Reinforced heat transfer method for horizontal pyrolysis rotary furnace

Abstract

The invention discloses an enhanced heat transfer method for a horizontal pyrolysis rotary furnace, which comprises the following steps of: additionally arranging steel fins with the thickness of 4-6mm on the outer surface of a pyrolysis chamber of the horizontal rotary furnace, adding an enhanced heat transfer material and solid waste into a stock bin according to the mass ratio of (2: 5)-(3: 5), and conveying the enhanced heat transfer material and the solid waste into the horizontal pyrolysis rotary furnace by a belt conveyor; the solid wastes are medical wastes or waste tire particles; the enhanced heat transfer material is carborundum or steel balls; when the horizontal pyrolysis rotary furnace is in a cold state, starting an adjustable-speed motor to drive the horizontal pyrolysis rotary furnace to rotate so as to mix the enhanced heat transfer material and the solid waste; starting a combustor, and pyrolyzing the solid wastes; and solid residues discharged from the pyrolyzing furnace are screened, and carborundum or steel balls in the solid residues are separated out. After the method is adopted, the convective heat transfer coefficient of the outer surface of the pyrolysis chamber can be increased by 28-33% and averagely increased by about 30%, and the apparent heat transfer coefficient between the pyrolysis material and the interior of the pyrolysis chamber is increased by 20-40%.

Description

Technical Field

[0001] The invention relates to a method for pyrolyzing solid waste such as medical waste, waste tires and biomass, and in particular to a method for enhancing heat transfer in a horizontal pyrolysis rotary furnace based on mixing solid waste with good heat conductors such as steel balls and corundum and installing heat exchange fins on the outer wall of the pyrolysis chamber. Background Art

[0002] Horizontal pyrolysis rotary furnaces are increasingly being used and valued in the resource utilization, reduction and harmless utilization of solid wastes such as medical waste and waste tires. However, the existing pyrolysis furnaces have smooth outer walls with small heat transfer areas, low heat transfer coefficients, and large external heat transfer resistance. In addition, the external hot gas and the internal pyrolysis materials are indirectly exchanged with each other. Due to the poor thermal conductivity, large thermal resistance, poor overall heat transfer effect, low pyrolysis yield, high pyrolysis energy consumption and poor economy of materials such as medical waste, the large-scale promotion and application of horizontal pyrolysis rotary furnaces in the field of medical waste and waste tire treatment is still subject to various conditions. With the rapid increase in the amount of medical waste and waste tires, the development of an efficient horizontal pyrolysis rotary furnace that takes both internal and external enhanced heat transfer measures has become an urgent problem to be solved.

[0003] Figure 1 It is a traditional solid waste horizontal pyrolysis rotary furnace treatment process. Solid waste such as medical waste and waste tires are indirectly heated by an external combustion chamber in the pyrolysis chamber to undergo thermal cracking. The pyrolysis products include pyrolysis gas, pyrolysis oil and solid residue. However, this method has the disadvantages of poor heat transfer performance, slow pyrolysis speed, low pyrolysis efficiency, high pyrolysis energy consumption and pyrolysis cost. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for simultaneously enhancing heat transfer inside and outside the pyrolysis chamber of a horizontal rotary furnace, which can quickly increase the temperature of solid waste, thereby improving heat transfer efficiency and pyrolysis rate, and reducing energy consumption and cost of the pyrolysis process.

[0005] A method for enhancing heat transfer in a horizontal pyrolysis rotary furnace of the present invention comprises the following steps:

[0006] Step 1: Install steel fins with a thickness of 4 to 6 mm on the outer surface of the pyrolysis chamber of the horizontal rotary furnace, wherein the rib coefficient of the steel fins is 1.3 to 1.5;

[0007] Step 2: adding the heat transfer enhancing material and solid waste into a silo at a mass ratio of 2:5 to 3:5, and then conveying them into the pyrolysis chamber of the horizontal pyrolysis rotary furnace by a belt conveyor; the solid waste is medical waste or waste tire particles; the heat transfer enhancing material is corundum or steel balls;

[0008] Step 3: When the horizontal pyrolysis rotary furnace is in a cold state and the pressure inside the horizontal pyrolysis rotary furnace is at normal pressure, the speed regulating motor is started to drive the horizontal pyrolysis rotary furnace to rotate at a speed of 1.0-2 revolutions per minute for 10-20 minutes, and the enhanced heat transfer material is always sunk near the wall of the horizontal pyrolysis rotary furnace, and keeps in contact and collision with the inner wall of the pyrolysis chamber of the horizontal pyrolysis rotary furnace;

