WO1998023707A1

WO1998023707A1 - Two-zone molten metal hydrogen-rich and carbon monoxide-rich gas generation process

Info

Publication number: WO1998023707A1
Application number: PCT/US1996/019081
Authority: WO
Inventors: Thomas C. Holcombe; Donald P. Malone
Original assignee: Ashland Inc.
Priority date: 1996-11-25
Filing date: 1996-11-25
Publication date: 1998-06-04
Also published as: AU1275697A; JP2001507050A; EP0946680A4; EP0946680A1

Abstract

A high pressure two-zone molten iron gasification process for converting solid, liquid and gaseous hydrocarbon feeds into separate substantially hydrogen-rich and carbon monoxide-rich streams at 2 to 200 atmospheres pressure by feeding hydrocarbons into the molten iron in a first zone (4) in which hydrogen-rich gas is formed and then circulating the molten iron into contact with an oxygen containing gas in a second zone (5) in which carbon monoxyide-rich gas is formed. The carbon level in the circulating molten iron is carefully controlled above 0.3 wt. % to minimize formation of FeO. Hydrogen sulfide and other volatile sulfur compounds are removed from the separate gas streams via scrubbing in downstream equipment (12 and 16).

Description

TWO-ZONE MOLTEN METAL HYDROGEN-RICH AND CARBON MONOXIDE-RICH GAS GENERATION PROCESS

This application is a Continuation-in-Part to USSN 08/421,102, filed April 13,

1995, (attorney's docket 6391NUS) now US 5,577,346.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to Attorney's Docket 6391QPC, filed November

25, 1996, and Attorney's Docket 6391PPC, filed November 25, 1996.

BACKGROUND OF THE INVENTION

I. FIELD OF THE INVENTION

This invention relates to a process of conversion of hydrocarbons via

gasification into two high pressure gas streams: a hydrogen-rich stream and a carbon-

monoxide-rich stream. More specifically, this invention relates to the use of a two-

zone predominantly molten iron or molten iron alloy system in conjunction with the

above gasification conversion.

II. DISCUSSION OF THE PRIOR ART

Two-zone molten iron gasifiers are disclosed by:

U.S. Patent 1,803,221 (1931) to Tyrer describes hydrogen-rich gas production

by feeding methane or a methane-steam mixture into one molten iron zone below the

surface of the metal, thereby assuring complete reaction of the gaseous feed. The carbon which dissolves in the molten iron in the first zone is bumed out of the molten

iron in the second zone with an oxygen containing gas. Additional oxygen containing

gas may be added to the combustion products leaving the second zone to completely

oxidize to carbon dioxide any carbon monoxide remaining.

The disadvantages of the process described in this patent include:

The feedstocks are limited to hydrocarbon gases such as methane and do not

include lower value hydrocarbon liquids or solids.

Operating pressure is nominally atmospheric pressure which is less economical

to operate than equipment producing hydrogen at elevated pressures; two atmospheres

and above.

The importance of controlling the carbon level in the molten iron is not

considered and thus production of only lower purity hydrogen-rich gas is possible. If

a minimum carbon level of at least 0.3% is not maintained, excess iron oxide will

form in the molten iron during oxidation and will be converted to carbon monoxide

and dilute the hydrogen-rich gas when hydrocarbon feeds are introduced to the

hydrogen-rich gas producing first zone.

U.S. Patents 4,187,672 (1980) and 4,244,180 (1981) to Rasor describe a

hydrocarbon gasification process in which solid hydrocarbons such as coal are

introduced on the surface of one molten iron bath zone in which high temperature

cracking of the hydrocarbons into lighter molecular weight materials takes place with residual carbon being dissolved in the molten iron. The cracked hydrocarbon products

are removed via outlets in the shaft through which the feed hydrocarbon solids enter

the molten iron. The molten iron containing the carbon is transferred to the second

molten iron zone in which an oxygen containing gas is introduced to convert the

carbon into carbon monoxide and raise the temperature of the iron for transfer back

to the carbonization section. The carbon monoxide is further oxidized above the

molten iron bath and the heat recovered via a boiler or similar system. Sulfur, if

present in the feed, is removed via slag formation on top of the molten iron. The

disadvantages of the process described in this patent include:

The feedstocks are limited to solid hydrocarbons such as coal and do not

include lower value hydrocarbon liquids or gases.

Since the solid hydrocarbon feeds are introduced above the surface of the

molten iron, cracking of the feeds occurs such that a very impure hydrogen gas stream

is produced because of the presence of cracked hydrocarbon gases.

Since the product gas from the oxidation zone is further oxidized for energy

recovery in, for example, a steam boiler, no attempt is made to produce a carbon

monoxide-rich gas.

Sulfur removal from the solid feed via reaction with and removal of slag from

the equipment is complicated and expensive. Operating pressure is nominally atmospheric pressure, which is less

economical to operate that equipment producing hydrogen at elevated pressures; two

atmospheres and above.

The importance of controlling the carbon level above 0.3% in the molten iron

is not considered and thus production of only lower purity hydrogen-rich gas is

possible.

