JPH08141364A - Method and device for purifying exhaust combustion gas - Google Patents

Abstract

PURPOSE: To solve problems such as generation of chloride dew-point corrosion of the material constituting a flow path of exhaust gas and increase of ventilation loss, and to remove hydrogen chloride contained in exhaust gas by a smallest possible modification of a conventional device. CONSTITUTION: Hydrogen chloride contained in exhaust combustion gas discharged from a refuse incineration boiler 1 is neutralized by alkaline substance (Ca(OH)2 or the like) and produced chloride is removed by using a dust collector. In this method for purifying exhaust combustion gas, one kind or the mixture of alkali metal carbonate such as Na2 CO3 or K2 CO3 is added to exhaust gas in an alkali metal carbonate-charging system 18 provided at the front flow side of the part (bag filter 8) in the flow path of exhaust gas in which chloride dew point corrosion is feared to be produced. The produced chloride is changed into another chloride in which rise in dew point and boiling point is little.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a problem in a system for recovering and removing harmful hydrogen chloride contained in combustion exhaust gas discharged from combustion equipment such as various boilers and waste treatment equipment as chloride. A method for preventing chloride dew point corrosion.

[0002]

2. Description of the Related Art In recent years, the control of carbon dioxide (CO ₂ ) emissions has become an issue from the viewpoint of preventing global warming. Therefore, in a thermal power plant, which is a large source of CO ₂ ,
Improvement of power generation efficiency is being promoted in order to reduce CO ₂ emissions per unit power generation amount, and a high efficiency power generation system such as a coal gasification combined cycle is planned and constructed. In addition, the construction of a refuse incineration power generation system is expanding to make effective use of the heat generated by the incineration of waste such as municipal waste. In these power generation systems, the chloride contained in the fuel is released into the exhaust gas as hydrogen chloride as it burns. As a method for removing this harmful hydrogen chloride, an alkaline agent as shown in formula (1) is blown into the exhaust gas to neutralize the hydrogen chloride and form a chloride (for example, calcium chloride: CaCl ₂ ) and A method of filtering and collecting with a bag filter is used. As an alkaline agent, calcium hydroxide (Ca (O
H) ₂ ) is often used. 2HCl + Ca (OH) ₂ → 2H ₂ O + CaCl ₂ (1)

FIG. 5 shows an outline of a conventional fluidized bed type refuse incineration power generation system. In the refuse incineration boiler 1, air is blown from the lower part of the boiler 1 to burn the refuse introduced from the refuse inlet 2, the generated high temperature combustion gas is heat-exchanged through the heat transfer tube in the upper part of the boiler 1, and then the refuse is incinerated. It is discharged from the boiler 1. The combustion exhaust gas passes through the exhaust gas duct 10 at about 300 ° C., is then heat-recovered by the economizer 6, passes through the exhaust gas duct 11 at about 250 ° C., and is cooled to 150 ° C. by the desuperheater 7, Hydrogen chloride is removed in the exhaust gas duct 12. Here, as described above, blown from Ca (OH) _2-on system 16 Ca a (OH) ₂ in the exhaust gas duct 12, to neutralize the hydrogen chloride, the bag filter which is installed the generated CaCl ₂ after the exhaust gas duct 12 It is filtered and collected by 8.

Further, in the refuse incinerator with a steam generator shown in FIG. 5, the steam for combustion is steam that is not corrosive.
It was supplied to the steam air heater 9 from 7 and was used here for heating the combustion air. Then, in the refuse incineration boiler 1, the refuse input port 2 is heated by the combustion air heated.
The waste injected from the above is combusted, and the superheated steam obtained in the boiler 1 is supplied to the steam turbine 3 and used for power generation by the generator 4. The used steam is cooled by the condenser 5 and passes through the condensate path 13 to save the coal in the exhaust gas flow path.
Is heat-exchanged and is supplied to the refuse incineration boiler 1 via the condensate path 14. The temperature of the exhaust gas heat recovery system is determined by the efficiency of heat recovery, the prevention of dioxin generation and the performance of the bag filter 8 that removes and collects dust and chloride, which are problems in municipal waste incineration facilities. It has been done.

