Today in Energy

October 31, 2017

Petra Nova is one of two carbon capture and sequestration power plants in the world

image of Petra Nova, as explained in the article text
Source: Petra Nova, a joint venture between NRG Energy and JX Nippon Oil & Gas Exploration

The Petra Nova facility, a coal-fired power plant located near Houston, Texas, is one of only two operating power plants with carbon capture and storage (CCS) in the world, and it is the only such facility in the United States. The 110 megawatt (MW) Boundary Dam plant in Saskatchewan, Canada, near the border with North Dakota, is the other electric utility facility using a CCS system.

A third power plant in Kemper County, Mississippi, is capable of burning natural gas as well as lignite coal and was expected to be fully operational and capable of using CCS by mid-2014. However, Kemper has operated primarily on natural gas, essentially as a combined-cycle plant, since August 2014. In June 2017, Mississippi Power made the decision to suspend operations activities relating to the coal gasification process, electing to operate Kemper strictly as a natural gas-fired combined-cycle plant. Kemper has also abandoned plans to use technology to capture its greenhouse gas emissions.

CCS technology mitigates the release of carbon dioxide (CO2) from the combustion of fossil fuels. Three potential approaches allow power plants to capture CO2:

  • Post-combustion capture involves sending the power plant’s emissions through an absorption process where a solvent captures up to 90% of the CO2. The recovered CO2 goes through a regenerator that strips the CO2 from the solvent while the remaining emissions (primarily nitrogen) are vented to the atmosphere.
  • With oxy-combustion capture, the fossil fuel is burned in pure oxygen instead of air. The result of this process captures nearly pure CO2.
  • With pre-combustion capture, the fossil fuel is turned into a synthetic gas consisting of relatively pure hydrogen and CO2. 

Petra Nova’s post-combustion CO2 capture system began operations in January 2017. The 240-megawatt (MW) carbon capture system that was added to Unit 8 (654 MW capacity) of the existing W.A. Parish pulverized coal-fired generating plant receives about 37% of Unit 8’s emissions, which are diverted through a flue gas slipstream. Petra Nova’s carbon-capture system is designed to capture about 90% of the carbon dioxide (CO2) emitted from the flue gas slipstream, or about 33% of the total emissions from Unit 8. The post-combustion process is energy intensive and requires a dedicated natural gas unit to accommodate the energy requirements of the carbon-capture process.

graph of carbon dioxide emission intensity at W.A. Parish Unit 8, as explained in the article text
Source: U.S. Energy Information Administration, based on U.S. Environmental Protection Agency Air Markets Program Data

The carbon dioxide captured by Petra Nova’s system is then used in enhanced oil recovery at nearby oil fields. Enhanced oil recovery involves injecting water, chemicals, or gases (such as carbon dioxide) into oil reservoirs to increase the ability of oil to flow to a well.

By comparison, Kemper had been designed to capture about 65% of the plant’s CO2 using a pre-combustion system. The capital costs associated with the Kemper project were initially estimated at $2.4 billion, or about $4,100 per kilowatt (kW), but cost overruns led to construction costs in excess of $7.5 billion (nearly $13,000/kW). Petra Nova CCS retrofit costs were reported to be $1 billion, or $4,200/kW, and the project was completed on budget and on time.

Principal contributor: Kenneth Dubin