US2918024A - Fuel burning method - Google Patents

Description

H. SEIDL FUEL BURNING METHOD Dec. 22, 1959 Filed Feb. 26, 1952 FIG.2

INVENTOR. .JZ/uef Jezdl ATTORNEY 2,918,024 Patented Dec. 22, 1959 FUEL BURNING METHOD l Hubert Seidl. Duisburg, Germany, assiguor to The Babcock & Wilcox Company, JerseyCity, NJ., a corporation of New Jersey' Application February 26, 1952, Serial No. 273,424

Claims priority, application Germany March 3, 1951 2 Claims. (4Cl. v110-28) The present invention relates to the gasification and combustion of ash-containing solid'fuels and especially to the accomplishment of such processes through the useof cyclone furnaces of the type disclosed,for example, in U.S. patent Bailey 2,357,301, issued September 5, 1944. rIn one form, therefore, a cyclone furnace is essentially a horizontally inclined cylinder of fluid cooled construction,

and is especially adapted to utilize a gas-yielding solid fuel, such as coal, which has been initially crushed or otherwise reduced to a relatively coarse granular condition so as to provide particle sizes of 1% and under, together with a proportion of dustlike particles known as fines In the operation of a cyclone furnace, as customarily practiced, the reduced fuel and 'the total combustion air are introduced tangentially so as to maintain a whirling stream of coal Vand air which is burned at temperatures above the ash fusion temperature. The yrelatively low fusing temperature of the ash released and the centrifugal effect thereon combine to form a lm or layer of molten ash or slag on the furnace walls, and particularly on the circumferential Wall areas. The lighter fuel particles mainly burn in suspension, whilethe heavier particles are thrown outwardly and caught on the slag layer which rapidly reaches an equilibrium thickness and, as additional ash is deposi-ted, the excess slag drains to a slag discharge opening adjacent the gas discharge end of the furnace. A vigorous scrubbing action takes place between the air and entrapped coal particles, resulting in extremely active combustion which is completed wholly within the cylindrical cyclone chamber. Accordingly, no additional air nee-d be supplied exteriorly of the chamber to complete the combustion of gases discharging from the furnace. v

As an alternative to the foregoing procedure, cyclon furnaces maybe operated with an air deficiency for the purpose of gasifying the fuel in such a manner as to pro- '50 duce a combustion gas consisting mainly of CO and H2, in addition to N2, which gas can be used as desired. In the case of coal of low gas content, therefore, which cannot be directly burned in a cyclone furnace, it is possible to Vgasify such a coal completely in a cyclone furnace 'at a high temperature.

According to the present invention, in order to render Ia cyclone furnace useful as a furnace device for both gasrich and gas-poor coals, that is, coals of high and low gas content, respectively, means are provided adjacent the cyclone furnace outlet whereby a regulable supply of quaternary air may be combined with the discharging gases. Such a means may desirably be arranged to include an annular channel or duct protected against oxidation, and formed with a circular row of nozzles through which air from the duct is blown in jets whose axes, as the generating elements of a' cone having its tip on the prolonged longitudinal axis of the cyclone chamber, penetrate into the current of gas issuing from -the cyclone out-V let. Thus, with means for providing' Quaternary air in suitable manner when required, a cyclone furnace can be operated either as a combustion chamber, with no quaternary air being supplied, or as a gasifying chamber, when the supply of secondary air is sharply throttled and, to compensate for the deficiency of secondary air, quaternary air is provided exteriorly of the chamber to support combustion of the issuing gases.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specication. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention has been illustrated and described.

Of the drawings:

Fig. 1 is a side elevation, in section, of part of a cyclone furnace installation including an embodiment of my invention; and

Fig. 2 is a front View, partly in section, along line 2 2 of Fig. l.

