JP4817333B2 - Desulfurization method using waste concrete - Google Patents

Description

  The present invention relates to a recycling technology for producing a flue gas desulfurization material from a concrete waste material, and a flue gas desulfurization technology using the produced desulfurization material.

2. Description of the Related Art Conventionally, a technique for removing sulfur oxides emitted from coal-fired power plant flue gas has been proposed for the purpose of preventing air pollution caused by sulfur oxides.
Existing desulfurization technologies can be broadly classified into three. That is, a wet desulfurization process, a semi-dry desulfurization process, and a dry desulfurization process.
Among these, the dry desulfurization process is a process of performing desulfurization under a high temperature condition of 800 to 1100 ° C. using a compound such as calcium carbonate (CaCO ₃ ) or calcium oxide (CaO) as a desulfurization agent. The dry desulfurization process has the advantage that it can be easily installed with desulfurization equipment using almost no water. On the other hand, compared to wet and semi-dry desulfurization processes, the sulfur removal rate and the utilization rate of input calcium are low, and the process requires high temperatures.

In recent years, a novel dry desulfurization process using calcium silicate hydrate (C—S—H gel) as a desulfurizing agent has been studied (Non-Patent Documents 1 to 5). In this process, fly ash discharged from a coal combustion facility or the like is coated with calcium hydroxide (Ca (OH) ₂ ) so that silicon in the fly ash reacts with Ca (OH) ₂ to form C- An S—H gel is produced and used as a desulfurizing agent. In this process, it is reported that desulfurization is possible at a low temperature of 57 to 400 ° C., and Ca utilization efficiency in the desulfurization agent is high. However, there are drawbacks in that it takes time to adjust the desulfurizing agent, the price of calcium hydroxide is high, and the desulfurization cost is high.

Here, calcium silicate hydrate is nothing but the main component of cement after hydraulic hardening. The high reactivity between basic cement and sulfur oxides has been pointed out when considering the effect of acid rain on concrete structures. If the cement waste that is currently being used effectively can be directly used as a dry desulfurization material, it is possible to reduce the amount of waste and to build a low-cost desulfurization process.
Several proposals have already been made for using such concrete waste or cement waste as a dry desulfurization agent.

For example, Patent Document 1 discloses concrete in which concrete waste is crushed and sized to 0.59 to 1.19 mm as a solid absorbent that absorbs and removes acidic gases such as sulfur oxides and hydrogen chloride contained in exhaust gas. The use of particles is described.
Patent Document 2 proposes a method for producing a flue gas desulfurization material from a fine powder mortar obtained by crushing concrete as construction waste material. This method regenerates calcium carbonate (CaCO ₃ ) and calcium hydroxide Ca (OH) ₂ contained in the concrete as a flue gas desulfurization material, and was obtained by crushing and regenerating the concrete waste of construction waste. The pulverized mortar is used as a flue gas desulfurization material, and cement paste (mortar) and aggregates such as gravel and crushed stone using the difference in compressive strength between the materials constituting the concrete waste To obtain a fine powder mortar.
According to the method described in Patent Document 2, the mixture of reprocessing materials is composed of medium aggregate made of gravel with a particle size of 15 to 20 mm, small aggregate made of gravel with a particle size of 5 to 15 mm, particle size Are divided into fine aggregates having a particle size of 5 mm or less, and fine aggregates having a particle size of 5 mm or less include fine aggregates made of sand or the like of 0.13 to 5 mm, and mortar components having a particle size of 0.13 mm or less. Separated into fine particles 16.

There are two reasons why calcium silicate hydrate has a high desulfurization ability: high basicity and a large surface area (see Non-Patent Document 6).
In addition, calcium silicate hydrate crystals have a lot of pore water, and it is considered that calcium hydroxide dissolved in the pore water greatly contributes to desulfurization.
Furthermore, according to past studies, the desulfurization effect of compounds such as CaO · SiO ₂ · H ₂ O or 4CaO · Al ₂ O ₃ · 13H ₂ O is particularly high (Non-patent Document 2), in the presence of water or NOx. It has been reported that the desulfurization effect is high (Non-Patent Document 4).
Japanese Utility Model Publication No. 59-184930 Japanese Patent No. 2646938 CSHo and SMShih, 1992, Ind. Ehg. Chem. Res., 31 [4], 1130-1135. JFSanders, TCKeener, and J. Wang, 1995, Ind. Eng. Chem. Res., 34 [1], 302-307. Jung, G.-H., Kim, H., and Kim, S.-G., 2000, Ind. Eng. Chem. Res., 39 [5], 1264-1270. Li, Y., Loh, B., Matsushima, N., Nishioka, and M., Sadakata, M., 2002, Energy & Fuel, 16 [1], 155-160. Renedo, MJ, and Fernandez, J., 2002, Ind. Eng. Chem. Res., 41 [10], 241-2417. Reed.GD, Davis.WT, and Pudelek, RE, 1984, Environ.Sci.Technol. 18,54.

