GB2187546A

GB2187546A - Grain dryer

Info

Publication number: GB2187546A
Application number: GB08704260A
Authority: GB
Inventors: Ernest George Benfield
Original assignee: CARIER
Current assignee: CARIER
Priority date: 1986-03-06
Filing date: 1987-02-24
Publication date: 1987-09-09
Also published as: GB8704260D0

Abstract

A grain dryer comprising an air outlet to a water scrubbing dust removal unit arranged to scrub the exhaust air prior to releasing it to atmosphere. The air from the outlet is preferably drawn by a fan and delivered into a generally vertical duct 6 provided with spray nozzles 43 directing water towards the opposed wall of the duct to scrub the air stream. A water curtain is formed at the bottom of the duct 6 to provide a secondary scrubbing. The duct 6 debouches onto the surface of water in a shallow tank 48, and the air turns through 180 DEG through the water curtain. The water is recirculated from the tank 48, over a weir into a collecting trough and through a rotary filter to a pump 47 feeding a common delivery line 46 for the spray nozzles 43. The rotary filter may be provided with a cleaning means for removing the cake from its exterior and extracting it from the system. In another embodiment only a water curtain is provided (Figs. 1 to 5). <IMAGE>

Description

SPECIFICATION Grain dryer This invention relates to grain dryers.

Conventionally, a grain dryer consists of a burner or burners from which the products of combustion, normally admixed with secondary air, are passed through a body of grain. In their passage through the grain, the gases pick up a considerable amount of solid material, including dust and husks, which is subsequently released into the atmosphere.

In an increasingly environmentally-aware age, this may present a problem, particularly if the grain dryer is located close to human habitation or public roads or footpaths.

In accordance with a first aspect of the invention, there is provided a grain dryer comprising an air outlet to a water scrubbing dust removal unit arranged to scrub the exhaust air prior to releasing it to atmosphere.

In accordance with a second aspect of the invention, there is provided a grain dryer comprising an air outlet to a water-curtain dust removal unit arranged to scrub the exhaust air prior to releasing it to atmosphere.

In a water curtain version, the air from the outlet may be drawn by a fan into a generally vertical duct debouching into the water curtain, which may be generated by water recirculated from a tank located below the duct. In such an arrangememt, air from the vertical duct may impinge on the water in the tank and be turned through 1800 into a discharge duct surrounding the vertical duct, so that the air stream passes through the water curtain during the 1800 degree turn.

The duct is conveniently of generally rectangular section, and the water curtain is formed by a horizontal channel and weir associated with each side of the rectangle.

In an alternative arrangement in which the air from the outlet may be drawn into a generally vertical duct in which it is exposed to sprays of water, and the water from the sprays impinges on the walls of the duct and runs down to form a water curtain at the bottom of the duct.

Preferably, a shallow tank is located below the lower end of the duct, and a collecting trough surrounds the tank to collect water overflowing horizontal and co-planar upper edges to bounding walls of the tank for recirculation to the sprays.

The base of the collecting trough is conveniently inclined to assist drainage to a discharge zone, whence it is re-circulated.

The sprays are preferably formed by multiple full bore nozzles fitted with deflectors to form the spray and debouching substantially horizontally into the duct and fed from a common re-circulation pump.

In order to remove collected solzd material scrubbed out of the air, the recirculating water may be drawn through a rotary filter while being recirculated and the rotary filter is conveniently provided with a cleaning means for removing the cake from its exterior and extracting it from the system.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a grain dryer with an air cleaning unit in accordance with a preferred form of the invention Figure 2 is an end elevation of the dryer of figure 1; Figure 3 is an opposite side elevation of part of the air cleaning unit, to an enlarged scale; Figure 4 is a section on the line IV-IV of figure 3; Figure 5 is an end elevation of the air cleaning unit; and Figure 6 is a diagrammatic perspective view showing some modifications.

Turning first to figures 1 and 2, a grain dryer is illustrated as comprising multiple body sections 1 which hold the grain to be dried and are mounted on a support frame 2. The body sections 1 are located beside burners 3, which draw air in the direction indicated by the arrow 3a, and the combustion gases from the burners are mixed with secondary air and pass upwards in a duct 4a and then through the body of grain within the sections 1, emerging into ducting 4.

From the ducting 4, the now dust-laden air is drawn by one or more large diameter fan units 5 and passed into a generally vertical square or rectangular section duct 6 which projects downwards into a dust removal unit 7, which is shown in greater detail in figures 3 and 4.

