Gas-to-Liquids Expansion Cooling for Hydrocarbon Separation
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Solution Overview
Problem
In remote oil production areas without existing gas transportation infrastructure, associated natural gas is typically disposed of by flaring or re-injection, both of which are environmentally or operationally suboptimal, as flaring is no longer acceptable and re-injection can harm oil production quality.
Innovation Solution
A gas-to-liquids plant process that subjects natural gas to expansion through a flow restrictor for cooling via the Joule Thomson effect, separates longer-chain hydrocarbons, processes the gas to form synthesis gas with excess hydrogen, and uses Fischer-Tropsch synthesis to convert methane into longer-chain hydrocarbons, with integrated steam reforming and oxygenate addition to prevent hydrate formation and optimize hydrocarbon recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural gas is cooled to below -10°C to increase recovery of higher hydrocarbons, then the quantity of longer-chain hydrocarbons increases, but the compression requirements and cost increase significantly
Solution Approach 1:
The patent changes the temperature parameter from extreme cooling (below -10°C) to moderate cooling (above -10°C, preferably above -5°C), and adjusts the pressure parameter to optimize hydrocarbon recovery while minimizing compression energy costs. This parameter optimization resolves the contradiction between maximizing hydrocarbon quantity and minimizing energy consumption.
2Reliability
If a pre-reformer is added to convert longer-chain hydrocarbons to methane, then the Fischer-Tropsch catalyst performance improves, but the device complexity and capital cost increase
Solution Approach 1:
The patent combines the pre-reforming function with the existing reformer unit, eliminating the need for a separate pre-reformer. The reformer is designed to handle both pre-reforming of longer-chain hydrocarbons and steam methane reforming in a single integrated unit, thereby reducing device complexity while maintaining catalyst performance.
Solution Approach 2:
The reformer unit is designed to perform multiple functions: pre-reforming of longer-chain hydrocarbons, steam methane reforming, and serving as the reaction zone for Fischer-Tropsch synthesis. This multi-functional design eliminates the need for separate pre-reforming equipment while ensuring adequate catalyst protection and performance.
3Duration of action of stationary object
If the Fischer-Tropsch conversion is limited to no more than 70% to protect the catalyst from water vapour, then the catalyst lifespan is extended, but the process requires an additional Fischer-Tropsch stage
Solution Approach 1:
The patent combines the Fischer-Tropsch synthesis reaction and the water-gas shift reaction within a single reactor unit. The reformer serves as both the reforming zone and the Fischer-Tropsch synthesis zone, eliminating the need for a separate second Fischer-Tropsch stage while maintaining catalyst protection through controlled conversion and water management.
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 process reduces the need for pre-reformers, decreases plant size and cost, and allows for efficient conversion of natural gas to longer-chain hydrocarbons, enabling the gas to be processed without significant heat transfer and minimizing environmental impact by avoiding flaring and optimizing oil production.
Implementation Method 1
the natural gas is subjected to expansion through a flow restrictor so as to undergo cooling through the Joule Thomson effect
Implementation Method 2
the expansion takes place without significant transfer of heat from the surroundings, the natural gas expanding into a lower pressure state
Implementation Method 3
with the consequence that longer-chain hydrocarbons condense from the vapour state into the liquid state, and can be separated from the remaining natural gas
Data Source
Figure 1
AI summary
A gas-to-liquids process and plant (10) for treating natural gas (5), in which the natural gas is subjected to expansion through a flow restrictor (16) so as to undergo cooling through the Joule Thomson effect, enables liquids (21, 22) to be separated from the gas stream. The natural gas may be cooled before it reaches the flow restrictor (16) by heat exchange with fluid that has passed through the flow restrictor (16). This decreases the proportion of longer-chain hydrocarbons in the natural gas, which may simplify subsequent processing, and may enable the size of the plant to be decreased.