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10
NEW SUBMARINE DISTILLING SYSTEMS
 
INTRODUCTION
 
As of the date of revision of this text (Jan. 1955) there are a number of new types of submarines in commission or being built. Fresh water requirements, space availability, and other variable conditions have brought about the installation of several different distilling systems on these submarines.

In Section 6A1 mention is made of these new models. In this chapter, a section is devoted to a brief description of each. Some of them have not yet been fully evaluated under actual operating

  conditions, and it is possible that some changes will be made. Therefore, no detailed descriptions are attempted in this discussion.

All of these models except the Soloshell employ the vapor compression principle and all are entirely electric. They differ from the Model X-1 (AAA-1) only in capacity, physical size, and small mechanical and operational details. The Soloshell is a steam evaporator operating on the vacuum principle.

 
A. BADGER MODEL V-1
 
10A1. General information. This is a vapor compression unit of the same rated capacity and similar in size and appearance to the Model X-1 (or AAA-1) but of modified design.

The Model V-1 was designed to operate under a vacuum of approximately 22 inches of Hg. This meant that the boiling temperature of the sea water feed could be lowered, with a resulting lower rate of scale formation and a softer type of scale deposit. The unit could, as a result, be operated for longer periods before cleaning. Also, since the unit is completely sealed of from the atmosphere, the pressure fluctuations when snorkeling should have no affect on the operation of the unit.

Two of these units were installed on each of the SS563 class submarines. Under actual operating conditions they failed to prove entirely satisfactory and some alterations to the original design were necessary.

The following is a brief description of the original installations, a discussion of some of the problems encountered under actual operating conditions and the alterations made to insure satisfactory operation.

10A2. Description. The distilling unit consists of two main parts, the evaporator and the heat exchanger. (See Figure 10-1.) The evaporator has a vertical tube steam chest with a vapor separator above the steam chest for separation of

  liquid particles from the vapor. A 3-lobed vapor compressor, fitted with a bypass valve for starting, is mounted on top of the evaporator. A 12-hp electric motor is mounted on top of the evaporator and drives the compressor.

The heat exchanger, connected to the evaporator by piping, is of the double tube type. Its function is to heat the incoming feed water by absorbing heat from the condensate and the brine overflow. All of these features are similar in construction and location to the Model X-1.

10A3. Distilling cycle. The cycle is started by two horizontally placed electric heaters which heat the distilled water in the bottom of the steam chest. Heat from the distilled water is transferred through the tubes of the steam chest to the feed water inside of the tubes (after the unit is in operation, the feed water is also preheated in the heat exchanger). The vapor from the boiling feed passes through a vapor separator to the vapor compressor, where its pressure (and temperature) is raised.

The compressed steam, still under a vacuum relative to the atmospheric pressure, passes from the compressor to the steam chest where it gives up its latent heat of vaporization to the feed water as the steam condenses.

A distillate trap in the steam chest keeps the level of the distilled water high enough to cover

 
(70)

Figure 10-1. Schematic sketch vapor compression distilling unit Model V1.
Figure 10-1. Schematic sketch vapor compression distilling unit Model V1.
 
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the two heating elements. These two thermostatically controlled heaters supply the additional heat to the distillate necessary to balance the heat losses. The heat from the distillate is transferred to the incoming feed water in the heat exchanger.

10A4. Pumps. In order to maintain a vacuum, a horizontal centrifugal displacement type vacuum pump is used to draw the air and noncondensable gases from the steam chest through a pipe extending into the steam chest. An arrangement of baffles is used to direct the air to this perforated pipe. These noncondensable gases are discharged through the heat exchanger and into the atmosphere.

Since the unit operates on a vacuum, a brine pump is required to pump the brine from the evaporator to the heat exchanger, and a condensate pump is required to remove the distillate and pump it through the heat exchanger.

10A5. Alterations. As previously mentioned, this model did not prove entirely satisfactory as designed. Under actual operating conditions, it was extremely sensitive to the variable conditions encountered. It proved difficult to maintain the vacuum. Considerable trouble was experienced with the compressor seals and when the unit was under a vacuum, it was very difficult to locate and rectify air leaks into the system.

As a result, changes were made to the original installations. Conversion kits were supplied which, after installation, permitted operation of the units under a pressure (similar to the converted Model X-1) instead of a vacuum. This conversion greatly increased the capacity of these units.

In order to accomplish this conversion, several mechanical changes were made:

a. The vacuum pump, no longer necessary, was eliminated.

  b. The vacuum operated compressor was replaced with one designed for pressure operation.

c. A new compressor drive was installed to suit the new pressure conditions.

d. A pressure controlled (pressure-static) switch was provided to replace the temperature controlled (thermostatic) switch for control of the heaters.

e. Vacuum gages were replaced with pressure gages.

f. Changes were made in lines and flowmeters to accommodate the increased capacity obtained by pressure operation. (Before conversion the output of distilled water was 50 to 55 gph; after conversion the condensate rate with a clean unit increased to 75 to 80 gph.)

g. At present the brine and condensate pumps are retained. Since the unit now operates under pressure, they are not needed to remove the liquids from the evaporator, but the brine pump is used to pump the brine overboard, and the condensate pump is used to deliver the fresh water through the heat exchanger to the distillate tank, which is at a higher level than the heat exchanger. A proposed rearrangement, whereby the distillate tank is lowered and the method of brine disposal changed, would render these pumps unnecessary.

h. Operating under pressure, a desuperheating system became necessary. A line equipped with an orifice from the distillate pump to the compressor provides the desuperheating water.

With the described alteration, the methods of operation, control, and maintenance are very nearly the same as those described for the converted Model AAA-1. The increased capacity and other advantages gained by conversion, more than offset the decrease in operating time between cleanings.

 
B. BADGER MODEL WS-1,300 GPD DISTILLER
 
10B1. General description. The Model WS-1 vapor compression distilling unit is similar to the Model X-1 in its principles of operation. It is a small compact unit requiring little space, thus its selection for use aboard the T-Class of submarines. One of these units is installed on each of this class vessel.

The distilling unit consists of three main parts;

  the evaporator, the heat exchanger, and the vapor compressor.

a. The evaporator has a vertical tube type steam chest with a vapor separator space above it for separating liquid particles out of the vapor. A motor-driven water sealed type vapor compressor, fitted with a bypass valve for starting, is mounted in the upper section of the evaporator.

 
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Figure 10-2. SCHEMATIC WS-1 DISTILLING SYSTEM

The lower portion is fitted with a boiler section in which two 2,000-watt electric heaters are mounted horizontally. One of the two heaters is controlled automatically to maintain proper evaporator operating pressures.

These heating elements project into the lower part of the boiler section, which acts as a reservoir for the distillate. With this arrangement, the heaters add heat to the distillate instead of directly to the sea water feed. Same of this added heat is transmitted to the feed water in the upper part of the boiler section through the plating separating the two liquids, and some of the heat is given up to the cool feed water in the heat exchanger.

b. The heat exchanger is the horizontal double tube type, with all features of the heat exchangers used with Model X-1.

c. The vapor compressor is the liquid sealing ring type, installed in the evaporator. Motive power is supplied by a 5-hp motor, with a belt drive, mounted on the evaporator casing.