[0009] Step 4: While the horizontal pyrolysis rotary furnace continues to rotate, start the burner installed in the heating chamber of the horizontal pyrolysis furnace, and indirectly heat the pyrolysis chamber of the horizontal pyrolysis rotary furnace by burning the natural gas transported by the natural gas pipeline connected to the burner. When the temperature inside the pyrolysis chamber rises to 250°C, some solid wastes begin to gradually pyrolyze. When the temperature inside the pyrolysis chamber rises to above 350°C, most of the solid wastes begin to rapidly pyrolyze, and the pyrolysis gas generated is sufficient to meet the heat required for pyrolysis of the material. Close the valve of the natural gas pipeline connected to the burner, and introduce the pyrolysis gas generated by the pyrolysis chamber into the inlet of the burner through the pipeline. The pyrolysis chamber is continuously heated by the combustion of the pyrolysis gas generated by the pyrolysis chamber itself to maintain a normal pyrolysis process. At the same time, when the enhanced heat transfer material rotates to a certain position above with the horizontal pyrolysis rotary furnace, it falls into the solid waste under the action of gravity, transfers heat to the solid waste, and contacts and heats the solid waste. The continuous friction and collision between the enhanced heat transfer material and the solid waste makes the solid waste loose during the pyrolysis process.

[0010] Step 4: The gas-liquid mixture generated during the pyrolysis process is separated into pyrolysis gas and fuel oil through a cooling system connected to the pyrolysis product outlet of the horizontal pyrolysis furnace. The pyrolysis gas is a combustible gas and circulates to the inlet of the burner for combustion. The pyrolysis oil is directly sold as fuel oil or used as a chemical raw material. The solid residue discharged from the pyrolysis furnace is screened to separate the corundum or steel balls therein. The flue gas generated in the combustion chamber is subjected to a flue gas purification system to remove organic compounds and solid particulate matter, so that the emission index meets the standard before being discharged.

[0011] The present invention is beneficial in that:

[0012] 1) The fins installed on the outer wall of the pyrolysis chamber of the horizontal rotary furnace can not only increase the heat exchange area, but also create disturbances and turbulence on the high-temperature flue gas, increase the convective heat transfer coefficient on the outer surface of the pyrolysis chamber, and reduce the heat transfer thermal resistance. According to simulation optimization and experiments, when the rib coefficient (the ratio of the outer surface area of ​​the fin tube to the inner wall area of ​​the pyrolysis chamber after the fins are installed on the outer surface of the pyrolysis chamber) is in the range of 1.3 to 1.5, the convective heat transfer coefficient on the outer surface of the pyrolysis chamber can be increased by 28 to 33%, an average increase of about 30%, and the enhanced heat transfer effect is very significant;

[0013] 2) After adding 40-60% corundum or steel balls to medical waste or waste tires, since the thermal conductivity and specific gravity of corundum or steel balls are much greater than those of medical waste or waste tires, and the added corundum or steel balls are always located at the bottom of the material and directly contact the inner wall of the pyrolysis chamber cylinder, the heat transferred from the combustion chamber can be quickly absorbed. During the rotation of the pyrolysis chamber, these rapidly heated corundum or steel balls will fall into the pyrolysis material and transfer heat to the material, so that the temperature of the medical waste or waste tires rises rapidly and more evenly, improving the heat transfer efficiency. According to actual measurements, the apparent heat transfer coefficient between the pyrolysis material and the inside of the pyrolysis chamber can be increased by 20-40% after adopting this method.

[0014] 3) After adding corundum or steel balls to the pyrolysis material, the agglomeration of the material during the pyrolysis process is significantly improved because the corundum or steel balls are mixed with the material and collide with each other. In the later stage of pyrolysis, the material is no longer stuck together and is in a loose state. In this way, the contact area between the material and the inner wall of the pyrolysis chamber will also be greatly increased, which can enhance the heat transfer effect, improve the heat transfer speed and the degree of pyrolysis.

[0015] 4) Since the blended corundum or steel balls have a relatively high melting point, above 1500°C, and are relatively wear-resistant, and the pyrolysis temperature of medical waste or waste tires is below 500°C, these enhanced heat transfer materials are basically not lost during the pyrolysis process and can be completely recycled. The method is simple and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0018] Figure 1 Flow chart of the traditional solid waste horizontal pyrolysis rotary furnace treatment process;

[0019] Figure 2 The invention discloses a process flow chart of a method for simultaneously enhancing heat transfer inside and outside a horizontal pyrolysis rotary furnace. DETAILED DESCRIPTION

[0020] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0021] In the following description, many specific details are set forth to facilitate a full understanding of the technical solution of the present disclosure, but the technical solution of the present disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only part of the embodiments of the technical solution of the present disclosure, rather than all of the embodiments.

