JPH04310279A - Oxidizing apparatus of sulfite compound-containing ash - Google Patents

Abstract

PURPOSE:To accelerate the reaction speed of an oxidation reaction of calcium sulfite compound-containing ashes with oxygen and carry out the oxidation treatment by a simple apparatus. CONSTITUTION:In a discharged smoke desulfurization apparatus wherein ashes are collected by a dust collecting apparatus 5 after desulfurization of combustion gas is carried out using a desulfurizing agent, the sulfite compound-containing ashes collected by the dust collecting apparatus 5 are put in a reactor 9, a gas mixture consisting of compressed air, oxygen-rich air and nitrogen monoxide-containing high temperature gas (waste gas) from a device 7 is led to the reactor to oxidize the sulfite compound-containing ashes. In the reaction; SO3+1/2H2O+1/2O2 CaSO4.1/2H2O, when high temperature flue gas is used for increasing the gas temperature, oxidizing efficiency is improved owing to NO in the reaction gas and denitrification reaction; CaSO3+1/2H2O+ NO CaSO4.1/2H2O+1/2N2 is also carried out.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to the treatment of ash containing sulfite compounds generated from a flue gas desulfurization device, and in particular, the present invention relates to the treatment of ash containing sulfite compounds generated from a flue gas desulfurization equipment, and in particular, the ash containing sulfite compounds is treated by pressurized air with increased moisture pressure and oxygen-enriched air. It relates to the process of oxidizing ash.

0002

[Prior Art] Sulfur compounds (SOx) are contained in the exhaust gas discharged from heavy oil-fired and coal-fired boilers in thermal power plants.
Acidic toxic substances such as
ppm, and is said to be a causative agent of acid rain and photochemical smog, so effective treatment means are desired. Conventionally, wet methods (e.g. limestone-gypsum method) or dry methods (activated carbon method) have been used, but while the wet method has a high removal rate of harmful substances, it is difficult to treat wastewater and requires reheating of exhaust gas. However, there were problems in that the equipment costs and operating costs were high, and a high removal rate could not be obtained with the dry method. For this reason, it is desired to develop a desulfurization method that can obtain a high removal rate in a low-cost process without waste water. A dry method has been proposed in which acidic harmful substances are removed by directly dispersing limestone in the water, and the dry method is characterized by low equipment and operating costs.

FIG. 8 shows a typical flow sheet of a method in which slaked lime or quicklime is sprayed into exhaust gas to react with SO2 in the exhaust gas, and then removed by a dust collector. The temperature of the exhaust gas from the boiler 1 is lowered by an air heater 3, and then guided to a desulfurization tower 2. A desulfurizing agent such as slaked lime is supplied as a spray into the flue or into the desulfurizing tower 2, and water 4 is also supplied at this time to lower the temperature of the exhaust gas and increase the humidity. At this time, the water 4 may be supplied separately from the desulfurizing agent, or the desulfurizing agent may be supplied simultaneously as a slurry. The reacted desulfurizing agent is collected together with the ash in the exhaust gas by the dust collector 5 and discarded.

[0004] In such a method, the removal rate of acidic harmful substances is said to be dominated by the moisture (relative humidity) in the exhaust gas. That is, in order to increase the removal rate, it is necessary to lower the temperature of the exhaust gas and increase the moisture content. In order to increase the moisture concentration, methods of spraying water or slaked lime slurry have been proposed, but such methods of increasing the moisture concentration in the gas do not sufficiently improve the removal rate. If the removal rate is low, add water or steam to the particles containing unreacted desulfurization agent collected by the dust collector to destroy the shell of reaction products formed on the surface, and then remove some of the particles. A method of improving the removal rate by again spraying into the exhaust gas has also been proposed (for example, U.S. Pat. No. 3,431,289,
JP-A No. 61-35827). In such a semi-dry method, when the desulfurization reaction is completed, ash containing calcium sulfite is generated as waste. Conventionally, this ash has been treated by heat-treating the ash in an oxidizing atmosphere using oxygen to oxidize the calcium sulfite in the ash to calcium sulfate.