U.S. Patent 5,435,814 (1995) to Miller and Malone (Ashland) describes the

general concept of a two-zone molten iron system process operating at high pressures,

up to J 00 atmospheres, with solid and liquid feed introduction below the surface of

the molten iron and production of a hydrogen-rich and carbon monoxide rich gas

streams. The disadvantages of the process described in this patent include:

There is no method described for handling the feedstock sulfur.

The importance of controlling the carbon level in the molten iron is not

considered and thus production of only lower purity hydrogen-rich gas may be

possible. The process is restricted to a particular method of circulating molten iron.

In summary, all of the above patents operate at atmospheric pressure and do not

control carbon at a minimum of 0.3% in molten iron. Furthermore, the Rasor patents

do not inject feed below the surface of the molten iron and are restricted to solids

feeds. Furthermore, all the patents ignore sulfur in the feed or use slag to remove it.

One-zone molten metal gasifiers are disclosed by: U.S. Patents 4,496,369 (1985) to Tomeman and 4,511,372 (1985) to Axelsson

in which coal or other liquid hydrocarbons are injected advantageously below the

surface of the molten iron along with oxygen and water vapor to form a mixed

hydrogen and carbon monoxide gas. Iron oxides are also added to the molten iron to

act as a coolant for the melt. The primary objective of the invention is to produce

gasified hydrocarbons and it is disclosed that production can be increased by operating

at high pressures. The high pressures are not only economic because of the reduced

size of equipment but it is also disclosed that high pressure decreases the degree of

refractory wear in the reactor and the amount of dust cany-over in the gas from the

reactor. In addition, it is disclosed that a higher sulfiir level in the molten bath will

also reduce the amount of dust carry-over from the reactor. The process disclosed

cites the advantage of maintaining the carbon content of the bath below 0.8% carbon

to reduce the amount of dust carry-over from the reactor.

The primary disadvantage of the process described in this patent include the

lack of separate molten iron zones for gasification and thereby does not permit

production of individual hydrogen-rich and carbon monoxide-rich gas streams.

U.S. Patents 4,574,714 and 4,602,574 (1986) to Bach and Nagel in which solid

or liquid toxic and/or lower value hydrocarbons are injected advantageously below

the surface of the molten iron alloy, along with oxygen specifically to destroy the toxic

compounds. With appropriate feeds a mixed hydrogen and carbon monoxide gas can be formed and Cl chemistry may be utilized to advantage at times to produce useful

products. It is further disclosed that maintaining a carbon level of 0.5-6% carbon,

preferably 2-3% carbon in the molten metal is desired to prevent refractory

degradation and facilitate reaction kinetics by providing a high concentration gradient

for toxics destruction. Sulfiir, when present in the feed, is removed via absoφtion in

the slag. The disadvantages of the process described in this patent include:

The feedstocks are introduced to the molten iron single zone system for

destruction as hazardous materials and not to produce hydrogen-rich or carbon

monoxide-rich gases and thereby misses the advantages of feeding non-hazardous

feedstocks.

Sulfiir removal from the solid feed via reaction with and removal of slag from

the equipment is complicated and expensive.

Operating pressure is nominally atmospheric, which is less economical to

operate than equipment producing gases at elevated pressures; two atmospheres and

above. Also, rotating gasification vessels on trunnions for slag removal makes

operating at higher pressures impractical.

The importance of controlling the carbon level in the molten iron at more than

0.3% is not considered and thus production of only lower purity hydrogen-rich gas is

possible. The primary disadvantage of the process described in this patent include the

lack of separate molten iron zones for gasification and thereby does not permit

production of individual hydrogen-rich and carbon monoxide-rich gas streams.

The following foreign patents also disclose processes related to that of this

application.

U.K. Patent 1,187,782 (1970) to Nixon discloses a reactor in which a

hydrocarbon is introduced to one zone resulting in the production of a hydrogen-rich

gas and oxygen is introduced into a second zone where the carbon which was

dissolved in the first zone is bu ed with oxygen to give the exothermic heat to

maintain the appropriate temperature in the first zone. It is noted that the two zone

system as described has an advantage over hydrogen production in a single zone

system wliich is operated in "blocked out" operations equivalent to that of a two zone

system. It is further disclosed that sulfur present in the iron may be removed,

purifying to some extent the iron. The disadvantages of the process described in this

patent include:

Since no attempt is made to produce a carbon monoxide-rich gas in the

oxidation zone, only a hydrogen-rich gas stream is produced.

Operating pressure is nominally atmospheric pressure, wliich is less economical

and above. The importance of controlling the carbon level above 0.3% in the molten iron

is not considered and thus production of only lower purity hydrogen-rich gas is

possible.

One embodiment of U.K. Patent 1,437,750 (1976) to Agarwal and Aimer

describes producing a combustible gas containing a ratio of hydrogen to carbon

monoxide of between 2:5 to 10:1 using a two-zone molten iron reactor with a coal

feed to the top of one zone. Although the gases are produced in separate zones after

further conversion with, for example, the water gas shift reaction, they are combined

so the product from the system is a single combustible gas. Carbon concentrations in

the molten iron are between 1 and 3% in the first zone and between 3 and 5% in the

second zone. The disadvantages of the process described in this patent include:

The feedstocks are limited to solid hydrocarbons such as coal and do not

include lower value hydrocarbon liquids or gases.

