Flash or Foul, 2008 Engineering, Pulping and Environmental Conference

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Condensate stripper preheater fouling is a significant problem in the pulp and paper industry. Fouling reduces energy efficiency, increases maintenance costs for cleaning, and lowers availability in condensate stripping systems. High condensate stripper availability is needed to comply with environmental regulations. The preheater is often the major cause of downtime in condensate strippers. Many types of heat exchanger designs have been used as preheaters, including plate-and-frame, shell-and-tube, and spiral heat exchangers. All of these designs have been plagued by the reaction-type fouling that occurs on both the foul and the stripped condensate sides of the exchangers. A new preheater design was developed and implemented at the Charleston mill. It consists of a series of flash tanks and shell-and-tube heat exchangers. Stripped condensate is cooled by flashing in the flash tanks, and the flash steam is used on the shell side of the shell-and-tube heat exchangers. The flash steam is clean and does not cause the shell side fouling that occurs when condensate itself is used on the shell side. The foul condensate is heated in the tube side of the exchangers, and results in fouling that is easily removed by chemical cleaning. The preheater avoids the high temperatures on heat exchanger surfaces which promote chemical reaction-type fouling. The new preheater was installed in 2006 in the Charleston mill condensate stripper system, which has a flow rate of 3.8 m³/min and a bottoms temperature of about 150 °C. It has performed well and has resulted in excellent preheater availability.