Steam conditions

Plant Coolant temperature (°C) Steam conditions (at turbine inlet, full power)  

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Water as an impurity accelerates the oxidation rate. Figure 4 compares growth curves for Si02 under dry and steam conditions. Halogens can also be introduced to the oxidation process, thereby reducing sodium ion contamination. This improves dielectric breakdown strength, and reduces interface trap density (15). 

Selection of the high pressure steam conditions is an economic optimisation based on energy savings and equipment costs. Heat recovery iato the high pressure system is usually available from the process ia the secondary reformer and ammonia converter effluents, and the flue gas ia the reformer convection section. Recovery is ia the form of latent, superheat, or high pressure boiler feedwater sensible heat. Low level heat recovery is limited by the operating conditions of the deaerator. 

PWRs operate differendy from BWRs. In PWRs, no boiling takes place in the primary heat-transfer loop. Instead, only heating of highly pressurized water occurs. In a separate heat-exchanger vessel, heat is transferred from the pressurized water circuit to a secondary water circuit that operates at a lower pressure and therefore enables boiling. Because of thermal transfer limitations, ultimate steam conditions in PWR power plants ate similar to those in BWR plants. For this reason, materials used in nuclear plant steam turbines and piping must be more resistant to erosion and thermal stresses than those used in conventional units. 

The supply steam conditions should not be allowed to vary greatly. Pressure below design ean lower capacity. Pressure above design usually doesn t increase capacity and can even lower capacity. 

As steam temperatures increase, more expensive materials must be used to manufacture the turbine. Above 750" F, the price increase will be about 5% to about 850°F. Another 5% will be added for temperatures between 850°F and 900°F, and another 5% for temperatures above 900°F Steam turbine designers have selected as a standard for single-stage turbines a limit of 600 psia and 750°F maximum inlet steam conditions. 

Driver. If steam is available, a common choice is a steam turbine driver for the main pump and an electric motor for standby. Some plants prefer two electric motor-driven pumps. Give the minimum steam condition. Give the expected voltage drop on the electric system if more than 10% is expected, especially on large systems. 

Since the early 1960s, advanced steam conditions have not been pursued. In the 1960s and early 1970s there was little motivation to continue lowering heat rates of fossil-fired plants due to the expected increase in nuclear power generation for base-load application and the availability of relatively inexpensive fossil fuel. Therefore the metallurgical development required to provide material X for advanced steam conditions was never undertaken. 

Since 1900, manufacturers have made many step changes in the basic design of steam turbines. New technology and materials have been developed to support the industry s elevation of steam conditions, optimization of thermal cycles and unit capacity. Steam turbines will continue to be the principal prime mover for electricity generation well into the twenty-first century. 

Silvestri, G. J., Jr. Bannister, R. L. Fujikawa, T. and Hizume, A. (1992). Optimization of Advanced Steam Conditions Power Plants. Transactions of the ASA4E, Journal of Engineering for Gas Turbine and Power 114 612-620. 

S° = Degrees of superheat in a steam condition, degrees I above saturated (not the actual temperature)... 

Determine the internal steam rate for the steam conditions and reduce speed by... 

The overall efficiency of the condensing thermal cycle, as discussed, is dictated primarily by the steam conditions used. There are some small industrial stations with outputs up to 2 MW using shell-type boilers for the generation of steam. Here the steam conditions are limited to approximately 17 bara and 250°C. For larger installations these conditions will rise sharply when watertube boilers become attractive and more common steam conditions are of above 60 bara and 540°C. 

Having ascertained the process steam flow and developed some ideas on the boiler pressure, the following step is to analyze the power available. Figure 15.23 provides a ready means of determining the approximate relationship between power available and process steam for specific steam conditions. Use of this and similar charts will allow an assessment to be made of the potential of a CHP scheme with a backpressure turbine. The conditions can be changed to give the required balance for heat and power. 

The single-stage, single-valve turbine is the simplest option. Such a machine is suitable for applications requiring powers up to 300 kW, steam conditions up to a nominal 115 bar, 530°C and rotational speeds... 

Steam is the preferred atomizing medium, since it is more economic than compressed air. Steam consumption is typically less than 0.5 per cent of the fuel burnt on a mass basis, although this rises in direct proportion to turndown ratio. On very large burners, the steam flow is modulated in proportion to fuel burnt. Turndown ratios range from about 5 1 for small shell boilers to 12 1 in watertube applications, making this one of the most versatile burners. The steam condition is important in that it must be dry saturated or slightly superheated at the nozzle to avoid condensate formation. On small or non-continuously running plant where no steam is available for start-up a compressed air supply must be provided until steam becomes available from the boiler. 

A steam turbine operates with inlet steam conditions of 40 barg and 420°C and can be assumed to operate with an isentropic efficiency of 80% and a mechanical efficiency of 95%. Calculate the power production for a steam flowrate of 10 kg s-1 and the heat available per kg in the exhaust steam (i.e. superheat plus latent heat) for outlet conditions of ... 

Lou and Zeng spotted the work of Park et al. and sought to improve on it by developing an aqueous synthetic route. In this method, water and sodium sulfate are added to freshly prepared tungstic acid and autoclaved at up to 200°C for up to 24 h (assuming saturated steam conditions, this corresponds to pressures of up to 15.5 bars). 

Unless otherwise specified, steam turbine drivers shall conform to ISO 10436 (API Standard 6II). Steam turbine drivers shall be sized to deliver continuously 110 percent of the maximum power required for the purchaser s specified conditions while operating at corresponding speed with specified steam conditions. 

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