Membrane permeation treatment with adjustment of the temperature of the first retentate as a function of the CH.SUB.4 .concentration in the third and/or fourth permeate

Abstract

A facility and method for membrane permeation treatment of a feed gas flow containing at least methane and carbon dioxide that includes a compressor, a pressure measurement device, at least one valve, and first, second, third, and fourth membrane separation units for separation of CO.sub.2 from CH.sub.4 to permeates enriched in CO.sub.2 and retentates enriched in CH.sub.4, respectively. A temperature of the first retentate is adjusted at an inlet of the second membrane separation unit with at least one heat exchanger as a function of the measured CH.sub.4 concentration in such a way so as to reduce the determined difference.

Claims

1. A facility for the membrane permeation treatment of a feed gas flow containing at least methane and carbon dioxide, comprising: a compressor for compressing the feed gas flow; a first membrane separation unit able to receive a flow of gas coming from the compressor and supply a first permeate and a first retentate; a second membrane separation unit able to receive the first retentate and supply a second permeate and a second retentate; a third membrane separation unit able to receive the first permeate and supply a third permeate and a third retentate; a fourth membrane separation unit able to receive the third retentate and supply a fourth permeate and a fourth retentate; a gas analyzer adapted to measure a CH.sub.4 concentration of the third permeate, of the fourth permeate, or of a flow that is comprised of a combination of the third permeate and the fourth permeate; and at least one heat exchanger for adjusting a temperature of the first retentate at an inlet of the second membrane separation unit as a function of the measured CH.sub.4 concentration, 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 at least one heat exchanger receives a secondary flow having a temperature higher or lower than a temperature of the first retentate.

3. The facility of claim 1, wherein the fourth retentate is recycled to the compressor.

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

5. The facility of claim 1, wherein at least one membrane separation unit uses a membrane with a selectivity different from the selectivity of the membranes of the other membrane separation units.

6. The facility of claim 1, wherein at least one membrane separation unit comprises at least two membranes with a same selectivity.

7. The facility of claim 1, wherein at least one membrane separation unit comprises at least two membranes with different selectivities.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic of an example of the multi-stage separation of the invention.

(2) FIG. 2 is a process flow chart illustrating an aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) Depending on the case, the facility according to the invention may have one or more of the following features:

(4) the first measuring means is carried out by a gas analyzer;

(5) the adjusting means is a heat exchanger using a secondary flow having a temperature higher or lower than the temperature of the first retentate. It should be noted that this secondary flow may be liquid or gas. Its temperature will preferably be higher and will preferably be between 1.2 times the temperature of the first retentate and 100 times the temperature of the first retentate, more preferentially between 2 times the temperature of the first retentate and 80 times the temperature of the first retentate, even more preferentially between 2.5 times the temperature of the first retentate and 50 times the temperature of the first retentate; FIG. 1 illustrates an example of a facility according to the invention with a secondary flow having a temperature higher than the temperature of the first retentate;

(6) the fourth retentate is recycled to the compressor for compressing the feed gas flow.

(7) the membranes used in the membrane separation units have the same selectivity.

(8) at least one membrane separation unit comprises at least two membranes with the same selectivity.

(9) at least one membrane separation unit comprises at least two membranes with different selectivities.

(10) at least one membrane separation unit uses a membrane with a selectivity different from the selectivity of the membranes of the other membrane separation units.

(11) A subject of the present invention is also a method for controlling a facility as defined in the invention, comprising the following steps:

(12) a step of measuring the CH.sub.4 concentration in the third permeate or the fourth permeate or in a flow combining the third permeate or the fourth permeate. The measurement will preferably be carried out by a gas analyzer;

(13) a step of comparing this measurement with a setpoint value, and of determining the difference with respect to this setpoint value, and

(14) a step of adjusting the temperature of the first retentate at the inlet of the second membrane separation unit such a way as to reduce the determined difference.

(15) FIG. 2 illustrates the method according to the invention.

(16) As appropriate, the method according to the invention can exhibit one or more of the features below:

(17) the adjusting of the temperature of the first retentate is carried out by heat exchange between a secondary flow having a temperature higher or lower than the temperature of the first retentate. The heat exchange is carried out within the heat exchanger of the facility according to the invention;

(18) the adjusting step comprises an increase or a decrease in the temperature;

(19) the feed gas flow is biogas;

(20) the comparing step and the adjusting step are carried out automatically by data transmission and data processing means. A data transmission and data processing means may for example be an industrial processor of the programmable controller type.

(21) 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.

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

(23) “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”.

(24) “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.

(25) 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.

(26) 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.

(27) 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.