The drawings illustrate the invention as incorporatedv in a vapor generating unit having as its source of heat Aa plurality of cyclone furnaces 1, 2, 3 and 4 which are installed at the front of the unit as shown in Fig. 1, and

which are arranged in pairs at separate elevations as inf dicated more particularly in Fig. 2. The cyclone furnaces thus provide primary furnace chambers which open through suitable outlets directly into the gas inlet chamber A of a secondary furnace which forms an integral part of the vapor generator structure `and is dened by walls including fluid cooled tubes suitably connected into the fluid circulation system of the vapor generator. The chamber A has a slag outlet 61 formed in the bottom thereof and is separated from a radiation chamber B of the secondary furnace by a partition 55 and screen 54 formed by fluid cooled tubes. Each cyclone furnace is lsimilar in form and construction to furnaces disclosed in che aforesaid U.S. Patent 2,357,301, and thus comprises a circular-cylindrical housing formed of cooling tubes 5 suitably connected into the uid circulation system of the vapor generating unit, and lined with a refractory composition 6 on the inside and with an insulating composition 7 on the outside. All of the lluid cooled tubes ofthe secondary furnace and the cyclone furnaces are constructed and larranged so as to maintain a natural circulation of fluid therethrough between a lower drum 3@ and upper drums 32 and 35. Certain features disclosed in the copending application of Kerr et al., Serial No. 552,120, led August 31, 1944, now Patent No. 2,841,343, are also incorporated, as will later appear.

Each cyclone housing is extended outwardly and conically to form a tapered inlet section S into which the mixture consisting of granular fuel `and heated primary air under pressure'is introduced tangentially. The fuel lis taken from a bunker 9, for example, and is directed by means of screw conveyors 11 into separate pressure sealing feeders 12 and thence into primary air conduits 13 which lead from a main air conduit 14 and which open tangentially into the respective furnace inlet sections 8. Another current of air, derived from air conduit 14, and directed through conduit 15, is caused to enter each cylindrical housing 16 tangentially so as to provide a rotating core of tertiary air.

Secondary air, also from conduit 14, is directed through conduits 17 and introduced tangentially into each cy clone chamber at the cylindrical periphery of the charnber and in the same direction of rotation vas the entering primary air-fuel stream. Each secondary air conduit 17, at and adjacent its discharge end, is longitudinally partitioned so as to form a seriesvof nozzles 18 through which the secondary air is discharged into the furnace. All conduits 13, 15 and 17, for example, and individual nozzles 18, through which air, or an air-fuel mixture, is conducted to the furnace, are provided with suitable means, such as separately operable dampers, not shown, `for regulating and blocking fluid flow therethrough..

At the end adjacent the secondary furnace, each cyclone furnace is closed by a cooling tube Wall 19 arranged perpendicular to the horizontally inclined cylinder axis, in which wall there is provided a central circular outlet 21 through which all gaseous products derived from the fuel are discharged into the secondary furnace chamber A. At the periphery of wall 19, for the upper furnace 3, for example, an annular air manifold or header 23 is provided for the purpose of supplying air to nozzles 24 which are formed thereon, the manifold 23 having its entire inner periphery in contact with the tube-cooled cyclone wall 19 so as to be protected against oxidation as a result of exposure to hot furnace gases. Quaternary air may be supplied in regulable quantity to manifold 23 through conduit 25 which is connected as shown so as to receive air from the main air conduit 14. The manifold nozzles 24 are arranged in a circular row and formed about axes which are generatrices of a cone whose tip lies on the prolonged longitudinal axis of the corresponding cyclone furnace 3. As will be understood, provision is made whereby through suitable known devices, not shown, the supply of air to air nozzles 24 may be regulated, or entirely cut off, as desired.

In the lower portion of the peripheral Wall of furnace 3, directly adjacent the air manifold 23, there extends over a portion of the circumference a slag outlet,such as slot 26, through which the liquid slag drains directly into the secondary furnace 10, without interfering with the discharge of quaternary air through nozzles 24. In the embodiment illustrated, the lower cyclone furnace 1 is provided with a slag outlet 27 which may be formed in the end wall 19 since no air manifold 23 is included. As indicated in Fig. l, the end wall 19 of the lower primary furnace 1 lies in a plane with the inclined front wall 28 of the secondary furnace whereas the corresponding outlet end wall of the upper furnace 3 lies in an inclined plane which is voffset from the lower portion of wall 28 so as to provide space for the slag outlet 26. As will be noted, the furnace wall 28 is inclined forwardly toward the bottom and thus permits slag from each of the outlets to fall clear of the wall. In addition, a slag drip ledge 29 may be provided on wall 28 below each of the slag outlets 26 and 27 so as to minimize slag accumulation on the wall.