Since the solid hydrocarbon feeds are introduced above the surface of the

is produced because of the presence of cracked hydrocarbon gases.

Since the product gas from the oxidation zone is combined with the gas from

the first zone, no attempt is made to produce a carbon monoxide-rich gas.

No disclosure is made concerning sulfiir removal from the solid feed via

reaction in the molten metal zones. Operating pressure is nominally atmospheric pressure, which is less economical

to operate that equipment producing hydrogen at elevated pressures; two atmospheres

and above.

U.K. Patent 2,189,504 (1987) to Herforth describes a two-zone molten iron

reactor in which low grade solids fuels are gasified in one zone and high grade solid

fiiels are gasified in the second zone. This permits the low grade solid fuels and waste

materials to be consumed and produce a low quality off-gas where as the gasification

of high grade fuels in the second zone permits production of a high quality off-gas

unmixed with the low quality off-gas while still peπnitting destruction of the low grade

fiiels or waste materials. The sulfur is removed in the slag formed in the reactors. The

disadvantages of the process described in this patent include:

The feedstocks are limited to solid hydrocarbons such as coal and do not

include lower value hydrocarbon liquids or gases.

Since the solid hydrocarbon feeds are introduced above the surface of the

is produced because of the presence of cracked hydrocarbon gases.

No attempts are made to produce either a hydrogen-rich or carbon monoxide-

rich off-gas.

Sulfiir removal from the solid feed via reaction with and removal of slag from

the equipment is complicated and expensive. Operating pressure is nominally atmospheric pressure, which is less economical

and above.

French Patent 2,186,524 (1974) to Vayssiere describes a two-zone molten iron

system with a hydrogen-rich gas generated from hydrocarbons injected beneath the

surface of the molten iron in one zone and either a carbon monoxide-rich gas or

mixture of hydrogen and carbon monoxide gas generated by injecting oxygen or

oxygen and hydrocarbon into the second zone. The disadvantages of the process

described in this patent include:

There is no provision for removal of the sulfiir in the feed.

Operating pressure is atmospheric pressure, wliich is less economical to operate

that equipment producing gases at elevated pressures; two atmospheres and above.

The importance of controlling the carbon level above 0.3% in the molten iron

is not considered.

In summary, while such systems referenced above may provide reasonable

results, none of them effect the production of a separate hydrogen-rich stream and a

separate carbon monoxide-rich stream at elevated pressures by feeding hydrocarbons

below the surface of the molten iron and with controlled carbon contents of the molten

metal above 0.3%. Furthermore, these systems either have no provision for handling

feed sulfiir or use a complicated and costly slag technique for sulfiir removal. Sulfiir capture in the slag requires slagging materials to be added to the molten metal zones

and a more complicated means of regularly drawing off the sulfiir containing slag.

When sulfur is captured in slag the slag must then be disposed of, typically in

uneconomic and environmentally unsound landfills

5 Thus, our survey of prior practices indicates that the prior art has not combined

the use of two zone molten iron gasifiers for separate hydrogen-rich and carbon

monoxide-rich gas production, feed introduction below the molten iron surface, high

pressure operation and carbon content control of the molten iron in the manner we

have.

l o SUMMARY OF THE INVENTION

Broadly, this invention involves a process for producing in separate streams a

hydrogen-rich gas and a carbon monoxide-rich gas from two molten metal zones and

necessary ancillary equipment. Molten metal components are intended to include any

molten material layer within a particular zone; e.g., molten metals, such as iron and

15 its alloys, which are always present and slag components, if present, that would foπn

a second molten layer with such molten metals. The molten metal employed in this

invention is preferably molten iron but may be copper, zinc, especially chromium,

manganese, or nickel, or other meltable metal in which carbon is somewhat soluble

and which is at least 50% molten iron by weight. In the first molten metal zone, a hydrocarbon feed in the form of a relatively

dry gas or liquid or solid or solid-liquid slurry or atomized solid or liquid is fed

beneath the molten metal surface and a hydrogen-rich gas is produced. By relatively

dry is meant below 1 % by weight of water. By introducing the feed below the surface

of the molten metal substantially complete chemical reactions and conversions to

hydrogen and carbon of the feed can be acliieved. The carbon in the hydrocarbon feed

dissolves in the molten metal.

In the second molten metal zone, into which molten metal from the first molten

metal zone flows, an oxygen bearing stream is introduced to convert the carbon

dissolved in the molten metal from the first zone into a carbon monoxide-rich gas

stream which exits from above the molten metal bath in a gas stream separate from the

hydrogen-rich gas stream from the first molten metal zone. Molten metal from which

the carbon has been gasified by oxygen in the second zone is returned to the first

molten metal zone.

