Framo Hydraulic Cargo Pumping System on Ships
The framo hydraulic cargo pumping system is designed for a flexible and safe cargo and tank cleaning operation on ships. It consists of one hydraulic motor driven cargo pump installed in each cargo tank, ballast pumps, tank cleaning pumps, portable pumps and other consumers, all connected via a hydraulic ring line system to a hydraulic power unit as shown in figure below. The submerged cargo pump is a single stage centrifugal pump with the impeller close to the tank top, giving a good pumping performance of all kinds of liquids and with excellent stripping performance. The hydraulic section is surrounded by a cofferdam that completely segregates the hydraulic oil from the cargo.
The hydraulic power unit consists of electric motor and/or diesel engine driven hydraulic power packs, where the hydraulic pumps are of axial piston type and swash plate design with variable displacement. The pump displacement is hydraulically controlled via the pressure regulator on each pump and by this system, the oil delivery from the hydraulic pumps will always be the same as the oil consumption for the hydraulic motors. To control and limit the speed of the motor, a control valve is fitted for each motor.
To keep the hydraulic oil clean and hydraulic oil temperature within desired range, a full flow filter and cooler are installed in the main return line. To regulate the oil temperature, a cooling water inlet valve is controlled from the framo control system. To prevent impurities from entering the hydraulic system, the system is also pressurized (2-6 bar) when not in operation. Depending on the installation, this is done by a jockey or feed pump.
The discharge from all cargo, ballast and other pumps connected to the system may be remotely controlled from framo control panel, vessel’s integrated control system (ICS) or locally at each pump via the control valve. The portable pump is controlled locally at the pump via the control valve. The equipment is manufactured in Norway ‘Framo’ facility and the most important benefits of the system are:
- Segregation of cargoes for vessel’s safety and the environment.
- Maximum transport volume.
- Efficient stripping and tank cleaning.
- Hydraulic system without any electrical power equipment in cargo area.
- Automatic regulation of power needed and impossible to overload.
System Description
The Framo cargo pumping system is controlled by a Programmable Logic Control (PLC) installed inside the control panel. The PLC is programmed by Framo and provides the logic for safe operation of the system.
ALARM SYSTEM
All alarm inputs, except “Wear indication” are normally closed, meaning that the system is built up on normally closed contacts. Hence if a contact opens or there is a loose wire, an alarm condition occurs, i.e. FAIL TO SAFE.
The alarms are divided into two groups:
a) Shut down
b) Alarm for indication (pre-warning) only
Each alarm is indicated with a flickering light and an acoustic signal. The “Horn silence” button must be operated before it is possible to confirm the alarm by the “Acknowledge” button.
Group a) alarms: The “Reset” button must be operated to clear the alarm.
Group b) alarms: Automatic reset
POWER SUPPLY
Most hydraulic system control panels are supplied via two separate power feeders, main and back-up. In case of failure to main feeder, automatic change-over to back-up will take place. For increased availability and simplified trouble shooting, the control system is electrically divided into separate sub-systems. Each sub-system has its own 24VDC power supply. Failure in one system is not likely to interfere with other systems.
The feeders and DC power supplies are monitored by relays provided with status lamps. The lamps illuminate when corresponding feeder/ supply is in good condition. A failure on any of the feeders/ supplies or short circuit will generate a potential free (dry contact) power failure alarm to the engine control room in addition to alarm at the control panel.
FEED PUMPS
The feed pumps are started/stopped manually from control panel or from the electric starter cabinet. However, when initiating start of the first main power pack, two of the feed pumps will automatically be started (high capacity mode) before the power pack is started. When the power packs are stopped, the feed pump will switch from high capacity mode to low capacity mode (only one feed pump running) automatically after 10 minutes if this is not done by operator. A running signal is provided for indication on the control panel. The high capacity mode is used to keep feed pressure on the suction side of the main hydraulic pumps. Two feed pumps must therefore be running before the main power packs can be started. If one of the feed pumps stops when running in high capacity mode and the power packs are running, the third feed pump will start automatically. If the running signal for the third feed pump is not obtained within 3 seconds, the feed pressure low alarm will be initiated and the system will be shut down. One of the feed pumps must always be running when the system is not in operation and if it stops, the protection pressure low alarm is initiated.
