Model MicroCEM

Instruction Manual

748467-A January 2002

SECTION 1

DESCRIPTION AND SPECIFICATIONS

1-1 OVERVIEW

The MicroCEM Analyzer Module is designed to continuously determine the concentration of O2 , CO, and NOx in a flowing gaseous mix- ture. The concentration is expressed in percent (%) or parts-per-million (PPM).

The sampled gas is collected from the stack and prepared by the Probe/Sample Handling System for analysis and processing by the Analysis Enclosure. The Analysis Enclosure shall be a standalone, computer-controlled unit, utilizing PC/104 as the system bus.

The MicroCEM is enclosed in a rugged NEMA 4X, IP65 type enclosure, for harsh environ- ment. The analysis enclosure utilizes convection cooling with no air intake and air vents. The analysis enclosure is modular, general purpose and easily expandable. It utilizes industry standard components such as PC/104 boards, and modular signal conditioning mod- ules.

1-2 TYPICAL APPLICATIONS

SCR

Emission Compliance per EPA 40 CFR Part 60

Gas Turbines

Natural Gas Fired Boilers Process Heaters

1-3 THEORY OF OPERATION

a.Chemiluminescense NOX

The NOx analyzer continuously analyzes a flowing gas sample for NOx [nitric oxide

(NO) plus nitrogen dioxide (NO2)]. The sum of the concentrations is continuously reported as NOx.

The MicroCEM NOx Analyzer Module uses the chemiluminescense method of detection. This technology is based on NO’s reaction with ozone (O3) to produce

NO2 and oxygen (O2). Some of the NO2 molecules produced are in an electronically excited state (NO2* where the * refers to the excitation). These revert to the ground state, with emission of photons (essentially, red light). The reactions involved are:

NO2 + O3 → NO2* + O2

NO2* → NO2 + red light

The sample is continuously passed through a heated bed of vitreous carbon, in which NO2 is reduced to NO. Any NO initially present in the sample passes through the converter unchanged, and any NO2 is converted to an approximately equivalent (95%) amount of NO.

The NO is quantitatively converted to NO2 by gas-phase oxidation with molecular ozone produced within the analyzer form air supplied by an external source. During the reaction, approximately 10% of the NO2 molecules are elevated to an electronically excited state, followed by immediate decay to the non-excited state, accompanied by emission of photons. These photons are detected by a photo- multiplier tube which produces an output proportional to the concentration of NOx in the sample.

To minimize system response time, an internal sample bypass feature provides high-velocity sample flow through the analyzer.

b.Non-Dispersive Infrared (NDIR) CO

The optical bench can selectively meas- ure multiple components in a compact design by using a unique dual optical bench design. Depending on the applica- tion, any two combinations of NDIR chan- nels can be combined on a single chopper motor/dual source assembly.

Rosemount Analytical Inc. A Division of Emerson Process Management

Description and Specifications

1-1