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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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In early acid plant designs this energy was considered low grade heat and the energy was simply rejected to the environment usually via a cooling water system. Early acid cooling systems consisted of cast iron 'serpentine' coolers, so-called because of their shape. They were generally cooled with cooling water being sprayed on the outside with the acid flowing on the inside.
Some cast iron cooler installations still exist in a few acid plants.
In the mid 1960's CIL (Canada) began the search for a better alternative. After many years of development work and testing, the anodically protected shell and tube stainless steel acid cooler was introduced to the industry. The shell and tube units were more compact than the cast iron coolers and the all welded construction virtually eliminated the potential for leaks. The key to the success of the shell and tube acid cooler is the use of anodic protection.
Plate heat exchangers are a popular alternative to shell and tube acid coolers because of their compact size and lower costs. They offer very high heat transfer coefficients compares to shell and tube acid coolers. Materials of construction such as alloy C-276 allow the units to operate without anodic protection. The price advantage is still maintained even though more corrosion resistant and expensive materials are used compared to 316L SS because the plates are very thin. Anodic protection of plate heat exchanger using 316L SS plates was attempted but ran into the same problems as the attempt to commercialize anodically protected air coolers. Alloy C-276 plate heat exchangers were limited to a maximum inlet temperatues of 90°C (194°F) for corrosion reasons. The introduction of Hastelly D-205 and Cronifer 2803 Mo as a plate material allows acid temperatures to go beyond the 90°C (194°F) restriction. Spiral heat exchangers are another option for acid cooling. They offer many of the same advantages as plate heat exchangers. A seldom used cooling option are PTFE tank coils. There unique design do not lend itself to the typical acid plant and are used in special cases where other exchangers are not suitable. A fairly recent advancement are shell and tube coolers constructed entirely of high silicon stainless steels such as Sandvik SX. Using this material eliminates the need for anodic protection. Acid is no longer restricted to the shell side of the exchanger as is the requirement for anodically protected acid coolers.
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Copyright© 2005,
2006, 2007, 2008 DKL
Engineering, Inc., All Rights Reserved |
The absorption of water and sulphur
trioxide into sulphuric acid is an exothemic reaction resulting in an increase in the acid
temperature as it exits the tower. This heat must be removed before the acid is
returned to the tower. The function of the acid cooler is remove this heat from the
acid stream and to reject it to the environment or recover the heat as useful energy.
These coolers had several disadvantages, such as:
