WO2014044518A1 - Method for influencing the thermal flux density on the walls of the reaction tube in a reformer - Google Patents

Abstract

The invention relates to a method for influencing the thermal flux density on the walls of reaction tubes (2) in a reformer (3) into which combustion gas (8) and air (9) are fed, the reformer (3) being provided with a furnace chamber (5), which is surrounded by a peripheral furnace wall, at least one burner (6) on the furnace ceiling (7), and a plurality of vertical, parallel reaction tubes (2), hot exhaust gas (13) being expelled downwards from the furnace chamber (5) and the reaction tubes (2), which are filled with catalyser, being heated and subjected to hydrocarbonaceous gas and water vapour from above, endothermic separation of the hydrogen from the hydrocarbons being induced by the catalyser in the tubes (12) by the heat generated by the resulting flames and by the hot exhaust gases (13) at an exit pressure in the furnace chamber (5) of greater than 200 kPa. In order to develop the method such that the thermal distribution in the furnace chamber (5) and the thermal transfer to the reaction tubes (2) are significantly improved, a portion of the combustion gas (8), which is greater than 60 %, is also fed into the furnace chamber (5) as a portion of the air (9), which is greater than 60 %, at a respective angle of at least 30° relative to the vertical (10) of the furnace ceiling (7).

Description

 Method for influencing the heat flow density on the walls of the reaction tubes in a reformer

The invention relates to a method according to the preamble of claim 1.

In addition, the invention relates to a device for carrying out the method.

A method of the type mentioned is known from EP 1 085 261 AI.

In the process of the type mentioned in the reaction tubes of reformers hydrocarbons are cleaved in the presence of water vapor, these reactions are strongly endothermic. With the length of the reaction tubes thereby decrease the concentrations of the hydrocarbons to be reformed and those of the starting materials. As a result, the tube length also decreases the reaction rate, the endothermic effects and the absorption capacity of the heat. At the end of the reaction tubes, the endothermic reactions are often complete and the gases in the reaction tubes are close to the thermodynamic equilibrium, which is why the heat demand there is low. If the reaction tubes are heated intensively, the catalyst is overheated and damaged by the reaction tubes, resulting in undesirable reactions.

Since the combustion takes place under the ceiling of the reformer and the exhaust of the exhaust gases in the bottom region of the reformer, it is initially assumed in the prior art of intensive heating of the reaction tubes under the ceiling and an ever weaker heating on the way down because such profiles the heating correspond to the heat demand in the reaction tubes. However, significantly less favorable heating profiles are found in the furnace of the operated reformers. Hot strands and cold circulation areas are observed, causing the reaction tubes to be locally overheated or slightly heated.

In order to remedy this situation, in WO 2005/053834 it has been decided to To improve unfavorable flow and temperature conditions in a reformer with identically aligned burners by changing the orientation of the burner in the edge zone of the furnace chamber. A burner with a modified orientation in the edge zone is also disclosed in EP 2 369 229 A2.

Another known method to improve the flow and temperature conditions is to increase the air velocity in the outer burners.

However, large reformers are equipped with several hundred burners and the corrections of the flames in the edge zone of the furnace chamber have virtually no effect on the distribution of the flow and the temperature. Despite corrections of the flames in the peripheral zone, flames are concentrated in the central area and cold circulations occur. In areas with "hot spots", the catalyst is overheated and damaged. As a result, the selectivity is deteriorated, whereas in the cold zones not enough heat is transferred into the reaction tubes, which in turn reduces the sales.

From the prior art is also known to control the flow rate of the individual reaction tubes according to the individual heating of the reaction tubes. Experience has shown, however, that the circulation areas change both their position and their size, and these changes are often unpredictable and comprehensible. Since the heating of the individual reaction tubes is unpredictable and measurement of the parameters and control of the individual reaction tubes is therefore out of the question because of the high costs (for example 1000 tubes / reformer), this method has hardly gained any practical significance.

In reformer burners, the combustion air is also fed substantially downwards, usually divided into the so-called primary air, which flows around the fuel nozzles in the burners, and the secondary air, which later mixed with the fuel gas or the flame. In this case, fuel gas is preferably fed through a plurality of nozzles obliquely downwards, wherein preferably additionally relatively small fuel nozzles, which provide a stable pilot flame within the burner. ners are used. The obliquely downwardly fed gas jets are mixed and ignited in the burner near zone with the downwardly flowing air. For complete combustion, a mass mixing ratio of air / gas of about 20 is required, the direction of the burning gas jets depending on the mixing ratio air / fuel gas. The more is sucked by the vertically fed air through the gas jet, the steeper down the flames are inclined. In addition, the obliquely downwardly directed fuel gas jets cause a vacuum below the burner head which contracts the oblique downward jets in the burner near zone, forming a round downward jet.