However, CaCl ₂ produced by the process shown in FIG. 5 has high hygroscopicity, and the boiling point of its aqueous solution is Ca.
It increases with increasing Cl ₂ concentration. FIG. 6 shows the results of examining the temperature dependence of the boiling points of the CaCl ₂ aqueous solution (dashed line) and the MgCl ₂ aqueous solution (solid line). In FIG. 6, the 6 molal concentration of CaCl _{2 in} an aqueous solution corresponds to about 60 weight percent, and the boiling point at this concentration is 15%.
Reach 5 ° C. Chlorides are seen to show such a tendency that the boiling point of the aqueous solution thereof greatly increases as the concentration increases, and in the low temperature parts such as the desuperheater 7, the bag filter 8 and the exhaust gas duct 12, the chloride is contained in the exhaust gas. Condensation of the water content of the water forms a chloride solution, which causes chloride dew point corrosion of the exhaust gas flow path constituent material. Further, if the high-concentration CaCl ₂ in a wet state adheres to the bag filter 8 and stays therein, not only the ventilation loss in the bag filter 8 increases but also the removal thereof becomes difficult.

[0006]

The dew point is 150 to 250.
As a method to prevent chloride corrosion of exhaust gas flow path constituent materials that also rises to ℃, operate all exhaust gas treatment system system temperatures above the dew point Ni-based high Cr high Mo material that is corrosion resistant to chloride dew point corrosion However, the former causes a decrease in thermal efficiency and a lower dust removal performance, and the latter causes a material cost of 10 times or more, which cannot be adopted from an economical point of view. As described above, in the method of recovering hydrogen chloride in combustion exhaust gas as calcium chloride CaCl ₂ , measures against chloride dew point corrosion of exhaust gas flow path constituent materials, increase of ventilation power in exhaust gas flow path constituent materials, bag filter 8 There was a problem that the economic burden and loss such as a decrease in the amount of power generation due to the start and stop of the plant due to the cleaning of the above became large. The object of the present invention is to solve the problems of chloride dew point corrosion occurrence and ventilation loss increase of the material constituting the exhaust gas flow path in the prior art,
It is to remove hydrogen chloride in the exhaust gas with a minimum change to the conventional device.

[0007]

The above objects of the present invention can be achieved by the following constitutions. That is, in the combustion exhaust gas purification method of neutralizing hydrogen chloride in the combustion exhaust gas with an alkaline substance, and removing the produced chloride using a dust collector,
This is a combustion exhaust gas purification method in which an alkali metal carbonate is added to a chloride formed by a neutralization reaction of hydrogen chloride and an alkaline substance to change to another chloride having a small increase in dew point and boiling point. In the above combustion exhaust gas purification method of the present invention, chloride dew point corrosion may occur in order to change the chloride produced by the neutralization reaction of hydrogen chloride and an alkaline substance to another chloride having a smaller dew point and boiling point increase. A method of adding an alkali metal carbonate to the upstream side of the exhaust gas flow passage can be used. As the alkali metal carbonate, sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ C)
O ₃ ) may be used alone or as a mixture. Further, the combustion exhaust gas in the combustion exhaust gas purification method of the present invention is an exhaust gas discharged from a refuse incinerator or a coal gasification furnace.

The above object of the present invention is achieved by the following constitution. In other words, in a combustion exhaust gas purification device that installs an alkaline substance addition device in the combustion exhaust gas flow path to neutralize hydrogen chloride in the exhaust gas and remove the generated chloride using a dust collector, a neutralization reaction between hydrogen chloride and an alkaline substance A combustion exhaust gas purification device in which an alkali metal carbonate addition device that changes the chloride generated in step 2 into another chloride with little increase in dew point and boiling point is placed on the upstream side of the exhaust gas flow passage where there is a risk of dew point corrosion. is there.

[0009]