[0005]

[Problems to be Solved by the Invention] The method of oxidizing calcium sulfite-containing ash, which is a waste product of the desulfurization reaction, in the semi-dry method described above has a problem in that the reaction rate is slow, the treatment time is long, and the treatment efficiency is low. There was a point. Furthermore, this treatment method requires the installation of a calcium sulfite oxidation treatment device separate from the combustion device, which poses a problem in that the device becomes complicated and expensive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to increase the reaction rate of oxidation reaction of calcium sulfite-containing ash with oxygen and to carry out the oxidation treatment using a simple device.

[0007]

[Means for Solving the Problems] The above objects of the present invention are achieved by the following main configuration. In other words, in a flue gas desulfurization device that desulfurizes combustion exhaust gas with a desulfurizing agent and then collects the ash in a dust collector, pressurized air, oxygen-enriched air, and In an oxidizing device for ash containing sulfite compounds that introduces a mixed gas consisting of high-temperature gas containing nitrogen oxide, or in a flue gas desulfurization device that collects ash in a dust collector after desulfurizing combustion exhaust gas with a desulfurizing agent,
This is an oxidation device for sulfite compound-containing ash that introduces a high-temperature mixed gas consisting of pressurized air and oxygen-enriched air into the sulfite compound-containing ash collected by a dust collector.

[0008] The ash collected by the dust collector is sufficiently humidified with compressed air and then subjected to PSA (Pressure Swing).
The mixture is mixed with oxygen-enriched air using the adsorption method or gas separation membrane, and the temperature inside the reaction vessel is lowered to 1.
It is desirable that the temperature be 00°C or higher. At this time, the water concentration is preferably adjusted to 100 mmHg or higher. Combustion exhaust gas may be used as the nitrogen monoxide-containing mixed gas after being monitored so that the concentration of nitrogen oxides and sulfur oxides in the combustion exhaust gas satisfies the exhaust gas regulation standard values. When a high temperature gas containing nitrogen monoxide is not used as the mixed gas, it can be heated using the heat of combustion exhaust gas.

[0009]

[Action] When the above ash is heated to 100°C or above and the compressed air and oxygen-rich air produced by the compressor are introduced into the reaction vessel, the ash containing calcium sulfite is introduced into the reaction vessel.Since the air is compressed, the pressure of water vapor is high. This results in a state similar to that of spraying water vapor. Therefore, CaSO3+1/2H20+1/2O2→CaSO
It is thought that a reaction of 4.1/2H20 is occurring. At this time, even if high-temperature flue gas is used to raise the gas temperature, the oxidation rate is improved by NO in the reaction gas, and the denitrification reaction expressed by the following equation also occurs. CaSO3+1/2H20+NO→CaSO4・1
/2H20+1/2N2

0010

EXAMPLES The present invention will be explained in more detail by the following examples, but is not limited thereto.

Example 1 The case of desulfurizing exhaust gas from a coal-fired boiler using slaked lime as a desulfurizing agent will be explained using an example to which the present invention is applied.

[0012] In FIG. 1, exhaust gas 6 from a boiler 1 is added with the desulfurizing agent, then its temperature is lowered by an air heater 3, and then led to a desulfurization tower 2. The reacted desulfurizing agent is collected together with the ash in the exhaust gas by the dust collector 5 and discarded.

Using this apparatus, the desulfurization performance was measured when coal A (sulfur content in coal was 1%) was burned. however,
Slaked lime is used as the desulfurization agent, and slaked lime is used to remove S contained in exhaust gas.
It was added in a molar ratio twice that of O2 (hereinafter abbreviated as Ca/S=2). Furthermore, in the desulfurization tower 2, 5% water by weight was added to the slaked lime. The temperature inside the tower at the time of water introduction was 70°C. In addition, the desulfurization agent was sampled just before being supplied to the desulfurization tower 2, and dried in an atmosphere of 110°C until the weight of the desulfurization agent became constant.The water content was measured from the weight loss at that time, and it was 0.5%. Met.

