How to operate a coke oven plant
Patent Information
- Application Number
- JP2024524379
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2021-10-25
- Filing Date
- 2022-10-20
- Publication Date
- 2025-10-03
- Estimated Expiration
- 2042-10-20
AI Technical Summary
The operation of coke oven plants using blast furnace gas is challenging due to its lower heating value and highly variable composition, leading to unstable and inefficient heating in underfire systems, which is exacerbated by the variability of coke oven gas composition.
A method involving the conversion of carbon monoxide in blast furnace gas to carbon dioxide, followed by mixing with coke oven gas to create a controlled gas stream with stable properties, using analyzers to adjust the proportions of blast furnace and coke oven gases to optimize the underfire system's operation.
This approach stabilizes the gas properties, enhances heating efficiency, reduces emissions, and provides flexible control over combustion parameters, achieving significant reductions in carbon monoxide and carbon dioxide emissions.
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Abstract
Description
[Technical field]
[0001] The present invention generally relates to a method for operating a coke oven plant, as well as to a corresponding coke oven plant. [Background technology]
[0002] As is well known, modern coke making plants or coke oven plants are arranged in rows which may contain as few as 10 to as many as 100 or more coke oven chambers. Due to the physical dimensions of the coking chambers (narrow, long, tall), they are sometimes called slot ovens. The ovens are designed and operated in such a way that they allow the recovery of volatile products evolved from the coal during the carbonization process. The carbonization process is usually operated in cycles, repeating the following main steps: loading; carbonization; and emptying.
[0003] The heat required to operate the carbonization process is generally provided by the combustion of combustible gases, which can be of any suitable nature, but for economic reasons blast furnace gases can be used, if available in the coke oven plant.
[0004] Furthermore, the operation of a blast furnace is complex and many parameters and modifying input variables must be constantly taken into account in order to produce good quality and high yield pig iron, so that the composition of the resulting blast furnace gas varies more or less significantly over time.
[0005] Therefore, operation of coke oven heating / underfiring systems with blast furnace gas is far from ideal not only due to its low heating value but also due to its highly variable composition. Technical problems
[0006] The object of the present invention is to provide a method for operating a coke oven plant that can be heated with blast furnace gas, and to provide a better and more reliable heating in the underfire system by providing a significantly enhanced and more flexible control of the underfire gases, in particular aiming at maintaining the best combustion parameters and efficiency of the coke oven at all times. Preferably, the method should be applicable not only to new coke oven plants, but also to existing plants. Summary of the Invention
[0007] To this end, in a first aspect, the present invention provides a method of operating a coke oven plant, comprising: a) providing a blast furnace gas stream containing carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2), and a coke oven gas stream containing hydrogen, carbon monoxide and methane (CH4) (and other hydrocarbons); b) treating (at least) a portion of the blast furnace gas stream by converting carbon monoxide to carbon dioxide in a CO conversion unit to obtain a treated blast furnace gas stream; c) subjecting the treated blast furnace gas stream from step b) to carbon dioxide removal in a CO2-depletion unit to obtain a primary CO2-depleted blast furnace gas stream; d) mixing the first CO2-depleted blast furnace gas stream from step c) and a fixed proportion of the blast furnace gas stream in a first mixing unit to obtain a second CO2-depleted blast furnace gas stream; e) mixing a proportion of the secondary CO2-depleted blast furnace gas stream and the coke oven gas stream from step d) in a second mixing unit to obtain a tertiary CO2-depleted gas stream; f) feeding said tertiary CO2-depleted gas stream from a coke oven plant into an underfire system of a coke oven for converting coal into coke, thereby producing coke oven gas and tail gas.
[0008] According to the invention, one or more properties of the secondary CO2-depleted blast furnace gas stream are determined by a first analyzer downstream of the first mixing unit, and one or more properties of the tertiary CO2-depleted gas stream are determined by a second analyzer downstream of the second mixing unit. A proportion of the blast furnace gas stream and a proportion of the coke oven gas stream are controlled to adjust at least one of the one or more properties selected from the CO2 content (or concentration of CO2), the CO content (or concentration of CO), the H2 content (or concentration of H2), the Wobbe index, the stoichiometric combustion air / oxygen demand, and the Lower Heating Value in the tertiary CO2-depleted gas stream based on the properties determined by the first and second analyzers, thereby controlling the operation of the underfire system.
[0009] In a second aspect, the present invention provides a coke oven plant preferably configured to carry out the method of operating a coke oven plant described herein, comprising: a) a blast furnace gas supply, in particular a blast furnace gas network configured to provide a blast furnace gas stream comprising carbon monoxide CO, carbon dioxide CO2 and hydrogen H2, and a coke oven gas supply, in particular a coke oven gas network configured to provide a coke oven gas stream comprising hydrogen H2, carbon monoxide CO and methane CH4 (and other hydrocarbons) or coke oven gas generated in the coke oven plant itself; b) a CO conversion unit fluidly connected to said blast furnace gas source and configured to treat (at least) a portion of the blast furnace gas stream by converting carbon monoxide to carbon dioxide to obtain a treated blast furnace gas stream; c) a CO2-depletion unit fluidly connected to the CO conversion unit and configured to remove carbon dioxide from the treated blast furnace gas stream to obtain a primary CO2-depleted blast furnace gas stream; d) a first mixing unit fluidly connected to the CO2-depletion unit and controllably fluidly connected to the blast furnace gas source, the first mixing unit including a controllable blast furnace bypass flow regulator, e.g., a first controllable valve, the first mixing unit configured to mix a primary CO2-depleted blast furnace gas stream from the CO2-depletion unit with a fixed proportion of the blast furnace gas stream to obtain a secondary CO2-depleted blast furnace gas stream; e) a second mixing unit fluidly connected to the first mixing unit and controllably fluidly connected to the coke oven gas source, the second mixing unit including a controllable coke oven gas flow regulator, such as a second controllable valve, the second mixing unit configured to mix a proportion of the coke oven gas stream with the secondary CO2-depleted blast furnace gas stream from the first mixing unit to obtain a tertiary CO2-depleted gas stream; and f) a coke oven of the coke oven plant including an underfire system fluidly connected to the second mixing unit and configured to combust the tertiary CO2-depleted gas stream to convert coal into coke, thereby generating coke oven gas and tail gas.
[0010] The coke oven plant according to the invention further comprises a first analyzer downstream of the first mixing unit (and upstream of the second mixing unit) configured to determine one or more characteristics of the secondary CO2-depleted blast furnace gas stream, a second analyzer downstream of the second mixing unit (and upstream of the underfire system) configured to determine one or more characteristics of the tertiary CO2-depleted gas stream, and a control unit configured to control the operation of the underfire system by determining a fixed proportion of the blast furnace gas stream and a fixed proportion of the coke oven gas stream based on the characteristics provided by the first and second analyzers, and by controlling the controllable blast furnace bypass flow regulator and the controllable coke oven gas flow regulator to regulate at least one of said one or more characteristics selected from the CO2 content (or concentration of CO2), CO content (or concentration of CO), H2 content (or concentration of H2), Wobbe index, stoichiometric combustion air / oxygen demand, and lower heating value in the tertiary CO2-depleted gas stream.
[0011] Blast furnace gas (BFG), also called top gas, is a by-product of blast furnace operation that occurs when iron ore is reduced to metallic iron with coke. Blast furnace gas is composed mainly of nitrogen, carbon dioxide, carbon monoxide, and some hydrogen. In conventional processes, blast furnace gas typically contains about 45-55% N2, about 15-25% CO, about 15-25% CO2, and about 1-10% H2. Depending on the blast furnace operation and process, for example in blast furnaces injected with natural gas, the volume fraction of carbon monoxide can exceed 25%, while the volume fraction of hydrogen can exceed 10% and H2 can reach 15%.
[0012] Although blast furnace gas generally has a relatively poor calorific value and is not an ideal gas, it can be used in the underfire system of a coke oven (train). Its main drawback, apart from its generally poor calorific value, is that it is an unavoidable residue or by-product from the metallurgical process, which is operated to best produce pig iron whatever the composition of this residue. As a result, this composition can vary greatly over time based on the actual operating conditions of the blast furnace. Thus, not only is a large amount of blast furnace gas required to operate a coke oven, but, more importantly, it is very difficult to operate in a stable and controlled manner.
[0013] Although it is known that the addition of a proportion of coke oven gas, i.e. the gas produced during the carbonization operation, has a high calorific value and thus alleviates the problem of the poor calorific value of the blast furnace gas, this does not significantly mitigate the variability of the blast furnace gas composition and therefore of some of its properties related to its use in the underfire system of the coke oven.In fact, the coke oven gas is itself a by-product, the composition of which may vary independently over time, thereby potentially exacerbating the unstable operation of the underfire system.
[0014] The inventors have concluded that even the controlled combined use of blast furnace gas and coke oven gas cannot reliably provide a gas whose properties are adequate and sufficiently constant for optimal operation of the underfire system. However, the inventors have found that both problems can be significantly reduced by excluding a large proportion of CO2 from a portion of the blast furnace gas, leaving a larger proportion of calorific gases in the resulting stream, albeit at a reduced overall throughput. Moreover, the inventors have found that by processing in such a way, one can actually benefit from a real and additional degree of freedom in the control of the properties of the underfire gas, thereby allowing independent and therefore more reliable control of the different properties of the resulting gas. In fact, the inventors have not only found that the main cause of variation in the composition of blast furnace gas is the variation in its CO2 content, but also that removing it (at least partially) results in a gas with significantly different desirable properties. Indeed, by preferably (essentially) depleting the blast furnace gas of all its CO2, not only is the calorific value of the resulting gas increased, but particularly more important properties of the resulting CO2-depleted blast furnace gas are improved compared to the original blast furnace gas, such as its Wobbe Index, which is an important property of combustible gases, and burners used in underfire systems are generally set up to function optimally when this property is kept within reasonable limits.
[0015] The fact of having two gases with very different properties but derived from the same cheap blast furnace gas provides a large and flexible spectrum of combinations with which better combustion parameters and efficiency of the coke oven can be achieved. Last but not least, a further important advantage of the present invention is that these advantages are obtained accompanied by a significant reduction in CO2 emissions in the exhaust stack of the coke oven.
[0016] The amount of CO contained in the blast furnace gas also varies greatly, so that it is advantageous to subtract this gas from the blast furnace gas. However, in contrast to CO2, CO is highly toxic and its removal requires much stricter safety measures, which is on the one hand more problematic. The invention therefore provides for the conversion of carbon monoxide to carbon dioxide by any suitable process. The original CO2 and the newly formed CO2 can then be removed in one operation by known methods, as will be explained in more detail below. On the other hand, and also in contrast to CO2, CO still provides a constant heating value and can be usefully used in downstream underfire systems. As will be explained further below, the conversion of CO to CO2 preferably used in the advantageous embodiment is the so-called water gas shift reaction. As will be understood by the skilled person, this further reduces the CO2 emissions in the exhaust stack of the coke oven.
[0017] As a result, the present invention allows for better control of calorific value variations and other properties such as the Wobbe index, by providing a secondary CO2-depleted blast furnace gas, obtained by adding a reasonable and controlled amount of original raw blast furnace gas by determining the appropriate properties of the gas downstream of the first mixing unit, and by diverting an appropriate amount of raw blast furnace gas to the first mixing unit, thus allowing for increased flexibility and reliability in the operation of the coke oven. Preferably, the corresponding properties of the blast furnace gas are already available, e.g. by monitoring in the blast furnace gas network, or can be determined separately in a third analyzer and sent to the control unit in order to reduce even more precisely the variations of the properties of the tertiary CO2-depleted stream.
[0018] Furthermore, by foreseeing that a certain percentage of coke oven gas is introduced into the now combined at least partially CO2-depleted blast furnace gas stream (i.e., the second CO2-depleted blast furnace gas), the heating value of at least the gas fed to the underfire system is increased. In fact, coke oven gas is generally formed by heating coal to 1100°C in the absence of air / oxygen. A typical composition of coke oven gas is e.g. hydrogen (H2-55%), methane (CH4-24%), carbon monoxide (CO-8%), other hydrocarbons (C n H m -1.5-3%). The corresponding properties of the coke oven gas are preferably already available, e.g. by monitoring in the coke oven gas network, or can be determined separately in a fourth analyzer and sent to the control unit in order to reduce even more accurately the fluctuations in the properties of the tertiary CO2-depleted stream.
[0019] Overall monitoring and control of the method is achieved by continuously determining or monitoring one or more characteristics of the secondary CO2-depleted blast furnace gas stream (i.e., CO2-depleted blast furnace gas mixed with untreated blast furnace gas, if necessary) and the tertiary CO2-depleted gas stream (i.e., CO2-depleted blast furnace gas mixed with untreated blast furnace gas and coke oven gas, if necessary), and by controlling or commanding stream regulators, such as controllable valves, located in the blast furnace gas bypass and in the coke oven gas supply. Of course, further monitoring and / or control points may be provided if deemed necessary or useful.
[0020] Advantageously, the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are controlled based on the characteristics determined by the first and second analyzers to adjust at least one of the Wobbe Index and the lower heating value in the tertiary CO2-depleted gas stream.
[0021] The Wobbe Index (commonly called IW) is given as follows (MJ / Nm 3 ) is defined as: If JPEG2024539249000002.jpg1016VC has a higher heating value (or a higher calorific value) and GS has a specific gravity, then JPEG2024539249000003.jpg1031, where ρ STP is the density of the gas under standard conditions (0°C, 101.325 kPa), ρ air , STP is the density of air at standard conditions, M is the molar mass of the gas, and M air is the molar mass of air, approximately 28.96 kg / kmol.
[0022] Lower Heating Value (LHV; net heating value; NCV, or lower calorific value; LCV) is a measure of the available heat energy produced by the combustion of a fuel, expressed in kJ / Nm3, assuming that the water component of the combustion process remains in the vapor state at the end of combustion. 3 LHV is measured as units of energy per unit mass or volume of material, such as 150°C. Thus, LHV is generally defined as the amount of heat released by combustion when the products are cooled to 150°C, meaning that the latent heat of vaporization of water (and possibly other reaction products) is not recovered.