In a vapor generating unit of the construction described, each of the cyclone furnaces 1 to 4 may be operated in known manner at capacities sufficiently high sol that, despite the intensive wall cooling, a temperature is maintained within each furnace which is above the lmelting point of the slag. Furthermore, all cyclone furnaces 1 to 4 may be operated simultaneously or one or more may be operated, and the remaining furnaces or furnace allowed to remain idle.

When any one of the cyclone furnaces is operated in the customary manner, using a coal of high gas content,

vthe granular solid fuel is introduced with a stream of primary air tangentially into the fuel inlet section 8, while secondary air is supplied through nozzles 18, and tertiary air admitted axially of the primary air-fuel stream. Thus, the total air required for complete combustion of a gas-rich coal is available interiorly of the cyclone combustion chamber, and the resultant hot gases of combustion are discharged into the secondary furnace chamber A for further separation of slag, and thence into the adjoining chamber B for radiation of heat to lwall tubes associated therewith. However, when the fuel fed to the chamber is a low gas content coal, and total air is supplied as above described, the extent of fuel gasilication is insufficient to enable complete combustion to be effected within the cyclone furnace chamber.

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Temperatures within the furnace are therefore lower than when burning a coal/of high gas content and in consequence the slag iiow will ultimately cease and the furnace will come to a stoppage.

However, when a gas-poor fuel is fed to the furnace in a stream of primary air, and tertiary air is added if necessary, and secondary air is added only in small measure or not at all, then the fuel will gasify within the furnace at a high temperature and the slag will remain liquid and drain from the chamber. As a result of such gasification, a combustible gas, consisting predominantly of nitrogen and carbon monoxide will then discharge through the outlet 21. In order to supply the proportion of air lacking for complete combustion, a supply, of quaternary air is provided and directed through nozzles Z4 into the stream of gas issuing from outlet 21.

Since solid fuels have different gas contents, it will not always be possible to carry out this mode of operation on the basis that in one case, the combustion is completed within the furnace and that, in another case, only gasification takes place within the furnace and that combustion is effected only exteriorly of the furnace. Intermediate conditions will undoubtedly occur in which gasifying and burning must in part be effected in the cyclone chamber and secondary combustion -must be effected in chamber A by the addition of quaternary air from nozzles 24. The simplest guide for regulating the addition of combustion air is to maintain cyclone furnace temperatures at a minimum of about 15500-1600 C., for example, so as to exceed the ash fusion temperature of -the fuel. If desired, the regulation may be effected automatically so that upon cyclone furnace temperatures falling below a predetermined desirable minimum, a temperature responsive apparatus will cause the supply of air to the secondary air nozzles 18 to be reduced and the supply of quaternary air to nozzles 24 to be increased. The return to a selected permanent condition, for example, the desired outlet gas temperature or CO2-content, may suitably be effected by the steam pressure, orlsteam temperature, or by the air pressure itself.

For the gasification of a particular fuel, instead Vof introducing the fuel directly into any one of the cyclone furnaces 1 to 4, it may be advantageous to preheat and preheat the fuel in a pregasiier, similarly in the form of a cyclone furnace, and discharging to one or more of the cyclone furnaces 1 to 4. If a fuel very diflicult to gasify is to be used, the gasification can be supported by using a nitrogen-poor air (as for example by oxygen enrichment) as the primary or secondary air. l

Since for partial-load operation also there must be maintained a predetermined furnace temperature which is sufficiently above the fusion temperature of the slag, partial load operation of a cyclone furnace is permissible only for a limited period. The vapor generator can nevertheless be operated at any desired partial load if a relatively large number of cyclone furnaces are employed so that heating gases are continuously available from at least one cyclone furnace operating alone at full load capacity. The secondary furnace chamber A is so dimensioned that the slag received therein will also remain liquid during partial load operation of the total cyclone furnace firing means.

When a plurality of cyclone furnaces are employed. it is advantageous to arrange the furnaces in successive vertical rows. Thus, with an upper cyclone furnace in one vertical row operating as a gasifying chamber, and a lower cyclone furnace in the same row operating as a combustion chamber, the hot gas stream issuing from the lower furnace serves as a pilot for igniting the gasair stream issuing from the upper furnace, and vice versa. An example of such an arrangement is illustrated in Fig. 2, wherein the lower cyclone furnace 1, in one vertical row, is arranged to operate as a combustion chamber, and the upper cyclone furnace 3, in the same vertical row, is arranged to operate as a gasifying chamber. In the adjacent vertical row, the upper cyclone furnace 4 is arranged to operate as a combustion charnber, while the lower cyclone furnace 2 is arranged to operate as a gasifying chamber. Alternatively however, both furnaces 1 and 4 which are operable either as cornbustion chambers or gasifying chambers may occupy one row at one elevation, and the other furnaces 2 and 3 which are normally operated only as combustion chambers may occupy a second row at a different elevation.

When operating entirely with gasified solid fuel as described, the size of radiation chamber B may be made somewhat smaller, or convection heating surface may be provided by spaced liuid conducting tubes arranged across an upper portion of the chamber. The almost complete separation of molten slag in the cyclone chamber or chambers makes this last named arrangement appear applicable also to cyclone furnace fired units when the combustion of fuel is substantially completed within the respective cyclone furnaces.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from .the spirit of the invention covered by my claims, and that certain featutres of the invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

l. The method of burning an ash containing solid fuel of relatively low gas yielding properties which comprises continuously introducing a stream of air and said fuel in suspension at a high velocity into a substantially cylindrical chamber of generally horizontal arrangement so as to move at a high velocity along the circumferential wall thereof in a continuous helical path throughout the length of the chamber while maintaining a mean temperature therein above the fuel ash fusion temperature, introducing additional air tangentially into said chamber at a location between the point of entry of the airfuel stream at one end of the chamber and the chamber gas outlet at the opposite end of the chamber, said additional air being introduced in an amount sufficient to promote gasification of the fuel and less than the amount required to complete combustion of said fuel within the chamber, causing the fuel and air so introduced to move axially of the furnace chamber through said helical path which is of sufficient length to result in gasification of said fuel and the release within said chamber of substantially all of the recoverable ash in the fuel and the deposition of slag on wall areas of the chamber, causing the resulting furnace gases to be reversed in their direction of axial movement in an annular pocket surrounding said gas outlet prior to discharge from said chamber through said gas outlet, causing the ash separated in said chamber to be discharged from a lower portion of said pocket in molten condition, and causing air to be mingled with the discharging gases in an amount sucient to complete the combustion thereof exteriorly of said chamber. 2. In the production of a common body of heating gases from solid fuels of different gas yielding properties, one of said fuels having a relatively high gas content and a second fuel having a relatively low gas content, introducing each of said fuels in suspension in a stream of primary air into a separate substantially cylindrical chamber of substantially horizontal arrangement so as to move throughout its total length at a high velocity along the circumferential wall thereof while maintaining a mean temperature therein above the fuel ash fusion temperature, introducing additional air tangentially into each of said chambers at a location between the point of entry of the air-fuel stream adjacent one end of each chamber and the chamber gas outletrat the opposite end, said additional air being introduced into one of said chambers in an amount sufficient to complete combustion of the fuel of relative high gas content thereing, said additional air being introduced into the other of said chambers in an amount sufficient to promote gasication of the fuel of relatively low gas content therein and less than the amount required to complete combustion of said low-gas-content fuel, causing the fuel and air so introduced to move axially of the respective furnace chambers through helical paths along the circumferential walls thereof to cause combustion of said high-gas-content fuel in said one chamber and to cause gasification of said low-gas-content fuel in said other chamber, causing the resulting furnace gases to discharge from said chambers through the respective gas outlets in separate streams, causing the ash separated in each of said chambers to be discharged from a lower portion thereof in molten condition, directing air into the discharging stream of gases resulting from the gasiication of said low-gas-content fuel in jets circumferentally distributed about the discharging stream and in an amount sufficient to complete the combustion thereof, and causing said streams of combustion gases to combine to form said common body of heating gases.

References Cited in the file of this patent UNITED STATES PATENTS 867,177 Welles Sept. 24, 1907 1,617,694 Schwartz Feb. 15, 1927 1,849,095 Keenan Mar. 15, 1932 1,910,735 Zikesch May 23, 1933 1,943,286 Burg Jan. 16, 1934 1,982,803 Greenawalt Dec. 4, 1934 2,029,725 Kuhner Feb. 4, 1936 2,357,301 Bailey et al. Sept. 5, 1944 2,368,827 Hanson et al. Feb. 6, 1945 FOREIGN PATENTS 270,295 Great Britain Ian. 5, 1928 302,255 Great Britain Dec. 11, 1928 675,113 Germany Apr. 28, 1939

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