Heat exchange – Expansion and contraction relieving or absorbing means – Relieving or absorbing means supports temperature modifier...
Patent
1999-04-19
2000-11-07
Leo, Leonard
Heat exchange
Expansion and contraction relieving or absorbing means
Relieving or absorbing means supports temperature modifier...
165 81, 165154, F28F 700, F28D 710
Patent
active
061422185
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a heat-exchanger unit for recovering heat from the flue gases from a cylinder steam boiler.
More specifically the invention relates to a heat exchanger unit of the type comprising a flue-gas tube open at both ends for fitting in vertical position in a pressure vessel situated above the boiler's combustion appliance in order to form a flue-gas channel running vertically therethrough, and a heat-exchanging tube dosed at both ends which is supported concentrically inside the flue-gas tube at one end by a bent inlet pipe extending from a first lower opening in the peripheral wall of the flue-gas tube to an inlet opening in a lower outwardly bulging end wall of the heat-exchanging tube and at the other end by a straight outlet pipe extending from an outlet opening in an upper part of the peripheral wall of the heat-exchanging tube to a second, upper opening in the peripheral wall of the flue-gas tube, the inlet pipe having a first, horizontal, straight end portion by which it is connected to the flue-gas tube, and a second, upwardly directed, straight end portion by which it is connection to the lower end wall of the heat-exchanging tube, and also an intermediate, curved portion joining said two end portions together.
In previously known heat exchanger units of the type described above the curved portion of the inlet pipe has always been bent at an angle of 90.degree.. Furthermore, the other end portion of the inlet pipe has extended in strictly vertical direction towards the inlet opening, the latter being arranged concentrically in relation to the central longitudinal axis of the heat-exchanging tube in the lower end wall of the heat-exchanging tube.
A drawback of these known heat exchanger units has been that cracks can easily occur at the weld between inlet pipe and flue-gas tube. The reason for this cracking is that the hot flue gases produced in the boiler's combustion appliance subjects the heat-exchanging tube to considerably greater thermal influence than the flue-gas tube which means that, when the boiler is in operation, the heat-exchanging tube undergoes considerably greater longitudinal expansion than the flue-gas tube. This is particularly so when, as is usually the case, the heat-exchanging tube is provided with external surface-enlarging elements in the form of a large number of pins protruding radially from the tubular body of the heat-exchanging tube, for instance. Since the outlet pipe is normally considerably shorter than the inlet pipe and also generally considerably greater in diameter, this difference in the longitudinal expansion between heat-exchanging tube and flue-gas tube will give rise to considerably higher mechanical strain at the joint between inlet pipe and flue-gas tube than at the joint between outlet pipe and flue-gas tube. The risk of fatigue cracks eventually appearing is therefore much greater in the former joint than in the latter.
The object of the invention is to obtain an improved heat exchanger unit of the type described in the introduction, with reduced risk of fatigue cracks of the type described above appearing, and therefore having increased service life in comparison with previously known heat exchanger units.
The heat exchanger unit proposed according to the invention for this purpose is characterized primarily in that the bending angle of the intermediate, curved portion of the inlet pipe exceeds 90.degree. and that the other end portion of the inlet pipe extends with an inclination determined by said bending angle, towards the centre of curvature of a partially spherical portion of the lower end wall of the heat-exchanging tube, in which wall the inlet opening is arranged eccentrically in relation to the central longitudinal axis of the heat-exchanging tube.
Giving the bent portion of the inlet pipe a bending angle exceeding 90.degree. achieves increased flexibility in the inlet pipe. The increased bending angle thus also results in an increase in the total length of said pipe as well as an increase in the length of the bent po
REFERENCES:
patent: 1326277 (1919-12-01), Latourelle
patent: 2961221 (1960-11-01), Friese et al.
patent: 3026092 (1962-03-01), Pellegrini
patent: 3572430 (1971-03-01), Charnock, Jr.
patent: 3989100 (1976-11-01), McDonald
patent: 4276928 (1981-07-01), Blaskowski
patent: 5626187 (1997-05-01), Nilsson
Nilsson H.ang.kan
Sabelstrom Wilhelm
Aalborg Industries A/S
Leo Leonard
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