In-Furnace Combustion Balancing to Increase Steam Temperatures

Ottumwa Generating Station

Alliant Energy Sarah Martz Electric Power Research Institute Rick Himes Zolo Technologies Eric Huelson

Agenda

1. Ottumwa Objectives 2. Boiler Balancing Strategies 3. Manual Balancing Exercise 4. Results and Next Steps

Ottumwa Objectives

1. Operate within regulatory NOx limits. 2. Operate within regulatory CO limits. 3. Maintain superheat and reheat temperatures.

NOx < 100 ppm CO < 200 ppm

ReHeat > 1000F

Problem

• Difficult to maintain all three objectives. Pro: CO and NOx targets largely met via NeuCo biasing. Con: Steam temperature generally below 1000F. Issue: Conditions that allow for increased steam temperatures also promote increased emissions.

• NeuCo CombustionOpt Optimizer Pro: Has available MPC and Neural Net optimization tools to optimize combustion and respond to emission variances. Con: Ottumwa’s available controls (> 300 burner & aux air dampers and tilts) and Indicators (>200 on ZoloBOSS alone) make autonomously optimizing combustion problematic.

Combustion Balance Effort

Theory By balancing in-furnace combustion the plant can maintain NOx, CO and Reheat objectives.

Manual Balancing Objectives Evaluate Combustion: Identify fuel rich burner zones and fuel lean burnout zones. Evaluate Controls: Determine controls that can be used to balance fuel rich/lean regions of the boiler. Balance Combustion: Identify a control strategy that can be used to balance combustion with controls and indicators. Integrate Results: Integrate balancing into NeuCo CombustionOpt.

Balancing Concept

Balanced In-Furnace

Combustion

• Reduced Emissions (CO, NOx) • Uniform Heat Transfer

Reduced slag, Balanced steam temperatures

• Allows for Reduced Excess O2 Heat Rate and Efficiency gains

Combustion Curve Target: Low CO, Low NOx, Efficient

Difficulty: Local Imbalances will dominate stack emissions. Objective: Balance combustion across entire furnace.

Balancing Integration Steps

1. Plan Identify controls and indicators available.

2. Test Demonstrate indicator response to control changes.

3. Balance Identify control strategy to maintain balanced combustion.

4. Quantify Confirm balancing strategy and benefit of balanced combustion.

5. Integrate Incorporate balancing into Optimizer or DCS.

Plan Controls and Indicators Available

OFA • 8 Upper Rear OFA ports. • 8 Lower Corner OFA ports. Burner and Aux Air • Burners – 8 columns, 7 rows • Aux Air – 8 columns, 8 rows ZoloBOSS • 8x5 grid above OFA. • Temp, O2, CO and H2O. O2 Probes • 7 West Side, 7 East Side. Steam Temperatures • Reheat and Superheat Emissions • CO and NOx

Ottumwa Generation Station Twin Tangential Fired, 715 MW

Test Parametric Testing for Control Impact

Tested Controls Upper Rear OFA Lower OFA Aux-Air

Findings Upper Rear OFA

West to East Air Biasing: Effective at moving air to/from each side of the boiler Lower OFA

Mitigating CO Hot spots: Effective at mitigating CO regions within the boiler Aux-Air:

No obvious effect: Typically combustion can be centered through Aux-Air changes. More testing to identify tuning relationship.

Balance Ottumwa Balancing Strategy

1. Equilibrate East and West Furnace.

2. Balancing Combustion Within Each Furnace.

Balance Equilibrating East and West

• Control: Upper Rear OFA ports – Alternate Controls: WB Biases, Aux Air Bias

• Indicator Validation Oxygen Biasing: Zolo O2% , O2 Probes In-furnace Temperature Biasing: Zolo Temp(F) • Steam Temperature Biasing: Superheat (F), Reheat (F)

Balance Balancing In-Furnace Combustion

• Control: Lower OFA Conner Ports – Alternate Control: Aux Air, Secondary Air, Boundary Air

• Indicator Validation ZoloBOSS Quadrants: Zolo O2% , Zolo CO(ppm)

Qualify Manual Balancing Exercise

1. Collect Baseline Data. 2. Balance Combustion (Iterative Process).

– Equilibrating East and West – Balance In-Furnace Combustion – Optimize excess O2

3. Document optimal control strategy.

Manual Balancing Baseline

Overview – Objective Provide baseline data for current boiler performance.

– Actions Collected two hours of baseline performance data with NeuCo enabled.

– Next Step Reduce Excess O2 and determine in-furnace balance.

