Heat Recovery Steam Generators.pptx

8/14/2019 Heat Recovery Steam Generators.pptx

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Firetube HRSG: A shell-and-tube heatexchanger in which steam is generated on theshell side by heat transferred from hot fluidflowing through the tubes.

Attemporator==Desuperheater.

Pinch temperature=Heating mediumtemperature leaving the steam generator

section - the steams saturation temperature

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High-temperature heating mediums (exceeding480C [900F])

Resulting in high boiling flux rates (in excess of)94,600 W/m2 (30,000 Btu/hr-ft2).

Typical steam side operating pressures range from as

low as 1,050 kPa(g) (150 psig) for fluid catalyticcracker and sulfur plant applications to as high as 12,400 kPa(g) (1,800 psig)

for ammonia and ethylene facilities

as temperaturesexceeding 1090C (2000F) andflux rates to 315,500 W/m2 (100,000 Btu/hr-ft2) canbe accommodated in firetube HRSGs



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Hot fluid temperatures not exceeding 480C(900F) with flux rates of 94,600 W/m2(30,000 Btu/ hr-ft2) and below.

Any hot fluid stream with a sufficienttemperature above the steam saturationtemperature can be utilized.

Steam side operating pressures range from

350 kPa(g) (50 psig) 4,150 kPa(g) (600psig).

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Maximum velocity limitations with respect tothe erosive nature of particulate bearingstreams.

Process conditions: Maximum allowable pressure drop

Maximum heat flux



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Fluid catalytic cracking slurry steam generators aregenerally designed for a velocity of 1.5 m/s 2.1m/s (5 ft/sec 7 ft/sec) to avoid settling out thesolids constituents.

For sulfur condensers, rho-v2 should not exceed 890kg/msec2 (600 lb/ft-sec2) to prevent fogging ofthe gas stream. Rho-v2 is the product of the densityof a fluid and the square of the velocity of the fluid.This represents the force the fluid flow is exerting onan area. It is commonly used in heat exchangers todetermine if the fluid flow can exert sufficient forceon the exchanger tubes to create tube vibration



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As the design pinch temperature is reduced,the log mean temperature difference (LMTD)decreases and the surface area requirementincreases.

HRSGs with large pinch temperatures tend touse larger diameter or shorter tubes thanthose with small pinch temperatures.

The typical pinch temperature range is 8C 14C (15F 25F).


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Heat Recovery Steam Generators.pptx