GB2402387A

GB2402387A - Method of producing salt from seawater and a related apparatus

Info

Publication number: GB2402387A
Application number: GB0327603A
Authority: GB
Inventors: Shunzo Tagami
Original assignee: TAGAMI FOOD Manufacturing Co
Current assignee: TAGAMI FOOD Manufacturing Co
Priority date: 2003-06-05
Filing date: 2003-11-27
Publication date: 2004-12-08
Anticipated expiration: 2023-11-27
Also published as: JP2004359510A; GB0327603D0; JP3855238B2; GB2402387B

Abstract

The invention provides for the spreading of salt powder from a spreading nozzle (30) to an outer surface of a heated rotary drum (3) before seawater is blasted form a nozzle (14) onto the outer surface of the heated rotary drum (3) and wherein the spreading of the salt powder is performed at a position immediately preceding a position at which the outer surface of the rotary drum is blasted with seawater and wherein the salt powder assists with the recovery of salt from the sea water.

Description

( 27.lO\1 703 J 1 2402387

METHOD OF PRODUCING SALT FROM SEAWATER

AND A RELATED APPARATUS

The present invention relates to a method of and an apparatus for producing salt of a high quality from seawater using a drying machine ofthe rotary drum type to obtain high productivity.

As a common salt production method of the type mentioned, a method disclosed in Japanese Patent No. 3,077,062 has been proposed by the assignee of the present application. According to the method, a first drying machine of the rotary drum type including a drum body having a double cylinder structure and a second drying machine of the rotary drum type including a drum body having a double cylinder structure similar to said first drum machine are used.

The insides of the first and second drying machines are arranged to communicate with each other. Flame from a burner is blown into a space between the outer cylinder and the inner cylinder of the first drying machine of the rotary drum type to heat the outer cylinder from the inside. Similarly the outer cylinder ofthe second drying machine of the rotary drum type is also heated from the inside. In this state, seawater is blasted at the outer surface of the rotating outer cylinder of the first drum type drying machine so that the water evaporates to concentrate the seawater to obtain salt water. The salt water is recovered and blasted at the outer surface of the rotating outer cylinder of the second drying machine of the rotary drum type so that the water of the salt water evaporates while the salt remains on the outer surface of the outer cylinder. Then, the salt a&Bring to the outer surface of the outer cylinder of the! second drying machine of the rotary drum type is exfoliated and collected. ; The method described ensures a high productivity and a high heat efficiency because the seawater is first concentrated once by the first drying machine of the rotary drum type and then dried to produce baked salt by the second drying machine of the rotary drum type ofthe same structure.

In this instance, however, since the seawater recovered from the first r drying machine of the rotary drum type is in a concentrated state, when baked salt is produced from the seawater by the second drying machine of the rotary drum type, calcium carbonate, calcium sulfate and other substances are isolated and adhere firmly to the outer surface of the drum, that is, to the outer surface of the outer cylinder, as a result of the heat used for heating the outer cylinder of the second drying machine of the rotary drum type. The a&Bring calcium carbonate, calcium sulfate and so forth cannot be exfoliated from the outer surface of the drum, and they form a layer, the thickness of which gradually 3 increases as time passes. Therefore, a problem with this method is that not only is the productivity adversely affected by the layer but also the quality of the common salt produced using the method is also adversely affected.

Further, a seawater intake apparatus for taking in seawater includes a water collector embedded in a seabed filter installation constructed by excavating the seabed. The seawater is filtered at the seabed and collected by the water collector, and is drawn in as clean seawater to an apparatus on the ground through an intake pipe by means of an intake pump.

With the seawater intake apparatus, the seabed filter installation in which the water collector is embedded is constructed by excavating the seabed as described above. Therefore, if ocean currents always flow on the seabed, then the upper face of the seabed filter installation is washed incessantly by the ocean currents and unlikely to be covered with precipitates and like substances.