10B2. Cycle. (See Figure 10-2.) Feed is supplied by a feed pump through the rate-of-flow controller (feed pressure regulator), feed control valve, and feed rotameter to the heat exchanger, where it is preheated by the hot distillate. Feed water leaves the heat exchanger and goes to the evaporator, where it is fed into the central downtake tube. It then picks up heat from the distillate and steam in the steam chest as it rises up through the tubes.

Vapor, from the boiling feed at the top of the steam chest, passes up through the vapor separator where any entrained liquid particles will be separated from the vapor. The compressor takes a suction from the separator and discharges down to the steam chest where the steam, on the outside of the tubes, gives up its latent heat to the incoming feed inside the tubes, as the steam condenses. Every pound of steam that condenses generates a pound of vapor from the feed water for the compressor suction.

The distillate then flows down the distillate return pipe to the boiler section where it is drawn off through the heat exchanger to storage. The condensate discharge line is at such a height as to keep the heaters in the boiler section covered continuously.

  These heaters start the operation of the unit by heating the initial distillate, which in turn, heats the cold sea water feed above it to its filing point and generates the steam to start the vapor compression cycle. During operation, the electric heaters supply additional heat so that a sufficiently high overflow rate can be maintained to retard the formation of scale and balance the heat losses, and so that the proper operating pressure can be maintained in the unit. One of these heaters is controlled, during the operation, by a pressure operated switch to automatically maintain the proper balance.

The hot distillate flows from the boiler section, through the heat exchanger, where it gives up heat to the incoming sea water. It then flows from the heat exchanger to a suitable distillate collecting tank, here it can be tested and transferred to the ship's fresh water stowage tanks.

The brine overflow in the upper section of the steam chest is drawn off through a funnel and brine overflow line and passed through the heat exchanger to the bilge. In the heat exchanger, the brine gives up much of its heat to the sea water feed.

Air and noncondensable gases are directed by a system of baffles to a vent line in the steam chest. These noncondensable gases are passed through the heat exchanger and to atmosphere. The amount of vapor and noncondensable gases vented from the steam chest can be controlled by a needle valve installed in the vent line.

20B3. Operation. The distilling plant is balanced and kept in a stable condition by slight adjustments of the feed rate and by the number of electric heaters used. The unit operates on a very sensitive heat balance and operates best when all conditions remain constant. Balance is indicated by a compound gage which indicates the pressure (or vacuum) of the vapor from the boiling feed.

The temperature of the sea water feed is a determining factor controlling the amount of heat necessary to hold the compound gage reading at the proper pressure. Under most conditions the automatically operated heater will be sufficient to maintain this pressure. However, if the feed water is very warm, the heat supplied by the compressor might be all that is necessary; or if extremely cold, both heaters, on continuously, might

 
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be necessary to maintain the proper operating pressure.

Under the varying conditions usually encountered such as rough seas, snorkeling, etc., the plant is balanced with a compound gage pressure of 6 to 12 inches of water and a feed rate between 24 1/2 gph and 30 gph, depending on the condition of scaling in the unit. As the heating surfaces become scaled, the feed rate should be increased.

During operation, the compressor discharge pressure should be between 2 and 4 pounds. The compressor sealing water valve should be adjusted to keep the discharge pressure at a minimum.

  If operating properly, this unit will produce about 16 gallons of fresh water per hour (rated capacity is 300 gallons per day) from an input of about 25 gallons per hour of sea water. The distillate, made from sea water, will have less than one part per million of salt.

10B4. Cleaning. The system is designed to be cleaned by an acid cleaning method as was described for the Model X-1.

Need for cleaning is indicated by a rise in compressor discharge pressure. When the compressor pressure rises to 5 3/4 pounds the distilling unit must be cleaned.

 
C. CLEAVER-BROOKS, 300-GPD DISTILLER
 
10C1. General information. The Cleaver-Brooks 300-gpd vapor compression distilling unit is a small compact unit, adapted for use aboard the K-Class submarines. One unit of this type is installed on board each boat of this class.

The distilling unit consists of three main sections:

1. Evaporator, consisting of the following:

a. Evaporator-condenser section.

b. Vapor head, containing two steam separators.

c. Bottom head and boiler section, containing the two heaters.

2. Heat exchangers consisting of two heat exchangers connected in series.

3. Vapor compressor with drive.

10C2. Description. (See Figure 10-3.)

1. Evaporator.

a. The evaporator-condenser section of this unit performs the same fluctions as the steam chest in the Model X-1 or Model WS-1. Vaporization of the sea water feed inside of the tubes and condensation of the steam around the outside of the tubes, are the main functions.

b. The vapor head section contains two vapor separators, a centrifugal separator, and a cyclone separator. Circuitous passage through the separator baffles causes the vapor passing through these separators to give up any entrained liquid particles. The vapor head is also fitted with a bypass valve which is used when starting or cleaning.

c. The bottom head and boiler section is bolted to the bottom, of the shell under the evaporator-condenser

  section. The lens-shaped space between the lower tube sheet of the evaporator-condenser section and the bottom head forms a reservoir for the feed water. Below this "feed well" is the boiler, which acts as a reservoir for the distillate. The 2 immersion type heaters project horizontally into the boiler.

2. Heat exchangers.

Two identical heat exchangers of the interlocking coil type, connected in series, serve the same purpose as the straight tube type used in other models. The feed water passes around the coils and the distillate and brine pass through the coils. The feed water is heated and the brine and distillate are cooled in these heat exchangers.

3. Vapor compressor.

The vapor compressor is of the centrifugal blade type driven through belts by a 3-hp electric motor.

10C3. Distilling cycle. The cycle is started by the initial heating of the distillate in the boiler by the two electric heaters. The boiling distillate, and the vapor from it circulating around the tubes of the evaporator-condenser section, heats the feed water inside of the tubes to the boiling point.

This boiling action in the evaporator causes the feed water from the feed well to percolate upward through the tubes, some of it being converted to vapor and the remainder returning to the bottom section through the downtakes. (A trough welded around the upper part of the shell, is connected by 3 channels, or downtakes, to the feed well below the bottom tube sheet.)

During operation, a portion of this boiling sea water feed is continuously discharged as "blowdown"

 
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Figure 10-3. SCHEMATIC CLEAVER BROOKS 300 G.P.D. DVC 1.5 UNIT

(brine) to prevent too high a salt concentration. This brine, or blowdown, is directed through the heat exchangers to recover some of the heat before the brine is discharged as waste. Sea water feed is supplied continuously to the unit to make up for the amount discharged as brine plus the amount converted to vapor.

The sea water supply passes through a pressure reducing valve and a flowmeter (flowrator) on its way to the heat exchangers. In the two heat exchangers, the feed receives heat from the brine and from the distillate flowing (counterflow) away from the evaporator.

The hot feed from the heat exchangers enters the side of the evaporator-condenser section and flows into the bottom section or feed well through one of the three downtakes. In the feed well, the sea water receives more heat from the boiler section directly below it. Then, as it rises through the tubes, the hot feed receives the latent heat from the condensing steam on the outside of the tubes. Part of the feed is vaporized as it rises through the tubes and part of it returns to the feed well. A portion of the boiling feed drains away through the blowdown outlet to the heat exchangers.

The vapor, rising from the boiling feed water passes through the 2 separators in the vapor head and into the compressor suction. Particles of salt water which are removed from the vapor in the separators are collected and drained back to the bottom section.

