Elsevier

Biosystems Engineering

Volume 200, December 2020, Pages 284-297
Biosystems Engineering

Research Paper
Rheology of fibre suspension flows in the pipeline hydro-transport of biomass feedstock

https://doi.org/10.1016/j.biosystemseng.2020.10.009Get rights and content

Highlights

  • Rheological characteristics of untreated wood chip biomass slurries were studied.

  • Biomass slurry samples were made off a closed-circuit pipeline facility.

  • Rotational viscometer with vane-in-cup geometry was used over range of temperatures.

  • Corresponding rheological parameters were approximated using well-known models.

  • A pressure drop-based method proposed to approximate viscosity of slurry flows.

In the hydro-transport of biomass feedstock by pipeline to bio-refineries, the rheology of the biomass slurry directly impacts the specifications and, therefore the cost of pipeline components. In this study, the rheological characteristics of untreated fine wood chip slurries across a broad range of slurry temperatures (5–15 °C) and solids concentrations (3–15 wt% dry-matter) were experimentally studied. Slurry samples were pumped in a closed-circuit pipeline facility where slurry flow longitudinal pressure drops were simultaneously measured. The rheological characteristics of the samples were then measured using a rotational viscometer with a vane-in-cup geometry. At low slurry concentrations (˂6 wt% dry-matter), the biomass slurry exhibited Newtonian behaviour; however, non-Newtonian (shear-thinning) behaviour was seen at higher slurry concentrations. In order to approximate the corresponding rheological parameters, different well-known non-Newtonian viscosity models (power-law, Bingham, Casson, and Herschel-Bulkley) were applied to experimental data. In addition, a new approach for approximating the apparent viscosity of biomass slurries using longitudinal pressure drop measurements was introduced and validated. The method has not been previously applied to non-Newtonian biomass slurries under turbulent flow regimes.

Introduction

Fossil fuel-based generating facilities continue to be the primary supplier of energy worldwide. However, adverse environmental effects, as well as issues associated with the secure supply of fossil fuels, have increased the interest in renewable sources of energy (Vakulchuk, Overland, & Scholten, 2020). Among those, biomass often holds a top rank primarily because of its carbon neutrality over its life cycle as well as its utility as a feedstock for direct conversion to fuels and chemicals (Pootakham & Kumar, 2010). However, ‘as-received’ biomass has low bulk and low energy density. As a result, the costs associated with transporting biomass by vehicle can contribute 12–80% to the delivered cost (Vaezi, Nimana, & Kumar, 2015). This is the main barrier towards enabling biomass-based facilities to compete on grounds of capacity and scale with fossil-fuel based plants (Kumar, Cameron, Flynn, 2004, 2005a, 2005b).

Truck delivery is the most common mode of biomass transport. However, there are issues caused by the number and frequency of large capacity trucks (Kumar, Cameron, & Flynn, 2003; Kumar et al., 2005a). Using alternative modes of delivery of biomass could be socially, environmentally, and economically more beneficial (Vaezi, Katta, & Kumar, 2014). Pipeline hydro-transport (the transportation of solids in a liquid carrier stream) is a reliable and economic mode of solid transport at large scales and over long distances and it has recently attracted attention in the bioenergy sector (Kumar & Sokhansanj, 2007; Morey, Kaliyan, Schmidt, & Tiffany, 2009; Vaezi et al., 2015). Research studies on the pipeline hydro-transport of biomass feedstock has demonstrated the overall cost of delivery is less than by truck beyond certain scales and distances (Vaezi et al., 2015). Moreover, Vaezi et al. in various studies (Vaezi et al., 2014; Vaezi & Kumar 2014a, 2014b; Vaezi, Verma, & Kumar, 2018) demonstrated the mechanical and chemical feasibility of the pipeline in transporting agricultural and forest residue biomass.

