Making Clean Electricity using Coal Gasification
The gasifier is the core system component in the gasification process. It determines both the primary requirements for raw material inputs and the product gas composition. The gasifier is generally a high temperature/pressure vessel where oxygen (or air) and steam are directly contacted with a fuel, such as coal, causing a series of chemical reactions to occur that result in production of a fuel gas. This fuel gas (also referred to either as synthesis gas or syngas) consists primarily of hydrogen, carbon monoxide, and carbon dioxide. Minor constituents present in the feedstock are converted to such products as hydrogen sulfide, ammonia, and ash/slag (mineral residues from coal). These products can be separated and captured for use or safe disposal. After cleaning to remove contaminants, the syngas consists mainly of carbon monoxide and hydrogen. According to the Department of Energy's vision for coal gasification, at this point steam may be added and the syngas sent through a water-gas shift (WGS) reactor to convert the carbon monoxide to nothing but carbon dioxide and additional hydrogen. After a gas separation process, the carbon dioxide is ready for utilization (such as for Enhanced Oil Recovery) or safe storage, and the hydrogen can be fired in a gas-turbine/steam-turbine generator set to produce electricity with stack emissions containing no greenhouse gases. Alternately, syngas or hydrogen can be used to produce highly-valued fuels and chemicals. Co-production of combinations of these products and electricity is also possible.
The Gasifier Optimization and Plant Supporting Systems area focuses on the development of technologies and models to improve the performance and reduce costs of advanced gasifiers. Specifically, current projects focus on development of more durable refractory materials, creating models to better understand the kinetics and particulate behavior of fuel inside a gasifier, and developing practical solutions to mitigate the plugging and fouling of syngas coolers. The direction of this work leads toward development of a highly advanced gasifier, which would incorporate the most aggressive and successful technologies resulting from both Gasification Systems program and other DOE programs. Anticipated improvements will allow much expanded use of low-cost, low rank coals, expanding opportunities for gasification systems and lowering feedstock costs. Optimization also includes the aim of reducing water consumption in gasification plants, and systems integration to increase efficiency and reduce costs plant-wide.
Development of Reacting Multiphase Models for Advanced Gasification Processes and Experimentation for Model Development and Validation
NETL’s Office of Research and Development (ORD) is developing validated models for advanced gasification technology so that new concepts can be developed with less empirical testing, and yielding improved performance. Computational models are being developed to simulate and understand performance before a design is finalized, which is important for reducing cost. During new technology development empirical scale up information is not available because reactors at the large-scales that are required have not been built. Science-based models with quantified uncertainty are important tools for reducing the cost and time required for development because traditional scale-up methods do not work well for multiphase flow reactors, such as the ones used for gasification.
- Development of Reacting Multiphase Models for Advanced Gasification Processes
- Experimentation for Model Development and Validation
New Concepts for Gasification and Fuel Conversion
ORD is accelerating deployment of advanced gasification systems by aligning its core strengths with industry’s needs and technology gaps. Efforts are focused on technological advancement of novel gasification concepts to (1) reduce the coal gasification costs; (2) increase overall efficiency of the gasification system; and (3) reduce emissions including carbon. The overall goal of this task is to design a compact, low temperature, and economically viable gasifier to produce value-added chemicals from coal.
- New Concepts for Gasification and Fuel Conversion
Material Interactions during Gasification
ORD is focusing its refractory material research in two areas, (1) improving refractory material service life; and (2) modeling and controlling slag chemistry – both of which have specific tasks targeting refractory material development, sensor development, ash/slag management, and vanadium phase studies. Ash agglomeration data is being used in models of fluidized bed gasification systems. Ash particles can become sticky during gasification, causing agglomeration in fluidized beds, leading to poor gas flows or gasifier shutdown in fluidized bed systems.
Conversion and Fouling
Research is establishing how chemistry affects slag viscosity, so that the impact that fuel properties have on slag and refractory interaction, and plugging and fouling throughout the syngas cooling system, can be understood and ameliorated. Simulation tools will lead to confident use of low-rank coal and mixed feeds, aiding in gasifier design and performance.
Gasifiers for High H2 Syngas Production
Gas Technology Institute is working on a hybrid molten bed (HMB) gasification process to produce high-hydrogen syngas from coal and natural gas as a co-feed, with syngas used to produce power and diesel fuel.
Aerojet Rocketdyne is further developing an advanced pilot-scale gasifier for use in a first-of-a-kind, commercially relevant demonstration plant. Research is being conducted on advanced water-gas shift processes and catalysts for testing at pilot-plant scale, to reduce the cost of high-hydrogen syngas production.
Enhancing Microbial Conversion of Coal to Methane
Research is being conducted to enhance and optimize microbially converting coal to methane at a production rate and purity to be industrially relevant to support power generation, or the production of transportation fuels/fertilizer/chemicals.
National Carbon Capture Center
Transport Reactor Integrated Gasification (TRIG™), originally developed by Kellogg, Brown, and Root (KBR) based on the company's fluidized catalytic cracking technology, has been enhanced through extensive testing by Southern Company at the Power Systems Development Facility in cooperation with NETL. Testing corroborated that the gasifier effectively handles low-rank coals (e.g., Powder River Basin lignite), which account for half of the worldwide coal reserves but are often considered uneconomic as energy sources due to high moisture and ash contents.
As part of the support for the Gasifier Optimization and Plant Supporting Systems key technology area, systems studies are being conducted to provide unbiased comparisons of competing technologies, determine the best way to integrate process technology steps, and predict the economic and environmental impacts of successful development.
Recently Completed Projects:
Other key technologies within Gasification Systems include the following: