Pressurized Fluidized Bed Combustion Plants Research Articles

Condensed phase corrosion of P91 and DSS 2205 steels at advanced oxygen‐fired pressurized fluidized bed combustion plants

AbstractTo achieve the targets of high energy efficiency and reduced CO2 emission, advanced oxygen‐fired pressurized fluidized bed combustion technology is being developed. The generated flue gas condensates are very corrosive, but very limited information is available to select appropriate alloys for the cost‐effective construction and long‐term safe operation of flue gas components. Thus, this study investigated the corrosion performance of P91 and DSS 2205 steels in the simulated condensates at 60°C–150°C. The dominant reactions on the two steels were considerable oxide formation and high chemical dissolution of the formed oxides instead of localized pitting. The increase in temperature leads to an exponential increase in the long‐term corrosion rates of the steels. Benefited from its high Cr and Mo contents, DSS 2205 steel exhibited much better corrosion resistance, and the formed surface scales consisted of inner Fe‐enriched and outer Cr‐enriched oxides in which Cr2O3 was transformed into Cr(OH)3 with the increase in temperature. The corrosion products on P91 steel consisted of inner Cr–Fr–Mo oxides and outer Fe‐enriched oxides, which were porous and unable to protect the steel.

Corrosion of duplex stainless steel 2205 in hot flue gas environments produced at advanced oxy-fired pressurized fluidized bed combustion plants

The selection of constructional material of flue gas components is crucial for the successful deployment and long-term safe operation of the newly developed oxy-fired pressurized fluidized bed combustion plants. In this study, the corrosion performance of a candidate steel, duplex stainless steel 2205 (DSS 2205) was investigated in simulated flue gas mainly composed of CO2/H2O/O2/N2/SO2/HCl with a total pressure of 1.50–1.64 MPa at 270−320 °C. The oxidation kinetics of DSS 2205 followed parabolic law, and the formed surface oxide was a double-layer structure with outer Fe-rich oxide and inner Cr-rich oxide. Besides general oxidation, SO2 and HCl-induced pitting also occurred. Increasing temperature led to enhanced general oxidation and accelerated pitting. Extending exposure duration resulted in increased pit density, but did not noticeably affect the maximum pit depth. These results indicate that the steel is a promising candidate for further pilot- and industrial-scale assessments.

Application of the severity parameter for predicting viscosity during hydrothermal processing of dewatered sewage sludge for a commercial PFBC plant

Dewatered sewage sludge (approximately 80% water, but with low fluidity) was liquidized by hydrothermal treatment in order to make coal–water paste (CWP) for use in a pressurized-fluidized-bed-combustion (PFBC) power plant. Prediction of the viscosity of the dewatered sewage sludge during batch reactor hydrothermal liquefaction is important in order to avoid inputting excess energy. A single parameter, the severity parameter, has been used to predict viscosity during the hydrothermal process. The relationship between the viscosity of the slurry made from dewatered sewage sludge and the severity value was investigated. Viscosity reduction was associated with an increase in the severity value and was dependent on reaction temperature and time. It was concluded that predicting the viscosity of dewatered sewage sludge during the hydrothermal process by means of the severity parameter is possible. This method is expected to provide a useful guideline for choosing reaction conditions based on prediction of the viscosity of the sludge slurry during the hydrothermal process.

97/02170 PFBC with high ash coals: experience of Bharat Heavy Electricals Limited

Bharat Heavy Electricals Limited (BHEL) has proved the Pressurized Fluidized Bed Combustion (PFBC) process for high ash content coals, by testing different grades of coals, by testing different grades of coals in their test facility. Combustion efficiency has been found to be more than 98%. Load following capability of PFBC plants has been verified by conducting experiments at various bed heights. A test facility is being established to study the hydrodynamic characteristics of large fluidized beds in small, cold, geometrically similar beds using a nondimensional approach. Details of test facility, test results, operating experience and proposed cold studies are discussed in this paper.

96/04133 Formation of solid deposits in the gas circuit of a pressurized fluidized bed combustion plant

96/04133 Formation of solid deposits in the gas circuit of a pressurized fluidized bed combustion plant

Formation of solid deposits in the gas circuit of a pressurized fluidized bed combustion plant

Analysis of solid deposits from the gas circuit of the pressurized fluid bed combustion (PFBC) plant in Escatron (N.E. Spain) showed them to be mainly composed of particles of anhydrite (CaSO 4) with a mean diameter of 6 μm, cemented by a partially devitrified glassy matrix comprising complex sulfates, including langbeinite, K 2Mg 2(SO 4) 3. Formation of these deposits is interpreted using phase diagrams for the systems CaSO 4-MgSO 4-K 2SO 4 and CaSO 4-MgSO 4-Na 2SO 4. Deposit compositions are located in the primary crystallization field of anhydrite, with first liquid formation below 690°C.

95/00616 Effect of pressure on second-generation pressurized fluidized bed combustion plants

95/00616 Effect of pressure on second-generation pressurized fluidized bed combustion plants

Effect of Pressure on Second-Generation Pressurized Fluidized Bed Combustion Plants

In the search for a more efficient, less costly, and more environmentally responsible method for generating electrical power from coal, research and development has turned to advanced pressurized fluidized bed combustion (PFBC) and coal gasification technologies. A logical extension of this work is the second-generation PFBC plant, which incorporates key components of each of these technologies. In this new type of plant, coal is devolatilized/carbonized before it is injected into the PFB combustor bed, and the low-Btu fuel gas produced by this process is burned in a gas turbine topping combustor. By integrating coal carbonization with PFB coal/char combustion, gas turbine inlet temperatures higher than 1149°C (2100°F) can be achieved. The carbonizer, PFB combustor, and particulate-capturing hot gas cleanup systems operate at 871°C (1600°F), permitting sulfur capture by time-based sorbents and minimizing the release of coal contaminants to the gases. This paper presents the performance and economics of this new type of plant and provides a brief overview of the pilot plant test programs being conducted to support its development.

超々臨界圧発電

Steam conditions of 246kgf/cm2g, 538/566°C, super critical pressure single reheating has been dominant as a standard type of the thermal power plants in Japan in recent years. There was no significant progress in steam conditions since the 1960s when the above mentioned conditions were established until June 1989 when the epoch making Kawagoe No.1 unit started commercial operation with the steam conditions of 316kgf/cm2g, 566/566/566°C ultra super critical pressure double reheating.This was because the current materials were used near their limits and enormous funding and time for research and development were needed to improve and develop mate-rials. Also, the investment for improving efficiency could not be compensated by the fuel cost reduction.But the sudden jump of energy price caused by the Oil Shock, steady progress in mate-rial technology, and accumulated experience in designing, manufacturing, and operation of boilers and turbines made a good start in improving steam conditions and led to the comple-tion of the first large scale ultra super critical pressure plants in the world.316kgf/cm2g, 566/566/566°C class steam conditions will be adopted to new coal fired plants in Japan. There are some elements to be developed to realize 352kgf/cm2g, 649/593/593°C class steam conditions, and it will take a little more time.When we survey future technology, ultra super critical pressure technology contri-butes to the improvement of the efficiency of not only pulverized coal firing and PFBC (Pressurized Fluidized Bed Combustion) plants, but also of the steam cycle in combined cycle plants.