Both molten metal zones are operated at elevated pressures, above two

ahnospheres, to reduce the size of the equipment need to produce and further treat, if

necessary, the hydrogen-rich and carbon-monoxide rich gases. In addition, as

disclosed is U.S. Patent 4,511,372 incoφorated by reference, operation at high

pressures reduces dust carry over and wear on refractory walls of the vessel.

Furthermore, the capital and operating costs of compression, of these gases to pressures at which they are utilized commercially are eliminated or substantially

reduced.

Furthermore, in this process the amount of carbon in the molten iron to which

the hydrocarbon feed is introduced is carefully controlled to above 0.3% to minimize

formation of high levels of FeO, ferrous oxide, which could include a separate FeO

phase. High levels of FeO will react with the carbon in the hydrocarbon feed and

produce high levels of carbon monoxide, thereby contaminating the hydrogen-rich

stream. If a separate phase of FeO is present it will attack the refractory of the vessels

holding the molten iron. The amount of carbon in the molten iron should not normally

exceed an upper limit as determined by its solubility in molten iron.

This invention also includes having the hydrogen-rich and carbon monoxide-rich

gases flowing from the molten metal zones through separate product gas lines to pass

through successive downstream coolers, scrubbers or other gaseous impurity removal

devices, and knock-out drums to cool the gases and to remove any solids and any

condensed liquids from the gas streams. The gases may further be fed to proven

scrubbers which remove hydrogen sulfide and other volatile sulfiir compounds

produced in the molten metal zones and emit a substantially sulfur-free and carbon

oxide-free hydrogen-rich product gas and a substantially sulfur-free carbon monoxide-

rich product gas. Suitable feeds for the process include carbonaceous reactant feedstocks

selected from the group consisting of: light gaseous hydrocarbons such as methane,

ethane, propane, butane, natural gas, and refinery gas; heavier liquid hydrocarbons

such as naphtha, kerosene, asphalt, hydrocarbon residua produced by distillation or

other treatment of crude oil, fuel oil, cycle oil, slurry oil, gas oil, heavy crude oil,

pitch, coal tars, coal distillates, natural tar, crude bottoms, and used crankcase oil;

solid hydrocarbon such as coal, rubber, tar sand, oil shale, and hydrocarbon polymers;

and mixtures of the foregoing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a drawing of the basic process of this invention.

Figure 2 is a drawing of a variation of the process of this invention

incoφorating scrubbing systems to remove hydrogen sulfide and other volatile sulfur

compounds from the hydrogen-rich and carbon monoxide-rich gases made in the

process.

Figure 3 is a drawing of a variation of the process of this invention

incoφorating the use of feed and product valving systems to/from two molten metal

reactors to duplicate the effect of creating two molten metal zones separately by feed

and product control systems instead of transferring the molten metal between two

zones of a single reactor. DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates the invention in a simplified diagram of an apparatus for

carrying out the basic process. Molten iron 2 is contained in the vessel 1. The molten

iron in vessel 1 is maintained at a temperatures between 1 150° and 1750°C

(2102°-3182°F) to keep it substantially liquid. Partition 3 divides the vessel into two

zones 4 and 5. A hydrocarbon feed in the foπn of a relatively dry liquid or solid or

solid-liquid slurry or atomized solid or liquid in a gas is fed through tuyere pipe 6 or

lance pipe 7 beneath the molten metal surface of zone 4 in which the hydrocarbon is

converted to a hydrogen-rich gas which escapes from the surface of the molten metal

and carbon which dissolves in the molten metal. The hydrogen-rich gas exits zone 4

via pipe 10 and enters a cooling system 11 where it is cooled to temperatures suitable

for its introduction into commercial hydrogen-rich gas consuming processes. Suitable

equipment for controlling the pressure above 2 atmospheres is provided before the

hydrogen-rich gas is sent to a consuming process via pipe 13. Molten iron containing

dissolved carbon from zone 4 is transferred to zone 5 and oxygen is introduced

beneath the molten metal surface in zone 5 through tuyere pipe 8 or lance pipe 9. The

carbon in the molten iron in zone 5 is converted to a carbon monoxide-rich gas in zone

5 and exits the vessel via pipe 14 and enters a cooling system 15 where it is cooled to

temperatures suitable for its introduction into commercial carbon monoxide-rich gas

consuming processes. Suitable equipment for controlling the pressure above 2 atmospheres is provided before the carbon-monoxide-rich gas is sent to a consuming

process via pipe 17.

The following additional features characterize the process illustrated in

Figure 1 :

Suitable feeds for the process introduced via tuyere pipe 6 or lance pipe 7

include carbonaceous reactant feedstocks selected from the group consisting of: light

gaseous hydrocarbons such as methane, ethane, propane, butane, natural gas, and

refinery gas; heavier liquid hydrocarbons such as naphtha, kerosene, asphalt,

hydrocarbon residua produced by distillation or other treatment of crude oil, fuel oil,

cycle oil, slurry oil, gas oil, heavy cmde oil, pitch, coal tars, coal distillates, natural

tar, cmde bottoms, and used crankcase oil; solid hydrocarbon such as coal, mbber, tar

sand, oil shale, and hydrocarbon polymers; and mixtures of the foregoing.

