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Magnesium Oxide Wet Scrubbing for Flue Gas Desulferization

Magnesium Oxide Wet Scrubbing for Flue Gas Desulferization
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Magnesium Oxide Wet Scrubbing for Flue Gas Desulferization - 1

Application Data Sheet Power Magnesium Oxide Wet Scrubbing System for ■ Reduced sulfur dioxide (S02) emissions ■ Improved corrosion resistance ■ Reduced sorbent consumption Wet scrubbers are used in utilities, paper mills, and chemical plants to remove sulfur dioxide (S02) and other pollutants from gas streams. Undesirable pollutants are removed by contacting the gases with an aqueous solution or slurry containing a sorbent. Lime / limestone systems are most common for S02 removal but magnesium oxide (MgO) slurry is sometimes used as an alternative. After fly ash removal, the flue gas enters the scrubber (Figure 1) where it comes in contact with the MgO slurry. The S02 is absorbed in the scrubber slurry and forms insoluble magnesium sulfite Oxygen injected at the base of the scrubber further oxidizes the MgS03 to magnesium sulfate (MgS04). A bleed line from the scrubber recirculation line carries the slurry to a centrifuge where MgS03 crystals are separated from the scrubber slurry. The MgS03 and MgS04 is used in the acid plant to produce S02 for sulfuric acid production. The MgO reagent is regenerated and returned to the scrubber system. The pH of the slurry must be carefully maintained between 4.5 and 5.0 because the MgS03 has a very limited solubility above pH 5.0. Proportional control, using the 4-20 mA current output, is desirable when hold-up time in the recirculating tank is five minutes or less. When hold-up time is fifteen minutes or more, a less expensive on- off control by the pH analyzer is adequate. If the pH of the scrubber slurry is too low, S02 will not be absorbed, corrosion will result, and S02 regulatory emissions standards will be violated. S02 will be absorbed if the pH is too high, but reagent usage will be excessive, and scale will form inside the scrubber leading to plugging due to formation of calcium carbonate (CaC03) Since the MgO slurry has a tendency to coat the pH sensor, the 3400 HT PERpH-X or the 396 TUpH1 pH sensor should be used in line, with a sample velocity of at least 3 ft / sec. The 3400 HT features a rebuildable reference while the 396 is a disposable design. Appropriate analyzers include the dual input 1056, which offers a large display, intuitive menus, and four optional alarm relays for basic process control. If more advanced control features are required, the 56 offers four programmable relays with Time Proportional Control ' TUpH is a trademark of Rosemount Analytical ROSEMOUNT EMERSON. Analytical Process Management

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Magnesium Oxide Wet Scrubbing for Flue Gas Desulferization - 2

Power 1056 Dual Input Intelligent Analyzer Dual configurable inputs and outputs Large, bright LCD display Intuitive menus with advanced diagnostics Four alarm relays with timers Optional HART® or Profibus DP Polycarbonate NEMA 4X (IP65) enclosure Fast, Accurate, & Stable Measurement Rugged, Versatile Design Quick Connect Cable or Integral Cable Long lasting rebuildable Reference SOLUTIONS Compliant Design Large, high resolution full-color screen displays process trends Four configurable 4–20 mA current outputs Data and event logging accessed via USB 2.0 data port PID control outputs and...

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