As fuel gas is in the reformers in the process of the type mentioned natural gas or a mixture of natural gas and process gases, the z. As H ₂ , CO, C0 ₂ and hydrocarbons used. When these gases are burned in the air, the flame temperature is usually in the range between 1500 and 2200 ° C. Such hot flames must not flow directly to the reaction tubes, so that the reaction tubes and the catalyst are not destroyed by overheating. In order for the hot flames in the ceiling-fired reformers to cool rapidly and without contact with reaction tubes, usually fast, downwardly directed jet flames are used midway between the heated reaction tubes. The flame temperature is thereby reduced predominantly by suction of the colder gases from the environment. The higher the flame velocity, the higher the negative pressure in the initial region of a jet and the mass flow of the gas drawn in from the environment. However, the negative pressure in the vicinity of the flames causes the intake and contraction of the adjacent flames, which in turn hot strands and cold circulation areas are formed.

In addition, the distribution of the heat flow in the furnace space depends on the height of the reformer. The hydrogen reformers (natural gas is decomposed into H ₂ and CO) are usually much higher than reformers for dehydrogenation of hydrocarbons. In the high hydrogen reformers, the flames spread in the upper Half of it, so that the lower half is flowed through evenly in the ideal case. The maximum heat flux density occurs approximately at the point where the propagating gas jets reach the reaction tubes, i. E. typically at a distance from the ceiling of 0.3 to 0.5 of the total height. In the low reformers, the flames flow to the bottom of the reformer or to the roof of the exhaust tunnel, where they are deflected towards the reaction tubes. The maximum heat flux density is to be expected in the lower half of the reaction tubes. However, this involves a further disadvantage because the endothermic reactions in the lower half are significantly weaker, whereby the catalyst is overheated and damaged at the bottom, whereas the upper part of the reaction tubes is under-utilized, since there the absorption capacity of the heat is higher than the heat supply ,

Based on the disadvantages resulting from the prior art, it is therefore an object of the present invention to provide a method of the type mentioned above, in which the heat distribution in the furnace chamber and the entire heat transfer to the Reaktionsrohe in structurally and control technology as simple as possible being greatly improved, in particular

- The heat flux density at the reaction tubes to the heat demand of

 endothermic reactions in a catalyst bed is adjusted;

 - Flames or "hot spots" on the reaction tubes do not occur;

- Reducing gases such as H ₂ , CO do not occur on the reaction tubes and a low pollutant production in the form of, for example, NO _x , CO, soot is given.

This object is achieved with the features of claim 1.

Advantageous embodiments of the invention will become apparent from the dependent claims.

The invention provides that both a part of the fuel gas, which is greater than 60%, and a part of the air, which is greater than 60%, in each case at an angle of at least 30 ° relative to the vertical in the furnace chamber is fed.

A basic idea of the invention is not to direct the downward flow of hot gases produced by combustion as fast gas jets through the middle between reaction tubes, but more slowly into the environment of the reaction tubes or in cross section and in co-current with the reformed gas. As a result, below the burners, there are no fast downward flames that attract each other. This avoids concentrated hot strands and colder circulation areas and temperature imbalances.

The method according to the invention also ensures that at least a portion of the hot gases flows first downwards in the direction of the reaction tubes and then along the reaction tubes, in direct current with the process gas within the tubes. Since the concentration of the reagents, the rate of endothermic reactions and the absorption capacity of the heat at the beginning of the tubes are particularly high, this area can be heated very intensively, without overheating of the catalyst. The gas flowing down along the reaction tubes cools down, so that the heat flow density is reduced with the length of the reaction tubes, whereby overheating in the further course of the tube is likewise prevented.

A further advantage of the invention is that bundling is prevented by producing no fast individual flames, but wide and much slower flames, which mainly suck in their own exhaust gases.

An advantageous development of the invention provides that the part of the injected air is fed at a different angle than the fuel gas in the furnace chamber, wherein the proportion of the air is changed. By changing the proportion of air, the axial distribution of the heat flow density can be adjusted to the reaction tubes. A practicable variant of the invention provides that the fuel gas and the air are deflected below the burner. The deflection also achieves an advantageous flow distribution in the furnace chamber.

