Note: Descriptions are shown in the official language in which they were submitted.
CA 02521982 2005-10-03
Attorney ~ket No. 2245-t~0a2
APPARATUS AND METHOD FC?R
C~~t_ GASIFIG~TIQN
BA~KGRt3Ul~ll~ OF THE INVENTION
[1~00~1The invention concerns an apparatus and process for converting
coal into a substitute natural gas. More particularly, the invention concerns
converting, via non-catalytic partial oxidation, liquid condensates Pram a
primary
gasification process into secondary synthesis gas, resulting in utilization of
substantially all lay-product streams for production of additional raw gas,
thereby
minimizing undesirable effluent produced by the gasification process.
[Clt~l~~ Coal gasification technology is well known and has been in
commercial use, for example, in South Africa for many years. The most
comrnoniy
employed coal gasifier is that developed by Irurgi k~vhle and
I~ineraloeltechnik
GmbH. The l..urgi process utilizes a fixed bed gasifier into which coal of a
selected
particle size is fed countercurrently to a stream of steam and oxygen.
[~~~D3~ Goal gasification processes are accompanied by the generation of
by-products essentially comprised of oil, tar and phenolics. Disposition of
this
by-product presents significant environmental and economic problems.
[tf0~4Therefore, there is seen to be a need in the art for an apparatus
and process which will utilize essentially all of the by-pr~l~t streams of a
gasification process for production of further raw gas to maximize the
synthesis gas
produced by the gasificatit~n process.
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CA 02521982 2005-10-03
Att~~ney Dt>cket No. 2245-t~.7~52
SUMMARY OF THEONVENTtON
[t~O] Accordingly, process for converting coal into a substitute natural
gas begins by placing a charge of coat into a coal gasification unit and
causing
gasification of at least a portion crf the charge by exposing the charge to a
gasifying
agent and heat. Primary raw gas is recovered at an outlet of the coal
gasification
unit and at least a pardon of the primary raw gas is passed into a port-
catalytic
partial oxidation unit where a partial oxidation agent and the temperature is
maintained to convert the at least portion of the primary raw gas Into a
secondary
raw synthesis gas substantially devoid of higher hydrocarbons.
~0001~] In another aspect of the invention, a process for converting coal
into a substitute natural gas begins by placing a charge of coal into a coal
gasification unit and causing gasification of at least a portion of the charge
by
exposing the charge to a gasifying agent and heat in the coal gasification
unit.
Primary rave gay is ~ecavered at an outlet of the coal gasification unit and
subjected
to quenching to separate condensable hydrocarbon containing liquid therefrom.
The
liquid is then subjected to a non-catalytic parCial oxidation in the presence
of a partial
oxidizing agent at a temperature sufificient to convert the liquid into a
secondary raw
synthesis gas substantially devoid of hydrocarbons other than carbon monoxide,
carbon dioxide and methane.
[!gQ01] In still another aspect of the invention, apparatus for converting
coal
iryto substitute natural gas includes a plurality of coal gasiftcation units,
each
operable to cause c~asification of at least a portion of a charge of coal fed
thereto
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CA 02521982 2005-10-03
Attorney Docket No. 2245-D~?~0~2
and to produce a primary raw gas at a gasifieatian unit output. A quenching
system
having an input coupled to each of the gasification unit outputs receives the
primary
raw gas therefrom and is operative to separate condensable hydrocarbons in
liquid
form from the primary rarrr gas, to deliver the liquid to a quenching system
liquid
output and t0 deliver cooled raw gay as the substitute natural gas to a
quenching
system gas output. A partial oxidation unit having an input coupled to the
quenching
system liquid output is operative to subject received liquid hydrocarbons t0
partial
oxidation at a temperature sufficient to convert the liquid hydrocarbons into
a
seCOndary raw synthesis gas substantially devoid of hydrocarbons at a gas
r~utput of
the partial oxidation unit.
BRIEF DESCRIPTIt~I~ OF THE DRAWING
[Ot?01~~ The objects arrd features of the invention will became apparent
from a reading of a detailed description, taken in conjunction with the
drawing, in
which:
jOQ(t] Figure 1 is a block diagram of a coal gasification system arranged
in accordance with the principles of the invention;
[~01~~ Figure 2 is a block diagram showing a primary gasification unit and
a partial oxidation unit coupled via an optional quenching system; and
[t?01't~ Figure 3 is a block diagram c~f an exemplary gasification plant using
a single partial oxidation unit with four primary coal gasification units and
a
mufti-stage quenching system, arranged in accordance with the principles of
the
invention.
