Combined Cycle Units Research Articles

Cogeneration steam turbines from Siemens: New solutions

The Enhanced Platform system intended for the design and manufacture of Siemens AG turbines is presented. It combines organizational and production measures allowing the production of various types of steam-turbine units with a power of up to 250 MWel from standard components. The Enhanced Platform designs feature higher efficiency, improved reliability, better flexibility, longer overhaul intervals, and lower production costs. The design features of SST-700 and SST-900 steam turbines are outlined. The SST-700 turbine is used in backpressure steam-turbine units (STU) or as a high-pressure cylinder in a two-cylinder condensing turbine with steam reheat. The design of an SST-700 single-cylinder turbine with a casing without horizontal split featuring better flexibility of the turbine unit is presented. An SST-900 turbine can be used as a combined IP and LP cylinder (IPLPC) in steam-turbine or combined-cycle power units with steam reheat. The arrangements of a turbine unit based on a combination of SST-700 and SST-900 turbines or SST-500 and SST-800 turbines are presented. Examples of this combination include, respectively, PGU-410 combinedcycle units (CCU) with a condensing turbine and PGU-420 CCUs with a cogeneration turbine. The main equipment items of a PGU-410 CCU comprise an SGT5-4000F gas-turbine unit (GTU) and STU consisting of SST-700 and SST-900RH steam turbines. The steam-turbine section of a PGU-420 cogeneration power unit has a single-shaft turbine unit with two SST-800 turbines and one SST-500 turbine giving a power output of Nel. STU = 150 MW under condensing conditions.

Development of a thermal scheme for a cogeneration combined-cycle unit with an SVBR-100 reactor

At present, the prospects for development of district heating that can increase the effectiveness of nuclear power stations (NPS), cut down their payback period, and improve protection of the environment against harmful emissions are being examined in the nuclear power industry of Russia. It is noted that the efficiency of nuclear cogeneration power stations (NCPS) is drastically affected by the expenses for heat networks and heat losses during transportation of a heat carrier through them, since NPSs are usually located far away from urban area boundaries as required for radiation safety of the population. The prospects for using cogeneration power units with small or medium power reactors at NPSs, including combined-cycle units and their performance indices, are described. The developed thermal scheme of a cogeneration combined-cycle unit (CCU) with an SBVR-100 nuclear reactor (NCCU) is presented. This NCCU should use a GE 6FA gasturbine unit (GTU) and a steam-turbine unit (STU) with a two-stage district heating plant. Saturated steam from the nuclear reactor is superheated in a heat-recovery steam generator (HRSG) to 560–580°C so that a separator–superheater can be excluded from the thermal cycle of the turbine unit. In addition, supplemental fuel firing in HRSG is examined. NCCU effectiveness indices are given as a function of the ambient air temperature. Results of calculations of the thermal cycle performance under condensing operating conditions indicate that the gross electric efficiency ηel NCCUgr of = 48% and Nel NCCUgr = 345 MW can be achieved. This efficiency is at maximum for NCCU with an SVBR-100 reactor. The conclusion is made that the cost of NCCU installed kW should be estimated, and the issue associated with NCCUs siting with reference to urban area boundaries must be solved.

The influence of carbon capture and compression unit on the characteristics of ultramodern combined cycle power plant

In this paper, the influence of carbon capture and compression unit on the characteristics of ultramodern combined cycle power plant is presented. The chemical absorption of the CO2 from the flue gases using MEA in the carbon capture unit was used. The effective use of heat recovered from the turbine blade cooling air in order to increase the efficiency of combined cycle power plant with the carbon capture and compression unit is proposed. The power plant is analysed in a wide range of compression ratios and temperatures in the gas turbine. Thermodynamic and ecological characteristics of this combined cycle unit as a function of the basic operating parameters are made. The equation connecting the efficiency of combined cycle power plant with and without the carbon capture and compression unit is proposed. The calculations indicate that the reduction of energy consumption of the absorbent by 1 MJ/kgCO2 causes an increase in net electric efficiency of the unit by 1.25 percentage points. The analysed combined cycle power plants are characterised by the highest electricity generation efficiency achievable for large energy units and exceptionally low CO2 emissions, lower than 41 kg/MWh throughout the analysed range of compression ratio.

