JPS621562B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a raw material switching method in a hydrogen production device for producing a constant amount of hydrogen without causing any disturbance to the device when switching from hydrocarbon gas to backup naphtha.

In petroleum refining and petrochemical plants, hydrogen is sometimes produced by a steam reforming method using hydrocarbon gas discharged from various petroleum refining or petrochemical equipment, so-called off gas (OFF gas), as a raw material.

In this type of hydrogen production equipment, if a problem occurs with the off-gas supply equipment and the supply of off-gas decreases or stops, hydrogen production becomes impossible, so naphtha can be supplied for backup purposes. . Conventionally, equal volume backup, in which an equal volume of naphtha is added when the supply of off-gas is reduced or stopped, requires a great deal of man-hours and temporarily makes the operation of the equipment unstable.

The present invention has been made in view of these points, and is designed to supply an equal amount of naphtha based on various data during normal operation when the off-gas flow rate fluctuates and it becomes difficult to continue operating the equipment. At the same time, in order to replenish the volume reduction of the raw material caused by switching from off-gas to naphtha, a part of the generated hydrogen is recycled into the raw material supply, thereby compensating for fluctuations in off-gas and maintaining a constant level without causing disturbance to the control system. It is designed to be able to produce large amounts of hydrogen.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

The figure is a configuration diagram showing an embodiment of a hydrogen production apparatus for explaining the present invention. The figure shows an example in which two systems of off-gas and backup naphtha are used as raw materials. In the figure, F ₁ to F ₃ are flow rate detectors installed in the raw material flow paths of each system, and C ₁ to C ₃ are flow rate controllers that adjust the raw material flow rate in response to the outputs of the detectors F ₁ to F ₃ . , V ₁ to V ₃ are control valves driven by controllers C ₁ to C ₃ , respectively.
The raw materials that have passed through each flow path join together at point A and enter the heating furnace 1. The raw material heated in the heating furnace 1 is reformed into hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) by steam in the presence of a catalyst in the reforming furnace 2, and then enters the decarboxylation device 3 where it is carbonated. The gas is removed and becomes a product (hydrogen).

C ₄ is a flow rate controller that adjusts the amount of hydrogen recycled from a part of the product, V ₄ is a control valve driven by the controller, and F ₄ is a flow rate detector that detects the amount of recycled hydrogen, and its output is It is input to controller _C4 .

T ₁ is a temperature detector that detects the temperature at the outlet of heating furnace 1, C ₆ is a sampling type temperature controller that outputs a control signal in response to the output of the temperature detector, and C ₇
is a flow rate controller that uses the output of the temperature controller as a set value to adjust the flow rate of fuel flowing into the heating furnace 1, _V5 is a control valve that receives the output of the controller, and _F5 is a flow rate detector that detects the fuel flow rate. The output is input to controller _C7 . _T2 is a temperature detector that detects the temperature inside the reforming furnace 2, and _C8 is a temperature controller that receives the output of the temperature detector and outputs a control signal.

F ₆ and F ₇ are flow rate detectors that detect the fuel flow rate supplied to the reforming furnace 2, and C ₉ and C ₁₀ are flow rate regulators that receive the output of each flow rate detector F ₆ and F ₇ and output a control signal. _T3 is a temperature detector that detects the gas temperature at the outlet of the reforming furnace 2, and _C11 is a temperature controller that receives the output of the detector and outputs a control signal. _C12 is a pressure controller which receives the output of either one of temperature controller _C8 or flow controller _C9 as a set value, and _SW1 is its changeover switch. C ₁₃ is a pressure regulator which receives the output of either one of the temperature regulator C ₁₁ or the flow regulator C ₁₀ as a set value, and SW ₂ is its changeover switch.
V ₆ and V ₇ are control valves driven by pressure regulators C ₁₂ and C ₁₃ , respectively, and P ₃ and P ₄ are pressure detectors that detect the pressure (back pressure) that fuel is applied to the nozzle section, and are driven by regulators C 12 and C 13, respectively. ₁₂ and C ₁₃ . Reference numeral 7 denotes an arithmetic control device that receives the outputs of the respective detectors and provides set value signals to the controllers C ₃ to C ₅ and C ₉ to _{C 10} , as well as performs various arithmetic controls. As the arithmetic and control device, for example, a microcomputer is used. In the figure, connection lines from each detector to the arithmetic and control unit are omitted.
To explain the operation of the device configured in this way,
It is as follows.

First, a normal operating state in which off-gas is normally supplied will be described. In normal operating conditions, control valves V ₃ and V ₄ are closed and no naphtha is being supplied and there is no partial recycling of generated hydrogen. That is, a predetermined amount of hydrogen is produced only by supplying from offgases 1 and 2. Further, the setting values of each controller set by the arithmetic and control device 7 are stored in advance in the built-in memory at certain fixed time intervals. Furthermore, the control output of temperature controller _C8 is connected to the setting input of pressure controller _C12 , and the control output of temperature controller _C11 is connected to the setting input of pressure controller _C13 . is controlled so that the temperature inside the furnace and the passing gas are constant.

Next, an explanation will be given of an abnormal operation when the supply of off-gas decreases and stops.

