Heat exchange – With scraper removing product from temperature modifying...
Patent
1983-06-07
1986-01-07
Davis, Jr., Albert W.
Heat exchange
With scraper removing product from temperature modifying...
165 95, 122379, 1510416, 1510419, F28G 106, F28G 164, F28G 110
Patent
active
045628866
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a device for the internal cleaning, under operation, of the tubes of a heat exchanger containing a plurality of substantially straight tubes, a shell surrounding said tubes, and head chambers at the ends of the heat exchanger. The number of tubes may vary from a few to thousands of tubes. The heat exchanger is part of equipment, and it may be built into said equipment, or it may be combined with said equipment, or it may stand separate from said equipment. In the first two types of heat exchanger the shell or the head chambers may be parts of the equipment. The heat exchanger may be mounted in a horizontal or vertical position.
PRIOR ART
The nominal effect of a heat exchanger is based on the assumption that the heat transfer from the tube wall to the medium inside the tube, or the reverse, is not deteriorated by any coating which insulates and which reduces the flow velocity in the tube. Such a coating occurs, however, in most processes. It is very inconvenient, particularly in continuous processes, to have to reckon with a sinking effect of the heat exchangers. In addition, such a coating may stop the production, and may deteriorate the yield by changing the ratio of the desired to the undesired product. It may also increase the consumption of steam.
Such a coating on the tube wall may be of various types. In heat exchangers for a comparatively low temperature, for example in waterworks and sewage treating plants, the coating may consist of soft sludge. In heat exchangers for a comparatively high temperature, for example in chemical and petrochemical processing industries, the coating may consist of viscous tar, coke, and soot. In other heat exchangers, for example in the cellulose processing industry, the coating may form brittle deposits.
Few heat exchangers have means for the internal cleaning of the tubes under operation. The majority of heat exchangers are cleaned after having been taken apart during a stop of operation. Heat exchangers are often made oversize, to prolong the interval between cleaning operations. A cleaned heat exchanger is often kept in reserve, to minimize the time for the stop of operation. Such measures, however, necessitate an increased investment. Generally, the cost for cleaning the tubes and associated operations during the lifetime of a heat exchanger, say 5 years, correspond to 3 times the investment for the heat exchanger. To said cost must be added the costs for the interruptions of operation, the reduced production, and the lower yield, said additional costs being often considerable. The cleaning of the tubes after discontinuing the operation and taking the heat exchanger apart is considered to be one of the dirtiest industrial jobs.
Several methods have been suggested for cleaning the tubes under operation. In one known method cleaning pistons are moved forward and backward through the tubes by means of rods, a common driving plate, and a pressurized cylinder. It is an inconvenience of said method that the loss of pressure is comparatively large, and that there is a risk of deposition on the cleaning pistons because they have a large surface in contact with the tube wall. It is another inconvenience that the device requires a large space, and that it can be used only for heat exchangers containing short tubes.
According to the Swedish Pat. No. 317,394 loose brushes are driven by the pumped medium forward and backward through the tubes. A catching basket for the brush is placed at each end of the tube. It is an inconvenience that the medium has to be pumped, that a system of valves and shunt conduits has to be arranged to reverse the flow of the medium, that a comparatively large loss of pressure is caused by the catching basket just outside the tube ends and by the brush inside said catching basket, that the mounting of the catching basket requires a deformation of the valuerable tube end, and that the plastic parts and the brush limit the use of the device to heat exchangers operating mainly with water and aqueous sol
REFERENCES:
patent: 502223 (1893-07-01), Burpee
patent: 514514 (1894-02-01), Stafford
patent: 813739 (1906-02-01), Ross
patent: 1007423 (1911-10-01), Bernhardt
patent: 1448048 (1923-03-01), Bahr
patent: 1611820 (1926-12-01), Delo
patent: 2233066 (1941-02-01), Watson
patent: 2628380 (1953-02-01), Therrien
patent: 3460180 (1969-08-01), Girard
Davis Jr. Albert W.
Ford John K.
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