JP6878913B2 - How to make carbon dioxide - Google Patents

Description

The present invention relates to a method for producing carbon dioxide, and more particularly to a method for producing carbon dioxide using exhaust gas from an ethylene plant operated under negative pressure as a raw material.

Carbon dioxide is used in various fields such as a shield gas for welding, a gas for manufacturing castings, a gas for filling foods, a purge gas, a soft drink, and dry ice. And this carbon dioxide has mainly used carbon dioxide produced as a by-product in the ammonia production process.
However, due to the balance between supply and demand of ammonia, the ammonia manufacturing plant has been shut down, and a new source of carbon dioxide is needed. As such a new source, ethane, propane, naphtha, gas oil in industrial equipment such as boilers and gas turbines used as power generation equipment such as thermal power plants that use a large amount of fossil fuel, and in cracking furnaces. A wide range of hydrocarbon raw materials such as benzene, etc. are thermally decomposed at high temperature for a short time under no catalyst to produce olefins such as ethylene, propylene and butene and aromatic compounds such as benzene, toluene and xylene, which are separated and purified. Ethane plants, etc. will be considered.

The technology that uses carbon dioxide in the exhaust gas generated from the above industrial equipment such as boilers and gas turbines is intended to fix carbon dioxide as an environmental measure, and its application is to boiler turbines such as power plants that generate a large amount of electricity. This is a technology that is being studied mainly for equipment, and is a technology that extracts part or all of the exhaust gas containing exhaust gas and sends it to carbon capture equipment (Patent Document 1).

In addition, the above ethylene plant has a thermal decomposition step and a separation and purification step. In the thermal decomposition step, the raw material hydrocarbon and steam are mixed, introduced into the reaction tube in the ethylene decomposition furnace, and heated from the outside of the tube by a burner, and a reaction product such as ethylene is obtained. The reaction product obtained by the heat exchanger is then rapidly cooled and sent to a separation and purification step where it is separated into individual components. During this quenching, the uncondensed gas component is discharged to the outside as exhaust gas. This exhaust gas contains carbon dioxide, which is a complete combustion product of the raw material hydrocarbon.

Japanese Unexamined Patent Publication No. 2010-17617

Gato et.al. (2005): “Dynamic behavior of high-pressure natural gas flow in pipelines”, Int. J. Heat and Fluid flow, Vol26,817-825

However, since the exhaust gas from the equipment described in Patent Document 1 contains impurities such as sulfur and other heavy metal components, it is difficult to utilize the recovered carbon dioxide for food applications.

On the other hand, the exhaust gas from the above ethylene plant does not contain impurities such as sulfur and other heavy metal components, and the carbon dioxide recovered from this can be utilized for food applications.
By the way, the decomposition furnace of the above ethylene plant is often operated under the condition of a slight negative pressure of −35 PaG to −15 PaG, in contrast to the power plant boiler. Then, in the unlikely event that the exhaust gas containing carbon dioxide is recovered from the ethylene plant and the carbon dioxide recovery facility malfunctions, the recovery rate of the exhaust gas changes, and as a result, a shock wave due to pressure fluctuation, that is, pressure It is known that fluctuating waves are generated (Non-Patent Document 1). When the pressure fluctuation wave propagates to the ethylene cracking furnace of the ethylene plant, the pressure of the cracking furnace fluctuates, and in some cases, it may change to positive pressure, which may hinder the stable operation of the cracking furnace.

Therefore, in the present invention, when exhaust gas containing carbon dioxide is recovered from an ethylene plant to produce high-purity carbon dioxide, a shock wave generated due to a malfunction in the carbon dioxide production facility causes an ethylene decomposition furnace of the ethylene plant. The purpose is to prevent the inside of the ethylene cracking furnace from becoming positive pressure and to ensure stable operation of the ethylene cracking furnace.

As a result of studies by the present inventors, they have found that the above problems can be solved by providing an exhaust gas facility, a carbon dioxide production facility, and an exhaust gas extraction pipe that satisfy specific conditions, and have completed the present invention.
That is, the gist of the present invention is as follows.

