NO20150152A1

NO20150152A1 - Device and Method for Emptying Cargo from a Tank

Info

Publication number: NO20150152A1
Application number: NO20150152A
Authority: NO
Inventors: John Magne Oppedal; Petter Solberg
Original assignee: Vitallic As
Priority date: 2015-02-03
Filing date: 2015-02-03
Publication date: 2016-02-08
Also published as: WO2016126164A1; NO337187B1

Description

Inventors Information

1 DESCRIPTION OF INVENTION

Title of invention

The name of the invention, Zeres, is a composed name made up by Zero and Residuals. The name Zeres illustrates that by using the invention, Zeres, the result will be zero residuals in the cargo tanks after completion of emptying sequences.

The technical field of the invention is mechanical and fluid technique.

Background for the invention

Forexisting chemical cargo tankens pumping systems, the re are challenges related to the removal of remaining residuals after ended conventional pumping and stripping sequences.

The remaining residuals represent a part of the actual shipped cargo, and for some cargos, the re will be an important economic benefit to deliver all the shipped liquids. This is difficult, and not adequate, for most tankers with today^s conventional tank stripping arrangement.

From an environmental point of view, this new invention will reduce the quantity of waste residuals. This also means a reduced need forwashing water to dean the tanks and following reduced amount of delivered waste to cargo terminals at completion of a cargo operation. If one single washing sequence is cancelled by installing Zeres, it means that the generated waste volume will be noticeably reduced, saving both cost and environment.

Chemical cargo tank vessels carries different kinds of cargos, and it is important to make sure that tanks are sufficiently cleaned and all remaining cargo and washing water are re mo ved before new cargo is loaded.

The fully removal of remaining residuals in today's tanks are done manually by ship^s crew. This can be an unsafe solution seen from a HES point of view. For many of the different shipped cargos, the content can be dangerous and represent a high risk for explosion ortoxicity, which restricts the possibility to enter cargo tanks.

State of art

Following, a brief description of the state of art for conventional stripping sequence: Normal remaining quantity of cargo in the cargo tanks at completed discharge sequence for existing systems can va ry from 25 to 250 L, depending on pump type, tank design and condition of pump and stripping systems. In addition to the cargo, the re will be the same amount of washing water collected in the tanks after ended washing sequences. Removal of remaining cargo and washing water will have to take place. The crew of the ship often perform this job manually, which demands unnecessary time and labour.

Cargo lines, depending of design/layout, are emptied completely by use of pressurized nitrogen or air at ended stripping sequence.

Remaining cargo in the cargo pipe from the pumps are emptied through the stripping pipe by adding pressurized inert gas through the cargo pipe purging valve while pump is running. The cargo discharge valve is closed during the stripping sequence and the pump is continuously running to maintain backpressure for the cargo pipe from the pump while nitrogen is pushing the liquid column down to the assembly point for the cargo and stripping pipe. When the stripping sequence of cargo is completed, remaining residual liquids will be remained in the pump suction well.

The liquid can, for designs as explained f urt he r below, be removed by vacuum stripping systems. The efficiency for vacuum systems is normally poor, and the designs are limited concerning density and viscosity for cargos and lifting heights.

Following, a brief description of the state of art for vacuum stripping sequence:

Vacuum stripping arrangement is an optional stripping method, which can be used for smaller size chemical cargo tankers carrying low viscosious cargos. Vacuum stripping system is mainly used to remove washing water after tank cleaning.

Use of vacuum systems for removing residual cargo is an option, but the re are seve ra I uncertain issues and challenges related to the method.

Vacuum stripping arrangement is installed on fewvessels due to its need for high capacity of purging medium and rf s uncertain ability to collect cargo with high viscosity index, high density and for tank applications with a tank height above certain critical limits for vacuum lifting.

Some challenges related to vacuum as stripping method are:

• The ejector system's ability to create a sufficient vacuum for removal of cargo. • Vacuum stripping has a limitation for lifting capacity, which is directly dependent of tank height and cargo density. • Consumption of a large amount of nitrogen to empty the cargo pipe, followed by driving the ejector system and again emptying the cargo pipe after collecting residuals from the pump suction well. • A large number of operations for the stripping sequence cause a gre a te r consumption of operation time, which results in increased time at terminals. This might also result in less cargo operations per year.