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CA 02521982 2005-10-03
Attorney Docket t~ia. X245-UC>Ut~52
DETAILED ~ESCRIPT1(~N
[00~12~ As used in this description, the term "higher hydroca~ans" refers to
hydrocarbons having a composition GnH",, where n and m are integers and n is 2
or
higher.
[tt'tWith refierence to I=ig. 1, a basic block diagram sl~ca~rving the
optional arrangements of the invention is displayed. Primary gasifier 10~
directs raw
gas at ifs output 11 ~i to either a quench and liquor separation unit 1 Q6 via
path 11 UA
or via path 110B to a non-catalytic partial oxidizer unit 104. If path llt~B
is utilized,
then the input to partial oxidizer 104 is basically in gaseous fiarm. If the
quench and
liquor separation unit 106 is used, then the input 116 to partial oxidizer
unit 104 is in
liquid form, being condensate generated by the cooling process taking place in
unit
1 Ofi.
[Otll ~.It will be apparent to those skilled in the art, that only a portion
of
the raw gas 110 may be fed via optional path 1108 to the partial oxidizer unit
1 t14.
j~016] When the raw gas 110 is subjected to quenching via path 110A
prior to being fed to partial oxidizer it34, the resultant generated secondary
synthesis
gas at output 114 would then be routed' via path 114A back to an input ofi
quenching
system 1(36 for fiurther cooling. t~therwise, if quenching is not perfiormed
prior to
partial oxidation, the secondary raw synthesis gas at 114 may be directed to
system
output 11 ~ via path 114B.
[00't~6~ What differentiates the instant invention firam known gasificatian
processes is the inclusion of a non-catalytic partial oxidation unit 10~..
Unit 104
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CA 02521982 2005-10-03
A~ffJrll~~ DC~~Cet ~0. 22~~-~2
produces additic~nai raw synthesis gas from the tars and oils present in raw
gas
stream 110 in gaseous form or at input 116 in liquid form. Hence, aI6 by-
producf
streams are utilized for the production of raw gas, minimizing the effluent
produced
from the process.
[~0~ 7~ Partial oxidizer 1 Q4 converts higher hydrocarbons into carbon
monoxide and hydrogen and some inadvertent carbon diaxide. This is
accomplished at a very high temperature using direct contact with a hot flame
burner
in a substoichiometric oxygen atmosphere which prevents a vast majority of the
generated carbon mont~xide from converting to carbon dioxide.
[0018, C~irect feed of raw gas 11fl via path llflB makes sense in those
applications where methane is not desired in the final substitute natural gas
end
product. However, when using the quench and liquor separation system 1 f~~,
only
the derived liquor is passed to the partial oxidizer and not the raw gas
exiting at path
11 t~. In this type of application, methane is usually a desirable component
of the raw
substitute gas at system output 1' 12 and will be passed directly thereto via
system
1 U6 without going to partial oxidizer 104. ,
[t3t~19~ Wifih reference to Fig. 2, a basic arrangement of the primary
gasifier, nan-catalytic partial oxidizer and an optianal quenching system 212
are
depicted.
[~fl2~#~ A coal lock hopper 2~4 is a pressure vessel and allows the gasafier
2~6 to be fed in a batch operation. Coa! lock 204 has a bottom and top closure
which are operated hydraulically. Goal flows through a disposal chute 2iJ2
into the
coal lock 2fi34 when coal lock 244 is at atmospheric pressure (with the bottom
cone
CA 02521982 2005-10-03
Attflmey C?flcket ~Ifl. 2245-D~~052
enclosed and the tap cane open). After coal lack 204 ifull, the tap cone is
closed
and coal lack 2g4 is pressurized with a raw gas taken downstream of the, gas
cooling
unit. Final pressurizing is dare through a direct Line Pram the tap section of
the
gasifier 2g6 to the coal loch 204.
[pp2l~ When coal lath 2p4 is at the gasifier pressure, a bottom cone
opens and coal begins flay#~in g into gesifier 20~ uia a distri~utar 208,
preferably
comprised of a cyclone skirt. When coal lock U4 is empty the bottom cone
closes
and is ready for r~cyclinc~.
[~U22] Gasifier 2018 is a double-walled pressure vessel. High pressure
boiler feed water is kept i~ the jacket farmed by the double walls so as to
limit jacket
and gasifier wall temperatures. High pressure boiler feed water is circulated
through
the jacket by dawncarne~s. During operation, a considerable amount of heat is
transferred from the fuel bed to the jacket. The jacket steam is added to the
high
pressure steam and the total steam is mixed with oxygen at a ratio of
approximately
U.4 pounds of steam per SGF oxygen. This gasificatian agent is routed via a
rotating
grate 2g9 into the gasifier fuel beck. Gansequently, grate 2t~9 is cooled by
the
gasification agent. Grate 2C~9 is papered by alternating current drives and
serves to
first, enable distribution of the gasificatian agent an the cross section of
gasifier 2~8
via gasificatian agent ring slats. The distribution is completed in the ash
bed.
