Combined slag flow model for entrained flow gasificationby Dapeng Bi, Qingliang Guan, Weiwei Xuan, Jiansheng Zhang

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Combined slag flow mode

Weiw

Engineer refractory wall gasifier based on thermal resistance. ation of sla sifier, the yer and me wall. For the refractory gasifier, thermal resistance of the refractory lining and environment con were the major parts.  2015 Elsevier Ltd. All rights re ⇑ Corresponding author. Tel.: +86 10 62795930; fax: +86 10 62781743.

E-mail address: zhang-jsh@tsinghua.edu.cn (J. Zhang).

Fuel 150 (2015) 565–572

Contents lists available at ScienceDirect

Fue jourthermal corrosion. The larger particle was beneficial to the capture efficiency and form while the smaller one favors high carbon conversion. For the membrane wall ga resistance of the solid slag layer contributed to the protection of the silicon carbide lahttp://dx.doi.org/10.1016/j.fuel.2015.02.028 0016-2361/ 2015 Elsevier Ltd. All rights reserved.g layer, thermal mbrane vection served.Keywords:

Gasification

Slag model

Particle behavior

Sensitivity

Thermal resistance liquid slag layers as well as the temperature distribution across the slag layer. Further study investigated the influence of particle behavior on slagging in the gasifier. In addition, a comparison was made between the membrane wall gasifier and the refractory wall gasifier. The results indicated that temperature of critical viscosity and the thermal conductivity of the slag were crucial factors in determining the accuracy of the combined model. The slag of the membrane wall consisted of both a solid and liquid slag layer. The internal surface temperature of the steel was lower than 540 K, which decreases the occurrence ofa r t i c l e i n f o

Article history:

Received 23 October 2014

Received in revised form 6 February 2015

Accepted 8 February 2015

Available online 2 March 2015was developed to describe the slag characteristics and gasification process in entrained flow gasifier. A criterion for particle capture was used to evaluate the interaction of particles colliding with the wall.

Two kinds of gasifiers were simulated using the developed model: the membrane wall gasifier and the refractory wall gasifier. The model was proved reliable by comparing the simulation with industrial results. Sensitivity of the model was analyzed. The model predicted the local thickness of the solid andTg a b s t r a c t

A slag flow and heat transfer model coupled with a particle capture sub-model and 3-D gasifier model A comparison was made between the membrane wall gasifier and theDapeng Bi, Qingliang Guan,

Key Laboratory for Thermal Science and Power h i g h l i g h t s  A combined slag model was developed to describe the slag characteristics and gasification process in entrained flow gasifier.  The influence of particle behavior on slagging is demonstrated.l for entrained flow gasification ei Xuan, Jiansheng Zhang ⇑ ing of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China g r a p h i c a l a b s t r a c t

Objective of the simulation and structure of the slag model. nal homepage: www.elsevier .com/locate / fuell 501. Introduction

Gasification is a technological process that is conventionally employed to convert the solid feedstock, such as coal, petcoke and biomass, into clean syngas consisting primarily of hydrogen and carbon monoxide [1]. Among the various gasification technologies, entrained flow coal gasification is mostly widely used in the production of numerous chemicals and shows favorable prospects on the Integrated Gasification Combined Cycle (IGCC).

Nomenclature

Symbols

Ai area (m2)

Cp specific heat (kJ kg1 K1)

FT flowing temperature (K)

G capture probability (%) min particle feeding rate (kg m2 s1)

Pw pressure of cooling water (K) qin heat flux into the slag (w) qout heat flux out the slag (w) qm heat flux out the SiC (w) qmo heat flux out the membrane wall (w)

Tcv temperature of critical viscosity (K)

Tf outlet temperature of cooling water (K)

Tg temperature of gas (K)

Tin particle temperature (K)

Tl mean temperature of the liquid slag (K)

To surface temperature of the slag (K)

Tm temperature of the membrane wall (K)

Ts temperature of the slag (K)

Tw inlet temperature of cooling water (K) u velocity of the gas (m s1) 566 D. Bi et al. / Fuel 1Generally, entrained flow gasification is classified by the lining type of the gasifier chamber. Two types of lining (refractory brick wall or water-cooling membrane wall) are used in the gasifier chamber to protect the steel walls. During the operation of the gasifier, the inorganic compounds in the coal form an incombustible ash residue. In an entrained coal gasifier, most of the ash is deposited on the inner wall of the chamber and then flows down as molten slag. The remaining ash is entrained as fly-ash by the syngas and enters the scrubbing system. In order to avoid any obstruction, the fusibility and flow properties of the ash and the temperature inside the gasifier must enable the unobstructed removal of the slag through the tap hole. Therefore, understanding the behavior of the slag is necessary and critical for further improvements to the reliability and availability of entrained flow gasifier. Due to the difficulties associated with real-time observations, constructing a comprehensive slag model is an effective way to investigate the slag behavior in the gasifier.

Severalmodels have been proposed to predict slag formation and its flow characteristics in an entrained flow gasifier. Chen et al. [2] studied the slag behavior in an oxy-coal combustor by introducing the effect of wall burning and the Weber number. Bockelie et al. [3] investigated the slag thickness of the GE and MHI gasifier with a new numerical scheme. Yang et al. [4] discussed an oxygen-staged slagging gasifier with a reactor networkmodel. The slagmodel used inOtaka et al. [5] provided an evaluationmethod for themolten-slag from coal gasifier without taking the particle effects into account.

Essentially, modeling the slag behavior of the entrained gasifier primarily involves three aspects: 3-dimensional CFD simulation of the gasifier, the slag flow and heat transfer model, and the particle capture model. A lot of researchers have developed 3-D gasifier modelsand showed their reliability [6–9]. Seggiani [10] proposed a onedimensional time-varying slag flow and transfer model that has been widely accepted in previous studies [11,12]. However, for the particle capture model, various opinions exist as to the most viable model. For example, Ni et al. [13] simplified the collision of particles with the wall as liquid–solid wall interactions and introduced the maximal rebounded energy, Ee⁄, to classify the particles. But the collision of particles to the wall is more like solid–solid interaction.