Installation and method for the treatment by membrane permeation of a gas stream with the aspiration pressure of the second permeate adjusted

Abstract

Installation for membrane permeation treatment of feed gas containing methane and carbon dioxide that includes first, second, and third membrane separation units. The permeate from the first membrane separation unit is fed to the third membrane separation unit and the retentate from the first membrane separation unit is fed to the second membrane separation unit. The aspiration pressure of the second permeate is adjusted with a compressor according to the aspiration pressure of the second permeate before recycling thereof to the feed gas flow fed to the first membrane separation unit.

Claims

1. The method for controlling membrane permeation treatment of a feed gas flow containing at least methane and carbon dioxide, comprising the following steps: providing an installation that comprises: a compressor A for compressing the combined flows of feed gas and a third retentate, a first membrane separation unit able to receive the compressed combined flow of feed gas and third retentate that is admixed with a second permeate and to supply a first permeate and a first retentate, a second membrane separation unit able to receive the first retentate and to supply the second permeate and a second retentate, a third membrane separation unit able to receive the first permeate and to supply a third permeate and the third retentate, and at least one compressor B for aspirating the second permeate, feeding the aspirated second permeate to the compressed combined flows of the feed gas and the third retentate, and adjusting the aspiration pressure of the second permeate, wherein each membrane separation unit comprises at least one membrane that is more permeable to carbon dioxide than to methane; measuring the aspiration pressure of the second permeate at a location in between the second membrane separation unit and the compressor B; comparing the measured aspiration pressure with an associated setpoint value; and adjusting the aspiration pressure of the second permeate by the compressor B in order to keep the pressure value equal to the setpoint value associated with the aspiration pressure.

2. The method of claim 1, wherein, in the adjustment step, the compressor B is accelerated or decelerated.

3. The method of claim 1, wherein the measurement, comparison and adjustment steps are carried out automatically by data transmission means.

4. The method of claim 1, wherein the feed gas flow is biogas.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 depicts an example of an installation according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) Depending on the case, the installation according to the invention may have one or more of the following features: at least one measurement means for measuring the CH.sub.4 concentration in the second retentate, and at least one pressure adjustment means for adjusting the pressure of the feed gas flow depending on the CH.sub.4 concentration measured, the at least one measurement means for measuring the CH.sub.4 concentration typically being a CH.sub.4 analyzer. the adjustment means for adjusting the pressure of the feed gas flow is a compressor or a progressive shut-off and pressurizing valve. the third retentate is recycled to the compressor used for compressing the feed gas flow. the membranes used in the membrane separation units have the same selectivity.

(3) The present invention also relates to a method for controlling an installation as defined in the invention, comprising the following steps:

(4) a step of measuring the aspiration pressure of the second permeate,

(5) a step of comparing this measurement with a fixed setpoint value, and

(6) a step of adjusting the aspiration pressure of the second permeate by the compressor B in order to keep the pressure value equal to the setpoint value.

(7) As the case may be, the method according to the invention can exhibit one or more of the following features: in the adjustment step, the compressor B is accelerated or decelerated; note that an acceleration of the compressor B will lead to a decrease in the pressure level in the membranes, and a deceleration of the compressor B will lead to an increase in the pressure level in the membranes; the measurement, comparison and adjustment steps are carried out automatically by data transmission means; said method comprises: a step of measuring the CH.sub.4 concentration in the second retentate, a step of comparing this measurement against a setpoint value, and a step of adjusting the pressure of the feed gas flow in such a way as to reduce the determined discrepancy; the pressure of the feed gas flow is adjusted using the compressor A or using a progressive cut-off and pressurizing valve. the adjustment step for adjusting the feed gas flow involves increasing or decreasing the pressure; the comparison step and the adjustments step are performed automatically by data transmission and data processing means; the feed gas flow is biogas.

(8) A data transmission and data processing means may for example be an industrial processor of the programmable controller type.

(9) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(10) The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

(11) “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

(12) “Providing” in a claim is defined to mean furnishing, supplying; making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(13) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(14) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed; it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(15) All references identified herein are each hereby incorporated by reference into this application in their entireties; as well as for the specific information for which each is cited.