[0023] In short, the present invention allows a significantly enhanced and reliable control of the operation of the coke oven underfire system by providing and controlling the combination of two different gases from the same blast furnace gas, allowing the flexible adjustment within a significantly wider range of important properties of the underfire gas, such as the Wobbe Index, and further by adjusting other properties of the underfire gas, such as its lower heating value, by adding coke oven gas, if necessary or desired. Moreover, these advantages are achieved together with a significant reduction in the carbon emissions of the entire carbonization process.
[0024] Preferably, the proportion of blast furnace gas flow and the proportion of coke oven gas flow are particularly or primarily controlled to reduce fluctuations in the operation of the underfire system.
[0025] In an advantageous embodiment, the variation of one or more properties selected from the CO content, CO content, H content, stoichiometric combustion air / oxygen demand, Wobbe index and lower heating value of the tertiary CO2-depleted stream is reduced by at least 5%, preferably at least 10%, more preferably at least 20% compared to the variation of one or more of the same properties of blast furnace gas from a blast furnace gas source or network.
[0026] Alternatively or additionally, the proportion of the blast furnace gas flow and the proportion of the coke oven gas flow are particularly or primarily controlled to bring the Wobbe Index closer to a target value and / or to increase the lower heating value of the blast furnace gas.
[0027] In an advantageous embodiment, the Wobbe Index of the tertiary CO2-depleted stream is controlled to be within + / - 20%, preferably + / - 15%, more preferably + / - 10% of a preset / target value of the Wobbe Index (specific to the underfire system).
[0028] In a further advantageous embodiment, the lower heating value of the tertiary CO2-depleted stream is increased by at least 10%, preferably at least 20%, more preferably at least 30% compared to the LHV of the blast furnace gas from the blast furnace gas source or network. Thus, typically, the LHV of the tertiary CO2-depleted stream is between 3700 and 5300 kJ / Nm 3 Within the range of 4100 to 5000 kJ / Nm 3 is adjusted to be within the range.
[0029] Alternatively or additionally, the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are particularly or mainly controlled in order to reduce the CO2 content in the exhaust gas, i.e. to reduce the carbon emissions of the carbonization process.
[0030] In yet another advantageous embodiment, the CO2 emissions of the coke oven exhaust gas are reduced by at least 30%, preferably at least 60%, more preferably at least 90% compared to the CO2 emissions when operated without CO2-depletion (i.e. only blast furnace gas and coke oven gas from the blast furnace gas source through the bypass), all other conditions being equal.
[0031] As already briefly mentioned above, in a preferred embodiment, the method comprises in step b) the treatment of (at least) a part of the blast furnace gas stream in a CO conversion unit, in which a water-gas shift reaction is carried out and CO is converted in the presence of water (steam) into CO2 and hydrogen. In a coke oven plant, the CO conversion unit thus preferably comprises a water-gas shift reactor. In that case, the production of additional hydrogen is added to the calorific value of the gas obtained, while still allowing the removal of CO, which is converted here into CO2.
[0032] The removal of carbon dioxide in the CO2-depletion unit can be carried out using any known suitable method, such as one or more steps of chemical absorption and / or physical absorption. The CO2-depletion steps preferably include one or more of physical absorption and / or chemical absorption, such as pressure swing absorption (PSA), vacuum pressure swing absorption (VPSA), capture by a washing liquid, etc.
[0033] A CO2-depletion unit may, for example, include an absorber and a stripper unit. In the absorber, a wash liquid (such as an aqueous amine solution) absorbs the CO2 (and possibly other acid gases such as H2S) from the blast furnace gas. The wash liquid, enriched in the absorbed CO2, is sent to the stripper where it is heated. This allows the wash liquid to release the absorbed CO2, allowing it to be reused in the absorber. The released CO2 can be captured, stored and used for other purposes.
[0034] The scrubbing liquid may be any scrubbing liquid suitable for removing CO2 from the gas. For example, the scrubbing liquid may include a solution of monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), diisopropylamine (DIPA) and / or diglycolamine (DGA).
[0035] Pressure Swing Absorption (PSA) is a technique used to separate some gas species from a gas mixture under pressure, depending on the molecular properties of the species and their affinity for the absorbent. It operates at temperatures close to ambient. Selective absorbents (zeolites, activated carbon, etc.) are used as trapping materials to preferentially absorb the target gas species at high pressure. The process then swings to a lower pressure to desorb the absorbed gas. Vacuum Pressure Swing Absorption (VPSA) separates gases from a gas mixture at close to ambient pressure; the process then goes to a vacuum to regenerate the absorbent.
[0036] In certain embodiments, the water gas shift reaction (step b)) can be combined with pressure swing absorption (step c)) in a so-called sorption enhanced water gas shift (SEWGS) reactor, e.g. a multi-bed pressure swing absorption (PSA) unit in which the vessel is filled with a water gas shift catalyst and a CO2 absorbent. The SEWGS reactor combines the catalytic water gas shift reaction with a solid sorbent-based CO2 separation (such as K-promoted hydrotalcite sorbent) to achieve both CO conversion and CO2 capture in one unit.