Advantageously, the shape of the flames resulting from the combustion is changed. Here, the flame shape is to be adapted such that the temperature is lowered in the upper region of the reaction tube and increased in the lower region of the reaction tube. For this purpose, the distribution of the fuel gas injected at different angles and the air can be changed, for example by the proportion of obliquely fed air, e.g. is lowered from 100% to 80% to the vertical from 100% to 80% at an angle of 40 ° air and the remaining 20% air is fed in vertically. Alternatively, the deflection of the fuel gas or the air in the burner can be changed by lowering the position of deflection surfaces, which are hit by the fuel gas and the air, in the burner. These measures serve to adapt the flame shape so that the temperature distribution is again adapted in the burner chamber to a changed heat requirement, which results primarily from a change in the local maximum heat flux density at the reaction tubes and the axial heat profiles.

In the following the invention will be explained in more detail with reference to the drawings. It shows in a schematic representation:

Fig. 1a and b show a method according to the invention, which is shown in a device designed as a reformer, wherein the device is shown in a side view and in a plan view, and

Fig. FIG. 2 shows a section of the device from FIG. 1 with burner-near. FIG

 Deflection.

From Fig. 1, the procedure of the method in a device 1 in the form of a Reformers 3 forth. The device 1 has a furnace chamber 5 enclosed by a circumferential furnace wall and is equipped with a plurality of burners 6 arranged in rows and a plurality of vertical, parallel reaction tubes 2. The fuel feed takes place through a plurality of separate nozzles of the burner 6. The furnace roof 7 represents an end face of the furnace chamber 5.

The process begins with the supply of both a portion of the fuel gas 8 and a portion of the air 9, in each case at an angle aa ₂ , which is at least 30 ° relative to the vertical 10 of the furnace roof 7 in the furnace chamber 5. In the in Fig. 1 illustrated embodiment of the invention, the air 9 is fed obliquely downward through a correspondingly arranged gap or more openings in the furnace chamber 5.

Notwithstanding the in Fig. 1 illustrated embodiment of the invention nozzles or columns for gas and air feed can be arranged in the burner head in several levels and aligned differently, so that both the majority of the fuel gas 8 and the majority of the air 9 in a significantly different from the vertical 10 Direction flows into the furnace chamber 5.

The combustion of the fuel gas 8 in air 9 resulting hot exhaust gases 13 flow through the furnace chamber 5 along the reaction tubes 2 in the downward direction. The exhaust gases 13 cool down and flow between the reaction tubes 2 in the upper region of the furnace chamber 5. Here, a corresponding heat demand is transmitted to the reaction tubes 2. The hot exhaust gas 13 heats the catalyst tubes filled with reaction tubes 2, which are acted upon from above with hydrocarbon-containing gas and water vapor. In the reaction tubes 2, an endothermic removal of the hydrogen from the hydrocarbons is effected by the heating of the flames and hot exhaust gases at an outlet pressure in the furnace chamber of over 200 kPa by the catalyst. The hot exhaust gas 13 is carried down from the furnace chamber 5. For this purpose, the exhaust passage 11, through the opening 12, the exhaust gas 13 is derived from the furnace chamber 5.

For the implementation of the method as well as to be able to estimate an optimal heat and power distribution in the environment of the reaction tubes 2 and a heat transfer to the reaction tubes 2, takes place in the in FIG. 1 embodiment of the invention, the feeding of the fuel gas 8 over ten nozzles at a speed of 500 m / s. The gas throughput is 500 kW. The fuel gas 8 is fed at an angle Ch of 50 ° in the furnace chamber 5. The feeding of the air 9 at a speed of 20 m / s takes place at an angle a ₂ of 40 °, so that an average angle of 45 ° results in the feed.

Under these conditions, the burner 6 consumes 20 kg of air per 1 kg of fuel gas 8 in a stoichiometric combustion. Here, the burner generates 1.3 m ³ / s of hot exhaust gas 13 having a temperature T ₀ = 2000 ° C.

The speed w _{hg of} this generated hot exhaust gas 13 can be estimated at a stoichiometric combustion with the momentum equation: w _hg = (m _f * w _f + m _air * w _air ) / (m _f + m _air ) where m _f , w _f - mass flow and initial velocity of the fuel gas 8 and m _a ir, w _air - mass flow and initial velocity of the air are 9.

From the volume flow 0.13 m ³ / s of a gas jet of the exhaust gas 13 and the determined speed w _hg , the initial diameter d _{0 of} the jet of the exhaust gas 13 can be given as 62 mm.

