WO1998023708A1

WO1998023708A1 - H2s production from a molten metal reactor

Info

Publication number: WO1998023708A1
Application number: PCT/US1996/019112
Authority: WO
Inventors: 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: AU1460997A

Abstract

Hydrogen sulfide is produced by charging a sulfur containing feed to a molten metal bath containing over 3 wt.% dissolved carbon. Allowing dissolved carbon levels to build up in the bath, preferably by controlling oxygen addition to ensure a large inventory of dissolved carbon, creates a reducing 'atmosphere' in the molten metal bath which allows most of the feed sulfur to be converted to H2S, which can be converted to elemental sulfur using a Claus unit or similar technology. Oxygen addition, to burn carbon from the bath, preferably occurs at a different time or place in the bath than the time or place of sulfur containing feed addition.

Description

H₂S PRODUCTION FROM A MOLTEN METAL REACTOR

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of prior co-pending application USSN

08/421 ,102, filed April 13, 1995, (attorney docket 6391NUS), now US 5,577,346

granted November 26, 1996.

The application is somewhat related to USSN 08/163,468, filed December 7,

1993, (attorney docket 6431MUS).

CROSS REFERENCE TO RELATED PATENTS

This application is related to US 5,435,814, issued July 25, 1995, teaching a

two-zone molten metal decomposition apparatus and process.

BACKGROUND OF THE INVENTION

I. FIELD OF THE INVENTION:

This invention relates to gasification of sulfur and hydrocarbon containing

streams in molten metal.

II. DESCRIPTION OF THE PRIOR ART:

Molten metal, especially molten iron, baths are well known and widely used as

gasifiers. The high temperatures in such baths rapidly decompose, by theπΗal action,

a variety of solid, liquid and gaseous feeds into hydrogen and/or carbon oxides. Such processes are well known, e.g., U.S. Patents 4,574,714 and 4,602,574 to Bach teach

a molten iron gasifier. Another, and preferred, molten metal reactor is disclosed in US

5,435,814, MOLTEN METAL DECOMPOSITION APPARATUS, Chailes B. Miller

and Donald P. Malone.

One of the problems of molten metal processing is that the feeds to such

processes are rarely pure materials. If the feed were a pure hydrocarbon, such as

methane with no significant amount of chlorides, trash metals, sulfur or other

impurities, design and operation of the molten metal reactor is simple. Consider the

case of methane conversion. The reactor need only be designed to thermally convert

the CH₄ into hydrogen (which is thermally stable and rapidly released as pure

hydrogen gas) and carbon (which rapidly dissolves in the molten iron). There are no

feed impurities and no slag forms.

Once the refiner has to depart from such ideal fuels as methane, design of the

reactor becomes complicated. Molten metal reactors are best at converting difficult

streams not otherwise amenable to processing - resids, ground up tires, old pesticides

and the like. Such materials present many challenges to the engineer charged with

converting them to useful products (or at least making the offending material go

away), but for now the focus is on one pervasive impurity - sulfur. The problem of

sulfiir in the feed is pervasive in refinery processing, coal combustion and molten metal processing. It is instructive to review how each of these processes has dealt

with feed sulfur.

Crude oil invariably contains sulfiir. Sulfiir is so pervasive in crude oil that its

presence in greater or lessor amounts makes crude oil sour or sweet. Refiners have

evolved efficient ways to convert sulfiir in feed into solid sulfiir product. Sulfur is a

valuable product in its elemental foπn. In refineries, the crude is generally

catalytically hydrotreated to convert sulfur compounds to H₂S which is eventually

converted in a Claus unit to elemental sulfur. The processing is expensive, both in

teπns of operating and capital expense required to hydrotreat feeds, but essential.

In coal processing, sulfur is generally dealt with by stack gas scrubbing or by

burning the coal in a bed of ground up limestone or dolomite. It is possible to burn

coal in California if a Circulating Fluidized Bed (CFB) coal combustor is used.

Relatively small amounts of coal are added to a much larger circulating inventory of

crushed alkaline material. The sulfiir components in the coal are oxidized to fonri

sulfur oxides, which then react with tons of circulating, high temperature, ground

dolomite.