In the compressor, the pressure of the vapor is raised to about 5 pounds per square inch. This compression also raises the temperature of the steam. The compressed steam from the compressor is forced into the steam chest, where it condenses and gives up its latent heat to the feed water.

  The condensate, or distillate, drains back to the boiler and then through an overflow outlet in the boiler to the heat exchangers where it imparts heat to the cold feed water before being discharged to stowage tanks. The distillate overflow outlet in the boiler insures that the heaters remain immersed. These heaters remain on when the unit is in operation and would burn out unless covered. During operation, vaporization of part of the distillate is continuous. Some of the distillate is used as a water seal for the compressor, a needle valve and a "flowrator" being used to regulate the amount of distillate flowing to the compressor.

10C4. Operation. This unit produces about 15 gallons of distilled water per hour. Approximately 2 gallons of sea water are required to produce 1 gallon of distillate.

The unit should operate continuously for 500 hours before cleaning is necessary.

10C5. Cleaning.

Indications of need for cleaning are:

1. Rise in compressor discharge pressure above the normal 5 psi.

2. Reduction in distillation rate of more than 10 percent.

3. Reduction in quantity of distillate compared to the amount of power consumed.

There are 2 methods of cleaning used; the chemical method, and the mechanical method.

The chemical method of scale removal employs a sodium-acid-sulphate solution. One method is very similar to the one described for acid cleaning the Model AAA-1.

Mechanical cleaning; a drill type tube cleaner is run through each tube separately, if a type of scale has been formed which chemical cleaning cannot remove. The coil type heat exchangers cannot be cleaned by this method.

 
D. VAPOR COMPRESSION DISTILLING UNIT MODEL Y-1
 
10D1. General description. The Model Y-1 vapor compression distilling unit is entirely electric and rated at 1,000 gallons per day of distilled water. It makes 45 to 50 gallons per hour of distilled water, containing less than one part per million of sea salt, from about 70 gallons per hour of normal sea water and has a, constant blowdown (overflow) of 20 to 25 gallons per hour. The   temperature of the distilled water (condensate) will be within 15 degrees F. to 30 degrees F. of the sea water feed temperature. The overflow temperature will be about 30 degrees F. to 40 degrees F. above the feed water temperature.

A distilling unit consists of three parts-the evaporator, the heat exchanger, and the compressor. The evaporator has a vertical tube steam

 
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chest with a vapor space above it fitted with baffles to separate the liquid from the vapor. Three electric heaters are mounted horizontally in the boiler section, and are automatically controlled to maintain the proper evaporator operating pressure. A three-lobe, positive displacement type compressor is mounted on top of the vapor chamber, and its motive power is supplied by a 7 1/2 horsepower electric motor. The heat exchanger is essentially a horizontal double pipe cooler.

Figure 10-4. Vapor compression distilling unit,
Model Y-1.
Figure 10-4. Vapor compression distilling unit, Model Y-1.

10D2. Evaporator. The evaporator (see Figure 10-13) consists of four main parts; the boiler section, the vertical steam chest, the vapor separator, and the vapor compressor.

The boiler section is 22 inches in diameter by 9 1/4 inches high. It has connections for the three 2,000-watt immersion heaters which are mounted

  horizontally in it. It also has a distillate drawoff connection, the lower connection for the gage glass and a 1/4-inch I.P.S. drain connection. As this section contains the heaters it must always be filled with distillate when heaters are in operation to prevent them from burning out. During operation of the unit, water in the boiler section is maintained at the boiling point. Hot vapors rise through the 3/4-inch I.P.S. vapor pipe to the steam chest. Distillate made in the steam chest flows down through the 3/4-inch I.P.S. distillate return pipe to the boiler section. The 1-inch I.P.S. distillate drawoff connection from the boiler section is so located to maintain a level of water high enough to keep the heaters covered with water at all times.

The vertical steam chest (see Figure 10-13) is 22 inches in diameter and contains 379 copper nickel tubes 3/4-inch o.d. x 16 1/4 inches long. It has a 4-inch o.d. tube as a central downtake or circulating tube, and an overflow pipe which maintains the proper liquid level in this section. This overflow pipe consists of a funnel and a 1 1/4-inch I.P.S. tube centered in the central downtake and connected to the shell of the evaporator in the feed water return section. The overflow flows from the unit, passes through the heat exchanger, and discharges into the brine receiver.

The sea water feed boils inside the 3/4-inch o.d. tubes at a pressure of between 6 and 12 inches of water, while the steam from the compressor condenses on the outside of the 3/4-inch o.d. tubes at approximately three pounds gage pressure. The hot distillate (condensate) flows from the boiler section, through the heat exchanger, and on to the distillate water receiver. Suitable baffles in the steam chest direct the flow of vapor around the tubes, and also direct the noncondensable gases to a central point. A vent line is installed at this point in the steam chest of the evaporator to prevent the noncondensable gases from accumulating. To control the amount of vapor and noncondensable gases vented during the operation of the unit an orifice plate (with 3/64-inch orifice) is placed in the flanged joint at the vent outlet of the evaporator.

Besides the connections mentioned above, the steam chest also has the top gage glass connection, and a 3/4-inch I.P.S. fill connection. The gage glass allows a visual check of the height

 
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Figure 10-5. Evaporator fittings.
Figure 10-5. Evaporator fittings.
of the distillate. The fill connection is used to fill the boiling section with enough water to cover the immersion heaters.

Between the steam chest and the boiler section is a feed water return section which contains a 4 1/4-inch x 8-inch handhole, a 1-inch I.P.S. overflow connection, and a 3/4-inch I.P.S. flush and drain connection.

The vapor separator (see Figure 10-13) which is fastened by brackets to the top head of the evaporator, consists of a 22-inch shell containing two concentric baffles. This baffle arrangement allows the steam to pass into the compressor but prevents any liquid entrainment from so doing. Small particles of water separated by this arrangement collect on the bottom of the vapor separator and flow into the seal cup. The liquid overflows the seal cup to the boiling sea water, and relatively pure vapor passes on to the suction side of the compressor. The pressure in the evaporator above the boiling sea water is indicated by a compound indicating pressure gage connected to the side of the evaporator. This section also

  has connections for the following items located in the outer shell; a 3/4-inch I.P.S. sea water feed connection, and a 10-inch manhole.

10D3. Vapor compressor. The vapor compressor (see Figure 10-12) is a three-lobe, positive displacement type consisting of two rotors enclosed in a special compact housing designed for bolting on the top head of the evaporator. Each rotor has three helical lobes designed to produce a continuous uniform flow of vapor. The vapor enters the specially designed compressor housing at the bottom and passes upward between the inner and outer walls to the rotor chamber where it fills the spaces between the rotor lobes as they roll apart. This vapor is then carried by the rotors in the spaces between the lobes around the cylindrical sides of the housing producing a pressure at the bottom as the lobes roll together. Clearance is provided between the rotors and the housing to prevent the rotors from touching each other or the surrounding housing.

