Operational experience of USC steam condition plant and PFBC combined cycle system with material performance

Abstract

In Japan, many conventional coal-fired power plants have been introduced, because coal fuel has many advantages in terms of price and availability, compared with oil and gas. In December 1997, the Kyoto Protocol that was adopted at the COP3 meeting (the Third Conference of the Parties to the United Nations Framework Convention on Climate Change) committed Japan to reduce its greenhouse gas emissions to 6% below 1990 levels during the commitment period to 2012. To help meet such environmental requirements, coal-fired plants need to improve their thermal efficiency. Promising candidates of high efficiency coal-fired power plant are Ultra Super Critical (USC) steam condition pulverised coal plant and Pressurised Fluidised Bed Combustion (PFBC) combined cycle.Recently most of Japanese thermal power plants have adopted USC steam conditions, because in Japan there are a lot of fully developed materials whose costs are compatible with the excellent performance of these plants.In April 2002 EPDC (Electric Power Development Co., Ltd) 600MW Isogo New Unit 1 began commercial operation, with the highest steam condition in Japan. It replaced two former coal-fired 265MW plants. This boiler was designed and manufactured by Ishikawajima-Harima Heavy Industries Co., Ltd (IHI). In this unit, 12Cr ferritic heat resistance materials (ASME P122 & T122) were applied to the main pressure parts in high-temperature regions, because of their excellent properties such as high creep rupture strength and high oxidation resistance up to 650°C. These properties play an important role to reduce tube and pipe wall thickness and hence costs.PFBC combined cycle system is a new coal utilization system capable of higher thermal efficiency with compact unit size and excellent environmental adaptability. IHI had intensive research and development efforts for commercialization of PFBC with 3MW test facility in IHI’s workshop and a license agreement concluded with ABB Carbon AB in Sweden (Alstom Power Sweden at present) for the PFBC technology in 1990. Then IHI designed and fabricated EPDC Wakamatsu 71MW pilot plant and Kyushu Electric Power Co., Inc. (KyEPCO) developed the Karita 360MW commercial plant. Karita, using a former pulverized coal-fired unit infrastructure, is the largest PFBC combined cycle system in the world. In this unit, many new materials have been applied in the boiler systems. SPV490, developed by IHI and Japanese steel manufacturers, was used for the pressure vessel and contributes to a weight and cost reduction of approximately 10%. A new austenitic steel, NAR-AH4 having excellent erosion/ corrosion resistance and high creep rupture strength, developed by IHI and SMI (Sumitomo Metal Industries Co., Ltd) was used for high-temperature components (cyclone and hot gas ducts, etc). This steel is expected to be used widely as a candidate material for high-temperature components.This paper presents operational experience from high efficiency coal-fired thermal power plants focussing on material performance, which play a key role of these plants.