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ABSTRACT Preliminary corrosion measurements have been made on high-temperature alloys exposed in a steam-10% CO2 mixture intended to simulate the environment produced in a novel combustion process. Exposures were made up to 1000h at 900°C, and 740h at 1135°C at a pressure of 2 MPa. Data were also collected from exposures in ambient pressure air at 900°C to provide a basis for comparison. Representative wrought, high-temperature alloys produced the expected protective external scales in the steam-CO2 mixture, but also suffered internal penetration, the importance of which increased with temperature. On the basis of a simple linear extrapolation of these limited data, and using an acceptability criterion of less than 100 nm/h (34 mpy) metal loss, only two of the wrought alloys were considered to be acceptable at 900°C, and none at 1135°C. An alumina scale-forming, oxide dispersion-strengthened alloy met the criterion at both temperatures, and aluminized samples of chromia-forming alloys showed good promise. INTRODUCTION A technology proposed by Clean Energy Systems Inc. (CES) of Sacramento, California?zero emissions steam technology (ZEST)(1)?promises to generate electric power from the combustion of a hydrocarbon fuel with oxygen while minimizing the cost of isolating and sequestering the CO2 produced. Natural gas, or methane which may be derived from coal, is burned in stoichiometric proportions with oxygen to give a two-species gas that comprises approximately 90% H2O and 10% CO2 by volume. After expansion through a series of turbines and steam generators or reheaters, the gases are delivered to a condenser where most of the water vapor condenses and the CO2 separates from the gaseous mixture. The humid CO2 from the condenser is dewatered, compressed to the required down-hole pressure (approximately 20 MPa) and delivered to a sequestration site such as an injection well. With a maximum rotor inlet temperature (RIT) of 1427°C at a pressure of 2.6 MPa, it is estimated that net plant efficiencies of the order of 55% will be obtainable with essentially total CO2 sequestration. The energy penalty for this CO2 separation process is only 3.4%, which is significantly lower than the 20-45% required for other fossil fuel plants(1). Figure 1a is a schematic diagram of the process, and Fig. 1b shows a detailed schematic diagram of the steam generator. By employing numerous mixing and cool-down sections in the combustor/steam generator, the temperature of the combustion products can be matched to the required inlet temperature of the expansion gas turbines. Nevertheless, some components are likely to be required to operate in a steam-CO2 gas mixture at high pressures and at temperatures significantly higher than normally encountered. The pressures and temperatures at various locations in Fig. 1 are indicated in Table 1 for three sets of conditions representing current, near-term, and advanced technologies. It is evident that this concept involves some significant materials challenges, since there are few alloys capable of operating at the highest temperatures envisioned, and few if any data on compatibility with steam under these conditions. The present work was initiated to begin generating data on the performance of high-temperature alloys in steam at temperatures representative of their highest service capabilities. EXPERIMENTAL PROCEDURES The alloys chosen for study represent the typical classes of high-temperature alloys available for use as tubes and pipes. The compositions are listed in Table 2. No turbine airfoil alloys were included. Alloy samples of thickness 2.8-3.0 mm (except for alloy 214, which was only available at 0.8 mm) and surface areas of approximately 4 cm2 or 28 c
- Energy > Power Industry (1.00)
- Energy > Oil & Gas > Upstream (1.00)
ABSTRACT Model austenitic alloys are being studied as part of an alloy development program for high temperature (¡Ý650°C) recuperators for small gas turbine engines. In many cases, the recuperator design requires an alloy foil with both high temperature strength and corrosion resistance in an exhaust gas environment. Previous work showed that type 347 stainless steel would not have sufficient corrosion resistance for this application. Long-term testing is being conducted to better understand the effect of composition on corrosion resistance in humid air at 650°-800°C. Current results show that Fe-20Cr-20Ni with additions of Mn and Si has excellent corrosion resistance in humid air for more than 5,000h at 650° and 700°C. Increasing the Ni content of the alloy is critical to improving corrosion resistance. INTRODUCTION The August 2003 blackout in the United States has bolstered the case for distributed generation as a solution for overloaded transmission lines and improved reliability. One element in the distributed generation portfolio are small (30-250 kW) single-shaft, gas turbine engines or microturbines.1-2 With a footprint of approximately 3m x 4m, these engines could be sited at the user?s facility and provide base or peak load electricity while delivering waste heat for climate control or heating water. One potential market uses methane from landfills and sewage plants as fuel.3 Microturbines are environmentally attractive because of their low NOx emissions. However, one of the drawbacks of current microturbines is their relatively low electrical generation efficiency (¡Ö30%) compared to large gas turbines. (An overall efficiency increase is obtained by using the waste heat for other uses.) Thus, one goal of the Department of Energy?s Distributed Energy Resources program is to improve the efficiency of next-generation microturbines.4 Increasing the turbine inlet temperature is a primary method for increasing engine efficiency. Higher operating temperatures require the selection or development of cost-competitive materials for advanced microturbines. One of the most critical areas is the recuperator or heat exchanger, which significantly boosts the efficiency of small turbine engines.5 Increasing the temperature of the recuperator