Fouling heat exchangers

Suspended solid.s Clogs pipelines Fouls heat exchanger Surfaces Settling Filtration... 

It is a general principle of heat exchange that low flows tend to promote fouling and fouling promotes corrosion. The corroded, fouled heat-exchanger surface retards flow and creates a vicious cycle. We will see this problem again in shell-and-tube heat exchangers, as discussed in Chap. 21. 

In many plants it may not be possible to shut down a fouled heat exchanger or other vital item of equipment. Thus it may prove impossible to either collect a sample of the foulant or to subsequently clean the unit off-line. Under these circumstances, some detective work is required to deduce the most likely cause of the fouling problem. Many times, however, some of the foulant material will be found in more accessible parts of the... 

The economic loss term includes two types of losses i) economic loss associated with failed equipments that have not been repaired (for example, a fouled heat exchanger can continue operating but at reduced heat transfer rate, ii) economic loss due to imavailability of equipment during repair time. The economic loss is calculated as a loss rate ( per day) multiplied by the duration of the period within which the loss is realized. To determine economic loss rates, an analysis is carried out on each piece of equipment to determine the economical effects of equipment failure, which include reduced production rate or even shutdown, the deterioration of product quality, etc. 

FIGURE 2.1. Temperature distribution across fouled heat exchanger surfaces... 

Dust in recycling streams fouls heat exchanger surfeces or causes difficulties in direct combustion systems. 

Used solvent is liable to foul heat exchanger surfaces and so will almost always be on the tube side of a shell and tube heat exchanger with steam on the shell side. While it is possible to use a natural circulation external calandria if the solvent to be evaporated is clean, forced circulation is more reliable if the solvent contains residue (Fig. 4.1) despite the fact that it may be a diliicult duty as regards both cavitation and seal maintenance. 

Contaminated MEG from textile uses may contain antimony and from vehicle fleet operation it may be contaminated with inorganic acid inhibitors so that from both sources the residues arising from MEG recovery is liable to foul heat exchanger surfaces and may be very toxic. 

Certain low-sulfur waxy crudes rapidly foul heat exchanger tubes. An easy method that has worked in some services to restore lost heat-transfer capacity partially is as follows ... 

Asomaning, S.A. Watkinson, A.P. Petroleum stability and heteroatoms species effects on fouling heat exchangers by asphaltenes. Heat Transfer Eng., 2000,12,10-16. 

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