JP2846399B2 - Desulfurization in boiler furnace and flue - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for removing sulfur oxides (hereinafter referred to as SOx) from combustion exhaust gas of a power generation boiler or the like, and particularly relates to a boiler furnace with a simple facility cost. The present invention relates to a method for improving the desulfurization performance of a method combining desulfurization in a furnace and desulfurization in a flue by spraying a desulfurizing agent into the inside.

[Conventional technology]

2. Description of the Related Art Conventionally, a wet desulfurization method called a limestone-gypsum method is mainly used as a desulfurization apparatus for a power generation boiler. The limestone-gypsum method is a high-performance desulfurization method in which fine limestone is slurried in water and brought into contact with exhaust gas to absorb sulfur oxides and collect gypsum. On the other hand, a typical example of the dry method is an activated carbon desulfurization method. In each case, the desulfurization performance is high, but there is a problem that the number of incidental facilities is large and the facility costs are high.

The limestone-gypsum method requires wastewater treatment, reheating of exhaust gas, and the like. On the other hand, in recent years, a combined desulfurization method of spraying a fine powder desulfurizing agent into a boiler furnace and performing desulfurization in a flue has attracted attention. However, this desulfurization method has low desulfurization performance and the utilization rate of the supplied desulfurization agent is low, so it has been adopted as a desulfurization method for combustion exhaust gas for boilers for thermal power generation requiring high desulfurization performance. There is no current situation.

In order to increase the desulfurization performance, it is necessary to take measures such as making the particle size of the desulfurizing agent sprayed into the furnace ultra-fine or increasing the desulfurizing agent supply amount. However, there is a limit in making the desulfurizing agent ultrafine. Further, if the supply amount of the desulfurizing agent is increased in order to enhance the desulfurizing performance, there is a problem that unreacted desulfurizing agent is mixed into the coal ash, and new secondary pollution is generated at the time of the disposal of the coal ash.

[Problems to be solved by the invention]

In the boiler furnace and flue gas desulfurization methods described above, in the boiler furnace, the boiler can be considered to be a reactor for decarboxylation of limestone, and some desulfurization occurs. It is done in Hokkaido. That is, it is important to generate highly active quicklime in the boiler furnace in order to increase the desulfurization performance and the utilization rate of the desulfurizing agent.

However, up to now, in the above desulfurization method, the quick calcification reaction in the furnace has not been sufficiently performed, and therefore, there has been a disadvantage that desulfurization in the furnace and desulfurization in the flue are not performed smoothly.

In view of the above, an object of the present invention is to provide a desulfurization method capable of solving the above-mentioned drawbacks, allowing a sufficient desulfurization reaction to proceed in a furnace and a flue, and improving the desulfurization performance and the utilization rate of a desulfurizing agent. I do.

[Means for solving the problem]

In order to achieve the above object, in the present invention, in a boiler furnace, a fine powder desulfurizing agent consisting of one or more of a salt, oxide or hydroxide of a metal selected from calcium, sodium and magnesium is sprayed. In a furnace and flue gas desulfurization method in which desulfurization is performed in a furnace and in a flue, the desulfurizing agent is calcined to generate CaO, MgO, and Na ₂ O, and the desulfurizing agent containing these oxides is used as a carrier fluid. Along with spraying into the furnace together with the furnace, the supply amount of the desulfurizing agent and the amount of the oxide generated by the preliminary calcination are changed according to the boiler load. In the desulfurization method,
After the desulfurizing agent is calcined, it is classified by gravity with a carrier fluid, and light desulfurizing agent particles are sprayed into a furnace, while heavy desulfurizing agent particles are circulated to a pulverizing step.

And, in the desulfurization method of the present invention, as the desulfurization agent, one or more kinds of salts, oxides or hydroxides of metals selected from calcium, sodium or magnesium can be used, and further, the desulfurization agent A dispersant can be added, and as the dispersant, a part of the coal ash recovered from the electrostatic precipitator can be used and mixed with the above desulfurizing agent in the calcining step. Further, any one of heated air, fuel exhaust gas, and steam can be used as the carrier fluid.

The calcination step of the desulfurizing agent in the present invention is performed at a calcination temperature of 950.
The temperature is maintained at a temperature of less than or equal to ° C. and is retained for a predetermined time, and the position where the desulfurizing agent is sprayed into the boiler furnace by the carrier fluid is preferably a position where the temperature in the boiler furnace is 1000 ° C. or less.

