US 3260227 A
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United States Patent 3,260,227 SYSTEM FOR DRYING AND BURNING WET COAL Ernest L. Daman, Westfield, N.J., and Gilbert C. Whitney,
Jr., Dansviile, N.Y., assignors to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Filed Aug. 24, 1964, Ser. No. 391,576 6 Claims. (Cl. 110-7) This invention relates to coal burning furnaces. In particular, it relates to an apparatus for burning slurry mixtures of coal and water.
Flowing slurry mixtures of coal and water have been used to transport coal through pipe lines from the coal mines to the ultimate plant consumer. Conventional coal burners may be used to burn the coal in slurry mixtures, but they require that the coal be dried for optimum operation. The present methods for drying of slurry mixtures of coal and water for burning by conventional burners have necessitated expensive drying equipment and costly procedures. One method that has been used for drying slurry mixtures was to pass the slurry mixture through vacuum filters to remove the water and then to pass the dried product through a fired heater stack for further drying. In this method, huge thermal losses and an uneconomical operation were experienced.
Therefore, it is an object of the present invention to provide an economical method and apparatus for drying a slurry mixture of coal and water.
In particular, it is an object of the present invention to provide a method and apparatus by which a slurry mixture of coal and water can be dried with hot furnace gases.
In accordance with the present invention, there is provided a hot gas passageway communicating with the interior of a furnace, hot gases passing from the furnace into the passageway. A slurry mixture is injected into the passageway as a spray and is dried by the hot gases. A gas recirculation fan in the passageway draws the hot gases from the furnace into the passageway and propels the injected slurry and coal as it is being dried to a conventional coal burner.
The slurry mixture is spray injected into the passageway by means of an atomizer to provide greater surface area and to promote the evaporation of the slurry water content therein. The slurry also is injected into the passageway upstream of the gas recirculation fan at a point sufiiciently removed from the fan to temper and cool the hot gases before they reach the fan, thereby, protecting the fan. However, to avoid accumulation of coal on the passageway walls, the slurry preferably is injected within the fan suction.
A cool air channel may also be provided which communicates with the hot gas passageway for tempering the gas on the upstream side of the recirculation fan and for providing additional temperature-control for the drying operation and preventing damage to the passageway. The amount of cool air introduced into the gas recirculated may be made responsive to the temperature of the mixture of the air, fuel and gas downstream of the fan to avoid overheating of the fan.
By cooling the hot gases before they pass through the fan, relatively inexpensive power requirements for the fan and less exotic and expensive fan materials are required. Other advantages will be apparent from a reading of the following description and accompanying drawing in which:
There is shown a system and apparatus for recycle of furnace gas for slurry drying and burning in accordance with the present invention.
Referring now to the drawing, a passageway 11 is pro- 3,260,227 Patented July 12, 1966 vided which communicates with the interior of a furnace 20 for receiving hot furnace gases in the range of 2000 F. and higher which are drawn into the passageway by a fan 13 provided in the passageway. Coal mixed with water in slurry tank 8 is injected by pump 1 into the passageway at a position intermediate to the fan 13 and the hot gas passageway entrance 25. The pump 1 causes the slurry to be pumped into conduit 2 from which it is transported via slurry tube 24 into throat 6 of spray nozzle 4 located in the passageway 11 between the fan and the hot gas passageway entrance 25. High pressure air supply conduit 3 transports air under high pressure from a high pressure air supply (not shown) via annular chamber 23. The chamber 23 communicates with circularly symmetric nozzle jets 26, the latter opening into frustoconical section 7. The openings for the jets are equally spaced preferably defining a circle adjacent the narrowmost portion of frustoconical section 7 for causing the slurry passing into the section from throat 6 to become atomized and dispersed on entering passageway 11.
Further details of the spray nozzle are described in co-pending application, Serial No. 391,566 filed August 24, 1964, by'Gilbert C. Whitney, Jr., Ernest L. Daman, and Jay L. Clark, and entitled Slurry Burner. Preferably, the jets 26 are oriented to direct pressurized air into the frustoconical section 7 in three vectorial components. One component is tangential to the circle formed by the jet openings in the frustoconical section 7. The second component is in a direction parallel to the axis of the frustoconical section, and the third component is radial to the axis of the frustoconical section. Together they cause a helical swirling air movement within the area bounded by the section 7 to cause the coal passing through throat 6 to enter the passageway 11 as an atomized spray. The wet coal exiting from throat 6 is caught up in this swirling air movement becoming dispersed and spray atomized.
Although nozzle 4 has been described as a particular type of nozzle which has been found satisfactory to cause the spray atomization required for the proper functioning of the present invention, it should be noted that any type of atomization device may be utilized without departing from the scope and spirit of the present invention.
The atomized slurry provides a large surface area so that the hot furnace gases in passageway 11 evaporate the moisture content in the slurry. Furthermore, the hot gases drawn from the furnace into the passageway are tempered by the cooler slurry mixture between the fan 13 and the hot passageway entrance 25 to about 200 F. for preventing damage to the passageway and fan by the hot gases. Cool air from air box 16, cont-rolled by butterfly valve 18 in channel 12 may also be used to reduce the temperature of the mixture in the fan 13.
