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.
Robust Sensor Development
Gas Technology Institute (GTI) is improving its optical flame sensor, which will be used to monitor coal gasifier flame characteristics to help support increased availability and reliability of gasifiers. This project builds on GTI's previously developed technology, and will add real-time temperature monitoring, improve reliability, perform long-term testing, and assess commercial viability of the sensor system.
Researchers at NETL have been working on an advanced, durable refractory material for coal gasifiers that extends the refractory service life an estimated 50 percent beyond that normally achieved with conventional materials, and which has equivalent or better resistance to chemical deposition, a primary wear mechanism that impacts refractory service life. Work continues in terms of studying ash/slag chemistry so as to understand and control slag/refractory interactions, and reducing ash species that may negatively affect gasifier operation such as heat exchanger fouling.
Conversion and Fouling
Research will establish 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.
Low-Rank Coal Optimization
Research in this area will focus on the development of gasification performance prediction models to reduce uncertainties associated with the use of low-rank coals and co-feeds, including biomass.
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.
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.
National Carbon Capture Center at the Power Systems Development Facility
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: