JPS623082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling gas components in an SO ₂ reduction tower, particularly when the SO ₂ component concentration in exhaust gas changes due to boiler load fluctuations - that is, the SO ₂ gas flowing into the reduction tower The present invention relates to a method for controlling gas components in an SO ₂ reduction tower, which is suitable for application when the amount changes.

First, the equipment configuration of a conventional SO ₂ reduction tower will be explained with reference to FIG.

In the figure, 1 is an SO ₂ reduction tower, 2 is a gas mixer, 3 is a gas component analyzer, 4 is an air flow rate regulator,
5 is a bypass gas amount regulator, 6 and 7 are gas temperature detectors in the SO ₂ reduction tower 1, and 8 is a control device.

During operation, the incoming gas containing SO ₂ , H ₂ O, etc.
The SO ₂ is sent into the reduction tower 1, where it comes into contact with carbon and undergoes reduction and other reactions as described below. And, at the exit of SO ₂ reduction tower 1,
The resulting gas contains CO ₂ , S ₂ , H ₂ S, H ₂ , SO ₂ (unreacted amount), etc.

This gas is mixed with the gas that has bypassed the SO ₂ reduction tower 1 in the gas mixer 2 and sent to the Claus reactor. As _is well known, the Claus reactor is supplied with SO ₂ and H ₂ S,
This is a separation reaction into H ₂ O. In order for this reaction to occur, the ratio of SO ₂ and H ₂ S must be 1:2.
It is desirable that the ratio be as follows.

In such a device, at the outlet of the gas mixer 2,
The composition of the gas is controlled as follows. first,
Air is sent to the SO ₂ reduction tower 1 via the air flow regulator 4 to burn carbon in the SO ₂ reduction tower,
The temperature is raised within the column 1 to a point at which the reduction reaction can easily proceed.

As a result, in the reduction tower 1, according to formulas (1) to (4), C+SO ₂ →1/2S ₂ +CO ₂ ...(1) C+H ₂ O→CO+H ₂ ...(2) CO+H ₂ O→CO ₂ +H ₂ ...(3) H ₂ +1/2S ₂ →H ₂ S ...(4) The reaction shown occurs. As a result, SO ₂ and H ₂ O contained in the input gas are changed to S ₂ and H ₂ S.

Here, each of the above-mentioned reactions is not completed instantaneously, but the reaction rate is determined by temperature and gas component partial pressure, and also changes depending on the residence time of the gas in the column.

As a method for controlling the gas components of such an SO ₂ reduction tower, the temperature inside the reduction tower 1 is controlled to be constant by controlling the amount of inflowing air, and the S ₂ recovery rate inside the reduction tower 1 is maximized. It is known.

When the above-mentioned control is performed, reduction tower 1
It is no longer possible to maintain the ratio of H ₂ S and SO ₂ at a predetermined value (2:1) at the outlet of the reactor.

For this purpose, conventionally, the component amounts of H ₂ S and SO ₂ are detected by a gas component analyzer 3, and on the other hand, as shown in FIG. 5, and by adjusting the bypass amount of the inflow gas, the amount of H ₂ S sent to the Claus reactor is
and SO ₂ was maintained at a predetermined value (2:1).

However, with this control method, it takes a relatively long time (currently about 10 minutes) to obtain the analysis results from the gas component analyzer 3, and the response speed is slow, making it difficult to adjust the bypass amount of inflow gas. There was a drawback that it could not be done properly. In addition, when the flow rate of the inflowing exhaust gas changes, the residence time in the reduction tower 1 cannot be accurately determined, making it impossible to accurately determine the reaction amount.
This method had the disadvantage of not being able to accurately control the amount of gas components.

The purpose of the present invention is to eliminate such drawbacks of the conventional technology, estimate the reaction amount from accurate residence time and temperature in the reduction column, and enable accurate gas composition control.
The present invention provides a method for controlling gas components in an SO ₂ reduction tower.

The present invention estimates the temperature distribution inside the SO ₂ reduction tower from gas temperature detection values at two or more points along the flow of the reduction tower, and estimates the residence time inside the reduction tower from the gas flow rate. The feature is that the operation amount (air amount) is controlled while accurately estimating the component concentration of SO ₂ contained in the inflow gas from the estimated value.

FIG. 2 shows a schematic configuration of an SO ₂ reduction column suitable for carrying out the present invention. The same reference numerals in the figure as in FIG. 1 represent the same or equivalent parts, so the explanation thereof will be omitted.