Description of the invention

The invention is made on the principles of gra vi ty filling and evacuation by pressurization of cargo from a closable volume.

The idea is to use inert gas pressure for driving the cargo to the top. For enabling this, the tank has to be equipped with a closable volume with an automatic closing mechanism, which is the new invention, Zeres.

How this invention solves the problems of the prior art

This invention solves the problems of the prior art as it has the possibility to completely remove all remaining cargo, after completion of normal pumping and stripping sequences, in a safe and effective way, nearly independent of viscosity and density of the shipped cargos, and nearly independent of tank heights and size for cargo tanks.

The invention also enables complete emptying of washing water from cargo tanks without need for manual work in the tank. This is not possible in a good way with existing inventions, due to excessive time consumption and limitation for cargo tank heights. (Vacuum systems are normally limited to maximum 10 meters lifting height depending on cargo density).

What makes this invention new and unique

The use of a Closable Cargo Collector Volume (hereby referred to as CCCV) is new and unique for the invention. CCCV means a small pressure tank volume for collection of cargo. Further, the volume are being pressurized by inert gas to force the cargo out through a stripping pipe further to the cargo pipe on the outside of the tank.

The CCCV will be integrated below the suction well of the cargo tanks and gives the unique possibility to have all cargo collected by gra vi ty and forced out by use of pressurized gas.

The benefit with this invention compared to known technology

The benefit with this invention is the innovative use of a minor space in the ballast tank area of the vessels, which gives a greater collective volume for residual cargo. When this open volume is tu rn ed into a closable volume by use of the re mote closable inlet valve, it gives a benefit that no other stripping systems have tåken into use as of today.

New Invention

Zeres will be located in the ballast tanks below the cargo tank floor, and below the cargo pump in each of the respective cargo tanks.

Zeres will be an extension of the pump's suction well. Zeres will be installed into the existing double bottom tank below pumps suction well, and take a minor part of the volume in the ballast tank. Installation of the system is available for both new vessels and as an upgrade for existing vessels. The Zeres arrangement includes a new customized pump suction well for maintaining the function for both the pump system and Zeres.

The principle of Zeres is to push the remaining cargo in the suction well through a pipe to the cargo pipes on ship deck by applying pressurized inert gas to a closable cargo collector volume (CCCV) arranged below the existing suction well. The remaining cargo will first drain to the pump suction well from the sloped cargo tank floor. Since Zeres is below the suction well, all cargo will drain into the CCCV. Inert gas is applied through a gas inlet pipe to pressurize the actuator volume inside Zeres. Pressurised inert gas pressure will be tåken from the existing systems on board on the vessel and connected to Zeres by tubing.

The seal plug moves upwards and seals and doses the CCCV.

The CCCV is then pressurized from gas pressure coming through an orifice in the actuator volume. Cargo is being forced through a cargo outlet pipe located in the lowest point in the tank. Detailed decription of the invention Zeres - design and operation

Description of the components of Zeres related to figure 4

All the main components of Zeres are assembled to the top plate (10) that is assembled to the CCCV (1) with a wing nut (11). The top plate (10) and the wing nut (11) are equipped with o-rings (8) for sealing purposes.

The inlet (3) and outlet (4) -pipe are assembled, both below and above the top plate (10), with fittings for easy assembly/disassembly. The pipe extension will be fitted and routed on the side of the cargo tank reaching through to deck.

This design allows easy service access to the CCCV (1) and components assembled to the top plate. Removal of parts for relocation to a workshop for service will be easy.

CCCV (1) will be welded in relation to the pump suction well. One side of the CCCV will face towards ballast tank.

The sealing piston top (2) will be made of chemical resistant high shore elastomer that seals towards the tank top (10).

All material selection will take antistatic electricity into consideration.

The orifice nozzle (5) will be a flow restrictor, which secures that the piston will lift up and close the CCCV before start of pressurization. The check valve (12) will prevent cargo from entering inside the piston arrangement (9) when the system is not in operation.