The desulfurizing agent is sprayed into the boiler furnace by the carrier fluid, and the desulfurizing agent sprayed into the boiler furnace is light desulfurizing agent particles. Here, the light desulfurizing agent particles are mainly CaO when limestone is used as the desulfurizing agent, and the heavier desulfurizing agent is mainly CaCO ₃ , which is circulated to the grinding step. Adjustment of the particle size of the desulfurizing agent sprayed into the boiler furnace and the CaO / CaCO ₃ ratio at the outlet of the calcining step is performed by adjusting the supply amount of the carrier fluid.

Further, it is preferable to control the desulfurizing agent supply amount, the calcination conditions, the carrier fluid supply amount, and the like according to the sulfurous acid gas concentration in the exhaust gas and the change in the boiler load. For example, control of the desulfurizing agent supply amount sprayed into the boiler furnace and the calcination conditions are performed according to the concentration of sulfurous acid gas in the exhaust gas at the outlet of the electrostatic precipitator, or
Control of the calcination conditions of the desulfurizing agent and the supply amount of the carrier fluid are performed according to the change in boiler load or the concentration of sulfurous acid gas in the exhaust gas on the outlet side of the electrostatic precipitator, and further, the CaO at the calcination process outlet based on the carrier fluid supply amount The control of the ratio of / CaCO ₃ can be performed according to the change in boiler load.

[Action]

Sulfur oxides generated by the combustion of coal are desulfurizing agents sprayed into the furnace, that is, salts, oxides, and hydroxides of metals such as calcium, sodium, and magnesium, and specifically, limestone, dolomite, slaked lime, and the like. And desulfurized. When these desulfurizing agents are sprayed into the furnace of a boiler, the following decarboxylation reaction and desulfurization reaction occur in parallel.

 In limestone, the following thermal decomposition reaction occurs.

CaCO ₃ → CaO + CO ₂ (1) For dolomite (CaCO ₃ .MgCO ₃ ), (2) ~
A thermal decomposition reaction occurs as shown in equation (4).

CaCO ₃ . MgCO ₃ → CaCO ₃ .MgO + CO ₂ (2) CaCO ₃ .MgO → CaO.MgO + CO ₂ (3) MgCO ₃ → MgO + CO ₂ (4) Similarly, slaked lime, magnesium hydroxide, and caustic soda undergo a thermal decomposition reaction, which causes a desulfurization reaction. Produces active CaO, MgO, Na ₂ O.

Next, CaO, MgO, Na ₂ O is primarily reacts as follows SO _2, O ₂ in the combustion exhaust gas in the boiler furnace.

^{_{CaO + SO 2 + 1/2}} O 2 → CaSO 4 (5) Na 2 O + SO 2 + 1/2 O 2 → Na 2 SO 4 (6) MgO + SO 2 + 1/2 O 2 → MgSO 4 (7) unreacted CaO, etc. Is accompanied by coal ash and flue gas, and a desulfurization reaction occurs in the flue. The desulfurization reaction at this time is shown by equation (8).

CaO + to _{H 2 O + SO 2 → CaSO} 3 + H 2 O (8) already (8) formation reaction of CaSO ₃ of formula is found that a large effect of moisture in the combustion exhaust gas. Moreover, the O ₂ in the flue contained in the combustion exhaust gas, CaSO
₃ is partially oxidized to CaSO ₄ , but the proportion is small.

It has been clarified that the firing temperature of limestone is important for enhancing the reaction of the formula (8), that is, the desulfurization reaction.

In order to increase the desulfurization reaction of quicklime in the flue, the firing temperature of the limestone sprayed into the boiler furnace is important, but when the boiler furnace is used as a quicklime reactor for limestone, the limestone is sprayed into the furnace and burned. The time that can accompany and stay with the exhaust gas varies slightly depending on the type of boiler, but is as short as 1 to 3 seconds. During this residence time, the quicklime reaction of limestone and partial desulfurization are performed.

The firing temperature at which the decarboxylation of limestone actively proceeds is about
600 ° C to about 900 ° C. Examining the limestone firing temperature and the activity related to the desulfurization reaction in the flue, the highest and most effective temperature is around 900 ° C where the quick calcification reaction is completed.

In order to obtain quicklime in the boiler furnace under the optimum firing conditions for limestone, the residence time was short, and the necessity of spraying limestone into a temperature zone of a high-temperature atmosphere to cause quicklime reaction was met.