Note that the gas mixer 2 and the bypass gas amount regulator 5 are shown with chain lines to indicate that these are theoretically unnecessary for carrying out the present invention.

In order to understand the operating principle of the present invention, first examine the reaction rates of equations (1) and (4) listed above. According to the law of chemical equilibrium, the reaction rates r ₁ and r ₂ of each are as follows. This is shown by equations (5) and (6).

r ₁ = k ₁ e ^-E1/RT [P _SO2 ] (m ² /sec) ...(5) r ₂ = k ₂ e ^-E2/RT [P _H2 ] [P _S2 ] ^1/2 (m ² / sec) ...(6) Here, k ₁ , k ₂ : Reaction rate constant E ₁ , E ₂ : Activation energy R : Gas constant T : Absolute temperature [P _SO2 ], [P _H2 ], [P _S2 ]: Partial pressure of SO ₂ , H ₂ , and S ₂ Therefore, the reaction amounts of SO ₂ and H ₂ S in the reduction column 1 can be expressed by the following equations (7) and (8). .

Here, Fg: Total gas flow rate A: Cross-sectional area of the tower l: Height of the tower Therefore, if the amount of SO ₂ contained in the gas that flowed into the reduction tower is denoted by F _SO2 , then this SO ₂ It can be seen that F _SO2 −Δ(SO ₂ ) flows out from the reduction tower 1. Therefore, SO ₂ and H ₂ S contained in the effluent gas
The ratio of is given by equation (9).

SO ₂ /H ₂ S=F _SO2 -Δ(SO ₂ )/Δ(H ₂ S)...
(9) As mentioned above, _{the SO 2 and}
The ratio of H ₂ S needs to be 1/2. In order to reduce the ratio of equation (9) to 1/2, make sure that equation (10) holds true. It turns out that it is sufficient to determine the temperature T inside the tower.

Here, if the temperature inside the column is represented by the average temperature 〒, then ∫ ^l ₀ Adx=V, so equation (10) can be transformed into equation (11).

Here, V: Internal volume of the column. Therefore, find the average temperature 〒r that satisfies equation (11),
It can be seen that by setting 〒r as a set value or target value, the amount of air can be adjusted so that the average temperature inside the column matches 〒r.

However, the problem here is that the amount of SO ₂ contained in the inflow gas F _SO2 cannot be directly measured. Therefore, it is necessary to estimate F _SO2 indirectly.

Here, the amount of SO ₂ measured by the gas component analyzer 3 is expressed as F _SO2a , the concentration of SO ₂ contained in the gas flowing into the tower is ρ _SO2 , and the amount of gas flowing in from the bypass valve 5 is F' If g, then equations (12) and (13) hold true.

Here, since F _SO2 =Fg·ρ _SO2 (13A), F _SO2 can be estimated by substituting ρ _SO2 obtained by equation (13) into equation (13A).

The above analysis shows that the specific control method should be as follows. That is, first, assuming the average temperature 〒, the SO ₂ of the incoming gas is determined by equation (13).
Find the concentration ρ _SO2 .

Next, by equation (13A), F _SO2 is Fg・ρ _SO2
Estimation calculation is performed by , and the average temperature inside the column is calculated using equation (11). Here, if the average temperature obtained from equation (11) is equal to the value assumed earlier, this is set as the target value 〒r for the average temperature in the column.

At this time, if the two do not match,
The average temperature 〒 assumed in equation (13) is corrected by a minute amount, and similar calculations are performed to determine the target value 〒r of the temperature inside the column by the so-called convergence calculation method.

In this case, the average temperature in the column is usually assumed based on the current or previous measured value of the temperature in the column.

Therefore, even if the average temperature obtained from equation (11) differs from the average temperature assumed when calculating equation (13), the difference is small and the comparison can be made using the convergence calculation method. Easily set the target value of the temperature inside the column〒r
can be determined.

Once the target value 〒r has been determined as described above, the average temperature is obtained using the temperature detectors 6 and 7, and the air flow rate regulator 4 is controlled, for example, by feedback, so that the average temperature matches 〒r. Good.

As detailed above, in the SO ₂ reduction column component control method of the present invention, the concentration ρ _SO2 of SO ₂ in the inflow gas is calculated using equation (a) (13). In addition, at this time, the average temperature inside the column is assumed to be a value close to the current or previous actual measurement value of the temperature inside the column.

