Combustion of off-gasses for producing a steam feed for electrolysis section

Abstract

A chemical plant is provided, in which an electrolysis section is arranged to receive at least a portion of a first steam feed and electrolyze it to provide a hydrogen stream and an oxygen- enriched stream. A first heat exchanger is arranged to receive at least a portion of the oxygen-enriched stream and a combustion air stream to transfer heat from the oxygen- enriched stream to the combustion air stream. The heated combustion air stream and at least a portion of an off-gas stream are arranged to be combusted in at least one burner so as to provide a combusted gas stream. A second heat exchanger is arranged to receive at least a portion of said combusted gas stream and said water stream. The second heat exchanger is arranged to transfer heat from the at least a portion of the combusted gas stream to the water stream so as to provide a cooled combusted gas stream and a steam stream. A process for production of a steam stream using a combustible off-gas stream in the chemical plant is also provided.

Description

[0001] COMBUSTION OF OFF-GASSES FOR PRODUCING A STEAM FEED FOR ELECTROLYSIS

[0002] SECTION

[0003] TECHNICAL FIELD

[0004] The present invention relates to a chemical plant and a process for production of a steam stream using a combustible off-gas stream.

[0005] BACKGROUND

[0006] When producing e.g. ammonia or methanol, in a chemical plant, a purge of combustible gases is emitted from the synthesis loop (a "purge stream" or "off-gas stream"). In conventional natural gas plants these purge streams are normally used as fuel in the reformer or fired heater.

[0007] In chemical plants based on electrolysis, which may not comprise fired heaters, such purge streams are currently a waste / export stream. There is a desire to make effective use of purge streams in chemical plants. This would improve the efficiency of the plant and make use of what might otherwise be a waste stream.

[0008] SUMMARY

[0009] This invention utilizes the heating value of the purge stream by combusting the stream in a duct burner with a combustion air stream heated with the enriched air from the electrolysis process. This improves the efficiency of the plant and make use of a stream, which is otherwise treated as a waste stream.

[0010] So, in a first aspect the present invention relates to a chemical plant, said plant comprising : an electrolysis section (20) a first steam feed (5) a combustible off-gas stream (12) a combustion air stream (25) a first heat exchanger (24) at least one burner (30) a second heat exchanger (40) a water stream (51) wherein said electrolysis section (20) is arranged to receive at least a portion of said first steam feed (5) and electrolyze it to provide a hydrogen stream (22) and an oxygen-enriched stream (21); wherein said first heat exchanger (24) is arranged to receive at least a portion of said oxygen-enriched stream (21) and said combustion air stream (25), and where said first heat exchanger (24) is arranged to transfer heat from the at least a portion of said oxygen-enriched stream (21) to said combustion air stream (25) so as to provide a cooled oxygen-enriched stream (23) and a heated combustion air stream (26); wherein at least a portion of said heated combustion air stream (26) and at least a portion of said off-gas stream (12) are arranged to be combusted in said at least one burner (30) so as to provide a combusted gas stream (31); wherein said second heat exchanger (40) is arranged to receive at least a portion of said combusted gas stream (31), and said water stream (51), where said second heat exchanger (40) is arranged to transfer heat from the at least a portion of said combusted gas stream (31) to said water stream (51) so as to provide a cooled combusted gas stream (42) and a steam stream (52); and wherein said plant comprises a steam drum (50), said steam drum (50) being arranged to receive at least a portion of said steam stream (52) from the second heat exchanger (40), output a dry steam stream (52b) and provide a portion of said dry steam stream (52a) as at least a portion of said first steam feed (5) to the electrolysis section (20).

[0011] In another aspect, a process for production of a steam stream is provided using a combustible off-gas stream in a chemical plant as described herein, said process comprising the steps of: providing a plant as described herein; feeding at least a first portion of said first steam feed (5) to said electrolysis section (20) and electrolyzing said first portion to provide a hydrogen stream (22) and an oxygen-enriched stream (21); supplying at least a portion of said oxygen-enriched stream (21) and said combustion air stream (25) to said first heat exchanger (24) and allowing heat transfer from the at least a portion of said oxygen-enriched stream (21) to the combustion air stream (25) to take place, so as to provide a heated combustion air stream (26) and a cooled oxygen-enriched stream (23); feeding at least a portion of said heated combustion air stream (26) and at least a portion of said off-gas stream (12) to at least one burner (30) to provide a combusted gas stream (31); supplying at least a portion of said combusted gas stream (31) and said water stream (51) to said second heat exchanger (40) and allowing heat transfer from the at least a portion of said combusted gas stream (31) to said water stream (51) to take place, so as to provide a cooled combusted gas stream (42) and a steam stream (52); feeding at least a portion of said steam stream (52) from the second heat exchanger (40) to said steam drum (50), outputting a dry steam stream (52b) and providing a portion of said steam stream (52a) as at least a portion of said first steam feed (5) to the electrolysis section (20).

