Utilizing waste tail gas from a separation unit biogas upgrade systems as beneficial fuel
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Publication Number
US-8158378-B2
Publication Date
2012-04-17
Expiration Date
Abstract
The invention relates to a method for utilizing low-quality tail gas derived from a pressure swing adsorption system or membrane system, which is used to upgrade biogas, as a beneficial fuel for the facility and/or digester boiler.
Core Innovation
The described invention relates to upgrading biogas produced in an anaerobic digestion system. A biogas feed stream is compressed and at least a portion is passed to a separation unit that discharges a purified, methane-containing product gas and a low-quality gas stream comprising a minor amount of methane, carbon dioxide and other impurities present in the biogas feed stream.
Instead of flaring the low-quality gas stream, the invention combines the low-quality gas stream with a portion of the biogas feed stream and/or with a portion of the purified, methane-containing product gas. The combined product is used as a fuel in the anaerobic digestion system, including for a digester boiler, rather than thermal oxidizer flaring of the low-quality stream.
The approach supports creating an intermediate-quality fuel suitable for facility/boiler use by blending streams and/or by adjusting the PSA or membrane operating cycles. The described rationale is based on fuel heating value and parasitic load, and the document discusses analyzer signal controlled blending and operational ranges, including methane concentration ranges for the blended boiler fuel.
An example is described that compares prior art using tail gas flared versus reusing the tail gas by blending it, resulting in improved fuel utilization and reduced flaring and capital cost.
Claims Coverage
The provided material identifies one independent claim covering a compressed anaerobic digestion biogas stream that is separated into a purified methane-containing product gas and a low-quality gas stream, where the low-quality stream is combined with biogas and/or product gas for fuel use within the anaerobic digestion system.
Separating compressed anaerobic digestion biogas into purified product gas and low-quality gas
Passes at least a portion of the compressed biogas feed stream to a separation unit that discharges a purified, methane-containing product gas and a low-quality gas stream comprising a minor amount of methane, carbon dioxide and other impurities.
Reusing low-quality gas stream by combining for fuel in the anaerobic digestion system
Either combines the low-quality gas stream with a portion of the biogas feed stream, or combines it with a portion of the purified, methane-containing product gas, for use as a fuel in the anaerobic digestion system.
Pressure swing adsorption separation producing methane-containing product gas and tail gas
The separation unit is a pressure swing adsorption system that discharges a purified, methane-containing product gas as the less readily adsorbable component and a tail gas as the low-quality stream containing a minor amount of methane, carbon dioxide and other impurities.
Membrane separation with non-permeate purified product and permeate low-quality gas
The separation unit is a membrane system that discharges a purified, methane-containing product gas as non-permeate and permeates a low-quality gas stream.
Analyzer-controlled blending using methane, carbon dioxide and/or heating value
Controls combining by analyzing methane, carbon dioxide and/or heating value of the combined stream and controlling the portion size of the product gas mixed with the low-quality gas stream.
Methane-containing product gas to low-quality gas mixing ratio range
Uses a ratio of the methane-containing product gas portion combined with the low-quality gas stream to the purified methane-containing product gas stream of 10-60%.
Combined fuel methane content constraint
Either combined gas stream contains 40-50% methane.
The claim set covers producing and compressing an anaerobic digestion biogas feed stream, separating it into a purified methane-containing product gas and a low-quality gas stream, and reusing the low-quality gas stream by blending it with biogas and/or product gas for fuel use in the anaerobic digestion system. Coverage includes specific separation-unit implementations and combining controls or constraints based on methane, carbon dioxide, heating value, and defined methane and mixing ratio ranges.
Stated Advantages
Improved fuel utilization.
Reduced flaring.
Reduced capital cost.
Documented Applications
Using the combined gas stream as a fuel in the anaerobic digestion system, including for a digester boiler.
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