Preliminary results from field testing an improved refractory material for slagging coal gasifiers

Slag attack of refractory materials used to line the hot face of slagging gasifiers limits their service life to between 3 and 24 months. These gasifiers use coal, petroleum coke, or combinations of them as raw materials to produce chemicals, liquid fuel, and/or electricity; with future consideration being given to the use of other abundant, low cost feedstock such as biomass. The ash from these materials generate liquid slags during gasification at temperature between 1300 - 1575 C and pressures up to 1000 psi, leading to severe slag attack of a vessel lining and causing unacceptable gasifier reliability and on-line availability. To maximize refractory life and provide protection of the gasifier metal shell, the best liners have contained a minimum of 60-70 pct chromia in combination with alumina, alumina/zirconia, or magnesia. The Albany Research Center of DOE has developed a phosphate containing high chrome oxide refractory liner that indicates potential for increased service life over currently used materials. This new liner has been produced commercially by a refractory company and installed in a gasifier for performance evaluation. Refractory issues in slagging gasifiers, the development and properties of the phosphate containing high chrome oxide material, and the preliminary results from the plant trial of this material will be presented

Refractory failure in IGCC fossil fuel power systems

Current generation refractory materials used in slagging gasifiers employed in Integrated Gasification Combined Cycle (IGCC) fossil fuel power systems have unacceptably short service lives, limiting the reliability and cost effectiveness of gasification as a means to generate power. The short service life of the refractory lining results from exposure to the extreme environment inside the operating gasifier, where the materials challenges include temperatures to 1650 C, thermal cycling, alternating reducing and oxidizing conditions, and the presence of corrosive slags and gases. Compounding these challenges is the current push within the industry for fuel flexibility, which results in slag chemistries and operating conditions that can vary widely as the feedstock for the gasifier is supplemented with alternative sources of carbon, such as petroleum coke and biomass. As a step toward our goal of developing improved refractory materials for this application, we have characterized refractory-slag interactions, under a variety of simulated gasifier conditions, utilizing laboratory exposure tests such as the static cup test and a gravimetric test. Combining this information with that gained from the post-mortem analyses of spent refractories removed from working gasifiers, we have developed a better understanding of refractory failure in gasifier environments. In this paper, we discuss refractory failures in slagging gasifiers and possible strategies to reduce them. Emphasis focuses on the refractories employed in gasifier systems which utilize coal as the primary feedstock

Development of improved performance refractory liner materials for slagging gasifiers

Refractory liners for slagging gasifiers used in power generation, chemical production, or as a possible future source of hydrogen for a hydrogen based economy, suffer from a short service life. These liner materials are made of high Cr2O3 and lower levels of Al2O3 and/or ZrO2. As a working face lining in the gasifier, refractories are exposed to molten slags at elevated temperature that originate from ash in the carbon feedstock, including coal and/or petroleum coke. The molten slag causes refractory failure by corrosion dissolution and by spalling. The Albany Research Center is working to improve the performance of Cr2O3 refractories and to develop refractories without Cr2O3 or with Cr2O3 content under 30 wt pct. Research on high Cr2O3 materials has resulted in an improved refractory with phosphate additions that is undergoing field testing. Results to date of field trials, along with research direction on refractories with no or low Cr2O3, will be discussed

An update on the development of an improved performance refractory material for slagging coal gasifiers

Severe slag attack of high temperature materials that line coal gasifiers used in the production of chemicals, liquid fuels, and/or electricity result in their unacceptably short lifetimes, lasting anywhere from 3 months to 24 months. Lengthening of this short service life to increase gasifier reliability and increase on-line availability of a gasifier is viewed as critical for greater technology acceptance and utilization. A phosphate containing high chrome oxide refractory has been developed by the Albany Research Center of DOE and scaled up by an industrial producer of refractories for plant trials. An update of this material and its properties will be presented

Improved Refractories for Slagging Gasifiers in IGCC Power Systems

The gasification of coal and other carbon-containing fuels provides the opportunity to produce energy more efficiently, and with significantly less environmental impact, than more-conventional combustion-based processes. In addition, the synthesis gas that is the product of the gasification process offers the option of ''polygeneration,'' i.e., the production of alternative products instead of power should it be economically favorable to do so. Because of these advantages, gasification is viewed as one of the key processes in the U.S. Department of Energy's Vision 21 power system. However, issues with both the reliability and the economics of gasifier operation will have to be resolved before gasification will be widely adopted by the power industry. Central to both enhanced reliability and economics is the development of materials with longer service lives in gasifier systems that can provide extended periods of continuous, trouble-free gasifier operation. The focus of the Advanced Refractories for Gasification project at the Albany Research Center is to develop improved refractory materials capable of withstanding the harsh, high-temperature environment created by the gasification reaction, and includes both the refractory lining that protects and insulates the slagging gasifier, as well as the thermocouple assemblies that are utilized to monitor gasifier operating temperatures. Current generation refractory liners in slagging gasifiers are typically replaced every four to 18 months, at costs ranging up to $2,000,000, depending upon the size of the gasification vessel. Compounding materials and installation costs are the lost-opportunity costs for the time that the gasifier is off-line for the refractory exchange. Current generation thermocouple devices rarely survive the gasifier start-up process, leaving the operator with no real means of temperature measurement during routine operation. Reliable, efficient, and economical gasifier operation that includes the 90 to 95% on-line availability desired by the industry clearly requires improvements in refractory liner materials and in thermocouple protection strategies. As a result, the goals of this project include the development of a refractory liner with a service life at least double that of current generation refractory materials, and the design of a thermocouple protection system that will allow accurate temperature monitoring for extended periods of gasifier operation