In the design and operation of pipelines to hydro-transport energy commodities, the rheological and transport properties (density, apparent viscosity, concentration, temperature and velocity) of the solid–liquid flow mixture (slurry) directly impact the size and cost of pipeline components (e.g., pipes, pumps, instrumentation) (Abulnaga, 2002; Wilson, Addie, Sellgren, & Clift, 2006). It is therefore critical to determine the apparent viscosity (for non-Newtonian fluids the ratio of shear stress to shear rate) before the pipeline to hydro-transport solid materials can be specified (Chhabra & Richardson, 2011; Chin, 2001).

Several studies have been conducted to evaluate the effects of biomass slurry concentrations as well as biomass fibre characteristics (size and geometry) on slurry apparent viscosity in biofuel production applications (Ghosh, Holwerda, Worthen, Lynd, & Epps, 2018; Pimenova & Hanley, 2003; Pimenova & Hanley, 2004; Rosgaard, Andric, Dam-Johansen, Pedersen, & Meyer, 2007; Viamajala, McMillan, Schell, & Elander, 2009). The rheological properties of pre-treated corn (maize) stover (plant residue left after removal of kernels) suspensions were experimentally studied by Pimenova and Hanley (2004) over a range of concentrations from 5 to 30 wt% dry-matter. The yield stress of acid-hydrolysed corn stover suspensions was approximated using three different non-Newtonian viscosity models – Bingham (Bingham, 1917), Casson (Casson, 1959), and Herschel-Bulkley (Herschel-Bulkley, 1926). The results indicated that the Herschel-Bulkley model agreed better than the others for the experimental measurements.

The rheology of two different batches of dilute-acid pre-treated corn stover was also studied by Knutsen and Liberatore (2009). Their study showed that pre-treated corn stover suspensions at concentrations of 5–17 wt% dry-matter behave as soft solids and exhibit elastic deformation at low strains prior to yielding. Moreover, strong shear thinning behaviour was reported even at solid concentrations as low as 5 wt% dry-matter.

Viamajala et al. (2009) investigated the rheological characteristics of treated and untreated corn stover using plate–plate viscosity measurement geometry over a range of concentrations from 10 to 40 wt% dry-matter. They reported the behaviour of both treated and untreated mixtures to be shear thinning and the Casson model was used to describe it well. They found the viscosity and yield stress of treated corn stover slurries to be less than those of untreated slurries.

Using a torque rheometry method, Ehrhardt et al. (2010) investigated the rheological properties of acid hydrolysed corn stover slurries at high concentrations (20–30 wt% dry-matter) in batches. The results indicated that acid hydrolysed corn stover slurries behaved as Bingham plastic fluids in which yield stress decreased with increasing acid concentration, rheometer temperature, and hydrolysis reaction temperature but increased with increasing solids concentration. These results demonstrated that the Bingham model was capable of describing the rheological behaviour of acid hydrolysed corn stover slurries.

In other research, Klingenberg et al. (2017) designed and fabricated a rheometer in order to measure the rheological properties of lignocellulosic biomass slurries at high temperatures and solids contents (>25 wt% dry-matter). The results confirmed the shear-thinning behaviour occurred with chopped and milled corn stover-water mixtures and they also demonstrated an inverse relationship between apparent viscosity and temperature.

Research has been carried out on the rheological characteristics of biomass slurries where the apparent viscosity was either measured in a batch using a torque rheometry method (Klingenberg et al., 2017; Novotna, Landfeld, Kyhos, Houska, & Strohalm, 2001; Pimenova & Hanley, 2003, 2004) or where samples were directly made from the batch and tested in rheometers (Bhattacharya & Bhat, 1997; Ehrhardt et al., 2010; Grigelmo-Miguel, Ibarz-Ribas, Martı́n-Belloso, 1999; Knutsen & Liberatore, 2009; Viamajala et al., 2009). In the pipeline hydro-transport of biomass feedstock, however, slurries are pumped over a range of velocities, pressures, and temperatures (depending on the feedstock type, pipe material, design and topography of the pipeline, and the climate) these factors can change the rheological characteristics of the biomass slurries. Hence, it appears that if the sample under test is made from a batch and not in situ, i.e., right drawn off from the pipeline, it will not properly represent the rheological specifications of the slurry that is being pumped through a pipeline. Therefore, in this research, an experimental facility comprised of a 25 m long and 50 mm diameter closed-circuit pipeline was fabricated, the biomass slurry was prepared and circulated, longitudinal pressure drops were measured, and samples were made directly from the pipeline (Vaezi et al. 2014, 2018; Vaezi & Kumar, 2014b). In addition, while all previous research studies have investigated the rheological characteristics of agricultural residue biomass slurries, the present research focused on the slurries made from forest residue biomass, e.g., wood chips which is commonly used in biofuel industries (Ragauskas et al., 2006; Sahoo, Bilek, Bergman, & Mani, 2018) and paper production (Duffy, 2006; Pécora, Ruiz, & Soriano, 2007).

