# Presentation: 520612

## Findings from Field Tests of PEMS and Portable Analyzers

- John Schakenbach, USEPA
- Scott Shanklin, Karen Wesson, Penny Kellar The Cadmus Group, Inc.
- Electric Power Research Institute
- CEM Users Group Conference
- Savannah, GA
- May 6, 2005

## What’s a PEMS?

- Predictive Emissions Monitoring System
- A set of mathematical models that develops a numerical relationship between a unit’s operating parameters and a pollutant
- Does not directly measure emissions

## History of PEMS

- PEMS used for emissions since 1980
- EPRI studied PEMS in the mid-90s
- PEMS have been approved:
- for gas-fired boilers (<250 mmBtu/hr) under NSPS subpart Db by several states
- for gas-fired turbines by Texas TNRCC rule
- PEMS allowed under final CAM Rule (10/97)
- Three Part 75 NOx PEMS conditionally approved on gas-fired turbines and boiler

## Types of PEMS

- First principles
- material balances, thermodynamics, reaction kinetics
- Regression
- establishes statistical relationship
- Neural network
- iterative process using weighting factors
- Hybrid

## Potential Part 75 PEMS Users

- Gas-fired (possibly oil-fired) turbine where NOx CEMS will be replaced
- Low mass emitters
- Existing App. E peaking units transitioning to baseload operation
- Possibly 100-200 new turbines would use PEMS

**Notes:**
We believe that the market for NOx PEMS is ....
We also believe that NOx PEMS are not suitable for units with post-combustion NOx controls, for example, SCR, because of the uncertainties regarding catalyst consumption or other variables involved in post-combustion controls.

## Field Test

- Host site:  Dominion Chesterfield #8 in VA, gas-fired, GE Frame 7F turbine, 160MW, unfired HRSG, steam injection for NOx control
- 8 month duration to capture summer, fall, winter ambient temperature and humidity variations
- 1 PEMS was compared to Part 75-certified NOx CEMS, using Subpart E
- Quarterly RATAs
- Test sensor failure
- Determine appropriate QA/QC

## Field Test

- Host site: KUA, Cane Island, Unit 2 in FL, gas-fired, GE Frame 7EA turbine, 80 MW, unfired HRSG, with dry low NOx
- 7 month duration to capture summer, fall, winter temperature and humidity
- 1 PEMS and 4 portable NOx analyzers were compared to Part 75-certified NOx CEMs, RM 7E & Subpart E criteria
- Quarterly RATAs
- Test sensor failure
- Determine appropriate QA/QC

## Findings

- PEMS inputs must stay within operating envelope
- Abbreviated Subpart E statistical tests when coupled with 3-level initial RATA appear to provide adequate initial QA
- Certain statistical test allowances should be made for low emitting and/or low emission variability sources
- PEMS can be accurate for gas-fired combustion turbines where NOx is controlled by either water or steam injection or by dry-low-NOx if proper training and QA are performed

## Findings

- Compared to contracting out, purchasing portable analyzer for PEMS QA can be accurate and lower cost
- PEMS can be a lower cost alternative to CEMS for certain applications
- PEMS were unable to successfully predict NOx emissions during startup or shutdown

## Example Turbine PEMS Operating Envelope

| PEMS Input | Minimum Value | Maximum Value |
| --- | --- | --- |
| Splitter valve (steps open) | 60.0 | 100.8 |
| Gas flow (lbs/sec) | 2.0 | 4.0 |
| Load (MW) | 16.9 | 27.1 |
| Inlet air temp (°F) | 40 | 123 |
| Exhaust gas temp (°F) | 476 | 667 |
| Burner mode | 2 | 2 |

## Subpart E Test Results Chesterfield Unit 8*

| Data Set | n | Pass r-test? | Pass t-test? | Pass F-test? |
| --- | --- | --- | --- | --- |
| First 720 hours of data** | 720 | Yes | Yes | Yes |
| All 2002 data | 1112 | Yes | Yes | No |
| February 2003 data | 165 | Yes | Yes | No |
| All data | 1277 | Yes | Yes | No |

- *Mean NOx concentration is about 21 ppm.
- ** No startups or shutdowns

## Subpart E Test Results KUA Unit 2*

| Data Set | n | Pass r-test? | Pass t-test? | Pass F-test? |
| --- | --- | --- | --- | --- |
| All data | 962 | No | No | Yes |
| Data without shutdowns | 915 | Yes | No** | Yes |
| Data without startups | 905 | No | No | Yes |
| Data without startups and shutdowns | 958 | No | Yes | Yes |

- *Mean NOx concentration is about 8 ppm.
- **Actually “Yes”.  Subpart E requires t-test only be applied to data at normal load. Therefore, because data w/o startups and shutdowns passed t-test, all data sets passed t-test.

