JPH0450879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a post-treatment method and device equipped with a small limestone kiln for converting fresh water obtained by a desalination device into water quality suitable for tap water.

Even if some of the lime in limestone contains dolomite (dolomite), which is replaced by dolomite, the reaction will be exactly the same, so a detailed explanation will be omitted in the present invention.
All portions indicated by Ca include cases where Ca+Mg is present.

Since the fresh water obtained by the desalination equipment contains almost no mineral components, it corrodes the piping materials of the subsequent water supply system and has a poor taste as drinking water. To compensate for these shortcomings,
The method used is to add calcium carbonate or slaked lime and carbon dioxide gas to fresh water to make manufactured water.Generally, a container filled with limestone, a so-called limestone filter, is installed, and the fresh water that has absorbed carbon dioxide gas is passed through it. After passing through, calcium hydrogen carbonate is produced by the following reaction and hardness increases.

CaCO ₃ + H ₂ O + CO ₂ → Ca (HCO ₃ ) ₂ ...(1) This limestone filter is usually filled with readily available and inexpensive limestone with a particle size of 2 to 20 mm, but in many cases the purity is low and contains impurities,
In addition, the dissolution rate is slow, and even if hardness is added, the quality of the water may be poor.This limestone filter has a low throughput of fresh water despite its capacity, and large-scale desalination equipment requires dozens of such filters. Since these filters were to be installed together, equipment costs were high, and limestone had to be added to each filter, and this replenishment work, along with the work of discharging insoluble slime, was quite complicated.

On the other hand, carbon dioxide gas can sometimes be obtained by decomposing and extracting bicarbonate components in seawater in desalination equipment, so it is reasonable to use this gas, but in this case, it may contain impurities such as ammonia, oil, and bromine. This is dangerous, and if hydrazine is used as a deoxidizing agent for the boiler of steam for the bleed ejector, there is a risk that hydrazine or the like will be mixed into the carbon dioxide gas in the bleed gas, which is a problem.

In addition, carbon dioxide gas can be obtained through the process of recovering carbon dioxide gas produced by burning oil or gas using a solvent such as ethanolamine;
Alternatively, it is possible to use purchased liquefied carbon dioxide, but in the former case, the equipment would be of the same type as a large-scale device, which would not only be complicated and require more power for pumps, etc., but also require a large number of equipment and be expensive to construct. Therefore, health problems remain. The latter is impractical as it causes a rise in price (running costs). In other words, in this case, the former is an unreasonable scale-down for the requirement of about number + Nm ³ /H (as CO ₂ ).
In the latter case, the amount consumed is a little too high and there is also the fear of running out of supply.

As mentioned above, the required amount of carbon dioxide gas is number + Nm ³ /
H (as CO ₂ ), and also as limestone.
The handling quantity is only about 100Kg/H, and the small-diameter limestone corresponding to this quantity has to be continuously processed, and the decomposition time is an order of magnitude higher than that for limestone larger than the number + mmφ used in industrial-scale lime furnaces. In short,
Therefore, the retention amount is small, and it is suitable for heating in a special furnace that is orders of magnitude smaller than a general lime furnace.As the concept is completely different from that of conventional lime furnaces, the present invention is a newly developed lime furnace. By organically combining a small-scale limestone decomposition furnace with a desalination device, even in the case of slightly low-grade limestone, a higher purity slaked lime solution or lime milk containing fine particles can be produced, Next, by absorbing carbon dioxide gas generated from the limestone kiln and, if necessary, carbon dioxide gas obtained from other sources, into the liquid, calcium hydrogen carbonate is efficiently produced from the fresh water.

That is, before the above reaction formula (1), a part of it reacts with carbon dioxide gas to produce calcium carbonate through the following reaction Ca(OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O...(2). Since this calcium carbonate is under conditions where it is dissolved at the same time as it is produced, its particle size is extremely small, and at the same time, fresh water and carbon dioxide gas are reacted according to equation (1), and calcium hydrogen carbonate is dissolved in fresh water. This was done for the purpose of being economical, downsizing and continuous equipment, and obtaining stable drinking water that passes water quality standards.

The present invention will now be described with reference to the accompanying drawings.

