Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1984-05-14
1987-01-13
Schwartz, Larry I.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34 28, 34 35, 34182, 110228, F26B 304
Patent
active
046353798
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of drying primarily solid fuels, such as bark, forestry waste material and the like. The drying method, of course, can be used also for other materials.
The drying is carried out indirectly in known manner, i.e. saturated steam from the fuel is superheated indirectly in a heat exchanger by heat of a higher temperature. The steam driven off can thereafter be converted in a suitable way, for example to process steam, or be utilized in some other way.
On the market a developed system is available, at which drying energy is recovered as process steam. Said system implies that the fuel is atomized and dried in a steam flow, which is superheated in steps during its passage through the drying system. Subsequent to the drying process, the fuel is separated from the steam in a cyclone, whereafter the fuel normally is used for dust firing. The particle size is limited by the relatively short staying time of the fuel in the drying process.
The present invention has the object to be a further development of the "dust drying process" described and is intended to be applied in firing installations where particles exceeding in size those mentioned above can and should be used, for example at grate firing or in a fluidized bed.
The invention offers the advantage, that the fuel need not be finely ground and be cleaned thereby from solid impurities, as required at dust firing in order to prevent rapid wear of the grinding and drying equipment. A further advantage is the very low speed of the drying steam at its contact with the fuel, implying that the cyclone equipment, which is required at dust drying where the entire fuel amount at a high speed follows along with the drying steam through the installation, can be abandoned. Solid fuels can according to known art be dried indirectly to a high dry content and be combusted in powder state. At the drying process the entire fuel amount follows along with the drying steam through the heat exchangers and is thereafter separated in a cyclone. After separation, the powder normally is blown to a burner. Other types of firing, of course, are possible, but are rarely used because the fuel must be well atomized for obtaining a sufficient dry content. The particle size normally should be <5 mm when a high dry content should be obtainable, and .ltoreq.1 mm at dust drying. The atomization of fuel to the aforesaid particle size implies high requirements on machinery equipment. As solid domestic fuels, such as bark and forestry waste material, normally include great amounts of impurities, such as sand, stones and metal pieces, the fuel must be cleaned carefully prior to its grinding in order to prevent costly wear of grinding and drying equipment. Such equipment is expensive and, of course, requires corresponding maintenance.
At firing methods such as grate firing and fluidized bed, the requirement on the particle size of the fuel is entirely different from what is required in the aforesaid dust drier. Particles with substantially greater dimensions, up to 25-30 mm for fluidized bed and even greater for grate firing, can be used. The firing installations, besides, are relatively insensitive to impurities of the aforesaid kind. When the impurities follow along with the fuel into the boiler, they normally leave the boiler together with the ashes without causing much trouble.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a schematic view of the preferred embodiment for carrying out the process of the invention.
FIG. 2 is an enlarged schematic view taken along the length of the conveyor 6.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The present invention relates to a method of drying a fuel adapted for grate firing, fluidized bed and the like. Impurities following along with the fuel pass through the drier without causing damage thereon. The fuel is dried at overpressure and passed slowly on a belt of the type chain grate or the like through the drier. The water vapour driven off is utilized according to known art. The superheated drying steam i
REFERENCES:
patent: 2671968 (1954-03-01), Criner
patent: 2816372 (1957-12-01), Myers et al.
patent: 3783527 (1974-01-01), Driscoll et al.
patent: 4253825 (1981-03-01), Fasano
patent: 4290269 (1981-09-01), Hedstrom et al.
The Btab Drier-Swedish Paper Journal-Jun. 10, 1984.
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