Claims:We claim:

1. A paddy straw feeding system for vibrating grate boiler furnace comprising input belt conveyors operatively connected to plurality of silos (4) for creating a buffer storage of paddy straw loosened from strings obtained from each input belt conveyor and stoker feeders (2) for feeding loosened paddy straw and untied strings of said straw, discharged from said silos (4) to vibrating grate, each silo being provided with bottom screws for discharging said loosened paddy straw and the untied strings, to said stoker feeders (2) characterized in that the silo screws (1) are inclined to horizontal and are twin screws driven by single drive rotating in opposite direction, the screws being variable pitch, variable diameter (7) and open at outlet for discharging paddy straw with said strings to stoker feeders (2) via intermediate chute and in that each stoker feeder (2) has feeder screws (21) which are twin tapered screws with conical shaft, variable pitch and variable diameter, each screw having separate drive (16) and rotating in opposite direction, whereby feeding paddy straw to the furnace in an uninterrupted manner is ensured.

2. The paddy straw feeding system as claimed in claim 1, wherein the silo bottom screws (1) are of cantilever design having bearing (5) at drive (11) end only and open shaft (6) without bearing at non drive end.

3. The paddy straw feeding system as claimed in claim 1, wherein stoker feeder screws (21) are placed side by side in a water cooled trough and thus have water cooled construction and said screws (21) are cantilever with open ends.

4. The paddy straw feeding system as claimed in claims 1, 2 and 3, wherein the screws (1, 21) are constructed of material suitably selected to prevent corrosion.
5. The paddy straw feeding system as claimed in claim 1, wherein each said stoker feeder (2) is designed to feed paddy straw to vibrating grate through water cooled tunnel (3) with shark fin arrangement (22) connected to boiler furnace, each said water cooled tunnel (3) is located after each stoker feeder (2).

6. The paddy straw feeding system as claimed in claim 5, wherein the roof of said tunnel (3) is provided with the shark fin arrangement (22) which acts as retainer to ensure a dense plug of material in the tunnel.

7. The paddy straw feeding system as claimed in claim 6, wherein the shark fin arrangement (22) can be pneumatically operated.

8. The paddy straw feeding system as claimed in any one of claims 6 or 7, wherein the tunnel (3) is of jacketed construction with the inner shell made up of corrosion resistant duplex stainless steel and outer shell is made of carbon steel.

9. The paddy straw feeding system as claimed in claims 6 to 8, wherein the tunnel (3) is equipped with a cooling water circuit (23) within it, whereby cooling water is circulated through the annulus of the tunnel body with a circulating water pump and cold make up water is added to maintain the desired cooling water temperature.

Dated this 12th day of October, 2020.

(SOUMEN MUKHERJEE)
IN/PA - 214
Applicants’ Agent
for seenergi IPR
, Description:
PADDY STRAW FEEDING SYSTEM

FIELD OF THE INVENTION

The present invention in general, relates to a paddy straw feeding system for a vibrating grate boiler furnace.

More particularly, the present invention relates to a paddy straw feeding system which has specially designed components for smooth and uninterrupted feeding of loosened paddy straw and the ropes/strings untied from the loosened paddy straw to vibrating grate boiler furnace.

In the instant invention, loosened paddy straw acts as the fuel for vibrating grate boiler.

TECHNICAL BACKGROUND OF THE INVENTION

It is known that paddy straw is transported in bales for feeding to boiler which needs the loosened straw to fire on vibrating grate.

Now, for that purpose, bales are tied with nylon rope/strings along the length of the bale and for loosening the straw the rope/strings have to suitably cut for loading the loosened straw on feeding belt conveyor, which is invariably manual.

Furthermore, the cut rope/strings are carried into the furnace along with the loosened straw and often entangles with the rotating components like the shafts resulting in jamming and chocking of the components, thereby hampering the required flow of the feeding system to the vibrating grate boiler. This is a very major technical problem.
Also, loosened straw should have storage to cater fluctuations in input feeding system due to manual loading of bales onto the feeding belt conveyor, as it often happens.

