Shell-and-tube condenser

Vertical vapor-in-tube downdraft condensers offer several advantages over horizontal condensers. Many of the sante advantages are offered by vertical vapor-in-shell condensers that use baffles designed to permit condensate to remain on the tube. The advantages of vertical condensers and differences between vertical and horizontal condensers are  

Countercurrent flow is accomplished resulting in maximum possible subcooling of condensate. Noncondensable gases, which always exist in a condenser, are contacted with the lowest available temperature before removal. Vent losses are therefore at a minimum. 

Pressure drop is generally lower for vertical vapor-in-tube condensers. However, for very low operating pressures (below 50 torr) shellside condensing will provide lower pressure drop if equipment is appropriate designed. 

More accurate control is afforded for vertical vapor-in-tube condensers. 

With few exceptions, vertical downdraft condensers provide better heat transfer than updraft condensers. Occasionally, updraft condensers are used when minimum condensate subcooling is desired or when the remaining vapors will not condense in the presence of previously obtained condensate. Sonte-tinaes corrosion is minimized by preventing condensate and uncondensed vapors from contacting. Chemical reactions may also be avoided. 

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Evaporative condensers (Fig. 11-88) are widely used due to lower condensing temperatures than in the air-cooled condensers and also lower than the water-cooled condenser combined with the cooling tower. Water demands are far lower than for water-cooled condensers. The chemical industry uses shell-and-tube condensers widely, although the use of air-cooled condensing equipment and evaporative condensers is on the increase. 

Condensers The vapor from the last effect of an evaporator is usually removed by a condenser. Surface condensers are employed when mixing of condensate with condenser coohng water is not desired. They are for the most part shell-and-tube condensers with vapor on the shell side and a multipass flow of cooling water on the... 

Many shell-and-tube condensers use copper alloy tubes, such as admiralty brasses (those containing small concentrations of arsenic, phosphorus, or antimony are called inhibited grades), aluminum brasses, and cupronickel austenitic stainless steel and titanium are also often used. Utility surface condensers have used and continue to use these alloys routinely. Titanium is gaining wider acceptance for use in sea water and severe service environments but often is rejected based on perceived economic disadvantages. 

Condensers may be of one or two general types depending on the specific application. Contact condensers operate with the coolant, vapors, and condensate intimately mixed. In surface condensers, the coolant does not come in contact with either the vapors or the condensate. The usual shell-and-tube condenser is of the surface type. Figure 29-14 illustrates a contact condenser which might be used to clean or preclean a hot corrosive gas. 

Figure 6.4 Shell-and-tube condenser (Courtesy of APV Baker Ltd (Hall Division))...

Figure 6.5 Double-bundle shell-and-tube condenser...

Shell-and-tube condensers can be installed with the axis vertical and will be one-pass, the water falling to an outlet tank below. This arrangement permits tube cleaning while the plant is operating. 

Advance warning should be had from the plant running log of any build-up of scale on water-cooled surfaces. Scale within the tubes of a straight double-pipe or shell-and-tube condenser can be mechanically removed with suitable wire brushes or high-pressure water lances, once the end covers have been removed. Tubes which cannot be dealt with in this way must be chemically cleaned (see also Chapter 33). 

Water connections to a shell-and-tube condenser must always be arranged so that the end covers can easily be removed for inspection, cleaning, and repair of the tubes. Heavy end covers require the use of lifting tackle, and supports above the lifting points should be provided on installation to facilitate this work. 

Operated in this manner, the shell-and-tube type is a flooded evaporator (see Figure 7.3) and has oil drainage pots if using ammonia, or a mixture bleed system if the refrigerant is one of the halocarbons. The speed of the liquid within the tubes should be about 1 m/ s or more, to promote internal turbulence for good heat transfer. End cover baffles will constrain the flow to a number of passes, as with the shell-and-tube condenser. (See Section 6.4.)... 

