Indirect heating low-rank coal pyrolysis rotary kiln and working method thereof

Abstract

The invention relates to an indirect heating low-rank coal pyrolysis rotary kiln and a working method thereof. A tube nest heat exchange assembly and a central heat exchange sleeve are arranged in the rotary kiln; the center heat exchange sleeve is arranged in the center of the rotary kiln in the axial direction of the rotary kiln. The tube nest heat exchange assembly comprises a plurality of sets of heat exchange tube nests arranged in the circumferential direction of the rotary kiln, and each set of heat exchange tube nests comprises a plurality of heat exchange tubes arranged in the radial direction of the rotary kiln. The mode of indirect heat exchange between the central heat exchange sleeve and the heat exchange tubes and the low-rank coal is adopted, so that the equipment cost is reduced, and the pyrolysis capacity is improved; the interior of the barrel is divided into a plurality of independent bins through the partition plates, low-rank coal moves towards the kiln tail in the independent bins, the low-rank coal can be in close contact with the heat exchange tube nest, the center heat exchange sleeve and the partition plates when the independent bins rotate to any position, and therefore uniform heating and efficient pyrolysis of the low-rank coal are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of low-rank coal pyrolysis, and in particular to an indirectly heated low-rank coal pyrolysis rotary kiln and a working method thereof. Background Art

[0002] Coal chemical industry, oil shale and pyrolysis of biomass are important energy conversion methods. Through the pyrolysis process, low-rank coal and other raw materials can be converted into high-value fuel gas and chemicals, and the performance of the pyrolysis equipment directly affects the pyrolysis efficiency and economic benefits. Among the existing pyrolysis equipment, low-rank coal pyrolysis rotary kiln is widely used due to its large processing capacity and strong adaptability to coal particle size. The heat exchange methods of low-rank coal pyrolysis rotary kiln include direct heat exchange (internal heat) and indirect heat exchange (external heat). The heat carriers include solid heat carriers and gas heat carriers. Among them, the indirect heat exchange rotary kiln with hot air as the heating medium is the most representative. For the indirect heat exchange rotary kiln with hot air as the heating medium, the conventional heating methods mainly include hot air jacket heating, hot air tube heating, "jacket + tube" heating and other methods (such as coal running inside the tube and hot air running outside the tube).

[0003] Although the existing indirect heat exchange rotary kiln using hot air as the heating medium can achieve pyrolysis of low-rank coal to a certain extent, there are still some problems in the actual production process, which restricts its promotion and application.

[0004] First, the pyrolysis of low-rank coal needs to be achieved through contact heat exchange, and when the rotary kiln is in operation, the material filling rate needs to be controlled within a reasonable range (usually not more than 20%); in this case, only a small amount of tubes buried by the material at the bottom of the rotary kiln shell or part of the jacket in contact with the material participate in the contact heat exchange, resulting in low heat exchange efficiency.

[0005] Secondly, if a hot air jacket heat exchange structure is used, since there is no insulation layer inside the rotary kiln cylinder, the hot air heats the outer wall of the cylinder, and the heat from the outer wall is transferred to the coal inside the cylinder for pyrolysis. In this case, the cylinder is mostly made of heat-resistant steel, which leads to a sharp increase in equipment cost. At the same time, in order to ensure the mechanical strength of the rotary kiln equipment and control the deformation within a certain range, the upper limit of the air supply temperature cannot be too high, which in turn limits the pyrolysis capacity. In addition, the use of a hot air jacket is not conducive to the installation of multiple support levels in the rotary kiln (for each additional support level, the hot air jacket is cut off at the corresponding wheel belt), and the large ring gear cannot be set in a reasonable position, which restricts the development of rotary kiln equipment towards large-scale development.