[1] In a method for producing carbon dioxide using an exhaust gas discharged from an ethylene decomposition furnace and an exhaust gas plant having an exhaust gas facility for collecting and discharging the exhaust gas discharged from the ethylene decomposition furnace. The exhaust gas equipment and the carbon dioxide production equipment that produces the carbon dioxide are connected by an exhaust gas take-out pipe, and one end of the exhaust gas take-out pipe is inserted into the exhaust gas equipment and flows through the exhaust gas take-out pipe. When the amount of exhaust gas decreases, the time from the start of the decrease to the end of the decrease is t1 seconds, and the exhaust gas in the portion of the exhaust gas with an opening at one end of the exhaust gas take-out pipe inserted inside the exhaust gas facility. When the flow direction is used as a reference, the direction in which the opening at one end of the exhaust gas extraction pipe faces is θrad (0 ≤ θ ≤ π), and the pressure generated when the amount of the exhaust gas flowing through the exhaust gas extraction pipe decreases. The time for the fluctuating wave to reach the ethylene decomposition furnace is t2 seconds, and the amount of decrease in kinetic energy caused by the decrease in the speed of the exhaust gas flowing through the exhaust gas extraction pipe is ΔU (J).
Then, by satisfying the following formula (1), the pressure fluctuation range caused by the malfunction of the carbon dioxide production equipment is suppressed to 100 Pa or less, which is a method for producing carbon dioxide.
(-7.29349) × t1 + (-18.52513) × θ + (-138.68) × t2 + (0.4040007) × ΔU + 149.9496 ≦ 100… (1)
[2] The production of carbon dioxide according to [1], wherein the ethylene cracking furnace is operated at −150 PaG or more and less than -100 PaG, and the pressure of the ethylene cracking furnace due to the pressure fluctuation is maintained at a negative pressure. Method.

According to the present invention, since the exhaust gas equipment, the carbon dioxide production equipment and the exhaust gas extraction pipe are provided so as to satisfy the condition of the equation (1), the pressure fluctuation width due to the pressure fluctuation wave caused by the malfunction of the carbon dioxide production equipment is within 100 Pa. Therefore, the ethylene cracking furnace can be maintained in a negative pressure state, and stable operation of the ethylene cracking furnace can be ensured.

(A) (b) (c) Schematic diagram showing the relationship between the ethylene decomposition furnace, the exhaust gas equipment, and the exhaust gas extraction pipe according to the present invention. Schematic diagram of carbon dioxide production equipment according to the present invention Schematic diagram showing the relationship between the exhaust gas equipment according to the present invention and one end of the exhaust gas extraction pipe. Graph showing an example of slowdown of exhaust gas flowing through the exhaust gas extraction pipe

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

The present invention is a method for producing carbon dioxide, which recovers carbon dioxide from an ethylene cracking furnace and an exhaust gas of an ethylene plant having an exhaust gas facility for recovering and discharging the exhaust gas discharged from the ethylene cracking furnace.

The ethylene cracking furnace 10 uses saturated hydrocarbons, mainly ethane, propane, butane, LNG (liquefied natural gas), naphtha, gas oil, etc. as raw materials, and has a temperature of 500 to 875 ° C. and a pressure of −150 PaG to −100 PaG in the cracking furnace. Driven in range. The decomposed gas is cooled by a cooler as needed and sent to the exhaust gas equipment 11.

As shown in FIG. 1A, the above exhaust gas facility 11 includes a decomposition furnace duct 12 for recovering exhaust gas having carbon dioxide generated in a plurality of ethylene decomposition furnaces 10, and a connecting duct 13 for connecting each decomposition furnace duct 12. It is composed of an exhaust gas collecting duct 14 that collects the exhaust gas in the connecting duct 13, and an exhaust gas chimney 15 that discharges the exhaust gas collected in the collecting duct 14 to the outside.
The exhaust gas equipment 11 recovers the exhaust gas containing carbon dioxide generated in the ethylene decomposition furnace 10 and discharges it to the outside from the chimney.