An internal direct heating limestone calcining furnace 2 is installed close to the installation location of a desalination device, for example, a seawater desalination evaporation device 1, and the distilled water, which is fresh water produced from the evaporator 3, contains only a few ppm of TDS. Since it is not suitable for drinking as it is, it is introduced into a calcium dissolving device 5, which will be described in detail later, through a pipe 4 to impart hardness.

On the other hand, the limestone kiln 2 shown in an enlarged manner is of an internal direct heating type, and the limestone 7 charged into the kiln from the hopper 6 is used for internal heating, for example, by introducing fuel oil from a pipe 8 and burning it. by burner 9
The limestone is directly heated to over 900℃, decomposing it into quicklime and carbon dioxide gas, and the quicklime is cooled in the cooling zone 1 at the bottom of the furnace.
0, it is directly contacted and cooled by the cold air flow introduced from the blower 11 through the pipe 12, and then falls into the quicklime digester 13 in the lower part. The combustion air is preheated by appropriately exchanging heat in the indirect cooler 14 in the upper part of the kiln 2 and the cooling zone 10 in the lower part mentioned above, and then used. Note that the cooling operation for the upper and lower parts can be performed by either direct or indirect contact. The firing furnace is not limited to the method shown in the drawings, but can also be modified from a top-type, Kunii-type, or other suitable method for miniaturization.

A part of the fresh water generated in the desalination device 1 is charged into the quicklime digester 13 via a pipe 15 to produce a slaked lime solution or lime milk, and if there are impurities, a thickener installed in the digester 13 16, impurities are turned into silt and discharged from the lower part 17.
In the quicklime digester 13, when the purity of the quicklime to be charged is high, a long pipe can be used instead of a container.

The slaked lime solution or milk of lime purified in this way passes through a pump 18 and a pipe 19, for example 0.5%
It reaches the calcium dissolving device 5 at a certain concentration and is mixed with the fresh water passing through the branch pipe 20.

In the above description, a portion of the produced fresh water is introduced into the quicklime digester 13, but in some cases, the pipe 20 may be omitted and the entire amount of produced fresh water may be introduced. In this case as well, if the limestone is of high purity and contains almost no impurities, the container 13 may be omitted and a long pipe may be used instead.

The carbon dioxide gas generated by the decomposition of limestone in the limestone kiln 2 has a somewhat inferior purity due to the presence of air in addition to the carbon dioxide in the combustion gas, but it enters the calcium dissolving device 5 through the pipe 21 and becomes fresh water. Even if CaCO 3 is dissolved and the reaction proceeds according to the reaction equations (1, 2) and generates CaCO ₃ , the reaction proceeds in the dissolving device 5 according to the equation (1).
CaCO ₃ , H ₂ O, and CO ₂ react to form Ca(HCO ₃ ) ₂ by dissolution.The particle size of CaCO ₃ is minute and dissolves quickly without any time to grow, giving hardness to fresh water and forming pipes. 22 as treated water.

At this time, since CaCO ₃ has a small particle size as described above, the reaction rate is high, and a large-scale device such as a conventional limestone filter is not required. The hardness required for the fresh water taken out from the pipe 22 after treatment is approximately several ppm in terms of hydrogen carbonate ions,
The production of this level of bicarbonate ions from the approximately 0.5% CaCO ₃ flowing through the pipe 19 is coupled with the fact that the carbon dioxide used is highly pure and easily dissolved, and the reaction time is shortened. It can be made small and the internal mechanism is extremely simple, and although in this embodiment the side baffle plates 23 are protruded to change the flow path, such a configuration can be omitted and the device can be made simple. Also, if CO ₂ is easily removed from other sources,
Of course, if it can be obtained, it may be used.