The function of the present invention will be described below.
Immediately after neutralizing the hydrogen chloride with Ca (OH) ₂ , the CaCl ₂ produced there, for example sodium carbonate (Na ₂
CaC which reacts with CO ₃ ) and has a small increase in boiling point of the aqueous solution
O ₃ and sodium chloride (NaCl) are produced. Formula (2) shows the reaction between CaCl ₂ and Na ₂ CO ₃ . _{CaCl 2 + Na 2 CO 3 →} CaCO 3 ↓ + 2NaCl ···· (2) 4 CaCl ₂ aqueous solution the results of examining the concentration dependency of the boiling point of the aqueous solution mixed with CaCl ₂ and Na ₂ CO ₃ (dashed line) And the results with the MgCl ₂ aqueous solution (solid line). The boiling point of the aqueous solution (broken line) in which CaCl ₂ and Na ₂ CO ₃ were mixed hardly increased with increasing concentration over the range up to 4.3 molal concentration, and the value was about 102 to 103 ° C. When Na ₂ CO ₃ is added to the CaCl ₂ aqueous solution, Ca as shown in the formula (2) is obtained.
Since Cl ₂ changes to CaCO ₃ and precipitates, it becomes a NaCl solution that does not raise the dew point and boiling point, and dew point corrosion can be prevented. Thus, the reaction product is filtered and collected in a dry state while keeping the dew point lower than the exhaust gas duct temperature.
INDUSTRIAL APPLICABILITY The chloride dew point corrosion prevention technology of the present invention can be applied to chloride dew point corrosion prevention of a coal gasification combined cycle power generation plant, which is likely to become the mainstream in a high efficiency power generation system in the near future.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. Example 1 FIG. 1 is an example of a refuse incineration power generation system for carrying out the method for removing hydrogen chloride in combustion exhaust gas according to this example.
Devices having the same functions as those of the refuse incineration power generation system shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, C in the conventional refuse incineration power generation system shown in FIG.
N in the exhaust gas duct 12 downstream of the a (OH) ₂ charging system 16
a Alkali metal carbonate injection system 18 represented by a ₂ CO ₃ is added, and finally CaCO ₃ and NaCl are produced from the exhaust gas, and the dew point of chloride is 150 to 250 ° C. to 150 ° C.
At temperatures above the final dew point,
The chloride and dust are collected by the bag filter 8. Note that the optimum distance between the Ca (OH) ₂ charging system 16 and the Na ₂ CO ₃ charging system 18, the residence time of the exhaust gas in the exhaust gas duct 12, and the optimum Na ₂ CO ₃ charging amount are the gas temperature and the target. Since it varies depending on the conditions of the reaction rate and the final dew point, specific numerical values do not fall within the scope of the present invention.

In FIG. 1, an alkali metal carbonate injection system 18
Is provided on the downstream side of the Ca (OH) ₂ charging system 16,
This can prevent chloride dew point corrosion due to CaCl ₂ . However, in the low temperature part of the desuperheater 7, iron chloride (F
eCl ₂ or FeCl ₃ ) and high boiling chlorides (eg CaC) formed by the reaction of hydrogen chloride with dust particles or substances in combustion ash.
l ₂ , MgCl ₂ , NH ₄ Cl, AlCl ₃ , ZnCl ₂ )
May deposit on the wall surface, which also raises the dew point and causes corrosion of structural materials. In order to prevent the dew point corrosion caused by the chloride thus generated, a system capable of injecting an alkali metal carbonate such as Na ₂ CO ₃ may be installed in front of the part where the corrosion becomes a problem, for example, the desuperheater 7.

Embodiment 2 Another embodiment of the present invention is shown in FIG. Devices having the same functions as those of the refuse incineration power generation system shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. The temperature reducer 7 in FIG. 1 is omitted, and an alkali metal carbonate injection system 18 such as Na ₂ CO ₃ and an exhaust gas heat utilizing air heater 19 are installed at that position. In the conventional refuse incinerator with a steam generator, non-corrosive steam was used to heat the combustion air (see FIG. 5), but in this embodiment, an air heater (air heater) 19 using combustion exhaust gas is used. The combustion air is heated by. This is to focus on the fact that chloride dew point corrosion of the constituent members of the exhaust gas passage can be prevented by adding an alkali metal carbonate to the combustion exhaust gas. An alkali metal carbonate injection system 18 such as Na ₂ CO ₃ is installed. In the present embodiment shown in FIG. 2, the heat of the combustion exhaust gas can be utilized without using the steam generated for heating the combustion air, so that the thermal efficiency and the power generation efficiency can be improved. Further, the desuperheater 7 in FIG. 1 can be omitted, which is also effective for downsizing.

Embodiment 3 FIG. 3 shows a flow of a coal gasification combined power generation system according to another embodiment of the present invention. In the conventional coal gasification combined power generation system, the steam generator (evaporator, superheater) 2 uses the retained heat of the coal gas emitted from the coal gasification furnace 20.
The superheated steam is obtained by 1, and the steam turbine 26 uses the superheated steam to generate electricity by the generator 25. Then, the coal gas used in the steam generator (evaporator, superheater) 21 is cooled by the gas / gas heater 22, and after removing ash and solids by the gas purifier 23, it is burned by the gas turbine 24 to generate a power generator. Power is generated at 25. Further gas turbine 24
The exhaust gas emitted from the exhaust gas is supplied to the exhaust heat recovery steam generator 28 to heat the supply water to the steam generator (steamer, superheater) 21. The steam turbine 26 is provided in the exhaust heat recovery steam generator 28.
The steam used in 1. is condensed by the condenser 27 and then supplied. Further, a denitration device 29 is arranged in the middle of the two exhaust heat recovery steam generators 28 to discharge the purified exhaust gas 30.