[0012] Further aspects of the present invention are set out in the following description text, figures and the appended claims.

[0013] LEGENDS

[0014] The technology is illustrated by means of the following schematic illustrations, in which:

[0015] Figure 1 shows a simple layout of the burner unit part of the invention.

[0016] Figure 2 shows a first layout of the invention, where a burner combusts a combustible offgas (25) to produce heat which is used for heating a water stream (51) in a second heat exchanger (40) before sending it to a steam drum (50) to produce dry steam (52b).

[0017] Figure 3 shows another layout of the invention.

[0018] Figure 4 shows another layout of the invention.

[0019] Figure 5 shows another layout of the invention. Figure 6 shows another layout of the invention.

[0020] DETAILED DISCLOSURE

[0021] Unless otherwise specified, any given percentages for gas content are % by volume. All feeds are preheated as required.

[0022] A "stage" comprises one or more "units" which perform a change in the chemical composition of a feed, and may additionally comprise elements such as e.g. heat exchanger, mixer or compressor, which do not change the chemical composition of a feed or stream.

[0023] The term "synthesis gas" (abbreviated to "syngas") is meant to denote a gas comprising hydrogen, carbon monoxide, carbon dioxide and small amounts of other gasses, such as argon, nitrogen, methane, steam, etc.

[0024] In a first aspect, a chemical plant is provided, said plant comprises: a combustible off-gas stream, an electrolysis section, a first steam feed, a combustible off-gas stream a combustion air stream a first heat exchanger at least one burner, a second heat exchanger, and a water stream.

[0025] Combustible off-gas stream

[0026] A combustible off-gas stream refers to an off-gas stream comprising at least one combustible component, wherein said off-gas stream is produced within said chemical plant e.g. a purge gas stream or a waste gas stream from a purification section. A typical combustible off-gas stream composition may e.g comprise CO, CO2, H2, CH4and inert gases (N2, Ar etc.). Optionally, the off-gas stream may further comprise unsaturated hydrocarbons, such as olefins or alkenes (CnH2n; n>2). The specific composition of the combustible off-gas stream may vary, depending on the production purpose of the chemical plant. The combustible offgas stream typically comprises a mixture of components in contrast to the syngas, which is typically is rich in the components reacting (incl combusting) in a synthesis section. The combustible off-gas stream may in an embodiment comprise 15-70 mole % H2, such as 20-70 mole %. The combustible off-gas stream may in an embodiment comprise less than 25 mole % CO. The combustible off-gas stream may in an embodiment comprise 0-25 mole % CO, such as 0.1-5 mole % or 10-25 mole %. The combustible off-gas stream may in an embodiment comprise less than 35 mole % CH4. The combustible off-gas stream may in an embodiment comprise 0-35 mole % CH4, such as 0.1-5 mole % or 10-25 mole %. The combustible off-gas stream may in an embodiment comprise less than 20 mole % NH3. The combustible off-gas stream may in an embodiment comprise 0-20 mole % NH3, such as 0.1- 10 mole %. The combustible off-gas stream may comprise one or more of these combustible components in any combination with the proviso that the total amount of these combustible components amounts to 100% or less of the total combustible off-gas stream. The total amount of these combustible components may thus amount to 40 - 100 mole % of the total combustible off-gas stream, such as 50 - 90 mole % or 50-80 mole % of the total combustible off-gas stream. Other components may be present such as CO2, Argon and / or N2.

[0027] In one aspect, said chemical plant further comprises a syngas stream and a synthesis section wherein said synthesis section is arranged to receive said syngas stream and convert it into a product stream and an off-gas stream, and wherein said synthesis section is arranged to provide at least a portion of said off-gas stream to said burner.

[0028] In one embodiment, the synthesis section (also referred to as a synthesis loop) is arranged to provide at least a portion of the off-gas stream to said burner, wherein said off-gas stream is a purge gas stream. In said embodiment, the synthesis section partly converts the syngas stream to a product stream and a recycle stream, where the recycle stream receives a second syngas steam (referred to as make-up syngas stream) followed by the recycle stream being recycled such that it re-enters the synthesis section such as into a synthesis reactor. To control the content of by-products and inert gasses, which may accumulate due to said recycle stream, at least a portion of the recycle stream is provide as an off-gas stream to said burner, preferably before adding make-up syngas. In this way, the off-gas stream may comprise unconverted syngas, by-products produced within said synthesis section and inert gases.

