JPH0472597B2 - - Google Patents

Description

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

Even if dolomite (dolomite), in which some of the lime in limestone is replaced by magnesia, the reaction is 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, 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 placed, 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 imparted, the quality of the water may be poor, and the amount of freshwater that can be processed by this limestone filter is low relative to its capacity. As a result, equipment costs were high, and limestone had to be added to each filter, and this replenishment work, along with the work of discharging the dissolved 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 the steam for the bleed ejector, there is a risk that hydrazine or the like will be mixed into the extracted carbon dioxide 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 not practical as it would lead to a rise in price (running costs). That is, in this case, the former is an unreasonable scale-down for the requirement of about 3000 ml + Nm ³ /H (as CO ₂ ), and the latter requires a little too much consumption and is accompanied by concerns about running out of supply.

As per the above air, the required amount of carbon dioxide + Nm ³ /H
(as _CO2 ) and as limestone 100
The amount handled is very small, about Kg/H, and the small diameter limestone corresponding to this amount is continuously processed, and the decomposition time is orders of magnitude shorter than that for industrial-scale limestone larger than number + mmφ. The amount of stagnation is also small, and the concept is completely different from that of conventional limestone furnaces, as it is suitable for heating inside pipes such as ceramic pipes, which will be described later.The present invention is based on a newly developed ultra-small limestone decomposition furnace. organically combined with a desalination device to produce a higher purity slaked lime solution or lime milk even in the case of slightly lower grade limestone, and then using lower purity carbon dioxide gas to first produce a higher purity slaked lime solution or lime milk. A slurry of calcium carbonate particles is produced, and the calcium carbonate particles are reacted with generated carbon dioxide gas in fresh water to efficiently produce calcium hydrogen carbonate. That is, before the above reaction formula (1), the following reaction Ca(OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O ...(2) captures even dilute carbon dioxide gas to generate calcium carbonate. This is a method of dissolving calcium bicarbonate in fresh water by reacting calcium carbonate with carbon dioxide gas in fresh water using the formula (1), and is economical, allows for miniaturization and continuous use of equipment, and is stable enough to pass water quality standards. This was done for the purpose of obtaining drinking water. The present invention will now be described with reference to the accompanying drawings.

An external heating limestone decomposition 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, in order to reform it, pipe 4
After that, it is introduced into a calcium dissolving device 5 whose details will be described later, and hardness is imparted as described later.

On the other hand, the limestone decomposition furnace 2 shown in an enlarged manner is of an external heating type. A tube as small as +mm can be used, and the limestone 8, which is about several mm in size, is charged into the furnace from the upper hopper 6 through the charging double valve 7, and is It is heated to 900°C or more through the furnace wall 10 by a heater 9 such as a burner using petroleum as fuel, decomposing quicklime into carbon dioxide gas, and while the quicklime passes through the cooling zone 11 at the bottom of the furnace, After being indirectly cooled by a cooler 13 through which air from 12 flows, it falls through a pipe 15 with a discharge valve 14 into a quicklime digester 16 in the lower part. It goes without saying that a device other than a burner can be used as the heater 9, and it is considered advantageous to use electricity as the heat source, especially when the heater is small. The charging valve 7 and the discharge valve 14 are each provided with a sealing mechanism (not shown) to prevent air from entering, and the pipe 15 is filled with a sealing gas to prevent the generated carbon dioxide from leaking to the outside. Of course, other means may be taken, but it is particularly preferable to use water vapor, which will condense in a later step, for sealing or sweeping without lowering the purity of the carbon dioxide gas. The material for the furnace wall is heat-resistant metal such as Inconel, and ceramics such as SiC,
Use Al ₂ O ₃ and other heat-resistant materials such as pyroceram and cermet.

The fresh water before entering the desalination device 1 and calcium dissolving device 5 is charged into the quicklime digester 16 via a branch pipe 17, and a slaked lime solution or lime milk is produced in the device, and is then processed by a thickener 18 provided inside. Impurities become silt and are discharged from the lower part 19, and purified products are sent to the first stage carbon dioxide absorber 21 through a pipe 20. In the quicklime digester 16, when the purity of the charged quicklime is high, a long pipe can be used instead of a container. First stage carbon dioxide absorption tower 21
The combustion exhaust gas from the burner passes through the outer periphery of the thermal decomposition tower 2', passes through the duct 22, and passes through the pipe 2 in the heat exchanger 23.
After being cooled by heat exchange with the combustion air passing through 4, it is ejected to the bottom 26 through a pipe 25, and the carbon dioxide in the exhaust gas reacts with the slaked lime solution or milk of lime in the vessel to produce CaCO ₃ . do. This CaCO ₃ has a small particle size and is convenient for subsequent transport and reaction. Excess exhaust gas is discharged to the atmosphere through the upper pipe 27. In this way, low-purity carbon dioxide gas can be used for CaCO ₃ production, which is economical.

Note that a circulating water guide cylinder 28 is provided inside the first stage carbon dioxide absorber 21 to allow the reaction to occur smoothly. Since the CaCO ₃ generated here has a small particle size, it becomes a slurry and flows through the pump 29 and the pipe 30.
CaCO ₃ reaches the calcium dissolving device 5 at a concentration of, for example, about 0.5% and is mixed with the fresh water passing therethrough. In addition to the above-mentioned combustion exhaust gas, the first stage carbon dioxide absorber 21 also contains some limestone decomposition gas, carbon dioxide obtained from other sources, such as boiler exhaust gas, seawater desalination equipment exhaust gas, or purity levels in the air. Low carbon dioxide gas may be used alone or in combination.

In the above description, a portion of the produced fresh water is introduced into the quicklime digester 16, but in some cases, the pipe 4 may be omitted and the entire amount of produced fresh water may be introduced. In this case, if the limestone is of good purity and has almost no impurities, container 1
It is also possible to use a long pipe instead of 6.

The carbon dioxide gas generated by the decomposition of limestone inside the thermal decomposition tower 2' of the limestone decomposition furnace 2 maintains high purity.
Calcium enters the dissolving device 5 through the pipe 31 and is dissolved in fresh water, and CaCO ₃ , H ₂ O, and CO ₂ react in the dissolving device 5 to dissolve and generate Ca (HCO ₃ ), which imparts hardness to the fresh water. do. 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 32 after treatment is approximately several ppm in terms of hydrogen carbonate ions, so the production of this level of hydrogen carbonate ions from the approximately 0.5% CaCO ₃ flowing through the pipe 30 is limited to the amount of carbon dioxide gas used. Coupled with the high purity and ease of dissolution, the reaction time is short and the calcium dissolution device 5
It can be made small and the internal mechanism is extremely simple.In short, it only needs to be able to mix and dissolve sufficiently, and the carbon dioxide absorption part that carries out the reaction with a simple tower type or piping as shown in the figure with an appropriate length can be used. 33 is sufficient.

When some of the produced lime can be used for purposes other than the main post-treatment in the vicinity, a portion of the high-purity carbon dioxide generated by heating the limestone can be used instead of the low-purity carbon dioxide. Although it can be used, the amount of heat required to heat the limestone to produce the carbon dioxide gas in this area consumes too much energy, making it impractical unless a small amount of quicklime is always needed at that location.

