DESC:FIELD
The present disclosure relates to waste combustion systems.
BACKGROUND
Liquid wastes generated by industries and distilleries cause considerable pollution, as almost 88% of such liquid wastes get discharged directly into the fields and water bodies. Various methods for the disposal of such wastes are used conventionally, like incineration, composting, bio-methanation and the like. However, the conventional methods of liquid waste disposal have their own limitations. For example, a typical distillery generates about 1,000 tons of liquid waste every day. However, even after its disposal by using conventional methods such as bio-composting, large quantities of liquid waste still remains in its original form, posing a serious threat to local water bodies. Moreover, bio-composting has inherent limitations, including the requirement of large tracts of land to carry out the process and is generally hampered by rain. With regard to incineration of liquid wastes, the process is comparatively efficient and is widely accepted under zero liquid discharge norms laid down by various governing authorities worldwide.
During incineration, the liquid waste is typically co-fired with oil and gas. However, as both oil and gas are expensive, coal can also be used as a substitute. However, due to depletion of coal reserves and due to the issues with logistics and the quality of coal being supplied, the use of coal as a fuel is not an efficient solution. Also, the conventional furnaces used for the combustion of such wastes, suffer from certain inherent constructional issues. For example, a typical waste combustion furnace for the combustion of solid-liquid waste uses a grate, which rotates from a posterior wall side towards a feeder wall side of the furnace. The solid waste is typically fed from a point on the feeder wall and is thrown towards the posterior wall, while the liquid waste is sprayed on the solid waste moving on the grate. Generally, the liquid waste is sprayed from a sprayer, which is positioned operatively above the grate.
It is observed that in a conventional co-fired waste combustion furnace, there is no provision for mixing of the solid and liquid wastes. As a result, a non-homogeneous mixture of solid-liquid waste is formed, which does not combust completely. Further, the spraying of liquid waste locally over the solid waste leads to “blackout” areas at certain portions of the waste because of localized cooling of the solid waste that is being co-fired. Further, the liquid waste percolates through the solid waste without proper combustion, as a result of the spraying. In addition, waste seepage below the grate is an operational hazard because of the fire below the grate.
OBJECTS
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
It is an object of the present disclosure to provide a waste combustion system suitable for the disposal of solid and/or liquid wastes.
Another object of the present disclosure is to avert the percolation of liquid wastes through the solid wastes, so as to obviate incomplete combustion.
Yet another object of the present disclosure is to retain the heat generated during the combustion of wastes, which helps in sustaining continuous combustion without any blackout areas.
Still another object of the present disclosure is to avert the seepage of liquid wastes below the grate and hence reduce or eliminate back-fire and damage to the grate components.
Yet another object of the present disclosure is to homogeneously blend the liquid and solid wastes in predetermined quantities to facilitate complete combustion of the wastes.
Yet another object of the present disclosure is to provide an improved feeding of the solid and/or liquid wastes on the grate, to achieve sustained combustion.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
Described herein is a waste combustion system for combusting solid and/or liquid wastes, comprising a furnace section for receiving solid and/or liquid wastes through a fuel feeder, the fuel feeder having a compartmentalized structure having an operational top segment placed above an operation bottom segment; the top segment having a first screw conveyor for feeding solid and/or liquid wastes through a first conduit onto a combustion grate of the furnace section; the bottom segment having a second screw conveyor for feeding solid wastes through a second conduit onto the combustion grate, wherein the feeding from the second conduit is done prior to the feeding from the first conduit.
In one embodiment, at least one sprinkler is provided near an exit of the first screw conveyor for sprinkling liquid wastes onto the solid wastes moving inside the first screw conveyor, to provide a homogenized mixture. However, sprinklers may be provided at any other positions inside the first screw conveyor.
The combustion grate can rotate in a direction starting from a feeding side to an opposing side, inside the furnace section.
The first and second screw conveyors can comprise at least one screw, wherein the screw has a stepped shaft with flights. The flights can be at least one of ribbon flight, paddle flight, continuous flight, serrated flight and cut flight.