If the feeds introduced via tuyere pipe 6 or lance pipe 7 include sulfur, the

sulfiir will be removed from the system via its capture in a slag floating on the molten

iron in zones 4 and 5. Or the sulfur will remain as hydrogen sulfide or other volatile

sulfiir compounds in the hydrogen-rich and carbon monoxide-rich gas streams and go

to the gas consuming processes via pipes 13 and 17.

Any dust and fume generated as part of the process in zones 4 and 5 will be

removed from the hydrogen-rich and carbon monoxide-rich gas streams via

conventional means such as bag filters which are part of the gas cooling systems 11 and 15.

The amount of carbon in the molten iron which is returned to zone 4 from

zone 5 to which the hydrocarbon feed is introduced is carefully controlled to above

0.3%) at all times to minimize foπnation of a separate phase of FeO, ferrous oxide. If

present in substantial amounts, the FeO will react with the carbon in the hydrocarbon

feed entering via tuyere pipe 6 or lance pipe 7 and produce carbon monoxide thereby

diluting the hydrogen-rich stream exiting zone 4 via pipe 10. In addition, FeO in a

separate phase will attack the refractory lining of vessels holding the molten iron. The

amount of carbon in the molten iron which passes from zone 4 to zone 5 should not

nonnally exceed an upper limit as set by the solubility of carbon in molten iron.

The molten metal employed in this invention as bath 2 is preferably and

predominantly molten iron but may be copper, zinc, especially chromium, manganese,

or nickel, or other meltable metal in which carbon is somewhat soluble but is at all

times at least 50 wt.% molten iron.

5 Figure 2 is drawing of a variation of the basic process. In addition to

incorporating all the elements of Figure 1 including the description above, in this

variation the sulfiir in the feed is allowed to build up to equilibrium levels in the

molten metal and slag in zones 4 and 5. At equilibrium, the sulfur compounds in the

slag and metals will be converted to hydrogen sulfide and other volatile sulfiir

o compounds in zones 4 and 5 and exit in the hydrogen-rich and carbon monoxide-rich gases via lines 10 and 14. After cooling in systems 11 and 15 the sulfur compounds

are removed from the gases by conventional means such as amine scmbbing, caustic

scrubbing, or other suitable sulfur compound removing devices, etc. in sulfiir removal

systems 12 and 16 before the now essentially sulfur-free gases enter the gas

consuming processes via pipes 13 and 17. The advantage of this mode of operation

is a reduced production of slag and reduced dust fonnation as shown in the prior art,

U.S. Patent 4,51 1,372 which is hereby incoφorated by reference.

Figure 3 is a drawing of another variation of the process incoφoration all of the

applicable descriptions of Figures 1 and 2 and incoφorating the use of feed and

product valving systems to/from two molten metal reactors to duplicate the effect of

creating two molten metal zones separated by feed and product control systems

instead of transferring the molten metal between two zones of a single reactor.

In this variation, as shown in Figure 3, the process comprises two (or more)

identical systems perfoπning functions comparable to the systems in Figures 1 and 2

and including: vessels 1 1 and 21 holding molten iron in baths 12 and 22; feed tuyere

pipes 16 and 26 and alternative feed lance pipes 17 and 27 for introducing

hydrocarbon feeds below the surface of the molten iron 12 and 22; feed tuyere pipes

18 and 28 and alternative feed lance pipes 19 and 29 for introducing oxygen below the

surface of the molten iron 12 and 22; vessel exit pipes 10 and 20; gas cooling systems

13 and 23; and product gas pipes 60 and 50. This system duplicates the two-zone reactor system of Figures 1 and 2 by

creating the equivalent of two zones with the use of suitable valves and control

systems on the feeds to vessels 11 and 21 and the product gases exiting the cooling

systems 13 and 23 via pipes 60 and 50. Thus, the control systems are operated such

that while hydrogen-rich gas is being made in vessel 1 1 and carbon monoxide-rich gas

is being made in vessel 21. After an appropriate length of time operating in this mode

the feed and product control systems switches the feeds and products and hydrogen-

rich gas is made in vessel 21 and carbon monoxide-rich gas is made in vessel 1 1. The

hydrocarbon feed system is described as follows: hydrocarbons are conducted to the

system in pipe 40 which divides into pipes 41 and 44; pipe 41 leads to valve 42 and

pipe 43 which is connected to tuyere pipe 26 or lance pipe 27 in vessel 21; pipe 44

leads to valve 45 and pipe 46 which is connected to tuyere pipe 16 or lance pipe 17

in vessel 1 1 . The oxygen feed system is described as follows: oxygen is conducted

to the system in pipe 30 wliich divides into pipes 31 and 34; pipe 31 leads to valve 32

and pipe 343 which is connected to tuyere pipe 28 or lance pipe 29 in vessel 21 ; pipe

34 leads to valve 35 and pipe 36 which is connected to tuyere pipe 18 or lance pipe

