and efficiency in resource and energy use increation of high-value products [Reinerte et al., 2017], steam explosion could prove to be a wise investmentfor HempFlax or start-up companies. Extensive research in this treatment process will be conducted tofind the possibilities of implementing steam explosion. Because HempFlax is part of the innovation hub,a company located closely, and open for communication, this research will include a design based on thepossibilities for HempFlax to invest in steam explosion. A techno-economic evaluation will be made to findout the technological feasibility, costs and scale to which the technique could be executed. The outputof the research will be advice and information on the implementation of steam explosion, including thetechno-economic evaluation.

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2 Context

Hemp is one of the raw materials, produced in Groningen, with many application possibilities and marketpotential due to it’s advantages in soil improvement and structural properties of the bast fibres. However,these advantages are currently not being exploited, as HempFlax produces their hemp in bulk for large, lessvaluable markets. The usage of hemp in higher value markets requires additional production steps or rawmaterial of a higher quality. Figure 1 shows a flowchart of the hemp production process at HempFlax. Afterthe basic treatment processes, retting and decortication, fibres are converted into products and sold in largequantities. In order to use the hemp in more valuable markets, a pre-treatment step is required subsequentto the basic treatment processes.

Figure 1: Flowchart of HempFlax hemp production

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2.1 Problem analysis

2.1.1 Problem statement

At this moment, HempFlax does not make use of pre-treatment to further process their hemp, making itfit to use in high value products. Implementing the process of steam explosion to obtain a high qualityhemp fibre could, therefore, be a promising investment for HempFlax. This leads to the following problemstatement: Currently, the costs and technical/economic feasibility of implementing the technique of steamexplosion, and the extent to how much it should be executed is unknown.

2.1.2 Problem owner/Stakeholder analysis

This section discusses the main problem owner and different stakeholders in the research. Identifyingstakeholders is important because it shows all parties interested and potentially affected by the researchand to which extent. Each stakeholder will be designated to one of the four quadrants in the stakeholderanalysis diagram. This diagram can be found in figure 2 and shows the possible stakeholder types.

The main problem owner in this research is dr. Andre Heeres representing ‘Innovatie Hub Oost Groningen’(IHOG). This collaboration between different scientists and companies is exploring innovative possibilitiesof creating new applications for raw materials such as hemp, potatoes and magnesium salts to enhance theregional economy of east Groningen. ‘Innovatie Hub Oost Groningen’ is a stakeholder that can be describedas a key player in this research because their influence and interest are both high.

A second key player in this research is the University of Groningen (RUG). The research is carried outas a Bachelor Integration Project for the bachelor program of Industrial Engineering and Management,specifically the Product and Process Technology track. This stakeholder is represented by prof. dr. ir. ErikHeeres as first supervisor to the project. Because the research is initiated via the University of Groningen,this stakeholder is positioned in the top right quadrant of the stakeholder analysis diagram.

Another stakeholder is the CEO of HempFlax, Mark Reinders. HempFlax is a company located in OudePekela in the east of Groningen and is one of the largest hemp producers in the Netherlands. They producehemp for a large number of applications in construction, industrial applications, animal care, horticultureand nutraceuticals [HempFlax, 2019]. The outcome of this research will provide HempFlax with an advicethat can prove to be profitable. Therefore, HempFlax has a high interest in the research. The research is notinitiated by HempFlax, making their influence low. Because of the high interest and relative low influencein the research, HempFlax is positioned in the bottom right quadrant of the stakeholder analysis diagram.

Besides HempFlax, Syncom is also one of the stakeholders. Syncom, also represented by dr. Andre Heeres, isa company providing industries with custom synthesis solutions [Syncom, 2019]. Therefore, they can deliverrefining processes for hemp products if necessary. This research is of interest to Syncom as it could leadto (further) collaboration between HempFlax and Syncom. Syncom is, therefore, positioned in the samequadrant as HempFlax in the stakeholder analysis diagram.

Other stakeholders are, for example, hemp farmers as they produce the hemp used in further processes.The outcome of the research does affect them. Their stake is only financial. Therefore, hemp farmers areplaced in the bottom left quadrant of the diagram and can be described as ’least important’ stakeholders.

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Figure 2: Stakeholder analysis diagram

2.2 System description

The system focused in this research is depicted in figure 3. The input of the system is hemp fibres ofcertain quality. These fibres already have endured primary treatment. The input is assumed to be of aconstant quality. Different factors influencing this quality fall outside of the scope of this research. The nextstep is further processing by steam explosion to obtain high quality fibres. The process of steam explosionand the obtained fibres are studied in this research and, therefore, fall within the system. The technicalfeasibility and possible implementations of steam explosion will be studied besides an extensive cost analysiscontributing to a techno-economic evaluation. The processed fibres will be assessed on quality/value andpossible applications in high value products. Finally, the output of the system will be advice on implementingsteam explosion as pre-treatment technique based on the techno-economic evaluation.

Figure 3: Visual representation of system description

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2.3 Design (research) goal and questions

The overall goal of this research can be divided into two goals, one research oriented and the other designoriented. To accomplish the final design goal, extensive research is required to get familiarized with thesubject, and to help making design decisions all within the previously described system. The techniqueof steam explosion, and how it affects the hemp fibres, must be thoroughly investigated. Besides this,information about applications of the processed product is required. After realizing the research goal, thedesign goal can be achieved: giving advice on implementing the pre-treatment technique of steam explosionto process hemp fibres. This advice is based on techno-economic evaluations, stating technical and economicfeasibility of the technique. Achieving the design goal will provide the output of the previously describedsystem.

The research goal and design goal both lead to their own set of questions, knowledge and practical (design)questions. Both types of questions are mutually nested as design is needed to answer knowledge questionsand vice versa [Wieringa, 2010].

Knowledge questions

• What are the chemical and structural properties of hemp fibres?

• What does the pre-treatment technique of steam explosion entail?

• Which materials are needed to perform steam explosion?

• On what scale can steam explosion be performed?

• What is the price of steam explosion processed hemp fibres?

• What are the different applications for steam explosion processed hemp fibres?

Design questions

• What is the most suitable steam explosion set-up for HempFlax?

• How much does it cost to install a steam explosion hemp fibre treatment unit?

• Is implementing the pre-treatment technique of steam explosion economically feasible for HempFlax?