[0029] In one aspect, the chemical plant comprises a syngas stream, a synthesis section, and a purification section, wherein said synthesis section is arranged to receive said syngas stream and convert it into a product stream and an off-gas stream and wherein said purification section is arranged to receive said product stream and convert it into a purified product stream and a further off-gas stream, and wherein said purification section is arranged to provide at least a portion of said further off-gas stream to said burner. Within these aspects, at least a portion of said off-gas stream arranged to be combusted in said at least one burner may be provided i) solely from one or more synthesis section(s), ii) solely from one or more purification section(s) or iii) a combination of off-gas streams from said synthesis section(s) and purification section(s) or iv) any of i-iii) combined with one or more alternative streams. In this way, the specific composition depends on conditions comprising the following conditions: a) the composition of the provided feed(s) e.g. syngas stream; b) type and combinations of stage / section / reactor(s) specifically the specification of the synthesis section and hence optionally the applied catalysts; c) arrangement of optional purification sections comprising recovery and / or separation section or units such as CO2recovery units and d) process conditions applied throughout the chemical plant such as temperature and pressure.

[0030] In aspects, the chemical plant comprises a syngas stream. Said syngas stream may be a gas stream comprising primarily hydrogen (H2) and nitrogen (N2). Alternatively, said syngas stream may be a gas stream comprising hydrogen, carbon monoxide, carbon dioxide and small amounts of other gasses, such as argon, nitrogen, methane, steam. Said syngas stream may be fed as a feed to said synthesis section.

[0031] In one aspect, the chemical plant comprises a synthesis section, wherein said synthesis section is an ammonia synthesis section, a methanol synthesis section, a methanol-to-olefins synthesis section, methanol-to-gasoline (TIGAS) synthesis section, a methanation section or a Fischer-Tropsch (FT) synthesis section.

[0032] In one embodiment, the chemical plant comprises an ammonia synthesis section. In said embodiment, the chemical plant comprises a syngas stream comprising primarily H2and N2. An electrolysis section may provide the H2or alternatively the H2may be provided from a production plant, wherein H2is produced from natural gas or fossil fuel. An air fractionation unit may provide the N2. The ammonia synthesis section may receive the syngas and provide an off-gas stream, which is fed to the burner.

[0033] In other embodiments, the chemical plant comprises a methanol synthesis section, a methanol-to-olefins synthesis section, a methanol-to-gasoline (TIGAS) synthesis section, a methanation section or a Fischer-Tropsch (FT) synthesis section. In said embodiments the syngas stream fed to the synthesis may comprise H2and CO2. An electrolysis section may provide the H2or alternatively the H2may be provided from said chemical plant such that H2is produced from natural gas or fossil fuel. Typically, the provided CO2is recovered from a flue gas from combustion of a fossil fuel or a non-fossil biomass. The synthesis section receives the syngas and provide an off-gas stream, which is fed to the burner. In embodiments wherein the chemical plant comprises a purification section, said purification section may comprise a CO2recovery unit.

[0034] The electrolysis section

[0035] The electrolysis section is arranged to receive at least a portion of said first steam feed and electrolyze it to provide a hydrogen stream and an oxygen-enriched stream.

[0036] A first steam feed is required as a feed for the electrolysis section. Preferably, the first steam feed is a dry steam feed of high purity. To obtain a steam feed of high purity, it is generally known to expose a water stream to some kind of water treatment prior to using it in industrial systems (may be referred to as a process steam). Untreated water may contain impurities causing damage or wear to the system. Such impurities may cause formation of scales, corrosion, deposits etc. Also, oxygen may be unwanted in the process steam since it may cause corrosion, e.g. in piping and heat exchangers. Furthermore droplets / entrainment are unwanted due to high concentration of impurities in the boiler water.

[0037] One way of obtaining a steam feed of high purity, is to first treat raw water in an ionexchanger to remove minerals. Demineralized water is then passed through a deaerator to produce deaerated water which is then passed to a boiler with a steam drum where dry steam is produced, which is then ready for use as a process steam. In the deaerator oxygen is stripped from the water and the stripped water is collected in a surge vessel. In the boiler, the deaerated water is heated in a heat exchanger and the heated mixture of water and steam is then separated in a steam drum to produce the dry steam for use as feed.

[0038] The electrolysis section may comprise solid oxide electrolysis cell (SOEC) electrodes such that the splitting of H2O occurs within a SOEC. Multiple cells may be combined into SOEC stacks, and multiple stacks may in turn be combined into an SOEC plant. A solid oxide cell (SOC) is an electrochemical conversion device having two compartments (an anode side and a cathode side) divided by an electrolyte material made of a solid oxide or a ceramic electrolyte. Such a cell is fully reversible e.g. for the components H2O<->H2.

[0039] The first steam feed may enter the process side of the SOEC where it is (partly) converted into the hydrogen stream and an oxygen-enriched stream. The oxygen produced in the conversion on the fuel side is transferred through the electrochemical cell to the oxy side of the SOEC, where it is recombined as gaseous oxygen. It is typically transported away from the SOEC with a flushing stream. In one aspect, said plant comprises a flushing stream where the flushing stream is arranged to be supplied to the anode of said electrolysis section as flushing stream for flushing of oxygen, and thereby provide an oxygen-enriched stream. In one aspect, the flushing stream is air, a nitrogen-rich stream or a CO2-rich stream.

