STEAM REFORMER WITH INTERNAL HEAT RECOVERY

X

S.ΦHA.M HBSOEMBR MUffi IKI BEHAL HΞAT REGGVERY

The presently described invention is relevant to an apparatus for 10 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 refers to a process for producing a hydrogen-rich gas by utilizing said apparatus. The r -gas obtained may be used in NH.,- and/or 15 CH₃0H-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 20 mixture containing hydrogen and carbon monoxide, the process is known as "steam reforming".

Said reaction may be represented in a general formula:

^{25 C}n_.Am + a H,20 + b 0,2 -*==≥. c H2₉ + d CO + e CO,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 in direct flame-firing through a num¬ ber of burners.

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

Steam reformers with electrical heating are also known:

6B patent 866 085 teaches a process for the decomposition of hydrocarbons under addition of steam to hydrogen and carbon mon¬ oxide. According to the said GB patent steam of about 383 K is produced in boiler 5 by utilizing the heat-energy from an exother- mic, external reaction. Said 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 heat¬ ing. 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 of h.e.at_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.

10 The said 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 15 2809 126 utilizes the heat-energy in the cooling medium of a High Temperature Helium Cooled Reactor (HTHR) and, additionally, elect¬ rical heat, to convert gaseous hydrocarbons and steam to hydrogen and carbon oxides, i.a. The structure is suited for high tempera¬ ture but not for elevated pressure (compensators for dilatation, 20 exchangeable containers for catalysts).

EP, Publ. No. 0020 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, 25 are placed the electric heating elements.

In clear technical distinction therefrom the inventive apparatus shows a steam reformer with inner cooling of the container wall by the feed substances, with internal heat recovery and with thermo-

30 dynamically and process-technologically advantageous arrangements of the catalyst and the heating device. All said components can be

<ς installed in a pressure vessel, which allows the process to pro¬ ceed at elevated pressure, a very important requirement in the hydrogen-technology. The heating element can be an electrical

35 heating device or a burner. The process for obtainment of 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 mix¬ tures a.s.o.; further the different reactions are easily con- trolled.

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

- an inner isolating hull 13 for conveying 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 said 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 said tubes with heat delivery to the entering feed substances to the outlet of the apparatus

and

- the arrangement of all said 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'. 5

A second special realization 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 10 heat exchanger.

A third form of the general apparatus is further characterized in that the heating means is a combined device of electrical heating elements and of a burner, both components being operated separa- 15 tely and independently, whereby the said heating means is arranged within the lower part of the upper block of catalytic material and outside of the tubes of said heat exchanger.

All said apparatus show an inner isolating hull of metallic and/or 20 ceramic material(s) and the said 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

25 baskets outside the tubes of said heat exchanger and the second one being material placed in the passage of the reactants after said 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 reac-

30 tants after its rise in temperature by heat recovery, whereby - after the further heating of the reactants by the exothermic reac¬ tion with the oxygen-containing gas - said reactants enter the said second block of catalytic material.

35 In the second kind of the inventive apparatus the catalytic material is arranged as layers within baskets outside the tubes of said 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 mate- rial but separated therefrom and also outside the tubes of said heat exchanger.

In the third form of said apparatus the catalytic material is arranged in two parts, the first one being material positioned as layers in baskets outside the tubes of said heat exchanger and the second one being material placed in the passage of the reactants after said burner, whereby the reactants flow through both said catalyst material blocks, the electric heating elements are arranged in the lower region of the baskets with catalytic mate- rial but separated therefrom and also outside the tubes of said heat exchanger and the burner is an injector arrangement for mixing the oxygen-containing gas into the reducing gaseous reac¬ tants after its rise in temperature by heat recovery, whereby - after the further heating of the reactants by the exothermic reac- tion with the oxygen-containing gas - said reactants enter the said 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 sub- stances 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 reac¬ tion products are withdrawn. Said process may serve as base for the production of the feed stock to be used in the NH-- and/or CH₃0H-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 steam reformer with a combined burner-electrical heating (Fig. 3).

In Figures 4 to 6 finally, some important thermodynamical rela¬ tions 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.

Figur I illustrates the special inventive apparatus according to dipendent claims 2 and 6.

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

After entrance the feed substances flow within the clearance bet¬ ween the vessel wall 11 and the inner thermal isolation 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,said 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 cata¬ lyst. 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.

Figur 2 shows a second special embodiment; that one corresponding to Claims 3 and 7.

E stands here also for the inlet of the gaseous feed substances and A for the outlet of the gaseous reaction products. The compo¬ nents 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 execution form of the inventive apparatus, the one defined in Claims 4 and 8, is illustrated.

E is the inlet for the feed substances, E' the one for the oxy¬ gen-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 bet¬ ween 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 14 the gaseous feed substances flow around and outside the tubes 19 of the heat exchanger 19. Starting from a predetermined height, said 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 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.

