Transfer line heat exchangers

The crossover temperature must satisfy an overall heat balance around the furnace system, including transfer line heat exchangers and feed preheaters, and must not exceed certain limits to avoid incipient cracking. 

Immediately after cracking, the cracked gases are reduced in temperature as quickly as possible to stop the cracking processes and prevent the cracked gases forming coke. This quenching is often referred to as the transfer-line-heat-exchange (TEE). Excess steam is condensed and the water recycled (not shown). Heat from the TEE is recovered as process steam. 

The first and most obvious approach is to use a water quench. This does not permit any of the sensible heat to be recovered and results in a substantial "dirty" waste water stream which must be treated. The other approach, which was finally adopted, was to use a recycle gas quench (about 4 to 1) which cooled the reactor gas to 700°C. Following this, the total gas stream was passed through a series of Transfer Line (heat) Exchangers (TLE). 

Transfer-line heat exchangers are characterized by the following design objectives ... 

The transfer line heat exchanger behind the cracking furnace realizes fast quenching and recovers the heat energy in the form of steam. The steam is applied to operate the compressors for pygas condensation. 

Carbon steel, low-alloy steels Transfer lines, beat exchanger shells, baffles, pump components, heat exchanger tubing, fan blades and shrouds, valves, screens, fasteners... 

Age, centrifuge, charge, clean, cool, concentrate, crystallize, decant, distill, dry, evacuate, extract filter, filter-in-place, heat, heat-to-reflux-and-age, line-blow, line-flush, open/close-vent, pH-adjust, pressurize, purge, QC-test, quench, quench-in-place, react, react-distill, start-sweep, sto sweep, transfer, transfer-through-heat-exchanger, utilize, vent, wash-cake, yield-react Elute-column, equilibrate-column, load-column, regenerate-column, wash-column Crystallize-continuously, Distill-continuously, Dry-continuously, Extract-continuously, filter-continuously, react-continuously... 

Hardness Calcium and magnesium salts in the forms of CaCOj, Ca, Mg. This is the primary source of scaling in heat exchange equipment, boilers, pipelines/transfer lines, etc. Tends to form curds with soap and interferes with dyeing applications as well. 

In an indirect bath heat exchanger, the heating medium provides Iil u to an intermediary fluid, which then transfers the heat to the fluid h)cuig heated. An example of this is the common line heater used on many gas well streams to keep the temperature above the hydrate formal ion lem perature. A fire tube heats a water bath, which provides heat to tlie v.all siieam flowing through a coil immersed in the bath. Details pertaining to dcsi jit of indirect bath heaters are presented in Chapter 5. 

Blowdown and heat recovery system (BDHR) flash tanks and heat exchangers are potential candidates for sludging, leading to restrictions in the drain line or heat transfer surfaces. Deposits in the BDHR heat exchanger may lead to under-deposit corrosion and leaks. 

An example of integrated heat-transfer modehng and reactor design is shown in Figure 11.6. A predicted thermal profile for the reactor section of a combined reactor-heat exchanger is the solid line, while the discrete points are experimentally measured temperatures along the reactor length. The thermal profile is controlled... 

The coil or zigzag fin shape provides a relatively large heat exchange surface area. This permits a larger amount of heat to be transferred to the cooler environment as compared to a return duct running in a straight line between the upper- and the lower-reversal points. 

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