Facility and method for the treatment by membrane permeation of a gas stream with adjustment of the third-permeate suctioning pressure

Abstract

Facility and method for membrane permeation treatment of a feed gas stream containing at least methane and carbon dioxide including first, second, and third membrane separation units each including at least one membrane that is more permeable to carbon dioxide than to methane, wherein a permeate from the first membrane separation unit is fed to the third membrane separation unit and a retentate from the first membrane separation unit is fed to the second membrane separation unit. A compressor B adjusts the third-permeate suctioning pressure as a function of the feed gas stream pressure and the second retentate methane concentration.

Claims

1. A facility for membrane permeation treatment of a feed gas stream containing at least methane and carbon dioxide, comprising: a compressor A for compressing the feed gas stream; a first membrane separation unit able to receive the feed gas stream coming from the compressor A and to supply a first permeate and a first retentate; a second membrane separation unit able to receive the first retentate and to supply a second permeate and a second retentate; a third membrane separation unit able to receive the first permeate and to supply a third permeate and a third retentate; at least one means for measuring a pressure of the feed gas stream at an inlet of the first membrane separation unit; at least one means for measuring a CH.sub.4 concentration in the second retentate; and at least one compressor B for adjusting a third-permeate suctioning pressure as a function of a measured pressure of the feed gas stream and of a measured methane concentration of the second retentate, wherein each membrane separation unit comprises at least one membrane that is more permeable to carbon dioxide than to methane.

2. The facility of claim 1, wherein the third retentate is recycled to the feed gas stream upstream of the compressor A.

3. The facility of claim 1, wherein the second permeate is recycled to the feed gas stream upstream of the compressor A.

4. The facility of claim 1, wherein the membranes used in the membrane separation units have a same selectivity.

5. The facility of claim 1, wherein at least one of said first, second, and third membrane separation units comprises at least two membranes.

6. The method for controlling the facility recited in claim 1, comprising the steps of: a) measuring a pressure of the feed gas stream at the inlet of the first membrane separation unit using the at least one means for measuring a pressure, wherein the at least one means for measuring a pressure comprises at least one pressure sensor; b) measuring a CH.sub.4 concentration in the second retentate using the at least one means for measuring a CH.sub.4 concentration, wherein the at least one means for measuring a CH.sub.4 concentration comprises at least one CH.sub.4 analyzer; c) comparing the measured pressure of the feed gas stream and the measured CH.sub.4 concentration in the second retentate with associated setpoint values and determining the differences between the measured pressure of the feed gas stream and the measured CH.sub.4 concentration in the second retentate and the associated setpoint values; and d) adjusting the third-permeate suctioning pressure of the compressor B.

7. The method of claim 6, wherein the third-permeate suctioning pressure is adjusted by the compressor B and the pressure of the feed gas stream is adjusted by the compressor A or by a progressive shut-off and pressurizing valve.

8. The method of claim 7, wherein the adjusting of the pressure of the feed gas stream comprises increasing or decreasing the pressure.

9. The method of claim 6, wherein, in said step of adjusting, the compressor B is subjected to an acceleration or deceleration.

10. The method of claim 6, wherein the comparing, determining, and adjusting steps are performed automatically by a data transmission and data processing means.

11. The method of claim 6, wherein the feed gas stream is biogas.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The FIGURE represents an example of a facility according to the invention, wherein the compressor B is likened to a vacuum pump P.

DETAILED DESCRIPTION OF THE INVENTION

(2) Depending on the case, the facility according to the invention may have one or more of the following features: the third retentate is recycled to the feed gas stream upstream of the compressor A; the second permeate is recycled to the feed gas stream upstream of the compressor A; the membranes used in the membrane separation units have the same selectivity; at least one membrane separation unit comprises at least two membranes.

(3) A subject of the present invention is also a method for controlling a facility as defined in the invention, comprising the following steps: a) measuring the pressure of the feed gas stream at the inlet of the first membrane separation unit, b) measuring the CH.sub.4 concentration in the second retentate, c) comparing the pressure measured in step a) and the concentration measured in step b) with setpoint values, and determining the difference relative to these setpoint values, and d) a step of adjusting the third-permeate suctioning pressure by means of the compressor B.

(4) Depending on the case, the method according to the invention may have one or more of the features below: in step d), the third-permeate suctioning pressure is adjusted by means of the compressor B and the pressure of the feed gas stream is adjusted by means of the compressor A or by means of a progressive shut-off and pressurizing valve; the adjusting of the pressure of the feed gas stream comprises increasing or decreasing the pressure; in the adjusting step, the compressor B is subjected to an acceleration or deceleration. It should be noted that an acceleration of the compressor B will make it possible to reduce the pressure level of the third permeate, while a deceleration of the compressor B will make it possible to increase the pressure level of the third permeate; the comparison step and the adjustment step are carried out automatically by data transmission and data processing means; the feed gas stream is biogas.

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

(6) 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.

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

(8) “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

(9) “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”.

(10) “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.

(11) 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.

(12) 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.

(13) 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.