[0037] In the context of the present invention, steps b) and / or c) may be integrated into a single stage or apparatus; each step may alternatively comprise a number of processes of the same or different types, in series or in parallel, as necessary or desired.
[0038] Furthermore, in another advantageous embodiment, the stoichiometric combustion air demand or requirement, or the stoichiometric combustion oxygen demand (i.e., the amount of air or oxygen required to achieve maximum combustion efficiency) is determined by at least the second analyzer to enable control of the amount of oxygen or air supplied to the underfire system.
[0039] In the context of the present invention, the term "CO2-depleted" or "depletion" in the context of blast furnace gas is used to refer to a gas with a reduced CO2 concentration (or the action of reducing said concentration) compared to the original blast furnace gas provided by a blast furnace gas source, such as a blast furnace gas network or blast furnace gas obtained directly from the top of a blast furnace. After removing CO2, a residual concentration of CO2 may still remain in the blast furnace gas. Thus, "CO2-depleted blast furnace gas" generally means "blast furnace gas with a reduced CO2 concentration". In particular, the removal of carbon dioxide in a CO2-depletion unit results in a CO2 content or concentration in the primary CO2-depleted blast furnace gas stream of at most 10 vol.-%, generally at most 7.5 vol.-%, preferably at most 5 vol.-%, more preferably at most 2.5 vol.-%.
[0040] Therefore, in yet another aspect, the present invention proposes using the method of operating a coke oven plant as described herein or using said coke oven plant to reduce fluctuations in the operation of an underfire system heated with blast furnace gas.
[0041] Alternatively or additionally, the present invention proposes using the method of operating a coke oven plant described herein or using said coke oven plant in order to maintain the Wobbe Index close to a preset or target value and to increase the lower heating value of the blast furnace gas.
[0042] Alternatively or additionally, the invention proposes using the method for operating a coke oven plant described herein or using said coke oven plant to reduce the (non-renewable) CO2 content in the flue gas, i.e. to reduce the CO2 emissions of the flue gas or the entire carbonization process.
[0043] The method and coke oven plant according to one or more embodiments described herein achieves at least some of the following results and advantages:
[0044] CO2 emissions in the stack of coke oven plants are reduced by 30%-90% and beyond.
[0045] The final CO2 emissions can be adjusted according to the thermal tuning of new or existing coke oven trains, and the bypass and tuning described herein can maintain the best combustion conditions for the heating flues and adjust the LHV and / or Wobbe Index of the input gases to the coke oven gases.
[0046] A dedicated control unit / automation system (integrated into an existing automation system or as a stand-alone module) can manage set points and target points to meet optimal combustion conditions and / or minimal CO2 emissions.
[0047] Standard instrumentation is generally sufficient to analyze and provide the data necessary to perform on-line calculations of the flow characteristics necessary to evaluate the optimum set points of the regulating loops.
[0048] A dedicated automation module can be provided for continuous recording of the hot gas input and adjusts the set point of the regulator valve to maintain the required heat input to the battery in order to adjust the LHV and Wobbe index of the coke oven gas relative to the input gas depending on the combustion result. The flow rate of the CO2-depleted blast furnace gas stream can be adjusted in order to achieve both minimal CO2 emissions in the stack and efficient combustion while controlling the Wobbe index and minimum LHV in the regenerative heating system.
[0049] The CO2-depleted blast furnace gas stream can be used as a replacement for conventional blast furnace gas for heating only, but with a higher LHV and adjusted Wobbe Index in all cases compared to the upstream blast furnace gas, and with lower CO2 emissions than pure blast furnace gas or gas blends.
[0050] Furthermore, even if the CO2-depletion unit is temporarily unavailable, there is no need to shut down the coke oven train and the enrichment of the coke oven gas can be supplied via the blast furnace gas bypass.
[0051] The method of the present invention can be implemented in both new and existing coke oven plants, thereby providing a cost-effective method for upgrading existing plants, allowing new flexibility in operation, better control and efficiency of underfire systems, and / or reduced CO2 emissions.
[0052] The disclosed method of operating a coke plant allows flexible management of the different streams by algorithms aimed at optimizing at least one of the following: CO2 emissions (by prioritizing the primary CO2-depleted BFG stream in the first mixing unit), stabilization of coke oven combustion parameters (by stabilizing the Wobbe Index or by adjusting the LHV in the tertiary CO2-depleted stream), and / or heat input (by reducing the fluctuations of one or more properties, such as the Wobbe Index and / or the LHV, in the tertiary CO2-depleted stream).
[0053] Finally, it is a particular advantage of the present invention that it can be implemented in both new and existing coke oven plants. [Brief description of the drawings]
[0054] Preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram of an embodiment of (a part of) a coke oven plant.
[0055] Further details and advantages of the invention will become apparent from the following detailed description of some non-limiting embodiments, with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0056] An embodiment of a method for operating a coke oven plant, or an embodiment of such a coke oven plant itself, is shown diagrammatically in FIG.
