A pyrolysis furnace and a pyrolysis method using direct current for heating

Abstract

This invention belongs to the field of pyrolysis and relates to a pyrolysis furnace and method using direct current (DC) heating. The pyrolysis furnace includes a preheating section, a pyrolysis section, and subsequent units. Each of the preheating and pyrolysis sections is independently equipped with a DC heating system, which consists of a DC power supply, a voltage regulator, electrodes, electric heating conductors, heating cables, communication cables, and a data acquisition / control unit. The metal furnace tubes of the preheating and pyrolysis sections serve as the electric heating conductors. Temperature sensors are installed on the inner wall of the metal furnace tubes, and ground wires are installed at the inlet and outlet. The electrodes are located on the outer walls at both ends of the preheating and pyrolysis sections. The DC power supply is connected to the voltage regulator and then connected to the electrodes on the outer walls of the preheating and pyrolysis sections via heating cables. The data acquisition / control unit is connected to the temperature sensors on the inner wall of the metal furnace tubes via communication cables. This invention directly heats the metal furnace tubes with electricity, resulting in high thermal efficiency, low heat loss, and rapid heating.

Description

Technical Field

[0001] This invention belongs to the field of pyrolysis, specifically relating to a pyrolysis furnace and pyrolysis method that utilize direct current for heating. Background Technology

[0002] In recent years, with the advancement of global science and technology and the significant increase in industrial production activities, coupled with massive emissions of carbon dioxide, global warming has become an increasingly serious concern. Therefore, countries around the world are enacting relevant laws to control emissions of greenhouse gases such as carbon dioxide, thereby mitigating the climate crisis facing humanity.

[0003] Traditional ethylene cracking furnaces typically use fuel combustion for heating, but this process produces large amounts of carbon dioxide, carbon monoxide, nitrogen oxides, and sulfides. Nitrogen oxides and sulfides cause environmental pollution, while carbon dioxide contributes to the greenhouse effect, leading to global warming.

[0004] To address this, some research institutions have proposed using electric heating to heat the pyrolysis furnace. CN1315489A and CN113652246A employ resistance wire heating or electric heating elements to heat the pyrolysis furnace. However, the biggest problem with using electric heating elements to heat the furnace to high temperatures via thermal radiation is that these elements are easily damaged during operation, leading to temperature imbalances within the furnace and even preventing the pyrolysis temperature from being reached. This necessitates stopping the furnace and replacing the heating elements. Therefore, indirect heating cannot guarantee long-term stable operation of the pyrolysis furnace.

[0005] In summary, traditional pyrolysis furnaces use fuel oil or gaseous hydrocarbons to heat the furnace tubes and incorporate a convection section to recover the heat carried by the high-temperature fuel gas within the furnace. Using electric heating for pyrolysis eliminates the need for heat recovery from the high-temperature fuel gas. Furthermore, while indirect resistance wire heating followed by radiant heating of the furnace tubes is simple to operate and allows for convenient temperature control, the furnace lining structure used for furnace insulation is complex, resulting in high investment costs. Additionally, the heating wires are prone to damage, and locating and replacing broken wires is difficult, leading to significant maintenance workload and disruptions to continuous production. This indirect heating method has low thermal efficiency and is therefore unsuitable.

[0006] CN112805509A and CN107079535A proposed the concept of using direct current (DC) to directly heat the fluid inside the pipeline, but there are still many issues to consider in practical applications for different pyrolysis furnaces. CN202111239737.5 and CN202111239740.7 proposed a method for directly heating hydrocarbons by passing electricity through the pyrolysis furnace tube in a small-scale experiment. This method requires the use of special MoSi2 or MoSi2-containing metal furnace tubes as conductors for heating, and the output voltage can only be a fixed value when using a transformer to regulate the voltage. It is not possible to adjust the output voltage and heating current in a timely manner, which is difficult to implement in industrial plants. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this paper proposes a cracking furnace and cracking method that utilizes direct current (DC) heating for ethylene cracking. The method proposes using the existing cracking furnace tubes in industrial plants as conductors, directly heating the furnace tubes with DC electricity to supply heat for hydrocarbon cracking. Since the cracking furnace tubes typically have a wall thickness of 6–10 mm and a diameter of 50–165 mm, the burnout of conventional electric heating elements during operation can be avoided.

[0008] To achieve the above objectives, a first aspect of the present invention provides a pyrolysis furnace that uses direct current for heating, the pyrolysis furnace comprising a preheating section, a pyrolysis section, and a subsequent unit;

[0009] The preheating section and the pyrolysis section are each independently equipped with a DC electric heating system, which consists of a DC power supply, a voltage regulator, electrodes, electric heating conductors, heating cables, communication cables, and a data acquisition / control unit.

[0010] The metal furnace tubes of the preheating section and the pyrolysis section are used as electric heating conductors. The inner wall of the metal furnace tube is equipped with a temperature sensor, and the inlet and outlet are equipped with ground wires. The electrodes are located on the outer walls of both ends of the preheating section and the pyrolysis section.

[0011] After the DC power supply is connected to the voltage regulator, it is connected to the electrodes on the outer walls of both ends of the preheating section and the pyrolysis section via heating cables. The data acquisition / control unit is connected to the temperature sensor on the inner wall of the metal furnace tube via a communication cable.

[0012] A second aspect of the invention provides the application of the described cracking furnace heated by direct current in the cracking preparation of olefins.

[0013] A third aspect of the present invention provides a pyrolysis method, which employs the aforementioned pyrolysis furnace heated by direct current, and includes the following steps:

[0014] (1) The pyrolysis feedstock and diluent enter the preheating section. The pressure regulator is adjusted to preheat the pyrolysis feedstock and diluent in the preheating section to obtain the preheated material.

[0015] (2) The preheated material enters the pyrolysis section, and the pressure regulator is adjusted to pyrolyze the preheated material to obtain the pyrolyzed material, which then enters the subsequent system.

[0016] The present invention has the following advantages:

[0017] (1) High thermal efficiency

[0018] Unlike traditional pyrolysis furnaces that transfer heat through conduction and radiation, this invention directly heats the metal furnace tubes by applying electricity. The furnace tubes themselves are the heating element, and the heat is generated directly from the heated pyrolysis furnace tubes, rather than being transferred from the outside. Therefore, it has high thermal efficiency, low heat loss, and fast heating speed.

[0019] (2) Sensitive temperature regulation

[0020] By installing a temperature sensor inside the pyrolysis furnace tube, the output voltage can be controlled at any time according to the temperature inside the pyrolysis furnace tube. This allows for rapid changes in the current and temperature of the pyrolysis furnace tube, thereby reducing the lag in controlling the reaction temperature.

[0021] (3) Safe and easy to maintain

[0022] This invention features a voltage regulator to adjust the power supply voltage of the metal furnace tubes to 10-150V, and grounding at the inlet and outlet of the pipeline, ensuring safety and preventing electric shock accidents. The metal furnace tubes have high mechanical strength and are not easily damaged like electric heating wires, making maintenance convenient. The pyrolysis furnace body only serves an insulation function and is simple to construct. Unlike fuel-fired furnaces, it does not require complex linings to ensure good combustion conditions, nor does it require complex furnace linings like indirect resistance wire heating.

[0023] (4) Uniform heat distribution

[0024] In existing pyrolysis units, the wall thickness of the pyrolysis furnace tubes is 6–10 mm, and the tube diameter is 50–165 mm. The skin effect when direct current passes through the conductor is negligible, so heat is generated uniformly along the cross-section of the pyrolysis furnace tube. Simultaneously, under the condition of uniform resistance per unit length (such as the pyrolysis section), the heat generated along the pipe axis is also uniform, which is unattainable by other heating methods. Other methods, due to the unequal distances between different parts of the pyrolysis tube and the heat source, inevitably result in different amounts of heat received, thus causing temperature differences. Because hydrocarbon thermal pyrolysis reactions are very sensitive to reaction temperature, the uniformity of heat generated by direct electric heating is highly beneficial to the pyrolysis reaction.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0026] Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0027] Figure 1 A schematic diagram of the DC electric heating pyrolysis furnace process is shown.

