Note: Descriptions are shown in the official language in which they were submitted.
~2~3~
BACK~ROUND OF_ THE INVE2iTIO
This invention relates to the partial oxidation of
liquid hydrocarbonaceous fuels, including oxygen-containing
hydrocarbonaceous fuels and slurries of solid carbonaceous
fuels. More specifically, it relates to a pollution
abatement process for the environmentally safe disposal of
toxic CN-containing sludge produced during the treatment of
water used to quench cool and/or scrub the hot effluent gas
stream from a synkhesis gas generator.
The hot effluent synthesis gas stream i.e., mixtures
of H2 ~ C0 from a free-flow non-catalytic partial oxidation
~as generator may include trace amounts of HCN, i.e. 0.5 to
100 parts per million (PPM) by weight as well as entrained
particulate matter such as soot, ash, slag, and bits of
refractory. Water is most commonly used to quench cool
and/or scrub the hot effluent gas stream from the reaction
~one in order to remove the entrained matter. A portion of
the l-lCN in the synthesis gas stream will be absorbed by the
water in the quench and/or cooling zones, along with trace
amounts of other ~ater soluble impurities in the gas stream
such as formates and halides.
Since large quantities of water are employed in the
process for producing synthesis gas, reducing gas, or fuel
gas by the partial oxidation of liquid hydrocarbonaceous
fuels, including oxygen-containing hydrocarbonaceous fuels
and slurries of solid carbonaceous fuels, it is important
especially in arid locations to reclaim the quench and/or
scrubbing water and to recycle them back to the gas
quenching and/or scrubbing zones for reuse. In fact, for
--1--
~2~33~319
economic and environmental reasons, water recovery and upgrading,
and recycling the upgraded water to the process have now become
necessary.
U.S. Patent 4,211,646, pertains to a method for the
t-reatment of waste waters having toxic and corrosive properties
due to the presence of cyanides, formates and halides. A toxic
inorganic sludge and an upgraded waste water stream are produced
by this method. No procedure is provided in U.S. Patent
~,211,646 for safely disposing of concentrated toxic inorganic
sludges.
Sludge disposal would represent a major operating cost
in a plant producing synthesis gas from petroleum and coal feed.
~ree and complexed cyanides in the sludge must be destroyed before
any sludge disposal system is environmentally acceptable. Com-
plex cyanides are resistant to chemical destruction. Sunlight
nay break down complexed cyanide, but free cyanides are then re-
leased. If the inorganic sludge is landfarmed, contamination of
ground water is a potential hazard.
These problems and others are eliminated by the subject
process by which substantially all of the free and complexed
cyanides in the inorganic sludge are destroyed in the reaction
~one of the partial oxidation gas generator.
--2--
3~2~33~
SUMM~RY OF THE INVENTION
According -to one aspec-t of the present invention there is provided a
pollwtion abatement process for a toxic inorganic CN-con-taining sludge compri-
s ing
(1) mixing together the toxic CN-containing sludge from (6) and a
liquid hydrocarbonaceous fuel to produce a fuel mixture;
(2) reacting the fuel mixture from (1) by partial oxida-tion wi-th a
Eree-oxygen con-taininy gas and a temperature moderakor in the reac-tion zone of
a Eree-Elow partial oxidation gas generator at an autogenous tempera-ture in
the range of about 1700 to 3000F. and a pressure in the range of about 10 to
200 atmospheres to produce an effluent gas stream substantially comprising H2,
CO, CO2, at least one gas from the group consisting of H2O, CH4, H2S, COS, N2,
and ~r, and containi.ng particulate carbon, ash and trace amounts of EiCN, HCL
and NH3;
(3) introducing the effluent gas strearn from (2) in-to a gas quench
coo:l:i.ng and/or scrubbing zone, and producing a carbon-water dispersion contain-
:i~g d:Lsso:Lved formic acid and a separate stream of raw synthesis gas, reducing
gas or fuel gas;
(4) resolving said carbon-water dispersion in a decanting zone to
produce a carbon-liquid hydrocarbonaceous fuel slurry and water containing Eree
and combined cyanides; halides of ammoni~n or a metal selected from the group
sodium, calcium, iron, nickel, and mixtures thereof; formates; sulfides; thio-
cyanates; ammonia; and metal constituents selected from the group consis-ting
of nickel, vanadium, iron, and mixtures thereof;
(5) mixing at least a portion of the water from (~) at a temperature
in the range of about 125 to 200F. and a pH in the range of about 7 to 9
with a ferrous salt thereby converting a substantial portion of said cyanides
to iron cyanides, adding a base to increase the pH to a value in the range o-E
about 9-ll., and precipi-tating said toxic inorganic CN-containing sludge in said
water; and
(6) separating the suspended CN-containing sludge from the wa-ter in
--3--
~2~33~
a separating zone.
