JPS637112B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention aims to dispose of coal ash, which is a fuel, and limestone, which is a desulfurizing agent, generated during fluidized bed combustion in a fluidized bed, and ash, which is composed of a desulfurized desulfurizing agent, by burying it in seawater. Or a dumping method, specifically, by subjecting the fluidized bed combustion ash to a humidified granulation process to form granular compacts and then curing them in the air at room temperature, the landfill efficiency (Dry-t/m3 ⁾ can be improved. :Fluidized bed combustion ash that improves the amount of fluidized bed combustion ash that can be disposed of per unit volume of ash disposal site, and maintains the PH of immersed seawater in the disposal site at 9.0 or less, which is within the regulated value in the drainage standards. This relates to a processing method. In recent years, in Japan, in order to deal with the international oil supply instability that has been occurring since the oil crisis of the 1970s, the development of oil-alternative energy has become a national issue, and coal energy has been highlighted as one of these. Conventionally, pulverized coal combustion has been the main combustion method when coal is used as fuel, but recently fluidized bed combustion has been attracting attention as a new combustion method. This is a method in which lime, which is a fuel, and limestone, which is a desulfurization agent for in-furnace desulfurization, are input to form a fluidized bed inside the boiler. Compared to the conventional pulverized coal combustion method, the fluidized bed combustion method requires a smaller furnace volume, resulting in a smaller boiler volume.Secondly, there are fewer restrictions regarding the type of combustion lime, and thirdly, the combustion temperature is between 750 and 950℃. It has advantages such as low-temperature combustion and low generation of thermal NOx, and fourthly, a large overall heat transfer coefficient on the surface of the heat transfer water tube. On the other hand, one of the issues related to the practical application of fluidized bed combustion is the problem of ash treatment due to the unique characteristics of fluidized bed combustion ash. Compared to conventional pulverized coal combustion ash, fluidized bed combustion ash has a lower combustion temperature and is unmelted ash, and it also contains a desulfurized desulfurization agent consisting of quicklime (CaO) and type anhydrous ash (CaSO ₄ ). This is the main feature. Traditionally, most of the coal ash generated in Japan has come from pulverized coal combustion, with some of it being reused as cement admixtures and cement raw materials, and the rest being disposed of in landfills or dumped. Therefore, although it is possible that fluidized bed combustion ash can be used effectively as a resource or disposed of in landfills, it is still necessary to establish a unique effective utilization or disposal method that fully takes into account the unique characteristics of fluidized bed combustion ash. This is extremely important for the practical application of bed-fired boilers, and especially for the large-scale treatment of fluidized-bed combustion ash, it is essential to first establish technology that can smoothly carry out landfill or dumping disposal. When disposing of fluidized bed combustion ash in a landfill or dumping, the main problems caused by the unique characteristics of fluidized bed combustion ash are: firstly, the combustion temperature is low and it is unmelted ash, so the shape is non-spherical; The second reason is that unreacted quicklime is present in the desulfurized desulfurization agent, and fluidized bed combustion ash usually contains 5 to 30% by weight of quicklime, and this large amount of alkaline content makes it difficult to dispose of in landfills. The PH level of leftover water from landfilling at disposal sites is rising, and PH countermeasures are required when discharging leftover water into public water bodies. Generally, fluidized bed combustion ash is classified into combustion furnace overflow ash and dust collector-collected ash (cyclone ash, electrostatically collected ash) depending on the generation system. The proportion of combustion ash generated at these generation locations varies greatly depending on the combustion system and operating conditions during fluidized bed combustion, but is roughly as follows. Combustion furnace overflow ash 0-40wt% Cyclone ash 30-60wt% Electrostatic precipitated ash 30-40wt% Of these, combustion furnace overflow ash is usually in the form of lumps of several mm, and the landfill efficiency is 1.4-1.5Dry-t/m3 ^. big. In addition, because the elution rate of alkaline components is low, the pH of immersed seawater in landfills is usually 9.0.
It is as follows. Therefore, the combustion furnace overflow ash can be directly disposed of in a landfill or dumped. On the other hand, the ash collected by dust collectors (cyclone ash, electrostatic precipitated ash) is usually fine particles of several microns to several tens of microns, and is non-spherical in shape because it is unmelted ash, and the landfill efficiency is 0.2 to 0.5 Dry-t. / ^m3 , which is quite small. Incidentally, the landfill efficiency of ordinary pulverized coal combustion ash is approximately
It is 0.8Dry-t/ ^m3 . Note that the landfill efficiency at the time of landfill disposal generally corresponds to the bulk density when no treatment such as compaction, compaction, or vibration is applied. For this reason, the method for measuring landfill efficiency is
This is in accordance with JIS5101, and measurements are taken by filling granular and lumpy materials into a container while allowing them to fall naturally. In other words, the method for measuring landfill efficiency is to hold the bulk measuring device horizontally, attach a funnel to the funnel stand, place a sieve on the funnel, and place the sieve below the funnel.
Stack the receivers correctly on the receiver stand, place one spoonful of the sample on the sieve, and lightly wipe the entire surface of the sieve with a small sieve of slightly different diameter to disperse the sample, then open the funnel. Repeat this operation until the sample is piled up in the receiver. Next, scrape off the peak with a straight-sided spatula, then measure the mass of the contents in the receiver, and use the following formula. It seeks landfill efficiency. Landfill efficiency (Dry-t/m ³ ) = Fluidized bed combustion ash weight / Receiver internal volume In the case of granular or lumpy materials, the granulated fluidized bed combustion ash falls naturally into a measuring cylinder. The weight of the packed fluidized bed combustion ash (however, the amount of ash reduction before granulation treatment) and the apparent volume were measured, and the bulk density (corresponding to landfill efficiency) was calculated using the following formula.
