Subsea Gas Dew Point Control by Water Knockout Cooling
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Solution Overview
Problem
Current methods for subsea transport of produced gas face challenges with hydrate formation due to water condensation, leading to pipeline blockages, and require excessive use of hydrate inhibitors and complex regeneration processes, which are costly and inefficient.
Innovation Solution
A method and system for water dew point depression that involves separating the hydrocarbon fluid stream, controlled cooling to remove water, and subsequent separation to reduce the water dew point, allowing for reduced hydrate inhibitor usage and avoiding hydrate formation during long-distance transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrate inhibitors are added to prevent hydrate formation during long-distance subsea transport, then hydrate deposition is avoided, but the cost and complexity of the system increases due to required regeneration processes
Solution Approach 1:
The patent applies preliminary action by cooling the hydrocarbon stream below the hydrate formation temperature before it enters the pipeline, and removing water in advance through a dehydration unit. This preliminary water removal prevents hydrate formation during transport, eliminating the need for continuous hydrate inhibitor addition and complex regeneration processes at the receiving end.
Solution Approach 2:
The patent extracts water from the hydrocarbon stream through a dehydration unit that separates and removes water before the stream enters the transport pipeline. By taking out the water that would otherwise form hydrates, the system avoids the need for hydrate inhibitors and their associated regeneration infrastructure.
2Reliability
If electric heating is used to maintain pipeline temperature above hydrate formation temperature, then hydrate formation is prevented, but installation and operational costs increase significantly
Solution Approach 1:
The patent converts the harmful effect of cold temperatures (which cause hydrate formation) into a beneficial process by utilizing the cold ambient temperature to cool and condense water from the hydrocarbon stream. This preliminary cooling and dehydration before transport eliminates the need for energy-intensive heating during transport, as the stream is already in a hydrate-free state.
3Loss of energy
If pipeline diameter is reduced to increase flow rate and reduce temperature loss, then energy loss is minimized, but the operational window is reduced and future capacity is limited
Solution Approach 1:
The patent changes the key parameter of water content in the hydrocarbon stream through preliminary dehydration. By reducing water content before transport, the system enables the use of smaller pipeline diameters without risking hydrate formation, as the stream temperature can be maintained above hydrate formation temperature more easily. This parameter change (water content reduction) provides flexibility for future capacity increases without requiring pipeline replacement.
4Quantity of substance
If the hydrocarbon stream is cooled to remove water before transport, then hydrate formation is prevented, but the stream temperature drops below hydrate formation temperature requiring careful temperature control
Solution Approach 1:
The patent applies preliminary action by performing water removal through condensation and separation before the stream enters the transport pipeline. The stream is cooled to condense water, separated in a dehydration unit, and then reheated to a temperature above hydrate formation temperature before entering the pipeline. This preliminary water removal ensures hydrate-free transport without requiring continuous temperature control during transit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the need for hydrate inhibitors, minimizes regeneration costs, and prevents hydrate formation over long distances, enabling flexible and efficient subsea gas transport with reduced maintenance and infrastructure requirements.
Implementation Method 1
cooling the first gas phase in a controlled manner to knock out water or condense water and optionally other condensates into a second liquid phase
Implementation Method 2
separating the hydrocarbon fluid stream into a first liquid phase and a first gas phase
Data Source
AI summary
The present invention concerns a method for lowering the water dew point subsea in a produced multiphase hydrocarbon fluid stream containing water, the method comprising the steps of: separating (10) the hydrocarbon fluid stream (1) into a liquid phase (3) and a first gas phase (2); cooling (20) the first gas phase in a controlled manner to knock out water or condensing water and optionally other condensates while keeping the fluid above a hydrate formation temperature thereof; separating off condensed liquids (6) and a second gas phase; wherein the second gas phase (8) has a water dew point which is lower than that of the initial multiphase hydrocarbon fluid stream. The invention also concerns a system for lowering the water dew point subsea.