Heat exchange apparatus and process

Details Heat exchange apparatus and process Heat exchange apparatus and process

1997-05-27

1999-09-28

Lewis, Michael

Chemistry of inorganic compounds

Hydrogen or compound thereof

Elemental hydrogen

165110, 165160, 165174, C01B 326, F28B 100

Patent

active

059583649

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a heat exchange apparatus and process and in particular to a process and apparatus wherein there is liable to be significant differential thermal expansion between tubes carrying a process fluid and means, such as a tube sheet, defining a boundary of the zone through which a heat exchange medium passes in heat exchange with the process fluid passing through the tubes.
In a heat exchanger of the above type a process fluid is passed from a process fluid feed zone, through heat exchange tubes disposed within a heat exchange zone defined by a casing through which a heat exchange medium passes, and then into a process fluid off-take zone. Means, such as tube sheets, are provided to separate the zones. Thus a tube sheet may separate the heat exchange zone through which the heat exchange medium passes from a zone, such as a plenum chamber, communicating with the interior of the heat exchange tubes to permit feed of process fluid to the tubes or off-take of process fluid from the tubes. An alternative arrangement involves the use of header pipes disposed within the heat exchange zone to define the process fluid feed zone: the process fluid is fed to the header pipes from whence it flows into and through the heat exchange tubes. Similarly header pipes may be provided for the off-take of process fluid from the tubes. Alternatively there may be a combination of tube sheets and header pipes, for example the process fluid may be fed to the heat exchange tubes from a plenum chamber separated from the heat exchange zone by a tube sheet while header pipes are provided disposed within the heat exchange zone for off-take of process fluid from the tubes. Such tube sheets or headers are herein termed boundary means as they define boundaries between the heat exchange zone and the process fluid feed and off-take zones.
In some applications, such as steam reforming of hydrocarbons, the heat exchange tubes are of considerable length, typically several meters, and there is a large temperature difference, often several hundred .degree. C., e.g. 500 to 1000.degree. C. or more, between the cold, i.e. ambient, state and normal process operation. As a result the tubes expand longitudinally by a considerable amount, often 10 cm or more, relative to the casing to which the boundary means is fastened. Normal practice is to provide pigtails at one or both ends of the tubes to permit such differential expansion so that the pigtails, rather than the tubes themselves are fastened to boundary means. Alternatively bellows arrangements are often employed to permit such expansion. However pigtails or bellows arrangements able to accommodate differential expansion of the order of 10 cm or more present practical difficulties.
In some types of heat exchange apparatus, the heating exchange medium is the process fluid that has passed through the tubes but which has been subjected to further processing before being used as the heat exchange medium. For example the tubes may be filled with a steam reforming catalyst and a hydrocarbon feedstock mixed with steam is passed through the tubes: the latter are heated by a heat exchange medium to supply the necessary heat for the endothermic primary steam reforming reaction to give a primary reformed gas. The resultant primary reformed gas is then subjected to partial oxidation where the primary reformed gas is partially combusted with oxygen or air and, in some cases, the process known as secondary reforming, is then passed through a secondary reforming catalyst bed. The resultant partially combusted gas, by which term we include secondary reformed gas, is then used as the heat exchange medium heating the tubes. An example of this type of process and heat exchange apparatus for effecting the primary reforming is described in GB 1 578 270.
In a modification of this type of process the boundary means at the outlet end of the heat exchange tubes is omitted. The tubes open into a zone into which a gas such as air or oxygen is introduced so that partial combustion of the primary reformed g

REFERENCES:
patent: 2458756 (1949-01-01), Watson
patent: 4871014 (1989-10-01), Sulzberger

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