Primary reformer with secondary inlet channels supplying the burner

p0001The invention relates to a reactor for the catalytic reforming of hydrocarbons with steam under elevated pressure, with which synthesis gas is produced. Such synthesis gas serves, for example, for the production of ammonia, hydrogen and methanol.

p0002Reactors for the catalytic reforming of hydrocarbons with steam have been known and in a Vi elzahl of embodiments known. In large systems, a design has been used in which a ceiling-fired box furnace with vertical reaction tubes or slit tubes is used. In this case, the slit tubes are arranged in rows. The tubes are flowed through process gas, which forms the feed gas, from top to bottom. The feed gas is subjected to a so-called cracking process.

p0003The gas exit temperatures are typically 850 ° C. and above. The process gas is collected in the lower area - inside or outside the furnace - in so-called exit collectors. In the "alleys" located between the rows of tubes, burners are arranged which are arranged vertically downwards. This area is referred to as a furnace box. The generated flue gas flows through the furnace from the top downwards and is withdrawn through so-called smoke gas tunnels lying on the floor. The temperatures in the oven box average 1000 to 1250 ° C. The furnace walls are lined with a fire-resistant protective layer for thermal insulation and protection against the high temperatures prevailing through the heating.

p0004The reaction chamber heated by the furnace usually has a plurality of gas-tight closed vertical tubes arranged in rows and suitable for filling with catalyst. These are used for process control and have devices for feeding the hydrocarbon to be reformed and the water vapor heated up to 650 ° C. to the reaction space, as well as means for removing the reformed synthesis gas from the reaction space.

p0005The furnace chamber in which the firing devices are arranged has, in the lower region of the space, a chamber for collecting the flue gases, as well as a plurality of substantially horizontally arranged tunnels running parallel to one another and perpendicular to the vertical pipes, These brick-built tunnels have openings at the sides to allow the flue gases to escape from the furnace chamber. The tunnels are usually made of masonry materials.

p0006<patcit id="pcit0001" dnum="WO2005018793A1"><text>WO2005 / 018793 A1</text></patcit> Describes a typical furnace system and method for the catalytic reforming of hydrocarbons with water vapor to synthesis gas under elevated pressure. A special configuration of the outer walls of the tunnels is used to improve the smoothing of the flue gas flow and for a more uniform temperature distribution of the combustion system.<patcit id="pcit0002" dnum="WO2006119812A1"><text>WO2006 / 119812 A1</text></patcit> Describes a typical furnace system and method for the catalytic reforming of hydrocarbons with water vapor to synthesis gas with the addition of oxygen to adjust the stoichiometry and a special downstream pore burner to avoid soot formation.

p0007All the described reforming systems have in common that a firing device, which consists of a plurality of burners arranged between the process-conducting reaction tubes, heats the furnace chamber with the reforming tubes leading through it. The burners serving for firing the furnace chamber are usually fed with heating gas and air via separate ducts. The supply of the heating gas into the burner chamber is carried out separately from the air supply. The passage of the gas feeds into the burner chamber takes place through the fire-resistant furnace lining or directly in front of it. In the case of the previously used constructions, the heating-gas-air ratio for the burners is controlled by a throttle valve or a similar device for setting the gas flow of the air supply. The burner control system and thus the furnace temperature can be controlled via this device. This design is effective, but has the disadvantage that the local air supply at the burners can be poorly controlled and, in places, leads to unfavorable ratios of heating gas to air.

p0008The oxygen-to-fuel ratio can be technically described by the so-called lambda (λ) value. When a stoichiometric molar ratio of oxygen to heating gas is used, a lambda value of 1.0 is obtained. When a stoichiometric combustion ratio is used, the oxygen content is lower, the lambda value is less than 1.0. When a higher oxygen content is used in the stoichiometric combustion ratio, a lambda value higher than 1.0 is obtained. A combustion is therefore optimal when the lambda value is 1.0. In conventional designs, lambda values ​​are obtained at the individual burners, which can fluctuate as a function of the operating condition and can temporarily have elevated values.

p0009This has a detrimental effect on the combustion process. The result may be a higher consumption of heating gas compared to the conversion of the reforming process. When the fuel is changed, the air supply is difficult to adjust to the changed stoichiometry. This can temporarily lead to an unwanted increase in the flame temperature and with the increased inflow in air to an increased formation of nitrogen oxides of the type NO_x come. Nitrogen oxides contribute to the acid rain as pollutants in the atmosphere.

p0010It is therefore an object of the invention to find a possibility to improve the air supply into the burner system in such a way that the air supply into the burner can be adjusted optimally over the entire duration of the process. This improves the combustion of the fuel gas and thus the heating gas yield of the reforming process. Optimal lambda values ​​should always be set on the individual burners so that the flame temperature always has the only necessary height. As a result, the formation of the harmful nitrogen oxides can be significantly reduced or completely eliminated.

