JPH07172825A - Production of highly reactive quick lime by hydration-redehydration treatment of quick lime - Google Patents

Abstract

PURPOSE:To obtain highly reactive quick lime by hydrating quick lime and redehydrating the resulting slaked lime by heating. CONSTITUTION:Quick lime obtd. by heating calcium carbonate such as limestone to >=700 deg.C is hydrated by the action of water in an atmosphere at 100-400 deg.C to obtain slaked lime. This slaked lime is redehydrated by heating to 450-900 deg.C to produce the objective highly reactive quick lime.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing highly reactive quicklime having a stable capacity, which is used as a quicklime-based reactive adsorbent or the like.

[0002]

2. Description of the Related Art Conventionally, in order to obtain quick-reacting lime by firing limestone, it has been necessary to carry out a decarboxylation reaction of calcium carbonate at a temperature as low as possible.

Decarbonation temperature (decomposition temperature) of calcium carbonate
Changes with CO ₂ partial pressure. Decarboxylation reaction is about 60 at 0 partial pressure
Although it starts at 0 ° C, a temperature of about 900 ° C is required to normally calcine limestone under atmospheric pressure. In industrial production, a higher firing temperature is used because of the productivity.

Crystals of quick lime remain after decarboxylation, but when the decomposition temperature is raised, the crystals gradually adhere to each other and grow into large crystals. Therefore, as the firing temperature of limestone is increased, the reactivity of the quicklime obtained is reduced.

In order to calcine limestone at a temperature as low as possible, a "reduced pressure calcining method" in which limestone is calcined in a decompression container is also conceivable. However, as the partial pressure of CO ₂ in the decompression container is further reduced, it becomes necessary to secure the airtightness, resulting in an increase in manufacturing cost.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to produce highly reactive quicklime.

[0007]

Means for Solving the Problems As a result of intensive studies by the present inventors, quick lime obtained by firing under normal conditions is once hydrated to obtain slaked lime, and then this slaked lime is re-dehydrated to obtain quick lime. It was found that highly reactive quick lime can be obtained by

That is, the method for producing highly reactive quicklime of the present invention is characterized in that quicklime is hydrated in an atmosphere of 100 to 400 ° C. and then dehydrated at 450 to 900 ° C.

[0009]

The reactivity of quicklime obtained by calcining calcium carbonate changes depending on the calcining temperature, and the higher the calcining temperature, the worse the reactivity.

When quicklime obtained by firing is hydrated, it becomes slaked lime. When this slaked lime is dehydrated at the decomposition temperature of calcium hydroxide and made into quick lime again, the reactivity is high,
In addition, regardless of the degree of reactivity of the original quicklime with the firing temperature, it is possible to obtain quicklime having a substantially constant reactivity.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Quicklime is obtained, for example, by heating calcium carbonate such as limestone at 700 ° C. or higher.

Since the decarboxylation temperature of limestone is about 600 ° C,
It is virtually impossible to obtain quicklime at temperatures below 700 ° C. There is no particular limitation on the high temperature side, but calcination at 1300 ° C. or higher is meaningless in the case of obtaining quick lime by a normal operation. Further, when the temperature for firing limestone is increased, the reactivity of the obtained quick lime decreases as the firing temperature rises.

Next, quick lime is placed in an atmosphere at 100 to 400 ° C. and hydrated by making water act on it to obtain slaked lime. 1
If the temperature is lower than 00 ° C, water vapor is likely to be condensed and lime cannot be digested cleanly. When the temperature is higher than 400 ° C, a reversible reaction of dehydration of slaked lime occurs. The hydration treatment with water can be performed by spraying quick lime with water or by applying steam.

Further, this slaked lime is added to 450-90 this time.
It is re-dehydrated by heating to 0 ° C, preferably 450 to 600 ° C, and returned to quicklime. At temperatures lower than 450 ° C, dehydration of slaked lime becomes difficult due to the above reversible reaction. When the temperature is higher than 600 ° C., as in the case of a normal decarboxylation reaction, the remaining quicklime crystals raise the decomposition temperature, so that the crystallites gradually adhere to each other and grow into large crystals. for that reason,
As the temperature rises, the reactivity of quicklime obtained becomes worse, and the limit is 900 ° C. Moreover, the temperature exceeding 900 ° C. is also a normal manufacturing temperature. By this re-dehydration treatment, the highly reactive quicklime of the present invention is obtained.

[0015]

The highly reactive quicklime obtained according to the present invention has higher reactivity than the raw quicklime before the hydration / redehydration treatment. Moreover, although the raw material quicklime has a large difference in reactivity (high or low reactivity) depending on the firing conditions,
The highly reactive quicklime after the re-dehydration treatment has a substantially constant high reactivity regardless of which quicklime is used regardless of the firing temperature of the raw quicklime.

[0016]

EXAMPLES In each of the following examples, limestone was heated to a predetermined temperature (7
The raw material quick lime was obtained by firing at 0 to 1200 ° C.) and hydrated and re-dehydrated to obtain high reaction quick lime.

Recalcification was carried out for the raw material quicklime and highly reactive quicklime, and the reaction rate (recarbonation rate) with respect to the reaction time was measured. The results are shown in FIG. 1 (raw material quicklime) and FIG. 2 (highly reactive quicklime). )Pointing out toungue.

The re-carbonation rate is N _{2 at} a constant temperature of 700 ° C.
-CO ₂ mixed gas (CO ₂ concentration: 72.4mmHg) flowed to measure the reaction rate for each reaction time.

From FIG. 1, it can be seen that in calcination of limestone, the reactivity of the quicklime obtained differs depending on the firing temperature, and the higher the firing temperature, the lower the reactivity of quicklime.

It can be seen from FIG. 2 that the reactivity of quicklime is enhanced by the hydration / redehydration treatment. Moreover, in the case of the raw quicklime having a low reactivity, the reactivity is significantly improved, and regardless of the degree of the reactivity based on the firing temperature of the raw quicklime, the quicklime having a constant high reactivity is obtained.

Example 1 Limestone was calcined at 700 ° C. to obtain raw quicklime, and the reactivity of this quicklime was measured and shown in FIG.

Next, this quicklime was sprayed with water at 160 ° C. to hydrate the quicklime to obtain slaked lime.

Thereafter, the slaked lime was further heated at 500 ° C. and re-dehydrated to return to quick lime. The reactivity of highly reactive quicklime after re-dehydration was measured and is shown in FIG.

Examples 2 to 6 The reactivities of raw quicklime and highly reactive quicklime were measured in the same manner as in Example 1 except that the firing temperature of limestone was changed as shown in Table 1 below. In Figure 2,
The results are shown in FIG.

[0025]

[Table 1]

[Brief description of the drawings] [Fig. 1] Quick lime after burning limestone (quick lime raw material)
2 is a graph showing the reactivity of [Fig. 2] Quick lime after hydration and re-dehydration (quickly reactive lime)
It is a graph which shows the reactivity regarding.

 ─────────────────────────────────────────────────── --- Continued from the front page (72) Inventor Hitoki Matsuda 94-3 Ueda Ipponmatsu, Tenpaku-cho, Tenpaku-ku, Nagoya, Aichi Prefecture

Claims (1)

[Claims] 1. A method for producing highly reactive quicklime, which comprises hydrating quicklime in an atmosphere of 100 to 400 ° C. and then re-dehydrating at 450 to 900 ° C.