However, the conventional desulfurization material using the concrete waste material has a problem that its desulfurization effect is not yet sufficient as compared with calcium silicate hydrate (C—S—H gel).
This invention is made | formed in view of the above situations, Comprising: It aims at manufacturing a cheap and highly efficient desulfurization material using a concrete waste material, and performing a desulfurization. .

  As a result of intensive studies to achieve the above object, the inventors have extracted the calcium content in the interior of the particle by adding an acid extraction treatment, and covered the particle surface with calcium carbonate, thereby desulfurization reaction rate. And gained knowledge that calcium utilization efficiency can be improved.

The present invention has been completed based on these findings, and is as follows.
(1) A desulfurization material comprising an extraction residue obtained by subjecting a waste cement fine powder obtained from a concrete waste to an extraction treatment with an acid.
(2) was crushed concrete waste to give a waste cement powder, method for producing a desulfurizing material to said Rukoto obtain an extract residue was extracted treated with an acid this resulting waste cement fine powder.
(3) Exhaust gas characterized by removing sulfur oxide from flue gas using desulfurization material consisting of extraction residue obtained by adding extraction treatment with acid to waste cement fine powder obtained from concrete waste Smoke desulfurization method.

  According to the present invention, calcium silicate hydrate, which has high reactivity with sulfur dioxide and is obtained from waste concrete waste, is used to desulfurize at low temperature at low cost with low water consumption. A desulfurizing agent that can be provided can be provided.

Until now, the high reactivity of calcium silicate and sulfur dioxide has been pointed out.
In the present invention, the cement hydrate part obtained from the concrete waste material is refined and further subjected to acid treatment to extract the calcium content in the interior of the particles, thereby improving the desulfurization reaction rate and the calcium utilization rate. is there.
Examples of the acid used for the acid treatment of the present invention include inorganic acids such as carbonic acid, hydrochloric acid, nitric acid, and sulfuric acid, and organic acids such as acetic acid, citric acid, and humic acid, and it is particularly preferable to use carbonic acid. That is, when carbonic acid is used as the acid, the extracted calcium is precipitated as calcium carbonate on the particle surface, and this calcium carbonate also contributes to desulfurization.

  The waste cement fine powder used in the present invention is a fine powder obtained when crushing concrete waste, and has a particle size of 5 mm or less, preferably 1 mm or less, more preferably 0.2 mm or less. .

  In the present invention, the waste cement fine powder is subjected to an extraction treatment with an acid. At this time, the amount of acid is adjusted from the stoichiometric ratio of the reaction so that calcium in the waste cement is extracted to the particle surface. .

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

<Example 1>
(Calcium extraction treatment with carbonic acid)
As a sample, waste cement fine powder (provided by Tateishi Construction Co., Ltd.) discharged when reclaiming aggregate from waste concrete was used.
In the desulfurization test, two types of waste cement fine powder that had not been modified and an extraction residue subjected to calcium extraction treatment with carbonic acid were used. The calcium extraction conditions were: waste cement fine powder / water charge ratio: 0.057, reaction temperature: 30 ° C., carbon dioxide partial pressure: 1.1 MPa, reaction time: 60 minutes. After calcium extraction, the extraction residue was suction filtered with a filter, washed with ion-exchanged water, and then dried.
Table 1 shows the compound composition of each sample measured by a fluorescent X-ray analyzer and a differential thermal balance. The values of CaCO ₃ and Ca (OH) ₂ are theoretical values.

(Desulfurization performance test)
In order to investigate the effect of the waste cement fine powder as a desulfurization material, a desulfurization performance test was performed in the following procedure. FIG. 1 is a diagram showing an apparatus used for a desulfurization test.
When SO ₂ is absorbed and fixed in the waste cement fine powder, some weight change should occur. Therefore, using a differential thermal balance (H60 manufactured by Shimadzu Corporation), add the waste cement fine powder and carbonation treatment. The change over time of the weight of the waste cement fine powder in an SO ₂ atmosphere (gas flow rate 100 mL / min, SO ₂ 1000 ppm, N ₂ balance) was measured to determine the desulfurization rate. A test was also conducted on calcium carbonate powder.
After placing the sample on an alumina top plate and placing the top plate on a thermobalance, the sample was pretreated in a nitrogen gas atmosphere. After no change in weight was observed, the sample was switched to the SO ₂ atmosphere. While the gas supply was started and the temperature was kept constant, the change in the weight of the sample was measured. The non-patent document 4 was referred as the experimental method.
The test results are shown in FIGS.

