The present invention relates to a method of controlling a plant for processing a gas by adsorption, having N adsorption units.
It also relates to a plant for processing a gas by adsorption, which is controlled using such a method.
In order to ensure correct operation of a plant for processing a gas by adsorption provided with a plurality of cyclically working adsorbers, it is known to employ a sequencer, that is to say an ordered set of control operations of the adsorbers. These sequencers prove particularly useful when the plant has a large number of adsorbers, which are subjected selectively or simultaneously on the one hand to external supply and regeneration flows and, on the other hand, to flows coming from the other adsorbers, with a sequencer grouping together in a structured way hundreds of commands for actuating valves of these adsorbers, with a view to ensuring cyclic operation of the plant.
Furthermore, there is an ever-increasing demand for processing plants using adsorbers to operate with a high level of reliability and stability. Hence, even if one or more adsorbers are temporarily out of service because of a maintenance operation or an unforeseen incident, such as a valve breakage, it is desirable for these plants to continue to operate in an exceptional mode, that is to say for them to be able to continue to produce a flow of processed gas, with a flow rate and a purity which are substantially similar to those of the processed gas flow in the normal mode.
The transition between the normal mode and an exceptional mode needs to be fast and to entail the least possible perturbations of the outgoing processed gas flow, with a view to ensuring continuity of downstream plants consuming the processed gas.
It proves particularly complex for the control method of such a plant to take these various operating modes into account, because of the very large number of envisageable situations. It is hence necessary to accommodate all the possibilities for isolation of adsorbers and occurrence of a production incident, without thereby lengthening the reaction time of the plant.
It is an object of the invention to provide a method of controlling a plant for processing a gas by adsorption, of the aforementioned type, which makes it possible to reduce greatly the programming workload of a control unit reproducing this method, and to improve the reaction capacities of a corresponding plant.
To that end, the invention relates to a method of controlling a plant for processing a gas by adsorption, which plant has N adsorption units, N being greater than or equal to two, operating according to a cycle which is distributed uniformly into at most N phase times and during a part of which at least one of the adsorption units is subjected to the output flow of at least one of the other adsorption units, in which at least one control sequencer is used which determines the control steps of the N adsorption units over a cycle and which ensures, in a loop on itself, cyclic operation of the processing plant, and in which, on the basis of the control steps of the processing plant which occur during a given phase time of a cycle of an operating mode of the plant, said sequencer of said operating mode is obtained by extrapolation to the other phase times of the cycle.
According to other characteristics of this method, taken individually or in any technically feasible combinations:
a mobile parameter for identifying the operating state of the adsorption unit which is in each successive phase time of the cycle is firstly associated with said phase time; for the given phase time, a parameterized sequence of control steps of the processing plant during said given phase time is then defined, each adsorption unit controlled by the steps of said sequence being denoted by the parameter for identifying the operating state of said adsorption unit; and a control sequencer of the processing plant is lastly generated by matching an adsorption unit with each mobile parameter of the parameterized sequence during each phase time of the cycle, so as to cause the succession of phase times of the cycle to be followed at all the adsorption units in operation;
a normal-mode control sequencer of the processing plant is generated for N adsorption units in operation;
each step of the parameterized sequence of the normal-mode sequencer is denoted by a mobile parameter and a step number;
for each isolated adsorption unit, a fixed parameter for identifying the isolated state of the isolated unit is introduced before defining the parameterized sequence, and when the control sequencer of the processing plant is being generated, the or one of the isolated adsorption units is matched with the or each fixed parameter during all the phase times of the cycle, generating an exceptional-mode control sequencer of the processing plant;
each step of the parameterized sequence of the exceptional-mode sequencer is denoted by the fixed parameter or parameters, a mobile parameter and a step number;
at least one parameterized sequence is provided for transition between the parameterized sequence of the normal-mode sequencer and the parameterized sequence of the exceptional-mode sequencer of the processing plant;
each step of the parameterized position transition sequence is denoted by a mobile parameter of the sequence of the normal-mode sequencer, the fixed parameter or parameters, a mobile parameter of the sequence of the exceptional-mode sequencer and a reference number;
the exceptional-mode sequencer is a maintenance-mode control sequencer of the processing plant for substantially half the isolated adsorbers;
the generated sequencer is obtained by looping the parameterized sequence on itself as many times as the cycle has phase times, and by matching the corresponding adsorption unit with each parameter during each loop; and
the corresponding adsorption unit is matched with each parameter by means of a correspondence table.
The invention also relates to a plant for processing a gas by adsorption, having on the one hand N adsorption units, N being greater than or equal to 2, which operate according to a cycle which is distributed uniformly into at most N phase times and during a part of which at least one of the adsorption units is subjected to the output flow of at least one of the other adsorption units, said N adsorption units being connected to a pipe for supplying gas to be processed, to a pipe for producing processed gas, to a pipe for collecting a residual gas flow, and being provided with pipes and valves both for connecting the adsorption units to one another and for connecting the adsorption units to said supply, production and connection pipes; and on the other hand a unit for controlling the plant, which defines at least one control sequencer of the adsorption units, ensuring cyclic operation of the plant, in which at least one sequencer of the control unit is obtained by applying the control method as defined above, and at least some of the connection valves are respectively denoted by a parameter of the parameterized sequence generating at least one sequencer of the control unit.
According to one advantageous characteristic of this plant, the valves denoted by a parameter of the parameterized sequence are distributed into sets of valves as a function of the use of the gas which passes through the valves of the same set, and each of the valves denoted by a parameter is also denoted by the number of the set to which the corresponding valve belongs.