JPS6038087A - Drinking water making apparatus - Google Patents

Abstract

PURPOSE:To sufficiently perform the dissolution of an alkali stock material into prepared water, by adding an acid to replenished seawater or recirculated brine in an evaporation type seawater desalting apparatus, and adding carbon dioxide generated in an evaporation chamber to prepared water. CONSTITUTION:After the concn. ratio of a multi-stage flash evaporation apparatus is set to 1.8 and the addition amount of sulfuric acid 28 is adjusted by a valve 29, sulfuric acid 28 is added to replenished seawater at the outlet of a degassing tower 6 or recirculated brine at the inlet of a recirculation pump 9. In this case, the addition rate of sulfuric acid is adjusted on the basis or the M- alkalinity of replenished seawater. In order to obtain a carbon dioxide amount 1.86kg-mol/hr required in adding 15ppm of M-alkalinity (on the basis of CaCO3) to prepared water, it is necessary to decompose 53% of total carbonic acid in replenished seawater. By the above mentioned method, the dissolution of an alkali stock material into prepard water can be sufficiently performed and good drinking water is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for converting water produced by an evaporative seawater desalination apparatus into drinking water.

A system for converting produced water into drinking water in a conventional multi-stage 7-run evaporator will be explained with reference to the system diagram shown in FIG.

In the multi-stage flood complete evaporator A, raw seawater is sent to the heat exchanger tube 3 of the heat release section 2 by the seawater supply pump 1, heat is exchanged with the steam generated in the evaporation chamber of the heat release section, and the water vapor is cooled and condensed. The other side is heated. A portion of this heated seawater is supplied as make-up sea water via a make-up sea water pump 4, after which an antifoaming agent 5 is added thereto, and then sent to a degassing tower 6 where gases such as dissolved oxygen are degassed. A scale inhibitor 7 is added to this deaerated seawater, and in the final stage evaporation chamber FL of the heat release section 2, it is mixed with the concentrated brine that has been partially blown with the blowdown pump 8 (blowdown brine) and circulated as circulating brine. The heat is sent to the heat transfer tube 11 of the heat recovery section 10 via the pump 9. Heat recovery section 10
The circulating brine in the heat transfer tubes is heated while cooling and condensing the evaporated water vapor in the evaporation chamber of the heat recovery section 10, and is heated while increasing the temperature through the condenser chambers of each stage to the brine heater 12.
sent to. After the circulation pline is heated to a predetermined temperature by the steam 13 sent from the steam generator in the brine heater 12, it enters the first stage evaporation chamber F1 and is successively sent to the next stage evaporation chamber. Each evaporation chamber is sequentially reduced in pressure by an ejector 14 so that the pressure on the final stage side is lower, and the steam generated in each evaporation chamber contacts the heat transfer tube to exchange heat, and the steam is condensed and sent to each evaporation chamber. The condensed water is collected in a provided condensed water tray 15. Heat recovery section 10 and heat release section 2
The condensed water receivers 15 installed in each evaporation chamber are in communication with each other, and the produced water is sent to the drinking water converting device B by a pump 16.

The prine in the evaporation chamber is transferred to the evaporation chamber of the heat release section 2 through successive evaporation chambers from the first stage to the second stage and the third stage, where it is concentrated and becomes a concentrated pline. The carbon dioxide gas generated in the evaporation chamber is sucked by the ejector 14 as a bleed gas together with the steam that has not been condensed in the heat transfer tube and the leak air from the evaporation chamber.

The alkaline raw material used to add M-alkalinity to the produced water in the drinking water converting apparatus B usually includes slaked lime, limestone, and dolomite, but in the conventional example, dolomite is used.

Dolomite (CaO03 = 74%, MgO = 26
When using the bleed gas 17 containing carbon dioxide at the outlet of the ejector 14 as the carbon dioxide raw material for dissolving %), the bleed gas 17 is pressurized by the compressor 18 and injected into the produced water. In addition, when the carbon dioxide gas raw material is supplied from a carbon dioxide gas generator 19 installed separately, it is injected into the produced water while adjusting the supply amount necessary for reaction and dissolution of M-alkalinity at a predetermined concentration with the valve 20. Mix and dissolve using the line mixer 21. Next, manufactured water 22 in which carbon dioxide gas has been dissolved is poured into a dolomite filter 28 (filled with dolomite having a particle diameter of approximately 5 marks φ or less to a height of 2.0 to 2.5 m).
The carbonated water is reacted with calcium carbonate and magnesium hydroxide to dissolve the M-alkalinity of calcium bicarbonate 0a(HCO2)2 and magnesium bicarbonate Mg-(HCOs)2 in the produced water, and to obtain a predetermined concentration of M-alkalinity. - Producing hard water with added alkalinity.

