JPH11128659A - Device for treating waste gas in starting coal gasification plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the corrosion of an equipment constituting material at the time of starting, in a gas treating device for bringing the gas generated in starting a pressurized coal gasification plant into contact with water to cool and purify the gas. SOLUTION: The gas generated in starting a pressurized coal gasification plant is brought into contact with water, purified and cooled in this gas treating device. In this case, the hydrogen ion concn. (pH) of the circulating water to be brought into contact with the generated gas is kept at 6 to 9 to prevent the corrosion of the equipment constituting material. As the means, a pH meter 33 for measuring the pH of the circulating water in a decanter 26 attached to a gas purifier 3, a pH controller 34 for controlling the supply of a pH regulator (sodium hydroxide, etc.), to the circulating water based on the output of the pH meter 33, a pressure reducing valve 28 for reducing the pressure of the circulating water in the decanter 26 and a pressure reducer 7 for liberating the acidic gas from the pressure-reduced cooling water are provided. Further, a cooler 24 for cooling the cooling water to 50 deg.C or a heater for heating it to 130 deg.C is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a starting apparatus for a gasification plant in which a raw material such as coal is gasified at high temperature and high pressure with a gasifying agent containing oxygen to obtain a product gas. Gas treatment for cleaning and removing small amounts of acidic gas components such as nitrogen oxides such as nitric oxide and nitrogen dioxide and sulfur dioxide gas contained in the gas by contacting the exhaust gas generated when combusting gas with water TECHNICAL FIELD The present invention relates to an apparatus for preventing corrosion of equipment constituent materials by carbon dioxide or the like contained in exhaust gas at the time of startup in a water circulation system of a process.

[0002]

2. Description of the Related Art Coal is a useful energy source with abundant reserves. However, coal contains more than 10% of ash (alumina, silica, calcium, etc.) and harmful metals (Cr, Hg, etc.).
The processing method was difficult and narrowed the applicable range. In spouted bed coal gasifiers, however, coal is partially burned at high temperatures with a gasifying agent such as oxygen to produce useful gas,
It can be taken out of the system as a slag that melts ash and hardly elutes harmful components. For this reason, the field of application is expanding, and it is expected to be particularly useful as a fuel for power generation or a raw material for industrial use.

FIG. 2 is a system diagram of a conventional pressurized spouted bed gasification plant from a gasifier to a wet gas processing apparatus. In this apparatus, first, the fuel oil 14 and the air 15 are supplied to the oil burner 13 and burned, so that the temperature and pressure of the system from the gasifier 1 to the heat recovery boiler 2 and the filter 6 are increased, and the predetermined temperature is increased. And the pressure is reached to prepare for startup. In this system, the generated gas 11
Is passed through the cleaning device 3 which is a wet type gas processing device, and the pressure of the system is gradually increased to a predetermined value by the pressure regulating valve 16 provided at the outlet. After the temperature increase and the pressure increase are completed, the pulverized coal 17 and the oxidizer 18 as the fuel are charged into the gasification furnace 1, and the operation is gradually switched to the gasification operation. Washer 3
Then, the valve 42 is opened, the circulating water 20 is circulated by the pump 9, and brought into gas-liquid contact with the generated gas 11, whereby the gas components and unburned components contained in the generated gas 11 in trace amounts are wet-removed.

That is, the scrubber 3 removes an acidic gas component that degrades the performance of the subsequent desulfurization equipment at the time of start-up and at the time of switching to the gasification operation, and removes uncollected fine particles during the coal gasification operation. The main purpose is to remove dust and other trace gas components such as ammonia and halogen compounds, and to adjust the gas temperature. During the gasification operation, a solid content such as dust contained in the generated gas 11 is collected by a gas scrubber, and the solid content is settled by the decanter 26.
The settled solids are extracted together with the water while adjusting the drain valve 22, and the appropriate replenishment water is supplied.

Here, a heat recovery boiler 2 connected to a gasification furnace 1 and a cyclone 1 connected to the heat recovery boiler 2
2, the filter 6 connected to the cyclone 12, the gas-gas heat exchanger 19 connected to the filter 6, the gas scrubber 3 connected to the gas-gas heat exchanger 19, and a pipe disposed under the gas scrubber 3 at the bottom. Decanter 2 connected by 38
6. A drain valve 2 is disposed below the decanter 26 and is provided at the bottom thereof.
Wastewater treatment equipment 23 connected by a pipeline 37 interposed
The circulating water pump 9, the suction side of which is connected to the bottom of the decanter 26 via a pipe 42 via a valve 42, and a pipe 36 that communicates the discharge side of the circulating water pump 9 with the upper part of the gas scrubber 3. A series of devices including a cooler 24, a make-up water supply means 21 connected to an upper part of a decanter 26, a desulfurization tower 4 connected to an upper part of the gas scrubber 3, and a pipe and a valve connecting these devices. Is referred to as a starting exhaust gas treatment device. The interior of the decanter 26 is divided into two by a partition wall extending from the bottom surface to a predetermined height, and a pipe 37 provided with the drain valve 22 and a pipe 27 provided with the valve 42 are connected to different sections from each other. The pipe 38 is connected to a position above the section to which the pipe 37 is connected, and the makeup water supply means 21 is connected to a position above the section to which the pipe 27 is connected. That is, pipeline 3
The circulating water flowing from 8 into the decanter 26 accumulates in the section to which the line 37 is connected (the drain valve 22 is normally closed), and the circulating water overflowing from the section exceeds the partition wall and the line 27 It flows into the connected compartment.

[0006]

However, when the gasification plant is started, when the generated gas 11 which is the combustion exhaust gas from the oil burner 13 is passed through the cleaning device 3 to be washed and cooled, the generated gas 11 Oxides (NO ₂
And NO ₃ ), sulfur dioxide (SO ₂ and SO ₃ ), carbon dioxide (CO ₂ ), etc., are more likely to be absorbed by the circulating water 20 as the pressure increases, and the circulating water 20 becomes acidic water, and the gas treatment equipment However, there is a problem that the equipment material constituting the material significantly corrodes.

Emission gas 11 when starting coal gas plant
Is a high-temperature combustion exhaust gas from the oil burner 13, and is generally sulfur contained in oil or nitrogen oxides (NO ₂ , NO and N ₂ O) and sulfur dioxide (S ₂ ) generated by high-temperature combustion.
O ₂ and SO ₃ ) are included together with carbon dioxide (CO ₂ ). It is known that these gases dissociate into anions and protons (hydrogen ions) when absorbed by water according to the following formula, and are called acid gases because water exhibits acidity.

[0008]

Embedded image

[0009] Normally, under the normal temperature and pressure, these acidic gases are not too many absorbed in water, the NO ₂ 20
%, About 50% for SO _{2 and} about 0.1% or less for CO ₂ . However, as in this system, in the exhaust gas generated when starting a pressurized coal gas plant, the partial pressure of each acid gas component increases with the increase in pressure, and when the total pressure is about 1 MPa, NO ₂ and SO ₂
In this case, almost 100% is absorbed, and about 1% is absorbed by CO ₂ . Therefore, as shown above (Equations 2, 5, 6,
According to 7), the hydrogen ion concentration increases as the pressure increases, and the pH of the circulating water 20 repeatedly used for washing is increased.
Drops sharply.

The iron material constituting the gas treatment apparatus contains carbon dioxide, hydrogen sulfide (H ₂ S), hydrogen chloride (HCl) and the like in the generated gas 11 during the coal gasification operation.
Carbon steel, low alloy steel, etc. are used in anticipation of a certain amount of corrosion. FIG. 3 shows the effect of temperature on the corrosion rate of iron in an aqueous solution containing carbon dioxide. From room temperature to about 50 ° C, iron sulfide (FeS
x) and iron oxide (Fe ₂ O ₃ ) serve as a protective film, and the corrosion rate is relatively low. However, as the temperature increases, the amount of corrosion increases due to carbon dioxide gas, peaking at around 100 ° C., and furthermore, in high-temperature water of 130 ° C. or more, corrosion occurs due to the formation of a bivalent metal carbonate such as iron carbonate (FeCO ₃ ) due to a protective film. (Reference literature examples: Materials and Environment, Vol. 44 (39), p. 142-150, 19).
95). However, for example, if the total pressure is 3 MPa and 1
500 m ³ N with 00 ppm NO ₂ and 5% CO ₂
/ H gas is washed with 5 m ³ of circulating water.
H begins to decrease with washing, and eventually shows a strong acidity with a pH of 3 or less, and these iron materials, which are component materials of the device, are severely corroded and cannot be operated continuously.

