JP2017194184A - Exhaust gas treatment equipment and exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect an element inside a heat exchanger and also a liner of a chimney against corrosion by sulfur oxide while effectively utilizing heat of exhaust gas.SOLUTION: There are provided an exhaust gas flow passage 1 for guiding exhaust gas to a chimney 12; an air flow passage 2 where combustion air passes; a heat exchanger 4 for heat exchanging between the exhaust gas flow passage 1 and the air flow passage 2; a flowing-in air flow rate adjustment part for adjusting a flow rate of combustion air heat exchanged by the heat exchanger 4 through the air flow passage 2; a first temperature sensor 9 for detecting an exhaust gas outlet side temperature GT; a second temperature sensor 10 for detecting a chimney temperature CT; and a flowing-in air flow rate adjustment part 11 for adjusting a flow rate of combustion air heat exchanged by the heat exchanger 4 through the flowing-in air flow rate adjustment part in such a way that the exhaust gas outlet side temperature GT may become or more than an exhaust gas outlet side temperature control lower limit value TL2 and the chimney temperature CT may become or more than a chimney temperature control lower limit value TL1 on the basis of the detected temperatures of the first and second temperature sensors 9, 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas treatment technique that effectively uses the heat of exhaust gas as preheating of combustion air before dissipating high-temperature exhaust gas generated from a hot blast furnace, a boiler, or the like, which is a blast furnace auxiliary equipment, from a chimney.

Patent Document 1 describes preheating the combustion air with the heat of exhaust gas using a heat exchanger.
Here, as described in Patent Document 1, a large amount of sulfur oxide is contained in exhaust gas burned in a hot stove or the like, and sulfur that is a gas when the exhaust gas temperature falls below a certain temperature. There is concern that the oxide becomes liquid sulfuric acid and corrodes the internal elements of the heat exchanger.

Therefore, it is necessary to keep the exhaust gas temperature above a certain temperature, and it is necessary to protect the element by adjusting the exhaust gas temperature passing through the element by the restriction of the fluid that exchanges heat.
In view of this problem, Patent Document 1 discloses that the desired performance cannot be achieved by detecting the exhaust gas outlet temperature on the outlet side of the heat exchanger and controlling the amount of heat exchange using the bypass. In addition, it is described that preheating control of the air flowing into the heat exchanger is separately performed with a heater.

Japanese Patent Laid-Open No. 54-6165 (for example, page 1)

The inventors have found that it is preferable to protect the chimney liner from corrosion caused by sulfur oxide contained in the exhaust gas as well as protect the element of the heat exchanger from corrosion caused by sulfur oxide contained in the exhaust gas. Obtained.
The present invention has been made paying attention to the above points, and aims to protect the liner of the chimney together with the elements inside the heat exchanger from corrosion by sulfur oxide while effectively utilizing the heat of the exhaust gas. To do.

  In order to solve the problem, an exhaust gas treatment apparatus according to an aspect of the present invention includes an exhaust gas channel that guides exhaust gas to a chimney, an air channel through which combustion air passes, the exhaust gas channel, and the air channel. A heat exchanger that lowers the temperature of the exhaust gas flowing through the exhaust gas flow path by exchanging heat with the air flow path and increases the temperature of the combustion air flowing through the air flow path, and the heat exchanger through the air flow path An inflow air flow rate adjustment unit that adjusts the flow rate of combustion air to be heat-exchanged, and a first temperature sensor that detects an exhaust gas outlet side temperature that is a temperature at the outlet side of the heat exchanger of the exhaust gas flowing through the exhaust gas passage And the second temperature sensor for detecting the chimney temperature, which is the temperature in the chimney, the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor, and Set exhaust gas outlet temperature Adjust the flow rate of the combustion air heat exchanged by the heat exchanger via the inflow air flow rate adjustment unit so that the chimney temperature is equal to or higher than the lower limit value and the chimney temperature is higher than the preset chimney temperature control lower limit value. Air flow rate control means.

According to the aspect of the present invention, it is possible to protect the chimney liner as well as the elements inside the heat exchanger from corrosion by sulfur oxide while effectively using the heat of the exhaust gas.
Here, the exhaust gas temperature and the chimney temperature on the outlet side of the heat exchanger are estimated to have a temperature transition that substantially follows in a steady state, but it is assumed that the followability may deteriorate due to disturbances at various places.

