Process for producing process steam

Abstract

The invention relates to a process for producing process steam, comprising: (a) providing steam (9; 35, 55) having a pressure in a range from 50 to 150 mbar(abs); (b) compressing the steam (9; 35, 55) in a first compression step to obtain pre-compressed steam (19) having a pressure in a range from 75 to 500 bar(abs); (c) compressing the pre-compressed steam (19) in a second compression step to obtain process steam (23) having a pressure in a range from 0.9 to 10 bar(abs), wherein the first compression step is carried out in an axial compressor (17) or in at least two compressors or blowers (57.1, 57.2, 57.3, 57.4), which are arranged in parallel, and the second compression step is carried out in a geared turbo compressor (21) comprising a plurality of compressor stages (21.1, 21.2, 21.3, 21.4, 21.5, 21.6).

Description

[0001] 240424W001

[0002] Process for producing process steam

[0003] Description

[0004] The invention relates to a process for producing process steam from steam having a pressure in a range from 50 to 150 mbar (abs).

[0005] Steam is a major thermal energy carrier in industry, for example in chemical industry. Conventional fossil steam production comes along with significant carbon dioxide emissions.

[0006] In many industrial processes, heat has to be dissipated for cooling. For this purpose, generally heat exchangers are used, in which process heat is transferred to a cooling medium. Depending on the process and the amount of heat to be dissipated, cooling water is used.

[0007] Particularly in processes that have to be cooled at low temperatures, presently the cooling medium is cooled after passing the heat exchanger. For cooling the cooling medium for example a coolant cooling system, an air cooling system or a cooling tower may be used. In all of these processes, the heat transferred from the process to the cooling medium is dissipated and not used. Due to the low temperature of the stream or apparatus to be cooled, it is necessary to depressurize the water to low pressures to evaporate a part of the water and obtain steam.

[0008] Evaporating water at low pressures and subsequent recompression of the steam presently is used for example for distillation of water or other liquids as described in US-A 2022 / 0289595. Here the steam of the evaporation is compressed and then used as heating medium for evaporation.

[0009] A parallel control system of a steam recompression plant with two steam compressors is disclosed in WO-A 2017 / 152813.

[0010] However, none of the known processes can be used for utilizing the energy dissipated from a process at low temperatures for producing process steam.

[0011] Therefore, it is an object of the present invention to provide a process for producing process steam using energy of processes which are cooled at low pressures.

[0012] This object is achieved by a producing process steam, comprising:

[0013] (a) providing steam having a pressure in a range from 50 to 150 mbar(abs);

[0014] (b) compressing the steam in a first compression step to obtain pre-compressed steam having a pressure in a range from 75 to 500 mbar(abs); 240424W001

[0015] 2

[0016] (c) compressing the pre-compressed steam in a second compression step to obtain steam having a pressure in a range from 0.9 to 10 bar(abs), wherein the first compression step is carried out in an axial compressor or in at least two compressors or blowers, which are arranged in parallel, and the second compression step is carried out in a geared turbo compressor comprising a plurality of compressor stages.

[0017] The steam obtained in step (c) having a pressure in a range from 0.9 to 10 bar(abs) can be used in industrial processes as a thermal energy carrier.

[0018] By compressing the steam in two compression steps, it is possible to efficiently compress steam having a pressure in a range from 50 to 150 mbar(abs). This allows to use energy of processes, which are cooled at low temperatures, for producing steam. By using the energy of processes being operated and cooled at low temperatures for producing steam, the amount of steam produced by using fossil energy can be reduced.

[0019] The steam may be obtained by any process in which steam having a pressure in a range from 50 to 150 mbar(abs), preferably having a pressure in a range from 75 to 150 mbar(abs) and particularly in a range from 100 to 150 mbar(abs) is produced. Preferably, the steam is obtained by cooling a process step.