It is also a fact that paddy straw has high silica and alkali content which leads to erosion and corrosion of the fuel feeding system of vibrating grate boilers. Furthermore, paddy straw has low to high moisture content in tropical conditions where, these paddy straw is often stored in open fields in bales.

Apart from the above, paddy straw being fed in plug form to the furnace, certain pyrolysis of fuel in the feeding tunnel closer to the furnace is possible and the corrosive gases may condense at the cooler surfaces of the tunnel leading to corrosion.

Accordingly, there is a need for a technically enhanced paddy straw feeding system for vibrating grate boiler which successfully solves the aforementioned technical difficulties commonly encountered in feeding loosened paddy straw into vibrating grate boilers.

The present invention meets the abovementioned needs and other associated needs by providing a technically enhanced paddy straw feeding system for a vibrating grate boiler furnace, primarily by providing a smooth working interrelation between suitably designed silo feeding screws, water cooled stoker feeder screws in combination with other features, as it would be clear to persons skilled in the art, on reading the contents of this specification.

OBJECTIVES OF THE INVENTION

It is the prime objective of the present invention to provide a paddy straw feeding system for a vibrating grate boiler furnace which ensures smooth and uninterrupted feeding of loosened paddy straw and the ropes/strings untied from the loosened paddy straw that are carried with loosened straw, to vibrating grate boiler furnace.
It is yet another objective of the present invention to provide a paddy straw feeding system for a vibrating grate boiler furnace which substantially minimizes erosion and corrosion of the components.

It is a further objective of the present invention to provide a paddy straw feeding system for a vibrating grate boiler furnace which ensures to accommodate variations in moisture content of paddy straw fed to the boiler furnace, so that the process is not hampered.

How the foregoing objectives are achieved should be clear from the contents of the specification hereinafter.

All through the specification including the claims, the words “vibrating grate”, “boiler furnace”, “silo”, “stoker feeder”, “tunnel”, “shark fin arrangement”, “screws”, “strings/ropes of bales” are to be interpreted in the broadest sense of the respective terms and includes all similar items in the field known by other terms, as may be clear to persons skilled in the art. Restriction/limitation, if any, referred to in the specification, is solely by way of example and understanding the present invention.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a paddy straw feeding system for vibrating grate boiler furnace comprising input belt conveyors operatively connected to plurality of silos for creating a buffer storage of paddy straw loosened from strings obtained from each input belt conveyor and stoker feeders for feeding loosened paddy straw and untied strings of said straw discharged from said silos to vibrating grate. Each silo is provided with bottom screws for discharging said paddy straw and untied strings to said stoker feeders. The silo screws are inclined to horizontal and are twin screws driven by single drive and rotating in opposite direction, the screws being variable pitch, variable diameter and open at outlet for discharging paddy straw with said strings to stoker feeders via intermediate chute. Each stoker feeder has feeder screws which are twin tapered screws with conical shaft, variable pitch and variable diameter. Each screw has separate drive rotating in opposite direction, whereby feeding paddy straw to the furnace in an uninterrupted manner is ensured.

Preferably, the silo bottom screws are of cantilever design having bearing at drive end only and open shaft without bearing at non drive end.

More preferably, stoker feeder screws are placed side by side in a water cooled trough and thus have water cooled construction and said screws are cantilever with open ends.

Even more preferably, each said stoker feeder is designed to feed paddy straw to vibrating grate through water cooled tunnel with shark fin arrangement connected to boiler furnace, said water cooled tunnel is located after each stoker feeder.

Most preferably, the roof of each tunnel is provided with the shark fin arrangement which acts as retainer to ensure a dense plug of material in the tunnel.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Having described the main features of the invention above, a more detailed and non-limiting description of some exemplary embodiments will be given in the following with reference to the drawings.

Figure 1 is a view of the general arrangement of the paddy straw feeding system of the present invention.
Figure 2 is an enlarged top view of the silo bottom screws of the present invention.

