Method to control the extraction rate in a membrane based biogas upgrading plant

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 gas analyser, 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 pressure of the feed gas flow is adjusted according to a CH.sub.4 concentration of the second retentate.

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 first gas analyzer disposed downstream of the second membrane separation unit that is adapted to measure a CH.sub.4 concentration of the second retentate; and a pressure adjustment means for adjusting the pressure of the feed gas flow according to the CH.sub.4 concentration measured by the first gas analyzer, wherein the pressure adjustment means is disposed downstream of the first gas analyzer and each membrane separation unit comprising at least one membrane that is more permeable to carbon dioxide than to methane.

2. The facility of claim 1, wherein said installation further comprises a second gas analyser adapted to measure a CH.sub.4 concentration in the feed gas flow and the pressure adjustment means is further able to adjust the pressure of the feed gas flow according to both the CH.sub.4 concentration measured by the first gas analyzer and the CH.sub.4 concentration measured by the second gas analyzer.

3. The facility of claim 1, wherein the pressure adjustment means is a compressor.

4. The facility of claim 1, wherein the pressure adjustment means is a progressive shut-off and pressurizing valve.

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

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

7. 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.

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

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

10. A method for the membrane permeation treatment of a feed gas flow containing at least methane and carbon dioxide, comprising the steps of: compressing the feed gas flow with a compressor; receiving a flow of gas coming from the compressor at a first membrane separation unit that supplies a first permeate and a first retentate; receiving the first retentate at a second membrane separation unit that supplies a second permeate and a second retentate; receiving the first permeate at a third membrane separation unit that supplies a third permeate and a third retentate; receiving the third retentate at a fourth membrane separation unit that supplies a fourth permeate and a fourth retentate; with a first gas analyser disposed downstream of the second membrane separation unit, measuring a CH.sub.4 concentration of the second retentate; adjusting, using a pressure adjustment means disposed downstream of the first gas analyzer, the pressure of the feed gas flow according to the CH.sub.4 concentration measured by the first gas analyzer, wherein each membrane separation unit comprising at least one membrane that is more permeable to carbon dioxide than to methane; comparing a CH.sub.4 concentration measured by the first gas analyzer against a setpoint CH.sub.4 concentration and determining a difference therebetween; and adjusting a pressure of the feed gas flow in such a way as to reduce the determined difference.

11. The method of claim 10, wherein the pressure of the feed gas flow is adjusted using the compressor.

12. The method of claim 10, wherein the pressure of the feed gas flow is adjusted using a progressive cut-off and pressurizing valve.

13. The method of claim 10, wherein said step of adjusting involves increasing or decreasing the pressure of the feed gas flow.

14. The method of claim 10, wherein the feed gas flow is biogas.

15. The method of claim 10, wherein said steps of comparing and adjusting are performed automatically by a programmable controller.

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) An example of an installation according to the invention is depicted in FIG. 1. Depending on the case, the installation according to the invention may have one or more of the following features:

(4) the said installation comprises at least a second measurement means for measuring the CH4 concentration in the feed gas flow and the pressure adjustment means for adjusting the pressure of the feed gas flow is able to adjust the pressure of the feed gas flow according to the measurement taken by the first measurement means and the second measurement means.

(5) the first measurement means and/or the second measurement means is/are gas analysers.

(6) the adjustment means is a compressor or a progressive shut-off and pressurizing valve.

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

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

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

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

(11) 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.

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

(13) a step of measuring the CH4 concentration in the second retentate,

(14) a step of comparing this measurement against a setpoint value, and of determining the discrepancy with respect to this setpoint value, and

(15) a step of adjusting the pressure of the feed gas flow according to the determined discrepancy.

(16) The CH4 concentration is measured using a gas analyser.

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

(18) As the case may be, the method according to the invention can exhibit one or more of the following features:

(19) the pressure of the feed gas flow is adjusted using the compressor or using a progressive cut-off and pressurizing valve.

(20) the adjustment step involves increasing or decreasing the pressure.

(21) the feed gas flow is biogas.

(22) the comparison step and the adjustments step are performed 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.

(23) 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.

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

(25) “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”.

(26) “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.

(27) 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.

(28) 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.

(29) 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.