CN1235846C - Method for preparing acetylene by hot plasma cracking methane containing gas - Google Patents

Abstract

The present invention discloses a method for preparing acetylene by cracking gas containing methane by hot plasma. Argon, nitrogen or hydrogen gas is ionized into plasma jets by a plasma generator, and high temperature environment is formed in the reactor; an air inlet device for raw gas is opposite to and symmetrical with multiple air inlet rings, and raw gas is sprayed into the reactor via the air inlet rings to be mixed with the plasma jets penetrating the air inlet rings to be quickly and sufficiently soaked; the used reactor is a telescopic reactor, and mixed gas is limited in the reactor, which leads that a temperature in the reactor is unchanged; a used cooling device is a pneumatic cooling and expanding cavity and is combined with the reactor, and cracked gas is quenched in the expanding cavity; accordingly, a laboratory technique is successfully turned into an engineering technique. In the method, acetylene is mainly prepared together with black carbon, hydrogen gas is prepared in an auxiliary mode, and black carbon can also be mainly prepared. When the method is used for preparing acetylene, major techniques and economic indicator achieve or exceed the existing experiment level of abroad laboratories, and the present invention has the advantages of good economic and environmental benefits.

Description

Method for producing acetylene by pyrolysis of methane-containing gas by thermal plasma

technical field

The invention relates to a method for preparing acetylene, in particular to a method for producing acetylene by plasma cracking methane-containing gas. The technical scheme of the invention is a mature industrial method, which can be directly applied to the field of chemical engineering in which methane-containing gas is used as raw material to prepare acetylene.

Background technique

At present, the methods for domestic production of acetylene are calcium carbide hydrolysis and natural gas partial oxidation, and there are also electric arc methods abroad.

To produce acetylene by calcium carbide hydrolysis, calcium carbonate (CaCO ₃ ) is first smelted in an electric arc furnace to obtain calcium oxide (CaO), which then reacts with water (H ₂ O) to form acetylene. A large amount of CO ₂ and calcium carbide slag (CaOH) are produced in the whole process, which pollutes the environment very much and is difficult to control centrally. Partial oxidation of natural gas is the incomplete combustion of natural gas in an oxygen environment to obtain acetylene. The process also produces a large amount of waste gas such as CO ₂ and CO, and the natural gas consumption per unit product is large and the yield is low. Generally, it takes 6,500 cubic meters of natural gas to produce one ton of acetylene, and the utilization rate of non-renewable energy is low. The method of producing acetylene by arc cracking natural gas is limited by the reaction temperature, so the conversion rate of natural gas is low, the yield of acetylene is low, and the natural gas consumption per unit product is high. The typical representatives of foreign countries who produce acetylene by arc cracking natural gas include German Huels Company and American Dupont Company, Huels Company The reported specific energy is 12.1KWh/kg, the one-way conversion rate is about 50%, the yield is about 33%, and the natural gas consumed per ton of acetylene is 4500m ³ .

Plasma jet pyrolysis of natural gas to produce acetylene is a brand-new method, which is to discharge and start arcing in the working gas (nitrogen, argon, hydrogen, etc.) to form a high-speed jet of plasma jet, resulting in a high-temperature environment, where the methane component of natural gas is oxygen-free , high temperature, and normal pressure environment, it is dehydrogenated and coupled to generate cracked gas containing acetylene, and the target product acetylene is obtained through subsequent processing. It has nothing in common with the process of calcium carbide hydrolysis to acetylene; compared with the partial oxidation of natural gas, the heat source used is essentially different. The partial oxidation of natural gas uses natural gas to burn in an aerobic environment to obtain heat energy, plasma Jet pyrolysis of natural gas to produce acetylene uses electric arc to convert electrical energy into heat energy; compared with arc cracking method, plasma method can form a temperature environment more suitable for natural gas cracking and obtain higher single-pass yield. The high-temperature environment is formed by direct discharge arcing in the middle, and no additional working gas is needed, but the generated temperature is low, and the cracking of methane is not complete.

The National Engineering and Environmental Laboratory (INEEL) in Idaho, USA and the National Energy Technology Laboratory (NETL) in Pittsburgh are representative of the research work on plasma jet cracking natural gas to acetylene. The best result they published in 2002 was that the plasma power was 60KW, 7.25m ³ of natural gas was cracked per hour, the conversion rate of natural gas was 96%, and the yield of acetylene was 93%. Based on this calculation, every ton of acetylene produced consumes 1550m ³ of natural gas and the specific energy is 12.9KWh/kg.