19 in vessel 11. The detennination of whether hydrocarbons or oxygen are fed to

either vessel 1 1 or 21 is deteπnined by whether valves 32, 35, 42 and 45 are open or

shut; these settings, in turn, being established by the control system. The product gas systems from vessel 11 is described as follows: product gases

exit vessel 1 1 via pipe 10, pass through cooling system 13 and enter pipe 60; the gases

may then go via pipe 61 through valve 62 into pipe 63 and pipe 54 connecting with the

commercial processes using hydrogen-rich gas; or the gases may go via pipe 65

through valve 66 into pipe 67 and pipe 58 connecting with the commercial processes

using carbon monoxide-rich gas. The product gas systems from vessel 21 is described

as follows: product gases exit vessel 21 via pipe 20, pass through cooling system 23

and enter pipe 50; the gases may then go via pipe 51 through valve 52 into pipe 53 and

pipe 54 connecting with the commercial processes using hydrogen-rich gas; or the

gases may go via pipe 55 through valve 56 into pipe 57 and pipe 58 connecting with

the commercial processes using carbon monoxide-rich gas. The routing of each gas

is deteπnined by whether valves 62, 66, 52 and 56 are open or shut; these settings,

in turn, being established by the control system.

As an example of the operation of the system in Figure 3, if hydrogen-rich gas

were being produced in vessel 1 1 and carbon monoxide-rich gas were being produced

in vessel 21, the following valves would be open; 45, 32, 62, 56, and closed; 42, 35,

66, 52. These valve settings would be reversed when hydrogen-rich gas were being

produced in vessel 21 and carbon monoxide-rich gas were being produced in vessel

11. The system for Figure 3 has been described in simple terms for the general

concept. A more detailed description of the operation is given in USSN 08/425,938, filed April 19, 1995, (attorney's docket 6501AUS) which is incoφorated by reference.

This application also describes the use of three molten metal vessels, instead of two,

with a similar valving and control system to peπnit continuous gasification operations

when one reactor must be out of service for repairs, etc. This feature is also included

in the present disclosure by reference.

Another variation of the process is to use an oxygen enriched gas as the source

of oxygen through tuyere pipe 8 or lance pipe 9 (Figures 1 and 2) for gasifying the

dissolved carbon in the molten metal in zone 5.

Another variation of the process is to use liquid feedstocks prior to their

introduction to the system via tuyere pipe 6 or lance pipe 7 as a scmbbing medium in

the cooling sections 11 and 15 for dust and fume removal from the hydrogen-rich and

carbon monoxide-rich product gases exiting vessel 1 through pipes 10 and 14 (Figures

1 and 2).

Another variation of the process is to use a quantity of hydrogen-rich gas from

pipe 13 (Figures 1 and 2) or elsewhere in the system to atomize liquid hydrocarbon

feeds as they are introduced to zone 4 via tuyere pipe 6 or lance pipe 7.

Another variation of the process is to use a quantity of carbon monoxide-rich

gas pipe 17 (Figures 1 and 2) or elsewhere in the system to cool tuyere pipe 8 or lance

pipe 9 introducing the oxygen to the molten metal in zone 5. Another variation of the process is to use a quantity of water vapor or steam to

cool tuyere pipe 8 or lance pipe 9 introducing the oxygen to the molten metal in zone

5 and to moderate the temperature in zone 5.

Another variation of the process is to use a quantity of carbon dioxide gas to

5 and to moderate the temperature in zone 5.

Another variation of the process is to use a quantity of methane gas to cool

tuyere pipe 6 or lance pipe 7 introducing the feed to the molten metal in zone 4 and

to moderate the temperature in zone 4.

The following explanation details the importance to this invention of controlling the

amount of oxygen introduced to the carbon monoxide-rich gas generation section such

that the carbon content of the molten iron returned to the hydrogen-rich gas generation

section is above a minimum value and thereby ensures that the hydrogen-rich gas

contains a minimum of impurities. It also emphasizes the importance of these controls

particularly when operating at the high pressures of this invention. Reference (by

page number and/or figure number) are made to the data in the book, "The Making,

and Steel Engineers. The desired primary chemical reaction taking place in the hydrogen-rich gas

generation section of this invention involves the gasification of a hydrocarbon feed

(CH_n):

CH_n = n/2 H₂ (hydrogen gas) + C- Fe (carbon dissolved in molten iron) (1)

However, two important and undesirable secondary reactions will take place between

the carbon in the feed and any oxygen and iron oxide (FeO) which is present in the

molten iron:

C + O - Fe (oxygen dissolved in molten iron) = CO (carbon monoxide gas) +

Fe(molten) (2)

C + FeO (separate phase in molten iron) = CO (carbon monoxide gas) + Fe

(molten) (3)

Reactions (2) and (3) are undesirable since carbon monoxide gas is generated which

dilutes the hydrogen gas produced by reaction (1) and thereby requires more extensive

hydrogen-rich gas purification facilities. In addition, it is known that FeO in a

separate phase will attack refractory linings of vessels holding molten iron to a greater

extent than just molten iron so that the conditions for Reaction 3 to take place should

be minimized or eliminated, that is, there should be no separate FeO phase present

with the molten iron. Similarly, the desired chemical reaction taking place in the carbon monoxide-

rich gas generation section of the invention involves the oxidation of the carbon

dissolved in the molten iron coining from the hydrogen-rich gas generation section:

