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Air Pressure

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REVERSE OSMOSIS PLANT
(FRESH WATER GENERATOR)

Introduction

There are two reverse osmosis plant (fresh water generator) are installed onboard ship. One is fitted in Aux Machinery Room and other is fitted in Fwd Main Machinery Room. Each plant capacity is 15 tons /day.

Purpose

To generate fresh water to meet ship’s requirement.

Major Parts and Function

Centrifugal Pump: PK130 filter pump, delivers the feed water at a pressure of up to 4 bar through the cartridge filter and from there to the high pressure pump PP160. This centrifugal pump has its own integral electric motor.

High-Pressure Pump: PP160 is a positive displacement pump. (plunger pump) this pump delivers feed to the PT modules at a pressure of up to 65 bar. (note: pressure is controlled by VS160). The pump is powered through a belt drive from a three-phase motor. Minimum feed pressure to this pump is 0.5 bars.
Pulsation Damper: The pulsation damper fitted on the high-pressure pump discharge converts the pressure fluctuations, common for a plunger pump, into a steady pressure. It consists of a pressure vessel, internally separated by an diaphragm into two sections. The outermost section is filled with nitrogen at a pressure of 30 bar. The pulsation’s from the 3 plungers of the HP pump are absorbed by the gas pressurized membrane. It is normal to observe pulsation’s in the pointer of PI160 when pointer is rising through 25 to 32 bar, (resistance against gas pressure).
Sand filter: The sand filter retains all sediment particles over 50 (m in size. As the density of these particles increases, the pressure drop across the inlet and outlet increases. To reduce this pressure drop and remove these particles, the sand filter is backwashed by air and feed water (generally when 2 to 2.5 bars are reached).
Cartridge Filter: Within cartridge filter FC140 sediment particles of 10 (m or more in size are retained within the filter element. These cartridge filter elements have to be replaced when dirty, they cannot be cleaned.
PT Module: Inside the PT module(s) of module block FM160 the feed water is pumped at the operating pressure through a stack of membrane cushions. Hydraulic discs between the membrane cushions direct the water flow. The pure water passes through the membranes and enters the pure water channel, leaving behind the salt molecules and other impurities of the water, which cannot pass through the membrane (e.g. retention of NaCl: 98.5-99%). As the steadily flowing water carries these rejected particles away they become more concentrated after passing over each membrane cushion. The feed water is finally discharged (in case of sea-water desalination back into the sea) as brine “concentrate”.
Motorizing Valve: The pressure in the PT module or modules, is automatically controlled and adjusted by motor valve VS160, which in turn is controlled by the PLC. The plant is designed for a maximum operating pressure of 65 bars. The operating pressure is 65 bar with normal sea water. This valve should never be fully closed during operation. When in operation this valve reduces the flow area to increase the pressure between the HP pump discharge and the outlet of the modules. If this valve closes a fault will show. This valve can be manually operated by a hand wheel should the power unit fail.
Pressure switch PS150: Is activated by the water pressure before the high pressure pump and switches the plant off in the event of insufficient feed (to protect the pump against cavitation). It is de activated when the pressure drops below a set value of 0.5 bar. High pressure pump will not start if this pressure switch is not activated. When not activated fault will show.
Pressure switch PS170: (If installed) monitors the pressure in the concentrate line from the PT module. It stops the plant at a pressure of 6 bar, in order to avoid damage to the module. Most probable cause for this to be activated is that a valve on the concentrate discharge is closed. This pressure switch is activated when the pressure goes above the 6 bar setting. When activated fault will show.
Pressure switch PS180: Pressure switch PS180 STOPS the plant when the pressure in the permeate line rises to 3 bar. This is to save the PT module from damage. This pressure switch is activated when the pressure goes above 3 bars. When activated fault will show.
Conductivity Sensor: A conductivity sensor transmits the conductivity of the permeate to the conductivity meter, (measuring the remaining salt content). An increase in conductivity implies a higher salt content. The value displayed in the conductivity meter is in µs/cm. As a rough guide, if the reading shown is divided by 2 the figure obtained would be the approximate value of salts as p.p.m.(mg/l).
Solenoid Valve: The pure water solenoid valve VE1801 is automatically controlled by the conductivity of the permeate. If the maximum pre-set value (1000 (S/cm for sea-water desalination, 50 (S/cm for mains water purification) is exceeded, VE1801 sends the permeate into the cleaning tank (from there to drain). When good permeate is produced, at a quality with a lower conductivity than the maximum pre-set value, then VE1801 sends this water to fresh water storage. If the plant operates more than 15 to 20 minutes at high conductivity (over the set limit), it automatically shuts down and a fault signal is displayed.
Working Principle

