A Brief Review of Viscosity Models for Slag in Coal Gasification

Massoudi, Mehrdad; Wang, Ping

doi:10.2172/1036735

Cited by 13 publications

(8 citation statements)

References 109 publications

(138 reference statements)

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“…The viscosity of a non-Newtonian fluid is a function of shear rate due to the interactions between solid particles suspended in the liquid phase; moreover, the shear rate dependence may itself vary as a function of time. The critical viscosity temperature (T cv ) is defined as the temperature at which solid phase formation causes a transition from Newtonian to non-Newtonian flow in molten coal ash slags [34]. Johnson reviewed viscosity data for slagging gasifier operations, and proposed a Bingham plastic model to describe the non-Newtonian slag flow [35].…”

Section: Critical Viscosity Temperaturementioning

confidence: 99%

Correlation between the critical viscosity and ash fusion temperatures of coal gasifier ashes

Hsieh

Kwong

Bennett

2016

Fuel Processing Technology

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Coal gasification yields synthesis gas, an important intermediate in chemical manufacturing. It is also vital to the production of liquid fuels through the Fischer-Tropsch process and electricity in Integrated Gasification Combined Cycle power generation. Minerals naturally present in coal become molten in entrained-flow slagging gasifiers. Molten coal ash slag penetrates and dissolves refractory bricks, leading to costly plant shutdowns. The extent of coal ash slag penetration and refractory brick dissolution depends on the slag viscosity, the gasification temperature, and the composition of slag and bricks. We measured the viscosity of several synthetic coal ash slags with a high-temperature rotary viscometer and their ash fusion temperatures through optical image analysis. All measurements were made in a carbon monoxide-carbon dioxide reducing atmosphere that approximates coal gasification conditions. Empirical correlation models based on ash fusion temperatures were used to calculate critical viscosity temperatures based on the coal ash compositions. These values were then compared with those obtained from thermodynamic phase-transition models. An understanding of slag viscosity as a function of ash composition is important to reducing refractory wear in slagging coal gasifiers, which would help to reduce the cost and environmental impact of coal for chemical and electricity production.Published by Elsevier B.V.

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Section: Critical Viscosity Temperaturementioning

confidence: 99%

Correlation between the critical viscosity and ash fusion temperatures of coal gasifier ashes

Hsieh

Kwong

Bennett

2016

Fuel Processing Technology

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“…The rheological properties of molten coal ash slag with certain particle concentrations, with the exception of viscosity, also includes other characteristics, such as flow pattern, shear thinning, and eventually the onset of yield stress (i.e., minimum shear stress that initiates viscous flow) . Understanding the complexities of the rheology of molten coal ash slag, including ash deposition behaviors, corrosion on heat exchanger tubes, slag formation, and tapping from furnace, is the key to determining and modeling the slagging processes .…”

Section: Introductionmentioning

confidence: 99%

Rheological evolution and crystallization response of molten coal ash slag at high temperatures

et al. 2013

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Ash-related problems are often the main reason for entrained-flow gasifiers and boilers unscheduled shut downs. Thus, understanding the high-temperature physical properties of molten coal ash slag may enable an accurate description of the condition of ash deposition in the gasifier and boiler. The evolution of the time dependence of rheological behaviors, including the viscosity and yield stress of the molten coal ash slag containing 0-35.51 vol % crystals at decreasing temperatures (1400-1280 C) and within 1.05 3 10 5 s, were investigated. Non-Newtonian behaviors, including shear thinning, become obvious with an increasing crystal contents. The trends in the change of crystal nucleation rate in molten coal ash slag are similar with those of the growth rate. Finally, the experimental results and the crystal-size distribution method are used to develop a semiempirical parameterization that describes the complex non-Newtonian rheology of crystal-bearing molten coal ash slag.

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“…Viscosity is strongly dependent on the temperature and chemical compositions of ash. For a more detailed discussion of the constitutive modeling related to the rheological studies of slag see Massoudi and Wang [62]. Figure 5 shows a simplified relationship between ash fluid properties and chemical composition [20] Slag viscosity could be measured using a high-temperature rotational viscometer/rheometer, or it could be estimated from the composition of the ash in the gasifier feed stream.…”

Section: Slag Viscositymentioning

confidence: 99%

Slag Behavior in Gasifiers. Part I: Influence of Coal Properties and Gasification Conditions

2013

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Abstract:In the entrained-flow gasifiers used in integrated gasification combined cycle (IGCC) plants, the majority of mineral matter transforms to liquid slag on the wall of the gasifier and flows out the bottom. However, a small fraction of the mineral matter is entrained (as fly ash) with the raw syngas out of the gasifier to downstream processing. This molten/sticky fly ash could cause fouling of the syngas cooler. To improve gasification availability through better design and operation of the gasification process, a better understanding of slag behavior and the characteristics of the slagging process is needed. Char/ash properties, gas compositions in the gasifier, the gasifier wall structure, fluid dynamics, and plant operating conditions (mainly temperature and oxygen/carbon ratio) all affect slagging behavior. Because coal has varying ash content and composition, different operating conditions are required to maintain the slag flow and limit problems downstream. In Part I, we review the main types and the operating conditions of entrained-flow gasifiers and coal properties used in IGCC plants; we identify and discuss the key coal ash properties and the operating conditions impacting slag behavior; finally, we summarize the coal quality criteria and the operating conditions in entrained-flow gasifiers. In Part II, we discuss the constitutive modeling related to the rheological studies of slag flow.

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A Brief Review of Viscosity Models for Slag in Coal Gasification

Cited by 13 publications

References 109 publications

Correlation between the critical viscosity and ash fusion temperatures of coal gasifier ashes

Correlation between the critical viscosity and ash fusion temperatures of coal gasifier ashes

Rheological evolution and crystallization response of molten coal ash slag at high temperatures

Slag Behavior in Gasifiers. Part I: Influence of Coal Properties and Gasification Conditions

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