[0028] Figure 2 A schematic diagram of a DC single-phase heating system is shown.

[0029] Figure 3 A schematic diagram of a DC parallel electric heating system is shown.

[0030] Figure 4 A schematic diagram of a DC series electric heating system is shown.

[0031] Explanation of reference numerals in the attached figures

[0032] A-Preheating section; B-Cracking section; 1-DC power supply; 2-Voltage regulator; 3-Electrode; 4-Metal furnace tube; 5-Data acquisition / control unit; 6-Heating cable; 7-Communication cable. Detailed Implementation

[0033] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0034] To achieve the above objectives, a first aspect of the present invention provides a pyrolysis furnace that utilizes direct current for heating, such as... Figure 1 As shown, the pyrolysis furnace includes a preheating section A, a pyrolysis section B, and subsequent units;

[0035] The preheating section and the pyrolysis section are each equipped with an independent electric heating system, such as... Figure 2 As shown, the electric heating system consists of a power supply 1, a voltage regulator 2, electrodes 3, a metal furnace tube 4, a heating cable 6, a communication cable 7, and a data acquisition / control unit 5;

[0036] The metal furnace tubes of the preheating section and the pyrolysis section are used as electric heating conductors. The inner wall of the metal furnace tube is equipped with a temperature sensor, and the inlet and outlet are equipped with ground wires. The electrodes are located on the outer walls of both ends of the preheating section and the pyrolysis section.

[0037] After the DC power supply is connected to the voltage regulator, it is connected to the electrodes on the outer walls of both ends of the preheating section and the pyrolysis section via heating cables. The data acquisition / control unit is connected to the temperature sensor on the inner wall of the metal furnace tube via a communication cable.

[0038] In this invention, the preheating section is used to preheat the pyrolysis raw materials and diluent, and the pyrolysis section is used to pyrolyze the preheated pyrolysis raw materials in the presence of the preheated diluent; the data acquisition / control unit is used to adjust the output voltage and current of the DC power supply in a timely manner based on the temperature feedback data of the inner and outer walls of the pyrolysis furnace tube, thereby controlling the temperature of the pyrolysis furnace tube.

[0039] In this invention, the heat source for the preheating section A and the pyrolysis section B is an electric heat source. The pyrolysis furnace tube is used as a conductor, and direct current flows through the tube to generate heat, directly heating the preheating section A and the pyrolysis section B. This invention uses clean energy electricity (such as solar, nuclear, wind, and tidal energy) as the heat source for the pyrolysis reaction, which can significantly reduce carbon emissions during the pyrolysis process. Furthermore, by not using natural gas or fuel oil to heat the pyrolysis furnace, emissions of nitrogen oxides and sulfides can be reduced. In addition, the preheating section A directly electrically heats the pyrolysis feedstock and diluent, reducing the convection section in existing pyrolysis units. There is no heat exchange between the pyrolysis feedstock, diluent, and flue gas, resulting in a smaller footprint, simpler process, and lower equipment cost. The absence of flue gas exceeding 100°C found in traditional pyrolysis furnaces allows for direct venting, improving the thermal efficiency of the pyrolysis furnace. Furthermore, the significantly reduced width of the preheating and pyrolysis sections reduces the furnace volume and floor space required.

[0040] According to the present invention, preferably, the preheating section and the pyrolysis section are each independently single-pass or multi-pass, each pass including at least one metal furnace tube, and when there are ≥2 metal furnace tubes, the metal furnace tubes are connected in parallel (e.g. Figure 3 (as shown) or in series (such as) Figure 4 (As shown in the image) settings.

[0041] In this invention, "multi-pass" refers to a number of passes ≥ 2, and the shape of the metal furnace tube varies according to the requirements of the pyrolysis process. It can be single-pass, two-pass, or even multi-pass. For example, single-pass tubes and two-pass tubes commonly used in pyrolysis devices are type 1-1, type 2-1, type 4-1, or type 8-1.