Chloride dew point corrosion in prior art coal gasification combine cycle power generation systems can occur in the gas / gas heater 22 and the gas purifier 23.
The coal gas before refining contains SO ₂ and hydrogen chloride in addition to ash, and if dew-point corrosion occurs at the portion where ash or the like adheres or when it becomes wet at the time of stoppage, corrosion due to acidic chloride occurs. Therefore, in the system of FIG. 3 described above, an alkali metal carbonate injection device 31 such as Na ₂ CO ₃ is installed in the exhaust gas passage on the upstream side of the arrangement positions of the gas / gas heater 22 and the gas purification device 23, respectively. When the dew point in the system is expected to rise or become wet, Na
_When an alkali metal carbonate such as ₂ CO ₃ is added into the exhaust gas passage from the alkali metal carbonate injecting device 31, the dew point rises, and the pH of the solution can be brought to the alkali side even under wet conditions. Can prevent corrosion.

[0015]

EFFECTS OF THE INVENTION According to the present invention, when hydrogen chloride is removed, it is possible to recover the generated chloride at a temperature below the dew point of the exhaust gas duct. The ventilation loss of the filter is less likely to increase, and the number of plant shutdowns for collecting the reaction products can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a refuse incineration power generation system to which a method for removing hydrogen chloride in combustion exhaust gas according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing another embodiment of a refuse incineration power generation system that prevents chloride dew point corrosion according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example in which the chloride dew point corrosion prevention method according to the present invention is applied to a coal gasification combined cycle power generation system.

FIG. 4 is a diagram showing the concentration dependence of the boiling point of an aqueous solution in which CaCl ₂ and Na ₂ CO ₃ are mixed.

FIG. 5 is a diagram showing an outline flow of a refuse incineration power generation system according to a conventional technique.

FIG. 6 is a diagram showing concentration dependence of boiling points of CaCl ₂ aqueous solution and MgCl ₂ aqueous solution.

[Explanation of symbols]

1 ... Waste incineration boiler, 3, 26 ... Steam turbine, 4
… Generator, 5, 27… Condenser, 6… Economizer, 7…
Desuperheater, 8 ... Bag filter, 9 ... Steam air heater, 12 ... Exhaust gas duct, 16 ... Ca (OH) ₂ charging system, 18 ... Alkali metal carbonate charging system, 19 ... Air heater, 20 ... Coal gasifier , 21 ... Steam generator, 22 ...
Gas / gas heater, 23 ... Gas purification device, 24 ... Gas turbine, 28 ... Exhaust heat recovery steam generator, 29 ... Denitration device,
31 ... Alkali metal carbonate injection device

Claims (5)

[Claims] 1. A combustion exhaust gas purification method in which hydrogen chloride in a combustion exhaust gas is neutralized with an alkaline substance, and the generated chloride is removed using a dust collector, and a chloride produced by a neutralization reaction between hydrogen chloride and an alkaline substance. A method for purifying combustion exhaust gas, which comprises adding an alkali metal carbonate to a chloride to change it to another chloride having a small increase in dew point and boiling point. 2. In order to change the chloride produced by the neutralization reaction of hydrogen chloride and an alkaline substance into another chloride having a small increase in dew point and boiling point, the exhaust gas flow passage portion where chloride dew point corrosion may occur The combustion exhaust gas purification method according to claim 1, wherein an alkali metal carbonate is added to the upstream side. 3. The combustion exhaust gas purification method according to claim 1, wherein sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ CO ₃ ) is used alone or as a mixture as the alkali metal carbonate. 4. The combustion exhaust gas purification method according to claim 1, wherein the combustion exhaust gas is discharged from a refuse incinerator or a coal gasification furnace. 5. A combustion exhaust gas purifying apparatus, which is provided with an alkaline substance addition device in a combustion exhaust gas passage, neutralizes hydrogen chloride in exhaust gas, and removes generated chloride using a dust collector. The addition device of the alkali metal carbonate that changes the chloride generated by the neutralization reaction to another chloride with less increase in dew point and boiling point was placed on the upstream side of the exhaust gas flow passage where dew point corrosion might occur. Characteristic combustion exhaust gas purification device.