Note: Descriptions are shown in the official language in which they were submitted.
2~689:~1
1 56,682
SEPARATION OF POLLUTA~TS IN TIIE
INCINERATION OF MUI~ICIPAL SOLID '.!AST~
BACKGROUND OF THE INVENTION
This invention relates to the disposal of munici-
pal solid waste (MSI~) and it has particular relationsh~p
to such disposal by incineration. ~his invention is inti-
mately related to incineration of ~ISIr and is uniquelyapplicable to thls way o~ disposing o~ MSI7. But it is to
be understood that this invention may find ada~tation in
other areas, for example, in the treatment o~ flue gases of
power plants whose primary source of power is fossil fuel,
and that such adaptatlon is within the scope of equivalents
of this application and of any patent which may issue on or
as a result thereof.
As landfills for MS~J become filled and it becomes
more and more n~cessary totrespass on residential areas
where the landfills are decidedly unwelcome, 1t has become
indispensible to create other facilities than deposit in
landfills for disposing of rlSI~. Among these facilities is
the incineration of the MSW, usually, at the same time t-o
generate electrical power. This alternative to landfills
has been put into use in a number Or states in the US, In-
cineration Or the waste generates pollutants,-specirically
hydrochloric acid, hydrofluorlc acid, sulfur oxides, nitro-
gen oxides, carbon monoxide and flyash containing unburned
carbon. It is ~ssential ~hat these pollutants be separated
from the flue gas which is released to the atmosphere or
that their content in the gas be reduced to a very small,
harmless magnitude. Indeed~ one of the handicaps, under
' '' ' , ; ;.
.:
2~911
2 56,682
which inclneration Or waste ln accordance wlth prior art
practice suffers, ls the failure to separate or reduce the
pollutants to a harmess magnitude at a reasonable cost.
It is an obJect Or this invention to suppress the
toxlcity of the flue gases and the ash in the incineration
of ~lSll by separating the pollutants from the gas which is
discharged to the atmosphere and rrom the ash which is de-
posited.
Commercial emissions control technology, in accor-
dance with thé teachings of the prior art, generally performsthe functions of particulate control, sulfur oxides (herein
S0x) control, ]ICl/HF control, and nitrogen oxides (herein
N0x) control in a step-wise fashion, requiring large plant
space and high equipment cost. Commercial particulate con-
trol devices that will remove small particles such as bag-
house ~abric filters and electrostatic precipitators, operate
only at limited low temperatures (~250C) (482F), are very
large devices and are sensitive to flue gas and particulate
conditions. They may not, for example, be efrective in the
removal of very fine particles or sticky particles may raise
reliability concerns, and may not ~unction well under certain
flue~gas compositions.
Commercial technology of the prior art for Sx and
HCl/~F removal includes both wet and dry systems operated
as once-through or recovery processes. The commercial mar-
~et is dominated by lime-based and sodium-based systems.
These commercial processés may be able to function with MSW
incinerators, but n~aintenance, reliability and cost factors
are ma~or concerns. The temperature limitations for these
3 commercial processes would place them generally after all
heat transfer equipment in the plant, so none of the equip-
ment would be protected from the potentlally corrosive and
fouling nature Or the combustion products.
The commerclal N0x flue gas treatment processes
` 35 are large and generally expensive, and some are very sensi-
tive to particulate and to flue gas conditions, requirlng
particulate removal before accepting the rlue gas, and opera-
tin~ over limlted temperature ranges with uniform gas flow
re~luired .
:, . . .
2~8~11
3 5~,682
It ls an ob~ect of this invention to overcome
the drawbacks and deficiencies Or the prlor art and to
provide for the suppression of the toxicity and corroslve
erfects in the incineration o~ MSI~ reliably and economically
and with mlnimum maintenance requirement.
SUMMARY OF THE INVEI~TION
In accordance with this invention, there is pro-
vided a method o~ separating pollutants in the incineration
of municipal solid waste in whose practice the MSW is burned
and converted into flue gas and ash. The flue gas is passed
to a pseudo-liquid fluid-bed filter contactor in which there
are filters, typically ceramic candle ~'ilters. The gas
which drives the fluid-bed may be the flue gas itself,
driven, ~sually by positive and negative pressure, at a high
enough velocity to produce the pseudo~ uid condition. The
fluid-bed may also be driven by a separate pump-driYen gas
in addition to the rlue gas which can be reactive wlth the
gaseous pollutants in the flue gas. The particulate which
constitutes the bed may be particulate in the flue gas or
2~ separate particulate such as aluminum oxide. Or it may be
separate particulate sorbents which react with the pollutants
or serve as a catalyst in pollutant reactions.