[0~2~] Secondly, grate 2~6 carries ash towards the ash lock hopper 210,
helps disintegrate ash aglamerates and grinds ash lumps to a maximum size to
avail blockages of the ash lack canes. Finally, grate 209 heaps the fuel bed
in
oration.
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CA 02521982 2005-10-03
AttdfrsEy C30e~et h~4. 22~~-~~U052
[U~4] Grate 2(79 is automatically speed controlled by the oxygen flow to
adapt the ash turn out to the ash production. Manual corrections of the grate
speed
are also possible. The turn-out capacity of grate 2(79 is determined by the
number of
plows installed underneath the grate and the speed of the grate 209. Crate 209
runs
continuously and is only stopped for chart periods when the ash lack 21 U
cycle
begins.
[gt725~ The gasificatian agent, far example, a mixture of oxygen at conduit
233 and steam at conduit 23~, is passed through the following reaction zones
in
vessel 2g6.
~~~6~ In the ash bed 206A, the gasification agent is superheated by ash
leaving combustion zone 20613 at a temperature of approximately
273t?°F. lender
the assumption that a sufficient ash bed 206A is established, the ash is
coated dawn
to a temperature higher than that of the gasification agent while the
gasification
agent is heated up gentry into vessel 206.
[U627j In a combustion zone 2068, carbon and oxygen are converted to
carbon dioxide and heat. The temperatures of the gaseous flaw going upwards
and
the ash which has a carbon content of approximately 2°la) sinking
downwards,
increases to nearly 27f33°1~.
[OtI~B~ The gas streaming upwards frarn the combustion zone 268
consists mainly of carbon dioxide and steam and reacts in the gasificatian
zone
2060 at an average temperature of approximately 15607°F. The dominating
reaction
in gasification zone 2g60 is the conversion of carbon and water into carbon
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CA 02521982 2005-10-03
Attorney Docket No. 2245-OOflt152
monoxide, hydrogen and heat. A methanation reaction has a minor influence on
the
composition of the gas leaving gasif(cation zone 2U6C.
~g029] In a carbonization zone 2(~&D, volatiies in the coal are expelled.
The carbonization reaction is heat consuming. Consequently, the gasification
raw
gas streaming upwards from the asif(cation zone 2Q~~ must heat up the
downflowing coai and de(iver heat for carbonization. Additionally, in
carbonization
zone 2ga, recycled dusty tar is cracked to oil and coke.
~00~~ Ash lock 210 is pressure vessel having hydraulically operated
bottom and flop closures, Ash lock 210 serves to remove ash from gasifier 2Q6
and
is operated in cycles, each having the following steps.
[gg~'1 ] The continuously running grate 209 turns the ash out of gasifier 2f~6
through hydraulically actuated top cone into ash lock 21 ~ with its bottom
cone closed
at gasifier pressure. As soon as ash lock 2~0 (s full, grate 209 is stopped.
After the
ash lock top cone is shut and sealed, grate 2g~ is restarted.
jt~0~2] Ash lock 210 is then lowered to atmospheric pressure, the bottom
cone of the ash lock 210 is Opened and ash flows out of ash lock ~1g into a
sluice-way 25where it is quenched and hydraulically carried away to an ash
plant.
[t1Q3a Flaw gas generated by gas(fier unit 2Uf> ex(ts at conduit 235 and is
directed -to optional quenching system 2t2 whose o~rtput X37 contains liquid
candensates from the quenching process. Alternatively, in a direct feed system
quenching system X12 is not utilized and raw gas is fed to partial oxidizer
unit 266..
[004 In the optional scrubbing/cooling apparatus 212, excess water,
certain condensable hydrocarbons and a small quantity of solids are separated
from
8
CA 02521982 2005-10-03
Att~!rney ar.,cket Na. 2245-OtH7052
the raw gas stream in conduit 235. The liquid stream in conduit X37 serves as
a
feedstack to the partial oxidation unit 2~ 6.
[C11751 In the non-catalytic partial oxidation unit 216 the feedstock reacts
with oxygen in the presence of steam as ~ moderator to raw synthesis gas, Hot
raw
gas is cooled by direct injection of water in quench pipe X18 and quench
uessel 2~t~.
