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The world market-place for steam turbine products is becoming increasingly competitive, and manufacturers must routinely produce designs which are extensively optimised whilst working within demanding tender and contract lead-times. The objective of the research work has been to develop a methodology whereby established turbomachinery analysis methods can be integrated within a framework of optimising algorithms. A rule-base, numerical optimisation, fuzzy logic, and genetic algorithms are used to optimise bladepath configurations, with particular emphasis on the minimisation of life-cycle operating costs. Significantly, automation of the design process is increased, design lead-times can be reduced, and performance improvements are predicted. The optimisation procedure relies on a sequential approach, with much emphasis placed on the iterative running of simple design codes. Simplified design methods are often reliant on correlated loss data to predict turbine performance, and in some cases this data is inaccurate or incomplete. An example of this is in the design of partially-admitted control stages, where little published data is available. It is suggested that CFD methods can, in some cases, be applied to derive new performance correlations or re-assess the validity of existing models. The application of an unsteady CFD solver to typical control stage geometries is presented in detail, and the approach is extended to include the development of a new control stage optimisation method.

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Unlike in oil firing, the effective role of additives to alleviate deposition in coal fired power generation is still regarded with much scepticism and controversy amongst the power generators and boiler operators. The objectives of this research study were principally to explore the mechanisms involved in formation of coal ash deposits and thus determine the effectiveness of a magnesium based additive, namely Lycal 93HS, in reducing the bonding strength of ash deposits on boiler tube surfaces, by making them friable and easily removed by sootblowers during normal operation of the boiler. The experimental techniques developed involved visual, optical and scanning electron microscopy examination of a wide range of matured deposit samples collected over a period of two years, with and without injection of Lycal 93HS into the boilers at West Belfast power station. Specimen deposit samples "fashioned" into the form of Seger cones and "reconstituted" from their crushed, powder form were tested for their softening behaviour at elevated temperatures with and without further additions of Lycal 93HS. This technique was further used to evaluate the effect of Lycal 93HS on the softening behaviour of a range of coal ash components separated by high temperature ashing of coarse particles of coal as well as the bulk ash from the coarse and fine sizes of coal particles. The softening behaviour on heating and crystallisation tendency behaviour on cooling for a selected range of the ash components was investigated without and with additions of Lycal 93HS, using Hot-Stage Microscopy. The possibility of surface adhesion between the fly ash and injected Lycal 93HS within the boiler environment was investigated through a series of laboratory based Surface leaching experiments of deposit and particulate samples with and without injection of Lycal 93HS. The variation in concentration profiles of silicon, iron and magnesium within the collected solutions over a period of time were analysed, using Atomic Absorption Flame Spectroscopy. The elemental chemical composition of bulk deposit samples, the average high temperature ash and its separated components was carried out using X-Ray Fluorescence. Qualitative study of the mineralogy of low temperature ash, selected ash components, as well as a range of deposit samples with Lycal injection was conducted using X-Ray Diffractometry. The results of Lycal injection into a boiler were clearly evident from inspections of the boiler where Lycal injection over different periods of time had resulted in significantly cleaner boiler tube surfaces. Examination of deposit samples with Lycal injection showed lightly sintered, porous, friable textures compared to the highly sintered, fused and dense structures for samples without Lycal injection. The effect of Lycal on the softening behaviour of reconstituted deposit samples and various components of ash was shown to be dependent on their chemical composition, with iron oxide playing an important role. For a number of highly acidic ash components, additions of 5 and 10 mass% Lycal promoted crystallisation of their fluid melt, when cooled to specific temperatures. For the more ferriferous ash components, additions of 1 and 3 mass% Lycal enhanced the surface formation of spikes when their melts were cooled to specific temperatures. The results of leaching experiments showed that the initial magnesia concentrations were generally much higher for the deposit samples and fly ash particles from ash hoppers and grit arrestors with Lycal injection than those without.