An object of the present invention is to suppress corrosion of a ferrous material or the like which is a constituent material of a wet gas processing apparatus at the time of starting a coal gasification plant.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gas treatment apparatus for bringing generated gas into contact with circulating water, in which a circulating water which has absorbed an acidic gas such as nitrogen oxide, sulfurous acid gas, carbon dioxide gas by a gas scrubber is depressurized. This is achieved by providing a decompression means for dispersing acid gas (carbon dioxide gas or the like) once absorbed in the circulating water as a gas. A circulating water pressurizing pump for pressurizing the depressurized circulating water again may be provided, and the pressurized circulating water may be sent to the suction side of the circulating water pump.

In addition to the above-mentioned depressurizing means, a pH adjusting means for adjusting the hydrogen ion concentration (pH) of the circulating water having absorbed the acidic gas is provided, and the hydrogen ion concentration (pH) of the circulating water is adjusted to be 6 to 9 slightly acidic or weak. You may make it alkaline.

In particular, the generated gas 1 introduced into the gas cleaning device 3
When the total concentration of the acid gas except for the carbon dioxide gas such as nitrogen oxide and sulfur dioxide gas in 1 is low at several tens ppm or less,
By providing only the pressure reducing means and the circulating water pump and dispersing the carbon dioxide gas once absorbed in the circulating water 20, corrosion can be prevented, and a means for adjusting the hydrogen ion concentration (pH) is unnecessary.
When the gas temperature of the generated gas 11 introduced into the gas cleaning device 3 is high at about 100 ° C. or higher, the circulating water of the gas cleaning device 3 is cooled to 50 ° C. or lower by a cooler, or Heating to 130 ° C. or higher can prevent corrosion. In general, this cooler or heater can also serve as the cooler 24 used during the gasification operation shown in the conventional example of FIG. 2 (when used as a heater, a heat source such as steam is required. Become). The pressure reducing means can be dealt with by providing a pressure reducing valve and a pressure reducing device, or by using a drum such as a decanter used for gasification operation as a pressure reducing device and providing a pressure reducing valve in front of the device.

By using the gas treatment apparatus according to the present invention, when the circulating water 20 containing the acidic gas once absorbed by the washing is reduced in pressure and extracted to the decompressor, mainly the carbon dioxide gas which is physically absorbed is mainly removed. A part of the acidic gas as a component is diffused, the pH of the circulating water rises, and the temperature of the circulating water decreases due to the evaporation of water under reduced pressure. The temperature of the generated gas 11 is about 100 ° C. or less, and the NOx and SOx concentrations are
If it is low at 0 ppm, reduce the pressure to reduce the pH of circulating water.
Has a weak acidity of about 6 and a temperature of 50 ° C. or lower, so that corrosion of inexpensive iron materials and the like constituting the gas treatment apparatus can be suppressed, and the circulating water 20 can be pressurized by the pressurized circulation pump and used for cleaning. become.

On the other hand, NOx and SOx in the generated gas 11
When the concentration of the trace acid gas is higher than 100 ppm, the NOx and SOx gases absorbed in the circulating water 20 increase, and the NO ₃ ~ and SO ₃ ² ~ concentrations increase.
The pH is adjusted to 6 to 9 by neutralizing the hydrogen ions (H +) generated by the above formulas (2) and (5) using an H regulator.
By making it weakly acidic or weakly alkaline, corrosion of the gas treatment device is suppressed. Further, when the temperature of the generated gas 11 is high and is about 100 ° C. or more, the temperature of the circulating water 20 rises to 50 ° C. or more due to washing. Alternatively, corrosion of the material can be suppressed by forming a protective film such as iron oxide (Fe ₂ O ₃ ) or iron carbonate (FeCO ₃ ) by heating to 130 ° C. or more by a heater.