while maintaining durability requirements has proven to be a critical problem. Most recuperator designs have used type 347 stainless steel because of its combination of creep and corrosion resistance. However, it has been well documented that increasing the exposure temperature to ¡Ý650°C has resulted in accelerated attack of type 347 stainless steel due to the presence of water vapor in the exhaust gas.6-10 Accelerated attack due to water vapor has been observed for both ferritic and austenitic alloys in the 600°-900°C range11-16 and is currently being investigated by a number of research groups. An increase in the corrosion rate is a particular concern for recuperators because most designs employ thin-walled alloy components having a limited Cr reservoir. The Cr reservoir is an important factor in determining corrosion lifetime because, as Cr is depleted from the foil, at some critical Cr content the foil will no longer be able to form a protective Cr-rich surface oxide. In order to meet recuperator durability goals of ¡Ö40,000h, a stainless steel must be identified with a low Cr consumption rate and which will make it resistant to accelerated attack. As described in previous papers,9,10 the goal of this program is to develop a low-cost alternative to type 347 stainless steel by (1) identifying the base Cr and Ni contents needed for resistance in these environments; (2) identifying beneficial minor alloying additions and (3) combining
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.34)
- Materials > Metals & Mining > Steel (1.00)
- Energy > Power Industry (1.00)
- Government > Regional Government > North America Government > United States Government (0.46)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation (1.00)
- Health, Safety, Environment & Sustainability > Sustainability/Social Responsibility > Sustainable development (0.86)
Performance of Materials in Black Liquor Gasification Environments
Pint, Bruce A. (Oak Ridge National Laboratories) | Tortorelli, Peter F. (Oak Ridge National Laboratories) | Hemrick, James G. (Oak Ridge National Laboratories) | Peascoe, Roberta (Oak Ridge National Laboratories) | Hubbard, Camden R. (Oak Ridge National Laboratories) | Keiser, James R. (Oak Ridge National Laboratories)
ABSTRACT Black liquor gasification systems have the potential to replace black liquor recovery boilers because of their increased energy efficiency, reduced emission of pollutants and inherently safer designs. However, there are significant problems that must be addressed, not the least of which is the selection of suitable materials for containment of the processes associated with gasification. There are two systems that are considerably ahead of all others in terms of development efforts and commercialization: a low-temperature process that operates below the melting point of the salts and one that operates well above it. Descriptions of both systems and the operating environments are presented, as well as a summary of the performance of materials in these systems. Laboratory studies that simulate the gasifier environments are currently underway, and initial results of these studies indicate there are significant materials issues to be resolved. Predictions of corrosion rate have also been made using proprietary software, and results of these projections are summarized. INTRODUCTION AND BACKGROUND In North America, the kraft process is the predominant chemical method used to separate the wood fibers in the pulping stage of papermaking. Black liquor, which is a by product of this pulping process, is an aqueous solution containing both organic and inorganic material. The organic material is derived from the unused portion of the wood and is generally recovered and burned in the recovery boiler to produce heat and steam. The inorganic material is a result of the reaction between the pulping chemicals (sodium sulfide and sodium hydroxide) and the wood. The goal of the chemical recovery process in kraft mills is to regenerate these pulping chemicals. The combustion of the organic material and recovery of the chemicals are accomplished in a black liquor recovery boiler, but there are many shortcomings to this approach. These boilers are relatively inefficient with respect to production of steam and power, have relatively high pollutant emission levels and present safety issues associated the molten salt produced in the boiler. Black liquor gasification offers an alternative to recovery boilers, and a recent publication indicated that there are energy and financial benefits to be gained by switching to gasification of black liquor. In addition to the kraft process, two less 1 frequently used pulping processes, known as the semi-chem process and the sulfite process, produce waste streams that can be gasified in the same fashion as the kraft black liquor. The most significant difference is the sulfur content of the liquor: that from the semichem process has small or negligible amounts while liquor from the sulfite process contains about twice the sulfur of kraft liquor. Two black liquor gasification processes have been developed to the extent that a number of pilot and/or demonstration scale units have been or are being built. These two processes are fundamentally different. In the low temperature process developed by Manufacturing and Technology Conversion International, Inc. of Baltimore, MD, steam 2 reforming occurs in a fluidized bed where the temperature is currently limited to about 605°C. By keeping the temperature at or below this point, the alkali salts remain as solids rather than melting and forming a liquid phase that can attack the structural components as well as form dense plugs in the reformer/gasifier vessel. In the high temperature gasification process developed by Chemrec AB, Stockholm, Sweden, the temperature of the process is maintained 3 well above the melting point of the salt. As a result of the higher temperature operation, gasification reactions occur at a much higher
- North America > United States > Maryland > Baltimore County > Baltimore (0.24)
- Europe > Sweden > Stockholm > Stockholm (0.24)