Efficiency Improvements & Emission Reductions

Efficiency Improvements

We've installed several technologies to reduce emissions and improve efficiency at our coal-fired plants. Going forward, replacing Hoot Lake Plant with wind and natural gas-fired generation will reduce emissions even further. We expect system-wide carbon emissions to decrease by at least 40% from 2005 levels by 2022.

Pollution Control Equipment Upgrades at Coal-Fired Plants

Pollutant

Hoot Lake Plant

Coyote Station

Big Stone Plant

Sulfur Dioxide None Spray Dryer (1981) Circulating Dry Scrubber (2015)
Nitrogen Oxides (NOx) Low-NOx Burners and Separated Over-Fire Air (2006) Separated Over-Fire Air (2015-2016) Separated Over-Fire Air & Selected Catalytic Reduction (2015)
Particulate Matter Electrostatic Precipitator (2014)  Baghouse (2009) Baghouse (2015)
Mercury Activated Carbon Injection (2014) Activated Carbon Injection (2014) Activated Carbon Injection (2015)

Net Plant Heat Rate

Improving net plant heat rate (NPHR) reduces emissions because it takes less fuel to produce the same amount of energy. NPHR is most commonly expressed as Btu/kWh, representing a measure of the amount of energy it takes to produce one kilowatt-hour of electricity. From 2005 to 2019 we've improved our system average NPHR by approximately 22%. That average includes owned generation sources and long-term wind power purchase agreements. We expect an additional 17% NPHR improvement by 2022.

Thermal Generation Efficiency

In 2019 we improved efficiencies at Coyote Station by installing a combustion optimization neural network. In the chart below, we calculated efficiency by dividing the electric energy produced by our thermal generating units by the total energy content of the fuel burned.

 2019 Thermal Generator Efficiency By Fuel Type

Coal

Natural Gas

Oil

30.64%

33.3%

26.28%

Emission Reductions 

We continue to reduce air emissions with state-of-the-art technologies and wind generation investments.

Declining Emissions

 Percent reductions are the expected reductions from 2005 to 2022.

 

Carbon System Intensity

 

Carbon Emissions (Metric Tons)

Reporting content: Direct (Scope 1) CO2 emissions from owned generation, and Indirect (Scope 2) CO2 emissions from purchased generation

Year

2005

2009

2012

2015

2019

2022

Coal Generation

3,844,070

3,293,265

3,155,212

1,998,067

2,727,559

2,130,470

Natural Gas/Other

30,356

18,847

35,714

10,214

30,834

212,973*

Purchased

824,053

596,944

734,640

1,256,540

1,044,478

889,845

Total

4,698,479

3,909,056

3,925,567

3,264,821

3,802,871

3,233,288

Owned + Purchased

(Intensity)

0.940

0.840

0.832

0.692

0.729

0.577

Owned

(Intensity)

1.103

0.955

0.932

0.871

0.916

0.652

*Increase in 2022 Natural Gas/Other carbon emissions is due to Astoria Station becoming operational in 2020

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