Steam reformer with internal heat recovery

Abstract

The inventive apparatus for the execution of endothermic reactions between gaseous reactants at heightened temperture and increased pressure encompasses the following main components:an inner isolating hull (33) for conveying the feed substances from their inlet (E) along the clearance between the pressure wall (31) of the apparatus and the hull,a tube-bundle heat exchanger (39'), placed within the hull for the internal heat recovery, whereby the feed substances are outside of the tubes (39) of the heat exchanger,a catalyst material, disposed in the lower part of the heat exchanger and/or after it in flowing direction.heating means (37, 37") arranged within the catalyst material for the supply of heat energy to the reactants at the region of the final conversion, whereby the reaction products proceed inside of the tubes, with heat delivery to the entering feed substances to the outlet of the apparatus.Processes for producing a hydrogen-rich gas may be carred out by using an apparatus as indicated. For that the necessary amount of feed substances in form of steam and hydrocarbons and the necessary heat-energy in form of electrical energy and/or oxygen-containing gas for the partial oxydation of the reducing components in the feed substances are fed into said apparatus and the hydrogen-rich reaction products are withdrawn therefrom.Such processes are useful for the production of the feed stock to be used in the NH.sub.3 -- and/or CH.sub.3 OH-synthesis.

Description

The presently described invention provides an apparatus for the execution of endothermic catalyzed reactions between gaseous reactants at heightened temperature and increased pressure, with internal heat recovery and energy supply. The invention further describes a process for producing a hydrogen-rich gas by utilizing the apparatus. The H.sub.2 -gas obtained may be used in NH.sub.3 -and/or CH.sub.3 OH-synthesis.

The process carried out in the inventive apparatus is known per se. It is the catalyzed reaction of hydrocarbons and steam at temperatures of over 850 K and at increased pressure to a gas mixture containing hydrogen and carbon monoxide , the process is known as "steam reforming".

The reaction may be represented by the general formula:

C.sub.n H.sub.m +a H.sub.2 O+b O.sub.2 .revreaction.c H.sub.2 +d CO+e CO.sub.2 +. . . The conversion is, over wide temperature- and component-limits, endothermic, i.e. for the attainment of a high yield, heat-energy has to be supplied from outside.

In most of the known steam reformers the feed substances are fed into tubes filled with catalytic material. The tubes are arranged in a furnace and are heated by direct flame-firing through a number of burners.

As actual heat-recovery from reaction products to feed substances within the furnace is neither foreseen nor realized in known steam reformers.

Steam reformers with elecrical heating are also known:

GB patent No. 866 085 teaches a process for the decomposition of hydrocarbons under addition of stream to hydrogen and carbon monoxide. According to the GB patent steam of about 383 k is produced in boiler 5 by utilizing the heat-energy from an exothermic, external reaction. The steam is heated by heat exchange to about 673 K and mixed with hydrocarbon-vapours and/or -gases of the same temperature.

This mixture is then fed into reactor 4 and heated to reaction temperature (about 1223 K) by means of electrical induction heating. The hot reaction products are then used, outside the reactor 4 in a special heat exchanger, to produce the above mentioned steam.

The heat energy is added, as shown before, at low temperature levels. The plant to implement the above conversions encompasses at least three apparatus:

the reaction chamber 4, wherein no heat exchange or heat from reaction products to feed compounds occurs, the boiler 5, wherein the product gases give off heat-energy for the evaporation of water and for the heating of steam to about 383 K and the superheater 6, in which the steam from boiler 5 is heated to higher temperatures.

The plant consisting of different and separated apparatus, it is evident that, compared to an all-in-one-apparatus, it must be of a much more complex construction.

The reforming furnace according to DE Offenlegungsschrift No. 2 809 126 utilizes the heat-energy in the cooling medium of a High Temperature Helium Cooled Reactor (HTHR) and, additionally, electrical heat, to convert gaseous hydrocarbons and steam to hydrogen and carbon oxides, The structure is suited for high temperature but not for elevated pressure (compensators for dilatation, exchangeable containers for catalysts).

