Increasing Steam Parameters Research Articles

Zavarivost između čelika tipa 304H i čelika tipa P91 za primene na visokim temperaturama

This paper presents research about weldability between two dissimilar steels, martensitic steel P91 and 304H austenitic steel. Both materials are being preferred as a structural material for higher temperature applications due to their good mechanical properties at high temperatures. The mechanical properties at high temperature, such as tensile strength and creep resistance, are very important factors that ensure the application of materials. The P91 is modified martensitic Cr steel with higher amount of chromium which improves the higher temperature strength and molybdenum that increases creep resistance. On the other hand, the 304H represents advance austenitic stainless steel with controlled carbon content, which makes it ideal for applications requiring good mechanical properties at elevated temperatures. With increasing the demand of high efficiency in the power generation industry the high temperature applications usually require joints between advanced austenitic stainless steels and new class martensitic stainless steels in order to achieve the goal with the increased steam parameters. Therefore, this paper focuses on the weldability assessment between these two different steels and the characteristics of the weld metal.

FACTOR ANALYSIS OF THE THERMAL SCHEME OF CHP WITH SUPER CRITICAL STEAM CYCLE ON THE BASIS OF EXERGY METHOD

The most promising direction of CHP modernization is the introduction of power units on supercritical steam parameters. Increasing steam parameters is one of the most effective ways to increase the efficiency of a CHP plant. Thus, the development of the concept of thermal schemes turbines for supercritical steam parameters, taking into account the characteristics of their operation at the existing CHP Ukraine is an actual scientific problem. The solution to this problem will make it possible to replace or modernize the power generating equipment that has exhausted its resource with modern power units that meet world economic and environmental standards. The method of exergy analysis is adapted to the study of thermal schemes of CHP plants with supercritical steam cycle. As an example of application of a method the exergy analysis of the power plant working on the one-stage thermal scheme is carried out. Within the framework of the proposed method, a thermodynamic and topology-exergetic model of the power plant is created. Based on the topology-exergetic model the indicators of thermodynamic efficiency of the power plant operating on supercritical parameters of steam are determined. It is proposed to apply the theory of experiment planning in exergy analysis of the thermal circuit of a CHP. With the involvement of this theory, a multifactor numerical experiment was conducted to determine the impact on the exergetic efficiency of the thermal scheme of CHP of the main determining variable factors, such as adiabatic and thermal efficiency of the plant, as well as the operating parameters. The generalized equation of functional interrelation of exergetic efficiency of system and exergetic efficiency of elements of thermal scheme of CHP is received. The proposed equation can be used as a tool for further training of neural networks and their application both in the design and in the diagnosis of energy efficiency of CHP. According to the results of the factor analysis, a rather high conservatism of the considered one-stage scheme of CHP to the change of the varied parameters was revealed. This indicates the presence of more rigid structural links between the elements, which is generally a positive aspect of the reconstruction.

A Technical Analysis of Oil Shale Firing Power Units Retrofitting for Carbon Capture and Storage (CCS)

In Estonia the significant part of power generation is still based on firing oil shale fuel in thermal power plants despite of the growth of the share of the green energy in recent years. Electricity generation is based on power units utilizing different combustion technologies. A significant part still comprises old units with capacity 185-195 MWe commissioned in early 70s of last century. These pulverized combustion (PC) based units utilize oil shale as a fuel and are operating with subcritical steam parameters, characterizing by relatively low efficiency 26 - 30% (net, LHV based). Due to their low performance, operational issues (intensive fouling of heating surfaces), and remarkable environmental impact, these units were decommissioned or retrofitted with boilers implementing circulating fluidized bed combustion (CFBC) technology in 2004-2005. Implementation of CFBC technology for oil shale combustion significantly reduced both operational issues and environmental impact. With some additional modifications in turbine island allowing to increase rated capacity up to 215 MWe and after increasing steam parameters, the net efficiency of up to 37% was achieved. Consequently, the specific CO2 emissions in the range of 0.99 – 1.05 t/MWhe depending on quality of oil-shale used, was achieved. Recently, the new 300 MWe CFBC based power unit was commissioned. It is operating with subcritical steam parameters: live steam temperature 565 °C and pressure 17 MPa. Net efficiency (LHV based) of that unit is 40 % and specific CO2 emissions up to 0.9 t/MWhe in case of firing only oil shale. In this study the technical viability of retrofitting oil shale based power generation units with CC is described. In the analysis two CC methods were considered: post-combustion (assuming conventional amine process) and oxy-fuel combustion. Among other CC technologies these processes are at the present time characterized by higher technical readiness level, can be applied for existing units with minimal modifications and are applicable for oil shale fuel with it specifics. Besides power generation, Estonia has for almost 100 years of experience in production of shale oil through thermal decomposition of oil shale kerogen in retorts. Currently, solid heat carrier (SHC) method is the main method used for producing shale oil. In this method, direct CO2 emission comes from the preparation of SHC by combustion of solid retorting residue (semi-coke). Mainly two combustion methods are presently applied: lift pipe combustion and CFBC which was recently successfully integrated into shale oil production process. The possibility of utilizing CC technologies in shale oil production units and their technical analysis is described in this study.