[0006] Thirdly, the passability of materials in the rotary kiln cylinder mainly depends on the inclination of the cylinder and the rotation speed adjustment of the rotary kiln. When the number of components in the rotary kiln is large and the structure is complex, it will increase the difficulty of material passing, resulting in a decrease in production efficiency. Summary of the Invention

[0007] The present invention provides an indirectly heated low-rank coal pyrolysis rotary kiln and a working method thereof, which adopts a "central heat exchange sleeve + heat exchange tube" method to indirectly exchange heat with low-rank coal, which not only reduces equipment cost but also improves pyrolysis capacity; a number of independent silos are separated from the cylinder by partitions, and the low-rank coal moves toward the kiln tail in the independent silos. When the independent silos rotate to any position, the low-rank coal will maintain close contact with the heat exchange tubes, the central heat exchange sleeve and the partitions, thereby achieving uniform heating and efficient pyrolysis of the low-rank coal.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] An indirectly heated low-rank coal pyrolysis rotary kiln comprises a rotary kiln, wherein the kiln head of the rotary kiln is higher than the kiln tail, a feeding device is provided at the kiln head, and a discharging device is provided at the kiln tail; a tube-and-tube heat exchange assembly and a central heat exchange sleeve are provided in the rotary kiln; the central heat exchange sleeve is provided at the center of the rotary kiln along the axial direction of the rotary kiln; the tube-and-tube heat exchange assembly comprises a plurality of groups of heat exchange tubes arranged along the circumference of the rotary kiln, each group of heat exchange tubes comprises a plurality of heat exchange tubes arranged along the radial direction of the rotary kiln, and all the heat exchange tubes are arranged parallel to the axial direction of the rotary kiln; an air supply section is provided at the kiln tail, and an air outlet section is provided at the kiln head, the hot air inlet of the heat exchange tube and the hot air inlet of the central heat exchange sleeve are both connected to the hot air supply duct through the air supply section, and the hot air outlet of the heat exchange tube and the hot air outlet of the central heat exchange sleeve are both connected to the hot air outlet duct through the air outlet section.

[0010] The cylinder of the rotary kiln is composed of a steel cylinder and an insulation layer inside the cylinder, and the steel cylinder is made of ordinary carbon steel.

[0011] A plurality of partitions are evenly arranged along the circumferential direction in the annular space between the cylinder and the central heat exchange sleeve of the rotary kiln, so as to divide the annular space into a plurality of independent chambers, and a plurality of groups of heat exchange tubes are respectively arranged in each independent chamber.

[0012] In the same group of heat exchange tubes arranged along the radial direction, the diameters of the heat exchange tubes increase successively from the inside to the outside.

[0013] The heat exchange tubes in the same group arranged radially are supported and fixed by the same hosting bracket; the hosting bracket consists of a vertical plate and two side plates. The vertical plate has holes for the heat exchange tubes to pass through. The two side plates are symmetrically arranged on both sides of the vertical plate, and the side plates are inclined along the axial direction of the rotary kiln. The spacing between the side plates toward the kiln tail end is smaller than the spacing between the side plates toward the kiln head end.

[0014] A plurality of annular fins are axially arranged on the outer wall of the central heat exchange sleeve.

[0015] The cylinder of the air supply section is provided with multiple air inlets, some of which are provided with 90° elbows, and other parts are provided with straight pipes; each heat exchange tube is connected to the hot air supply duct through a corresponding 90° elbow; the central heat exchange sleeve located at the tail of the kiln is provided with multiple hot air inlets along the circumferential and axial directions, which are connected to the hot air supply duct through corresponding straight pipes.

[0016] The air outlet section is provided with an air collecting hood on the periphery of the feeding device, and the annular space between the air collecting hood and the feeding device is the air outlet channel; the hot air outlet of the heat exchange tube is directly connected to the air outlet channel; the central heat exchange sleeve located at the kiln head is provided with multiple hot air outlets along the circumferential and axial directions and connected to the air outlet channel; the hot air outlet is provided on the air collecting hood and connected to the hot air outlet duct.

[0017] The hot air supply duct and the hot air outlet duct are connected to form a hot air circulation duct, and the hot air circulation duct is provided with a hot air circulation fan and a supplementary hot air inlet.