In Figures 4 to 6 important thermodynamic relations of the process for producing hydrogen-rich gas utilizing the inventive steam re- formers are given. Figure 4 illustrates the process in the appara¬ tus according to Figure 1 with air, Figure 5 the same process with oxygen. Figure 6 illustrates the process carried out in the appa¬ ratus according to Figure 2.

In the following tables I to III which are to be read in connec¬ tion with the Figures 4 to 6 the abbreviations stand for the following units:

T is the temperature axis (K), H the enthalpy axis (kJ/mol),

H-, is the enthalpy recovered by heat exchange,

H« is the enthalpy recovered by heat exchange plus conversion and H the enthalpy recovered during the internal heating, Hr is the enthalpy added by electrical heating,

ΔT 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, - - - - the curve obtained by heat exchange plus (endothermic '• ) conversion and 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 A

Heating of the feed substances by heat recovery.

Units In the tubes Outside the tubes

Reaction products Feed substanc Inflow Outflow Inflow Outf

Data concerning fluid

Mean moleculary weight g/mol 17,4 17,4 17,7 17,7

Pressure bar 30,05 30,0' 31,4 31,3

Temperature^K 5 560 800

Specific mass kg/π3 850 62 T 7,38 12,8 8,3

Isobaric heat capacity J/(mol K) 36,4 35,4 46,2 43,

Dynamic

Viscosity mg/(s m) 33,9 25,6 19,8 28,

Heat conductivi I y mW/(K m) 122 92,8 54,0 82,

Prandtl-No. — 0,581 0,563 0,958 0,

Data concerning flow of mass

Mass velocity kg/s 0,89 0,58

Volume velocity m³/s 0,121 0,088 0,045 0,

Heat flow kW 420

Heat flow density kW/m² 16 11

Reynolds-No. — 17200 22700 17800 12

Pressure drop mbar 50 100 2. Process along curve B

Reforming with heat addition alone by heat recovery

Units In the tubes Outside the tubes

Reaction products Feed substances Inflow Outflow Inflow Outflo

Data concerning fluid

Mean moleculary weight g/mol 17,4 17,4 17,7 15,5

Pressure bar 30,1 30,05 31,3 30,8

Temperature 1228

^K 3 850 800 950

Specific mass kg/πT 5,10 7,38 8,38 6,05

Isobaric heat capacity JΛmol K) 39,4 36,4 43,7 41,2

Dynamic

Viscosity mg/(s m) 45,2 33,9 28,8 35,1

Heat conductivii y mW/(K m) 166 122 82,8 144

Prandtl-No. — 0,618 0,581 0,859 0,646

Data concerning flow of mass

Mass velocity kg/s 0,89 0,58

Volume velocity m³/s 0,175 0,121 0,069 0,096

Heat flow kW 730

Heat flow density kW/m 40 28

Reynolds-No. — 12900 17200 12200 10000

Pressure drop mbar 50 500

3. Process along curve A and B

Heating of air by heat recovery

£

Units In the tubes

Air

Inflow Outflow

Data concerning fluid

Mean moleculary weight g/mol 28,85 28,85

Pressure bar 31,0 30,8

Temperature 400 900

Specific mass^Kkg/πr3 27,2 11,9

Isobaric heat capacity J/(mol K) 29,1 30,1

Dynamic viscosity mg/(s m) 23,0 40,1

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 m³/s 0,011 0,026

Heat flow kW 166

Heat flow density kW/m² 14

Reynolds-No. — 26300 15600

Pressure drop bar 200 The following Table II shows special values of the representation in Fig. 5 (oxygen)

Table II

1. Process along curve A

Heating of the feed substances by heat recovery..

