Patent Application
20080187877
The gasification process involves turning coal or other carbon-containing materials into synthesis gas. Because coal costs less than natural gas and oil, there is a large economic incentive to develop gasification technology. An issue with existing gasification technologies is that they generally have high capital costs and/or relatively low availability. Availability refers to the amount of time the equipment is on-line and making products. One cause of low availability is complex or short-lived gasifier liner designs. Examples of liners currently being used in gasifiers are refractory liners, membrane liners, and regeneratively cooled liners. Refractory liners require annual replacement of the refractory, with an availability of approximately 90%. While membrane liners have a longer life than refractory liners, the complexity of the liner can increase the cost of the gasifier up to 2 to 3 times.
Regeneratively cooled liners are also used in the gasification process and generally present a lower cost, longer life alternative to refractory liners and membrane liners. These benefits are a result of freezing a layer of slag on the wall of the regeneratively cooled liner. Regeneratively cooled liners can significantly reduce the cost of electricity, hydrogen, and synthesis gas produced by gasification plants when compared to gasification plants using refractory liners and membrane liners. An example of a regeneratively cooled liner is disclosed in U.S. Pat. No. 6,920,836 (Sprouse), which is herein incorporated by reference.
While regeneratively cooled liners provide significant benefits in gasification technology when compared to refractory liners and membrane liners, one of the technical challenges of using regeneratively cooled liners is managing the thermal growth of the liner. The liner, which may be formed of ceramic, is usually attached to a metal backing structure of the gasifier. Thus, as the temperature inside the gasifier increases, the rates of thermal expansion of the ceramic liner and the metal backing structure are mismatched.
Another challenge with regard to regeneratively cooled liners is the specific implementation of the metal/ceramic joining required to establish a closed-loop (regenerative) cooling circuit. In addition, there is a risk that a small crack in the liner could alter the performance and efficiency of the gasifier, eliminating the ability to co-generate power.
Thus, a need exists for a gasifier liner that offers the advantages of a ceramic lining while addressing the challenges of ceramic/metal joining and ceramic/metal thermal growth mismatch.
A liner having controlled thermal expansion for use within a gasifier vessel includes a plurality of elongated channels and a plurality of ceramic sheaths. The elongated channels pass coolant through the gasifier. The ceramic sheaths surround the elongated channels.
Coolant channels 12 extend along a length of vessel 16 and have a head end 28, aft end 30, and body 32. Coolant channels 12 are connected to mounting flange 44, which contacts vessel 16, injector 20, and coolant inlet manifold 22 by mechanical seals 34. As can be seen in
Liner 14 envelops coolant channels 12 shielding coolant channels 12 from the corrosive, high temperature environment of gasifier reactor 10. Liner 14 covers approximately 100% of coolant channels 12 exposed to the gasification reaction in reaction chamber 26. Any exposed metal of coolant channels 12 that is not covered by liner 14 is kept sufficiently cooled or protected by the face of injector 20 or by the quench spray in quench section 24 so that the metal does not corrode. In an exemplary embodiment, liner 14 may be formed of materials including, but not limited to: ceramics and ceramic matrix composites. The thermal expansion of a ceramic matrix composite sheath is between approximately 1.7 E-06 in/in-° F. and approximately 3.3 E-06 in/in-° F.
Vessel 16 is positioned above quench section 24 and contains reaction chamber 26. Vessel 16 houses coolant channels 12, liner 14, and insulator 18 of gasifier reactor 10. Insulator 18 is positioned between liner 14 and vessel 16 to help maintain the temperature of coolant channels 12, liner 14, and vessel 16 within operating limits. A suitable temperature range for liner 14 is between approximately 1000° F. (538° C.) and approximately 2000° F. (1093° C.). A particularly suitable temperature range for liner 14 is between approximately 1200° F. (649° C.) and approximately 1800° F. (982° C.). Although
Coolant inlet manifold 22 supplies the coolant to coolant channels 12 and is contained between Injector 20 and head ends 28 of coolant channels 12. To prevent coolant flowing from coolant inlet manifold 22 to coolant tubes 12 from leaking into vessel 16 or out of vessel 16 to the atmosphere, coolant tubes 12 are sealed where coolant channels 12 seal against injector 20, where coolant channels 12 seal against vessel 16, and where vessel 16 seals against injector 20. Head ends 28 of coolant channels 12 are attached to injector 20 over only a few inches, resulting in manageable loads between injector 20 and coolant channels 12. Although gasifier reactor 10 is discussed as including coolant inlet manifold 22, gasifier reactor 10 may alternatively be constructed without a manifold or with a manifold of different arrangement without departing from the intended scope of the invention.