[0040] In one aspect, at least a portion of the hydrogen stream provided by the electrolysis section is arranged to be fed as a feed to the synthesis section, optionally in admixture with syngas stream.

[0041] Combustion Air Stream

[0042] A combustion air stream is meant to refer to a gas atmosphere suitable for providing oxygen for a combustion of the combustible off-gas stream. It preferably comprises between 5-30 mole % oxygen (O2), such as 20-25 mole % oxygen (O2). In one embodiment the combustion air stream is ambient air.

[0043] Burner Unit

[0044] The purpose of the burner unit is to use heat from the oxygen-enriched stream to preheat a combustion air stream and use the thus heated combustion air stream to combust the combustible off-gas in a burner to provide a combusted gas stream.

[0045] At least a portion of said oxygen-enriched stream is arranged to transfer heat in a first heat exchanger to a combustion air stream to provide a heated combustion air stream and a cooled oxygen-enriched stream. The heated combustion air stream and at least a portion of said off-gas stream are arranged to be combusted in said at least one burner so as to provide a combusted gas stream.

[0046] In an embodiment the combustion air stream is heated in the first heat exchanger to a temperature in the range of from 50 to 500 °C, such as from 200 to 400 °C. An advantage of such a preheating is that the combustion is more easily controlled yet the heating value in the oxygen-enriched stream is exploited.

[0047] Off-gases with a high heating value can be combusted alone. Off-gases with a low heating value might need additional support fuel, which could be H2and / or syngas. Therefore, if required, an additional fuel stream, preferably being a portion of said hydrogen stream or a portion of said syngas stream, may be arranged to be provided to the at least one burner. Heat exchanger

[0048] A second heat exchanger is arranged to receive at least a portion of said combusted gas stream, and said water stream. The second heat exchanger is arranged to transfer heat from the at least a portion of said combusted gas stream to said water stream so as to provide a cooled combusted gas stream and a steam stream.

[0049] In an embodiment, a portion of the oxygen-enriched stream not used for heating the combustion air stream and / or the cooled oxygen-enriched stream may be combined with the combusted off gas before sending it to the second heat exchanger.

[0050] In one aspect, at least a portion of said steam stream is fed to the electrolysis section as at least a portion of said first steam feed to the electrolysis section.

[0051] Steam drum and additional heat exchangers

[0052] The steam drum is arranged to receive at least a portion of said steam stream from the second heat exchanger and provide a dry steam stream of which at least a portion of said first steam feed to the electrolysis section.

[0053] In one aspect, said plant further comprises a third heat exchanger, said third heat exchanger being arranged to heat a second water stream to produce a second steam stream and to feed said second steam stream to said steam drum. In this way, the third heat exchanger provides the remaining necessary heat to produce the steam stream.

[0054] In one aspect, said steam drum is arranged to receive a first water stream and said steam drum is arranged to provide said water stream to at least the second heat exchanger and / or provide said second water stream to the third heat exchanger.

[0055] In one aspect, the third heat exchanger comprises multiple heat exchanger units. Typically, the multiple heat exchangers are arranged in parallel. In one aspect, the third heat exchanger is heated by means of an electrical heater, a steam fired heater, by heat recovery from hot streams and / or by heat recovery using one or more heat pumps. Each heat exchanger unit may have different, multiple heat sources, either in sequence or in combination. A steam drum is a standard feature of a water-tube boiler. It is a reservoir of water / steam at the top end of the water tubes. The drum stores the steam generated in the water tubes and acts as a phase-separator for the steam / water mixture.

[0056] Process for production of a steam stream

[0057] In a second aspect, a process for production of a steam stream using a combustible off-gas stream in a chemical plant is also provided. Said process comprises the steps of: providing a plant as described herein; feeding at least a first portion of said first steam feed to said electrolysis section and electrolyzing said first portion to provide a hydrogen stream and an oxygen- enriched stream; supplying at least a portion of said oxygen-enriched stream and said combustion air stream to said first heat exchanger and allowing heat transfer from the at least a portion of said oxygen-enriched stream to the combustion air stream to take place, so as to provide a heated combustion air stream and a cooled oxygen- enriched stream; feeding at least a portion of said heated combustion air stream and at least a portion of said off-gas stream to at least one burner to provide a combusted gas stream; supplying at least a portion of said combusted gas stream and said water stream to said second heat exchanger and allowing heat transfer from the at least a portion of said combusted gas stream to said water stream to take place, so as to provide a cooled combusted gas stream and a steam stream; feeding at least a portion of said steam stream from the second heat exchanger to said steam drum (50), outputting a dry steam stream (52b) and providing a portion of said steam stream (52a) as at least a portion of said first steam feed (5) to the electrolysis section (20).

[0058] In one aspect, the process further comprises the step, wherein at least a portion of said steam stream from said second heat exchanger is fed to the electrolysis section as at least a portion of said first steam feed to the electrolysis section.

