Furnaces – Process
Patent
1986-04-14
1988-01-05
Yuen, Henry C.
Furnaces
Process
110229, 110347, F23B 700, F23G 500
Patent
active
047168447
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and device by which fossil fuels may be converted nearly nitric oxide-free into heat and transferred in a steam generator into the water or steam.
2. Description of the Prior Art
In the field of steam generator construction, steam generators heated with fossil fuels are normally equipped with a fire chamber in which the fossil fuel, which may be coal, oil or gas, is burned in a flame.
Said combustion produces at least locally temperatures which are close to the theoretical combustion temperature. Said temperatures are above the kinetic temperature for forming nitric oxides of 1300 centigrade.
This produces varying concentrations of nitric oxide in the off-gas depending on the firing principle, which may be a cyclone firing or front firing system, a combustion chamber with an elongated flame or also a fluidized bed-type firing system; however, more or less large combustion zones with nearly stoichiometric mixture formation and with a clearly notable formation of nitric oxide will always occur locally.
Now, the objective of the invention is to create at all sites or in all locations of the steam generator system conditions such that no formation of nitric oxide is possible. This requires creating in all locations conditions of such a type that the nitric oxide formation temperature of 1300.degree. C. is not exceeded in an oxidizing atmosphere.
SUMMARY OF THE INVENTION
This is not possible in a flame combustion. For this reason, the combustion takes place flamelessly in excess air in a ceramic system, or catalytically, if need be.
A gasification step with subsequent cooling of the gases produced in said step is preconnected to the flameless combustion in the ceramic system. Said gasification stage consists of a ceramically insulated combustion chamber, preferably a cyclone combustion chamber, which converts the fuel used, for example coal, with a partial stream of air into a fuel gas with a low caloric value.
Thus the conversion of the fossil fuel in the first stage is a partial oxidation. When adding about 45 to 70% of the theoretic amount of air for the combustion, approximately 35 to 55% of the combustion heat is generated in said first stage because a portion of the combustion heat so generated is consumed by the heat-consuming reactions.
The gasification temperature adjusts itself to about 1500.degree. to 1900.degree. C. The high gasification temperature permits on the one hand the discharge of the slags in the liquid state; on the other hand, the reaction is accelerated in such a way that a relatively complete reaction of the coal or solids-containing oils is assured.
A precondition for said high temperature is the well-insulating ceramic lining of the combustion chamber, for example with wear-resisting and insulating ceramic materials such as silicon nitrite and silicon carbide
The formation of the liquid ash is additionally promoted by the fact that in the reducing atmosphere of the gasification stage, the ash particles remain liquid for a longer period at lower temperatures, which means that the lower temperatures found in smaller plants and in the initial phase will suffice to achieve a liquid ash discharge.
However, said lower ash melting point of the 1st stage means that the fission gas has to be cooled in the injection space to lower temperatures before entering the contact heating surface areas. Said temperature is about 900.degree. C. without additives in the coal, and up to about 1050.degree. C. with additives added to the coal.
For achieving said high gasification temperature or temperature of partial oxidation, it is necessary, furthermore, to preheat the combustion air to a relatively high temperature ranging between 300.degree. and 700.degree. C. Said preheating takes place in the heat exchangers or air heater, which are connected after the oxidation stages.
The heat exchangers connected downstream of the oxidation stages contain not only the air heater, but also heating surfaces for heating the wa
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patent: 3818869 (1974-06-01), Blaskowski
patent: 4290269 (1981-09-01), Hedstrom et al.
patent: 4336769 (1982-06-01), Daman
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patent: 4430094 (1984-02-01), Gorzegno
patent: 4437416 (1984-03-01), Ishii et al.
patent: 4558651 (1985-12-01), Ying et al.
patent: 4602573 (1986-07-01), Tanca
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