US 6,146,605 AGranted

Combined SCR/SNCR process

AssigneeHera, LLC

InventorFelix E. Spokoyny

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Abstract

In many situations where the maximum NOx reduction capabilities of conventional SCR systems are not necessary, and alternative SNCR systems may not economically provide desired NOx reduction, a staged SCR/SNCR system is believed to be the most appropriate solution available. By means of the present invention, a system has been developed for delivering NOx reduction agents from a common urea feedstock, when it appropriate to use combined NOx treatment stages (i.e. SNCR within the boiler followed by in-duct SCR and/or catalyzed air preheater elements). For the SNCR stage, the urea from the common feedstock is diluted prior to injection into the boiler and, for the SCR stage, the urea from the common feedstock is used to produce ammonia using hydrolysis. Urea solution which is not converted to ammonia in the SCR phase, is used for dilution of the solution being delivered to the SNCR system.

Claims9

Dependent claims

In a combined SNCR/SCR system for removing NOx from a flue gas stream of a fossil fuel burning facility, such as a power plant, the improvement in the method of providing the nitrogenous compound necessary for the respective process reactions, comprising the steps of:

providing a stored source of a urea based compound;
continuously directing a first portion of said compound to the SNCR section of the system for injection into the flue gas stream in a form, location and temperature zone which are appropriate for efficient selective non-catalytic reduction of NOx in the presence of such first portion;
selectively directing a second portion of said compound to an intermediate conversion system which is operative to convert a portion of said second portion of said compound to a gaseous mixture containing ammonia, and to leave a remaining portion;
after said last mentioned conversion, continuously integrating said remaining portion with said first portion;
and
directing to and consuming said gaseous mixture in said SCR section of the system.

3 more elements

Dependencies are inferred from the claim text.