JPH0351641B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention calculates the steam carbon molar ratio S/C, converts this S/C into a ratio value, and controls the steam amount in a hydrogen production device using the ratio value and the raw material flow rate. Concerning quantity control methods.

In petroleum refining or petrochemical plants, hydrocarbon gas such as so-called off gas (OFF GAS) discharged from various petroleum refining or petrochemical equipment may be used as a raw material for hydrogen production.

By the way, when producing hydrogen from off-gas,
The composition of the raw material gas changes significantly depending on the operating conditions of the equipment that generates off-gas, so it is analyzed using a gas chromatography analyzer installed at the inlet of the reformer, the number of carbons in the raw material is calculated, and the steam flow rate at that load is determined. has been decided. However, in such conventional methods, the steam flow rate has to be set somewhat higher in order to compensate for short-term fluctuations in the off-gas composition and flow rate, and steam is wasted.

The present invention has been made in view of these points, and is a method of determining the steam carbon molar ratio S/C from flow rate, temperature, carbon, and pressure detectors installed in the raw material flow path and the steam flow path. , the S/C
The value is input to the controller, and the ratio is changed using the control signal, and the steam flow rate is controlled based on the ratio and the raw material flow rate value, thereby minimizing the amount of steam used. The carbon molar ratio S/C can be controlled to be constant.

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. In the figure A ₁ ,
T ₁ , P ₁ , F ₁ are detectors installed in the off-gas supply flow path, A ₁ is an analyzer to detect gas composition, T ₁ is a temperature detector to detect temperature, and P ₁ is to detect pressure. The pressure detector, F ₁ is a flow rate detector that detects the flow rate. As the analyzer _A1 , for example, a gas chromatography analyzer is used. V ₁ is a control valve that adjusts the raw material flow rate, and C ₁ is a flow rate controller that adjusts the control valve V ₁ so that the output of the flow rate detector F ₁ is constant. _P2 ,
F ₂ is a detector installed in the steam supply flow path,
_P2 is a pressure detector that detects pressure, and _F2 is a flow rate detector that detects flow rate. V ₂ is a control valve that adjusts the steam flow rate, and C ₂ is a flow controller that adjusts the control valve V ₂ so that the output of the flow rate detector F ₂ is constant.

CA ₁ is a computing unit that receives the output of each detector A ₁ , T ₁ , P ₁ , F ₁ and corrects the temperature, pressure, and specific gravity of the off-gas to calculate the number of carbon moles in the gas;
CA ₂ is an arithmetic unit that receives the outputs of detectors F ₂ and _{P 2} and corrects the specific gravity of _the steam flow rate to calculate the _number of steam moles. This is a calculator that receives the steam mole number output and calculates the steam carbon molar ratio S/C. C ₃ receives the output of the arithmetic unit CA ₃ and outputs the corresponding S/C
A controller such as a PID controller that outputs a control signal according to the difference between the value and the set S/C value, 1 is a flow rate detector
Receives the output of F ₁ and the control signal of controller C ₃ , converts it into a ratio value α between the steam flow rate and the raw material gas flow rate,
This is a ratio setting device that calculates the steam flow rate necessary to maintain a predetermined steam carbon molar ratio S/C based on the ratio value α. The output of the ratio setter is input to controller _C2 as the steam flow rate set value. 2 is a reforming furnace that reformes the mixed gas of off-gas and steam combined at point A into hydrogen and carbon dioxide; 3
is a carbon dioxide removal device that removes carbon dioxide produced in the reforming furnace. The operation of the device configured in this way will be explained below.

In the device shown in the figure, the temperature and pressure correction for converting the flow rate value of the raw material adjusted by the controller C ₁ to the value at 0°C and 1 atm, and the correction of the specific gravity error that occurs when the raw material fluctuates, are performed using the calculator CA ₁ . , the specific gravity of the steam adjusted by the controller _C2 is corrected by the calculator _CA2 . A calculator CA ₁ is used to calculate the number of moles of carbon from the corrected raw material flow rate value, and a calculator CA ₂ is used to calculate the number of moles of steam from the corrected steam flow rate value.

First, the case where the number of carbon moles is calculated by the calculator CA ₁ will be explained. The off-gas component is _CO
Let it be represented by H _2o+2 . Here n is the number of carbons. If the molecular weight of this C _o H _2o+2 is MW, the following formula holds true.

n x atomic weight of carbon + (2n+2) x atomic weight of hydrogen = MW (1) Since the atomic weight of carbon C is 12 and the atomic weight of hydrogen is 1, converting C _o H _2o+2 into molecular weight gives the following formula.