EP, Publ. No. 0 020 358, teaches an ordinary electro-reformer, with a reactor having an inside thermal isolation and the catalyst placed in the tubes. In the same tubes within, the catalytic mass, are placed the electric heating elements.

In clear technical distinction therefrom the inventive apparatus shows a stream reformer with inner cooling of the container wall by the feed substances, with internal heat recovery and with thermodynamically and process-technologically advantageous arrangements of the catalyst and the heating device. All components can be installed in a pressure vessel, which allows the process to proceed at elevated pressure, a very important requirement in the hydrogen-technology. The heating element can be an electrical heating device or a burner.

The process for obtaining hydrogen-rich gas, carried out in the inventive apparatus, may be adapted to a wide range of feed substances, i.e. to different hydrocarbons, air, air-oxygen mixtures; further the different reactions are easily controlled.

The apparatus for the execution of endothermic reactions between gaseous reactants at heightened temperature and increased pressure, with internal heat recovery from reaction products to feed substances, with catalysis and heat supply, according to this invention, is characterized by

and inner isolating hull 13 for coveying the feed substances from their inlet along the clearance between the pressure wall of the apparatus and said hull, a tube-bundle heat exchanger, placed within said hull for the internal heat recovery, whereby the feed substances are outside of the tubes of said heat exchanger, a catalyst material, disposed in the lower part of said heat exchanger and/or after it in flowing direction, heating means arranged in the region of the catalyst material for the supply of heat energy to the reactants at the point of the final conversion, whereby the reaction products proceed inside of the tubes with heat delivery to the entering feed substances to the outlet of the apparatus and the arrangement of all parts within a pressure vessel.

A first special embodiment of the above apparatus is further characterized in that the heating means is a burner, to which oxygen-containing gas is conveyed from outside-- and with heat exchange --, which gas is exothermically reacted with a part of the reducing feed substances, whereby the burner is placed between the catalytic material, here arranged in two blocks 15, 15'.

As second special embodiment of the inventive apparatus is further characterized in that the heating means is an electrical heater and in that the heating elements are arranged in the lower part of the region with the catalytic material, outside the tubes of the heat exchanger.

A third form of the general apparatus is further characterized in that the heating means is combined device of electrical heating elements and of a burner, both components being operated separately and independently, whereby the heating means is arranged within the lower part of the upper block of catalytic material and outside of the tubes of the heat exchanger.

All apparatus show an inner isolating hull or metallic and/or ceramic material(s) and the pressure vessel has an outside thermal isolation.

In the first special embodiment the catalytic material is arranged in two parts, the first one being material positioned as layers in baskets outside the tubes of the heat exchanger and the second one being material placed in the passage of the reactants after the burner, whereby the reactants flow through both said catalyst material blocks and the burner is an injector arrangement for mixing the oxygen-containing gas into the reducing gaseous reactants after it rise in temperature by heat recovery, whereby--after the further heating of the reactants by the exothermic reaction with the oxygen-containing gas--, the reactants enter the second block of catalytic material.

In the second form of the inventive apparatus the catalytic material is arranged as layers within baskets outside the tubes of the heat exchanger through which layers the feed compounds flow in more than one passage and the electric heating elements are arranged in the lower region of the baskets with catalytic material but separated therefrom and also outside the tubes of the heat exchanger.

In the third form of the apparatus the catalytic material is arranged in two parts the first one being material positioned as layers in baskets outside the tubes of the heat exchanger and the second one being material placed in the passage of the reactants after the burner, whereby the reactants flow through both the catalyst material blocks, the electric heating elements are arranged in the lower region of the baskets with catalytic material but separated therefrom and also outside the tubes of the heat exchanger and the burner is an injector arrangement for mixing the oxygen-containing gas into the reducing gaseous reactants after it rise in temperature by heat recovery, whereby--after the further heating of the reactants by the exothermic reaction with the oxygen-containing gas--the reactants enter the the second block of catalytic material.

For implementing the process for producing a hydrogen-rich gas by using the inventive apparatus the necessary amount of feed substances in form of stream and hydrocarbons and the necessary heat-energy in form of electrical energy and/or oxygen-containing gas for the partial oxydation of the reducing components in the feed substances are fed into the apparatus and the hydrogen-rich reaction products are withdrawn. The process may serve as the basis for the production of the feed stock to be used in the NH.sub.3 - and/or CH.sub.3 OH-synthesis.