Bracket (6) for guiding of the piston (2) is fitted to the top plate (10) for easy access and service (Full disassembly possibility)

Spring for piston return (7) will force the piston back to rest position (open position) when sequence is completed. The spring is fitted to supplement the gravity force on the piston (2) for conquer the friction force between the dynamic seals (13) forensuring open position while not in operation.

There will be installed rubber seals (8) between the CCCV (1) and the actuator volume (9). This is in order to prevent cargo from entering the actuator volume (9). Nitrogen pressure en ters the actuator volume (9), forcing the piston to upper position due to increased pressure in the actuator volume (9). This will isolate the collector volume CCCV (1). Following gas will flow through orifice (5) and check valve (12) to build up pressure in the CCCV (1).

Description of Zeres operation principles related to figure 3 and 4

After a conventional pumping and stripping operation for a cargo tank is complete, the residual cargo located in the pump suction well (C) for the cargo tank will be drained into the CCCV (1).

Pressurized inert gas will be applied to the inlet pipe (3). The actuator volume (9) will be pressurized and the piston will move the seal plug (2) upwards forclosing of the cargo collector volume (1). Inert gas will then start to flow through the flow restrictor orifice (5), further through the check valve (12), and finally out to the CCCV (1). The orifice (5) represents a particularly resistance and ensures that the piston (2) moves and seals prior to the gas pressure build-up in the CCCV (1). As the pressure increases in the CCCV, the cargo, which represents a higher density than the inert gas will be forced into the cargo outlet pipe (4). The check valve (5) prevents cargo to leak inside the actuator volume (9) when the system is not pressurized. The operation continues until all residual cargo in the cargo collector volume (1) is forced out through the cargo outlet pipe (4). Completion of this Zeres cargo stripping sequence can e.g be detected by noise change from free flow of inert gas in the cargo pipe.

When gas pressure in the inlet port for inert gas (3) is released, the piston returns by the force of the spring (7) and ensures that the sealing plug (2) will open for refill of cargo from the suction well into the CCCV (1). This sequence will be repeated for as many times as required for emptying all cargo in the pump suction well.

Benefits by us ing Zeres

• Few operations: open/closing of one purging valve and one stripping valve for few repeated sequences and enable completely removal of remaining cargo or washing water. • Good service ability, as all the vital parts are removable along with top plate.

• No need for unnecessary tank entries.

• Important feed to HSE prospective on board the vessels.

• Small probability for making mistakes during operations.

• All handling of cargo liquid are made inside closed volumes, which restricts physical contact for operators • Great reduction in usage of purging medium compared with co m pa ra ti ve systems. • Operation time is faster due to the invention is based on the closable volume principle.

Zeres tank volume and components will be designed in accordance with the actual design pressure and in accordance with applicable pressure vessels standards.

Zeres will include a complete extended suction well for cargo pumps with integrated CCCV.

The suction well will have a unique design for Zeres to fit and with slopes for cargo to drain.

Claims

The following claims shall be protected by this application: 1. A system to pressurize a closable volume below and in relation to a chemical cargo tank, or another cargo tank, to build up a differential pressure to the environment to force out any residual cargo from the cargo tank which prior have been drained into the closable volume through a valve.
2. System in accordance with claim 1, with a self-forcing seal plug, which will obtain an even larger sealing force by the pressure from the cargo collector volume due to surface ratio from the engagement by the actuator volume.
3. System in accordance with claim 1 or 2,

Characterized in that the regulation system with an orifice nozzle size that ensures the piston to actuate and seal/isolate the cargo collector volume fully from the environment before pressurizing of the cargo collector volume, with the same source of pressure.
4. System in accordance with claim 1 or 2,

Characterized in that for the design of main system, which is fully removable and mobile for easy service access.
5. System in accordance with claim 1, 2 and 3,

Characterized in that the design is based on automatic operated mechanism with few remoted operations.
6. System in accordance with claim 1, 4 and 5,

Characterized in that the system can be used for all types of cargo tanker vessels and floating sto rage and production units (shipping and offshore)
7. System in accordance with claim 1, 2 and 5,

Characterized in that the system is driven from the tank vessels existing compression aggregate.