Integrated Gasification Combined-Cycle Generation

A technology under current study that could play a significant role in Alliant Energy's future energy mix is Integrated Gasification Combined-Cycle (IGCC) generation.

This method of generating electricity from fossil fuels (typically coal, pet coke or oil) produces fewer emissions than conventional coal generation alternatives - but at a considerably higher cost.

How does it work?

In a conventional coal power plant, coal is pulverized to a very fine powder and burned. The heat is used to produce steam, which in turn spins a turbine to generate electricity. This generation process is referred to as the “steam cycle.”

In an IGCC facility, coal is fed into a vessel called a gasifier, where heat and pressure cause the coal to be converted to combustible gas compounds, or “syngas.” This syngas is cleaned to remove sulfur and other contaminants before it is burned in a combustion turbine, which spins a generator.

Additionally, the exhaust heat from the combustion turbine is recovered and used to produce steam in a boiler that spins another generator. Thus, the “combined cycle” portion of IGCC — both a combustion turbine cycle and a steam cycle — are used to produce electricity.

View a diagram of the IGCC generation process [PDF]

What's the status of current technology?

While the gasification process has existed since the 1800s, only recently have greater strides been made in improving the technology.

Although gasification is commonly used in the chemical industry, only a few IGCC projects have been built worldwide for electric generation. To date, only two have been built in the United States to use coal (Florida, Indiana). Several are in the planning stages.

The projects thus far have provided valid demonstrations of performance characteristics for anticipated capacity, efficiency and environmental emissions. However, they have also shown that higher cost and lower reliability make this technology more expensive than conventional coal generation at this point in time.

Why consider IGCC?

• Technology: GCC technology produces air emissions that are already considerably lower than required by current U.S. Clean Air standards. Significant reductions in sulfur dioxide (SOX), nitrogen oxides (NO
• Carbon dioxide reduction: Carbon dioxide (CO2), considered a major source of global warming, could be captured more economically with IGCC than with conventional technologies. The CO
• Efficiency: Overall efficiency is approximately 40 to 45 percent of the energy value of coal converted to electricity. In comparison, conventional coal plants are approximately 30 to 35 percent efficient.
• Water requirements: Water requirements are typically about 50 percent less for IGCC applications than for conventional coal generation.
• By-products: Marketable by-products from the IGCC process can be sold, such as sulfur.

What are the risks?

• Cost: IGCC facilities are more expensive to build than conventional coal plants. Only recently have suppliers begun to emerge that can offer comprehensive, integrated designs with packaged systems and compatible equipment. Due to the industry's limited experience with the technology, truly accurate cost estimates for construction and operating costs are not yet available for use in planning future facilities.
• Maintenance: IGCC technology requires more frequent maintenance with longer maintenance outages, requiring that power be purchased from other resources when the IGCC plant is unavailable.
• Unproven fuel experience: Neither of the U.S.-based IGCC projects has used Powder River Basin, or western, coal, which is the type used most frequently in the Midwest.
• Performance guarantees: The industry is encouraging suppliers to offer performance contracts for next-generation IGCC plants, but for now, the risk of reduced reliability and availability add significant cost to the project's financing.

What's ahead?

Improvements in performance and cost are expected in the next several years. However, the technology benefits and risks, as well as financing options, must be clearly evaluated and understood prior to Alliant Energy's decision to make major capital investments in IGCC plants.

With coal being an abundant, readily available and low-cost resource in the United States, it is prudent for utilities like Alliant Energy to encourage development of clean coal technologies such as IGCC. In support of such a strategy, we are investing significant amounts in collaborative research of IGCC technology in order to make future decisions on when to employ IGCC technology.