RU2810311C1 - Grate - Google Patents

Abstract

FIELD: thermal power engineering.

SUBSTANCE: design of a fixed volumetric grate for burning and drying solid fuels, including fuels with different particle fractions. The grate contains an upper part, including at least one row of grate plates, the width of which is less than the width of the gap between them, a lower part, located under the upper part and including at least one row of grate plates, the width of which is greater than the width of the gap between them, in this case, the size of the gap between the grate plates in the upper part of the grate is made smaller than the size of the retained particles, the size of the gap in the lower part of the grate is made greater than the size of the particles, the distance between adjacent rows of grate plates in the upper and lower parts of the grate is made no less than the width of the gap between grate plates of the upper row. The grate plates of the lower row are located under the slots of the upper row of grate plates in the upper and lower parts of the grate. The grate contains several rows of grate plates, while the size of the gap between the plates and the distance between adjacent rows in the upper part of the grate decreases from the top rows to the bottom.

EFFECT: ensuring complete combustion of raw material particles of mixed fractional composition.

10 cl, 3 dwg

Description

The invention relates to the field of thermal power engineering, namely to the design of a fixed volumetric grate for burning and drying solid fuels, including fuels with different particle fractions, and can be used in the furnaces of solid fuel heat generators, furnaces, steam and hot water boilers.

In thermal power engineering, there are a number of problems that arise when burning and drying fuel with different fractional compositions and a high content of small particles:

1) The problem of uniform distribution of raw materials with uniform access of oxygen for oxidation/drying and complete combustion of different fractions of raw materials.

This problem arises due to the fact that:

- on grates with a live section (the ratio of the total area of the holes to the total area of the grates) from 5% to 60%, the thickness of the layer of raw materials is different, the air movement is uneven, as a result of which small particles are blown out only in some places with a through hole in the grate with subsequent combustion only in a given place with access to oxygen (“crater” mode), while plugging of holes in other places occurs, which leads to different combustion times in different zones and under-combustion (incomplete combustion) of raw materials;

- on grates with a live cross section of up to 5% (for example, according to the decision on RF patent No. 2312273, published on December 10, 2007), the gas-dynamic resistance is significantly higher (due to the smaller number of holes compared to the number of holes with a live grate cross section of more than 5%) , which leads to significant energy costs to overcome it;

- with vortex combustion, the process of maintaining aerodynamics is unstable and also energy-consuming due to the fact that it is necessary to keep all the raw materials in the air during drying and combustion, while with strong air flows there is a significant volume of small particles (up to half of the supplied small particles of raw materials and an even larger volume the resulting ash, since it has a lower weight and particle size) rises and is carried away from the combustion chamber, which requires significant costs for their capture.

2) Insufficient use of the entire volume of the firebox

a) The basic scheme for using grates in the volume of fixed fireboxes is single-level with this level located on a plane at angles close to the horizontal, or on a plane broken in the middle with a slope towards the center.

In this case, the grates can be stationary with devices for turning the raw materials or movable.

The reason for the prevalence of the single-level scheme is the complexity of organizing controlled combustion and movement of raw materials at each level of the multi-level scheme at temperatures of 800-1000°C. The more levels, the higher the combustion area of raw materials in the same volume, which leads to an increase in power per unit volume of the furnace, which improves all equipment indicators (material intensity, capital intensity).

b) The use of moving combustion chambers or furnaces leads to increased costs and complexity of technical solutions, since it increases the requirements for all structural elements operating under high temperatures of 800-1000 ° C and under severe structural loads and mechanical stress. Accordingly, the cost of the entire structure increases with the same power indicators.

3) The problem of turning raw materials and moving raw materials and ash.

During combustion, ash envelops unburned particles, which creates the need to turn the raw material to ensure access to oxygen. In this case, the ash must be pushed down for subsequent removal. It is highly advisable to do this without a strong upward air flow in order to prevent the carryover of ash particles and unburned raw materials into the atmosphere.

4) Energy recovery to increase efficiency.

To maximize the use of energy released during combustion and increase efficiency, it is necessary to make full use of the exhaust hot gases, for example, for pre-drying the incoming raw materials.

