Dennis M. Bachovchin

Topping Combustor Status for Second-Generation Pressurized Fluidized Bed Cycle Application

Second-generation Pressurized Fluidized Bed (PFB) combined cycles employ topping combustion to raise the turbine inlet temperature for enhanced cycle efficiency. This concept creates special combustion system requirements that are very different from requirements of conventional gas turbine systems. The topping combustor provides the means for achieving state-of-the-art turbine inlet temperatures and is the main contributor to enhanced plant performance. The objective of this program is to develop a topping combustor that provides low emissions, and is a durable, efficient device exhibiting stable combustion and manageable wall temperatures. The combustor will be required to burn a low-Btu Syngas under normal “coal-fired” conditions. However, for start-up and/or carbonizer outage, it may be necessary to fire a clean fuel, such as oil or natural gas. Prior testing has shown the Westinghouse Multi-Annular Swirl Burner (MASB) to have excellent potential for this application. Metal wall temperatures can be maintained at acceptable levels, even though most “cooling” is done by 1600°F vitiated air. Good pattern factors and combustion efficiencies have been obtained. Additionally, low conversion rates of fuel bound nitrogen to NOx have been demonstrated. This paper presents an update of the status of an ongoing topping combustor development and test program for application to “Second-Generation Pressurized Fluidized Bed Combined Cycles (PFBCC).” The program is sponsored by the Department of Energy’s Morgantown Energy Technology Center (DOE/METC) and will first be applied commercially into the Clean Coal Technology Round V Four Rivers Energy Modernization Project. Phase 1 of the program involved a conceptual and economic study (Robertson et al., 1988); Phase 2 addresses design and subscale testing of components; and Phase 3 will cover pilot plant testing of components integrated into one system.

Topping Combustor Development for Second-Generation Pressurized Fluidized Bed Combined Cycles

A project team consisting of Foster Wheeler Development Corporation, Westinghouse Electric Corporation, Gilbert/Commonwealth and the Institute of Gas Technology, are developing a Second Generation Pressurized Fluidized Bed System. Foster Wheeler is developing a carbonizer (a partial gasifier) and a pressurized fluidized bed combustor. Both these units operate a nominal 1600°F (870°C) for optimal sulfur capture. Since this temperature is well below the current combustion turbine combustor outlet operating temperature of 2350°F (1290°C) to reach commercialization, a topping combustor and hot gas cleanup (HGCU) equipment must be developed.Westinghouse is participating in the development of the high temperature gas cleanup equipment and the topping combustor. This paper concentrates on the design and test of the topping combustor. The topping combustor in this cycle must utilize a low heating value syngas from the carbonizer at approximately 1600°F (870°C) and 150 to 210 psi (1.0 to 1.4 MPa). The syngas entering the topping combustor has been previously cleaned of particulates and alkali by the hot gas cleanup (HGCU) system. It also contains significant fuel bound nitrogen present as ammonia and other compounds. The fuel-bound nitrogen is significant because it will selectively convert to NOx if the fuel is burned under the highly oxidizing conditions of standard combustion turbine combustors.The fuel must be burned with the vitiated air from the pressurized fluidized bed combustor (PFBC). Oxidizer has been cleaned of particulates and alkali by HGCU system, and has also been partially depleted in oxygen. The 1600°F (870°C) oxidizer must also be utilized to cool the combustor as much as possible, though a small amount of compressor discharge air at a lower temperature 700°F (about 370°C) may be used.The application requirements indicate that a rich-quench-lean (RQL) combustor is necessary and the multi-annular swirl burner (MASB) was selected for further development. This paper provides an update on the development and testing of this MASB combustor. Additionally, Westinghouse has been conducting computational fluid dynamic (CFD) and chemical kinetic studies to assist in the design of the combustor and to help optimize the operation of the combustor. Results of these models are presented and compared to the test results.Copyright

Solid oxide fuel cell combined cycles

The integration of the solid oxide fuel cell and combustion turbine technologies can result in combined-cycle power plants, fueled with natural gas, that have high efficiencies and clean gaseous emissions. Results of a study are presented in which conceptual designs were developed for 3 power plants based upon such an integration, and ranging in rating from 3 to 10 MW net ac. The plant cycles are described and characteristics of key components summarized. Also, plant design-point efficiency estimates are presented as well as values of other plant performance parameters.