According to another aspect of the presen-t invention there is provi-
ded a process for disposing oE a toxic inorganic CN-containing sludge produced
by removing entrained particulate matter from the water used to quench cool
and/or scrub the hot raw effluent gas stream produced in the reaction ~one oE
a partial oxidation gas generator by the partial oxlda-tion of a liquid hydro-
carbonaceous fuel and mixing at least a portion of the water -thereby produced
with ferrous sulfa-te or ferrous chloride, adjusting the pH of said mixture to
a value in the range of about 9-11 by the addition of sodium or calcium hydro-
xide, precipitating in said water an inorganic sludge in which iron cyanide is
present, and separating said inorganic sludge from the water; which process
cont,istCJ essent:ially of mixing said inorganic CN-containing sludge with at
least a portion of said liquid hydrocarbonaceous fuel feed to -the reaction
xone of-the partial oxidation gas generator, and reacting said mixture wi-th a
free-oxygen containing gas in the reaction ~one of the partial oxidation gas
genc!rator at a temperature in the range of about 1700F. to 3000F. and a pre-
ssure :in the range of about 1-250 atmospheres t:hereby destroying said iron
cyanides, and recovering -the ash components of said sludge as a portion of the
slag from the generator.
In this pollution abatement process, the hot raw effluent synthesis
gas stream comprising H2 and CO from the partial oxidation of liquid hydrocar-
bonaceous fuels, including oxygenated hydrocarbonaceous organic materials and
slurries of solid carbonaceous fuels and containing toxic gaseous impuri-ties
such as H2S and COS as well as trace amounts of HCN and HCL is quench cooled
and/or scrubbed with wa-ter. A small amount of these toxic materials remain in
the water after the rest of the synthesis gas is separated. Formic acid and
Nl13 may also be present in the quench and/or scrLlbbing water. A toxic inorga-
ni.c CN-con-taining sludge is produced by mixing a-t leas-t a portion of the quench
and/or scrubbing water at a -tempera-ture in the range of about 60 -to 210F. and
a pH in the range of about 7 to 9 wi-th ferrous sulfa-te or ferrous chloride,
and adding sodium or calcium hydroxide to said treated water thereby adjus-ting
-3a-
"i~,' ~-.
33~Gi
the pH to a value in -the range oE about 9-11 and precipitating said inorganic
CN-con-taining sludge. To preven-t the formation of calcium sulfate, the pre-
ferred combinations of ~errous salt and base are (a) ferrous sulfate and sod-
iUM hydroxide, and (b) ferrous chloride and calcium hydroxide. The toxic in-
oryanic CN-containing sludge is separated from the water and -then safely dis-
posed of without creating environmental problems by mixing it with -the liquid
hydrocarbonaceolls fuel feeds-tream and reacting the mixture in -the gas genera-
tor by partial oxida-tion at a ternperature in the range of about 1700F. to
30~0~F'. and a pressure in the
-3b-
3~
ranye of about 1 to 250 atmospheres, such as about 10 to
200 atmospheres. The water which is separated from the
sludge is upgraded by steam stripping the ammonia,
adjusting the pH to a value in the range of abou'c 6-8, and
removing organic matter such as formates in a conventional
biological reactor. A biological residue is formed which
may be recycled to the gas generator as a portion of the
feed. The upgraded watex may be recycled ~o the quench
cooling and/or scrubbing zone. Alternatively, the upgraded
water, biological residue, or both may be discharged from
the system, without polluting the environment.
B~IEF DESCRIPTION OF THE DRAWING
The invention will be further understood by reference
to the accompanying drawing showing a schematic
representation of a preferred embodiment of the process.
DESCRIPTION OF THE INVE,NTION
The present invention pertains to an environmentally
safe continuous method for disposing of toxic material
produced in the partial oxidation process for the
production of a stream of synthesis gas, fuel gas, or
reducing gas from liquid hydrocarbonaceous fuels, including
oxygen-containing hydrocarbonaceous fuels and slurries of
solid carbonaceous fuels in a liquid carrier. Also
included in the feedstock to the gas generator is the toxic
inorganic cyanide-containing sludge derived downstream in
the process. The product gas may be used with or without
further processing and/or purification by conventional
methods, depending on the composition of the liquid
hydrocarbonaceous fuel feed. Further, water which becomes
3~
contamlnated with toxic materials during quench cooling and/or
scrubbing the hot raw gas stream may be upgraded for reuse or Eor
safe disposal without polluting the environment.