It is stored in the water storage tank 24. Then, after taking out the hard water from the water storage tank and injecting chlorine gas 01226 at a predetermined concentration,
Sodium hydroxide, NaOH, still sodium carbonate, Na2
00327 and adjusted to the specified pH to make drinking water 25
becomes.

The alkali scale suppression effect of the chemical addition method in a multi-stage 7-ranoshi complete evaporator is that calcium carbonate 0aO03, which is precipitated by heating and concentrating seawater, increases the solubility of magnesium hydroxide Mg(OH)2, and suppresses its precipitation. The main effect is suppression. The bicarbonate ion HOOi and carbonate ion C, which are self-containing carbonate substances, are (1)
, ' Generate carbon dioxide ao2 by the reaction of (2),
Generates carbon dioxide gas in the gas phase along with steam.

↑ 2HCO-3→CO3+C02+H20(1)00%-
+H20→co21+ 20H- (2) If we calculate this carbon dioxide generation as the carbon dioxide generation rate as shown in equation (3) based on the total carbon dioxide (nCo; +cc is also -) contained in the make-up seawater, then the prine maximum It changes depending on the temperature (TMAx) and the concentration ratio of equation (4), and in the operation of a two-stage, usually multi-stage flannel type evaporator.

The characteristics of carbon dioxide generation rate are shown in FIG.

The following water quality is close to standard seawater: Chlorine ion (CI-) = 18000 ppmM-Alkalinity = 120/7 (asoao03) pH
= 8.2 (a is also 25℃) When measuring the total carbonic acid concentration at density = 1.02 (/7), + HOOi + 0
OS-=2.16 mol/rrt. On the other hand, in the case of adding M-alkalinity to manufactured water in drinking water production equipment, the concentration range of M-alkalinity added is usually 15.
(1-150 ppm (ascia003)), and slaked lime 1 limestone and dolomite are used as alkaline raw materials.The reaction between these alkaline raw materials and carbon dioxide gas is as follows.

Slaked lime Oa (OH)2 +2 C! 02 →Oa (H2O
2) 2' (5) Limestone 0aCO3+ 002 ten [20-* Ca (HCO3
)2 ((1) Dolomite (Ca003 = 74%,
MgO = 26%) CaO03+002+ H2O-
+0a(IIO03)2 (7)MgO+ 2002+
H20→Mg (aco3)2(8) Here, as a planning condition for the multi-stage flash evaporator, the amount of make-up seawater =
1500 awakenings/h, concentration ratio = 18°, maximum prine temperature = 9
Set to 0℃ or 112℃.

The amount of water produced and the amount of carbon dioxide gas generated were calculated as shown in the table below. The carbon dioxide generation rate was determined from Figure 2.

Dolomite (Oa) is used as an alkaline raw material in drinking water production equipment.
003 = 74%, Mg0 = 26%), and when adding this produced water G 67 nf / IIK M-alkalinity to 150 ppm (as Ca00a),
The theoretical amount of carbon dioxide gas is as follows.

Oa (II-T, CO3)2+Mg (uco3)2
= 15'Opp (aa 0aO03) = 1.5
mol/r& (as Ca003) However, the density of hard water is assumed to be 1.00.

X 1.5mol/n? X'667n? /bX 10
-” = 0.588kg-mol/hX 1.5m
o l/rr? X 667m/ b X 10-” =
0.984kg-mo I/h However, 100 is CaO
03 and 40 are the molecular weights of MgO.