However, where the flow rate of the ocean currents is low or the amount of precipitates and like substances is relatively high, the upper face of the seabed filter installation is soon covered with precipitates and so forth. Also, such precipitates and so forth can be found to advance into the seabed filter installation. Consequently, the seabed installation is likely to suffer from clogging. Therefore, there is the possibility that the filter action of the seabed filter installation may deteriorate and/or the intake efficiency of the seabed filter installation may deteriorate.

The present invention seeks to provide for a method of producing common salt from seawater, and a related apparatus, having advantages over known such apparatus and methods.

According to an aspect of the present invention, there is provided a method of producing common salt from seawater, comprising the steps of depositing salt powder upon an outer surface of a heated rotary drum and subsequently delivering seawater to the heated outer surface of the rotary drum on which the salt powder has been deposited so that water in the seawater evaporates due to the heated outer surface of the rotary drum while salt remains a&Bring to the outer surface of the rotary drum; and recovering the salt a&Bring to the outer surface of the rotary drum so as to provide for the said salt.

According to another aspect of the present invention, there is provided a common salt production apparatus, comprising a rotatable drum arranged to be heated, means for delivering seawater to an outer surface of the rotary drum so that water in the seawater evaporates due to the heated outer surface of the rotary drum while salt remains a&Bring to the outer surface of the rotary drum, means for recovering the salt a&Bring to the outer surface of the rotary drum and means for depositing powdered salt on the outer surface of the rotary drum before the seawater is delivered thereto, The present invention can therefore advantageously provide a method of and an apparatus for producing common salt from seawater wherein, upon production of baked salt, the adherence of calcium carbonate, calcium sulfate and other substances, which are isolated during the production of baked salt, to the outer surface of a drum, can be prevented.

In the common salt production method and the common salt production apparatus, heating for drying seawater is arranged to be performed in a state wherein the seawater is absorbed in salt powder spread on the outer surface of the rotary drum. Therefore, the sea water does not directly contact with the ! outer surface of the rotary drum. Consequently, a situation where calcium carbonate, calcium sulfate and other substances are isolated and adhere fixedly to the outer surface of the rotary drum are eliminated.

Preferably, the salt powder spreading means is located at a position such that powdered salt is spread on the outer surface of the rotary drum prior to the delivery of seawater to the outer surface of the rotary drum.

Preferably, the salt recovered from the outer surface of the rotary drum is used as the salt powder to be spread. This makes it possible to maintain a uniform quality.

Preferably, the concentrated seawater is used as the seawater to be blasted at the outer surface ofthe rotary drum. However, where seawater is not yet concentrated is used as the seawater to be blasted, adhesion of calcium carbonate, calcium sulfate and some other substances can be prevented.

Preferably, the seawater intake apparatus includes a water collector embedded in a seabed filter installation constructed by excavating the seabed, for filtering and collecting seawater on the seabed, a water intake pump for taking in seawater collected by the water collector and feeding the collected seawater toward the rotary drum through an intake pipe, a seawater tank for reserving the collected seawater, and a cleaning back flow pump for feeding the seawater in the seawater tank back to the water collector through the intake pipe to clean the water collector and the seabed filter installation.

The present invention can further advantageously provide a method of and an apparatus for producing common salt from seawater wherein a seabed filter installation constructed by excavating the seabed can be cleaned readily at any time from a location on the ground so that normally clean seawater can be taken in.

In the seawater intake apparatus, seawater contained in the seawater tank on the ground is fed back to the water collector of the seabed filter installation through the water intake pipe. Consequently, the seabed filter installation constructed by excavating the seabed can be cleaned readily at any time from a location on the ground, and normally clean seawater can be taken in.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic view showing a system configuration of a form of seawater intake apparatus used in a common salt production apparatus to which the present invention is applied; Fig. 2 is a perspective view of a water collector ofthe seawater intake apparatus of Fig. 1; Fig, 3 is a schematic view showing a system configuration of the common salt production apparatus to which the present invention is applied; Fig. 4 is a schematic cross sectional view of a first drying machine of the common salt production apparatus of Fig. 3; Fig. 5 is a schematic cross sectional view of a second drying machine of the common salt production apparatus of Fig. 3; and Fig. 6 is a schematic view showing a system configuration of another common salt production apparatus to which the present invention is applied.