A separation vessel carries away slag at its output 249.
jl~Ct36~ flan-catalytic partial oxidation unit 216 partially oxidizes the
heavy
fractions at a temperature of approximately 25011°F. and at a pressure
of about
435 psig. C7xygen at conduit 239 and steam at conduit X41 are added to the
incoming feedstock in conduit 237 via a partial oxidation burner unit 214.
Burner
21 ~ ensures intensive mixing of the feed, which is necessary far a high
conversion
into the desired raw synthesis gas.
[4~7~ In ors injection zone of reactor ~~6, the feed is partly oxidized in the
flame of burner 214. The gross reactions in unit 216 essentially convert
higher
hydrocarl3ons to carbon monoxide and hydrogen in two phases.
[U038~ lr~ a first heating and cracking phase, feed and oxygen leave burner
214 at respective preheating temperatures. Prior to actual combustion, the
reactants are further heated by the heat reflected from the flame and glowing
brickwork of vessel 216f the high hydrocarbons of the feed crack into
radicals.
[Otl~9~ Next, in a reaction phase, on reaching ignition temperature, a
portion of the hydrocarbons react with the oxygen in an exothermic reaction
forming
carbon dioxide and water. Practically, all of the oxygen available is consumed
in this
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CA 02521982 2005-10-03
Attorney Doei~et No. 2245-OOOt352
phase. The non-oxidized portion of the hydrocarbons reacts with steam and the
reaction products are mainly carbon monoxide and hydrogen.
[004g~ ~s mentioned previously, feedstock, oxygen and steam enter
reactor 216 via burner 214, which is mounted at a top portion of reactor 216.
~umer
214 preferably has a four-nozzle design with a central dummy tube which takes
up
the start-up burner. At start-up, the central tube bears the ignition and
start-up
burner, which is equipped with a flame control sensor. For heating up reactor
216,
plant air and fuel gas are fed via the start-up burner at conduit 243. At
higher
temperatures, when higher heating duties are required, air and fuel gas are
also fed
via four lances of the burner. At a reactor temperature well above the self-
ignition
temperature of the fuel gas, normally at about 1470°F, the start-up
burner is
removed and replaced by a steam-purged dummy.- wring the final heating up to
approximately 2260°F, fuel gas and air are fed through the four burner
nozzles.
[~~41To maximize the volumetric capacity of partial oxidation reactor
216, fine coal may optionally be added to the liquid feedstock via lance
burner 2i 4.
[~t14~~ burner 21 ~4 is cooled with cooling water and by the media passing
therethrough. The reactor outlet to quench pipe 218 is also cooled in order to
minimize refractory wear at this point.
~~t143~ The conversion of hydrocarbons by partial oxidation occurs in
refractory lined reactor 216. The refractory material is selected according to
ash
load and ash properties of the feed stock. The ash must melt at the reactor
operating temperature to guarantee free flow of molten ash from reactor 216 to
the
quench vessel 226 and tc~ avoid blockage of reactor 216 and quench pipe 218.
CA 02521982 2005-10-03
A'~ftSrrlG'Y CJOG~G~~ CIO. ~~45~~2
[Ott~~~ Hot raw secondary synthesis gas from reactor 2U6 is routed via
quench pipe 218 to quench vessel 22Q. The secondary synthesis gas is
instantar~eouly cooled from about 247°F to an equilibrium temperature
of
approximately 4t~~F by water injection. i_iquid slag flowing with the gas
solidifies
into particles. The particles could be leached in either an acid or alkali
medium.
Gas is separated from surplus guench water and slag particles below quench
pipe
21 ~ and the quench vessel 220. Gas is withdrawn through a separate nozzle and
the slag water collected is routed via level control to slag separator 222.
The slag is
separated from the soot water leaving the quench vessel via conduit 25~ in a
slag-like system having slag separation vessel 222. The heavy slag particles
settle
from the soot water in the slag separation vessel 222 and are collected in a
bottom
cone for discharge via conduit 243.
i0tt45~ Collected soot and ash may be mixed info a soot slurry and sent to
a metal ash recovery system where the soot slurry is flashed to atmospheric
pressure in a slurry tank. The slurry is filtered resulting in a filter cake
and clear
water usable for quenching and scrubbing operations.
[0~4~~ Fig. 3 presents a block diagram of a gasification plant using a
single non~cata,lytic partial oxidation unit with four primary coal
gasification units.
