POEMA

Production of Coatings for New Efficient and Clean Coal Power Plant Materials

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 Obiettivo del progetto (Objective)

'The overall objective is the development of new coatings for supercritical steam power plants for efficient and clean coal utilization. A significant reduction of emissions is expected by increasing efficiencies to Å‹ > 50%. Currently, an efficiencies of 45% have been achieved in the last 30 years from subcritical 180 bar/540ºC to ultra-supercritical 300 bar/600-620ºC corresponding to a specific reduction of 20% of CO2 emissions. Efficiencies of 50% and more can be achieved by further raising the temperature, but conventional ferritic steels are not sufficiently oxidation resistant, since the temperature designed for operation was 550º C. From the mechanical properties perspective, ferritic steels can be used at temperatures up to 650º C and for higher temperatures austenic steels and Ni base alloys are being considered. One of the main objectives of this project is therefore to develop advanced coatings for steam environments which can resist the chemical attack of steam and fireside corrosion at temperatures higher than 620ºC employing materials with the required high temperature mechanical properties in particular creep strength. Ferritic–martensitic steels will be considered as substrate materials for up to 650º C whereas, austenitic steels will be explored for higher temperatures. In general higher temperatures mean higher oxidation rates, in particular when the oxidant is water vapour instead of oxygen. The introduction of carbon capture and sequestration (CCS) technologies also aiming to reduce emissions in power generation has also increased the interest in developing new material solutions able to reduce the economical and environmental penalty associated to energy production systems when CO2 is generated. For instance oxy-fuel combustion takes place in a N2 free atmosphere so oxygen is burned in near stoichiometric conditions with the fuel (pulverized carbon) producing and exhaust gases mainly composed of CO2 and H2O.'

Introduzione (Teaser)

Much greater efficiencies of coal-fired power plants can be achieved by raising steam turbine temperatures and employing innovative combustion processes. Scientists are developing anti-corrosion coatings to facilitate implementation and fewer emissions.

Descrizione progetto (Article)

Reducing both emissions and dependence on fossil fuels is an important area of energy research. The former is easier to address in the short term until a transition to renewable energy sources is more cost effective. Scientists launched the EU-funded project 'Production of coatings for new efficient and clean coal power plant materials' (POEMA) to protect materials from the corrosion that becomes more problematic in high-efficiency scenarios.

The target temperature range is 700 to 750 degrees Celsius. Higher temperatures create steam oxidation and steam-grown oxide scales on the inside of tubing. Fireside corrosion is a synergistic effect among metal alloy materials, flue gas and deposits. It is the leading cause of failure in coal-burning furnaces.

A novel coal-burning process that is the topic of global research could increase the likelihood of corrosion. Oxy-fuel coal combustion, in which coal is burned in an almost pure stream of oxygen, is a more efficient process that uses less fuel. In addition, it produces flue gases consisting mainly of water and carbon dioxide (CO2). The concentrated CO2 stream is easier to purify in carbon capture and sequestration schemes designed to reduce CO2 release into the atmosphere.

Scientists evaluated nano-structured and micro-structured coatings in both air and oxy-fuel combustion. During the first 18 months of the project, work progressed from selection of substrates and coatings for screening, to application and characterisation, to the beginnings of life-cycle assessment.

Metal alloy substrates consisting of a ferritic steel (P92), an austenitic (HR3C) and two alternative nickel-based alloys are being utilised. From the original 31 coatings, scientists have chosen 6 coatings to be optimised for the steam oxidation application and 5 for fireside oxidation protection. To date, all coatings have been applied to the ferritic substrate, and both uncoated and coated samples have been characterised. Lifetime models of some of the coated systems are under development.

Increasing the efficiency of coal-fired power plants will enable significant reductions in CO2 emissions. Corrosion-protection coatings being developed by POEMA scientists promise to enable long-term operation under the required operating conditions with important environmental benefits.