JP4095262B2 - Air preheater management device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air preheater management device, and more specifically, measures the dew point of a gas supplied with heat by the air preheater, and the temperature of the air that enjoys heat by the air preheater so that the gas does not fall below the dew point. The present invention relates to an air preheater management device for adjusting the air temperature.
[0002]
[Prior art]
In a chemical factory, heated gas such as combustion gas in a boiler plant is generally discharged by an air preheater, which is a heat exchanger, after supplying heat to the air used for combustion in the boiler.
[0003]
The exhausted gas often contains sulfurous acid gas (SO ₃ ), and if the temperature is lowered too much by heat exchange, the sulfurous acid gas reacts with water and liquefies into sulfuric acid. The components contained in the gas discharged from the gas liquefy. If it does so, dew point corrosion may arise in an air preheater and its piping, and it may cause a problem in facilities management.
[0004]
On the other hand, a method of reducing the amount of heat exchange in the air preheater and reducing the temperature of the exhaust gas by heating the air that receives heat by heat exchange in the air preheater in advance by steam or the like is considered. It is done.
[0005]
[Problems to be solved by the invention]
However, the greater the difference between the exhaust gas temperature and the dew point, the lower the heat utilization of the exhaust gas and the greater the amount of steam added to the air. For this reason, thermal efficiency will fall as a whole.
[0006]
Therefore, an object of the present invention is to increase the thermal efficiency by measuring the dew point of the gas after supplying heat with an air preheater.
[0007]
[Means for Solving the Problems]
The present invention relates to an air preheater having a gas pipe through which a gas for supplying heat passes and an air pipe through which air for receiving heat is passed, and the gas pipe, wherein the air preheater supplies heat. It consists of an electrochemical sensor having an electrode part attached to the part of the piping through which the gas passes later. The electrode part has a plurality of electrodes and an air introduction part for introducing air into the electrode part. Since the above problem has been solved by using an air preheater management device that brings the end face into contact with the gas after supplying the heat and the other end face of the electrode into contact with the air introduced from the air introduction section. is there.
[0008]
By introducing air from the air introduction part into the electrode part and cooling the electrode from the other end surface side, the temperature of the entire electrode can be lowered. When cooled to some extent, the gas brought into contact with one end surface of the electrode starts to liquefy. Since the liquefied liquid contains an electrolyte, electrochemical current noise and electrochemical potential noise are generated between the electrodes. That is, the dew point can be measured by sensing the occurrence of the electrochemical current noise and electrochemical potential noise. And the introduction temperature of the air which enjoys heat with an air preheater is adjusted so that the temperature of the said gas may be hold | maintained at the temperature more than the measured dew point. Thereby, it can prevent that dew point corrosion arises with the said gas.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
As shown in FIG. 1, the air preheater management device according to the present invention includes an air preheater 1 and an electrochemical sensor 3 having an electrode portion 2.
[0010]
The air preheater 1 is a heat exchanger, and as shown in FIG. 1, a gas pipe 4 through which gas for supplying heat (hereinafter referred to as “heating gas”) p <b> 1 passes and heat is received. Air pipe (hereinafter referred to as “supply air”) q1. The heated gas p1 sent to the air preheater 1 through the gas pipe 4 gives heat to the supply air q1 sent through the air pipe 5 in the air preheater 1. Then, the heated gas (hereinafter referred to as “heat exchanged gas”) p <b> 2 after the heat is supplied is subjected to a process such as atmospheric release through the gas pipe 4.
[0011]
On the other hand, the supply air q1 is sent to the air preheater 1 through the air pipe 5, and receives heat as described above. The supplied air (hereinafter referred to as “combustion air”) q2 that has enjoyed heat is sent to a boiler or the like and used for combustion.
[0012]
The electrochemical sensor 3 is the gas pipe 4 described above, and is a control section that processes measurement data at the electrode section 2 and the electrode section 2 attached to the heat insulating material 10 of the pipe through which the heat-exchanged gas p2 is passed. 6 is composed. Data of the dew point (Tr) of the heat exchanged gas p2 detected by the control unit 6 is sent to the management system 7, and the temperature of the heat exchanged gas p2 in the gas pipe 4 ( T2) data is also sent. From these data, the temperature (T1) of the supply air q1 is expressed by the following equation (2).
Tr <(T1 + T2) / 2 (1)
That is, T1> 2 × Tr−T2 (2)
The temperature (T1) of the supply air q1 is adjusted while operating the steam valve 8 and adjusting the amount of the supply steam s so as to satisfy the condition. Thereby, it adjusts so that heat-exchanged gas p2 may not become below a dew point, and can prevent dew point corrosion.
