EPRI FINDS BUGGENUM THE MOST EFFICIENT OPERATING LARGE IGCC PLANT

Coal-based Integrated Gasification Combined-Cycle (IGCC) plants have been developed to commercial size over the past 2 decades. They have only been built as demonstration plants but are operating as commercial units. These units have now accumulated several years of operating experience and have shown that an IGCC plant can meet extremely stringent air emission standards while also achieving high plant efficiencies. N. Holt of Electric Power Research Institute (EPRI) summarized the technical status, trends and future improvements of IGCC at the 219th American Chemical Society National Meeting held in San Francisco, California, in March.

Three coal-based, commercial-sized (but partially government-funded) IGCC demonstration plant projects are currently operating in the United States and two in Europe, as summarized in Table 1.

Table 1

The three ongoing United States IGCC projects are all based on different gasification technologies and illustrate different application opportunities. All three plants are based on General Electric F gas turbines with turbine inlet temperatures of about 1,260ēC and equipped with multiple can combustors. The European IGCC projects are both based on Siemens gas turbines equipped with dual silo combustion chambers.

The Piņon Pine and ELCOGAS projects have seen limited operations to date, but both the GE 6FA at Piņon Pine and the Siemens V 94.3 at ELCOGAS have been running well on natural gas at their design outputs. Although only extended multiyear operations can really test the durability of gas turbines in an IGCC application, the results to date from the projects with the GE F-class gas turbines are encouraging.

Table 2 presents the major component and overall design performance of these plants, and compares these design values with the operational results achieved to date.

Table 2

Both the Texaco gasifier at Tampa and the Destec gasifier at Wabash River have demonstrated that they can supply sufficient syngas to fully fuel their combustion turbines. At Tampa, fouling downstream of the gasifier and corrosion in the lower gas temperature range of 250 to 300ēC have been the main causes of outages to date. At Wabash River the main remaining problem area seems to be the dry gas filter, where corrosion and blinding of the metallic candles continue to occur. The most recent operations at these sites are encouraging and show considerable progress, with both projects experiencing long runs and higher availability.

The SEP/Demkolec (Buggenum) project started operations in early 1994. The tight integration has led to some operational sensitivities and complexities, leading SEP to recommend only partial integration for future installations. The main problem encountered in the early years of operation at the Buggenum plant (also later encountered at Puertollano) has been combustion-induced vibrations and overheating in the gas turbine combustors. Design changes made in early 1997 have markedly improved the vibration problem, and since that time several long runs have been conducted, with an availability of over 80 percent in each quarter since the third-quarter of 1997 (with the exception of the second quarters when the required annual inspection is conducted). In the third- and fourth-quarters of 1998, the Gasification Island was in continuous operation for over 2,000 hours. The Shell gasifier has generally performed well and has achieved its design cold gas efficiency.

In summary, these demonstration plants show that IGCC systems can provide power at higher efficiency than pulverized coal plants, with significantly lower air emissions and a more benign solid byproduct. While the reliability/availability of these units has improved since they were first brought on-line, they are not yet operating at commercially acceptable availability levels (only 56 to 61 percent in 1998). Based on past experience in the development of new technologies, and assuming continued support by the various government and private parties involved, it is reasonable to expect that the remaining problems will be solved within the next 5 years.

A number of IGCC plants (many of 500 megawatts) will be commissioned over the next 3 years based on the use of petroleum residuals and located adjacent to large petroleum refineries. The shrinking market for high-sulfur fuel oil and the impact of tightening fuel specifications and new environmental legislation is the impetus behind these projects. Most of these projects have multiple coproducts, typically power, steam and hydrogen for the refinery plus sale of power to the grid or other nearby industrial customers. The projects in Europe are mostly based on heavy oil while the majority of the United States projects are based on low-value petroleum coke. The experience gained from these projects should aid in reducing the capital cost of IGCC equipment and in providing greater confidence in the reliable operation of this technology.

The larger higher efficiency G and H gas turbines, with firing temperatures of about 1,500ēC, are now entering commercial service based on natural gas. When applied to IGCC plants these turbines will provide further gains in efficiency and reductions in capital cost through economy-of-scale. The United States Department of Energy through its Vision 21 initiative has a comprehensive research and development program with gasification as a key core technology. This program should result in a stream of new developments improving the performance and reducing the capital cost of IGCC plants, says Holt.