Units In the tubes Outside the tubes

Reaction products Feed substance Inflow Outflow Inflow Outflo

Data concerning fluid

Mean moleculary weight g/mol 15,5 15,5 17,8 17,8

Pressure bar 30,05 30,0 31,4 31,3

Temperature 25 560 800

Specific mass^Kkg/r 3 850 6 rf 6,60 a,n 12,8 8,52

Isobaric heat capacity ύ7(mo1 K) 37,7 37,1 46,2 43,3

Dyna ic viskosity mg/(s m) 32,5 23,9 19,9 28,9

Heat conductiviity mW/(K m) 133 99,2 53,1 81,3

Prandtl-No. — 0,594 0,576 0,975 0,86

Data concerning flow of mass

Mass velocity kg/s 0,75 0,68

Volume velocity m³/s 0,112 0,081 0,053 0,08

Heat flow kW 407

Heat flow density kW/m 17 12

Reynolds-No. — 14900 20200 20700 1430

Pressure drop mbar 50 100 2. Process along curve B

Reforming with heat addition alone by heat recovery

Units In the tubes Outside the tubes

Reaction procucts Feed substances Inflow Outflow Inflow Outflow

Data concerning fluid

Mean moleculary weight g/mol 15,5 15,5 17,8 15,6

Pressure bar 30,1 30,05 31,3 30,8

Temperature ecific mass 3 1263 850 800 950

Sp kg/πT 4,40 6,59 8,51 6,13

Isobaric heat capacity J/(mol K) 41,2 37,7 43,3 40,9

Dynamic viskosity mg/(s m) 45,2 32,5 28,9 35,2

Heat conductiviity . mW/(K-m) , 188 133 81,4 142

Prandtl-No. — 0,640 0,594 0,867 0,652

Data concerning flow of mass

Mass velocity kg/s 0,75 0,68

Volume velocity m³/s 0,167 0,112 0,080 0,112

Heat flow kW 765

Heat flow density kW/m 50 35

Reynolds-No. — 10600 14900 14300 11700

Pressure drop mbar 50 500 3. Process along curve A and B

Heating of oxygen by heat recovery

Units In the tubes

Oxygen

Inflow Outflow

Data concerning fluid

Mean moleculary weight g/mol 32 32

Pressure bar 31 30,8

Temperature ecific mass^K 400 900

Sp kg/m3^J 30,2 13,2

Isobaric heat capacity J/(mol K) 30,1 34,4

Dynamic viskosity mg/(s m) 25,8 44,7

Heat conductiviity 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 m³/s 0,002 0,005

Heat flow kW 37

Heat flow density kW/m² 2,0

Reynolds-No. — 4900 2900

Pressure drop mbar 200

Λl

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

Table III

1. Process along curve A

Heating of the feed substances by heat recovery.

Units In the tubes Outside the tubes

Reaction products Feed substances Inflow Outflow Inflow Outflo

Data concerning fluid

Mean moleculary weight g/mol 12,7 12,7 17,6 17,6

Pressure bar 30,2 30,0 31,4 31,0

Temperature^K 3 870 650 560 800

Specific mass kg/πT 5,26 7,02 12,6 8,3

Isobaric heat capacity J/(mol K) 35,3 34,2 46,0 44,2

Dynamic viscosity mg(s m) 32,9 25,2 19,8 27,1

Heat conductiviity mW/(K m) 180 140,2 55,9 80,7

Prandtl-No. — 0,510 0,486 0,925 0,842

Data concerning flow of mass

Mass velocity kg/s 0,58 0,58

Volume velocity m³/s 0,110 0^',083 0,046 0,069

Heat flow kW 350

Heat flow density kW/m² 21,1 14,8

Reynolds-No. — 11500 15100 17700 12900

Pressure drop mbar 40 50 2. Process along curve B

Reforming with heat addition alone by heat recovery

Units In the tubes Outside the tubes

Reaction products Feed substances Inflow Outflow Inflow Outflo

Data concerning fluid

Mean moleculary weight g/mol 12,7 12,7 17,6 17,5

Pressure bar 30,3 30,2 31,0 30,0

Temperature^K 0 800 870

Specific mass kg/n3 940 87 f 4,88 5,26 8,33 7,57

Isobaric heat capacity J/(mol ) 35,7 35,3 44,2 45,7

Dynamic viscosity mg/(s m) 35,2 32,9 27,1 31,1

Heat conductiviity mW/(K m) 192 180 80,7 95,8

Prandtl-No. — 0,517 0,510 0,986 0,991

Data concerning flow of mass

Mass velocity kg/s 0,58 0,58

Volume velocity m³/s 0,119 0,110 0,069 0,077

Heat flow kW 116

Heat flow density kW/m² 21,0 14,7

Reynolds-No. — 10800 11500 12900 11300

Pressure drop mbar 40 200 19

3. Process along curve C

Reforming by heating with heat recocery and electrical heating

Units In the tubes Outside the tubes

Reaction products Feed substances Inflow Outflow Inflow Ourflow

Data concerning fluid

Mean moleculary weight g/mol 12,7 12,7 17,6 12,7

Pressure bar 30,6 30,3 30,9 30,6

Temperature 1285 940 870 1285

Specific mass kg/πr 3,60 4,88 7,57 3,60

Isobaric heat capacity J/(mol K) 38,2 35,7 45,7 38,2

Dynamic viscosity • mg/(s m) 44,6 35,2 31,1 44,6

Heat conductiviity mW/(K m) 248 192 95,8 248

Prandtl-No. — 0,543 0,517 0,843 0,543

Data concerning flow of mass

Mass velocity kg/s 0,58 0,58

Volume velocity m³/s 0,161 0,119 0,077 0,161

Heat flow kW 585

Heat flow density kW/tτT 28,9 20,2

Reynolds-No. 8500 10800 11300 .7900

Pressure drop mbar 60 350

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