Comparative Analysis of Low-Grade Heat Utilization Methods for Thermal Power Plants with Back-Pressure Steam Turbines

Thermal power plants (TPPs) with back-pressure steam turbines (BPSTs) were widely used for electricity and steam production in the Union of Soviet Socialist Republics (USSR) due to their high efficiency. The collapse of the USSR in 1991 led to a decrease in industrial production, as a result of which, steam production in Russia was reduced and BPSTs were left without load. To resume the operation of TPPs with BPSTs, it is necessary to modernize the existing power units. This paper presents the results of the thermodynamic analysis of different methods of modernization of TPPs with BPSTs: the superstructure of the steam low-pressure turbine (LPT) and the superstructure of the power unit operating on low-boiling-point fluid. The influence of ambient temperature on the developed cycles’ efficiency was evaluated. It was found that the usage of low-boiling-point fluid is thermodynamically efficient for an ambient temperature lower than 7 °C. Moreover, recommendations for the choice of reconstruction method were formulated based on technical assessments.

Numerical investigations on non-synchronous vibration and frequency lock-in of low-pressure steam turbine last stage

The flow phenomenon of rotating instability (RI) and its induced non-synchronous vibrations (NSV) in the last stage have gradually become a security problem that restricts the long-term flexible operations of modern large-scaled low-pressure steam turbines. Especially, if one structural mode of the last stage moving blade (LSMB) is excited, significant blade vibrations may potentially lead to high-cycle fatigue failure. A loosely coupled computational fluid dynamics reduced model with prescribed blade vibrations has been established to investigate NSV of the LSMB and the potential lock-in phenomenon under low-load conditions. Firstly, calculations with reduced multi-passage domain have been verified by comparing with the results of the full-annulus one, and an appropriate reduced domain is determined. Secondly, a set of calculations by controlling blade vibration parameters indicate that lock-in phenomenon between RI frequency and blade vibration frequency may occur when nodal diameters of cascade vibrations is coincident with the wave number of RI. Furthermore, dynamic modal decomposition technology has been employed to identify the unsteady pressure field around the blade surface and to reveal the interaction relationship between the flow modes of RI and vibration-induced pressure disturbance. Finally, the blade response evaluation based on harmonic analysis shows that in NSV, the global maximum dynamic response level of locked-in case is nearly 20 times than that of unlocked one.

Feasibility of Boosting Low-Energy-Quality Steam by Using Wave Rotor

Owing to the difficult utilization of the low-pressure level in the process industry, the low-energy-quality steam is often condensed to recover the demineralized water or just discharged directly, causing a huge waste of thermal energy. A novel technology of enhancing the steam’s energy quality by using the wave rotor based on the principle of moving shockwave compression is proposed. The supercharging ability of 3-port wave rotor is studied by meaning of 1-dimension unsteady theory and computational fluid dynamic. A practical thermodynamic flowsheet of boosting the low-pressure steam driven by high-pressure steam is also proposed and analysed in detail. As an example, to boost the saturated steam of pressure 1.0 MPa to 1.953 MPa, a three-stage wave rotor solution is proposed and is verified its feasibility. The high supercharging ratio and entrainment ratio of the wave rotor are much higher than the traditional steam ejector shows the feasibility of enhancing energy-quality of low-pressure steam.

Numerical and experimental study of droplet-film-interaction for low pressure steam turbine erosion protection applications

One common approach for anti-erosion measures in low pressure steam turbines is to equip a hollow stator vane with slots on the airfoil surface in order to remove the water film by suction and consequently reduce the amount of secondary droplets. The purpose of this paper is to build an understanding of the predominant effects in fluid-film interaction and to examine the suitability of modern numerical methods for the design process of such slots. The performance of a suction slot in terms of collection rate and air leakage is investigated numerically in a flatplate setup with upstream injection of water. In order to model the relevant phenomena (film transport, edge stripping of droplets, transport of droplets in the surrounding fluid, wall impingement of droplets) an unsteady Eulerian-Lagrangian simulation setup is applied. The accuracy of the numerical approach is assessed by comparison with experimental measurements. The comparison of four cases with the measured data demonstrates that the chosen simulation approach is able to predict the main features of film flow and interaction with the surrounding fluid. The collection rate as well as fluid film properties show the same qualitative dependency from water mass flow rate and air velocity.

Life Cycle Assessment of Cogeneration Systems Using Raw and Torrefied Dichrostachys Cinerea (L.) Wight & Arm. (Marabou).

Purpose This study aims to assess environmentally three different alternatives related to the valorization of Dichrostachys cinerea (L.) Wight & Arm. (marabou), identified as an invasive tree, as a feedstock for cogeneration facilities installed in the sugarcane industry in Cuba. The alternatives are (A-1) Electricity generation from marabou in a conventional back-pressure steam turbine cycle, (A-2) Electricity generation from torrefied marabou in a back-pressure steam turbine cycle, and (A-3) Electricity generation from torrefied marabou using extraction-condensing turbines.Methods SimaPro 9.0.0.35 software was used for the modeling of the inventory, based on different operational parameters. The ReCiPe environmental impact assessment method was used in the hierarchical perspective, assessing 18 impact categories (midpoint), and 3 damage categories (endpoint).Results and discussion The results demonstrated that A-3 shows the lower environmental impacts (Fine Particulate Matter Formation, Terrestrial Acidification, and Water Consumption) as compared to A-2 and A-1. This performance is explained by a lower normalized marabou consumption (1.85 kg marabou/kWh generated), and lower emissions associated with marabou harvesting, transportation, and processing. The cogeneration stage was the main contributor to the environmental burdens in Water Consumption (100% in A-1; 87% in A-2 and A-3). Marine Ecotoxicity was the impact category with better environmental performance due to the substitution of synthetic mineral fertilizers by ashes produced during combustion. The human health damage category reached the higher impacts on the torrefaction subsystem in the A-3 scenario, representing over 94% of the total environmental burden of the process. PM<10, NO2, and SO2 contributed the most over this damage category, mainly in marabou combustion, causing injuries in respiratory systems by aspiration of organic compounds.Conclusions The use of more efficient technology (extraction-condensing steam turbine), using torrefied marabou as feedstock, compared with the previous alternatives, impacts beneficially on the environment. Thus, a combination of marabou torrefaction with cogeneration facilities in sugarcane industries can be considered as an environmental-friendly technology in the Cuban context. The current study results will help decision-makers implement more sustainable policies in the Cuban energy sector, using marabou as feedstock as an attractive bioenergy route pathway.