Elsevier

Energy

Volume 33, Issue 8, August 2008, Pages 1206-1223
Energy

Pre-treatment technologies, and their effect on international bioenergy supply chain logistics. Techno-economic evaluation of torrefaction, fast pyrolysis and pelletisation

https://doi.org/10.1016/j.energy.2008.03.007Get rights and content

Abstract

The pre-treatment step has a significant influence on the performance of bioenergy chains, especially on logistics. Torrefaction, pelletisation and pyrolysis technologies can convert biomass at modest scales into dense energy carriers that ease transportation and handling.

Torrefaction is a very promising technology due to its high process efficiency (94%) compared to pelletisation (84%) and pyrolysis (64%).1 When torrefaction is combined with pelletisation, the product (TOP2) energy content is as high as 20.4–22.7 GJ/ton. The primary energy requirement for TOP delivery from Latin America to Rotterdam harbour can be as low as 0.05 GJ/GJ, in contrast to 0.12 GJ/GJ for pellets and 0.08 GJ/GJHHV for pyrolysis oil. TOP can be delivered to Europe at over 74 €/ton (3.3 €/GJ) and electricity could be produced as cheap as 4.4 €cent/kWhe from an existing co-firing plant. Fisher Tropisch fuel costs 6 €/GJHHV for TOP, 7 €/GJ for conventional pellets and 9.5 €/GJHHV for pyrolysis oil. Consequently, fuel production from TOP and conventional pellets is comparable to the current gasoline production cost ranging from 3 to 7 €/GJHHV and diesel from 2 to 7 €/GJHHV, depending on the oil market.3 Thus, well designed supply chains make international trade of biomass feasible from energy efficiency and economic perspective.

Introduction

Sustained energy supply is an essential objective to achieve and depends on ensuring secure and reliable energy sources. However, the European Union (EU) import dependency is rising. Unless domestic energy becomes more competitive in the next 20–30 years around 70% of the EU's energy needs are expected to be met by imported products—some from regions threatened by insecurity [1]. On the other hand, fossil fuel consumption causes substantial environmental harm notably, climate change. Energy production and consumption account for 81.5% of the total green house gas (GHG) emissions in the EU-25 [2].

In addressing those threats, the EU is increasingly shifting towards policies favouring use of renewable energy sources. Currently biomass delivers around 4% of the EU's primary energy (Eurostat) and in order to reach the future targets set out by the EU, significant amounts of biomass will be required. The renewable energy target in the EU's overall mix is determined as 20% by 2020, which corresponds to 230–250 MtOE bioenergy depending on various assumptions [3].3 Furthermore as a substitute for transportation fuels, the EU set itself a minimum binding target of 10% biofuel use by 2020. Moreover, bioenergy contributes 22% of the primary energy supply in developing countries, and around 10% of global energy demand [4].

Since some countries have larger land areas used at lower densities compared to others, they may become net suppliers of renewable bioenergy. While biomass production costs in such countries may be relatively low, there will be additional logistic costs, energy uses and material losses [5]. However, several studies have given indications that international trade in biofuel could be economically feasible [6], [7], [8]. These studies, concerning long distance bio-energy transportation, analysed several cases to calculate biomass delivery and final energy production costs. Hamelinck developed a tool with which different bioenergy chains were analysed [5], [6]. This work clarified that densification prior to international transportation of biomass is crucial, as converting biomass into a densified intermediate can save transport and handling costs. In addition, it can improve the efficiency of the final conversion stage. Subsequently, pre-treatment is a key step in the total supply chain. Broadly, feedstock costs contribute around 20–65% of the total delivery cost whereas pre-treatment and transport contribute 20–25% and 25–40%, respectively, depending on the location of the biomass resources [5]. However, recent and potential future improvements of pre-treatment technologies and their subsequent impacts on the overall bioenergy chain have not been addressed in detail.

