Radiant tubes

Example 5 Radiation in a Furnace Chamber A furnace chamber of rectangular paraUelepipedal form is heated hy the combustion of gas inside vertical radiant tubes hningthe sidewalls. The tubes are of 0.127-m (5-in) outside diameter on 0.305-m (12-in) centers. The stock forms a continuous plane on the hearth. Roof and end walls are refractory. Dimensions are shown in Fig. 5-20. The radiant tubes and stock are gray bodies having emissivities of 0.8 and 0.9 respectively. What is the net rate of heat transmission to the stock by radiation when the mean temperature of the tube surface is SIG C (1500 F) and that of the stock is 649 C (1200 F) ... 

This problem must be broken up into two parts, first considering the walls with their refractory-backed tubes. To imaginary planes A of area 1.83 by 3.05 m (6 by 10 ft) and located parallel to and inside the rows of radiant tubes, the tubes emit radiation gTiAj i2, which equals gTiA2 3 2i- To find S 2i. ise Fig. 5-17, curve 5, from which F21 = 0.81. Then from Eq. (10-200)... 

The arbor (wicket) heater is a substantially vertical design in which the radiant tubes are inverted Us connecting the inlet and outlet terminal manifolds in parallel. An overhead crossflow convection bank is usually included. This type of design is good for heating large gas flows with low pressure drop. Typical duties are 53 to 106 GJ/h (50 to 100 10 Btu/h). 

Indirect Heating If the process material cannot tolerate exposure to the combustion gas or if a vacuum or an atmosphere other than air is needed in the furnace chamber, indirect firing must be employed. This is accomplished in a muffle furnace or a radiant-tube furnace (tubes carrying the hot combustion gas run through the furnace). 

RADIANT TUBES OD " TUBE WALL ASTM SPEC. ... 

Alloy 800 (32% nickel, 20% chromium and 46% iron) is used for furnace equipment such as muffles, trays and radiant tubes and in oil and petrochemical plants as furnace coils for the reforming and pyrolysis of... 

Flaimiiable gas Radiant tube Potential for Improve reactor... 

Absorbed heat duty, Btu./hr. Design pressure, psig. Radiant tube material... 

Mulching of radiant tubes for heating by warm water PP. 

Advantages of this technology include the precise solid waste retention time and reduction of gas flows that are obtained by indirectly heating the soil with radiant tubes. This technology is commercially available. 

A = surface area of the radiant tubes in the firebox, ft2 e = emissivity factor... 

Tt = the receiving metal temperature, °F (this is the radiant tube metal or tube skin temperature). 

Figure 8.19. Some types of process fired heaters (See also Fig. 17.16 for a radiation panel heater), (a) Radiant, shield, and convection sections of a box-type heater, (b) Heater with a split convection section for preheating before and soaking after the radiant section (Lobo and Evans, 1939). (c) Vertical radiant tubes in a cylindrical shell, (d) Two radiant chambers with a common convection section.

The 90 radiant tubes are arranged as shown on Figure 8.22 4 shields, 14 at the ceiling, and 36 on each wall. Dimensions of the shell are shown. 

Figure 17.15. A fired heater as a high temperature reactor, (a) Arrangement of tubes and burners (1) radiant tubes (2) radiant panel burners (3) stack (4) convection chamber tubes (Sukhanov, Petroleum Processing, Mir, Moscow, 1982). (b) Radiant (surface-combustion) panel burner (1) housing (2) ceramic perforated prism (3) tube (4) injector (5) fuel gas nozzle (6) air throttle Sukhanov, Petroleum Processing, Mir, Moscow, 1982). (c) Fired tubular cracking furnace for the preparation of ethylene from naphtha.

Radiant tube burners are made by using CMC. These are used for indirect-fired, high-temperature zones, controlled atmosphere heating and melting applications. 

Direct-fired furnace. Fired heaters are designed to increase the process temperature of oil and gas streams. This increase of temperature in most every case does not change molecular structure. Thus, temperatures up to 500°F maximum with 400°F design are very common. Designs are usually cylindrical, with vertical radiant tube banks fired by oil/gas combination burners. 

Radiant Section. Changes in the radiant section can be difficult to justify based on capacity alone. However, if the radiant tubes are near the end of their useful life, an upgrade to this section may provide more capacity. Changes in metallurgy since the mid-1970s have allowed changes in radiant section operating conditions. 

Radiant tubes, carburizing boxes, annealing boxes... 

Cost of process furnaces, box type with horizontal radiant tubes. 

Michael C. Kasprzyk, Large Silicon Carbide Radiant Tube Production Process, in Silicon Carbide 87, ed. D. Cawley, The American Ceramic Society, Columbus, OH, 1989, pp. 387-394. 

Example 10 Furnace Simulation via Zoning The furnace chamber depicted in Fig. 5-20 is heated by combustion gases passing through 20 vertical radiant tubes which are backed by refractory sidewalls. The tubes have an outside diameter of D = 5 in (12.7 cm) mounted on C = 12 in (4.72 cm) centers and a gray body emissivity of 0.8. The interior (radiant) portion of the furnace is a 6 x 8 x 10 ft rectangular parallelepiped with a total surface area of 376 ft2 (34.932 m2). A 50-fL (4.645-m2) sink is positioned centrally on the floor of the furnace. The tube and sink temperatures are measured with embedded thermocouples as 1500 and 1200°F, respectively. The gray refractory emissivity may be taken as 0.5. While all other refractories are assumed to be radiatively adia-... 

Montedison Low-Pressure Process. The Montedison low-pressure process [940], [1036], [1128], [1129] involves a split flow to two primary reformers. About 65% of the feed-steam mixture flows conventionally through the radiant tubes of a fired primary reformer followed by a secondary reformer. The balance of the feed-steam mixture passes through the tubes of a vertical exchanger reformer. This exchanger reformer has a tube sheet for the catalyst tubes at the mixed feed inlet. There is no tube sheet at the bottom of the tubes, where the reformed gas mixes directly with the secondary reformer effluent. The combined streams flow on the shell side to heat the reformer tubes in a manner similar to that described for the M. W. Kellogg KRES reformer, see Sections 4.1.1.8 and 5.1.4.3). The process air flow is stoichiometric. Synthesis is performed at 60 bar in a proprietary three-bed indirectly cooled converter with am-... 

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