Prospects for the use of SMR and IGCC technologies for power generation in Poland

This study is a preliminary assessment of prospects for new power generation technologies that are of particular interest in Poland. We analysed the economic competitiveness of small size integrated gasification combined cycle units (IGCC) and small modular reactors (SMR). For comparison we used one of the most widely applied and universal metric i.e. Levelized Cost of Electricity (LCOE). The LCOE results were complemented with the results of energy-economic model TIMES-PL in order to analyse the economic viability of these technologies under operation regime of the entire power system. The results show that with techno-economic assumptions presented in the paper SMRs are more competitive option as compared to small IGCC units.

燃气–蒸汽联合循环机组控制系统与性能监测诊断系统的数据交互

以“E”级燃气–蒸汽联合循环供热机组为研究对象，在“DCS + Mark VIe”的控制模式基础上，利用OC6000e平台开发了该机组的性能监测诊断系统。文中对“DCS + Mark VIe”的控制系统的控制模式、系统结构，特别是其与性能监测诊断系统的数据交互方式进行了详尽的分析。 Taking the “E” class gas-steam combined cycle unit as the research object, the performance moni-toring and diagnosis system of the unit is developed by using OC6000e platform based on the con-trol model of “DCS + Mark VIe”. In this paper, the control mode and system structure of “DCS + Mark VIe” control system are analyzed in detail, especially the mode of data interaction with the performance monitoring and diagnosis system.

Опыт организации водно-химического режима с применением пленкообразующих аминов на тепловых электрических станциях с парогазовыми установками

The list of thermal power stations equipped with combined-cycle plants (CCPs) at which chelamine is used as a correcting reagent is presented. The advantages of this reagent and advisability of using it are pointed out. The main drawbacks of cycle chemistries based on film-forming amines are formulated, namely, low pH values in the low-pressure boiler water with high pH values in superheated low-pressure steam and high concentrations of ammonia in superheated steam. The effect the concentration of a complex reagent has on the water and steam quality parameters during the operation of a 110 MW combined-cycle unit in its nominal mode is outlined. Measures taken for optimally conducting the cycle chemistry with metering complex reagents as applied to a CCP are considered. The results from regime-adjustment tests of the cycle chemistry of a heat recovery steam generator with metering a complex reagent are described. It has been revealed that in case of using Type 906 H chelamine, the specific electrical conductivity of the H-cation sample of high-pressure superheated steam exceeds the values prescribed by the temporary regulations, and that the pH of the low-pressure circuit's boiler water is at the lower limit of the range prescribed by these regulations. A transition for using Type BRW 150H reagent, which is characterized by a lower distribution ratio between boiling water and saturated steam, has been done. The results obtained from the regime-adjustment tests in the cases of using chelamine of types 906H and BRW 150H were subjected to a comparative analysis. It has been revealed that the replacement of the chelamine type (with the reagent concentration remaining the same) resulted in a higher concentration of sodium, higher conductivity of the H-cation sample, and higher pH value of low-pressure feed water. It has been shown that with a lower concentration of Type BRW 150H reagent, the main quality indicators of feed water, boiler water, and low- and high-pressure steam are within the their standardized ranges and have stable values. It is pointed out that the specific consumption of Type BRW 150H reagent is a factor of 2 lower than in case of metering Type 906H reagent.

Co-gasification of coal and biomass wastes in an entrained flow gasifier: Modelling, simulation and integration opportunities

