Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen; Reversible storage of hydrogen
  • C01B3/02—Production of hydrogen; Production of gaseous mixtures containing hydrogen
  • C01B3/32—Production of hydrogen; Production of gaseous mixtures containing hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide or air
  • C01B3/34—Production of hydrogen; Production of gaseous mixtures containing hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide or air by reaction of hydrocarbons with gasifying agents
  • C01B3/38—Production of hydrogen; Production of gaseous mixtures containing hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide or air by reaction of hydrocarbons with gasifying agents using catalysts
  • C01B3/384—Production of hydrogen; Production of gaseous mixtures containing hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide or air by reaction of hydrocarbons with gasifying agents using catalysts with external heating of the catalyst
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/02—Processes for making hydrogen or synthesis gas
  • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
  • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
  • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/08—Methods of heating or cooling
  • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
  • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
  • C01B2203/0816—Heating by flames
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/08—Methods of heating or cooling
  • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
  • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
  • C01B2203/0822—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel the fuel containing hydrogen
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/08—Methods of heating or cooling
  • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
  • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
  • C01B2203/0827—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel at least part of the fuel being a recycle stream
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/16—Controlling the process
  • C01B2203/1604—Starting up the process
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency

Definitions

• the present invention relates to a method of regulating the flow of fuel gas sent to the steam reformer furnace burners for controlling the flow of fuel gas supplying the burners on said furnace.
• SMR Steam reforming
• synthesis gas a mixture composed mainly of hydrogen and carbon monoxide from a gaseous feed of reactants consisting essentially of hydrocarbons and carbon monoxide. water vapor which react together in a catalytic tubular reactor.
• This technology one of the most used for the production of hydrogen in particular, is based on the catalytic reactions at high temperature (800-950 ° C) of light hydrocarbons with water vapor. Highly endothermic, these reactions require heat input.
• This heat is usually provided by the combustion of a fuel with air using burners located in a radiant furnace in which the reforming tubes are arranged.
• the fumes from the combustion flow outside the tubes in the furnace and provide the reactants, by radiation and convection, the heat required for reforming.
• the reformers we are considering here are steam reformers of usual geometry.
• the furnaces have a number of burners arranged in rows on side walls in the case of so-called “sidefired” SMRs and so-called “terrace wall” SMRs, or at the oven vault in the case of SMRs known as “terrace walls”. top-fired “; more rarely, the burners are placed in the floor of the oven in the case of "bottom-fired”. In all cases, the burners are relatively spaced relative to each other.
• One of the difficulties of the implementation of this technology is the control of the equilibrium between heat supply and demand, ie the balance between the quantities of heat generated by the combustion and the quantities of heat. heat demanded by endothermic reactions. However, this balance is essential to maintain tube temperatures below the recommended maximum temperatures (commonly known as design temperatures), otherwise the materials constituting said tubes can become fragile or even crack, causing incidents and unexpected stops.
• the temperature control of the tubes is particularly delicate during the start-up phases (whether cold or hot). In fact, during these start-up phases, the feed gas is not introduced into the tubes, only an inert gas is circulated therein, the heat consumption is therefore low (due to the absence of endothermic reactions in the atmosphere). inside the tubes during these phases).
• the burners are often able to operate with a wide variety of fuels.
• this will especially be purge gas from the cold box (for the production of CO) and / or offgaz from the purification unit H 2 by adsorption by Pressure swing modulation (PSA), as well as the source of hydrocarbons (often natural gas) for the supplement.
• PSA Pressure swing modulation
• the entire heating system including among others the design
• a fuel gas consisting mainly of recycled gas (including offgaz from PSA, typically 90%) and hydrocarbons (natural gas for example).
• the different burners are equipped with individual ignition systems; those who participate in the startup are distributed in the oven so that the provided heat is evenly distributed over the entire oven, so as to minimize hot spots. For the same reason, ignition sequences are also defined for these burners.
• excess air is here defined as the percentage of combustion air in excess of the air necessary to ensure the stoichiometry of the combustion reaction. Sufficient excess air guarantees lower flame temperatures and thus reduces the risk of overheating of the tubes.