In the present invention, in order to enhance the desulfurization reaction in the flue, before spraying the limestone into the boiler furnace, the limestone is preliminarily calcined at the optimal calcination condition temperature in a considerable ratio in the calcination step, and The temperature range sprayed into the furnace indicates at least the optimum temperature for the quick calcification of limestone
It is characterized by having a temperature atmosphere of 900 ° C.

FIG. 2 shows the results of examining the firing temperature of limestone and the water adsorption rate. The water adsorption rate is highest when the limestone firing temperature is around 900 ° C (the completion temperature of the limestone quick calcification reaction). Below that temperature, it is low because the quick lime reaction is insufficient, and above that temperature, the lime is gradually reduced. It can be said that melting begins and the pore volume decreases due to a decrease in pore volume.

Furthermore, different for lime of calcination temperature of limestone, the result of obtaining SO ₂ adsorption amount in the combustion exhaust gas conditions flue third
Shown in the figure. The SO ₂ adsorption amount of lime having different limestone firing temperatures has a close relationship with the moisture adsorption amount shown in FIG. 2, and it is apparent that the limestone firing temperature can be highest near 900 ° C.

From the above, to increase the desulfurization performance in the flue, that is, in the combined desulfurization method in the boiler furnace and in the flue, firing the limestone at a very high firing temperature is disadvantageous in terms of increasing the overall desulfurization performance. .

However, conventionally, in order to complete the quick calcification reaction of limestone within a short residence time in a boiler furnace, it was necessary to spray the limestone into a high-temperature atmosphere.

In the present invention, in the desulfurization method combining desulfurization in a boiler furnace and flue gas desulfurization, in order to enhance the desulfurization reaction in the flue,
The desulfurization performance can be enhanced by spraying into a boiler furnace having a temperature atmosphere of at least 1000 ° C. after a considerable portion of the quick lime reaction has been promoted in the limestone pre-firing step.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

Example 1 FIG. 1 is a process chart showing an example of the desulfurization method of the present invention.
In FIG. 1, pulverized coal 2 and air 3 are supplied to a boiler 1. In the furnace desulfurization method of the present invention, the desulfurizing agent 7 is
The crushed desulfurizing agent 9 is supplied to the calcination furnace 10 and calcined. The lime 11 is guided to the classifier 12 by the carrier fluid 14, and the desulfurizing agent 13 having a predetermined particle size or less is sprayed to the boiler 1, and the limestone Is completed to the quicklime, and the above-mentioned formula (5),
A desulfurization reaction as shown in equations (6) and (7) occurs. The above process is the desulfurization process in the boiler furnace.

Unreacted CaO from the boiler furnace accompanies the coal ash and flue gas and is directed to the flue from streams 15 to 22, where flue desulfurization takes place.

CaO accompanying the flue gas from the boiler 1 undergoes the desulfurization reaction of the formula (8) while adsorbing moisture in the flue gas. It is effective to supply water to the flue line to regulate the moisture concentration in the flue.

The flue gas 15 is subjected to gas-phase reduction and desulfurization of ammonia gas 17 and nitrogen oxides supplied to a flue in a desulfurization device 16. The flue gas 18 is then led to an air preheater 19,
The air supplied to the boiler 1 is heated. In the desulfurizing agent supply system, a part 14 of the heated air is used for conveying the desulfurizing agent.

Further, a part of the solid matter mainly composed of coal ash 25 collected by the electrostatic precipitator 21 is supplied from the crusher 8 of the desulfurizing agent supply system to the line of the classifier 12 to increase the classification of the desulfurizing agent. In addition, unreacted CaO or Ca (OH) _{2 in} coal ash can be reused. Further, it is effective to add a dispersing agent to the fine-particle desulfurizing agent from the pulverizer when pre-baking is smoothly performed. Addition of sodium stearate, calcium stearate, or the like as a dispersant is more effective for dispersion. Fine particles of the calcined quicklime are sprayed into a boiler furnace by gravity classification or the like. The weight ratio between the particles of advanced quick calcification and the particles of unreacted limestone is 56: 100, and the unreacted limestone 27 having a large particle diameter is effectively returned to the crusher 8, re-crushed, and used. .

As the mechanical disperser, a method in which the desulfurizing agent particles are conveyed to air and made to collide at a high speed, or a method in which ultrasonic waves are irradiated on a conveying line is also effective.