(b) Using the concentration ρ _SO2 determined in (a) above, (13A)
From the formula, calculate the SO ₂ amount F _SO2 in the inflow gas.

(c) Substitute the SO ₂ amount F _SO2 determined in (b) above into equation (11) to calculate the average temperature in the column 〒.

(d) If the average temperature obtained in (c) above is not equal to the previously assumed average temperature in the column, gradually change the assumed average temperature in the column and perform the calculations in (a) to (c) above. Iterate - that is, by convergence calculation - until they are equal.

(E) Using the average temperature inside the tower determined as above as a target value, the opening degree of the air flow rate regulator 4 is controlled so that the actual value of the average temperature inside the tower becomes equal to the target value, and air is supplied. Adjust the amount.

Through this step, the ratio of the SO ₂ component to the H ₂ S component at the outlet of the SO ₂ reduction tower 1 is always maintained at 1:2.

Therefore, if the control method of the present invention is applied,
There is no need to bypass the inflow gas and supply it to the outlet side of the reduction tower 1, and theoretically the gas mixer 2 and the bypass gas amount regulator 5 can be omitted.

In addition, in the present invention, since the temperature inside the reduction tower is controlled based on the amount of inflow gas, the control response time is shorter than in the conventional example, and the SO ₂ and H ₂ S supplied to the Claus reactor are reduced. This has the advantage that the component ratio can be controlled more reliably.

However, in reality, the target value of the average temperature inside the column 〒r
There may be a deviation between the actual average temperature and the actual average temperature. Particularly during a transient period when the amount of inflowing gas increases rapidly, the temperature deviation increases and it becomes difficult to maintain the component ratio at the outlet of the reduction tower at a predetermined value.

In FIG. 2, the gas mixer 2 and the bypass gas amount regulator 5, which are indicated by chain lines, are used to remove SO ₂ and H ₂ S that are generated due to transient temperature deviations when the control method of the present invention is implemented. This is a preliminary provision to compensate for component deviations. These bypass gas flow control systems are adjusted as follows.

That is, if the target average temperature is 〒r and the actual average temperature is 〒a, then ΔF _S expressed by equation (14)
There will be a shortage of SO ₂ on the outlet side of the reduction tower 1 by the amount of _{O 2} . Therefore, via the bypass flow control system, It is necessary to replenish SO ₂ to compensate for this shortage.

F'g=ΔF _SO2 /ρ _SO2 (15) That is, it is necessary to control the bypass gas amount regulator 5 with F'g determined from equation (15) as the target. Here, if SO ₂ is insufficient, it can be compensated for using the above idea, but if SO ₂ becomes excessive, it becomes uncontrollable. Therefore, in order to ensure compensation by the bypass gas flow rate control system, the SO ₂ and
It is necessary to set the ratio with H ₂ S to 1:2 or more in advance.

The control method described above is realized by the control device 8A.

FIG. 3 is a block diagram illustrating the algorithm of the control method of the present invention described above. This algorithm can be easily implemented using a microcomputer or the like.

In the figure, the block 100 first includes the reduction tower 1
This is a function to input the actually measured temperature inside the gas, the components obtained by the gas component analyzer 3, etc. into the computer. In block 101, assuming the average temperature inside the column, (13)
The SO ₂ concentration ρ _SO2 in the inflow gas is estimated using the formula, and the inflow SO ₂ amount F _SO2 is further calculated using the formula (13A).
Estimate and calculate.

Next, in block 102, the target temperature in the column r is determined using equation (11). In this case, the average temperature in the column (target value) obtained from equation (11)
If the assumed value is different from the previously assumed value, the assumed value is slightly changed and the functions 101 and 102 are repeatedly executed. When the two values become equal, the target temperature in the column r is determined and block 1
Proceed to 03.

In block 103, an appropriate algorithm such as known proportional/integral control is executed so that the temperature inside the column 〒a matches this target temperature 〒r, and a target opening degree 200 of the air flow rate regulator 4 is determined. .

Next, if necessary, in block 104, (14),
Find F′g using equation (15). Furthermore, in block 105, a target opening 201 of the bypass gas amount regulator 5 is determined so that the bypass gas flow rate matches this F'g.

Finally, in block 106, the opening degree targets 200 and 201 of these two valves (of regulators 4 and 5) are outputted to the corresponding control valves as outputs of the computer, and the flow rate control of each is performed using a known method. Execute by appropriate method.

