The inner tube surfaces of shell-and-tube heat exchangers are often fouled by deposits. In order to reach required performances or temperatures, the heat transfer surface is overdesigned by applying an exaggerated fouling factor. If tubes are cleaned continuously by means of sponge rubber balls, this overdesign is no longer necessary.
Sponge rubber balls can be used for easy cleaning of the inner tube walls of shell-and-tube heat exchangers. They are available with diameters from 12 to 45 mm and produce the best cleaning effect if their diameter is 1 to 2 mm larger than the inner tube diameter of the heat exchanger. The ball material is individually adapted to the respective tube material in order to avoid material wear and tear. The oversize of the balls creates a pressure drop inside the tube which transports the cleaning balls through the system. The balls continuously loosen the fouling from the tube walls, thus avoiding deposits which may impair the heat transfer. Depending on the tube material, the cleaning balls are worn down after about 4 to 7 weeks, when they must be replaced. The number of balls in circulation is equivalent to 20 to 30% of the number of tubes per pass.
Easy ball replacement
The main components of the cleaning system are the ball recirculating unit, the strainer section and the control system (Fig. 1). The ball recirculating unit comprises a stainless steel housing with a sight glass as its cover and a pump designed for an installed load of approximately 1.5kW mounted on it. The transparent cover allows both easy monitoring of the circulating balls and their quick replacement. One DN 80 pipe connects each ball collector with the inlet pipe of the heat exchanger, and then continues from the strainer section back to the recirculating unit. The strainer section is an adapter pipe with a screen fitted inside. The screen can be either fixed or movable, or alternatively designed as a funnel, depending on the diameter of the pipe and on the type of fouling prevailing in the cooling water. The degree of fouling can be monitored by connecting addi-tional pressure gauges upstream and downstream of the strainer. The control system allows different time intervals to be programmed, so that the cleaning frequency can be individually adapted to suit actual requirements.
Simple operational principle
The pump of the ball recirculating unit transports the balls to the inlet area of the heat exchanger. The cooling water flow carries the balls, distributing them over the individual tubes. The almost identical hydraulic conditions within the tubes guarantee uniform distribution. After each passage, the balls are separated from the cooling water by the strainer section and trapped in the ball collector. Apart from simply checking the ball dimensions, the system is maintenance-free.
Potential cost savings
There are a number of advantages if a heat exchanger is operated together with a tube cleaning system. The constant heat transfer enables efficiency to be optimised in the long run. Continuous cleaning prevents corrosion and prolongs the life of the heat exchanger. Since manual cleaning is no longer necessary, labour costs are reduced and the environmental impact is lessened by eliminating the need for cleaning chemicals. Finally, the cleaning system allows smaller cooling surfaces to be installed and thus cuts the cost of new systems.
Taprogge
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Further information cpp-256
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