In the process, a hot effluent gas stream is made by
the partial oxidation of liquid hydrocarbonaceous fuels, includ-
ing oxygen-containing hydrocarbonaceous fuels and slurries of
solid carbonaceous fuels in a liquid carrier with a free-oxygen
containing gas and in the pre.sence of a temperature moderator.
The gas generator is a vertical cylindrical steel pres-
sure vessel lined on the inside with a thermal refractory mate-
rial. A typical partial oxidation synthesis gas generator is
shown in co-assigned U.S. Patent No. 2,818,326 and U.S. Patent
3,5~ ,291. A burner is located in the top oE the gas generator
along the central vert-lcal axis for introducing the feed streams.
A suitable annulus-type burner is shown in co-assigned U.S.
Patent 2,928,~60,
The term liquid hydrocarbonaceous fuel as used herein,
is intended to include various materials, such as petroleum dis-
tillates and residues, gasoline, naphtha, kerosene, crude
petroleum, asphalt, gas oil, residual oil, tar-sand and shale oil,
oil derived from coal, aromatic hydrocarbons (such as benzene,
toluene, and xylene fractions), coal tar, cycle gas oil from
fluid-catalytic-cracking operation, furfural extract of coker gas
oil, and mixtures ~hereof~ Included within the deEinition of
liquid hydrocarbonaceous fuel are oxygenated hydrocarbonaceous
organic materials
--5--
33~
including carbohydrates, cellulosic materials, aldehydes,
organic acids, alcohols, ketones, oxygenated fuel oil,
waste liquid and by-products from chemical processes
containing oxygenated hydrocarbonaceous oryanic materials,
and mixtures thereof.
Also included within the definition of liquid
hydrocarbonaceous fuel are pumpable slurries of solid
carbonaceous fuels. Pumpable slurries of solid
carbonaceous fuels may have a solids content in the range
of about 25-70 wt.% such as 45-68 wt.%, dependiny on the
characteristics of the fuel and the slurrying medium. The
slurrying medium may be water, liquid hydrocarbonaceous
fuel, or both.
The term solid carbonaceous fuel includes coal, such a
anthracite, bltuminous, subbituminous; coke from coal;
lignite; r~sidue derived from coal liquefaction, oil
shale; tar sands; petroleum coke; asphalt; pitch;
par~iculate carbon (soot); concentrated sewer sludge; and
mixtures thereof. The solid carbonaceous fuel may be
ground to a particle size so that 100% passes through an
ASTM E11-70 Sie~e Designation Standard (SDS) 1.4mm
Alternative No. 14.
The use of a temperature modera-tor to moderate the
temperature in the reaction ~one of the gas generator
depends in general on the carbon to hydrogen ratio of the
feed stoc~ and -the oxygen content of the oxidant stream.
Suitable temperature moderators include steam~ water,
C02-rich gas, liquid C02, coole~ effluent gas ~rom the gas
generator, by-product nitroyen from the air separation unit
~)3;~
used to produce substantially pure oxygen, and mixtures of
the aforesaid temperature moderators. The temperature
moderator may be introduced into the gas generator in
admixture ~Jith either the liquid hydrocarbonaceous fuel
feed, the free-oxygen containing stream, or both.
Alternatively, the temperature moderator may be introduced
into the reaction zone of the gas generator by way of a
separate conduit in the fuel burner. When H20 is
introduced into the gas generator either as a temperature
moderator,a slurrying me~ium, or bo.h, the weight ratio of
water to the hydrocarbonaceous fuel is in the range of
about 0.3 to 2.0 and preferably in the range of about 0.5
to 1Ø
The term free-oxygen con~aininc~ gas, as used herein is
intended to include air, oxygen-enriched air, i.e., greater
than 21 mole % oxygen, and substantially pure oxygen, i.e.,
greater than 95 mole % oxygen, (the remainder comprising N2
and rare gases). Free-oxygen containing gas may be
introduced into the burner at a temperature in the range of
about ambient to 1200F. The atomic ratio of free-oxygen
in the oxidant to carbon in the feed stock tO/C, atom/atom)
is preferably ln the range of about 0.7 to 1.5, such as
about 0.80 to 1.2.
