Review DRAFT

CAM T ECHNICAL G UIDANCE D OCUMENT B.16 NONSELECTIVE CATALYTIC REDUCTION B-134 4/02 B.16 NONSELECTIVE CATALYTIC REDUCTION 28,29,30

B.16.1 Background

Nonselective catalytic reduction (NSCR) is an add-on NO

x control technology for exhaust streams with low O 2 content. Nonselective catalytic reduction uses a catalyst reaction to simultaneously reduce NO

x , CO, and hydrocarbon (HC) to water, carbon dioxide, and nitrogen. The catalyst is usually a noble metal. The conversion occurs in two sequential steps, as shown in the following equations:

Step 1 Reactions: 2CO + O 2 

### ÿ 2CO 2 2H 2 + O 2 

### ÿ 2H 2 O HC + O 2 

### ÿ CO 2 + H 2 O

Step 2 Reactions: NO

x + CO 

### ÿ CO 2 + N 2 NO

x + H 2 

### ÿ H 2 O + N 2 NO

x + HC 

### ÿ CO 2 + H 2 O + N 2
The step 1 reactions remove excess O 2 from the exhaust gas because CO and HC will more readily react with O 2 than with NO

x . The O 2 content of the stream must be kept below approximately 0.5 percent to ensure NO

x reduction.

One type of NSCR system injects a reducing agent into the exhaust gas stream prior to the catalyst reactor to reduce the NO

x . Another type of NSCR system has an afterburner and two catalytic reactors (one reduction catalyst and one oxidation catalyst). In this system, natural gas is injected into the afterburner to combust unburned HC (at a minimum temperature of 1700°F). The gas stream is cooled prior to entering the first catalytic reactor where CO and NO

x are reduced. A second heat exchanger cools the gas stream (to reduce any NO

x reformation) before the second catalytic reactor where remaining CO is converted to CO 2 .
The control efficiency achieved for NO

x ranges from 80 to 90 percent. The NO

x reduction efficiency is controlled by similar factors as for SCR, including the catalyst material and condition, the space velocity, and the catalyst bed operating temperature. Other factors include the air-to-fuel (A/F) ratio, the exhaust gas temperature, and the presence of masking or poisoning agents. The discussions in section B.15 for SCR relating to catalyst issues and space velocity also apply to NSCR. The operating temperatures for NSCR system range from approximately 700° to 1500°F, depending on the catalyst. For NO

x reductions of 90 percent, the temperature must be between 800° to 1200°F. One source indicates that the O 2 concentration for NSCR must be less than 4 percent, and another source indicates that the O 2 concentration must be at or below approximately 0.5 percent.

B.16.2 Indicators of NSCR PerformanceReview DRAFT

CAM T ECHNICAL G UIDANCE D OCUMENT B.16 NONSELECTIVE CATALYTIC REDUCTION 4/02 B-135 The key indicators for NSCR are the same performance indicators for SCR with a few exceptions (minus the NH 3 /NO

x ratio, outlet NH 3 concentration, and sulfur content of the fuel). Outlet NO

x concentration, catalyst bed inlet temperature, catalyst activity, pressure differential across the catalyst bed, catalyst bed outlet temperature, inlet gas flow rate, and outlet O 2 concentration were discussed above. Table B-16 lists these indicators and illustrates potential monitoring approaches for NSCR.

B.16.3 Illustrations

The following illustration presents an example of compliance assurance monitoring for NSCR:

16a: Monitoring catalyst bed inlet temperature, catalyst bed outlet temperature, and catalyst activity.