Oa 003 10 Co2 reaction amount for MgO = 0.
588 kg-mol/h 10.9 F! 4kg-m
o I/h = 1.467 kg mol/h Manufactured water in which carbon dioxide gas was dissolved was passed through a dolomite filter to 1M
-Alkalinity = 150 ppm (asoa003) To dissolve, the amount of carbon dioxide gas is required to be approximately 1.2 times the theoretical amount, so the required amount of carbon dioxide gas is 1.467 kg.
-mol/h x 1.2 = 1.760kg-mo
l/b-. Therefore, the amount of carbon dioxide gas generated in the evaporation chamber is insufficient as follows.

coz deficiency at TMAx90℃ = 1.76 okg-
mol/h-” 1.00kg-mol/h20.76
kg mol/h TMAX] CO2 deficiency at 12°C = 1.760 kg
mol/b-138kg-mol/It=0.481
(g-mol/h) Therefore, in the conventional device, there was a serious problem in that the insufficient amount of carbon dioxide gas had to be replenished from another carbon dioxide gas generating device.

Therefore, the present invention aims at adding M-
The present invention proposes a drinking water desalination device that can completely supplement the carbon dioxide gas required for alkalinity with the carbon dioxide gas generated from the evaporation chamber of the evaporative seawater desalination device. In other words, acid (hydrochloric acid or hydrochloric acid) is added to the make-up seawater of the desalination equipment or to the circulation line (preferably the circulation line at the inlet of the circulation pump), and 1M - Decomposes alkalinity to produce carbonic acid H2CO3.

M'003+ H2so4→MSO4+■2CO3(9
)M(HCi03)2+I(2804→Mtao4
+ 2 H2CO3θQH200310OS-→2)
Ioo, -0υ This carbonic acid reacts with the carbonate ions C' - contained in large quantities in the circulation line in the heat exchanger tube of the pre-recovery section, as shown in the 0υ equation, and changes into bicarbonate ions H,co,,''. When this circulation line enters the evaporation chamber, bicarbonate ions (
1) Carbon dioxide gas is generated by the reaction of formula. In this way, the amount of carbon dioxide gas generated by adding acid is

Since there is a fixed relationship with the amount of acid added, it is possible to control the amount of carbon dioxide gas generated by changing the amount of acid added in the range of the carbon dioxide gas generation rate shown in FIG. 2 or higher.

Hereinafter, one embodiment of the present invention will be described based on the system diagram shown in FIG. 3 (in the figure, the same reference numerals as in FIG. 1 indicate the same items). The concentration ratio of the multi-stage flash evaporator was set to 18.

After adjusting the amount of sulfuric acid 28 added with valve 29.

It is added to the make-up seawater at the outlet of the degassing tower 6 or to the circulation line of the circulation pump 9. In addition, the addition rate of sulfuric acid 28 is 02
As shown in the formula, it can be adjusted based on the M-alkalinity of the make-up seawater.

Xl, 00QJ As a result, the phenomenon shown in FIG. 4 appeared regarding the rate of carbon dioxide gas generation relative to the addition rate of sulfuric acid 28.

M-alkalinity was added to the produced water at 150 ppm (as 0a
O03) Amount of carbon dioxide required to add 1.86 kg-
In order to obtain mol/h, it is necessary to decompose 53% of the total carbonic acid in the supplementary seawater as shown in the second order.

Total carbon dioxide content of make-up seawater = 1500ff? /hX2.16
mol/nf
) is 45% at 90°C and 25% at 112°C.

As described above, the gist of the present invention is to add an acid to make-up seawater or circulating brine in an evaporative seawater desalination apparatus, and to add carbon dioxide gas generated in an evaporation chamber to produced water. By adding an acid, sufficient carbon dioxide gas can be obtained, and by adding this carbon dioxide gas to the produced water, the alkaline raw material can be sufficiently dissolved in the produced water, and good drinking water can be obtained. Therefore, there is no need to replenish the insufficient amount of carbon dioxide gas from another carbon dioxide gas generating device as in the conventional case.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a conventional drinking water conversion device, Fig. 2 is a graph showing the carbon dioxide generation rate with respect to concentration ratio, Fig. 3 is a system diagram of a drinking water conversion device according to the present invention, and Fig. 4 is a sulfuric acid It is a graph showing the generation rate of carbon dioxide gas with respect to the addition rate. 28...Sulfuric acid, 29...Valve, 14...Ejector t17...Bleed gas residue, 18...Compressor.

Claims (1)

[Claims] A drinking water desalination device characterized in that an acid is added to make-up seawater or circulating brine in an evaporative seawater desalination device, and carbon dioxide gas generated in an evaporation chamber is added to produced water.