Use for Power Generation

The important considerations for increasing the system efficiency while using steam shall be based on requirement of power to mn the plant, possibility of exporting surplus power or to use the steam partly for generating power and partly use it as a heating medium. 

The selection of steam turbines and generators depends on the internal demand for power and heating duty. The surplus steam (available from exhaust of a steam turbine after power generation) can be used as follows (cogeneration system) 

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Steam costs vary with the price of fuel. If steam is only generated at low pressure and not used for power generation in steam turbines, then the cost can be estimated from local fuel costs assuming a boiler efficiency of around 75 percent (but can be significantly higher) and distribution losses of perhaps another 10 percent, giving an overall efficiency of around 65 percent. 

The increasing number of atomic reactors used for power generation has been questioned from several environmental points of view. A modern atomic plant, as shown in Fig. 28-3, appears to be relatively pollution free compared to the more familiar fossil fuel-fired plant, which emits carbon monoxide and carbon dioxide, oxides of nitrogen and sulfur, hydrocarbons, and fly ash. However, waste and spent-fuel disposal problems may offset the apparent advantages. These problems (along with steam generator leaks) caused the plant shown in Fig. 28-3 to close permanently in 199T. 

Tests conducted in Finland and Sweden have indicated the viability of using waste paper and plastic packaging as a fuel in a conventional power plant rather than in a municipal solid waste incinerator. If the process is accepted, as much as 30 million tonnes of the 50 million tonnes of combustible packaging which Europe consumes each year could be used for power generation. The feasibility of the initiative is discussed, and its implications in terms of future power plant construction. APME... 

Biomass gasification offers the potential for producing a fuel gas that can be used for power generation system or synthesis gas applications. The volatile matter contains a considerable amount of tar which is a complex mixture of aromatics. Despite extensive research efforts tar formation which causes the pipe plugging and the reduction of conversion efficiency is still a major problem in biomass gasification systems [1-6]. 

Figure 23.20 illustrates the features of a typical steam system. It is usual to have at least three levels of steam. On larger sites, steam may also be generated at a very high pressure, which will only be used for power generation in the boiler house. Steam would then be distributed typically at three pressures around the site. Back-pressure turbines let steam down from the high-pressure mains to... 

While this basic definition of cogeneration efficiency seems straightforward, complications are created by the process steam generated from waste heat recovery that can be used for power generation or process heating and that does not require any fuel to be fired in the utility system. The heat supply can be defined as the sum of the heat from fuel (both in the utility boilers and fired heaters) and steam generation from the waste heat recovery (see Figure 23.44)17 ... 

Raffinate-II typically consists of40 % 1-butene, 40 % 2-butene and 20 % butane isomers. [RhH(CO)(TPPTS)3] does not catalyze the hydroformylation of internal olefins, neither their isomerization to terminal alkenes. It follows, that in addition to the 20 % butane in the feed, the 2-butene content will not react either. Following separation of the aqueous catalyts phase and the organic phase of aldehydes, the latter is freed from dissolved 2-butene and butane with a counter flow of synthesis gas. The crude aldehyde mixture is fractionated to yield n-valeraldehyde (95 %) and isovaleraldehyde (5 %) which are then oxidized to valeric add. Esters of n-valeric acid are used as lubricants. Unreacted butenes (mostly 2-butene) are hydroformylated and hydrogenated in a high pressure cobalt-catalyzed process to a mixture of isomeric amyl alcohols, while the remaining unreactive components (mostly butane) are used for power generation. Production of valeraldehydes was 12.000 t in 1995 [8] and was expected to increase later. 

Waste heat from farming, animal manure, crop production, and municipal solid residues could also be used for power generation. 

The idea for using diodes for generation and amplification of power at microwave frequencies was suggested by A. Uhlir, Jr. Frequency multipliers have been used for power generation since 1958. These devices depend on the nonlinear reactance or resistance characteristics of semiconductor diodes. Generally, there are three types of multiplier diodes—step recovety diodes, variable resistance multiplier diodes, and variable capacitance multiplier diodes. 

Coal forms about 60% of the global fossil fuel resources that are relatively evenly distributed around the world in more than 90 countries. The relative share of the coal consumption had a peak of 70% around 1900, but since then the relative importance has been on decline. Nowadays approximately % of the global fossil fuel consumption is by solids, from which 60 % is used for power generation. 

Armenia owns some 1800 km high-pressure gas transmission and approximately 9000 km gas distribution network. In 1990 Armenia consumed some 4.5 bcm of gas, which declined to 1.5 bcm p.a. (2000), of which more than 75% is used for power generation. 

This same report discusses the potential for additional requirements for liquid fuels due to a one or two year delay in completion of coal and nuclear plants. If electricity growth averages 5.6% per year compounded, an additional 1,041,000 BPD could be required if such a delay occurred. The experience of 1977 where liquid fuels were utilized to cope with the combination of a severe winter that curtailed natural gas supplies used for power generation and a coal strike demonstrate that liquid fuels can be quickly utilized to meet emergency situations. 

Some examples of the phenomenon of breakaway corrosion are encountered in nuclear reactors used for power generation. In some reactors carbon dioxide is used as a coolant. Mild steel is chosen for use in gas-cooled reactors at 400°C, steel containing chrominum... 

Most bulk coal transportation is by rail, with trucks used for local transport. For reasons of economics, most of the world s coal consumption is in power plants located nearby coal mines, which minimizes the necessity for long-distance transportation. More than 60 percent of the coal used for power generation worldwide is consumed within 50 km of the mine site. In the United States, the average distance that coal is shipped by rail is farther, at about 800 miles. That distance has increased in recent years owing to the move toward greater use of coals with lower sulfur content (found mainly in the West) to meet sulfur oxide emissions standards in plants located mainly in the South and the East. As coal is currently shipped over great distances in the United States,... 

While the Seebeck effect enables TE devices to be used for power generation, the Peltier effect allows them to be used for cooling. In Peltier effect devices, heat flows in the same direction as majority carriers. The appropriate metric for this apphcation is called the TE efficiency, t], which is simply the ratio between the load s power input and the net heat flowrate. Essentially, rj gives the fraction of Camot efficiency attainable... 

Figure 4.48. Schematic of a thermoelectric device, which may be used for power generation or refrigeration.

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