At present, the method of plasma jet cracking natural gas to acetylene is still in the laboratory stage and has not yet entered the stage of industrial scale. The reason is that the essence of the method for producing acetylene by plasma jet cracking natural gas is a high-temperature chemical reaction process, and the reaction speed is extremely fast, measured in milliseconds, which can be regarded as a thermodynamic process in theory. Different, when large-scale raw material gas enters the reaction on an industrial scale, there are the following difficulties:

After the raw material gas enters the reactor, it cannot be heated quickly with the stream gas, which directly affects the reaction effect of the raw material gas, the methane conversion rate is low, and the product yield is low; The residence time is not easy to control, and the yield of the target product acetylene and the by-product carbon black cannot be controlled according to the needs; there is no economical and effective rapid cooling measure for the cracked gas after the reaction, and the produced acetylene is cracked into carbon black, and the yield of acetylene is low; The reactor has carbon formation, which is not easy to handle.

Contents of the invention

The present invention proposes a new method, which effectively overcomes the above-mentioned difficulties and avoids corresponding unfavorable consequences, and is a mature industrial method that can be implemented. This method mainly produces acetylene, co-produces carbon black, and by-products hydrogen (H ₂ ↑); using this method to produce acetylene, the main technical and economic indicators will reach or exceed the experimental level of foreign laboratories, and the economic and environmental benefits will be comprehensive. The benefits will be significantly improved compared with any existing industrial method for producing acetylene.

The method for producing acetylene from methane-containing gas by thermal plasma cracking of the present invention is to send the streamed gas of the working gas into the plasma generator, and be discharged and ionized under the action of a strong electric field to form a high-temperature plasma jet, and the high-temperature jet flows in the reactor A high-temperature environment above 5000K is formed. The raw material gas containing methane enters the reactor through the inlet device, and is mixed with the working gas for heat transfer. The temperature of the mixed gas after soaking is 2000-4500K. Combined to generate cracked gas containing acetylene, the cracked gas is quenched by the cooling device and the temperature is reduced to 350-1000K, the carbon black in the cracked gas is removed through the gas-solid separator, and the acetylene in the cracked gas is separated according to the conventional method. : The air intake device is a symmetrical multi-channel intake ring, the raw material gas is injected into the reactor through the intake ring, and its trajectory is directed from the circumference to the center of the circle in a radially converging shape, mixed with the plasma jet penetrating the intake ring, and rapidly Sufficient heat soaking; the reactor is a funnel-shaped contraction type "Y" reactor, and the mixed gas after soaking is restrained in the "Y" reactor so that the temperature in the reactor is maintained at 2000-4500K; The cooling device is a pneumatic cooling expansion chamber, the cracked gas is buffered in the expansion chamber, the volume suddenly expands, the flow rate decreases sharply, and the heat exchange with the cooling medium is quenched, and the temperature drops to 350-1000K; the raw material gas and the working The gas flow ratio is 0.7-2:1; the residence time of the raw material gas in the reactor is 0.4-40ms.

The temperature of the plasma jet is preferably 5000-30000K, preferably 8000-20000K.

The temperature of the mixed gas after soaking is preferably 2800-4000K, preferably 3100-3500K.

The cracked gas is cooled down to a temperature of preferably 400-800K, preferably 500-700K;

The flow ratio of the raw material gas and working gas is preferably 0.7-1.5:1, more preferably 0.7-1:1.

The working gas is argon, nitrogen or hydrogen.

The raw material gas is any one or several methane-containing gases of natural gas, coal bed methane, and coal coke gas.

The method for producing acetylene mainly produces acetylene, co-produces carbon black, and produces hydrogen by-product. The selectivity of acetylene or carbon black is changed by changing the ambient temperature in the reactor or the residence time of the mixed gas in the reactor.

The selectivity of the acetylene or carbon black is realized by changing the input electric power of the plasma generator.

The selectivity of the acetylene or carbon black is realized by changing the flow rate of raw gas.

The selectivity of the acetylene or carbon black is realized by simultaneously changing the flow rate of the raw material gas and the input electric power of the plasma generator.

The selectivity of the acetylene or carbon black is achieved by changing the geometry of the reactor.

The beneficial effect of this method is:

1. The opposite symmetrical multi-channel air intake method is adopted, the raw material gas and the high-temperature jet are fully heated when entering the reaction, the methane is completely cracked in the high-temperature reaction zone, the conversion rate is high, and the product yield is high.

