Operating parameters steam turbines

A steam turbine is operating between inlet steam of 40 barg and 420°C and outlet steam of 5 barg. Using the Willans Line Model with parameters from Table 23.1 for large turbines and intercept ratio of 0.05, calculate the power production for a turbine at full load with a flowrate of steam of 10 kg s-1. 

Several parameters affect the efficiency of steam turbines, as shown partially on Figure 4.1. Closer examination will need to take into account specific mechanical details which usually are left to the manufacturer. Geared turbines [the dashed line of Fig. 4.1(b)] have higher efficiencies, even with reduction gear losses, because they operate with especially high bucket speeds. For example, for a service of 500 HP with 300psig steam, a geared turbine has an efficiency of 49.5% and one with a direct drive at 1800 rpm has an efficiency of 24%. 

The turbine has to be protected against overspeeding, its critical operating parameters have to be monitored, and if a condition exists that could cause equipment damage, the turbine has to be stopped by closing the steam supply valve. 

All parameter changes were within the operational permissible limits, and they were easily compensated by the automatic control systems without intervention of the operators. Personnel support was only required on the water-steam circuit in order to bring parameters of No.6 turbine generator back to the normal values after all the transients were over (pressure regulator of TG No.6 was opened for pressure reduction in the controlled stage chamber of the turbine). 

At the present time efforts to analyse an additional measures to reduce the capital cost are continued. A successful operation of BN-600 NPP testifies to the fact that the parameters and steam cycle efficiency of large reactor could be improved in comparison with BN-800 NPP. From the time the basic decision on this plant was taken, more than 20 years have passed. During this period, the steam parameters in fossil fuelled plants were increased (24 MPa, 560°C) and industry has started turning out turbines and generators from 500-800 to 1000-1200 MW(e). The main steam temperatures are 540 to 560°C is achieved. The decision on the use of such steam cycle and standard turbines is studied. 

According to the design concept, the UNITHERM can be used as a source of energy for the generation of electricity, district heating, seawater desalination and process steam production either in a complex or to meet specific demands. The purpose of the NPP would impact not only the mix of components but may also determine the characteristics of the reactor [II-5]. For instance, the use of steam at low parameters for district heating and potable water production allows the application of a turbine generator unit operated at backpressure. This sufficiently increases total plant efficiency and allows the use of the thermal siphon as an... 

The choice of a candidate turbine generator plant for the UNITHERM NPP depends on the plant capacity and operation mode (electricity generation or cogeneration) as requested by its users. It is planned to use standard turbine equipment, for example, manufactured by the Kaluga Turbine Works (AO KTZ) [II-6], These turbine-generators use steam of low parameters. 

The turbine operates using dry saturated steam in the mode of a steam outlet backpressure of 1.2-1.05 bar. With consideration of the continuous transfer of 5 % of heat to the independent heat removal system, the total efficiency of the UNITHERM NPP would in this case amount to 74 %. This very high value is achieved due to the utilization of low-parameter heat at the turbine exhaust. 

Reactors with nuclear steam reheat were also developed in the former Soviet Union. The Beloyarsk Nuclear Power Plant (BNPP) was the first NPP in the world where nuclear steam reheat was implemented on industrial level. Two reactors (100 MWei and 200 MWei) were installed with identical steam parameters at the turbine inlet (Pjj, = 8.8 MPa and T n = 500—510°C). The first reactor (Unit 1) was put into operation on April 26, 1964, and the second reactor (Unit 2) on December 29, 1967. Both reactors had similar dimensions and design. However, the flow diagram and the core arrangement were significanfly simplified in Unit 2 compared to that of Unit 1. Schematics and simplified layouts of the BNPP Units 1 and 2 are shown in Figs. A5.1 and A5.2. 

Layouts (b—e) were not recommended due to unpredictable water chemistry regimes at various locations throughout the thermodynamic cycle. Layout (a) with the secondary steam reheat required high pressures and temperatures in the primary loop. Circulation pumps with different parameters (power and pressure) would have to be used to feed common header upstream of the channels of the primary group. In this respect, Layout (a) was considerably more complex and expensive than Layout (f). Activation of SHS, which could occur in Layout (f), was not considered to be posing any significant complications to the turbine operation and hence remained a viable option (Dollezhal et al., 1958). 

At 1 22 a.m., the reactor parameters were approximately stable, and the decision was made to start the actual turbine test. But in case they wanted to repeat the test again quickly, the operators blocked the emergency protection signals from the turbine stop valve, which they were about to close, so that it would not trip the reactor. Also, just before they shut off the steam to the turbine, they sharply reduced the feedwater flow back to the initial level required for the test conditions. This boosted the coolant inlet temperature, creating a transient situation that could not be addressed because safety systems were cut off. 

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