2.4 Cycle choice/design steps

In the IEM field, integrating design science in a research project is of great importance. The design sciencecan be described by making use of the three cycles of Hevner. These cycles are depicted in figure 4. Therelevance cycle initiates design science research with an application context that provides the requirementsfor the research [Hevner, 2007]. Using the relevance cycle provided the context of this report. Secondly,the rigor cycle provides past knowledge to the research project to ensure its innovation [Hevner, 2007].Current knowledge about certain subjects, in this case steam explosion and hemp fibres, shows where thepossibilities lie for innovation and improvement. Finally, the design cycle encompasses repetitive generationand evaluation of potential designs to obtain a final satisfactory design [Hevner, 2007]. For this research, themost relevant cycle is the central one, the design cycle. This is because the output of the research shouldbe an artifact: advice on implementing steam explosion. However, due to the need of extensive researchand cost analysis to answer all the knowledge questions, the rigor cycle will also be important to the designscience of this research project.

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Figure 4: Cycles of Hevner [Hevner, 2007]

2.5 Resources

While conducting this research, multiple methods are used to arrive to the final output of the system. Toobtain a final advice on implementing steam explosion, the main method of gathering usable information isliterature research. This research has to be accompanied by techno-economic evaluations determining thetechnical and economic feasibility of steam explosion. Besides literature, an important source of informationwill be personal communication in the form of, for instance, interviews or casual conversation with expertsin the field and stakeholders in this project. Visiting HempFlax and asking questions can provide valuableinformation and insights that cannot be found in literature.

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3 Literature review

The literature review provides answers to the knowledge questions stated in section 2.3. These questions arementioned again below and answers are given in following sections.

Knowledge questions

• What are the chemical and structural properties of hemp fibres?

• What does the pre-treatment technique of steam explosion entail?

• Which materials are needed to perform steam explosion?

• On what scale can steam explosion be performed?

• What is the price of steam explosion processed hemp fibres?

• What are the different applications for steam explosion processed hemp fibres?

3.1 Hemp

Cannabis Sativa L., better known as hemp, is one of the world’s earliest developed source of plant bast fibreand it is widely used due to its fiber’s high length [Paridah et al., 2011]. Besides this, the fibres from theindustrial hemp plant are among the strongest and stiffest available natural fibres [Pickering et al., 2007].Cultivation of hemp has a low requirement for fertilizers and herbicides [Ranalli and Venturi, 2004], andis therefore considered as highly suitable for modern agricultural systems that are environmentally friendly[Amaducci and Gusovius, 2010]. Compared to other synthetic fibres (e.g. glass fibre), hemp has a lower costand a lower density [Faruk et al., 2012], which makes it an interesting crop centering the attention of muchresearch.

Figure 5: Different applications of Cannabis Sativa L.

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Figure 6: Cross section of Hemp stem [Narep, 2017]Figure 7: Schematic representation of lignocellulosicbiomass

Different parts of Cannabis Sativa L. are used in a wide variety of applications (figure 5). Usable componentsare the stalk, leaves, flowers, and the seeds. This research focuses primarily on the fibres which can be foundin stalk of the plant (figure 6). These fibres consist mainly of cellulose and are located in the shivs, thewoody inner core of the stem, and in fibre bundles in the outside layer of the stem. The fibre bundles containthe highest percentage of cellulose [Dupeyre et al., 1998]. Besides cellulose, plant biomass such as hemp,generally consists of three other significant organic components: hemicellulose, lignin, and pectin [Jung et al.,2015]. The cellulose is linked by van der Waals bonds and packed closely together while being protectedby hemicellulose, lignin and pectin (figure 6) [Perez et al., 2002]. Cellulose is a lineal polymer composedof cellobiose molecules forming long chains linked together by hydrogen bonds and van der Waals forces.Hemicellulose is a complex carbohydrate polymer with a lower molecular weight than cellulose. In contrastto cellulose, hemicellulose is prone to hydrolize. The bonds and complex structural properties cause for highprocessing costs of lignocellulosic biomass [Banerjee et al., 2010].

The first step in obtaining the fibre bundles from the hemp stem is the retting process [Dupeyre et al.,1998]. This is a fermentation process, involving several bacteria and fungi, which degrades the pectins andother cementing compounds in order to separate fibres from other stem tissues [Ribeiro et al., 2015]. Toobtain fine, clean, and strong fibres, applicable in higher value markets such as textiles and composites, itis necessary to further break the hemicellulose, lignin, and pectin seal, and disrupt the crystalline structureof cellulose [Dreyer et al., 2002][Mosier et al., 2005][Kumar et al., 2009]. This can be achieved by furtherpre-treatment of the hemp fibres. This research focuses on the pre-treatment technique of steam explosion.

In order to determine the effectiveness of any pre-treatment technique, it is wise to be familiar with thedifferent properties of hemp. Comparing these properties before and after steam explosion provides valuableinformation about the effectiveness of pre-treatment and the value of the pre-treated hemp fibres. Comparingthe mechanical properties and chemical composition of hemp to synthetic alternatives also shows the valueof hemp and why it is a promising alternative.

3.1.1 Mechanical properties

Table 1 shows some of the mechanical properties of Hemp and cotton, two natural fibres, and E-glass andCarbon, two synthetic fibres. The different mechanical properties are compared by taking into account thehigh value markets in which hemp fibres are expected to be used: composites and textiles. One of themechanical properties that show the advantage of hemp fibres is the density. For instance, E-glass and hempcan share similarities in stiffness while the density of hemp fibres is approximately 1 g/cm3 lower. Thismeans that using hemp, rather than E-glass, in composites will result in a product with the same qualitiesand a lower weight. Carbon fibre use in composites prove to be more brittle, the fibres are more costly and

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it is a non-renewable source [Jawaid and Khalil, 2011]. In the textiles industry, the 3-d structure of thefibres is of a greater importance. Because the fibres need to be spun, the fibre length and diameter are keyproperties. Synthetic fibres are produced manually and can therefore be structured to specific requirements.The question remains whether hemp fibres meet the requirements for the textile industry. To contribute tothe positive qualities of textile yarn, fibres need to be longer than 15 mm and no longer than between 30 and60 mm [van ’t Geloof et al., 2018]. Fibres which are finer than 10 µm tend to be too fragile for conversioninto yarn, while fibres thicker than 50 µm convert into a yarn structure too course and thick for comfortableuse [NPTEL, 2014]. Table 1 shows that hemp fibres are suitable for textile use. The higher tensile strengthand stiffness of hemp compared to cotton, alongside the fact that hemp cultivation requires less water andpesticides [Ranalli and Venturi, 2004], prove that hemp is a strong alternative.