|This fresh water generator uses the principle of the Reverse Osmosis. |
|If two saline liquids are separated from another by a semi-permeable membrane, which does only allow molecules over a certain size to pass |
|through, then, these liquids will tend to equalize their concentrations. This process is called Osmosis. Should one of these liquids be salt|
|water and the other pure water, water molecules would diffuse through the membrane towards the salt water and dilute this. A certain |
|pressure would occur in the system when this happens this pressure is called the Osmotic Pressure. |
|For water desalination or dechlorination this process is artificially reversed, Reverse Osmosis. The system is subjected to a pressure above|
|the Osmotic Pressure, causing a molecule movement into the reverse direction: Only the water molecules diffuse from the salt water through |
|the membrane to the pure water side. The ions of the salt water cannot pass through and remain on the salt water side. |
|Within the Rochem PT modules the REVERSE OSMOSIS process takes place whilst the feed water is in motion, flowing over the membrane surfaces.|
|About 30% of the water in the feed water passes through the membrane, the remaining 70% retaining the rejected salts. The feed water is |
|gradually increasing in salt concentration as it flows through the module. The salts filtered out and left behind by the membrane are |
|carried away and discharged, in case of sea water desalination they are returned to the sea as brine (concentrate). The pure water |
|“permeate” produced flows to a fresh water storage facility. |
|The amount of pure water that can be produced depends on the following factors: |
|1- The operating pressure, |
|2- The salt content of the feed water, |
|3- The feed water temperature. |
| |
|For example the oceans have a salt content of approximately 3½ %. whereas the Red Sea has a much higher salt content of approximately 4½ %, |
|To overcome the increase in salinity the operating pressure is increased. |
|Each standard system has been designed for a certain production rate of pure water, assuming a feed water temperature of 25°C. For each 1°C |
|drop in feed water temperature the permeate production drops by 3%. For example: Designed output at 25°C is 100 l/h. |
|Then with a feed temperature of say 15°C the permeate output is 100-30% = 70 l/h. |
|A rise in temperature above 25°C increases the pure water production only slightly. 25°C is the optimum feed temperature. |
|General arrangement of the RO1020 (individual deviations not allowed for) |
|[pic] |
|Sketch of operating principle |

Designed Parameters

➢ Feed Water Temperature: 25oC

➢ Maximum output: 15 ton/day

➢ Operating pressure: 65 bar

➢ Maximum operating pressure: 73 bar

➢ Feed pressure after filter pump: 4 bar

➢ Pressure of discharged concentrate (max): 6 bar

➢ Pressure of delivered permeate (max. pressure): 3 bar

➢ Conductivity of permeate (max. value) 1000 µS/cm

Safety Remarks

➢ The fresh water generator must not be operated within harbour area. Or in waters polluted with oil.

➢ Plant not to be operated for day trip (OEM Recommended).

➢ Plant to be operated approx after 50 NM.

➢ Do not allow to operate the RO unit in areas of river especially in regions with low draft.

➢ Protection, such as pulley / belt guards, may be removed only for maintenance or repair and must be re-installed immediately after any such repair or maintenance has been completed.

➢ There must not be any visible movement (vibration/pulsation) of the pointer on pressure gauge.

➢ The feed pressure to the high pressure pump PP160 must not fall below 0.5 bar. If this happens, the pump will be damaged by cavitations.

Starting Procedure

| Step |Action |Effect |Lamp signal |
|No. | | | |
|1 |Open all valves to and from the RO unit. | | |((((( |
|2 |Open VK111 |- |Drain all water from cleaning tank. |((((( |
|3 |Set valves to Normal operation: | | |
| |VK121 |VK132 |VK134 |VK133 |VK171 |
|normal operation |[pic] |[pic] |[pic] |[pic] |[pic] |
|4 |Turn master-switch to “I” (On). |- |Conductivity display illuminated. |((((( |
|5 |Press lamp button 1. |- |Motor control valve VS160 is open. |◙(((( |
| | |- |When WS161 sends signal "valve completely open“ to the | |
| | | |PLC, filter pump PK130 starts. | |
| | |- |High pressure pump PP160 starts 300 seconds. after | |
| | | |pressure switch PS150 has given start signal. | |
| | |- |Motor control valve VS160 runs towards close to bring up| |
| | | |pressure. | |
| | |- |Pressure transmitter PT160 stops pressure rise when | |
| | | |maximum pressure or maximum permeate flow rate is | |
| | | |reached. VE1801 sends permeate into tank B111, since | |
| | | |conductivity limit is exceeded. | |
| | |- |Conductivity of permeate drops below allowed maximum. |((((( |
| | | |VE1801 switches to permeate discharge, i.e. fresh water | |
| | | |storage. | |

[pic]

CIRCUIT DIAGRAM- REVERSE OSMOSIS PLANT

Running checks

|Parameter |Device |Set values |
|Feed pressure |pressure switch PS150 (min. pressure) |0,5 bar |
|Pressure at inlet to module |pressure transmitter PT160 (max. pressure) |73 bar |
|Pressure of discharged concentrate |pressure switch PS170 (max. pressure) |6 bar |
|Pressure of delivered permeate |pressure switch PS180 (max. pressure) |3 bar |
|Flow rate of permeate |flow meter FIS 180 (nominal capacity), shut-down delayed |225 l/h per module |
|Conductivity of permeate |conductivity sensor/meter CIT80 (max. value) |1000 (S/cm (sea water) |
| | |or 50 (S/cm (town mains |
| | |water) |
|Amperage of electric motors |motor circuit-breakers |(see electric schematics|
| | |and rating plates) |