Thermodynamic cycle analysis and optimization to improve efficiency in a 700 °C ultra-supercritical double reheat system

When increasing steam parameters, the incomplete thermodynamic cycle and large irreversible system losses are bottlenecks in improving thermal efficiency in ultra-supercritical power plants. In this study, a comprehensive analysis of both parameter optimization and system cycle analysis is carried out for a 1000-MW double reheat ultra-supercritical thermal power plant. First, the genetic algorithm is used to optimize the primary and double thermal pressure, as well as the steam extraction parameters of the steam turbine. Then, a thermodynamic optimization model is proposed to analyze performance. Moreover, the exergy analysis method is applied to reveal the irreversibility mechanism in the thermodynamic cycle. In order to further solve the energy-grade mismatch problem, the performance of a regenerative steam turbine thermal system is improved based on the optimized system. The results indicate that the power generation efficiency of the optimized system is 0.31% higher than that of the prototype system, and the heat consumption rate is decreased by 43.67 kJ (kW h)−1. The power generation efficiency in the regenerative steam turbine system is up to 52.42%, which is 1.44% higher than that of the optimized system. Therefore, an effective method to improve the thermal efficiency is obtained through the thermodynamic cycle analysis and optimization for 700 °C ultra-supercritical double reheats systems.

Waste to energy efficiency improvements: Integration with solar thermal energy.

Hybridisation of waste to energy with solar facility can take competing energy technologies and make them complementary. However, realising the benefits of solar integration requires careful consideration of the technical feasibility as well as the economic and environmental benefits of a proposed system. In this work, a solar-integrated waste-to-energy plant scheme is proposed and analysed from an energy, environmental and economic point of view. The new system integrates a traditional waste-to-energy plant with a concentrated solar power plant, by superheating the steam produced by the waste-to-energy flue gas boiler in the solar facility. The original waste-to-energy plant - that is, the base case before introducing the integration with concentrated solar power - has a thermal power input of 50 MW and operates with superheated steam at 40 bar and 400 °C; net power output is 10.7 MW, and the net energy efficiency is equal to 21.65%. By combining waste-to-energy plant with the solar facility, the power plant could provide higher net efficiency (from 1.4 to 3.7 p.p. higher), lower specific CO2 emissions (from 69 to 180 kg MWh-1 lower) and lower levellised cost of electricity (from 13.4 to 42.3 EUR MWh-1 lower) comparing with the standalone waste to energy case. The study shows that: (i) in the integrated case and for the increasing steam parameters energy, economic and ecological performances are improved; (ii) increasing the solar contribution could be an efficient way to improve the process and system performances. In general, we can conclude that concentrated solar-power technology holds significant promise for extending and developing the waste to energy systems.

