US2101423A - Furnace - Google Patents

Description

Dec. 7, 37. s E 2,101,423

FURNACE Filed June 26, 1935 Patented Dec. 7, 1937 UNITED STATES PATENT OFFICE Application June 26,

1935, Serial No. 28,515

In Austria and Czechoslovakia April 20, 1935 2 Claims.

My invention relates to furnaces and more particularly to furnaces operated with highly volatile low-class fuels, such as lignite, which are equipped with a charging duct.

Among the furnaces which have been designed for the most complete combustion of such fuels, those equipped with a charging duct and a combustion chamber are comparatively cheap and small and well adapted for their purpose. In the charging duct the fuel is heated and the grate is supplied gradually, while in the combustion chamber the flame develops freely, which is very important in highly volatile fuels, and the gases of combustion are easily conducted away.

Notwithstanding its favorable features this furnace which will be briefly referred to as the twoduct furnace is not altogether satisfactory. It was hitherto believed that high temperature was indispensable for complete combustion and that the gases must not come in contact with cold walls. Therefore everything was done to produce high temperature in the combustion zone. More particularly the walls of the furnace were lined with heat insulating material such as fireclay. This involved a large size of the furnace, high cost, an inferior efficiency and the possibility that cold air might enter the furnace.

I have found that it is not necessary to make the furnace large, and that complete gasification of highly volatile fuel may be effected at a comparatively low temperature, preferably below 600 C. It is an object of my invention to design a furnace in which such combustion can be performed.

To this end I provide in the furnace charging ducts in which the fuel descends, means for admitting combustion air to the ducts and means positioned in the region of the air-admitting means for increasing the descending velocity of 10 the fuel in the duct by restricting the free sectional area of each charging duct to not more than 25% of the area of the grate, the said charging ducts being arranged between cooling chamhers.

In this manner the velocity of descent is made equal to the velocity at which the combustion of the fuel is propagated in upward direction.

In the drawing affixed to this specification and forming part thereof a furnace for sectional boilers, embodying my invention is illustrated diagrammatically by way of example.

In the drawing Fig. 1 is an elevation of a boiler unit designed for a sectional boiler and modified in accordance with my invention,

Fig. 2 is a section on the line 2-2 in Fig. 1.

In these figures the adaptation of my invention to a boiler with a central combustion chamber is shown. In such boilers each unit is built up from two sections (12 and as, and in the boilers as heretofore designed, the two sections were similar and both designed like section as, with a substantially vertical rib 6 defining one side of the combustion chamber 15, and a vertical baflie b1 extending upwardly from the grate e and subdividing the space into two flues c1 and C2. The combustion chamber if made up by the two ribs 6 was charged with coke from above.

In a boiler according to my invention the sections as are not modified, but the sections a2 are equipped with charging ducts d formed by ribs l and 8, and the vanes h are provided at the lower end of rib 8, above a horizontal portion (21 of the grate e. 9 is a charging hopper at the top of the charging ducts d. As shown for three sections 002 in Fig. 2, charging ducts d alternate with water chambers f. The grate is shown as comprising one horizontal portion 61 at the side of section (12, and another horizontal portion e below the combustion chamber t, with an inclined portion connecting the two horizontal portions. Preferably the bars of the grate portions are hollow and cast integral with the water chambers ,f. The water chambers extend not only above, but also below the grates in this boiler and this effectively prevents caking of the fuel.

The furnace illustrated can be operated with highly volatile fuel without a fore-hearth, and the extra space such hearth occupies, is therefore dispensed with. Only the patterns for casting the sections :12 require alteration by removing the rib b1 and a portion of the rib B, and replacing them by the ribs 1 and 8, the vanes h, and the corresponding grate portions. The sections as remain as they are.

The fuel from hopper 9 is conducted to the combustion chamber 2? through the individual ducts d. The free sectional area of each charging duct d is reduced above the incandescent fuel bed at m, or at least at m, as and for the purpose specified. The gases produced from the descending fuel by low-temperature distillation and the still unconsumed particles of fuel flow towards the grate e. Combustion is completed in the chamber 15, and the waste gases flow to the chimney, as indicated by the arrows.

As mentioned above, it is an object of my invention to dispense with large-sized furnaces and with combustion at high temperature and to cffect complete combustion in a small and unlined furnace at comparatively low temperature.

In order to effect a complete and smokeless combustion of the gases which are ignited at various temperatures, the combustion must be performed under such conditions that the gases are completely burned, including those gases which are the most difiicultly inflammable. A difficultly inflammable product is, for instance, tar vapor, a low-temperature distillation product of the bitumen in the coal, and one of the principal causes of smoke and incomplete combustion.

The composition of the gases formed when the fuel is heated, depends on various factors, among which are the temperature of degasification and the quantity of air which is admitted. By varying the factors, the composition of the gases can be so determined that they are completely burnt at low temperature and in short time. My invention is based on the knowledge that gases mixed with a sufficient quantity of air, produced at low temperature and conducted through a layer of glowing fuel, have a chemical composition such that they will be burnt in a furnace which is much smaller, and at a much lower temperature, than in existing furnaces, with a completeness heretofore not attained, and without developing smoke.