2. The funnel-shaped shrinking "Y" type reactor is adopted, and the mixed gas after soaking is restrained in the "Y" type reactor, so that the temperature in the reactor is kept stable, the cracking reaction is completely controlled, and the production process is stabilized ; And the residence time of the mixed gas in the reactor can be controlled and adjusted, so as to meet the needs of producing acetylene and carbon black products with different yields.

3. The shrinkable "Y" type reactor is organically combined with the pneumatic cooling expansion chamber to form a reasonable cooling structure, which effectively prevents acetylene from being cracked into carbon black, increases the yield of acetylene, and avoids carbon formation in the reactor. .

By solving the technical problems in the above three aspects, the method becomes a mature industrial method and can be directly applied in actual engineering. The current design scale is a single set of equipment with a power supply of 200KW, a production capacity of 100 tons of acetylene per year, a conversion rate of natural gas of 97%, a yield of acetylene of 90%, a specific energy of 13KW/kg, a power consumption of 12987 degrees per ton of acetylene, and a natural gas of 1558m ³ . The concentration of acetylene in the gas phase product is greater than 13%.

Description of drawings

Fig. 1 is the process flow chart of this method.

Figure 2 is a schematic diagram of the structure of the intake ring and the flow of raw gas and working gas.

Figure 3 is a schematic diagram of the reactor structure.

Fig. 4 is a schematic diagram of the structure of the cooling expansion chamber.

Detailed ways

The present invention will be described in detail below.

Referring to Fig. 1: implement the method for producing acetylene from methane-containing gas by plasma cracking, at first a device for implementing the method is set, which includes high-power DC power supply 1, plasma generator 2, feed gas inlet device 4, reaction Device 5, cooling device 6, gas-solid separator 7, plasma generator 2 is provided with a working gas inlet 3.

The method includes the following steps: the direct current power supply 1 supplies energy to the plasma generator 2, and the flow gas of the working gas is sent into the plasma generator 2 through the inlet 3, and the flow gas of the working gas is discharged and ionized under the action of a strong electric field A high-temperature plasma jet is formed, and the high-temperature jet forms a high-temperature environment above 5000K in the reactor 5. The raw material gas containing methane enters the reactor 5 through the air inlet device 4, and is mixed with the working gas plasma jet to transfer heat. The temperature of the mixed gas is 2000-4500K. The methane component of the raw material gas is dehydrogenated and coupled at this temperature to generate cracked gas containing acetylene. The cracked gas also contains carbon black, H ₂ , CH ₄ , C ₂ H ₄ , C ₂ H ₆ , and working gas components such as N ₂ , the cracked gas is quenched by the cooling device 6, and the temperature drops to 350-1000K, and the carbon black in the cracked gas is removed by the gas-solid separator 7, and then the carbon black in the cracked gas is separated by a conventional method. Acetylene, the whole process is carried out in an oxygen-free, atmospheric pressure environment.

The above are the common basic features of the method for producing acetylene by plasma cracking natural gas, which belongs to the existing known laboratory technology.

In addition to the above-mentioned basic features, the present invention also has the following distinguishing features, which constitute the inventive point of the method and are the key to transforming laboratory technology into engineering technology. include

See Figure 2: The raw material gas inlet device 4 is a ring-shaped multi-channel structure. The raw material gas ② is injected into the reactor 5 through the inlet ring to form a symmetrical intake mode, that is, the movement track of the raw material gas is radiated from the circumference to the center of the circle. Mixed with the plasma jet ① that runs through the inlet ring, the raw material gas ② and the working gas ① are quickly and fully heated, so that methane is completely cracked in the high-temperature reaction zone, with high conversion rate and high product yield.

See Figure 3: Reactor 5 is a shrinking "Y" type reactor, that is, a funnel-shaped reactor. Its front section is a conical structure, and the rear section is a tubular structure with a small diameter and a long length. The resistance is great. The mixed gas after soaking ③ is confined in the "Y" type reactor 5, so that the temperature in the reactor 5 is kept within the range of design requirements (2000-4500K), and the reaction process can be carried out effectively and stably. (Note: the outer wall of the tubular section of the reactor 5 has cooling water ⑥ cooling.)