Referring first to Fig. 1, there is shown a seawater intake apparatus used in a common salt production apparatus to which the present invention is applied. A seabed filter installation 51 is constructed on the seabed which includes a hole 52 excavated into the seabed below the level of the seabed BE and having a circular truncated conical cross section. The hole 52 is filled from the bottom to the top with a base layer 53 formed from stones, ballast and so forth, a coarse tertiary filter layer 54 formed from stones, ballast and so forth, a dense secondary filter layer 55 formed from a filter material and a denser primary filter layer (surface layer) 56 formed from a filter material. A water collector 57 is embedded in the tertiary filter layer 54.

Referring now to Fig. 2, the water collector 57 includes a filter 58 disposed there around and forming a cylindrical shape. The water collector 57 is closed at the opposite ends thereof with side plates 59, and an intake (connecting port) 60 is provided on an outer face of one of the side plates 59.

An intake pipe 61 is connected to the intake 60 as shown in Fig. 1 such that seawater in the proximity of the seabed can be filtered and collected as clean seawater by the drawing action of an intake pump located at ground level as described below.

Referring back to Fig. 1, the intake pipe 61 branches into a salt producing intake duct line 61a and a cleaning duct line bib. The salt producing a intake duct line 61a extends to a common salt production apparatus described hereinafter which is provided at ground level downstream of a salt producing water intake pump P1. The cleaning duct line 61b branches into a cleaning water intake duct line 61c and a cleaning back flow duct line did. The cleaning water intake duct line 61c extends to a cleaning seawater tank 62 at ground level via a cleaning water intake pump P2. The cleaning back flow duct line 61d extends from the cleaning seawater tank 62 back to the cleaning duct line 61b via a cleaning back flow pump P3.

In normal operation for water intake into the common salt production apparatus, the cleaning water intake pump P2 and the cleaning back flow pump P3 are rendered inoperative while the salt producing water intake pump P1 is rendered operative to take in water.

When the sea bottom filter installation 51 is to be cleaned, the salt producing water intake pump P1 and the cleaning back flow pump P3 are rendered inoperative while the cleaning water intake pump P2 is rendered operative to take in water so that the seawater is pumped into the cleaning seawater tank 62. Then, the salt producing water intake pump P1 and the cleaning water intake pump P2 are rendered inoperative while the cleaning back flow pump P3 is rendered operative to feed the seawater in the cleaning seawater tank 62 back into the sea bottom filter installation 51 through the intake pipe 61.

Now, the common salt production apparatus installed at ground level is described.

Referring to Fig. 3, a first drying machine 1 of the rotary drum type and a second drying machine 2 of the rotary drum type are installed in a serially juxtaposed relationship with each other.

Each ofthe drying machines 1 and 2 includes a rotary drum (drum body) 3 made of a metal and having a horizontally elongated cylindrical shape. The rotary drum 3 is supported for rotation by bearings 4 at opposite ends thereof.

A chain 8 extends between and around a sprocket wheel 5 provided on an outer periphery of an end portion of the rotary drum 3 and a sprocket wheel 7 on a motor 6 so that the rotary drum 3 is arranged to be driven to rotate in the direction of an arrow mark by the motor 6 by way of the chain 8.

Each rotary drum 3 has a double cylinder structure including an outer cylinder 3a and an inner cylinder 3b as shown in Figs. 4 and 5. The inner cylinder 3b is closed at opposite ends thereof while the outer cylinder 3a is open at the opposite ends thereof. An end of the first drying machine 1 is connected to a heat source 10 by a horn 9 such that a heating medium (water vapor, flame, heated gas or the like) from the heat source 10 may be blown directly into a space between the outer cylinder 3a and the inner cylinder 3b of the rotary drum 3 of the first drying machine 1.