[0057] The coke oven or coke oven train 80 is fed with a coke oven feed stream, the so-called tertiary CO2-depleted stream F, which is mainly produced from an (n-initial) blast furnace gas (BFG) stream B from a BFG source such as a BFG network 10, and a certain proportion of a coke oven gas (COG) stream C from a COG source such as a COG network or directly using a coke oven gas stream H from the coke oven.
[0058] As is evident from Figure 1, a portion B1, i.e. a first portion, of the BFG stream B is first fed to a CO conversion unit 30 in which at least a portion, preferably essentially all, of the carbon monoxide CO contained in the BFG is converted to carbon dioxide, e.g. >90 mol-%, preferably >95 mol-%, more preferably >99 mol-%. Advantageously, the CO conversion unit comprises a water-gas shift reactor, which converts CO in the presence of water steam into CO2 and H2. This CO conversion not only significantly reduces the content of toxic CO, but also allows it to be removed together with the original CO2 in a subsequent step, allowing the recovery of the energy still contained in the CO by producing additional hydrogen.
[0059] The resulting treated BFG then enters the CO2-depletion unit 40 to capture and remove most of the CO2 (original and produced by the CO conversion unit 30). The capture and removal can be by any suitable technique, for example one or more physical and / or chemical absorption processes, such as pressure swing absorption (PSA), vacuum pressure swing absorption (VPSA), capture by a washing solution. The overall reduction in CO2 depends on the initial content of CO and CO2, and the processes used in both the CO conversion unit and the CO2-depletion unit. However, a reduction of more than 85%, more preferably more than 90%, or even more than 95% of the CO2 emissions can generally be achieved in the primary CO2-depleted BFG stream leaving the CO2-depletion unit, compared to the initial BFG B (or B1 or B2).
[0060] The resulting primary CO2-depleted BFG stream D is then fed to a first mixing unit 60 where it is or can be mixed as required with a constant proportion B2 of the initial BFG, i.e. a second part, in order to adjust one or more properties thereof, such as its CO2 content, CO content, H2 content, Wobbe index and lower heating value. The adjustment of these one or more properties is controlled by a control unit (not shown) based on measurements of these properties made by a first analyzer 65 located downstream of the first mixing unit 60 and by operating a BFG bypass flow regulator 15, which can be for example a controllable valve, to control the amount of BFG B2 added to the first mixing unit 60 via the BFG bypass line. The sum of the BFG process stream, i.e. part B1, and the BFG bypass stream, i.e. the constant proportion B2, amounts to a total amount of BFG stream B.
[0061] The control of the BFG bypass flow regulator 15 can be such that the CO2-depleted BFG is mainly used by prioritizing the use of the primary CO2-depleted BFG stream D, thereby significantly reducing the overall CO2 content in the exhaust G in the stack 90 of the coke oven 80. Alternatively, the control of the BFG bypass flow regulator 15 can be such that the fluctuations of one or more of the above-mentioned characteristics are mainly reduced by adjusting the flow through the bypass pipe to best straighten said characteristic(s), at least as far as this is possible within the rates of the mixed streams B2 and D. The control of the BFG bypass flow regulator 15 can of course also be such that the best compromise between reducing the overall CO2 content in the exhaust G and reducing the fluctuations is achieved.
[0062] Although reduction in variability in one or more of the above properties can be achieved by using at least some primary CO2-depleted BFG stream D instead of initially only BFG stream B2, for the same reasons, i.e. to reduce variability and / or increase the heating value of gas stream D, it will generally be necessary or desirable to further controllably add a certain proportion of coke oven gas.
[0063] Thus, the primary CO2-depleted BFG stream E leaving the first mixing unit 60 is fed to the second mixing unit 70 together with a proportion of the coke oven gas GOG stream C, said proportion being controllable via the COG flow regulator 25. Again, control of said regulator is advantageously based on one or more of the aforementioned characteristics determined by a second analyzer 75 downstream of the second mixing unit 70.
[0064] Similarly, the COG flow regulator 25 can be controlled to mainly use the secondary CO2-depleted BFG E, thereby "maintaining" the reduction of the overall content of CO2 in the exhaust G in the stack 90 of the coke oven 80. Alternatively, the COG flow regulator 25 can be controlled to mainly reduce the fluctuations of one or more of the above-mentioned characteristics in the tertiary CO2-depleted stream, by adjusting the flow of the COG stream C in order to best straighten said characteristic(s), at least as far as this is possible within the flow rates of the mixed streams C and E. Again, the COG flow regulator 25 can of course be controlled to best compromise between reducing the overall content of CO2 in the exhaust G and reducing said fluctuations.
[0065] If necessary or desirable, further analyzers may be provided, such as a third analyzer 10.5 for determining one or more properties of the initial BFG stream B and / or a fourth analyzer 20.5 for determining one or more properties of the COG stream C. Values of the determined properties may be provided to a control unit to further improve control of the composition, and therefore the properties, of the tertiary CO2-depleted stream that is fed to the underfire system of the coke oven 80.
