Flameless Pressurized Oxy-combustion Large Pilot Design, Construction, and Operation (Final Technical Report)

Abstract

The team of Southwest Research Institute® (SwRI®), ITEA, Sargent & Lundy (S&L), University of Wyoming (UW), Electric Power Research Institute, Inc. (EPRI), General Electric Global Research (GE), designed a research pilot for Flameless Pressurized Oxy-Combustion (FPO), a novel coal technology. The current United States (U.S.) electricity market is reliant on increasing renewable penetration, drastically shifting how coal-fired power plants are needed for operation. Rather than typical baseload resources, these plants are needed as load-following resources to support electricity generated from intermittent renewable capacity, as well as to provide critical ancillary services to the grid. Under the flameless conditions created in the combustor, fuel is combusted with no flame front at uniformly (isothermal) high temperatures of 1,400 to 1,700°C. As the combustor is refractory lined, there is minimal heat transfer loss during combustion; instead, the hot flue gases are sent to a separate heat recovery steam generation system, with a greater than 97% efficiency, where the heat exchange takes place. In a full-scale FPO scheme design, which would operate closer to 12 bar pressure, improved heat recovery would result, as the combustion and flue gas energy recovery and recycle schemes operating together are in a closed ‘power cycle’ with power production at 45.5% of HHV heat input. The minimization of auxiliary power usages, currently estimated to be 12.3% of HHV heat input, will dictate future avenues of technology development in the long term. Operating under FPO conditions, combustion is stoichiometric, and dioxin, polyaromatic hydrocarbons, and soot are consumed and do not pass into the exhaust gases. Similarly, carbon monoxide levels produced are less than 1 ppm by volume. This means that minimal post-treatment to the flue gas exiting the combustor is required, allowing pressurized flue gas to be recycled to temper combustion. Other than the possible need to neutralize the offtake carbon dioxide (CO2) and water streams, no further post-treatment is required, and any airborne pollution emissions in the CO2 output stream conform to the strictest environmental regulations. From ‘hot’ standby conditions – 5% operating capacity, the FPO combustor can ramp up to a full 100% load within half an hour and exhibits stable efficient power generation across this range. Therefore, there is no direct energy penalty associated with capacity utilization extremes. Under FPO combustion conditions, the output products are energy, CO2, and water together with a quantity of a benign vitrified slag. Heat exchangers to recuperate energy are air-cooled. Thus, fired with high water content coals such as lignite and sub-bituminous varieties, the FPO technology produces more water than it consumes. As FPO is a simple 3-stage process consisting essentially of: coal pretreatment and preparation, the combustor, and the once-through steam generator (OTSG). The firing loop can be prefabricated in modular form and brought to site, ready for site assembly and integration. FPO technology is especially suited to modularization, as it is scalable. Adopting discrete sub-packages which are easily and quickly assembled on-site, means that commissioning of equipment can take place off-site before its arrival. From a cold start, FPO uses natural gas to establish equilibrium conditions in the combustor before solid fuels are added. Therefore, co-firing coal and natural gas together is simple and has been proven. Further, the ability of FPO technology to combust multiple fuels alone or together, ranging from gas to residual liquids, waste, and biomass feedstocks, as well as coal has been studied. The ability to co-fire biomass and coal allows FPO technology with CO2 utilization can generate a negative carbon footprint practically and distinctly. FPO technology is unique in that it is a technical performance-proven clean-coal technology solution that is neither categorized as a pre- or post-combustion carbon capture solution; rather it represents a versatile integrated carbon capture and combustion solution. There is minimal parasitic load designated to capture CO2, and while some energy is consumed to produce oxygen, at the system level, efficiency is comparable or superior to the latest generation supercritical pulverized coal and ultra-supercritical pulverized coal-fired boiler technology, which do not have carbon capture. This project for the development of a research pilot resulted in a front-end engineering design study, AACE Class III cost estimate, techno-economic analysis, NEPA environmental assessment, and permitting applications.