Fouling services

They are not recommended for dirty or fouling services, because of plugging of the pilot valve and small-bore pressure-sensing lines. If the pilot valve or pilot cormections become fouled, the valve will automatically open. In special cases where fouling is a function of entrained solids, this limitation may be countered by the use of a nonflowing pilot valve and a pilot line filter. With a nonflowing pilot valve, there is no normal flow in the pilot system and therefore solids entrainment is reduced. 

The usual applications for finned tubes are in heat transfer involving gases on the outside of the tube. Other applications also exist, such as condensers, and in fouling service where the finned tube has been shown to be beneficial. The total gross external surface in a finned exchanger is many times that of the same number of plain or bare tubes. 

CHANTRY, W. A. and Church, D. M. (1958) Chem. Eng. Prog. 54 (Oct.) 64. Design of high velocity forced circulation reboilers for fouling service. 

Easy to shut down and clean for fouling service (A) ... 

This all results in reduced capital cost. The disadvantage of this tube pitch is that, except for the outer few rows of tubes, the shell side cannot be cleaned by hydroblasting. Obviously, this sort of arrangement should never be used in a fouling service, unless the deposits can be chemically removed. 

The third example shown in Fig. 19.7 is my favorite for sensible-heat transfer in fouling service. This consists of 1-in tubes set on lV2-in rotated square pitch. The pitch layout is the same as that of the square pitch. It is just the tube bundle that is rotated by 45°. The shell-side fluid cannot flow without interference between the tubes. Hence, the tubes promote turbulence, and improve heat transfer. The large tubes,... 

Actually, retrofitting a tube bundle with low fin tubes often reduces heat-transfer capacity. This happens when the controlling resistance to heat transfer is shell-side fouling. The fouling deposits get trapped between the tiny fins. This acts as an insulator between the shell-side fluid and the surface of the tubes. In severe shell-side fouling services, I have replaced fin tubes with bare tubes, and doubled the heat-transfer duty on the exchanger. 

On the debit side, the plugging tendency increases exponentially as hole diameters diminish. Smaller holes are also more prone to corrosion. While 5-mm (j -in) holes easily plug even by scale and rust, 13-mm (-ill) holes are quite robust and are therefore very common. The small holes are only used in clean, noncorrosive services. Holes smaller than 5 mm are usually avoided because they require drilling (larger holes are punched), which is much more expensive. For highly fouling services, 19- to 25-mm (f- to 1-in) holes are preferred. 

With large holes (16 to 25 mm), these trays are some of the most fouling-resistant and corrosion-resistant devices in the industry. This defines their main application highly fouling services, slurries, and corrosive services. Dual-flow trays are also the least expensive and easiest to install and maintain. 

Good and repeatable seat tightness, before and after cycle Limited on dirty or fouling service, unless with special configuration... 

The best type of valve unit depends on the corrosive and fouling tendencies of the service, as some valve units tend to pop out of their seats in corrosive services, while others tend to stick to their seats in fouling services. 

Hole diameter. A good choice of size for clean services is Vie in, while Vi in is preferred for fouling services (1). Assuming that the depropanizer is a mildly fouling service, Vis-in holes are appropriate. 

Description The spiral-plate heat exchanger (SHE) may be one exchanger selected primarily on its virtues and not on its initial cost. SHEs offer high reliability and on-line performance in many severely fouling services such as slurries. 

Because of the minimal internals for solids to grow on, both types of contactors are common in fouling services. The spray nozzle based devices are also inherently low pressure drop. 

They can be used for viscous and/or fouling service. formance Characteristics ... 

Low-fouling services (clean fluids) Where mechanical cleaning is required Where mechanical cleaning is required... 

Refs. Oversurfacing of heat exchangers in fouling service results not only in increased equipment costs but also in more cleaning waste, because operating velocities will be lower than the design velocity, and the reduced turbulence results in increased deposits (see Ref. [5]). 

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