The Role of High Efficiency Coal in a Low Carbon Energy Future

A global shift in the energy industry is well underway, with rapid build out of wind and solar capacity worldwide and deployment of advanced metering infrastructure to support a smarter electric grid. Such smart grid technologies and distributed energy will transform the way electricity is produced and delivered. Along with the focus on achieving a low carbon energy system to mitigate the impacts from climate change, many people have declared coal power dying or already dead. Characteristic of numerous headlines, a recent Power Magazine article painted a grim picture of the coal power industry: “Industry in Turmoil: Coal Plants Shutting Down Around the World.” Given a global focus on climate change, does the coal power industry have a future in a low carbon energy system?

Coal still provides the bulk of electricity generation around the world. In the U.S., coal provided 38.7% of electric power in 2014 while renewables other than hydropower provided 7% (EIA 2014 data). Worldwide, coal provides about 40% of electric power. However, as the coal fleet ages and older inefficient units are retired, there is an opportunity for coal to play a vital role in reducing carbon emissions. Currently, the average efficiency of the global coal-fired generation is 35% (lower heating value basis, or LHV). In comparison, the efficiency of natural gas generation is 48%, which also emits half as much carbon as coal. However, natural gas is not economically competitive in many regions of the world and still represents energy security risks for some countries.

The map below from the World Energy Council shows the average efficiency of coal-fired power in countries around the world. Japan and Nordic countries have the most efficient plants, having been among the first to install high-efficiency, low-emissions (HELE) coal technology. HELE coal technologies can achieve efficiencies of 45% or higher, reducing CO2 emissions by 20% or more compared to a subcritical coal unit under similar operations.

Efficiency of coal-fired power plants

So what is HELE technology? Above the supercritical point (22.1 MPa/3208 psi) water changes phase from liquid to superheated steam without boiling, eliminating the requirement for water and vapor separation. Supercritical boilers (or steam generators) produce steam above 530°C; these elevated temperatures and pressures cause greater vapor expansion through the steam turbine, creating more power. Ultra-supercritical (USC) units achieve pressures above 25 MPa (3,640 psi) and steam temperatures of 580°C to 600°C (definition varies by manufacturer). While some supercritical units have been able to generate steam at USC pressures, continuous operation at such high temperatures could damage steam turbine blades and rotors. Developments in materials science including chrome and nickel-based superalloys have supported steam turbine designs that can withstand USC conditions. Superalloys retain their strength even after long exposure times to high temperatures (resistance to creep and fatigue) and offer corrosion and oxidation resistance.

Although integrated gasification combined cycle (IGCC) and fluidized bed combustion are also promising technologies for achieving high efficiency coal power, HELE technology based on supercritical and USC steam generator designs have already been widely commercialized – and this is an important point. This is technology that can be utilized today to reduce carbon emissions.

The potential for carbon reductions by improving the efficiency of coal power was recently analyzed by the International Energy Agency’s (IEA) Clean Coal Centre. Ian Barnes from IEA wrote a terrific article for Cornerstone magazine on how upgrading the efficiency of the global coal fleet could help lower carbon emissions, particularly for emerging economies where coal consumption is projected to increase to support expanding electrification.

The most efficient coal power plants in the world today were built to meet simultaneous goals of reducing emissions and maintaining reliable energy supply. Tau Technical profiled these plants for Cornerstone, illustrating how HELE technology could help coal serve an important role in a low carbon energy future. Read more: “Setting the Benchmark: The World’s Most Efficient Coal-Fired Power Plants.”

 

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