[0022] As shown in the accompanying drawings, a method for enhancing heat transfer in a horizontal pyrolysis rotary furnace of the present invention comprises the following steps:

[0023] Step 1: Install steel fins with a thickness of 4 to 6 mm on the outer surface of the pyrolysis chamber of the horizontal rotary furnace. The rib coefficient of the steel fins is 1.3 to 1.5. The height of the steel fins is determined according to the distance between the inner and outer cylinders. Considering the thermal expansion and the flow resistance of the flue gas, it is recommended to leave a gap of 5 to 10 mm between the top of the steel fins and the inner wall of the outer cylinder of the horizontal rotary furnace.

[0024] Step 2: adding the heat transfer enhancing material and solid waste into a silo at a mass ratio of 2:5 to 3:5, and then conveying them into the pyrolysis chamber of the horizontal pyrolysis rotary furnace by a belt conveyor; the solid waste is medical waste or waste tire particles; the heat transfer enhancing material is corundum or steel balls; the diameter of the corundum or steel balls is preferably 1-3 mm;

[0025] According to the experimental results, the optimal mass mixing ratio between the heat transfer enhancing material and the solid waste is 2:5 to 3:5. If too little heat transfer enhancing material is added, the heat transfer enhancing effect is not obvious. If too much heat transfer enhancing material is added, it will absorb too much heat and affect the heating rate and pyrolysis rate of the solid waste.

[0026] Step 3: When the horizontal pyrolysis rotary furnace is in a cold state (not heated) and the pressure inside the horizontal pyrolysis rotary furnace is at normal pressure, start the speed regulating motor to drive the horizontal pyrolysis rotary furnace to rotate at a speed of 1.0-2 revolutions per minute for 10-20 minutes to ensure that all transmission parts can operate normally. Since the specific gravity of corundum (steel balls) is much greater than that of medical waste (waste tires), the enhanced heat transfer material will be deposited near the inner wall of the pyrolysis chamber of the horizontal rotary furnace, and maintain contact and frequent collision with the inner wall of the pyrolysis chamber of the horizontal pyrolysis rotary furnace;

[0027] Step 4: While the horizontal pyrolysis rotary furnace continues to rotate, start the burner installed in the heating chamber of the horizontal pyrolysis furnace, and indirectly heat the pyrolysis chamber of the horizontal pyrolysis rotary furnace by burning the natural gas transported by the natural gas pipeline connected to the burner. In the initial heating stage, the solid waste basically does not undergo pyrolysis. When the temperature inside the pyrolysis chamber rises to above 250°C, some solid waste begins to undergo pyrolysis. When the temperature inside the pyrolysis chamber rises to above 350°C, most of the organic solid waste undergoes rapid pyrolysis. The heat provided by the combustion of the pyrolysis gas generated by the pyrolysis furnace is sufficient to meet the heat required for heating the pyrolysis chamber. Close the valve of the natural gas pipeline connected to the burner, introduce the pyrolysis gas generated by the pyrolysis chamber into the inlet of the burner through the pipeline, and use the pyrolysis gas generated by the pyrolysis chamber itself to continuously heat the pyrolysis chamber to maintain a normal pyrolysis process.

[0028] At the same time, when the enhanced heat transfer material rotates to a certain position above with the horizontal pyrolysis rotary furnace, it falls into the medical waste or waste tires under the action of gravity, transfers heat to the solid waste, and conducts contact heating on the solid waste. The enhanced heat transfer material and the solid waste are constantly rubbed and collided with each other, making the solid waste loose during the pyrolysis process. Since the enhanced heat transfer material with a large thermal conductivity coefficient is mixed into the solid waste, the overall thermal conductivity will also be improved, the heat transfer performance of the material will be better, the temperature will be more uniform, and the pyrolysis rate will be faster.

[0029] Since steel fins are installed on the outer wall of the pyrolysis chamber of the horizontal rotary furnace, compared with the smooth wall, the heat transfer area is increased, and the high-temperature flue gas flowing through the steel fins is disturbed and turbulent, which plays a role in enhancing heat transfer, thereby increasing the convection heat transfer coefficient of the outer surface of the pyrolysis chamber and reducing the external heat transfer thermal resistance. Through this heat transfer enhancement method, the convection heat transfer coefficient of the outer surface of the pyrolysis chamber can be increased by 28-33%, an average increase of about 30%, and the heat transfer enhancement effect is very significant.

[0030] Since corundum and steel balls are good thermal conductors, their thermal conductivity is much higher than that of medical waste and waste tires, and they always maintain good contact and collision with the inner wall of the pyrolysis chamber during the rotation of the pyrolysis furnace, they can quickly absorb the heat from the combustion chamber outside the cylinder to increase the temperature. At the same time, when the enhanced heat transfer material rotates to a certain position above with the horizontal pyrolysis rotary furnace, it falls into the medical waste or waste tires under the action of gravity, transfers heat to the solid waste, heats the material, and accelerates the temperature increase rate and pyrolysis rate of the material. Through this enhanced heat transfer method, the apparent heat transfer coefficient between the pyrolysis material and the inside of the pyrolysis chamber can be increased by 20-40%.