The relative proportions of solid carbonaceous fuel,
liquid hydrocarbon fuel if any, water or other temperature
moderator, and oxygen in the feed streams to the gas
generator are carefully regulated to convert a substantial
portion of the carbon in the fuel feed to the partial
oxidation gas generator e.g. 75 to 95 wt.%, such as 80 to
--7--
~ ~33~1
90 wt.~ of the carbon to carbon o~ides e.g~, C0 and C02 and
to maintain an autogenous reaction zone temperature in the
range of about 1700 to 3000F., such as about 2350 to
2900F. Advantageously, with ash-containing solid
carbonaceous slurry feeds, the ash in the solid
carbonaceous fuel forms molten slag at such later reaction
temperatures. Molten slag is much easier to separate from
the hot effluent gas than fly-ash. The pressure in the
reaction zone is in the range of about l to 250
atmospheres, such as abou~ 10 to 200 atmospheres. The time
in the reaction zone of the partia-l oxidation gas generator
in seconds is in the range of about 0.5 to 20, such as
normally about 1.0 to 5.
The effluent gas stream leaving the partiaI oxidation
yas generator has the following composition in mole %
depending on the amount and composition of the feedstreams:
~12 ~ to 60.0, C0 8.0 to 70.0, C02 1.0 to 50.0, ~I20 2.0 to
50.0, CH4 0.0 to 2.0, H2S 0.0 to 2.0, COS 0.0 to 1.0, N2
0.0 to 80.0, and Ar 0~0 to 2Ø Trace amounts of the
following gaseous impurities may also be present in the gas
stream in parts per million (ppm~: HCN 0.5 to about 100,
such as about 2 to 20, HCl 0 to about 20,000, such as about
200 to 2,000 and NH3 0 to about 10,000, such as about 100
to 1,000. Entrained in the effluent gas stream is about
0.5 to 20 wt.~, such as 1 to 4 wt.~ of particulate carbon
(basis welght of carbon in the feed to the gas generator)
and the remalning portion of the uncon~erted ash-containing
solid carbonaceous fuel feed. Molten slag resulting from
3~
the Eusion oE the ash content of the coal may be also entrained in
the gas stream leaving the generator.
The effluent gas stream leaving the reaction zone of the
noncatalytic partial oxidation gas generator at a temperature in
the range of about 1700 F. to 3000F. may be either (1) quench
cooled and scrubbed with water, (2) cooled in a gas cooler and
then scrubbed with water, or both (1) and (2). When the gas gene-
rator is operated at elevated pressure i.e. above about 10 atmos-
pheres small amounts of formic acid may be produced in the system
and dissolves in the water in the quench cooling and scrubbing
zones. Clarifying the quench cooling and/or scrubbing water by re-
moving dispersed solids such as soot and ash have been previously
dLsclosed. For example, in coassigned U.S. Patent 4,0]4,786, a
llquld organ:Lc extractant ls employed in a decanter system to re-
move soot from carbon-water dlsperslon produced durlng gas quench
coollng and/or scrubblng. In coassigned U.S. Patent 3,544,291 a
settler :Ls used to separate a stream of clarified water from two
water streams of carbon and ash.
Even though soot and other sol:ids have been removed from
the quench and/or scrubbing water in the manner previously des-
cribed, there remains in the water a mixture comprising small
amounts of cyanides, metal halldes, forrnates and posslbly other by-
products of the partial oxidation reaction such as ammonia and the
metals nickel~ vanadium, iron, and the oxldes and/or sulfldes there-
of. These constltuents may bulld up ln the system when the
_g_
~33~
wa-ter streams are recycled and may corrode or deposit out
in downstream equipment. By the subject process, these
contaminants may be concentrated as a toxic inorganlc
CN-containing sludge and be safely disposed of in the
partial oxidation gas yenerator in admixture with the
liquid hydrocarbonaceous fuel.
On a weight basis in parts per million (ppm) the
quench and/or scrubbing water from the partial oxidation
process may contain the following impurities: total
cyanide (free and combined) from 5 to 1,000 or more, such
as 10 to 100; halides of ammonium or a metal selected from
the group sodium, calcium iron, nickel, and mixtures
thereof about 25 to 20,000, such as about 50 to 5,000;
formates about 100 to 20,000, such as about 500 to 10,000;
lS a metal constituent selected from the group nickel,
vanadium, iron and mixtures thereof about 5 to 1,000 each,
such as about 10 to 250 each; sulEides and thiocyanates
about 5 to 1,000 each, such as about 10 to 250 each;
ammonia about 0 to 10,000, such as about 100 to 5,000.