The alkali used for pH adjustment is Na.
It is desirable to use an alkali hydroxide such as OH or KOH, a nonvolatile amine or ammonia (NH ₃ , NH ₄ OH). It is desirable that alkaline earth metal salts such as Ca compounds are not used because they easily react with carbon dioxide gas to form carbonates having low solubility and cause clogging of equipment. Further, when the pH of the circulating water 20 is made alkaline at 9 or more, the carbon dioxide (CO ₂ ) contained in the generated gas 11 is easily absorbed at the time of shifting to the gasification operation, and the flow rate of the gas as fuel decreases. Therefore, it is not suitable for a power generation system using GT, so that it is desirable to be in the above pH range.
According to the present invention, since the carbon dioxide gas once absorbed is diffused, when switching to the gasification operation after startup,
Calcium compounds contained as dust in coal gas,
The effect of reducing the problem of generating scale by reacting with carbon dioxide dissolved in circulating water can be expected.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 shows a first embodiment in which the present invention is applied to a wet gas processing apparatus in a coal gasification plant.
This embodiment is different from the configuration of the conventional example shown in FIG. 2 in that the gas cleaning device 3 is brought into contact with the generated gas 11 containing carbon dioxide gas or the like.
And a decanter 26, a circulating water pump 9 and a cooler 24, a pressure reducing valve is provided upstream of a valve 42 interposed in a pipe line 27 connecting the decanter 26 and the suction side of the circulating water pump 9. The circulating water pressurizing pump 41 having a suction side connected to the bottom of the depressurizing device 7 is disposed at the bottom of the depressurizing device 7.
The pipe 27 on the downstream side of the pipe is communicated by the pipe 35 and the pipe 3
5 is connected to an alkali supply pipe line 29 interposed with an alkali supply adjustment valve 30, and a pH measuring device 33 for measuring a hydrogen ion concentration (pH) is disposed inside the decanter 26.
Using the output of the measuring device 33 as an input, the alkali supply regulating valve 30
The point is that a pH adjuster 34 for controlling the opening degree is provided. Above the decompressor 7 (gas phase part), means for releasing gas is provided. The alkali supply pipe line 29, the alkali supply adjustment valve 30, and the pH adjuster 34 serve as pH adjustment means. Total pressure is increased to 3MPa, about 100ppm
Of NOx, a 150~300 ℃, 1000m ³ N / h of gas containing SOx and 5% CO ₂ for about 50 ppm 10
The case of washing with m ³ circulating water was shown.

The operation and effect of this embodiment will be described below. First, at startup, the combustion exhaust gas of the oil burner 13 is washed and cooled by the circulating water 20 through the gas washer 3. By this operation, the acidic gas contained in the generated gas 11 is absorbed by the circulating water 20, and the pH meter 33 becomes acidic. Therefore, by closing the valve 42 and opening the pressure reducing valve 28 to guide the circulating water 20 to the pressure reducing device 7 and reducing the pressure of the circulating water containing the acidic gas absorbed by the washing, mainly the carbon dioxide gas physically absorbed is mainly contained. A part of the acid gas is released from the circulating water in the pressure reducer 7.

Further, alkali is controlled by an alkali supply adjusting valve 30 according to a signal from a pH adjuster 34 to which an output signal of the pH measuring device 33 is input, and is supplied to a pipeline 35. 7 circulating water 20
The hydrogen ions (H +) in the circulating water 20 generated by absorbing NOx and SOx and the like are reduced by being sent to the suction side of the circulating water pump 9 through the
The pH of the circulating water 20 can be maintained at a weakly acidic or weakly alkaline pH of 6 to 9. In addition, since the temperature of the circulating water rises to 50 ° C. or more due to the sensible heat of the generated gas 11, by supplying the cooling water 25 to the cooler 24,
The temperature of the circulating water 20 can be maintained at 50 ° C. or lower. This suppresses corrosion of the iron material constituting the gas processing device.

