Gasification: The Technology of Choice

The Power Systems Development Facility (PSDF) is an engineering scale demonstration of advanced coal-fired power systems and high-temperature, high-pressure gas filtration systems. The PSDF was designed at sufficient scale so that advanced power system components and the Department of Energy’s Clean Coal Roadmap program elements could be tested in an integrated fashion to provide data for commercial scale-up. The PSDF is funded by the U. S. Department of Energy (DOE), the Electric Power Research Institute, Southern Company, Kellogg Brown & Root, Inc. (KBR), Siemens Power Generation, Inc. (SPG), Peabody Energy, Lignite Energy Council, and Burlington Northern Santa Fe Corporation (BNSF). Currently, the primary focus of the PSDF is research and advancement of the gasification process, with focus also on particulate removal and syngas cleanup systems. Gasification at the PSDF is based on the KBR Transport GasifierTM, which is an advanced circulating fluidized bed reactor designed to operate at considerably higher circulation rates, velocities, and riser densities than a conventional circulating bed. These conditions result in higher throughput, better mixing, and higher mass and heat transfer rates. The Transport Gasifier began operation in September 1999, and through March 2006 has achieved about 8,300 hours of gasification. A total of 6,841 hours of gasification were using Powder River Basin, while additional hours were devoted to North Dakota lignite and bituminous coals from Utah, Illinois, Indiana, and Alabama. Approximately 5,100 hours of testing have occurred in air-blown gasification with the remaining hours in oxygen-blown operation. The gasifier typically operates at temperatures between 1,600 and 1,800°F, pressures up to 275 psig, and coal rates between 2,500 and 5,500 pounds per hour. These conditions yield carbon conversions up to 97 percent and produce commercially projected syngas lower heating values up to 145 Btu/SCF in air-blown gasification and 300 Btu/SCF in oxygen-blown gasification. The technology being demonstrated at the PSDF is also the basis for an advanced 285-megawatt coal gasification project located in Orlando, Florida, which was selected by DOE under its Clean Coal Power Initiative (CCPI). This paper discusses the performance of the Transport Gasifier during recent testing in air-blown and oxygen-blown mode as well as future plans of the PSDF and the Orlando Gasification Project (OGP). INTRODUCTION The PSDF is an engineering scale demonstration of advanced coal-fired power systems with high-temperature, high-pressure gas filtration. The PSDF was designed at a scale sufficient to test advanced power system components and Clean Coal Technology Roadmap program elements in an integrated fashion to provide data for commercial scale-up. Clean coal research at the PSDF focuses on testing the Transport Gasifier, a particulate control device (PCD, a high temperature, high pressure gas filter), and a number of auxiliary systems essential for any gasification process. The Transport Gasifier is an advanced pressurized circulating fluidized bed system designed to operate in air or oxygen-blown modes using a variety of fuels such as subbituminous, bituminous and lignite coals and biomass. Syngas produced by the Transport Gasifier can be used as fuel for a combustion gas turbine or a fuel cell, or can be used for processing into chemicals such as methanol or transportation fuels. The gasifier operates at considerably higher circulation rates, velocities, and riser densities than a conventional circulating bed, resulting in higher throughput, better mixing, and higher mass and heat transfer rates. PROCESS DESCRIPTION Figure 1 illustrates the general flow diagram used for testing the Transport Gasifier and PCD at the PSDF. A series of lock hoppers feed coal to the Transport Gasifier, while a separate set of lock hoppers feed sorbent, if necessary, to capture sulfur in the coal as calcium sulfide. The gasifier also has feed lines so air and steam can be fed as reactants, along with nitrogen and recycle gas for fluidizing the system. The syngas exiting the Transport Gasifier cyclone is sent through a primary gas cooler, where the temperature is reduced to around 800°F before entering the PCD for final particulate cleanup. In the PCD, virtually all of the particulates remaining in the syngas are removed using filter elements. After exiting the PCD, the syngas may be sent to gas cleanup, a piloted syngas burner and combustion turbine, or the secondary gas cooler. Most of the syngas is typically sent to the secondary gas cooler and is later depressurized to around 2 psig using a pressure control valve. Next, the gas is sent to an atmospheric syngas combustor where it is combusted and all reduced sulfur compounds (H2S, COS, CS2) and reduced nitrogen compounds (NH3, HCN) are oxidized. Upon leaving the combustor, the oxidized syngas, or flue gas, flows through a heat recovery boiler to cool the gas and produce steam. The gas then travels through a baghouse, and out the stack. The Transport Gasifier produces both fine and coarse ash. Fine ash, which is collected by the PCD, is cooled and removed via a continuous fine ash depressurization (CFAD) system. Coarse ash accumulates in the standpipe and is removed via a continuous coarse ash depressurization (CCAD) system. Both the fine and coarse ash streams are pneumatically conveyed into an ash silo for disposal. A ir /O x yg en S team A ir S team O x yg en P res s u re L etd ow n V a lv e A s h G as ifica tion A s h G as ifica tion A s h S orben t C oa l T ran s p or t G as ifier D is en g ag er C yc lon e P ar t icu la te C on tro l D ev ice A tm os p h er ic S yn g as C om bu s to r S tack B ag h ou se A s h T ran s p o r t S ys tem S tar tu p B u rn er