[0066] In the coke oven (train), coal is converted to coke with heat generated by an underfire system burning a tertiary CO2-depleted stream F. The combustion produces exhaust stream G, and the carbonization operation produces coke oven gas H, which can be used as a source of COG for the COG stream C, as mentioned earlier.
[0067] As an example of what can be achieved with the present invention, see the table below which shows some improvements when operating with the present invention (tertiary CO2-depleted gas) compared to operating with non-CO2-depleted mixed BFG (conventional blast furnace gas and coke oven gas mix) and COG: while allowing a moderate increase in LHV and a significant reduction in stack CO2 emissions.
[0068] [Table 1] [Explanation of symbols]
[0069] 10 Blast Furnace Gas (BFG) Network 10.5 The Third Analyzer 15 BFG bypass flow regulator B Initially BFG style B1 BFG processing stream, part of the so-called initial BFG stream B2 BFG bypass flow, a certain percentage of the initial BFG flow 20 Coke Oven Gas (COG) Network 20.5 The Fourth Analyzer 25 COG flow regulator C COG style 30 CO conversion units 40 CO2-depletion units D Primary CO2-depleted BFG flow 60 First Mixing Unit 65 First Analyzer E Secondary CO2-depleted BFG flow 70 Second Mixing Unit 75 Second Analyzer F 3rd CO2-depleted BFG flow 80 Coke ovens, coke oven rows G Coke oven exhaust gas flow, exhaust gas flow 90 Exhaust stack H Coke oven gas produced in a coke oven
Claims
1. a) Carbon monoxide CO, carbon dioxide CO ２ and hydrogen H ２ a blast furnace gas stream (B) containing hydrogen H ２ , carbon monoxide CO and methane CH ４ providing a coke oven gas stream (C) comprising: b) treating a portion (B1) of the blast furnace gas stream (B) by converting carbon monoxide to carbon dioxide in a CO conversion unit (30) to obtain a treated blast furnace gas stream; c) adding CO to the treated blast furnace gas stream from step b) ２ - subjecting to removal of carbon dioxide in a depletion unit (40) to primary CO ２ - Obtaining a depleted blast furnace gas stream (D); d) Primary CO from step c) ２ - mixing the depleted blast furnace gas stream (D) with a proportion (B2) of the blast furnace gas stream (B) in a first mixing unit (60) to produce a secondary CO ２ - Obtaining a depleted blast furnace gas stream (E); e) Secondary CO from step d) ２ - A proportion of the depleted blast furnace gas stream (E) and the coke oven gas stream (C) are mixed in a second mixing unit (70) to produce a tertiary CO ２ - Obtaining the depleted gas stream (F); f) the tertiary CO ２ - feeding the depleted gas stream (F) from the coke oven plant to the underfire system of the coke oven (80) to convert the coal into coke, thereby producing coke oven gas (H) and flue gas (G); A method for operating a coke oven plant, comprising the steps of: Secondary CO ２ The characteristics of the depleted blast furnace gas stream (E) are determined by a first analyzer (65) downstream of the first mixing unit (60) and a tertiary CO ２ the characteristics of the depleted gas stream (F) are determined by a second analyzer (75) downstream of the second mixing unit (70); A certain percentage (B2) of the blast furnace gas stream (B) and a certain percentage of the coke oven gas stream (C) are analyzed by the first (65) and second (75) analyzers to determine the tertiary CO ２ - CO in the depleted gas stream (F) ２ Content, CO content, H ２ The method for operating a coke oven plant controls to adjust at least one of the content, Wobbe index, stoichiometric combustion air demand, and lower heating value, thereby controlling the operation of the underfire system.
2. A certain percentage (B2) of the blast furnace gas stream (B) and a certain percentage of the coke oven gas stream (C) are added to the tertiary CO ２ 2. The method of claim 1, wherein the control is based on the characteristics determined by the first (65) and second (75) analyzers to adjust at least one of the Wobbe index and the lower heating value in the depleted gas stream (F).
3. 3. The method according to claim 1 or 2, wherein the constant proportion (B2) of the blast furnace gas flow (B) and the constant proportion of the coke oven gas flow (C) are controlled to reduce fluctuations in the operation of the underfire system.
4. A certain percentage (B2) of the blast furnace gas stream (B) and a certain percentage of the coke oven gas stream (C) are added to the CO in the exhaust gas (G). ２ Content and / or CO of exhaust gas (G) ２ 3. The method of claim 1 or 2, wherein the method is controlled to reduce emissions.
5. The constant proportion (B2) of the blast furnace gas stream (B) and the constant proportion of the coke oven gas stream (C) are determined to achieve the target value of the Wobbe index and / or to achieve the tertiary CO ２ 3. The process according to claim 1 or 2, wherein the lower heating value of the depleted gas stream (F) is controlled to increase.
