Heat exchangers fouling problems

Printed circuit heat exchangers, fouling problems 553... 

Cooling System Corrosion Corrosion can be defined as the destmction of a metal by chemical or electrochemical reaction with its environment. In cooling systems, corrosion causes two basic problems. The first and most obvious is the failure of equipment with the resultant cost of replacement and plant downtime. The second is decreased plant efficiency to loss of heat transfer, the result of heat exchanger fouling caused by the accumulation of corrosion products. 

Heat-exchanger fouling, or scale build-up, can be a major factor limiting the kind and concentration of solids in feed that can be processed. The plugging problem can be dealt with by periodically flushing the exchanger with warm water or diluted nitric acid, as in conventional processes. 

Six mechanisms have been identified as being responsible for heat exchanger fouling, but it is seldom that one mechanism is responsible for a particular fouling problem a combination of mechanisms is much more likely, although one mechanism may be dominant. The variables that have the greatest influence on these mechanisms, apart from the nature of the fluids being processed, are temperature and flow rate. 

The problems associated with heat exchanger fouling have been known since the first heat exchanger was invented. The momentum of the industrial revolution depended on the raising of steam, usually from coal combustion. In the early days serious problems arose in steam raising equipment on account of the accumulation of deposits on the water side of boilers. The presence of these deposits, usually crystalline in character originating from the dissolved salts in the feed water. 

The problem of heat exchanger fouling therefore represents a challenge [Bott... 

Kolaczkowski, S.T., Crittenden, B.D. and Varley, R., 1988, Operability of crude oil preheat exchangers - computer software tools for managing the problems of heat exchanger fouling in oil refining and petrochemical plants. In. Conf Fouling in Process Plant. Inst. Cor. Sci. Tech, and I. Chem. E. University of Oxford, Oxford, 52 - 67. 

An unusually large error of closure (in absolute value) suggests an abnormal event, for example, a malfunctioning sensor or an equipment problem, such as heat exchanger fouling, as illustrated by Example 10.2. 

Oil and hydrocarbon leaks that return with the condensate coat heat-exchange surfaces and cause FW system fouling and deposit binding. These materials must be removed or they will reenter the boiler to produce nonwettable boiler surfaces, and create serious problems. Oil in condensate should be removed by the use of an inline pre-coat filter. The pre-coating should be either aluminum hydroxide ox ferric hydroxide becaue both these hydrous oxide gels have an affinity for oil. 

A note of caution on the use of photo-etched channels has been offered by RAMSHAWfl3 ) who points out that the system is attractive in principle provided that severe practical problems such as fouling are not encountered. With laminar flow in matrices with a mean plate spacing of 0.3-1 mm, volumetric heat transfer coefficients of 7 MW/m3 K have been obtained with modest pressure drops. Such values compare with 0.2 MW/m3 K for shell and tube exchangers and 1.2 MW/m3 K for plate heat exchangers. 

---