Short Loop Regeneration for Gas Dehydration Units
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Solution Overview
Problem
Conventional gas dehydration units using molecular sieve adsorbent beds face challenges with high pressure regeneration, leading to water and hydrocarbon refluxing, incomplete desorption, contaminant buildup, and reduced molecular sieve performance, resulting in economic losses and operational inefficiencies.
Innovation Solution
A system with parallel vessels in adsorption and regeneration modes, utilizing a short loop for increased regeneration gas flow and pressure reduction, allowing for efficient water desorption and contaminant removal, and optionally incorporating a secondary dehydration unit for further moisture removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pressure regeneration is used to desorb water from molecular sieve, then regeneration speed is improved, but water and hydrocarbon refluxing occurs and desorption efficiency decreases
Solution Approach 1:
The system implements periodic pressure cycling between high pressure (for rapid water desorption) and low pressure (for hydrocarbon removal and preventing refluxing). The controller alternates between these pressure states to achieve complete regeneration while avoiding the harmful effects of sustained high pressure
Solution Approach 2:
The system dynamically changes pressure parameters during the regeneration process, using high pressure initially for rapid water removal, then reducing to low pressure for hydrocarbon desorption. Temperature parameters are also adjusted to optimize desorption at different stages
2Loss of time
If high pressure regeneration is used, then regeneration time is reduced, but contaminant buildup increases and molecular sieve performance deteriorates
Solution Approach 1:
The system uses periodic pressure cycling to alternately remove water (at high pressure) and hydrocarbons/contaminants (at low pressure), preventing contaminant buildup while maintaining short regeneration cycles
Solution Approach 2:
The multi-vessel configuration allows continuous operation where one vessel is always in adsorption mode while another is regenerated, ensuring uninterrupted gas treatment and continuous contaminant removal
3Productivity
If large vessel diameters are used for high pressure regeneration, then processing capacity is improved, but heat load on regeneration system increases
Solution Approach 1:
The system divides the regeneration process into multiple vessels operating in parallel, with each vessel handling a portion of the total gas flow. This segmentation reduces the diameter of individual vessels while maintaining overall processing capacity and reducing heat load on each unit
4Reliability
If regeneration gas is used to heat molecular sieve bed, then water desorption is improved, but oxygen reacts with hydrogen and hydrocarbons forming unwanted by-products
Solution Approach 1:
The system uses periodic pressure cycling to separate the water desorption phase (high pressure) from the hydrocarbon removal phase (low pressure), preventing the formation of unwanted by-products by avoiding simultaneous presence of oxygen, hydrogen, and hydrocarbons at high temperatures
Solution Approach 2:
The system extracts and removes hydrocarbons from the regeneration gas stream at low pressure before they can react with oxygen and hydrogen to form unwanted by-products like sulfur and carbon dioxide
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 enhances regeneration efficiency, reduces regeneration time, and improves molecular sieve performance, increasing LNG throughput while reducing capital and operating expenses and extending molecular sieve life.
Implementation Method 1
Dehydration of natural gas is typically accomplished by flowing the gas over zeolite-based molecular sieve adsorbent. Water in the gas is preferentially adsorbed by the molecular sieve.
Implementation Method 2
The adsorbent is regenerated in vessel 2R at high temperature by flowing dry regeneration gas 3 over the bed of molecular sieve adsorbent material
Implementation Method 3
The regeneration gas is then cooled in a condenser 5, free water 6 is separated in a separator 11 and removed
Implementation Method 4
The remaining gas 7 is compressed by a compressor 8 and returned through line 46 to the front-end of the plant
Data Source
AI summary
Water saturated molecular sieve in a gas dehydration unit is regenerated. A short loop is used in which regeneration gas is recycled to a heater upstream of a vessel in regeneration mode. The regeneration gas passes over the molecular sieve in the vessel to desorb water thereby regenerating the molecular sieve. The short loop also includes a condenser, a water separator and a compressor. The regeneration gas is not recycled to the AGRU at the front-end of the plant, thus the regeneration gas flow rate can be increased, as it is not limited by the front-end capacity of the plant. Moreover, the pressure of the system during regeneration can be reduced within the limits of system hydraulics. By using the short loop, the total time required for regeneration can also be reduced. The embodiments disclosed can de-bottleneck molecular sieve regeneration constraints in LNG, LPG or cryogenic gas plants.