A part or all of the exhaust gas recovered in the exhaust gas equipment 11 is extracted, and at least a part of carbon dioxide contained in the extracted exhaust gas is recovered to produce high-purity carbon dioxide, which is shown in FIG. Such carbon dioxide production equipment 21 is provided.

The carbon dioxide production facility 21 is not particularly limited, but is an exhaust gas take-out pipe 22 that extracts a part or all of the exhaust gas from the exhaust gas facility 11, and a water washing tower 23 that cleans the exhaust gas extracted by the exhaust gas take-out pipe 22 with water. , A blower 24 that sucks the exhaust gas washed with water in the water washing tower 23, an absorption tower 25 that absorbs carbon dioxide from the sucked exhaust gas, a processing facility (not shown) that processes and purifies the absorbing liquid that has absorbed carbon dioxide, etc. It is a facility to have. Although only one blower 24 may be provided, it is preferable to provide a plurality, that is, at least two in parallel in order to prevent the entire carbon dioxide production facility 21 from stopping due to a malfunction or failure of the blower 24. ..

As described above, the exhaust gas equipment 11 and the carbon dioxide production equipment 21 are connected by the exhaust gas extraction pipe 22. One end of the exhaust gas take-out pipe 22 is inserted into the exhaust gas equipment 11, and the other end is connected to, for example, a washing tower 23.

The position of the exhaust gas equipment 11 into which one end of the exhaust gas take-out pipe 22 is inserted is located on one surface of the aggregation duct 14 as shown in FIG. 1 (a) and the exhaust gas chimney 15 as shown in FIG. 1 (b). The lower end surface, the upper end opening of the exhaust gas chimney 15 as shown in FIG. 1C, and the like can be mentioned.
Then, one end of the exhaust gas take-out pipe 22 is inserted into the exhaust gas equipment 11 from the above position, and this end is arranged under the conditions described later.

The opening 22a provided at one end of the exhaust gas extraction pipe 22 is provided at the end face or side surface of the end, for example, as shown in FIG. Specifically, the exhaust gas take-out pipe 22 inserted into the exhaust gas equipment 11 is bent in the flow direction of the exhaust gas flowing in the exhaust gas equipment 11, and the opening 22a at the end of the exhaust gas take-out pipe 22 is passed through the exhaust gas flow. As shown in FIG. 3, it is preferable to form the shape so as to be inclined at a predetermined angle (θrad, 0 ≦ θ ≦ π) with respect to the direction. Specifically, this angle θ is an angle formed between the flow direction of the exhaust gas and the surface on which the opening 22a is formed and the vertical direction. This angle will be described later.
The angle θ is 90 ° with respect to the flow direction of the exhaust gas on the surface of the exhaust gas take-out pipe 22 opposite to the surface closest to the wall surface of the exhaust gas facility 11, with the flow direction of the exhaust gas as 0 rad. The angle of the opening 22a formed with an angle of = π / 2 rad) is 90 ° (= π / 2 rad). Similarly, the angle of the opening 22a formed on the surface of the exhaust gas take-out pipe 22 closest to the wall surface of the exhaust gas equipment 11 at an angle of 90 ° (= π / 2rad) with respect to the flow direction of the exhaust gas. Also set to 90 ° (= π / 2 rad).

In the present invention, in order to suppress the pressure fluctuation range generated in the ethylene decomposition furnace 10 to 100 Pa or less due to the malfunction of the carbon dioxide production facility 21, it is necessary to satisfy the following formula (1).
(-7.29349) × t1 + (-18.52513) × θ + (-138.68) × t2 + (0.4040007) × ΔU + 149.9496 ≦ 100… (1)

In the formula (1), t1 (second) indicates the time from the start of the decrease to the end of the decrease when the amount of the exhaust gas flowing through the exhaust gas take-out pipe 22 decreases.
t1 (second) is also applied when the carbon dioxide production facility 21 is intentionally stopped, but the sign of the constant is negative, and the amount of the exhaust gas flowing through the exhaust gas extraction pipe 22 is reduced in a short time. If it occurs, specifically, it will be short due to the shutdown or malfunction of one or more of the blowers 24, the decrease in the amount of exhaust gas due to the malfunction of the other carbon dioxide production equipment 21, the emergency shutdown of the carbon dioxide production equipment 21, etc. When the amount of exhaust gas decreases in time, it has a great influence on the result of the equation (1).