Such a dimensioned jet of hot exhaust gas 13 sucks gas from his Environment having a temperature T _u of 900 ° C. The cooling caused by the suction of the surrounding gas can be estimated using the known free-jet formulas. To be able to estimate to what extent a probate heat and power distribution is given, the temperature T _{x of} the jet of exhaust gas 13 via the equation

(Tx-Tu) / (T ₀ -Tu) =% * do / 0.3 / x is calculated, where x is the distance from the nozzle of the burner 6 (see Figure lb).

The distance x can in turn be determined by geometric considerations. Here, the distance d between tube row and burner 6, the average angle α and the angle ß between distance d and the direction r of the beam is taken into account. After determining the temperature of the wall of the reaction tubes 2, it is examined to what extent the selected parameters can be the basis for a proven heat and power distribution or heat transfer. As shown in FIG. 2 also shows, 6 deflecting surfaces 14 are arranged below the burner to deflect in particular vertically fed into the furnace chamber 5 and fed fuel gas 8 to achieve a deviating from the vertical 10 of the furnace roof 7 extending flow direction of the air 9 and the fuel gas 8.

The average angle α for all media fed through the burner 6 can also be calculated using momentum equations using the horizontal and vertical velocity components in the momentum equation: w _n

 α = arctg

w _v where w _v = Σ (m, ^■ W | ^■ cos di) / Σ (m, ^■ w,) the average vertical and w _h = Σ (m, ^■ w, ^■ sin α,) / Σ (m, ^■ w, ) the average horizontal velocity component as well as m ,, w, which are the masses and velocities of the particles. According to the invention, the average angle α is at least 20 ° and at most 70 °.

Bezuaszeichenliste:

1 device

2 reaction tubes

3 reformers

5 oven room

6 burners

 7 oven ceiling

8 fuel gas

9 air

 10 verticals

11 exhaust duct

12 opening

 13 exhaust

 14 deflection surface

Claims

claims: 1. A method for influencing the heat flow density on walls of reaction tubes (2) in a reformer (3), in the fuel gas (8) and air (9) is fed, wherein the reformer (3) with an enclosed by a rotating furnace wall furnace space ( 5) and at least one burner (6) on the furnace roof (7) and a plurality of vertical, parallel reaction tubes (2) is provided, wherein hot exhaust gas (13) down from the furnace chamber (5) is carried out while the with catalysts filled reaction tubes (2) heated, which are acted upon from above with hydrocarbonaceous gas and water vapor, wherein in the tubes (2) by the catalyst, an endothermic separation of the hydrogen from the hydrocarbons by the heating by the resulting flames and hot exhaust gases (13) an outlet pressure in the furnace chamber (5) of over 200 kPa is effected and the fuel gas (8) and the air (9) relative to the vertical (10) of the furnace roof (7) each at an angle in de n furnace space (5) is fed, characterized, in that both a part of the fuel gas (8) which is greater than 60%, and a part of the air (9) which is greater than 60%, each at an angle of at least 30 ° with respect to the vertical (10) of the furnace roof (7 ) is fed into the furnace chamber (5). 2. The method according to claim 1, characterized, that the part of the injected air (9) at an angle other than the fuel gas (8) in the furnace chamber (5) is fed, wherein the proportion of the air (9) is changed. 3. The method according to claim 1 or 2, characterized, the average angle α calculated with momentum equations for all media fed by the burner (6) is at least 20 ° and at most 70 °. 4. The method according to any one of claims 1 to 3, characterized, that fuel gas (8) and / or air (9) within a burner (6) are fed offset in height, wherein the angle of the uppermost feed is at least 10 ° greater than the angle of the lowermost feed. 5. The method according to any one of claims 1 to 4, characterized, that the fuel gas (8) and the air (9) are deflected below the burner (6). 6. The method according to any one of the preceding claims, characterized, that the shape of the flames is changed. 7. Device (1) for carrying out the method according to one of the preceding claims, characterized, a plurality of burners (6) are provided in the furnace roof (7) with fuel nozzles or openings in the burner head and with one or more nozzles, channels or openings for feeding the air (9) in alignment with the vertical (10) of the furnace roof (7) that both the majority of the fuel gas (8) and the majority of the air (9) in a direction other than the vertical (10) flow into the furnace chamber (5). 8. Apparatus according to claim 7, characterized, in that the burners (6) are provided with a substantially vertical air injection, wherein a deflection surface (14) is provided for deflecting the vertical flows below the burner (6). 9. Apparatus according to claim 7 or 8, characterized, that the deflection surface (14) is acted upon by both the fuel gas (8) and the air (9). 10. Device according to one of claims 7 to 9, characterized, in that, in order to influence the flame shape and the heat flow density on the tubes (2), the deflecting surface (14) is displaceably positioned underneath the burners (6).