Method and system for obtaining hydrogen from a feed mixture which contains hydrogen and hydrocarbons
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Solution Overview
Problem
Low pressure demethanizers used in hydrogen recovery from gas mixtures containing hydrogen, methane, and hydrocarbons with two carbon atoms face inefficiencies due to the need for additional cooling and the use of high-maintenance, energy-intensive turboexpanders, particularly in conjunction with pressure swing adsorption processes.
Innovation Solution
A method that involves cooling the feed mixture to precipitate condensates, using counterflow absorption with a gaseous fluid from the low pressure demethanizer compressed to the first pressure level, eliminating the need for expansion cooling and reducing the energy requirements by avoiding the use of turboexpanders and recompression, thus enabling efficient hydrogen recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low pressure demethanizers are used for hydrogen recovery, then separation efficiency is improved and equipment cost is reduced, but additional cooling requirements and energy consumption increase
Solution Approach 1:
The patent combines the demethanizer and absorption column into an integrated system where the demethanizer operates at low pressure (improving ease of manufacture) while the absorption column recovers hydrocarbons that would otherwise require additional cooling and energy-intensive processing. The absorbed hydrocarbons are then desorbed and recycled, eliminating the need for separate cooling and recompression steps.
Solution Approach 2:
The patent changes the operating parameters by using a two-stage process: first demethanization at low pressure (reducing equipment cost), then absorption at controlled temperature and pressure conditions. This parameter optimization allows the system to achieve both low equipment cost and reduced energy consumption by avoiding the need for extensive additional cooling.
2Temperature
If turboexpanders are used for expansion cooling in pressure swing adsorption, then cooling capacity is improved, but device complexity and maintenance requirements increase
Solution Approach 1:
The patent extracts the cooling function from the complex turboexpander system and replaces it with a simpler absorption-based cooling mechanism. The absorption column uses the natural heat of absorption to achieve the required cooling effect, eliminating the need for turboexpanders and their associated complexity and maintenance requirements.
Solution Approach 2:
The patent replaces the mechanical turboexpander system with a chemical/physical absorption system. Instead of using mechanical expansion to achieve cooling, the system uses the exothermic absorption process followed by controlled desorption to achieve the desired temperature effects, thereby eliminating complex mechanical equipment.
3Productivity
If compression to first pressure level is performed for counterflow absorption, then absorption efficiency is improved, but energy consumption increases
Solution Approach 1:
The patent performs preliminary compression of the gaseous fluid from the demethanizer to the first pressure level before it enters the absorption column. This preliminary action ensures that the absorption process operates at optimal pressure conditions, maximizing absorption efficiency. The energy cost of this compression is offset by the elimination of subsequent energy-intensive cooling and recompression steps.
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 allows for the economical and efficient production of pure hydrogen by eliminating the need for costly and energy-intensive rotary equipment, reducing energy consumption, and simplifying the process by eliminating the need for further cooling and recompression, thereby improving the overall efficiency of hydrogen recovery.
Implementation Method 1
cooling the feed mixture to a second temperature level such that one or more condensates are precipitated from the fluid of the feed mixture
Implementation Method 2
compressed to the first pressure level in gaseous form
Data Source
AI summary
To obtain hydrogen from a gaseous C2minus feed, it is cooled from a first to a second temperature level at a first pressure level forming one or more condensates. A gaseous remainder is cooled to a third temperature level and subjected to a counterflow absorption at the first pressure level, obtaining a top gas rich in hydrogen and methane and a sump liquid. The former is heated and subjected to pressure swing adsorption at the first pressure level, forming a product stream rich in hydrogen and depleted in or free from methane. The condensate(s) and/or the sump liquid is/are expanded to and fed into a low pressure demethanizer at the second pressure level. The counterflow absorption is carried out using fluid taken from the demethanizer at the second pressure level, compressed in gaseous form to the first pressure level and cooled to the third temperature level.