Pipe coils

The heatable areas of the diyer are the vessel wall and the screw. The diyer makes maximum use of the product-heated areas—the filling volume of the vessel (up to the knuckle of the dished head) is the usable product loading. The top cover of the vessel is easily heated by either a half-pipe coil or heat tracing, which ensures that no vapor condensation will occur in the process area. In addition to the conical vessel heated area, heating the screw effectively increases the heat exchange area by 15-30 percent. This is accomphshed via rotary joints at the base of the screw. The screw can be neated with the same... 

Vibrating-conveyor dryers are suitable for free-flowing solids containing mainly surface moisture. Retention is limited by conveying speeds which range from 0.02 to 0.12 m/s. Bed depth rarely exceeds 7 cm, although units are fabricated to carry 30- to 46-cm-deep beds these also employ plate and pipe coils suspended in the bed to provide additional heat-transfer area. Vibrating dryers are not suit le for fibrous materials which mat or for sticky sohds which may ball or adhere to the deck. 

Superimposed on the double spiral, there may be a double eddy [Van Tongeran, Mech. Eflg., 57, 753 (1935) and Wellmann, Feuer-ungstechnik, 26, 137 (193 ] similar to that encountered in pipe coils. Measurements on cyclones of the type shown in Fig. 17-36 indicate, however, that such double-eddy velocities are small compared with the spiral velocity (Shepherd and Lapple, op. cit.). Recent analyses of flow patterns can be found in Hoffman et al.. Powder Tech., 70, 83... 

Pipe Coil Pipe coil for submersion in coil-box of water or sprayed with water Is simplest type of exchanger. Condensing, or relatively low heat loads on sensible transfer. Transfer coefficient is low, requires relatively large space if heat load is high. 0.5-0.7... 

Open Tube Sections (Water cooled) Tubes require no shell, only end headers, usually long, water sprays over surface, sheds scales on outside tubes by expansion and contraction. Can also be used in water box. Condensing, relatively low heat loads on sensible transfer. Transfer coefficient is low, takes up less space than pipe coil. 0.8-1.1... 

Half-pipe coil jacket Laminar flow... 

Half-pipe coil jacket Half-pipe coil jacket... 

In predicting the time required to cool or heat a process fluid in a full-scale batch reactor for unsteady state heat transfer, consider a batch reactor (Figure 13-2) with an external half-pipe coil jacket and non-isothermal cooling medium (see Chapter 7). From the derivation, the time 6 to heat the batch system is ... 

Pipe Coil 10-5 A Pipe coil for submersion in Condensing, or relatively low Transfer coefficient is low. 0.5-0.7... 

I. Baudelot coolers (see Figures 7.7 and 7.8a). The evaporator stands above a collection tank, and the water runs down the outside surface in a thin layer. Evaporator construction can be pipe coils or embossed plates. The latter are now usually of stainless steel, to avoid corrosion troubles. Evaporators maybe flooded or dry expansion. During operation, a Baudelot cooler... 

Pipe coils within a water tank (see Figures 7.1c, 7.5 and 7.6). Both flooded and dry expansion evaporators are in use. Water is circulated by pumps and/ or special agitators. This type of water chiller maybe operated without formation of ice, or ice maybe allowed to accumulate intentionally (see below). 

Providing the surrounding air is reasonably still, the lids may be omitted. It helps to have glass walls at the sides to reduce draughts, which would disturb the layer of very cold air in the cabinet. The evaporator may be pipe coils on the outside of the inner wall, but is more usually a finned coil at the back or sides. It is important that produce is kept below the design level of the cold air blanket. The construction with discrete cold trays is now taken a stage further, where several trays may be arranged one above the other. 

High purity ethylene gas plus recycle ethylene are fed to a compression chamber, compressed and then fed along with catalyst previously dissolved in a suitable solvent into, parallel horizontal reactors, as many- as eight in parallel. Each reactor consists of a water-filled shell containing a single pipe, coiled to give maximum contact with the water. Reaction conditions are 350-425 F and 2000-3000 psi. 