In the fluid-bed filter contactor, certain pollu-
tants are converted into nontoxic particulate, by dry in~ec-
tion of sorbents, ~iltered out by the filters and removedas ash. The treatment of these pollutants is a once-through
operation. Other o~ the pollutants are converted into atmos-
pheric gases which pass through the filters and are vented.
Specirically, the HC1 and HF are converted into salts Or
3 calcium, strontlum or sodium and o~ other alkaline or alkaline-
earth elements. The SOx, SO2 and SO3 are converted into par-
ticulate sulfates. The i30X, i.e., NO, NO2, N20, N204, is
converted into atmospheric gases, nitrogen and oxygen, in a
catalytic reaction. The carbon monoxide is converted into
carbon dioxide, an atmospheric gas, by oxidation by the air
ln the bed. The flyash is partlally agglomerated into lar~er
particles and filtered out as ash. Since the flue gas in the
'I ` ~-`
: .
- 2~
4 56,6~2
fluid-bed fllter contactor is at an elevated temperature,
the reactions with the pollutants are accelerated.
Specifically, the lnvention comprehends the
separation Or the pollutants in a fluid-bed filter contactor
having high-temperature resistant ceramic filters by dr~
in~ection of HCl, HF, and desulfurizatlon sorbents and con-
version of NOX by reductants operating in a catalytic re-
action. The ceramic filters provide nearly complete parti-
culate removal.
BRIEF DESCRIPTION OF THE DRAIrI~GS
For a better understanding Or this invention, both
as to its organization and as to its operation, together
with additional ob~ects and advan~ages thereof, reference
is made to the following description taken in connectlon
with the accompanying drawlngs, in which:
Figure 1 is a flow block diagram showing the
practice of this invention and presenting as blocks typical
apparatus used in the practice o~ thls invention;
Fig. 2 is a diagrar~matic view generally in longitu-
dinal section showing a fluid-bed used in the practice o~
this invention;
Fig. 3 is a diagrammatic view in longitudinal
section showin~ a bubblin~ fluid-bed used ln the practice
o~ this invention;
Fig. 4 is a diagrammatic view in longitudinal
section showing a turbulent fluid-bed used in the practice
of this lnvention;
~i~. 5 is a dia~rammatic view in longitudinal
section showing an entrained bed used in the practice of -
this invention; and
Fig. 6 is a rlow block dia~rammatic view showing
specific practice of this lnvention.
DETAILED D~SCRIPTIOM OF IIIVENTIOII
.
Fig. 1 shows incineration apparatus 10 in which
the block 11 represents the storage and the ~eeding Or the
MSW. The II~W is red, ror example, by a conveyor, into the
burner 13 where it is burned~ producing flue gas and leavin~
., .
` ' : , , . ~, . r:.,., ",,
: :
` ~'' ' ,: :
` '; '
.
2~S~9~1
56,682
a residual ash which is removed from the burner. The burner
is supplied wlth alr, usuall,y forced draft to erfectuate the
combustion. The flue gas, the combustion ~roducts of the
burner, heats a SteaM generator 15 which, as is customary
in the incineration of MSI~, generates steam to drlve a tur-
bine to produce power. Typically, the steam generator 15
includes a boller, a super-heater and an evaporator (all not
shown). The combustion products pass from the steam genera-
tor 15 into a fluid-bed fllter contactor 17. In ~ig. 1 the
fluid-bed contactor 17 is shown connected between the steam
generator and a heat exchan~er 19. In actual practice the
contactor 17 may be interposed between any two Or the above
three listed components, for example, between the boiler and
the super-heater or between the super-heater and the evapora-
tor. The flue gas which rlows into the contactor 17 is typi-
cally at a tem~erature o~ about 90~F (483.5C). If the
contactor 17 is interposed between the boiler and the super-
heater, the flue gas tem~erature is about 1500F (815.5C).
In contactor 17 the pollutants are removed from the combustlon
2~ products or reduced to a small harmless content, The result-
ing cleaned gas flows into the heat exhan~er 19 whére it is
cooled and then flows lnto and out of a stack 21. Some heat
derived from the heat exchan~er 19 may be su~plied to preheat
the combustion air for the burner 13. There is provided
facilities 23 for storing and feeding the sorbents, As shown
in Fig. 1, the sorbents may be ln,~ected in one or more of a
number of points in the system 10, namely, into the feed chan-
nel 25, conducting the flue ~as from the burner 13 to the
steam generator 15; between any two of the three components
3~ of the steam generator 15, but, in this caseS the fluid-bed
contactor 17 must be downstream of the ~olnt of in,~ection;
into the feed channel 27 between the boiler and the bed 17,
and/or dlrectly into the fluid-bed 17. There is also ~rovlded
a facility 29 for storin~ and feeAin~ a reductant for N0x.
