Note: Descriptions are shown in the official language in which they were submitted.
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BACKG~OUND OF THE INVENTION
The present invention relates to gasifica-
tion and more particularly to a continuous process for
yielding a combustible gas from the gasification of
char or coke.
There is a present day growing concern with
the rapid depletion of natural gas and oil resources
resulting from the rise in the industrial civilization
level throughout the world. With this concern comes
an acute awareness that immediate steps must be taken
to conserve our gas and oil resources and to develop
prccesses whereby greater use can be made of our ample
coal reserves.
The use of coal as a fuel in e~ectric gen-
erating power plants has been on a decline in recent
years due to environmental constraints which rendered
the conversion of coal to electricity uneconomical.
; Since coal is by far the most abundant of all fossil
fuel reserves, the development of a process for pro-
ducing clean fuel gas from coal or its by-products
would reduce our dependence on natural gas and oil
while providing an economical fuel capable of meeting ~ -
the new environmental standards.
The basic process for converting solid
coal to fuel gas in the form of carbon monoxide is
well ~no-~n. In fact, the "town gas", used before the
a~ailability of nat~ral gas, was produced by burning
coal under a reducing atmosphere.
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Present day coal gasification processes
inuolve the combustion of char or coke with oxygen
to yield a combustible gas through the following
reaction:
C + 1/2 2 D C0
Another process for the use of air in
lieu of oxygen and its reaction is expressed below:
- C + 1/2 2 + 1.88 N~ ~ C0 + 1.88 N2
.
Depending on the type of process, the upper
temperature level during gasification is of prime
concern due to reaction rates or kinetics.
In air-blown entrainment gasification, the
short residence time in the high-temperature zone
determines gas quality and the fraction of coal gasi-
fied. Any variable that reduces temperature, such as
a heat loss or presence of steam, detracts from gas
quality. The disadvantage of this proces$ stems from
the fact that air tends to dilute the coal gas pro-
duced to an unsatisfactory low heat content and intro-
duces nitrogen which cannot be economically removed
from the produced coal gas.
- Where the process uses oxygen instead of
air, there are generated such extreme temperatures
that some steam addition is necessary to moderate
the ~asification temperature. With steam addition,
a second consuming reaction occurs to reduce heat liber-
ation and produce hydrogen and carbon monoxide. 'rhe
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1038165
disadvantage of oxygen-blown gas~fication is the high
- cost of the associated oxygen plant.
SUMMA~Y OF THE INVENTION
The present invention relates to processes
for obtaining carbon monoxide fuel gas from the reaction
of gaseous sulfur dioxide with char or coke.
Accordingly, there is provided a main embodi-
ment whereby hot char or coke is brought into direct contact
with heated gaseous sulfur dioxide to produce a gaseous
mixture of carbon monoxide and elemental sulfur. En-
trained solids are removed from the gaseous mixture and
the latter is cooled through indirect heat exchange so
as to condense the sulfur thereby leaving a gas com-
prised primarily of carbon monoxide and having the pre-
- requisite heat value to qualify as a fuel.
The condensed sulfur is burned in the presence
of heated air to produce a gaseous mixture of sulfur
dioxide and nitrcgen which is then passed through a con- -
ventional sulfur dioxide recovery system to effect
separation of the nitrogen and sulfur dioxide, the latter
is then heated preparatory to use as the gasifying agent.
Oxygen, from a separate source, may be added during the
sulfur dioxide heating stage in the event that the gasi-
fication temperature drops below the level required for
sustained reaction.
An alternate embodiment of the invention
dispenses with the need for a separate source of oxygen
by providing a process whereby the heated gaseous sulfur
dioxide used for the gasification stage can be enriched
3 with up to 33% oxygen. This is achieved by conveying
:
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1038165
the gaseous mixture of sulfur dioxide and nitrogen,
produced in the sulfur burning stage, through a eon-
ventional system,-such as that used for the manu-
facture of oleum, and whieh subjects the gaseous
mixture to eatalytie oxidation in the presenee of air ~ `
thereby producing a gaseous mixture of sulfur trioxide
and nitrogen and which thereafter separates the nitrogen
and the sulfur trioxide, the latter is then heated to
a temperature level causing the dissociation of sulfur
trioxide into oxygen enriched sulfur dioxide to be
used as the gasifying agent.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of a
system embodying the invention as related to a process
for yielding a eombustible gas from the gasification
of ehar or coke.
