Patent Application
20180187837
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French patent application No. FR1750088, filed Jan. 5, 2017, the entire contents of which are incorporated herein by reference.
The present invention relates to a method for reheating an atmospheric vaporizer using a gas originating from a cryogenic air separation unit.
In a cryogenic air separation unit (ASU), a backup system may be necessary to supply a gaseous product, for example oxygen, nitrogen or argon, in case of shutdown of the ASU for a limited period. The backup system is generally composed of a cryogenic liquid storage and a liquid vaporization system.
Different vaporization systems can be used depending on the atmospheric conditions, on the production capacity, etc. (e.g. an exchanger with a heat transfer fluid such as steam or water, a vaporizer of pool type heated by steam, an atmospheric vaporizer, etc.).
An atmospheric vaporization system constitutes an economical option and offers the advantage of using the “free” heat while it is in service. However, its main drawback is that it has a limited service time because of the icing on the outer surface of the vaporizer because of the presence of moisture in the air.
The de-icing of an atmospheric vaporizer can be done naturally if the temperature of the air is hot enough, for example above 0° C. However, if the ambient temperature may remain cold for a long period (for example a few weeks or even a few months), the installation of a heating system for the de-icing of the vaporizer may prove necessary.
The conventional de-icing methods consist in installing either a dedicated reheater (generally electrical) in line or an electrical reheater outside of the vaporizer but within a closed enclosure, combined with forced ventilation. These de-icing means present a significant cost overhead and, in the case of an in-line electrical reheater for an oxygen vaporizer, there is also a potential risk of high temperature oxygen fire.
In certain embodiments of the invention, solutions are proposed that are more economical and easier to implement, which do not require any dedicated reheater installation.
According to one object of the invention, a method for reheating, even de-icing, an atmospheric vaporizer is provided in which:
i) in normal operation, a cryogenic liquid having as its main component oxygen, nitrogen or argon originating from a source is vapourized by heat exchange with the ambient air in the atmospheric vaporizer and in which
ii) in reheating phase, to reheat, even de-ice the vaporizer, the cryogenic liquid is no longer sent from the source to the atmospheric vaporizer but, instead, a gas is sent thereto at a temperature of at least 0° C., preferably of at least 20° C., this gas originating from a cryogenic distillation air separation unit, the gas being either
a) a stream of air purified of water and of carbon dioxide taken from the air supply of the air separation unit or
b) a gas originating from a column of the air separation unit reheated in a heat exchanger by the air intended for the distillation.
According to other optional aspects of the invention:
The method can make it possible to operate an atmospheric vaporizer intended to supply gas for a limited period, in care of failure of an ASU.
In some cases, the gas is supplied during a programmed shutdown of the air separation unit.
In other cases, when the ambient temperature is below zero, the atmospheric vaporizer is covered with ice and cannot be used until the ambient temperature rises sufficiently. In this case, a means of de-icing the vaporizer has to be found.
The design and the dimensioning of the atmospheric vaporizer must guarantee the supply of the gas for a predefined period before the bulk formation of ice.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawing(s). It is to be noted, however, that the drawing(s) illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.
The method according to the invention will be described in more detail with reference to the figures.
In normal operation, a cryogenic liquid 1 having as its main component oxygen, nitrogen or argon is withdrawn from a storage S. The liquid is sent through a valve V1 to a vaporizer V by a duct 5. The liquid is vaporized in the vaporizer by heat exchange with the air and the gas formed is sent through the valve V3 to a duct 11 by which it supplies a client.
In the case where the vaporizer is covered with ice, it is necessary to heat the vaporizer V and, for this, the sending of the liquid 1 to the vaporizer is stopped.
In normal operation, air is sent to an air separation unit ASU where it is purified of water and of carbon dioxide in a purification unit. At the output of the purification unit, it is cooled and sent to a distillation column to be separated.
When the vaporizer V has to be reheated, at the output of the purification unit, the air is divided into two parts. A first part is cooled and sent to a distillation column to be separated. A second part 3 is heated to at least 0° C., maybe to at least 20° C., and preferably to at least 50° C. in a reheater R, for example an electrical reheater or steam reheater.
This air is sent to the atmosphere by the valve V3, V5 and the duct 9 after having circulated in the vaporizer V to reheat it.
The main drawback with this solution is the need to restore the content of the vaporizers V after the de-icing operation.
According to the method of
In normal operation, a cryogenic liquid 1 having as its main component oxygen, nitrogen or argon is withdrawn from a storage S. The liquid is sent through a valve V1 to a vaporizer V by a duct 5. The liquid is vaporized in the vaporizer by heat exchange with the air and the gas formed is sent through the valve V3 to a duct 11 by which it supplies a client.
In the case where the vaporizer is covered with ice, it is necessary to heat the vaporizer V and, for this, the sending of the liquid 1 to the vaporizer is stopped.
In normal operation, air is sent to an air separation unit ASU where it is purified of water and of carbon dioxide in a purification unit. At the output of the purification unit, it is cooled and sent to a distillation column to be separated to form a gas having as its main component oxygen, nitrogen or argon 2. The gas is either output from a distillation column in gaseous form and reheated in a heat exchanger where the air supply is cooled or output from a distillation column in liquid form and vapourized and reheated in a heat exchanger where the air supply is cooled. In this way, it is at a minimum temperature of 0° C. in most cases.
When the vaporizer V has to be reheated, at the output of the purification unit, at least a part of the gas 3 is sent to the vaporizer to reheat it and preferably de-ice it, possibly after reheating in a reheater (not illustrated). If the main component of the gas 3 and that of the liquid 1 are the same, the gas 3 can be sent to the client by the duct 11. Otherwise, it can be rejected to the atmosphere.
In a particular case illustrated in
A valve V4 can be closed in order to send the gas which was used for the reheating to the air via the duct 15. In this case, it is possible to reheat, even de-ice, the vaporizer V and to vent the reheating gas, even de-icing gas, to the atmosphere, while a part of the production 13 is sent to the client.
Once the de-icing is done, normal operation of the method is resumed.
The main advantages of this solution are:
The main drawback is the need to increase the pressure of the gas produced in order to compensate for the headloss of the vaporizers. This may prove difficult when the gas is produced at low pressure, for example nitrogen originating from the low-pressure column of a double column. In this case, the solution of
In the case of the two figures, the storage S can be supplied from the air separation unit ASU or not.
The reheating gas 3 can be used in addition to a reheater.
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.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“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” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR 1750088 | Jan 2017 | FR | national |