The inventive reactor will now be exemplified by means of three special embodiments. These are

the steam reformer with burner (FIG. 1),

the steam reformer with electrical heating (FIG. 2) and

the stream reformer with a combined burner-electrical heating (FIG. 3).

In FIGS. 4 to 6 finally, some important thermodynamical relations of the processes carried out in the inventive apparatus are given; these graphical representations are to be read in relation with the tables I to III, further below.

FIG. I illustrates a inventive apparatus according to the present invention.

E is the inlet for the feed substances, i.e. substantially gaseous and/or vaporized hydrocarbons and steam in an appropriate proportion. E' is the inlet for the oxygen containing gas, i.e. air or oxygen-enriched air; steam may be added here too. Through the outlet A the gaseous reaction products leave the apparatus.

After entrance the feed substances flow within the clearance between the vessel wall 11 and the inner thermal isoltion hull 13 along practically the whole height of the apparatus. Directed by deflector plates 14 the gaseous feed substances flow around and outside the tubes 19 of the heat exchanger 19'. Starting from a predetermined height, the flow continues, but now within the layers of catalytic material (first block). The gases having been heated (mainly by the previous heat exchange) the reaction will start immediately after contact of the reactants with catalyst. After a certain degree of conversion the gases enter the region 17, where oxygen-containing gas is passed in, after having been heated within the special tubes 16. A predetermined part of the reducing species in the feed substances is now burned with the introduced oxygen, whereby the reaction of the gases is raised to a reaction optimum level. In the second catalyst-block, consisting of the elements 15 and 15' the reforming conversion is brought to the equilibrium and the gaseous reaction products leave through the tubes 19 and outlet A. Thereby they give off heat-energy to the entering reactants and (indirectly) also to the entering oxygen-containing gases.

FIG. 2 shows a second special embodiment; of the present invention.

E stands here also for the inlet of the gaseous feed substances and A for the outlet of the gaseous reaction products. The components numerated with 21, 22, 23, 24 and 29 correspond to those with 11, 12, 13, 14 and 19 in FIG. 1. 26 is the electrical heating element which is fixed outside the tubes and separated from the catalyst. The electrical wires are designated with 27.

In FIG. 3 a third special embodiment of the invention is illustrated.

E is the inlet for the feed substances, E' the one for the oxygen-containing gas plus if necessary steam. With A is designated the outlet for the gaseous reaction products, i.e. the hydrogen containing gas.

After entrance the feed substances flow within the clearance between the vessel wall 31 (with outer insulation 32) and the inner thermal isolation hull 33 along practically the whole height of the apparatus. Directed by deflector plates 34 the gaseous feed substances flow around and outside the tubes 39 of the heat exchanger 39. Starting from a predetermined height, flow continues, but now within the layers of catalytic material (first block). The gases having been heated (mainly by the previous heat exchange) the reaction will start immediately after contact of the reactants with the catalyst. After a certain degree of conversion and with being heated by the electrical heating elements 37 with wires 37', the gases enter the region 37, where oxygen-containing gas is passed in, after having been heated within the special tubes 36. A predetermined part of the reducing species in the feed substances is now burned with the introduced oxygen, whereby the reaction of the gases is raised to a reaction optimum level. In the second catalyst-block, consisting of the elements 35 and 35' the reforming conversion is brought to the equilibrium and the gaseous reaction products leave through the tubes 39 and outlet A. Thereby they give off heat-energy to the entering reactants and (indirectly) also to the entering oxygen-containing gases.

In FIGS. 4 to 6 important thermodynamic relations of the process for producing hydrogen-rich gas utilizing the inventive steam reformers are given. FIG. 4 illustrates the process in the apparatus according to FIG. 1 with air, FIG. 5 the same process with oxygen. FIG. 6 illustrates the process carried out in the apparatus according to FIG. 2.

