API RP 534:2007 pdf download
API RP 534:2007 pdf download.Heat Recovery Steam Generators.
2.5.3 High-pressure Steam Applications
For cases involving high-pressure steam. typically 10,400 kPa(g) (1,500 psig) and above, firctube HRSGs require heavier wall shell cylinders and tubes. This is particularly true for high capacity systems. For this reason firetube HRSGs in high-pressure stcam systems weigh more than their watertube counterparts.
2.5.4 Hot Tubesheet Construction
The hot tubcshcct design of firetubc FIRSGs, particularly its attachment to thc shell and the tubes may be complex. The severity of service relates to the coexistence of multiple conditions, such as:
a. High inlet gas temperature.
b. High pressure on the steam side.
c. Loading imposed by the tubes due to axial differential thermal growth relative to the shell.
d. Potential erosive effects of particulate bearing gases.
e. Potential for corrosive attack from the process and steam sides.
The tubcsheet is commonly made of Cr-Mo ferritic steels which require special attention during fabrication and testing. Many firctube LIRSGs require a thermal and stress analysis to prove the construction acceptable for all anticipated operating conditions.
2.6 MECHANICAL DESCRIPTION
2.6.1 High-temperaturelHigh-flux Units
2.6.1.1 Refractory Lined Inlet Channel
Inlet channels of high-temperature units are internally refractory lined to insulate the pressure components. A number of refractoiy systems are available including dual and monolithic layers. east and gunned. or with and without internal liners. Various types of refractory anchoring systems are also used. Metallic needles may be considered as a means to further reinforce the castable.
The selection of refractory materials and their application method must be compatible with the hot side service conditions. The design must account for concerns such as:
a. Insulating capability, including effect of hydrogen content on the refractory thermal conductivity. The presence of hydrogen
will increase the thcrnial conductivity of the refractory.
b. Chemical compatibility with the process fluid.
c. Gas dew point relative to cold face temperature.
d. Erosion resistance against particulate bearing streams.
e. Potential for coking under ferrules.
2.6.1.2 Channels
Several channel construction options exist. The gas connections may be in-line axial or installed radially on a straight channel section. In-line is preferred fur designs with low-pressure drop to ensure complete distribution of gas to all tubes. The channel should be designed to minimize flow turbulence and erosion of the refractory liner, if present. Access into the channel compartment is generally through a manway in large diameter units, or through a full access cover in small units.
2.6.1.3 Tubesheets
The single niost distinguishing feature of high-temperature firetube HRSGS is the thin tubesheet construction. Conventional shell- and-tube exchangers operating at moderate temperatures incorporate tubesheets traditionally designed according to the requirements of TF.MA. prior to 2004. However. ASME Section VIII, Division I Part UHX has replaced the TEMA method for tubesheet design. Typical tubesheet thicknesses in such units range from 50mm (2 in.) 150mm (6 in.)or more. Use of TEMA or ASME Part UHX tubesheets in high-temperature, high-flux (severe service) firetube HRSGs is not recommended because the tubesheet metal temperature gradient would be excessive and high stresses would result.
The thin tubesheet design is based on the use of the tubes as stays to provide the necessary support for the tubesheets. Tubesheet thicknesses typically range from 16 mm (5/x in.) — 38 mm (11/2 in.).
Tubesheet temperature can be further minimized by limiting heat flow to the tubesheet with the use of insulated frrules inserted in each tube inlet. The ferrules project 75 mm (3 in.) – 100 mm (4 in.) from the tubesheet face. The space between the ferrules is packed with refractory, which secures the ferrules and insulates the tubesheet face. Ferrules are either a high-temperature resistant metallie or ceramic material, wrapped with an insulating paper for a lightly snug fit in the tube bore. Overcompression of the insulation will reduce its effectiveness. Figures 4 and 5 show details of one style each of a metallice and ceramic ferrule. Other configurations have been used.