Vapor is taken from the separator (see Figure 10-12) at a pressure of between six and twelve

 
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Figure 10-6. Heat exchanger.
Figure 10-6. Heat exchanger.
inches of water and is discharged from the compressor at approximately three pounds gage pressure, through a 3-inch i.d. tube within the shell of the evaporator, into the steam chest. A bypass valve (starting valve only) is attached to the top head of the evaporator and is connected to the 3-inch o.d. pipe on the pressure side of the compressor. The bypass valve discharges into the vapor separator on the suction side of the compressor. A relief valve, set at 7 1/2 pounds, is installed on the compressor discharges. A zero to 15 psi pressure gage indicates the compressor discharge pressure. A 7 1/2 horsepower electric motor is mounted on the vapor compressor to supply the motive power.

10D4. Heat exchanger. A double pipe heat exchanger (see Figure 10-14) is connected to the evaporator (see Figure 10-12). The function of

  the heat exchanger is to preheat the incoming feed water, cool the brine overflow and condensate, and condense any vented steam.

The heat exchanger consists of fifty 1 1/4-inch i.d. tubes, arranged in seven rows of six tubes across, with two rows of four tubes, one at the center and one at the bottom. Inside each 1 1/4-inch i.d. tube is one 3/4-inch o.d. externally finned or wired tube. The condensate flows inside forty-eight of the 1 1/4-inch i. d. tubes in series, entering hot at the bottom and emerging cool from the top. Steam and noncondensable gases from the steam chest vent flow inside the two remaining 1 1/4-inch i.d. tubes where the steam is condensed and the gases cooled.

The heat exchanger is divided in such a way that sea water feed flows in series through the 3/4-inch o.d. tubes inside 36 of the 1 1/4-inch i.d.

 
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Figure 10-7. Immersion heater.
Figure 10-7. Immersion heater.

tubes, and brine overflow passes in series through the 3/4-inch o.d. tubes inside 14 of the 1 1/4-inch i.d. tubes.

The cold sea water feed enters at the top of the exchanger and after being heated by flowing through 36 of the inner tubes in series, flows from the exchanger to the evaporator (see Figure 1014). The hot brine overflow enters the heat exchanger at the bottom and is cooled by flowing through 14 of the inner tubes in series, then leaves the heat exchanger at the top (see Figure 10-14).

The hot condensate from the evaporator enters the heat exchanger at the bottom and flows in series through the annular spaces between 48 of the inner and outer tubes as noted previously. During this circuit, it is alternately cooled by the incoming feed and heated by the brine overflow.

Figure 10-8. Equipment for evaporator pressure
control.
Figure 10-8. Equipment for evaporator pressure control.

  The heat picked up from the brine is transferred again to the feed, and the condensate flows from the top of the exchanger after being cooled to within about 30 degrees F. of the feed temperature.

This arrangement of flows makes it possible to have the sea water feed and the brine overflow inside the small tubes where any scale which forms can be removed easily.

The heat exchanger is insulated by vermiculite enclosed by a light metal shell.

10D5. Electric heaters (Figure 10-7). The three 2,000-watt electric heaters (see Figure 10-13) are located horizontally and parallel to each other in the boiler section. They are special chromolox heaters of the tubular hairpin immersion type with the heater section of tubing formed to a triangular shape. The immersed length is 9 1/2 inches. The heaters are used on starting the plant to heat the initial cold feed to boiling and to generate the initial steam for compression. During operation the electric heaters supply additional

Figure 10-9. Flow-control valve.
Figure 10-9. Flow-control valve.

 
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338450 O-55-7

heat so that a sufficiently high overflow rate can be maintained to retard the formation of scale and balance the heat losses. Proper inside operating pressure, indicated by the compound indicating pressure gage, is held by the automatic control of these heaters which are turned on and off by a pressure operated switch set to within the operating pressure limits of the plant.

10D6. Pressure controlled switch (Figure 10-8). The pressure controlled switch is essentially a pressure type contact maker, set to, break the circuit to the electric heater at a pressure of 12 inches of water, and make the circuit at a pressure of 6 inches of water. Attachment is on the mounting plate next to the compound indicating pressure gage. The mounting plate is located near the top of the evaporator (see Figure 10-13).

10D7. Compound indicating pressure gage. The dial of the compound indicating pressure gage is graduated to indicate zero to 120 inches of water for pressure, and zero to 15 inches of mercury for vacuum. (See Figure 10-8.)

10D8. Compressor discharge pressure gage. The graduations of the compressor discharge pressure gage are zero to 15 pounds per square inch. Mounting is on top of the evaporator beside the compressor discharge relief valve. (See Figure 10-5.

10D9. Compressor discharge relief valve. The compressor discharge relief valve is set to relieve at 7 1/2 pounds gage pressure. (See Figure 10-5.)

10D10. Bypass, valve. The 1-inch bypass valve (V2) which is mounted on top of the evaporator is connected to the 3-inch i.d. pipe on the pressure side of the compressor, and discharges into the vapor separator on the suction side of the compressor. (See Figure 10-5.)

10D11. Flo-control valve. The 1/2-inch flo-control valve is provided to control the flow of salt water feed to the distilling unit. The valve is located between the feed rotameter and the water regulating valve. (See Figure 10-9.)

10D12. Filter. The filter screens on the two 3/4-inch filters supplied with the unit will be removed and will be used in the duplex strainer in the feed water line.

10D13. Brine rotameter. The brine rotameter measures the flow of brine in gallons per hour.

  Figure 10-10. Rotameter.
Figure 10-10. Rotameter.

(See Figure 10-10.) Calibrated capacity=105 gph.

10D14. Feed rotameter. The feed rotameter measures the flow of feed water in gallons per

Figure 10-11. Water regulating valve.
Figure 10-11. Water regulating valve.

 
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Figure 10-12. Schematic sketch.

Figure 10-13. Evaporator section.
Figure 10-13. Evaporator section.
 
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Figure 10-14. Heat exchanger cutaway and flows.
Figure 10-14. Heat exchanger cutaway and flows.
 
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hour. (See Figure 10-10.) Calibrated capacity=105 gph. Both the feed and brine rotameters are the armored type.

10D15. Water regulating valve. The water regulating valve which keeps the feed flow through the rotameter to the distilling unit at a constant rate is located between the feed rotameter and the filters. (See Figure 10-11.)

  10D16. Sight feed valve. A 1/4-inch sight feed valve (V3) is located on the desuperheater line to enable the operator to observe the flow of water to the compressor. This line is tapped to the distillate drawoff line just as it leaves the evaporator and provides the water needed for desuperheating purposes.
 
E. SOLOSHELL TWO EFFECT DISTILLING PLANT
 
10E1. Introduction. With the application of nuclear power to submarine propulsion there has been installed the first steam evaporator in submarine distilling systems, the Soloshell, double effect, low pressure distilling plant. The principles of operation of this and other types of steam distilling plants can be found in Naval Machinery Part III. The discussion herein will be confined solely to the type to be found on submarines with nuclear steam plants.

The principle of operation of the Soloshell is not unlike that of the vapor compression type of distilling plant. Sea water is heated to the point of vaporization, condensed to make fresh water and the resulting brine pumped overboard. The heat source of the vapor compressor is electricity whereas the heat source of the Soloshell is steam.

10E2. General. This distilling plant is of the low pressure, two effect, Soloshell type.

