Technical Field of the Invention

The present invention relates to a heating system and a method for heating a liquid of any type contained in at least one tank on marine installations or vessels, based on circulation of a thermal liquid, such as water and/or glycol. Each tanks is provided with at least one heating element and associated piping system for supply and discharge of the thermal fluid, and an inlet for loading the fluid to be stored and an outlet for discharging the stored fluid. Further, each tank is preferably provided with a primary circulation system including a pipe system with at least a valve and pumping unit associated with said inlet and outlet for circulation of the fluid in the tank, and with an interconnecting pipe system for secondary circulation of the thermal liquid in order to heat the liquid in the tank.

Background for the Invention

On vessels and on board offshore platforms there is a need for storing fluids, such as oil or other types of liquids, either for transport and storage and/or for consumption. Such liquids have a tendency to have a low viscosity, reducing the pumping ability of the liquid. In such tanks, it is well known to apply a primary and a secondary circulation system. The primary circulation system is applied for filling and emptying the tank of its liquid content and also for circulating the liquid while stored inside the tank. As a consequence, it is also well known to heat the liquid while stored in the tank by circulating a heated liquid, such as water through a piping system inside the tank. Said circulating system of a heated liquid is through relatively long pipelines inside the tank. Thus, the circulation pipeline system of the tanks functions as heating elements, said pipes being plain pipes arranged on the bottom of the tank. For connecting said pipeline to a central, main circulation pipeline system onboard the vessel, the tank is provided with an inlet and an outlet.

For circulating the heated liquid in the pipeline system inside the tank, the pipeline system comprises a pump and valve(s) and a loop connecting the inlet and the outlet, so that the fluid in the tank may be circulated through the system, for example during heating. The circulation system is a closed system, making it possible to circulate hot fluid to each tank for individual heating by opening and closing the valves associated with each tank. The hot fluid may for example be steam, hot water, glycol, or thermal oil. One circulation pump is also usually introduced in the circulation system and the circulation pipeline system is connected to a heat exchanger for supply of heat from an external source to the liquid circulating through the system. Also, a conventional expansion tank is incorporated into the closed circulation system. For heating of ORO cargo (Oil Recovery

Operation cargo) steam delivered by a steam generator system is the most common medium for heating the tank fluid, such steam being introduced directly into the tank.

As an alternative for circulating a hot fluid through a closed piping system inside the tank, steam may be injected directly into the content of the tank. Summary of the Invention

An object of the present invention is to provide an improved heating system for tanks containing a fluid, and an improved method for heating fluids contained in tanks.

A further object of the present invention is to provide a system using "green energy", i.e. energy recovered from one or more cooling systems on the marine installation, such energy otherwise would have been lost or wasted.

Another object of the present invention is to provide a system which effectively and quickly may be installed in and removed from a tank without any significant installation activity.

Another object of the present invention is to provide a solution enhancing the cleaning process of the tank, allowing the region around the heating element to be thoroughly cleaned, without leaving any un-accessible area of the tank to be cleaned.

According to the present invention highly effective spiral coils may be used for heating the fluid in the tanks, said coils being of a type and being configured in such way that they quickly may be installed and removed from the tank in an efficient and cost effective manner. The coils are preferably attached to the tank wall, thus avoiding any detrimental permanent fixing or attachment brackets or other types of attaching means fixed to the tank bottom.

Further, according to the present invention an efficient control system is provided, enabling use of "green energy" and individual control and monitoring of the heating of each tank by individual regulation of the opening of each of the valves for supply of heated fluid on an individual basis for circulation through each separate heating coil. The control of the valves may be on an open/closed basis.

The objects of the present invention are achieved by means of a heating system and a method as further defined in the independent claims while alternatives and embodiments of the invention are defined by the dependent claims.

The heating system is provided with a secondary circulation system in a closed circulation system, comprising a heat delivering heat exchanger, a circulation pipeline system delivering heat to at least one heating element in a tank and an actuated valve arranged in the supply line for each tank for separately controlling the rate of circulation of heated liquid through the heating element, the heating element comprising at least one small sized, high performance removable heating coil, and that the system includes a system for controlling the volume of heat delivered separately and independently to each tank.

According to one embodiment, the heating element is in the form of a plain, smooth coil provided with a flange arrangement for attachment to the tank wall, above the tank floor.

Further, one or more temperature sensing sensors are provided in the system, measuring the temperature of the heating fluid delivered to the tank(s), the valves being preferably individually controlled by the control system, opening or closing the valve individually based on temperature measurements compared with

corresponding set values stored in the control system.

According to the method proposed herein, green energy in the form of recovered heat, is delivered from heat producing units, such as cooling liquid for cooling engines, exhaust gas, combustors and incinerators used for heating the liquid in said tank(s).

Said heated liquid is preferably circulated in a closed system where heat is delivered by a heat exchanger, supplying heat from said cooling liquid to said tanks individually. The volume of heated liquid circulating through one or more tanks may preferably be individually controlled by regulating the opening of an actuated valve, based on signals from a control unit, the unit comparing temperature measurements from one or more temperature sensors and comparing said registered temperature with predefined set values for the required temperature.

According to one embodiment of the method described, the valve opening is regulated such that the volume of heat energy supplied to all tanks are equal.