Table 1: Mechanical properties of Hemp, Cotton, E-glass, and Carbon 1

Fibre Density Length Diameter Tensile strength Stiffness(g/cm3) (mm) (µm) (MPa) (GPa)

Hemp 1.4-1.6 5-55 20-40 550-900 25-70Cotton 1.51 10-60 20 400 12E-glass 2.55 - - 2500 70Carbon 1.8 - - 2000 400

3.1.2 Chemical composition

Table 2 gives the chemical composition of hemp fibres according to multiple sources. Hemp fibres aregenerally composed of 53.9-86.1% cellulose, 4.0-18.2% hemicellulose, 6.0-25.0% pectin, and 2.7-21.0% lignin(all in % by weight, wt%)(table 2). Besides these four organic compounds, hemp fibres also contain smallamounts of fats and proteins [Dupeyre et al., 1998]. The chemical composition of untreated hemp fibresvaries greatly. This is due to differences in cultivation conditions, the age of the plants, and the harvest andseparation techniques used prior to pre-treatment [Friedl, 2012].

Table 2: Wt% of Cellulose, Hemicellulose, and Lignin in Hemp fibreSource %Cellulose %Hemicellulose %Pectin %Lignin

[Jankauskiene et al., 2015] 86.1 6.08 - 11.6[Cronier et al., 2005] 65.0-84.0 6.0-8.1 9.4-25.0 2.7-4.5

[Liu et al., 2015] 64.0-71.0 4.0-6.0 6.0-10.0 3.0-8.0[Dupeyre et al., 1998] 55.0 16.0 - 4.0

[Thomsen et al., 2005] 75.0 8.0 - 5.0[Zhang et al., 2014] 53.9-57.6 16.3-18.2 6.5-7.1 20.0-21.0

[Le Troedec et al., 2008] 58.7 14.2 16.8 6.0[Bonatti et al., 2004] 55.0 16.0 8.0 4.0

[Bledzki and Gassan, 1996] 74.4 17.9 - 3.7

1Sources: [Sawpan et al., 2011] [Beckermann and Pickering, 2008] [Wambua et al., 2003] [Mwaikambo et al., 2006] [Fu et al.,2000] [Dupeyre et al., 1998] [Haigler et al., 2005]

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3.2 Steam explosion

As mentioned in section 3.1, fibre bundles from the hemp stem are mainly composed of the four organiccompounds: cellulose, hemicellulose, lignin, and pectin. The cellulose, closely packed together, is protectedby hemicelullose, lignin and pectin. In order to use the hemp fibres in high value markets such as textiles andcomposites, these fibres need to be of certain quality. The quality of fibres is often indicated by the smoothnessof the fibre and the weight percentage of non-fibre material in the fibre[van ’t Geloof et al., 2018]. Related tothe smoothness are the impurities, remaining hemicellulose, lignin, and pectin or chemical/biological residuesfrom processing steps, present in the fibre. According to van ’t Geloof, fibres with weight percentages ofnon-fibre material between 1-1.5% are considered to be high quality fibres. Weight percentages of morethan 7% are are categorized as bad quality [van ’t Geloof et al., 2018]. Pre-treatment is a necessary stepin degumming cellulose and achieving high quality fibres. A schematic illustration of the pre-treatmentprocess can be found in figure 8. Degumming the cellulose can be done in different ways such as physically(steam explosion), enzymatically, chemically, by use of ultrasonic waves, and using a recent developmentin degumming techniques called Crailar technology [Hemmes, 2019]. Steam explosion proved to be one ofthe most promising techniques, reaching solid biomass yields of 97%, due to its simplicity in machinery andefficiency in resource and energy use in creation of high-value products [Shahrukh et al., 2015][Reinerte et al.,2017]. Research shows that steam explosion could increase the cellulose content of hemp fibres from 73% to85%-90% [Kukle et al., 2011]. This is by steam exploding fibres that already underwent the retting process.Cellulose content of raw hemp fibres increased from 60%-64% to 73%-75% [Kukle et al., 2011]. Therefore,the retting process is recommended to be included before steam explosion.

Figure 8: Schematic illustration of the effect of pre-treating lignocellulosic biomass [Hsu et al., 1980]

3.2.1 Basic method

As hemicellulose is prone to hydrolysis, steam explosion is used as a hydrolytic pre-treatment technique thatreleases the constitutive components of biomass, thereby increasing the enzyme and solvent accessibility ofcellulose [Glasser and Wright, 1998]. Pectins and hemicellulose are rapidly hydrolyzed to an extend thatallows their solubilization in water. The process of steam explosion can be divided into two phases. Thefirst phase is the treating of the biomass with high temperature steam, creating a high pressure. Thisfirst phase essentially functions as a thermochemical reaction, which is similar to other steam and thermalpre-treatment techniques [Yu et al., 2012]. Temperatures can range from 190-230◦C and pressures can reachup to 3.0 MPa [Wolbers et al., 2018]. The second phase is an adiabatic process, where thermal energy isconverted into mechanical energy, and involves releasing the steam, resulting in an explosive discharge toatmospheric pressure [Hendriks and Zeeman, 2009]. Hot steam softens the material and the fibres separateby the mechanical action at the discharge [Vignon et al., 1995]. During steam explosion, important processvariables are reaction temperature, time and pressure [Thomsen et al., 2005]. Steam explosion is commonlyperformed on lab-scale in a batch reactor. However, there are possibilities of operating steam explosion ina continuous fashion, which could be a better alternative to scaling up a batch reactor in order to achieveindustrial scale pre-treatment.

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3.2.2 Parameters

In this section, an overview is given of different studies using different parameters on different scale steamexplosion reactors. This will give an insight in distinct options and may result in a possible optimal parameterdecision. Table 3 presents a summary of process conditions employed in various batch applications, table 4presents a summary of numerous continuous applications.

Table 3: Summary of steam explosion process conditions employed in various batch applicationsBiomass Reactor size Temperature Pressure Time Source

(◦C) (MPa) (min)Lab scale

Hemp 1 L 200-240 - 2 [Vignon et al., 1995]Hemp 6.1 g biomass 180-220 1-2.3 1 [Kukle et al., 2011]Hemp 5 L 200 - 10 [Thomsen et al., 2006]Hybrid aspen 0.5 L biomass 235 3.2 1-5 [Reinerte et al., 2017]Aspen 5 L 185-220 - 5-10 [Li et al., 2007]Sunflower 2 L 180-230 4.12 5 [Ruiz et al., 2008]Corn 10 L 180-200 - 5 [Zimbardi et al., 2007]

Industrial scaleCorn 5 m3 175.1-204.1 0.8-1.6 5 [Li and Chen, 2008]Spruce 3x11 m3 220 2.2 10 [Wolbers et al., 2018]

[Brusletto and Kleinert, 2018]Sugarcane 2.5 m3 180-200 - 15 [Oliveira et al., 2013]

Table 4: Summary of steam explosion process conditions employed in various continuous applicationsBiomass Reactor size Temperature Pressure Reaction time Source