5) Purification of flue gases from entrained particles.

During combustion, both ash and light fuel particles are carried away in the flue gas stream. Depending on environmental requirements, it is necessary to use various cleaning methods, which involves the use of additional equipment with chambers (cyclones, sedimentation chambers) to organize filtration and requires quite significant energy costs to create pressure/exhaust of exhaust gases and overcome gas-dynamic resistance. Therefore, minimizing the amount of entrained particles will significantly simplify and reduce the cost of such activities.

A grate is known (RF patent No. 2234641, published on August 20, 2004), containing rows of grate plates located in the volume of a rotating combustion chamber in a checkerboard pattern under each other and rotated relative to the axis of rotation of the combustion chamber at an angle of 10-15°.

Thanks to this design of the grate, maximum contact of fuel particles with air oxygen is ensured both during the fall of the fuel from the grate plates and while it is on the plates.

However, in this case, the grate plates are attached to the inner walls of the chamber and rotate with it, that is, the firebox with the plates rotates to mix the raw materials. This design requires especially strong, heat-resistant materials, has a short service life and high wear, since it rotates under conditions of high temperatures during combustion up to 800-1000°C. In this case, the raw material is not distributed independently, but as a result of the rotation of the chamber. To maintain the axis of rotation and to avoid deformation, the design of the chamber with a grate must have high frame strength. Also, the size of the firebox will be limited, since it is impossible to rotate a huge structure heated to 800-1000°C for a long time without breakdowns.

In this case, before loading the raw materials, preliminary preparation will be required, which involves grinding and bringing the fuel to approximately the same fraction. This is necessary because in this installation all particles, both large and small, move inside the firebox at the same speed. There is no way to regulate the residence time of raw material particles of different sizes in the furnace, retaining large particles for a longer time. If you load different fractions of raw materials, a fast speed will lead to incomplete combustion of large particles, or, when choosing a slow feed rate of raw materials (focusing on the combustion rate of large particles), there will be an excessive time for small particles to remain in the furnace, and as a result, the productivity of the device will be less.

All of the above ultimately indicates the ineffectiveness of using such a grate and the significant costs of its operation.

A grate is known (RF patent No. 2206823, published June 20, 2003), taken as the closest analogue to the claimed solution, containing vertically arranged rows of grate plates arranged in a checkerboard pattern within the furnace volume. In this case, the plates of the grate are made vibrating and are located to form gaps relative to one of the walls of the firebox.

Thanks to this design, fuel particles are poured from top to bottom. However, such movement of particles is ensured only due to the presence of vibration during the operation of vibration drives and motors. In the absence of such vibration, raw materials will accumulate on the upper rows of grate plates and clog the passage of raw material particles to the underlying levels. That is, in this case there is no self-distribution of raw materials throughout the entire volume of the furnace and no self-regulation of the thickness of the raw materials remaining on the grate plates.

Also in this patent there is no possibility of distributing raw material particles of different sizes at different levels in the volume of the furnace and storing them there for pre-drying for a longer time. It is necessary to pre-grind the raw materials and achieve approximately the same fractional composition for uniform drying and combustion, since all raw materials will move down at the same speed (you will have to choose the feed rate of the raw materials, focusing on the largest particles, which worsens the performance of the device, see above). In addition, the presence of vibration of the grate plates attached to the edges of the combustion chamber will require high strength from them. For large firebox sizes, such grate plates will require either a significant increase in their thickness, which will limit the number of rows in the volume of the furnace, or the presence of intermediate fastenings that will allow transmission and withstand vibrations, which, taking into account temperatures of 800-1000 ° C, is extremely difficult and costly.

The technical objective of the present invention is to create a grate that eliminates the disadvantages inherent in analogues, ensures that the entire volume of the furnace with air gaps for access of gases is filled with raw materials, and increases the efficiency of combustion of different fractions of raw materials.

The technical result of the invention is to ensure complete combustion of raw material particles of mixed fractional composition due to the design features of the solution, which allow for self-distribution of raw materials throughout the entire volume of the furnace from top to bottom under the force of gravity and self-regulation of the residence time of particles of different sizes in the furnace until complete combustion.