seek. Bulk density (Dry-t/ ^m3 ) = Fluidized bed combustion ash weight/apparent volume Combustion ash with low landfill efficiency significantly shortens the useful life of the landfill site, and when transported to the disposal site. The volumetric efficiency of trucks, etc. will decrease and transportation costs will increase. In addition, since the ash collected by the dust collector is fine, it has a large surface area and has a low settling rate in seawater at disposal sites, etc., and the amount of alkaline components leached from the fluidized bed combustion ash becomes large when it is disposed of in a landfill or dumped. Normally, the pH of immersed seawater is between 9 and 11. The quality of water when immersed seawater is discharged into public waters such as sea areas is regulated to a pH of 5.0 to 9.0 by wastewater standards based on the Water Pollution Control Law, and countermeasures such as neutralization treatment are essential. In addition, when disposing of pulverized coal combustion ash in a landfill, etc., humidification treatment or humidification kneading treatment by adding 20 to 40% water is carried out to prevent dust, and when disposing of fluidized bed combustion ash in a landfill, etc. A similar humidification treatment or humidification kneading treatment can also be considered. However, although fluidized bed combustion humidification treatment or humidification kneading treatment is effective in preventing dust, it is not effective in improving landfill efficiency or suppressing the pH of immersed seawater in landfill sites. In other words, in humidification treatment or humidification kneading treatment with a mixed water content of 10 to 60%, there is almost no difference in landfill efficiency from that of powder, and no effect on the PH of flooded seawater at landfill sites was observed. In fact, the PH may increase. For this reason, for smooth landfill disposal or dumping of dust collector-collected ash (cyclone ash, electrostatic precipitated ash) among fluidized bed combustion ash, it is possible to improve the landfill efficiency of fluidized bed combustion ash with simple operations and at low cost. There is a need for a treatment method that can increase the pH of immersed seawater at landfill sites and other sites and keep it within the regulated values in wastewater standards. In view of the above points, the present invention was made with the aim of improving the landfill efficiency and suppressing the PH of immersed seawater to below the regulatory value, in order to smoothly carry out the landfill disposal or dumping of fluidized bed combustion ash. , Coal ash generated during fluidized bed combustion in a fluidized bed consisting of coal as a fuel and limestone as a desulfurizing agent and fluidized bed combustion ash consisting of a desulfurized desulfurizing agent are collected using a cyclone or an electrostatic precipitator, which is a dust collector. The Ca/S molar ratio in the collected combustion ash is 6.
When the following combustion ash is disposed of in a landfill or dumped in seawater, the amount of mixed water is 20 to 70%, preferably 30 to 60%.
While adding seawater or fresh water to the fluidized bed combustion ash so that the particle size is 2 to 10 mm, preferably 3 to 6 mm.
The present invention provides a method for treating ash generated from a lime-fired fluidized bed boiler, which comprises granulating the ash so that the ash becomes granulated, then curing it in the air at room temperature for 5 to 120 hours, and then disposing of it in a landfill or dumping. be. Hereinafter, the configuration of the present invention will be explained in detail. First, in humidified granulation of fluidized bed combustion ash, the porosity of the granules is reduced due to the compaction effect that occurs during the granulation process, increasing landfill efficiency. In addition, due to the quicklime contained in the desulfurized desulfurization agent in the fluidized bed combustion ash, and the self-condensation property of molded anhydrous slag in the presence of moisture, it has mechanical strength that does not collapse during transportation or handling even immediately after granulation. Express. On the other hand, during the curing period at room temperature after the granulation process, ettringite (3CaO.
Al ₂ O ₃ .3CaSO ₄ .32H ₂ O) is generated, and the strength of the granules further increases. In this way, fluidized bed combustion ash can be made into granules with high landfill efficiency by subjecting it to appropriate granulation treatment due to its unique properties. In addition, curing in the atmosphere after granulation of fluidized bed combustion ash reduces the pH of immersed seawater during landfill disposal.
The low value of 9.0 or less is due to the following phenomenon. (1) The granulation process reduces the surface area in contact with seawater at the disposal site, increases the sedimentation rate in the seawater, and reduces the amount of alkaline components dissolved from the fluidized bed combustion ash. (2) Due to the hydration reaction between the components in the fluidized bed combustion ash and moisture, an ettringite layer is formed on the surface of the fluidized bed combustion ash, and alkaline components such as quicklime are trapped inside. (3) When the granules of fluidized bed combustion ash come into contact with seawater, magnesium chloride present in the seawater reacts with quicklime and/or slaked lime in the fluidized bed combustion ash. A magnesium hydroxide film is formed on the surface, suppressing the elution of alkaline components. The particle size of the granulated material is 2 to 10 mm, preferably 3 to 10 mm.
6mm is appropriate. Although various commercially available granulators can be used as the granulator used for humidified granulation of fluidized bed combustion ash, consideration must be given to formability, equipment costs, running costs, and maintenance. For example, a rolling plate type granulator, a drum type granulator, and a briquette type compression granulator are suitable. As described above, the purpose of the present invention is to improve the landfill efficiency of fluidized bed combustion ash and reduce the pH of immersed seawater to 9.0 or less by curing the fluidized bed combustion ash in the air at room temperature after humidification and granulation. There it is. Next, Examples and Comparative Examples will be described. The constituent components of the fluidized bed combustion ash used in the Examples and Comparative Examples are shown in Table 1. The methods described above were used to measure the landfill efficiency of fluidized bed combustion ash and the landfill efficiency of fluidized bed combustion ash granules. To measure the pH of seawater immersed in fluidized bed combustion ash, 900ml of seawater is poured into a measuring cylinder for 1, and 100g of fluidized bed combustion ash (humidified kneaded product, granulated product) is allowed to fall naturally from the top, and then the PH is measured. We used the following method.