Figure 3a is a detailed view of the silo bottom screws showing the drive arrangment.

Figure 3b is a side view of the silo bottom screws shown in figure 3a.

Figure 4 is an enlarged elevation view of the stoker feeder according to the present invention.

Figures 5a, 5b and 5c are elevation view, side view and top view respectively of the water cooled tunnel with pneumatically operated shark fin arrangement according to the present invention.

Figure 6a is a sectional view of the cooling water circuit inside the tunnel leading to the boiler furnace, the cross section being taken along the line A-A, shown in figure 6b.

Figure 6b is a view of the schematic of the cooling water circuit inside the tunnel leading to the boiler furnace.

DETAILED DESCRIPTION OF THE INVENTION

The following describes a preferred embodiment of the present invention which is for the sake of understanding the invention and non-limiting.

It should be understood that the figures show one silo, one stoker feeder, one tunnel but in practice there can be a plurality of such units and the present invention embodies such units including variations in the number of components shown and orientation thereof. Furthermore, vibrating grate boiler furnace is not shown in the figures, since it is known, and the present invention is applicable on all types of vibrating grate boiler furnaces.
In all the figures, like reference numerals represent like features.

As stated hereinbefore, while discussing technical background of the invention, paddy straw, fuel for vibrating grate boiler furnaces, are carried in bales and are tied with nylon ropes/strings. These are cut to loosen the paddy straw. Further, paddy straw gets loosened when bales are manually loaded to feeding belt conveyors for its free fall from input belt conveyor to storage silos. This also brings the cut strings/ropes which are also fed to the boiler furnace along with the loosened paddy straw.

The general flow of loosened paddy straw to vibrating grate boiler furnace is somewhat as under.
-Paddy straw gets loosened due to its free fall from input conveyor to silo 4.
-Common silo is provided to store fuel with storage capacity of 5 minutes of total fuel required for boiler. This may vary and such variation is within the ambit of the present invention.
-Silo front plates are inclined to vertical for ensuring smooth fuel (loosened paddy straw and untied strings/ropes) flow to each stoker feeder 2.
-Silo bottom twin screws 1 are placed beneath each silo. The screws are inclined to horizontal. These by virtue of their construction ensure free flow of fuel to stoker feeder 2 without any hindrance/interruption of any type such as entanglement of strings/ropes with components.
-Water cooled stoker screws feed the fuel forward by virtue of their technically advanced construction.
-The fuel is propelled to water cooled tunnel 3 placed after each stoker feeder to feed the fuel to the grate.
Now, the constructional features of the components and functions of such features are described in more detail to explain how the technical deficiencies as discussed under “Technical background of the invention” are sorted out and how the objectives of the instant invention, as stated under the heading “Objectives of the invention” are met.

Referring to figure 1, it shows storage silo 4 having specially designed bottom screws 1 for delivering the stored paddy straw from storage silo 4 to stoker feeder 2. Stoker feeders 2 are connected to water cooled tunnel 3 with shark fin arrangement which leads the fuel to the vibrating grate boiler furnace. These are elaborately described a little later.

The silo bottom screws 1 are more vividly illustrated in the enlarged view in figure 2. When, figure 2 and figure 1 are seen together, it would be clear that the silo bottom screws, beneath each silo are inclined twin screws 7 with tapered shaft 6 and are variable pitch, variable diameter and open at outlet.

The bottom screws rotate in opposite directions and are driven by a single drive 11 (shown in Figure 1). Figure 2 also shows the screw bearings 5 and solid shaft outside casing 8. The opposite direction of rotation of the twin screws is indicated by arrows in figure 2.

Referring to figure 3a it would be further clear that the silo front plates are inclined at an angle of 70? to the horizontal in this particular arrangement. It also elaborately shows the drive arrangement 11. The solid shaft 8 outside the casing 10 connects the inclined screws 7 with the single drive arrangement 11 for both the screws. Paddy straw gets loosened due to its free fall from input belt conveyor (not shown) as explained before. Common silo is provided to store fuel with a storage capacity of 5 minutes of total fuel required for boiler. Inclined silo front plates ensure smooth fuel flow to each stoker feeder 2.