In this study, the rheology of untreated wood chips slurries, sampled across a broad range of slurry temperatures and solids concentrations from 3 to 15 wt% dry-matter was experimentally studied. In addition, to evaluate the rheological behaviour of biomass slurries (e.g., Newtonian, shear-thinning, etc.) and to approximate the corresponding rheological parameters (e.g., yield stress, consistency index, fluid behaviour index), three different well-known viscosity models – Bingham (Bingham, 1917), Casson (Casson, 1959) and Herschel-Bulkley (Herschel & Bulkley, 1926) were applied to the experimental data in order to ascertain the best representative model. Finally, a novel approach for approximating the apparent viscosity of biomass slurries based on longitudinal pressure drop data was introduced and validated. This technique makes it possible to estimate the in situ apparent viscosity of the slurries through pipelines at large Reynolds numbers.

Section snippets

Material preparation

The wood chips (aspen and poplar) were supplied by Weyerhaeuser Company Ltd. (Pembina Timberland, Alberta, Canada). Large chips were hammer-milled using a Gisiger–Technik 2301 hammermill (GT Zesor AG, Messen, Switzerland) with a 3 mm round hole screen and refined into fine chips. The size distribution and shape analysis were performed using a Camsizer P4 (Microtrac (2014) Retsch GmbH, Haan, Duesseldorf, Germany). The measurements indicated a number of characteristics such as cumulative

Experimental results

To evaluate the rheological behaviour of the biomass slurry, the change in shear stress with respect to shear rate was experimentally measured over a wide range of concentrations (3, 5, 6, 8, 10, 11, 13 and 15 wt% dry-matter). At low slurry concentrations of 3 and 5 wt% dry-matter, the results showed a linear relation between shear stress and shear rate, i.e., the results demonstrated Newtonian behaviour of the slurry (Fig. 8). However, experimental results showed a nonlinear relation between

Conclusions

In this research, the rheological behaviour of untreated fine wood chip biomass slurries at various slurry concentrations and temperatures was investigated. Samples were taken from a closed-circuit pipeline facility, and the apparent viscosity of the slurries was investigated using a rotational viscometer with vane-in-cup geometry as well as from slurry pressure drop data. The results indicate Newtonian, power-law, and Bingham plastic rheological behaviours at different slurry concentrations.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors are grateful to the National Sciences and Engineering Research Council of Canada (NSERC), Canada, University of Alberta Future Energy Systems research initiative, Canada and the Division of Research and Innovation Partnerships (RIPs) at Northern Illinois University, USA for their financial support. They also thank Astrid Blodgett for editing the paper. All the results, justifications, and conclusions are solely the authors' and have not been endorsed by any other party.

References (65)

  • T. Pootakham et al.

    A comparison of pipeline versus truck transport of bio-oil

    Bioresource Technology

    (2010)
  • G. Roberts et al.

    Modelling the flow behaviour of very shear-thinning liquids

    Chemical Engineering Science

    (2001)
  • J. Simuang et al.

    Effects of fat content and temperature on the apparent viscosity of coconut milk

    Journal of Food Engineering

    (2004)
  • H. Toǧrul et al.

    Mathematical model for prediction of apparent viscosity of molasses

    Journal of Food Engineering

    (2004)
  • M. Vaezi et al.