The solid wastes can comprise agriculture waste, lignocellulose waste, bagasse and the like.
The liquid wastes can comprise wastes from distilleries and industries.
At least one wall of the furnace section can be arched to retain the combustion heat.
The first conduit from the top segment connects the first screw conveyor to a furnace wall at a first position and the second conduit connects the second screw conveyor to the furnace wall at a second position, directly below the first position.
The inclination of the first and second conduits connecting the screw conveyors and the furnace wall can be greater than the angle of repose of the wastes fed into the furnace section.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a schematic view of a conventional co-fired furnace, wherein liquid and solid wastes are fed separately;
Figure 2 illustrates a schematic view of a waste combustion system in accordance with one embodiment of the present disclosure;
Figure 3A illustrates a side schematic view of a screw conveyor of the waste combustion system of Figure 2; and
Figure 3B illustrates a front schematic view of the screw conveyor of the waste combustion system of Figure 2.
DETAILED DESCRIPTION
A waste combustion system of the present disclosure will now be described with reference to the embodiments which do not limit the scope and ambit of the disclosure.
The embodiments herein, the various features and the advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so that there is no unnecessary confusion about the embodiments herein. The description hereinafter, of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Figure 1 illustrates a schematic view of a conventional co-fired furnace (100), wherein liquid wastes and solid wastes are separately fed. The co-fired furnace (100) comprises a fuel feeder (10), a screw conveyor (12), a conduit (14), a feeder wall (22), a posterior wall (24), a grate (18), a sprinkler/spray gun (20), an economizer (28), an outlet conduit (30), and a hopper (26). Particularly, the solid waste is provided on the grate (18) away from the feeder wall (22) while the liquid waste is sprayed from the sprinkler/spray gun (20). For this purpose, the solid waste (for example, agriculture waste, lignocellulose waste, and bagasse) is fed from the fuel feeder (10) to a screw conveyor (12), which facilitates the transfer of solid waste into the co-fired furnace (100) through the conduit (14). The conduit (14) is inclined at an angle such that the waste inside the screw conveyor (12) moves under the gravitational force. The solid waste from the conduit (14) reaches an inside of the furnace at a point (16) on the grate (18) away from the feeder wall (22). The grate (18) is rotated in an anti-clockwise direction from a posterior wall (24) to the feeder wall (22), while the liquid waste is sprayed by the sprinkler /spray gun (20) on solid waste.
The heat generated by the combustion of the wastes is utilized by various heat exchangers including a super-heater (27), an evaporator (29), a recuperator (not shown), the economizer (28), an air preheater (not shown), make-up water heater (not shown), a de-aerator (not shown) for desired applications, while the flue gas after exchanging the heat with the heat exchangers is fed into the atmosphere from the outlet conduit (30). Further, the ash produced during the combustion is collected in the hopper (26).
It is observed that the liquid waste, which is sprayed on the solid waste, does not form a uniform layer on the solid waste, and which results in incomplete combustion of the solid waste. Further, the liquid waste percolates through the solid waste and this again hampers complete combustion of the solid waste. Still further, the seepage of the liquid waste below the grate (18) may result in an operational hazard as it may catch fire.
Figure 2 illustrates a schematic view of a waste combustion system (200) in accordance with an embodiment of the present disclosure, wherein the waste combustion system (200) can utilize a blend of liquid wastes and solid wastes. The waste combustion system (200) is a furnace having a furnace section, a dual-discharge fuel feeder (32), a first conduit (38) and a second conduit (42), a feeder wall (48), a posterior wall (50), and a hopper (52). At least one wall of the furnace section can have at least one arch (54) for retaining the heat generated by the combustion of wastes and sustaining combustion with high moisture wastes. The fuel feeder (32) holds solid wastes, which may include agriculture waste, lignocellulose waste, bagasse and the like.