[0018] An operating method of an indirectly heated low-rank coal pyrolysis rotary kiln includes the following steps:

[0019] 1) Low-rank coal enters the kiln head of the rotary kiln through the feeding device, enters the independent chambers and moves to the kiln tail as the cylinder rotates;

[0020] 2) Hot air enters the tube heat exchange assembly and the central heat exchange sleeve from the air supply section at the kiln tail, and flows toward the kiln head;

[0021] 3) As the low-rank coal moves toward the kiln tail, it rotates with the drum in the corresponding independent chamber, and indirectly exchanges heat with the multiple heat exchange tubes in the independent chamber and the hot air flowing in the opposite direction in the central heat exchange sleeve, thereby achieving pyrolysis;

[0022] 4) The upgraded coal after pyrolysis is discharged from the discharge device at the kiln tail. The hot air reaching the kiln head after heat exchange flows out from each heat exchange tube and the central heat exchange sleeve and is discharged outside through the air outlet section. The discharged hot air returns to the air supply section at the kiln tail through the hot air circulation pipe for recycling.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The low-rank coal pyrolysis rotary kiln described in the present invention adopts a "central heat exchange sleeve + heat exchange tube" method for indirect heat exchange with low-rank coal, which can not only reduce equipment costs but also effectively improve the pyrolysis capacity; specifically, the central heat exchange sleeve is coaxially arranged with the cylinder of the rotary kiln, and the annular space between the two is divided into several independent chambers by partitions, and each independent chamber has multiple groups of heat exchange tubes passing through; hot air is introduced from the tail of the kiln into the tube heat exchange assembly and the central heat exchange sleeve, and the low-rank coal entering the rotary kiln cylinder from the kiln head moves to the tail of the kiln in each independent chamber. When the rotary kiln rotates to any angle, the low-rank coal can indirectly exchange heat with multiple heat exchange tubes and the hot air in the central heat exchange sleeve, thereby achieving rapid pyrolysis of the low-rank coal while ensuring heating uniformity and improving pyrolysis efficiency.

[0025] 2) The low-rank coal pyrolysis rotary kiln of the present invention adopts an internal insulation method, and the material of the steel cylinder can be ordinary carbon steel, which greatly reduces the equipment cost; the rotary kiln can be equipped with multiple support gears according to production capacity requirements, and the transmission device can also be set in a reasonable position, which is beneficial to improving the reliability of the rotary kiln and facilitating the large-scale design of the rotary kiln.

[0026] 3) In the low-rank coal pyrolysis rotary kiln described in the present invention, the two side panels on the supporting bracket used to support each group of heat exchange tubes adopt a special design of "wide spacing toward the kiln head end and narrow spacing toward the kiln tail end". When the cylinder rotates, the low-rank coal will be lifted and will naturally slide along the inclined surface of the side panels toward the kiln tail end, which is beneficial to improving the passability of the material.

[0027] 4) In the low-rank coal pyrolysis rotary kiln of the present invention, annular fins can be further provided on the outer side of the inner casing, and the partition itself is also a fin structure, thereby further increasing the heat exchange area and improving the pyrolysis efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the three-dimensional structure of the indirectly heated low-rank coal pyrolysis rotary kiln of the present invention (the support and rotation systems are not shown).

[0029] Figure 2 yes Figure 1 Enlarged view of the middle kiln tail.

[0030] Figure 3 yes Figure 1 An enlarged view of the middle kiln head.

[0031] Figure 4 It is a middle cross-sectional view of the indirectly heated low-rank coal pyrolysis rotary kiln according to the present invention.

[0032] Figure 5 Schematic diagram of the hosting bracket of the present invention.