The present invention installs a desalination device and an externally heated limestone decomposition furnace in the vicinity, organically communicates with each other, and directs a part or all of the produced fresh water to the quicklime produced in the limestone decomposition furnace to turn it into lime milk or slaked lime solution. If there are impurities, they are first separated by sedimentation, and then low-purity carbon dioxide such as externally heated limestone decomposition furnace combustion exhaust gas, some limestone decomposition gas, and carbon dioxide obtained from other sources are absorbed singly or in combination. After that, the high-purity carbon dioxide gas generated from the furnace is further reacted to produce calcium hydrogen carbonate in fresh water, so low-purity carbon dioxide gas in the combustion exhaust gas can be used effectively without being discarded. Unlike conventional limestone filters, the calcium dissolving device does not require intermittent and troublesome work such as filling and replenishing limestone, but can improve work efficiency because it is continuous. When the amount of carbon dioxide from the decomposition furnace alone is insufficient due to the furnace conditions or the type of fuel used in the heater 9, the permeated water may absorb carbon dioxide depending on the type of membrane, such as during desalination by reverse osmosis. When there is not much carbon dioxide in the air, or when there is no carbon dioxide source such as combustion exhaust gas or bleed gas nearby, several hundred ppm of carbon dioxide in the air can be captured by installing an absorption tower due to the strong reactivity of Ca(OH) ₂ . You can also fill in the gaps by doing so. 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 leeway in the pipe length, it can be made smaller by using a part of it, or new additional equipment can be omitted, and it also has the effect of reducing the amount of limestone with inferior purity. It is also possible to operate using small particles as raw material.
Weathered shells mixed with sand are also considered as targets.
On the other hand, even if the concentration of carbon dioxide gas is low,
CaCO ₃ can be converted into a high-grade product, and low-concentration carbon dioxide gas, or even the atmosphere in extreme cases, can be used for the reaction in equation (2), and the carbon dioxide in equation (1) can be self-sufficient. In the post-treatment of freshwater, each component is well balanced and there is no waste, and if there is a limestone quarry near the desalination equipment, even if low-grade limestone cannot be mined, it can be used effectively. is large.

[Brief explanation of drawings]

The figure is a flow sheet showing an enlarged part of one embodiment of the present invention. 1... Desalination equipment, 2... External heating limestone decomposition furnace, 2'... Thermal decomposition tower, 3... Evaporator, 5...
Calcium dissolving device, 6...hopper, 7...double valve for charging, 9...heater, 12...blower,
13...Cooler, 14...Discharge valve, 16...Quicklime digester, 18...Sickener, 21...First stage carbon dioxide absorber, 33...CO ₂ absorption part.

Claims (1)

[Claims] 1. An externally heated limestone or limestone containing magnesium (hereinafter referred to as limestone) decomposition furnace is installed near the desalination equipment, and a part of the produced fresh water is led to the limestone decomposition furnace, and the produced quicklime is This is mixed with lime milk or slaked lime solution, and this is used to absorb limestone decomposition furnace combustion exhaust gas, some limestone decomposition gas, and carbon dioxide gas obtained from other sources, alone or in combination, and this and the limestone decomposition furnace generates. A method for post-processing produced fresh water, characterized in that hardness is imparted by mixing and absorbing high-purity carbon dioxide gas and remaining produced fresh water. 2. An externally heated limestone decomposition furnace is installed near the desalination equipment, and the produced fresh water is guided to the limestone decomposition furnace side and mixed with the produced quicklime to form a slaked lime solution. It is characterized by imparting hardness to the produced fresh water by absorbing gas or carbon dioxide obtained from other sources alone or in combination, and mixing and absorbing high-purity carbon dioxide generated from the limestone decomposition furnace. A method for post-treatment of produced fresh water. 3. A part of the fresh water produced by the desalination equipment is led to a quicklime digester through piping, etc. to make lime milk or slaked lime solution, and then the lime milk or slaked lime solution is led to the first stage carbon dioxide absorber through piping, etc. After reacting with carbon dioxide in the combustion exhaust gas generated in the thermal decomposition tower, carbon dioxide gas generated by thermal decomposition of limestone, etc. in the thermal decomposition tower is further led to the calcium dissolving device through a piping, etc. A produced freshwater after-treatment device configured to mix and dissolve produced freshwater with the remainder of the produced freshwater. 4. The produced fresh water post-treatment device according to claim 3, wherein the desalination device is an evaporator and the produced fresh water is distilled water. 5. The produced fresh water post-treatment device according to claim 3, wherein the desalination device is a reverse osmosis device, and the produced fresh water is permeated water. 6. The produced freshwater after-treatment device according to claim 3, wherein the calcium dissolution device is a carbon dioxide absorption section consisting of a tower type or long piping. 7. The produced freshwater after-treatment device according to claims 3, 4, 5, and 6, wherein the charging valve and the discharge valve have a sealing mechanism.