Electrostatic precipitator reliability

If a wet method for collection is selected, such as a wet electrostatic precipitator, fiber-type self-draining mist eliminator, or wet scrubber, ammonia can be regenerated from the salt solution by reaction with a readily available metal oxide such as lime or zinc oxide with formation of a stable sulfur product for disposal. These metal oxides, however, as well as their reaction products, are insoluble and could cause deposition on heat transfer surfaces and/or clogging in the regenerating equipment. Therefore, as indicated in Figure 2, to ensure continuity and reliability of the process, a soluble metal oxide was utilized (in the form of sodium hydroxide solution) to regenerate the ammonia in the experimental work described. This procedure also allows more eflFective utilization of the metal oxide the soluble oxide (NaOH) can be regenerated in batch equipment outside the continuous portion of the process by reaction with either the aforestated insoluble reactants, lime, or zinc oxide. Better control is aflForded in a batch reactor with more eflBcient use of reactants. However, in full-scale equipment undersirable deposition of reactant and product may be controllable so that batch operation may not be necessary. 

Reliability of electrostatic precipitators (ESP) has been excellent except where the inlet gases have been too cold or too hot. Entering flue gas temperatures must be kept above 177 C (350 F) to prevent dew point corrosion of electrostatic precipitators (ESP). But entering flue gas temperatures also must be kept below 260 (500 F) to prevent high temperature chloride corrosion. 

Heat exchanger tubes for the cooler situated between the phosphorus burner and the hydrator towers are also made of graphite, and the gas path in the electrostatic precipitator consists of carbon tubes with cathode elements of stainless steel wire to ensure reliable operation. 

Based on fuel type, flue gas conditions, boiler type, NO removal requirements, new or retroflt application, cost and reliability, the SCR converter in a power plant can be located immediately after the boiler (and the economizer) (high dust arrangement, HD), after the removal of the particulate by the electrostatic precipitator and upstream of the APH Row dust arrangement, LD), and after the particulate collection and/or the removal of sulfur dioxide by a flue gas desulfurization (FGD) system (tail end arrangement, TE) (Figure 3). 

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