Engineered refractoriers for slagging coal gasifiers

The widespread commercial adaptation of slagging gasifier technology to produce power, fuel, and/or chemicals from coal will depend in large measure on the technology's ability to prove itself both economic and reliable. Improvements in gasifier reliability, availability, and maintainability will in part depend on the development of improved structural materials with longer service life in this application. Current generation refractory materials used to line the gasifier vessel, and contain the gasification reaction, often last no more than three to 18 months in commercial applications. The downtime required for tear-out and replacement of these critical materials results in gasifier on-line availabilities that fall short of targeted goals. In this talk we will discuss the development of improved refractory materials engineered specifically for longer service life in this application, with emphasis on the design of new refractories that contain little or no chrome

Improving thermocouple service life in slagging gasifiers

The measurement of temperature within slagging gasifiers for long periods of time is difficult/impossible because of sensor failure or blockage of inputs used to monitor gasifier temperature. One of the most common means of temperature measurement in a gasifier is physically, through the use of thermocouples in a gasifier sidewall. These units can fail during startup, standby, or during the first 40-90 days of gasifier service. Failure can be caused by a number of issues; including thermocouple design, construction, placement in the gasifier, gasifier operation, and molten slag attack of the materials used in a thermocouple assembly. Lack of temperature control in a gasifier can lead to improper preheating, slag buildup on gasifier sidewalls, slag attack of gasifier refractories used to line a gasifier, or changes in desired gas output from a gasifier. A general outline of thermocouple failure issues and attempts by the Albany Research Center to improve the service life of thermocouples will be discussed

An analysis of the causes of failure in high chrome oxide refractory materials from slagging gasifiers

High Cr2O3 refractory materials are used to line the hot face of slagging gasifiers. Gasifiers are reaction chambers that convert water, oxygen, and a carbon feedstock into CO, H2, and methane at temperatures as high as 1575DGC and pressures up to 1000 psi. Ash in the carbon feedstock liquefies, erodes and corrodes the gasifier's refractory liner, contributing to liner failure within a few months to two years. The failure of a refractory liner decreases a gasifier's on-line availability and causes costly system downtime and repairs. Many factors contribute to refractory lining failure, including slag penetration and corrosion, thermal cycling, gasifier environment, and mechanical loads. The results of refractory post-mortem failure analysis and how observations relate to gasifier service life will be discussed

Improved Refractory Materials for Slagging Gasifiers in IGCC Power Systems

Gasifiers are the heart of Integrated Gasification Combined Cycle (IGCC) power system currently being developed as part of the DOE's Vision 21 Fossil Fuel Power Plant. A gasification chamber is a high pressure/high temperature reaction vessel used to contain a mixture of O2, H2O, and coal (or other carbon containing materials) while it is converted into thermal energy and chemicals (H2, CO, and CH4). IGCC systems are expected to play a dominant role in meeting the Nation's future energy needs. Gasifiers are also used to produce chemicals that serve as feedstock for other industrial processes, and are considered a potential source of H2 in applications such as fuel cells. A distinct advantage of gasifiers is their ability to meet or exceed current and anticipated future environmental emission regulations. Also, because gasification systems are part of a closed circuit, gasifiers are considered process ready to capture CO2 emissions for reuse or processing should that become necessary or economically feasible in the future. The service life of refractory liners for gasifiers has been identified by users as a critical barrier to IG

New developments in gasifier refractories

For Integrated Gasification Combined Cycle (IGCC) systems, operational reliability depends in part upon the ability of the materials of construction to tolerate harsh, high-temperature environments for extended periods of time. The harshest conditions within an IGCC system occur inside the gasifier itself, where for slagging systems the environment includes elevated temperature and pressure, as well as the presence of corrosive slags and gases. Attempts to enhance gasifier performance by operating at higher temperatures, with higher throughputs, and/or with variable feedstocks, put additional stress on the materials exposed to the operating environment, often resulting in a corresponding decrease in their useful service life. Current generation refractory materials commonly used at the hot face of commercial slagging systems will typically last from four to 18 months, depending on the operating conditions of the specific gasifier. However, as gasification technology matures, the need for new and improved materials will increase as the time between required maintenance shutdowns, and hence the economics and reliability of operation, are defined more and more by the service life of the materials from which the system is built. To address this need for materials development, the U.S. Department of Energy's Office of Fossil Energy and the Albany Research Center are exploring ways to extend the service life of the refractory liner that contains the gasification reaction in slagging gasifiers. In this paper, we examine how refractory materials fail in the gasifier environment, and introduce a new refractory designed specifically to resist such failures. Based on laboratory exposure tests, this new refractory is predicted to significantly enhance gasifier reliability and availability through increased service life