Turning now to figures 3 and 4, the duct 6 is shown as extending into the unit 7 which is a water curtain scrubbing unit and consists essentially of a water tank 8 which in operation is filled with water to the level indicated by the line 9. Above the water tank 8, which is of generally square section larger than the section of the duct 6, there are located outer panels 10 and 11 which, with the ouside surface of the duct 6, define an exhaust air passage 12 surrounding the duct 6.

Along the outer side of each panel defining the bottom part of the duct 6 there is located a channel 14 having a lip 15 forming a weir.

The weir thus extends continuously around all four sides of the air duct. Support pillars 16 are provided for the channels 14.

Each channel 14 is provided with a water supply connection 17 attached to a hose 18.

The hoses 18 are all fed from a common pressure connection 19 of a water pump 20 which has a suction hose 21 connected to a union 21a on an extension 8a of the tank 8.

A rotary filter drum 22 is mounted on a rotary shaft 23 and is partially submerged in the water in the tank extension 8a. The shaft 23 carries a sprocket 23a teeth, engaged by a drive chain C. An outer surface of the drum 22 is formed by a cladding 22a of perforated galvanised mild steel sheet. For example, to form a suitable filter, the perforations may be 3/32 inch (2.4mm) diameter and closely spaced. The cladding 22a is supported by discs 22b, which have large apertures 22c therein to allow free flow of water within and through the ends of the drum 22. The ends of the cladding 22a overhang somewhat the diametral portions of the discs 22b, as shown at 22d, so as to allow only a small clearance between the effective end of the drum 22 and the walls 8b of the tank extension 8a. Bypassing of the filter formed by the cladding 22a is thus effectively avoided.

The water supply to the pump 20 is thus drawn through the filter formed by the cladding 22a and filter cake building thereon, and then through the interior of the drum 22 and out of the ends thereof, so that the solids suspended therein are collected on the outside of the drum cladding 22a to form a filter cake which is continually removed by means of a hinged doctor blade 25 of spring steel. This solid cake removed by the doctor blade 25 is fed to an auger 26 which carries the cake, in substantially pelletised form, into an auger tube 27. The auger 26 is driven from the chain drive C by means of a small sprocket 26a.

The lower outer panels 10 on two sides of the arrangement are provided with sealed inspection doors 35 having locking handles 36.

It will be seen thus that the water from the tank is recycled by the pump 20 through the filter drum 22 and is thus substantially cleaned before it forms the water curtain by passing over the weirs 15.

The dust-laden gases from the dryer pass down the duct 6 towards the water in the tank 8, as indicated by the vertical arrows 31, and the airflow has then to turn through 1800, as indicated by the arrows 32, before passing up through the duct 12 to exhaust, as indicated by the arrows 33.

This 180 change of direction has a very considerable effect in centrifugally separating the larger solid particles from the air, and during this change of direction, the air also has to pass through the water curtain which is indicated by the reference numeral 34 and this removes a further substantial proportion of the suspended particles.

It will also be seen that the particles suspended or floating on the water in the tank are removed by the filter drum 22 as the water is recycled by the pump 20.

Figure 6 illustrates an alternative form of scrubbing unit, which has a principal spray scrubbing action and a secondary water curtain. In this figure, the duct 6 is shown inside panelling 41 forming an outer wall for the vertically upward discharge of the clean air to atmosphere. The path of the air is shown by the U shaped arrows 42 showing the 180 change of direction of the air as it leaves the duct 6.

The duct 6 is provided with a plurality of full bore nozzles 43, provided with deflectors to form and distribute a spray in the duct, and each located near one wall of the duct and directing a spray towards the opposite wall.

Although only two nozzles 43 are actually illustrated, it will be understood that normally at least one nozzle will be located adjacent each wall, and possibly more if the duct 6 is of large dimension. The nozzles 43 are at different levels, so that air passing down the ducting will pass through several layers of spray and be scrubbed thereby. The nozzles are made full bore, rather than of jet form, to obviate the need for expensive and unnecessary fine filtration equipment.

The nozzles are fed via individual hoses 44 (of which four are shown in figure 6) from a manifold 45 fitted to a common delivery line 46 from a pump 47.

The water from each of the sprays impinges on the wall of the duct 6 opposite the respective nozzle 43 and runs down the wall to cascade off the lower edge of the wall to form a water curtain as it drops into a shallow tank 48 below the bottom of the duct 6.