The arithmetic and control device 7 closes the control valve (V ₁ or V ₂ ) of the off-gas flow path where the pressure has decreased. At the same time, a setting value is given to the flow controller C ₃ to supply the naphtha required to generate the same amount of hydrogen as the amount of hydrogen generated immediately before the abnormality, and based on this, the controller V _{3 opens and the naphtha is supplied to the flow controller C 3} . is supplied. Next, give the set value to flow controller C ₄ , open controller V ₄ ,
A part of the product hydrogen is recycled to the heating furnace 1 inlet. The reason why part of the hydrogen is recycled to the input side in this way is as follows. Naphtha contains more hydrogen atoms per unit mole than off-gas, so if the amount of hydrogen generated is kept constant and the raw material is switched from off-gas to naphtha, it is necessary to pass through the heating furnace 1 to the reforming furnace. The number of molecular moles per unit time of the raw material supplied to No. 2 can be small. By the way, naphtha is supplied in a liquid state, but after being supplied, it is heated in the heating furnace 1 and immediately vaporized. Furthermore, since the pressure and temperature within the system of the hydrogen production apparatus are maintained approximately constant, the volume decreases by the amount of decrease in the number of moles of molecules of the raw material per unit time. For this reason, the difference between the number of molecular moles per unit time during off-gas and the number of molecular moles per unit time of naphtha, and the amount of volume reduction based on this, are calculated in the arithmetic and control device 7, and the volume reduction is A corresponding set value is applied from the arithmetic and control unit 7 to the flow regulator C ₄ , which opens the regulator V ₄ and the hydrogen is recycled. In other words, when switching the raw material from off-gas to naphtha, the number of molecular moles per unit time supplied to the heating furnace 1 and reforming furnace 2, that is, the volume of gas present in the device, is
Hydrogen is used to supply the same amount of hydrogen before and after switching the raw materials.

In addition to the above operations, the arithmetic and control unit 7 disconnects the cascade connection of the flowmeter C ₇ and operates only the flowmeter C ₇ in an independent loop, and controls the heating furnace 1 due to changes in raw materials.
Give a setting value that is commensurate with the load.

Furthermore, the arithmetic and control unit 7 connects the pressure regulators C ₁₂ and C ₁₃ in cascade to the temperature regulators C ₈ and C ₁₁ .
Switch from flow controller C ₉ to C ₁₀ . When the state of the process control system changes, if the change in the process is interpreted as a change in temperature, it will not be possible to perform appropriate control because temperature has a large time delay compared to other process variables. Therefore, the control is switched to flow rate control with good responsiveness. Simultaneously with the switching, set values are given to the flow rate controllers C ₉ and C ₁₀ from the arithmetic and control unit 7. Next, how to give these setting values will be explained.

When the above-mentioned abnormality occurs, the arithmetic and control unit 7 calls out the setting value data of each controller stored in the above-mentioned built-in memory and outputs it to each controller.

In order to provide the set values to the flow rate controllers C ₉ and C ₁₀ described above, the fuel flow rate value required to maintain the same furnace temperature as before the abnormality is calculated by adjusting the load change of the reformer 2 due to the change in raw materials. The flow rate value is determined by calculation, and the signals necessary to obtain the flow rate value are given as set values to the controllers C ₉ and C ₁₀ , respectively.

In addition, after the above operations are completed, the manipulated output of each controller is changed to a predetermined value with a rate of change limit taken into consideration for safety, so that the process is prevented from being disrupted by sudden changes in set values. It is prevented. Even if it becomes difficult to continue operation of the equipment, it is possible to switch to an equal volume backup system using naphtha without bumping by performing the various operations described above.

Note that hydrogen recycling may be appropriately stopped after a predetermined period of time after switching to naphtha, or may be stopped after switching to off-gas again, as will be described later.

While operating in such an equal volume backup state, the pressure in the stopped off-gas flow path recovers to the predetermined value, and the detector output value of each control loop becomes the predetermined value, and the set value and measured value return to the predetermined value. When it is confirmed that the difference in value is within a predetermined tolerance, the arithmetic and control unit 7 terminates the equal volume backup state and returns to the normal operating state. In other words, the off-gas flow path controller (V ₁ or V ₂
) and at the same time close the control valve _V3 to stop the supply of naphtha. Furthermore, the arithmetic and control device 7
Control valve V ₄ is closed to cut off part of the product hydrogen from being recycled, and the cascade connection of pressure regulators C ₁₂ and C ₁₃ is returned from flow regulators C ₉ and C ₁₀ to temperature regulators C ₈ and C ₁₁ .

In the above description, the case where there are two systems for off-gas of the raw material is taken as an example, but the present invention is not limited to this, and any number of systems may be used.

As explained above in detail, according to the present invention, when the off-gas flow rate fluctuates and the control system is about to go down, an equal amount of naphtha is supplied based on various data during normal operation, and the amount of naphtha is supplied per unit time of the raw material. In order to maintain the number of moles of molecules supplied at the same amount as under normal conditions, that is, to replenish the volume loss caused by switching from off-gas to naphtha, a portion of the generated hydrogen is recycled to the raw material supply section to reduce fluctuations in off-gas. It is possible to realize a hydrogen production device that can automatically compensate and produce a constant amount of hydrogen without causing any disturbance to the control system.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an embodiment of the present invention. 1...Heating furnace, 2...Reforming furnace, 3...Decarboxylation device, 7...Arithmetic control unit, _C1 to _C13 ...Controller,
V ₁ to V ₇ ... Control valve, F ₁ to _{F 7} ... Flow rate detector, P ₂
~ _P4 ...Pressure detector, _T1 ~ _T3 ...Temperature detector,
SW ₁ , SW ₂ ...Selector switch.

Claims (1)

[Claims] 1. In an apparatus for producing hydrogen by steam reforming using hydrocarbon gas and naphtha for backup, when switching to naphtha for backup, an amount of hydrogen is added to compensate for the volume reduction caused by switching from the hydrocarbon gas to naphtha. A raw material switching method in a hydrogen production device, characterized in that the raw material is recycled to a raw material supply section.