Simple Solutions for High Ash Content Levels

Many sulfur burning plants are plagued by high ash content levels , and then contamination of the waste heat boiler and catalyst bed in the converter of the acid plant. The answer to this problem is the installation of a liquid sulphur polishing filter after the pressure leaf filter. The liquid sulphur polishing filter with ceramic elements will drastically improve the run time of the sulfuric acid plant.

The filter holds ceramic filter tubes. This is a combination of surface and depth filtration. The sulfur flows from the outside of the filter element. Solids are retained on the surface of the filter tube and clean sulphur comes through the outlet of the sulphur storage. The filter is cleaned by injecting steam into the reverse direction. The operation of a liquid sulphur polishing filter is demanding and, in some cases, problematic. Some of the possible problems, along with recommended solutions are:

  • Design: Most filters are designed on flow rate, containing ash levels as low as 20 ppm at the inlet. However, when problems are encountered at the pre-filter, the ash content can build up fast and the polishing filter will be plugged. A flow-based overdesign of 10-20 percent is a must to avoid possible breakthrough of ash, preventing short cycles and overloading the filter with solids.
  • Cleaning: the ceramic filter tubes are cleaned by injecting high pressure steam in reverse. The steam will follow the path of lowest pressure drop, so clean filter tubes will allow steam to pass through, while plugged filter tubes will not be cleaned efficiently. The solution in this case is to use individual outlets. One register on filter tubes is cleaned, followed by the next. The cleaning will be much more efficient, and the life time of the filter tubes often doubles.
  • Sealing of ceramic filter tubes: ceramic filter tubes have glued-on gaskets. Often, due to high temperatures, the sealant gets damaged and the gaskets get loose. A specially designed filter rube holder keeps the gaskets in place and assures a good seal. The tube holder also makes it possible to expand the length to fit a double length filter tube.
  • Blocking cake discharge outlet: when high amounts of solids are accumulated in the polishing filter, the solids can block the cake discharge opening. This can be prevented with a special heated cake outlet valve, which can be supplied with an up to 16-inch opening.
  • Steam vapours around the filter: when the filter is cleaned by back flushing with steam, vapours will be released from the bottom outlet. This is a dangerous situation for operators around the filter and can cause corrosion on the filter and surrounding equipment. Sulphurnet has designed a special cake discharge drum so the steam can be directed to a safe zone. When using this cake discharge drum, high pressure air can be used for a thorough and efficient cleaning instead of steam.

Implementation of the above features not only provides ceramic filter tubes with a longer lifetime it also makes the operation safer and more reliable. Reliability can be obtained by installing pressure instruments to measure the pressure differential, and by automating the system.

For more information about the polishing filter and its features, do not hesitate to contact us at sulphur@sulphurnet.com .

Article published in the print edition of Sulfuric Acid Today Fall / Winter 2013 and written by Jan Hermans.

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