[Table] Examples 1 and 2 Combustion ashes A, B, and C shown in Table 1 were granulated using a rolling dish granulator (dish diameter: 1 m). Table 2 shows the granulation conditions.
It was as shown below. The granulated material had a particle size of 3 to 6 mm, and even when the granulated material was dropped from a height of 2 m onto a concrete floor, it did not break at all.

[Table] Example 1 is the case where combustion ash A in Table 2 is cured in the air at room temperature for 2 days, Example 2 is the case where combustion ash B is cured in the air at room temperature for 2 days, and the landfill efficiency is as shown in Table 3. Ta. Comparative Examples 1 to 3 Combustion ashes A and B shown in Table 1 were subjected to humidification treatment (in this case, the amount of mixed water was 40%), which is carried out on ordinary pulverized coal combustion ashes to prevent dust generation. Comparative Example 1 for combustion ash A, Comparative Example 2 for combustion ash B
And so. Comparative Example 3 was obtained by curing granulated combustion ash C shown in Table 2 in the air at room temperature for 2 days. The landfill efficiency of these items was determined as shown in Table 3. In addition, the pH of seawater before fluidized bed combustion ash is added.
was 8.2-8.3.

[Table] From Table 3, it can be seen that by humidifying and granulating the ash collected by the dust collector among the fluidized bed combustion ash and then curing it in the air at room temperature, the landfill efficiency is significantly improved, and the immersed seawater It can be seen that the PH can be suppressed to within the regulated values in the wastewater standards. As explained above, according to the present invention, it is possible to significantly improve the landfill efficiency when the fluidized bed combustion ash generated during fluidized bed combustion using coal as fuel is disposed of in a sea area or disposed of in a landfill or dumped. At the same time, it is possible to reduce the PH of the immersed seawater to 9.0 or less, which is within the regulated value in the wastewater standards.The present invention is a technology that smoothly implements the landfill or dumping of fluidized bed combustion ash and contributes to the utilization of national land. Extremely useful.

Claims (1)

[Claims] 1 Among coal ash generated during fluidized bed combustion in a fluidized bed consisting of coal as a fuel and limestone as a desulfurizing agent and fluidized bed combustion ash consisting of a desulfurized desulfurizing agent, cyclone and/or electric dust collectors are used. In the combustion ash collected by the dust collector
When combustion ash with a Ca/S molar ratio of 6 or less is landfilled or dumped in seawater, the amount of mixed water is 20 to 70%.
While adding seawater or fresh water to the fluidized bed combustion ash, it is granulated to a particle size of 2 to 10 mm, then cured in the air at room temperature for 5 to 120 hours, and then disposed of in a landfill or dumped. A method for processing ash generated from a coal-fired fluidized bed boiler, the method comprising: disposing of the ash.