Closed Loop LPG Regeneration for Gas Dehydration Molecular Sieves
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Solution Overview
Problem
Conventional natural gas dehydration units face inefficiencies in regenerating molecular sieves due to high pressure regeneration leading to hydrocarbon and water refluxing, corrosion, and incomplete contaminant removal, resulting in sub-optimal performance and reduced sieve life.
Innovation Solution
A closed loop regeneration system using liquid propane (LPG) as a regeneration medium, which is superheated, passed through the saturated molecular sieve to regenerate it, and then recycled after condensation, with additional treatment steps to remove contaminants, allowing for independent adsorption and regeneration processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pressure regeneration is used to regenerate molecular sieve, then regeneration speed is improved, but hydrocarbon and water refluxing occurs causing poor water desorption and corrosion
Solution Approach 1:
The patent changes the pressure parameter during regeneration by using a pressure swing process: high pressure is applied during the drainage phase to remove liquid hydrocarbons and water, then low pressure is applied during the vacuum phase to achieve complete water desorption without refluxing. This dynamic parameter change resolves the contradiction between regeneration speed and water desorption quality.
Solution Approach 2:
The regeneration process is divided into periodic phases: high-pressure drainage phase followed by low-pressure vacuum phase. This periodic action allows the system to alternately achieve rapid liquid removal and complete water desorption, resolving the contradiction between regeneration speed and desorption quality.
2Productivity
If high pressure regeneration is used, then regeneration efficiency is improved, but vessel thickness and material requirements increase creating additional heat load
Solution Approach 1:
The patent uses periodic pressure swing with alternating high and low pressure phases. The high pressure phase is brief and used only for drainage, while the majority of the regeneration occurs at low pressure. This reduces the cumulative heat load on the vessel walls compared to sustained high pressure operation, thereby reducing vessel thickness and material requirements.
3Device complexity
If contaminants are present in regeneration gas, then regeneration process is simpler, but complete regeneration of molecular sieve is not achieved resulting in sub-optimal performance
Solution Approach 1:
The patent extracts and removes contaminants (liquid hydrocarbons and water) from the regeneration gas stream during the high-pressure drainage phase before the vacuum phase. This extraction of harmful contaminants allows the use of relatively simple regeneration gas (even air with contaminants) while still achieving complete molecular sieve regeneration in the subsequent low-pressure vacuum phase.
Solution Approach 2:
The periodic pressure swing separates contaminant removal (high-pressure drainage phase) from water desorption (low-pressure vacuum phase). This temporal separation allows contaminants to be removed first, enabling complete regeneration during the vacuum phase without interference from contaminant reactions.
4Object-affected harmful factors
If contaminants react at high regeneration temperatures, then by-products are formed causing fouling and off-specification products, but reducing temperature prevents complete contaminant removal
Solution Approach 1:
The patent uses periodic pressure swing where high temperature is applied during the brief high-pressure drainage phase for contaminant removal, then the system transitions to low-pressure vacuum phase where complete water desorption occurs at lower temperatures. This temporal separation prevents prolonged high-temperature exposure that would cause excessive by-product formation while still achieving effective contaminant and water removal.
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 reduces water refluxing, improves regeneration efficiency, extends sieve life, and meets stringent moisture specifications by providing a cleaner regeneration medium, reducing equipment sizes and operational costs while ensuring safer and more reliable operations.
Implementation Method 1
a pump for pumping the LPG from the storage tank
Implementation Method 2
at least two heat exchangers in series for receiving and converting the LPG to a hot (superheated) propane and/or butane gas
Implementation Method 3
converting the LPG to a hot (superheated) propane and/or butane gas
Implementation Method 4
the hot propane and/or butane gas passes across the water saturated mole sieve thereby regenerating the water saturated mole sieve
Implementation Method 5
During dehydration mode, water and other contaminants are adsorbed onto the mole sieve material; and during regeneration mode, they are desorbed from the mole sieve
Implementation Method 6
a condenser in communication with a regeneration gas outlet in the gas dehydration unit for receiving an overhead stream containing the hot propane and/or butane gas from the gas dehydration unit and dropping the temperature to form a fluid stream containing LPG, water and non-condensable gases
Implementation Method 7
a three phase separator in communication with the condenser for separating the fluid stream into a gas stream, a water stream, and a liquid stream comprising LPG
Data Source
AI summary
A system is disclosed in which water-saturated desiccant in a dehydration unit, having previously been used to dehydrate natural gas, is regenerated in a closed loop process using liquid petroleum gas (LPG). LPG is pumped from a storage tank, vaporized and superheated. The superheated LPG gas enters the dehydration unit such that the hot gas passes over the desiccant thereby regenerating the desiccant. An overhead stream from the dehydration unit passes to a condenser where the temperature of the hot gas from the dehydration unit is dropped to form a fluid stream containing LPG, water and non-condensable gases. The fluid stream passes to a three phase separator for separating the fluid stream into a gas stream, a water stream, and a liquid stream containing LPG which is then returned to the storage tank for reuse in the closed loop process.