卷 66, 编号 2 (2019)

Vacuum condensers for steam turbines are usually designed at design conditions when all condenser sections are cooled identically with the flowrate of cooling water (or air for air-cooled condensers) and the same air inleakage in each section. A deviation from the design operating conditions occurs due to several causes, such as nonuniform cooling of the condenser heat transfer surface because of its fouling or a fan failure (in air-cooled condensers) and local air inleakage. To investigate condensation under nonuniform cooling conditions, a test facility simulating a condenser was constructed. It consists of two parallel channels. Nonuniformity of cooling in one of the channels was simulated by reducing the cooling water flow. There were regimes with steam feeding into air to model air inleakage occurring in actual condensing units. The experiments were performed in the condensation pressure range of p_c = 8–20 kPa. The previous predictions suggest that installation of orifices with a low-pressure drop can reduce the condenser pressure in case of nonuniform cooling. The effect of orifices with different diameters on the condensation process parameters was studied in this test facility. It has been demonstrated that installation of the orifices facilitates a decrease in the condenser pressure with a cooling water flow rate through one of the channels less than 50% of the design value. A range of optimal orifice diameters for this experimental condenser model was determined. According to the experiments, the benefit of orifice installation is observed only in case of joint operation of the condenser with a volumetric degasser, such as a steam jet ejector. The experimental data demonstrate an increase in the efficiency of joint operation of a condenser and an ejector under nonuniform cooling conditions due to installation of orifices in the line of steam-air mixture ejection.

Turbine generators can be used for utilization of the potential of steam lost in pressure-reducing and cooling units of operating boiler houses. This approach brings about an independent source of power the price of which can be much lower than the established tariff. The features in reconstruction of a boiler house in the city of Bratsk, Irkutsk oblast, carried out in 2012 are examined. Steam generated in a KE-50-14-225 boiler is routed to a 0.3–0.5 MPa common header for use in deaerators and steam-water heaters. Considering an increase in the electricity tariffs, a decision was made to install a 500-kW backpressure turbine generator in the boiler house in parallel with the pressure-reducing unit to generate auxiliary power. The criteria for selecting the number and power of turbine generator units depending on the required steam generation, operating conditions of the consumer, the level of electric loads of the boiler house, and the existing heat supply system are shown. The specifics in operation of the turbine generator unit are examined. To ensure safe and reliable operation of the unit, it is advisable to increase the number of monitored parameters through extension of the normal instrumentation system. The discounted payback period for the reconstruction cost and additional costs for installation of a second turbine generator unit are estimated. The boiler house regimes, a change in the prices for fuel and electricity, and the operator’s labor cost are considered. After installation of the turbine generator, the specific fuel consumption for electricity generation amounts to 180 g.c.e /(kW h). In 2017, the electricity generation cost was 1.23 rubles/(kW h) with the average tariff of 2.13 rubles/(kW h). The discounted payback period for the performed reconstruction does not exceed 6 years, and that for further reconstruction is 8 years.

The paper considers the make-up water heating capability and conditions in the built-in tube bundles when cooling water is concurrently piped through the main turbine condenser bundles. Based on the analysis of experimental and calculated data, a technique is proposed for estimating heat fluxes entering the condenser when the turbine plant operates in the heat production mode. It is shown that, for efficient operation of the built-in bundle as part of the condensing system, all heat fluxes coming in addition to the wheelspace should be directed into the regenerative heating zone under the built-in condenser bundles through special water distribution devices, and the inlet zone itself should be separated from the condenser chamber by enclosing shields. The calculation studies were carried out using a mathematical condenser model of a cogeneration steam turbine plant with built-in condenser bundles. The studies were performed on the model of a turbine plant T-50-12.8 for three seal levels of the low-pressure sliding grid and different make-up water flows and temperatures. The conducted researches made it possible to determine the heat distribution in the condenser between the condenser bundles in different turbine operating modes and to reveal the absence of pressure constraints in the condenser and make-up water temperature constraints at the outlet of the built-in bundle. Based on the turbine plant T-50-12.8 mathematical model, thermal efficiency calculations were performed using the built-in make-up water condenser bundles when the main bundles operate in the cooling mode. It is shown that the heat economy of the turbine plant operating in the considered regimes in the heat production mode with the make-up water flows close to the nominal make up 70% and more of the condenser heat load.