The Influence of In Situ Reheat on Turbine-Combustor Performance

This paper presents a numerical and experimental investigation of the in situ reheat necessary for the development of a turbine-combustor. The flow and combustion were modeled by the Reynolds-averaged Navier-Stokes equations coupled with the species conservation equations. The chemistry model used herein was a two-step, global, finite rate combustion model for methane and combustion gases. A numerical simulation was used to investigate the validity of the combustion model by comparing the numerical results against experimental data obtained for an isolated vane with fuel injection at its trailing edge. The numerical investigation was then used to explore the unsteady transport phenomena in a four-stage turbine-combustor. In situ reheat simulations investigated the influence of various fuel injection parameters on power increase, airfoil temperature variation, and turbine blade loading. The in situ reheat decreased the power of the first stage, but increased more the power of the following stages, such that the power of the turbine increased between 2.8% and 5.1%, depending on the parameters of the fuel injection. The largest blade excitation in the turbine-combustor corresponded to the fourth-stage rotor, with or without combustion. In all cases analyzed, the highest excitation corresponded to the first blade passing frequency.

Biomass Gasification Hot Gas Cleanup for Power Generation

In support of the U.S. Department of Energy’s Biomass Power Program, a Westinghouse Electric led team consisting of the Institute of Gas Technology, Gilbert/Commonwealth, and the Pacific International Center for High Technology Research, is conducting a 30-month research and development program to provide validation of hot gas cleanup technology with a pressurized fluidized bed, air-blown, biomass gasifier for operation of a combustion turbine. This paper discusses the gasification and hot gas cleanup processes, scope of work and approach, and the program’s status.Copyright

Rich-Quench-Lean Combustion for Multiple Fuels

Westinghouse has developed a rich-quench-lean gas turbine combustor for use on multiple gaseous fuels. The design is based on variants of the Multi-Annular Swirl Burner (MASB) that was invented as a low-NOx topping combustor for the second generation PFBC process, utilizing high temperature vitiated air and high temperature NH3-rich fuel gas, both derived from coal. This Westinghouse RQL combustor is also capable of low-NOx performance using either natural gas or propane in vitiated air, as well as compressor air operation using syngas (coal- or biomass-derived fuel gas for IGCC), propane, or natural gas. The current status of the Westinghouse RQL combustor with regard to each such application is discussed, including design basis, design status, test experience, and expected emissions and operating characteristics.Copyright

Development of Hot Gas Cleaning Systems for Advanced, Coal Based Gas Turbine Cycles

Westinghouse is developing hot gas cleaning systems for advanced, coal based gas turbine cycles. This paper summarizes the Westinghouse hot gas filter concept and reports on recent in-house and field test programs supporting its design and development. Basic materials issues related to ceramic material stability and hot metals structures are reviewed. Results of recent filter system testing are presented comparing candle and cross flow designs operating in both “simulated” and actual coal derived gas streams. Laboratory tests and analysis are reported relating to integrating sulfur and alkali control with the particle filter function.© 1992 ASME

ANALYSIS OF UNSTEADY AEROTHERMODYNAMIC EFFECTS IN A TURBINE-COMBUSTOR

This paper presents a numerical investigation of the unsteady transport phenomena in a turbine-combustor. The flow and combustion are modeled by the Reynolds-averaged Navier-Stokes equations coupled with the species conservation equations. The chemistry model used herein is a two-step, global, finite rate combustion model for methane and combustion gases. The governing equations are written in the strong conservation form and solved using a fully implicit, finite difference approximation. This numerical algorithm has been used to investigate the airfoil temperature variation and the unsteady blade loading in a four-stage turbine-combustor. The numerical simulations indicated that in situ reheat increased the turbine power by up to 5.1%. The turbine combustion also increased blade temperature and unsteady blade loading. Neither the temperature increase nor the blade loading increase exceeded acceptable values for the turbine investigated.