The rated capacity of the two-effect unit is 4,000 gallons per clay of condensate, and the overload, clean tube capacity, is 5,200 gallons per day with the chlorine content of the condensate not exceeding one-fourth grain per gallon (produced from sea water). The first effect steam will be at a pressure not exceeding 5-psi gage and the distilling condenser at a vacuum of 26" Hg, the density of the brine overboard discharge not exceeding one and one-half thirty seconds.

The two effect unit consists of a horizontal rectangular shell, within which are incorporated the evaporating units, vapor feed heater, distilling condenser, vapor separators, and water level controllers. A vertical longitudinal wall divides this single shell into first and second effect evaporator shells. The first effect shell contains the first effect evaporator tube nest, vapor separator and

  vapor feed heater; the second effect shell contains the second effect evaporator tube nest, vapor separator and distilling condenser.

10E3. Principles of operation. For the purpose of explaining the operation of the Soloshell, the distilling plant is divided into seven different circulating systems as follows:

1. Distiller condenser circulating water circuit.

2. Evaporator feed water circuit.

3. Vapor circuit.

4. Fresh water circuit.

5. Brine circuit.

6. Primary steam circuit.

7. Air removal circuit.

To fully understand the operation of the Soloshell and become familiar with the terminology of the various units, the circuits should be followed on the diagrammatic sketch as the text below is read. (See Figure 10-15.)

1. Distiller condenser circulating water circuit. The distiller condenser circulating water pump takes a suction from sea and discharges through the condensate cooler and the distilling condenser. A strainer is provided in the pump suction piping. The cooling water makes one pass through the tubes of the condensate cooler and four passes through the tubes of the distiller condenser. The cooling water is then discharged overboard through an orifice which is designed to maintain 8 pounds per square inch back pressure on the distiller condenser tubes and heads.

2. Evaporator feed water circuit. The feed water for the evaporator is taken from the distiller condenser circulating water overboard. The orifice installed in the circulating water discharge line (1 above) maintains a minimum back pressure on the evaporator feed line and forces

 
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the evaporator feed through a pressure reducing valve. This valve is provided in the feed line to reduce the high pressure in the circulating water line, which would be encountered under submerged conditions, to a low pressure suitable to the design of the evaporator shell. The feed then passes through the feed heating section of the distilling condenser, and in series, through the air ejector condenser, the flowrator, first effect vapor feed heater, and into the first effect evaporator shell.

The pressure differential between the first and second effect shell permits the second effect feed to be discharged from the first effect shell, through an internal fixed weir-type level control into the second effect shell. Brine is continuously discharged overboard from the second effect evaporator shell through the internal fixed weir-type level controller by the brine discharge pump.

It will be noted that the system is arranged so that the feed water passes from-one heater to the next in the order of the temperature levels in the various units, i.e. the heating medium for the feed heating section of the distiller condenser is the vapor produced in the second effect evaporator which is at a lower temperature than the heating medium for the first effect vapor feed heater, etc. The only exception to this order of heating is that the air ejector condenser is placed early in the series in order that a substantial temperature difference will exist between the condensing steam and the feed water, so that the size of this unit can be reasonably small.

In well designed plants, the evaporator feed water is heated to within about 10 degrees F. of the temperature in the first effect evaporator shell by the series of feed heaters provided for the distilling plant installation. After passing through the last feed heater in the series, the feed water is discharged to the first effect evaporator shell.

3. Vapor circuit. The vapor formed in the first effect passes through a vapor separator to remove any entrained moisture carried, over, and then to a vapor feed heater. Here it gives up some of its latent heat to the feed water going to the first effect shell. The remaining vapor passes into the second effect tube nest where it condenses causing the brine in the second effect to boil.

During the evaporating process, the vapor is disengaged from the brine at the water surface

  and, although the vapor itself is pure, small particles of raw, unevaporated feed water are entrained by, and carried over with, the vapor. The inclusion of these particles of feed water in the vapor generated is known as "priming," or "carry over." These particles of feed water are removed from the vapor by vapor separators of the hook baffle type. They have large vapor areas, and are bolted directly over the vapor inlet connections to the vapor feed heater and distilling condenser. The vapor is forced to change its direction of motion several times in passing around the edges of the baffles or vanes at high velocity. The particles of entrained moisture are entrapped and removed by the hooked shape edges of the baffles. All moisture collecting hooks and baffles are inclined to provide for satisfactory drainage. Drainpipes leading below the surface of the water are provided for discharging the separated moisture as far away as possible from the tube nest in the evaporator shell.

After passing through the vapor separator on its way to the second effect tube nest, the vapor generated in the first effect passes through the first effect vapor feed water heater, where part of the vapor is condensed giving up its latent heat of vaporization to the feed water passing through the tubes of the heater. Vapor feed heaters are shell-and-tube type heat exchangers.

4. Fresh water circuit. The condensate formed by the condensation of the first effect vapor in the second effect tube nest is combined with the condensate from the distiller condenser. This combined total of the condensed vapors is routed through a shell-and-tube type heat exchanger called a condensate cooler, where some of the heat remaining in the condensate is transferred to the circulating water on its way to the distiller condenser. By virtue of the different pressures (and boiling points) within the second effect coils and the distiller, the drain from the two are led to a flash chamber. When the second effect drains reach the lower pressure of the flash chamber, part of the hot water will flash into steam and be vented into the distiller condenser where it is finally condensed. A float controlled drain regulator is provided in the second effect drain to maintain a water seal. The distiller condensate pump (a centrifugal type) takes suction from the flash chamber, raises the pressure of the condensate to

 
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Figure 10-15. THE GRISCOM-RUSSEL CO SOLOSHELL L.P. DISTILLING PLANT-TWO EFFECT WITH WEIR LEVEL CONTROLLERS, FLOWRATER AND SOLENOID TRIP VALVE

a few pounds above atmospheric pressure, discharges to the condensate cooler and delivers it to a solenoid valve. The solenoid valve is so wired that flow can be directed to the ship's tanks only when the solenoid is energized. An increase in salinity to more than 0.25 grains per gallon de-energizes the solenoid and thus trips the valve to the bilge. This arrangement makes it impossible to reset the valve to discharge to the ship's tanks until the salinity is below 0.25 grains per gallon and the solenoid is again energized. In the event of a power failure at the panel, the valve will trip and discharge to the bilge.

5. Brine circuit. Fixed weir-type level controllers are installed in each shell. These consist of a weir pipe, open at the top, connected to a weir well at the bottom of the shell. All of the feed water in excess of that which is evaporated spills over the weir pipe and into the weir well and out of the shell. After being partially evaporated in the first effect evaporator shell, the density or salinity of the feed water is increased and it is then referred to as brine to distinguish it from sea water. When sufficient room is not available beneath the distilling plant for the full loop seal, as is the case in submarine installations, a short loop is installed with a valve for controlling the flow. In order to insure proper operation of these overflow weirs in the absence of a full loop seal, a water level must be maintained in the gage glass on the first effect weir well. This is accomplished by hand regulating the valve between the first effect weir well and the second effect shell. Although this procedure still involves some hand regulation, control is much easier because a level anywhere in the gage glass is satisfactory. Also, once the proper valve setting has been obtained with the plant operating at full capacity, it may be left in that position and not disturbed when starting or securing the plant.