And by setting the exhaust gas outlet side temperature control lower limit to the exhaust gas temperature at the heat exchanger outlet side to be higher, if you try to protect the chimney liner from corrosion by sulfur oxides, the heat utilization efficiency of the exhaust gas will be Min, lower.
Similarly, instead of the exhaust gas temperature at the outlet side of the heat exchanger, the air flow rate into the heat exchanger is adjusted only by the chimney temperature, and the chimney liner as well as the elements inside the heat exchanger are protected from corrosion by sulfur oxides. Even in the case of protection, the exhaust gas temperature on the outlet side of the heat exchanger becomes high, and the heat utilization efficiency of the exhaust gas becomes low.

It is a conceptual diagram which shows the equipment structure which concerns on embodiment based on this invention. It is a figure explaining the structure of the inflow air flow volume adjustment part which concerns on embodiment based on this invention. It is a figure explaining the example of a process of an exhaust gas temperature control part. It is a figure explaining the process example of a chimney temperature control part. It is a figure which shows an example of the time transition of the example of exhaust gas temperature control.

Next, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, the exhaust gas burned in the hot stove will be described as an example, but the present invention can be applied to exhaust gas generated from other equipment as long as it contains corrosive fluid. .
(Constitution)
In the exhaust gas treatment apparatus of the present embodiment, as shown in FIG. 1 which is a conceptual diagram, the exhaust gas 20 generated in each hot stove is appropriately supplied to the chimney 12 through the exhaust gas passage 1. Here, the exhaust gas 20 from one hot air furnace appropriately selected from a plurality of hot air furnaces is supplied to the exhaust gas passage 1.

Further, combustion air can be supplied to the combustion burner for the combustion chamber 21 of the hot stove through the air flow path 2.
An air supply device 3 such as a blower is provided upstream of the air flow path 2, and air is pumped to the air flow path 2 by the air supply device 3. The air supply device 3 pumps the supply air amount of the air amount command value to the air flow path 2 based on the air amount command value necessary for combustion in the combustion chamber 21 of the hot stove.

A heat exchanger 4 is interposed in the middle of the exhaust gas channel 1 and in the middle of the air channel 2, and heat exchange is performed between the exhaust gas channel 1 and the air channel 2. That is, heat exchange is performed so that the temperature of the exhaust gas flowing through the exhaust gas flow path 1 is lowered and the temperature of the combustion air flowing through the air flow path 2 is increased.
The air flow path 2 has an air bypass path 5 that communicates the upstream side (incoming side) and the downstream side (outside side) of the heat exchanger 4 position, and the air bypass path 5 has an air A bypass valve 6 (air open / close valve) is provided. The air bypass valve 6 includes a flow control valve, a pressure adjustment valve, and the like. The opening degree of the air bypass valve 6 is, for example, fully closed as an initial value.

The amount of air flowing into the heat exchanger 4 can be adjusted by the air bypass passage 5 and the air bypass valve 6 without changing the amount of air supplied to the burner of the combustion chamber.
The air bypass path 5 and the air bypass valve 6 constitute an inflow air flow rate adjustment unit.
Further, the exhaust gas passage 1 has an exhaust gas bypass passage 7 that communicates the upstream side (incoming side) and the downstream side (outside side) of the heat exchanger 4, and the exhaust gas bypass passage 7 is connected to the exhaust gas bypass passage 7. A valve 8 (exhaust gas on-off valve) is provided. The initial value of the exhaust gas bypass valve 8 is fully closed.

Further, a first temperature sensor 9 for detecting the exhaust gas outlet side temperature GT, which is the temperature of the exhaust gas flowing through the exhaust gas passage 1 on the outlet side of the heat exchanger 4, and a chimney temperature CT, which is the temperature in the chimney 12, are detected. Second temperature sensor 10. Each of the temperature sensors 9 and 10 supplies a detection signal corresponding to the detected temperature to the inflow air flow rate adjusting unit 11.
Moreover, the inflow air flow volume adjustment part 11 which adjusts the air inflow amount to the heat exchanger 4 is provided.

  The inflow air flow rate adjusting unit 11 has an exhaust gas outlet side temperature GT equal to or higher than a preset exhaust gas outlet side temperature control lower limit TL2 based on the detected temperature of the first temperature sensor 9 and the detected temperature of the second temperature sensor 10. At the same time, the air bypass valve 6 is adjusted so that the chimney temperature CT becomes equal to or higher than the preset chimney temperature control lower limit value TL1, and the flow rate of the combustion air exchanged by the heat exchanger 4 is adjusted.

