Radiant tube removal

EXHIBIT 7-16 Radiant Tube Removal in a Circular Furnace... 

Exhibit 7-43 also shows the product outlet line and its decoking hook-up. Line A is set up in its usual operation configuration line B is set in the decoking mode. As the steam and air are blown through the radiant tubes, any waste is carried to the sewer or, if preferred, to a drum for removal. The vent line is run to the stack. Once again, the plant layout designer... 

Larger-si2ed heaters are usually hori2ontal box heaters. The radiant coils can be located either on the side walls so that the units are fired from underneath, or in a center row of tubes in which the heater is fired from both sides to provide a higher heat flux for reducing the radiant surface. An access area at one end of the box is required in order to remove the tubes. Sometimes multiple coils are included in the same box, which may require access to both ends of the box. 

The first pump removes air at a rate of 500 1/min and the second at about 300 1/min. The pressure in the first vacuum-lock is maintained at about 1 to 20 torr and that in the second about 0.1 to 0.5 torr. As a consequence the mass spectrometer source can be easily operated at about 10 torr. Flash vaporization of the solute occurs by radiant heating in a small chamber that butts directly onto the solid probe entrance to the ionization chamber and the vapor passes through a small hole directly into the ion source. The flash heater is either a nichrom coil or a quartz heater tube. The slots in the vacuum-locks are made of sapphire strips. An example of the use of the belt interface to monitor the separation of a pesticide mixture is shown in figure 20. 

A principal factor governing the operating cycle of ethylene steam crackers (ESC) is coke formation on the inside surfaces of the radiantly heated pyrolysis tubes. Steam is used as the carrier for the hydrocarbon feedstock as it is known empirically to minimise this coking. It is probable that the observed deposition is a net process representing the difference between formation and removal, primarily by thermal oxidation. A fundamental requirement of any detailed understanding of the overall processes involved, therefore, is knowledge of the oxidation behaviour of such deposits. Although several studies have been undertaken on various carbons considered to simulate ESC pyrolysis tube coke (e.g. ( )) no relevant information has been published for plant material. To provide these data, therefore, the oxidation behaviour of a coke formed on an ESC tube has now been examined in water vapour. 

Carbonaceous deposition during steam cracking is the net result of steady state formation and removal processes. If the measured oxidation rates in water vapour did represent the removal of the deposit in situ, then this would be an extremely rapid process over the temperature range at which deposition on radiantly heated process tubes is most significant. Thus, 1 mm thickness of deposit would be oxidised by 362 mm Hg water partial pressure in 300 h at 800°C, 33 h at 900°C and 5 h at 1000°C. If a hydrocarbon, or its decomposition products, enhanced the oxidation rate these times could be decreased. Coke removal by thermal oxidation cannot be ignored, therefore, although its extent would depend on specific plant operating conditions. 

Convection section This compartment houses rows )f primarily horizontal tubes located downstream fom the radiant section that are used for additional leating in a process unit, Pa.ssing the hot flue gases >ver these tubes can provide additional duty. Exam-ties include preheating process streams, steam super-leating, and additional steam generation. Provisions aust be made to remove these tubes for inspection, epair, Of replacement. 

Because furnace tubes must be periodically replaced, clear areas are provided directly in line with the tubes. The removal mechanism may be a trolley beam located on the stack of a circular furnace, a crane, or a cherry picker. If only one or two tubes require removal, a tube extraaor, similar to the type used for extracting shell and tube exchanger bundles, may be used. As can be seen in Exhibit 7-l6, radiant... 

The bulk of worldwide annual commercial production of ethylene is based on steam cracking. In this petrochemical process saturated hydrocarbons are broken down into smaller, often unsaturated, hydrocarbons. It is the principal industrial method for producing lighter alkenes, mainly ethylene and propylene. The steam cracking operation involves heating the hydrocarbon (ethane, propane, butane, naphtha or gas oil) in radiant coils in the presence of steam in a furnace. The heat is transferred to the coils by radiation. This technology has been commercially practiced since early 1940s. Hydrocarbon feed is heated with steam up to 1050°C and fed to Cr-Ni reactor tubes. Cracked products exit at 850°C and are rapidly quenched to 300°C to prevent secondary reactions. The product is scrubbed to remove H S and CO, and then dried. and Cj components are separated by low temperature fractional distillation. 

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