Main Area: Gas Cleaning
Novel gas cleaning and conditioning are crucial technologies for achieving near-zero emissions, while meeting gasification system performance and cost targets. DOE's Gasification Systems program supports technology development in the area of gas cleaning and conditioning, including advanced sorbents and solvents, particulate filters, and other novel gas-cleaning approaches that remove and convert gas contaminants into benign and marketable by-products. To avoid the cost and efficiency penalties associated with cooling the gas stream to temperatures at which conventional gas clean-up systems operate, novel processes are being developed that operate at mild to high temperatures and incorporate multi-contaminant control to parts-per-billion levels.
Chemicals from Coal Complex
The various downstream uses of syngas require that most of the contaminants present in coal or other feedstocks be removed to very low levels prior to use. Many of these contaminants can contribute to erosion, corrosion, and loss of strength in gas turbine components, and can act as poisons to fuel cells and to the catalysts that are often used in chemical processing steps.
Conventional methods for removing sulfur and other contaminants from syngas typically rely on chemical or physical absorption processes operating at temperatures of 100°F or less. When cooled to this level, nearly all of the steam present in the syngas condenses. Then, after contaminant removal, the gas has to be reheated and often additional steam needs to be added for downstream hydrogen production. These process swings adversely impact the plant's thermal efficiency and cost. Economic analysis shows that gas-cleaning processes that are amenable to higher operating temperatures could significantly reduce this efficiency loss and improve the gasification plant's commercial viability.
Because syngas streams contain a wide variety of contaminants at low concentrations—ammonia, hydrogen chloride, hydrogen sulfide, and carbonyl sulfide, as well as various forms of trace metals, including arsenic, mercury, selenium, and cadmium—multiple unit operations are often needed to effect removal to acceptable levels. Unit operations that could remove multiple contaminants at elevated temperatures would simplify plant design and operation and improve process economics.
Scale-Up of Warm Syngas Cleaning Technology
Research Triangle Institute (RTI) is leading a project at Tampa Electric Company's (TECO) 250-megawatt (MW) Polk Power Station – an IGCC plant located near Tampa, Florida. The project will remove multiple contaminants, including total sulfur down to less than 1 part per million, from a slip stream of coal-derived syngas at elevated temperature produced by the utility's coal gasifier. Ninety percent of the carbon dioxide in the cleaned stream will be captured and sequestered deep underground. This project will also clean the syngas of trace contaminants such as mercury and arsenic, and clean ammonia, to very low levels in an integrated test system. Pure, marketable solid sulfur will be created from the sulfur captured. Carbon dioxide will be captured using an activated MDEA system, with the intention of accelerating commercial deployment of these technologies for gasification of coal and petroleum coke. The activated MDEA process has been commercially used in numerous oil refineries, natural gas sweetening and ammonia plants, but its relatively non-selective hydrogen sulfide/carbon dioxide removal characteristics have prohibited its potential use in gasification plants using high-sulfur fuels (like coal and petroleum coke), to produce a low-sulfur carbon dioxide product required for sequestration. However, RTI's warm syngas cleaning system is capable of achieving very high levels of sulfur removal in syngas produced from the gasification of high-sulfur fuels. The activated MDEA process can then be applied to the low-sulfur syngas stream to recover a carbon dioxide product for sequestration, and, simultaneously, remove any trace sulfur from the syngas. It is anticipated that this technology will be ready for commercial scale demonstration in 2015. Novel membranes, with operating temperatures of 535-825°F, are also being developed for separating carbon dioxide from syngas and are compatible with RTI's warm gas-cleaning technology, enabling even better thermal efficiency and process economics for future coal-to-hydrogen plants using both technologies.
The goal of this research is to develop and test technologies that can remove a variety of contaminants from the syngas stream at elevated temperatures, including hydrogen sulfide, carbonyl sulfide, ammonia, hydrogen chloride, as well as trace metals including arsenic, mercury, selenium, and cadmium. These contaminants can potentially impair downstream processes, damage the environment, and present a human health hazard if not removed. NETL has supported several projects involving novel technologies and methods that remove multiple contaminants down to extremely low levels.
Completed Contaminant Control Projects
Archived ProjectsSystems 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 main areas within Gasification Systems include the following: