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Employment of Two-Stage Oxygen Feeding to Control Temperature in a Downdraft entrained-flow Coal Gasifier

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International Journal of Clean Coal and Energy 2014年第3期3卷 29-45页

作者： Ting Wang Xijia Lu Heng-Wen Hsu Cheng-Hsien Shen Energy Conversion & Conservation Center University of New Orleans New Orleans LA USA Green Energy and Environment Research Laboratory Industrial Technology Research Institute Hsinchu City Taiwan

The traditional practice of employing a two-stage coal-fed gasification process is to feed all of the oxygen to provide a vigorous amount of combustion in the first stage but only feed the coal without oxygen in the second stage to allow the endothermic gasification process to occur downstream of the second stage. One of the merits of this 2-stage practice is to keep the gasifier temperature low downstream from the 2nd stage. This helps to extend the life of refractory bricks, decrease gasifier shut-down frequency for scheduled maintenance, and reduce the maintenance costs. In this traditional 2-stage practice, the temperature reduction in the second stage is achieved at the expense of a higher than normal temperature in the first stage. This study investigates a concept totally opposite to the traditional two-stage coal feeding practices in which the injected oxygen is split between the two stages, while all the coal is fed into the first stage. The hypothesis of this two-stage oxygen injection is that a distributed oxygen injection scheme can also distribute the release of heat to a larger gasifier volume and, thus, reduce the peak temperature distribution in the gasifier. The increased life expectancy and reduced maintenance of the refractory bricks can prevail in the entire gasifier and not just downstream from the second stage. In this study, both experiments and computational simulations have been performed to verify the hypothesis. A series of experiments conducted at 2.5 - 3.0 bars shows that the peak temperature and temperature range in the gasifier do decrease from 600?C - 1550?C with one stage oxygen injection to 950?C - 1230?C with a 60 - 40 oxygen split-injection. The CFD results conducted at 2.5 bars show that 1) the carbon conversion ratio for different oxygen injection schemes are all above 95%;2) H2 (about 70% vol.) dominates the syngas composition at the exit;3) the 80% - 20% case yields the lowest peak temperature and the most uniform temperature

关键词： Two-Stage Oxygen Feeding entrained-flow Coal Gasification Gasification Simulation Syngas Composition Clean Coal Technology Multiphase flow Simulation

Implementation of a Demoisturization and Devolatilization Model in Multi-Phase Simulation of a Hybrid entrained-flow and Fluidized Bed Mild Gasifier

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International Journal of Clean Coal and Energy 2013年第3期2卷 35-53页

作者： Jobaidur Khan Ting Wang Energy Conversion & Conservation Center University of New Orleans New Orleans USA

A mild gasification process has been implemented to provide an alternative form of clean coal technology called the Integrated Mild Gasification Combined Cycle (IMGCC), which can be utilized to build a new, highly efficient, and compact power plant or to retrofit an existing coal-fired power plant in order to achieve lower emissions and significantly improved thermal efficiency. The core technology of the mild gasification power plant lies on the design of a compact and effective mild gasifier that can produce synthesis gases with high energy volatiles through a hybrid system: utilizing the features of both entrained-flow and fluidized bed gasifiers. To aid in the design of the mild gasifier, a computational model has been implemented to investigate the thermal-flow and gasification process inside this mild gasifier using the commercial CFD (Computational Fluid Dynamics) solver ANSYS/FLUENT. The Eulerian-Eulerian method is employed to model both the primary phase (air) and the secondary phase (coal particles). However, the Eulerian-Eulerian model used in the software does not facilitate any built-in devolatilization model. The objective of this study is therefore to implement a devolatilization model (along with demoisturization) and incorporate it into the existing code. The Navier-Stokes equations and seven species transport equations are solved with three heterogeneous (gas-solid) and two homogeneous (gas-gas) global gasification reactions. Implementation of the complete model starts from adding demoisturization first, then devolatilization, and then adding one chemical equation at a time until finally all reactions are included in the multiphase flow. The result shows that the demoisturization and devolatilization models are successfully incorporated and a large amount of volatiles are preserved as high-energy fuels in the syngas stream without being further cracked or reacted into lighter gases. The overall results are encouraging but require future experimenta

关键词： Multi-Phase Simulation Gasification Simulation entrained-flow Gasifier Fluidized Bed Mild Gasifier Clean Coal Technology

An Investigation on Performance of a Horizontal entrained flow Gasifier

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Journal of Power and Energy Engineering 2018年第3期6卷 28-37页

作者： Isack A. Legonda Department of Mechanical and Industrial Engineering University of Dar es Salaam Dar es Salaam Tanzania

A novel study on biomassair gasification using a horizontal entrained-flow gasifier has been conducted. The use of a horizontal entrained-flow gasifier reactor was employed to assess the effect of the gasifier reactor orientation on the gasification process. The gasification experiments were conducted at 800℃ and equivalence ratio of 0.23 while maintaining gas hourly space velocity (GHSV) of 8000 h-1. Preparation and characterisation of wood powder were performed using classical methods. The research findings showed that maximum fuel conversion and cold gas efficiency using a horizontal entrained-flow gasifier were 99% and 70% respectively compared to 91% and 62% respectively of the vertical design. Moreover, the gasifier length can also be reduced from the common 1000 - 2000 mm to 500 mm. In general, the results of this study suggest that there exists a sensitivity to the gasifier orientation on the overall gasification process.

关键词： Gasification entrained-flow Syngas

Characterization of Size and Density Separated Fractions of a Bituminous Coal as a Feedstock for entrained Slagging Gasification

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International Journal of Clean Coal and Energy 2013年第4期2卷 58-67页

作者： Nari Soundarrajan Nandakumar Krishnamurthy Sarma V. Pisupati John and Willie Leonie Family Department of Energy and Mineral Engineering and EMS Energy Institute The Pennsylvania State University University Park USA National Energy Technology Laboratory US Department of Energy Morgantown USA

Coal is one of the main sources of energy in many parts of the world and has one of the largest reserves/production ratios amongst all the non-renewable energy sources. Gasification of coal is one among the advanced technologies that has potential to be used in a carbon constrained economy. However, gasification availability at several commercial demonstrations had run into problems associated with fouling of syngas coolers due to unpredictable flyash formation and unburnt carbon losses. Computer models of gasifiers are emerging as a powerful tool to predict gasifier performance and reliability, without expensive testing. Most computer models used to simulate gasifiers tend to model coal as a homogenous entity based on bulk properties. However, coal is a heterogeneous material and comminution during feedstock preparation produces particle classes with different physical and chemical properties. It is crucial to characterize the heterogeneity of the feedstocks used by entrained flow gasifiers. To this end, a low ash US bituminous coal that could be used as a gasifier feedstock was segregated into density and size fractions to represent the major mineral matter distributions in the coal. Float and sink method and sieving were employed to partition the ground coal. The organic and inorganic content of all density fractions was characterized for particle size distribution, heating value, ultimate analysis, proximate analysis, mineral matter composition, ash composition, and petrographic components, while size fractions were characterized for heating value, ash composition, ultimate and proximate analysis. The proximate, ultimate and high heating value analysis showed that variation in these values is limited across the range of size fractions, while the heterogeneity is significant over the range of density fractions. With respect to inorganics, the mineral matter in the heavy density fractions contribute significantly to the ash yield in the coal while contributing ver

关键词： Slag Fly-Ash entrained-flow Gasifier Clean Coal Technology Mineral Transformations Partioning