Technical and Economic Advances in Steam Reforming of

8

Hydrogen: Production and Marketing Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 02/25/16. For personal use only.

Technical and Economic Advances in Steam Reforming of Hydrocarbons R. G. MINET

KTI Corporation, 221 East Walnut Street, Pasadena, CA 91101 O. OLESEN

United Technologies Corporation, South Windsor, CT 06074 For several decades, the process of high temperature steam

reforming (HTSR) has been the most efficient, economical and

practical technique available for conversion of light hydrocarbons

to hydrogen and hydrogen/carbon monoxide mixtures for eventual

manufacture of ammonia, methanol, oxo-alcohols, pure hydrogen

and a wide range of petrochemicals, chemicals and chemical treatment atmospheres.

Raw materials used range from natural

gas, methane, and methane containing refinery gases through various combinations of light hydrocarbons including ethane, propane, butane, pentane, light naphtha and heavy naphtha (420F end point). Systems have been developed to remove various impurities, principally sulfur compounds, from the feedstock to limit poisoning of the HTSR catalyst which is usually nickel based, promoted with various combinations of alkalai and exotic metals.

The reforming reaction typically is carried out with steam to carbon ratios in the range of 2.5 to 5.0 at process temperatures from 1300 to 1600F and pressures up to 500 psig. Since 1970, significant advances have been introduced in the design, fab-

rication and operation of HTSR equipment and systems which extend the operating range, improve efficiency of use of feed and fuel,

reduce capital cost,

and in the foreseeable future will extend

the technique to include distillate fuel oils as an acceptable

feedstock on a commercial basis. Many of the innovations are essentially extensions of the state of the art which permit

improved efficiency by more complete heat recovery, closer

temperature approaches, and use of superior materials of construction. Some recent advances involve new process steps, new

catalyst and new process engineering ideas. In addition to presenting a brief review of recent improvements, innovations and design approaches, this paper will describe an advance design reformer developed originally by United Technologies Corporation using space age technology concepts

which will soon be placed on-stream to produce hydrogen for fuel

cell use in the generation of electric power (1_). Adoption of

the steam reformer in this system in commercial HTSR facilities

American Chemicaf

0-841&j^^/^tf?fÛ6-147$07.25

© 19ö(T American t^nemical Society

1155 16th St. N. W.

Washington, D. C. 20036

148

HYDROGEN: PRODUCTION AND MARKETING

will significantly alter the size and improve the efficiency, and flexibility of this class of equipment in future process plants making hydrogen from hydrocarbon raw materials.


Conventional Design

A wide variety of basic mechanical designs and arrangements have been used for conventional high temperature steam reforming reactors.

All furnaces include fuel combustion systems, a radiant

heat transfer section where the high temperature required is attained within the reaction tubes, a convection section where the hot gases are cooled to recover the available heat and various auxiliary systems required to supply combustion air, control the combustion process and integrate the furnace with the process unit it serves. There are advantages and disadvantages to all possible flow schemes. By way of illustration, Figure 1 shows several of the most common arrangements which are also summarized in

Table 1.

Various combinations of these configurations are in service in facilities designed to produce hydrogen, hydrogen and carbon monoxide mixtures for ammonia synthesis gas, methanol synthesis gas and carbon monoxide/hydrogen mixtures for the production of a wide range of chemical products ranging from simple alcohols to complex organic chemical molecules.

Since the mid 1970' s , changes in the design of reformers have produced improvements in overall thermal efficiency, accomplished primarily by improved heat recovery in the convection section, ultimately reducing the temperature of the flue gas to the limit imposed by the condensation point of water, or in the case of

some fuels, sulfur trioxide. Extensive use of air preheat in newer designs lowers fired fuel requirements. Fuels utilized in steam reformers have included various

gaseous streams ranging from natural gas to hydrogen-rich fuel gases, process gases of various kinds, purge gases, coke oven gas and various light liquid fuels from naphtha to the No. 2 distillate. The vaporized fuel oil technique licensed by Allied Chemical Company has permitted an extension of the range of liquid fuels which can be handled in radiant burners (2J. Fuel oils heavier than No. 2 have been utilized for firing reformers but these are limited to low sulfur and metal contents by the

metallurgy of the reformer tubes and convection section. Improvements in overall thermal efficiency have been coupled with the introduction of extensive air preheat to decrease the fired fuel requirements. Additional decreases in fired fuel requirements can be obtained by materially improving the radiant box efficiency through changes in radiant box geometry. Usually a balance was struck between the fired fuel requirement to meet

the thermal reactor duty, and the overall need for additional heat for generation of high pressure steam required for the process as a reactant or for driving pumps, compressors, or

8. minet and OLESEN

Steam Reforming of Hydrocarbons


.

5

cc

co

d

coô

149

Od

1

co

2 sags

i

. ^ ^ O

O

»H -P 5J OTi ü H p et O CJ et *h co

TS

O 4et

-P Ö ß O CD

Ct -H

G >

o

|> > .h 4^ o o rd cj rH JQ cd CJ

O -P

O cd JH W

eu

o

H O Jh O

O «H

4^>

co

3 rH

P(

C d p-t c1 cd ct -h

O o

faet '

Hct

d

H

^

^

_j

^

rC

.^ &H

rH

^dCDJH'd

H t

OXîH^dcocr' 4JkrHO O G Ct «H

Ô O !h

-P G

G

-P et

CD

O

Td +> «H

et

^ H

U

_,

S

+5

«n

rH

73 U

O 0

^

^

CD

g

(D tû

etp^rHfj

.G

ß

ctJHCO

H îh O -rCDO GJCt

Eh Ph]

O CD

CD -H 'd

eta)

Ph

5H

-H


8. minet and OLESEN


151

blowers. A typical schematic presentation of the overall flow scheme in a modern high temperature steam reformer loop is given in Figure 2 for a 10 million scf/day hydrogen plant. Using the materials of construction and mechanical design procedures which are typical of the late 1970' s , a conventional high temperature steam reformer would have operating and design parameters approximately as given in Table 2 for a 10 million scf/day hydrogen plant.

Mechanical and Process Innovations (Sections A - H) Designers of HTSR equipment continuously introduce new technology to reduce cost, to improve efficiency and to increase the range of feedstocks and fuels which can be handled. In today's economy, it is clear that yery high thermal efficiency coupled with reasonable flexibility in feedstock and fuel characteristics is required for a viable hydrogen production system. Improvements in technology introduced in the last few years deserve detailed study and evaluation for any current design project. The following paragraphs provide an indication of the effect of the improvement on the overall HTSR design. Burners - Section A

Various processing schemes involving steam reformers require use of fuels having a yery wide range of combustion properties.

At startup, a steam reformer may burn natural gas, LPG or No.

2 fuel oil. When the system is on-stream, at least part of the fuel may be a low heating value gas generated by a process recovery system, as for example, Pressure Swing Adsorption (PSA) purification, or it may be a purge gas from ammonia or methanol synthesis. Such a gas may have a heating value as low as 90 to 150 Btu/cubic foot.

In some cases, the reformer may be fired at

some time during its cycle, utilizing high hydrogen off gas from

a refinery or from some outside process step producing an excess

of fuel. A modern, well designed reformer must accommodate variations in fuel composition without loss of firing efficiency or disruption of the control system.

Multiple gun burners, piped up to handle the anticipated range of fuels for the particular operation are being incorporated in finely tuned steam reformers currently under construction.

A

diagram showing schematic details (3) for such a burner is shown in Figure 3.

Newly available burners can handle both low and

high heating value gaseous fuels with a liquid fuel as well while remaining within permissible limit for noise and N0X restrictions.

Such burners can be used for natural draft and forced draft

installations, with or without air preheat.

152


CM


$ it

s

I

£

.Sr— ¦-

Is" r— ' «

il

Lfi

g W

U-J

—à— f

Hf

.

¦

«

I

I

-s

"8s

____________ |

r^*""^

i

„ — it1]!«

^rHITTa 1 1 r— « « »I « i .^_

**

I

1

| S

DC

—Hi

8. minet and OLESEN


153


ß o •H 4J CJ

d

o u

Ph

ß CD u o

ÎH TÎ

&

ICD

rd

4J

^

co

fi: Eh

rH

Ah rQ CJ CD

O

pq

U

CD

ft

cj cd

«M c, O rH d • w

Eh

43 CD CO fi cd d

_•

T

CD

CD

H rÛ

ft j>>

cd

Eh

Eh

ß CL) ß O rH O -H ? -r4 43 4J H H-> Vr< CdCJCd'H ß cd cj to +3 W ft 'H O rC •H d S ft tCM ß CD B «H

O

P

CdrdOCD

rH CD rd

.HrH'H+3

eIooîsoc/duîsîo

O 4^

ß

H Tl

O O

-H 4*

tû a d JH

ft g CD EH

-j -rH X O

O

0 cj -H > ÎH

cd

,ß 4) 10 ß CD rn

K cd ttO +3

0 4J O

cooQpd

cd

CD

ft

O

I

I

.H o:

to O . -=r

ft CQ EH rd

ft O

ft o rß CO

rH O ft to 43 ß •H

cd rß 43 rd ft cd ß

C

£ 3 -P

•» O ft ft

CD CJ rH ßo 'H r-\ ^ »H CD cd Ti 43 rH ß CD Cd

to Cd to H Cd

CdßrßHrH43

rH

rH «H feO ft O CO 43 X «H £ rß CO cd CD O A*1 43 ßStsoo-H o d > o

to CD 43 ^ ß -H g

-d CD TJ CD CO CO H T} rH «H o ß d o CJßCDOß -H 43 rß £3 43 > OX^cdOO JHOßOH ft 0 d o H vo •» CO CD H X JH043 O