Example 2 FIG. 4 is a schematic sectional view showing the application of the desulfurization method of the present invention to a 50 kg / h hard pulverized coal combustion furnace. In FIG. 4, a combustion furnace main body 100 is provided with a pulverized coal burner 101 at an upper portion, and further, a limestone spray nozzle 104 is provided at a central portion of the combustion furnace 100. The experiment is a comparative experiment in which a mixture of quicklime and limestone obtained by calcining limestone at 900 ° C. for about 30 minutes was sprayed into a combustion furnace.

In the pulverized coal combustion shown in Fig. 4, the sulfur content of less than 200 mesh
Using coal 102 containing 0.95%, air 103
Supplied with A portion of the flue gas was sampled from the flue gas sample seat 105, and the sulfur dioxide concentration was continuously measured by infrared absorption spectrum. Before the addition of the desulfurizing agent, the sulfurous acid gas concentration in the combustion exhaust gas was 810 to 825 ppm, and the desulfurization rate was determined from the sulfurous acid gas concentrations before and after the supply of the desulfurizing agent.

In FIG. 5, the number of moles of limestone supplied to the number of moles of sulfur supplied on the horizontal axis is shown by Ca / S. A is limestone preliminarily calcined at 900 ° C for 30 minutes to produce quicklime. Compared to limestone B without the process, Ca / S = 2 in desulfurization rate.
Thus, the effect of the present invention was confirmed by 8 to 10%.

Example 3 FIG. 6 is a cross-sectional view of an experimental device simulating the flue gas desulfurization. In FIG. 6, the reaction tube 201 has an inner diameter of 60 mmφ × length of 2.5 mm.
m was heated by an electric furnace 202 to control the temperature to 150 ° C. As the simulated flue gas 204 from the upper portion 203 of the reaction tube 201, SO ₂ 1
A gas preheated to 150 ° C. adjusted to 000 ppm, 200 ppm of NO, 10% of CO _2, 10% of H ₂ O, 6% of O ₂ and the remaining N ₂ was passed. The desulfurizing agent was sprayed from the nozzle 206 and brought into contact with the combustion exhaust gas in parallel. And SO ₂ concentrations in the inlet simulated combustion exhaust gas into the reaction tube,
The SO ₂ concentration in the flue gas after desulfurization at the outlet of the reaction tube was continuously sampled from 205 and 207, respectively, and measured by an infrared absorption monitor to evaluate the desulfurization rate.

FIG. 7 shows the relationship between the amount of desulfurizing agent sprayed from the upper part of the reaction tube and the desulfurization rate. (A) in the figure is a limestone fired at 1200 ° C.
(B) shows the test results using CaO obtained by calcining limestone at 900 ° C. for 30 minutes using CaO produced by calcining for 30 minutes and changing the supply amount. (C) shows the test results when the moisture concentration in the simulated combustion exhaust gas was increased from 10% to 15% using the CaO of (B). CaO obtained by calcining limestone at 900 ° C can increase the desulfurization rate more than CaO obtained by calcining limestone at 1200 ° C. In addition, the higher the water concentration in the exhaust gas, the higher the desulfurization rate can be. From the above results, the effect of calcining limestone before spraying into the boiler furnace according to the present invention is clear.

In a thermal power boiler, operation is performed with a daily load change of 25 to 100%. For this reason, in order to perform optimal operation with a constant desulfurization performance according to the load amount, it is necessary to change the spray amount of the desulfurizing agent to the boiler, the spray position, and the like.
By detecting the SO ₂ concentration at the outlet of the electrostatic precipitator and changing and controlling the firing conditions and the supply amount of the carrier fluid, it is possible to follow the boiler load.

Further, by adjusting the firing conditions and the amount of the transported fluid, CaO / CaCO ₃ at the outlet of the firing device can be controlled, and the operation following the change in boiler load can be performed. The carrier fluid is heated air, combustion exhaust gas,
Steam or the like can be used, and the quick calcification ratio can be adjusted by adjusting the temperature of the carrier fluid. Spraying a concentrated CaO particle fluid into a boiler furnace using gravity classification by a gas-solid contact device such as a spouted bed or fluidized bed can improve desulfurization performance in the furnace. It is valid.

CaO that accompanies the flue gas in the flue adsorbs water vapor in the flue gas at about 200 ° C. or lower, and the desulfurization reaction proceeds using the water vapor as a sulfurous acid gas adsorption site. Therefore, desulfurization performance can be enhanced by forcibly spraying steam or water into the flue. In order to increase the water vapor concentration in the combustion exhaust gas, it is effective to use water vapor as the carrier fluid in the firing step in order to enhance the desulfurization reaction in the flue.

