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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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There are two important dew points that are important in the operation of an acid plant. The most important is the acid dew point which has an impact on the life of the process equipment. The second is the dew point of instrument air. The acid dewpoint is important to know because excessive acid
condensation will lead to increased corrosion of process equipment. The areas in the
plant where this is critical are points in the process where the gas has been cooled close
to or below its dewpoint. These areas are:
The dewpoint of the gas is approximately 140°C to 180°C. Knowing the
exact dewpoint of the gas can enable the acid plant to recover the maximum amount of heat
in heat recovery equipment (ie. economizers and boilers) by cooling the gas closer to its
dewpoint temperature. A dewpoint monitor is sometimes specified for an instrument air system where
the air quality is important for the proper operation of a plant. Instances where
this is important are plant locations where the ambient temperatures are very low
(-40°C/°F). If the instrument air is not dried to the required dewpoint, water
will condense and freeze in instrument air lines resulting in instrument failures, safety
hazards, and possibly a plant shutdown. Condensed Liquid Film - A probe is inserted into the gas stream and the
detector is gradually cooled by increasing the flow of air to the probe. As the
detector temperature falls, a point is reached where a thin film of acid begins to
condense onto its surface. Two electrodes are fused into the detector surface, and
as the acid condenses, a current begins to flow between them. The magnitude of the
current depends on the thickness of the acid film. The air flow to the probe is
adjusted until a steady current is obtained indicating that the thickness of the film is
constant. At that point the rate of condensation of acid is equal to the rate of
evaporation, and the temperature at which this occurs is the acid dew point
temperature. The precise temperature is measured by the probe thermocouple which
indicates the temperature of the detector surface. The following instruments are available for measuring acid dew points.
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2006, 2007, 2008 DKL
Engineering, Inc., All Rights Reserved |
