The V-Temp Economizer System and Method for SCR Temperature Control

Presented at: Power-Gen International
December 13-15, 2011
Las Vegas, Nevada, U.S.A.

M.J. Albrecht
J.T. Buckler
S.A. Scavuzzo

ABSTRACT

Emission requirements for fossil-fired boilers mandate that the boiler’s air quality control system (AQCS) be capable of meeting emission standards from minimum load through full load. This flexibility is more critical than ever so that coal-fired power plants remain competitive with other sources of renewable fuels and power generation methods.

One major component in the boiler’s AQCS is the selective catalytic reduction (SCR) system for nitrogen oxides (NOx) control. For optimum NOx reduction, the gas temperature entering the SCR must be maintained above the temperature at which ammonium bisulfate forms. The formation of ammonium bisulfate will degrade the SCR’s NOx removal efficiency resulting in shorter catalyst life. At loads that cannot maintain at least this temperature, typically 70 to 80% load, the SCR will require a means to increase the boiler’s economizer exit gas temperature (EEGT). The solutions currently available to resolve the EEGT issue do not provide the turndown required by most power plants for loads of 40% and below.

Babcock & Wilcox Power Generation Group, Inc. (B&W PGG) has patented the V-TempTM system to control the flue gas temperature leaving the boiler and entering the SCR, within the SCR’s desired operating load range. This system controls the distribution and flow of the economizer fluid so that the EEGT can be increased at reduced loads. The V-Temp system maintains an application-specific minimum EEGT at reduced loads, permitting the SCR to remain in service and to control NOx emissions, while minimizing the
risk of ammonium bisulfate formation in the downstream flue, at the SCR inlet, or in the SCR catalyst.

This paper will include results from successful installations of the V-Temp system on both supercritical and subcritical boilers. Optimization of this system is currently being developed to allow for operation of the boiler down to 25% load with the SCR in service while maintaining unit efficiency at full load.

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