See Figure 4: The cooling device 6 is a pneumatically cooled expansion chamber, which has a large volume and a built-in heat exchanger ⑤. The outer wall of the expansion chamber is cooled by cooling water ⑥. The built-in heat exchanger ⑤ also passes cooling water ⑥. Therefore, the expansion chamber The heat capacity is also large. The pneumatic cooling expansion chamber is organically combined with the "Y" type reactor 5 to realize rapid cooling of the cracked gas ④. The principle is that the long and narrow tubular section of the "Y" reactor 5 constitutes a throttling area, and the pyrolysis gas ④ forms a high-speed jet in the throttling area, which is sprayed into the pneumatic cooling expansion chamber 6, the volume suddenly expands, and the temperature drops sharply, realizing the first secondary cooling; at the same time, the flow rate of the expanded cracked gas ④ decreases sharply, and it contacts with the large surface of the cooling medium to achieve the second cooling; the cracked gas ④ is quenched under this dual action, and the temperature drops to 350-1000K, thus effectively It avoids the cracking of acetylene into carbon black and improves the yield of acetylene. Simultaneously, since the pyrolysis gas ④ forms a high-speed jet in the throttling area, it flushes the reactor 5 and avoids carbon formation in the reactor 5. (Note: There will be carbon formation on the inner wall of the cooling expansion chamber and the surface of the heat exchanger ⑤, so the cooling expansion chamber is also equipped with a carbon removal mechanism, which is not shown in the figure.)

Through the above reaction process, the methane component of the raw material gas ② is dehydrogenated and coupled to generate cracked gas ④ containing acetylene. The cracked gas ④ also contains carbon black, H ₂ , CH ₄ , C ₂ H ₄ , C ₂ H ₆ , and working gas components such as N ₂ ; the gas-solid separator 7 removes the carbon black in the pyrolysis gas, and the gas-solid separator 7 can adopt common separation equipment such as a bag trap to separate the pyrolysis gas of carbon black ④ and then press Acetylene is separated by conventional methods.

The relevant parameters of each step are as follows:

The flowing gas of the working gas is ionized into a plasma jet, and the temperature is above 5000K, preferably 5000-30000K, preferably 8000-20000K.

The temperature after mixing the raw material gas and the working gas is 2000-4500K, preferably 2800-4000K, preferably 3100-3500K.

The cracked gas is quenched and the temperature is reduced to 350-1000K, preferably 400-800K, preferably 500-700K.

The flow ratio of raw material gas to working gas is 0.7-2:1, preferably 0.7-1.5:1, most preferably 0.7-1:1.

The residence time of raw material gas in the reactor is 0.4-40ms.

There are two kinds of carbon black produced by this method, one is the carbon black produced by the direct cracking of natural gas, which is produced when the temperature is lower; the other is that the acetylene produced in the cracked gas fails to leave the high temperature zone for cooling in time, and then cracks itself into carbon black , the quality of this carbon black is better than the carbon black produced by direct cracking of natural gas, and is closer to acetylene carbon black.

When implementing this method, can change the ambient temperature in the reactor or/and the residence time of mixed gas in the reactor by changing the geometrical dimensions of the reactor, or the feed gas flow rate, or the electric power of the input plasma generator, can Change the selectivity of acetylene or carbon black to meet the needs of producing acetylene and carbon black products with different yields. For example

The flow rate of the raw material gas and the electric power input to the plasma generator remain unchanged, the length of the reactor increases, the resistance of the medium increases, the flow rate slows down, the residence time of the raw material gas in the reactor becomes longer, and the reaction tends to be carbon black selectivity;

The geometric size of the reactor and the flow rate of the raw material gas remain unchanged, the electric power input to the plasma generator is increased, the reaction temperature is increased, and the time required for the reaction is shortened. When the reactor is longer, the reaction tends to be carbon black selectivity;

The geometric size of the reactor and the electric power input to the plasma generator remain unchanged, and increasing the flow rate of the raw material gas is essentially equivalent to reducing the reaction temperature, and the reaction tends to be carbon black selective.

For a given reactor, its geometry is given, so usually only the latter two ways are used to change the selectivity of acetylene or carbon black.

Thus, this method can also utilize the above-mentioned method of changing product selectivity to mainly produce carbon black, and use one or several methods comprehensively to realize the purpose of mainly producing carbon black. However, if the main production of carbon black is the long-term goal, it is better to use a longer-sized reactor to prolong the residence time of the pyrolysis gas in the reactor, so that the acetylene in the pyrolysis gas is also cracked into carbon black to obtain high-quality carbon black.