The problem of reducing my invention to practice in'a two-duct furnace is by no means an easy one. In the charging ducts d the fuel is stored and heated before and during its downward movement. The rate at which the fuel descends, is a function of the quantity of fuel consumed on the grate e. If, with the object of performing the above-said degasification at low temperature while air is admitted, the quantity admitted through h is such as to effect complete combustion, the fuel in the charging ducts d burns rapidly in upward direction, asit hasbeen heated, and an abrupt and intense gas production will be the consequence. This often occurs in the old two-duct furnaces.

Such intense gas production, on the one hand, is contrary to the condition that the degasification of the highly volatile fuels should be gradual, and, on the other hand, the temperature at which the fuel burns rapidly in upward direction, is high, not low, as it should be for the degasification performed according to my invention.

In order to obtain complete combustion at low temperature the abrupt upward burning of the fuel in the charging ducts d must be prevented While at the same time a sufiicient quantity of air is admitted to the duct. 7

This is effected by the means described, i. e., b increasing the velocity at which the fuel descends in the ducts 12, through the medium of a restriction of the sectional area of the duct d above the hot fuel bed on the grate e, at least where air is admitted through h, so that the velocity of descent is increased by the restriction. The velocity-of descent should be equal to the velocity of burning. By these means fresh particles reach the air inlet h from the lower end of the fuel column in the charging ducts d in more rapid succession than heretofore, and there is no intense and thorough heating of the fuel in the ducts d. At this higher velocity of descent the required quantity of air can be admitted to the charging ducts d throughh without any risk of abrupt burning of the fuel in the duct. In other words, according to my invention the rapid upward. burning. at. high. temperature replaced by degasification at low temperature, preferably below 600.

Since the rate at which a given fuel burns upwards in the charging ducts d is known or can easily be ascertained, the restriction of the free sectional area of the ducts d at h, or at least at h, as the duct may also be restricted elsewhere, if desired, is determined by the ratio of the velocities of descent and burning. The quantity of fuel charged into the charging ducts d to make up for the fuel consumed on the grate, is determined by. the grate area. It has been found that the descending and burning velocities are equal for average fuels and for normal draft in the furnace, if the restriction at the air inlet 11. of each individual charging duct d is at most of the grate area.

As described above, that portion of the charging duct which is above the incandescent bed of fuel, is bordered at its outer side by air inlet means such as a vertical or inclined wall having air inlet openings or the vanes it making up a vertical or inclined grid. At its opposite or inner side it is bordered by a substantially unbroken wall made up by the ribs, by which the gases produced upon degasification are compelled to flow through the incandescent fuel bed, instead of flowing directly to the combustion chamber t. Since, however, degasification is effected at comparatively low temperature, this wall is made of a good conductor of heat and cooled by the water in the water chambers 1 instead of the walls of fire clay heretofore provided which are too thick and favor upward burning.

This novel type of furnace presents several advantages over the existing two-duct furnace. Firstly it is muchsmaller; secondly it is not necessary to provide' an extra system of pipes for connecting the unbroken, water-cooled metal wall to the circulation of the boiler, and thirdly the assembly provides a much better utilization of radiated heat and a considerable reduction in the cost of manufacture.

In sectional boilers for highly volatile fuels the individual units were heretofore lined with insulating material, such as fireclay, to avoid cooling of the gases to a temperature below the proper one by direct heat exchange with cold metal walls. In a boiler according to my invention such precaution is unnecessary since the gases are immediately admitted to the incandescent bed of fuel on the grate e, and are not cooled to any appreciable extent by the portions of the water chambers 1.

As all charging ducts d open together into the central chamber t, which is a combustion chamber exclusively, a forehearth is dispensed with, as mentioned above, and the size of the plant and its manufacturing cost are reduced. I wish it to be understood that I do not desire to be limited to the exactdetails of construction shown and described for obvious modifications will occur to a person skilled in the art.

I claim:-

1. ma furnace in combination, a grate, charging ducts for supplying fuel to said grate from above, means for admitting combustion air' to the fuel in each charging duct above the incandescent layer of fuel on the grate, means positioned in each charging duct and in the region of the airadmitting means for restricting the free sectional area of each charging duct to not more than of the area of said grate, and coolingchambers inserted between said charging ducts said charging ducts being delimitedby the walls of the cooling chambers and by walls branched 01f the cooling chamber walls and extending between adjoining cooling chambers.

2. In a furnace for sectional boilers in combination, units making up the boiler and defining a combustion chamber extending along the boiler, a grate at the bottom of said combustion chamber, charging ducts defined by said units for supplying fuel to said grate from above, means for 10 admitting combustion air to the fuel in each charging duct above the incandescent layer of fuel on the grate, means positioned in each charging duct and in the region of the air-admitting means for restricting the free sectional area of each charging duct to not more than 25% of the area of said grate, and cooling chambers defined by said units and alternating with said charging ducts.

STEFAN BECK.

Images