GB2079915A

GB2079915A - Solids drier

Info

Publication number: GB2079915A
Application number: GB8118580A
Authority: GB
Original assignee: Wormser Engineering Inc
Current assignee: Wormser Engineering Inc
Priority date: 1979-04-20
Filing date: 1980-04-18
Publication date: 1982-01-27
Also published as: DE3015232A1; GB2074890A; FR2468832A1; DE3015232C2; FR2454581A1; CA1174905A; AU542456B2; FR2485178A1; NO801111L; GB2049134B; GB2074890B; GB2049134A; AU5751480A; DE3050901C2

Abstract

An apparatus (340) for drying solid material comprises a trough (350), an agitator preferably having bars (354) supported by two wheels (353) rotatable about shaft (352), a hot air duct (358) and a perforated distributor plate (359). The material enters the drier down chute (341), is contacted by the hot air in the trough (350), and leaves over lip (362). The material may be coal, which is dried and crushed before being fed by air blast (376) through a pipe (374) to a fluidized bed combustor. Coarse lumps of coal are removed from the trough (350) by pins (356) on the bars (354). Fines remaining in the trough (350) are dried there in a fluidized state. <IMAGE>

Description

1

GB 2 079 915 A 1

SPECIFICATION Solids drier

The present invention relates to a solids drier.

The drier is particularly, although not 5 exclusively, adapted to dry coal for supply to a coal burner. The burner may especially be a combustor-desulfurizer utilizing fluidized beds and as described in our copending British Patent Application No. 8012826 and another application 10 divided therefrom.

According to the present invention, there is provided a solids drier comprising a housing, an agitator movably supported relative to said housing, a distributor located beneath said - 15 agitator and having therein a multiplicity of holes arranged to cause hot gas movement therethrough at similar velocities over said distributor, and means to deliver hot gas through said holes.

20 An embodiment of the invention will now be more particularly described by way of example and with reference to the accompanying drawing, in which Fig. 1 shows a side elevation view, partly in section of an apparatus for drying and crushing 25 solids and transporting it to a subsequent operation.

Referring now to the drawing, which will be described with reference to the use of the apparatus for feeding coal to a combustor-30 desulfurizer, Fig. 1 shows a variable-speed screw feeder 348, a coal drier 340, a crusher 342, a rotary air lock 368 and a coal pot 344. Coal from a coal bin 346 passes through the screw feeder 348 and enters the drier 340 through a chute 341. 35 From the chute it falls into a trough 350, partially semicircular in cross section, in which is positioned a revolving shaft 352 carrying at each end a wheel 353 (one shown) between the two of which extend bars 354. One of the bars 354 40 carries smaller transverse pins 356 (1" in length), which are spaced with 1/4" gaps therebetween to rake along larger lumps of coal but not to catch smaller pieces of coal and the fines. At the base of the trough 350 is fitted a hot air duct 358, which 45 introduces hot air (500—700°F) into the trough 350 through a perforated distributor plate 359 to fluidize the smaller particles and heat by jet impingement the larger ones. This air may be first heated by pasSing it through a coil (not shown) in 50 the combustion bed. Enclosing trough 350 is a cover 360, and a vent 361 permits hot air and any gases emitted by the coal to be vented. The revolving assembly promotes the drying of coarse . lumps of coal, when only large sizes are being fed 55 (e.g., stoker coal, sized 1 1/4 x 1/4") by stirring the lumps, thereby eliminating pockets of moisture that might otherwise be left between coal pieces. When the drier is being used to dry coal containing both coarse and fine coal (e.g., nut 60 and slack coal, sized 1 1/2 x 28 mesh), the raking motion of the pins 356 removes coarse lumps, these lumps not requiring as much drying as the fines, thus allowing the remaining coal to be dried in the fluidized state. Coal moistures of up to 15%

65 can be handled by the drier, while using air that is safely below the coal gas explosion point, because of the relatively long residence time (typically 15 seconds) of the coal in the trough, which permits the drying air access to a relatively large amount 70 of coal surface, thereby promoting the transfer of heat to the coal. At the side of the trough 350 opposite the screw feeder 348 is an outlet lip 362, which is at the end of a radius 15° below a horizontal radius, and directs dried coal to piping 75 364 and from there to the crusher 342 (designed to crush the coal to a particle diameter of 95% — 1/2". 50% + 8 mesh) and into the rotary air lock 368. Vent 369 prevents pressure build-up upstream of the air lock, and is vented to 80 atmosphere.

Pockets of crushed coal are then dumped from the air lock 368 into the coal pot 344. Coal pot 344 has mounted in it a perforated distributor plate 370 below which air inlet pipe 372 enters 85 the pot to direct fluidizing air through the plate 370. Coal outlet pipe 374 extends from the pot above the plate 370, and is connected to the pot by reducer 375. Blast air tube 376 is directed into the reducer 375 to assist in carrying coal out 90 through the pipe 374 pneumatically to a coal feed pipe of a combustor-desulfurizer as disclosed in our co-pending applications.

The purpose of the coal pot is to smooth out the fluctuations in the coal feed rate that would 95 otherwise occur when the rotary air valve empties each pocket.

An alternative design has the rotary air lock 368 placed between the feed screw 348 and the drier 340, allowing heated air leaving the drier at 100 vent 361 to be used as coal transport air, entering the coal pot at pipe 372 before driving the coal to the fluid bed combustor. This eliminates the thermal loss and fuel loss associated with venting the drier's exhaust gases to atmosphere, and 105 eliminates the need for any particulate collector system that would otherwise be required with an atmospheric vent system.

Further alternatives are possible, for example the agitator of the coal drier 340 may be of a different 110 design than that shown; for example, a spiral or pair of spirals may be used instead of the bars 354. Also, transverse pins 356 are optional, particularly with coal that contains few fines below 1/4 inch. The temperature of the air 115 entering the drier may be thermostatically controlled to create the optimum coal outlet temperature of about 200° F, regardless of the moisture. This avoids the possibility of overheating the coal, and starting a fire in the coal drier during 120 shutdowns. It also allows the drying of coals whose moisture content is greater than 15%, by increasing the drier's air inlet temperature above 700°F. The heat for the drier may come from a separately-fueled duct burner, rather than from a 125 heating coil as described in the preferred embodiment.

Although in the embodiment described, the apparatus has been adapted for drying coal, it may of course be used for drying any other particulate

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GB 2 079 915 A 2

solids. Neither is it always necessary to provide the remaining parts of the apparatus described such as the crusher, coal pot or screw feeder.

Claims

5 1. A solids drier comprising a housing, an agitator movably supported relative to said housing, a distributor located beneath said agitator and having therein a multiplicity of holes arranged to cause hot gas movement 10 therethrough at similar velocities over said distributor, and means to deliver hot gas through said holes.
2. A drier as claimed in claim 1, in which said distributor is generally a portion of a circular

15 cylinder annulus.
3. A drier as claimed in either claim 1 or claim

2, in which said holes are spaced to facilitate fluidizing solids fines.
4. A drier as claimed in any one of the

20 preceding claims, in which said agitator comprises a pair of disks and a multiplicity of spaced rods extending therebetween.
5. A drier as claimed in any one of the preceding claims, in which said distributor

25 includes, at the downstream end thereof, a raised lip.
6. A drier as claimed in any one of the preceding claims, in which said agitator comprises mixing elements adapted to move larger pieces of

30 solid through the drier faster than finer particles of solid.
7. A solids drier substantially as described herein with reference to the accompanying drawing.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1982. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.