[0042] According to the present invention, preferably, the voltage regulator is at least one of an off-load voltage regulating transformer, an induction voltage regulator, a thyristor voltage regulator, and a magnetic voltage regulator, and preferably a magnetic voltage regulator.

[0043] In this invention, the voltage regulator can adjust the output voltage in real time based on feedback from the set temperature and the actual temperature to control the heating power.

[0044] According to the present invention, preferably, the electrode material is at least one selected from copper, silver, platinum, graphite and carbon nanotubes, and preferably copper.

[0045] In this invention, the metal furnace tube is an alloy commonly used in the convection and pyrolysis sections of existing pyrolysis furnaces. It has high resistivity, low temperature coefficient of resistance, and is not easily oxidized at high temperatures. NiCr alloy furnace tubes are preferred. The wall thickness of the metal furnace tube is 6-10 mm and the tube diameter is 50-165 mm.

[0046] A second aspect of the invention provides the application of the described cracking furnace heated by direct current in the cracking preparation of olefins.

[0047] A third aspect of the present invention provides a pyrolysis method, which employs the aforementioned pyrolysis furnace heated by direct current, and includes the following steps:

[0048] (1) The pyrolysis feedstock and diluent enter the preheating section. The pressure regulator is adjusted to preheat the pyrolysis feedstock and diluent in the preheating section to obtain the preheated material.

[0049] (2) The preheated material enters the pyrolysis section, and the pressure regulator is adjusted to pyrolyze the preheated material to obtain the pyrolyzed material, which then enters the subsequent system.

[0050] According to the present invention, preferably, the voltage of the DC output of the voltage regulator is adjusted to 10-150V in steps (1) and (2).

[0051] According to the present invention, preferably, the preheating temperature is 550-650°C, and the mass ratio of diluent to pyrolysis feedstock is 0.3-0.8.

[0052] According to the present invention, preferably, the pyrolysis temperature is 700-1100℃, the pyrolysis residence time is 0.05-0.5s, and the outlet pressure is 0.1-0.3MPa.

[0053] According to the present invention, preferably, the pyrolysis feedstock is at least one selected from ethane, propane, light hydrocarbons, naphtha, hydrotreated tail oil, and diesel oil; and the diluent is at least one selected from water vapor, hydrogen, nitrogen, methane, and argon.

[0054] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0055] Example 1

[0056] The ethane cracking to olefins is carried out in an electrically heated cracking furnace, using direct current (DC) as the heating power source. In the preheating section, the DC voltage is transformed to 30-50V by a no-load tap-changing transformer. Copper electrodes are connected to both ends of a single Cr25Ni20 cracking furnace tube in the preheating section, maintaining the furnace tube outlet temperature at 600℃ after heating. In the cracking section, the DC voltage is transformed to 37-63V by a no-load tap-changing transformer. Copper electrodes are connected to both ends of a single Cr25Ni35 cracking furnace tube in the cracking section, maintaining the cracking furnace tube outlet temperature at 860℃ after heating.

[0057] (1) The dilution steam and ethane are fed directly into the preheating section of the electric heating cracking furnace at a weight ratio of 0.3 for mixing and preheating. The temperature of the preheated ethane is 600℃.

[0058] (2) The mixed gas obtained from the preheating section is introduced into the cracking section. The outlet temperature of the cracking section furnace tube is 860℃, the outlet pressure of the cracking section is 0.17MPa, the residence time is 0.29s, the ethane feed rate is 1.1 tons / hour, and cracked gas is obtained after cracking.

[0059] (3) The obtained pyrolysis gas was separated by a subsequent system, and the composition of the pyrolysis gas was analyzed by gas chromatography, as detailed in Table 1.