[0059] In one aspect, said plant further comprises a steam drum, and said process further comprises feeding at least a portion of said steam stream from the first heat exchanger to said steam drum and optionally providing a portion of said steam stream as at least a portion of said first steam feed to the electrolysis section.

[0060] In one aspect, said process further comprises feeding a first water stream to said steam drum so as to provide said water stream for at least the second heat exchanger.

[0061] In one aspect, said plant further comprises a third heat exchanger, and wherein said process comprises allowing heat transfer from said third heat exchanger to a second water stream provided from said steam drum to produce a second steam stream and feeding said second steam stream to said steam drum.

[0062] In one aspect, said process further comprises supplying a flushing stream such as an air or CO2-rich stream to the anode of said electrolysis section and flushing the oxygen with said flushing stream to provide an oxygen-enriched stream. In a more specific aspect, said flushing stream is oxygen poor and said process further comprises feeding a separate oxygen-containing stream to the at least one burner.

[0063] In one aspect, said chemical plant further comprises said syngas stream and said synthesis section, and wherein said process further comprises feeding a syngas to said synthesis section to provide a product stream and off-gas stream, and wherein at least a portion of said off-gas stream is fed as a feed to said burner.

[0064] In one aspect, said chemical plant further comprises the syngas stream, the synthesis section and the purification section, and said process further comprises feeding said syngas to said synthesis section to provide a product stream and off-gas stream and comprises feeding said product stream to said purification section to provide a purified product stream and an offgas stream, wherein at least a portion of said off-gas stream provided from said purification section is fed as a feed to said burner.

[0065] In one aspect, said process further comprises feeding at least a portion of the hydrogen stream from the electrolysis section to the synthesis section, optionally in admixture with a syngas stream. In another aspect, said process further comprises feeding an additional fuel stream, preferably being a portion of said hydrogen stream portion of said syngas stream, to the at least one burner.

[0066] In one aspect, said plant further comprises a synthesis section, and said process further comprises feeding least a portion of said steam stream to said synthesis section for use in a distillation process. The synthesis section may be a methanol synthesis section, or other general synthesis section. In a further aspect, said plant comprises said purification section comprising a CO2recovery unit, and wherein said process comprises feeding least a portion of said steam stream to said purification section for regeneration of said CO2recovery unit.

[0067] Specific embodiments

[0068] Position numbers:

[0069] 1 syngas stream

[0070] 5 first steam feed

[0071] 6 flushing stream

[0072] 8 fuel stream

[0073] 10 synthesis section

[0074] 11 product gas stream

[0075] 12 combustible off-gas stream

[0076] 12b off-gas stream

[0077] 15 purification section

[0078] 15a CO2 recovery unit

[0079] 16 purified product stream

[0080] 20 electrolysis section

[0081] 21 oxygen-enriched stream

[0082] 21a first portion of oxygen-enriched stream

[0083] 21b second portion of oxygen-enriched stream

[0084] 22 hydrogen stream

[0085] 23 cooled oxygen-enriched stream

[0086] 23a portion of cooled oxygen-enriched stream

[0087] 24 first heat exchanger

[0088] 25 combustion air stream

[0089] 26 heated combustion air stream

[0090] 30 at least one burner

[0091] 31 combusted gas stream

[0092] 40 second heat exchanger

[0093] 42 cooled combusted gas stream

[0094] 50 steam drum

[0095] 51 water stream

[0096] 51b first water stream

[0097] 52 steam stream

[0098] 52a at least a portion of dry steam stream

[0099] 52b dry steam stream 52c at least a portion of second steam stream

[0100] 52d at least a portion of steam stream

[0101] 60 third heat exchanger

[0102] 100 chemical plant

[0103] In a chemical plant (100), illustrated in figure 2, an electrolysis section (20) receives at least a portion of a first steam feed (5) and electrolyze it to provide a hydrogen stream (22) and an oxygen-enriched stream (21). Additionally, said chemical plant (100) provides a combustible off-gas stream (12). A first heat exchanger (24) receives at least a portion of the oxygen-enriched stream (21) and at least a combustion air stream (25) to provide a heated combustion air stream (26) and a cooled oxygen-enriched stream (23). At least one burner (30) receives at least a portion of the heated combustion air stream (26) and at least a portion of the combustible off-gas stream (12), such that said streams may be combusted within the at least one burner (30) so as to provide a combusted gas stream (31). A second heat exchanger (40) receives at least a portion of said combusted gas stream (31), and a water stream (51) such that the second heat exchanger (40) allows for heat transfer from the at least a portion of said combusted gas stream (31) to said water stream (51). In this way, the second heat exchanger (40) provides a cooled combusted gas stream (42) and a steam stream (52). A third heat exchanger (60) receives and heats a first water stream (51c) to produce a second steam stream (52c). A steam drum (50) receives at least a portion of said steam stream (52) and at least a portion of the second steam stream (52c) and produces the steam stream (52b). Optionally, the electrolysis section (20) receives a portion (52a) of said steam stream (52b) such as in admixture with the said first steam feed (5).