(◦C) (MPa) (min)Lab scale

Spruce 50-200 kg/hr - 1.2-1.5 7.2-14.4 rpm [Fang et al., 2011]biomass (screw rotation

speed)Wheat 150 kg/hr 193-225 - 2-6 [Zimbardi et al., 1999]

biomassWheat 150 kg/hr 195-198 - 1.5-2.5 [Viola et al., 2008]Barley biomassOatHybrid poplar 1.5 L 208-238 1.7-3.1 2-20 [Grous et al., 1986]

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3.2.3 Chemical impregnation

There are studies that implement impregnating the biomass with chemicals prior to steam explosion in orderto obtain higher cellulose percentages2. As hydrolysis can be catalyzed by both acidic and alkaline conditions,common chemicals used for chemical pre-treatment are sulfuric acid (H2SO4) and Sodium Hydroxide (NaOH).In his research on woody hemp chenevotte, Vignon found that acid catalyzed treatment is more effective atlower temperature, alkali-catalyzed conditions results in a very homogeneous material in which low levelsof cellulose degradation are observed, and neutral conditions (water treatment) required high temperatures(>240◦C)[Vignon et al., 1996]. However, more recent studies show that chemical pre-treatment does notimprove the level of fibre disintegration [Kukle et al., 2011]. Retted hemp fibres could therefore be subjectedto steam explosion without prior chemical impregnation. As the focus of this research is specifically on steamexplosion, chemical impregnation will not fall inside the scope and will, therefore, not be further discussed.

3.2.4 Batch process

Figure 9 shows a schematic representation of a steam explosion batch plant. Biomass, in this case hemp, isfed through a pneumatic loading valve into a reaction chamber: a stainless steel pressure vessel. Inside thereactor, the biomass is soaked with saturated steam and the reaction time is controlled after the requiredtemperature is reached. After the elapsed time, the blow valve is opened, decreasing the pressure drasticallyin a short period of time, discharging the biomass into an expansion chamber. Connected to the expansionchamber is a water condenser in order to recover and remove liquid waste, volatile organic compounds,produced during the process. The necessary saturated steam is provided by an external boiler. As seen insection 3.2.2, batch reactors can be scaled up to an industrial size.

Figure 9: Scheme of steam explosion batch plant [ENEA, 2015]

3.2.5 Continuous process

As mentioned in section 3.2.1, steam explosion can also be performed continuously on a larger scale. Multipleinstitutes are studying the principles of continuous steam explosion [ENEA, 2015][Fang et al., 2011][Zimbardiet al., 1999]. Figure 10 shows a schematic overview of a continuous reactor.

Biomass is soaked with steam while being conveyed towards the reactor. Inside a feeder, the biomass iscompressed into a dense ’plug’ which seals the reactor and is continuously fed into the reactor. ENEAuses a tubular reactor with a diameter of 30 centimeters and a length of 3 meters [ENEA, 2015]. Thesteel reactor is designed to withstand pressures up to 30 kg/cm2. Steam is pumped into the reactor from an

2[Dupeyre et al., 1998][Vignon et al., 1996][Hendriks and Zeeman, 2009][Vignon et al., 1995]

12

external boiler continuously pressurizing the reactor. The biomass is moved through the reactor by a rotatingscrew conveyor. The speed of this screw determines the time of treatment. At the end of the reactor, anexpansion valve opens at regular intervals for a preset amount of time to control the biomass being releasedto atmospheric pressure. The exploded biomass, mixed with steam from the reactor, is transported to anexpansion tank where the two are separated. Using this continuous steam explosion reactor, it is possible toprocess up to 300 kilograms per hour.

In his research on dilute acid treatment of black spruce, Fang used a continuous steam explosion reactorwhich was modified from an Andritz 22-in. refiner [Fang et al., 2011]. The throughput of this reactor couldvary from 50-200 kilograms per hour. Conventional steam explosion processes achieve defibration, breakingbiomass into fibres, by means of an explosion at the end of the treatment. In this reactor, the explosionis replaced with a refining step. Instead of an explosive discharge to atmospheric pressure, the biomass ispassed to a refiner.

Continuous reactors can be scaled up easily and are more efficient to utilize. However, not many studiesinclude large scale continuous set-ups which indicates the need for further development.

Figure 10: Scheme of continuous steam explosion reactor [ENEA, 2015]

3.2.6 Severity factor

In order to optimize a steam explosion process, Overend and Chornet developed a severity index that is widelyused [Overend and Chornet, 1987]. In their study, they show that it was imperative to find a representativefactor that compares different parameters of steam explosion. The severity index (S) is a function of thereaction time (t) in seconds and temperature (T ) in kelvin, and can be described as shown in equation(1). Process parameters and the severity index are chosen based on the purpose of the pre-treatment. Theseverity index is typically chosen to be between 2 and 4 because at high severity (S>4), sugars start todegrade due to dehydration and condensation reactions [Lam, 2011].

S = log

(∫ t

0

exp

(T (t) − 100

14.75

)dt

)(1)

Although this model is used widely, there are some limitations. The model developed by Overend andChornet does not include factors such as the feedstock moisture content and particle size while these factors

13

have a strong influence on the steam explosion process kinetics. For example, high moisture contents of thefeedstock have been shown to slow down kinetics [Lam, 2011]. This is due to the voids in the biomass thatare filled before the steam temperature is reached.

3.2.7 Loss of biomass

Steam explosion appears to be a very promising pre-treatment technique. However, this process does nothave a 100% efficiency. As mentioned in section 3.2.4, some of the volatile solids of the biomass are lostduring steam explosion treatment due to the mechanical force of decompression [Bauer et al., 2014]. Biomassyield can vary from 79% to 97%3. This depends on the specific biomass used, process design, and parameterschosen for the steam explosion process. The amount of biomass loss can be estimated by looking at the ashcontent of the untreated and steam exploded biomass. Formula 2 shows this basic calculation.

(Mass loss/M) =XASE −XAuntreated

XASE(2)

where M = the total mass of untreated biomass

XASE = the ash content of steam exploded biomass

XAuntreated = the ash content of untreated biomass

3.3 Processed fibres

Once the relevant information about steam explosion is established, it is wise to get familiar with the finalproduct. In this section, the applications of the pre-treated, degummed fibres will be discussed along withthe current price of these processed fibres. As discussed briefly in section 3.1 and shown in figure 5, thehemp plant has a wide variety of applications. Raw hemp fibres can already be used in different marketssuch as construction, animal care or nutraceuticals. When pre-treated, hemp fibres are pertinent for use inhigher valued products. Keijsers et al. costructed a cellulose resource matrix including the different marketsfor cellulose fibre applications [Keijsers et al., 2013]. Some of these markets and their price range are shownin table 5. This table shows that the raw material price in the textile market ranges from 1200-1900 e/ton.The composites market, currently about 14% of the hemp fibre market, is estimated to have a large growthpotential and has an indicated price of around e750 per tonne [Carus et al., 2013]. Therefore, in his research,Hemmes argued that the composites and textiles market are most interesting for hemp fibre use [Hemmes,2019]. These markets are looked into in the following sections.