2C - Fe (carbon dissolved in molten iron) + 0₂ = 2CO + Fe(molten) (4)

Again, there are two undesirable secondary reactions which take place between the

iron and the oxygen fed to this section:

Fe + 0₂ = O - Fe (oxygen dissolved in molten iron) (5)

2Fe + 0₂ = 2FeO (separate phase in molten iron) (6)

Note that the chemical elements shown in the above equations are illustrative

of the materials involved and the processes taking place but may not necessarily

represent the actual molecular species which may be present. For example,

experimental evidence has shown that: a) oxygen dissolved in molten iron may be

present as dissolved FeO or in other iron/oxygen ratios; b) carbon dissolved in molten

iron may be present as dissolved FeC or in other iron/carbon ratios.

It is an important feature of this invention that the process must be controlled

based on a complete understanding of the factors which control the degree to which

all the above reactions, and in particular the secondary reactions (reactions 2, 3, 5, 6)

will take place. The following quantitative relationships are critical to this

understanding. When oxygen and molten iron are present, oxygen is soluble to a limited extent

in molten iron; the maximum solubility being 0.16% at 1527°C (2781 °F) (page 405 in

reference). Graphically, the solubility of oxygen at other temperatures is presented

in Figure 13-542 while mathematically it is described by (page 406):

log [wt.% O] = - 6320/T(°K) + 2.734 (7)

If more oxygen is added to molten iron than will be soluble according to the above,

the oxygen reacts with the iron and a separate FeO phase is foπned (page 405).

When oxygen and carbon and molten iron are present, the amount of oxygen

in the molten iron as well as the amount of carbon in the molten iron are related

according to the following reaction (page 674):

CO (pressure above molten iron) = O + C (concentrations in molten iron)(8)

and equation

K = [ t.%C]x[wt.% 0]/Pco (partial pressure CO, atm) (9)

log K = -1168/T (°K) - 2.07 (10)

The fact that the concentrations of carbon and oxygen dissolved in molten iron are

proportional to and affected by the partial pressure of the carbon monoxide above the

molten iron is critical to the process control and successful commercial application of

this invention. This trend is illustrated by the following example.

According to Equation 7 the solubility of oxygen in molten iron at 1482°C

(2700°F) is 0.136 wt.%. Thus, if more than 0.136 wt.% oxygen is present in the molten iron, it will be present as a separate phase of FeO. According to Equation 9,

the following amounts of oxygen will be present in molten iron at 1482°C (2700°F)

when the molten iron contains 0.3 wt.% and 4.5 wt.% carbon at various pressures of

carbon monoxide above the molten iron bath:

CO Pressure, psia wt.% O at 0.3% Carbon wt.% Oat 4.5% Carbon

0.147 0.000061 0.000004

1.47 0.000613 0.000041

14.7 0.00613 0.00041

294.0 0.1226 0.0082

485.1 0.2023 0.0135

735.0 0.3060 0.0204

It is observed that, when the CO pressure is at 485.1 or 735.0 psia and the

carbon in the molten iron is at 0.3 wt.%, the amount of oxygen is present in the

molten iron is above 0.136 wt.%> (the maximum solubility of oxygen) and thus a

separate FeO phase will also be present. These are conditions under which the carbon

monoxide-rich section of the invention could be operated and would be the

composition of the molten iron circulated to the hydrogen-rich gas generation section.

When circulated back to the hydrogen-rich gas generation section the pressure of the

carbon monoxide would be minimum and the dissolved oxygen and FeO would react

be released as carbon monoxide into the hydrogen-rich gas by Reactions 2 and 3

above and thereby dilute the hydrogen-rich gas. In addition the refractory holding the

molten iron would be subject to attack by the FeO. Although, the amount of dissolved

oxygen in the molten iron cannot be controlled, the amount of FeO as a separate phase can by controlling the amount of carbon in the molten iron in the carbon monoxide-

rich gas generation section. This would be done by regulating the amount of oxygen

introduced into the carbon monoxide-rich gas generation section such that the amount

of carbon in the molten iron did not fall below a specific prescribed level for the given

operating conditions. According to Equation 9 at 1482°C (2700°F) the amount of

carbon in the molten iron to minimize the foπnation of a separate phase of FeO should

be above 0.446 wt.% at 485.1 psia and 0.676 wt.% at 735 psia.

While using specific quantities for demonstration puφoses, the above example

illustrates the trends involved in the control of the operations of the invention but in

no way limits the operating conditions to those shown. Other operating temperatures

and pressures will deteπnine appropriate carbon and oxygen content limitations for the

molten iron.