[0060] Example 2

[0061] The cracking of naphtha to olefins is carried out in an electrically heated cracking furnace, using direct current (DC) as the heating power source. In the preheating section, the DC voltage is transformed to 60-100V by an induction voltage regulator. Silver electrodes are connected to both ends of two Cr25Ni20 cracking furnace tubes connected in series in the preheating section, maintaining the furnace tube outlet temperature at 600℃ after heating. In the cracking section, the DC voltage is transformed to 74-126V by an induction voltage regulator. Platinum electrodes are connected to both ends of two Cr25Ni35 cracking furnace tubes connected in series in the cracking section, maintaining the cracking furnace tube outlet temperature at 838℃ after heating.

[0062] (1) The dilution steam and naphtha are directly fed into the preheating section of the electric heating pyrolysis furnace at a weight ratio of 0.5 for mixing and preheating. The temperature of the naphtha after preheating is 600℃.

[0063] (2) The mixed gas obtained from the preheating section is introduced into the cracking section. The outlet temperature of the cracking section furnace tube is 838℃, the outlet pressure of the cracking section is 0.17MPa, the residence time is 0.29s, the naphtha feed rate is 400kg / h, and cracked gas is obtained after cracking.

[0064] (3) The obtained pyrolysis gas was separated by a subsequent system, and the composition of the pyrolysis gas was analyzed by gas chromatography, as detailed in Table 1.

[0065] Example 3

[0066] The diesel cracking to olefins process is carried out in an electrically heated cracking furnace, using direct current (DC) as the heating power source. In the preheating section, the DC voltage is transformed to 30-50V via a silicon controlled rectifier (SCR) regulator. Graphite electrodes are connected to both ends of eight parallel Cr25Ni20 cracking furnace tubes in the preheating section, maintaining the furnace tube outlet temperature at 600℃ after heating. In the cracking section, the DC voltage is transformed to 37-63V via a magnetic regulator. Carbon nanotube electrodes are connected to both ends of eight parallel Cr25Ni35 cracking furnace tubes in the cracking section, maintaining the cracking furnace tube outlet temperature at 817℃ after heating.

[0067] (1) The dilution steam and diesel oil are directly fed into the preheating section of the electric heating pyrolysis furnace at a weight ratio of 0.8 for mixing and preheating. The temperature of the diesel oil after preheating is 600℃.

[0068] (2) The mixed gas obtained from the preheating section is introduced into the cracking section. The outlet temperature of the cracking section furnace tube is 817℃, the outlet pressure of the cracking section furnace is 0.17MPa, the residence time is 0.29s, the diesel feed rate is 1600kg / h, and cracked gas is obtained after cracking.

[0069] (3) The obtained pyrolysis gas was separated by a subsequent system, and the composition of the pyrolysis gas was analyzed by gas chromatography, as detailed in Table 1.

[0070] Comparative Example 1

[0071] Ethane cracking to olefins is carried out in a conventional cracking furnace, with the same metal furnace tube alloys as in Example 1 for the preheating and cracking sections. The cracking section is heated by the combustion of methane and hydrogen. The high-temperature flue gas in the combustion chamber preheats the cracking feedstock and produces ultra-high-pressure steam through heat exchange in the convection section. The specific process is as follows:

[0072] (1) A dilution steam / ethane with a weight ratio of 0.3 is mixed and preheated in the convection section, and the temperature of the preheated steam and ethane mixture is 600℃;

[0073] (2) The ethane and steam mixture after preheating in the convection section is introduced into the cracking section. The mixture in the cracking tube undergoes a cracking reaction. The outlet temperature of the cracking furnace tube is 860℃, the outlet pressure of the cracking furnace tube is 0.17MPa, the residence time is 0.29s, the ethane feed rate of a single cracking furnace tube is 110kg / h, and cracked gas is obtained after cracking.

[0074] (3) The obtained pyrolysis gas was separated by a subsequent system, and the composition of the pyrolysis gas was analyzed by gas chromatography after sampling. See Table 1 for details.

[0075] Comparative Example 2

[0076] The only difference between this comparative example and Example 1 is that a magnetic voltage regulator was not installed, a fixed voltage of 40V was used in the preheating section, and a fixed voltage of 50V was used in the pyrolysis section.