Table 5: Cellulose fibre markets volumes and market price [Keijsers et al., 2013]Cellulose market Price range Market volume

(raw material price e/tonne) Global estimation (Mt/y)Textiles 1200-1900 70 (fibre)Non-woven 200-400 0.6Wood, timber 450-600e/m3 1200-1500Pulp, paper and board 450-650 380 paper

186 pulp (2003)19-21 (non-wood pulp)

Building materialsCellulosic fibre composites 200-400 0.07-0.8 (automotive)Green chemicals 50-100

3[Shahrukh et al., 2015][Wolbers et al., 2018][Thomsen et al., 2006][Bauer et al., 2014]

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3.3.1 Textiles

As table 5 shows, the textiles market is the largest high-value market for cellulose fibres. With a raw materialprice range of e1200-1900, textiles create the highest added value for, for instance, pre-treated hemp fibres.The textile industry shows a couple of main competitors to hemp. These competitors are other natural fibressuch as cotton, jute, and wool, and synthetic fibres such as polyesters and nylon. As of now, the textileindustry consists mainly of cotton fibres and the fossil-based synthetic fibres [van Dam, 2014]. Due to thecurrent environmental impact of the textile industry, interest in hemp fibres is expected to rise drastically.Hemp fibre is a non fossil-based, less water intensive substitute to synthetic and cotton fibres. Within thetextile industry, interesting niche markets for hemp fibre use could be apparel, carpet backing, upholsterysacking, and geo-textiles [Keijsers et al., 2013].

3.3.2 Composites

The growth of the natural fibres based composites markets is due to the same sustainability reasons whichretailers and consumers desire. Because of the weight advantages and improved recyclability, automotiveindustries are increasingly interested in producing lignocellulosic fibre reinforced composite materials insteadof composites that are glass fibre reinforced [van Dam, 2014]. These composite materials can be used forinterior parts as well as exterior automotive body parts.

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4 Design/Techno-economic evaluation

In this section, a techno-economic evaluation of steam explosion is conducted making use of the foundliterature. In order to evaluate steam explosion, a process is designed including a small supply chainassessment. The designed process is assessed based on cost estimations and technological possibilities. Thegoal of this design phase is to eventually being able to answer the design questions formulated in section 2.3.These design questions are mentioned again below.

Design questions

• What is the most suitable steam explosion set-up for HempFlax?

• How much does it cost to install a steam explosion hemp fibre treatment unit?

• Is implementing the pre-treatment technique of steam explosion economically feasible for HempFlax?

4.1 Batch set-up versus continuous set-up

In section 3.2 it became clear that steam explosion can be performed either in a batch reactor or in acontinuous reactor. For the techno-economic evaluation, a design of the process is constructed in order toassess the costs. Due to the superior availability of information about industrial scale steam explosion batchreactors, the designed process will consider a batch reactor. Besides the availability of information, as thisresearch is focused towards HempFlax, a batch reactor set-up is a more realistic choice. This is becausethe implementation of continuous steam explosion will require a significantly larger investment involving amuch higher risk. HempFlax is a relatively small company which is more likely to start investing in a batchset-up. Furthermore, for a start-up company to invest in steam explosion, a batch set-up is certainly thebetter choice as it is more easy to control.

4.2 Supply chain analysis

A small analysis is conducted in order to get a clear overview of the different steps in the hemp treatmentsupply chain. This analysis shows different factors that should be considered and taken into account. Aschematic process diagram of the supply chain can be seen in figure 11.

Figure 11: Supply chain of steam explosion hemp treatment

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Hemp is grown and retted on the field for a certain amount of weeks. The retted hemp fibres are the inputof the steam explosion process. Fibres can be conditioned in order to fulfill specific requirements in termsof moisture content before or after steam explosion. A water feed and fuel are input for the water boiler,providing steam for conditioning and steam explosion. After the steam explosion, waste is recovered andremoved for further treatment or disposal. Steam exploded fibres are transported to storage in order toeventually be used in the high value markets of textiles and composites.

4.3 Process design

For the steam explosion step in the supply chain, a design is made based on values found in literature,assumption, and estimations. The process and all the equipment needed, the dimensions of the reactor, theprocess parameters, and the feed material are elaborated on in this section.

4.3.1 Process

Figure 12: Schematic process diagram for steam explosion treatment unit design

Figure 12 shows a schematic diagram of the steam explosion design, including all required steps andequipment. Retted hemp fibres are fed into the steam explosion vessel. A natural gas powered boilerconverts water into steam and this steam is then also fed into the vessel. Once the vessel has reached thedesired temperature and pressure for a certain period of time, the pressure is discharged to atmosphericpressure and blown into an expansion chamber. The expansion chamber is cooled in order to condensatethe steam, making the separation of solid fibres and the condensate possible via filtration. Cooling can beachieved via a simple shower installation, sprinkling water in the expansion chamber. Recycling of waterback into the boiler is a possibility. However, this would require an additional cleaning step to remove organicvolatile compounds and is, therefore, not included in this design. The steam exploded fibres are dried in anatmospheric single drum dryer.

4.3.2 Dimensions

The dimensions of the steam explosion reactor for this design are based on the hemp production of HempFlaxin the Netherlands. In 2015, HempFlax grew approximately 1,600 hectares of fibre hemp in three differentcountries. Half of this amount was grown in the Netherlands. As HempFlax is expecting to grow around3,500 hectares by 2020 [HempFlax, 2019], current production in the Netherlands is estimated to be 1,500hectares. Average fibre hemp yield per hectare is about 2 tonnes [DNFI, 2018]. Therefore, about 3,000tonnes of hemp was cultivated for fibre use in the Netherlands. The assumption is made that a third of this

17

will be used for pre-treatment. A reactor of 2.5 m3 is chosen, which is capable of treating 135 kg rettedhemp fibres each batch. Oliveira et al. studied a batch steam explosion reactor with the same dimension fortreatment of sugarcane straw [Oliveira et al., 2013].The cylindrical vessel with hemispherical head is assumedto have a length and diameter of approximately 1.4 meters. Fibres are blown into an expansion chamber of10 m3 with a length of 2.1 meters and a diameter of 2.3 meters.