Furthermore, the reaction rate constant k ₂ in equation (8) also changes depending on pressure and temperature. Therefore, it is desirable to correct this according to the result (H ₂ S gas amount) of the gas component analyzer 3.

FIG. 4 shows the algorithm for _k2 correction. Basically, the average gas temperature of n groups is
i, gas flow rate Fgi and _H2S gas amount measurement value F _H2Sai
(Here, the above i is 1 to n). _k2 is estimated by regression analysis of the data.

In FIG. 4, block 300 represents the collection function of this n set of data. Next, in block 301, evaluation criterion J shown in equation (16) is introduced from n sets of data.

and Find k ₂ that minimizes the evaluation criterion J. That is, by setting ∂J/∂k ₂ = 0 and rearranging,
Equation (17) is obtained, and k ₂ can be found from this.

Finally, in block 302, k ₂ in equation (11) is corrected using k ₂ found in the above manner.

By employing the method of correcting the reaction rate constant k ₂ as shown above, it becomes possible to estimate the reaction amount in the column even more accurately. Therefore, it becomes even more reliable to always maintain the ratio of SO ₂ and H ₂ S at a predetermined value at the outlet of the reduction tower.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the equipment configuration of a conventional SO ₂ reduction tower, and FIG. 2 is a diagram showing a schematic configuration of an SO ₂ reduction tower suitable for implementing the gas component control method of the present invention.
3 and 4 are block diagrams showing the control algorithm of the present invention. 1... SO ₂ reduction tower, 2... gas mixer, 3...
Gas component analyzer, 4...Air flow rate regulator, 5...
Bypass gas flow rate regulator, 6, 7... Gas temperature detector, 8, 8A... Control device.

Claims (1)

[Claims] 1 Gas containing SO ₂ is flowed into a reduction tower, SO ₂ in the flowed gas is reduced to H ₂ S in the presence of a reducing agent, and SO ₂ and H ₂ are exchanged at the exit of the reduction tower. A method for controlling gas components in an SO ₂ reduction tower that maintains a ratio of S to
Estimating the amount of SO ₂ in the inflow gas from the amount of SO 2 at the outlet of the reduction tower and the gas temperature in the reduction tower, and calculating the amount of SO ₂ at the exit of the reduction tower from the amount _{of SO 2 in} the inflow gas determined in this way. Determine the gas temperature target value in the reduction tower necessary to make the ratio with H ₂ S a predetermined value, and adjust the flow of air into the reduction tower so that the gas temperature in the reduction tower becomes equal to the target value. A method for controlling gas components in an SO ₂ reduction tower, characterized by controlling the amount. 2 Detect the amount of H ₂ S at the outlet of the reduction tower, use this to determine the correction value of the reaction rate constant of the H ₂ S production reaction in the reduction tower, and use this to determine the amount of H 2 S in the incoming gas.
A method for controlling gas components in an SO ₂ reduction tower according to claim 1, characterized in that the amount of SO ₂ is corrected. 3 Gas containing SO ₂ , air and reducing agent are injected, producing SO ₂ and H ₂ S at the outlet.
an SO ₂ reduction tower, an inflow air flow rate adjustment means, a means for detecting the gas temperature in the reduction tower, a means for detecting the inflow gas flow rate, a means for analyzing the gas component (SO ₂ ) at the exit of the reduction tower, The flow rate of incoming gas, the amount of SO ₂ at the outlet of the reduction tower, and the gas temperature in the reduction tower are input, and the amount of SO ₂ in the inflow gas is estimated, and the amount of SO ₂ and H ₂ S at the exit of the reduction tower is calculated. Calculate the gas temperature target value in the reduction tower necessary to bring the ratio to a predetermined value, calculate the amount of air flowing into the reduction tower necessary for this purpose, and make sure that the necessary amount of air inflow is obtained. 1. A gas component control device for an SO ₂ reduction tower, comprising: a control device for controlling an inflow air flow rate regulating means. 4 Detect the amount of H ₂ S at the outlet of the reduction tower, use this to determine the correction value of the reaction rate constant of the H ₂ S production reaction in the reduction tower, and use this to determine the amount of H 2 S in the inflow gas.
4. The gas composition control device for an SO ₂ reduction tower according to claim 3, wherein the SO ₂ amount is adjusted.