The feed stock, usually topped or reduced crude oil, is heated in pipe coils (Figure 1) from about 900° to 950° F. The oil is then fed to one of two or more vertical, insulated coke drums. The coke drums are connected by valves so that they can be switched onstream for filling, then switched off-stream for coke removal. The temperature in the drum will ordinarily be 775° to 850° F. and the pressure 4 to 60 pounds per square inch gage. Hot, coke-still vapors from the coke drum pass to a fractionator where gas and gasoline, intermediate gas oil, and heavy gas oil are separated. More or less of the heavy gas oil is recycled. The ratio of recycled heavy gas oil to fresh feed is usually less than 1 but may go up to about 1.6 (5,15,28, 40). 

A theoretically derived equation for laminar flow in helical pipe coils by Ruthven (Chem. Eng. Sci, 26, 1113-1121 [1971] 33, 628-629 [1978]) is given by... 

Half-pipe coil jacket Laminar flow 18.6(NRe)0 33(Npr)0 33(De/L)0 33( ab/pw)014 When pipe coils are made with a semicircular cross-section, De = Jtdci/2, where dci is the inner diameter of the pipe, in feet. For calculating the velocity, the cross-sectional flow area equals Jtd2 /8. When pipe coils are made with a 120° central angle, De = 0.0708 dci and the cross-sectional area equals 0.154(dci)2. 

Half-pipe coil jacket Transition flow Use the above equations depending of the value of NRe. 

Lead is immune to distilled water free from C02 and oxygen. Air free from C02 in distilled water corrodes lead. In presence of C02 a film of basic lead carbonate in formed, which prevents further attack. The successful use of lead pipe coils for steam boiler applications depends on the use of pure water condensate, which is free from oxygen and carbon dioxide. In the event of the presence of oxygen, oxygen scavengers such as hydrazine or sodium sulfite together with cobalt nitrate may be used. 

Select steam traps for the following five types of equipment (1) where the steam directly heats solid materials, as in autoclaves, retorts, and sterilizers (2) where the steam indirectly heats a liquid through a metallic surface, as in heat exchangers and kettles where the quantity of liquid heated is known and unknown (3) where the steam indirectly heats a solid through a metallic surface, as in dryers using cylinders or chambers and platen presses and (4) where the steam indirectly heats air through metallic surfaces, as in unit heaters, pipe coils, and radiators. 

Based on initial heat flow calorimetry studies, a process development engineer must choose the appropriate reactor vessels for pilot plant studies. A pilot plant typically has vessels that range from 80 to 5000 L, some constructed of alloy and others that are glass lined. In addition some vessels may have half-pipe coils for heat transfer, while others have jackets with agitation nozzles. A process drawing for a typical glass-lined vessel is shown in Figure 4. In Sections 3.1.4.1 and 3.1.4.2 we review fundamental heat transfer relationships in order to predict overall heat transfer coefficients. In Section 3.1.4.3 we review experimental techniques to estimate heat transfer coefficients in process vessels. 

Chapter 7, Reactor Design, discusses continuous and batch stirred-tank reactors and die packed-bed catalytic reactor, which are frequently used. Heat exchangers for stirred-tank reactors described are the simple jacket, simple jacket with a spiral baffle, simple jacket with agitation nozzles, partial pipe-coil jacket, dimple jacket, and the internal pipe coil. The amount of heat removed or added determines what jacket is selected. Other topics discussed are jacket pressure drop and mechanical considerations. Chapter 7 also describes methods for removing or adding heat in packed-bed catalytic reactors. Also considered are flow distribution methods to approach plug flow in packed beds. 

Figure 7.3 compares calculated overall heat-transfer coefficients for several reactor heat exchangers, using water for both the jacket and reactor fluid. The figure shows that the highest heat-transfer coefficient is obtained with internal coils and the lowest with the simple jacket (called the conventional jacket in Figure 7.3) without a spiral baffle or agitation. It is assumed that the flow rate for the internal coil is the coil flow rate and not the jacket flow rate, as plotted in Figure 7.3. Heat-transfer coefficients for the half-pipe coil, agitated, and baffled jackets are conparable.

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