The inorganic C~-containing sludge is precipitated in
at least a portion i.e., about 10 to 100 wt.%, such as
about 20 to 50 wt.~ of the quench and/or scrubbing water
after at least a portion of the entrained solids are
removed in the following manner.
(1) Ferrous sulfate or ferrous chloride is mixed with -the
water at a temperature in the range of about 60 to 210F.,
such as 125 to 200F. and a pH in the range of about 7.0 to
3Ø By definition pH = -log[H30 ]. The moles of ferrous
ions added are in the range of about 1.2 to 10, such as 2
-to 6, times the moles of total cyanides in the water.
--10--
~2~33~6~
(2) At substantially the same temperature and preferably
in the range of about 125 to 200F., sodium hydroxide or
calcium hydroxide is added with constant mixiny to raise
the pH of the water treated in (1) to a value in the range
of 9-11, To avold the formation in the system of calcium
sulfate (scale), which deposits out at elevated
temperatures such as in the ammonia stripper, the
preferable improved combinations of ferro~s salts and bases
are (a) ferrous sulfate and sodium hydroxide, and (b)
ferrous chloride and calcium hydroxide~
With the addition of the base, an inorganic
CN~containing sludye forms or precipitates substantially
comprising ash and a mixture of the cyanides, hydroxides
and sulfides of iron. Ash may comprise the metals and the
sulfides of the metals selected from the group nickel,
vanadium, iron, and mixtures thereof. In addition, when
the base is calcium hydroxide as in the (b) combination
above, then calcium carbonate will also be present in-said
CN-containing sludge. Further, should the combination of
ferrous sulfate and calcium hydroxide be used in a specific
case then in addition the carbonate and sulfate of calcium
will also be present in said CN-containing sludge.
Optionally, to increase the settling rate of the
inorganic CN-containing sludge that takes place next in a
conventional settler, colloidal clay or other conventional
weighting agent followed by about 0.05 wt.~ of a
conventional flocculant/coagulant such as a polyelectrolyte
polymer may be mixed in with the sludge forming mixture.
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~33~
5ettling of the suspension of CN-containing sludge in
water takes place in a conventional settler or clarifier.
The underflow toxic sludge stream may be then introduced
into a mixing tank where it is mi~ed with at least one
S other liquid hydrocarbonaceous fuel feed stream and safely
disposed of in the partial oxidation gas generator.
The ash components in the CN-containing sludge would
then be recovered as slag from the gas generator. Another
benefit may arise when coal is included in the feed and the
CN-containing sludge contains calcium compounds which serve
to catalyze the endothermic coal-steam reaction during
gasification. Further, the calcium compounds will act as
fluxing agents for ash in the generator charge, thereby
lowering the coal ash fusion temperature. By this means
lS the synthesis gas generator may be c,perated at a lower
temperature while still producing molten slag. The oxygen
consumption is thereby reduced at a si~3nifi~ant economic
savings.
(3) Most of the ammonia in the substantially solid-free
overflow from the settler may be removed by steam
stripping. Optionally, this ammonia may be used to
supplement the base in adjusting the pH of the quench
and/or scrubbing water in (1) and/or the ferrous ion
treated water in (2), above.
(4) To remove formates and other any other organic
matter that may be present in the stripped water fxom (3),
the pH of the water is adjusted to a value in the range of
about 6 to 8 by conventional means. The water is then
lntroduced into a conventional biological reactor where -the
-12-
~Z~33~
oryanic matter, including formates, are converted into C02
and a biological residue tha-t may be safely disposed of
without polluting the environment. Alternatively, the
biological residue may be recycled to the partial oxidation
gas generator in admixture with the other fuel streams and
the inorganic CN-csntaining sludge stream.
The upgraded water from the biological reactor may be
recycled to the gas quench and/or scrubbing zone or safely
disposed of without polluting the environment. The
composition of the upgraded water having a pH of about 7.5
is less than the following in parts per million: CN total
3.0, C~ free :L.0, SCN 1.0, sulfide 1.0, formate 50, NH3 20,
nickel-vanadium-iron 1, total suspended solids 40, and
BOD's, unfiltered 40.
DESCRIPTION OF THE DRAWING
A more complete understanding of the invention may be
had by reference to the accompanying drawing which
illustrates a preferred embodiment of the invention.
