Research

871 KiB

Open AccessArticle

Conditional Methods in Modeling CO₂ Capture from Coal Syngas

by Dmitry N. Saulov, Shuhei Watanabe, Junjun Yin, Dimitri A. Klimenko, Kamel Hooman, Bo Feng, Matthew J. Cleary and Alexander Y. Klimenko

Energies 2014, 7(4), 1899-1916; https://doi.org/10.3390/en7041899 - 27 Mar 2014

Cited by 1 | Viewed by 4880

Abstract

Gasification of coal or biomass with in-situ CO₂ capture is an emerging technology aiming to address the problem of climate change. Development of a CO₂ sorbent with desirable properties and understanding the behavior of such a material in carbonation/calcination reactions is [...] Read more.

Gasification of coal or biomass with in-situ CO₂ capture is an emerging technology aiming to address the problem of climate change. Development of a CO₂ sorbent with desirable properties and understanding the behavior of such a material in carbonation/calcination reactions is an important part of developing the technology. In this paper, we report experimental results describing the carbonation behavior of three synthetic CaO-based sorbents. We also present a physically-based model of the reactive transport processes in sorbent particles, which have complicated pore structures. This modeling is based on the conditional approach (i.e., conditional moment closure (CMC)), which has proven to be successful in modeling reactive transport phenomena in porous media. The model predictions are in good agreement with the experimental data. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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1311 KiB

Open AccessArticle

Accidental Continuous Releases from Coal Processing in Semi-Confined Environment

by Emilio Palazzi, Fabio Currò and Bruno Fabiano

Energies 2013, 6(10), 5003-5022; https://doi.org/10.3390/en6105003 - 27 Sep 2013

Cited by 33 | Viewed by 5408 | Correction

Abstract

Notwithstanding the enforcement of ATEX EU Directives (94/9/EC of 23 March 1994) and safety management system application, explosions in the coal sector still claim lives and cause huge economic losses. Even a consolidated activity like coke dry distillation allows the opportunity of preventing [...] Read more.

Notwithstanding the enforcement of ATEX EU Directives (94/9/EC of 23 March 1994) and safety management system application, explosions in the coal sector still claim lives and cause huge economic losses. Even a consolidated activity like coke dry distillation allows the opportunity of preventing explosion risk connected to fugitive emissions of coke oven gas. Considering accidental releases under semi-confined conditions, a simplified mathematical approach to the maximum allowed gaseous build-up is developed on the basis of the intrinsic hazards of the released compound. The results will help identifying and assessing low rate release consequences therefore to set-up appropriate prevention and control measures. The developed methodology was tested at the real-scale and validated by numerical computational fluid dynamics (CFD) simulations showing the effectiveness of the methodology to evaluate and mitigate the risk connected to confined hazardous releases. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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381 KiB

Open AccessArticle

A New Agro/Forestry Residues Co-Firing Model in a Large Pulverized Coal Furnace: Technical and Economic Assessments

by Weigang Xu, Yanqing Niu, Houzhang Tan, Denghui Wang, Wenzhi Du and Shien Hui

Energies 2013, 6(9), 4377-4393; https://doi.org/10.3390/en6094377 - 23 Aug 2013

Cited by 17 | Viewed by 6550

Abstract

Based on the existing biomass co-firing technologies and the known innate drawbacks of dedicated biomass firing, including slagging, corrosion and the dependence on fuel, a new model of agro/forestry residue pellets/shreds and coal co-fired in a large Pulverized Coal (PC) furnace was proposed, [...] Read more.

Based on the existing biomass co-firing technologies and the known innate drawbacks of dedicated biomass firing, including slagging, corrosion and the dependence on fuel, a new model of agro/forestry residue pellets/shreds and coal co-fired in a large Pulverized Coal (PC) furnace was proposed, and the corresponding technical and economic assessments were performed by co-firing testing in a 300 MW PC furnace and discounted cash flow technique. The developed model is more dependent on injection co-firing and combined with co-milling co-firing. Co-firing not only reduces CO₂ emission, but also does not significantly affect the fly ash use in cement industry, construction industry and agriculture. Moreover, economic assessments show that in comparison with dedicated firing in grate furnace, agro/forestry residues and coal co-firing in a large PC furnace is highly economic. Otherwise, when the co-firing ratio was below 5 wt%, the boiler co-firing efficiency was 0.05%–0.31% higher than that of dedicated PC combustion, and boiler efficiencies were about 0.2% higher with agro/forestry residues co-firing in the bottom and top burner systems than that in a middle burner system. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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666 KiB

Open AccessArticle

A Dynamic Model for the Normal Impact of Fly Ash Particle with a Planar Surface

by Ming Dong, Jian Han, Sufen Li and Hang Pu

Energies 2013, 6(8), 4288-4307; https://doi.org/10.3390/en6084288 - 20 Aug 2013

Cited by 17 | Viewed by 5540

Abstract

The rebound behavior of fly ash particles normally impacting a planar surface is investigated by using a dynamic model. The three forms of soft sphere physical model are obtained using static/quasi-static contact mechanics and energy dissipation theory. The influences of the particle size, [...] Read more.