  Here, the chimney temperature control lower limit value TL1 is set to a value lower than the exhaust gas outlet side temperature control lower limit value TL2. Further, a setting switching temperature TL4 described later is set to a setting value that is higher than the chimney temperature control lower limit value TL1 and lower than the exhaust gas outlet side temperature control lower limit value TL2. The chimney temperature control lower limit value TL1 and the exhaust gas outlet side temperature control lower limit value TL2 are set to a temperature higher than the dew point temperature of sulfur oxide (about 120 ° C.).

  As shown in FIG. 2, the inflow air flow rate adjustment unit 11 of the present embodiment includes two control units, an exhaust gas temperature control unit 11A and a chimney temperature control unit 11B, according to the chimney temperature CT as described later. By switching between the control by the exhaust gas temperature control unit 11A and the control by the chimney temperature control unit 11B, the flow rate of air flowing into the heat exchanger 4 is adjusted by both the exhaust gas temperature control unit 11A and the chimney temperature control unit 11B. To do. The inflow air flow rate adjusting unit 11 operates every predetermined sampling time.

The exhaust gas temperature control unit 11A exchanges heat with the heat exchanger 4 by adjusting the opening degree of the air bypass valve 6 so that the exhaust gas outlet side temperature GT becomes equal to or higher than the exhaust gas outlet side temperature control lower limit TL2. Adjust the flow rate of combustion air.
A processing example of the exhaust gas temperature control unit 11A will be described with reference to FIG.
First, in step S10, the exhaust gas temperature control unit 11A determines whether or not the chimney temperature CT is equal to or lower than the chimney temperature control lower limit value TL1. When it is determined that the chimney temperature CT is equal to or lower than the chimney temperature control lower limit TL1, the process proceeds to the process of the chimney temperature control unit 11B. On the other hand, if it determines with the chimney temperature CT being higher than the chimney temperature control lower limit TL1, it will transfer to step S20 as flow control based on exhaust gas exit side temperature GT.

In step S20, it is determined whether or not the exhaust gas outlet side temperature GT is equal to or lower than the exhaust gas outlet side temperature control lower limit value TL2. If it determines with exhaust gas exit side temperature GT being below exhaust gas exit side temperature control lower limit TL2, it will transfer to step S30. On the other hand, if it is determined that the exhaust gas outlet side temperature GT is higher than the exhaust gas outlet side temperature control lower limit TL2, the process proceeds to step S50.
In step S30, the opening degree of the air bypass valve 6 is changed in the opening direction by a predetermined opening degree. That is, the amount of air flowing through the air bypass 5 is increased, the process is terminated, and the process returns to step S10.

  In step S50, it is determined whether the exhaust gas outlet temperature GT is equal to or higher than the exhaust gas outlet temperature control upper limit value TL3. When the exhaust gas outlet side temperature GT is equal to or higher than the exhaust gas outlet side temperature control upper limit value TL3, the process proceeds to step S60. On the other hand, when the exhaust gas outlet side temperature GT is less than the exhaust gas outlet side temperature control upper limit TL3, the process ends and returns to step S10. Here, the exhaust gas outlet side temperature control upper limit value TL3 is set to a temperature higher than the exhaust gas outlet side temperature control lower limit value TL2 in advance by a set temperature.

In step S60, the opening degree of the air bypass valve 6 is changed in the closing direction by a predetermined opening degree, and the amount of air flowing through the air bypass path 5 is reduced.
Next, a processing example of the chimney temperature control unit 11B will be described with reference to FIG.
The chimney temperature control unit 11B adjusts the opening degree of the air bypass valve 6 so that the chimney temperature CT becomes equal to or higher than the chimney temperature control lower limit value TL1, so that the heat of the combustion air exchanged by the heat exchanger 4 is adjusted. Control the flow rate.

  First, in step S100, the chimney temperature control unit 11B determines whether or not the chimney temperature CT is equal to or higher than a set switching temperature TL4 that is higher than the chimney temperature control lower limit value TL1. When it is determined that the chimney temperature CT is equal to or higher than the set switching temperature TL4, the process proceeds to the process of the exhaust gas temperature control unit 11A. On the other hand, when it is determined that the chimney temperature CT is lower than the setting switching temperature TL4, the process proceeds to step S110.

In step S110, the opening degree of the air bypass valve 6 is changed in the opening direction by a predetermined opening degree, and the amount of air flowing through the air bypass path 5 is increased. Thereafter, the process ends and the process proceeds to step S100.
The exhaust gas bypass valve 8 changes the opening degree appropriately according to the gas leak from the piping, the deterioration of the heat exchanger 4, and the fluctuation of the amount of the exhaust gas flowing into the exhaust gas passage 1. Adjust the amount of exhaust gas to be supplied.