θ (rad) indicates the above angle.
As described above, θ is the angle of the opening 22a, and generally, depending on other conditions, the direction may be opposite to the flow direction of the exhaust gas, but the flow direction of the exhaust gas, that is, More preferably, it is provided in the direction opposite to the direction toward the ethylene cracking furnace. A more preferable range is 0 to 90 ° (= π / 2 rad). At 270 ° (= 3π / 2rad) to 0 ° (360 °), the opening 22a faces the wall surface of the exhaust gas equipment 11, but it is the same as at 0 ° to 90 ° (= π / 2rad). It is thought that the effect will be obtained. That is, in the present invention, 0 to 180 ° and 360 to 180 ° are not distinguished, and the direction of the opening at one end of the exhaust gas extraction pipe is set to θrad (0 ≦ θ ≦ π).

t2 (seconds) indicates the time for the pressure fluctuation wave generated when the amount of exhaust gas flowing through the exhaust gas extraction pipe 22 decreases to reach the ethylene cracking furnace.
t2 (seconds) is the time for the pressure fluctuation wave to reach the ethylene cracking furnace, but since the pressure fluctuation wave propagates in the gas, it has almost the same speed as the sound wave. Therefore, this time t2 is substantially the distance from the decomposition furnace 10 to the carbon dioxide production facility 21, that is, the length of the exhaust gas extraction pipe 22, and the decomposition furnace from the opening at one end of the exhaust gas extraction pipe 22. It is determined by the total value of the distances of the shortest routes up to 10.

ΔU (J) indicates the amount of decrease in kinetic energy caused by the decrease in the speed of the exhaust gas flowing through the exhaust gas extraction pipe 22.
ΔU is the amount of decrease in kinetic energy caused by the decrease in the speed of the exhaust gas flowing through the exhaust gas extraction pipe 22. Since the mass of the exhaust gas flowing through the exhaust gas take-out pipe 22 is constant per unit volume, it becomes constant once the diameter of the exhaust gas take-out pipe 22 is determined, and can be incorporated into a constant. Therefore, for example, as shown in FIG. 4, if the velocity decreases from v1 to v2, ΔU becomes a constant multiple of ^{((v1) 2-} (v2) ^2).

The reduced speed v2 becomes v2 = 0 when the carbon dioxide production facility 21 is stopped. Further, when the carbon dioxide production facility 21 does not stop but a malfunction occurs, such as when some of the plurality of blowers 24 stop, v2> 0.

The coefficients of t1, θ, t2 and ΔU described above are coefficients determined so that the data of the pressure fluctuation width in the ethylene decomposition furnace when these conditions are changed can be reproduced. When this coefficient is positive, the variable is increased and the pressure fluctuation range is increased. On the contrary, when this coefficient is negative, the variable is increased and the pressure fluctuation range is decreased.
Therefore, the value of "(-7.29349) x t1 + (-18.5213) x θ + (-138.68) x t2 + (0.4040007) x ΔU + 149.9494" in the above formula (1) is said to be 100 or less. Means that the pressure fluctuation range in the ethylene decomposition furnace is 100 Pa or less.

Therefore, in this formula (1), t1 and ΔU change depending on the degree of malfunction of the carbon dioxide production facility 21, so that t2 and θ, that is, the distance and the opening from the ethylene decomposition furnace to the carbon dioxide production facility 21. By optimizing the angle of 22a, the pressure fluctuation range can be set to 100 Pa or less even if t1 and ΔU change.

By the way, in the above equation (1), various factors including t1, t2, θ, and ΔU are set, the pressure fluctuation width (ΔP) in the ethylene decomposition furnace is calculated by fluid analysis, and a statistical regression model that reproduces this result is reproduced. It is an equation derived by constructing. The calculation method by this fluid analysis will be shown in the column of Examples described later.

