The VOCON system is developed by Intertanko outlining how to limit the manual release to a tank pressure around the TVP of the cargo, rather than far below it. It is a prudent and logical step forward in managing cargo loss and involves two pieces of equipment:
a) Constant pressure valves.
b) An automated release valve that operates according to the VOCON procedure.
The individual valves are referred to as the VOC stop system. The central, automated system for gas release is referred to as the VOCON valve system.
The key element of the VOCON valve system is a centralized release valve that features:
The system is primarily used on oil carriers.
The system works with either hydraulic or electrical actuators, or with a self-contained Ex-approved hydraulic/electric actuator in order to avoid interference with an existing hydraulic system – e.g. for system upgrades. The opening and closing pressure are remotely controlled from the C.C.R. via a PLC-unit, which incorporates the physical properties of any given crude oil.
The VOCON venting system is controlled by an electrical actuator maintaining the tank pressure between the set-pressure and the re-seating pressure. The VOCON system is installed on the mast riser bypass line and controls the vapour pressure in all the cargo tanks during the voyage for direct emission control.
By controlling the pressure in the venting system, it is possible to fully control the VOC emissions.
The VOCON system can be programmed to enable adjustment of the opening setting on the valve, according to what is optimal for the specific cargo.
The valve actuator is analogue controlled and can be set to open partly instead of full. This feature can be used to reduce the flow rate for measuring more accurately and keep the pressure on the cargo avoiding boil off. Approved for hazardous area installation.
A built-up piston controlled inline pressure vacuum valve in stainless steel for breathing purposes and full flow capacity performance. Covering a range from 2.400 Nm3/h to 26.000 Nm3/h.
The VOCON System is operated from an HMI (Human Machine Interface) touch screen in the front of the cabinet. It is possible to run in automatic or manual. Settings can be adjusted within the max/min limitation for safe operation. The control cabinet must be placed indoors in a non-hazardous area, e.g. in the Cargo Control Room.
The relative pressure transmitter (gauge pressure) is placed on the IG Main ine. The transmitter is used to measure the pressure in the tank venting system and reports back to the control cabinet for action. Approved for hazardous area installation.