CHALLENGES AND OPPORTUNITIES OF UTILIZATION OF ASH AND SLAG WASTE OF TPP (THERMAL POWER PLANT). PART 2

For existing and already constructed coal TPP plants, known methods of utilization of fly ash and slag wastes (FASW) may be in de­mand when all emerging environmental and economic risks are taken into account. But for the new power generating source when choosing coal combustion technology, it is necessary to increase the significance of the environmental component of the project more essentially. It is known that the most promising technologies for coal combustion, which increase environmental safety exactly by burning, are technolo­gies based on a circulating fluidized bed. These technologies can sig­nificantly reduce sulfur and nitrogen oxide emissions behind the boiler, but the solution to the problem of flay ash and slag waste remains at the same level. It is proposed to solve the problem of FASW utilization during the implementation of new energy projects or when replacing the decommissioning capacities of coal generation by replacing the method of coal combustion in a stream or fluidized bed with meth­ods of burning solid fuel in a bubbling slag melt. The descriptions and schemes of these methods are given. The comparison of the main qual­itative technical and ecological parameters of pulverized coal combus­tion and technologies of coal combustion in slag melt is presented. The development of coal generation is expected in two main areas: coal combustion with increasing steam parameters and gas generation with a combined cycle of electricity generation: steam and gas, based on the gasification of solid fuels. These directions will allow achieving electric efficiency of steam-power plants from 30 – 36 %, up to 44 – 45 % on supercritical steam parameters, and using a combined steam-gas cycle up to 50 – 55 %. A technological scheme of gasification of coal in a slag melt is proposed, which increases the electrical efficiency of the installation. The ecological and economic efficiency of the gasifica­tion method for solid fuel and the simplicity of the production of slag products by casting are shown. The quality of cast slagstone products is much higher than similar cement-sand products with the addition of fly ash, and the ease of transition from one casting mold to another allows quickly responding to market demands.

Weldability assessment and high-temperature properties of advanced creep resisting austenitic steel X6CrNiNbN25-20 (DMV310N/HR3C)

The modern Ultra Super Critical Power Plants (USC PP) applying the 600 °C technology require advanced stainless steels in superheater/reheater systems in order to cope with the increased steam parameters. Different grades of stainless steels have been developed by increasing Cr-contents, alloying with stabilizing and precipitating elements as well as thermomechanical heat treatments resulting in high creep rupture strengths and improved oxidation/corrosion resistance. In the context of a collaborative research project, X6CrNiNbN25-20 (DMV310N/HR3C) has been investigated. The main focus of the research project was on characterization and weldability assessment. As a result, the base metal under investigation was compared with governing code cases and specifications. Base metal chemical composition, microstructures, mechanical properties, reheat cracking sensitivity, and hot ductility as well as creep rupture strengths have been investigated. A weldability assessment, including thermal simulation and welding procedure qualifications, has been performed to establish parameter windows for similar and dissimilar welding. Dissimilar welding between grade 92 and austenitic steel tubes has been performed. The project also took the opportunity to investigate the behavior of a recently developed gas tungsten arc welding (GTAW) P87 consumable for dissimilar welding. Cross-weld creep rupture tests have been conducted for both similar and dissimilar welding, while aging tests addressed microstructural stability.

Experience of using municipal solid waste in the energy industry (An Overview)

The status of municipal solid waste (MSW) utilization for energy purposes in Europe, the United States, and China is revealed, showing that MSW has long been among alternative fuels abroad and is widely used as a renewable energy source. Energy utilities often deal with the construction and operation of thermal waste-to-energy facilities. Currently, thanks to the use of the best available technologies (BAT), among which are incineration in mechanical grate stokers and in vertex fluidized-bed furnaces, and multistage gas treatment, the problems of environmentally safe operation of facilities for MSW-to-energy utilization have been fully resolved. The main research is aimed at improving the energy efficiency of these facilities, primarily, by increasing steam parameters and organizing its intermediate superheating. It is shown that a high efficiency of converting the MSW energy potential into electricity can also be reached by integrating MSW incinerators into the heat flow scheme of thermal power plants, whose main fuel is coal or gas. Examples are given of active foreign MSW-to-energy facilities improved to increase electricity efficiency to 30% and more.

New Austenitic Creep Resistant Steels for Superheaters of USC Boilers

Current trend in increasing steam parameters in ultra-supercritical (USC) boilers requires new materials not only for membrane walls, headers and pipelines but also for superheater and reheater tubes. Newly developed austentitic steels Super304H, TP347HFG and HR3C exhibit superior resistance in steam thanks to their fine-grained microstructure, especially in case of Super304H and TP347HFG. The paper presents the results of verification of properties of these steels tubes including creep resistance of the base metal and welded joints, which show promising level of long-term creep strength of the base metal and weld joints and these results are supplemented by some new knowledge about the development of the microstructure of these steels, especially sigma phase appearance.