Gasification processes convert carbon-containing material into syngas through chemical reactions in the presence of gasifying agents such as air, oxygen, and steam. Syngas mixtures produced from such processes consist mainly of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2), and methane (CH4); this gas can be directly utilised as a fuel to produce electricity or steam. Besides, it is regarded as a basic feedstock within the petrochemical and conventional refining industries, producing various useful products like methanol, hydrogen, ammonia, and acetic acid. In this work, a rigorous process model is developed to simulate the co-gasification of coal-biomass blends through an entrained flow gasifier. The proposed model is tested originally for American coal. The model validation is made against literature data and results show good agreement with these practical data, providing a robust basis for integration and retrofitting applications. Effects of critical parameters, comprising gasification temperature, steam/O2 ratio, and feedstock variability on the syngas composition and gasifier efficiency are studied. The developed model is further applied in a project to revamp an existing Egyptian natural gas-based power plant, replacing its standard fuel with coal-rice straw blends. The revamping project integrates the existing plant with a gasification unit burning a blend of coal and rice straw to replace the conventional fuel used. The feedstock used constitutes a dry Egyptian coal and a coal-rice straw blend (10 wt% rice straw), gathered locally. Different blending scenarios are investigated and the best performance is achieved with coal to rice straw ratio of 90:10 on weight basis, attaining 85.7% cold gas efficiency and significant economic savings. Results showed that the total annualised cost of the revamped process decreased by 52.7% compared with a newly built integrated gasification combined cycle (IGCC) unit.

Economic competitiveness of small modular reactors versus coal and combined cycle plants

Small modular reactors (SMRs) may be an option to cover the electricity needs of isolated regions, distributed generation grids and countries with small electrical grids. Previous analyses show that the overnight capital cost for SMRs is between 4500 US$/kW and 5350 US$/kW, which is between a 6% and a 26% higher than the average cost of a current large nuclear reactor. This study analyzes the economic competitiveness of small modular reactors against thermal plants using coal and natural gas combined cycle plants. To assess the economic competitiveness of SMRs, three overnight capital costs are considered 4500 US$/kW, 5000 US$/kW and 5350 US$/kW along with three discount rates for each overnight cost considered, these are 3, 7, and 10%. To compare with natural gas combined cycle (CC) units, four different gas prices are considered, these are 4.74 US$/GJ (5 US$/mmBTU), 9.48 US$/GJ (10 US$/mmBTU), 14.22 US$/GJ (15 US$/mmBTU), and 18.96 US$/GJ (20 US$/mmBTU). To compare against coal, two different coal prices are considered 80 and 120 US$/ton of coal. The carbon tax considered, for both CC and coal, is 30 US$/ton CO2. The results show what scenarios make SMRs competitive against coal and/or combined cycle plants. In addition, because the price of electricity is a key component to guarantee the feasibility of a new project, this analysis calculates the price of electricity for the economically viable deployment of SMRs in all the above scenarios. In particular, this study shows that a minimum price of electricity of 175 US$/MWh is needed to guarantee the feasibility of a new SMR, if its overnight capital cost is 5350 US$/kWe and the discount rate is 10%. Another result is that when the price of electricity is around 100 US$/MWh then the discount rate must be around 7% or less to provide appropriate financial conditions to make SMRs economically feasible.

Greenhouse Gas Mitigation in Chinese Eco-Industrial Parks by Targeting Energy Infrastructure: A Vintage Stock Model.

Mitigating greenhouse gas (GHG) emissions in China's industrial sector is crucial for addressing climate change. We developed a vintage stock model to quantify the GHG mitigation potential and cost effectiveness in Chinese eco-industrial parks by targeting energy infrastructure with five key measures. The model, integrating energy efficiency assessments, GHG emission accounting, cost-effectiveness analyses, and scenario analyses, was applied to 548 units of energy infrastructure in 106 parks. The results indicate that two measures (shifting coal-fired boilers to natural gas-fired boilers and replacing coal-fired units with natural gas combined cycle units) present a substantial potential to mitigate GHGs (42%-46%) compared with the baseline scenario. The other three measures (installation of municipal solid waste-to-energy units, replacement of small-capacity coal-fired units with large units, and implementation of turbine retrofitting) present potential mitigation values of 6.7%, 0.3%, and 2.1%, respectively. In most cases, substantial economic benefits also can be achieved by GHG emission mitigation. An uncertainty analysis showed that enhancing the annual working time or serviceable lifetime levels could strengthen the GHG mitigation potential at a lower cost for all of the measures.