The technical result is achieved by using a grate containing:

- the upper part, including at least one row of grate plates, the width of which is less than the width of the gap between them;

- the lower part, located under the upper part and including at least one row of grate plates, the width of which is greater than the width of the gap between them;

- in this case, the size of the gap between the grate plates in the upper part of the grate is made smaller than the size of the retained particles;

- the size of the slot in the lower part of the grating is larger than the size of the particles;

- the distance between adjacent rows of grate plates in the upper and lower parts of the grate is made no less than the width of the gap between the grate plates of the upper row;

- the grate plates of the lower row are placed under the slots of the upper row of grate plates in the upper and lower parts of the grate.

In a particular case, the upper part of the grate contains several rows (two or more) of grate plates, while the size of the gap between the plates and the distance between adjacent rows in the upper part of the grate decreases from the top rows to the bottom to gradually retain smaller particles.

In a particular case, the size of the slots in one row of grate plates is different. But at the same time, the condition is met that in the upper part of the lattice the slits retain the particles of raw materials, and in the lower part of the lattice the slits allow the particles of raw materials to pass further down.

In a particular case, the lower row of grate plates is located at an angle horizontally relative to the upper row of grate plates.

In a particular case, the rows of grate plates are made with the same distance between them.

In a particular case, rows of grate plates are made with different distances between them.

In a particular case, the size of the gap between the plates in the lower part of the grid from the upper rows to the lower ones is reduced to effectively use the space and regulate the gas flow rate and the speed of particle movement.

In a particular case, the width of the plates in the lower part of the grate increases from the upper rows to the lower ones for more efficient use of space, achieving the necessary retention dynamics and complete combustion of smaller particles.

In a particular case, the grate plates of the upper part of the grate retain particles larger than 50 mm in size.

In a particular case, the grate plates of the lower part of the grate retain particles smaller than 50 mm in size.

In a particular case, the distance between the rows of grate plates is ensured by using a support-stand, the height of which is greater than the width of the gap between the grate plates of the row that is located on top of the support-stand.

In a particular case, the support-stand at the top of the grille consists of one or two horizontal slats and two vertical slats.

In a particular case, the support-stand in the upper part of the grille is made solid.

In a particular case, the support-stand at the bottom of the grille is made solid.

Also, nozzles 7 are installed in the furnace walls near the grate to supply air to blow off ash and raw material particles from the grate plates.

Making the width of the grate plates located in the upper part of the grate smaller than the width of the gap between them allows large particles of raw materials, the size of which exceeds the width of the gap between these plates, to be retained between the plates, but at the same time allow small particles to pass to the underlying levels, thereby distribution of raw materials across levels in the furnace volume and reducing the time spent in the furnace of small particles and increasing the time spent in the furnace of large particles.

When burned and dried, the size of the pieces will decrease, they will fall down and collapse, which will lead to independent grinding and complete combustion of the raw material. In this case, the residence time of large particles of raw materials in the furnace will depend on the rate of their burning and downward movement. Thus, large, wet, poorly burning pieces will remain in the firebox longer.

Reducing the size of the gap from the upper levels to the lower allows you to gradually pass large pieces that decrease in the process of drying, crushing and burning down until they are completely crushed, for each piece for a different time, depending on their initial moisture, fragility and size.

This ensures self-regulation of the time each particle of raw material spends in the furnace.

Making the width of the grate plates located in the lower part of the grate no less than the width of the gap between them allows you to retain unburned particles of raw materials, preventing them from quickly falling into the ash pan, and to collect on the plates particles of raw materials that have fallen from above, which are under the force of gravity and influence heavier particles falling from above roll down from the plates and then through cracks, the size of which is larger than the size of the particles of the raw material falling on this level, fall onto the grate plates of the lower row of the lower part of the grate (if the number of rows of plates in the lower part of the grate is more than one) , which are located under the slots of the upper row of plates, from which the raw material particles fell. As they move, the particles are dried, freed from the ash enveloping them, further crushed and burned out.