[0033] In the figure: 1-feeding device; 2.1-insulation layer inside the cylinder; 2.2-steel cylinder; 2.3-heat exchange tubes; 2.4-central heat exchange sleeve; 2.5-annular fins; 2.6-partition; 2.7-cushion bracket; 3-discharge device. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0035] like Figure 1-Figure 4 As shown, the present invention describes an indirectly heated low-rank coal pyrolysis rotary kiln, which includes a rotary kiln. The kiln head of the rotary kiln is higher than the kiln tail, and a feeding device 1 is provided at the kiln head and a discharging device 3 is provided at the kiln tail; a tube-in-tube heat exchange assembly and a central heat exchange sleeve 2.4 are provided in the rotary kiln; the central heat exchange sleeve 2.4 is provided at the center of the rotary kiln along the axial direction of the rotary kiln; the tube-in-tube heat exchange assembly includes a plurality of groups of heat exchange tubes 2.3 arranged along the circumference of the rotary kiln, each group of heat exchange tubes 2.3 includes a plurality of heat exchange tubes arranged along the radial direction of the rotary kiln, and all heat exchange tubes are arranged parallel to the axial direction of the rotary kiln; an air supply section is provided at the kiln tail and an air outlet section is provided at the kiln head, the hot air inlet of the heat exchange tube and the hot air inlet of the central heat exchange sleeve 2.4 are both connected to the hot air supply duct through the air supply section, and the hot air outlet of the heat exchange tube and the hot air outlet of the central heat exchange sleeve 2.4 are both connected to the hot air outlet duct through the air outlet section.

[0036] The cylinder of the rotary kiln is composed of a steel cylinder 2.2 and an insulation layer 2.1 inside the cylinder. The steel cylinder 2.2 is made of ordinary carbon steel.

[0037] A plurality of partitions 2.6 are evenly arranged along the circumference in the annular space between the cylinder of the rotary kiln and the central heat exchange sleeve 2.4, dividing the annular space into a plurality of independent chambers, each of which is provided with a plurality of groups of heat exchange tubes 2.3.

[0038] In the same group of heat exchange tubes 2.3 arranged along the radial direction, the diameters of the heat exchange tubes increase successively from the inside to the outside.

[0039] The heat exchange tubes in the same group arranged radially are supported and fixed by the same hosting bracket 2.7; Figure 5 As shown, the hosting bracket 2.7 consists of a vertical plate and two side plates. The vertical plate has holes for the heat exchange tubes to pass through. The two side plates are symmetrically arranged on both sides of the vertical plate, and the side plates are inclined along the axial direction of the rotary kiln. The spacing between the side plates toward the kiln tail end is smaller than the spacing between the side plates toward the kiln head end.

[0040] A plurality of annular fins 2.5 are axially arranged on the outer wall of the central heat exchange sleeve 2.4.

[0041] The cylinder of the air supply section is provided with multiple air inlets, some of which are provided with 90° elbows, and some of which are provided with straight pipes; each heat exchange tube is connected to the hot air supply duct through a corresponding 90° elbow; the central heat exchange sleeve 2.4 located at the tail of the kiln is provided with multiple hot air inlets along the circumferential and axial directions, which are connected to the hot air supply duct through corresponding straight pipes.

[0042] The air outlet section is provided with an air collecting hood outside the feeding device, and the annular space between the air collecting hood and the feeding device is the air outlet channel; the hot air outlet of the heat exchange tube is directly connected to the air outlet channel; the central heat exchange sleeve 2.4 located at the kiln head is provided with multiple hot air outlets along the circumferential and axial directions and connected to the air outlet channel; the hot air outlet is provided on the air collecting hood and connected to the hot air outlet duct.

[0043] The hot air supply duct and the hot air outlet duct are connected to form a hot air circulation duct, and the hot air circulation duct is provided with a hot air circulation fan and a supplementary hot air inlet.

[0044] The working method of the indirect heating low-rank coal pyrolysis rotary kiln of the present invention includes the following steps:

[0045] 1) Low-rank coal enters the kiln head through the feeding device 1, enters the independent chambers and moves to the kiln tail as the cylinder rotates;

[0046] 2) Hot air enters the tube heat exchange assembly and the central heat exchange sleeve 2.4 from the air supply section at the kiln tail, and flows toward the kiln head;

[0047] 3) As the low-rank coal moves toward the kiln tail, it rotates with the drum in the corresponding independent chamber, indirectly exchanging heat with the multiple heat exchange tubes in the independent chamber and the hot air flowing in the opposite direction in the central heat exchange sleeve 2.4, achieving pyrolysis;

[0048] 4) The upgraded coal after pyrolysis is discharged from the discharge device 3 at the kiln tail. The hot air reaching the kiln head after heat exchange flows out from each heat exchange tube and the central heat exchange sleeve 2.4 and is discharged outside through the air outlet section. The discharged hot air returns to the air supply section at the kiln tail through the hot air circulation pipe for recycling.