It is not necessary to maintain a water level in the weir well between the second effect shell and the brine pump. This level may be anywhere in the glass or out of sight below it. However when the gage glass becomes completely flooded, a stoppage or reduction in flow of brine overboard due to improper operation of the brine pump or other difficulty is indicated. When the overflow weir-type level controls are provided no attempt should be made to regulate the brine pump discharge

  valve. This valve is left in a fixed open position so that the pump is able to discharge whatever amount of brine overflows the second effect weir pipe. In order to increase the flow of brine overboard and thus reduce the brine density it is merely necessary to increase the flow of feed to the first effect evaporator.

On submarine installations there are two brine pumps provided; a low pressure pump capable of discharging the brine overboard when operating the plant while surfaced or at depths down to periscope depth, and a high pressure pump which is used in series with the low pressure pump when operating the plant at depths below periscope depth.

When operating the low pressure pump alone, the discharge is led to the engine room circulating water discharge line. When operating the high pressure pump in series with the low pressure pump, the discharge of the low pressure pump is directed to a brine collecting tank in which there is a ball float. The ball float operates a valve in the discharge line of the high pressure pump. Thus when the water level in the brine collecting tank has reached a predetermined height the discharge valve of the high pressure pump is opened and the high pressure pump then takes a suction on the tank and the discharge line of the low pressure pump. It is evident then, that the ball float operated high pressure pump discharge valve prevents the high pressure pump from taking a suction on the low pressure pump discharge line which would exceed the gallon per minute discharge rate of the low pressure pump.

The first and second effect shell drains are also connected to the low pressure brine pump through stop valves.

6. Primary steam circuit. Main steam is supplied to the first effect evaporator tubes through a spring loaded, 5-psi reducer. An orifice plate is installed below this valve to permit operating with steam in the tubes at a pressure below atmospheric. The thermometer in the steam line between the orifice and the first effect evaporator tube nest will usually indicate superheat, due to the initial condition of the main steam and the throttling action through the reducing valve and the orifice. As this temperature might be too high, resulting in scale formation, the steam temperature

 
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is lowered to the saturation temperature by means of a desuperheating spray line through which condensate is brought back from the discharge side of the engineroom condensate removal system and is sprayed into the incoming steam, removing any superheat present. The condensed main steam, called "first effect drain" is drained to the engineroom condensate collecting system, which is operating under a vacuum. A float controlled drain regulator is provided in the drain line to maintain a water seal. It should be borne in mind that the main steam is the immediate source of all the heat used by the entire plant with the exception of the heat absorbed from the air ejector jet steam.

7. Air removal circuit. Air and noncondensable vapors enter the plant mainly with the evaporator feed water in which they are dissolved. As the feed water is heated, the dissolved air is freed and tends to collect in various units of the plant. Air also enters the plant with the incoming steam and through various small leaks at pump glands and imperfect joints. Since the distilling condenser is at the lower end of the heat flow cycle of the distilling plant, the absolute pressure within this unit is lower than that within any other unit of the plant and all air and noncondensable gases, which leak into the system, tend to collect in the condenser. In order that the required vacuum may be maintained, the noncondensable gases must be removed so that they will not insulate the condensing tubes and render the cooling surfaces ineffective.

Air enters the distiller condenser with vapor from the second effect evaporator and flash chamber as well as through a series of vent lines which are led from various units of the plant to the distiller condenser. The proper functioning of these vents is essential to the satisfactory operation of the plant. Two single stage air ejectors having an after condenser common to both are provided for removing the noncondensable vapors and air which accumulate in the distilling condenser. Either of these ejectors is capable of removing the air from the plant under normal conditions of air leakage, the second ejector being available as a spare or for use under abnormal conditions of air leakage.

The air ejector suction piping is connected to the air precooling section of the distilling condenser.

  The main function of the air precooler is to cool and remove all possible water vapor from the air to be handled by the ejectors, thereby reducing the total volume of the gas as much as practicable.

The motive steam is supplied to the air ejectors from the main steam line through a reducing valve which reduces the pressure to about 150 psi.

The steam jet issuing from the nozzle of the air ejector entrains the air and noncondensable vapors from the distiller condenser and raises the pressure of the mixture lightly above atmospheric. This steam is condensed and the air is cooled in the air ejector condenser where the vapor gives up its latent heat to the evaporator feed water passing through the condensing tubes of this unit. The air and noncondensable vapors are vented to the atmosphere. The condensate is returned to the engineroom condensate removal system.

10E4. Starting and securing.

STARTING

1. Open wide all valves in the circulating water circuit from the sea suction to the overboard discharge.

2. Start the circulating pump.

3. Open all air vent cocks on the distilling condenser, vapor feed heater, and air ejector condenser heads until the air is expelled, then shut them.

4. Open the feed valves until the tube nests are fully covered, regulate the second feed valve to maintain the proper water level in the first effect shell.

5. Open the necessary valves in the brine overboard discharge system and start the low pressure brine discharge pump. If below periscope depth, the low pressure pump must be used in series with the high pressure brine discharge pump.

6. Open the second effect evaporator tube nest vent valves wide. The first effect tube nest vent valve should remain shut.

7. Insure that the first effect tube nest and air ejector condenser drain valves to the bilge are open, and that the valves in these drain lines to the ship's condensate return system are shut.

8. Open-air suction to the ejector. Open supply steam to the ejector, insuring that full pressure required (stamped on nameplate) is available at the nozzle, and that steam supply is properly drained.

9. Test the salinity of the air ejector condenser

 
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drain. When less than 0.25 grains per gallon, shut bilge drain and open drain to tank.

10. When second effect shell vacuum is about 16 inches, open first effect tube nest steam supply valve wide. Adjust regulating valve to maintain steam pressure of, about 5 psi above the orifice. Last effect shell vacuum should continue to increase to 26 inches or more.

11. When condensate discharges from the first effect drain line to the bilge, test for salinity. When satisfactory, shut the bilge discharge line and open valves as necessary to discharge the condensate to the return system and open the first effect tube nest vent valve one full turn.

12. When condensate appears in the second effect drainer, see that drainer discharge valve is open, and adjust second effect tube nest vent valve to the operating position (approximately one turn open).

13. When condensate appears in the flash chamber or distilling condenser hot well, make sure the condensate cooler discharge is directed to the bilge by manually tripping the solenoid actuated valve. Then start the condensate pump.

14. Regulate the first effect feed valve so as to obtain a rate of feed flow of approximately three times the normal distilling plant output. Open the second effect feed valve so as to maintain a level in the first effect weir well gage glass.

15. When the salinity of the condensate leaving the condensate cooler is less than 0.25 grains/gallon, set the solenoid valve to discharge to the ship's tanks.

16. Open and adjust feed treatment injection valve if feed treatment is to be practiced.

17. When the plant has been in full operation for 15 to 20 minutes, determine the rate of distilled water production by means of the meter in the condensate cooler discharge line. The rate of production may be increased or decreased through a small range by increasing the steam pressure above the orifice.

18. When the desired rate of output has been set, determine the density of the evaporator feed, then adjust the evaporator feed valve to obtain a rate of flow in accordance with the table below. The rate of feed flow will be indicated by the flowrator in the feed line.