Embodiment 2 FIG. 4 shows a second embodiment in which the present invention is applied to a wet gas processing apparatus in a coal gasification plant. This embodiment differs from the first embodiment shown in FIG. 1 in that the cooler 24 provided in the pipe 36 is omitted and the pipe 35 is located downstream of the connection point of the alkali supply pipe 29 in the pipe 35. The point is that the heater 32 is interposed. In the present embodiment, the circulating water pump 9 and the circulating water
0 is circulated between the gas scrubber 3 and the decompressor 7 at about 300 ° C.
High-temperature evolved gas 11 is passed through a gas scrubber 3 to circulate water 2
This is an apparatus for removing impurities such as a trace amount of acidic gas contained in the generated gas 11 by bringing the generated gas 11 into contact with zero.

According to this configuration, when the generated gas 11 is washed and cooled, a part of the circulating water 20 is evaporated by the sensible heat of the gas, and the supply amount of the steam 31 supplied to the heater 32 is adjusted. As a result, the temperature of the circulating water 20 becomes 13
It can be maintained at 0 ° C. or higher. When the inlet temperature of the generated gas 11 is as high as about 300 ° C. as in this example, the temperature of the circulating water 20 can be easily maintained at 120 ° C. or more by the sensible heat. A small amount of steam is required. The shortage of the circulating water 20 that is lost due to evaporation needs to be supplied with makeup water. Further, in order to compensate for a decrease in pH due to the acidic gas absorbed in the circulating water 20, the opening degree (or opening and closing) of the alkali supply adjusting valve 30 is controlled by the pH controller 34 in accordance with the value of the hydrogen ion concentration (pH) measuring instrument 33. ) To maintain the pH of the circulating water at a weakly acidic or slightly alkaline pH of 6 to 9. In this case, the temperature of the circulating water 20 is about 13
Since the temperature is as high as 0 ° C. or higher, the amount of absorption of the carbon dioxide gas among the acidic gases is particularly reduced, and the supply amount of the alkali required for neutralization is extremely small as compared with Example 1 in which the circulating water temperature is low.

Embodiment 3 FIG. 5 shows a third embodiment in which the present invention is applied to a wet gas processing apparatus in a coal gasification plant. This embodiment is different from the prior art shown in FIG. 2 in that a line 3 connecting the gas scrubber 3 and the decanter 26 is connected.
8, a pressure reducing valve 28 is interposed, a gas line portion of the decanter 26 is connected to a pipe 39 interposed with a valve 44, and an alkali supply adjustment is performed on the pipe 36 at an upstream side of the cooler 24. The alkali supply pipe line 29 interposed with the valve 30 is connected, and the hydrogen ion concentration (pH) is set inside the decanter 26.
That the pH measuring device 33 for measuring
Using the output of the measuring device 33 as an input, the alkali supply regulating valve 30
Is provided with a pH adjuster 34 for controlling the opening degree (or opening and closing).

In this embodiment, instead of the decompressor 7 in the first embodiment, a drum such as a decanter 26 conventionally used for gasification operation is also used as a depressurizer, and the decanter 26 and the gas cleaning device 3 38 that leads circulating water to
Is provided with a pressure reducing valve 28. At the time of starting the gasification furnace, the circulating water 20 is depressurized by the pressure reducing valve 28, and the depressurized circulating water is guided to the decanter 26, so that the acidic gas 8 dissolved in the circulating water 20 is diffused in the decanter 26, The diffused acid gas 8 is discharged from the pipe 39 through the valve 44 to the outside of the system. The pH adjuster 34 receives the output of the pH meter 33 as an input, controls the opening (or opening and closing) of the alkali supply adjusting valve 30, supplies alkali from the alkali supply line 29 to the line 36, and supplies the circulating water 20. Can be adjusted by neutralizing with an alkali.

During the gasification operation, the gas can be washed by circulating with the circulating water pump 9 while introducing the circulating water 20 into the decanter 26 without reducing the pressure as in the conventional case.
According to the present embodiment, there is no need to newly install a decompressor, and it is economical at low cost.