2

"P

tf

>J

S

d rß O rH rH 43 UD IX! «^ CD CD £ Cd«H O ft > O rdrd^-rHOftft

u 43 43

ß

to

•H 00 CD

rQ S I

Q

CD

g

S 43 •H H •H ßrd Ocd .H 43 43rH cdO oft «H CO rH ß

•H

»2Cd

?rH

>> CD 43 CO î» 43 O ß ^ CJ -H ß CD CJßftH Cd £ O CD d »H ß ß 43. H rOr^CDO C0O43'H4343^h rö ,H ^ x CD ß «H CDftcd o ft

-H 'd ß o O

o

s

cd ü

rH

CD

'd CD • O H O -H CDdftPnOCDH CD ft • K O H CD ft ft ft O ft ft

43 O rH ft

43

£ c3 (D 43 Iß

•

43

rH CD -p cd ^

ß


170


PSA SKID

FUEL GAS SURGE

10000J O ' TURBO-COMPRESSOR

SHIFT CONVERTOR SKID

& DEAERATOR

¦» ¦ 4:e Q O il D-

REFORMER & HDS SKID

o

1

=j *

50'

Mar1 :©E II

CC\

V

ttp

Id I. ?

Figure 10. UTC reformer-PSA hydrogen plant (schematic plot plan — KTI Corporation design)

8. minet and OLESEN


171

limitations of HTS reforming systems in use to date is the


process side pressure which can be accommodated and controlled

by the metallurgy and permissible thickness of the reformer tubes. The maximum process side pressure in use today is in the range of 500 psig. By operating the combustion side at an elevated pressure level, it is possible to project to reformer systems which can operate with process side pressures at the level required for methanol synthesis or eventually, certain types of ammonia synthesis utilizing advanced catalytic materials. While such developments are not available at this time for commercial use, design studies made to date by KTI have uncovered no serious obstacle to their realization.

Reforming Distillate Fuel Oils- Section H

The extension of the range of usable feedstocks to include distillate fuel for high temperature steam reforming is under serious and potentially successful development. The objective is to provide a process which can convert commercially available No. 2 fuel oil, having sulfur contents in the range of 0.4 weight %, to hydrogen and carbon monoxide mixtures for production of

ammonia, methanol and hydrogen with the overall efficiency and economy attainable with the high temperature steam reforming process for light hydrocarbon feedstocks.

The approach being used to achieve this result was described recently by KTI reporting on work carried out for the Electric

Power Research Institute (13j. The basic scheme, in block

diagram form, is shown in Figure 12. It consists of a hybrid reactor combining an advanced tubular steam reformer with an autothermal catalytic reformer. This combination overcomes the

limitations of lower catalytic activity in HTSR systems toward the heavier hydrocarbons while retaining a significant part of

the desired process characteristics. Development of the hybrid reactor technique is entering

a bench scale experimental program, to be followed with a small scale prototype unit scheduled for operation late in 1979. Summary and Conclusions Advances in the technology of high temperature steam re-

forming are being made continuously to provide improvements in efficiency, feedstock range and operating parameters. A review of recent advances gives unmistakable evidence that vigorous development activity with fresh view points will materially im-

prove cost and operating factors for this extremely useful process

technique. Application of the new heat recovery techniques, mechanical materials of construction and combustion systems to conventional reformer furnace design will help to keep the HTSR even with material and feedstock cost escalation. Adoption of the


172


Figure 11. Steam reformer modules conceptual arrangement for 1000 tons /day ammonia plant

BURNER FUEL INLET

-j- n/ I

8" FLANGE

^^__'

\ BURNER

^^ — ^^^^

^^^¦fr

^^K^nU

^" i DIAMETER i

.BURNER

^\X IGNITOR

112"

-

^^KL /- — \ /^ BURNER ^^^K f*^£X ^-^^ EXHAUST ^^^B (•mmtX^^^

F/l^K

! m^^m

P0RT

Jfäj 6" FLANGE

JzM^^K^mtf^\sS

/^ ^k /process

ôAf gas EXIT

PROCESS GAS INLET

Figure 12. Steam reformer under construction for 4.8-MW fuel cell demonstrator power plant (to be operated by Con Edison in New York City)


8. minet and OLESEN


-

cc

r

"1

*

Technical and Economic Advances in Steam Reforming of

Recommend Documents