Figure 2 is a schematic representation o~ an
alternate system embodying the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE I~ENTION
Figures 1 and 2 are schematic illustrations
of systems which are related to processes whereby sulfur
dioxide is used to gasify earbonaeeous matter to yield
a eombustible fuel gas.
In aeeordanee with the present invention,
hot earbonaceous matter 12 is supplied to a gasifier 14
to be contacted therein by a heated eontinuous stream 16
of eoneentrated sulfur dioxide. The earbonaeeous matter
12 must contain less than 1%, by weight~ of hydrogen and
is either ehar derived from a conventional gasificatlon
proeess or eoke sueh as that used for various metal-
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lurgical processes.
The sulfur dioxide reacts with the char or coke to
produce a gaseous mixture 18 of carbon monoxide and elemental
sulfur.
The reaction in the system depicted in Figure 1 is
as follows:
2C (Char or Coke) + S02 ~ 2C0 + 1/2 S
The reaction in the system depicted in Figure 2
includes enrichment with up to 33% oxygen and is as follows:
3C + S02 + 1/2 2 ~ 3C0 + 1/2 S2
The char or coke contained within the gasifier 14 may
be either in a fixed or fluidized state, the latter condi~ion
being maintained by the flowing stream of heated sulfur dioxide.
The gaseous mixture 18 is conveyed from the gasifier
14 to a gas-solids separator for the removal of ungasified parti-
culates 22. The gas-solids separator 20 is one of many presently
known in the art, for example, a mechanical or bed-filter type
separator.
The substantially solids-free gaseous mixture 24
of carbon monoxide and elemental sulfur exiting from the
separator 20 is conveyed to a sulfur condenser 26 which is a
known indirect type heat exchanger, for example, a shell and
tube heat exchanger, preferably one having the gaseous mixture
24 flowing through theltubes and the entering coolant 28 passing
over the tubes, and exiting as shown by 28A. The heat exchanger
parameters are such that the gaseous mixture 24, within the con- ;
denser 26, is maintained at a controlled temperature in the range
of 280F to 315F to dissociate the carbon monoxide and elemental
sulfur as follows:
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2co + 1/2 S2(Gas) . ~ 2cO (100% CO) + S(Li id)
- The combustible fuel gas 30, produced in
accordance with the present invention,has a carbon
monoxide content in the range of 95% to 100% and a
heat value in excess of 300 Btu/scf. The fuel gas 30
leaving the condenser 26 is a high quality clean gas
which may be used as fuel in a second stage combustion
device or as a feed gas for petrochemical applications.
- The elemental sulfur contained within thegaseous mixture 24 is liquified in the condenser 26 and
is thereafter conveyed as liquid sulfur 32 to a sulfur
burner 34 and associated combustion chamber 36 of a
type known in the art, for example, the burner and
combustion chamber disclosed in U.S. Pat. No. 3,723,068
issued on March 27, 1973, in the name of R.A. McIlroy
et al. The liquid sulfur 32 is entrained by a regulated
quantity of heated air 38 and burned to produce a gaseous ;~
mixture 40 of sulfur dioxide and nit~ogen as follows:
s + 4.76 Air ~ S02 + 3 - 76 N2
.
The gaseous mixture 40 is conveyed, to a fluid
heater 42 of a type known in the art, for example, the
fluid heater disclosed in U.S. Pat. No. 2,447,306 issued
on August 17, 1948, in the name of E.G. Bailey et al.
The fluid heater 42 has communicating upper and lower
chambers 44 and 46, respectively, and includes an
elevator 48 which receives cooled refractory particles
from the lower chamber 46 and returns them to the upper
chamber 44 to be reheated. The gaseous mixture 40 gives
up heat to the refractory particles as it passes through
the upper chamber 44. The heated refractory particles
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flow into the lower chamber 46 where they, in turn~
- give up heat to the gases passing therethrough.