In the present invention, an internal direct heating limestone calcining furnace is installed near the desalination equipment, and part or all of the generated fresh water is guided to the limestone calcining furnace side and mixed with the generated quicklime to form a slaked lime solution or lime milk. A method for after-treatment of produced fresh water, characterized by imparting hardness to the produced fresh water by mixing and absorbing carbon dioxide gas generated from a limestone kiln, and if necessary, carbon dioxide obtained from other sources, into the produced fresh water. Because of this, it is possible to utilize both the decomposed carbon dioxide gas obtained in a direct heating limestone kiln and the carbon dioxide gas in the combustion gas, and the calcium dissolving device does not require intermittent troubles such as limestone filling and replenishment, unlike conventional limestone filters. Work efficiency can be improved because there is no repetitive work and the work is continuous. In cases where the amount of carbon dioxide from the firing furnace alone is insufficient due to the conditions of the furnace or the type of fuel in the tube 8, the permeated water may contain too much carbon dioxide depending on the type of membrane, such as during desalination by reverse osmosis. When there is no carbon dioxide gas source such as combustion exhaust gas or bleed gas nearby, due to the strong reactivity of Ca(OH) ₂ ,
It is also possible to make up for the shortage by installing an absorption tower to capture several hundred ppm of carbon dioxide gas in the air. Furthermore, if there is sulfur in the fuel, the amount captured as CaSO ₄ etc. can also be an effective source of calcium.

Moreover, since CaCO ₃ having a small particle size is generated by adding carbon dioxide gas, the reaction rate with easily soluble high purity carbon dioxide gas in the subsequent calcium dissolving device increases. Incidentally, since the calcium carbonate fine particles of the present invention have a specific surface area several hundred to tens of thousands of times larger than that of a limestone filter made of limestone, which is about several millimeters in size, the dissolving device can be small and simple in shape, and the passing speed of fresh water can be increased. This has the effect of increasing the processing capacity, and if there is some extra space in the pipe length, it can be made smaller by using a part of it, and it is also possible to use limestone, which has lower purity, as a raw material. Limestone mixed with sand can also be considered as a target; on the other hand, even if the concentration of carbon dioxide gas is low, the generated CaCO ₃ can be converted into a high-grade one, and up to the reaction of equation (2), low concentration carbon dioxide gas, In extreme cases, even the atmosphere can be used, and the carbon dioxide in equation (1) can be self-sufficient, so
In the post-treatment of fresh water, each component is well balanced and there is no waste, and if there is a limestone quarry near the desalination equipment, it can be used effectively even if only low-grade limestone can be mined. It's large.

[Brief explanation of the drawing]

The figure is a flow sheet showing an enlarged part of one embodiment of the present invention. 1...Seawater desalination evaporator, 2...Internal direct heating limestone calcining furnace, 3...Evaporator, 4...Pipe, 5...
...Calcium dissolving device, 6...Hopper, 7...
limestone, 8... tube, 9... burner for internal heating,
10...Cooling zone, 11...Blower, 12...
Pipe, 13...Quicklime digester, 14...Indirect cooler, 15...Pipe, 16...Sickener, 17...
Lower part, 18...Pump, 19...Pipe, 20...Branch pipe, 21...Pipe, 22...Pipe, 23...Baffle plate.

Claims (1)

[Claims] 1. A calcining furnace for internally directly heated limestone or limestone containing magnesium (hereinafter referred to as limestone) is installed near the desalination equipment, and a part of the generated fresh water is guided to the limestone calcining furnace to It is produced by mixing with quicklime to form lime milk or slaked lime solution, and mixing and absorbing this with carbon dioxide gas generated from the limestone kiln, and carbon dioxide gas obtained from other sources if necessary, into the remaining fresh water produced. A method for post-treatment of produced fresh water, characterized by imparting hardness to the fresh water. 2. An internal direct heating limestone calcining furnace is installed near the desalination equipment, and the generated fresh water is guided to the limestone calcining furnace.
It is characterized by imparting hardness to fresh water by mixing with generated quicklime and allowing the mixed solution to mix and absorb carbon dioxide gas generated from the limestone kiln, and if necessary, carbon dioxide obtained from other sources. Method for post-treatment of generated fresh water. 3. A part of the fresh water produced by the desalination equipment is led by piping, etc. to a quicklime digester connected to a thermal decomposition tower having a hopper, a charging valve, and a discharge valve, and is led to a calcium dissolving device by piping, etc. via a pump. is a post-treatment device for freshwater generated by guiding it to a calcium dissolving device through piping, etc. 4. The produced freshwater after-treatment device according to claim 3, wherein the calcium dissolution device is a container with a plurality of baffle plates projecting from the side.