Feed Density (32nds) 1/2 3/4 1 1 1/8 1 1/4
Ratio of Feed to Fresh Water Output 1.5 2 3 4 6
  19. After the plant has been in operation about an hour, and occasionally thereafter, check the density of the brine pump discharge, and adjust the first effect feed valve as necessary to maintain a brine density of 1 1/2 thirty-seconds. The brine density is reduced by increasing the rate of feed, and increased by reducing the rate of feed.

10E5. Securing.

1. Shut steam supply to first effect tube nest.

2. Shut the first effect tube nest drain to return system and open drains to bilge.

3. Shut first effect tube nest vent valve.

4. Shut air suction and steam supply valves to air ejector.

5. Open second effect tube nest vent valve wide.

6. Secure the condensate pump.

7. Continue operation of circulating water and brine overboard discharge pumps for 10 minutes or longer to cool all parts of the distilling plant.

8. Secure the brine overboard pump.

9. When both tube nests are fully covered with water, secure the circulating pump.

10. Shut feed valve to the first effect and to the second effect.

11. Shut the suction and overboard sea chests.

12. Shut air ejector and condenser drain lines to return system and open drains to bilge.

13. Trip the solenoid actuated valve to discharge to the bilge.

10E6. General notes.

1. Pumps must not be run dry. Before starting any pump, make certain that the suction, vent, and gland seal valves are open, and that the pump casing is full of water. On centrifugal pumps, it is preferable to leave the discharge valve closed until after the pump has been started.

2. It is permissible to run a centrifugal pump with the discharge valve shut for periods of 15 to 20 minutes.

10E7. Feed and brine density. The salt content of sea water is measured in thirty-seconds, and is called its density. Thus, sea water is said to have a density of 1/32 if a 32-pound sample contains 1 pound of salts. Sea water feed is partially boiled off in the distilling plant, and the remaining brine which is discharged overboard has a higher "density" than the initial feed. For best results, the brine density must be held constant at 1 1/2 thirty-seconds. A higher density will result in more scale throughout the plant, while a lower density

 
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results in a needless waste of heat because of the unnecessarily large amount of brine discharged overboard. The brine (or feed) density is measured by salinometers which are calibrated to read directly in thirty-seconds. Salinometers are not to be confused with electrical salinity indicators which measure the salt content of the distillate.

A suitable salinometer must be available for each distilling plant. It should be calibrated for temperatures of 110 degrees, 115 degrees, 120 degrees, and 125 degrees F. If the salinometer is misplaced or lost, a new one should be procured immediately.

With the overflow weir-type level controllers the brine density is maintained at the appropriate value of 1 1/2 thirty-seconds by regulating the feed valve to the first effect evaporator.

No attempt should be made to regulate the brine pump discharge valve. This valve is left in a fixed open position so that the pump is able to discharge whatever amount of brine overflows the second effect weir pipe. In order to increase the flow of brine overboard, and thus reduce the brine density, it is merely necessary to increase the flow of feed to the first effect evaporator.

Samples of brine are usually obtained through a sampling cock at the brine pump discharge. It is important to obtain a sample truly representative of the brine in the last effect shell. The temperature of the sample drawn into the sampling pot should agree closely with the reading of the thermometer on the last effect shell. A difference of more than 3 degrees or 4 degrees usually indicates faulty operation of the brine pump, or dilution of the brine between the last effect shell and the sampling cock.

If the pump gland is located on the same side of the pump casing as the pump inlet, the brine may be diluted by sealing water. In such cases it may be possible to obtain a correct sample by closing the valve in the gland sealing line temporarily. Some installations have been made with a brine diluting line connected from the circulating pump discharge to the brine pump suction to improve the operation of the pump. This line is not necessary, and, unless the flow through it is very carefully adjusted, the flow of brine from the last effect shell to the brine pump may be stopped altogether.

A true sample can always be obtained by means of a vacuum test pot connected to the last effect

  shell. Such a sampling pot is not as convenient as a petcock at the brine pump discharge, but is recommended where the danger of dilution exists because of the type of pump used, because of the presence of a brine diluting line, or because drain lines from other effects (besides the last) are connected to the brine pump.

The amount of brine which must be discharged overboard in order to maintain a constant last effect shell density of 1 1/2 thirty-seconds varies through a wide range, depending on the density of the initial feed. Feed density is not constant. It varies from less than 1 to more than 1.2 thirty-seconds in open oceans, and through an even greater range when inland seas (such as the Red Sea) and sheltered bays are considered. The higher values are usually found in tropical waters, and the lower values in northern waters.

The amount of brine to be discharged overboard for each pound of distillate is given by the following term:

(f) / (1.5-f)

where f is initial feed density in thirty-seconds. Thus for an initial density of 1 thirty-seconds, two pounds of brine must be discharged overboard for every pound of distillate; for an initial density of 1 1/4 thirty-seconds, five pounds must be discharged, etc. It is evident, therefore, that a fixed quantity of feed water will not result in a constant brine density of 1 1/2 thirty-seconds in the last effect shell. It is essential that the brine density be checked at hourly intervals, and that the brine regulating feed control valve be adjusted as necessary. The amount of feed required in order to maintain a brine density of 1 1/2 thirty-seconds in the last effect is given by the following expression:.

(1.5) / (1.5-f) X distillate in gal/min

where f again is the initial feed density in thirty-seconds. Since rotameters are usually calibrated in gallons per minute, the distillate must also be in gallons per minute. Thus for a plant producing 10 gals/min of distillate, feed flow required when the initial density is 1 thirty-seconds is 30 gals/min; feed flow required when the initial density is 1 1/4 thirty-seconds is 60 gals/min, etc.

Feed samples for density test may be obtained from the vent or drain connections on the distilling

 
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condenser or air ejector condenser heads at a temperature within the range of the salinometer.

When using a flowrator to regulate the feed rate, brine samples should be obtained and the density checked by the salinometer at regular intervals to prevent possibility of excessive density because of incorrect readings of the flowmeter.

10E8. Scale. The character and amount of scale deposited on the tube surfaces will depend not only upon proper operation in accordance with the manufacturer's instructions, but also upon the quality of the feed water. In low pressure distilling plants, scale results primarily from calcium carbonate and other minor constituents of sea water. The ratio of these minor constituents to the total solids in sea water is not always the same. Hence, it does not follow that two waters having the same density (same total solids) will necessarily result in the same amount of scale under the same operating conditions. Some bay and harbor waters of very low density may result in far more scale than ocean water. In the oceans, more scale should be expected near coral islands than in other regions even though the feed density may be the same. In open waters, away from the effects of fresh water rivers, coral islands, etc. the feed density is an index of scale forming properties. Scale deposits may be reduced by proper feed treatment. This subject will be taken up later in the text.

When no feed treatment is used, a relatively brittle scale is usually formed. This can be partially removed by chill-shocking the plant daily, thus prolonging the period between shutdowns for cleaning. If the plant is usually secured a part of each day, no other chill-shocking is necessary as the scale will automatically crack off when the plant is started up again. When feed treatment is used, the deposit builds up very slowly, and does not crack as readily as untreated scale. Daily chill-shocking may be beneficial, but a longer interval may be entirely satisfactory. The optimum chill-shocking period must be determined from experience.

10E9. Chill-shocking. Most distilling plants are provided with special flushing pipes over the evaporator tubes to facilitate chill-shocking. The procedure is as follows:

  1. Secure the following: Steam supply to the air ejector, the air ejector condenser drain line, the steam supply to the first effect tube nest, the first effect tube nest drain line to the condenser, the feed valve to the first effect, the condensate pump and the brine pump.