Although the drawing illustrates a preferred
embodiment of the invention, it is not intended to limit
the subject invention to the particular apparatus or
materials described.
Gas generator 1 is a vertical cylindrically shaped
unpacked free-~low non-catalytic steel pressure vessel
lined with refractory 2. Annulus-type burner 3 is mounted
in upper inlet 4 for introducing the reactant feedstreams
into reaction zone 5.
Burner 3 includes central passage 10, through which a
stream of free-oxygen containing gas from line 11 is
-13-
~3~
introduced, and annular passage 12 through which a mixture
of hydrocarbonaceous fuel and a stream of temperature
moderator, such as steam from line 13 is introduced. Fresh
liquid hydrocarbonaceous fuel feed in line 14 is passed
through lines 15-16 and into mixing tank 17. In tank 17,
the fresh liquid h~drocarbonaceous fuel is mixed with a
recycled liquid hydrocarbonaceous soot slurry stream from
line 18 and an inorganic CN-containing sludge which is
pumped into tank 17 by pump 19 from the bottom of settler
or clarifier 20 through lines 21-23. This fuel feed
mixture is passed through lines 24-25 and mixed in line 13
with a temperature moderator from line 26, valve 27, and
line 28 and/o:r steam from gas cooler 29 by way of lines
30-31, valve 32, and lines 33 and 25. By-product steam may
be passed through line 34, valve 36, and line 35 for use
elsewhere in the system or for export. Fresh boiler feed
water (~FW) enters yas cooler 29 through line 40.
The raw effluent gas stream frc~m reaction zone 5
splits into two gas streams in chamber 41. The two gas
streams in passages 42 and 43 are simultaneously and
separately cooled, cleaned, and scrubbed with water to
remove entrained soot. Thus, the hot gas stream in passage
42 is passed through dip-tube 44 and quenched in water 45
contained in the bottom of quench tank 46. A recycle
stream of water is in-troduced into quench tank 46 via line
47.
The quenched gas leaves through line 48 and is
scrubbed again ln nozzle scrubber 49 before passing through
dip-tube 50 into water 51 contained in the bottom of gas
-14-
~33~3~D
scrubber 52. The gas stream then passes up through shower 53
where it is contacted with water before leaving through line 54 at
the top of gas scrubber 52 as a clean stream of product synthesis
gas saturated with water. Nozzle scrubber 49 and gas scrubber 53
may be fed with fresh or upgraded recycle water from lines 55 and
56 respectively.
When the principal feed to -the gas generator comprises
an ash-containing solid carbonaceous fuel such as coal, then uncon-
verted carbon, ash, and any molten slag formed in the reaction
zone drops through the dip-tube 44 into the pool of water 45 in
quench tank 46. Any molten slag is quickly cooled to form
granular sol-id particles. Water is supplied to quench chamber 46
through line /~7. Accumulations of solid material, such as solidi-
fied slag or ash, unconverted carbon and bits of refractory are
wi.thdrawn as required from quench tank 46 through :Line 60, valve
61, 62 and a conventional lock hopper system (not shown). A suit-
abLe lock hopper arrangement is shown and descr:Lbed in coassigned
U.S. Patent 3,544,291. The solid residue and water are discharged
from the lock hopper into a conventional solids-liquid separation
means such as a settler, filter or centrifuge (not shown).
In the embodiment of the process in which the liquid
hydrocarbonaceous fuel comprises a liquid hydrocarbon such as
petroleum oil or a slurry of solid carbonaceous fuel in a liquid
hydrocarbonaceous fuel, additional unreacted carbon i.e. soot is
formed in the gasifier and is removed when the gas stream is
quenched in water 45. In such case,
3~
a stream of soot-water dispersion from the bottom of quench
tank 46 is pumped through line 70 and mixed ln line 71 with
a stream o~ soot-water dispersion from line 72. The later
stream of soot-water is obtained by scrubbing the second
split stream of hot raw synthesis gas from line 43 with
water after the gas stream is cooled by indirect heat
exchange with BFW in gas cooler 29. Thus, the cooled
stream of raw synthesis gas in line 73 is quenched and
scrubbed with water 74 in conventional yas scrubber 75 and
leaves through line 76 at the top. The gas stream is
cooled below the dew point in gas cooler 77. Separation of
water 78 takes place in separating tank 79, and a clean
dewatered stream of product synthesis gas leaves through
over head line 80.
