Turbine Internal Efficiency Research Articles

The high-temperature retrofit research and application of subcritical units

Under the pressure of reducing CO2 and pollutants emissions, The Chinese Government requires that all the existing coal-fired power units shall achieve an average net efficiency higher than 39.6% (LHV) by 2020. Considering the fact that the typical annual average net efficiency level of subcritical units is about 37%, some are even lower than 35%, it seems to be overambitious to achieve this target. The high temperature retrofit of subcritical units, however, find a technically and economically feasible solution for this problem, mainly on 4 aspects: 1) By improving the main and reheat steam temperatures from 538 °C to 600 °C, both the cycle efficiency and turbine internal efficiency are greatly improved. 2) By keeping the main and reheat steam pressures unchanged, combined with innovative boiler heating surfaces retrofit, the pressure parts of the boiler and feedwater system are utilized as much as possible thus the 600 °C steam temperatures are achieved with reasonable cost. 3) Combined with other energy-saving technologies, like flue gas heat recovery technology and generalized regeneration technologies, the unit efficiency is further improved under rated load, and even larger under part load. 4) By applying special startup technology and other efficiency preservation technologies, the solid particle erosion problem is suppressed thus the unit can operate efficiently in long term. Now the high temperature retrofit is being conducted in a typical 320 MW subcritical unit in Xuzhou, China. The target net efficiency under rated condition is higher than 42.36%, much better than those of all existing supercritical units and even some ultra-supercritical units. This project is expected to be a demonstration, setting a benchmark for the high efficiency retrofit of subcritical units.

Mid and low-temperature solar–coal hybridization mechanism and validation

A higher solar-to-electricity conversion efficiency was one of the major advantages of the solar-fossil hybrid systems, compared to the solar-only power plants. In this paper, a new mechanism to reveal the reasons for the improved solar-to-electricity efficiency in a solar-hybrid power plant was given. A correlation was built to describe the main influencing factors of its thermodynamic performances, including higher collector efficiency, higher turbine internal efficiency and upgraded energy level of the mid and low-temperature solar heat. This proposed mechanism can be used to integrate solar–coal hybridization system effectively. A case study was taken as the typical 200 MW coal-fired power plant hybridized with solar heat at approximately 300 °C, where the solar heat was used to preheat the feed water before entering the boiler. Furthermore, simulation results of this mid and low-temperature solar-hybridization system was conducted to prove the proposed mechanism. It is expected that the theoretical values have a good agreement with the simulation ones. The results obtained indicate that why development of mid and low-temperature solar–coal hybridization technology may provide a promising direction to efficient utilization of low-grade solar thermal energy, and provide the direction to enhance system performances of this kind of solar–coal hybrid power plants.

A Typical Solar-coal Hybrid Power Plant in China

This paper proposes a 330 MW coal-fired power plant hybridized with solar heat, which will be demonstrated in Sinkiang province of China. In this solar hybrid plant, solar heat at around 300°C is used to replace the steam extracted from the high- pressure turbine, to pre-heat the feed water before the economizer of the boiler. In this way, the replaced high-temperture and pressure steam can be further expanded in the turbine, boosting output work of the coal-fired power plant. At the same time, compared to present solar-only thermal power technology, the solar heat at around 300°C here can be converted into electricity by the aid of larger capacity units of the coal-fired plant with higher turbine internal efficiency. Furthermore, this kind of solar hybrid power plant can be operated at a fully rated output during periods of low solar radiation such as the evening and overcast days without storage device. As a result, the annual net solar-to-electric efficiency could reach up to 21%, with the improvement of nearly 3 percentage points, compared to the state-of-the art parabolic trough plants, such as SEGSs. And the levelized cost of electricity generation (LCOE) could be reduced to 0.8-1.0▪/kWh, about 20-30% lower than that of the solar-only thermal power plant (1.1-1.3▪/kWh). This kind of solar-coal hybrid power plant would offer a promissing approach to the cost-effective and scalable utilization of mid-temperature solar heat in the near and mid term.