The working gas used in the method may be argon, nitrogen, or hydrogen. Argon is usually not used, but relatively low-cost nitrogen is used, preferably hydrogen, because its enthalpy is higher than that of nitrogen, the effect of methane cracking will be better, and hydrogen can be directly from the separated gas in this process without additional preparation Or purchase; at the same time, there are no nitrogen, argon and other components in the cracking gas, and the separation process will be simpler and easier. The working gas can also use nitrogen and hydrogen mixed gas, and the methane cracking effect is good and economical.

The raw material gas used in this method can be any methane-containing gas such as natural gas, coal bed methane, and coal coke gas, or several kinds of methane-containing mixed gases.

The measurement of various gases described in this method is based on standard volume (standard M ³ ), and the flow measurement unit is standard volume/unit time.

Claims (10)

1. A method for thermal plasma cracking of methane-containing gas to produce acetylene, which is to send the stream of working gas into the plasma generator, ionize under the action of a strong electric field to form a high-temperature plasma jet, and this high-temperature jet is formed in the reactor In a high-temperature environment above 5000K, the raw material gas containing methane enters the reactor through the inlet device, and is mixed with the working gas for heat transfer. The temperature of the mixed gas after soaking is 2000-4500K, and the methane component of the raw gas is dehydrogenated and coupled at this temperature , generate the cracked gas containing acetylene, the cracked gas is rapidly cooled to 350-1000K by the cooling device, the carbon black in the cracked gas is removed through the gas-solid separator, and the acetylene in the cracked gas is separated according to a conventional method, and it is characterized in that: The air intake device is a symmetrical multi-channel air intake ring, and the raw material gas is injected into the reactor through each channel of the air intake ring, and its trajectory is directed from the circumference to the center of the circle in a radially converging shape, and is mixed with the plasma jet penetrating the air intake ring. The reactor is quickly and fully heated; the reactor is a funnel-shaped shrinkage "Y" reactor, and the mixed gas after soaking is confined in the "Y" reactor, so that the temperature in the reactor is maintained at 2000 -4500K; the cooling device is a pneumatic cooling expansion chamber, the cracked gas is buffered in the expansion chamber, the flow rate is suddenly reduced and quenched, and the temperature is reduced to 350-1000K; the flow ratio of the raw material gas to the working gas is 0.7-2: 1; The residence time of the raw material gas in the reactor is 0.4-40ms. 2. The method for producing acetylene by thermal plasma cracking of methane-containing gas according to claim 1, characterized in that: the temperature of the plasma jet is 5000-30000K, and the temperature of the mixed gas after the soaking is 2800-4000K. The temperature of the cracked gas is rapidly cooled to 400-800K, and the flow ratio of the raw material gas to the working gas is 0.7-1.5:1. 3. The method for producing acetylene by thermal plasma cracking of methane-containing gas according to claim 1, characterized in that: the temperature of the plasma jet is 8000-20000K, and the temperature of the mixed gas after the soaking is 3100-3500K. The temperature of the cracked gas is rapidly cooled to 500-700K, and the flow ratio of the raw material gas to the working gas is 0.7-1:1. 4. The method according to any one of claims 1 to 3, characterized in that: the working gas is argon, nitrogen or hydrogen. 5. The method for producing acetylene by thermal plasma cracking methane-containing gas according to any one of claims 1 to 3, characterized in that: the feed gas is any one or several of natural gas, coalbed methane, and coal coke gas Contains methane gas. 6. The method for producing acetylene by thermal plasma cracking of methane-containing gas according to claim 1, characterized in that: the method for producing acetylene mainly produces acetylene, co-produces carbon black, and by-products hydrogen, by changing the environment in the reactor The temperature or the residence time of the mixed gas in the reactor changes the selectivity of acetylene or carbon black. 7. The method for producing acetylene by thermal plasma cracking of methane-containing gas according to claim 6, characterized in that: the selectivity of the acetylene or carbon black is realized by changing the input electric power of the plasma generator. 8. The method for producing acetylene by thermal plasma cracking of methane-containing gas according to claim 6, characterized in that: the selectivity of the acetylene or carbon black is realized by changing the flow rate of the raw material gas. 9. The method for producing acetylene by thermal plasma cracking of methane-containing gas according to claim 6, characterized in that: the selectivity of said acetylene or carbon black is realized by simultaneously changing the flow rate of feed gas and the input electric power of plasma generator . 10. The method for producing acetylene by thermal plasma cracking of methane-containing gas according to claim 6, characterized in that: the selectivity of the acetylene or carbon black is realized by changing the geometrical dimensions of the reactor.

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