4.3.3 Parameters

Parameters for the treatment of hemp should be chosen based on specific requirements and applicationswhile keeping in mind the severity factor. Process parameters in this design are chosen based on researchby Thomsen et al., investigating steam explosion specifically of hemp fibres to be used in the textile andcomposite industry [Thomsen et al., 2006]. The designed process operates at a temperature of 200◦C witha pressure inside the reactor of 2.2 MPa. With a temperature of 200◦C and a reaction time of 10 minutes,the severity factor is calculated to be 3.9, which falls within the desired range mentioned in section 3.2.6(table 6). Thomsen et al. managed to obtain steam exploded fibres with a cellulose content of 86-90% whilelosing 17% dry matter. The yield from this designed steam explosion process is, therefore, assumed to be83% of the biomass fed into the reactor. With a yield of 83%, and a throughput of 1,000 tonnes, this reactorproduces 830 tonnes of high quality hemp fibres per year.

4.3.4 Feed material

Retted hemp fibres, produced by HempFlax, are considered to be the input of the process. The specificationsof HempFlax’s fibres are listed in a data sheet in appendix A. A summary including some of the specificationsis depicted in table 7. The cost of the retted hemp fibres is e700 per metric ton as indicated by HempFlax.

Table 6: Chosen process parametersParameter ValueTemperature (T) 200◦CPressure (P) 2.2 MPaReaction time (t) 10 minSeverity factor (S) 3.9

Table 7: HempFlax fibre specificationsProperty ValueBiomass EU certified hempHumidity <12%Retting and rettingdegree Dew retted, well rettedCellulose content 66%Hemicellulose content 16%Pectin content 4%

4.4 Cost estimations

In this section, the costs of the designed process are estimated. Costs of a process are divided into two differentkinds of expenditures: capital expenditures (CAPEX) and operational expenditures (OPEX). CAPEX are toacquire and maintain physical assets such as equipment, land and a building [Kenton, 2019]. OPEX includeoperational costs such as raw material costs, labor costs, and utility costs. The book on chemical processdesign by Turton et al. is used as framework for the cost estimations alongside a cost engineering pricebooklet developed by the Dutch Association of Cost Engineers (DACE), and a report on process equipmentcost estimation by the United Stated Department of Energy (US DOE)4. Equipment costs are multiplied by afactor 4 in order to approximate the installed cost. Total installed cost include installation, instrumentation,and piping costs. This factor is called the ’Lang factor’ and is first described by Lang in 1947 [Lang, 1947].Table 8 and 9 summarize the estimations for CAPEX and OPEX of the relevant pieces of equipment. Theestimated values are clarified in the following sections.

4[Turton et al., 2008] [DACE, 2018][Loh et al., 2002]

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4.4.1 Capital expenditures

Steam explosion vessel

The cost of the steam explosion vessel is estimated by making use of the DACE price booklet. A 2.5 m3

carbon steel vessel with an average wall thickness of 16 millimeters is indicated to have a cost of approximatelye24,000. The largest value for wall thickness is chosen because the vessel needs to withstand high pressures.As parameters may change due to different process requirements, equipment has to be capable of dealingwith this change.

Expansion chamber

The cost of the expansion chamber is estimated similarly to the reaction vessel. While the reaction vessel isused under high pressure, the expansion chamber catches the products after being discharged to atmosphericpressure, and therefore does not require a large wall thickness. A thickness of 10 millimeters was assumedfor the expansion chamber. This resulted in a cost estimation of e28,000.

Filter

A simple plate filter can be used to separate the condensate from the steam exploded fibres. As thethroughput of the process per batch is approximately 830 kg, a filter with a net filtering surface of 2 m2 isassumed to be sufficient. According to the DACE price booklet, a filter with this filtering surface has anapproximated price of e17,000.

Drum dryer

The cost estimation of the dryer is based on the US DOE report. This report provides graph curves fordifferent process equipment with purchase cost depicted against specific parameters. The graph used toestimate the cost of the single atmospheric drum dryer can be found in appendix B. For dryers, the relevantparameter is the drying area. For this design, the area is assumed to be 2 m2, and this value is less thanthe area range covered in the US DOE report. The rule of six-tenths, described by Turton et al., is usedalongside the US DOE report information to approximate the equipment cost of the dryer (equation (3)).This rule describes a simple relationship between the cost and an attribute of the equipment related to unitsof capacity.

Cost1

Cost2=

(Size1

Size2

)0.6

(3)

Using the rule of six-tenths, the cost of the dryer is estimated to be e37,000.

Natural gas boiler

The cost estimation of the external boiler, providing the steam explosion vessel with steam, is also basedon information from the US DOE report. The graph used to estimate the cost of the external boiler can befound in appendix C. In order to estimate the cost of the boiler, it is necessary to know the amount of steamthat it is required to produce per hour. According to Yu et al., traditional explosion steam consumption isapproximately 0.8-1.0 tons of steam per ton of feed stock [Yu et al., 2012]. Keeping this in mind, with areactor able to handle 135 kg per batch, the amount of steam required for one batch is estimated to be thesame. As the batch cycle time is 15 minutes (including change-over time), the amount of steam required perhour is 540 kg (1,200 lbs/hr). Once again, equation (3) is used to estimate the equipment cost of the boiler.This resulted in an estimated cost of e23,000.

Land/building

Assuming that HempFlax can use land they already own, costs for land are not taken into account. Thebuilding cost is estimated using the DACE price booklet. A building with basic installation and an area of64 m2 is estimated to cost e55,000.

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4.4.2 Operational expenditures

Labor cost

One of the major operational expenses is the labor cost of the employees operating the process. Turton etal. describes a method of estimating the cost of operating labor by determining the amount of shifts andoperator required for a specific process. This method states that the cost for one operator corresponds toapproximately e23,000 for a 2000-hour year. Assuming the steam explosion process requires 3 operators,the labor cost are estimated to be e69,000 per year.

Natural gas cost

One of the more substantial utility costs in this process, is the fuel cost of the external boiler, providing thereactor with high pressure steam. As steam explosion utilizes the same amount of steam as it is processingbiomass, fuel costs of the steam boiler is an important factor to consider. For this evaluation, the externalboiler is assumed to be fueled by natural gas and operating with an efficiency of 90%. With a natural gasprize of approximately $1.55/GJ [FortisBC, 2019], and a required 1,000 tonnes of steam per year, the yearlyboiler fuel cost can be calculated using the utility cost estimation module described by Turton et al. Thecosts of natural gas as fuel for the external boiler are estimated to be e5,000 per year.

