IGCC combined cycle section : gas turbine and steam cycle models and simulators

Abstract

In order to answer the call for environmental friendly and high efficiency electric power production, in the scenario of the clean coal energy, the H2-IGCC Project Under the EU's 7th Framework Programme for R&D deals with providing and demonstrating technical solutions which will allow the use of state of the art high efficients and reliable gas turbines (GTs) in the next generation of Integrated Gasification Combined Cycle (IGCC) plants. The technical challenges being addressed by the H2-IGCC project are divided into four Sub-Projects (SP): Combustion (SP1), Materials (SP2), Turbo-Machinery (SP3) and System Analysis (SP4). Roma Tre University and Professor Cerri research group have been involved in SP3 and SP4 tasks. Accordingly, this thesis deals with features related to both the sub-projects. Aim of this work is to investigate and optimize the integration between the chemical island, in which Hydrogen Rich Syngas (HRS) and CO2 are obtained from the gasification of coal, and the power island, in which a Gas Turbine – Steam Turbine combined cycle provides for the power production. The major components of the chemical island are the Air Separation Unit, the gasifier, the sygnas cooler, the gas treatment section and the Carbon Capture and Storage (CCS) section. On the other hand, the combined cycle is made of a 300MW F Class Gas Turbine and by a three pressure level steam section made up by Heat Recovery Steam Generator fed by the GT exhaust and by a Steam Turbine, with steam admissions and extractions. To perform the various analysis on the system integration and to take the high level of integration between the various sections and complexity of the whole system into consideration, a plant simulator has been developed. By means of such simulator tool components sizes (e.g. heat transfer devices surface, etc.), plant performance, coal consumption, costs and other aspects concerning the integration of the H2-IGCC plant systems have been analysed. State of the art of such a kind of IGCC power plants and practical solutions based on the experience of managing the plants have been taken into consideration during the simulator development. Moreover, background of Roma Tre Fluid Machinery and Energy Conversion research group already simulated power plants is taken into account and existing component models have been up-dated and adapted to the H2-IGCC plant specifications and where no component models existed, new ad hoc ones have been built up. The simulator has been developed by following a modular approach. It means that elementary component models (i.e. compressor, pump, steam turbine, etc.) have been adopted to replicate this plant. A preliminary plant layot calculation, in which the best layout has been selected, has been performed. After this first step, under the optimal integration point of view, a sizing process of the various components leads to establish the quantities (e.g. geometric and others) required by the off-design models and characterizing the whole system. Accordingly, offdesign component models are in most cases based on the geometric description of the apparatuses and the machines. Moreover, properties of the material being selected and working fluid features are embedded in the models. In these models reality functions and actuality functions have been introduced to tailor ad hoc the plant simulator to the real one. Once the sizes have been found, they have been inputted in the off-design dedicated models. These off-design models have been test varying the degrees of freedom taking the feasible domain of the solution into consideration. At this point, the simulator of the components have been established and used to provide the off-design maps and stable and safe operating domain. Hence, all the plant components have been matched together to perform the whole plant simulator. Matching consists of two steps. The first one is the sizing of the connections among the components. Once such sizes have been established, they are dropped in the matched components plant layout and the part loan plant simulator is established. The use of such simulator is adopted to explore safe and stable plant behaviour domain, evaluating part of the control maps of the system. Due to the complexity of the processes, the H2-IGCC plant has been divided in sub-components and in sub-simulators that have been connected together to build up the global H2-IGCC simulator. The thesis is mainly focused on the power island simulator development, based on detailed models. The connections between the coal to the syngas fed into the gas turbine burners and to the produced CO2 have been taken into account by means of steady state transfer functions approach based on data given by the end-user. Accordingly, the gasification island simulator has been developed. Once the plant simulator has been built up, investigations on the real plant behaviour when operating conditions change have been performed. According to the above, safe, stable and optimal behaviour of the whole system have been ensured by the adoption of proper control rules that have been implemented and embedded into the simulator. Trends of Variable Inlet Guide Vane (VIGV) and of the exhaust temperature (Tex) versus gas turbine load and ambient temperature change have been presented. Accordingly, such control rules allow to maintain the values of temperature, pressure, power and others under some threshold values assuring economic revenues and safe operations.Mapping for optimal plant managing has been discussed taking temperature, pressure and other quantities variability domain into consideration. Analyses have been carried out for gas turbine load change from the nominal value to the 60%, under ISO conditions, and for ambient temperature change between 5°C and 45°C. Accordingly, Gas Turbine, Steam Cycle and whole plant performance in terms of pressure ratios, efficiencies, mass flows, temperature profiles, net power and others have been evaluated and monitored owing to the operating conditions change.