Stopping Procedure

|Step |Action |Effect |Lamp signal |
|No. | | | |
|1 |Close valve VK111. |- |To stop cleaning tank emptying |((((( |
|2 |Press lamp button 2 |- |VE1801 changes over to fill tank B111 with permeate. |◙(((( |
| |(STOP with rinse) | | | |
| | |- |Tank B111 full LS1113 activated | |
| | |- |Motor control valve opens to reduce operating | |
| | | |pressure. | |
| | |- |Unit stops. |(◙((( |
|3 |Set valves as below: |(to take suction from cleaning tank) | |
| |VK121 |VK132 |VK134 |VK133 |VK171 |
|stop rinse |[pic] |[pic] |[pic] |[pic] |[pic] |
|4 |Press lamp button 1 |- |Rinse with permeate starts. |((((( |
| | |- |Low level switch LS1111 activated (tank empty). Unit |((((( |
| | | |stops. | |
|5 |To protect the unit for external pressure | | |
| |fluctuations set the valves as below | | |
| |VK171 |[pic] |(delivery to cleaning tank) | |
| |VK121 |[pic] |(suction from cleaning tank) | |
| |Open valve VK111. |Tank B111 is drained. | |

Note: If a stand-still of more than 10 days is intended, a preservation must be carried out prior to shut down. This is to prevent bacterial fouling on the membranes.

CIRCUIT CLEANING

➢ Fresh Water Production dropped by 10-15%

➢ Every 3 to 4 Weeks

➢ After 500 running hours

Choice Of Cleaner:

Type AA For organic sedimentation and fouling

Type C To remove iron fouling

➢ For normal cleaning “AA” would be used.

➢ It is recommended that “C” is used every 4 months to remove iron deposits.

➢ If the type of deposits / fouling is not known, all cleaners C and AA should be used consecutively. Run the unit for a minimum of 3 hours

Preservation

More than 10 days when not in use

Preservation chemical

ROCHEM ROCIDE

(Contain Sodium Bi sulphate < 10%)

Disinfection

If the permeate found contaminated of bacterium's, or generally after a longer stand-still without a prior preservation.

Preservation chemical

Biocide Agent

CAUTION (Never Mix Different Cleaners)

If done, this will only neutralize the cleaning solution and the cleaning results will be minimal. This can also damage the membrane surfaces.

After every cleaning/preservation/disinfection cycle’s cartridge filter element must be replaced.

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...What is the normal temperature of human body in degrees Celsius? Convert this temperature into F, R and K? 5. The “standard” acceleration (at sea level and 45° latitude) due to gravity is 9.80665 m/s2. What is the force needed to hold a mass of 2 kg at rest in this gravitational field? How much mass can a force of 1 N support? 6. A gasoline line is connected to a pressure gage through a double-U manometer as shown in the figure. If the reading of the pressure gage is 370 kPa, determine the gage pressure of the gasoline line. 7. A tank has two rooms separated by a membrane. Room A has 0.5lbm air and volume 18ft3, room B has 30ft3 air with density 0.05lbm/ft3. The membrane is broken and the air comes to a uniform state. Find the final density of the air. 8. A hydraulic lift has a maximum fluid pressure of 80. What should the piston-cylinder diameter be so it can lift a mass of 1600 lbm? 9. At a certain location, wind is blowing steadily at 10 m/s. Determine the mechanical energy of air per unit mass and the power generation potential of a wind turbine with 60m-diameter blades at that location. Take the air density to be 1.25 kg/m3. 10. A. In what forms can energy cross the boundaries of a closed system? B. When is the energy crossing the boundaries of a closed system heat and when is it work? C. What is an adiabatic process? What is an adiabatic system? D. A gas in a piston–cylinder...

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Combined Gas Law

...is a gas law which combines Charles's law, Boyle's law, and Gay-Lussac's law. This law states: “The ratio between the pressure-volume product divided by the temperature of a system remains constant.” This can be stated mathematically as:  Where: p is the pressure, V is the volume, T is the temperature measured in kelvins, and k is a constant (with units of energy divided by temperature). Reminder: 1atm= 760 torr = 101.3 kPa & Celsius to Kelvin= add 273 and Kelvin to Celsius= subtract 273 For comparing the same substance under two different sets of conditions, the law can be written as:  If the problem does not state which unit to give the result in, then make sure that temperature is converted into Kelvin and for the Pressure and Volume just make sure you stay constant and use the same unit on both sides of the equation. Combination of 3 Laws: Boyle's Law states that the pressure-volume product is constant:  In other words as external pressure on a gas increases the volume decreases, and vice versa. Charles's Law shows that the volume is proportional to absolute temperature:  In other words as temperature increases the volume increases, and vice versa. Gay-Lussac's Law says that the pressure is proportional to the absolute temperature:  In other words as temperature increases the pressure increases, and vice versa. Where P is the pressure, V the volume and T the absolute temperature and of an ideal gas. By combining (1) and either of (2) or (3) we can gain...

Words: 611 - Pages: 3