Feed water cost

Turton et al. also describe a method of estimating the feed water cost. This method derives an estimationbased on certain assumptions. Feed water must be treated to reduce hardness and remove magnesium andcalcium salts. This is a necessity as any contaminants entering with the water can eventually deposit onboiler tubes, causing fouling or other damage. Dissolved oxygen and carbon dioxide should be removed inorder to avoid corrosion. Taking into account the cost of treatment for the boiler feed water and the coolingfeed water, total feed water adds another e3,000 per year.

Waste disposal

The cost of waste disposal is estimated using the general value of $36 per tonne described by Turton etal. Including water, the waste stream is assumed to be 1130 tonnes. The cost of disposing waste water is,therefore, estimated to be e36,000 per year.

4.5 Assessment

In his research, Hemmes argued that steam explosion is one of the most promising pre-treatment techniquesfor processing hemp fibres to be used in high value markets [Hemmes, 2019]. During the literature review,conducted for this work, this technique was investigated extensively in order to provide information andadvice on implementing a steam explosion treatment unit. In this techno-economic assessment, steamexplosion findings are once more evaluated based on different parameters Hemmes described in his parallelevaluation matrix. These parameters are sustainability, technological readiness level, scalability, quality, andcosts. The estimated costs of installing a steam explosion treatment unit are weighted against the processedfibre prices in order to assess the economic feasibility.

4.5.1 Sustainability

Sustainability describes the environmental impact of the pre-treatment technique in terms of renewabilityand resources required. Steam explosion can be described as a sustainable process due to the only input,besides the product, being high pressure steam. As discussed in section 3.2.3, use of chemicals prior to steamexplosion is not required. Although this is not considered in the design, the waste stream can be cleanedand reused for the production of steam. Besides the disposal of the waste stream, the only non-sustainablefactor in the designed process is the production of steam by making use of a natural gas powered boiler.This type of boiler was chosen for convenience in cost estimations. However, more sustainable options are

20

available. Wolbers already discussed possibilities of using a biomass powered boiler while indicating potentialcost savings [Wolbers et al., 2018].

4.5.2 Technological readiness level

Technological readiness level describes the extent to which the technology has developed and its readinessfor implementation. As described in section 3.2, steam explosion is already investigated thoroughly formany years, indicating its large development. Whereas steam explosion in a batch set-up is researched andperformed on different scales and sizes, continuous steam explosion is not performed widely yet and requiresfurther development. Due to its simplicity in machinery, availability of technology is not a limiting factor inimplementing steam explosion as treatment technique.

4.5.3 Scalability

The scalability of a process is the degree to which it can be scaled up to a more industrial size. Steamexplosion in a batch set-up is researched widely, using different size reactors and varying biomass input.Table 3 and 4 show different studies using reactors with sizes ranging from 1 liter to 11 m3. While moststudies focus on a lab scale steam explosion, more recent studies look at the possibilities of using steamexplosion on an industrial scale. The fact that steam explosion is possible in a continuous fashion indicatesthe broad scalability of this technique.

4.5.4 Quality

Quality refers to the quality of the product after the process. For steam exploding hemp fibres, this qualitycan be described in terms of cellulose content. Steam exploding retted hemp fibres increases cellulose contentfrom 73% to 85%-90% [Kukle et al., 2011]. Fibres with a cellulose content in this range can be classified asgreat quality, and are suitable for use in high value products. A downside to steam explosion quality is theloss of biomass that occurs, creating a production yield of about 80%-90%.

4.5.5 Costs/economic feasibility

The costs of a process are the expenses made in order to set up and operate the process. Costs estimationsof CAPEX and OPEX are made and elaborated on in section 4.4. These estimations are based on a steamexplosion process, designed specifically for this techno-economic evaluation. Based on the estimated costsof setting up and operating a steam explosion process, and the market price of hemp fibres in textilesand composites (section 3.3), the economic feasibility of implementing steam explosion can be assessed.Calculations are based on a process using a 2.5 m3 vessel, processing 1000 tonnes of retted hemp fibres (rawmaterial) per year. With a production yield of 83%, 830 tonnes of pre-treated hemp fibres are produced.Table 8 and 9 summarize the CAPEX and OPEX for the designed steam explosion process.

Table 8: Capital expendituresCapital expense Cost

(e)Steam explosion vessel 24,000Expansion chamber 28,000Dryer 37,000Boiler 23,000

112,000(Lang factor) 4

448,000Building 55,000

Total 503,000

Table 9: Operational expendituresOperational expense Cost

(e/tonne raw material)Raw material 700Labor 69Natural gas 5Water 3Waste disposal 36

Total 813

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In order to assess the costs of steam explosion, the cost of producing one tonne of high quality fibres needsto be determined. This can be done by looking at the different cost inputs required for the process (figure13). CAPEX are translated into cost per tonne raw material by assuming a depreciation time of 10 years.Figure 13 shows that the cost of producing 0.83 tonnes of steam exploded hemp fibres is e863. Therefore,the cost of producing 1 tonne of pre-treated fibres is approximately e1,040.

Figure 13: Overview of cost inputs for the steam explosion process

Section 3.3 mentions that the hemp fibre market value of textiles ranges from 1,200-1,900 euros per tonne.This means that for each tonne of steam exploded hemp fibres produced for the textile industry, an averageprofit of approximately e500 could be made, resulting in a yearly profit of e415,000. With the high rawmaterial price of e700 per tonne, the composite market already has a minimal added value. As the marketvalue of composites is approximately e750 per tonne, using this steam explosion set-up for composite hempfibres does not seem to be profitable.

4.6 Advice

Based on the different findings during the literature review, and the evaluation of the designed process,advice can be given on the implementation of steam explosion. Steam explosion is a process that is easyto implement and control, and does not require sophisticated expensive equipment. Steam exploded fibresincrease in cellulose content and, in the right market, can almost double their value. While the raw materialprice of retted hemp fibres is already relatively high, with a market value of e750 per tonne, the compositemarket does not turn out to be value adding. However, steam exploded hemp fibres can be sold in thetextile market for up to e1,900 per tonne. Including the capital investment and the yearly operationalexpenses, selling the fibres for textiles could already turn a large profit after 2 years. Therefore, due to theefficiency, simplicity and low cost, implementation of steam explosion for the treatment of hemp fibres ishighly recommended.

4.6.1 Challenges

Challenges that could be faced upon implementation include the deciding of parameters. Experimentingwith different parameters for a personal set-up, trial and error, is required for an efficient process. A secondchallenge is penetrating a new market. This requires more market analysis in order to determine the bestmarket positioning strategy. For HempFlax, the question remains whether it is wise to start penetratingmore niche focused markets, which would cost less effort when already familiar with people in the field andmaintaining connections. In addition, HempFlax should be capable of realizing multiple marketing strategies.

