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| Sulphuric Acid on the WebTM | Technology Manual | DKL Engineering, Inc. |
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Knowledge for
the Sulphuric Acid Industry Introduction
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The amount of work that a turbine
can extract from saturated steam is limited to about 10-15% moisture in the steam at the
exit of the turbine. Superheat is desirable
because the heat of superheat is essentially 100% recoverable in a turbine. Types and Location of Superheaters In acid plants, superheaters have
been designed as stand alone units, integral with a waste heat boiler and as units for
installation inside our converters. The stand alone units are simply
rectangular tube bundles contained inside the traditional box or cylindrical shells. The gas must be brought to and from the
superheater by ducting. A gas side bypass for
temperature control is possible with these units. Superheaters
designed as part of a waste heat boiler are simply tube bundles located in the gas flow. The superheater section will be located near the
gas inlet where the gas is hottest. However,
the superheater bundle will often be protected by a convection or screen bundle so the
tube metal temperature does not exceed the design limits. Locating
the superheater inside the converter has the same advantages as locating our gas/gas heat
exchangers inside the converter. The
superheater bundle is located in a cylindrical area where the gas flows from the exit of
the bed down through the tubes. A gas side
bypass for temperature control is possible but is difficult to implement. Process Gas Temperature Control When a superheater is located
between catalyst beds in the contact section of an acid plant, the temperature of the gas
exit the superheater to the next bed must be controlled.
When the supeheater is located outside the converter a gas bypass is used to
regulate the gas exit temperature. However,
when the superheater is located inside the converter, a steam side bypass is used. Superheated Steam
Temperature Control When a steam system is designed for
superheat, the designer should ensure that the steam exit the superheater is superheated
about 5.6oC (10oC) higher than the desired superheat temperature. The steam temperature is not controlled using
bypasses on the superheaters but by desuperheating equipment. In cases of high gas temperatures
(ie. downstream of a regeneration furnace) plain tubes are used because the added
thickness of the fins increases metal temperatures and thermal stresses beyond acceptable
limits. Where the temperatures are more
'moderate', finned tubes can be used to enhance heat transfer. This is typical for superheaters within the
contact section of the acid plant. |
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Copyright© 2005,
2006, 2007, 2008 DKL
Engineering, Inc., All Rights Reserved |
