In-Situ FT-IR Measurements at Industrial Combustion Facilities (1996)

This paper describes the development and testing ofa prototype Fourier transform infrared (FT-IR) based measurement system for continuous emission monitoring (CEM) and process control in fossil fuel­ fired power plants. On several occasions, prototype systems have been transported and assembled at full­ scale and pilot-scale fossil fuel-fired combustors. The in-situ version of the prototype is capable of measuring NH3 and HCl concentrations, which are difficult to measure extractively, as well as CO, CO2, NO H20, and SOx concentrations. The results of recent tests will be presented. which involve in-situ monitoring of selective non-catalytic reduction (SNCR) of NO, based on simultaneous measurement of NO, NH), and CO. INTRODUCTION The use ofFT-IR spectrometry as a CEM in fossil fuel-fired power plants offers several advantages. A single instrument can be used to simultaneously monitor several pollutant species, thereby greatly reducing the cost and complexity of the CEM system. Additionally, the flexibility ofFT-IR offers different sampling strategies depending on the type of analysis required. Extractive measurements provide a low maintenance approach for simultaneously determining concentrations of several species, including CO, CO2, NO, and SOz. Alternatively, in-situ measurements can be used to determine concentrations of species that are otherwise difficult to monitor, for example, NH) and HC\. The capability to measure NH) concentrations is particularly useful for monitoring and, potentially, controlling the urea injection process used for NO, reduction. In-situ FT-IR transmission measurements can also be used to determine the temperatures of gases, and the number density, particle size, and composition of particulates in the effluent [1-5]. Recent work has also demonstrated the feasibility of in-situ FT-IR emission measurements for determining the concentration of unburned carbon in flyash [6,7]. Although FT-IR is an established multicomponent sensor technology, the use ofFT-IR for CEM and process monitoring and control systems in power plants is still in the developmental stages, particularly in the case of in-situ measurements [1-6]. In this work, we describe the development and testing of an in-situ FT-IR Spectrometer system for process monitoring and control of selective non-catalytic reduction (SNCR) of NO, using the Nalco Fuel Tech (NFT) NO,OUTn .1 process. EXPERIMENTAL All field test measurements were performed at NFT's pilot-scale combustion facility (0.25 MBTU/hr) in Naperville, IL during the week of February 20-24, 1995. The objective of these measurements was to demonstrate quantitative in-situ FT-IR analysis of NO, CO, and NH) at elevated temperatures. The facility consisted of a horizontally-fired combustor with an 8-inch inner-diameter combustion zone, as shown in Figure 1. This unit was equipped with conventional CEM equipment for NO Oz, CO, and S02 analysis, and with a gas chromatograph for NzO measurement. The ammonia concentration was determined extractively using wet chemical analysis. Temperature and residence time within the unit could be adjusted, and urea or other reagents could be injected at several locations along the combustor. A nitro-containing compound was added to the fuel (oil) to provide the .desired NO, level in the combustion effluent. The NO,OUl'M reagent was injected in a temperature-controlled zone downstream from the combustor using a peristaltic pump interfaced to a personal computer.