(Operation other)
In the hot stove, before the generated high-temperature exhaust gas is dissipated from the chimney 12, the heat exchanger 4 performs heat exchange between the exhaust gas and the combustion air to effectively use the exhaust heat.
However, since sulfur oxides are mixed in the exhaust gas, from the viewpoint of protecting the elements of the heat exchanger 4, the exhaust gas temperature after heat exchange is controlled to a temperature higher than the dew point temperature of sulfur oxide (about 120 ° C). There is a need to.

For this reason, the inflow air flow rate adjustment unit 11 of the present embodiment is based on the exhaust gas temperature on the outlet side of the heat exchanger 4 so that the exhaust gas outlet side temperature GT becomes equal to or higher than the exhaust gas outlet side temperature control lower limit TL2. The opening degree of the air bypass valve 6 is controlled so as to adjust the flow rate of the combustion air flowing into the exchanger 4.
Further, when the inventors have obtained knowledge that the liner of the chimney 12 needs to be protected from sulfur oxides and the chimney temperature CT is determined to be the chimney temperature control lower limit value TL1, heat based on the exhaust gas outlet side temperature GT is obtained. Switching from adjustment of the air inflow amount to the exchanger 4 to adjustment of the air inflow amount to the heat exchanger 4 based on the chimney temperature CT, both the element of the heat exchanger 4 and the liner of the chimney 12 are sulfur oxides. To protect against corrosion.

However, the adjustment of the air inflow amount based on the chimney temperature CT is less efficient in the heat exchange in the heat exchanger 4 than the adjustment of the air inflow amount based on the exhaust gas outlet side temperature GT. If it determines with more than setting switching temperature TL4 higher than the chimney temperature control lower limit TL1, it will return to adjustment of the air inflow amount based on exhaust gas exit side temperature GT.
As described above, according to the present embodiment, it is possible to protect the liner of the chimney 12 together with the elements inside the heat exchanger 4 from corrosion due to sulfur oxides while suppressing a decrease in the efficiency of heat exchange between the exhaust gas and the combustion air. It becomes.

  Here, when the heat exchanger 4 is aged and the exhaust gas of the heat exchanger 4 and the sealing material of the flow path of the combustion air are deteriorated over time, low temperature air is mixed into the exhaust gas side, and the exhaust gas outlet temperature GT is lowered. Thus, the chimney temperature CT can be reduced. In response to such a situation, the chimney temperature CT can be maintained at the allowable lower limit value or more by temporarily performing flow rate control based on the chimney temperature CT under a predetermined condition.

FIG. 5 shows an example of a time transition when the exhaust gas temperature is controlled based on this embodiment.
In the example of FIG. 5, the chimney temperature control lower limit value TL1 is set to 140 ° C., the exhaust gas outlet side temperature control lower limit value TL2 is set to 150 ° C., the exhaust gas outlet side temperature control upper limit value TL3 is set to 160 ° C., and the setting switching temperature TL4 is set to 142 ° C. An example in case. The chimney temperature control lower limit value TL1 and the exhaust gas outlet side temperature control lower limit value TL2 may be set to a temperature higher than the dew point temperature of sulfur oxide (about 120 ° C.).

  As shown in FIG. 5, after the exhaust gas outlet temperature GT is set to 150 ° C. or higher and the chimney temperature CT is set to 140 ° C. or higher, the air inflow amount is reduced by automatic control even if the chimney temperature CT becomes lower than the allowable temperature. The exhaust gas outlet temperature GT rises, and the chimney temperature CT can also quickly return to the allowable temperature or higher. That is, by performing the temperature treatment of the exhaust gas according to the present invention, the liner of the chimney 12 as well as the elements inside the heat exchanger 4 can be protected from corrosion by sulfur oxides.

Further, by adjusting the inflow amount of the combustion air with reference to the chimney temperature CT, the exhaust gas outlet side temperature control lower limit value TL2 can be lowered than before, and the heat efficiency by the heat exchanger 4 is also made higher than before. It becomes possible.
Here, the temperature difference between the chimney temperature control lower limit value TL1 and the exhaust gas outlet side temperature control lower limit value TL2 is larger than the temperature difference between the chimney temperature control lower limit value TL1 and the setting switching temperature TL4. It is preferable because the control time can be set short.