[0077] Table 1

[0078]

[0079]

[0080] As can be seen from the results in Table 1, Examples 1-3, employing the technical solution of this invention, can achieve the cracking of light hydrocarbons to produce olefins. Compared with the conventional cracking furnace in Comparative Example 1, under the same cracking feedstock conditions, the yields of ethylene, propylene, and butadiene are slightly higher. It also boasts advantages such as high thermal efficiency, uniform heat distribution, reduced carbon emissions and emissions of nitrogen and sulfur-containing pollutants, and a simple structure. Direct DC heating, without a voltage regulator, results in inaccurate temperature control and low olefin yields.

[0081] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0082] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A cracking furnace for heating by direct current, characterized by comprising: The pyrolysis furnace includes a preheating section, a pyrolysis section, and subsequent units; The preheating section and the pyrolysis section are each independently equipped with a DC electric heating system, which consists of a DC power supply, a voltage regulator, electrodes, electric heating conductors, heating cables, communication cables, and a data acquisition / control unit. The metal furnace tubes of the preheating section and the pyrolysis section are used as electric heating conductors. The inner wall of the metal furnace tube is equipped with a temperature sensor, and the inlet and outlet are equipped with ground wires. The electrodes are located on the outer walls of both ends of the preheating section and the pyrolysis section. After the DC power supply is connected to the voltage regulator, it is connected to the electrodes on the outer walls of both ends of the preheating section and the pyrolysis section via heating cables. The data acquisition / control unit is connected to the temperature sensor on the inner wall of the metal furnace tube via a communication cable.

2. The pyrolysis furnace using direct current for heating according to claim 1, wherein, The preheating section and the pyrolysis section are each independently single-pass or multi-pass, and each pass includes at least one metal furnace tube. When there are ≥2 metal furnace tubes, the metal furnace tubes are arranged in parallel or in series.

3. The pyrolysis furnace using direct current for heating according to claim 1, wherein, The voltage regulator is at least one of the following: no-load voltage regulating transformer, induction voltage regulator, thyristor voltage regulator and magnetic voltage regulator, preferably a magnetic voltage regulator.

4. The pyrolysis furnace using direct current for heating according to claim 1, wherein, The electrode material is at least one of copper, silver, platinum, graphite, and carbon nanotubes, preferably copper.

5. The pyrolysis furnace using direct current for heating according to claim 1, wherein, The metal furnace tube is made of an alloy with high resistivity, low temperature coefficient of resistance, and is not easily oxidized at high temperatures, preferably a Ni-Cr alloy. The wall thickness of the metal furnace tube is 6-10 mm, and the tube diameter is 50-165 mm.

6. The application of the cracking furnace using direct current heating as described in any one of claims 1-5 in the cracking preparation of olefins.

7. A pyrolysis method, characterized in that, The pyrolysis furnace using direct current heating as described in any one of claims 1-5 is used, comprising the following steps: (1) The pyrolysis feedstock and diluent enter the preheating section. The pressure regulator is adjusted to preheat the pyrolysis feedstock and diluent in the preheating section to obtain the preheated material. (2) The preheated material enters the pyrolysis section, and the pressure regulator is adjusted to pyrolyze the preheated material to obtain the pyrolyzed material, which then enters the subsequent system.

8. The heating method according to claim 7, wherein, In steps (1) and (2), the voltage of the DC output of the voltage regulator is adjusted to 10-150V.

9. The heating method according to claim 8, wherein, The preheating temperature is 550-650℃, and the mass ratio of diluent to pyrolysis feedstock is 0.3-0.

8.

10. The heating method according to claim 8, wherein, The pyrolysis temperature is 700-1100℃, the pyrolysis residence time is 0.05-0.5s, and the outlet pressure is 0.1-0.3MPa.

11. The heating method according to claim 7, wherein, The pyrolysis feedstock is at least one of ethane, propane, light hydrocarbons, naphtha, hydrotreated tail oil, and diesel oil. The diluent is at least one of water vapor, hydrogen, nitrogen, methane, and argon.

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