[0013]
The above dew point refers to a temperature at which a component contained in the heat exchanged gas p2 starts to liquefy. In addition, dew point prevention means that when the dew point is reached, liquefaction of components in the gas occurs, and corrosion occurs due to the electrolyte components contained in the liquefied product.
[0014]
As shown in FIG. 2, the electrode part 2 has a plurality of electrodes 21 to 23 at the tip of a cylindrical socket 9 and air for introducing air into the electrode part 2 at the rear part of the socket 9. It has the introducing | transducing part 11, and has a cavity part inside. The electrodes 21 to 23 are provided via the insulating material 12 so as not to contact each other, and at least one end surface thereof is provided to contact the heat exchanged gas p2 in the gas pipe 4. Moreover, the gas thermometer 13 is provided so that the front-end | tip protrudes in the gas piping 4. FIG.
[0015]
Further, the other end surfaces of the electrodes 21 to 23 and the other end of the gas thermometer 13 are not covered with the insulating material 12 and face the hollow portion inside the socket 9.
And each electrode 21-23 and the gas thermometer 13 are formed from the same heat conductive material, for example, a metal. For this reason, when each electrode 21-23 and the gas thermometer 13 contact | connects the heat exchanged gas p2 which passes the gas piping 4 at one end surface, each electrode 21-23 and the gas thermometer 13 will be the heat exchanged gas. The temperature is p2.
[0016]
The dew point of the heat exchanged gas p2 is measured by the following method. First, the heat exchanged gas p2 is caused to flow through the gas pipe 4, and the temperatures of the electrodes 21 to 23 and the gas thermometer 13 are set as the temperature of the heat exchanged gas p2. Next, air is introduced into the socket 9 from the air introduction part 11. Then, the other end surfaces of the electrodes 21 to 23 and the other end of the gas thermometer 13 come into contact with the air, and the electrodes 21 to 23 and the gas thermometer 13 are cooled. By continuing the introduction of air from the air introduction portion 11 into the socket 9, the temperatures of the electrodes 21 to 23 and the gas thermometer 13 are gradually lowered. When the temperatures of the electrodes 21 to 23 and the gas thermometer 13 are lowered to the dew point of the heat exchanged gas p2, liquefaction of the heat exchanged gas p2 brought into contact with one end face of the electrodes 21 to 23 occurs. At this time, electrochemical current noise and electrochemical potential noise are generated between the electrodes 21 to 23. While detecting this with the control part 6, the dew point of the heat exchanged gas p2 can be measured by detecting the temperature at the time of the detection with the gas thermometer 13. FIG.
[0017]
By sending the dew point data to the management system 7 and adjusting the steam valve 8 so as to maintain the temperature (T2) of the heat exchanged gas p2 at a temperature equal to or higher than the dew point according to the above method, the air preheater The temperature (T1) of the supply air q1 that enjoys heat can be adjusted.
[0018]
As shown in FIG. 1, the electrochemical sensor 3 includes the electrode unit 2 and a control unit 6. Further, as shown in FIG. 3, the control unit 6 includes a current / voltage measuring means 30 for measuring electrochemical current noise and electrochemical potential noise between the electrodes 21 to 23, and the current / voltage measuring means. Data storage means for taking in the measurement data of electrochemical current noise and electrochemical potential noise measured in step 1 and storing this measurement data in time series, and electrochemical stored in time series in the data storage means A dew point determining means for extracting measurement data of static current noise or electrochemical potential noise and determining the dew point from the extracted measurement data of electrochemical current noise and electrochemical potential noise.
[0019]
The electrochemical sensor 3 will be described in more detail with reference to FIGS.
FIG. 3 is a block diagram showing an outline of the entire configuration of the electrochemical sensor including the present embodiment. Here, the configuration, operation, and effect of the entire electrochemical sensor including the present embodiment will be described.
[0020]
First, the corrosion current voltage measuring means 30 will be described. This is composed of the measurement electrode unit 2, the non-resistance ammeter 24, the buffer circuit 25, and the band-pass filters 26 and 27 among the electrochemical sensors shown in FIG. 3.
[0021]
The configuration of the electrode unit 2 is as described above, and the number of electrodes is three.
Further, a current measurement circuit having a substantially zero internal resistance, a so-called resistance resistance ammeter 24 is connected between the first electrode 21 and the second electrode 22, and the second electrode 22 is connected to the second electrode 22. Between the third electrodes 23, an amplifier circuit having a very large input impedance that can measure a signal voltage without affecting the electrode side, here a buffer circuit 25 is connected.
