New and strict pollution regulations in metallurgical plants worldwide are restricting particulate and acid gas emissions to extremely low levels. Because of that, sulphuric acid plants are being installed to remove and utilise S02 in gases resulting from the roasting of sulphide ores, smelting of ores, and burning or regeneration of spent acid or acid sludge from petroleum refining. To prevent the formation of 'black' or contaminated acid and to protect the catalyst beds from fouling and plugging, wet electrostatic precipitators are utilised to clean the off-gases before entry into the acid plant. The acid plants that must handle impure sulphur dioxide gases such as those emitted from metallurgical processes like ore roasters, flash smelters, and spent acid regeneration, require the removal of acid mist and residual dust and fume before the gases enter the drying tower.
Conventional scrubbing systems (wet or dry) are generally not effective in controlling submicron emissions, consisting primarily of acid gas mists, submicron particulates and condensed organics. Wet electrostatic precipitators (ESPs), because of their ability to generate multi-staged charging and strong electrical fields in a wet, cooled atmosphere, have proven effective in cleaning the flue gas.
The Beltran wet ESP
As a result of considerable research and development, Beltran Technologies, Inc. custom designs and engineers a unique wet electrostatic tubular precipitator. The Beltran Wet ESP in most cases is a vertical-flow hexagonal or rectangular tube type precipitator.
Typically the flue gases enter at the bottom and flow upward through the precipitator. There are generally two sets of spray headers, whereby the first set continually
cools and saturates the flue gases, if necessary. The second set of spray headers are at the top and directly below the collector, which wash the collector and electrodes. These are operated on a periodic, as needed basis.
The multi-stage tubular precipitator consists of a series of ionising sections and a collection section. The discharge electrode is in the form of a rod or tube with a number of sharp corona generating discharge points. Various collecting tube geometries have been utilised over the years, the most common being the round. The square configuration and/or the hexagonal shape is chosen because these geometries are much more space efficient than the round shape, and produce a greater collection efficiency in a given volume.
The Beltran wet electrostatic precipitator uses solid ionising rods instead of wires. Also, the unique electrode design allows for generation of a corona field 4 to 5 times more intense than standard wet or dry ESPs. This higher current and field strength results in higher particle migration velocities that translate into a higher efficiency or reduced collector area-Solid particulate matter and mist droplets that enter the electrostatic section are charged by the high voltage and current produced by the electrode and collected on the grounded plates. Most of the particulates are flushed down into the bottom of the housing.
Controlling acid gas mists