In the flue, CaO adsorbs water and a desulfurization reaction occurs simultaneously with the slaked lime reaction. Sulfurous gas is fixed as calcium sulfite and desulfurization occurs. Further, since about 6% of oxygen gas is contained in the combustion exhaust gas, part of the calcium sulfite becomes gypsum and is collected together with the coal ash by the electric dust collector. Since unreacted slaked lime and quick lime are contained in coal ash, by returning a part of the coal ash to the limestone firing step, the effective rate of limestone can be increased, and the particle dispersion effect of the firing step can be increased. . Sodium stearate, calcium stearate, etc. are effective as the particle dispersing agent in the firing step, and the decomposition temperature is lower than that of limestone, etc., and it does not hinder the desulfurization in the boiler furnace or the flue. Can be smoothly fired.

〔The invention's effect〕

According to the present invention, as a flue gas desulfurization method for a power generation boiler, in a desulfurization method combining desulfurization in a boiler furnace and desulfurization in a flue, before limestone is sprayed into the boiler furnace, calcination is performed,
Since the quick calcification reaction is advanced, flue gas desulfurization can be performed under the condition where the activity of limestone is the highest, so that the desulfurization performance can be enhanced. In addition, since the reactivity of the desulfurizing agent can be increased, Ca / S can be reduced as compared with the conventional method, the running cost can be reduced, and the desulfurization cost can be effectively reduced. Furthermore, by installing a calcination process for the desulfurizing agent,
By adjusting the baking conditions and the supply amount of the carrier fluid, there is an effect that stable desulfurization performance following a boiler load change or the like can be maintained.

[Brief description of the drawings]

FIG. 1 is a process diagram showing an example of a furnace desulfurization method of the present invention,
FIG. 2 is a graph showing the relationship between the calcination temperature of limestone and the amount of adsorbed moisture, FIG. 3 is a graph showing the change in the amount of adsorbed sulfurous acid gas of quicklime having different calcination temperatures, and FIG. FIG. 5 is a schematic sectional view of an apparatus showing another example of the method.
FIG. 6 is a graph showing the results of a furnace desulfurization test, FIG. 6 is a cross-sectional view of a flue gas desulfurization test device, and FIG. 1 boiler furnace, 2,102 fine coal, 3,103 air, 7 fine desulfurizing agent, 8 crusher, 10 calciner, 12 classifier, 14 carrier gas, 16 …… desulfurization equipment,
19 …… Air preheater, 21… Electric precipitator, 9,11,13 …… Desulfurizer and carrier fluid line, 100… Combustion furnace body, 101…
Pulverized coal burner, 104: Limestone spray nozzle, 201: Reaction tube, 202: Electric furnace, 204: Combustion exhaust gas, 206: Desulfurizer nozzle

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Shigeru Azuhata 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hiroshi Miyadera 4026 Kuji-machi, Hitachi City, Ibaraki Prefecture Hitachi Research, Ltd. In-house (72) Inventor Ichiichi Saito 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratory, Ltd. (72) Inventor Kiyoshi Narato 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture, Hitachi, Ltd. Person: Nishimura, 6-9 Takaracho, Kure City, Hiroshima Prefecture Inside the Kure Factory of Babcock Hitachi Ltd. (56) References JP-A-3-101811 (JP, A) JP-A-60-178288 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) F23C 11/00 F23J 7/00 F23J 15/00 B01D 53/34

Claims (3)

(57) [Claims] 1. A fine powder desulfurizing agent comprising at least one of a salt, an oxide and a hydroxide of a metal selected from calcium, sodium and magnesium is sprayed into a boiler furnace, and is sprayed in the furnace and in the flue. In an in-furnace and flue-gas desulfurization method for performing desulfurization, the desulfurizing agent is calcined to generate CaO, MgO, and Na ₂ O, and the desulfurizing agent containing these oxides is accompanied by a carrier fluid into the furnace. A method for in-furnace and in-flue desulfurization, comprising spraying and changing the supply amount of the desulfurizing agent and the amount of the oxide generated by the preliminary firing according to the boiler load. 2. The desulfurizing agent according to claim 1, wherein
In-furnace and in-flue desulfurization method characterized by using CaCO ₃ and calcining it to generate CaO and changing the supply amount of the desulfurizing agent and the ratio of CaO / CaCO ₃ according to the boiler load . 3. The in-furnace and flue-gas desulfurization method according to claim 1, wherein the steam concentration is increased in the combustion exhaust gas by using steam as the carrier fluid.