Exchanger Cleaning

The values of h, and AP, calculated by this procedure are for clean exchangers and are intended to be as accurate as possible, not conservative. A fouled exchanger will generally give lower heat-transfer rates, as reflected by the dirt resistances incorporated into Eq. (11-2), and higher pressure drops. Some estimate of fouling effects on pres-... 

The formation of a bis(guanidinate)-supported titanium imido complex has been achieved in different ways, two of which are illustrated in Scheme 90. The product is an effective catalyst for the hydroamination of alkynes (cf. Section V.B). It also undergoes clean exchange reactions with other aromatic amines to afford new imide complexes such as [Me2NC(NPr )2]2Ti = NC6F5. ... 

Overall Heat Transfer Coefficients. Overall resistance to heat transfer based upon the outside area for the clean exchanger ... 

Therefore, the overall heat transfer coefficient for the clean exchanger is Uoc = 407 W m-2 K-1. 

Note, in the above analysis for the dirty exchanger the fouling has been included as part of the wall. Neglecting fouling, i.e. for a clean exchanger, these temperatures become 106.5°C and 109.2°C, respectively. 

Thus, the clean exchanger comfortably exceeds the required duty. The dirty exchanger also exceeds the required duty and so this exchanger seems suitable. 

The value of U was provided in the calculation. Typical values of f/ for new, clean exchangers are available in the literature and are here assigned the symbol C/ iean-After several months of use, the tubes are fouled by scale or dirt. This scale causes a decrease in the overall heat-transfer coefficient, from (/clean t/diny- Th relation between these two C/s is given by... 

The ratio of pressure drops of fouled (Apf) and clean exchanger (Apc) for constant mass flow rate is given by [151] ... 

It is best to always assume that water is present on the other side of any valve which is about to be open during operation (e.g., cleaned exchanger, line to a spare pump, additional feed line, drain, vent, instrument, or sample line). Such a line must be thoroughly drained before the valve connecting it to the column is opened. Failure to do this has been a common cause of pressure surges (4, 145, 296). 

Typieal fouled exehanger pressure drops are 1.3—2 times that of elean exchangers (Barletta, 1998). For extreme cases, fouled exchanger pressure drops are much higher than that of clean exchangers. 

Heat transfer in crude exchangers often declines because of tube-side fouling. The difference in crude preheat may be 50 "F for a dirty vs a clean exchanger train. 

The preferred method of cleaning exchangers is the use of alkaline chemicals such as Oakite for removing oil films, and phosphate-type cleaners such as Calgon for removing water scale. Inhibited dilute hydrochloric... 

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