HEAT PUMP SYSTEM FOR SUBSEA PIPELINE HEAT GENERATION
Publication Date: 2015-Oct-09
The IP.com Prior Art Database
The invention relates to an apparatus and method for heating production fluids either oil or gas flowing in a subsea pipeline Over long distances heating is essential to avoid the formation of hydrates or waxes as the temperature of the production fluid drops due to heat losses to the surrounding seawater A heat pump system is used to increase the efficiency of the heating system over that of conventional methods such as direct electrical heating The condenser heat exchanger of the vapor cycle is incorporated directly into the pipeline It is possible to realize savings by utilization of the disclosed system by avoiding the installation of insulation and heat tracing
This invention relates to heat pump systems for subsea pipeline heat generation. Subsea pipelines are used to transport fluids such as oil or gas from offshore fields to onshore terminals, and for distribution to end users. Such pipelines may experience flow assurance issues with the transportation of produced fluids due to low temperatures. The main risk with cold production fluid is increased pressure drop in or blockage of the pipeline.
In subsea pipelines, heat is continually lost from the flowing production fluid to the surrounding seawater. Heavier components such as waxes and asphaltanes will begin to precipitate out once the temperature of the production fluid falls below a certain level. Typically these heavy components will deposit on the cooler pipe walls, and if untreated can cause blockages in the pipeline. By heating the production fluid, the heavier components will remain liquid and not deposit on the pipe walls. In transporting natural gas, any water present will combine with the hydrocarbons to form a hydrate below a certain temperature. As with waxes, hydrates too will deposit on pipe walls and if untreated could lead to blockages. For example, waxes and asphaltanes could precipitate out of the solution and deposit on the pipeline walls. Over time this would lead to a restriction and possible total blockage of the pipeline.
There are several existing methods for pipeline heating. One method is electric heat tracing in which resistive heaters or cables are built into the pipeline along its entire length. An electric current, supplied from a central location, is passed through these elements to generate heat. This requires a specially designed pipe. In another method, chemical injection inhibitor or antifreeze chemicals are injected into the production fluid that will lower the wax appearance temperature and thus prevent heavier elements in the production fluid dropping out of solution. These chemicals are then typically extracted at the exit of the pipeline and recycled. Both the injection and extraction requires chemical plant equipment that leads to increased capital and operation cost.
BRIEF DESCRIPTION OF DRAWINGS
The invention discloses apparatus and method for heating production fluids (either oil or gas) flowing in a subsea pipeline, wherein:
FIG. 1 shows a system of multiple heat pumps along a subsea pipeline carrying production fluids.
FIG. 2 illustrates a heat pump unit for subsea pipeline heating.
FIG. 3 illustrates a marinization scheme of a heat pump for pipeline heating.
FIG. 4 shows a schematic plot of pressure and temperature as a function of distance.
The present invention is directed toward a system of heat pumps for subsea pipeline heating to prevent solid formation and blockage of the pipeline. FIG. 1 illustrates a system of multiple heat pumps (4) arranged at a certain interval along the pipeline (1) with the pump (10) ...