In-Line Localized Monitoring of Catalyst Activity in Selective Catalytic NOx Reduction Systems

Abstract

Localized catalyst activity in an SCR unit for controlling emissions from a boiler, power plant, or any facility that generates NOx-containing flue gases is monitored by one or more modules that operate on-line without disrupting the normal operation of the facility. Each module is positioned over a designated lateral area of one of the catalyst beds in the SCR unit, and supplies ammonia, urea, or other suitable reductant to the catalyst in the designated area at a rate that produces an excess of the reductant over NOx on a molar basis through the designated area. Sampling probes upstream and downstream of the designated area draw samples of the gas stream for NOx analysis, and the catalyst activity is determined from the difference in NOx levels between the two probes.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application is a continuation of application Ser. No. 11 / 112,667, filed Apr. 21, 2005, which is related to U.S. Provisional Patent Application No. 60 / 571,100, filed May 14, 2004, and claims all benefits legally capable of being offered by both such applications. The entire contents of both such applications are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention resides in the field of NOx emissions from combustion facilities, and methods and plant equipment using selective catalytic reduction (SCR) for controlling and reducing the emissions.[0004]2. Description of the Prior Art[0005]A widely used process for the reduction of NOx emissions from coal-fired utility boilers and in combustion flue gases in general is the process known as selective catalytic NOx reduction (SCR). In this process, the NOx in the flue gas is reacted with oxygen and ammonia over a solid catalyst whi...

AI Technical Summary

Benefits of technology

Enables continuous, efficient monitoring of catalyst activity without shutdowns, allowing for timely adjustments to maintain NOx reduction performance, reducing ammonia slip, and optimizing catalyst usage by providing detailed, localized data on degradation rates across different layers.

Problems solved by technology

This in turn results in greater amounts of unreacted ammonia leaving the unit (the “ammonia slip”) and therefore greater cost in operating the unit, a greater risk of pollution, and possible adverse impacts on downstream equipment.

Catalyst degradation is further complicated by the fact that in large catalytic reactors the catalyst is deployed in two or more distinct and separated layers, with different layers tending to degrade at different rates.

Monitoring methods that are in current use introduce inefficiencies of their own, however.

These methods will not differentiate between situations in which all catalyst layers are losing activity at approximately the same rate from those in which upstream layers are losing activity at a greater rate than those downstream.

A further difficulty is that increases in the ammonia slip or in the ammonia content of the fly ash may be the result of factors other than catalyst activity, such as an ammonia injection grid that is not properly adjusted or any other irregularity in the ammonia injection system.

Unless the unit is expressly shut down for the sampling, the time interval between sampling opportunities will be dictated by the outage schedule of the unit rather than concerns over the catalyst activity and can be very long.

A further problem with the withdrawal of catalyst samples is that the analyses of these samples provide no information regarding how any observed decrease in catalyst activity occurred, i.e., whether the decrease occurred slowly and gradually over time or by a step change resulting from a boiler upset, a fuel change, or some other occurrence not related to the SCR unit itself.

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