Referring specifically to Figure 1, the
cooled gaseous mixture 40A, exiting from the fluid
heater 42, is conveyed to a sulfur dioxide concentrator
50 wherein the nitrogen 52 is removed thereby leaving
a concentrated gaseous stream 16A containing in excess
of 99% of sulfur dioxide. The concentrator 50 is of
a type known in the art, for example~ the recovery
system disciosed in U.S. Pat. No. 3,758,668 issued on
September 11, 1973, in the name of W.C. Lapple et al,
and which employs a slurry, containing magnesium oxide,
to absorb the sulfur dioxide from the gaseous mixture
40A, and to form magnesium sulfide crystals which are
thereafter separated from ~e slurry and heated to re-
duce the water of crystallization, and are pelletized
- with carbon and a binder to form pellets which are
thermally treated for dissociation into reactive magnesium
oxide particles and gaseous sulfur dioxide, ~he former
being returned to the absorption ~one of the recovery
system. s~
The gaseous stream 16A of sulfur dioxide,
exiting from the concentrator 50 is routed to the lower ~ -
chamber 46 of fluid heater 42 to be heated by the re-
fractory particles circulating therethrough. The heated
gaseous stream'16 of sulfur dioxide leaving the lower
chamber 46 is conveyed to the gasifier 14 for the manu-
facture of combustible fuel gas. A separate source 54
of nitrogen-free oxygen is available to supply a re-
gulated quantity of oxygen 56 to the lower chamber 46
for oxygen enrichment of the gaseous stream 16 of sulfur
dioxide, whenever required, to maintain the temperature
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necessary for sust ~ ne ~reaction within the gasifier
14.
Referring specifically to Figure 2, there
is shown a system which provides for the addition of
up to 33% oxygen to the heated gaseous stream 16 of sul-
fur dioxide, used for gasification, without resort to a
cryogenic oxygen plant. The system uses the reversible
sulfur dioxide to sulfur trioxide reaction in the
manner set forth below:
T< 1800F~
S2 + 1/2 2 so3
~ > l~OO~F
In accordance with the invention, the gaseous
mixture 40A of sulfur dioxide and nitrogen, exiting
from the upper chamber 44 of fluid heater 42, is routed
to a conventional system, such as that used in the manu-
facture of oleum, and including a catalytic oxidizer 62
wherein the sulfur dioxide ccntained in the gaseous
mixture 40A is oxidized by the air 60 in the presence
of a catalyst, for example, vanadiump~ntoxide orplatinum,
which speeds up the reaction without a~fecting the
equilibrium. The catalytic oxidation stage'takes place
at a reaction temperature of less than 1800F, usually
in the range of 700F to 850F and is expressed as
foll~ws: .
S2 + 3-76 N2 + 2.38 Air T= 750F to 8000F
The gaseous mixture 64, exiting from the
catalytic oxidizer 62, may contain up to 85% diluent
nitrogen with sulfur trioxide. The gaseous mixture 64
is fed to a sulfur trioxide co~centrator 66 for the
separation of nitrogen 68 and concentrated sulfur tri-
oxide 7. The separation stage is effected by using
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highly concentrated sulfuric acid to scrub out the
sulfur trioxide thereby obtaining sulfur trioxide
enriched sulfuric acid, the latter ls then conveyed to
an evaporator which gasifies the sulfur trioxide.
The gaseous stream 70 of sulfur trioxide,
exiting from the concentrator 66 is routed to thelower
chamber 46 of fluid heater 42 to be heated by the re-
fractory particles circulating therethrough. The heat
supplied in chamber 46 is at a temperature in excess
of 1800F thereby decomposing the gaseous sulfur tri-
oxide to oxygen enriched sulfur dioxide as expressed
below:
T ~ 1800F S0 + 1/2 0
The heated gaseous stream 16 of sulfur dioxide
enriched with up to 33% oxygen is conveyed to the gasi-
fier 14 for the manufacture of combustible fuel gas.
While in accordance with provisions of the
statutes there is illustrated and described herein a
specific embodiment of the invention, those skilled in
the art will understand that changes may be made in the
form of the invention covered by the claims; and that
certain features of the invention may sometimes be used
to advantage without a corresponding use of the other
features,