• the airflow also has the role of limiting the risk of explosion by keeping the atmosphere of the furnace below 25% of the low explosive limit (Low explosivity limit in English or LEL), and this even if the flames of some burners are blown. This air flow is distributed over all the burners, whether they are lit or not.
• the flow of the combustible gas is injected into the furnace through the burnt burner ports.
• the orifices being fixed, this flow rate is solely dependent on the pressure of said gas in the supply pipe upstream of the burners.
• Fuels generated during reforming are not available at startup.
• the only fuels available usually the gaseous filler (natural gas, naphtha, light hydrocarbon mixture, etc.), are of high calorific value.
• the gaseous filler Natural gas, naphtha, light hydrocarbon mixture, etc.
• the gas flow must therefore be all the lower as its heating value is important; the fuel gas pressure in the supply pipe located upstream of the burners must therefore be lower too.
• the nominal operating conditions are as follows:
• the relative pressure of combustible gas, in the supply pipe upstream of the burners is 200mbar
• the air flow rate corresponds to 100% of the nominal flow
• the heat released is 100%.
• relative pressure means the pressure measured with respect to the atmospheric pressure ... All the pressures expressed in the remainder of this text will be relative pressures, except explicit mention. If we replace, all the other conditions being identical, the fuel mixture (90/10) above with a gas consisting of 100% natural gas, it will significantly reduce the fuel flow to the burners. As the heating value of natural gas is generally at least 3 times higher than that of the PSA offgaz, the fuel flow must be reduced by at least 3 and the pressure should be reduced to 20mbar (the flow circulating in the burners being proportional at the root of the pressure difference).
• the air flow rate to be sent is fixed (generally 50% of the nominal flow rate for the reasons mentioned above).
• a limited number of burners are turned on to heat the entire oven and tubes.
• burner curves In order to determine the fuel gas pressure adapted during the start-up phase, those skilled in the art have curves called burner curves in English language. They allow to link together the two quantities released heat (heat release) and fuel gas pressure; they are specific to each type of fuel.
• those skilled in the art apply certain known rules, including that of limiting the starting power to a value less than a maximum starting power, so as not to damage the reforming tubes. It is generally accepted that this maximum power is 30% of the nominal power. In practice, we will rather set a power of 25%.
• the rated power would correspond to a natural gas pressure of 22 mbar.
• a curve of the burners such as the curve reproduced in FIG. 1 shows that the natural gas pressure corresponding to the maximum starting power (30% of the nominal power) is 2 mbar. The reading of the curve indicates that the natural gas pressure upstream of the burners during the start-up phase must not exceed 2 mbar.
• This upstream limit pressure is lower as the calorific value of the fuel is high.
• the synthesis gas production facilities generally have several separate circuits for supplying the burners with combustible gas.
• Each of the circuits is dimensioned according to the nature of the fuel gas or fuel gas mixture it conveys.
• the object of the present invention is therefore to provide a simpler, more compact and more economical alternative solution to the problem of overheating of the tubes. Reforming when starting the furnace of the SMR, the solution consisting in ensuring, during this start-up, the supply to the burners in operation, of a fuel gas of sufficiently low calorific value, suitable for supplying said burners at the start of operation. SMR oven.
• the invention thus relates to a method for regulating the flow rate of a fuel gas I intended to supply the burners of a steam reformer reforming furnace during a start-up phase of said furnace, comprising the steps of a) supplying a collector with a gaseous flow of said fuel gas I, b) feeding of said collector with an inert gas stream II, c) production at the outlet of the collector of a gas stream III consisting of the fuel gas mixture I and the inert gas II, d) supply of the lit burners of the reforming furnace in the gaseous mixture III from step c), via a distribution assembly of the gaseous mixture III to the burners on
• the fuel gas I may be of the natural gas, butane, propane or naphtha type alone or as a mixture.
• the inert gas II can be an inert gas, of the nitrogen type, but it is also possible to use a gas with a low calorific value.
• low calorific value is meant a heating value substantially lower than that of the gas I.