FIGS. 2 to 4 show the exposure temperature dependence of the time course of the amount of SO ₂ absorbed (wt%) for waste cement fine powder, extraction residue, and CaCO ₃ , respectively.
As shown in FIG. 2, the weight of the waste cement fine powder increased with the exposure time of SO ₂ . This increase in weight is thought to be due to the reaction of calcium silicate hydrate or calcium hydroxide in waste cement with SO ₂ to produce calcium sulfate. It was found that at 30 ° C. and 60 ° C., the reaction rate between the waste cement fine powder and SO ₂ was greatly improved. The reason for this is considered to suggest that the moisture adsorbed on the waste cement and the hydration water of the cement compound greatly contribute to desulfurization. That is, at a temperature of 100 ° C. or higher, the rate at which these water molecules are desorbed from the waste cement increases, so that a large reaction rate may not be obtained.
On the other hand, as shown in FIG. 3, the reaction rate between the extraction residue and SO ₂ decreased from the reaction temperature of 60 ° C. as the temperature increased (due to a decrease in water content), and increased again at a temperature of 700 ° C. or higher ( CaCO ₃ → CaO decomposition reaction). The reaction rate at a high temperature (700 ° C. or higher) exceeded the reaction rate of the waste cement fine powder even though the calcium content was low. This is because calcium contained in the waste cement particles is extracted by extraction of calcium with carbonic acid, and as a result of precipitation as calcium carbonate on the surface of the particles or outside the particles, the reaction with SO ₂ is carried out rapidly. it is conceivable that.

FIG. 5 is a graph showing the exposure temperature dependence of absorbed SO ₂ / Ca content (mol / mol) (5 minutes after the start of exposure).
As is apparent from the figure, the extraction residue exceeded the desulfurization efficiency of the waste cement fine powder and calcium carbonate that were not modified in the high temperature range (700 ° C. or higher). That is, it can be seen that the extraction residue can be applied as a more efficient dry desulfurization material because calcium carbonate exists in the vicinity of the particle surface.

<Example 2>
(Desulfurization experiment of waste cement fine powder treated with hydrochloric acid)
Each sample having a calcium extraction rate of 10% to 100% was obtained by using 0.006 mol / L hydrochloric acid and changing the addition amount of hydrochloric acid. Each sample was obtained in the same manner as in Example 1 by dissolving the waste cement fine powder and stirring for 20 minutes, followed by suction filtration, and separating the filtrate into a solid content. In addition, the calcium extraction rate of the obtained sample was calculated | required by measuring the calcium content rate in a filtrate by ICP.
(Desulfurization experiment)
The solid content of each sample having a Ca extraction rate of 10 to 100% was dried, and a desulfurization experiment was performed in the same manner as in Example 1.
The experimental conditions were as follows.
Gas flow rate: 100 mL / min
Gas composition: SO ₂ 1005ppm, N ₂ balance
Temperature rising process: Room temperature → (20 ° C./min)→Reaction temperature Reaction temperature: 850 ° C.

The experimental results are shown in FIG. FIG. 6 shows the time transition of the weight increase of each sample for the waste cement fine powder before treatment and each sample with a Ca extraction rate of 10% to a Ca extraction rate of 100%.
As can be seen from the figure, the desulfurization performance of the sample after 10% Ca extraction was higher than that of the sample before treatment. This is because calcium contained in fine particles of waste cement powder is extracted by extraction of calcium with hydrochloric acid, and precipitated as calcium hydrochloride on the particle surface or outside of the particle, so that the reaction with SO ₂ is performed quickly. It is thought that it was because of.
In addition, it was found that the desulfurization performance of the sample after 20% Ca extraction was higher in the initial reaction than the sample before the treatment, but after 40 minutes passed, the weight of the sample after extraction increased. It turned out to be a little flat, and it was found to be the same as the desulfurization performance of the untreated sample. However, the desulfurization performance of samples with a calcium extraction rate of 30% or lower was lower than that of the sample before treatment.

  The present invention makes it possible to propose an inexpensive desulfurization plant using waste as a raw material.

Diagram showing desulfurization test equipment It shows the exposure temperature dependence of the temporal transition of the absorbed SO 2 _/ waste cement powder (wt%) It shows the exposure temperature dependence of the temporal transition of the absorbed SO 2 _/ extraction residue (wt%) Shows the exposure temperature dependence of the temporal transition of the absorbed _{SO 2 / CaCO 3 (wt%} ) Shows the absorbed _SO 2 / Ca content (mol / mol) of the exposure temperature dependence (exposure start after 5 minutes) The figure which shows the relationship between the time transition of weight increase and Ca extraction rate

Claims (3)

A desulfurization material comprising an extraction residue obtained by applying an extraction treatment with an acid to waste cement fine powder obtained from concrete waste. Concrete waste and pulverized to obtain a waste cement powder, method for producing a desulfurizing material to said Rukoto obtain an extract residue was extracted treated with an acid this resulting waste cement fine powder. A flue gas desulfurization method characterized by removing sulfur oxides from flue gas using a desulfurization material consisting of an extraction residue obtained by adding extraction treatment with acid to waste cement fine powder obtained from concrete waste .

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