The rebound behavior of fly ash particles normally impacting a planar surface is investigated by using a dynamic model. The three forms of soft sphere physical model are obtained using static/quasi-static contact mechanics and energy dissipation theory. The influences of the particle size, the incident velocity of the particle on the damping coefficient and the impact contact time are all examined. We also predict the critical velocity for three particle sizes. It is found that the variation of the damping coefficient (η) with the normal incident velocity (v_in) can be roughly divided into the three parts. In the first part, η decreases with increasing v_in. In the second part, η is little changed with increasing v_in. In the third part, η rapidly increases with increasing v_in. For smaller impact velocities, the viscoelastic effect plays a dominant role in the impact process, while for higher incident velocities; the energy dissipation depends mainly on plastic deformation. In addition, the critical velocity shows a distinct dependence on the particle size. Finally, the contact displacement-contact time curves are examined. The work provides a solid basis for the development of a discrete-element-method approach to study ash deposition. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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1527 KiB

Open AccessArticle

Experimental Studies on the Normal Impact of Fly Ash Particles with Planar Surfaces

by Ming Dong, Sufen Li, Jun Xie and Jian Han

Energies 2013, 6(7), 3245-3262; https://doi.org/10.3390/en6073245 - 03 Jul 2013

Cited by 31 | Viewed by 6522

Abstract

This paper presents the results of a comprehensive program of experiments in which fly ash particles were impacted under controlled conditions against a flat steel surface. The overall aim of these experiments was to gain an understanding of the ash deposition process in [...] Read more.

This paper presents the results of a comprehensive program of experiments in which fly ash particles were impacted under controlled conditions against a flat steel surface. The overall aim of these experiments was to gain an understanding of the ash deposition process in a pulverized coal boiler system. A continuous nitrogen flow carrying fly ash particles was used to examine the effect of particle incident velocity and particle diameter (d_p) on the normal restitution coefficient, and of the particle diameter on the critical velocity. The effect of the incident normal velocity and particle diameter on the normal restitution coefficient was also examined. The results show that the normal restitution coefficient increases rapidly with increasing incident velocity when this incident velocity is less than the yield velocity, and rapidly decreases with increasing incident velocity when the incident velocity is greater than the yield velocity. The critical velocity, determined solely by the first-contact energy loss, is proportional to d_p^−5/6 and therefore becomes larger for smaller particles. For instance, in the present work, the velocity v_c of a particle with diameter of 85 μm is 0.19 m/s, which increases to 0.42 m/s for particles with a diameter of 65 μm. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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2129 KiB

Open AccessArticle

Evaluation of Structural Changes in the Coal Specimen Heating Process and UCG Model Experiments for Developing Efficient UCG Systems

by Faqiang Su, Takuya Nakanowataru, Ken-ichi Itakura, Koutarou Ohga and Gota Deguchi

Energies 2013, 6(5), 2386-2406; https://doi.org/10.3390/en6052386 - 03 May 2013

Cited by 39 | Viewed by 6589

Abstract

In the underground coal gasification (UCG) process, cavity growth with crack extension inside the coal seam is an important phenomenon that directly influences gasification efficiency. An efficient and environmentally friendly UCG system also relies upon the precise control and evaluation of the gasification [...] Read more.

In the underground coal gasification (UCG) process, cavity growth with crack extension inside the coal seam is an important phenomenon that directly influences gasification efficiency. An efficient and environmentally friendly UCG system also relies upon the precise control and evaluation of the gasification zone. This paper presents details of laboratory studies undertaken to evaluate structural changes that occur inside the coal under thermal stress and to evaluate underground coal-oxygen gasification simulated in an ex-situ reactor. The effects of feed temperature, the direction of the stratified plane, and the inherent microcracks on the coal fracture and crack extension were investigated using some heating experiments performed using plate-shaped and cylindrical coal specimens. To monitor the failure process and to measure the microcrack distribution inside the coal specimen before and after heating, acoustic emission (AE) analysis and X-ray CT were applied. We also introduce a laboratory-scale UCG model experiment conducted with set design and operating parameters. The temperature profiles, AE activities, product gas concentration as well as the gasifier weight lossess were measured successively during gasification. The product gas mainly comprised combustible components such as CO, CH₄, and H₂ (27.5, 5.5, and 17.2 vol% respectively), which produced a high average calorific value (9.1 MJ/m³). Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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Review

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385 KiB

Open AccessReview

Slag Behavior in Gasifiers. Part II: Constitutive Modeling of Slag

by Mehrdad Massoudi and Ping Wang

Energies 2013, 6(2), 807-838; https://doi.org/10.3390/en6020807 - 07 Feb 2013

Cited by 29 | Viewed by 7295

Abstract

The viscosity of slag and the thermal conductivity of ash deposits are among two of the most important constitutive parameters that need to be studied. The accurate formulation or representations of the (transport) properties of coal present a special challenge of modeling efforts [...] Read more.

The viscosity of slag and the thermal conductivity of ash deposits are among two of the most important constitutive parameters that need to be studied. The accurate formulation or representations of the (transport) properties of coal present a special challenge of modeling efforts in computational fluid dynamics applications. Studies have indicated that slag viscosity must be within a certain range of temperatures for tapping and the membrane wall to be accessible, for example, between 1,300 °C and 1,500 °C, the viscosity is approximately 25 Pa·s. As the operating temperature decreases, the slag cools and solid crystals begin to form. Since slag behaves as a non-linear fluid, we discuss the constitutive modeling of slag and the important parameters that must be studied. We propose a new constitutive model, where the stress tensor not only has a yield stress part, but it also has a viscous part with a shear rate dependency of the viscosity, along with temperature and concentration dependency, while allowing for the possibility of the normal stress effects. In Part I, we reviewed, identify and discuss the key coal ash properties and the operating conditions impacting slag behavior. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

1209 KiB

Open AccessReview

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

by Ping Wang and Mehrdad Massoudi

Energies 2013, 6(2), 784-806; https://doi.org/10.3390/en6020784 - 07 Feb 2013

Cited by 120 | Viewed by 12064

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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