• the inert gas II is nitrogen.
• the fuel gas I is natural gas.
• the flow of the gas mixture III feeding the burners of the furnace is at a pressure at least equal to 3 - 5 mbar.
• said flow of the gaseous mixture III supplying the burners of the furnace has a partial pressure of fuel gas I such that the heat released by the combustion of the fuel mixture III with the air supplying said burners is of the order of 25-30% of the nominal heat.
• the flow ratio of the injected II gas / injected fuel gas flow I is between 0.5 and 1.
• FIG. 2 illustrates the principle of the injection of nitrogen into a gas manifold located on the fuel supply circuit of the burners.
• a stream of natural gas I and a stream of nitrogen II supply via lines 1 and 2 respectively, a common gas manifold 3 for the production of a combustible gas mixture III;
• the mixture III is fed via the feed pipe 4 to the burners 5 of the SMR furnace. Only a part of the burners 5 is lit. Only these ignited burners are fed with combustible mixture III.
• the start of the SMR furnace is carried out with a constant air flow and equal to 50% of the nominal flow rate.
• This air flow is distributed in all burners 5, whether on or off. Natural gas flow through burning burners should be minimized to ensure a high excess of air combustion.
• This flow rate is proportional to the square root of the difference between the upstream pressure and the (relative) pressure in the furnace combustion chamber. This being considered constant (of the order of -1 mbar), it is therefore determined by the pressure measured upstream of the burners.
• heating power of 25% of the nominal power during startup. Since the heating power is proportional to the flow rate of the fuel gas, this means that the flow rate of the fuel gas must be reduced by a factor of four as well.
• the minimum value of the pressure which can in practice be stabilized is 3-5mbar, which, as shown in the curve of figure 1, corresponds for natural gas to a power of 40-50% of the nominal power at each burner and can therefore be an unacceptable value for the preservation of the reforming tubes.
• the nitrogen injection according to the invention makes it possible to overcome these difficulties.
• the following table shows the results obtained with different ratios of natural gas and nitrogen rates [the pressure of the mixture III (natural gas + nitrogen) as well as the air flow are fixed constant].
• the nitrogen circuit is available in most reforming plants (primarily for start-up and shutdown), little modification will be required for the implementation of the present invention; the quantities of nitrogen involved are also low, generally of the order of 500 to 2500 Nm3 / h for plants whose size ranges from 20 000 to 100 000 Nm3 / h of hydrogen.
• the additional operating cost therefore remains very marginal, especially considering the indirect gains obtained thanks to improved operational reliability.
• the nitrogen injection also offers other advantages, among which: the supply of inert gas with respect to the combustion makes it possible to increase the overall flow rate through the burners, thus helping to better regulate their operation and thus to obtain more stable flames, this makes it possible to substantially reduce the risk of deterioration of the tubes by unstable flames; the pressure of the mixture (fuel + nitrogen) III in the feed pipe may be greater, which facilitates its regulation and allows a better distribution of the flows between the burners, thus contributing to improving the thermal uniformity in the furnace; Since the proportion of combustible gas in the overall flow is lower for each burner, more burners can be ignited to reach a given heating power, which also contributes to improving the thermal uniformity in the furnace.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Inorganic Chemistry (AREA)
• Hydrogen, Water And Hydrids (AREA)
• Feeding And Controlling Fuel (AREA)

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• 2007
  • 2007-07-12 FR FR0756457A patent/FR2918656B1/fr not_active Expired - Fee Related
• 2008
  • 2008-07-07 WO PCT/FR2008/051261 patent/WO2009010681A2/fr not_active Ceased
  • 2008-07-07 EP EP08806176A patent/EP2176160A2/de not_active Withdrawn
  • 2008-07-07 US US12/668,468 patent/US20100255432A1/en not_active Abandoned
  • 2008-07-07 CN CN200880024471A patent/CN101687636A/zh active Pending
  • 2008-07-07 EA EA201070133A patent/EA018738B1/ru not_active IP Right Cessation
• 2010
  • 2010-01-04 ZA ZA2010/00052A patent/ZA201000052B/en unknown

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