Facility for producing gaseous methane by purifying biogas from landfill, combining membranes and cryogenic distillation for landfill biogas upgrading
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Solution Overview
Problem
Existing biogas upgrading technologies face challenges in efficiently separating methane from nitrogen and oxygen due to the presence of oxygen, which can lead to explosive mixtures and reduced methane recovery rates, especially in biogas from landfills.
Innovation Solution
Integration of a single-column, medium-pressure cryogenic distillation process downstream from a conventional membrane unit, utilizing a booster to increase pressure and a cryodistillation unit with a subcooler to produce two methane-enriched flows, which are then compressed and mixed to achieve safe and efficient separation of nitrogen and oxygen from methane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional membrane units are used for CO2 removal, then CO2 separation is achieved, but nitrogen and oxygen removal becomes inefficient and methane recovery rates decrease
Solution Approach 1:
The purification process is divided into distinct stages: a membrane separation unit for CO2 removal followed by a cryogenic distillation unit for nitrogen and oxygen removal. Each unit is optimized for its specific function, with the membrane unit handling CO2 separation and the distillation unit handling air gases, thereby maximizing overall methane recovery while achieving high separation precision for each component
Solution Approach 2:
The invention changes the operating parameters between stages: the membrane unit operates at ambient or elevated temperatures and pressures, while the cryogenic distillation unit operates at low temperatures (cryogenic conditions). This parameter change enables efficient nitrogen and oxygen separation in the second stage without compromising the CO2 removal efficiency of the first stage, thereby maintaining high methane recovery rates
2Manufacturing precision
If cryogenic distillation is applied to separate nitrogen from methane, then separation efficiency is improved, but the presence of oxygen creates explosive mixtures and reduces safety
Solution Approach 1:
The membrane separation unit is placed before the cryogenic distillation unit to perform preliminary CO2 removal. This preliminary action reduces the oxygen concentration in the feed to the distillation unit, preventing the formation of explosive methane-oxygen mixtures during cryogenic separation while maintaining high nitrogen removal efficiency
Solution Approach 2:
The membrane separation unit acts as an intermediary stage between the raw biogas and the cryogenic distillation unit. It pre-treats the gas by removing CO2 and reducing oxygen content, creating a safer feed composition for the distillation unit and enabling efficient nitrogen separation without explosive risks
3Device complexity
If single-column medium-pressure distillation is used, then equipment complexity is reduced, but methane recovery rates drop when nitrogen content is below 30%
Solution Approach 1:
The invention changes the operating pressure parameter by using medium-pressure distillation instead of low-pressure distillation. This parameter change allows the single-column system to maintain high methane recovery rates even when nitrogen content is below 30%, while keeping the equipment complexity low with only one distillation column
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 safe and efficient separation of methane from nitrogen and oxygen, maintaining high energy efficiency and methane recovery rates, even at low nitrogen concentrations, thereby producing high-quality Renewable Natural Gas (RNG).
Implementation Method 1
a membrane separation unit arranged downstream of the VOC purification unit to receive the VOC-depleted gas flow and subject the VOC-depleted gas flow to at least one membrane separation to partially separate the CO2 and O2 from the gas flow
Implementation Method 2
a volatile organic compound (VOC) purification unit arranged downstream of the compression unit to receive the compressed initial flow of the biogas and comprising at least one adsorber loaded with adsorbents capable of reversibly adsorbing VOCs
Implementation Method 3
a cryodistillation unit comprising a heat exchanger and a distillation column, arranged downstream of the CO2 polishing unit to receive the CO2 depleted gas flow and subject the CO2 depleted gas flow to a cryogenic separation to separate O2 and N2 from the CO2 depleted gas flow
Implementation Method 4
a cryodistillation unit comprising a heat exchanger and a distillation column, arranged downstream of the CO2 polishing unit to receive the CO2 depleted gas flow and subject the CO2 depleted gas flow to a cryogenic separation
Implementation Method 5
a compression unit for compressing an initial gas flow of the biogas to be purified
Data Source
AI summary
A facility for producing gaseous biomethane by purifying biogas from landfill, comprising: • a compression unit, • a volatile organic compound (VOC) purification unit; • a membrane separation unit, • a CO2 polishing unit, • a cryodistillation unit comprising a heat exchanger and a distillation column, • an O2 depletion unit, • a dryer arranged.