Patent Application
20140208798
This invention relates to an apparatus and integrated process for separating a mixture of carbon dioxide and at least one other gas and for separating air by cryogenic distillation.
It relates in particular to an apparatus and integrated process for separating a mixture of carbon dioxide and at least one other gas and for separating air by cryogenic distillation, with water cooling intended to cool the mixture and/or the air upstream of the separation.
Compression and purification apparatuses treating supplies that are rich in CO2 (more than 35% volume on a dry basis, preferably more than 70%) produce in essence a flow with less CO2 content than the supply and containing the gases that will have been extracted from the product. The purification of the CO2 can take place thanks to one or several partial condensation(s) or by membrane separation or any other process (adsorption, cryo-condensation, etc.). In certain processes such as those mentioned, the flow of impure gas is a dry product. This will not be the case for a separation by scrubbing with amines for example, wherein the two products of the separation (the CO2 and the residual gases) will be wet.
Most CO2 treatment units include a step of drying the gases treated. This can be drying via adsorption. A dry gas must then be used to regenerate the adsorbent when it is saturated with water. The state of the art provides as such to use the gases vaporised from the storage of CO2 or residual gases, at high or low pressure.
It is known from EP-A-1712858 to use a carbon dioxide depleted gas to cool the water in a water cooling tower.
EP-A-0503190 discloses a water cooling system for an apparatus for separating a mixture of carbon dioxide, oxygen and nitrogen wherein a water cooling tower is supplied with expanded nitrogen coming from an apparatus for separating air and water, with the cooled water then being used to cool the mixture to be separated. Before it is sent to the tower, the nitrogen is sent to the top condenser of a distillation column and then to the cooling exchanger of the mixture to be separated. This complicated arrangement requires the presence of a turbine so that the nitrogen has enough refrigeration to supply the required cold. Nothing makes it possible to think that this cold would be sufficient to cool both the water for the apparatus for separating the mixture and the apparatus for separating air.
In certain embodiment, the invention proposes, according to certain alternatives, another use for the dry residual gases. They can as such be saturated with water in a tower that operates by direct contact, making it possible as such to lower the temperature of the unevaporated water and produce chilled water. The method is commonly used on the apparatuses for separating air in “water-nitrogen towers” in order to cool the water by heat exchange and evaporation with the cold nitrogen coming from the apparatus for separating air.
For the case where the incondensable items have a flow rate relative to the total flow treated that is clearly lower than nitrogen in relation to the air, a first portion of the cooling of the water could be carried out in a “non-condensable water” tower, with the first portion of the cooling being supplemented by a second portion of cooling in a refrigeration unit.
When an apparatus for separating air having a water cooling tower located in the vicinity of an apparatus for separating a mixture of carbon dioxide and at least one other gas, using the water-nitrogen tower in order to produce cold water for the two apparatuses and also possibly saturating therein the incondensable items (which will then share the venting of the nitrogen) will allow for genuine gains in investment in relation to using two independent towers.
The CO2 contained in the incondensable items must be prevented at all cost from rising back up to the apparatus for separating air via the line for transferring the dry nitrogen to the water-nitrogen tower. In normal operation as in the case of degraded mode, there is a real risk of introducing CO2 into the apparatus for separating air and of clogging it when the CO2 has frozen.
It can as such be considered to introduce the CO2 at a second level in the tower, above the nitrogen.
Note however that the risk is similar to that of allowing moisture to enter the cold box of the apparatus for separating air, except in that the incondensables arrive under pressure whereas when the nitrogen has become wet, it necessarily is at a pressure that is lower than at which it was in the box since it comes from there.
A precautionary measure, which is claimed as inventive also, consists in expanding the incondensable items sufficiently far from the tower so that over a distance that will be deemed as reasonable, the pressure in the supply pipe of the tower is lower for the line of incondensable items than for the line of nitrogen.
According to a particularly simple alternative, the process consists in cooling the water by using nitrogen from an ASU and possibly at least one gas coming from a unit for separating a mixture of CO2 and at least one other gas, which can for example be nitrogen, oxygen, argon, carbon monoxide, hydrogen, methane, NO2 or a mixture of at least two of these gases.