It will be seen that as the air performs its 1800 turn it passes through this secondary water curtain and is further scrubbed.

The tank 48 is in the form of a tray having a square bounding wall 49, of which the upper edge is horizontal and level, so as to form a weir over which the water flows into a collecting tray 51 which slopes downwardly towards a discharge zone 52, whence the water is drawn into a housing 53 for a rotary filter 54, similar to that described hereinabove with particular reference to figures 3 and 4. An auger and auger tube, together with a discharge container are also illustrated in figure 6. A suction line 55 for the pump 47 draws the fltered water from the housing 53 for recirculation via the nozzles 43.

The use of a shallow tank in the form of a tray has the advantage of avoiding a large volume of polluted water which might tend to settle, and make the tank difficult to clean.

Also, the shallow tray is comparatively easy to drain into the collecting trough and filter housing if any sediment forms therein.

It will be noted that the downcoming air and water in the duct 6 tend to drive the water in the tank 48 towards the edge thereof so as to pass over the weir formed by the wall 49, and this means that chaff or other particles in the air stream impinging on the water surface are readily impelled towards the weir, on or below the water surface, and are rapidly removed from the air stream so that they are removed from the system rather than being re-entrained in the air stream as it turns upwardly for discharge. The sloping of the collecting tray, and the comparatively high flow rate through it, mean that the solid particles removed are rapidly conveyed to the filter.

Also, the air in the duct is scrubbed first the sprays and then turned through 1800 as it passes through the water curtain, so that if particles are not scrubbed out of the air stream by the sprays or by the water curtain, they may be discharged centrifugally during the 1800 turn.

Various other modifications may be made within the scope of the invention.

Claims

1. A grain dryer comprising an air outlet to a water scrubbing dust removal unit arranged to scrub the exhaust air prior to releasing it to atmosphere.

2. A grain dryer comprising an air outlet to a water-curtain dust removal unit arranged to scrub the exhaust air prior to releasing it to atmosphere.

3. A grain dryer as claimed in claim 2, in which the air from the outlet is drawn by a fan into a generally vertical duct debouching into the water curtain.

4. A grain dryer as claimed in claim 3, in which the water curtain is generated by water recirculated from a tank located below the duct.

5. A grain dryer as claimed in claim 4, in which air from the vertical duct impinges on the water in the tank and is turned through 180 into a discharge duct.

6. A grain dryer as claimed in claim 5, in which the discharge duct surrounds the vertical duct, and the air stream passes through the water curtain during the 1800 degree turn.

7. A grain dryer as claimed in any of claims 3 to 6, in which the duct is of generally rectangular section, and the water curtain is formed by a horizontal channel and weir associated with each side of the rectangle.

8. A grain dryer as claimed in claim 1, in which the air from the outlet is drawn into a generally vertical duct in which it is exposed to sprays of water.

9. A grain dryer as claimed in claim 8, in which the water from the sprays impinges on the walls of the duct and runs down to form a water curtain at the bottom of the duct.

10. A grain dryer as claimed in claim 8 or 9, comprising a tank, located below the lower end of the duct, and a collecting trough surrounding the tank to collect water overflowing the tank for re-circulation to the sprays.

11. A grain dryer as claimed in claim 10, in which the tank is shallow and has horizontal and co-planar upper edges to bounding walls to form a weir over which the overflowing water passes into the collecting trough.

12. A grain dryer as claimed in claim 10 or 11, in which the base of the collecting trough is inclined to assist drainage to a discharge zone, whence it is re-circulated.

13. A grain dryer as claimed in any of 8 to 12, in which the sprays are formed by multiple nozzles debouching substantially horizontally into the duct and fed from a common recirculation pump.

14. A grain dryer as claimed in claim 13, in which the nozzles are full bore nozzles fitted with deflectors to form the spray.

15. A grain dryer as claimed in any of claims 4 to 6 or 10 to 14, in which the recirculating water is drawn through a rotary filter while being recirculated.

16. A grain dryer as claimed in claim 15, in which the rotary filter is provided with a cleaning means for removing the cake from its exterior and extracting it from the system.

17. A grain dryer substantially as hereinbefore described with reference to figures 1 to 5 of the accompanying drawings.

18. A grain dryer substantially as hereinbefore described with reference to figure 6 of the accmpanying drawings.