In the following tables I to III which are to be read in connection with the FIGS. 4 to 6 the abbreviations stand for the following units:

T is the temperature axis (K), H the enthalpy axis (kJ/mol), H.sub.1 is the enthalpy recovered by heat exchange, H.sub.2 is the enthalpy recovered by heat exchange plus conversion and H.sub.3 the enthalpy recovered during the internal heating, H.sub.E is the enthalpy added by electrical heating, .DELTA.T is the temperature interval effective for the heat exchange between the two media, A is the heating curve of the feed substances by heat exchange alone, B the curve obtained by heat exchange plus (endothermic!) conversion and C the curve obtained by heat exchange, conversion plus internal heating. is the equivalence line, indicating the relation between the temperature and the enthalpy of the gases, when in chemical reaction equilibrium.

The following Table I shows special values of the representation in FIG. 4 (air).

TABLE I__________________________________________________________________________1. Process along curve AHeating of the feed substances by heat recovery. Outside the In the tubes tubes Reaction products Feed substances Units Inflow Outflow Inflow Outflow__________________________________________________________________________Data concerning fluidMean molecular weight g/mol 17,4 17,4 17,7 17,7Pressure bar 30,05 30,0 31,4 31,3Temperature K 850 625 560 800Specific mass kg/m.sup.3 7,38 12,8 8,38Isobaric heat J/(mol K) 36,4 35,4 46,2 43,7capacityDynamic mg/(s m) 33,9 25,6 19,8 28,8ViscosityHeat conductivity mW/(K m) 122 92,8 54,0 82,6Prandtl-No. -- 0,581 0,563 0,958 0,860Data concerningflow of massMass velocity kg/s 0,89 0,58Volume velocity m.sup.3 /s 0,121 0,088 0,045 0,069Heat flow kW 420Heat flow density kW/m.sup.2 16 11Reynolds-No. -- 17200 22700 17800 12200Pressure drop mbar 50 100__________________________________________________________________________2. Process along curve BReforming with heat addition alone by heat recovery Outside the In the tubes tubes Reaction products Feed substances Units Inflow Outflow Inflow Outflow__________________________________________________________________________Data concerning fluidMean molecular weight g/mol 17,4 17,4 17,7 15,5Pressure bar 30,1 30,05 31,3 30,8Temperature K 1228 850 800 950Specific mass kg/m.sup.3 5,10 7,38 8,38 6,05Isobaric heat J/(mol K) 39,4 36,4 43,7 41,2capacityDynamic mg/(s m) 45,2 33,9 28,8 35,1ViscosityHeat conductivity mW/(K m) 166 122 82,8 144Prandtl-No. -- 0,618 0,581 0,859 0,646Data concerningflow of massMass velocity kg/s 0,89 0,58Volume velocity m.sup.3 /s 0,175 0,121 0,069 0,096Heat flow kW 730 Heat flow density kW/m.sup.2 40 28Reynolds-No. -- 12900 17200 12200 10000Pressure drop mbar 50 500__________________________________________________________________________3. Process along curve A and BHeating of air by heat recovery In the tubes Air Units Inflow Outflow__________________________________________________________________________ Data concerning fluid Mean molecular weight g/mol 28,85 28,85 Pressure bar 31,0 30,8 Temperature K 400 900 Specific mass kg/m.sup.3 27,2 11,9 Isobaric heat J/(mol K) 29,1 30,1 capacity Dynamic mg/(s m) 23,0 40,1 viscosity Heat conductivity mW/(K m) 32,9 60,2 Prandtl-No. -- 0,71 0,75 Data concerning flow of mass Mass velocity kg/s 0,31 Volume velocity m.sup.3 /s 0,011 0,026 Heat flow kW 166 Heat flow density kW/m.sup.2 14 Reynolds-No. -- 26300 15600 Pressure drop mbar 200__________________________________________________________________________

The following Table II shows special values of the representation in FIG. 5 (oxygen)