DESCRIPTION OF SYMBOLS 1 Exhaust gas flow path 2 Air flow path 3 Air supply apparatus 4 Heat exchanger 5 Air bypass path 6 Air bypass valve 7 Exhaust gas bypass path 8 Exhaust gas bypass valve 9 1st temperature sensor 10 2nd temperature sensor 11 Inflow Air flow rate adjusting unit 11A Exhaust gas temperature control unit 11B Chimney temperature control unit 12 Chimney 20 Exhaust gas 21 Combustion chamber CT Chimney temperature GT Exhaust gas outlet side temperature TL1 Chimney temperature control lower limit value TL2 Exhaust gas outlet side temperature control lower limit value TL3 Exhaust gas outlet side temperature control upper limit Value TL4 Setting switching temperature

Claims (6)

An exhaust gas flow path for guiding the exhaust gas to the chimney;
An air flow path through which combustion air passes;
A heat exchanger that reduces the temperature of the exhaust gas flowing through the exhaust gas flow path by exchanging heat between the exhaust gas flow path and the air flow path and increases the temperature of combustion air flowing through the air flow path;
An inflow air flow rate adjusting unit that adjusts the flow rate of combustion air heat-exchanged by the heat exchanger through the air flow path;
A first temperature sensor for detecting an exhaust gas outlet side temperature which is a temperature of the exhaust gas flowing through the exhaust gas passage at the outlet side of the heat exchanger;
A second temperature sensor for detecting a chimney temperature which is a temperature in the chimney;
Based on the detected temperature of the first temperature sensor and the detected temperature of the second temperature sensor, the exhaust gas outlet side temperature is equal to or higher than the preset exhaust gas outlet side temperature control lower limit value, and the chimney temperature is preset. An air flow rate control means for adjusting the flow rate of combustion air heat-exchanged by the heat exchanger via the inflow air flow rate adjustment unit so as to be equal to or higher than a control lower limit value;
An exhaust gas treatment apparatus comprising: The chimney temperature control lower limit value is set lower than the exhaust gas outlet side temperature control lower limit value,
When it is determined that the chimney temperature is higher than the chimney temperature control lower limit value, the inflow air flow rate control means is configured so that the exhaust gas outlet side temperature is equal to or higher than the exhaust gas outlet side temperature control lower limit value. Adjusting the flow rate of the combustion air heat exchanged by the heat exchanger via the air flow rate adjusting unit, and determining that the chimney temperature is equal to or lower than the chimney temperature control lower limit value, the chimney temperature is lower than the chimney temperature control lower limit value. Until the set switching temperature is higher than the value, the combustion air to be heat-exchanged by the heat exchanger via the inflow air flow rate adjustment unit so that the chimney temperature becomes equal to or higher than the chimney temperature control lower limit value. The exhaust gas treatment apparatus according to claim 1, wherein the flow rate is adjusted.   The inflow air flow rate adjustment unit is provided in an air bypass path that communicates an inlet side and an outlet side of the heat exchanger in the air flow path to bypass the heat exchanger, and the air bypass path. The exhaust gas treatment apparatus according to claim 1, further comprising an air on-off valve.   An exhaust gas bypass passage that bypasses the heat exchanger by connecting an inlet side and an outlet side of the heat exchanger in the exhaust gas passage; and an exhaust gas on-off valve provided in the exhaust gas bypass passage. The exhaust gas treatment apparatus according to any one of claims 1 to 3. After exchanging high-temperature exhaust gas with combustion air with a heat exchanger, it is discharged from the chimney,
Adjusting the flow rate of the combustion air flowing into the heat exchanger so that the exhaust gas outlet temperature which is the exhaust gas temperature on the outlet side of the heat exchanger is equal to or higher than a preset exhaust gas outlet temperature control lower limit value,
When it is determined that the temperature in the chimney is equal to or lower than a preset chimney temperature control lower limit value, the temperature in the chimney is equal to or higher than the lower limit value of the chimney temperature control instead of the flow rate adjustment based on the exhaust gas outlet temperature. An exhaust gas treatment method comprising adjusting a flow rate of the combustion air flowing into the heat exchanger.   If it is determined that the temperature in the chimney is equal to or higher than the set switching temperature higher than the chimney temperature control lower limit value, the exhaust gas outlet side temperature control lower limit that the exhaust gas outlet side temperature is preset from the flow rate adjustment based on the temperature in the chimney 6. The exhaust gas treatment method according to claim 5, wherein the flow rate adjustment based on the exhaust gas outlet side temperature is switched so as to be equal to or higher than a value.

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