Giancarlo Benelli

VALIDATION OF DRUM BOILER MODELS THROUGH COMPLETE DYNAMIC TESTS

Abstract This paper describes the validation of a model library for the simulation of drum boilers on the basis of static and dynamic experimental data obtained from a small-scale plant. All the steps of the validation process are described in detail, with particular reference to the modelling principles, to the trade-off between model complexity and accuracy, to the solution strategy and to the data-reconciliation policy. The results of the validation have formed an important knowledge base, which might be made available to other research groups.

Pressurised Oxy-Coal Combustion Rankine-Cycle for Future Zero Emission Power Plants: Process Design and Energy Analysis

This paper presents the process design and the energy analysis for a coal-fired power plant based on pressurised oxycoal combustion and including carbon capture technologies. A combustion technology performing a pressurised combustion of coal in an atmosphere of O2 /CO2 /H2 O and including flue gases recycling has been selected. Combustion and steam production occur in separated equipments and the combustor’s design allows achieving high ash removal efficiency. The Rankine cycle has been chosen as the most viable thermodynamic cycle in a short-term scenario. Oxygen required by the combustion process is supplied by a cryogenic Air Separation Unit (ASU) and a double-reheat ultrasupercritical cycle is employed with main steam conditions of 250bar/605°C and reheat steam temperatures of 605°C/620°C. All choices related to thermal cycle selection and process design have been conducted upon the principle of feasibility and reliability. In order to increase net plant efficiency both sensible and latent heat is recovered from the flue gas stream before entering the purification and compression section. By operating in pressure it becomes possible to recover a larger amount of heat than in the atmospheric case. As a result, all low pressure steam bleedings and the corresponding regenerative heat exchangers can be eliminated. Process simulation is carried out in the paper and the expected efficiency is evaluated, as well as other cycle performance parameters. Since a relevant benefit may arise from the combustion of cheap coals, the impact of burning high-ash content and low ash-fusion-temperature coals is assessed. The impact of energy penalties associated to oxygen production and the benefit arising from high heat-transfer coefficients due to the increased pressure of the flue gas are deeply investigated.Copyright

Pressurised Oxy-Coal Combustion Rankine-Cycle for Future Zero Emission Power Plants: Technological Issues

Among possible options to capture carbon dioxide, pressurised oxy-fuel combustion is a promising one. Accordingly, Enel teamed with Itea and Enea to develop a pressurised oxy-combustion technology. Currently, extensive tests have been carried out at 4 bar on a 5 MWt facility based in Gioia del Colle (Southern Italy). By starting from the know-how gained on that scale, Enel planned to build by 2010 an experimental 48 MWt demo-plant, based on the same pressurised combustion process introduced above. This will be the necessary intermediate step for the further scale-up towards a zero emission plant of industrial scale. This paper is the prosecution of a previous publication presenting the process design and energy analysis of a power cycle integrating the developed pressurised oxy-coal combustion technology with a Rankine cycle including carbon capture. After having briefly presented the pressurised oxycombustion project carried out at Enel, the paper focuses on technology issues related to the proposed cycle and the related process integration, with respect to main components.Copyright

Scaling From Atmospheric Pressure Rig to Full-Scale Pressure for the Emission Measurements From a Gas Turbine Combustor

Investigating the pressure scalability of pollutant emissions from a heavy-duty diffusion flame type, natural gas fuelled gas turbine combustor a two steps approach is presented in the current paper. First a theoretical viewpoint is established using similitude theory to characterize the operation conditions chosen for atmospheric tests in relation to the real gas turbine pressurized conditions. Then the corresponding experimental tests are presented for the full-scale gas turbine combustor in the original version both under atmospheric and pressurized gas turbine conditions at the ENEL test facilities.The results from the theoretical study indicate, that similitude cannot be maintained rigorously between the atmospheric and pressurized tests. However the experimentally determined NOx-emissions obtained under the reduced similarity test conditions provide a pressure scaling relation that can be maintained between the original and the retrofitted version of the combustor.© 2001 ASME

Damage Analysis of Gas Turbine Vanes Using a Thermal Fluid Dynamic and Mechanical Approach

Gas turbine combined–cycle systems work with high inlet temperatures, requiring the use of components made of advanced high temperature resistant materials and coatings. These components must be controlled to avoid serious damage to the plants. The durability of these materials and coatings is of great concern to equipment users. This paper deals with a procedure based on thermal fluid dynamic and mechanical integrated analyses of high temperature loaded components. The methodology is applied to uncooled last stator stages vanes of an industrial 165 Mw gas turbine. Several cracks were revealed on these vanes during periodical inspection and mechanical and metallographic investigations were performed. These analyses were used to identify the critical areas of the vanes, from which the component residual life depends on. The procedure was applied to study the damage undergone by gas turbine vanes to discover the causes of crack nucleation and the nucleation mechanism connected to load histories. It has a diagnostic scope, not a predictive one, but it can be considered as the first step of a residual life evaluation and, consequently, of a load cycle optimization: by modifying the future load histories, it could be possible evaluate the best operating conditions to extend component life. The numerical results of these analyses were compared with the damage to vane rows determined during periodical inspections. A good agreement between the analyses results and the inspection data was obtained in terms of critical points and crack locations. The implemented methodology seems to be a powerful tool for increasing the reliability of critical components of gas turbine combined–cycle systems.Copyright