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 more than 30% 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 Circulating Dry Scrubber
Nitrogen Oxides (NOx) Low-NOx Burners and Separated Over-Fire Air Separated Over-Fire Air Separated Over-Fire Air & Selected Catalytic Reduction
Particulate Matter Electrostatic Precipitator  Baghouse Baghouse
Mercury Activated Carbon Injection Activated Carbon Injection Activated Carbon Injection

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 2018 we've improved our system average NPHR by approximately 20%. That average includes owned generation sources and long-term wind power purchase agreements. We expect an additional 20% NPHR improvement by 2022.

Thermal Generation Efficiency

In 2018 we improved efficiencies at Big Stone Plant by installing a new air preheater sealing system and continued upgrading to LED lighting. Coyote Station also underwent LED lighting upgrades. 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.

 2018 Thermal Generator Efficiency By Fuel Type

Coal

Natural Gas

Oil

30.92%

34.34%

26.28%

Emission Reductions 

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

 

 Percent reductions are the expected reductions from 2005 to 2022.

  

 

Carbon Emissions (Metric Tons)

Year

2005

2009

2012

2015

2018

2022

Coal Generation

3,844,070

3,293,265

3,155,212

1,998,067

3,287,689

2,130,470

Natural Gas/Other

30,356

18,847

35,714

10,214

39,475

212,973

Purchased

824,053

596,944

734,640

1,256,540

764,534

889,845

Total

4,698,479

3,909,056

3,925,567

3,264,821

4,091,698

3,233,288

Owned + Purchased

(Intensity)

0.940

0.840

0.832

0.692

0.778

0.577

Owned

(Intensity)

1.103

0.955

0.932

0.871

0.941

0.652

Reporting content: Direct (Scope 1) GHG emissions

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