Gas separation – Deflector – Impingement baffle
Reexamination Certificate
2002-07-11
2004-02-03
Noland, Thomas P. (Department: 2856)
Gas separation
Deflector
Impingement baffle
C055S464000, C096S147000, C096S154000, C073S863220, C073S028050
Reexamination Certificate
active
06685759
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to particulate sampling systems, and more specifically to devices, methods and systems for isokinetic sampling of particulate matter, in-situ, from a high-temperature and/or high-pressure gas stream.
2. Description of Related Art
Various industrial processes generate gas streams containing particulate matter. For example, coal-based power generation technologies produce particulate-loaded streams of process gas. The gas streams are often filtered to remove entrained particulate matter prior to release to the atmosphere to reduce emissions, and/or prior to introduction to process equipment that may be damaged by the particulate matter. For example, particulate control devices (PCDs), such as ceramic barrier filters or granular bed filters can be utilized to remove particulate matter from process gasses produced by coal gasification and combustion prior to their use in a turbine or fuel cell to generate electricity in a power generation plant. Gas turbines utilized in power generation typically require particulate loading in the gas supply stream of less than 20 ppmw (parts per million by weight) or less than 24 mg/m
3
, with less than one percent of the particulate matter being larger than 10 microns (&mgr;m). See McClung, et al., “Design and Operating Considerations for an Advanced PFBC Plant at Wilsonville”, in
Proceedings of the
13
th International Conference on Fluidized
-
Bed Combustion, Vol.
1, pp. 107-115, Published by American Society of Mechanical Engineers, 1995. Increasingly stringent environmental protection regulations typically limit particulate emissions to the environment to 30 ppmw or less, and advanced emission control systems may enable particulate removal to as low as 0.2 ppmw or less.
The characteristics of a gas stream containing particulate matter often must be determined by sampling the gas stream. Sampling may be required to determine the overall quantity of particulate matter in a given volume of gas, to determine the portion of the particulate matter that falls within one or more particle size ranges, and/or to determine various characteristics of the particulate matter or the overall gas stream (such as, for example, chemical content, pH, temperature, pressure, flowrate, etc.). A variety of sampling devices have been developed for these purposes. For example, extractive sampling techniques remove a portion of the particulate-laden gas from the gas stream for processing and/or analysis in an external sampler device. Extractive sampling suffers a number of disadvantages. For example, the particulate properties may be altered during extraction. Various components of the gas stream, such as, for example, alkali or tar vapors in the gas stream, may condense during extraction. To minimize the adverse effects of sample gas cooling, extractive sampling lines must be heat traced, and expensive, high-temperature isolation valves must be used. Unfortunately, these complicated and expensive heat tracing systems are only partially successful in minimizing condensation of gas stream components, and add considerably to the expense of the sampler. In addition, collisions of the particles with one another and with the walls of the sampling lines during extraction alter the particulate content and sizing. See Anand, et al., “Optimization of Aerosol Penetration Through Transport Lines,” Aerosol Science and Technology, Vol. 16, pp. 105-112 (1992). Thus, in-situ, isokinetic sampling of the gas stream has been found to be desirable. With an in-situ sampling system, it is not necessary to heat trace the external portion of the system, and it is possible to use less-expensive, low-temperature isolation valves. By allowing the use of less-expensive valves, the in-situ sampling system can be a more cost-effective means of sampling and provides more representative samples when compared to an extractive sampling system.
Enabling in-situ, isokinetic sampling, however, presents a number of challenges. The size of sampling devices for in-situ sampling is often severely constrained by the associated process equipment. For example, in situ sampling of a gas stream flowing within a twelve-inch (12″) process pipe typically requires that the sampler size be considerably less than twelve inches, and not present an unacceptable flow restriction within the pipe. Additional constraints on the size and configuration of a sampling device may result from the sampling technique. For example, a sampler may need to be specially configured for sampling at or near the wall of a process pipe, or at the midpoint of the flow. Access limitations and safety concerns also may dictate the need for remote control of the sampling equipment, and the need for seals, purge systems, and other substantial means for isolating the gas stream from the external environment during sampling.
Further challenges to the successful development of in-situ, isokinetic sampling are presented by the characteristics of the particulate-laden gas stream being sampled. For example, recent and ongoing developments in advanced technologies for power generation, such as coal-based advanced pressurized fluidized-bed combustion (APFBC) and integrated gasification combined cycle (IGCC) processes, result in the need for sampling of process gas streams at very high pressures, often up to and exceeding 150-400 psia (1.0-2.8 MPa), and at very high temperatures, often up to and exceeding 600-1600° F. (320-870° C.). The gas streams to be sampled may further contain one or more highly corrosive and/or abrasive constituents.
Previously-known sampling devices and methods are typically inadequate for sampling particulate-laden gas streams at such extreme conditions. For example, known cascade impactors for sampling particulate, such as those shown and described in U.S. Pat. Nos. 3,001,914; 3,693,457; and 3,795,135, which are hereby incorporated by reference herein, often suffer from galling, fusion of contacting components, deterioration of materials, and other damage at extreme conditions. For example, previously known samplers typically include separate spacer elements between adjacent stages, and/or separate spacer elements between the jet plate and associated collection substrate of a single stage. These spacer elements are commonly in the form of cross-shaped supports or rings that are placed between adjacent components of an impactor during assembly. These spacer elements may undergo fusion or material transfer by galling with adjacent components at elevated temperatures, potentially resulting in analysis errors. In addition, the numerous components of a typical impactor render assembly and disassembly time consuming and subject to error or damage.
In addition, previously-known cyclone samplers at best provide limited utility in high-temperature, high-pressure sampling applications. For example, a prior art five-stage cyclone assembly included threaded connections on each of its five cyclone separators, which require disassembly by unthreading these connections to access and analyze the particulate matter collected therein. Threaded connections typically present on such samplers have been found to seize due to galling from exposure to high-temperature gas streams. In addition, the cyclone separators of the conventional five-stage cyclone assembly are laid out on the manifold in a longitudinally-spaced arrangement that results in an overall sampler length that has been found unacceptable for in-situ sampling in certain process vessels. Still further, the configuration and materials of construction of the conventional five-stage cyclone assembly provide inadequate structural rigidity, and the assembly may deform under its own weight at high temperatures.
Through considerable experimentation, applicants have discovered advantages in combining two or more devices into a single sampling system, thereby overcoming constraints imposed by in-situ, isokinetic sampling at high-temperature and high-pressure. For example, a cyclone sampler or a cas
Dahlin Robert S.
Farthing William E.
Landham, Jr. Edward C.
Needle & Rosenberg P.C.
Noland Thomas P.
Southern Research Institute
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