In molten metal processing (and to some extent in steel making), sulfur is

oxidized during processing to fonri sulfiir oxides. The produced sulfiir oxides then

react with alkaline material added to the bath to foπn a slag layer. One example of this approach is a vitreous layer used above a molten metal bath, as taught in US

5,354,940. A typical vitreous layer was five inches of 40% calcium oxide, 40%

silicone dioxide and 20% aluminum oxide.

Although it has been known for years that it is possible to release some H₂S

from a molten iron bath no one has made any productive use of this finding. In

UK 1 , 187,782, Nixon taught that a molten metal conversion process converting

methane to hydrogen would also refine the iron bath:

"The hydrogen produced in the cracking zone has a refining effect on the metal contained in the molten metal bath in contact with it. For instance, the sulphur content of the molten iron tends to be reduced as a result of the reaction:

FeS + H2 = Fe + H₂S."

The EXAMPLE in the Nixon patent showed conversion of methane to high

purity hydrogen (H2 volume % purity was 99.86 and 99.70). The sulfur content of the

hydrogen gas was not reported, but presumably trace amounts of H₂S were present,

at least during the early stages of the process as sulfiir present in the iron was removed

by the refining effect of the hydrogen production. In this example, the sulfiir was in

the metal and no sulfiir in the feed.

Some use has been made of molten metal baths to absorb H₂S. though the bath

in question was not a molten iron bath and operated at a lower temperature than

molten iron baths. I did not like the conventional approach to dealing with feed sulphur. Now,

refiners add large amounts of alkaline material to foπn an alkaline slag layer which has

to be tliick enough to react with sulphur compounds as they fonn or extract dissolved

sulfur from the metal. The added alkaline material consumes significant amounts of

energy when dumped into the reactor to foπn a slag layer. This slag layer in turn

creates a removal problem and eventually a disposal problem.

I wanted to be able to deal with sulfur containing feeds without unnaturally

altering the heat balance of the reactor by adding large amounts of alkaline material

to deal with the feed sulfiir. I discovered a way convert much, and potentially all, of

the feed sulfur to H₂S. Such material, while highly toxic, is easily handled in any

modem refinery using conventional amine scrubbing, Claus conversion and the like

techniques. H₂S is a dangerous material, but refiners have been efficiently converting

it to elemental sulfiir for over 50 years.

The solution was surprisingly simple. Change the operating conditions in the

molten metal reactor so that strong reducing environment was created. Rather than

do this adding hydrogen at ruinous expense, do it cheaply by letting the carbon level

build up in the reactor. High dissolved carbon levels in a molten iron bath could be

used to create conditions where most, or all, of the feed sulfiir could be converted to

H₂S. BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for producing H₂S from

a sulfur containing feed in a molten metal bath comprising dissolving at least 3 wt.%

carbon in a molten metal bath comprising at least 50 wt.% Fe; charging a sulfur,

hydrogen and carbon containing feed to such bath and theπnally decomposing said

feed to produce H₂S and carbon, emitting the H₂S as a vapor product from or above

said molten metal bath and dissolving at least a portion of said carbon in said molten

metal bath; and at least periodically adding oxygen or an oxygen containing gas to

said molten metal bath to oxidize at least a portion of said dissolved carbon from said

bath.

DETAILED DESCRIPTION DESCRIPTION OF THE PREFERRED EMBODIMENTS

FEED MATERIALS:

Any sulfur containing feed may be used, ranging from noπnally gaseous

materials, such as sulfiir containing natural gas streams to noπnally liquid and even

solid materials. The invention is especially useful at converting heavy distillate,

vacuum and other resids, solvent deasphalted pitch (SDA), aromatic extracts, FCC

slurry oil and the like into useful products without hydrotreating. In addition, the

invention can also efficiently process many sulfur containing solids such as trash,

garbage, tires, coal, virtually any other sulfur-containing material. If the sulfur containing feed does not contain enough hydrogen, then some

hydrocarbon rich material can be added with the sulfiir containing feed to provide

sufficient hydrogen to theπnally decompose the feed to a reduced foπn or sulfiir rather

than an oxidized form of sulfiir.

PRODUCTS:

H₂S is the prefeπed product. Preferably most, and ideally essentially all, of the

feed sulfur is converted to ELS.

