Elsevier

Fuel

Volume 141, 1 February 2015, Pages 214-221
Fuel

Rheological properties and stability of lignite washery tailing suspensions

https://doi.org/10.1016/j.fuel.2014.10.067Get rights and content

Highlights

  • Rheological properties and stability of LWTS were studied.

  • LWTS has good stability and is suitable for long-term storage and transportation.

  • Rheological properties were studied by rotational viscometer and pipeline system.

  • The two rheological methods were compared and a rheological model was proposed.

  • Dispersant NDF has no effect on stability but improves the rheological properties.

Abstract

The rheological properties and stability of lignite washery tailing suspensions (LWTS) were studied as a special type of coal water slurry (CWS). The properties of LWTS in these aspects are all shown to meet the requirement of a CWS. Two test methods, i.e., a rotational viscometer and a pipeline test system, were used to study the rheological properties of the LWTS and to distinguish between theory and practice. Furthermore, a rheological model of LWTS transfer in the pipeline test system was proposed and proved to be suitable and useful in designing commercial pipeline systems. Moreover, the influence of an anionic dispersant NDF (a co-polymer of methylene naphthalene sulfonate, styrene sulfonate and maleate) on the stability and rheological properties of LWTS was studied. The dispersant NDF proved to have no effect on the stability of the LWTS, while it significantly improved the rheological properties of the LWTS.

Introduction

The lignite washery tailing (LWT) used in this study is a solid waste obtained from a power plant in Indonesia. Lignite from South Sumatra was first dried in a steam tube rotary dryer and subsequently combusted at the power plant. Pulverized lignite fines formed during drying were collected by wet scrubbing, and thus, a wastewater containing powdered lignite was produced. The LWT proper were obtained from this wastewater through precipitation (output of approximately 10–15 t/h). This LWT flow represents a great threat to the environment if it is disposed of incorrectly. However, the LWT is also hard to utilize, with its high water content, low calorific value and difficulties in transportation. Therefore, the disposal of LWTs is of great concern.

Coal water slurry (CWS) in China is commonly used as in clean energy applications. Considering its fine particle and high water contents, LWT is suitable for use as a CWS. Therefore, in this article, suspensions of LWTs (LWTS) were prepared for study as a CWS. Until now, the feedstock for preparing slurry has been widened from traditional bituminous coal to include biomass [1], [2], [3], [4], petroleum coke [5], [6], [7] and lignite [7], [8], [9], [10], [11]. However, no research has been reported until now on the use of LWTs as a CWS. The physicochemical properties of LWTs are different from those of common coal washery tailings: it has a volatile matter content higher than common coal washery tailings, which may be because it derives from lignite. Therefore, it is necessary to study the characteristics of LWTs in all respects to evaluate if LWTs are suitable for use as a CWS. The rheological properties are always the most important parameters of a CWS, and in this article, the rheological properties of the LWTS were first studied.

Researchers from all over the world, e.g., Boylu, Atesok and Dincer from Istanbul Technical University as well as Goudoulas et al. from Aristotle University of Thessaloniki, have extensively studied the rheological properties of CWS. The first group [12], [13], [14], [15], [16], [17] considered the effect of the addition of various chemicals on the viscosity and stability of a CWS. Goudoulas et al. [8], [10], [18] reviewed the rheological properties of lignite–water slurries as well as the solid-loading effects. Moreover, He et al. [19] summarized the methods used for studying slurry rheology, the empirical equations modeling rheological behavior. All of these studies indicated that the slurry rheology models need to be studied further and that a more fundamental approach is desirable to develop models that can be applied to the design of commercial units.

In this study, the stability and rheological properties of LWTS were studied to determine if LWTs are suitable for use as a CWS. Two test methods, i.e., a rotational viscometer and a pipeline test system, were used to study the rheological properties of the LWTS and to distinguish between theory and practice. A fundamental rheological model suitable for the LWTS that could be useful in designing a commercial LWTS reuse system for energy recovery and environment protection was proposed. In addition, the effects of dispersant NDF on the stability and rheological properties of the LWTS were studied.

Section snippets

Materials

The lignite washery tailings were collected from a power plant in Indonesia. The proximate and ultimate analysis results of the LWTs are presented in Table 1. The particle size distribution of the LWTs (Fig. 1) was measured by a Malvern MasterSizer 2000. Most particles were found to be between 1 and 100 μm, in accordance with the usual particle size requirements for a CWS. Therefore, the LWTS is suitable for further processing as a type of CWS.

An anionic dispersant NDF was selected for use in

Stability and apparent viscosity

The stability and apparent viscosity of the LWTS were measured based on the method described in Sections 2.2.1 Measuring stability, 2.2.2.1 Rotational viscometer, respectively. The apparent viscosity was defined as the average of the six values of the apparent viscosity at a 100 s−1 shear rate. The SWsta and apparent viscosity data of the LWTS with various NDF dosages under different solid concentrations are presented in Table 2. It can be observed that the stability and apparent viscosity of

Conclusions

The stability and apparent viscosity of LWTS were studied. The stability and apparent viscosity of LWTS increase with increasing solid concentration. The properties of LWTS in these two aspects all meet the requirements of a CWS.

An anionic dispersant NDF was used to study the influence of dispersant on the stability and rheological properties of the LWTS. We found that this dispersant has no effect on the stability of the LWTS, but it significantly improves the rheological properties of the

Acknowledgments

Financial supports are acknowledged from: the National Basic Research Program of China (Grant 2011CB201500), the National High Technology Research and Development Program (863 Program) of China (Grant 2012AA063505), the Special Fund for National Environmental Protection Public Welfare Program (Grant 201209023-4) and the Program of Introducing Talents of Discipline to University (Grant B08026). The authors want to thank Prof. Dr. Alfons Buekens from our Institute (ZJU) for improving the whole

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