[0031] Step 5. The gas-liquid mixture produced during the pyrolysis process is separated into pyrolysis gas and fuel oil through a cooling system (the existing structure can be used) connected to the outlet of the pyrolysis product of the horizontal pyrolysis furnace. The pyrolysis gas is a combustible gas that circulates to the inlet of the burner for combustion. The pyrolysis oil is directly sold as fuel oil or used as a chemical raw material; the solid residue discharged from the pyrolysis furnace is screened to separate the corundum or steel balls therein. Since the temperature of the entire pyrolysis process does not exceed 500°C, and the corundum or steel balls are wear-resistant materials with little loss, they can be recycled and reused in the mining industry. Therefore, this method has the advantages of simple implementation and low cost. The flue gas generated by the combustion chamber is subjected to the existing flue gas purification system to remove organic compounds such as SOx and NOx and solid particulate matter therein, so that the emission indicators meet the standards of Europe, the United States and other countries and meet the emission standards.

[0032] The embodiments of the present invention are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the invention.

Claims

1. A method for enhancing heat transfer in a horizontal pyrolysis rotary furnace, characterized in that The following steps are involved: Step 1: Install steel fins with a thickness of 4 to 6 mm on the outer surface of the pyrolysis chamber of the horizontal rotary furnace, wherein the rib coefficient of the steel fins is 1.3 to 1.5; Step 2: adding the heat transfer enhancing material and solid waste into a silo at a mass ratio of 2:5 to 3:5, and then conveying them into the pyrolysis chamber of the horizontal pyrolysis rotary furnace by a belt conveyor; the solid waste is medical waste or waste tire particles; the heat transfer enhancing material is corundum or steel balls; Step 3: When the horizontal pyrolysis rotary furnace is in a cold state and the pressure inside the horizontal pyrolysis rotary furnace is at normal pressure, the speed regulating motor is started to drive the horizontal pyrolysis rotary furnace to rotate at a speed of 1.0-2 revolutions per minute for 10-20 minutes, and the enhanced heat transfer material is always sunk near the wall of the horizontal pyrolysis rotary furnace, and keeps in contact and collision with the inner wall of the pyrolysis chamber of the horizontal pyrolysis rotary furnace; Step 4: while the horizontal pyrolysis rotary furnace continues to rotate, start the burner installed in the heating chamber of the horizontal pyrolysis furnace, and indirectly heat the pyrolysis chamber of the horizontal pyrolysis rotary furnace by burning the natural gas transported by the natural gas pipeline connected to the burner. When the temperature inside the pyrolysis chamber rises to 250°C, part of the solid waste begins to be gradually pyrolyzed. When the temperature inside the pyrolysis chamber rises to above 350°C, most of the solid waste begins to be rapidly pyrolyzed, and the generated pyrolysis gas is sufficient to meet the heat required for the pyrolysis of the material. Close the valve of the natural gas pipeline connected to the burner, and introduce the pyrolysis gas generated in the pyrolysis chamber into the inlet of the burner through the pipeline. The pyrolysis chamber is continuously heated by the combustion of the pyrolysis gas generated by the pyrolysis chamber itself to maintain a normal pyrolysis process. At the same time, when the enhanced heat transfer material rotates to a certain position above with the horizontal pyrolysis rotary furnace, it falls into the solid waste under the action of gravity, transfers heat to the solid waste, and contacts and heats the solid waste. The enhanced heat transfer material and the solid waste are constantly rubbed and collided, so that the solid waste is in a loose state during the pyrolysis process. Step 4: The gas-liquid mixture generated during the pyrolysis process is separated into pyrolysis gas and fuel oil through a cooling system connected to the pyrolysis product outlet of the horizontal pyrolysis furnace. The pyrolysis gas is a combustible gas and circulates to the inlet of the burner for combustion. The pyrolysis oil is directly sold as fuel oil or used as a chemical raw material. The solid residue discharged from the pyrolysis furnace is screened to separate the corundum or steel balls therein. The flue gas generated in the combustion chamber is subjected to a flue gas purification system to remove organic compounds and solid particulate matter, so that the emission index meets the standard before being discharged.

2. The method for enhancing heat transfer in a horizontal pyrolysis rotary furnace according to claim 1, characterized in that: The diameter of the diamond sand or steel ball is 1-3 mm.

3. The method for enhancing heat transfer in a horizontal pyrolysis rotary furnace according to claim 1 or 2, characterized in that: Leave a gap of 5 to 10 mm between the top of the steel fin and the inner wall of the outer tube of the horizontal rotary furnace.

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