Currently, the state-of-the-art (SOTA) biomass-to-energy chains are mostly based on pelletisation. However, the pre-treatment technologies such as fast pyrolysis and torrefaction may improve the economics of the overall production chain. However, these technologies are still under development and their economic and technical performances are unclear. There are no normalised data sets available in literature and the available information mainly discusses the technology and the intermediate products, rather than their influence on the performances of the whole production chains. The main objective in this study is therefore to assess which pre-treatment method(s), at what point of the chain, with which conversion technology (ies) would give the optimal power and fuel (syngas) delivery costs for international biomass supply chains.

The study focuses on detailed techno-economic analysis of key pre-treatment technologies, namely torrefaction, pyrolysis and pelletisation and their respective impacts, in terms of costs and energy uses in various chains for biomass production and use.

Section snippets

Methodology and evaluation criteria

A technology review was performed to collect design data of pre-treatment technologies. Mass yields, energy yields and process efficiencies of each technology were evaluated, partly by building simple models to determine energy and mass balances.

The economic evaluation of the technologies was based on component level cost data, which were obtained from literature and personal communication with experts. Since the capacities of the components affect the specific cost of a plant, economies of

Torrefaction

Torrefaction is a thermal pre-treatment technology performed at atmospheric pressure in the absence of oxygen. Temperatures between 200 and 300 °C are used, which produces a solid uniform product with very low moisture content and a high calorific value compared to fresh biomass.

Even though torrefaction is in its infancy, several studies show that torrefaction increases the energy density, hydrophobic nature and grindability properties of biomass [9], [10], [11]. Torrefied biomass typically

Approach and methodology

There are several factors influencing the overall production costs when international bio-energy trade is considered. The location of the pre-treatment process is one important factor since it influences the scale of the subsequent processes which are capital-intensive. Moreover it influences the further transportation and storage options. In this study, five transfer points were considered, namely: local biomass production site, central gathering point, export and import terminals and a final

Discussion and conclusion

The main objective of this study was to identify the optimum biomass-to-energy chains by analysing the pre-treatment technologies (torrefaction, pyrolysis and pelletisation) each of which differ significantly in terms of their impacts on transportation, storage and conversion. The potential and future technical and economic performance of these technologies was analysed. The influences of intermediate products (pre-treated biomass) on transportation cost and energy use were evaluated. The

References (49)

  • Agterberg AE, Faaij APC. Bio-energy trade: possibilities and constraints on short and longer term. Report EWAB 9841,...
  • Bergman PCA, Boersma AR, Kiel JHA, Zwart RWH. Development of torrefaction for biomass co-firing in existing coal-fired...
  • A new process for torrefied wood manufacturing

    Gen Bioenergy

    (2000)
  • Prins MJ. Thermodynamic analysis of biomass gasification and torrefaction. Ph.D. thesis, Eindhoven Technical...
  • Girard P, Shah N. Developments on torrefied wood—an alternative to charcoal for reducing deforestation. FAO paper,...
  • Lipinsky ES, Arcate JR, Reed TB. Enhanced wood fuels via torrefaction. Fuel chemistry division preprints,...
  • Reed T, Bryant B. Densified biomass a new form of solid fuel. Solar Energy Research Institute, US Department of Energy...
  • E.G. Koukios

    Progress in thermochemical, solid-state refining of biofuels—from research to commercialization

    Adv Thermochem Biomass Convers

    (2003)
  • Bergman PCA. Combined torrefaction and pelletisation—the TOP process. ECN report, The Netherlands, July...
  • S. Yaman

    Pyrolysis of biomass to produce fuels and chemical feedstock

    (2003)
  • Bridgwater AV, Evans GD. An assessment of thermochemical conversion systems for processing biomass and refuse. Aston...
  • Bridgwater AV, Toft AJ, Brammer JG. A techno-economic comparison of power production by biomass fast pyrolysis with...
  • Diebold JP, Bridgwater AV. Overview of fast pyrolysis of biomass for the production of liquid fuels, fast pyrolysis of...
  • DynaMotive Energy Systems Corporation. BioTherm TM a system for continuous quality, fast pyrolysis biooil. In: 4th...
  • Cited by (490)

    View all citing articles on Scopus
    1

    Process efficiency includes sizing and drying of biomass.

    2

    TOP: torrefied and pelletised biomass.

    View full text