The first drying machine 1 and the second drying machine 2 are connected to each other at intermediate portions ofthe outer cylinders 3a and the inner cylinders 3b thereof by a connecting horn 11. A chimney 12 for exhaustion of gas is connected to the opposite end of the second drying machine 2.

A horizontally elongated seawater atomizing nozzle 13 for blasting seawater in an atomized state is provided at a position opposing to an upper portion of an outer periphery of the rotary drum 3 of the first drying machine 1 such that it extends in parallel to the axial line of the rotary drum 3.

Meanwhile, another horizontally elongated salt water atomizing nozzle 14 for blasting salt water after concentration of the seawater by the first drying machine 1 in an atomized state similarly is provided at a position opposing to an upper portion of an outer periphery ofthe rotary drum 3 ofthe second drying machine 2 such that it extends in parallel to the axial line of the rotary drum 3 of the second drying machine 2. Each ofthe nozzles 13 and 14 has a large number of injection holes formed therein and disposed horizontally.

Further, the second drying machine 2 is provided with a horizontally elongated salt powder spreading nozzle 30 for spreading salt powder to the outer surface of the rotary drum 3 immediately before the salt water after the concentration of the seawater is blasted from the salt water atomizing nozzle 14. In particular, the salt powder spreading nozzle 30 is disposed in the proximity of the salt water atomizing nozzle 14 on the leading or upstream side with respect to the salt water atomizing nozzle 14 in the rotation direction ofthe I rotary drum 3. Further, a horizontally elongated stripper 15 for exfoliating the salt a&Bring to the outer surface of the rotary drum 3 is disposed on the trailing or downstream side with respect to the salt water atomizing nozzle 14 in the rotation direction of the rotary drum 3. Preferably, the stripper 15 is disposed at a location as far as possible in the rotation direction of the rotary drum 3 from the position where nozzle 14 blasts the drum with salt water in order to exfoliate the salt in a state wherein as much water as possible has evaporated.

Seawater taken in by the salt producing water intake pump Pi ofthe seawater intake apparatus shown in Fig. 1 in such a manner as described above is temporarily reserved in a seawater tank 16. Then, after the seawater has been filtered through a filter tank 17, it is fed into the seawater atomizing nozzle 13 of the first drying machine 1 by a water circulating pump 18. In order to automatically adjust the seawater blasting amount by the nozzle 13 in response to the surface temperature of the rotary drum 3 ofthe first drying machine 1, a temperature sensor 19 is disposed on the heating medium blasting side. The water circulating pump 18 (or a solenoid valve) is automatically controlled in response to a signal ofthe temperature sensor 19. A salt water recovery tray 20 is disposed below the first drying machine 1.

In the first drying machine 1, the outer surface of the rotating rotary drum 3 is blasted with seawater in an atomized state from the seawater atomizing nozzle 13. Consequently, the seawater is heated suddenly by the rotary drum 3, whereupon water in the seawater evaporates, leaving concentrated salt water. The concentrated salt water flows down into the salt water recovery tray 20 through a hopper 20a.

The salt water recovered in the salt water recovery tray 20 is fed to the salt water atomizing nozzle 14 of the second drying machine 2 by a water circulating pump 21. In order to automatically adjust the salt water blasting amount by the nozzle 14 in response to the surface temperature ofthe rotary drum 3 of the second drying machine 2, a temperature sensor 22 is disposed on the heated medium blasting side. The water circulating pump 21 (or solenoid valve) is automatically controlled in response to a signal of the temperature sensor 22. A screw conveyor 23 is disposed below the second drying machine 2.