In one embodiment of the present disclosure, the fuel feeder (32) has a compartmentalized structure with a top segment (X) placed operationally above a bottom segment (Y), the bottom segment (Y) is connected to the top segment (X) by a passage. The segments (X) and (Y) have a first and second screw conveyor (40') and (40?), collectively referred to as screw conveyors (40), at its base, which open up inside the furnace section of the waste combustion system (200). The fuel feeder (32) receives solid wastes such as bagasse, agriculture waste, lignocellulose fiber waste or other solid wastes, and/or liquid wastes such as wastes from distilleries and industries, from the top segment (X) and discharges the same into the furnace section of the waste combustion system (200) via its first screw conveyor (40') after preparing a homogeneous blend thereof. For this purpose, the top segment is provided with at least one sprinkler (36) at a discharge end of its first screw conveyor (40'). However, sprinklers may be provided at any other positions in the first screw conveyor. The sprinkler (36) sprays liquid wastes on top of the solid wastes to make the desired blend, which is fed into the waste combustion system (200). The first screw conveyor (40') of the top segment (X) feeds the solid/liquid wastes into the waste combustion system (200) via a first conduit (38), at a first position. In one embodiment, the ratio of the solid wastes and the liquid wastes ranges from 50:50 to 70:30.
The bottom segment (Y) is meant to discharge solely solid wastes into the waste combustion system (200). In an embodiment, a passage (not shown) is provided at a bottom of the top segment (X) through which the solid wastes received by the fuel feeder (32) passes from the top segment (X) to the bottom segment (Y). The second screw conveyor (40?) of the bottom segment (Y) feeds the solid wastes into the waste combustion system (200) via a second conduit (42), at a second position. In one embodiment, some quantity of solid wastes, before mixing in the first screw conveyor (40') of the top segment (X), is drawn in the bottom segment (Y) and is fed onto a combustion grate (46) of the furnace section as a bottom layer. The mixture or blend of the solid/liquid wastes is fed onto the combustion grate (46) subsequently as a top layer, above the bottom layer of solid wastes. In an embodiment, the two conduits (38) and (42) are inclined at pre-determined angles suitable for flow by gravity.
The screw conveyors (40) can comprise at least one screw, having a stepped shaft with flights. The screw conveyors (40), in one embodiment, have a twin-screw construction having special design features, including but not limited to predetermined flight shape, predetermined flight positioning, cuts on the flight, mixing and paddles. However, the screw conveyor is not limited to a twin-screw construction, and it can comprise one or more screws. The flights may include forward and reverse flights. The flight shapes include, but are not limited to ribbon flight, paddle flight, continuous flight, with variable pitch and variable diameter. The at least one sprinkler (36), which is used for spraying liquid wastes on the solid wastes, can be operated at low pressure and can be designed to give a wide angle spray.
In operation, the solid wastes from the bottom segment (Y) are fed at a point (44) on the combustion grate (46), in proximity to the feeder wall (48). The solid wastes that are fed in the furnace section, form a bottom layer on the combustion grate (46) whereas the homogeneous mixture, of solid and liquid wastes, is fed above the bottom layer. The combustion grate (46) rotates in a direction starting from the feeding side, i.e., point (44), to an opposing side. The combustion grate movement enables sufficient residence time for complete combustion of the wastes lying thereupon. The direction of rotation of the combustion grate is opposite to that of a conventional spreader stoker furnace. The reverse movement of the combustion grate (46) is suitable for mass burning of low grade wastes. The arrangement inside the furnace section can have refractory lining and arches (54), which is suitable for proper combustion of the wastes. In one embodiment, as shown in Figure 2, the combustion grate (46) rotates in a clockwise direction from the feeder wall (48) to the posterior wall (50).