TABLE II__________________________________________________________________________1. Process along curve AHeating of the feed substances by heat recovery. Outside the In the tubes tubes Reaction products Feed substances Units Inflow Outflow Inflow Outflow__________________________________________________________________________Data concerning fluidMean molecular weight g/mol 15,5 15,5 17,8 17,8Pressure bar 30,05 30,0 31,4 31,3Temperature K 850 625 560 800Specific mass kg/m.sup.3 6,60 9,11 12,8 8,52Isobaric heat J/(mol K) 37,7 37,1 46,2 43,3capacityDynamic mg/(s m) 32,5 23,9 19,9 28,9viscosityHeat conductivity mW/(K m) 133 99,2 53,1 81,3Prandtl-No. -- 0,594 0,576 0,975 0,868Data concerningflow of massMass velocity kg/s 0,75 0,68Volume velocity m.sup.3 /s 0,112 0,081 0,053 0,080Heat flow kW 407Heat flow density kW/m.sup.2 17 12Reynolds-No. -- 14900 20200 20700 14300Pressure drop mbar 50 100__________________________________________________________________________2. Process along curve BReforming with heat addition alone by heat recovery Outside the In the tubes tubes Reaction products Feed substances Units Inflow Outflow Inflow Outflow__________________________________________________________________________Data concerning fluidMean molecular weight g/mol 15,5 15,5 17,8 15,6Pressure bar 30,1 30,05 31,3 30,8Temperature K 1263 850 800 950Specific mass kg/m.sup.3 4,40 6,59 8,51 6,13Isobaric heat J/(mol K) 41,2 37,7 43,3 40,9capacityDynamic mg/(s m) 45,2 32,5 28,9 35,2viscosityHeat conductivity mW/(K m) 188 133 81,4 142Prandtl-No. -- 0,640 0,594 0,867 0,652Data concerningflow of massMass velocity kg/s 0,75 0,68Volume velocity m.sup.3 /s 0,167 0,112 0,080 0,112Heat flow kW 765Heat flow density kW/m.sup.2 50 35Reynolds-No. -- 10600 14900 14300 11700Pressure drop mbar 50 500__________________________________________________________________________3. Process along curve A and BHeating of oxygen by heat recovery In the tubes Oxygen Units Inflow Outflow__________________________________________________________________________ Data concerning fluid Mean molecular weight g/mol 32 32 Pressure bar 31 30,8 Temperature K 400 900 Specific mass kg/m.sup.3 30,2 13,2 Isobaric heat J/(mol K) 30,1 34,4 capacity Dynamic mg/(s m) 25,8 44,7 viscosity Heat conductivity mW/(K m) 34,2 66,1 Prandtl-No. -- 0,711 0,723 Data concerning flow of mass Mass velocity kg/s 0,07 Volume velocity m.sup.3 /s 0,002 0,005 Heat flow kW 37 Heat flow density kW/m.sup.2 2,0 Reynolds-No. -- 4900 2900 Pressure drop mbar 200__________________________________________________________________________

The following Table III shows special values of the representation in FIG. 6 (electrical heating)