p0011The invention solves the problem by a reactor for the catalytic primary reforming of hydrocarbons with steam under elevated pressure with a device for the ceiling heating of a reforming process<ul><li>The heating device heats a thermally insulated furnace chamber with process-conducting reforming tubes, which are sealed in gas-tight manner into the furnace chamber and which are to be fed with a catalyst suitable for reforming processes and through which a reforming gas mixture is passed through,</li><li>The firing device consists of a plurality of burners arranged between the reforming tubes, and</li><li>The firing device is fed with heating gas and air, and</li><li>In each of the burners, supply devices separate from the two gases, which are respectively arranged in alignment and can be shut off individually or in pairs, and</li><li>The mixture of the two gases is respectively carried out in the burner or immediately before it, and</li></ul>in which <ul><li>The supply means for air in each of the burners has a main intake passage and an additional secondary intake passage, and</li><li>Both inlet channels are equipped with means adapted to adjust the gas flow, and</li><li>Each secondary inlet channel being branched off from the respective main inlet channel after the gas flow adjusting means and the other continuing channel forming a primary air channel, and</li><li>The ratio of the cross-sectional areas of the secondary inlet channel to that of the main inlet channel before the branching of the secondary inlet channel is between 1: 2 and 1: 100.</li></ul>

p0012In this case, each burner is individually supplied with a heating gas-air mixture, and separate supply devices exist for both gases, and the main air supply channel allows additional air supply to the burner design through the refractory furnace lining ( "secondary inlet channel"). The mixture of heating gas and air is carried out in the burner.

p0013In an embodiment of the invention, secondary inlet ducts and main inlet ducts are equipped with feed devices which can be closed individually or in pairs.

p0014In a further embodiment of the invention, the secondary throttle flaps can be operated directly adjacent to the associated main throttle flaps. This allows the operator to adjust both feeders in one working step.

p0015Preferably, all the feed channels are directed downwardly into the firing chamber and are arranged in alignment. The feeding direction of the air inlet ducts can be inclined or led over heels, depending on the type of construction of the furnace, in order to ensure the technical feasibility of the firing. The devices for feeding the air into the burner chamber can be designed through slots through the fire-resistant furnace lining. This design allows a more accurate distribution of the air into the flame chamber. Optionally, depending on the design of the furnace chamber, this slot mold can also be designed for optimizing combustion by means of swirl elements or trouser tubes with manifolds.

p0016In further embodiments of the invention,<ul><li>The secondary inlet channels are guided vertically downwards into the combustion chamber from the branch point, or</li><li>The secondary inlet channels are inclined or have a shoulder, or</li><li>The secondary inlet channels in the burner inlet area are designed in the form of a slot or a twist body or a trouser tube.</li></ul>

p0017The invention also encompasses a process for the catalytic primary reforming of hydrocarbons with water vapor under elevated pressure with a device for ceiling heating of a reforming process using the device according to the invention. In this case, it is provided that<ul><li>The heating device heats a thermally insulated furnace chamber with process-conducting reforming tubes, which are sealed in gas-tight manner into the furnace chamber and which are to be fed with a catalyst suitable for reforming processes and through which a reforming gas mixture is passed through,</li><li>The firing device consists of a plurality of burners arranged between the reforming tubes, and</li><li>The firing device is fed with a heating gas and air, and</li><li>In each of the burners the feed for both gases is effected by separate supply devices which are arranged in alignment and which can be blocked together individually or in pairs, and</li><li>The mixture of the two gases is respectively carried out in the burner or immediately before it, and</li><li>Feeding air into each of the burners through a main inlet channel and an additional secondary inlet channel which are adjusted or also blocked by appropriate means in the gas flow, and</li><li>A constant stoichiometry with a lambda value of 1.05 to 1.15 is set as the mixing ratio of air to heating gas at the outlet of the primary inlet channel, and a lambda value of 1.1 to 1.5 is set in the flame, depending on air supply becomes. The outlet of the air / fuel mixture from the primary inlet channel is also referred to as a burner stone.</li></ul>

p0018For the embodiment of the primary reforming process according to the invention, a natural gas-air mixture is preferably used for heating. In a further embodiment of the process, the burner is heated with an LPG-air mixture instead of with a natural gas / air mixture. As LPG hydrocarbons, a mixture of C is usually referred to₃- and C₄Hydrocarbons obtained from the corresponding petroleum fraction and easily liquefied. Suitable as a heating gas are, instead of natural gas or LPG, other hydrocarbons which preferably have a boiling point below the room temperature.