New projects for CCGTs with coal gasification (Review)

Perspectives of using coal in combined-cycle gas turbine units (CCGTs), which are significantly more efficient than steam power plants, have been associated with preliminary coal gasification for a long time. Due to gasification, purification, and burning the resulting synthesis gas at an increased pressure, there is a possibility to intensify the processes occurring in them and reduce the size and mass of equipment. Physical heat evolving from gasification can be used without problems in the steam circuit of a CCGT. The downside of these opportunities is that the unit becomes more complex and expensive, and its competitiveness is affected, which was not achieved for CCGT power plants with coal gasification built in the 1990s. In recent years, based on the experience with these CCGTs, several powerful CCGTs of the next generation, which used higher-output and cost-effective gas-turbine plants (GTPs) and more advanced systems of gasification and purification of synthesis gas, were either built or designed. In a number of cases, the system of gasification includes devices of CO vapor reforming and removal of the emitted CO2 at a high pressure prior to fuel combustion. Gasifiers with air injection instead of oxygen injection, which is common in coal chemistry, also find application. In this case, the specific cost of the power station considerably decreases (by 15% and more). In units with air injection, up to 40% air required for separation is drawn from the intermediate stage of the cycle compressor. The range of gasified coals has broadened. In order to gasify lignites in one of the projects, a transfer reactor was used. The specific cost of a CCGT with coal gasification rose in comparison with the period when such units started being designed, from 3000 up to 5500 dollars/kW.

Simultaneous Optimisation and Integration of Igcc Plant Using Graphical Method

As a promising green technology, Integrated Gasification Combined Cycle (IGCC) plant is more efficient and low-pollution electricity generation choice than conventional thermal power plants. Its process is mainly consist of the gasifier, the air separation unit and the combined cycle unit. Going through those key blocks, the fuel, such as coal and biomass, could be converted to syngas and further combusted for power generation. In order to be a viable technology, the bottleneck is located on the high energy production cost, which could be overcame by improving the plant efficiency through process optimisation and Integration. The opportunity and challenge are given by the complicated configuration and extreme operation conditions, which also demands a flexible and robust IGCC plant simulation to complete deep process analysis. In this work, a novel simplified IGCC mathematical model is proposed considering thermodynamics constraints with energy and mass conservation. The gasification is simulated based on the principle of Gibbs free energy minimisation, which holds the good feature of avoiding potential bi-level optimisation problem. The proposed gasification model results in syngas composition similar to the experimental data provided in literature. Meanwhile, the cryogenic air separation unit is selected with the double distillation column configuration, which is simulated considering the novel simplification of thermal coupled distillation columns. What is more, the combined cycle unit is simulated with isentropic assumption plus efficiency to complete the process. To validate the novel simplified IGCC model, one base case is built and compared with literature data. Another highlight of this work is the simultaneous optimisation and integration methodology instead of conventional sequential one, which gives more guarantee for achieving global optimal solution. If the ideal property assumptions are occupied, a graphical approach could be generated for the simultaneous optimization and integration of IGCC plant. The best material and energy integration scheme in proper operation condition could be selected considered with respect to the overall thermal efficiency of the IGCC plant. The good performance is shown by about 10 % power increment compared with the base case in the case study.

Dynamic performance of a novel offshore power system integrated with a wind farm

Offshore wind technology is rapidly developing and a wind farm can be integrated with offshore power stations. This paper considers as case study a futuristic platform powered by a wind farm and three combined cycle units consisting of a gas turbine and an ORC (organic Rankine cycle) module. The first aim of this paper is to identify the maximum amount of wind power that can be integrated into the system, without compromising the electric grid balance. The stability of the grid is tested using a dynamic model of the power system based on first principles. Additionally, the dynamics of the system is compared with a simplified plant consisting of three gas turbines and a wind farm, in order to identify benefits of the installation of the ORC system. The maximum allowable wind power is 10 MW for a nominal platform load of 30 MW. The results show that the presence of the ORC system allows decreasing frequency oscillations and fuel consumptions of the platform, with respect to the simplified configuration. On the other hand, the dynamic response of the combined cycle units is slower due to the thermal inertia of the heat transfer equipment.

