Steam Power Plants – New Wave of Supercriticality

Peter Luby

INGCHEM

 Slovak Republic

 Miro R. Susta

IMTE AG Power Consulting Engimeers

Switzerland

POWERGEN-EUROPE 2002, MILAN, ITALY

June 2002

ABSTRACT

Forecast of a dramatic rise in natural gas prices, due within a short outlook of 2 years, causes coal to enjoy its resurgence once again.  Emerging interest in new coal-fired supercritical (SC) steam plants has fueled development of new, cutting-edge technologies. Power plants with record-breaking steam parameters approaching or breaking levels of 300 bar and 600°C have been commissioned in the last decade or are under construction in Denmark, Germany and Japan. Strange enough, this is not the case for the traditional developers of SC technology like the USA and Russia.

SC technology clearly prevailed over subcritical one in OECD countries in the second half of last decade. In this period, more than 20,000 MWe of new SC capacity against merely 3,000 MWe subcritical capacity were installed within the OECD region.  In non-OECD countries, however, the rate was vice-versa. Only 5% out of new installed capacity was based on SC technology. In OECD countries various collaborative programs like THERMIE 700 EUROPE, COST 522 EUR, EPRI 1403-50 USA or CRIEPI push the technical envelope of this important clean-coal technology.

The following projects with record-breaking efficiencies were commissioned, or are under construction: 

·    Denmark – Skaerbeakvaerket (Elsam, 1997), Nordjyllaendvaerket (Elsam, 1998), Avedoerevaerkaet (Elkraft, 12/2001). All of them are fired with bituminous coal, operating with efficiencies 46% - 48%.

·  Germany – Schwarze Pumpe (SVK Schwarze Pumpe, 1997/1998), Niederaussem (RWE Energie, 11/2002). Both are fired with lignite, operating with efficiencies up to 43%.

·    Japan – Isogo 1,2 (EPDC), Tachibanawan (Electric Power Development Co.), Haramachi 2 (Tohoku Electric Power Co.) and  Hitachi-Naka (TEPCO), all of them fired with bituminous coal and achieving steam temperatures over 600°C.

The core machinery of an SC plant is a once-through (OT) boiler. 70% of all OT boilers are Benson. More than 1000 Benson boilers have been installed world-wide. Since the year 1924 Siemens PG is the owner of licence certificate for Benson boiler. Siemens awarded licencees to 10 boiler manufacturers. 

Conventional SC  technology is based on spiral wound furnace tubes. A novel design of Benson boiler with horizontal furnace and internally rifled vertical tubes has been developed by Siemens. In association with EU-funded programme  Thermie 700 it has been designed for steam conditions 350 bar, 700°C /720°C. 

The reduced hight of the boiler minimises the amount of expensive high nickel. This may appear to become the decisive factor for even more intensive expansion of SC technology because this particular  problem of extremely high cost of special steels and alloys was traditionally the main obstacle with even wider application of SC technology.