Electricity generation with the use of secondary energy resources emerging as a by-product of industrial technologies is one of the promising lines for making the Russian power industry more efficient. The secondary energy resources produced during operation of some industrial installations (primarily the heat of high-temperature gaseous waste) have a significant potential for electricity generation. Apart from being efficiently used, this potential can also be further increased by subjecting the thermal and material flows of gaseous waste to integrated power and chemical accumulation on the basis of natural gas endothermic conversion reactions, with the high-temperature gaseous waste serving as an oxidizer and a heat source for the conversion. Mathematical models of industrial installations equipped with conversion reactors for carrying out integrated power and chemical accumulation are developed and investigated. An oxidizer consumption coefficient for the conversion process is used in the models, and the method for calculating it is described. The increase of secondary fuel chemical energy obtained for an industrial fuel installation in comparison with the converted natural gas is quite essential, making around 14%. With such an arrangement, the entire flow of gaseous waste becomes a high-quality secondary fuel. At the same time, the possibilities of decreasing the consumption of oxidizer for the conversion process to the optimal value equal to 1.0 are rather limited: its level should be no less than 3.0. The use of integrated power and chemical accumulation under the conditions of a fuel-free basic-oxygen converter is possible with the oxidizer consumption ratio for the conversion process down to 1.4, a level closer to its optimal value. The possibility to recycle in the integrated power and chemical accumulation process approximately 32% of the heat of gaseous waste with the entire mass flowrate of converter gas transformed into high-quality secondary fuel with a heat capacity of 2155°С is demonstrated. The use of integrated power and chemical accumulation in the basic oxygen furnace technology can make it possible to obtain an essential gain in the electricity generation potential in comparison with the direct use of natural gas for electricity generation purposes.

Improvement of the heat transfer is very important in different industries. It leads to modification of the performance of various industrial equipment and increases of their efficiency. Improving the heat transfer rate could be taken in different ways. Among them, the application of the baffles is remarkable, because of the lack of the energy sources including electricity and lower costs. In this work, the effect of shapes of asymmetric baffles on the thermal performance was investigated. Five different shapes as vertical Rectangular, Rectangular diagonal, Trapezoidal, Triangular and Semi Ellipsoid were used as baffles. Three different cases of thermal boundary conditions were used for channel wall and baffles. Three cases are: Case 1 (adiabatic baffles and constant temperature of channel walls), Case 2 (adiabatic baffles and constant heat flux of channel walls) and Case 3 (constant temperature of channel walls and baffles). Governing Equations (included the equations of continuity, momentum and energy) were solved using the finite volume method over the control volume. Results show in Case 3, with constant temperature of channel walls and baffles, the thermal performance with Triangular baffles is more than other shapes. But, in other two cases, the thermal performance with Semi Ellipsoid baffles is more than other shapes.

In this paper, we experimentally determined the conditions and characteristics of the ignition of the fuel mixture samples of various composition of crushed coal and wood in stationary air heated to high temperatures (from 600 to 1000°C). The heating of fuel mixtures under study that are promising for heat power engineering and their subsequent ignition and combustion were registered by using a high-speed video camera (image size is 1024 × 1024 pixels, frame rate is up to 10⁵ frame/s), which ensures high reliability of the obtained results. The ignition delay times of all the studied mixtures based on lean and long-flame coals were established to decrease with an increase in the wood fraction. The limits of the stable (with small deviations of the delay time from the average values) ignition of weights of the studied mixtures are selected. At an increase in the wood waste fraction up to 50%, the decrease in the ignition delay time of mixed fuel based on grade T coal was found to be 11.2% at 600°C and 55.3% at 1000°C. For fuel mixtures based on grade D coal and wood, similar indicators are 17.6 and 64.3%. At temperatures typical for the furnace environment (approximately 1000°C), the ignition delay time for such fuels was determined to be less than 1 s, which is significantly less than the similar ignition characteristics of long-flame and lean-coal dust. The ash content of the fuel mixture is established to be a nonadditive characteristic relative to the ash content of the corresponding coal and wood. The increase in the wood fraction to 50% leads to a decrease in ash content to 10.44% for grade D coal and to 11.08% for grade T coal.

Flow-accelerated corrosion of metal caused by single- or two-phase flow of working fluid leads to thinning and destruction of welds in NPP power unit pipelines. Field experience gained from the operation of Russian and foreign nuclear power plants testifies that there have been many cases of damages inflicted to welds due to local flow-accelerated corrosion, the number of which tends to grow with the time for which the power units have been in operation. The article gives examples of the most typical places and characteristic features pertinent to the way in which the flow-accelerated corrosion of weld elements' metal takes place. The role and influence of the chemical composition of the weld metal and heat-affected zone metal on the location and rate of local flow-accelerated corrosion thinning in welds are determined. The flow hydrodynamic characteristics having an essential effect on the rate of flow-accelerated corrosion processes and the local thinning occurrence places are determined. Results from numerical modeling of the flow-accelerated corrosion weld thinning development process for different contents of chromium in the weld and heat-affected zone metal are given. The possibility of increasing the flow-accelerated corrosion rate in pipelines downstream of a weld with a preceding extended straight pipeline segment made of metal not prone to flow-accelerated corrosion is analyzed. Methods aimed at preventing the occurrence of damage to pipelines of NPP power units due to flow-accelerated corrosion are discussed. The article gives information on the results of activities for modifying the standard programs for in-service inspection of pipelines at VVER-based NPPs and also on the use, at Russian NPPs, of software systems providing support to the personnel on optimizing the arrangement and scheduling of in-service monitoring of flow-accelerated corrosion wear of heat-affected zones in welds of the pipelines used at NPP power units equipped with VVER-440, VVER-1000, and BN-600 reactors. It can be expected that the application of regularly updated software systems for supporting the personnel will make it possible to timely prevent inadmissible thinning and abrupt flow-accelerated corrosion-induced failures of pipeline welds in the power units of Russian nuclear power plants.