In operation, coolant flows from injector 20 through coolant inlet manifold 22, where it is introduced into head ends 28 of coolant channels 12. Although there may be minor leakage of the coolant at the connection of coolant channels 12 and injector 20, and at the connection of coolant channels 12 and vessel 16, the leakage is acceptable because the coolant will eventually exit into vessel 16. In alternative configurations, coolant channels 12 may be joined into coolant manifolds, replacing the need for mechanical seals 34 to eliminate leakage. As the coolant passes through coolant channels 12 the coolant picks up heat from reaction chamber 26 and cools coolant channels 12. For a dump-cooled liner configuration, aft ends 30 of coolant channels 12 are suspended within vessel 16 and the coolant eventually dumps into vessel 16 immediately upstream of quench section 24. For a regeneratively-cooled liner configuration, aft ends 30 of coolant channels 12 are joined to a manifold that directs the coolant out of gasifier vessel 16. Examples of suitable coolants include, but are not limited to: steam, nitrogen, carbon dioxide, and synthesis gas. A suitable temperature range for the coolant is between approximately 100° F. (38° C.) and approximately 1200° F. (649° C.). A particularly suitable temperature range for a water coolant is between approximately 150° F. (66° C.) and approximately 400° F. (204° C.). A particularly suitable temperature range for gaseous coolants is between approximately 600° F. (316° C.) and approximately 1000° F. (760° C.).
The coolant flows through coolant channels 12 at a rate sufficient to freeze a slag layer 36 along an exposed inner surface 38 of liner 14. Slag layer 36 is formed from the ash content in the carbon-rich fuels flowing through reaction chamber 26. At the high temperatures in which gasifier reactor 10 operates, the ash becomes slag. The temperature of the coolant running through coolant channels 12 is low enough to keep liner 14 at a temperature to freeze slag layer 36 onto exposed inner surface 38. If pieces of liner 14 break off, slag layer 36 protects coolant channels 12 from abrasion by high velocity particulates and from chemical attack by gas phase reactive species in reaction chamber 26. Alternatively, if slag layer 36 is not deposited along exposed inner surface 38 of coolant channels 12, coolant channels 12 may be formed of bare metal that is hardened or coated to resist abrasion and that is cooled to achieve surface temperatures capable of withstanding chemical attack.
For a dump-cooled liner configuration, the exit velocity of the coolant from coolant channels 12 also provides a slag drip lip 40 at aft ends 30 of coolant channels 12. Slag drip lip 40 is a result of the expanding volume and rapid quench of the coolant exiting at aft ends 30 coolant channels 12 and prevents slag from building up at aft ends 30 of coolant channels 12. The presence of slag drip lip 40 thus reduces any maintenance time and cost that would be required to remove slag from aft ends 30 of coolant channels 12, as well as prevents slag from blocking the coolant from exiting coolant channels 12 and entering quench section 24.
Sheaths 46 may be positioned onto coolant channels 12 either by slipping sheaths 46 around coolant channels 12 from head end 28 toward aft end 30, or from aft end 30 toward head end 28. After enough sheaths 46 have been slipped over coolant channels 12 to cover substantially all of coolant channels 12, tips 52 are used to keep sheaths 46 in place on coolant channels 12. Tips 52 may be connected to coolant channels 12 in any manner known in the art, including, but not limited to: welding and brazing.
Metal and ceramic joining issues, leakage issues, and thermal growth mismatch issues prevalent in gasifiers can either be reduced or eliminated by using a liner formed of ceramic sheaths positioned over coolant channels of the gasifier. The ceramic sheaths may be formed of a monolithic ceramic or a ceramic matrix composite. The ceramic sheaths surround the coolant channels and cover substantially the entire length of the coolant channels. The liner may be used in gasifiers having coolant channels of various configurations.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