After removing moisture from the gas at the boiler 1 outlet and the dust collector 5 outlet, the SO2 concentration was measured and found to be 820 ppm and 80 ppm, respectively. In other words, 90% of SO2 in the exhaust gas was removed.

After the above reaction is completed, the ash collected from the dust collector 5 contains CaSO3/(CaSO3+CaS
O4)=0.5 of CaSO3 was included. This is transported into the reaction container 9 by a screw feeder 10. Compressed air pressurized by compressor 8 and PSA (Pressur
Compressed air (hereinafter referred to as compressed air) mixed with air (hereinafter referred to as oxygen-enriched air) whose oxygen concentration has been increased to 50% by an oxygen enrichment device 7 using the Swing Adsorption method is introduced from a gas conduit 11. N at about 100℃
Heated by O-containing high temperature gas. This NO-containing high-temperature gas is supplied from the high-temperature flue gas (300° C.) at the inlet of the air heater 3. At this time, although not shown, boiler 1
After monitoring NO gas and SO2 gas concentrations in the combustion exhaust gas to meet exhaust gas standards, the flue gas is introduced into the oxygen enrichment device 7 as a high-temperature NO-containing gas.

In this embodiment, the oxygen enrichment device 7 is provided with a dedicated compressor 8, but the compressor 8 for the reaction vessel 9 and the compressor 8 of the oxygen enrichment device 7 may also be used. Since the boiler 1 uses coal as fuel, a large amount of ash is generated, so a fluidized bed is formed inside the reaction vessel 9 to improve the contact between the gas in the reaction vessel 9 and the ash. However, if the amount of ash generated is small, the same effect can be obtained by using it as a fixed layer and increasing the reaction time slightly. The fluidized state of the fluidized bed in the reaction vessel 9 is controlled by the differential pressure by the opening degree of the valve 12 in the bypass 13.

Since compressed air is used for the mixed gas, the pressure of the water vapor is high and a state similar to that obtained by spraying water vapor can be obtained. However, if it is necessary to replenish the mixed gas with water, Although not shown, after dispersing the sulfite compound-containing ash into the NO-containing exhaust gas in the reaction vessel 9,
Water and/or steam may also be supplied.

In this example, when the relationship between water pressure and oxidation rate ratio was determined under conditions where the temperature was kept constant at 100° C. and the oxygen concentration was 30%, as shown in FIG.
This indicates that the oxidation rate increases if the temperature is 0 mmHg or higher. Also, under certain conditions of temperature 100℃, water pressure 100mmHg, and oxygen concentration 30%, 10kg
The increase in oxidation rate due to pressure changes below /cm2 is not significant as shown in FIG. On the other hand, if the temperature is constant at 100° C. and water pressure is 100 mmHg, the oxidation rate increases as the oxygen concentration increases (FIG. 4). Also, water pressure 100
Under conditions of mmHg and 30% oxygen concentration, the temperature is 1
When the temperature exceeds 00°C, the oxidation rate increases up to 700°C (Figure 5). In addition, the temperature is 100℃ and the water pressure is 100m
When the NO concentration of the high-temperature gas was varied under a constant mHg condition, it was found that the higher the NO concentration, the higher the oxidation rate (Figure 6).

From the above studies, it was found that under the conditions of a reaction temperature of 100° C. or higher and a water pressure of 100 mmHg or higher, the oxygen concentration or N
The oxidation rate of sulfite compounds will increase if the O concentration is increased as much as possible, but in this device, if the oxygen concentration is 15% or more,
It has been found that a sufficient oxidation rate can be achieved when the NO concentration is about 50 ppm or more.

Example 2 In this example, the oxygen enrichment device 7 using the PSA method of Example 1 was used.
The same device as in Example 1 was used, except that oxygen enrichment device 7 was used instead using the porous oxygen enrichment membrane method. The oxygen enrichment membrane is more cost-effective than the PSA method because there is no need to consider moisture removal when the required oxygen concentration is low as in this example in an area with high air humidity. The reaction conditions were a reaction temperature of 100°C and a water pressure of 100mm.
When the Hg and oxygen concentrations were set to 30% and the results were compared with those of Example 1, they almost matched.