What is claimed is:

Claims

1. A process for generating both a hydrogen-rich gas stream and a carbon

monoxide-rich gas stream at a pressure in the range of 2 to 200 atmospheres said

process comprising;

a) introducing into a first molten metal zone operating at

1200°-2550°C (2192°-4532°F) and at 2 to 200 atmospheres a hydrocarbon feed

in the fonn of a relatively dry, less than 1% by weight of water, gas or liquid or

solid or solid-liquid slurry or atomized solid or liquid in a gas beneath the

molten metal surface of the zone in which the hydrocarbon is converted to a

hydrogen-rich gas which escapes from the surface of the molten metal, and to

carbon which dissolves in the molten metal;

b) transferring at least a portion of the first molten metal zone to a

second molten metal zone; reducing the carbon content of the second molten

metal zone by adding a controlled amount an oxygen containing stream to

oxidize carbon in the second molten metal zone and to produce a carbon

monoxide-rich gas stream;

c) recycling at least a portion of the second molten metal zone back

to the first molten metal zone such that the amount of carbon in the molten iron

winch is returned to the first zone from the second zone is carefully controlled to be above 0.3 wt.% to minimize foπnation of a high level of FeO, ferrous

oxide, possibly including a separate phase of FeO;

d) passing said separate hydrogen-rich gas and carbon monoxide-

rich gas streams out of their respective zones and cooling them to temperatures

suitable for their introduction into commercial hydrogen-rich gas and carbon

monoxide-rich gas consuming processes and controlling the pressure of each

gas stream at above 2 atmospheres;

e) removing any sulfiir in the feeds via its capture in a slag floating

on the molten iron in both zones or allowing the sulfiir to build up to

equilibrium levels in the molten iron and leave as hydrogen sulfide or other

volatile sulfiir compounds in the hydrogen-rich and carbon monoxide-rich gas

streams and go to the commercial gas consuming processes;

f) removing any dust and fume generated as part of the process in the

molten metal zones generating the hydrogen-rich and carbon monoxide-rich gas

streams via conventional means such as bag filters which are part of the gas

cooling systems.

2. The process as defined in Claim 1 in which the molten metal employed

in this invention is preferably and predominantly molten iron but may be copper, zinc,

especially chromium, manganese, or nickel, or other meltable metal in which carbon

is somewhat soluble and which is at least 50% by weight molten iron .

3. The process as defined in Claim 2 in which suitable feeds for the process

gaseous hydrocarbons such as methane, ethane, propane, butane, natural gas, and

refinery gas; heavier liquid hydrocarbons such as naphtha, kerosene, asphalt,

cycle oil, slurry oil, gas oil, heavy crude oil, pitch, coal tars, coal distillates, natural

tar, cmde bottoms, and used crankcase oil; solid hydrocarbon such as coal, rubber, tar

sand, oil shale, and hydrocarbon polymers; and mixtures of the foregoing.

4. The process as defined in Claim 1 in which all the sulfiir in the feed is

allowed to build up to equilibrium levels in the molten metal and slag zones at which

point the sulfiir compounds in the slag and metals in will be converted to hydrogen

sulfide and other volatile sulfiir compounds in molten metal and slag zones and exit

with the hydrogen-rich and carbon monoxide-rich gases; and after cooling the sulfiir

compounds are removed from the gases by conventional means such as amine

5 scrubbing, caustic scmbbing, etc.; before the now essentially sulf ir-free gases pass

to the commercial gas consuming processes.

5. The process as defined in Claim 1 incoφorating the use of feed and

creating two molten metal zones separated by feed and product control systems

o instead of transferring the molten metal between two zones of a single reactor.

6. The process as defined in Claim 1 incoφorating the use of an oxygen

enriched gas as the source of oxygen for gasifying the dissolved carbon in the molten

metal in the oxidation zone.

7. The process as defined in Claim 1 incoφorating the use of a submerged

lance entering the molten metal in the oxidation zone through the top surface of the

molten metal zone instead of through a tuyere pipe.

8. The process as defined in Claim 1 incoφorating the use of liquid feed

stocks prior to their introduction to the first molten metal zone as a scmbbing medium

in the cooling for dust and fume removal from the hydrogen-rich and carbon

monoxide-rich product gases.

9. The process as defined in Claim 1 incoφorating the use of a quantity of

hydrogen-rich gas to atomize liquid hydrocarbon feeds as they are introduced into the

first molten metal zone 4.

10. The process as defined in Claim 1 incoφorating the use of a quantity of

carbon monoxide-rich gas cool the tuyere pipe introducing the oxygen from below or

a lance introducing the oxygen from above the second molten metal zone.

11. The process as defined in Claim 1 incorporating the use of a quantity of

water vapor or steam to cool the tuyere pipe introducing the oxygen from below or a

lance introducing the oxygen from above the molten metal in the second zone and to

moderate the temperature in the second molten metal zone.

12. The process as defined in Claim 1 incorporating the use of a quantity of

carbon dioxide gas to cool the tuyere pipe introducing the oxygen from below or a

moderate the temperature in the second molten metal zone.

13. The process as defined in Claim 1 incoφorating the use of a quantity

methane gas to cool the tuyere pipe introducing the feed from below or a lance

introducing the feed from above the molten metal in the first zone and to moderate the

temperature in the first molten metal zone.