Coils, steam heating

Coils, steam, heating by, 19. Composition of coal, 71. Compressed-air engine, 66. Conclusion, 141. 

Thermal expan sion. Equipment and pipehues which are liquid-full under normal operating conditions are subject to hydrauhc expansion if the temperature increases. Common sources of heat that can result in high pressures due to thermal expansion include solar radiation, steam or other heated tracing, heating coils, and heat transfer from other pieces of equipment. 

The shape of a vessel determines how well it drains (Figure 53.7). If the outlet is not at the very lowest point process liquid may be left inside. This will concentrate by evaporation unless cleaned out, and it will probably become more corrosive. This also applies to horizontal pipe runs and steam or cooling coils attached to vessels. Steam heating coils that do not drain adequately collect condensate. This is very often contaminated by chloride ions, which are soon concentrated to high enough levels (10-100 ppm) to pose serious pitting and stress corrosion cracking risks for 300-series austenitic stainless steel vessels and steam coils. 

Apart from meeting space heating demands, many HW (and LP) steam boilers provide a heat source for domestic HW systems by the incorporation of a bank of finned copper coils located within the top section of the boiler. From these coils indirectly heated water is deliv-... 

Small boiler plants often supplement the heat derived from CR by employing steam coils, steam sparge pipes, or electric heaters, whereas larger facilities use economizers, closed FW heaters, and deaerators (as discussed in Chapter 3). 

Water at 293 K is heated by passing through a 6.1 m coil of 25 mm internal diameter pipe. The thermal conductivity of the pipe wall is 20 W/m K and the wall thickness is 3.2 mm. The coil is heated by condensing steam at 373 K for which the film coefficient is 8 kW/m2 K. When the water velocity in the pipe is I tn/s, ils outlet temperature is 309 K. What will the outlet temperature be if the velocity is increased to 1.3 m/s, if the coefficient of heat transfer to the water in the tube is proportional to the velocity raised to the 0.8 power ... 

To tempo- this water assume that 30% of the water must be heated to 14deionized water, this will be done in a separate tank. This tank will be designed to have a 0.5 hr holdup. The vessel will have steam coils to heat the water. Assume the coils occupy 10% of the space, and the tank is 90% full. 

For very long, helically coiled steam generator tubes, and for conditions typical of liquid-metal fast breeder reactors (LMFBRs), where steam is generated on the tube side, an overall heat transfer correlation for the whole boiling length (from X = 0 to X = 1.0) has been deduced experimentally (Campolunghi et al., 1977b) ... 

The inlet air duct, starting at the roof level of the cubicle, leads to the inlet air flap, inlet air filters, and steam heated heat exchanger coils to heat the inlet air. This heated air is directed through a 1/2 supporting grid and 100 mesh screen on the bottom of the product container. 

The equipment operates by negative pressure differential generated by a turbine. Air is drawn in the inlet duct, throttled at the inlet flap, cleaned at the inlet filter, heated at the steam heated coils, and then used to fluidize the material resting on the screen in the bottom of the product bowl. The air is then cleaned at the outlet filter, throttled at the outlet flap, and accelerated through the turbine to the atmosphere. 

The flue gas tunnels are rectangular fire-brick structures at the reformer s bottom. They act as horizontal ducts for flue gas removal. The flue gas exits at 1,800°F to 1,900°F. A heat recovery unit is provided to recover heat from this gas. This unit contains a reformer feed preheat coil, steam superheat coil, steam generation coil and boiler feed water preheat coil. 

Crude oil is pumped from storage through a steam heated exchanger and into an electric desalter. Dilute caustic is injected into the line just before the desalting drum. The aqueous phase collects at the bottom of this vessel and is drained away to the sewer. The oil leaves the desalter at 190°F, and goes through heat exchanger E-2 and into a furnace coil. From the furnace, which it leaves at 600°F, the oil proceeds to a distillation tower. 

Fluidized bed reactors typrcally are vertical cylindrical vessels equipped with a support grid and feed sparger system for adequate fluidization and feed distribution, internal cooling coils for heat removal, and either external or internal cyclones to minimize catalyst carryover. Fluidizauon of the catalyst assures intimate contact between feed and product vapors, catalyst, and heat-transfer surfaces, and results in a uniform temperature within the reactor. Reaction heat can be removed by generating steam within the cooling coils or by some oilier heat-transfer medium. 

The coke on the inner surface of the coil decreases heat transfer coefficients for the large amounts of heat that need to be transferred from the hot combustion gases in the furnace to the hydrocarbon-steam mixtures flowing through the coils. As a result of coke, smaller fractions of the heat of combustion are transferred to the reaction mixtures, and the already large costs of the fuel to the furnace are increased. 

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