Installation and method for the treatment by membrane permeation of a gas stream with the methane concentration adjusted

Abstract

Installation for membrane permeation treatment of feed gas flow containing at least methane and carbon dioxide including first, second, and third membrane separation units and at least one compressor B for aspirating the second permeate, a permeate from the first membrane separation unit being fed to the third membrane separation unit, a retentate from the first membrane separation unit being fed to the second membrane separation. After measuring the aspiration pressure and methane concentration of the second permeate before it is recycled to the feed, the pressure of the second permeate is adjusted according to the measured aspiration pressure and methane concentration.

Claims

1. A method for controlling an installation for the membrane permeation treatment of a feed gas flow containing at least methane and carbon dioxide, comprising the steps of: providing an installation comprising: a compressor A for compressing a combination of the feed gas flow and a third retentate, a first membrane separation unit able to receive the gas flow coming from the compressor 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 the third retentate, at least CH.sub.4 analyzer for measuring the methane CH.sub.4 concentration in the second retentate, and at least one compressor B for aspirating the second permeate, adjusting the pressure of the second permeate according to the aspiration pressure measured and the methane concentration measured before recycling the second permeate into the feed gas flow downstream of the compressor A, and combining the pressure-adjusted second permeate with the compressed combined flows of the feed gas and the third retenate, wherein each membrane separation unit comprising at least one membrane that is more permeable to carbon dioxide than to methane, measuring the pressure of the second permeate at a location between the second membrane separation unit and the compressor B; measuring the methane CH.sub.4 concentration in the second retentate; comparing the measured pressure and the measured CH.sub.4 concentration against associated pressure and CH.sub.4 concentration setpoint values and determining a difference between the measured pressure and and CH.sub.4 concentration and the associated setpoint values; and adjusting the pressure of the second permeate using the compressor B in order to obtain a concentration of CH.sub.4 in the second retentate corresponding to the CH.sub.4 concentration setpoint.

2. The method of claim 1, wherein, in step d), both the pressure of the second permeate is adjusted using the compressor B and the pressure of the feed gas flow is adjusted using the compressor A or using a progressive cut-off and pressurizing valve.

3. The method of claim 2, wherein the adjustment of the pressure of the feed gas flow involves increasing or decreasing the pressure.

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

5. The method of claim 4, wherein the comparison step and the adjustment step are performed automatically by data transmission and data processing means.

6. 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: the said installation comprises at least one pressure adjustment means for adjusting the pressure of the feed gas flow depending on the CH.sub.4 concentration measured; 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; at least one membrane separation unit comprises at least two membranes with different selectivities.

(3) The present invention also relates to a method for controlling an installation as defined in the invention, comprising the following steps: a. a step of measuring the pressure of the second permeate, b. a step of measuring the methane CH.sub.4 concentration in the second retentate, c. a step of comparing the pressure measured in step a) and the concentration measured in step b) against setpoint values, and of determining the discrepancy with respect to these setpoint values, and d. a step of adjusting the pressure of the second permeate using the compressor B in order to keep the CH.sub.4 concentration value in the second retentate constant.

(4) As the case may be, the method according to the invention can exhibit one or more of the following features: in step d), both the pressure of the second permeate is adjusted using the compressor B and the pressure of the feed gas flow is adjusted using the compressor A or using a progressive cut-off and pressurizing valve; the adjustment of the pressure of the feed gas flow involves increasing or decreasing the pressure; 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 comparison step and the adjustment step are performed automatically by data transmission and data processing means the feed gas flow 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 “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”.

(9) “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.

(10) 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.

(11) 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.

(12) 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.