## PEMS Relative Accuracy Results

- At Chesterfield, 1,255 9-run rolling RATAs
- Startups and shutdowns excluded
- 98% met alt spec of ± 0.020 lb/mmBtu mean dif
- 75% met 10% RA
- At KUA, 851 9-run rolling RATAs
- Startups and shutdowns excluded
- 100% met alt spec of ± 0.020 lb/mmBtu mean dif
- 52% met 10% RA

## Initial Certification for NOx PEMS

| Test | Description | Perf. Spec |
| --- | --- | --- |
| Sensor validation | Determines failed sensor  | Check for production of ≥ 1 valid data point per 15 minutes |
| Train PEMS | Typically 1 week or more of paired PEMS input/output and reference method data | Linear correlation (r ≥ 0.8); and F-test (Fcritical ≥ F); minimize low bias |
| Alarm system set-up | Determines how many input sensors must fail before PEMS is OOC | Highest deviation from reference value exceeds ± 10.0% |

## Initial Certification for NOx PEMS

| Test | Description | Perf. Spec |
| --- | --- | --- |
| 3-level RATA | Similar to flow RATA, except results are in lb NOx/mmBtu | For semiannual frequency:
RA > 7.5% and ≤ 10.0%, or
For low emitter*, results acceptable if mean PEMS value is within ± 0.020 lb/mmBtu of reference mean
For annual frequency:
RA ≤ 7.5%, or
For low emitter*, results acceptable if mean PEMS value is within ± 0.015 lb/mmBtu of reference mean |

- *Mean reference value during RATA or RAA is ≤** **0.200 lb NOx/mmBtu

## Initial Certification for NOx PEMS

| Test | Description | Perf. Spec |
| --- | --- | --- |
| BAF | Adjusts low PEMS data to agree with reference method | If davg ≤ |cc| at normal operating level, bias test is passed |
| F-test, & correlation analysis | Determines how similar reference method and PEMS variances are,  and correlation, respectively | F-test (Fcritical ≥ F*) applied to each operating level (low, mid and high) separately; linear correlation (r ≥ 0.8) is applied to all data collected at the 3 operating levels combined**; use ≥ 30 runs at each level |

- *If reference method sd <** **3% span or 5 ppm, either of these values may be used when calculating F.
- **When reference method mean < 5 ppm for an operating level, that operating level may be removed from the correlation analysis.

## Hints for Using Portable Electrochemical Analyzers

- When performing stability check for 3 cells, purge with ambient air between gas injections to reduce degradation of cell performance
- For low NOx sources, analyzers must provide readings to 0.1 ppm
- For low NOx sources, provide an alternative perf spec of ± 1 ppm difference from reference value
- Analyzer should have a minimum calibration threshold appropriate to stack gas concentration being measured

## Modified ASTM Method D6522-00

| Performance Check | Gas | Acceptance Criteria |
| --- | --- | --- |
| Zero Cal Error | NO, NO2 | ≤ 3% of span gas conc or ± 1.0 ppm dif, whichever is less restrictive |
|  | O2 | ≤ 0.3% O2 |
| Span Cal Error | NO, NO2 | ≤ 5% of span gas conc or ± 1.0 ppm dif, whichever is less restrictive |
|  | O2 | ≤ 0.5% O2 |
| Interference | NO,NO2,O2 | ≤ 5% of avg stack NO conc for each test run (using span gas checks) |

## Modified ASTM Method D6522-00

| Performance Check | Gas | Acceptance Criteria |
| --- | --- | --- |
| Linearity | NO,O2 | ≤ 2.5% of span gas conc or ± 1.0 ppm dif, whichever is less restrictive |
|  | NO2 | ≤ 3.0% of span gas conc or ± 1.0 ppm dif, whichever is less restrictive |
| Stability | NO,O2NO2 | ≤ 2.0% of span gas conc or ± 1.0 ppm max-min dif, whichever is less restrictive, for 30 min period
≤ 1.0% of span gas conc or ± 1.0 ppm max-min dif, whichever is less restrictive, for 15 min period |
| Cell Temp |  | ± 5 °F from initial temp |