In the second drying machine 2, the outer surface of the rotating rotary drum 3 is blasted with salt water in an atomized state from the salt water atomizing nozzle 14. However, since salt powder is spread on the outer surface of the rotary drum 3 from the salt powder spreading nozzle 30 immediately before the blasting of the salt water, the salt water atomized from the salt water atomizing nozzle 14 is absorbed into the salt powder spread to the outer surface of the rotary drum 3. Thereupon, the salt water is heated suddenly by the metal surface of the rotary drum 3, and consequently, the water in the salt water evaporates to produce baked salt a&Bring to the outer surface of the rotary drum 3. Then, the baked salt is dried on the rotary drum 3 and then exfoliated from the rotary drum 3 by the stripper 15 and drops through a hopper 23a onto the screw conveyor 23. Part of the recovered salt is re-used as the salt powder to be spread from the salt powder spreading nozzle 30 while the majority of the recovered salt is refined as common salt by a refining processing section not shown.

Steam recovery units 24 and 25 for recovering exhausted steam evaporated from the seawater are disposed above the first drying machine 1 and the second drying machine 2, respectively.

In such an installation as described above, the seawater taken in by the seawater intake apparatus and reserved in the seawater tank 16 is filtered by the filter tank 17 and atomized from the nozzle 13 toward the outer surface of the rotating rotary drum 3 of the first drying machine 1 while the flow rate thereof is automatically adjusted in response to the temperature of the first drying machine 1 such that, as the temperature drops, the flow rate decreases, but as the temperature rises, the flow rate increases. A large amount of water from within the atomized seawater evaporates on the rotary drum 3 and is recovered by the steam recovery unit 24 while the seawater is concentrated and flows down into the salt water recovery tray 20.

The salt water concentrated and recovered in the salt water recovery tray is then atomized from the salt water atomizing nozzle 14 toward the outer surface of the rotating rotary drum 3 of the second drying machine 2 while the flow rate thereof is automatically adjusted in response to the temperature of the second drying machine 2. The atomized seawater permeates into salt powder which has been spread upon the outer surface of the rotary drum 3 prior to the application of the salt water, and therefore, separation and adhesion of calcium carbonate, calcium sulfate and some other substances to the outer surface of the rotary drum 3 by sudden heating is prevented. The salt water permeating in the salt powder is heated to a temperature higher than 100 C on the metal surface of the rotary drum 3 together with the salt powder, and consequently, the water in the salt water evaporates while the salt component is changed into baked salt and adheres to the metal surface of the rotary drum 3. The adhering salt dries on the metal surface of the rotary drum 3 and is then exfoliated by the stripper 15. Consequently, the salt drops into the screw conveyor 23 and is then transported to the refinement processing section by the screw conveyor 23.

Meanwhile, exhausted steam is recovered by the steam recovery units 24 and and cooled so that it is recovered as fresh water.

After production of common salt is continued by the common salt production apparatus while the seawater is taken in from the seabed by the seawater intake apparatus of Fig. 1 in such a manner as described, the upper face ofthe seabed filter installation 51 is likely to be covered with precipitates and so forth or such precipitates are likely to enter the seabed filter installation 51 to cause clogging thereby to adversely affect the filtering operation of the seabed filter installation and/or decrease the water intake efficiency from the seabed filter installation. In such an instance, the seabed filter installation 51 is cleaned.

In particular, the salt producing water intake pump PI and the cleaning back flow pump P3 are rendered inoperative and the cleaning water intake pump P2 is rendered operative to pump the sea water into the cleaning seawater tank 62. Then, the salt producing water intake pump Pi and the cleaning water intake pump P2 are rendered inoperative and the cleaning back flow pump P3 is rendered operative to cause the seawater in the cleaning seawater tank 62 to flow back into the seabed filter installation 51 through the intake pipe 61 as described above.

Consequently, the sea water flowing back into the water collector 57 is discharged upwardly into the sea through the filters 58, tertiary filter layer 54, secondary filter layer 55 and primary filter layer 56. As a result, the inside and the upper face ofthe sea bottom filter installation 51 including the water collector 57 are cleaned. Consequently, the clean sea water can thereafter be drawn in as described above.

It is to be noted that, while, in the embodiment described above, the cleaning seawater tank 62 and the salt producing seawater tank 16 are provided separately from each other, they may otherwise be formed commonly as a single tank.

In the common salt production apparatus described above, the two drying machines 1 and 2 of the rotary drum type are used to concentrate the seawater once and then produce baked salt. However, the concentration may otherwise be omitted. Fig. 6 shows a common salt production apparatus having the alternative configuration just described. The common salt production apparatus shown in Fig. 6 is equivalent to the common salt production apparatus of Fig. 3 but from which the first drying machine 1 has been removed.

In particular, in the common salt production apparatus shown in Fig. 6, seawater pumped from the seawater tank 16 is filtered by the filter tank 17 and is then atomized from the nozzle 14 toward the metal surface of the rotating rotary drum 3 while the flow rate thereof is automatically adjusted in response to the temperature of the second drying machine 2 such that, as the temperature drops, the flow rate decreases, but as the temperature rises the flow rate increases. Meanwhile, at the position immediately on the upstream side to the position at which seawater is atomized, salt powder is spread to the metal surface of the rotary drum 3 so that, when the seawater is atomized immediately later, the seawater may permeate into the salt powder. Then, baked salt produced later on the metal surface of the rotary drum 3 as described hereinabove is exfoliated by the stripper 15 and transported to the refining processing section by the screw conveyor 23.

While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the concept ofthe invention as defined in the following claims.

Claims

1. A method of producing salt from seawater, comprising the steps of depositing salt powder upon an outer surface of a heated rotary drum and subsequently delivering seawater to the heated outer surface of the rotary drum on which the salt powder has been deposited so that water in the seawater evaporates due to the heated outer surface of the rotary drum while salt remains adhering to the outer surface of the rotary drum; and recovering the salt adhering to the outer surface of the rotary drum so as to provide for the said salt.

2. A method as claimed in Claim 1 wherein the salt powder is spread to an outer surface of the heated drum.

3. A method as claimed in Claim 1 or 2, wherein the salt powder is deposited upon the outer surface ofthe rotary drum at a position preceding the position at which the seawater is delivered and based on the direction of rotation of the drum.

4. A method as claimed in any one or more ofthe preceding claims, wherein at least part of the said salt powder comprises salt previously recovered from seawater in accordance with the method.

5. A method as claimed in any one or more ofthe preceding claims, wherein concentrated seawater is used as the said seawater to be delivered to the outer surface of said rotary drum.

6. Salt production apparatus, comprising a rotatable drum arranged to be heated, means for delivering seawater to an outer surface of the rotary drum so that water in the seawater evaporates due to the heated outer surface of the rotary drum while salt remains adhering to the outer surface of the rotary drum, means for recovering the salt adhering to the outer surface of the rotary drum, and means for depositing powdered salt on the outer surface of the rotary drum before the seawater is delivered thereto.

7. Salt production apparatus as claimed in Claim 6, wherein the said means for depositing comprises salt spreading means.

8. Salt production apparatus as claimed in Claim 6 or 7, wherein the said means for depositing salt powder is arranged to employ salt previously recovered from the outer surface of said rotary drum.

9. Salt production apparatus as claimed in any one or more of Claims 6, 7 or 8, wherein and including seawater intake apparatus comprising: a water collector disposed in a seabed filter installation for filtering and collecting from in the region of the seabed; a water intake pump for drawing in seawater collected by said water collector and feeding the collected seawater toward said rotary drum through an intake pipe; a seawater tank for receiving the collected seawater; and a cleaning back flow pump for feeding seawater in said seawater tank back to said water collector through said intake pipe so as to clean said water collector and/or seabed filter installation.

9. A method of producing salt from seawater substantially as hereinbefore described with reference to, or as illustrated in Figures 1 to 6 of the accompanying drawings.

10. Salt production apparatus substantially as hereinbefore described with reference to, or as illustrated in Figures 1 to 6 ofthe accompanying drawings.