IGCC Project Examples
 
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Nuon Power’s - Buggenum, Netherlands

Nuon Power Buggenum IGCC Plant

Located in Buggenum, The Netherlands, Nuon Power’s 253 MW (net) integrated gasification combined cycle (IGCC) power plant began service in 1994 as a demonstration facility. It was originally constructed by Demkolec, a consortium of Dutch power producers, adjacent to an existing coal-fired power plant along the River Maas. This allowed the new IGCC demonstration plant use of existing coal reception and handling facilities. Following the completion of the demonstration phase of the plant and liberalization of the Dutch power sector, Nuon Power acquired the plant and has operated the plant commercially since.

Plant Description
The air separation unit (ASU) produces 95% pure oxygen for use in the gasifier, in addition to high purity nitrogen. Pure nitrogen generated by the ASU is used as a carrier gas for the dry-feed gasifier, in addition to use in purging. Additional nitrogen is compressed and used as dilution nitrogen in the gas turbine.  

Fuel is prepared in three 55% roller mills where coal particle size is ground to less than 100 microns. The pulverized coal is partly dried in the mills before final drying is done by burning syngas to heat the coal. Two trains of lock hoppers are employed to bring the coal to plant pressure, before it is conveyed pneumatically to the four side-mounted burners with high purity nitrogen as a carrier gas.

The gasifier is a single dry-feed Shell SCGP unit. The plant was designed for a wide range of imported coals; however the plant currently operates on local coal fired with up to 30% biomass to comply with Dutch renewable energy incentives. The gasifier operates at 360 psig and a temperature of 1,600°C (2,900°F) resulting in a carbon conversion rate of over 99%. The gasifier wall is surrounded with a steam generating membrane to contain high temperatures. Slag produced in the gasifier exits through a quench bath followed by lock hoppers. There is no slag crusher used at the slag lock hopper outlet.

As the raw syngas exits the gasifier it is quenched to a temperature of 900°C (1,650°F) by cool recycled particle-free syngas. A water-tube boiler then lowers the syngas temperature to 235°C (455°F) by generating high and intermediate pressure steam. A cyclone followed by a ceramic candle filter then removes particulate matter from the syngas.  Particulate matter is mostly fly ash along with a small amount of unconverted carbon. The last step of the gasification process is to scrub the syngas with water to remove ammonia and halides.

The acid gas removal unit entails a hydrogen cyanide/carbonyl sulfide (HCN/COS) Hydrolysis and a Sulfinol M Wash, which decreases sulfur content in the syngas to less than 20 ppm by volume. Sour gas is processed in a single Claus unit to produce elemental sulfur. Tail gas is not recycled; however it is hydrogenated and treated before discharge to the atmosphere through an incinerator.

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NUON IGCC Process Schematic

For nitrogen oxide (NOX) reduction, the syngas is mixed with nitrogen and water vapor before being sent to a Siemens V 94.2 gas turbine. The gas and steam turbines are both mounted on a single drive train which powers a 285-MW generator. After in-plant electricity consumption in the ASU, gas production areas, and the combined cycle unit is subtracted, total net power production is 252.5 MW.

Environmental Considerations
The Buggenum IGCC Plant has performed well environmentally in several areas. NOX emissions have been extremely low, typically below 10 ppm. Sulfur removal efficiency has been over 99%. This has resulted in total acidification components of the emissions (sulfur dioxide [SO2] and NOX) being less for operation on syngas produced from coal than natural gas. Particulate emissions including fly ash, chlorides and heavy metals have been virtually zero. Finally, the plant demonstrates zero waste water discharge, as water is treated and reused within the facility.

Operational History
The initial demonstration period of the project was completed at the end of 1997 and since 1998 the plant has been in commercial operation. Several issues were addressed during the demonstrations phase of the project including:

  • Gas turbine vibrations
  • Syngas scrubber erosion
  • Sulfinol degradation
  • Short ceramic candle filter lifespan
  • Slag lumps and fines discharge

Operation as a peak shaving unit began in 2002, resulting from restructuring and liberalization of the Dutch power sector. A ramp speed of 1.5 MW per minute was achieved in purely IGCC mode, while adding natural gas increased this figure to 3.5 MW per minute. Demand was cycled during this period on a four minute basis.

A critical change was made in 2002 to improve plant reliability. The IGCC plant had previously no control over coal procurement and was receiving the fuel from local PC plants. This caused more plant down time than otherwise would have occurred, as the plant required adjusting to the new coal parameters. Since then, this issue has been remedied with the plant taking an active role in coal procurement.

In 2004, as the plant was returned to base load operation, a further modification occurred. The existing dilution nitrogen compressor was modified to also serve as a startup air compressor for the ASU. This removed the limitation that the gas turbine was required to operate on natural gas for three days prior to bringing the ASU to operating temperature so the gasifier could begin operations. 

During 2005 the plant was modified to allow startup of the gas turbine on syngas, in addition to increasing the use of biomass as a fuel to take advantage of “green power” credits. These required modifications to both the fuel feed system and the gas turbine burners. 

Plant operation has run uninterrupted for durations of over 2,500 hours.

References/Further Reading

Power

 
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