Weldability assessment and high temperature properties of advanced creep resisting austenitic steel DMV304HCu

The modern (USC PP) applying the 600 °C technology require advanced austenitic stainless steels in superheater/reheater systems in order to cope with the increased steam parameters. Different grades of austenitic stainless steels have been developed by increasing Cr contents, alloying with stabilizing and precipitating elements as well as thermomechanical heat treatments resulting in high creep rupture strengths and improved oxidation/corrosion resistance. In the context of a collaborative research project, DMV304HCu (X10CrNiCuNb18-9-3) has been selected. The main focus of the research project was on characterization and weldability assessment. As a result, the base metal under investigation was compared with governing code cases and specifications. Base metal chemical composition, microstructures, mechanical properties, reheat cracking sensitivity, hot ductility as well as creep rupture strengths have been investigated. A weldability assessment, including thermal simulation and welding procedure qualifications, has been performed to establish parameter windows for similar and dissimilar welding. Dissimilar welding between Grade 92 and austenitic stainless steel tubes has been performed. The project also took the opportunity to investigate the behavior of a recently developed gas tungsten arc welding (GTAW) P87 consumable for dissimilar welding. Cross-weld creep rupture testing has been conducted for both similar and dissimilar welding, and aging tests addressed microstructural stability.

Assessment of Improved Molten Salt Solar Tower Plants

The temperature level increase of molten salt solar tower plants is one important task on the development schedule to increase the system's overall efficiency. In the conventional power plant technology, modern supercritical steam power plants work with life steam temperatures near 620°C. To apply these modern power blocks in molten salt solar tower plants, salt temperatures near 650°C are required. Today's molten salt tower plants reach salt temperatures of 565°C. To follow the positive development tendencies of fossil power plants, in the present work the combination of supercritical steam power plants with solar towers is analyzed. As stated in recent literature (Kolb, Kelly, Singer), the state of the art tubular central receiver concept coupled with increased steam parameters of the power block (300bar/600°C/610°C) shows a marginal potential to decrease LEC. The identification of future concept innovations with significant cost reduction potential in the field of molten salt tower plants, the enhancement of the receiver efficiency as well as the assessment of critical aspects related to their feasibility is the task of this paper.Therefore this work first focuses on the state of the art molten salt tower technology and related improved concepts with molten salt. The selected improvements follow on the one hand the aim to increase the receiver's maximum temperature level to approximately 650°C to be able to feed modern supercritical power blocks, on the other hand the aim to require a low development effort. After the reference concept is characterized, the objective is the systematic comparison of receiver technologies, which show a potential of improved thermal efficiencies.The assessed receiver candidates are tubular and direct absorption receivers, either external or located in a cavity. The analyzed power level is 125 MWel, while the steam process parameters are varied from low temperature level (550°C) and subcritical steam to high temperature level (620°C) and supercritical steam. With this, selected molten salt power plants were specified and then modeled with different sizes of solar fields and different storage capacities and analyzed on an annual basis. The results show, that the assessed concept options close to the state of the art require drastically decreased investment costs to end up with significant LEC reduction and cost-competitiveness. The increase in overall efficiency of these improved concepts is compensated by their higher financial effort. Results of further concept assessments as well as the sensitivity analysis of parameters and costs are described.

Gaseous corrosion of alloys and novel coatings in simulated environments for coal, waste and biomass boilers

The reduction of emissions from power generation plants is a key part of the Kyoto Protocol. Reduced emissions per unit of power produced can be achieved via increased thermal efficiency and this can be achieved by increasing steam parameters (i.e. temperature and pressure). Increased steam parameters in turn leads to accelerated corrosion of boiler components. Biomass and solid waste fuels introduce a number of aggressive species into process environments that result in enhanced rates of boiler degradation. This paper reports on studies, both theoretical and experimental, of the corrosion behaviour of high-alloy steels and Ni-base alloys as well as coatings for use in high efficiency coal and/or biomass- and waste-fired power plants. Coatings produced within the SUNASPO project have been laboratory tested in gaseous atmospheres representative of coal combustion, biomass combustion and waste incineration. Laboratory tests were carried out mainly in the temperature range 500 °C to 800 °C. Initial results showed the poor performance of traditional uncoated low-alloy boiler steels P91 (9% Cr) and HCM12A (12% Cr), as well as the higher alloy steel, 17Cr/13Ni. Results show the beneficial effects of coatings containing Al, Si, Al + Si, Al + Ti and Al + B in reducing the rate of corrosive attack. In a combustion product gas containing 100 ppm HCl and 1000 ppm SO2, aluminizing affords corrosion resistance of low-alloy steels such as HCM12A and P91 similar to that of Alloy 800 over 1000 h of test. The presence of Al inhibits internal, sometimes localized corrosion by promoting the formation of a protective surface oxide layer even at relatively low temperatures. The results of experiments in simulated coal; biomass and waste atmospheres are presented and discussed in terms of both corrosion kinetics and mechanisms of degradation.