Scrubbing water ~or gas scrubbers 52 and 75, may be
provided through lines 81 to 83 and 81 and 8~ to 86
respectively. The scrubbing water may comprise upgraded
water from line 81; Eresh make-up water from line 87,
valve 88, and line 89; and mixtures thereof.
The soot-water dispersion in line 71 and a recycle
portion of liquid organic extractant, such as naphtha, from
lines g5, valve 96 and line 97 are mixed together in line
98. The mixture o~ soot-water and naphtha passes into
decanter 10~ by way of inlet 105, an annular passage in
conduit sub-assembly 106, and lower horizontal radial
nozzle 107. The mixture is discharged below inter~ace
level 108. Simultaneously, the second stage naphtha is
introduced adjacent to or below the interface level 108 by
way of line 109, valve 110, line 111, inlet 112, central
~21~33~
conduit 113, and upper horizontal radial nozzle 114.
During the two-stage mixing, soot separates from the water
and forms a suspension with the liquid organic extractant.
In the decanter, a dispersion of particulate carbon-soot
and naphtha 115 forms in the upper portion of the decanter
and floats on water 116.
The water is passecl through lines 120 and 121,
pressure reducing valve 122, line 123, and flashed into
flash column 124. A stream of sulfur containing gaseous
impurities leave through line 125 and is sent to a Claus
unit for sulfur recovery. With valves 64 and 161 open and
valve 65 closed, at least a portion i.e. about 10 to 100
wt.%, such as about 20 to 50 wt.~ of the water in line 129
is treated in a water treatment facility, to be further
lS described. The remaining portion, if any, of the water
~ro~l line 129 may be passed through line 160, valve 161,
and line 162 and then through the lines leading into quench
tank 46 and/or gas scrubbers 52 and 75. Thus, by means of
valves 161 and 64, the degassed water in 129 may ~e split
20 between lines 160 and 132.
The soot-naphtha dispersion 115 in the upper section
of decanter 104 is passed through line 155 and mixed in
line 156 with fresh liquid hydrocarbonaceous fuel from
lines 14 and 154. Intimate mixing is achieved with mixing
25 valve 167, and the mixture i5 passed through line 168 into
naphtha still 169 equipped with reboiler 170.
Naphtha is vaporized in still 169 and leaves through
overhead line 171 along with a small amount of H20. This
stream is cooled be]ow the dew point in cooler 172. The
-17-
~;3 3~3~
liquid naphtha and water mixture is passed through line 173
and into separation vessel 17~. Gaseous impurities are
removed through overhead line 175 and sent to a Claus unit.
Water 180 is removed from the bottom of vessel 174 by way
of line 176, pump 177, and sent to flash column 124 by way
of lines 181, 121 and 123. Naphtha 182 is removed from
separation vessel 174 and recycled to decanter 104 by way
of lines 183, 184 and line 185. A portion of the naphtha
may be passed through line 186 and into still 169 as
reflux. Make-up naphtha may be introduced into the system
through line 187, valve 188, and line 189.
All of the liquid hydrocarbonaceous fuel-soot slurry
from the bottom of the naphtha stil] may be recycled to gas
generator 1 as a portion of the reactant fuel feed. Thus,
lS the bottom slurry from the naphtha still may be passed
through lines 18 and 16 into mixing tank 17 where it is
mi~ed with fresh liquid hydrocarbonaceous feed from lines
14-16, and CN-containing sludge from lines 21 to 23.
In order to produce a stream of upgraded water for
20 recycle to quench tank 46 and/or scrubbing unlts 52 and 75,
at least a portion of the stream of flashed grey water in
line 12~, or the water stream in line 67 from a settler
(not shown) or both are passed into mixing tank 63. For
example, both streams 132 and 67 may be processed together
in tank 63 when principal reactant fuel to the gasifier
comprises a slurry of solid carbonaceous fuel, i.e. coal
dispersed in a petroleum reslduum. Also, with low
soot-producing feed stocks such as coal-water slurries,
valves 64 and 161 may be closed and valve 65 opened since
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~33~)
in that embodiment the decanting zone may not be requlred.
In such case, at least a portion of the other solids, i.e.
about 10 to 100 wt.~, such as about 50 to 90 wt. 6, are
removed by conventional means from the water stream from
line 62, and the water is then passed throuyh lines 66, 67
and into the water upgrading facility.