At system shut down, the feed pumps will stop together with the first power pack.
POWER PACKS
The power packs are started/stopped manually from control panel or from the electric starter cabinet. The power packs can be started in any sequence. Maximum 4 starts should be made during an hour. Maximum 2 following starts can be made, then 15 minutes between each. The starts are controlled by the PLC, including starts from the electric starter cabinet.
”Closed” signal from limit switches on suction line for each power pack will stop or prevent start of the corresponding power pack only. An alarm light is provided for each power pack to indicate closed valve. If more than one power pack is loaded and the hydraulic oil temperature increases to 65°C or above, the control system will automatically unload all power packs in sequence except for one. The running light will start flashing for the unloaded power packs, and the high oil temperature alarm is re-initiated each time a new power pack is unloaded. The power packs will automatically be reloaded in sequence when the hydraulic oil temperature has decreased below 60°C.
SYSTEM PRESSURE CONTROL
System pressure is set by the potentiometer on the control panel, as a voltage input to the PLC. The PLC output is amplified by a proportional valve driver card controlling the proportional pressure control valve for the system pressure. The set pressure is automatically set to zero until one of the power packs has been loaded.
The manual set pressure is automatically compared to the actual pressure. If a pressure drop occurred, for example by starting too many consumers in proportion to number of power packs running, the PLC is limiting its output set pressure to maximum 60 bar above actual pressure. This is to avoid pressure peaks when starting another power pack or stopping a consumer. This function can be manually overruled in manual override mode 1 and is automatically overruled in mode 2.
REMOTE CONTROL OF HYDRAULICALLY DRIVEN PUMPS
The command signals from potentiometers at the front of the control panel are fed directly into the proportional valves for speed control. The built in pressure transmitters give a 4-20 mA (0-300 bar) feedback signal to the instruments on the control panel.
EMERGENCY STOP ARRANGEMENT
Following emergency stop arrangement is provided by Framo according to class requirements:
- Emergency stop push buttons located on deck are stopping the cargo pumps only, other consumers are not affected.
- Emergency stop push button located on hydraulic system control panel and central location outside engine room are stopping the hydraulic system.
SYSTEM SHUT DOWN
If a shut down function is initiated, the PLC will give shut down command to the power packs in sequence. The first power pack stops immediately and delay between shut down command of each following power pack is 0.75 seconds.
COOLING WATER INLET VALVE
The valve is automatically controlled and will open at hydraulic oil temperature above 50°C. It will stay open until the temperature decreases to below 30°C, then it will close. If no power packs are running and the hydraulic oil temperature is below 49°C, the valve will be closed. If there is a mismatch between command and feedback signal, an alarm will be released. If failure in the temperature monitoring loop, the valve will be opened.
ELECTRIC CONTROLLED BALLAST PUMP EJECTOR
The priming of ballast pump is done by creating vacuum in the pump casing. For creating vacuum, an air ejector is installed. The ejector for the priming system is automatically controlled by the PLC. The PLC receives input from a level switch installed in the pump casing and controls the solenoid valve for the ejector pilot air, starting and stopping the ejector. Time delay for start and stop is 2 seconds and the logic incorporates an interlock to prevent starting the ejector unless at least one power pack is running and operator’s hydraulic pressure command is more than 30 bar.
INERT GAS PRESSURE LOW
Input from external system for shut down of cargo pumps. Visual and audible alarm provided
CARGO PRESSURE HIGH
Input from external system for shut down of cargo pumps.Visual and audible alarm provided
INTERFACE TO VESSEL’S INTEGRATED CONTROL SYSTEM (ICS)
The Framo cargo pumping system can be operated/ monitored from Framo control panel or from ICS. The mode is selected in front of the Framo control panel.
INTERFACE TO POWER MANAGEMENT SYSTEM (PMS)
A “start request” signal is sent from the Framo electric starter to PMS. Start is prohibited until a “power available” signal is received from PMS.
Reference:
SERVICE MANUAL FOR CARGO PUMPING SYSTEM by Framo