Steam generation

In the steam generation system, heat from combustion causes steam to form in the primary steam generation coils (Stultz and Kitto, 1992). The steam vapor rises into the steam drum, where it is accumulated. The steam then successively passes to the convective and radiant superheaters, which use combustion heat to further heat the steam well above its previous temperature. The steam next flows to the turbine, which has both high- and low-pressure stages. 

High-temperature, high-pressure steam is generated in the boiler and then enters the steam turbine. At the other end of the steam turbine is the condenser, which is maintained at a low temperature and pressure. Steam rushing from the high-pressure boiler to the low-pressure condenser drives the turbine blades, which powers the electric generator. Steam expands as it works hence, the turbine is wider at the exit end of the steam. The theoretical thermal efficiency of the unit is dependent on the high pressure and tanperature in the boiler and the low temperature and pressure in condenser. 

Steam turbines typically have a thermal efficiency of about 35%, meaning that 35% of the heat of combustion is transformed into electricity. The remaining 65% of the heat either goes up the stack (typically 10%) or is discharged with the condenser cooling water (typically 55%). 

Low-pressure steam exiting the turbine enters the condenser shell and is condensed on the condenser tubes. The condenser tubes are maintained at a low temperature by the flow of cooling water. The condenser is necessary for efficient operation by providing a low-pressure sink for the exhausted steam. As the steam is cooled to condensate, the condensate is transported by the boiler 

A generator is mounted at one end of the turbine shaft and consists of carefully wound wire coils. Electricity is generated when these are rapidly rotated in a strong magnetic field. After passing through the turbine, the steam is condensed and returned to the boiler to be heated once again. 

In my experience, a reasonably good condensate recovery rate in a large, complex refinery is 70 percent. A substantial portion of the steam is used for process steam stripping, purging vessels, instrument connections, flare dispersal, and other nonrecoverable uses. Thus, the 70 percent rate is really rather good. 

On the other hand, 30 percent condensate recovery as a percentage of the steam generation rate is rather bad and represents sloppy operations and bad condensate recovery design practices. Very approximately, 10 percent of the cost of steam generation could be saved by recovering the condensate. The condensate contains few silicates, thus no blowdown (explained below) is needed, no chemical treatment or deaeration is required, and no energy that would otherwise be used to preheat the boiler feedwater will be wasted. 

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In design, the same rules must be obeyed around a utility pinch as around a process pinch. Heat should not be transferred across it by process-to-process transfer, and there should be no inappropriate use of utilities. In Fig. 6.13a this means that the only utility to be used above the utility pinch is steam generation and only cooling water below. In Fig. 6.136 this means that the only utility to be used above... 

Example 6.6 The problem table cascade for a process is given in Table 6.9 for — 10°C. It is proposed to provide process cooling by steam generation... 

These sources of waste from the steam system can be reduced by increasing the percentage of condensate returned (in addition to reducing steam generation by increased heat recovery). 

Reducing wastewater associated with steam generation by both reducing steam use through improved heat recovery and by making the steam system itself more efficient. 

The policy for waste heat recovery from the flue gas varies between incinerator operators. Incinerators located on the waste producer s site tend to be fitted with waste heat recovery systems, usually steam generation, which is fed into the site steam mains. Merchant incinerator operators, who incinerate other people s waste and... 

Figure 13.8 The grand composite curve for the whole process apparently requires only high-pressure steam generation from boiler feedwater.

Figure 16.19 shows the grand composite curve plotted from the problem table cascade. The two levels of steam generation are shown. 

Figure 16.19 Grand composite curve for Example 16.3 showing two levels of steam generation.

The problem with this approach is that if the steam generated in the boilers is at a very high pressure and/or the ratio of power to fuel costs is high, then the value of low-pressure steam can be extremely low or even negative. This is not sensible and discourages efficient use of low-pressure steam, since it leads to low-pressure steam with a value considerably less than its fuel value. 

Numerical Modeling of eddy current steam generator inspection Comparison with experimental data, P.O. Gros, Review of Progress in Quantitative Nondestructive Evaluation, Vol 16 A, D.O. Thompson D. Chimenti, Eds (Plenium, New York 1997) pp 257-261. 

Progress in mean of modelisation and inverse problem solving [1] let us hope to dispose soon of these tools for flaws 3D imaging in Non Destructive Control with eddy current sensors. This will achieve a real improvement of the actual methods, mainly based upon signature analysis. But the actual eddy current probes used for steam generators tubes inspection in nuclear industry do not produce the adequate measurements and/or are not modelisable. 

Our main application domain is the steam generator tubes of pressurized water nuclear plant. These tubes have 22.22 mm outer diameter and 1 27 mm thickness. 

The automatic acquisition and analysis system we developed within the scope of the Super-Phenix steam generator tube inspection by ultrasonic arrays is a remarkable example of an exhaustive acoustic verification system. It works for every type of probe for tube inspection. 

Q. Moreau, et al., Ultrasonic control system for Superphenix Steam Generator tubes , SMIRT 1997, Lyon... 

Due to the many problems concerning steam generators of nuclear power plants over the last decades, we developed our own inspection equipment and services. Next to this main activity, we provide inspections for nuclear power plants components such as thimbles, guide carts and baffle bolts. 

It has developed a real time method to compare successive non-destructive inspections of the steam generator tubes in nuclear power plants. Each tube provides a safety barrier between the primary and secondary coolant circuits. Each steam generator contains several thousands of tubes whose structural integrity must be ensured through the lifetime of the plant, Therefore, Laborelec performs extensive nondestructive tests after each plant outage. 

Using CD s streamlines the automatic comparison of data. Because of their large storage capacity and their reduced dimensions CD s provide a complete historical database for all steam generator tubes from a mobile inspection platform. 

The signal comparison function has been impieinented and tested during a steam generator tube inspection. A formal test in the real-life context was successfully done with a simple rule (parameters phase and amplitude) based on the central frequency for the distance signal. 

Figure 4. Laser Profile of Dented Steam Generator Tube...

Optical Probe for Steam Generator Tube Dent Measurement , EPRI NP-2863, Project SI81-1, February, 1983. 

Steam generator. For small scale work the steam generator D, Fig. 15, p. 33) is too cumbersome for the production of a small amount of steam. It is preferable to use a 250 ml. conical flask fitted with cork containing a vertical safety tube and an outlet-tube (Fig. 44). Care should be taken that the length of rubber tubing connecting the steam oudet tube to the flask containing the materi to be distilled should be as short as possible and should not contain kinks. 

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