The pH of the water in tank 63 is adjusted to a value
in the range of 7 to 9. Ferrous sulfate or ferrous
chloride is passed through line 68 to react with all of the
cyanides and sulfides present in tank 63 and to convert
them to iron cyanides and iron sulfides, respectively. The
treated waste water is then passed through line 133 into
mixing tank 134 where it is treated with a base from line
136 to adjust the pH to a value in the range of about 9.0
to 11Ø A sludge containing ferrous cyanide and other
compounds precipitates. Optionally, a weighting agent and
a polymeric flocculating agent to enhance the settling rate
may then be added through line 135. The mixture is then
passed through line 137 into a conventional clarifier or
settler 20. After settling, inorganic CN-containing sludge
i5 removed by way of line 21 and is pumped into mixing tank
17 as previously mentioned. The clarified water from
settler 20 is passed through line 138 into ammonia stripper
139 where it is stripped of ammonia by steam from line 140.
The NH3 and steam leave through overhead line 141; and,
the stripped water ls passed through line 142 into a
conventional biological reactor 143. Optionally, the NH3
in line 141 may be introduced into tanks 63 and/or 134 as a
portion of the base required for pH ad~ustment. The pH of
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~2~
the stripped water is adjusted to a value in the range cf
about 6-8. Organic matter, such as formates, are converted
in reactor 143 into C02 which leaves through line 144, and
a biological residue. Upgraded water leaves biological
reactor 143 through lines 145 and 81 and is recycled to
quench tank 45 and to gas scrubbers 52 and 75 in the manner
described previously. A portion of the upgraded water, now
being environmentally safe, may be optionally discharged
from the system through line 146, valve 147, and line 148.
Optionally, the biological residue may be passed through
line 149, valve 150, and lines 151 and 23 for reaction in
partial oxidation gas generator 1 after being mixed with
the other reactant fuel feedstreams in mixing -tank 17.
EXAMPLE
The following example illustrates an embodiment of the
process of this invention, and it should not be construed
~s limiting the scope of the inventionO
A slurry comprising 3724 tons per day of Kentucky
bituminous coal having the following Ultimate Analysis in
wt.% is reacted by partial oxidation to produce a raw
effluent gas stream: C 72.18, H 4.96, N 1.65, S 3.45, Ash
9.68 and 0 8.08.
About 0.2 - 0.3 wt.~ of the ash or about 1.08 tons per
day appears as soluble material in the gas quench cooling
and scrubbing system. To control the total dissolved
solids at 2500 parts per million (ppm), a blow down stream
of 72 gallons per minute of water is taken having the
following analysis in parts per million: S 20, CN 30, SCN
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10, NE~3 150n, formate 300, ash 200, and total inorganic C
30.
After removal of at least a portion of the entrained
solids, the pH of the water is adjusted to about 8. At a
temperature of 1~0F., 0.0106 lbs. of FeS04 . 7H20 per
gallon of water are mixed with the water. The pH is then
adjusted to about 10 by the addition of about 0.06 lbs. of
Na0H per gallon of water. About 1190 pounds per da~ (dry
basis) of an inorganic CM-containing sludge precipitates
out substantially having the following composition in
weight percent dry basis: ash 35.4, FeS 9.~, Fe(CN)2 5.6,
and Fe(0H)~ ~9.2. Optionally, to enhance the settling rate
of the sludge in a settler, a conventional weighting agent
such as colloidal clay may be mixed in followed by about
0.05 wt.% of a conventional flocculant coagulant, such as a
polyelectrolyte polymer.
The inorganic CN-containing sludge is then rnixed with
the coal slurry feed to the partial oxidation gas generator
as a portion of the feed.
The overflow water stream from the settler is stripped
! of NH3 in an ammonia stripper, and the formates and other
organlc matter are reacted in a conventional biological
reactor after a pH adjustment to about 7. A biological
residue and upgraded water are produced which are suitable
for disposal without effecting the environment. The free
CN and S contents in the upgraded water are less than 1
ppm, formates are less than 50 ppm and ammonia is less than
20 ppm. This upgraded water stream may be recycled to the
quench cooling and/or scrubbing zone. Further, by the
subject process, the toxic sludge having a CN content of
-21-
over 27,000 parts per million is safely disposed of in the
gas generator without effectiny the environmen-t. In one
embodim~nt, the biological residue is also recycled to the
gas generator as a portion of the feed.
The process of the invention has been described
generally and by examples with reference to a
hydrocarbonaceous fuel and gas streams of particular
compositions for purposes of clarity and illustration only.
It will be apparent to those skilled in the art from the
foregoing that various modification of the process and
materials disclosed herein can be made without departure
from the spirit of the invention.
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