According to an object of the invention, an integrated apparatus is provided for separating a mixture of carbon dioxide and at least one other gas and for separating air by air distillation comprising a unit for separating a gaseous mixture comprising carbon dioxide at and least one other gas in order to produce a carbon dioxide-enriched gas and a carbon dioxide depleted gas and a unit for separating air by cryogenic distillation in order to produce at least one nitrogen-enriched gas stream characterised in that it comprises a water cooling tower that operates by direct contact as well as a line for sending water to the top of the tower, a line for sending at least one portion of the nitrogen-enriched gas stream to a lower level of the tower, a cooled water line for withdrawing cooled water from the tower and means for cooling the air upstream of the air separation unit, the cooled water line being connected to means for cooling the air upstream of the air separation unit and to the inlet and/or to the outlet of the unit for separating the gaseous mixture.
According to other optional aspects of the invention:
According to another object of the invention, an integrated process is provided for separating a mixture of carbon dioxide and at least one other gas and for separating air by air distillation comprising a unit for separating a gaseous mixture comprising carbon dioxide and at least one other gas in order to produce a carbon dioxide-enriched gas and a carbon dioxide depleted gas and a unit for separating air by cryogenic distillation in order to produce at least one nitrogen-enriched gas stream characterised in that water is cooled in a water cooling tower that operates by direct contact with the nitrogen-enriched gas stream, the air intended for the air separation unit is cooled with the cooled water in the cooling tower and the gaseous mixture intended for the unit for separating the gaseous mixture and/or a product from the unit for separating the gaseous mixture is cooled using the cooled water coming from the cooling tower.
According to other optional aspects:
According to another object of the invention, an integrated apparatus is provided for separating a mixture of carbon dioxide and at least one other gas and for separating air by air distillation comprising a unit for separating a gaseous mixture comprising carbon dioxide and at least one other gas in order to produce a carbon dioxide-enriched gas and a carbon dioxide depleted gas and an air separation unit by cryogenic distillation in order to produce at least one nitrogen-enriched gas stream characterised in that it comprises a water cooling tower that operates by direct contact as well as a line for sending water to the top of the tower, a line for sending carbon dioxide depleted gas to a lower level of the tower, a line for sending at least one portion of the nitrogen-enriched gas stream to a lower level of the tower, a cooled water line for withdrawing cooled water from the tower, means for cooling the air upstream of the air separation unit, the cooled water line being connected to the means for cooling the air upstream of the air separation unit.
According to other optional aspects:
According to another objet of the invention, an integrated process is provided for separating a mixture of carbon dioxide and at least one other gas and for separating air by air distillation in an installation comprising a unit for separating a gaseous mixture comprising carbon dioxide and at least one other gas in order to produce a carbon dioxide-enriched gas and a carbon dioxide depleted gas and a unit for separating air by cryogenic distillation in order to produce at least one nitrogen-enriched gas stream characterised in that the installation comprises a water cooling tower that operates by direct contact as well as a line for sending water to the top of the tower, and wherein carbon dioxide depleted gas is sent to a lower level of the tower, at least one portion of the nitrogen-enriched gas stream is sent to a lower level of the tower, cooled water is withdrawn from the tower, the air is cooled in means in order to cool the air upstream of the air separation unit and cooled water is sent from the tank of the tower to the means for cooling the air upstream of the air separation unit.
According to other optional characteristics:
An advantage of this invention is that it allows for the integration of production of cold water for apparatuses for separating with as the only connection between the two apparatuses a cooled water line, although a solution according to prior art requires a nitrogen line under pressure that connects the two apparatuses.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings 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 invention shall be described in more detail by referring to the figures.
The nitrogen 17 is sent directly from the apparatus for separating air ASU to the pre-cooling unit P without passing through another means of treatment, such as a turbine or an exchanger other than the air cooling exchanger associated with the apparatus for separating air ASU.
The pre-cooling unit produces cold water which is sent either to the unit R as a stream 15 or is used in the unit P or both.
This unit comprises a cooling tower 33 wherein the water 31 comes into direct contact with nitrogen 17 coming from the apparatus for separating air ASU. The expanded gas 13 can be sent to the tower at a level higher than the inlet level of the nitrogen 17, possibly separated from the inlet level of the nitrogen by a lining stage. The nitrogen 17 comes from the apparatus ASU directly and arrives in the tower 33 without passing through the elements R or CPU.