Derive the Taylor-Prandtl modification of the Reynolds Analogy between momentum and heat transfer. In a shell and tube condenser, water flows through the tubes which are 10m long and 40 mm diameter. The... 

A condenser is required to condense n-propanol vapour leaving the top of a distillation column. The n-propanol is essentially pure, and is a saturated vapour at a pressure of 2.1 bara. The condensate needs to be sub-cooled to 45°C. Design a horizontal shell and tube condenser capable of handling a vapour rate of 30,000 kg/h. Cooling water is available at 30°C and the temperature rise is to be limited to 30° C. The pressure drop on the vapour stream is to be less than 50 kN/m2, and on the water stream less than 70 kN/m2. The preferred tube size is 16 mm inside diameter, 19 mm outside diameter, and 2.5 m long. 

Design a vertical shell and tube condenser for the duty given in question 12.7. Use the same preferred tube size. 

Figure 13.2 is a sketch of a depropanizer overhead condenser. Let s make a few assumptions about this shell-and-tube condenser ... 

Therefore, the liquid level in the overhead condenser would have to be somewhere in the condenser s shell. But then, the liquid in the condenser would be below the reflux drum. How, then, does the liquid get from the lower elevation of the condenser to the higher elevation in the reflux drum We will have to explain this hydraulic problem later. But for now, we can say that most reflux drums are elevated 20 or 30 ft above grade to provide net positive suction head (NPSH) for the reflux pump. Also, most shell-and-tube condensers are located at grade, for easier maintenance during unit turnarounds. 

Subcooling in a shell-and-tube condensers. Figure 13.3 is the same propane condenser shown in Fig. 13.2. Let s assume that the pressure drop through the shell side is zero. Again, we are dealing with a pure component propane. The inlet vapor is at its dew point. That means it is saturated vapor. Under these circumstances, the outlet liquid should be saturated liquid, or liquid at its bubble point. As the inlet dew-point temperature is 120°F, the outlet bubble-point temperature should be 120°F. But, as can be seen in Fig. 13.3, the outlet shell-side liquid temperature is 90°F, not 120°F. Why ... 

The solution is straightforward. Do not condense the steam by direct contact with cold water, as is done in the barometric condenser. Condense the steam by indirect contact, with the cold surface of the tubes in a shell-and-tube condenser. Hence the name surface condenser, a sketch of which is shown in Fig. 18.2. Compare Fig. 18.1 with the surface condenser. Is there really much difference Other than recovering clean steam condensate for reuse, there is no difference at all. I last used a surface condenser in 1976, on a sulfuric acid plant reactor feed gas boost blower, and it worked just fine. 

Figure 8.14. Some arrangements of shell-and-tube condensers, (a) Condensate inside tubes, vertical upflow. (b) Inside tubes, vertical downflow, (c) Outside tubes, vertical downflow, (d) Condensate outside horizontal tubes. (HEDH, 1983, 3.4.3).

The HPS condenser is made of 316L seamless tubes with a nominal outer diameter of 25 mm, a nominal wall thickness of 2.2 mm and a length of 6.4 m. The tube ends are joined to the tube sheet (100 mm thick) to form a bundle 1.1 m in diameter that is welded to the shell to make up the shell-and-tube condenser. The tubes are weld sealed at the top of the tube sheet as shown in Figure 7.72. The condenser is installed vertically with severe operating conditions1 at the inlet of the top tube sheet as the temperature reaches 150°C and pressure 250 psi. 

FIGURE 19.17 Shell-and-tube condenser surface as a function of vapor rate and system operating pressure (cooling water at 85°F). (From Chemical Engineering, January 17, 1977, copyright 1977 by McGraw-Hill, Inc., New York. Reprinted by special permission. )... 

Other variants of the gas clean up system have been tried including shell and tube condensers, rotary particle separation in a gas centrifuge and other various filters and demisters. These various unit operations were recommended and tested by Marick International however, success was extremely limited and is summarised in Table 1. 

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