In the present invention, the pressure fluctuation range can be suppressed to 100 Pa or less. The ethylene cracking furnace of the present application is operated under a negative pressure condition of −150 PaG or more and less than -100 PaG, but under this negative pressure condition, the ethylene cracking furnace may become positive pressure depending on the pressure fluctuation. In order to prevent this situation, it is necessary to adjust the values of t1, t2, θ, ΔU, especially t2 and θ, so that the value of the above formula (1) becomes smaller than the absolute value of the pressure of the ethylene decomposition furnace. As a result, even if the pressure fluctuates due to the malfunction of the carbon dioxide production facility, the pressure of the ethylene cracking furnace can be maintained at a negative pressure, and the stable operation of the ethylene cracking furnace can be ensured.

Next, the present invention will be described in more detail by way of examples. The present invention is not limited to these examples.
In the following examples and comparative examples, the pressure fluctuation value was calculated using software of computational fluid dynamics (CFD).

<Method of calculating pressure fluctuation value using equation (1)>
[Computational Fluid Dynamics (CFD) Software]
Computational fluid dynamics (CFD) is an engineering method for detailed calculation of fluids and other physical phenomena involving a target case. And with CFD software, the shape of the duct and chimney from the outlet of the ethylene decomposition furnace to the inlet of the carbon dioxide extraction facility, and the internal structure can be modeled in three dimensions as they are, such as the internal gas flow and pressure distribution. Can be obtained in detail. In addition, the calculation can be applied to both steady-state calculation and unsteady calculation. If the operation from the ethylene decomposition furnace to the carbon dioxide production equipment is in normal operation, the steady-state calculation is performed, and after the carbon dioxide production equipment malfunctions. The magnitude of the pressure wave propagating in the ethylene cracking furnace can be obtained and the pressure fluctuation range can be obtained by performing unsteady calculation when obtaining the pressure fluctuation in the equipment of the above.
-Software used: ANSYS CFX (manufactured by ANSYS, ver16.2)
The calculation procedure using this fluid analysis software is as follows.
1) The amount of gas generated in the decomposition furnace is set as the inlet condition for the decomposition furnace duct 12.
2) Set the flow rate at the outlet of the exhaust gas take-out pipe 22.
3) At the outlet of the exhaust gas take-out pipe 22, the flow rate is changed to decrease to a predetermined amount after a predetermined time has elapsed.
4) Calculate the pressure fluctuation value at the inlet of the decomposition furnace duct 12.

(Example 1)
Equipment to extract part of the exhaust gas (100,000 Nm ³ / hr, equivalent to 32%) of the ethylene decomposition furnace (total exhaust gas amount 440,000 Nm ³ / hr) from the exhaust gas extraction pipe (the extraction pipe is a circular pipe with a diameter of 1.5 m) From 100,000 Nm ³ / hr (gas linear speed 15.7 ^{m / sec) to 50,000 Nm 3} / hr (gas linear speed 7.9 m / sec) in 1 second. When the change occurs, the distance from the exhaust gas outlet (opening of the exhaust gas outlet pipe; the same applies hereinafter) is 318 m (assuming a sound velocity of 347 m / sec, propagation time = 0.92 sec), and the direction of the exhaust gas outlet pipe is It was installed so as to form an angle of 0 ° (= 0radian) with the gas flow direction. The calculated value of the equation (1) in this case was 53 Pa. Under these conditions, the pressure fluctuation value in the ethylene cracking furnace was calculated using fluid analysis software (CFX ver16.2). The calculation using the fluid analysis software was performed according to the following procedure.
1) Set the amount of gas generated in the cracking furnace as the cracking furnace inlet condition (440,000 Nm ³ / hr)
2) Set the flow rate at the outlet of the exhaust gas take-out pipe (100,000 Nm ³ / hr, gas linear speed 15.7 m / sec)
3) At the outlet of the exhaust gas take-out pipe, changed to 50,000 Nm ³ / hr (gas linear speed 7.9 m / sec) after 1 second. 4) Calculate the pressure fluctuation value at the cracker inlet. As a result, the ethylene cracker The pressure fluctuation in was 53 Pa, and it was found that there was no effect on the ethylene plant.