[0049] The indirect heating low-rank coal pyrolysis rotary kiln described in the present invention is different from the conventional rotary kiln in that it adopts the "tube-in-tube heat exchange component + central heat exchange sleeve" method for indirect heat exchange with low-rank coal, and the other components of the rotary kiln (such as the support and rotation system) all adopt conventional settings.

[0050] Since the shell-and-tube heat exchange assembly and the central heat exchange sleeve 2.4 are both built-in, no additional auxiliary equipment is required on the outer surface of the rotary kiln cylinder except for the kiln head and kiln tail. Moreover, since there is no jacket structure on the inner side of the cylinder, an inner cylinder insulation layer 2.1 can be provided on the inner side of the cylinder, and the steel cylinder 2.2 can be made of ordinary carbon steel. Compared with a solution in which the cylinder must be made of heat-resistant steel because an inner insulation layer cannot be provided, this greatly reduces the equipment manufacturing cost.

[0051] Conventional solutions for heat exchange by installing tubes within the rotary kiln cylinder have the tubes directly installed within the cylinder. As the cylinder rotates, the material is always at the bottom of the cylinder, resulting in most of the tubes not being in contact with the material for most of the time, leading to low heat exchange efficiency. However, in the present invention, a partition 2.6 is used within the rotary kiln cylinder to separate the annular space between the cylinder and the central heat exchange sleeve 2.4 into several independent chambers. Multiple groups of heat exchange tubes 2.3 are installed within each independent chamber. Hot air is introduced into all the heat exchange tubes composing the heat exchange tubes 2.3 and the central heat exchange sleeve 2.4. As the low-rank coal rotates within each independent chamber, it will always come into contact with the heat exchange tubes, the central heat exchange sleeve 2.4, and the partition 2.6, achieving indirect heat exchange, regardless of the angle at which it rotates. Furthermore, annular fins 2.5 can be added to the periphery of the central heat exchange sleeve 2.4 to further increase the heat exchange area. Therefore, the low-rank coal pyrolysis rotary kiln of the present invention can greatly improve pyrolysis efficiency.

[0052] In order to ensure the passability of materials, the present invention sets the side of the hosting bracket 2.7 as an inclined surface, that is, the two side panels "have a wide spacing toward the kiln head end and a narrow spacing toward the kiln tail end". The formed conical inclined surface has a guiding function. When the cylinder rotates, the low-rank coal in the independent chamber will be lifted and will naturally slide along the inclined surface of the side panel to the kiln tail end, thereby improving the passability.

[0053] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An indirect heating low-rank coal pyrolysis rotary kiln, comprising a rotary kiln, wherein the kiln head is higher than the kiln tail, the kiln head is provided with a feeding device, and the kiln tail is provided with a discharging device; characterized in that: The rotary kiln is provided with a tube-and-tube heat exchange assembly and a central heat exchange sleeve; the central heat exchange sleeve is arranged at the center of the rotary kiln along the axial direction of the rotary kiln; the tube-and-tube heat exchange assembly includes multiple groups of heat exchange tubes arranged along the circumference of the rotary kiln, each group of heat exchange tubes includes multiple heat exchange tubes arranged along the radial direction of the rotary kiln, and all heat exchange tubes are arranged in parallel along the axial direction of the rotary kiln; an air supply section is provided at the kiln tail of the rotary kiln, and an air outlet section is provided at the kiln head; the hot air inlet of the heat exchange tube and the hot air inlet of the central heat exchange sleeve are both connected to the hot air supply duct through the air supply section, and the hot air outlet of the heat exchange tube and the hot air outlet of the central heat exchange sleeve are both connected to the hot air outlet duct through the air outlet section.