    Investigation into the mechanisms of pipeline transport of slurries of wheat straw and corn stover to supply a bio-refinery

    Biosystems Engineering

    (2014)
  • M. Vaezi et al.

    Development of correlations for the flow of agricultural residues as slurries in pipes for Bio-refining

    Biosystems Engineering

    (2014)
  • M. Vaezi et al.

    The flow of wheat straw suspensions in an open-impeller centrifugal pump

    Biomass and Bioenergy

    (2014)
  • M. Vaezi et al.

    Application of high-frequency impedancemetry approach in measuring the deposition velocities of biomass and sand slurry flows in pipelines

    Chemical Engineering Research and Design

    (2018)
  • R. Vakulchuk et al.

    Renewable energy and geopolitics: A review

    Renewable and Sustainable Energy Reviews

    (2020)
  • S. Viamajala et al.

    Rheology of corn stover slurries at high solids concentrations–effects of saccharification and particle size

    Bioresource Technology

    (2009)
  • B.E. Abulnaga

    Slurry systems handbook

    (2002)
  • American Society of Agricultural and Biological Engineers

    Method of determining and expressing particle size of chopped forage materials

    (2007)
  • American Society of Agricultural and Biological Engineers

    Moisture measurement for forages

    (2008)
  • American Society for Testing and Materials

    Standard test method for density, relative density, and absorption of coarse aggregate

    (2012)
  • H. Barnes et al.

    The vane-in-cup as a novel rheometer geometry for shear thinning and thixotropic materials

    Journal of Rheology

    (1990)
  • E.C. Bingham

    An investigation of the laws of plastic flow

    (1917)
  • N. Casson

    Rheology of disperse systems

    (1959)
  • D. Cheng

    Viscosity-concentration equations and flow curves for suspensions

    Chemistry & Industry

    (1980)
  • R.P. Chhabra et al.

    Non-Newtonian flow and applied rheology: Engineering applications

    (2011)
  • W.C. Chin

    Computational rheology for pipeline and annular flow: Non-Newtonian flow modeling for drilling and production, and flow assurance methods in subsea pipeline design

    (2001)
  • R. Darby et al.

    How to predict the friction factor for flow of Bingham plastics

    Chemical Engineering

    (1981)
  • M. Djalili-Moghaddam et al.

    Fibre suspension rheology: Effect of concentration, aspect ratio and fibre size

    Rheologica Acta

    (2006)
  • Cited by (4)

    • Influence of the adopted rheological model of plant suspension on the predicted resistance of its flow in the pipe

      2022, Powder Technology
      Citation Excerpt :

      This offers an important contribution to the area (e.g. for bio-composite manufacturing techniques), but has little to do with conveying the slurry in the pipeline. Another example is the flow of fruit pulp (Leverrier et al. [22]) or the hydrotransport of wood chips (Faghani et al. [23]). However, there is little doubt here that the concentrated two-phase substance is a non-Newtonian fluid.

    • Impeller selection for mixing high-solids lignocellulosic biomass in stirred tank bioreactor for ethanol production

      2022, Bioresource Technology Reports
      Citation Excerpt :

      Also, the rheology and biomass properties change amid the enzymatic hydrolysis stage of SSF. Untreated or pretreated lignocellulosic biomass slurries exhibit shear-thinning behaviour with considerable yield stress (Faghani et al., 2020; Karungi et al., 2021). At a high-solids loading of approximately 20% (w/w), a pretreated corn stover becomes a tick paste that can undergo irreversible plastic deformation (Stickel et al., 2009).

    • Developing a standard platform to predict the drag coefficient of irregular shape particles

      2022, Powder Technology
      Citation Excerpt :

      Solid-fluid interactions are commonly observed in natural transport phenomena and industrial applications. A few examples include sedimentation in rivers [1], volcanic ash dissipation in the atmosphere [2], fixed and fluidized bed reactors [3], and pipeline hydro-transportation of coal [4], limestone [5], and biomass feedstock [6–10]. In all these examples, particle and fluid motions affect each other through drag, shear lift, virtual mass, and other force interactions [11].

    View full text