An Edge-Based Formulation for Combined-Cycle Units

As the number of combined-cycle units increases, efficient modeling approaches for these units play important roles for independent system operators (ISOs). Based on various combinations of combustion turbines (CTs) and steam turbines (STs), the combined-cycle unit could work at different configurations (modes) with different efficiencies. In this paper, we propose an edge-based formulation for the combined-cycle units in the unit commitment problem to improve the accuracy and effectiveness of current modeling approaches. Our formulation can 1) clearly describe the transition processes among different configurations so as to satisfy the ISO financial offer submission requirements and (2) capture physical constraints of each turbine, including the exact min-up/down time and time dependent startup cost, in the combined-cycle units so as to increase the operational flexibility while ensuring system feasibility. This model fits well with the current U.S. deregulated electricity market. The final numerical studies show that our approaches perform better than the current configuration-based modeling approach.

Modeling and Optimization of High-Performance Polymer Membrane Reactor Systems for Water–Gas Shift Reaction Applications

In production of electricity from coal, integrated gasification combined cycle plants typically operate with conventional packed bed reactors for the water-gas shift reaction, and a Selexol process for carbon dioxide removal. Implementation of membrane reactors in place of these two process units provides advantages such as increased carbon monoxide conversion, facilitated CO2 removal/sequestration and process intensification. Proposed H2-selective membranes for these reactors are typically of palladium alloy or ceramic due to their outstanding gas separation properties; however, on an industrial scale, the cost of such materials may become exorbitant. High-performance polymeric membranes, such as polybenzimidazoles (PBIs), present themselves as low-cost alternatives with gas separation properties suitable for use in such membrane reactors, given their significant thermal and chemical stability. In this work, the performance of a class of high-performance polymeric membranes is assessed for use in integrated gasification combined cycle (IGCC) units operated with carbon capture, subject to constraints on equipment and process streams. Several systems are considered for use with the polymeric membranes, including membrane reactors and permeative stage reactors. Based upon models developed for each configuration, constrained optimization problems are formulated which seek to more efficiently employ membrane surface area. From the optimization results, the limiting membrane parameter for achieving all carbon capture and H2 production specifications for water–gas shift reactor applications is determined to be the selectivity, α H 2 / C O 2, and thus a minimum value of this parameter which satisfies all the constraints is identified for each analyzed configuration. For a CO2 capture value of 90%, this value is found to be α = 61 for the membrane reactor and the 3-stage permeative stage reactor and α = 62 for the 2-stage permeative stage reactor. The proposed systems approach has the potential to be employed to identify performance limitations associated with membrane materials to guide the development of future polymeric and other advanced materials with desired membrane characteristics for energy and environmental applications.

Spatially and Temporally Resolved Analysis of Environmental Trade-Offs in Electricity Generation.

The US power sector is a leading contributor of emissions that affect air quality and climate. It also requires a lot of water for cooling thermoelectric power plants. Although these impacts affect ecosystems and human health unevenly in space and time, there has been very little quantification of these environmental trade-offs on decision-relevant scales. This work quantifies hourly water consumption, emissions (i.e., carbon dioxide, nitrogen oxides, and sulfur oxides), and marginal heat rates for 252 electricity generating units (EGUs) in the Electric Reliability Council of Texas (ERCOT) region in 2011 using a unit commitment and dispatch model (UC&D). Annual, seasonal, and daily variations, as well as spatial variability are assessed. When normalized over the grid, hourly average emissions and water consumption intensities (i.e., output per MWh) are found to be highest when electricity demand is the lowest, as baseload EGUs tend to be the most water and emissions intensive. Results suggest that a large fraction of emissions and water consumption are caused by a small number of power plants, mainly baseload coal-fired generators. Replacing 8-10 existing power plants with modern natural gas combined cycle units would result in reductions of 19-29%, 51-55%, 60-62%, and 13-27% in CO2 emissions, NOx emissions, SOx emissions, and water consumption, respectively, across the ERCOT region for two different conversion scenarios.