[0104] In an embodiment of the chemical plant (100), illustrated in figure 3, an electrolysis section (20) receives at least a portion of a first steam feed (5) and electrolyze it to provide a hydrogen stream (22) and an oxygen-enriched stream (21). A second addition to what is described above, comprises that said combustible off-gas stream (12) is provided from a synthesis section (10), where said synthesis section (10) receives a syngas stream (1) and provides a product gas stream (11) and a combustible off-gas stream (12). A first heat exchanger (24) receives a portion of oxygen-enriched stream (21a) and at least a combustion air stream (25) to provide a heated combustion air stream (26) and a cooled oxygen-enriched stream (23). At least one burner (30) receives at least a portion of the heated combustion air stream (26) and at least a portion of a combustible off-gas stream (12), such that said streams may be combusted within the at least one burner (30) so as to provide a combusted gas stream (31). Optionally, a second portion of said oxygen-enriched stream (21b) and at least a portion of said cooled oxygen-enriched stream (23a) are combined with the combusted gas stream (31). A second heat exchanger (40) receives at least a portion of said combusted gas stream (31) and a water stream (51) such that the second heat exchanger (40) allows for heat transfer from the at least a portion of said combusted gas stream (31) to said water stream (51). In this way, the second heat exchanger (40) provides a cooled combusted gas stream (42) and a steam stream (52). Optionally, the electrolysis section (20) receives a portion (52a) of said steam stream (52) such as in admixture with the first steam feed (5).

[0105] In further embodiments, illustrated in figure 4, the chemical plant (100), in addition to what is described for the above embodiments, comprises that said electrolysis section (20) receives a flushing stream (6) such that the anode of said electrolysis section (20) receives the flushing stream (6) for flushing of oxygen and said electrolysis section (20) thereby provides the oxygen-enriched stream (21).

[0106] In further embodiments, illustrated in figure 5, the chemical plant (100), addition to what is described in the above embodiments also comprises a purification section (15) for purifying the product gas stream (11). Said purification section (15) receives the product gas stream (11) from the synthesis section (10) and converts it into a purified product stream (16) and an off-gas stream (12b). In this way, the at least one burner (30) may receive the combustible off-gas (12, 12b) from the synthesis section (10), from the purification section (15) or from both the synthesis section (10) and the purification section (15), the latter optionally as admixed streams. A second addition to what is described in the proceeding specific embodiments, comprises that at least a portion (22a) of the hydrogen stream (22) from the electrolysis section (20) may be provided to the synthesis section (10) as an additional syngas, optionally in admixture with the syngas stream (1).

[0107] In a further embodiment, illustrated in figure 6, the at least one burner (30) receives an additional fuel stream (8), preferably being a portion of said hydrogen stream (22) from the electrolysis section (20) or a portion of said syngas stream (1).

[0108] EXAMPLES

[0109] Example 1 : ammonia synthesis

[0110] First example as illustrated in fig 3, comprises process simulation performed in relation to ammonia synthesis. Duty (energy transfer) in heat exchanger (40) in the oxygen-enriched stream (31) increases from 3.46 to 4.32 MW (25%) when the burner 30 is added to the system and stream 12 is fed to the burner 30. The electrical power for producing the steam required for the process (52a) in the electrolysis section (20) is reduced from 3.3 MW to 2.4 MW (Part of 60). This corresponds to (26.5 %). Ranges used : Off-gas [NH3] [Mole %]

[0111] Range: Typical

[0112] N2: 15-60 23

[0113] H2: 20-70 66

[0114] CH4: 0-25 0

[0115] Ar: 5-15 10

[0116] NH3: 0-2 1

[0117] Other: <1 <1

[0118] Example 2: Methanol synthesis

[0119] Second example as illustrated in fig. 3 comprises process simulation performed in relation to methanol synthesis. Duty (energy transfer) in heat exchanger (40) in the oxygen-enriched stream (31) increases from 1.8 MW to 2.3 MW (27.7 %). Electrical power for producing the steam required for the process (52a) in the electrolysis section (20) is reduced from 7.0 MW to 6.5 MW (Part of 60). This corresponds to (7.3%)

[0120] Off-gas (MeOH) [Mole %]

[0121] Range: Typical

[0122] H2: 40-60 50

[0123] CO2 : 35-55 45

[0124] CO: 0-2 1

[0125] CH4: 0-5 2

[0126] MeOH : 0-6 3

[0127] Others: 0-5 <1

[0128] Conclusion: Use of waste stream reduces power consumption in the chemical plant.

