Method and apparatus for regulating a plurality of fluids

In a method for regulating at least two fluids, a fluid feed flow Q is divided into n parts, the sum of the n parts being equal to Q, each of the n parts is sent to one of n processing units, each of the n processing units produces at least one processed flow, at least one processed flow of a first of the processing units is regulated by control means in order to keep the flow thereof constant at a value Q1 in nominal operation, at least one processed flow of a second of the processing units is regulated by control means in order to keep the pressure thereof constant in nominal operation and, in the event of a reduction of the feed flow Q, in reduced feed operation, if, preferably only if, the flow of the flow processed in the second processing unit of step v) drops and thus reaches a first minimum flow threshold, a processed flow in the first processing unit is regulated such that the processed flow having a value Q1 in nominal operation is reduced to a value less than Q1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a § 371 of International PCT Application PCT/FR2017/052363, filed Sep. 6, 2017, which claims the benefit of FR1658846, filed Sep. 21, 2016, both of which are herein incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a method and to an apparatus for regulating a plurality of fluids.

BACKGROUND OF THE INVENTION

The regulation of a plurality of fluids in parallel, coming from different sources, entails adaptation when:The balance of substances in terms of flow rate needs to be maintained.Certain fluids take priority over others, particularly during transient phases, for example if one of the fluids absolutely must be kept within a certain range of flow rates.

SUMMARY OF THE INVENTION

It is sometimes necessary to split a fluid into a plurality of parts in order to treat the parts separately using different treatment methods. The product or products of the treatment methods are then used by one or more clients. If there is a fluctuation in flow rate for a method in which a main source P supplies different treatment units P1and P2, regulation is performed as follows, as illustrated inFIG. 1:

The flow Q is divided into n (in this instance two) parts, the sum of the parts being equal to Q. Each of the parts1,2is sent to a treatment unit P1, P2through valves V1, V2. The fluid11coming from the unit P1will be regulated in terms of flow rate by a valve V11, and in this way the flow withdrawn will be at a fixed rate and the fluid12coming from the unit P2will be controlled in terms of pressure by the valve V12with a view to keeping the balance of substances stable. (FIG. 1). The treatment unit P1may produce products other than11. The treatment unit P2may produce products other than12. The valve V11regulates the flow rate of the product21in order to produce a constant flow rate Q1that takes account only of the flow rate of the flow11coming from the method P1by means of a controller FIC. The pressure of the product21can vary. The valve V12regulates the pressure of the product12so that this pressure is constant, using a controller PIC, the flow rate Q2of the product22potentially varying. The regulation takes account only of the flow rate of the flow12coming from the method P2.

The treatment units may operate the same treatment system, for example adsorption, distillation, absorption, etc., or else may each operate according to a different treatment system.

One aspect of the invention provides a method for regulating at least two fluids, in which:

i) A fluid supply flow Q is divided into n parts, the sum of the n parts being equal to Q.

ii) Each of the n parts is sent to one of n treatment units.

iii) Each of the n treatment units produces at least one treated flow.

iv) At least one treated flow from a first of the treatment units is regulated by control means in order to keep its flow rate constant at a value Q1in nominal operation.

v) At least one treated flow from a second of the treatment units is regulated by control means in order to keep its pressure constant in nominal operation.

vi) In the event of a reduction in the supply flow rate Q, in reduced-supply operation, if, and preferably only if, the flow rate of the flow treated in the second treatment unit of step v) drops and thus reaches a first minimum flow rate threshold, a flow treated in the first treatment unit is regulated so that the treated flow which in nominal operation has a flow rate Q1is reduced to a flow rate lower than Q1.

According to other optional aspects:n is equal to 2.n is equal to at least 3.the treated flow from a first of the treatment units, regulated by control means in order to keep its flow rate constant at a value Q1in nominal operation, is not regulated to keep its pressure constant in nominal operation.the treated flow from a second of the treatment units, regulated by control means in order to keep its pressure constant in nominal operation, is not regulated to keep its flow rate constant in nominal operation.the first unit produces two treated flows, each of the two being regulated by control means in order to keep its flow rate constant.in the event of a reduction in the fluid flow rate Q, if, and preferably only if, the flow rate of the flow treated in the second treatment unit of step v) drops below a threshold, just one flow treated in the first treatment unit is regulated to reduce its flow rate to a flow rate lower than Q1.the first treatment unit is a treatment unit performing adsorption and/or distillation, potentially cryogenic distillation.the second treatment unit is a treatment unit performing adsorption and/or distillation, potentially cryogenic distillation.

Another aspect of the invention provides an apparatus for regulating at least two fluids, comprising:

a) Means for dividing a fluid supply flow Q into n parts, the sum of the n parts being equal to Q

b) Means for sending each of the n parts to one of n treatment units

c) Means for extracting at least one treated flow from each of the n treatment units d) Means for regulating flow rate in order to keep the flow rate of at least one treated flow from a first of the treatment units constant so as to keep its flow rate constant at a flow rate Q1in nominal operation

e) Means for regulating pressure in order to keep the pressure of at least one treated flow from a second of the treatment units constant in nominal operation, and

f) Means for detecting the reduction in the flow rate of the flow treated in e), these detection means being capable of reducing the flow rate of a treated flow coming from the first of the treatment units when the flow treated in e) reaches a minimum flow rate threshold, so as to reduce the flow rate of a treated flow coming from the first of the treatment units to a flow rate lower than Q1.

