Date of Award

January 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

First Advisor

Steven A. Benson

Second Advisor

Gathaum Krishnamoorthy

Abstract

Coal combustion is responsible for the majority of electricity production in the United States. It is however, also the primary cause for carbon dioxide emissions, which contribute to global warming. With oil reaching its peak production in the near future, alternative fuel sources will be needed to meet the worlds growing energy demands. Coal is an abundant resource that has the potential to meet those demands. In contrast to coal combustion, coal gasification only partially oxidizes the coal to produce a syngas containing of hydrogen and carbon monoxide, which means less carbon dioxide emissions. Utilizing coal in gasification technologies is the key to using coal in a more environmentally friendly way. Coal utilized gasification technologies have a variety of different applications. These applications include production of synthetic natural gas, production of methanol, to converting the syngas to gasoline, or chemicals like ammonia or a more efficient method to produce electricity for power generation. There are some challenges associated with coal when trying to extract its energy. These challenges exist due to the impurities that are inherent in coal. These impurities get released upon combustion and gasification systems and cause corrosion and erosion which can lead to damaging of expensive equipment used in chemical processing plants. Therefore research is needed to address these challenges, in order to improve the gasification systems so they can become more efficient. One area of gasification technology that can utilize coal to generate useful products is fluidized bed gasification. Fluidized bed gasification is not as widely used as other gasification technologies in industry. This is because these systems have their own unique set of challenges associated with them. This research is focused on fluidized bed gasification with lignite as the design fuel. In this work a fluidized bed gasifier was designed, constructed, commissioned and optimized for hydrogen production. The design was based off of the literature and centered on the minimum fluidization velocity. Shakedown experiments were performed as part of commissioning the system. Experiments were run under combustion conditions, air blown gasification, oxygen blown gasification, oxygen combustion, and a hydrogen retort. A hydrogen rich syngas was produced, containing 58% hydrogen for the retort experiments and as high as 55% for oxygen blown gasification. This hydrogen rich stream was largely because of the water gas shift reaction that took place downstream of the gasifier. Along with these experiments, deposits from the impurities were formed under realistic conditions. The deposits were prepared and analyzed using scanning electron microscopy. The two methods which were used to characterize the deposits were morphology, which uses EDS to identify the atoms present in the sample, and point count (SEMPC) which uses a computer program to compare and classify the mineral phases present in the sample. Based on the results of the SEMPC analysis the mechanism from which the deposits formed was through viscous flow sintering. The atomic species most responsible for the sintering was found to be organically associated sodium and calcium in the lignite.

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