[0129] Example 3: Fischer-Tropsch

[0130] Third example as illustrated in fig. 3 comprises process simulation preformed in relation to Fischer-Tropsch synthesis. Duty (energy transfer) in heat exchanger (40) in the oxygen- enriched stream (31) increases from 1.96 MW to 2.62 MW (33.2 %). Electrical power for producing the steam required for the process (52a) in the electrolysis section (20) is reduced from 7.0 MW to 6.35 MW (Part of 60). This corresponds to (9.3%) Off-gas (F-T) [Mole %] Range: Typical

[0131] H2 15-25 17 CO2 20-50 33

[0132] CO 10-25 15

[0133] CH4 10-35 32

[0134] N2 0-5

[0135] C2+ 0-5 2

[0136] Conclusion: Use of waste stream reduces power consumption in the chemical plant.

[0137] While the invention has been described with reference to a number of embodiments and aspects, the overall scope of the invention is defined in the appended claims. The skilled person may combine embodiments and aspects as required, within the scope of the invention. All documents mentioned herein are incorporated by reference.

Claims

CLAIMS1. A chemical plant (100), said plant (100) comprising: an electrolysis section (20) a first steam feed (5) a combustible off-gas stream (12) a combustion air stream (25) a first heat exchanger (24) at least one burner (30) a second heat exchanger (40) a water stream (51) wherein said electrolysis section (20) is arranged to receive at least a portion of said first steam feed (5) and electrolyze it to provide a hydrogen stream (22) and an oxygen-enriched stream (21); wherein said first heat exchanger (24) is arranged to receive at least a portion of said oxygen-enriched stream (21) and said combustion air stream (25), and where said first heat exchanger (24) is arranged to transfer heat from the at least a portion of said oxygen-enriched stream (21) to said combustion air stream (25) so as to provide a cooled oxygen-enriched stream (23) and a heated combustion air stream (26); wherein at least a portion of said heated combustion air stream (26) and at least a portion of said off-gas stream (12) are arranged to be combusted in said at least one burner (30) so as to provide a combusted gas stream (31); wherein said second heat exchanger (40) is arranged to receive at least a portion of said combusted gas stream (31), and said water stream (51), where said second heat exchanger (40) is arranged to transfer heat from the at least a portion of said combusted gas stream (31) to said water stream (51) so as to provide a cooled combusted gas stream (42) and a steam stream (52); and wherein said plant comprises a steam drum (50), said steam drum (50) being arranged to receive at least a portion of said steam stream (52) from the second heat exchanger (40), output a dry steam stream (52b) and provide a portion of said dry steam stream (52a) as at least a portion of said first steam feed (5) to the electrolysis section (20).

2. The chemical plant according to claim 1, wherein said plant is arranged for said first heat exchanger (24) to receive a portion of said oxygen-enriched stream (21a) and optionally said plant is arranged for a portion of said oxygen-enriched stream (21b) and / or at least a portion of said cooled oxygen-enriched stream (23) to be combined with the combusted gas stream (31).

3. The chemical plant according to claim 2, wherein said plant comprises a third heat exchanger (60), said third heat exchanger (60) being arranged to heat a second water stream (51c) to produce a second steam stream (52c) and to feed said second steam stream (52c) to said steam drum (50).

4. The chemical plant according to any one of the preceding claims 2 or 3, wherein said steam drum (50) is arranged to receive a first water stream (51b) and said steam drum (50) is arranged to provide said water stream (51) to at least the second heat exchanger (40) and / or provide said second water stream (51c) to the third heat exchanger (60).

5. The chemical plant according to claim 4, wherein the third heat exchanger (60) comprises multiple heat exchanger units.

6. The chemical plant according to claim 4 or 5, wherein the third heat exchanger (60) is heated by means of an electrical heater, a steam fired heater, by heat recovery from hot streams and / or by heat recovery using one or more heat pumps.

7. The chemical plant according to any one of the proceeding claims, wherein said plant comprises a flushing stream (6) where the flushing stream is arranged to be supplied to the anode of said electrolysis section (20) as flushing stream for flushing of oxygen, and thereby provide an oxygen-enriched stream (21).

8. The chemical plant according to claim 7, wherein the flushing stream (6) is air, a nitrogen-rich stream or a CO2-rich stream.

9. The chemical plant according to any one of the proceeding claims, wherein said chemical plant further comprises a syngas stream (1) and a synthesis section (10) wherein said synthesis section (10) is arranged to receive said syngas stream (1) and convert it into a product stream (11) and an off-gas stream (12), and wherein said synthesis section (10) is arranged to provide at least a portion of said off-gas stream (12) to said burner (30).

10. The chemical plant according to any one of the proceeding claims, wherein said chemical plant comprises a syngas stream (1), a synthesis section (10), and a purification section (15), wherein said synthesis section (10) is arranged to receive said syngas stream (1) and convert it into a product stream (11) and an off-gas stream (12) and wherein said purification section (15) is arranged to receive said product stream (11) and convert it into a purified product stream (16) and a further off-gas stream (12b), and wherein said purification section (15) is arranged to provide at least a portion of said further off-gas stream (12b) to said burner (30).