The silo bottom screws 1 are placed at the bottom of each storage silo 4. As shown in figure 3a these screws 7 are inclined downward with 10? inclination to horizontal in this arrangement. The screws being variable diameter, variable pitch, inclined and open at outlet ensure free flow of loosened paddy straw to stoker feeder 2 through intermediate chute (not shown). The strings/ropes flow out along with loosened paddy straw from the inclined open end screws into the chute and thereby avoiding entanglement of strings over the screw bearing/shaft (5, 6, 8).

The screw flights are of variable pitch and variable diameter to handle paddy straw of high moisture. Screws are of cantilever design with bearings 5, at drive 11 end only as shown in figures 2 and 3a, non-drive end being with open shaft without bearing support. These screws 1, 7 extract high fuel moisture along with string/ropes and discharge to stoker feeder 2 through chute (not shown in detail) located above each stoker feeder 2.

Figure 3b is a side view of the silo bottom screws 1, 7 shown in figure 3a.

The screws are constructed of material suitably selected to prevent corrosion.

Figure 4 is an enlarged elevation view of the stoker feeder 2 according to the present invention. Stoker feeder is designed to feed paddy straw to vibrating grate (not shown) through tunnel 3 connected to boiler furnace (not shown). The stoker feeder screws 21 are twin screws with conical shaft, variable pitch and variable diameter. These screws are also open end cantilever screws as can be seen from figure 4, so that strings/ropes can be carried along with the loosened paddy straw to the grate. The screws are constructed of material suitably selected to prevent corrosion.

Referring to figure 4 the stoker feeder screws 21 are placed side by side in a water cooled trough. The cooling water inlet 18 and the cooling water outlet 12 can be seen in figure 4. Figure 4 also illustrates the outer casing 20, the inner casing 19, the chain arrangment 15, the bearing arrangement 14 and also the supporting frame 13 and the solid shaft 17. Each screw 21 has separate drive 16 rotating in opposite direction.

Figure 4 also shows the loosened paddy straws entering the stoker feeder 2 from silo bottom screws (shown in figures 1, 2, 3a and 3b) and the movement of paddy straws out of the stoker feeder 2 into the vibrating grate furnace via the tunnel 3 (shown in figures 5a, 5b, 5c). These are shown by arrows.

Referring to figures 5a, 5b and 5c, the water cooled tunnels 3 are placed one each after each stoker feeder 2 to propel the paddy straws and strings/ropes to the grate.

The roof of this tunnel 3 is provided with a shark fin arrangement 22 as very clearly shown figure 5c. This acts as retainer to ensure a dense plug of material in the tunnel. Shark fin is preferably operated through pneumatic power cylinder.

At the outlet of the feed tunnel 3 in the furnace, the straw expands onto the grate and ignite almost instantaneously due to the radiation and addition of air in the nozzles above the tunnel 3. The tunnel is of jacketed construction with the inner shell made up of corrosion resistant duplex stainless steel and outer shell made of carbon steel.

Cooling water to the tunnel is designed to maintain the temperature of water between 80? to 90? C and thus avoid condensation of corrosive gases due to pyrolysis of fuel in the tunnel and thereby reducing corrosion.

Cooling water is circulated through the annulus of the tunnel body with a circulating water pump and cold make up water added so as to maintain the cooling water temperature within the desired temperature.

The cross sectional view in figure 6a and the view in figure 6b clearly illustrate the aspects as described in the preceding two pragraphs in respect of schematic of the cooling water circuit inside tunnel 3.

It should be clear from the description hereinbefore and the various figures that all the objetives of the present invention have been met. This would be even more clear from the appended claims.

The present invention has been described with reference to a preferred embodiment and some drawings for the sake of understanding only and it should be clear to persons skilled in the art that the present invention includes all legitimate modifications within the ambit of what has been described hereinbefore and claimed in the appended claims.