TABLE III__________________________________________________________________________ Outside the In the tubes tubes Reaction products Feed substances Units Inflow Outflow Inflow Outflow__________________________________________________________________________1. Process along curve AHeating of the feed substances by heat recovery.Data concerning fluidMean molecular weight g/mol 12,7 12,7 17,6 17,6Pressure bar 30,2 30,0 31,4 31,0Temperature K 870 650 560 800Specific mass kg/m.sup.3 5,26 7,02 12,6 8,3Isobaric heat J/(mol K) 35,3 34,2 46,0 44,2capacityDynamic mg(s m) 32,9 25,2 19,8 27,1viscosityHeat conductivity mW/(K m) 180 140,2 55,9 80,7Prandtl-No. -- 0,510 0,486 0,925 0,842Data concerningflow of massMass velocity kg/s 0,58 0,58Volume velocity m.sup.3 /s 0,110 0,083 0,046 0,069Heat flow kW 350Heat flow density kW/m.sup.2 21,1 14,8Reynolds-No. -- 11500 15100 17700 12900Pressure drop mbar 40 502. Process along curve BReforming with heat addition alone by heat recoveryData concerning fluidMean molecular weight g/mol 12,7 12,7 17,6 17,5Pressure bar 30,3 30,2 31,0 30,0Temperature K 940 870 800 870Specific mass kg/m.sup.3 4,88 5,26 8,33 7,57Isobaric heat J/(mol K) 35,7 35,3 44,2 45,7capacityDynamic mg/(s m) 35,2 32,9 27,1 31,1viscosityHeat conductivity mW/(K m) 192 180 80,7 95,8Prandtl-No. -- 0,517 0,510 0,986 0,991Data concerningflow of massMass velocity kg/s 0,58 0,58Volume velocity m.sup.3 /s 0,119 0,110 0,069 0,077Heat flow kW 116Heat flow density kW/m.sup.2 21,0 14,7Reynolds-No. -- 10800 11500 12900 11300Pressure drop mbar 40 2003. Process along curve CReforming by heating with heat recovery and electrical heatingData concerning fluidMean molecular weight g/mol 12,7 12,7 17,6 12,7Pressure bar 30,6 30,3 30,9 30,6Temperature K 1285 940 870 1285Specific mass kg/m.sup.3 3,60 4,88 7,57 3,60Isobaric heat J/(mol K) 38,2 35,7 45,7 38,2capacityDynamic mg/(s m) 44,6 35,2 31,1 44,6viscosityHeat conductivity mW/(K m) 248 192 95,8 248Prandtl-No. -- 0,543 0,517 0,843 0,543Data concerningflow of massMass velocity kg/s 0,58 0,58Volume velocity m.sup.3 /s 0,161 0,119 0,077 0,161Heat flow kW 585Heat flow density kW/m.sup.2 28,9 20,2Reynolds-No. -- 8500 10800 11300 7900Pressure drop mbar 60 350__________________________________________________________________________

For the expert, the deduction of the corresponding data for processes carried out in the apparatus according to FIG. 3 is now, based on the above, an easy task.

Claims

1. An apparatus for endothermic catalytic reactions of gases at high temperature and pressure comprising:

(a) a pressure vessel having a gas inlet means at one end of said vessel for the introduction of feed substances, a second gas inlet means near an opposite end of said vessel for the introduction of an oxygen-containing gas, and a gas outlet at said opposite end of said vessel for removing gaseous reaction products;

(b) an inner thermal isolating hull open at one end and positioned within said vessel so as to provide a confined path between an inner wall of said vessel and an outer wall of said inner thermal isolating hull extending substantially throughout the length of said vessel for conveying said feed substances from said gas inlet to the open end of the hull;

(c) a tube bundle heat exchanger disposed within said inner thermal isolating hull extending from said open end of said hull toward a closed end of said hull, said heat exchanger having tubes in open communication with said gas outlet and gaseous reaction products formed near the closed end of the hull, and having tubes in closed communication with said gas inlet means for oxygen-containing gas;

(d) a mixing chamber with a burner defining a heating means disposed between an end of said heat exchanger and said closed end of said hull wherein partially reacted feed substances and said oxygen-containing gases enter and are combusted forming said gaseous reaction products in the presence of a second block of catalytic material heat energy is supplied to said gaseous reaction products where said gaseous reaction products enter said tubes and exit through said gas outlet;

(e) a first block of catalytic material disposed between said tubes of said tube bundle heat exchanger and said hull, wherein said feed substances flow around said tubes of said tube bundle heat exchanger and through said first block of catalytic material; and

(f) a second block of catalytic material disposed near said closed end of said hull wherein said gaseous reaction products exiting from said mixing chamber are allowed to reach thermodynamic equilibrium.

2. An apparatus according to claim 1, wherein said second block of catalytic material is arranged in two block portions and said burner is positioned between the two block portions.

3. An apparatus according to claim 1, wherein said burner comprises an electrical heating element, wherein said burner is arranged in a lower portion of said first block of catalytic material and outside of said tubes of said tube bundle heat exchanger.

4. An apparatus according to claim 1, wherein said inner isolating hull is made of a material which consists of a metallic or a ceramic material.

5. An apparatus as in claim 3, wherein said first block of catalytic material is arranged in baskets and said electrical heating element is arranged in the lower portion of said first block of catalytic material and said apparatus furhter comprises means for introducing oxygen into sai partially reacted feed substances exiting from said first catalyst block.