[0022]
Therefore, in this embodiment, a coupling current (coupling current: Imean) a corresponding to the degree of progress of corrosion on each electrode surface is generated between the first electrode 21 and the second electrode 22, respectively. The coupling current a is measured by the non-resistance ammeter 24, and after being subjected to signal processing described later, is stored in the data storage unit 72 of the computer 71 as data storage means in time series.
[0023]
At this time, regarding the electrochemical current noise (In) b, the fluctuation of the coupling current a is reduced by a filter circuit, particularly the bandpass filter circuit 26, in a low frequency region, particularly in a frequency region of about 1 Hz or less, preferably 0. It can be obtained by measuring current fluctuations in the frequency range of about .01 to 1 Hz, and the measured electrochemical current noise (In) b is also subjected to signal processing to be described later, and then stored in the data of the computer 71. The data is accumulated in the unit 72 in time series. Here, the electrochemical current noise (In) b can be obtained in the same manner by calculating the coupling current (Imean) a taken into the computer 71 and calculating its standard deviation.
[0024]
On the other hand, for the electrochemical potential noise (Vn) c, the potential difference (Vmean) between the second electrode 22 and the third electrode 23 is measured by the buffer circuit 25, and fluctuations in this potential difference are filtered out, In particular, the bandpass filter circuit 27 can obtain and measure the potential difference fluctuation in the low frequency region, particularly in the frequency region of about 1 Hz or less, preferably in the frequency region of about 0.01 to 1 Hz. The target potential noise (Vn) c is also accumulated in time series in the data storage unit 72 of the computer 71 after performing signal processing to be described later. Again, this electrochemical potential noise (Vn) c can be obtained in the same manner by taking the potential difference directly into the computer 71 and processing it accordingly and determining its standard deviation.
[0025]
Next, details of specific circuit means for data processing until each measurement data signal (each measurement data of current and voltage) is inputted to the computer 71 are shown in FIGS. 4 (a), 4 (b) and 5 (a). ) And (b).
[0026]
4A and 4B show an example when the data processing circuit is configured by an analog circuit. In this case, first, the current signal, that is, the coupling current a between the first electrode 21 and the second electrode 22 is measured by a non-resistance ammeter 24 as shown in FIG. At the same time, one of the current signals is an RMS circuit for obtaining the mean square of the signal → a DC circuit for converting the obtained signal into direct current → a converter comprising a LOG circuit for converting the signal converted into direct current into a logarithm (hereinafter, Logarithmically converted by a logarithmic converter (31) and further digitally converted by an analog / digital converter (hereinafter referred to as A / D converter) 32, and then input to the computer 71 as a coupling current (Imean) a, On the other hand, after the frequency component of about 1 Hz or less is extracted by the band-pass filter circuit 26, the logarithmic converter 4 is similarly used. Logarithmically converted by 1 and further digitally converted by the A / D converter 42 and then input to the computer 71 as electrochemical current noise (In) b.
[0027]
Next, the voltage signal, that is, the potential difference between the second electrode 22 and the third electrode 23 is measured by the buffer circuit 25 as shown in FIG. After the frequency component of about 1 Hz or less is extracted by the circuit 27, the logarithmic converter 51 again performs logarithmic conversion, and after the digital conversion by the A / D converter 52, the computer 71 receives the electrochemical potential noise. (Vn) is input as c.
[0028]
5 (a) and 5 (b) are examples when the data processing circuit is configured by a digital circuit corresponding to the analog circuit configuration of FIGS. 4 (a) and 4 (b). Indicate the same or corresponding parts, and the same operation can be obtained by the digital circuit configuration.
[0029]
On the other hand, the temperature detected by the gas thermometer 13 is accumulated in the data storage unit 72. The dew point determination means includes a rapid change in measurement data of electrochemical current noise (In) b and electrochemical potential noise (Vn) c accumulated in the data storage unit 72, and a gas temperature at that time. Judgment is made from the temperature measured by the total 13. That is, when the component of the heat exchanged gas p2 is liquefied, electrochemical current noise (In) b and electrochemical potential noise (Vn) c are generated, and the change is rapid. For this reason, it can be determined that the temperature at the time when these data are rapidly changed is the dew point of the heat-exchanged gas p2.
[0030]
The dew point data is sent to the management system 7 and is used for adjusting the temperature (T1) of the supply air q1 as described above.
[0031]
【Example】
The present invention will be described more specifically with reference to the following examples and comparative examples.
[0032]
Example 1
An electrode unit 2 as shown in FIG. 1 is provided in a portion of the gas pipe 4 of the air preheater 1 through which the heat-exchanged gas p2 passes, and a control unit 6 and a management system 7 are connected thereto. The electrochemical sensor 3 including the electrode unit 2 and the control unit 6 has the configuration and functions shown in FIGS.