Rotating the underlying row of plates horizontally at a certain angle (90 degrees) will allow pyramids of raw material particles to be formed on the underlying plate, thereby increasing the area of their contact with gases.

The number of rows in the lower part is selected in such a way that only burnt particles enter the ash pan from the bottom row of plates.

The location of the grate plates of the lower row under the slots of the higher row of grate plates in the upper and lower parts of the grate allows you to close the gap in the vertical projection between the plates of the upper level, preventing the particles of raw materials from immediately falling even lower, bypassing the plate of the lower level.

Making the distance between the rows of grate plates no less than the width of the gap between the grate plates of the upper row allows particles no larger than the size of the gap to roll freely (without getting stuck between the rows) from the top-level plate through the gap to the plate of the bottom row and then with a shift to the bottom rows , thereby distributing fallen raw material particles on the lower rows of grate plates, and also leaving a gap for air to pass in order to ensure complete combustion or drying of raw material particles throughout the entire volume of the furnace. That is, the distance between the rows of plates and, accordingly, the height of the support-stand are chosen so that the entire space between the rows of the grate is not covered with raw material particles, when gases stop passing to the overlying rows of the grate and the particles cannot roll down onto the underlying rows.

Thus, the dimensions and location of the grate plates in the grate, depending on the fractional composition of the raw material, are chosen in such a way that the raw material, after being fed to the upper part of the grate, is independently distributed over all the underlying rows of grate plates located throughout the entire volume of the furnace, under the force of gravity.

For periodic cleaning of the plates from raw materials and ash, cleaning of raw material particles from enveloping ash, nozzles 7 can be installed in the walls of the firebox/furnace for blowing with compressed air, and several nozzles can be installed on each row of grate plates. The nozzles are connected through a solenoid valve controlled by a program or via a timer.

As a result, a grate is being developed, which allows automatically, when feeding raw materials, to distribute it throughout the entire volume of the furnace (large particles will be located above, small ones - below), independently (due to the design) to regulate the time the raw materials are in the furnace and its movement down to the ash pan until full combustion, as well as radically reduce capital and operating costs for burning or drying raw materials.

Including the design of such a grate allows:

- increase the power of the furnace for burning/drying raw materials with the same weight and size of the furnace, using the entire volume of the furnace to maximize the area of combustion or drying of raw materials;

- improve the weight and size parameters of the furnace, reduce the specific costs of the materials used and, accordingly, reduce capital costs at the same power;

- reduce energy consumption for the operation of furnace mechanisms, increase the service life of the furnace and its elements, eliminating the presence of moving parts;

- increase the range of raw materials for combustion in terms of humidity and slagging, suitable for use, by maximizing the use of the energy of the burned raw materials for heating and drying the incoming feedstock, while increasing the efficiency of the combustion chamber;

- simplify and reduce the cost of manufacturing a grate by making it from standard simple parts: identical flat plates and stands without or with a minimum number of shaped elements;

- solve the problem of efficient combustion/drying of fines (sawdust, fine coal), ensuring access of oxygen/gases to the maximum surface of the raw material per unit of time without energy costs;

- reduce the harmfulness of emissions without additional costs through the interaction of incoming raw materials and exhaust gases and the deposition of entrained particles on the incoming raw materials.

In fig. 1 shows the design of the inventive grate.

In fig. Figure 2 shows the design of the inventive grate with additionally installed nozzles in the lower part of the grate.

In fig. Figure 3 shows grate plates in the lower part of the grate with piles of fuel particles.

According to FIG. 1, the grate contains an upper part with rows of grate plates 1 located vertically one below the other. The width of such grate plates 1 is less than the width of the slot 2 between them.

Between the indicated rows of plates in the upper part of the grate there is a support-stand 3, which is a solid or composite structure.

The grate also contains a lower part with rows of grate plates 4 located vertically one below the other. The width of such grate plates 4 is greater than the width of the slot 5 between them.

The rows of grate plates 4 in the lower part of the grate are arranged so that the plates of the underlying row are placed under the slots of the upper row of plates.

Between the indicated rows of plates in the lower part of the grate there is a support-stand 6, which is made solid.