How to model the cycling ability of thermal units in power systems

For thermal units in power systems, the importance of quick load changes increases along with the share of volatile renewable feed-in. An adequate representation of the cycling abilities of thermal units is therefore important in energy system modeling. Five different model techniques used in the literature to describe the cycling ability of thermal generation units are applied in the optimizing energy system model PERSEUS-NET-TS. The model calculates the dispatch of German generation units while restrictions of the transmission grid are considered. Differences in the cumulated dispatch of coal, lignite, and gas combined-cycle units in Germany due to the different modeling techniques are analyzed based on the PERSEUS-NET-TS results as well as the resulting dispatch of two exemplary single generation units. While the cumulated dispatch for Germany does not show any major differences for coal and lignite units, the cumulated dispatch of gas units differs slightly depending on the approach. Moreover, the dispatch of individual generation units may differ significantly. Even though the real commissioning strategies are not publicly known, it could be identified that the mostly applied modeling approaches based on technical restrictions increase computing time unnecessarily and that cost based approaches reduce on/off cycling more.

Tight and Compact MIP Formulation of Configuration-Based Combined-Cycle Units

Private investors, flexibility, efficiency and environmental requirements from deregulated markets have led the existence and building of a significant number of combined-cycle gas turbines (CCGTs) in many power systems. These plants represent a complex optimization problem for the short-term planning unit commitment (UC) carried out by independent system operators due to their multiple operating configurations. Accordingly, this paper proposes a mixed-integer linear programming (MIP) formulation of the configuration-based model of CCGTs, which is commonly utilized for bid/offering market processes. This formulation is simultaneously tighter and more compact than analogous MIP-based models; hence, it presents a lower computational burden. The computational efficiency of the proposed formulation is demonstrated by solving network-constrained UC case studies, of different size and complexity, using three of the leading commercial MIP solvers: CPLEX, GUROBI, and XPRESS.

Exergetic Analysis of Triple-Level Pressure Combined Power Plant with Supplementary Firing

AbstractThis work presents a thermodynamic analysis of a triple-level pressure combined power plant with supplementary firing. The supplementary firing is a technological development for improving and increasing the output power of a combined-cycle (CC) power plant. In Mexico, there is a plant operating with this configuration, which generates a net power of 1,170 MW, with a power ratio of the gas turbine (GT) to the steam turbine (ST) of 1.35∶1. This plant is composed of four combined-cycle units with supplementary firing, each providing an output power of 292.5 MW. The energetic and exergetic analyses of the combined cycle with and without supplementary firing are pursued, taking into account the combustion process of natural gas and humid air. These analyses are also carried out for the heat recovery steam generator, considering the waste gases of the gas turbine and of the supplementary firing as the energy sources. The obtained results are fuel, steam, and humid air flows; excess of air; gas and stea...

An efficient approach for solving mixed-integer programming problems under the monotonic condition

Many important integer and mixed-integer programming problems are difficult to solve. A representative example is unit commitment with combined cycle units and transmission capacity constraints. Complicated transitions within combined cycle units are difficult to follow, and system-wide coupling transmission capacity constraints are difficult to handle. Another example is the quadratic assignment problem. The presence of cross-products in the objective function leads to nonlinearity. In this study, building upon the novel integration of surrogate Lagrangian relaxation and branch-and-cut, such problems will be solved by relaxing selected coupling constraints. Monotonicity of the relaxed problem will be assumed and exploited and nonlinear terms will be dynamically linearised. The linearity of the resulting problem will be exploited using branch-and-cut. To achieve fast convergence, guidelines for selecting stepsizing parameters will be developed. The method opens up directions for solving nonlinear mixed-integer problems, and numerical results indicate that the new method is efficient.

Optimization of Start-Up of a Fully Fired Combined-Cycle Plant with GT13E2 Gas Turbine

The principles of starting up the steam power unit of the Hrazdan-5 fully fired combined-cycle power unit (Hrazdan, Armenia) are considered. This plant has neither a bypass stack for gas discharge from the gas turbine nor an external steam source for the steam-turbine gland and prestarting deaeration. Emphasis is placed on the differences between the start-up procedure followed at the plant and the procedure provided by the RD 34.25.512 Standard Instructions on Startup from Various Thermal States and Shutdown of 300-MW Boiler-Turbine Sets with K-300-240 LMZ Turbine.