[0026]

According to the present invention, corrosion of iron materials and the like in a wet gas treatment apparatus at the time of starting a coal gasification plant can be suppressed, so that an inexpensive and stable start-up operation can be performed without using expensive materials. And a gas processing device capable of providing the same.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment of a starting exhaust gas treatment apparatus for a coal gasification plant according to the present invention.

FIG. 2 is a system diagram showing a conventional example of a wet gas processing apparatus of a coal gasification plant.

FIG. 3 is a graph showing the relationship between the amount of iron corrosion in an aqueous solution containing carbon dioxide and temperature.

FIG. 4 is a system diagram showing a second embodiment of a starting exhaust gas treatment apparatus for a coal gasification plant according to the present invention.

FIG. 5 is a system diagram showing a third embodiment of a starting exhaust gas treatment apparatus for a coal gasification plant according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gasification furnace 2 Heat recovery boiler 3 Gas scrubber 4 Desulfurization tower 5 Slag 6 Filter 7 Pressure reducer 8 Acid gas 9 Circulating water pump 10 Slag hopper 11 Generated gas 12 Cyclone 13 Oil burner 14 Fuel oil 15 Air 16 Pressure control valve 17 Fine powder Charcoal 18 Oxidant 19 Gas-gas heat exchanger 20 Circulating water 21 Make-up water supply means 22 Drain valve 23 Drainage treatment equipment 24 Cooler 25 Cooling water 26 Decanter 29 Alkaline supply line 30 Alkaline supply regulating valve 31 Steam 32 Heater 33 pH measurement Apparatus 34 pH controller 35, 36, 37, 38, 39 Pipe line 40 Heater 41 Circulating water pressurizing pump 42, 43, 44 Valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01K 23/10 F01N 3/08 Z F01N 3/08 F02C 3/28 F02C 3/28 7/00 Z 7/00

Claims (6)

[Claims] 1. A gas washer for removing a trace gas component such as carbon monoxide or sulfur dioxide contained in an exhaust gas by contacting the exhaust gas at the time of starting a coal gasification plant with water to clean the gas. In a gas processing apparatus including a circulating water pump for circulating water supplied to a gas scrubber, a decompression means for decompressing circulating water having absorbed a gas component in the gas scrubber, and applying the depressurized circulating water to the gas processing apparatus. Circulating water pressurizing means for pressurizing and sending the circulating water to the circulating water pump. 2. The starting exhaust gas treatment apparatus for a coal gasification plant according to claim 1, wherein the circulating water having absorbed the gas component in the gas scrubber can have a pH of 6 to 9 weakly acidic or weakly alkaline. A start-up exhaust gas treatment device for a coal gasification plant, comprising a pH adjusting means. 3. The coal gasification plant according to claim 1, further comprising a cooler capable of cooling the temperature of the circulating water to 50 ° C. or less. Start-up exhaust gas treatment equipment for chemical plants. 4. A coal gasification plant starting exhaust gas treatment apparatus according to claim 1, further comprising a heater capable of heating the temperature of the circulating water to at least 130 ° C. Start-up exhaust gas treatment equipment for chemical plants. 5. A gas scrubber and a gas scrubber for removing a trace gas component such as carbon monoxide or sulfur dioxide contained in an exhaust gas by contacting the exhaust gas at the start of a coal gasification plant with water to clean the gas. In a gas treatment apparatus including a circulating water pump that circulates water supplied to a gas scrubber, a decompression unit that decompresses circulating water having absorbed a gas component in the gas scrubber, and a gas component in the gas scrubber. A start-up exhaust gas treatment apparatus for a coal gasification plant, comprising a pH adjusting means capable of adjusting the pH of absorbed circulating water to a weakly acidic or weakly alkaline of 6 to 9. 6. The starting exhaust gas treatment apparatus for a coal gasification plant according to any one of claims 2 to 5, further comprising a pH measuring device for detecting a pH of circulating water having absorbed a gas component in the gas cleaning device. Wherein the pH adjusting means
A starting exhaust gas treatment device for a coal gasification plant, which is configured to operate using an output of a measuring device as an input.