The horizontal size of the gap between the grate plates 1 in the upper part of the grate is selected in the following way:

- the width of the gap between the plates is taken slightly less than the size of the largest particles in order to allow small particles to fall down and not accumulate on the plates, and large particles to linger at the top;

- on the underlying rows of the upper part of the grate, the width of the gap between the grate plates must be gradually reduced.

As a result, the raw materials (large particles, often 50 mm in size or more) are automatically sorted by size from larger ones at the top to smaller ones at the bottom, distributed throughout the upper part of the grid.

Given the type of raw material available and the maximum particle sizes that come from the upper or lower level of the grate (the maximum particle size will be equal to the width of the slot of the last bottom row of the upper part of the grate), it is necessary to ensure that the maximum triangular pile of raw materials is formed on each plate of the underlying row (Fig. 3) did not block the gap between the plates of the overlying row and at the same time there remained a gap both for the passage of gases to the upper rows and for the rolling of falling particles along this slide onto the underlying rows. It is necessary to take into account the size of the particles of the raw material - they are guaranteed to pass to the lower levels, rolling down from one slide to another onto the underlying rows until they stop on one of the plates. In this case, the feed rate of the raw material must be such that the raw material has time to burn through and free up space on the plates for the raw material particles falling from above.

The width of the slit should at least allow a particle falling from the top row to pass into this slit, i.e. The minimum size of the slit is equal to the maximum size of particles falling onto it. In practice, to ensure stable operation, it is better to leave the slit width several times larger than the particle size.

Typically, the height of the pile of raw materials on the plate is no more than the width of the plate, so the distance between the rows of grate plates should be greater than the width of the slot in the overlying row of grate plates, and can be one plate width or more.

The length of the grate plates 1 and 4 is selected taking into account thermal expansion, so that the ends of the plates do not have a stop and a gap is provided for such expansion in order to prevent deformation of the plates. If the firebox is of significant size, it is better to take several plates along the length (for example, with a firebox width of 2 m, you can take four 50 cm plates with gaps between the plates for thermal expansion).

Between all rows of grate plates 1 and 4 there are supports-stands 3 and 6, on which the plates of the upper level rest perpendicularly and which press the plates of the lower level.

The support-stand can be made solid or with cutouts, or composite with a large distance between the rows.

The thickness of the support-stand must be sufficient to ensure the stability of this support and the rows of grate plates above (for example, 2-3 times greater than the thickness of the grate plates). The length of the support-stand can be any. It depends on the size of the grate and firebox. In this case, it is necessary to choose the length, taking into account thermal expansion, the presence of a gap at the ends, so that the support does not rest against other parts and does not deform when lengthened.

The attachment of the grate plates to the support-stand should not be made rigidly, but with gaps for thermal expansion of both the support-stand and the grate plates, or the support-stand can be made of a material with minimal thermal expansion. The distance between the supports is selected in such a way as to minimize or eliminate deflections of the grate plates over time, which depend on the thickness and material of the plates. For example, for a plate length of 50 cm, you can take two or three supports. In this case, it is not necessary to place the support-stand from the end of the plate; you can place one support-stand at a distance of 12 cm from the edge of the plate, then the second after 24 cm, which will be located at a distance of approximately 12 cm from the second edge, taking into account the thickness of the support-stands. Each next top row will rest on the previous one through supports. All connections must be made loosely, with gaps, so that deformation of the grate plates and grate does not occur.

It is possible to use cutouts or protrusions on the support-stand to fix the position of the grate plates on the support-stand relative to each other and maintain the width of the gap between the plates, as well as on the plates to better fix their position relative to the support of the stand along the length.

It is also possible to use inserts, holes, etc., which improve the fixation of the grate elements relative to each other.

In any case, all elements are pressed down by the overlying levels and fixed.

The dimensions of the grate can be any depending on the selected lengths of the plates and the length of the support.

The result is a three-dimensional grate from grate plates, for example, 50 cm x 50 cm with any height, for example, also 50 cm (one block). Depending on the size of the firebox, several such grate blocks can be placed inside one firebox, both in height and in length and width.