B.16.4 BibliographyCAM T ECHNICAL G UIDANCE D OCUMENT B.16 NONSELECTIVE CATALYTIC REDUCTION B-136 4/02Review DRAFTTABLE B-16. SUMMARY OF PERFORMANCE INDICATORS FOR NSCRsParameters Performance indicationApproach No. 1 2 3Illustration No. 16aExample CAM SubmittalsCommentPrimary Indicators of PerformanceOutlet NOXconcentrationDirect measure of outlet concentration. Mostdirect single indicator of NSCR performance. XCatalyst bed inlettemperatureIndicator that bed inlet is of sufficient temperature toinitiate reduction. Also an indicator that bed inlettemperature is not too high for catalyst longevity.X XCatalyst activity Periodic check of catalyst activity gives an indication of catalyst fouling or masking. Must periodicallyclean and/or replace catalyst to ensure reduction is occurring.XOther Performance IndicatorsCatalyst bed outlettemperatureIndicator of level of reduction occurring in the catalyst bed and that temperature does not exceed designlimits of catalyst. Higher temperatures improvereduction of CO and VOC but encourage generation ofNOX.X XPressure differentialacross catalyst bedIndicator of bed fouling or plugging. Increase in pressure differential indicates that bed is becomingfouled or plugged. Changes in pressuredifferential are likely to be gradual.XOutlet O2concentrationIndicator of dilution rate. Generally monitored in combination with NOX, VOC, or CO concentration toallow for correcting concentration to a specified percent O2.XComments: None.Review DRAFT

CAM T ECHNICAL G UIDANCE D OCUMENT B.16 NONSELECTIVE CATALYTIC REDUCTION 4/02 B-137 CAM ILLUSTRATION No. 16a. NONSELECTIVE CATALYTIC REDUCTION FOR NO X CONTROL

1. APPLICABILITY

1.1 Control Technology: Nonselective catalytic reduction [065] 1.2 Pollutants Primary: Nitrogen oxides (NO X ) Other: Nitric acid (HNO 3 ), ammonia (NH 3 ) 1.3 Process/Emission units: Internal combustion engines (ICE)

2. MONITORING APPROACH DESCRIPTION

2.1 Indicators Monitored: Catalyst bed inlet temperature, catalyst bed outlet temperature, and catalyst activity. 2.2 Rationale for Monitoring Approach • Catalyst bed inlet temperature: Indication that the gas stream is at sufficiency temperature to initiate reduction on the catalyst bed; too high a bed temperature may generate NO X rather than reduce NO X . • Catalyst bed outlet temperature: Indication that the reaction is occurring in the catalyst bed; too high a bed temperature may generate NO X rather than reduce NO X . • Catalyst activity: Indication of the catalyst’s ability to promote the reduction of NO X . 2.3 Monitoring Location • Catalyst bed inlet temperature: Inlet to the catalyst bed. • Catalyst bed outlet temperature: Outlet to the catalyst bed. • Catalyst activity: Removal of a small portion of catalyst for testing. 2.4 Analytical Devices Required: Thermocoupl es or other temperature instrumentation. 2.5 Data Acquisition and Measurement System Operation • Frequency of measurement: – Catalyst bed inlet temperature: Measure continuously. – Catalyst bed outlet temperature: Measure continuously. – Catalyst activity: Measure periodically. • Reporting units: – Catalyst bed inlet temperature: Degrees Celsius or Fahrenheit (C or F). – Catalyst bed outlet temperature: Degrees Celsius or Fahrenheit (C or F). – Catalyst activity: Percent active compared with new catalyst (or other as appropriate). • Recording process: – Catalyst bed inlet temperature: Recorded automatically on strip chart or data acquisition system. – Catalyst bed outlet temperature: Recorded automatically on strip chart or data acquisition system. – Catalyst activity: Manually recorded in NSCR maintenance log.Review DRAFT

CAM T ECHNICAL G UIDANCE D OCUMENT B.16 NONSELECTIVE CATALYTIC REDUCTION B-138 4/02 2.6 Data Requirements • Baseline catalyst bed inlet temperature, catalyst bed outlet temperature, and catalyst activity measurements concurrent with emission test. • Historical plant records of catalyst bed inlet temperature, catalyst bed outlet temperature, and catalyst activity measurements. 2.7 Specific QA/QC Procedures • Calibrate, maintain, and operate instrumentation using procedures that take into account manufacturer’s recommendations. 2.8 References: ______

3. COMMENTS

None.