Alternatives for Power Generation
With more than 180 countries committing to nationally determined climate targets, covering 99 percent of global emissions, and about 65 percent focused on mitigating greenhouse gas emissions (GHG), the Paris Climate Agreement has advanced global efforts to tackle climate change. Fossil fuels like coal, oil, and natural gas, which make up 65 percent of the total global GHG emissions, are increasingly under the spotlight as many countries look at new ways to transition their energy systems to cleaner sources.
In the United States, the Clean Power Plan (CPP)—the Environmental Protection Agency’s rule on reducing carbon pollution from power plants—has set in motion significant changes in utility markets across the country. It has also raised questions on what to do with retiring coal-fired plants. China’s new five-year plan also sets up the country for a low-carbon growth agenda under an economic, social, and environmental blueprint for national development through 2020. At the energy front, natural gas, which is increasingly becoming the alternative energy source to reduce greenhouse gas emissions, is projected to become the predominant fossil fuel. Whether it is natural gas, renewable energy, or energy efficiency measures to reduce electricity use, Bechtel’s priority should be to provide energy options that meet the unique resources and ambitions of our customers.
Challenge
Across the globe, about 1,200 new coal-fired plants are being proposed, with China and India together accounting for 76 percent of the proposed new coal power capacities, according to the World Resource Institute. Furthermore, even though the projected renewables share of the global energy mix by 2030 is expected to grow, fossil fuels will be a significant source of electric generation—about 44 percent. These trends show there is still more to be done if we are to achieve significant reductions in global carbon emissions.
Even for the United States, where a total of 60 gigawatts of coal-fired generation is expected to retire by 2020—partly as a result of the CPP and the implementation of the Mercury and Air Toxic Standards (MATS) , but primarily due to the low cost of natural gas—the question remains as to what should be done with a shut-down coal plant. Coal plants that are located in dense urban areas or near critical water resources can pose major health and environmental risks.
Substantial research and development effort must be dedicated to addressing the shortcomings in existing energy generation plans to help reduce or eliminate emissions of CO2 into the atmosphere.
Solution
Coal usage, which is a major source of GHG emissions, will increase significantly in developing economies such as China and India. However, for countries seeking to base their energy consumption on fossil fuels, taking the natural gas route might be a good near-term investment for the economy and for the climate.
Gas Turbine Combined Cycle Optimized for Post-Combustion CO2 Capture
Bechtel currently has a patent application pending for efficient and cost-effective removal of CO2 from a gas turbine combined-cycle (GTCC) power plant by applying two techniques in an innovative manner: high supplementary firing in a heat recovery steam generator (HRSG) and recirculation of a portion of its exhaust emissions. The advantage of the invention, compared to an existing natural gas-fired GTCC power plant with post-combustion capture (which uses a chemical solvent-based scrubbing system to separate the CO2 from the power plant emissions), is to reduce the CO2 capture penalty—power diverted away from generation—by almost 65 percent and the overall capital cost ($/kW) by about 35 percent. For a power plant with CO2 capture rated at 800 megawatts electrical (MWe), this translates into significant reduction in capital cost while producing 75 MWe extra power output. The end result is significant reduction in carbon footprint in the most cost-effective manner.
Repowering Aging Power Plants
Another solution involves adding to or replacing aging or obsolete power generation equipment (i.e., a coal-fired boiler plant with a steam turbine generator) with newer equipment comprising up-to-date technology while retaining still-usable components. It can increase power generation output and improve efficiency, extend plant life, improve environmental performance, and enhance operability and maintainability. The hurdle for repowering is the life-cycle cost of generation, which means that the new power plant must have better combination of capital expenditure, fuel, and operations and maintenance costs than the old one. Repowering can become a sustainable solution for retiring power plants. In terms of cost and environmental impact, repowering requires less upfront capital investment compared to an advanced GTCC. The GT powered plant emits less CO2 emissions—about 150,000 to 800,000 tons per year less CO2 than the original coal-fired plant. It also eliminates all toxic emissions such as mercury, arsenic, acid gases, etc.
The Bechtel Experience
For nearly a century, Bechtel has been a leader in clean energy solutions. We recently built (and currently building) GTCC power plants—Sherman, Temple I & II (Texas), and Stonewall (Virginia) for Panda Power Funds—that are among the cleanest natural-gas-fueled power plants operating in the United States, and comprise the most advanced emissions control technologies (they have zero liquid discharge systems). With our partners, Bechtel also provides retrofitting solutions for customers. For example, we have installed state-of-the-art air-quality-control systems for the 2,220 MWe Sammis coal-fired power complex in Ohio.
Taking innovative approaches in design and technology has enabled our teams to deliver to our customers the best possible projects that address cost and climate issues. In that vein, as the world works together to reduce or eliminate emissions of CO2 into the atmosphere, technological solutions like the optimized post-combustion CO2 capture and repowering can go a long way to deliver results.