[0020] For this purpose, the steam having a pressure in a range from 50 to 150 mbar(abs) may be obtained by cooling at least one process step using water having a pressure in a range from 0.5 to 5 bar(abs) as cooling medium and then depressurizing the heated water in a flash apparatus to the pressure in a range from 50 to 150 mbar(abs), so that a part of water evaporates. More preferred, the water used for cooling the process step has a pressure in a range from 0.75 to 3 bar(abs) and particularly in a range from 1 to 2 bar(abs).

[0021] Cooling the process step comprises cooling of a process stream and / or an apparatus used in the process step. Process steps, which are cooled for example are chemical reactions, absorptions, adsorptions, extractions, condensations including condensing reflux streams at the top of distillation columns or rectification columns. Apparatuses used in the process step may be for example are columns, tanks or pipes having a double jacket or being furnished with cooling coils on their jacket. Further, particularly when using columns or tanks, it is possible to provide cooling coils inside the apparatus.

[0022] Further apparatuses used in the process step that may be cooled for example are motors that have to be cooled.

[0023] For cooling a process stream, any suitable heat exchanger for indirect heat transfer known to the skilled person may be used. Suitable heat exchangers for example are shell-and-tube heat exchangers, plate heat exchangers or spiral heat exchangers. 240424W001

[0024] 3

[0025] The process stream may either be a stream fed into the process or obtained in the process or, alternatively, a stream of a cooling medium that is used for cooling the process step.

[0026] If a process stream is cooled, depending on the amount of heat to be transferred, the size of the water stream and the size of the process stream, only one heat exchanger may be used or at least two heat exchangers. If more than one heat exchanger is used, for example 2 to 12 heat exchangers, more preferred 2 to 8 heat exchangers and particularly 2 to 6 heat exchangers, it is possible to connect the heat exchangers in series or to connect the heat exchangers in parallel. Further, it is also possible to combine heat exchangers being connected in series and heat exchangers being connected in parallel. However, particularly preferably, cooling the process stream is carried out in at least two heat exchangers being arranged in parallel.

[0027] “Being connected in series” means that the water stream and the process stream each pass one heat exchanger after the other, whereas “being connected in parallel” means that the process stream and the water stream each are divided into partial streams, each partial stream passes one heat exchanger and after having passed the heat exchangers, the partial streams are combined to one water stream and one process stream again.

[0028] Besides connecting the heat exchangers in parallel or in series as described above, it is further possible to arrange the heat exchangers in such a way that the water stream or the process stream is divided into partial streams and passes the heat exchangers in parallel and the other stream passes the heat exchangers in series. In this case, it is particularly preferred that the water stream is divided into partial streams, so that the heat exchangers on the water side are connected in parallel and the process stream passes the heat exchangers in series.

[0029] For cooling the process step, the water used for cooling preferably has a temperature in a range from 32 to 54 °C, more preferred in a range from 40 to 54 °C and particularly in a range from 46 to 54 °C. By cooling the process step, the temperature of the water preferably increases by 5 to 20 K, more preferred by 8 to 15 K and particularly by 10 to 12 K by heat transfer from the process step.

[0030] Due to the pressure of the water, no evaporation takes place in the heat exchanger. For obtaining steam, the water is fed into the flash apparatus. While entering the flash apparatus, the water is depressurized to a pressure in a range from 50 to 150 mbar(abs), more preferred to a pressure in a range from 75 to 150 mbar(abs) and particularly to a pressure in a range from 100 to 150 mbar(abs). Due to depressurization, a part of the water evaporates. The part of the water that evaporates preferably is in a range from 0.5 to 5 wt-%, more preferred in a range from 0.5 to 3 wt-% and particularly in a range from 1 to 2.5 wt-%.

[0031] The flash apparatus may be any suitable flash apparatus known to the skilled person. The flash apparatus may be for example a flash tank or a flash column. For depressurizing the water on entering the flash apparatus, generally an expansion apparatus, for example a throttle is located at the inlet of the water into the flash apparatus. 240424W001

[0032] 4

[0033] In the flash apparatus the liquid phase comprising the non-evaporated water and the gas phase comprising the evaporated water are separated and the gas phase is withdrawn as the steam having a pressure in the range from 50 to 150 mbar(abs).

[0034] Besides obtaining the steam by flash evaporation of a liquid water stream to which heat was transferred from the at least one process step, in an alternative, the steam having a pressure in a range from 50 to 150 mbar(abs) may be obtained by using water having a pressure in the range from 50 to 150 mbar(abs) as cooling medium for the process step, wherein by heat transfer from the process step at least a part of the water evaporates.

[0035] If a part of the water evaporates by cooling the process step, it is particularly preferred to cool a process stream. For cooling the process stream by evaporating water at least partly, any suitable evaporator may be used. Suitable evaporators for example are shell-and-tube evaporators, falling film evaporators, thin film evaporators, or forced convection evaporators.

[0036] For providing the steam having the pressure in a range from 50 to 150 mbar(abs), more preferred in a range from 75 to 150 mbar(abs) and particularly in a range from 100 to 150 mbar(abs), the stream comprising the partly evaporated water is separated into a gas phase comprising the evaporated part of the water and a liquid phase comprising the non-evaporated part of the water. The gas phase then is withdrawn as the steam having the pressure in a range from 50 to 150 mbar(abs).

[0037] For separating the liquid phase and the gas phase any suitable phase separator may be used. Suitable phase separators for example are tanks or columns into which the two-phase stream is fed and then separated into the liquid phase and the gas phase. Usually, the liquid phase collects at the bottom of the tank or column and can be withdrawn via an outlet at the bottom and the gas phase collects at the top and can be withdrawn via an outlet at the top of the phase separator.

[0038] Independently of whether the process step is cooled by heating a liquid water stream or by at least partly evaporating the water stream, it is preferred that the evaporated part of the water is withdrawn as the steam having a pressure in the range from 50 to 150 mbar(abs) and the nonevaporated part of the water is recycled for cooling the process step. For this purpose, the water for cooling flows in a cooling circuit. If the temperature of the water increases by heat transfer from the process step, and the steam is obtained by flash evaporation, it is necessary to increase the pressure of the water before recycling it into the heat exchanger. Since by flash evaporation, the water cools to boiling temperature at the pressure to which it is depressurized, additionally cooling generally is not necessary.

[0039] Since the amount of water in the cooling circuit is reduced by withdrawing the steam, it is necessary to add fresh water to keep a constant amount of water in the system and flowing through the heat exchanger. Due to degassing, the fresh water generally has a temperature above the 240424W001

[0040] 5 temperature of the recycled water. Since, however, the amount of the recycled water usually is much larger than the amount of the freshly added water, the change in temperature is very low, so that cooling of the water by flash evaporation is sufficient.

[0041] If the process step is cooled by evaporating the water stream at least partly, for example in a falling film evaporator, it is necessary that the temperature of the water is below the temperature of the process step. During evaporation, the temperature of the water stream remains constant. In this case, the temperature of the water used for cooling remains constant in the whole cooling circuit, if the freshly added water also has the same temperature. If the freshly added water has a lower temperature, the water is heated by heat transfer from the process step until it reaches boiling temperature and then starts to evaporate.

[0042] Besides obtaining the steam by cooling only one process step, it is further possible to cool more than one process step, for example 2 to 10 process steps, more preferred 2 to 6 process steps and particularly 1 to 3 process steps. However, generally, only one process step is cooled.

[0043] If more than one process step is cooled, the water for cooling the process steps may pass the process steps in series and / or in parallel. If the water passes the process steps in series, it is necessary that the temperature of the water after having passed one process step still is low enough to cool the following process step or, if the water at least partly evaporates by cooling the process step, enough liquid water remains to be evaporated in the following process step.

[0044] For passing the process steps in parallel, the water stream is divided into partial streams and at least one partial stream is used for cooling each process step. After cooling the process steps, the partial streams are merged together and then either the steam is separated from the liquid phase or the water stream is at least partly evaporated by expansion.

[0045] To reduce the risk of corrosion in the lines through which the steam flows and to avoid damage of apparatuses and lines through which the steam flows, the water being used for cooling the process step and being evaporated for providing the steam preferably is demineralized and degassed water, for example boiler feed water.

[0046] According to the invention, the steam is pre-compressed in a first compression step to obtain pre-compressed steam having a pressure in a range from 75 to 500 mbar(abs). Preferably, the steam is compressed in the first compression step to a pressure in a range from 85 to 400 mbar(abs) and particularly to a pressure in a range from 100 to 300 mbar(abs).

[0047] For compressing the steam to a pressure in a range from 0.9 to 10 bar(abs), preferably 1.1 to 8 bar(abs) and particularly 2 to 7 bar(abs), any suitable blowers or compressors may be used.

[0048] As the differentiation between blowers and compressors is not unambiguous, pressure ratios of the impellers will be used to differentiate between the pre-compression and the second compression. 240424W001

[0049] 6

[0050] For the first stage compression blowers or compressors with a pressure ratio of 1 to 1 .5, preferably 1 .1 to 1 .4 and more preferably 1 .2 to 1 .3 are used. These blowers and compressors are well suited to handle large volume flows. The first compression stage can for example be implemented using a combination of an axial and radial compressor, radial compressors in series and / or in parallel, or impellers of a multistage turbo compressor. The first step of pressure increase may require two or more parallel impellers to handle the large volume flow.

[0051] After pre-compressing the steam to a pressure in a range from 75 to 500 mbar(abs), the steam is compressed in a second compression step to obtain the process steam. The pressure to which the steam is compressed in the second compression step depends on the intended use of the steam and is in a range from 0.9 to 10 bar(abs). Depending on the intended use, the steam may have any pressure in that range. Preferably, the process steam obtained by compression in the second compression step has a pressure in a range from 2 to 7 bar(abs).

[0052] Besides compressing the total amount of steam in each compressor stage, it is also possible to withdraw steam after at least one of the compressor stages, if steam of the respective pressure can be used.

[0053] Depending on the pressure to which the steam is compressed, the second compression step may comprise one or more compressor stages. Preferably, the second compression step is carried out in at least two compressor stages, more preferred in 3 to 8 compressor stages and particularly in 3 to 6 compressor stages.

[0054] According to the invention, the second compression step is carried out in a geared turbo compressor comprising a plurality of compressor stages. Generally, the geared turbo compressor comprises 3 to 8 compressor stages and particularly 3 to 6 compressor stages.

[0055] If the second compression step is carried out in a geared turbo compressor and the first compression step is carried out in at least two compressors being arranged in parallel, in one embodiment of the invention the at least two compressors of the first compression step form a first compressor stage of the geared turbo compressor.

[0056] Since the steam is overheated by compression, after compression the steam may be cooled. For this purpose and to increase the amount of steam, it is preferred to inject water into the steam after at least one compressor stage. Preferably, water is injected after each compressor stage. Further, water also may be added after each compressor or blower in the first compression step. Due to the temperature of the steam, the water completely evaporates, thereby cooling the steam and increasing the amount of steam. To ensure complete evaporation of the water injected into the steam, a sufficiently long injection section is provided.

[0057] The water being injected into the steam may be fresh water. Alternatively, it is also possible that the water being injected into the steam is a part of the non-evaporated part of the water. Fur- 240424W001

[0058] 7 ther, it is preferred to inject water having a temperature in a range from 40 to 150 °C into the steam leaving the at least one compressor stage. More preferred, the temperature of the water being injected into the steam after the at least one compressor stage has a temperature in a range from 60 to 130 °C and particularly in a range from 100 to 120 °C.

[0059] The process steam obtained by the inventive process may be fed into a steam grid or may be used directly in a process step for heating. Particularly preferably, the steam is used in another process step of the process in which the process step that is cooled takes place. Such process steps for example are distillation or rectification, pervaporation, crystallization, stripping, gas scrubbing, spray drying, drying, calcination, sintering, burning, e.g. brick burning in a kiln, chemical reaction or heat recovery.