6. Tertiary CO ２ A method according to claim 5, wherein the Wobbe Index of the depletion stream is controlled to be within + / - 20% of a preset target value of the Wobbe Index.
7. Tertiary CO ２ - The Wobbe index of the depleted flow is 3.5 to 7 MJ / Nm ３ 6. The method of claim 5, wherein the temperature is adjusted to within the range of
8. Tertiary CO ２ 6. The method of claim 5, wherein the lower heating value of the depleted stream is increased by at least 10% compared to the lower heating value of the blast furnace gas from the blast furnace gas source.
9. Tertiary CO ２ - The lower heating value of the depleted flow is 3700 to 5300 kJ / Nm ３ The method of claim 5, wherein the temperature is controlled to be within the range of
10. 3. The method according to claim 1 or 2, wherein in step b) the treatment of a proportion (B1) of the blast furnace gas stream (B) in the CO conversion unit (30) comprises a water gas shift reaction.
11. In step c), CO ２ A method according to claim 1 or 2, wherein the removal of carbon dioxide in the depletion unit comprises one or more of physical absorption and chemical absorption.
12. 3. The process of claim 1 or 2, wherein steps b) and c) are carried out in an absorption-enhanced water-gas shift reactor.
13. In step c), CO ２ - Carbon dioxide removal in the depletion unit is the primary CO ２ - CO in the depleted blast furnace gas stream (D) ２ 3. The method according to claim 1 or 2, wherein the content is at most 7.5% by volume.
14. a) Carbon monoxide CO, carbon dioxide CO ２ and hydrogen H ２ a blast furnace gas source configured to provide a blast furnace gas stream (B) comprising hydrogen H ２ , carbon monoxide CO and methane CH ４ a coke oven gas source configured to provide a coke oven gas stream (C) comprising: b) a CO conversion unit (30) connected to said blast furnace gas source and configured to treat a portion (B1) of the blast furnace gas stream (B) by converting carbon monoxide to carbon dioxide to obtain a treated blast furnace gas stream; c) a primary CO ２ - configured to remove carbon dioxide from said treated blast furnace gas stream to obtain a depleted blast furnace gas stream (D). ２ - depletion units (40); d) the CO ２ a first mixing unit (60) connected to the depletion unit (40) and controllably connected to said blast furnace gas source, comprising a controllable blast furnace bypass flow regulator (15), for controlling the CO ２ - Primary CO from the depletion unit (40) ２ - Mixing the depleted blast furnace gas stream (D) with a certain proportion (B2) of the blast furnace gas stream (B) to produce secondary CO ２ - said first mixing unit (70) adapted to obtain a depleted blast furnace gas stream (E); e) a second mixing unit (70) connected to said first mixing unit (60) and controllably connected to said coke oven gas supply, comprising a controllable coke oven gas flow regulator (25), for controlling the secondary CO from the first mixing unit (60); ２ - Mixing a certain proportion of the depleted blast furnace gas stream (E) with the coke oven gas stream (C) to produce tertiary CO ２ - said second mixing unit (70) adapted to obtain a depleted gas stream (F); f) connected to said second mixing unit (70) and using said tertiary CO 2 for converting coal into coke; ２ a coke oven (80) of a coke oven plant including an underfire system configured to combust a depleted gas stream (F) thereby producing coke oven gas (H) and exhaust gas (G); A coke oven plant comprising: Secondary CO ２ a first analyzer (65) downstream of the first mixing unit (60) configured to determine the characteristics of the depleted blast furnace gas stream (E), and a tertiary CO ２ a second analyzer (75) downstream of the second mixing unit (70), configured to determine a characteristic of the depleted gas stream (F); by determining a fixed proportion (B2) of the blast furnace gas stream (B) and a fixed proportion of the coke oven gas stream (C) based on said characteristic provided by said first (65) and second (75) analyzers, and by controlling the controllable blast furnace bypass flow regulator (15) and the controllable coke oven gas flow regulator (25) to control the tertiary CO ２ - CO in the depleted gas stream (F) ２ Content, CO content, H ２ a control unit configured to control operation of the underfire system by controlling to adjust at least one of the content, Wobbe index, stoichiometric combustion air demand, and lower heating value; Coke oven plant.
15. 15. The coke oven plant of claim 14, wherein the CO conversion unit (30) comprises a water gas shift reactor.
16. CO ２ A coke oven plant according to claim 14 or 15, wherein the depletion unit comprises one or more physical and chemical absorbers.
17. CO conversion unit (30) and CO ２ A coke oven plant according to claim 14, characterized in that each depletion unit (40) is formed by an absorption-enhanced water-gas shift reactor.
18. CO ２ - Depletion unit is the primary CO ２ - CO in the depleted blast furnace gas stream (D) ２ 16. A coke oven plant according to claim 14 or 15, operated so that the content is at most 7.5 vol-%.