Tube coil design

Fig. 2. Tube coil designs, (a) Spiral coil (b) meander coils (cooling basket) (c) tube bundles. (Reprinted with permission from the publisher, VCH Publishers, Inc., after Zlokarnik and Judat,...

Fig. 1.3 Tube coil design A - Spiral coil B - Single meander coil C - Double meander coil D - Tube bundles...

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

Coil Design Indirect-fired equipment is conventionally classified by tube orientation vertical and horizontal. Although there are many variations of each of these two principal configurations, they all are embraced within seven major types, as follows. 

The radiant section tube coils of horizontal fired heaters are arranged horizontally so as to line the sidewalls and the roof of the combustion chamber. In addition, tliere is a convection section of tube coils, winch are positioned as a horizontal bank of tubes above the combustion cham her. Nonnally the tubes are fired vertically from the floor, but they can also be fired horizontally by side wall mounted burners located below the tube coil. Tins economical, high dficiency design currently represents the majority of new horizontal-tube-t1icd heater installations. Duties run from 5 to 250 MMBtu/hr. Six types o) horizontal-tube-fired heaters arc-shown in Figure 3-21. 

This wide range of applications has resulted in an almost innumerable number of design permutations. These designs are normally based on multitube configurations but also include single-tube coil boilers. 

An often-used design is the high-pressure tube coil submerged in low-pressure vessels. Coils of high pressure tubes are easy to manufacture. 

A microwave-heated, flow-through digestion container (coiled Teflon tubing) was design for a commercial (Prolabo A300) focused microwave system (instead of microwave oven) and applied to the on-line preparation of biological samples, including milk, blood, and urine [108]. 

Small tubes are commonly employed where the reaction is rapid and/or the heat of reaction must be removed rapidly. The two conventional types of tubular reactors are (1) coils immersed in a constant-temperature bath and (2) a jacketed pipeline in which the inner tube is designed to withstand the reaction pressure. A modification of the conventional jacketed-pipe reactor can be used where it is desirable to minimize the thickness of the inner tube in order to reduce the area required for heat transfer. An example of this type of equipment is the liquid-phase heat exchanger of the Bureau of Mines, in which the outside pipe has an outside diameter of 4 2 ill- wall thickness of 1.005 in. The outside diameter of the inner tube is in., but the wall thickness is only 0.16 in. The worldng... 

Spontaneous growth of coils and tubes Spontaneous growth of coils and tubes Designed growth of microtubes, coils Designed growth of microtubes, coils... 

Helically finned tubes coiled around mandrels have been used for the compact Joule-Thomson heat exchangers. The high-pressure gas flows inside the tubes and the low pressure gas flows outside the tubes, in combined counter- and cross-flow. Heat exchanger designs were based on test data, some of which have been previously reported [6]. 

Answer by author Yes, we tested heat exchangers with many different designs, including pin fins, coiled fins, tubes coiled in spirals, etc. It is our opinion that the present helically finned and coiled exchanger design is the most useful design for the small compact exchangers. 

A commercially acceptable pyrolysis coil design is constrained by the limitations in available metallurgy. For any selected material, there exists a maximum operating temperature beyond which tube life is sharply reduced. This limitation in metal temperature must be considered in setting the coil design. 

The coil with the higher gas outlet temperatures requires higher heat transfer coefficients and/or higher heat transfer surface-to-volume ratio in order to not exceed the tube metal temperature limitation. This is achieved by utilizing a coil with relatively small diameter outlet tubes. This design, however, results in other undesirable effects due to simultaneous heat, mass and momentum transfer. 

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