FA L
LA L LS
PI VS
TI
TS
FS
FS
TI
TS TA
100¡C H VA
572
Lub Oil AW
072VX
Trip
Trip
FA L
TA L -60¡C
FA L
LA L LS
FA L FS
Trip
2.8.1 Vacuum pumps (See Illustration 2.8.1a)
Two vacuum pumps located in the cargo compressor room are used to evacuate the primary and secondary spaces atmosphere in the following cases:
1 To replace air with nitrogen for inerting;
2 To replace methane with nitrogen for gas freeing before dry docking after there has been leakage of cargo;
3 To test tightness of the membranes at regular intervals or after membrane repairs.
4 When the associated tank is opened up.
The pumps are driven by electric motors situated in the electric motors room through a gas tight bulkhead seal.
The two pumps are used in parallel to evacuate the primary and secondary spaces in order to reduce the time taken to achieve the vacuum of 200 mbar a.
The pumps are sea water cooled from the deck cooling sea water system (refer to 2.12). The pumps are started and stopped from the starter panel in the CCR. Auto from the CCR and local from the ECR.
! CAUTION
If there is a failure or stoppage and the vacuum pump is hot and the cooling water has stopped, await for room temperature before restarting in order to avoid shock due to cold water.
! CAUTION
If there is a computer control failure, the vacuum pumps can only be stopped from the ECR and not from the compressor room or CCR.
! CAUTION
If the primary space pressure were to be reduced below the secondary space pressure there is a danger of distorting the secondary barrier by lifting it off its supporting insulation. A maximum pressure difference of 30 mbar is allowed.
Discharge from the pumps is led to No. 3 mast riser.
Each vacuum pump will stop if the lubrication oil tank level, or flow is low, the discharge temperature is high or the suction temperature is low.
AF 621.01 Low suction temperature alarm AF 621.02 Set point: -60°C Trip the pumps AF 622.01 High discharge temperature alarm AF 622.02 Set point: +170°C Trip the pumps AF 619.01 High vacuum alarm
AF 619.02 Set point: 200 mbar a Trip the pumps AF 624.01 Low lubrication oil flow alarm
AF 624.02 6/10 drops per 10 seconds Trip the pumps AF 624.03 Low lubrication oil level alarm
AF 624.04 Set point: 5 cm Trip the pumps AF 623.01 Low cooling water flow alarm
AF 623.02 Normal flow rate 1500l/h Specification
Vacuum pumps:
Two horizontal rotary dry vacuum pumps, single staged type P8O manufactured by MPR industries, capable of creating a vacuum of 200 mbar a in the primary and secondary insulation spaces and driven at 875 rpm by 27 kW increased safety electric motors through a gas tight bulkhead seal (817 m3/h). Suction temperature -50°C to +45°C
Operating Procedures
1 Open the sea water cooling water inlet and outlet at the vacuum pump. Check through the pump drain valve that there is no water in the pump. A sample intake is fitted on the drain valve in order to permit sampling during operation. Then vent the pump cooling water lines. When evacuating the insulation spaces, the secondary barrier space is evacuated to 950 mbar a before the primary barrier space suction isolating valve is opened. Both spaces are taken down to 200 mbar a. This process ensures that it is not possible to lower the pressure in the primary barrier insulation space without having the same pressure in the secondary barrier insulation. Check pump lub-oil tank level.
pump and ensure oil drips are evident at each sight glass.
If the pump has been stopped for more than 24 hours it is essential to turn the rotor by hand 2 or 3 turns before starting the pump to ensure that the blades are not stuck on the cylinder.
3 The vacuum pumps can now be started.
2.8 Vacuum Pumps - Page 1 Issue: 1
2.9.1a Inert Gas and Dry Air Systems Issue: 1
Cargo Systems and Operating Manual LNG LERICI
2.9.1a Inert Gas and Dry Air System
Combustion Air Fans
Ignitor
Combustion Chamber Fuel Inlet
Steam Atomizing
Burner Unit and Combustion Chamber
From Ballast Pump
Scrubber
Effluent Seal
Vent to Funnel
Chiller Unit Pump
Intermediate Dryer Unit Demister
Vent to Funnel
Inert Gas to Deck Final Dryer Unit
Electric 80 kW Heater Fan Filter and Drain
Cooler Chiller Unit Sprayer
Bar
Light Ship Draught CI0
01VF
206
Effluent Pipe Not Lined
Combustion Air Steam Diesel Fuel Oil Chilled Water Sea Water Inert Gas
Sea Water Fiber Glass Lined Effluent Pipe Key
O2 Analyser
Refrigeration Compressor and Evaporator
Reactivation Dryer System Demister
Desiccant Vessel
Unit No.1
Desiccant Vessel
Unit No.2
Effluent Discharge Overboard Min.2m
B1 B2
2.9.1 Inert Gas and Dry Air Plant (XAI5321 and XD/5321 A through F)
The dry air / inert gas plant, installed in the engine room, produces dry air or inert gas which is used for the tank and piping treatments prior and after a dry docking or an inspection period.
The operating principle is based on the combustion of a low sulphur content fuel and the cleaning and drying of the exhaust gases.
The inert gas plant includes an inert gas generator, a scrubbing tower unit, two centrifugal fans, an effluent water seal, a fuel injection unit, an intermediate dryer unit (refrigeration type), a final dryer unit (adsorption type) and an instrumentation / control system.