The water cooling tower 33 is supplied at the top by a stream of water 31 at a temperature from 4° C. to 40° C. The pressure of the stream 13 is slightly less than that of the stream 17 at the inlet in the tower 33, thanks to the expansion in the valve V upstream of the tower, in order to prevent polluting the cooled water.
The gas 17 and possibly the gas 13 cool the water by direct contact and evaporation of a portion of the water in these dry gases and the mixture formed 39 exits at the top of the tower as venting. The water heated in the unit CPU can be sent back to the unit P via the supply 21.
The cooled water in the tank of the tower 33 is pumped by a pump 25 in order to be sent to the air cooling tower with water by the line 27. Otherwise the cooled water can be sent to an exchanger with indirect contact in order to transfer refrigeration to the air intended for the distillation. A portion of this water 27 can also be used to provide refrigeration to the unit CPU, for example upstream of the desiccation unit.
This process may possibly not use a mechanical refrigeration unit such as a refrigeration unit. The tower 33 will possibly be somewhat larger than that used solely for providing water for the air separation unit ASU.
For the processes of
This unit P comprises a cooling tower 33 wherein the water 31 comes into contact direct with nitrogen 17 coming from the apparatus for separating air ASU and an air cooling tower with water 133. The expanded gas 13 is possibly sent to the tower 33 at a level higher than the inlet level of the nitrogen 17. The nitrogen 17 comes from the apparatus ASU directly and arrives in the tower 33 without passing through the elements R or CPU.
The water cooling tower 33 is supplied at the top by a stream of water 31 at a temperature from 10° C. to 50° C.
The pressure of the stream 13 is slightly less than that of the stream 17 at the inlet in the tower 33, thanks to the expansion in the valve V upstream of the tower. The operating pressure of the tower 33 is substantially equal to the pressure at which the nitrogen 17 exits the apparatus for separating air ASU.
The gas 17 and possibly the gas 13 cool the water by direct contact and evaporation and the mixture formed 39 exits at the top of the tower as venting.
The cooled water in the tank of the tower 33 is pumped by a pump 25 in order to be sent to the top of the air cooling tower with water 133 as a stream 37. The air 1 intended for the distillation is cooled by being sent to the tank of the tower 133. The cooling water 21 is sent to an intermediate level of the tower 133 as a stream 121 and to the top of the tower 33 as a stream 31. The water cools the air by producing, at the top of the tower 133, a stream of cooled air 3 which is sent for purification and then for distillation in the air separation unit ASU.
The heated water 221 is collected in the tank of the tower 133 and is recycled in the tower 133 after exterior refrigeration (by using air coolers, through exchange with cold water, etc.). It can also be considered that the water 221 is not recycled but returns, for example, to a river or a water network downstream.
The cooled water 23 collected in the tank of the tower 33 is pressurised by the pump 25 and a portion 15 is sent to the separation unit CPU. The rest of the water is cooled by a refrigeration unit 35 in order to constitute the stream 37 sent to the top of the tower 133.
The cooled water 15 sent to the CPU can be used to cool the mixture to be separated or to cool a product from the separation. The unit CPU does not necessarily operate at sub-ambient temperature. The water heated in the unit CPU can be sent to the unit P via the supply 21.
The apparatus for separating air ASU does not necessarily supply an oxy-fuel combustion unit, if present, with oxygen. It is sufficient for the apparatus for separating air ASU to be located relatively close to the unit CPU to allow for the integration between the two.
For the case wherein the carbon dioxide depleted gas comprises carbon monoxide and/or methane and/or hydrogen, the gas can be sent to the cooling tower and the wet gas formed at the top of the tower can be used as a fuel, for example in a gas turbine.
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 a range is expressed, it is to be understood that another embodiment is from the one.
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 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 |
|---|---|---|---|
| 1154754 | May 2011 | FR | national |
This application is a §371 of International PCT Application PCT/FR2012/051203, filed May 29, 2012, which claims the benefit of FR1154754, filed May 31, 2011, both of which are herein incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2012/051203 | 5/29/2012 | WO | 00 | 3/31/2014 |