14n=MW−2 From this, the carbon number n becomes as shown in the following equation.

n=MW-2/14 (2) In the formula (2), n represents the number of carbons per mole. Therefore, the number of carbon moles Cmol can be determined by multiplying the ratio by the total mole Fmol. That is, the following formula holds.

Cmol=MW−2/14×Fmol (3) On the other hand, since the number of steam moles is calculated by the computing unit CA ₂ , the computing unit CA ₃ calculates the number of carbon moles from CA ₁ and the number of steam moles from CA ₂ . Then, the steam carbon molar ratio S/C is calculated. Next, a method for calculating the total number of moles Fmol of the source gas shown by equation (3) will be explained. Calculator CA ₁ sets value Fc ₁ , which is the output of flow rate detector F ₁ corrected for temperature, pressure, and specific gravity, to 0.
Divide by the volume 22.4 (equivalent to 1 mol) at ℃ and 1 atm to find the total number Fmol of the raw material gas. That is, Fmol is expressed by the following formula.

Fmol=Fc ₁ /22.4 (4) Next, the case of calculating the number of steam moles will be explained. Calculator CA ₂ uses the steam flow rate Fs obtained by flow rate detector F ₂ as saturated steam and converts it into a pressure detector.
Perform correction using the output of _P2 . Since specific gravity correction and pressure correction can be approximated near the design standard value, the corrected flow rate value Fsc is given by the following equation.

Fsc=FsxP ₂₁ /Pb (5) Here, Pb represents the design standard value of the orifice, and P ₂₁ represents the output of the pressure detector P ₂ . Once Fsc is determined, divide Fsc by the molecular weight of steam, 18, to determine the number of moles of steam, Fmols, in the same manner as in equation (4).

Fmols=Fsc/18 (6) Calculator CA ₃ calculates the steam carbon molar ratio S/C from the number of carbon moles obtained in this way and the number of steam moles. Controller _C3 is a calculator
In response to the difference between the S/C value calculated in CA ₃ and the set S/C value, a control signal corresponding to the S/C value is output. The ratio setting device 1 corrects the ratio α between the steam flow rate and the raw material gas flow rate using the control signal from the controller C ₃ , calculates a reference steam flow rate by multiplying the raw material flow rate by α, and uses this flow rate value as the controller C _2. The setting value shall be . As a result of such ratio control, steam flow rate control can be performed such that the steam carbon molar ratio S/C is constant. Therefore, the amount of steam used can be kept to the minimum necessary. Further, according to the present invention, even if the source gas composition analyzer _A1 fails, as long as the S/C ratio α is fixed at the value before the failure, control can be performed to keep the ratio constant. In addition, controllers C ₁ and C ₂
can also be operated with independent ratio control.

In the above description, two systems of raw materials are mixed, but in some cases, naphtha may be added to the off-gas for backup.
When naphtha is used, it is necessary to calculate the number of carbons and the number of moles for each naphtha and add them to those of the off-gas.

As described above in detail, according to the present invention, the steam carbon molar ratio S/C is determined from the flow rate, temperature, carbon, and pressure detectors installed in the raw material gas supply flow path and the steam flow path. , S/C
Since the steam flow rate is controlled by the ratio value corresponding to the value and the raw material flow rate value, the amount of steam used can be minimized, and even if the composition analyzer goes down, the steam carbon molar ratio S/C can be kept almost constant. Can be controlled at a constant level.

[Brief explanation of drawings]

The figure is a configuration diagram showing an embodiment of the present invention. 1...Ratio setter, 2...Reforming furnace, 3...Carbon dioxide removal device, _A1 ...Composition analyzer, _T1 ...Temperature detector, _P1 , _P2 ...Pressure detector, F ₁ , F ₂ ... Flow rate detector, V ₁ , V ₂ ... Control valve, C ₁ , C ₂ , C ₃ ...
Controller, CA ₁ , CA ₂ , CA ₃ ...Arithmetic unit.

Claims (1)

[Claims] 1. In a device that uses off-gas as a hydrocarbon source and produces hydrogen by steam reforming this gas, the flow rate, temperature, pressure,
A detector is installed in the steam supply line to detect the composition of the off-gas, and the number of carbon moles is calculated from the detected value.A detector is installed in the steam supply pipe to detect the flow rate and pressure, and the number of carbon moles is calculated from the detected value. In addition to calculating the number, the steam carbon molar ratio S/C is calculated from the number of carbon moles and the number of steam moles, and the steam flow rate and raw material gas flow rate are determined according to the difference between the relevant S/C value and the set S/C value. control of the steam amount in a hydrogen production device, characterized in that the steam amount is controlled via a ratio setting device having a function of converting the ratio value into a ratio value and fixing the ratio value based on the ratio value and the raw material flow rate value. Method.