2. Open the drain on the bottom of each shell and pump the shells. Shut the drain valves.

3. Open the water supply valve to the internal spray pipes and allow all evaporator tubes to become fully submerged.

4. Shut the water supply to the spray pipes and repeat step number 2.

5. Repeat step number 3. When the tubes are fully submerged, secure the water to the spray pipes, and quickly open the steam valve to the first effect tube nest. The flow of steam will be restricted by the orifice but may be increased for more effective "shocking" by increasing the pressure above the orifice. After the plant has been warmed up, this pressure should be brought back to normal.

6. To put the plant back in operation open the first effect tube nest drain valve to the condenser, supply steam to the air ejectors, open the air ejector condenser drain valve to the drain system, open the feed valve to the first effect and start the brine and condensate pumps.

10E10. Feed treatment. Vacuum type distilling plants can be operated for relatively long periods of time without overhaul and without feed treatment, if properly handled. However, it has been determined that the continuous injection of feed treatment into the first effect shell reduces the deposit on the evaporator tubes and in the brine lines.

Instructions for mixing and injecting a feed treatment mixture can be found in the manufacturer's instruction books.

10E11. Purity of condensate. It is very important that only pure condensate be sent to the ship's fresh water or reserve feed tanks. All distillate having a salt content in excess of a predetermined maximum (usually 0.25 grains per gallon) must be discharged to the bilge. In the case of submarine installations this is done automatically by the solenoid dump valve located on the discharge side of the condensate cooler. The manufacturer's instruction books should be consulted to aid in locating the source of excessive salinity.

 
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10E12. Operation with contaminated feed water. When operating in regions where the feed water may be contaminated with bacteria, such as in or near rivers, harbors, sheltered bays, etc., it is of the utmost importance to send only distillate of known purity to the ship's tanks as the health of the entire crew depends upon the production of sterile water. It has been determined that sterile distillate may be obtained without increasing the pressures and temperatures, providing the total impurities do not exceed 0.25 grains per gallon. This phenomenon occurs naturally when the sun's rays evaporate water free of bacteria at atmospheric temperatures and at low evaporation rates.

Evaporation of water, either at atmospheric pressure or at reduced pressures and temperatures, is a physical separation of water from its dissolved and suspended constituents. Bacteria are larger particles than molecules of salt, and therefore, are also left behind in the brine. The sterilization of water by subjection to high temperature is not necessary if contamination of the distillate by priming or salt water leakage is prevented.

The salinity of the distillate may be watched as an index of such priming or leakage and the discarding of all condensate having a saline content of more than 0.25 grains per gallon will protect the men. The solenoid valve for automatically dumping the distillate to the bilge whenever the salinity exceeds the maximum gives added protection. The distillate should also be tested chemically at frequent intervals in order to check the electrical indicator.

The U.S. Public Health Service stresses the importance of not operating the distilling plant in contaminated harbors because of the possibility of contamination of the distillate by distillation of oil or other volatile substances in the feed water. The U.S. Public Health Service further advises against operation of the plant in brackish or fresh contaminated water as the salinity indicator and solenoid valve are of little value in protecting the system against improper operation and carryover of impurities in the feed.

10E13. Materials. The evaporator division wall, shell, shell covers, tube sheets and tube nest covers of all units, evaporator tube support plates and all tubes are copper nickel alloy. All other tube support plates and vapor separators are naval rolled brass. Drain regulator bodies are gun

  metal. Replaceable zincs are provided in all salt water heads.

The evaporator tube bundles consist of 5/8-inch o.d. U-tubes, 0.049-inch wall thickness, expanded at both ends into a tube sheet and supported by a support plate. One tube sheet is bolted to the front of the shell so that the tube nest is free to expand. Support plates are supported on rails in the shell so that the tube nest is free to expand.

The U-tubes are arranged for two passes of the heating steam. The air vents to the second effect shell are taken from the second pass compartment in the tube nest cover through a perforated baffle. Sight glasses are fitted in the front of each evaporator shell for observing the operating condition within. Perforated spray pipes are fitted over the first and second effect tube nests for chill-shocking purposes and are externally connected through the front of the shell.

The vapor feed heater is of the straight tube type, having 5/8-inch o.d., 0.049-inch thick tubes expanded into a tube sheet at each end. Expansion of the tubes is permitted through the use of a floating head resting on guides in the vapor feed heater chamber.

The distilling condenser consists of two tube bundles, one being the condensing section, consisting of U-tubes; the other a feed heating section, consisting of straight tubes. The condensing section is of the U-tube type having 5/8-inch o.d., 0.065-inch thick tubes expanded at both ends into a tube sheet. A tube support plate supports the U-tube bundle. The feed heating section of the condenser is of the straight tube type, leaving 5/8-inch o.d., 0.049-inch thick tubes expanded into a tube sheet at each end. Expansion of the tubes is permitted through the use of a floating head resting on guides in the vapor feed beater chamber.

The air ejectors are of the single stage type. The air entering the ejector from the evaporator is entrained by the steam jet issuing from the nozzle and is carried through the diffuser, compressed to atmospheric pressure and discharged to the air ejector condenser where its heat is given up to the evaporator feed water. The air ejector condenser is of the straight tube type, having 5/8-inch o.d., 0.049 inch thick tubes expanded into a tube sheet at each end. The cylindrical shell is of copper, and differential thermal expansion

 
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between the shell and the tubes is provided for by the flanged ends of the shell. The air ejector steam passes through the shell and the evaporator feed makes several passes through the tubes. The air is discharged to the atmosphere through two vent pipes. The condensate drains from the bottom of the condenser to the drain collecting system.

The flash chamber is essentially a receptacle within which the vapor, liberated when the second effect drains are reduced to a pressure and temperature corresponding to the distilling condenser vacuum, is separated from the condensate and directed to the condenser. The total output of the plant is collected within the flash chamber and flows to the condensate pump. The flash chamber is attached to the second effect side of the evaporator shell.

The first and second effect tube nest drain regulators are of the style "F" (Griscomb-Russell) internal valve, piston type balance valve design with ball float. The regulators may be locked open in case of derangement. The condensate cooler is of the straight tube type, having 5/8-inch o.d., 0.065inch thick tubes, expanded into a tube sheet at each end.

  The firmed weir-type level controllers are located internally and are directly attached to the bottom of the first and second effect evaporator shell. The level controller is self-venting to its respective evaporator shell. Water level within the evaporator is maintained by the fixed weir pipes attached to the level controller body. This water level is indicated by gage glasses likewise fitted to the level controller.

The flowrator is located in the feed piping, between the feed water outlet connection on the air ejector condenser and the feed water inlet on the first effect vapor feed heater. It is calibrated in gallons per minute and visually indicates amount of feed water being supplied to the plant.

The feed reducing valve is provided to reduce the high pressures which may be encountered under submerged conditions to a low pressure suitable to the design of the evaporator shell, heaters and condenser bundles. For surface operation a back pressure valve is located on the circulating water piping overboard to maintain sufficient back pressure to force the feed through the reducing valve and heaters in the feed line and into the first effect shell.

 
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U. S. GOVERNMENT PRINTING OFFICE:1955 O-338450

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