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4.6.2 Opportunities

Opportunities in steam explosion include the economic advantage. The implementation of steam explosiondoes increase the value of HempFlax’s raw material. Steam exploded fibres can be sold with a high profitmargin. Besides, it would contribute to the desired economic boost in the east of Groningen due the newjob and market opportunities. This was the motive that started this research and got HempFlax involved inthe innovation hub. Moreover, producing hemp fibres for textiles could further increase the environmentalfriendly image of HempFlax for a broader, more consumer based, audience and expand the overall brandawareness.

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5 Discussion

The purpose of this research was to evaluate the pre-treatment technique of steam explosion for the productionof high purity hemp fibres. This evaluation was carried out by investigating existing literature extensivelyand designing a steam explosion process in order to estimate the costs. The goal was to provide an adviceand information, directed towards HempFlax, on the implementation of steam explosion. In this section,the applied methods, the process design, and recommendations for further research are discussed.

At the start of the study, a system was defined to focus the research and create a scope. This helpedwith recognizing the relevant subjects and keeping the project achievable within the restraining time limit.Because of the early choices that had to be made, some important factors were not discussed. For instance,retted hemp fibres, produced by HempFlax, were taken as input for the system without investigating theretting process. Information on prior processes to pre-treatment could prove to be useful as these havea great influence on the quality of the fibres. Besides, Hemmes argued that a ’green decortication’ stepcould replace retting in order to achieve a higher quality product which could contribute to this research[Hemmes, 2019]. Furthermore, additional processing steps for the production of textiles or composites werenot considered.

This study relies solely on the information obtained from literature and personal communication. Designdecisions were made based on literature review and conversations with experts. Thus, these decisions werenot backed up by self obtained experimental results. Performing steam explosion on lab scale with personalrequirements could help with finding the right parameters for an optimal process.

The research focused on the use of hemp fibres in the textile and composite industry as these marketsproved to be most promising and value adding. Keijsers et al. discuss multiple other cellulose fibre products,such as cellulose dissolving pulp and cellulosic film, that have an even higher market value [Keijsers et al.,2013]. However, these products are produced via cellulose regeneration technology which is not developedfor hemp yet. While these markets are not considered in this research, further research could look at thepossibilities of steam explosion in the production of other high value products. Overall, a comprehensivemarket analysis is vital before penetrating a new market.

As mentioned before, the designed steam explosion process was constructed by making assumptions basedon research and personal communication. Specific choices were made by focusing the design towardsthe possibilities of HempFlax and assuming their requirements. It should be kept in mind that manyimplementation factors depend on the specific requirements of a certain company. For example, changes inreactor scale and production capacity could influence the types of equipment required for an optimal steamexplosion process. For HempFlax, the choice was made to exclude the usage of the waste stream becausethis would require an extra cleaning step. Although the waste stream does contain components that couldbe sold or reused, the limiting amount of information available about the waste stream, and the relativelysmall scale of waste production, caused for the assumption that reusing the waste stream would not turn outprofitable. Further research could investigate the process thermodynamics in order to optimize equipmentand utility estimations, limit the amount of assumptions required, and construct a more efficient design.

Finally, cost estimations were made in 2019 and based on values that could change in the course of time.Hemp fibres will keep growing in interest, cellulose markets are still expanding, and pre-treatment techniquesare being developed. This has a large influence on different prices should be considered while reviewing thisstudy. Moreover, development of other techniques could result in more efficient or cheaper alternatives tosteam explosion.

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6 Conclusion

During this study, hemp fibres and steam explosion were investigated thoroughly by means of an extensiveliterature review in order to design and evaluate a steam explosion process. Previous research by Hemmesindicated that steam explosion was most promising for treating hemp, and concluded that the textile andcomposite markets were of high interest. This research elaborated on using steam explosion to prepare hempfibres for textile and composite products. Information was gathered on the properties of hemp fibres, themarket requirements, and the steam explosion treatment technique. Although the design was based on therequirements of HempFlax, findings in this report could be valuable for start-up companies interested inpre-treatment of hemp. These findings are concluded in this section.

Looking at mechanical properties, hemp fibres prove to be suitable for textiles and composites, and, at thesame time, be a strong competitor to synthetic fibres. This is due to a lower density, creating advantages instorage and transportation. Hemp fibres compete with cotton fibres because of a more sustainable cultivation,requiring less water and pesticides.

The chemical composition of untreated hemp fibres varies greatly. This is due to differences in cultivationconditions, the age of the plants, and the harvest and separation techniques used prior to pre-treatment. Forthe designed process, the hemp fibre feed was assumed to be of a constant quality.

Steam explosion is a relatively easy process to set-up and control, and does not require sophisticated expensiveequipment. Although being simplistic, it can increase hemp fibre cellulose content by approximately 15%.The process of steam explosion can be performed continuously or in a batch reactor. Continuous steamexplosion is not yet investigated widely and no continuous reactors are used industrially at the moment.However, steam explosion batch reactors can be scaled up largely and are already used in various industrialapplications. Therefore, also keeping in mind the production capacity of HempFlax, a batch reactor waschosen for the proposed design.

The designed process was evaluated by estimating its costs and comparing processing costs with the textileand composite market price. Pre-treating hemp fibres for use in the textile industry proved to be highlyprofitable. Due to the efficiency, simplicity and low cost, implementation of steam explosion for the treatmentof hemp fibres is highly recommended.

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A HempFlax data sheet

HempFlax BV

Product Data Sheet

1 Productname Automobile Fiber 2 Discription Bark Mechanic, extracted from the uncut hemp stalk. The hemp for automobile fibres comes from EU certified Hemp 3 Properties Fibre length: not determined, varying between 10 mm and 500 mm Humidity: <12% Ingredients: Fiber > 98% , dust shives etc, <2% Retting en rettingdegree: dew retted, well retted Components: Cellulose: 66% Hemicellulose: 16% Pectine: 4% Fat and wax: 1% Minerals: 2% Humidty: 12% Aggregates: additives possible Origin: Netherland/Germany 4 Scope None-woven textile, pulp, yarn, upholstery, isolation

5 Packaging Bales: 100 cm / 50 cm / 50 cm Ca. 110 kg heavy

6 Storage Dry storage normal humidity

7 Removal Composting and burning

8 Notes We take the responsibility for the quality of our products. Our warranty is based on tests and experience. In our commodities and products are from natural origin this could affect the quality. The reason for this are: the weather, climate, soil. With the publication of this product date sheet all others lose there validity.

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B Dryer cost estimation graph

[Loh et al., 2002]

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C Boiler cost estimation graph

[Loh et al., 2002]

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