## Portable NOx Analyzer Results KUA Unit 2*

| Analyzer | Portable
(lb/mmBtu) | Reference
(lb/mmBtu) | Mean Dif**
(lb/mmBtu) |
| --- | --- | --- | --- |
| TESTO | 0.0370 | 0.0286 | 0.0084 |
| ECOM | 0.0338 | 0.0282 | 0.0056 |
| Land | 0.0271 | 0.0286 | -0.0015 |
| Horiba*** | 0.0283 | 0.0282 | 0.0001 |

- *Mean NOx concentration is about 8 ppm.
- **All meet the alt perf spec of ±** **0.015 lb NOx/mmBtu of reference mean
- ***Chemiluminescence

## Portable NOx Analyzer Results KUA Unit 3*

| Analyzer | Portable
(lb/mmBtu) | Reference
(lb/mmBtu) | Mean Dif**
(lb/mmBtu) |
| --- | --- | --- | --- |
| TESTO | 0.0164 | 0.0110 | 0.0055 |
| ECOM | 0.0163 | 0.0110 | 0.0053 |
| Land | 0.0154 | 0.0106 | 0.0049 |
| Horiba*** | 0.011 | 0.0110 | 0.000 |

- *Mean NOx concentration is about 4 ppm.
- **All meet the alt perf spec of ±** **0.015 lb NOx/mmBtu of reference mean
- ***Chemiluminescence

## Ongoing NOx PEMS QA/QC Tests

| Test | Performance Spec | Frequency |
| --- | --- | --- |
| Daily QA/QC | ≤ 10.0% of reference NOx emission rate | Daily |
| 3-run RAA | Accuracy ≤ 10.0%
or
For low emitter*, results acceptable if mean PEMS value is within ± 0.020 lb/mmBtu of reference mean  | Monthly |

- *Mean reference value during RATA or RAA is ≤** **0.200 lb NOx/mmBtu

## Ongoing NOx PEMS QA/QC Tests

| Test | Performance Spec | Frequency |
| --- | --- | --- |
| Normal level RATA | For semiannual frequency:
RA > 7.5% and ≤ 10.0%, or
For low emitter*, results acceptable if mean PEMS value is within ± 0.020 lb/mmBtu of reference mean
For annual frequency:
RA ≤ 7.5%, or
For low emitter*, results acceptable if mean PEMS value is within ± 0.015 lb/mmBtu of reference mean | Annual or semiannual and after each PEMS training |

- *Mean reference value during RATA or RAA is ≤** **0.200 lb NOx/mmBtu

## Ongoing NOx PEMS QA/QC Tests

| Test | Performance Spec | Frequency |
| --- | --- | --- |
| Sensor validation
system | Check for production of ≥ 1 valid data point per 15 minutes | Daily |
| BAF | If davg ≤ |cc|, bias test is passed | After each RATA |
| PEMS training | Linear correlation (r ≥ 0.8), and F-test (Fcritical ≥ F) | Initial cert; and after operation changes |
| Alarm system set-up | Highest deviation from reference value exceeds ± 10.0% | After each PEMS training |

## Capital Cost Estimates for CEMS and PEMS

|  | CEMS | PEMS |
| --- | --- | --- |
| Sampling equip & analyzers | $110,000 | NA |
| PEMS planning & vendor selection | NA | $10,000 |
| Site mods, equip shelter | $0-$30,000 | $0 |
| Part 75 DAHS | $25,000 | $25,000 |
| PEMS computer/software | NA | $10K-$30K |
| PEMS test plan development | NA | $5K-$10K |
| PEMS training & installation | NA | $25K-$50K |
| Prepare QA/QC plan | $15,000 | $12,000 |
| Initial op/maintenance training  | $15,000 | $10,000 |
| Initial certification | $15K-$20K | $15K-$20K |
| Total Capital Costs | $180K-$215K | $112K-$167K |

## Estimated Annual Costs for CEMS and PEMS

|  | CEMS | PEMS |
| --- | --- | --- |
| Operation & maintenance | $20K-$50K | $10K-$20K |
| Periodic QA | $30,000 | $6,000 |
| Annual RATA | $3.8K-$5.5K | $3.8K-$5.5K |
| Periodic recertification | $0 | $0-$13,000 |
| Recordkeeping & reporting | $15,000 | $15,000 |
| Equipment replacement | $10,000 | $2,000 |
| Total Annual Costs | $78.8K-$110.5K | $36.8K-$61.5K |

## For a Copy of Presentation

- _[www.epa.gov/airmarkets](http://www.epa.gov/airmarkets)_, click on Recent Additions
- 			or
- John Schakenbach
- Phone:  202-343-9158
- schakenbach.john@epa.gov