Temp CO O2

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

O2

A

B

D

C

E

F

H

G

- -

- -

- -

- - Note: For all tomography plots displayed, Temp 2000-2800F, CO 2,000-16,000, O2 1.0% -8.0%. Blue = low, Green = Med, Red = High, Black = Max

Reducing O2

Temp CO O2

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

Overview – Objective Qualify state of combustion balance with reduced Excess O2.

– Findings Pro: Steam Temps ↑, NOx ↓, Aux Power ↓ Con: CO ↑

– Next Step Utilize West to East Balancing Strategies to move air to West Side.

Upper Rear OFA: +20% West Furnace, -20% East Furnace.

CO O2

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

- - + + + + - -

- -

- -

- -

- -

West to East Balance

Overview – Objective Balance West and East Furnace Averages

– Findings Pro: Reheat Temp ↑, Steam Split ↓, Aux Power ↓ Con: CO ↑ ↑

– Next Step Utilize In-Furnace Balancing to mitigate high CO and low O2. Lower OFA: Add Air to corners A & D, and E & H.

Temp CO O2

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

CO O2

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

+

+ - - +

+ - -

- - + + + + - -

In-Furnace Balancing

Temp CO O2

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

A

B

D

C

E

F

H

G

Overview – Objective Balance In-Furnace (Minimize Zolo CO and O2 hot spots, overall emission reduction)

– Actions Collected two hours of data with optimized combustion.

– Findings Pro: Stack CO ↓, Steam Split ↓, Aux Power ↓, In-furnace Zolo Balance ↓

+

+ -

- +

+ -

-

Overall Results

• Ottumwa Process 1. Reduced Excess O2

2. Balanced West to East Distribution

3. Balanced In-Furnace Combustion

• Result Highlights – Emissions: NOx ↓ by 5% (78 to 74ppm), Maintained CO limits < 200ppm

– Steam Temps: Superheat ↑ 6.4F, Reheat ↑ 18.0F (SH split - 0.1F, RH Split of 6.6F) – Auxiliary Power: ↓ 2.4 MW – Heat Rate Total Heat Rate Reduction ~0.9%

Dry gas loss + Aux Power + RH/SH temp of 92.9 btu/Kwh

* EPRI, “Heat Rate Awareness”, Table 4-2 Heat Rate and Generation Impacts of Controllable Losses for a Reheat Unit, 1997

Integration Integrate with NeuCo CombustionOpt

• Sustained Benefit – Relies on integrating balancing strategy into Optimizer or DCS.

• Items Needed – Control Logic: Translate balancing strategy into optimization based rules. – Limit Set Points: Set up optimizer control constraints.

• At Ottumwa – Looking to continue integration efforts in late August or September.

• Controls: Rear OFA Dampers – groupBA_W = (ROFA1, ROFA2, ROFA3, ROFA4)_level A&B – groupBA_E = (ROFA5, ROFA6, ROFA7, ROFA8) _level A&B

• Indicators: – ZB_W_O2Avg = Average(ZoloBOSS O2 (P1, P2, P3, & P4)) – ZB_E_O2Avg = Average(ZoloBOSS O2 (P5, P6, P7, & P8)) – Probe_W_O2Avg = West_O2 – Probe_E_O2Avg = East_O2

• Logic: – For a 30 minute window – If (ZB_W_O2Avg - ZB_E_O2Avg) > 0.2% & If (Probe_W_O2Avg -

Probe_E_O2Avg) > 0.2%, then +5%bias groupBA_W&-5% biasgroupBA_E – If (ZB_W_O2Avg - ZB_E_O2Avg) < -0.2% & If (Probe_W_O2Avg -

Probe_E_O2Avg) < -0.2%, then -5%bias groupBA_W& +5% bias groupBA_E

Example West to East Balancing Module

Conclusion

Process 1. Plan Identify controls and indicators available.

2. Test Demonstrate indicator response to control changes.

3. Balance Identify control strategy to maintain balanced combustion.

4. Quantify Confirm balancing strategy and benefit of balanced combustion.

5. Integrate Integrate balancing into Optimizer or DCS.

Ottumwa Results – Currently at Stage 5 in the process. – Results suggest sustained Ottumwa benefits *:

Aux power reduction ~ 1.2 MW NOx reduction ~ 5% CO reduction ~ 20% Superheat and Reheat Temps ~ 1000F (+/- 5F)

* Assumes sustained Excess O2 set point of 2.75% (2.25% during demonstration)

Thanks!

Alliant Energy Sarah Martz Electric Power Research Institute Rick Himes Zolo Technologies Eric Huelson