Spalling reduces the lifetime of hot-face refractory linings in slagging coal gasifiers, and has an important impact on the economics of coal gasification. Spalling is caused by ingress of the molten slag into the porous refractory, followed by reaction with the refractory to produce either volumetric expansion (compressive stresses) or volumetric shrinkage (tensile stresses). In this paper, ingress of the molten slag into the porous refractory is described by an effective diffusivity that treats simultaneous capillary and diffusive mechanisms in terms of the average pore radius and the slag viscosity. This effective diffusivity can be applied in spalling models to estimate spall thicknesses that are useful for determining whether the spall originated from tensile or compressive mechanisms.
Gasification is an important method of converting coal into clean-burning fuels and high-value industrial chemicals. However, gasifier reliability can be severely limited by rapid degradation of the refractory lining in hot-wall gasifiers. This paper describes an integrated approach to provide the experimental data and engineering models needed to better understand how to control gasifier operation for extended refractory life. The experimental program includes slag viscosity testing and measurement of slag penetration into refractories as a function of time and temperature. The experimental data is used in slag flow, slag penetration, and refractory damage models to predict the limits on operating temperature for increased refractory life. A simplified entrained flow gasifier model is also described to simulate one-dimensional axial flow with average axial velocity, coal devolatilization, and combustion kinetics. The goal of this experimental and model program is to predict coal and oxidant feed rates and to control the gasifier operation to balance coal conversion efficiency with increased refractory life.
This document was printed on recycled paper. Executive SummaryCombined heat and power fuel cell systems (CHP-FCSs) provide consistent electrical power and hot water with greater efficiency and lower emissions than alternative sources. These systems can be used either as baseload, grid-connected, or as off-the-grid power sources. This report presents a business case for CHP-FCSs in the range of 5 to 50 kWe. Systems in this power range are considered "micro"-CHP-FCS. For this particular business case, commercial applications rather than residential or industrial are targeted. To understand the benefits of implementing a micro-CHP-FCS, the characteristics that determine their competitive advantage must first be identified. Locations with high electricity prices and low natural-gas prices are ideal locations for micro-CHP-FCSs. Fortunately, these high "spark spread" locations are generally in the northeastern area of the United States and California where government incentives are already in place to offset the current high cost of the micro-CHP-FCSs. As a result of the inherently high efficiency of a fuel cell and their ability to use the waste heat that is generated as a CHP, they have higher efficiency. This results in lower fuel costs than comparable alternative small-scale power systems (e.g., microturbines and reciprocating engines).A variety of markets should consider micro-CHP-FCSs including those that require both heat and baseload electricity throughout the year. In addition, the reliable power of micro-CHP-FCSs could be beneficial to markets where electrical outages are especially frequent or costly. Greenhouse gas emission levels from micro-CHP-FCSs are 69% lower, and the human health costs are 99.9% lower, than those attributed to conventional coal-fired power plants. As a result, FCSs can allow a company to advertise as environmentally conscious and provide a bottom-line sales advantage. As a new technology in the early stages of adoption, micro-CHP-FCSs are currently more expensive than alternative technologies. As the technology gains a foothold in its target markets and demand increases, the costs will decline in response to improved manufacturing efficiencies, similar to trends seen with other technologies. Transparency Market Research forecasts suggest that the CHP-FCS market will grow at a compound annual growth rate of greater than 27% over the next 5 years. These production level increases, coupled with the expected low price of natural gas, indicate the economic payback period will move to less than 5 years over the course of the next 5 years.To better understand the benefits of micro-CHP-FCSs, the U.S. Department of Energy worked with ClearEdge Power to install fifteen 5-kWe fuel cells in the commercial markets of California and Oregon. Pacific Northwest National Laboratory is evaluating these systems in terms of economics, operations, and their environmental impact in real-world applications. As expected, the economic analysis has indicated that the high capital cost of the micro-CHP-FCSs ...
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