As the slurry is being dried in the passageway, fan 13 draws the slurry around baffle 9 disposed immediately adjacent the fan i-nlet causing the slurry mixture to flow over the bafiie edges in a tortuous path before entering the fan, and transports it via downstream conduit 14 to burner chamber 15 in communication with a conventional coal burner 21 wherein the dried coal is burned.
The atomizer 4 as shown injects the slurry mixture into the gas passageway 11 in a direction counter to the hot gas flow. As would be clear to those skilled in the art, the atomizer could also inject the slurry in the same direction with the gas flow, depending on various factors, such as the distance of the nozzle from the fan, the fan suction, the temperature of the gases, nozzle construction, etc. However, the nozzle may not be readily di rected toward the passageway walls since deposition of the coal slurry and clogging of the passageway walls could occur.
Passageway 11 may communicate with hot gas portions of the boiler gas passage, other than the furnace portion, where suitable temperatures are available for drying the slurry, without departing from the present invention. Where the slurry mixture contains some relatively coarse pulverized coal particles, the dried coarse coal may be conveyed to a pulverizer for further grinding after passage through the fan as would be apparent to those skilled in the art, or the coarse coal may be directly fired by the burner, without being further pulverized, by the addition of an undulating slag Wall disposed in the path of the burner flame. The wall functions to capture coarse coal causing a prolonged burning thereon as further described in co-pending patent application entitled Fly Ash Entrapment Wall, Serial No. 125,245, filed July 19, 1961.
Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.
What is claimed is:
1. A system for drying a slurry of coal and water with furnace combustion gases comprising,
conduit walls defining a gas conduit having a conduit inlet end adapted to receive combustion gases and a conduit outlet end,
a coal burner in communication with the conduit outlet end,
a fan disposed in the conduit at a position remote from the conduit inlet end, the fan establishing a fan suction region adjacent the fan extending upstream thereof for drawing hot combustion gases through the conduit,
atomizer means for supplying a slurry under pressure into the conduit for mixture with the combustion gases, said atomizer means including an atomizer disposed in the conduit in the fan suction region and oriented to direct the slurry into the conduit in a direction opposite to the flow of the combustion gases through the conduit,
bafide means disposed in the conduit between said atomizer and said fan immediately adjacent the fan for causing the mixture to flow through a tortuous path adjacent thereto,
a cooling channel communicating with the gas conduit upstream of said bafl le means adjacent the atomizer for attemperating the combustion gases,
a valve located within said cooling channel to control the degree of attemperation.
2. A system for drying a slurry of coal and water, according to claim 1, the burner further comprising a burner wind box, said cooling channel further in communication with said wind box for passing cool air from the wind box to the gas conduit.
3. A system for drying a slurry of coal and Water according to claim 2, wherein the baffie means comprises a plate, said plate disposed in the conduit perpendicular to the conduit walls in spaced relationship from said conduit walls.
4. A system for drying a slurry of coal and water according to claim 3, wherein said plate is axially connected to said fan.
5. A system for drying a slurry of coal and water according to claim 4, wherein said conduit includes an enlarged width portion adjacent said plate.
6. A system for combustion of a slurry of coal and water, comprising,
a furnace having an interior,
a coal burner having a flame burning end in communication with the interior of the furnace for burning a fuel in the furnace, said burner further including a fuel intake end and a burner wind box for supplying fuel and air, respectively, to the flame burning end,
conduit walls defining a gas conduit having a conduit inlet end in communication with the interior of the furnace adapted to receive combustion gases from the furnace and an outlet end in communication with the fuel intake end of the burner,
a fan disposed in the conduit at a position remote from the conduit inlet end, said fan establishing a fan suction region adjacent the fan extending upstream thereof for drawing the combustion gases through the conduit,
atomizer means for injecting a slurry under pressure into the conduit for mixture with the combustion gases, said atomizer means including an atomizer disposed in the conduit in the fan suction region and oriented to direct the slurry into the conduit in a direction opposite to the flow of the combustion gases through the conduit, said atomizer containing nozzle openings therein adapted to inject the slurry into the conduit in the form of a fine spray,
a bafiie plate disposed in the conduit between said atomizer and said fan immediately adjacent the fan and connected axial-1y thereto, the bafile disposed perpendicular to the conduit walls in spaced relationship from said walls for causing the mixture to flow through a tortuous path adjacent the baffle,
a cooling channel having two ends, one end in communication with the gas conduit at a point upstream of the circulating means, the other end connected to said Wind box, to pass cool air from the wind box to the conduit to attemperate the combustion gases,
a butterfly valve. in the cooling channel to control the degree of attemperation.
References Cited by the Examiner UNITED STATES PATENTS 2,148,447 2/1939 Dundas et a1. 110l5 2,535,730 12/1950 Gadret 1l07 X 2,648,950 8/1953 Miller 110-28 X 3,043,525 7/1962 Gilbert 110106 X 3,053,615 9/1962 Steinert. 3,124,086 3/1964 Sage et al 110-7 CHARLES J. MYHRE, Primary Examiner.