Improved analysis of Organic Rankine Cycle based on radial flow turbine

With attention to the drawback of specifying isentropic efficiency of expander (or turbine) in Organic Rankine Cycle (ORC) analysis, in order to enhance reliability of analysis results, this article replaces the constant isentropic efficiency by internal efficiency of optimal radial flow turbine for each condition. With both analysis methods, namely internal efficiency analysis method and conventional analysis method, 14 subcritical ORC working fluids are studied with hot water of 90 °C, pinch point temperature of 5 °C and condensing temperature of 30 °C. Results with both analysis methods are compared. The results show that turbine internal efficiency is determined by expansion ratio in rotor and decreases with the rise of expansion ratio in rotor. There are differences between cycle net power output with internal efficiency analysis method and that with conventional analysis method. The differences can change the results in optimizing fluid. It is significant to apply computational optimal efficiency instead of constant isentropic efficiency in ORC analysis.

The Development of Highly Loaded Turbine Rotating Blades by Using 3D Optimization Design Method of Turbomachinery Blades Based on Artificial Neural Network & Genetic Algorithm

In order to improve turbine internal efficiency and lower manufacturing cost, a new highly loaded rotating blade has been developed. The 3D optimization design method based on artificial neural network and genetic algorithm is adopted to construct the blade shape. The blade is stacked by the center of gravity in radial direction with five sections. For each blade section, independent suction and pressure sides are constructed from the camber line using Bezier curves. Three-dimensional flow analysis is carried out to verify the performance of the new blade. It is found that the new blade has improved the blade performance by 0.5%. Consequently, it is verified that the new blade is effective to improve the turbine internal efficiency and to lower the turbine weight and manufacturing cost by reducing the blade number by about 15%.

Development of a Highly Loaded Rotor Blade for Steam Turbines. 1st Report, Cascades Performance.

Turbine manufacturers have been concerned about efficient utilization of limited energy resources and prevention of environmental pollution. For steam turbine power plants, a higher efficiency gain is necessary to reduce the fuel consumption rate. Blade configurations have been studied for reductions of profile loss and endwall loss that lead to decreased steam turbine internal efficiency, by applying recent aerodynamic technologies based on advanced numerical analysis methods. This paper discusses increase of pitch-chord ratio by 14% (reduction of rotor blade numbers by 14%) and increased blade aerodynamic loading without deterioration of performance. A new rotor cascade is found which improves blade performance, especially at the root section where the reduction in the energy loss coefficient is about 40%. This rotor blade also provides lower manufacturing cost.

Development of a Highly Loaded Rotor Blade for Steam Turbines. 2nd Report. Three-Dimensional Stage Performance Verifications.

In order to improve steam turbine internal efficiency, a new highly loaded rotor blade for the high and intermediate pressure (HIP) stages, has been developed. The blade configuration is expressed by a 5th-order Bezier curve and an interactive technique is adopted in combination with a 2-D turbulent blade-to-blade flow analysis. The inverse method is adopted to modify the blade shape by optimizing the blade aerodynamic loading distribution near the root section which should decrease not only profile loss, but also endwall loss. Three-dimensional stage flow analysis and air turbine tests are carried out to verify the stage performance of the new blade. It is found that the new blade has improved blade performance near the root and the midspan; in particular, higher blade performance near the midspan contributes to an improvement in stage efficiency by about 0.3% at the design point. Consequently, it is verified that the new rotor blade is effective to improve steam turbine internal efficiency and to lower manufacturing cost by reducing the blade number by 15%.

Performance Characteristics of Hero's Turbine Using Hot Water as a Working Fluid

From the view point of energy saving and the development of new energy resources, it is important to utilize geothermal resources and waste heat from factories. As one of the energy conversion expanders, there is a radial outflow reaction turbine (that is, Hero's turbine). Performance characteristics of Hero's turbine using subcooled hot water as a working fluid are clarified analytically and experimentally. It is found that : (a) there is an optimum rotational speed at which maximum turbine efficiency can be obtained, (b) Hero's turbine internal efficiency can be expressed by an algebraic equation (7), and (c) nozzle loss amounts to almost 90 percent of the total turbine loss.

Performance characteristics of Hero's turbine using hot water as a working fluid.

From the view point of energy saving and the development of new energy resources, it is important to utilize geothermal resources and waste heat from factories. As one of the energy conversion expanders, there is a radial outflow reaction turbine (that is, Hero's turbine). Performance characteristics of Hero's turbine using subcooled hot water as a working fluid are clarified analytically and experimentally. It is found that : (a) there is an optimum rotational speed at which maximum turbine efficiency can be obtained, (b) Hero's turbine internal efficiency can be expressed by an algebraic equation (7), and (c) nozzle loss amounts to almost 90 percent of the total turbine loss.