By providing one or more temperature measuring sensors in main circulation line system it is possible to control the positions of the various valves, such valves preferably, but not exclusively, being of the open/close type, and/or to regulate the speed of the main circulation pump, based on comparison of the registered values with set values. Hence an automatically controlled system is obtained.

The system according to the present invention may be connected directly to the main heating system onboard the vessel, making it possible to supply heat from the heat recovery system, i.e. using heat which otherwise would have been wasted.

It should be noted that it is not always necessary to circulate the liquid inside the tank during heating, if the liquid is of a low viscosity type. Further, according to the present invention, it is not necessary to use a large number of temperature measuring sensors inside the tank. When measuring the temperature, the circulation pump may be stopped for a certain period of time, and also stopping then heating of the liquid in the tank, allowing the heated liquid to mix with the

surrounding liquid, and then restart the circulation, measuring the temperature in the circulation pipeline. Short Description of the Drawings

In the following one embodiment of the invention will be described in detail, referring to the accompanying drawing, wherein:

Figure 1 shows a system diagram of one embodiment of a rank heating system according to the invention.

Detailed Description of the Invention

Figure 1 shows a system diagram of one embodiment of a tank heating system 10 according to the invention. The system comprises a plurality of tanks 1 1 provided with an inlet 12 for loading a fluid, such as oil, into the tank. It should be noted that the system according to the present invention also may be applicable in respect to only one tankl . Further, the tank 1 1 is also provided with an outlet for discharging the liquid from the tank. The inlet 12 and the outlet of each tank 1 1 are associated with a main piping system (not shown) for loading or discharging liquid from the tank system 1 1 . According to the embodiment shown, each tank is also provided with a discharge and circulation pump 14 and a circulation pipeline 15, configured to allow circulation of the liquid stored in a tank in a closed loop from the tank 1 1 through the outlet 13, the circulation pump 14, the circulation pipeline 15, the inlet 12 and back to the tank 1 1 . A valve 16 is provided in the circulation pipeline 15. Such circulation system is not always required, if the liquid inside the tank has a low viscosity.

According to the present invention the tank is provided with a heating system comprising two heating element 17 arranged inside the tank 1 1 . The tank heating system according to the embodiment shown is a closed pressurized heating system for maritime installations based on thermal fluid (water) circulation and a working temperature up to 100 °C. The working pressure is normally up to 2 Bar. Even though two heating elements 17 are shown in the Figure, the number of heating elements 17 may be one or more, depending on the size of the tank 1 1 and the type of fluid to be stored in the tank 1 1 and the required heating in order to provide a liquid having a viscosity which enable pumping of the liquid..

The heating elements 17 in the tank 1 1 are preferably made of "small size" high performance heating coils with capacity normally up to 200kW and are flanged to the tank 1 1 close to the suction outlet line for easy and fast mounting and dismantling. If the liquid in the tank 1 1 is of low viscosity type, the pump 14 connected to the tank 1 1 could be used for circulation internally in the tank 1 1 . This will give more effective heat exchange. For example two coils of 200 kW may be used for each tank 1 1 , provided with flange arrangement for enabling welding to the tank wall and with use of flexible hoses for enabling quick and cost effective connection.

As disclosed the heating elements 7 are connected to an inlet pipeline 8 and an outlet pipeline 19 and all heating elements 17 being connected to a main circulation load pipeline 20 and discharging pipeline 21 . In the inlet pipelines 18, branched off the main inlet pipeline 19, an actuated valve 22 is arranged for flow control to individual heating coils 17/tank 1 1.

The thermal fluid circulating through the system is heated by a heat exchanger 23, connected to the central heating system (not shown). This gives an opportunity to utilize "green energy" from heat recovery system in HT-cooling system and/or exhaust gas economizer in the exhaust gas system. Such central heating system is disclosed in the applicant's co-pending Norwegian application No. 201 10336, filed on the same date as the present application, the content of which hereby being included by the reference. An expander tank 24 for thermal expansion between 10 and 100 degrees Celsius and a thermal fluid circulation pump or pumps 25 are connected to the main inlet and outlet circulation pipeline system. One or more actuated valves 26 are also incorporated into the main circulation system. Preferably two equal pumps 25, mounted on skid may be used, one running and one stand-by. Each pump 25 may preferably have capacity for delivering thermal fluid sufficient to meet the total heat consumption required. The pumps 25 may preferably be arranged in parallel with associated valve and piping system, always allowing one of the pumps to be in a stand-by mode. At the inlet and outlet side of the heat exchanger sensors for measuring the temperature of the thermal fluid in the closed loop entering and leaving the heat exchanger are arranged. The sensed temperature is sent to a control cabinet 28 through a signal line system 29.

The system according to the invention is automatically controlled and monitored by a control system on an on/off basis from the control cabinet 28 and can be interfaced to the main computer system (IAS). Manual control is standard features. The control system also control supply of power to the actuated valves

22,26, the status and the position of the actuated valves 22,26 also being controlled and monitored from the control cabinet 28. The control cabinet may for example be in the form of a 5,7" touch screen disclosing mimic diagram for the main pipeline 20,21 and all main components. The system may also have user interface for system operation and parameter setting, also displaying temperatures and valve status. Further, the system may also have an alarm display and an acknowledge system, interfacing and/or optionally being controlled by an Integrated Automation System (IAS) 31 on board the vessel.

The system is automatically controlled and monitored by a control system 30 and can be interfaced to the main computer system (IAS) 31 . Manual control is standard features.