Typically, the heat generated by combustion of wastes moving on the combustion grate (46) is utilized by various heat exchangers, which include, but are not restricted to screen tubes (53), a super heater (55), an evaporator (57), a re-cuperator (not shown in figure), an economizer (56), an air preheater (not shown in figure), a make-up water heater (not shown in figure), a de-aerator (not shown in figure), and the like for desired applications. Further, the flue gas is fed into the atmosphere by an outlet conduit (58). The arches (54) are refractory lined and positioned at selected locations for retaining the heat generated by the combustion of wastes. Further, the ash produced by the combustion of wastes is collected in the hopper (52).
The wastes that are fed from the two different entry points, can be fed at predetermined time intervals, in predetermined quantities & ratios, and at predetermined angles, depending on the type of wastes that are being fed.
Figure 3A and Figure 3B illustrate a side and a front schematic view respectively of a twin screw design of the screw conveyors (40), in accordance with one embodiment of the present disclosure. The screw conveyors (40), in the embodiment as shown in Figure 3A and Figure 3B, consists of stepped shafts (60) with variable pitch, and with serrated/cut flights for uniform feeding and mixing. Arrow (A) shows a forward motion of the wastes along the shaft (60), while arrow (B) shows a downward movement of the solid wastes from the top segment (X) to the bottom segment (Y). Implementation wise, the first screw conveyor (40') of the top segment (X) opens in the first conduit (38) towards the feeder wall (48), while the second screw conveyor (40?) of the bottom segment (Y), opens in the second conduit (42), below the first conduit. The first screw conveyor (40') provides a uniform and homogeneous blend of the solid and liquid wastes from the top segment (X).
The discharge of blended wastes from the first conduit (38) is independent of the discharge of the solid wastes from the second conduit (42). Further, the inclination of the conduits connecting the screw conveyors and the furnace wall is greater than the angle of repose of the wastes fed into the furnace section.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The waste combustion system of the present disclosure described herein above has several technical advantages including but not limited to the realization of:
? Avoiding seepage of liquid wastes below the combustion grate, blackout due to localized cooling, and incomplete combustion of the wastes;
? Homogenizing of the solid/liquid wastes, which facilitates proper combustion inside the waste combustion system; and
? Facilitating firing of liquid wastes in combination with solid wastes.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. ,CLAIMS:1. A waste combustion system for combusting solid and/or liquid wastes comprising:
a furnace section for receiving solid and/or liquid wastes through a fuel feeder, the fuel feeder having a compartmentalized structure having an operational top segment placed above an operation bottom segment; the top segment having a first screw conveyor for feeding solid and/or liquid wastes through a first conduit onto a combustion grate of the furnace section; the bottom segment having a second screw conveyor for feeding solid wastes through a second conduit, onto the combustion grate, wherein the feeding from the second conduit is done prior to the feeding from the first conduit.
2. The waste combustion system of claim 1, wherein at least one sprinkler is provided in the first screw conveyor for sprinkling liquid wastes onto the solid wastes moving inside the first screw conveyor, to provide a homogenized mixture.
3. The waste combustion system of claim 1, wherein the combustion grate rotates in a direction starting from a feeding side to an opposing side inside the furnace section.
4. The waste combustion system of claim 1, wherein the first screw conveyor and the second screw conveyor comprise at least one screw, said screw having a stepped shaft with flights.
5. The waste combustion system of claim 4, wherein said flight is at least one of ribbon flight, paddle flight, continuous flight, serrated flight and cut flight.
6. The waste combustion system of claim 1, wherein the solid wastes comprise agriculture waste, lignocellulose waste, and bagasse.
7. The waste combustion system of claim 1, wherein the liquid wastes comprise wastes from distilleries and industries.
8. The waste combustion system of claim 1, wherein at least one wall of the furnace section is arched.
9. The waste combustion system of claim 1, wherein the first conduit from the top segment connects the first screw conveyor to a furnace wall at a first position and the second conduit connects the second screw conveyor to a furnace wall at a second position, below the first position.
10. The waste combustion system of claim 1, wherein the inclination of the first and second conduits connecting the screw conveyors and the furnace wall are greater than the angle of repose of the wastes fed into the furnace section.