In the case of using a volumetric grate in a furnace for burning raw materials, after the raw materials burn out on the plates and ash forms, particles of raw materials falling from above will squeeze the ash to the lower levels and further to the bottom of the furnace, which occurs automatically without additional energy costs and auxiliary mechanisms such as a screw strip .

To periodically completely clean the plates, it is necessary to use a non-contact method, for example, with compressed air through nozzles located between the levels (Fig. 2). The direction of the nozzles is along the supports so that the air does not meet resistance.

These nozzles are connected through a solenoid valve controlled by a program or via a timer.

Thus, the proposed solution allows:

- the raw materials themselves, under the influence of gravity, are evenly distributed and heated throughout the entire volume of the furnace with predetermined characteristics (the thickness of the layer of raw materials on the plates, the width of the air passage between the piles of raw materials), thereby ensuring controllability of the combustion/drying process, setting the ignition rate and burning time during combustion raw materials or by setting the drying time through the established thickness of the raw materials on the plate;

- minimize the consumption of materials for the structure and expensive heat-resistant material for the manufacture of grates and, accordingly, reduce the weight of the finished system (furnace, grate, foundation), reduce the requirements for the strength of materials;

- eliminate or minimize energy costs for moving raw materials/turning in the furnace and removing ash from the grate, since when raw materials are supplied from above, the raw material is independently distributed over all plates of the grate, and the combustion ash is pushed down when adding new raw materials, which allows automatic remove ash from the grate to the bottom of the stove;

- eliminate or minimize thermal deformation of the grate for large firebox sizes, since the proposed grate design and method of its assembly leaves gaps between all elements, which ultimately leads to the absence of deformation due to thermal expansion and subsequent compression during cooling;

- increase the power of the furnace;

- increase the service life of all structural elements, since there are no mechanical movements of moving parts in the furnace or movements of grate plates or rustling strips inside the combustion space, which eliminates or minimizes mechanical wear of heat-resistant materials;

- ensure heat recovery from exhaust gases, which dry the incoming raw materials on the upper rows of the grate;

- ensure natural filtration, since flying ash particles and small unburned particles, meeting wet raw materials, are deposited on it, while the incoming wet raw materials play the role of a wet scrubber.

Claims (10)

1. A grate, characterized in that it contains an upper part, including at least one row of grate plates, the width of which is less than the width of the gap between them, a lower part, located under the upper part and including at least one row of grate plates, the width of which is greater , than the width of the gap between them, while the size of the gap between the grate plates in the upper part of the grate is made smaller than the size of the retained particles, the size of the gap in the lower part of the grate is made larger than the size of the particles, the distance between adjacent rows of grate plates in the upper and lower parts The grate is made no less than the width of the slot between the grate plates of the upper row; the grate plates of the lower row are placed under the slots of the upper row of grate plates in the upper and lower parts of the grate. 2. The grate according to claim 1, characterized in that it contains several rows of grate plates, while the size of the gap between the plates and the distance between adjacent rows in the upper part of the grate from the top rows to the bottom decreases to gradually retain smaller particles. 3. The grate according to claim 1, characterized in that the lower row of grate plates is located at an angle horizontally relative to the upper row of grate plates. 4. The grate according to claim 1, characterized in that the rows of grate plates are made with the same distance between them. 5. The grate according to claim 1, characterized in that the rows of grate plates are made with different distances between them. 6. The grate according to claim 1, characterized in that the size of the gap between the plates in the lower part of the grate from the top rows to the bottom is reduced for more efficient use of space and regulation of the gas flow rate and the speed of particle movement. 7. The grate according to claim 1, characterized in that the width of the plates in the lower part of the grate increases from the top rows to the bottom for more efficient use of space, achieving the necessary retention dynamics and complete combustion of smaller particles. 8. The grate according to claim 1, characterized in that the grate plates of the upper part of the grate retain particles larger than 50 mm. 9. The grate according to claim 1, characterized in that the grate plates of the lower part of the grate retain particles less than 50 mm in size. 10. The grate according to claim 1, characterized in that the distance between the rows of grate plates is provided by using a support-stand, the height of which is greater than the width of the gap between the grate plates of the row that is located on top of the support-stand.