Fluid heaters

Heat-transfer-fluid heaters maintain the temperature of a circulating liquid heating medium (e.g., a paraffinic hydrocarbon mixture, a Dowtherm, or a molten salt) at a level that may exceed 673 K (750°F). 

The nonuniform heat distribution in the radiant section of a nine-burner refinery process fluid heater... 

Effect of Process Fluid Changes. Composition of the process fluid sometimes changes during normal operations which requires a change in the amount of heat to be absorbed. The controller tries to modify the amount of heat supplied to the heater, accommodating the change in process fluid. But, again, wide fluctuations will be observed in process fluid heater outlet temperatures. 

Continuous liquid flow furnaces include boiler furnaces, fluid heaters (such as Dow-therm heaters), evaporators, cookers, and many liquid heaters used in the chemical process industries. (See figs. 1.12 and 4.25.) The tubing through which the liquid fluids flow is often built as an integral part of the furnace, for which many textbooks are readily available therefore, they will not be discussed at length here. 

Fired heaters, thermal fluid heaters, and packaged steam boilers... 

Indirect fluid heater Very useful for high-pressure or corrosive fluids where special metallurgy (i.e., corrosion-resistant metals) can be used in smaller, less costly containment than traditional shellside boiling. Heating medium (steam/ dowtherm/electric, etc.) heats an intermediate bath of water/NH3/Therminol or similar heat-transfer fluid that then heats a second coil at much lower cost than shellside heating or boiling. (See Fig. V-8.)... 

FIG. V-8 Indirect fluid heaters. (Source Armstrong Engineering Associates.)... 

Heaters, radiant Heat exchange Heat-exchange fluids Heat exchange media Heat exchanger Heat exchangers... 

The basic fluid-bed unit consists of a refractory-lined vessel, a perforated plate that supports a bed of granular material and distributes air, a section above the fluid bed referred to as freeboard, an air blower to move air through the unit, a cyclone to remove all but the smallest particulates and return them to the fluid bed, an air preheater for thermal economy, an auxiUary heater for start-up, and a system to move and distribute the feed in the bed. Air is distributed across the cross section of the bed by a distributor to fluidize the granular soflds. Over a proper range of airflow velocities, usually 0.8-3.0 m/s, the sohds become suspended in the air and move freely through the bed. 

PBT resins are very fluid in the melt and sometimes drooling from the injection no22le can be a problem in machines that do not have melt decompression. A simple free-flow no22le can be used satisfactorily to minimise drooling if its temperature can be adjusted by a separate heater band. PBT does not drool as badly as nylons. 

When manipulating a stream whose flow is independently determined, such as flow of a product or a heat-transfer fluid from a fired heater, a three-way valve is used to divert the required flow to the heat exchanger. This does not alter the linearity of the process or its sensitivity to supply variations and even adds the possibility of independent flow variations. The three-way valve shomd have equal-percentage characteristics, and heat-flow control may be even more beneficial. 

Bayonet Heaters A bayonet-tube element consists of an outer and an inner tube. These elements are inserted into tanks and process vessels for heating and cooling purposes. Often the outer tube is of expensive alloy or nonmetalhc (e.g., glass, impeivdous graphite), while the inner tube is of carbon steel. In glass construction, elements with 50.8- or 76.2-mm (2- or 3-in) glass pipe [with lengths to 2.7 m (9 ft)] are in contact with the external fluid, with an inner tube of metal. 

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