According to other optional aspects:the means for detecting the reduction in flow rate of the treated flow are capable of acting in such a way as to reduce the flow rate of the treated flow coming from the first of the treatment units to a flow rate lower than Q1by reducing the flow rate of this flow coming from the first of the treatment units.the means for detecting the reduction in flow rate of the treated flow are capable of acting in such a way as to reduce the flow rate of the treated flow coming from the first of the treatment units to a flow rate lower than Q1by reducing the flow rate of another flow coming from the first of the treatment units.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, the flow Q coming from a common source P is divided into n (in this instance two) parts, the sum of the parts being equal to Q. Each of the parts1,2is sent to a treatment unit P1, P2through valves V1, V2. The fluid11coming from the unit P1will be regulated in terms of flow rate by a valve V11, and in this way the flow withdrawn will be at a fixed flow rate and the fluid12coming from the unit P2will be controlled in terms of pressure by the valve V12with a view to keeping the balance of substances stable. The treatment unit P1may produce products other than11. The treatment unit P2may produce products other than12. The valve V11regulates the flow rate of the product21in order to produce a constant flow rate Q1. The pressure of the product21can vary. The valve V12regulates the pressure of the product12so that this pressure is constant, using a controller PIC, the flow rate Q2of the product22potentially varying. The regulation takes account only of the flow rate of the flow12coming from the method P2.

The treatment units may operate the same treatment system, for example adsorption, distillation, absorption, etc., or else may each operate according to a different treatment system.

Considering an alternative form ofFIG. 1, if there is a difference in the priority of production of the flows of the final products, the regulation will be adapted as follows, as illustrated inFIG. 2:

The fluid21coming from the unit P1will still be regulated in terms of flow rate in order to keep this flow rate constant when possible, and the fluid12coming from the unit P2will be regulated in terms of pressure with a view to keeping the balance of substances stable. If the flow rate of the fluid21needs to be stable whatever the operating scenario as far as possible, and if the second product22absolutely must not drop below a certain flow rate because such a drop would cause the method P2to halt, it is clear that the needs of the consumer of the flow22take priority over those of the consumer of the flow21. The consumer needs to be able to receive the product22when the supply Q is low even if, in order to do so, it is necessary to lower the production of the product21. To this end, a controller FIC2min will be added to the valve V11that regulates the pressure of the fluid22. Using this control loop, the FIC2min will always maintain a minimal flow rate through the method P2. A low-pass device will keep the flow21at the constant flow rate Q1, as long as doing so remains possible. However, when the minimum threshold for12is reached, the FIC2min will lower the flow rate of11in order, as a priority, to keep the flow22at a minimum flow rate threshold.

For example, let us consider a system in which the flow21is sent to a client which defines the flow rate Q1it needs. The flow22is sent to another client, for which the flow rate is unimportant (supplying a network or method downstream which is able to tolerate fluctuations in flow rate, etc.).

The method P2requires a minimum supply flow rate which corresponds to a flow rate of product22of 80 Nm3/h in order to function.

In normal operation, the two methods P1, P2produce productions21,22of 100 Nm3/h each, which in the case of the flow21corresponds to the desired flow rate Q1.

If the supply flow rate drops, initially, it is still possible to meet the needs of the two clients and the method P1produces a flow rate of 100 Nm3/h of the flow21whereas the method P2contents itself with producing 80 Nm3/h of the flow22, which corresponds to the minimum production.

If the supply flow rate drops further, it is no longer possible to produce 100 Nm3/h of the flow21and at the same time operate the method P2, because the flow rate of the flow12would drop below the minimum of 80 Nm3/h.

In that case, the controller lowers the flow rate of the flow21to a flow rate of 90 Nm3/h, which is therefore below 100 Nm3/h (Q1). By contrast, the flow produced by the method P2is kept at a flow rate of 80 Nm3/h.

Thus it is possible to keep P2functioning by limiting the supply to the Q1client, entirely automatically.

Without this control, P2would have tripped or functioned incorrectly, leading to a halt in the production of Q2. In this instance, the clients for Q1and Q2continue to be supplied even though the Q1client no longer receives the anticipated flow rate.

In another application of this idea, P1and P2are methods which are identical, but which experience a rapid degradation in performance when they are not operating at their nominal flow rates. Rather than having two units operating far from their optima, in this instance, P1is kept at its optimum.

In another application, the source P of the flow Q is made up of two units the operations of which can vary from 60 to 100. This source supplies four methods the operations of which vary from 30 to 20. If both sources are available, then Q(unit1)=Q(unit2)=60 and Q1=Q2=Q3=Q4=30. If Q (unit2) trips out, then Q(unit1) will increase its load to 100 and P1=P2=30 in order to maintain their optima, and P3=P4=20 in order to keep these units in operation.

The regulation control described hereinabove is valid whatever the number of fluids (n fluids).FIG. 3depicts an example of three fluids11,12,13produced by two treatment units P1, P2: the fluids11,13being produced by P1, and the fluid12by P2. The fluids11,13,12are regulated by the valves V11, V12, V13to produce the fluids21,23,22with flow rates Q1, Q3, Q2respectively.

The fluid11needs to be stable whatever the state of operation so that the flow rate of 21 downstream of the valve V11remains equal to Q1. The fluid22will be used to establish the balance of substances as long as the fluid22has not reached its minimum flow rate. Thus, if the flow rate of22reaches a minimum threshold, the flow rate of the flow13,23produced by the method P1will be lowered while the flow rate of11,21will remain constant.