2. The indirect heating low-rank coal pyrolysis rotary kiln according to claim 1, characterized in that: The cylinder of the rotary kiln is composed of a steel cylinder and an insulation layer inside the cylinder, and the steel cylinder is made of ordinary carbon steel.

3. The indirect heating low-rank coal pyrolysis rotary kiln according to claim 1, characterized in that: A plurality of partitions are evenly arranged along the circumferential direction in the annular space between the cylinder and the central heat exchange sleeve of the rotary kiln, so as to divide the annular space into a plurality of independent chambers, and a plurality of groups of heat exchange tubes are respectively arranged in each independent chamber.

4. An indirectly heated low-rank coal pyrolysis rotary kiln according to claim 1 or 3, characterized in that: In the same group of heat exchange tubes arranged along the radial direction, the diameters of the heat exchange tubes increase successively from the inside to the outside.

5. The indirect heating low-rank coal pyrolysis rotary kiln according to claim 1 or 3, characterized in that: The heat exchange tubes in the same group arranged radially are supported and fixed by the same hosting bracket; the hosting bracket consists of a vertical plate and two side plates. The vertical plate has holes for the heat exchange tubes to pass through. The two side plates are symmetrically arranged on both sides of the vertical plate, and the side plates are inclined along the axial direction of the rotary kiln. The spacing between the side plates toward the kiln tail end is smaller than the spacing between the side plates toward the kiln head end.

6. The indirect heating low-rank coal pyrolysis rotary kiln according to claim 1, characterized in that: A plurality of annular fins are axially arranged on the outer wall of the central heat exchange sleeve.

7. The indirect heating low-rank coal pyrolysis rotary kiln according to claim 1, characterized in that: The cylinder of the air supply section is provided with multiple air inlets, some of which are provided with 90° elbows, and other parts are provided with straight pipes; each heat exchange tube is connected to the hot air supply duct through a corresponding 90° elbow; the central heat exchange sleeve located at the tail of the kiln is provided with multiple hot air inlets along the circumferential and axial directions, which are connected to the hot air supply duct through corresponding straight pipes.

8. The indirect heating low-rank coal pyrolysis rotary kiln according to claim 1, characterized in that: The air outlet section is provided with an air collecting hood on the periphery of the feeding device, and the annular space between the air collecting hood and the feeding device is the air outlet channel; the hot air outlet of the heat exchange tube is directly connected to the air outlet channel; the central heat exchange sleeve located at the kiln head is provided with multiple hot air outlets along the circumferential and axial directions and connected to the air outlet channel; the hot air outlet is provided on the air collecting hood and connected to the hot air outlet duct.

9. The indirect heating low-rank coal pyrolysis rotary kiln according to claim 1, characterized in that: The hot air supply duct and the hot air outlet duct are connected to form a hot air circulation duct, and the hot air circulation duct is provided with a hot air circulation fan and a supplementary hot air inlet.

10. A method for operating the indirectly heated low-rank coal pyrolysis rotary kiln according to claim 1, 2, 3, 6, 7, 8, or 9, characterized in that: The process includes the following: 1) Low-rank coal enters the kiln head of the rotary kiln through the feeding device, enters the independent chambers and moves to the kiln tail as the cylinder rotates; 2) Hot air enters the tube heat exchange assembly and the central heat exchange sleeve from the air supply section at the kiln tail, and flows toward the kiln head; 3) As the low-rank coal moves toward the kiln tail, it rotates with the drum in the corresponding independent chamber, and indirectly exchanges heat with the multiple heat exchange tubes in the independent chamber and the hot air flowing in the opposite direction in the central heat exchange sleeve, thereby achieving pyrolysis; 4) The upgraded coal after pyrolysis is discharged from the discharge device at the kiln tail. The hot air reaching the kiln head after heat exchange flows out from each heat exchange tube and the central heat exchange sleeve and is discharged outside through the air outlet section. The discharged hot air returns to the air supply section at the kiln tail through the hot air circulation pipe for recycling.

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