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.

Increasing the corrosion resistance of turbine

The reliability of the vane apparatus of steam turbines largely determines the operation of the turbine as a whole. The results of scientific research indicate that the surface operation of the blades in the wet - steam flow is caused by a combination of corrosion and drip erosion. The presence of chemical elements and compounds in the working fluid intensifies the process of blade wear. The pH value of the working environment, which can fluctuate significantly during operation, has a significant effect on the wear characteristics. The influence of methods of strengthening the leading edges of steam turbine blades made of steel is analyzed 15Х11МФ on corrosion resistance. Corrosion tests of blade samples were carried out, the inlet edges of which were strengthened in three ways: high current amplification, electrospark alloying with T15K6 alloy, electrospark alloying with steel 15Х11МФ According to the results of the tests, the layer strengthened by hardening by high-frequency currents has the lowest corrosion rate, the layer strengthened by electrospark alloying with T15K6 hard alloy has the highest. The corrosion rate of the layer reinforced by electrospark alloying of steel 15H11MF is 2.1 less than that of the layer reinforced with T15K6 alloy.

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.

The Effect of Excess Heat Utilization on the Production Cost of Cement

Industrial excess heat is a largely untapped resource that has the potential for external use that would be beneficial to the cement industry. Therefore, this work studied the excess heat utilization for the optimization of production cost in a cement plant within a period of three years. The study of plant layout in the selected plant in Nigeria (Ewekoro II Cement Plant of 200 tonnes/hour) was carried out to identify areas where excess heat is generated. The temperature and static pressure of precalciner, kiln, and cyclone were taken using a temperature probe, pitot tube, digital manometer, and light-emitting diode temperature reader. These parameters were used to obtain the mass flow rate and heat transfer needed for the heat energy analysis of the system. The kiln was maintained at constant tonnage per hour through a clinker truck weighed using the weighbridge. The result showed that the heat generated from the kiln was 577,640,260 MJ/hr. through excess air draft of 780,000 m3/hr (89.4%) at 250 °C and induced draft fan of 900,000 m3/hr at 350 °C. The result showed that excess heat can be utilized in pre-heater and air quenched cooler boilers, steam turbines and auxiliaries, and generators. The total estimated heat that could be saved amounted to 344,648,250 MJ with a total annual capacity of 2.25 million tonnes of cement. A saving of over two billion dollars could be achieved in production cost per year.

A Thermodynamic Performance Analysis of Triple Effect Vapour Absorption Refrigeration System Using LiBr-H2O

Being an eco-friendly system and a cheaper way to produce cooling effect absorption refrigeration system (ARS) is becoming more popular as it can produce higher cooling capacity than vapor compression refrigeration systems, and it can be powered by other sources of energy (like waste heat from gas and steam turbines, or can utilizes renewable source of heat by sun, geothermal, biomass) other than electricity. In the recent years, the interest in absorption refrigeration system is growing because these systems have environmentally friendly refrigerant and absorbent pairs. In this study, a detail energetic analysis of triple stage LiBr-H20 absorption system using First law of thermodynamics is done. An Energy Equation Solver code are used to simulate the computer program is developed for the cycle and results are validated with past studies available is also done. Mass, energy and exergy balance equations and the various complementary relations constitute the simulation model of the triple effect refrigeration system. Further, the effect of exit temperature of generator, absorber, condenser and evaporator on COP, solution concentration and other parameters are studied. It was found in the study that COP increases with increasing the generator exit temperature keeping the absorber exit temperature constant but when the absorber exit temperature is increased COP tends to decrease and the concentration of weak solution leaving HP generator (Xw3), MP generator (Xw2) and LP generator (Xw1) also increases with increase in generator exit temperature, while it decreases with increase in condenser exit temperature. Keywords: Absorption Refrigeration System (ARS), LiBr + H2O, COP, solution concentration, Energy Equation Solver code, energetic analysis, triple effect refrigeration system.

Nonlinear Vibration Analysis of Turbine Bladed Disks with Mid-Span Dampers

Friction dampers are one of the most common secondary structures utilized to alleviate excessive vibration amplitudes in turbo-machinery applications. In this paper, the dynamic behavior of the turbine bladed disks coupled with one of the special damper designs, the so-called Mid-Span Dampers (MSDs) that is commonly used in steam turbines of Baker Hughes Company, is thoroughly studied. Friction between the blade and the damper is modeled through a large number of contact nodes by using 2D contact elements with a variable normal load. In the solution procedure, the coupled static/dynamic Harmonic Balance approach is utilized for the first time in the assessment of the dissipation capability of MSDs, computationally shown by predicting the forced response levels of the system at different resonances. Moreover, it is demonstrated that the nonlinear dynamic response is non-unique and it may vary considerably even if all the user-controlled inputs are kept identical. This phenomenon is a novel observation for MSDs and it is explained by an uncertainty present in the contact forces. Contact conditions corresponding to multiple responses are also investigated to unveil the different kinematics of the damper under the same nominal conditions.

Investigation of operational characteristics of axial displacement guides for thermal expansion systems of steam turbines

ТНЕ PURPOSE. To carry out a comparative analysis of the performance characteristics of the longitudinal movement guides of the external bearing housings of steam turbines, using the principle of rotation to ensure full contact of their lateral surfaces with the lateral surfaces of the guide groove at the base of the external bearing housing of the steam turbine. Compare the manufacturability of elements and their implementation for both existing and newly developed steam turbines .METHODS. The permissible transverse forces are determined from the strength conditions and compared for the traditional design of fixed longitudinal guides and the design of guides, in which the principle of rotation is used to avoid "biting" of the bearing housing on the guides when temperature misalignment appears along the flanges of the turbine cylinder. Also, the allowable forces are determined and compared from the condition of the absence of plastic deformations in any of the elements of the interface of the guides, the base frame and the bearing housing. Based on the results obtained, the value of the permissible temperature misalignment along the flanges of the turbine cylinder is estimated. The analysis was carried out in relation to the operating conditions of the front bearing housing and HPC of turbines of the T 100/120-130 UTZ family.RESULTS. It has been established that all the considered designs of guides with pivoting elements make it possible to exclude the occurrence of plastic deformations in the junction of the base frame and the outboard bearing housing at a temperature misalignment of 20°C regulated in most turbine operating instructions. CONCLUSION. The design of longitudinal keys proposed by UTZ does not require a change in the technology for manufacturing the foundation frames and allows the unit to be modernized during repairs in a CHP. The best performance disc guide design can be used in new turbine designs or factory retrofits.

Efficiency of steam turbines with bypass steam distribution for primary frequency control in power systems

This paper evaluates efficiency of steam turbines with bypass steam distribution involved in a process of primary frequency control in power systems. We calculated power of a steam turbine and power unit in general, and absolute electrical efficiency for both bypass and throttle steam distribution. It was found that bypass steam distribution increases absolute electrical efficiency of steam-gas units while operation under lower capacity. Economic indicators calculated for combined cycle gas units confirm effectiveness of steam turbines with bypass steam distribution involved in primary frequency control.