New advanced combined cycle coal-fired power generation systems are dependent on improvements in gas turbine technology and the development of hot gas cleaning techniques. These techniques are not only necessary to meet environmentally accepted emission limits for SOx and NOx but also to prevent downstream equipment from corrosion and erosion. Volatile alkali vapours in the exhaust gases produced by either coal gasification or combustion lead to corrosion of the gas turbine blades resulting in reduced operating life. Consequently, alkali removal systems which can operate upstream of the gas turbine have been incorporated into the development of the clean coal technologies. A number of studies on alkali removal systems have been performed in the temperature range of 800°C - 1000°C. Solid aluminosilicates, such as emathlite, activated bauxite, kaolinite and Fuller's Earth, react with alkali vapours at high temperatures and therefore have been characterised as suitable alkali sorbents. Fuller's Earth was identified as potentially the most suitable sorbent for use in the UK at the specified operating temperatures. This material was studied in detail by McLaughlin (1990) for use in a fixed bed configuration within the British Coal Air-Blown Gasification Cycle. Recently, it has been recognised that if ceramic filters are used for the removal of fine particulates, operating temperatures for alkali sorption will have to drop to 400°C-600°C, since these filters fail mechanically at higher temperatures. Much of the alkali will condense under these conditions and be removed by the filtration stages. However, the residual alkali levels may still exceed the revised turbine inlet specification of 24 ppb wt. Hence further studies of alkali sorption are required in this lower temperature region. During this work, it proved difficult to obtain accurate results at temperatures as low as 600°C, because of the low level of vapour phase alkali. However, experiments were performed successfully at 650°C and atmospheric pressure, on the fixed bed sorption rig used previously for tests at 827°C and 927°C. Tests comparing Fuller's Earth and kaolin, showed kaolin to have a higher sorption capacity at this temperature. Fixed bed tests with sodium and potassium were performed with Fuller's Earth pellets. The runs were of 200-600 hrs duration, with 4.58 ppm wt NaCl (1.8 ppm wt Na), 5 %vol H2O and up to 160 ppmv HCl in the inlet gas stream. Alkali uptake profiles were generated from chemical analysis of precise layers of pellets removed from the bed. Extensive modifications and improvements in analytical procedures enabled a closure of the mass balance of >99% to be achieved for a 600 hr run. Alkali exit levels measured using alumina wool filter pads in the exit gas were of the order of 5-6 ppb wt. Fuller's Earth pellets which had been pre-treated in gasifier gas and which were therefore contaminated with carbon, were tested and no difference was observed in their Na characteristics. Element mapping techniques based on Scanning Electron Microscopy, confirmed that a shrinking core model for Fuller's Earth grains and kaolin pellets was appropriate. The 'two-reaction' mechanism proposed by McLaughlin (1990), was used to fit the experimental results at 650°C. Albite was identified by X-ray diffraction studies as the reaction product under high-acid conditions and nepheline under non-acid conditions. Exit gas analysis studies with an on-line monitor for HCl, showed the production of HCl to be directly connected with the presence of NaCl vapour and to increase significantly with the presence of water vapour in the system. However, the detailed reaction mechanism has not been identified yet. The theoretical model developed for the high temperature studies (McLaughlin, 1990), using the pellet-grain model and the 'tank-in-series' method of solution has been applied successfully at 650°C. Parameters were extracted by curve fitting theoretical to experimental Na uptake concentration bed profiles. To test the numerical methods and the Szekely assumptions used in the McLaughlin program, two new computer programs were developed. The first, tested the pellet-grain model for a single pellet and the second was developed to solve the model more rigorously with a variable-order, variable-time-step numerical method. The new fixed bed model also incorporates the effects of temperature and pressure on selected parameters. It was used to predict the performance of a full-scale unit operating at 650°C and 24 bara. The results indicate that a bed of Fuller's Earth pellets, 3-10 mm in diameter, 4 m long and 4 m wide can achieve exit alkali levels below 20 ppb wt in continuous operation for up to 24,000 hrs.

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