Method and apparatus for cooling a flow containing at least 35% carbon dioxide and mercury

Abstract

In a method for cooling a flow containing at least 35% carbon dioxide and at least 0.2 ?g/Nm.sup.3 of mercury, the mercury being in liquid and/or gas form, the flow is cooled in a first brazed aluminum plate-fin heat exchanger from a first temperature to a second temperature higher than ?38.6? C. to form a cold flow at the second temperature, and the flow cooled to the second temperature is cooled in a second heat exchanger, which is a tube and shell heat exchanger, to a third temperature lower than ?38.6? C.

Claims

1. A process for cooling a flow containing at least 35% carbon dioxide and at least 0.2 ?g/Nm.sup.3 mercury, the mercury being in liquid and/or gaseous form, the process comprising the steps of: i) cooling the flow in a first brazed aluminum plate exchanger from a first temperature to a second temperature above ?38.6? C. in order to form a cooled flow; and ii) cooling the cooled flow or a gas derived from said cooled flow in a second exchanger to a third temperature below ?38.6? C. to form a second cooled flow, wherein the second exchanger is made of stainless steel, copper, nickel, tantalum or an alloy of two of these metals, wherein the second exchanger is a shell and tube exchanger or a brazed plate-fin exchanger or a plate and shell exchanger.

2. The process as claimed in claim 1, wherein the flow cooled to the second temperature containing at least 35% carbon dioxide and at least 0.2 ?g/Nm.sup.3 mercury is diphasic and is separated in a first phase separator in order to form a liquid mercury and the gas derived from the cooled flow that is purified of mercury.

3. The process as claimed in claim 1, wherein the flow is partially condensed in the first exchanger and is sent to a first phase separator, the gaseous portion originating from the first phase separator constituting the gas derived from the cooled flow, this gaseous portion being less rich in mercury than the flow cooled in the first exchanger.

4. The process as claimed in claim 1, wherein mercury is solidified and is deposited in the second exchanger and/or in a second phase separator supplied with mercury-enriched liquid or liquid mercury originating from a first phase separator.

5. The process as claimed in claim 4, wherein a liquid originating from the first phase separator is sent to the second phase separator at a level below a liquid level thereof.

6. The process as claimed in claim 1, wherein the second temperature is above ?36? C.

7. The process as claimed in claim 1, wherein the cooled flow is not purified in order to eliminate mercury by adsorption between the first and second exchangers.

8. The process as claimed in claim 7, wherein the cooled flow is not purified in order to eliminate mercury between the first and second exchangers.

9. The process as claimed in claim 1, wherein the second exchanger is a brazed plate-fin exchanger.

10. The process as claimed in claim 1, wherein the second cooled flow is then separated at a temperature equal to or below the third temperature in order to produce a liquid flow containing at least 80% carbon dioxide.

11. The process as claimed in claim 10, wherein the liquid flow comprises at least 95% carbon dioxide.

12. An apparatus for cooling a flow containing at least 35% carbon dioxide and at least 0.2 ?g/Nm.sup.3 mercury, the mercury being in liquid or gaseous form, the apparatus comprising: a first brazed aluminum plate heat exchanger configured to receive the flow at a first temperature and cool the flow to a second temperature above ?38.6? C. in order to form a cooled flow; a first phase separator for purifying the cooled flow of mercury thereby forming a gas stream having reduced amounts of mercury as compared to the cooled flow; a second heat exchanger made of stainless steel, copper, nickel, tantalum or an alloy of at least two of these metals, which is a shell and tube exchanger or a brazed plate-fin exchanger or a plate and shell exchanger, wherein the second heat exchanger is in fluid communication with the first phase separator such that the second heat exchanger is configured to receive the gas stream from the first phase separator and cool the gas stream to a third temperature below ?38.6? C.; means for sending a purge gas to the second exchanger and also means for discharging a mercury-laden purge gas from the second exchanger to a storage vessel or to a discharge stack; and means for discharging a purge stream comprising liquid mercury from the first phase separator.

13. The apparatus as claimed in claim 12, wherein the second heat exchanger is a shell and tube exchanger.

14. The apparatus as claimed in claim 12, wherein the second heat exchanger is a brazed plate-fin exchanger.

15. The apparatus as claimed in claim 12, wherein the second heat exchanger is a plate and shell exchanger.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) FIG. 1 provides an embodiment of the present invention.

(3) FIG. 2 provides an embodiment of the present invention.

(4) FIG. 3 provides an embodiment of the present invention.

(5) FIG. 4 provides an embodiment of the present invention.

(6) FIG. 5 provides an embodiment of the present invention.

DETAILED DESCRIPTION

(7) The flow may be gaseous or liquid.

(8) The percentages mentioned in this document relating to purities are molar purities.

(9) The flow may contain 45% carbon dioxide, 65% carbon dioxide or 85% carbon dioxide.

(10) Preferably, the flow contains less than 20% methane.

(11) Among other impurities, the flow may contain at least one of the following impurities: oxygen, nitrogen, argon, carbon monoxide, hydrogen. The invention will be described in greater detail by referring to the figures. FIG. 1 represents a variant of the process according to the invention, FIGS. 2 and 3 represent details from FIG. 1 and FIGS. 4 and 5 represent processes according to the invention.

(12) In FIG. 1, a mixture 1 contains at least 35 mol % carbon dioxide, at least 60 mol % carbon dioxide, or even at least 80 mol % carbon dioxide. It contains at least 0.2 ?g/Nm.sup.3 mercury, or even at least 2 ?g/Nm.sup.3 mercury.

(13) The remainder of the mixture 1 may contain one or more of the following components: oxygen, nitrogen, argon, nitrogen oxide (NO or NO.sub.2 or N.sub.2O), carbon monoxide, hydrogen, methane, etc.

(14) The mixture is filtered in a filter F in order to remove the dust, then compressed in a first compressor stage C1 in order to form a compressed flow 3. The compressed flow 3 at 35? C. is compressed in a second compressor stage C2, cooled in a cooler R2, compressed in a third compressor stage C3, cooled in a cooler R3, compressed in a fourth compressor stage C4, cooled in a cooler R4, compressed in a fifth compressor stage C5 and cooled in a cooler R5 in order to form a flow 5 at between 6 and 20 bar abs. This flow of the mixture 5 is purified of water in a bed of adsorbent A2 in order to form a purified flow 7 at 35? C. The purified flow 7 is partially condensed in a first heat exchanger 9, which is an aluminum exchanger consisting of a stack of plates separated by fins. The partially condensed flow is sent at a temperature above ?38.6? C., and below ?34? C., or even below ?34.5? C., for example at ?35? C., to a first phase separator 11. In this first phase separator, the mercury is partially condensed and is purged with the liquid 15. The gas formed 13 in the phase separator 11 also contains at least 0.2 ?g/Nm.sup.3 mercury and is sent to the tubes of a second heat exchanger 35, enabling an indirect exchange of heat between only two fluids, of shell and tube type. The figure does not illustrate the multiplicity of tubes where the gas 13 derived from the mixture is partially condensed. The liquid formed 43 at ?52? C. is sent to a second phase separator 17, where the liquid 15 from the first phase separator 11 is also sent. The phase separators 11,17 will preferably be made of stainless steel. The stainless steel may be of 316L type. The ducts connecting the first phase separator to the second exchanger and connecting the first phase separator to the second phase separator will preferably be made of stainless steel. On the other hand, the structured packings of the column 23 may be made of aluminum.

(15) Mercury solidifies in the second exchanger 35 which cools the flow 13 to a temperature below ?38.6? C., preferably below ?50? C. The cooling temperature is above ?54? C. in order to prevent any risk of the carbon dioxide freezing.

(16) Mercury also solidifies in the second phase separator 17.

(17) A gas 45 from the second phase separator 17 is heated in the first heat exchanger.

(18) The liquid 19 from the second separator 17 is expanded in a valve 21 and sent to the top of the distillation column 23.