11. The chemical plant according to any one of claim 9 or 10, wherein said synthesis section is an ammonia synthesis section, a methanol synthesis section, a methanol- to-olefins synthesis section, a methanol-to-gasoline (TIGAS) synthesis section, a methanation section or a Fischer-Tropsch (FT) synthesis section.

12. The chemical plant according to any one of claims 9-11, wherein at least a portion of the hydrogen stream (22) provided by the electrolysis section (20) is arranged to be fed as a feed to the synthesis section (10), optionally in admixture with a syngas stream (1).

13. The chemical plant according to any one of the proceeding claims, wherein an additional fuel stream (8) is arranged to be provided to the at least one burner (30).

14. A process for production of a steam stream (52) using a combustible off-gas stream (12) in a chemical plant (100) according to any one of the preceding claims, said process comprising the steps of: providing a plant according to any one of the preceding claims; feeding at least a first portion of said first steam feed (5) to said electrolysis section (20) and electrolyzing said first portion to provide a hydrogen stream (22) and an oxygen-enriched stream (21); supplying at least a portion of said oxygen-enriched stream (21) and said combustion air stream (25) to said first heat exchanger (24) and allowing heat transfer from the at least a portion of said oxygen-enriched stream (21) to the combustion air stream (25) to take place, so as to provide a heated combustion air stream (26) and a cooled oxygen-enriched stream (23); feeding at least a portion of said heated combustion air stream (26) and at least a portion of said off-gas stream (12) to at least one burner (30) to provide a combusted gas stream (31);supplying at least a portion of said combusted gas stream (31) and said water stream (51) to said second heat exchanger (40) and allowing heat transfer from the at least a portion of said combusted gas stream (31) to said water stream (51) to take place, so as to provide a cooled combusted gas stream (42) and a steam stream (52); feeding at least a portion of said steam stream (52) from the second heat exchanger (40) to said steam drum (50), outputting a dry steam stream (52b) and providing a portion of said steam stream (52a) as at least a portion of said first steam feed (5) to the electrolysis section (20).

15. The process according to claim 14, wherein said process comprises feeding a first water stream (51b) to said steam drum (50) so as to provide said water stream (51) for at least the second heat exchanger (40).

16. The process according to any one of claim 14 to 15, wherein said plant comprises a third heat exchanger (60), and wherein said process comprises allowing heat transfer from said third heat exchanger (60) to a second water stream (51c) provided from said steam drum (50) to produce a second steam stream (52c) and feeding said second steam stream (52c) to said steam drum (50).

17. The process according to any one of claims 14-16, wherein said process comprises supplying a flushing stream (6) such as an air or CO2-rich stream to the anode of said electrolysis section (20) and flushing the oxygen with said flushing stream (6) to provide an oxygen-enriched stream (21).

18. The process according to any one of claims 14-17, wherein said chemical plant comprises a syngas stream (1) and a synthesis section (10), and wherein said process comprises feeding the syngas (1) to said synthesis section (10) to provide a product stream (11) and off-gas stream (12), and wherein at least a portion of said off-gas stream is fed as a feed to said burner (30).

19. The process according to any one of claims 14-18, wherein said chemical plant comprises the syngas stream (1), the synthesis section (10) and a purification section (15), and wherein said process comprises feeding said syngas (1) to said synthesis section (10) to provide a product stream (11) and off-gas stream (12) and comprises feeding said product stream (11) to said purification section (15) to provide a purified product stream (16) and an off-gas stream (12b), wherein at least a portion of said off-gas stream (12b) provided from said purification section (15) is fed as a feed to said burner (30).

20. The process according to any one of claims 14-19, wherein the off-gas stream comprises between 15-70 mole % hydrogen (Hz), less than 25 mole % carbon monoxide (CO) and less than 35 mole % methane (CH4).

21. The process according to any one of claims 14-20, wherein the combustion air stream (25) comprises between 5-30 mole % oxygen (Oz), such as 20-25 mole %.

22. The process according to any one of claims 18-21, wherein said process comprises feeding at least a portion of the hydrogen stream (22) from the electrolysis section (20) to the synthesis section (10), optionally in admixture with a syngas stream (1).

23. The process according to any one of claims 18-22, wherein said process comprises feeding an additional fuel stream (8) to the at least one burner (30).

24. The process according to any one of claims 18-23, wherein said plant comprises a synthesis section (10), and wherein said process comprises feeding at least a portion (52d) of said steam stream (52) to said synthesis section (10) for use in a distillation process.

25. The process according to any one of claims 18-24, wherein said plant comprises said purification section (15) comprising a CO2recovery unit (15a), and wherein said process comprises feeding least a portion (52d) of said steam stream (52) to said purification section (15) for regeneration of said CO2recovery unit (15a).

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