The gasifier is the core system component in the gasification process. It sets the primary requirements for raw material inputs and determines the product gas composition. The gasifier is generally a high temperature and 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 consists primarily of hydrogen, carbon monoxide, and carbon dioxide (referred to either as synthesis gas or syngas). 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 reuse or safe disposal. After cleaning to remove contaminants, the syngas consists mainly of carbon monoxide and hydrogen. Steam is added and the syngas is sent through water-gas shift (WGS) reactors to convert the carbon monoxide to carbon dioxide and additional hydrogen. Finally, after a gas separation process, the carbon dioxide is ready for reuse or safe storage and the hydrogen rich syngas can be fired in a gas-turbine/steam-turbine generator set to produce electricity. A portion of the syngas can also be used to coproduce highly valued fuels and chemicals.
The Gasifier Optimization program element focuses on the development of new technology, improved system components and materials, and models designed to increase the efficiency and reliability of gasification, and to reduce the cost.
Gasifier Optimization R&D includes development of technologies to facilitate cost-effective gasification of both high- and low-rank coals and alternative feedstocks such as petcoke and biomass; development of novel high-pressure coal-feed systems; and development of technologies for co-feeding coal and biomass mixtures to high-pressure gasifiers. Promising technology developments will be tested and evaluated in large-scale pilot, demonstration, or commercial gasification systems. Examples of recent projects:
Reliability and Materials Improvements
Gasification occurs under conditions that present significant challenges, particularly from a materials perspective. The harsh conditions take their toll on all gasifier internals, especially refractory materials used as gasifier liners. Research is being directed at increasing gasifier availability and decreasing gasifier operations and maintenance costs. Efforts are focused on the development of corrosion- and erosion-resistant refractories for high temperature slagging coal gasifiers with a lifetime of at least 3 years; improved understanding of fundamental refractory failure mechanisms to provide insight into formulating new materials; evaluation of candidate materials under simulated gasifier conditions to identify promising materials; and testing of promising materials in a large-scale operating gasifier. An example of a recent success is AUREX™95P, a new refractory material developed by NETL, that has demonstrated increased reliability and service life in commercial gasifiers.
Process Measurement and Control Technologies
|Advanced Virtual Energy Simulation Training and Research facility - AVESTAR
The harsh environment created in the gasification process is also a challenge to invasive process instrumentation. Sensors must function reliably while exposed to high temperatures, high pressures, a highly reducing atmosphere, and molten ash or slag. The end result is often extremely short lives for critical instruments used for gasifier temperature measurement. Efforts are focused on development and testing of instrumentation that can provide reliable, accurate, and rapid response information on gasifier operation. Full-scale testing of such instrumentation is expected to increase both efficiency and reliability, leading to lower costs. Taking another approach to facilitate improved process control, the IGCC Dynamic Simulator Research & Training Center was created to provide research, education, and simulated demonstration capabilities, as well as immersive training for operation and control of advanced gasification systems. The Center is used to conduct leading-edge R&D in the areas of high-fidelity, real-time dynamic simulation, reduced order modeling, model predictive control, sensor placement, risk and safety analysis, and virtual engineering.
The Power Systems Development Facility (PSDF) is a state-of-the-art test center that was established by DOE in the early 1990s to accelerate the development of more efficient, advanced coal-based power plant technologies. The air-blown Transport Gasifier was developed at the PSDF and began operating in 1999. The PSDF now houses the National Carbon Capture Center (NCCC) that focuses national efforts on reducing greenhouse gas emissions through technological innovation, serves as a neutral test center for emerging carbon capture technologies, and continues to test advanced technologies with the potential for capital and operating cost reductions, such as syngas cleaning, water gas shift technologies, catalytic filter elements, and materials and sensors.
Completed Gasifier Optimization Projects include the following:
Systems Analyses – As part of the support for the Gas Cleaning program element, 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.
Other key areas within Gasification Systems include the following: