METHOD AND APPARATUS FOR THE UTILISATION OF WASTE HEAT FROM AN ELECTROLYSIS REACTION FOR THE GENERATION OF STEAM

Abstract

The invention relates to a method and an electrolysis arrangement, in which waste heat generated during an electrolysis reaction is utilised efficiently. The waste heat is transferred by means of a heat transfer medium to a water-containing medium. The thereby pre-heated water-containing medium is supplied to a degassing device. Due to the pre-heating of the water-containing medium, less steam from a steam-generating device is required for degassing of the water-containing medium.

Claims

1. A method comprising: generating at least one product gas by an electrolysis reaction by an electrolyser; providing a water-containing medium to generate steam; supplying the water-containing medium to a degassing device, and degassing the water-containing medium in the degassing device; supplying the degassed water-containing medium to a steam generating device, and generating steam from the degassed water-containing medium in the steam generating device; supplying a portion of the steam generated in the steam generating device to the degassing device, wherein degassing of the water-containing medium is effected by the supplied steam; transferring at least part of the waste heat generated during the electrolysis reaction to the water-containing medium by means of a heat transfer medium before the water-containing medium is supplied to the degassing device.

2. The method according to claim 1, wherein the water-containing medium is provided in the form of make-up water and/or the water-containing medium is provided in the form of a condensate by condensation of the steam after use of the steam in a steam user.

3. The method according to claim 2, wherein the waste heat generated by the electrolysis reaction is transferred to the make-up water and/or is transferred to the condensate, or is transferred to a mixture of the make-up water and the condensate.

4. The method according to claim 1, wherein the transfer of waste heat by means of the heat transfer medium is effected by a heat exchanger and/or a heat pump.

5. The method according to claim 4, wherein the transfer of waste heat is performed by means of the heat transfer medium through a heat exchanger to the make-up water, producing a preheated make-up water.

6. The method according to claim 5, wherein the transfer of waste heat by means of the heat transfer medium is effected by a heat pump to a mixture of the preheated make-up water and the condensate.

7. The method according to claim 1, wherein a first portion of the heat transfer medium is used to transfer waste heat to the water-containing medium, and a second portion of the heat transfer medium is re-cooled and afterwards used to cool the electrolyser.

8. The method according to claim 7, wherein the heat transfer medium is re-cooled after the waste heat has been transferred to the water-containing medium and is afterwards used to cool the electrolyser.

9. An electrolysis arrangement, comprising: an electrolyser configured to produce at least one product gas by an electrolysis reaction; a degassing device configured to degas a water-containing medium; a steam generating device configured to evaporate degassed water-containing medium to produce steam; means for feeding a portion of the generated steam from the steam generating device to the degassing device; at least one heat transfer device for transferring waste heat generated during the electrolysis reaction to the water-containing medium by means of a heat transfer medium, whereby the heat transfer device is arranged upstream of the degassing device.

10. The electrolysis arrangement according to claim 9, wherein the electrolysis arrangement comprises a device for providing the water-containing medium in the form of make-up water and/or comprises a device for providing the water-containing medium in the form of a condensate, the condensate being producible by condensation of the steam after use of the steam in a steam user.

11. The electrolysis arrangement according to claim 10, wherein the at least one heat transfer device is configured to transfer waste heat generated during the electrolysis reaction to the make-up water and/or is configured to transfer waste heat generated during the electrolysis reaction to the condensate, or is configured to transfer waste heat generated during the electrolysis reaction to a mixture of make-up water and condensate.

12. The electrolysis arrangement according to claim 9, wherein the at least one heat transfer device is a heat exchanger and/or a heat pump.

13. The electrolysis arrangement according to claim 9, wherein the electrolysis arrangement comprises a re-cooler, wherein the electrolysis arrangement is configured such that a portion of the heat transfer medium is used to transfer waste heat to the water-containing medium by means of the at least one heat transfer device, and a portion of the heat transfer medium is re-cooled in the re-cooler and used to cool the electrolyser.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0058] The invention will now be detailed by way of an exemplary embodiment with reference to the attached drawing. Unless otherwise stated, the drawing is not to scale. In the drawing FIG. 1 shows a simplified block flow diagram of an electrolysis arrangement according to the invention. The electrolysis arrangement as shown is configured for carrying out the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] The electrolysis arrangement according to FIG. 1 comprises an electrolyser 2, an air cooler 3, a supply of deionised make-up water 4, a heat exchanger 5, a heat pump 6, a deaerator 7, a steam boiler 8, and a steam user 9. Furthermore, the electrolysis arrangement 1 comprises six 3-way valves 10a to 10f. The aforementioned components are fluidically connected to each other by conduits 11a to 11j, 12a and 12b, 13a and 13b, 14, 15a to 15c, and 16. Conduits carrying a liquid medium are indicated by solid lines, whilst dashed lines indicate conduits carrying a gaseous medium. Furthermore, the electrolysis arrangement 1 has a conduit 17 for discharging hydrogen, whereby the hydrogen is subsequently fed to a further use (not shown).

[0060] The electrolyser 2 produces hydrogen and oxygen from a water-containing electrolysis medium, for example based on alkaline electrolysis with highly concentrated aqueous potash lye (aqueous KOH solution) as the electrolysis medium. The electrolyser 2 is shown in a highly simplified form as a block, but contains at least one electrolysis cell stack (not shown) in which the actual electrolysis reaction takes place. For the electrolysis reaction to take place, direct current with a working voltage up to the kV range is supplied to the electrolyser 2 with the aid of a rectifier (not shown). Part of the supplied electrical energy is converted into chemical energy by splitting water of the electrolysis medium into hydrogen and oxygen. Part of the electrical energy is not used in this respect and therefore accumulates in the form of thermal energy as waste heat, which is to be subjected to utilisation in the sense of the present invention. In the electrolysis cells of the electrolysis cell stack, a two-phase mixture of electrolysis medium and the respective product gas (hydrogen or oxygen) is produced. This mixture is separated in respective gas-liquid separators (not shown). Hydrogen produced on the cathode side is dried, freed from oxygen and afterwards discharged via conduit 17. It is then put to further use, for example for the production of methanol. Oxygen produced on the anode side is not utilised but released into the atmosphere (not shown). In the electrolysis medium depleted of water due to the electrolysis reaction, the original potassium hydroxide concentration, e.g. 3 mol/l, is restored by adding deionised water. The electrolysis medium is then recycled to the electrolysis cell stack (not shown).

[0061] The waste heat generated during the electrolysis reaction mainly accumulates in the electrolysis cell stack of the electrolyser 2. The electrolyser 2 is therefore cooled with cooling water supplied via conduit 11h. Typically, the cooling water is supplied via conduit 11h at a temperature of 20 to 30° C. The cooling water is then heated to 70 to 80° C. as a result of the electrolysis reaction taking place in the electrolyser, and is then discharged from the electrolyser 2 via conduit 11a. Part of the heated cooling water is fed to the air cooler 3 via the 3-way valves 10e and 10c and the conduits 11g and 11f with appropriate switching of the valves. In the air cooler 3 the cooling water is cooled back to 20 to 30° C.

[0062] A portion of the heated cooling water is fed to the heat exchanger 5 via conduits 11b and 11c, as well as the 3-way valves 10e and 10f with appropriate switching of the valves. Deionised water from the deionised make-up water supply 4 is fed to the heat exchanger 5 via conduit 12a. The heat exchanger 5 may be a shell and tube type heat exchanger for instance. The deionised water in line 12a has a temperature of about 10° C. and is pumped at a flow rate (mass flow) of 50 t/h. In the heat exchanger the deionised water is heated to 45° C., which is then passed on via conduit 12b. Thus, waste heat from the electrolysis reaction is transferred to deionised make-up water by means of the (heated) cooling water as a heat transfer medium. The deionised water is to be regarded as the water-containing medium in the sense of the invention. It is used in a further step to generate steam.

[0063] In turn, the heated cooling water supplied via line 11c is cooled in the heat exchanger 5. The method according to FIG. 1 is designed in such a way that the cooling water discharged from heat exchanger 5 via conduit 11d is not yet cold enough to be used directly to cool down the electrolyser again. It is therefore routed to the air cooler 3 via conduits 11e and 11f and the 3-way valves 10c and 10d with appropriate switching of the valves. The final cooling of the cooling water to the target temperature of 20 to 30° C. then takes place in the air cooler 3.

[0064] The pre-heated deionised water discharged from the heat exchanger 5 is continued via conduit 12b and combined with a condensate from conduit 16 via the 3-way valve 10b. The condensate in conduit 16 is obtained by condensation of steam in the steam user 9 and has a temperature of about 90° C. It is pumped at a flow rate (mass flow) of 50 t/h. By combining the condensate stream from conduit 16 and the stream of heated deionised water from conduit 12b, a stream of a deaerator feed water with a flow rate (mass flow) of 100 t/h is obtained in conduit 13a. The stream in conduit 13a has a temperature of about 50° C. This stream of conduit 13a is further heated to a temperature of 90° C. by means of the heat pump 6. The heat pump 6 uses the stream 11i as a heat source. Stream 11i represents a partial stream of the heated cooling water generated in the electrolyser and is branched off from conduit 11b with the aid of the 3-way valve 10f. Thus, waste heat from the electrolysis reaction is transferred to a mixture of deionised make-up water and condensate by means of the (heated) cooling water as a heat transfer medium, with the aid of a heat pump using the heat transfer medium as a heat source.

[0065] The stream discharged from the pressure side of the heat pump 6 has a temperature of 90° C. at a flow rate (mass flow) of 100 t/h. This stream is supplied to the deaerator 7 via conduit 13b. In the deaerator 7, the degassing device in the sense of the invention, the deaerator feed water supplied via conduit 13b is degassed. This is effected with the aid of steam, which is fed into the deaerator 7 via conduit 15b. The deaerator feed water is heated to at least 105° C. in the deaerator 7 and is thus freed from oxygen and other undesired gases. The steam supplied via conduit 15b represents a partial flow of the steam generated in the steam generator 8, which is branched off from conduit 15a with the aid of the 3-way valve 10a.

[0066] The degassed water is discharged from the deaerator 7 via conduit 14 and supplied to the steam boiler 8. Steam is generated in the steam boiler 8, the main quantity of which is passed on to the steam user 9 via conduit 15c. In steam user 9 the steam is used, for example, for heating an industrial chemical process. The used steam accumulates as condensate with a temperature of about 90° C. and is then available again as a water-containing medium for steam generation via conduit 16.

[0067] For the embodiment of FIG. 1 and as described above, 4.7 MW of thermal energy are extracted from the cooling water (heat transfer medium) and are transferred to the deionised make-up water and condensate (water-containing medium), which are supplied to the deaerator. Thus, less steam has to generated by the steam boiler 8 which is used for degassing the deaerator feed water in conduit 13b supplied to the deaerator 7. For a natural gas operated steam boiler working 8760 hours per year, this represents 44.7 GWh per year LHV of natural gas saved, based on the assumption that the steam boiler has an efficiency of 90%. Thus, 8400 tons of carbon dioxide emissions are avoided per year.

LIST OF REFERENCE SIGNS

[0068] 1 electrolysis arrangement configured to carry out method [0069] 2 electrolyser [0070] 3 air cooler [0071] 4 deionised make-up water supply [0072] 5 heat exchanger [0073] 6 heat pump [0074] 7 deaerator (degassing device) [0075] 8 steam boiler (steam generating device) [0076] 9 steam user [0077] 10a-10f 3-way valve [0078] 11a-11j cooling water conduit (heat transfer medium conduit) [0079] 12a, 12b deionised make-up water conduit [0080] 13a, 13b deaerator feed water conduit [0081] 14 boiler feed water conduit [0082] 15a-15c steam conduit [0083] 16 condensate conduit [0084] 17 hydrogen conduit