Using Data Analytics to Mitigate the Effects of Load Cycling and Low Load Operation

Elijah Caselman, P.E.Asset Management Engineer, Black & Veatch

18 February 2019

What are the challenges?

• Base-load design

• Multi-system modifications

• Reliability

• Heat Rate

• What else could go wrong?

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Quantifiable Effect on Reliability

• Load cycling units tend to experience higher forced outage rates.

• Problems can occur in unexpected places.

• How do we mitigate the effects?

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EFO

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Peaking Baseload

EFOR vs Load Profile

*Based on NERC GADS data (2006-2010)

Quantifiable Effect on Heat Rate

• Less efficient operation at lower loads

• How do we maximize equipment performance and reduce fuel costs?

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oad

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Heat Rate vs Load

Data Analytics

• Using data to provide insight into equipment performance and reliability• Improve operations and maintenance planning

• Advanced pattern recognition (APR) - Early detection of emerging issues

• Wide plant coverage across:• Boiler• Turbine• BOP

• Issue tracking and storage

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Modifications – Sliding Pressure Operation

• Sliding pressure operation can provide the following benefits:• Reduce boiler feed pump power• Reduce throttling losses across the HP turbine governor valves• Improve steam temperatures

• Potential concerns:• Metallurgical limits – drum temperature will change with pressure• Slower control response

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Modifications – Sliding Pressure Operation

• Data analytics used to quantify the impacts of sliding pressure operation• Net heat rate improvement driven by increased HPT efficiency and higher steam

temperatures

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Up to 15.5% increase in HPT efficiency observed during sliding

pressure operation

10-20+ degF increase in hot reheat temp

Minor increase in spray flows

Modifications – Air Quality Control Equipment• Impacts of cycling:

• Higher emissions and ammonia usage during low load operation: CO, NOx• Selective catalytic reduction (SCR) not designed for lower gas temperatures. • Gas temperatures limit load flexibility

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SCR Inlet NOx increases >33% when operating at ~180 MW

net vs 200 MW net

Modifications – Air Quality Control Equipment• Steps taken to mitigate cycling impacts:

• Boiler tuning to improve emissions at lower loads• Revised settings to allow combustion optimizer to remain enabled at lower loads

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Reduced ammonia flow by ~250 lb/hr or ~50%

Reduced SCR Inlet NOx by ~33% at 180 MW net

<190 MW net <190 MW net>190 MW net

Higher SCR Inlet NOx and ammonia flow at 180mwn

prior to tuning

Modifications – Boiler Feed Pump

• The boiler feed pump operates further away from the best efficiency point at lower loads which reduces pump life.

• Pump vibrations increase at lower loads

• Boiler feed pump recirculation line is more susceptible to flow-accelerated corrosion during low load operation due to lower temperatures and high pipe velocities

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Modifications – Boiler Feed Pump• Data analytics used to determine the

effect of operational changes on BFP

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Low Load -rated pressurerecirc CLOSED

Low Load -rated pressure

recirc OPEN

Low Load -sliding pressure

recirc OPEN

Reduced vibrations

• Pump operates closer to BEP with sliding pressure and recirc valve open

• Low vibrations when operating near BEP

FWH Drip Pump• HP FWH drip pump out of service for many years due to repeated failures.

• Pump not needed at full load• HR and cost impacts of operating with the pump out of service at low load were ~100 Btu/kWh and $100,000/yr

• FWH level fluctuations due to control room operators manually controlling drain valves at low loads.

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Condenser Performance• Advanced pattern recognition (APR) used to identify increase in condenser backpressure at low load.

• No significant change at full load

• Backpressure increased >1 inHg at low load. HR and cost impacts were >300 Btu/kWh and $50,000/month.

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Summary

• Market forces are driving a change in operation

• Not an easy task

• Equipment considerations

• Reliability and heat rate concerns

• Entering the unknown

• Additional steps are necessary to ensure reliable operation

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18 February 2019