This type of arrangement takes advantage of the fact that only the pyroiysis
products
from the ra~v gas generated from the primary gasification units are being
partially
oxidized. Hence, one needs only the capacity of a single partial oxidation
unit for
several pup to five} primary fixed bed degasifier units,
11
CA 02521982 2005-10-03
~1~8i'n~~ ~G~CBt N0. '~c4~-
[0Q47] As seen from Fig. 3, sources of coal to be gasified 361 a-d are
respectively fed to a disposal chute 3ia0 of each of four fixed hed gasifier
units
802a-302d. From input chute 350 the coal is passed into input lock hoper 352
which
is coupled to the processing vessel. Near the tap at the inlet to the
processing
vessel a cyclone skirt 354 assists in distributing the coal charge which flaws
dawnwardly through the vessel countercurrent to the flaw of the gasification
agent
supplied to respective inputs of vessels 3f?2a-d from oxygen source 3f?5 and
steam
source 3tt7. A rotating grate 356 distributes the gasificatian agent and
processes
ash within the system as described above with respect to Fig. 2.
~~Q~B~ Raw gas from the process is collected at outputs 303a-d which are
coupled tr~gether at conduit 313 as a gaseous input to quenching system 3U6.
As
mentioned above, the gasification agent is a mixture of oxygen and steam.
[0049 Quenching system 33G is comprised of a serial connection of five
heat exchange units ~i~8, 31t~, 312, 314 and 316. The initial stages 308 and
310
receive a relatively high temperature gas input and generate high pressure
steam
from the heat exchange process. Condensates from 308 and 31Q exit the units at
liquid outputs 30ga and 309b and are comprised primarily of thicker tars and
ash.
[I~il66Z Subsequent stages of the quenching system 306 result in
generation of medium pressure steam and the condensation of lighter oils. As
seen
from Fig. 3, the gas output of each stage is connected to the gas input of a
succeeding stage up until the final stage 316 whose output X11 farms the
primary
system output carrying cooled raw substitute natural gas.
12
CA 02521982 2005-10-03
Atfarn~y Docket No. 2245-00052
[005't] Hence, gaseous output 317 is coupled to an input of heat
exchanger 31 ~ whose gaseous output 319 is in turn coupled to the input of
heat
exchanger 312. Gaseous output 321 of unit 312 is connected to the input of
unit 313
and output 3~3 of unit 314 is coupled to an input of the final stage heat
exchanger
unit 1 ~.
jt?052The liquid outputs 30a-a are coupled together at one primary
quenching system liquid output 3C?9.
~~t13~ (liquid hydrocarbons in conduit 309 are coupled to an input of
non-catalytic partial oxidation unit 30~. Oxygen from source 365. and steam
from
source 307 are additionally coupled to the input of unit 3Qand the secondary
raw
synthesis gas comprised mostly of hydrogen and carbon monoxide exits unit 304
via
conduit 315 and directed back to an input 313 of the quenching system 3f~f for
further cooling.
~0~4~ Plant Output 311 therefore contains quenched raw substitute
natural gas at approximately 9~°I= which is essentially free of the
pyrolysi's products
generated in the primary gasifiers 3f72a-d.
E?CA1VIP~E
[O~tiS~ Unreactive coal ~i.e., coal containing more than about 3t?°l~
non-combust'sble cc~ntarninants~ having ash content up to about 50
wt.l°l° is fed to a
primary gasifier arranged as shown in Pigs. ~ or 3 and a primary raw gas is
produced at the output of the primary gasifier having a composition by volume
percent of ~8,°l° carbon dioxide, t3.65°~'°
hydrogen sulfide, 0.69°f° higher
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CA 02521982 2005-10-03
Attamey Docket ~Jo. 2245-Clf3~3CZ52
hydrocarbons, ~2.6fi°lp carbon monoxide, 38,51 °lQ hydrogen,
9.5°la methane and
.39°I~ nitrogen. Raw gas as produced above is then directed to a
quenching system
wherein the products of pyroiysis and other figuids are condensed out of the
gas
stream and passed to the input of a non-catalytic partial oxidation unit
running at a
reaction temperature of about 2578°F. The raw gas from the gasifier is
then
reformed in the partial oxidation unit, crackeei and hydrolysed, and the
established
process in c~asificatior3 reaction conditions result in the following typical
gas
compCanents at the output of the partial oxidation unit expressed by volume
percent:
1.9°!~ carbon dioxide, U.O~°lo hydrogen sulfide, ~% carbon
monoxide, 45.1°f~
hydrogen, ~.~°~ methane and ~.~2°l~ nitrogen.
[~~56] The application has been described with respect to a specific
embodiment for the sake of example only. The scope and spirit of the invention
are
to be determined from appropriately interpreted claims,
14