Other products of molten metal processing include CO, C0₂, H₂, perhaps some

methane and even some soot. In my process, a little soot can be a good thing in that

it ensures that the molten metal bath is saturated with carbon. The production of solid

soot is not especially beneficial, and will require some sort of filter or bag house

means to remove soot. Many units will have or can readily install such equipment

anyway. For these units with a baghouse or electrostatic precipitator or the like

filtering means to remove entrained solids, the presence of soot incurs no additional

capital expense and provides an easy way to ensure a reducing "atmosphere" is

always present in the molten metal CONTROLS:

Conventional analog or digital controls may be used, measuring temperature,

preferably with optical or infrared pyrometer or protected theπnocouple; carbon by

spectrometers; level by nuclear radiation and admitting feed, CH₃, C0₂, H₂0 to

maintain temperature, which must be high enough (e.g., at least 1150°C (2101°F) to

maintain the particular metal carbon composition liquid and dissolved carbon level and

H₂ production within preset limits. Temperature of the molten metal is preferably

1 150° to 1600°C (2102° to 2912°F), more preferably 1250° to 1500°C (2282° to

2732°F) during feed to the reactor or crucible and usually preferably 50° to 150°C

(122° to 302°F) higher during the oxidation cycle within the single-chamber reactors

or crucibles.

REACTOR DESIGN

The process does not require any special reactor design. Any molten metal

reactor apparatus can be used. Many people will prefer to use reactors similar to

those used in steel manufacturing, e. g. the design shown 4,574,714 or in US

5,322,547 (but preferably without the slag layer).

I prefer to use a pressurized system, such as that shown in US 5,435,814.

The hardware, per se, foπns no part of the present invention. PROCESS VARIABLES

Minimum dissolved carbon whenever the bed sees sulfiir containing feed should

be at least 2.0 wt.%, but preferably is higher.

Control of dissolved carbon level and other conditions in a molten metal reactor

allows a majority of the sulfur content of the feed to be converted to H₂S, rather than

sulfur oxides or required sulfur removal as slag. High dissolved carbon levels,

preferably in excess of 3 wt. % in a molten metal iron bath, and limited oxygen

addition, allow molten metal refiners to process sulfur containing feeds without

addition of lime or other similar alkaline materials, peπnitting slag foπnation to be

reduced or eliminated.

MODIFICATIONS

Reference to documents made in the specification is intended to incorporate

such patents or literature.

What is claimed is:

Claims

1. A process for producing H₂S from a sulfiir containing feed in a molten

metal bath comprising:

a) dissolving at least 3 wt.% carbon in a molten metal bath

comprising at least 50 wt.% Fe;

b) charging, at least periodically, a sulfur, hydrogen and carbon

containing feed to such bath;

c) theπnally decomposing said feed to produce H₂, H₂S and carbon;

d) recovering said H₂ and H₂S as a vapor product from or above said

molten metal bath;

e) dissolving at least a portion of said carbon in said molten metal

bath;

f) at least periodically adding oxygen or an oxygen containing gas

to said molten metal bath to oxidize a portion of said dissolved carbon from

said bath, while limiting oxidation so that said bath contains at least 3 wt. %

carbon at all times; and

g) repeating steps b-f to process additional amounts of sulfur

containing feed.

The process of claim 1 wherein the minimum carbon level is 4.0 wt.%.

3. The process of claim 1 wherein the minimum carbon level is 5.0 wt.%.

4. The process of claim 1 wherein the minimum carbon level is 6.0 wt.%.

5. The process of claim ] wherein the molten metal bath is at least

intermittently saturated with carbon and produces soot.

6. The process of claim 1 wherein said process occurs in a single molten

metal batch, with sequential addition of oxygen and feed.

7. The process of claim 1 wherein said process occurs in a circulating

molten metal bath with at least two physically isolated vapor regions above a

circulating molten metal bath, and wherein one of said vapor regions is a reducing

region receiving said feed and the other said region is an oxidizing region producing

a carbon oxide flue gas above a portion of said circulating molten metal bath receiving

said oxygen.

8. The process of claim 1 wherein the molten metal bath is essentially slag

free.

9. The process of claim 1 wherein at least 80 % of said feed sulfiir is

converted to H₂S.

10. A process of claim 1 wherein at least a portion, recovered as a vapor

product, of said hydrogen is recycled to said bath to enliance sulfur removal.

11 . A process of claim 1 wherein the temperature of the baths should range

between 2200° and 3000°F.