Liquid heaters and vaporizers – Plants – Feed water heaters
Patent
1995-02-03
1997-11-18
Sollecito, John M.
Liquid heaters and vaporizers
Plants
Feed water heaters
122 1C, 122420, 122421, 122DIG7, 110234, E22B 3300
Patent
active
056876742
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention describes a steam power plant for generating electric power which has a fossil-fuelled boiler, a water-steam cycle for generating high-tension, superheated steam for a steam turbine, an economizer to transmit flue gas heat to the feed-water, an air preheater to transmit flue gas heat to fresh air and devices for removing dust, sulphur and possibly nitrogen from the flue gases.
In steam power plants which are operated with fossil fuels, i.e. gaseous, fluid or solid fuels, the heat flux capacities (mass flow rate x specific heat capacity) of the flue gas which is to be cooled and the fresh air which is to be heated (combustion air) are different so that there is a temperature difference of up to 90.degree. C. at the cold end of the heat exchanger with a customary temperature difference between flue gas and fresh air of approximately 30.degree. C. at the warm end of the air preheater. These high differences in temperature result in corresponding energy losses and have a corresponding negative effect on the overall efficiency of the power plant.
Another disadvantage is that in power plants which are not equipped to further use the residual heat which is still at a relatively high temperature level in the flue gas which leaves the air preheater, be it through reheating the cleaned flue gas before it enters the chimney or be it through decoupling the heat for long-distance energy use, the residual heat is destroyed in the flue gas desulphurizing plant. The result is another decrease in the power plant's overall efficiency.
Another factor is that the start-up process in the known steam power plants described in the introduction is not advantageous. For example, before coal can be burnt in a coal-fuelled plant, considerable amounts of expensive auxiliary combustibles such as oil or gas must be burned in the boiler before the coal can be burnt until the parts of the plant--for example the mills for the lignite pulverizer dryer of the coal, the catalytic nitrogen removal reactor and the air preheater with its large regenerative heat accumulator masses, which must be heated with the help of the flue gas heat--reach their required minimum operating temperatures. Furthermore, the steam which is produced during the start-up but also during the shut down phase generally is precipitated in the capacitor of the steam power plant without utilizing the heat.
The invention was charged with reducing the loss of energy in a power plant as described in the introduction, to better utilize the heat of the flue gas and to make the start-up process more economical overall by using less oil or gas and by better utilizing the steam which is generated during the start-up phase.
SUMMARY OF THE INVENTION
This task is solved in accordance with the invention through a steam power plant which is characterized in that it has a first heat exchanger system with sections through which recirculated air and a heat vehicle medium flow and in which the section carrying the air is connected on the intake side to the fresh-air outlet of the air preheater and on the outlet side to the fresh-air intake of the air preheater.
Compared to the state of the art, the measures proposed in accordance with the invention result in a clear reduction of energy losses in the air preheater, in a considerably improved utilization of the heat which is contained in the flue gas, and therefore in a marked increase of the overall efficiency of such a steam power plant.
The recirculation air stream of the first heat exchanger system which is superimposed to the fresh air in the area of the air preheater makes it possible to almost completely align the heat flux capacities in the two heat exchanger sections of the air preheater. The result is that there are low temperature differences at the warm, as well as at the cold end, and correspondingly reduced energy losses. Some of the flue gas heat which is released in the air preheater which was transmitted to relatively cold fresh air in the customary design is now directly coupled
REFERENCES:
patent: 4319458 (1982-03-01), Berkley
patent: 5293841 (1994-03-01), Suhr et al.
Johanntgen Uwe
Marx Franz Josef
Creighton Wray James
Gravini Steve
Saarbergwerke Aktiengesellschaft
Sollecito John M.
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