Example 3 In this example, as shown in FIG. 7, the combustion exhaust gas of Example 1 was not used, but instead pressurized air and oxygen-enriched air were mixed and heated and introduced into the reaction vessel 9. It is something. That is, a mixture of pressurized air from the air compressor 8 and oxidation-enriched air from the oxygen enrichment device 7 is heated by the air heater 3 and introduced into the reaction vessel 9 to which calcium sulfite-containing ash is supplied. Although this method did not require a system such as a NO gas concentration monitor after oxidation treatment and was advantageous in terms of cost, the oxidation rate was slightly lower (0.95 times) than in Example 1. The effects of oxygen concentration, water pressure, and temperature on the oxidation rate were the same as in Example 1.

[0022]

Effects of the Invention According to the present invention, oxidation of sulfite compounds conventionally required long-term treatment using equipment such as a rotary kiln, but by increasing oxygen concentration and water pressure, oxidation of sulfite compounds can be done in a short time and by increasing the water pressure. Oxidation of sulfite compounds can be achieved at low cost. In this manner, the present invention can rapidly oxidize ash containing sulfite compounds generated from a combustion exhaust gas desulfurization device using a simple device.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of a desulfurization apparatus and a schematic diagram of an oxidation treatment apparatus according to Example 1 of the present invention.

FIG. 2 is a graph of experimental results showing the influence of water pressure on the oxidation rate ratio in the apparatus of Example 1.

FIG. 3 is a graph of experimental results showing the effect of total pressure on the oxidation rate ratio in the apparatus of Example 1.

FIG. 4 is a graph of experimental results showing the influence of O2 concentration on the oxidation rate ratio in the apparatus of Example 1.

FIG. 5 is a graph of experimental results showing the influence of reaction temperature on the oxidation rate ratio in the apparatus of Example 1.

FIG. 6 is a graph of experimental results showing the influence of NO concentration on the oxidation rate ratio in the apparatus of Example 1.

FIG. 7 is a flow sheet of a desulfurization apparatus and a schematic diagram of an oxidation treatment apparatus according to another embodiment of the present invention.

FIG. 8 is a flow sheet of a general desulfurization equipment.

[Explanation of symbols]

1 Boiler 2 Desulfurization tower 3 Air heater 4 Water 5 Dust collector 6 Exhaust gas 7 Oxygen enrichment device 8 Air compressor 9 Reaction container 10 Screw feeder 11 Gas pipe

Claims (6)

[Claims] [Claim 1] In a flue gas desulfurization device that desulfurizes combustion exhaust gas with a desulfurization agent and then collects ash in a dust collector, the sulfite compound-containing ash collected in the dust collector, pressurized air, and oxygen-enriched air are used. An oxidizing device for ash containing a sulfite compound, characterized in that the ash is reacted with a high-temperature mixed gas consisting of a nitrogen oxide-containing gas and a nitrogen oxide-containing gas. [Claim 2] A claim characterized in that the combustion exhaust gas is used as the high-temperature nitrogen monoxide-containing gas after monitoring the concentrations of nitrogen oxides and sulfur oxides in the combustion exhaust gas so that they meet exhaust gas regulation standard values. Item 1. The sulfite compound-containing ash oxidizing device according to item 1. [Claim 3] In a flue gas desulfurization device that desulfurizes combustion exhaust gas with a desulfurization agent and then collects ash in a dust collector, the sulfite compound-containing ash collected in the dust collector is enriched with pressurized air and oxygen. An oxidizing device for ash containing sulfite compounds, characterized by introducing a high-temperature mixed gas consisting of air. 4. The method for oxidizing ash containing sulfite compounds according to claim 3, wherein a combustion air preheater provided in a combustion exhaust gas path is used as the heating means for the high temperature gas. 5. The oxidizing device for ash containing sulfite compounds according to claim 1 or 3, wherein the temperature of the mixed gas is set to 100° C. or higher. [Claim 6] The moisture concentration in the mixed gas is 100 mmH.
The sulfite compound-containing ash oxidizing device according to claim 1 or 3, characterized in that the ash oxidation device has an oxidation capacity of at least 100 g.