Manufacturer Navalimpianti.
Inert gas delivery rate (Normal m3/h) 6500 Dry air delivery rate (Normal m3/h) 6500 Delivery pressure (bars) 0.3 Inert gas/dry air dew point (°C) -45 Inert gas composition (% vol) Oxygen 1
Carbon dioxide < 15
Carbon monoxide < 100 ppm Hydrogen < 100 ppm
Sulphur oxide < 2 ppm Nitrogen oxide < 65 ppm Nitrogen balance to 100%
Soot complete absence.
• The dry air/inert gas plant is locally operated.
The connection to the cargo piping system (refer to 2.2.1a) is made through two non-return valves and a spool piece which is in the normally closed position and the connection to the gas header is made through a removable bend (not normally connected).
Working Principle
Inert gas is produced by combustion of Gas Oil supplied by the Gas Oil Pump with air provided by blowers, in the combustion chamber of the Inert Gas Generator.
A good combustion is essential for the production of a good quality, soot free, low oxygen inert gas.
The products of the combustion are mainly carbon dioxide, water and small quantities of oxygen, carbon monoxide, sulphur oxides and hydrogen. The nitrogen content is generally unchanged during the combustion process and the inert gas produced consists mainly of 85% nitrogen and 15% carbon dioxide.
Initially, the hot combustion gases produced are cooled indirectly in the combustion chamber by a sea water jacket. Thereafter cooling of the gases mainly occurs in the scrubber section of the generator where the sulphur oxides are washed out. The sea water for the Inert Gas Generator is supplied by one of the ballast pumps via ballast main isolating valve 206.
Before delivery out of the generator, water droplets and trapped moisture are separated from the inert gases by a demister. Further removal of water occurs in the intermediate dryer stage, where the refrigeration unit cools the gas to a temperature of about 5°C. The bulk of the water in the gas condenses and is drained away with the gas leaving this stage via a demister. In the final stage, the water is removed by absorption process in a dual vessel desiccant dryer. The desiccant dryer units work on an automatic change over cycle, where the out of line desiccant unit is first reactivated with warm dry air which has gone through the reactivation dryer system.
A Pressure Control valve located at the outlet of the Dryer Unit maintains a constant pressure throughout the system, thus ensuring a stable flame at the generator.
Dewpoint and oxygen content of the Inert Gas produced are permanently monitored. The oxygen level controls the ratio of the air/fuel mixture supplied to the burner. The oxygen content must be below 1% by volume and the dewpoint up to a maximum of - 65°C with a minimum of -55°C. Both parameters are displayed locally and remotely through the Bailey IMS.
For delivery of Inert Gas to the cargo system, two combined remote air-operated control valves operated through solenoid valves are fitted on the distribution system, ie the Purge valve and the Delivery valve.
Dry-Air Production
The Inert Gas Generator can produce Dry-Air instead of Inert Gas with the same capacity.
However, for the production of Dry-Air:
a There is no combustion in generator;
The oxygen signal is overridden when the mode selector is on Dry-Air production.
After the processes of cooling and drying, and if the dewpoint is correct, the dry air is supplied to the cargo system through the delivery valve (with the purge valve closed).
Burner Description
The combustion air is supplied to the main burner by two
‘roots’ type blowers of 50% capacity each. The quantity of combustion air to the burner can be manually adjusted by a regulating valve in the excess air discharge line.
Fuel (Gas oil) is supplied at a constant pressure by the Gas oil electric pump which has a built-in pressure overflow valve.
Before ignition or start up of the unit, and with the pump running, all the fuel is pumped back via this fuel oil overflow valve which also serves to regulate the delivery pressure of the pump.
The fuel oil flows to the nozzle of the main burner via two solenoid valves and two fuel oil regulating valves.
A programme switch in the local control panel regulates one of the solenoid valves which also operates the pilot burner and initial firing.
The main burner is ignited by a pilot burner. The fuel oil is atomised in 2 steps. Firstly, the fuel oil is dispersed by a spray nozzle. Then it is subjected to a tangential impulse flow of steam which when it comes into contact with the axially orientated impulse flow of fuel, causes the ultrafine dispersion of the fuel oil.
Atomising steam for the ultramiser burner is fed via a special steam superheater. A pressure reducer stabilises the incoming steam pressure and the correct atomising pressure for the main burner can be adjusted.
The pneumatic valve in the steam line is opened a few seconds after ignition of the pilot burner. The steam superheater is fitted in the combustion chamber. The steam is further heated in the steam superheater, located in the combustion chamber to produce dry steam for efficient atomisation of fuel in the burner.
• For alarms and operating indications, refer to the manufacturer’s P & I diagrams.
2.9 Inert Gas and Dry Air Systems - Page 1 Issue: 1
2.10.1a Nitrogen Production System Issue: 1
Cargo Systems and Operating Manual LNG LERICI
TS 15
PI 35 PCV
35 PI
40
R12.
COOLER UNIT
PS 20 PS
L
Buffer Tank 7.5m3
8 bar
PT
DPS 5 DPS
PI PI PI
PI 35 PT
PT 35
Key
Gaseous Nitrogen Oxygen Enriched Air Air
Chilled Water Electrical