(19) An overhead gas 25 depleted in carbon dioxide but enriched in at least one of the impurities (oxygen, nitrogen, argon, nitrogen oxide (NO or NO.sub.2/N.sub.2O.sub.4 or N.sub.2O), carbon monoxide, hydrogen) is heated in the first heat exchanger 9.

(20) A bottoms liquid 27 is withdrawn from the bottom of the column and contains at least 80 mol % carbon dioxide. The liquid 27 is divided into two, one flow 29 is vaporized in the first heat exchanger 9 without having been expanded. A portion 30 of the gas formed is sent to the bottom of the distillation column. The remainder 32 forms part of the product of the process.

(21) The liquid 33 originating from the bottom of the column is expanded in a valve 31 up to a pressure equivalent to or slightly above that of the triple point of the carbon dioxide that it contains. The liquid is then sent to the shell of the second exchanger 35 where it is vaporized. The gas formed is heated in the exchanger 9 then is compressed by a compressor stage C6 and cooled in a cooler R6 before being mixed with the vaporized liquid 32. The gas thus formed is compressed by the stages C7, C8, C9 and cooled by the coolers R7, R8, R9, R10 in order to form a condensed gas. This condensed gas is mixed with the liquid purge 41 from the second exchanger and partly pumped by a pump P1 in order to form a pressurized liquid product 51, at at least 50 bar. The liquid purge 41 has previously been pumped in a pump P2. A portion 49 of the liquid is used as cycle liquid, is expanded at the triple point in the valve 53 and sent to the second exchanger 35, mixed with the flow 33.

(22) A portion of the mixture 47 is heated in an exchanger E1 and is used to regenerate the adsorbent bed A1 which is in the regeneration phase. The flow 55, having been used for the regeneration, is mixed with the flow 3 downstream of the stage C1.

(23) It is of course possible to vaporize the liquid 33 in the second exchanger 35 by indirect heat exchange with another fluid from the process, for example a portion of the vaporized bottoms liquid.

(24) When the apparatus is shut down, a purge gas at more than ?38.6? C. will be sent to the exchanger 35 in order to melt the solidified mercury and discharge it in gaseous form. These purge discharge ducts will be made of stainless steel.

(25) The connection between the two phase separators 11,17 is problematic since it is necessary to prevent the mercury from freezing in the duct coming from the phase separator 11, in order to prevent it from blocking the duct, but to send all the same the liquid CO.sub.2 coming from the phase separator 11 (at around ?35? C.) below the liquid level of the phase separator 17 (which is at ?52? C.). If it were introduced into the gaseous zone, solid mercury could be entrained by the gaseous fluid 45.

(26) In order to avoid entraining liquid mercury with the fluid 19, it is possible to install a dip tube in order to withdraw the fluid 19 without withdrawing the mercury which will sink to the bottom of the separation pot 17.

(27) Specifically, this makes it possible to reduce the portion of CO.sub.2 lost in the gas phase at the inlet to this phase separator 17 (since the hotter liquid is cooled by the cold liquid) and to avoid sending or entraining mercury in the gas phase 45 which is emitted into the atmosphere.

(28) TABLE-US-00001 TABLE 1 flow 3 7 13 43 P (bar a) 1 22 21.8 21.7 T (? C.) Composition 35 35 ?35 ?52 (vol % on dry basis) CO.sub.2 78 78 61 61 O.sub.2 8 8 14 14 Ar 5 5 9 9 N.sub.2 9 9 16 16 Mercury content 3 3 0.5 0.03 (?g/Nm.sup.3) Note: The remainder is The remainder is condensed and is trapped in the discharged in exchanger 35 the liquid 15

(29) In certain cases, it may prove that the simple partial condensation in the phase separator 11 is sufficient to remove enough mercury, that the gas 13 can be treated without taking additional precautions for protecting the components of the apparatus against the presence of mercury. In this case, it is not necessary to purge the exchanger 35 in order to remove the mercury, the latter being entrained in the liquid 15 toward the separator 17.

(30) FIGS. 2 and 3 show, in greater detail, arrangement options for a part of FIG. 1. In both figures, a mixture 7 contains at least 35 mol % carbon dioxide, at least 60 mol % carbon dioxide, or even at least 80 mol % carbon dioxide. It contains at least 0.2 ?g/Nm.sup.3 mercury, or even at least 2 ?g/Nm.sup.3 mercury.

(31) The remainder of the mixture 7 may contain one or more of the following components: oxygen, nitrogen, argon, nitrogen oxide (NO or NO.sub.2 or N.sub.2O), carbon monoxide, hydrogen, methane.

(32) The mixture 7 is cooled in a first exchanger 9 which is a brazed aluminum plate-fin exchanger. The mixture is cooled to a temperature above ?38.6? C. and below ?34? C., or even below ?34.5? C., and is sent to a first phase separator 11 made of stainless steel. The liquid produced 15 is removed from the phase separator and the gas 13 is sent to a second exchanger 35. This second exchanger 35 may be a shell and tube exchanger or a brazed plate-fin exchanger made of a metal other than aluminum or a plate and shell exchanger made of stainless steel. In the second exchanger 35, the flow is cooled to a third temperature below ?38.6? C.

(33) In the variant from FIG. 2, a portion of the mercury is liquefied in the first phase separator 11 which is made of stainless steel. As carbon dioxide is less dense than mercury, the liquefied carbon dioxide is found on top of mercury and may be removed by a dip tube 57 without removing the mercury. The liquid mercury can therefore be removed regularly via a duct 59 and a duct 61, or completely when the process is shut down. In this case, the mercury is not sent to the second phase separator 17, but is discharged from the apparatus and may be sold as product. The remainder of the mercury solidifies in the exchanger 35 and is removed by sending a purge gas into the exchanger 35 in order to vaporize the mercury and discharge it via the duct 63 and the valve 65.

(34) For the variant from FIG. 3, the liquid mercury passes from the first phase separator 11 to the second phase separator 17 via the duct 15.

(35) In this second pot, the mercury solidifies. During the shutdown of the process, the duct conveying the liquid from the second separator 17 to the column is closed, a purge gas vaporizes the mercury and the gas produced is purged via the duct 63 and the valve 65.

(36) The use of a second dip tube (like 57 in FIG. 2) may be recommended for withdrawing the liquid 19 from separator 17.

(37) In FIGS. 4 and 5, a mixture 7 contains at least 35 mol % carbon dioxide, at least 60 mol % carbon dioxide, or even at least 80 mol % carbon dioxide. It contains at least 0.2 ?g/Nm.sup.3 mercury, or even at least 2 ?g/Nm.sup.3 mercury.

(38) The remainder of the mixture 7 may contain one or more of the following components: oxygen, nitrogen, argon, nitrogen oxide (NO or NO.sub.2 or N.sub.2O), carbon monoxide, hydrogen, methane.

(39) The mixture 7 is cooled in a first exchanger 9 which is a brazed aluminum plate-fin exchanger. The mixture is cooled to a temperature above ?38.6? C. and below ?34? C., or even below ?34.5? C., and is sent to a phase separator 11 made of stainless steel. The liquid produced 15 is removed from the phase separator and the gas 13 is sent to a second exchanger 35. This second exchanger 35 may be a shell and tube exchanger or a brazed plate-fin exchanger made of a metal other than aluminum or a plate and shell exchanger made of stainless steel. In the second exchanger 35, the flow is cooled to a third temperature below ?38.6? C. and the mercury is deposited in solid form in the second exchanger.

(40) The second exchanger 35 may be a brazed plate-fin exchanger made of stainless steel or copper, nickel or tantalum or an alloy of at least two of these metals.

(41) Another fluid 45 is heated in both exchangers in order to provide frigories. Alternatively, two different fluids may each circulate in one of the exchangers. Next, the liquid formed 43 in the second exchanger may be treated in means that are sensitive to corrosion by mercury since the mercury concentration of the liquid will be less than 0.1 ?g/Nm.sup.3.

(42) As illustrated in FIG. 5, the presence of the phase separator 11 is not essential.

(43) 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.

(44) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(45) 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.

(46) 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.

(47) 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.

(48) 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.

(49) 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.