[0060] Embodiments of the invention are shown in the figures and explained in more detail in the following description.

[0061] In the figures:

[0062] Figure 1 shows a process for producing process steam in a first embodiment;

[0063] Figure 2 shows a process for producing process steam in a second embodiment; and

[0064] Figure 3 shows a process for producing process steam in a third embodiment.

[0065] Figure 1 shows a process for producing steam in a first embodiment.

[0066] For producing steam, water 1 , is fed into a heat exchanger 3. In the heat exchanger 3, the water 1 is used as a cooling medium for a process stream 5. By cooling the process stream, the water 1 absorbs heat and is heated to a temperature in a range from 35 to 75 °C.

[0067] After being heated in the heat exchanger 3, the water 1 is fed into a flash evaporator 7. On entry into the flash apparatus 7, the water 1 is depressurized to a pressure in a range from 50 to 150 mbar(abs). Due to the depressurization a part of the water evaporates. Generally, the amount of water that evaporates is in a range from 0.5 to 5 wt-%.

[0068] The evaporated part of the water is withdrawn from the flash apparatus 7 as steam 9. The nonevaporated part 11 is recycled into the heat exchanger 3. To keep the amount of water 1 being fed into the heat exchanger 3 constant, fresh water 13 is added. The fresh water preferably is demineralized and degassed water, for example boiler feed water. For circulating the water 1 and for compensation of level differences and pressure losses, a pump 15 is provided.

[0069] For producing process steam, the steam 9 having a pressure in a range from 50 to 150 mbar(abs) is fed into a first compression step, in which the steam is pre-compressed to a pressure in a range from 75 to 500 mbar(abs). In the embodiment shown in figure 1 , the first 240424W001

[0070] 8 compression step is carried out in a first compressor 17, preferably comprising an axial first compressor stage 17.1 and a radial second compressor stage 17.2, being arranged in series. For pre-compressing the steam, the first compressor 17 preferably is an axial / radial compressor.

[0071] After leaving the first compressor 17, the pre-compressed steam 19 is fed into a second compression step. The second compression step is carried out in a geared turbo compressor 21. In the embodiment shown here, the geared turbo compressor 21 comprises five compressor stages 21.1 , 21 .2, 21 .3, 21.4, 21 .5. In the geared turbo compressor 21 , the steam is compressed to obtain process steam 23. The process steam may be used in any process which uses steam for heating. Alternatively, the process steam may be fed into a steam grid.

[0072] By compression, the steam is superheated. To cool the steam after leaving a compressor stage, water 23 is injected. Injecting the water 23 has the additional effect that the amount of steam increases. In the embodiment shown here, water 23 is injected after each compressor stage 17.1 , 17.2 of the first compressor 17 and after each com pressor stage 21.1 , 21.2, 21.3, 21.4, 21.5 of the geared turbo compressor 21 . The water being injected into the steam preferably has a temperature in a range from 40 to 150 °C.

[0073] Figure 2 shows a process for producing process steam in a second embodiment.

[0074] In difference to the process shown in figure 1 , in the process shown here, a first process stream 27 and a second process stream 29 are cooled. The first process stream 27 and the second process stream 29 may have the same temperature or different temperatures. Further, the first process stream 27 and the second process stream 29 may originate from the same process step and be obtained for example by separating a process stream into a first partial stream and a second partial stream or the first process stream 27 and the second process stream 29 may originate from different process steps. Further, it is also possible that the first process stream 27 and the second process stream 29 originate from the same process step but may be different cooling streams or, for example, different intermediate product streams to be cooled.

[0075] The first process stream 27 is cooled in a first heat exchanger 31 and the second process stream 29 is cooled in a second heat exchanger 33. For cooling, water is used as cooling medium. The water 13 is divided into a first partial stream 35 and a second partial stream 37. The first partial stream 27 is fed into the first heat exchanger 31 for cooling the first process stream 27 and the second partial stream 37 is fed into the second heat exchanger 33 for cooling the second process stream 29.

[0076] After being heated by heat transfer from the process streams 27, 29, the first partial stream 35 and the second partial stream 37 are recombined again forming a heated water stream 39. Subsequently, the heated water stream 39 is divided into a first heated partial stream 41 and a second heated partial stream 43. The first heated partial stream 41 is fed into a first flash apparatus 45 and the second heated partial stream 43 is fed into a second flash apparatus 47. 240424W001

[0077] 9

[0078] By recombination of the first partial stream 37 and the second partial stream 39 to obtain the heated water stream 39 and the subsequent division of the heated water stream 39 into the first heated partial stream 41 and the second heated partial stream 43, it is achieved that the first flash apparatus 45 and the second flash apparatus 47 can be operated at the same operation conditions and that the steam obtained in the first flash apparatus 45 and the second flash apparatus 47 has the same pressure and temperature.

[0079] On entry into the first flash apparatus 45 a first gas phase containing steam and a first liquid phase containing non-evaporated water are formed and on entry into the second flash apparatus 47 a second gas phase containing steam and a second liquid phase containing non evaporated water are formed. The first liquid phase 49 and the second liquid phase 51 are combined and the fresh water 13 is added to the combined first and second liquid phases 49, 51. Subsequently, the water stream comprising the first liquid phase 49, the second liquid phase 51 and the fresh water 13 is divided into the first partial stream 35 and the second partial stream 37.

[0080] The first gas phase is withdrawn from the first flash apparatus 45 as a first steam stream 53 and the second gas phase 55 is withdrawn from the second flash apparatus 47 as a second steam stream 55. The first and second steam streams 53, 55 are pre-compressed by blowers being connected in series. In the embodiment shown here, four blowers 57.1 , 57.2, 57.3, 57.4 are used for pre-compressing the steam. Each of the blowers 57.1 , 57.2, 57.3, 57.4 comprises two blowers, wherein the first gas phase 53 and the second gas phase 55 pass the blowers 57.1 , 57.2, 57.3, 57.4 in parallel streams.

[0081] To reduce the necessary work for operating the blowers and to keep the temperature behind each blower 57.1 , 57.2, 57.3, 57.4 at 5 to 20 K above the boiling temperature, water 59 is added to the first and second steam streams 53, 55 before each of the blowers 57.1 , 57.2, 57.3, 57.4. The water being added to the first and second steam streams 53, 55 preferably has a temperature in a range from 40 to 120 °C.

[0082] After having passed the blowers 57.1 , 57.2, 57.3, 57.4, the pre-compressed first steam stream 53 and the pre-compressed second steam stream 55 are combined, to obtain pre-compressed steam 19. The pre-compressed steam 19 is fed into the geared turbo compressor 21 for further compression to obtain the process steam 23. Compressing the pre-compressed steam 19 in the geared turbo compressor 21 is carried out as described above for the embodiment of figure 1 .

[0083] A third embodiment of a process for producing process steam is shown in figure 3.

[0084] The process shown in figure 3 corresponds to the process shown in figure 1 with the difference that in the process shown in figure 3, a pre-compression stage of the geared turbo compressor 21 is used for pre-compressing the steam 9 having a pressure in a range from 50 to 150 mbar(abs) instead of two axial compressors being connected in series. 240424W001

[0085] 10

[0086] Further, in the embodiment shown here, five compressor stages of the geared turbocompressor are used for further compressing the pre-compressed steam in the second compression step.

[0087] For pre-compressing the steam 9 having a pressure in a range from 50 to 150 mbar(abs), the pre-compression is carried out by two impellers 21 .7, 21 .8, which are connected in parallel. Accordingly, the steam 9 having a pressure in a range from 50 to 150 mbar(abs) is divided into a first partial stream 9.1 being fed into the first impeller 21.7 and a second partial stream 9.2 being fed into the second impeller 21.8. After pre-compressing the steam to a pressure in a range from 75 to 500 mbar(abs), the first partial stream 9.1 and the second partial stream 9.2 are recombined and further compressed in the further compressor stages 21 .1 , 21.2, 21 .3, 21.4, 21.5, 21.6 of the geared turbo compressor 21 to obtain the process steam.

[0088] Besides a geared turbo compressor comprising five or six compressor stages for carrying out the second compression step, the geared turbo compressor may comprise any other number of compressor stages depending on the desired pressure of the process steam.

[0089] Further, it is possible to compress the whole steam to obtain process steam as shown here, or it is possible to withdraw a part of the steam behind any of the compressor stages. Thereby, it depends on the desired pressure of the steam after which compressor stage the steam is withdrawn.

[0090] The water may be heated in one heat exchanger 3 as shown in figures 1 and 3, in two heat exchangers 31 , 33 as shown in figure 2 or in more than two heat exchangers. The number of heat exchangers depends on the amount of water used for cooling the process stream and the necessary heat transfer surface and on the numbers of process streams to be cooled.

[0091] Besides arranging the heat exchangers as shown in figure 2, in which the water is divided into two partial streams that flow through the heat exchangers in parallel, it is also possible that the whole water stream flows through the heat exchangers in series. This is for example possible if the process streams to be cooled have different temperatures or the temperature of the water after being used as cooling medium in one heat exchanger is still low enough to be used as a cooling medium in a following heat exchanger.

Claims

240424W00111Claims1 . A process for producing process steam, comprising:(a) providing steam (9; 35, 55) having a pressure in a range from 50 to 150 mbar(abs);(b) compressing the steam (9; 35, 55) in a first compression step to obtain precompressed steam (19) having a pressure in a range from 75 to 500 mbar(abs);(c) compressing the pre-compressed steam (19) in a second compression step to obtain process steam (23) having a pressure in a range from 0.9 to 10 bar(abs), wherein the first compression step is carried out in an axial compressor (17) or in at least two compressors or blowers (57.1 , 57.2, 57.3, 57.4), which are arranged in parallel, and the second compression step is carried out in a geared turbo compressor (21) comprising a plurality of compressor stages (21 .1 , 21 .2, 21 .3, 21 .4, 21 .5, 21 .6).

2. The process according to claim 1 , wherein the steam (9; 35, 55) having a pressure in a range from 50 to 150 mbar(abs) is obtained by cooling at least one process step using water (1 ) having a pressure in a range from 0.5 to 5 bar(abs) as cooling medium and then depressurizing the water (1) in a flash apparatus (7; 45, 47) to the pressure in a range from 50 to 150 mbar(abs), so that a part of water evaporates.

3. The process according to claim 2, wherein by cooling the at least one process step the temperature of the water increases by 5 to 20 K by heat transfer from the at least one process step.

4. The process according to claim 2 or 3, wherein cooling the at least one process step is carried out in at least two heat exchangers (33, 31 ) being arranged in parallel.

5. The process according to claim 1 , wherein the steam (9; 35, 55) having a pressure in a range from 50 to 150 mbar(abs) is obtained by using water having a pressure in the range from 50 to 150 mbar(abs) as cooling medium for at least one process step, wherein by heat transfer from the at least one process step at least a part of the water evaporates.

6. The process according to any of claims 2 to 5, wherein the evaporated part of the water is withdrawn as the steam (9; 35, 55) having a pressure in the range from 50 to150 mbar(abs) and the non-evaporated part of the water (11 ; 49, 51) is recycled for cooling the at least one process step.240424W001127. The process according to any of claims 1 to 6, wherein the first compression step is carried out in at least two compressors (21.8, 21.9) being arranged in parallel and the at least two compressors (21 .

8. 21 .9) form a first compressor stage of the geared turbo compressor (21).

8. The process according to any of claims 1 to 7, wherein the geared turbo compressor (21 ) comprises 3 to 8 compressor stages (21.1 , 21 .2, 21 .3, 21.4, 21 .5, 21 .6).

9. The process according to any of claims 1 to 8, wherein after at least one compressor stage (21.1 , 21.2, 21.3, 21.4, 21.5, 21.6) water is injected into the steam.

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