Heat exchangers, condensers Heaters, fired

Maintain compressor inter-stage and process heat exchangers, condensers, reboilers and fired heaters with minimum fouling... 

FIG. 23-1 Heat transfer to stirred tank reactors, a) Jacket, (h) Internal coils, (c) Internal tubes, (d) External heat exchanger, (e) External reflux condenser. if) Fired heater. (Walas, Reaction Kinetics for Chemical Engineers, McGraw-Hill, 1959). 

Fresh waters are, in general, less corrosive towards copper than is sea-water, and copper is widely and satisfactorily used for distributing cold and hot waters in domestic and industrial installations . Copper and copper alloys are used for pipes, hot-water cylinders, fire-back boilers, ball floats, ball valves, taps, fittings, heater sheaths, etc. In condensers and heat exchangers using fresh water for cooling, tubes of 70/30 brass or Admiralty brass are usually used, and corrosion is rarely a problem. 

Figure 17.33. Heat transfer to stirred-tank reactors (a) jacket (b) internal coils (c) internal tubes (d) external heat exchanger (e) external reflux condenser (f) fired heater (Walas, 1959).

The overhead from the second stage is heated by an exchange with hot solvent. The fired heater further raises the temperature of the solvent/demetallized oil mixture to a point above the critical temperature of the solvent. This causes the demetallized oil to separate. It is then flashed and steam-stripped to remove all traces of solvent. The vapor streams from the demetallized oil and asphalt strippers are condensed, dewatered, and pumped up to process pressure for recycle. The bulk of the solvent goes overhead in the supercritical separator. This hot solvent stream is then effectively used for process heat exchange. The subcritical solvent recovery techniques, including multiple effect systems, allow much less heat recovery. Most of the low grade heat in the solvent vapors from the subcritical flash vaporization must be released to the atmosphere requiring additional heat input to the process. 

Armed with the thermodynamic fundamentals of heat management, we now take a closer look at the unit operation control loops for heat exchangers. We start with utility exchangers. These are used when heat is supplied to, or removed from, the process. Examples are steam-heated reboilers, electric heaters, fuel-fired furnaces, water-cooled condensers, and refrigerated coolers. 

FIGURE 23.22 Self-inertizing spray drying system (1) drying chamber with rotary atomizer (2) cyclone (3) scrubber condenser (4) direct-fired heater (5) heat exchanger for waste-heat recovery (6) exhaust to atmosphere (7) fuel (8) combustion air (9) cooler (10) condensate F, feed P product. 

The main target of a boiler is to capture the overall energy of the flue. This depends on the total heat exchanger surface, the resistance to corrosion, and the resistance to certain temperatures of raw material, for these reasons, the heat exchanger of a gas- or oil-fired water heater or combi can technically be seen as standard, low temperature, or condensing. 

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