(Comparative Example 1)
Equipment to extract part of the exhaust gas (140,000 Nm ³ / hr, equivalent to 32%) of the ethylene decomposition furnace (total exhaust gas amount 440,000 Nm ³ / hr) from the exhaust gas extraction pipe (the extraction pipe is a circular pipe with a diameter of 1.5 m) From 140,000 Nm ³ / hr (gas linear speed 22.0 m / sec) to 70,000 Nm ³ / hr (gas linear speed 11.0 m / sec) in one second. When the change occurs, the distance from the exhaust gas outlet to the ethylene decomposition furnace is 115 m (propagation time = 0.33 sec assuming a sound velocity of 347 m / sec), and the direction of the exhaust gas outlet pipe is 90 ° (= 1) with the gas flow direction. It was installed so as to form an angle of .57 radian). The calculated value of the equation (1) in this case was 132 Pa. Under these conditions, the pressure fluctuation value in the ethylene cracking furnace was calculated using fluid analysis software (CFX ver16.2). The calculation using the fluid analysis software was performed according to the following procedure.
1) Set the amount of gas generated in the cracking furnace as the cracking furnace inlet condition (440,000 Nm ³ / hr)
2) Set the flow rate at the outlet of the exhaust gas take-out pipe (140,000 Nm ³ / hr, gas linear speed 22.0 m / sec)
^{3) Change to 70,000 Nm 3} / hr (gas linear speed 11.0 m / sec) at the outlet of the exhaust gas take-out pipe after 1 second. 4) Calculate the pressure fluctuation value at the inlet of the cracking furnace. As a result, the ethylene cracking furnace The pressure fluctuation in was 141 Pa, which was found to have an effect on the ethylene plant.

10 Ethylene decomposition furnace 11 Exhaust gas equipment 12 Decomposition furnace duct 13 Connecting duct 14 Consolidation duct 15 Exhaust gas chimney 21 Carbon dioxide production equipment 22 Exhaust gas extraction piping 22a Opening 23 Water washing tower 24 Blower 25 Absorption tower

Claims (2)

In an ethylene cracking furnace and a method for producing carbon dioxide using exhaust gas discharged from an ethylene plant having an exhaust gas facility for recovering and discharging the exhaust gas discharged from the ethylene cracking furnace.
The exhaust gas equipment and the carbon dioxide production equipment for producing carbon dioxide are connected by an exhaust gas take-out pipe, and one end of the exhaust gas take-out pipe is inserted into the exhaust gas equipment.
When the amount of the exhaust gas flowing through the exhaust gas take-out pipe is reduced, the time from the start of the reduction to the end of the reduction is t1 second.
The direction in which the opening at one end of the exhaust gas take-out pipe faces, based on the flow direction of the exhaust gas at the portion having the opening at one end of the exhaust gas take-out pipe inserted inside the exhaust gas equipment. Θrad (0 ≤ θ ≤ π),
The time for the pressure fluctuation wave generated when the amount of the exhaust gas flowing through the exhaust gas extraction pipe decreases to reach the ethylene cracking furnace is t2 seconds.
The amount of decrease in kinetic energy caused by the decrease in the speed of the exhaust gas flowing through the exhaust gas extraction pipe is ΔU (J),
Then, by satisfying the following formula (1), the pressure fluctuation range caused by the malfunction of the carbon dioxide production equipment is suppressed to 100 Pa or less, which is a method for producing carbon dioxide.
(-7.29349) × t1 + (-18.52513) × θ + (-138.68) × t2 + (0.4040007) × ΔU + 149.9496 ≦ 100… (1) The method for producing carbon dioxide according to claim 1, wherein the ethylene cracking furnace is operated at −150 PaG or more and less than −100 PaG, and the pressure of the ethylene cracking furnace due to the pressure fluctuation is maintained at a negative pressure.

Images