Process and installation for treating a waste lye of a lye scrub

Abstract

The invention relates to a process for treating a waste lye of a lye scrub in which the waste lye is fed with oxygen or an oxygen-containing gas mixture and steam to an oxidation unit (1) and in the latter is subjected to a wet oxidation for a reaction time period at a first temperature level and a first pressure level, a three-phase component mixture, which comprises a gas phase, a liquid phase and solid particles, being removed from the oxidation unit (1) and subjected to a cooling and phase separation. It is provided that the three-phase component mixture in an unchanged composition is first subjected to an expansion from the first pressure level to a second pressure level and thereby cooled down to a second temperature level, and that the three-phase component mixture expanded to the second pressure level and cooled down to the second temperature level is subsequently subjected at least partly to a further cooling to a third temperature level and after that to a phase separation. A corresponding installation is likewise the subject of the present invention.

Claims

1. A process for treating a waste lye of a lye scrub in which the waste lye is fed with oxygen or an oxygen-containing gas mixture and steam to an oxidation unit (1) and in the latter is subjected to a wet oxidation for a reaction time period at a first temperature level and a first pressure level, a three-phase component mixture, which comprises a gas phase, a liquid phase and solid particles, being removed from the oxidation unit (1) and subjected to a cooling and phase separation, characterized in that at least part of the three-phase component mixture in an unchanged composition is first subjected to an expansion from the first pressure level to a second pressure level and thereby cooled down to a second temperature level, and in that the three-phase component mixture expanded to the second pressure level and cooled down to the second temperature level is subsequently subjected at least partly to a further cooling to a third temperature level and after that to a phase separation.

2. The process according to claim 1, in which the expansion to the second pressure level is carried out by using a valve arrangement (2) that has one or more expansion valves (21, 22) with in each case at least two flowed-through sealing edges and a maximum valve cross section of in each case at least 80%.

3. The process according to claim 2, in which expansion valves (21, 22) are formed as one or more ball valves.

4. The process according to claim 2, in which the valve arrangement (2) comprises two or more expansion valves (21, 22) arranged in parallel.

5. The process according to claim 1, in which the first temperature level lies at 180 to 220° C. and the second temperature level lies at 120 to 180° C. and at least 5° C. below the first temperature level.

6. The process according to claim 1, in which the third temperature level lies at ambient temperature up to 100° C.

7. The process according to claim 1, in which the first pressure level is at an absolute pressure of 20 to 50 bar and the second pressure level is at an absolute pressure of 1 to 10 bar.

8. The process according to claim 1, in which a first fraction of the three-phase component mixture expanded to the second pressure level and cooled down to the second temperature level is subjected to a further cooling to the third temperature level and after that to the phase separation, and a second fraction thereof is subjected to the phase separation without the further cooling to the third temperature level.

9. The process according to claim 8, in which the first and second fractions are set in relation to one another in accordance with a temperature control.

10. The process according to claim 8, in which the further cooling of the first fraction is carried out by using a heat exchanger unit (3) comprising one or more heat exchangers (31), past which the second fraction is at least partially led.

11. The process according to claim 1, in which the phase separation is carried out by using a phase separating unit (4) and in which a gas phase and a two-phase component mixture, which comprises a liquid phase and solid particles, are formed in the phase separation.

12. The process according to claim 11, in which the phase separating unit (4) is operated at a pressure level of 1 to 10 bar absolute pressure.

13. The process according to claim 1, in which the volume fraction of the gas phase in the three-phase component mixture lies at more than 25%.

14. The process according to claim 1, in which the three-phase component mixture is removed from the oxidation unit (1) at a first geodetic height, is fed to the at least partial expansion from the first pressure level to the second pressure level at a second geodetic height, and is subjected to the cooling to the second temperature level at a third geodetic height, the second geodetic height lying below the first geodetic height and the third geodetic height lying below the second geodetic height.

15. Installation for treating a waste lye of a lye scrub, with means which are set up for feeding the waste lye with oxygen or an oxygen-containing gas mixture and steam to an oxidation unit (1) and in the latter subjecting it to a wet oxidation for a reaction time period at a first temperature level and a first pressure level, and means which are set up for removing a three-phase component mixture, which comprises a gas phase, a liquid phase and solid particles, from the oxidation unit (1) and subjecting it to a cooling and phase separation, characterized in that means which are set up for first expanding at least part of the three-phase component mixture in an unchanged composition from the first pressure level to a second pressure level and thereby cooled down to a second temperature level are provided, and in that means which are set up for subsequently subjecting the three-phase component mixture expanded to the second pressure level and cooled down to the second temperature level at least partly to a further cooling to a third temperature level and after that to a phase separation are provided.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 illustrates in a simplified representation a process for treating a waste lye according to a configuration that is not according to the invention.

[0051] FIG. 2 illustrates in a simplified representation a process for treating a waste lye according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0052] In FIG. 1, a process according to a configuration not according to the invention for treating a waste lye is illustrated in the form of a greatly simplified process flow diagram.

[0053] In the process illustrated in FIG. 1, a wet oxidation of a waste lye is performed by means of an oxidation unit 1, which is illustrated here in an extremely simplified manner and may comprise one or more oxidation reactors. For this purpose, the oxidation unit is fed waste lye together with steam and oxygen or an oxygen-containing gas mixture and this is subjected in the oxidation unit to a wet oxidation for a reaction time period at a first temperature level and a first pressure level. For the pressures and temperatures used here, reference should be made expressly to the explanations above.

[0054] In the process illustrated in FIG. 1, a three-phase component mixture, which is illustrated here in the form of a substance stream 101, is removed from the oxidation unit 1 and cooled down in a heat exchanger unit 110 at the pressure and temperature level at which it was removed from the oxidation unit 1. The heat exchanger unit 110 is in this case operated by using a temperature control medium, which is illustrated here in the form of a flow stream 111 and a return stream 112.

[0055] In the process illustrated in FIG. 1, a three-phase component mixture cooled down in this way is fed in the form of a substance stream 102 to a first phase separating unit 120, which comprises a vessel 121. In the vessel 121, a liquid phase with particles, that is to say a two-phase mixture, separates out at the bottom. By means of a valve 122, this can be drawn off in accordance with a filling level control LC in the form of a substance stream 103 and transferred into a second phase separating unit 130. This is required here because, during the expansion of the two-component mixture from the first phase separating unit, dissolved gases outgas (flash). In the second phase separating unit 130, which once again comprises a vessel 131, a two-phase component mixture therefore once again separates out at the bottom.

[0056] By means of a valve 123, a gas phase in the form of a stream 104 is drawn off in accordance with a pressure control PC from the top of the phase separating unit 120. This stream may be combined with a gas phase in the form of a substance stream 106 that is correspondingly drawn off by means of a valve 133 in accordance with a pressure control PC from the phase separating unit 130, to form a collective stream 107.

[0057] By the process according to the prior art that is illustrated in FIG. 1, finally a liquid stream with particles, that is to say a two-phase stream 105, can be provided by means of a valve 132 in accordance with filling level control LC from the second phase separating unit 130 and can for example be passed on for storage or further treatment.

[0058] In FIG. 2, a process according to an embodiment of the present invention is illustrated in the form of a greatly simplified process flow diagram. Here, too, an oxidation unit 1 is used, with respect to which reference is made to the explanations relating to FIG. 1 and to the explanations given at the beginning.

[0059] A three-phase component mixture 201, which comprises a gas phase, a liquid phase and solid particles, is drawn off from the oxidation unit 1 at the pressure level at which the oxidation unit 1 is operated, and also at a corresponding temperature level. By contrast with the process illustrated in FIG. 1, however, it is then first expanded by means of an expansion unit 2. The expansion in this case takes place from a first pressure level to a second pressure level. For the pressure levels, reference is respectively made expressly to the explanations above. On the basis of the physical laws prevailing, the expansion results in a cooling of the three-phase component mixture 201 and a partial outgassing of dissolved gaseous components. A correspondingly formed, likewise three-phase component mixture is denoted by 202.

[0060] As is the case in the configuration of the present invention that is illustrated in FIG. 2, the expansion unit 2 may comprise here two expansion valves 21, 22 arranged in parallel, which may be formed in the way explained above. In this case, at least one of these expansion valves 21, 22 may be operated on the basis of a pressure control PC. Instead of a number of expansion valves 21, 22 being provided in parallel, however, valves may also be arranged in series or there may be a single valve. In the example represented, in particular switching valves 23 or shut-off valves are connected upstream or downstream of the expansion valves 21, 22.

[0061] In the embodiment of the present invention that is illustrated in FIG. 2, after it has been expanded from the first pressure level to the second pressure level in the expansion device 2, the three-phase component mixture 202 is divided into two partial streams 203 and 204. However, this is not absolutely necessary. It may also be merely that a treatment of the entire three-phase component mixture 202 in the manner of the substance stream 203 is provided. In such a case, the substance stream 204 is not formed.

[0062] In the example represented, the partial stream 203 is fed to a heat exchanger 31 in the heat exchanger unit 3, which, as already explained above with respect to the heat exchanger according to FIG. 1, may be flowed through by a refrigerant. This is represented here in the form of a flow 111 and a return 112, as illustrated in FIG. 1. However, on account of the different requirement for cold here, in particular a different refrigerant than in the process illustrated in FIG. 1 may be used. The three-phase component mixture 203 is cooled down further from the second temperature level to the third temperature level in the heat exchanger 31.

[0063] In parallel with this, in the embodiment illustrated in FIG. 2, optionally the partial stream 204 is led past the heat exchanger 31 by means of a valve 32 in accordance with a temperature control TC and is combined with the partial stream 203 cooled down there to form a collective stream 205. In this way, a temperature of the collective stream 205 can be set.

[0064] In the example represented, the collective stream 205 is fed into a phase separating unit 4, which has a vessel 41. This is provided with valves 42 and 43, which can be activated by means of a filling level control LC or a pressure control TC. By means of the phase separating unit 4 or the vessel 41, in this way a two-component mixture 206, which represents a liquid phase with particles, and a gas phase 207 can be formed.

[0065] By contrast with the embodiment according to the prior art that is illustrated in FIG. 1, according to this configuration of the invention the liquid phase 206 does not in this case have to be subjected to a further phase separation, since it has a smaller proportion of outgas components.