As the heating gas p1, a 120 ° C. boiler exhaust gas having a composition of 70.3% nitrogen, 4.1% oxygen, 16.4% water vapor, 9.2% carbon dioxide, and 7.6 ppm sulfurous acid gas is used. Also, room temperature air is used as the supply air q1.
[0033]
In the air preheater 1, the boiler exhaust gas is heat-exchanged to lower the temperature to around 100 ° C., and the heat-exchanged gas p2 is discharged.
In this state, air is introduced into the electrode part 2 from the air introduction part 11, and the temperatures of the electrodes 21 to 23 are changed to 70 ° C., 65 ° C., 60 ° C., and 70 ° C. as shown in FIG. Then, changes in electrochemical current noise (In) b and electrochemical potential noise (Vn) c at that time were observed. The result is shown in FIG.
In addition, in FIG. 6, the change was shown by making In / Vn into a corrosion rate (Corrosion Rate). “Gas Temp” represents the temperature (T2) of the heat exchanged gas p2, and “Probe Temp” represents the temperature of the electrode.
[0034]
As a result, it was found that the corrosion rate changed significantly at 60 ° C., and this temperature was the dew point of the heat exchanged gas.
[0035]
【The invention's effect】
According to the present invention, since the dew point of the gas supplied with heat by the air preheater can be measured, the occurrence of dew point corrosion of the gas pipe can be prevented, and the facility management of the air preheater and the piping connected thereto can be facilitated.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an air preheating management device according to the present invention. FIG. 2 is a schematic diagram showing an example of an electrode part of FIG. 1. FIG. 3 is an outline of the overall configuration of the electrochemical sensor of FIG. FIG. 4 is a block diagram showing an example when the processing circuit of each measurement data signal of current and voltage in the electrochemical sensor of FIG. 3 is constituted by an analog circuit. FIG. 5 is a diagram showing the current in the electrochemical sensor of FIG. FIG. 6 is a block diagram showing an example when a processing circuit for each voltage measurement data signal is configured by a digital circuit. FIG. 6 shows result data in the embodiment.
DESCRIPTION OF SYMBOLS 1 Air preheater 2 Electrode part 3 Electrochemical sensor 4 Gas piping 5 Air piping 6 Control part 7 Management system 8 Steam valve 9 Socket 10 Heat insulating material 11 Air introduction part 12 Insulating material 13 Gas thermometer 21, 22, 23 Electrode 24 None Resistance ammeter 25 Buffer circuit 26, 27 Band pass filter circuit 71 Computer 72 Data storage unit 73 Dew point determination a Coupling current (Imean)
b Electrochemical current noise (In)
c Electrochemical potential noise (Vn)
p1 heating gas p2 heat exchanged gas q1 supply air q2 combustion air s steam

Claims (4)

  An air preheater having a gas pipe for passing a gas for supplying heat and an air pipe for passing an air for receiving heat, and the gas after being supplied with heat by the air preheater. It consists of an electrochemical sensor having an electrode part attached to the part of the pipe to pass through, the electrode part has an air introduction part for introducing air into the plurality of electrodes and the electrode part, and the one end surface of the electrode is The electrode is brought into contact with the gas after the heat has been supplied, and the other end surface of the electrode is brought into contact with air introduced from the air introduction portion, and the electrochemical sensor has a coupling current corresponding to the degree of progress of corrosion of the electrode surface. The air preheater management apparatus which judges a dew point from the electrochemical electric current noise based on this, and the electrochemical electric potential noise based on the electric potential difference between the said electrodes.   Air is introduced from the air introduction part, and the electrode is cooled to cause liquefaction of the gas contacted at one end surface of the electrode, thereby generating electrochemical current noise and electrochemical potential noise. The dew point of the gas is measured by sensing, and the temperature of the air enjoying the heat is adjusted by the air preheater so that the temperature of the gas supplied with heat by the air preheater is maintained at a temperature higher than the dew point. The air preheater management device according to claim 1.   The electrochemical sensor includes the electrode part, a current / voltage measuring means for measuring electrochemical current noise and electrochemical potential noise generated between the electrodes of the electrode part, and an electric current measured by the current / voltage measuring means. Data storage means for taking in each measurement data of chemical current noise and electrochemical potential noise and accumulating the measurement data in time series, and electrochemical current noise accumulated in time series in the data storage means and 3. A sensor comprising dew point determination means for taking out each measurement data of electrochemical potential noise and judging the dew point from the obtained measurement data of electrochemical current noise and electrochemical potential noise. An air preheater management device according to claim 1.   The air preheater management device according to any one of claims 1 to 3, wherein the electrochemical current noise and the electrochemical potential noise are in a frequency band of 0.01 to 1 Hz.

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