p0019The air delivery into the burner is optimized by the described type of feeding of secondary air into the flame. This results in an optimum air-to-fuel ratio and optimal control of the flame, depending on the control. The maximum flame temperature in the furnace can be kept relatively low by this measure.

p0020Ordinary constructions for reforming synthesis usually have a lambda value of approximately 1.1 at the burners. This value can, however, fluctuate due to the operation. In the embodiment of the construction according to the invention, the secondary inlet channel can be opened, in particular, with a higher air supply, so that the additional air is bypassed at the primary outlet outlet channel. As a result, the local lambda value at the burner stone can be kept constant at 1.05 to 1.15, even if a lambda value of 1.1 to 1.5 is established in the flame.

p0021In one embodiment of the method according to the invention, the adjustment of the mixing ratio of heating gas to air at the outlet of the primary inlet duct is effected by adjusting the throttle flaps arranged in the inlet region in the feed ducts.

p0022In a further embodiment of the process according to the invention, the reforming gas contains methane and heated water vapor. In the device according to the invention, the reforming gas can be heated to a temperature of 500 ° to 650 ° C. by means of heat-exchanging devices in the exhaust gas tunnel outside the furnace chamber with the burner exhaust gas.

p0023In a further embodiment of the method according to the invention, the air required for heating the burner is heated to a temperature of 250 to 450 ° C. by means of heat-exchanging devices with the burner exhaust gas. In this case, the exhaust gases are used in the exhaust gas tunnel behind the heat-exchanging device for heating the reforming gas, so that the temperature at the tunnel-type chimney output is generally about 150-200 ° C.

p0024The combustion gases are discharged via the above-mentioned smoke tunnel of masonry. The tunnels have openings at the sides in order to allow the flue gases to escape from the furnace chamber. This measure ensures efficient removal of the flue gases over the entire furnace chamber. The tunnels are usually made of masonry materials.

p0025The mentioned embodiments have the advantage of an optimized adjustment of the air-fuel-gas ratio at the burners and an optimum control of the combustion with regard to setting an optimum lambda value. It is known that the nitrogen oxide content of NO_x Of an exhaust gas is significantly reduced by using a more favorable lambda value at the burner stone. It is also known that the nitrogen oxide content of NO_x Of an exhaust gas when a lower flame temperature is set. This can be found in relevant reference works. For example, the<nplcit id="ncit0001" npl-type="b"><text>Teaching "The John Zink Combustion Handbook", CE Baukel Jr., CRC-Press, London New York, 2001</text></nplcit>, called. Nitric oxides of the type NO_x Contribute to the acid rain.

p0026The design according to the invention of the burner and the feed system for heating gas and air is explained in more detail by means of two sketches, which show a section from the reforming furnace in a side view, the method according to the invention being not limited to these embodiments.

p0027<figref idrefs="f0001">FIG. 1</figref> Shows the schematic of the air and heating gas feed to the burner, starting from the main air supply duct 1. From this branch, the individual supply channels for air 2 to the individual burners, four of which are shown here by way of example, The individual main air supply ducts can be controlled by individually controllable and independent control devices 3. From these, the secondary inlet duct 4 according to the invention for air then branches off before the burner feed, which likewise has a separately controllable and independent control device 5. The main air supply channel is then passed on as a primary inlet channel of the air supply. The heating gas 6 is fed into these immediately before the burner. The feeding system passes through the refractory furnace lining 7 to ensure the flame guide 8 is inserted into the furnace chamber. By this firing, the reaction tubes 9 provided for the reforming reaction are then heated.

p0028<figref idrefs="f0002">FIG. 2</figref> Shows the feeding system again in a reduced form. Also shown is the schematic of the air and heating gas supply at the burner, starting from the main air supply duct 1. From this branch, the individual supply ducts for air 2 to the individual burners ab (for the sake of clarity, shown here fourfold exemplarily). The individual main air supply ducts can be controlled by individually controllable and independent control devices 3. From these, the secondary inlet duct 4 according to the invention for air then branches off before the burner feed, which likewise has a separately controllable and independent control device 5. The main air supply channel is then passed on as a primary inlet channel of the air supply. In these, the heating gas 6 is fed directly upstream of the burner via regulating devices. The feeding system passes through the refractory oven lining 7 to ensure the flame guide 8 is inserted into the furnace chamber.

Reference list

p0029<ol><li>1 air supply duct to the burner system</li><li>2 Main air supply channel of the individual burners</li><li>3 Air supply control device of the main intake channel</li><li>4 Secondary inlet channel</li><li>5 Air supply control of the secondary intake port</li><li>6 Heating gas supply</li><li>7 Passing through fireproof oven lining ( "Brennerstein")</li><li>8 Flame guide</li><li>9 Reformation gas tubes</li></ol>