The reductant may be supplied directly or throu~h c~lannel 27
into the flu~d-bed 1,. T~nicall~, the cat~lvser for the re-
duction is lncluded with the sorbents.
..
2 ~
~ 56~682
Instead of beln~ exhausted f'rom a stack, the
cleaned flue ~as can drive a turbine (not shown), typically
in a pressurized combustion plant. In this case, the heat
exchanger 19 would be omitted. ~oth the steam turblne and
the flue-gas turbine may be supplied or the boiler of the
steam ~enerator 15 and its turblne may be omitted. The
latter alternatlve has the advanta~e that the temperature Or
the flue ~as is not reduced by the boiler.
The fluid-bed filter contactor 17 ma~ be of the
type disclosed in Degnen et al., US 2,54R ~ 875 or Newby et al.,
4,9?3,548. Specifically~ it includes a container 31
(Fig. 2) havinga plenum 33 separated from a lower chamber
35 of the container by a tube sheet 37. A plurality of
ceramic candle filters 39 are suspended from the tube sheet
37 into chamber 35. The filters 39 are hollow and closed
at the bottom. They open into the plenum 33. Above the
lower wall of the chamber 35, there is a distributor screen
41. The ~aseous products of combustion (the flue gas) are
injected by a drive (not shown), usually positive and/or
negative pressure, in the plenum 45 below the screen 41 and
distributed above the screen where they produce a pseudo-
liquid fluid-bed 44 by reacting physically ~ith the particu-
late sorbents or with particulate of a separate material
in~rt to the pollutants such as aluminum oxide. The pollu-
tants HCl, HF, Sx are converted into solid particulatewhich is captured by the pores in the external surface of
the filters 39. The cleaned ~as, sans the particulate,
passes through the filters into the plenum 33 whencè it is
emitted to the stack 21 or to a turbine. The solid particu-
3 late is moved upwardly and do~lnwardly and in en~a~ement withouter surfaces Or the filters 39 and scours the surfaces,
removin~ the ca~tured particulate. The particulate which
forms the bed typically has a cross dimension (diameter) of
0.25-inch (o.64 cm) or less. The solid ~articulates which
` 35 result from the reaction of the sorbents and the pollutants
in the flue gas are discharged as ash, together with any
unused sorbent-inert particles and the f`lyash, which is also
captured by the filters 39 and by the solids in the fluld-bed.
- -, , ~; ; .; : . .. ' ;
,:
.
20~91 1
7 56,682
The N0x is reduced to nitrogen and oxygen by the
reductant in the presence of a catalyser which is included
in the sorbent. The nitrogen and oxygen pass through the
candles and are released as clean gas. ~he carbon monoxide
is oxidized to carbon dioxide, which is also passed throu~h
the candles and released as clean gas. In the proper tem-
perature range, typically 850C-1190C (1582F-2012F), the
N0x may be decomposed by an ammonia reductant alone without
a catalyst.
The sorbent particles mixing in the fluid-bed
fllter contactor 17 protect the filter elements from stic~y
particles and promotes the cleanin~ of the filter element
surfaces. The agglomeration of any sticky ashparticles,
fumes or tars in the combustion products, is also promoted
by the highly mixed fluid-bed particles. The fluid-bed
contactor environment may also provide catalytic conditions
or improved contacting for the further combustion of carbon
monoxide and flyash carbon. Ash particles that may accumu-
late in specif`ic regions Or the fluid-bed contactor are
drawn off for cooling, storage and disposal. Sorbent part-
icles are drawn off at a sorbent-rich zone of the fluid-bed
and are transported to separate or combined disposal with
the ash.
The hydrochlor~c and hydrofluoric acid sorbents
~5 Or pri~ary interest are calclum-based materials (limestones,
dolomites, quicklimes, hydrated li~es of various forms) and
sodium carbonate materials available in various mineral
forms. The sorbents perform effectively as either coarse
partlcles or fine entrained particles in the temperature
range of 600 to about 1100F (310.5C to 590.3C). Strontium
carbonate is effective at temperatures in the range of 900F
to 1900 (480.3C to 1030.~C).
The sulfur sorbents of interest to the generic
concept are:
Calcium hydrate sorbents in humidified flue
gas at temperatures less than about 150C
(330.9F).
"
2~9~1
8 56,682
Sodium-based sorbents for temperatures less
than about 315C (599F).
CuO-based sorbents in the range Or 350C to
500C (662F to g320~).
Calcium hydrate sorbents in the range of 400C
to 550C (752F to 1030F).
Calcium based sorbents (limestones, dolomiteS,
limes and hydrated limes) in the range of 700C
to 1100C (1292F to 2012F).
Strontium-based sorbents in the range of 980C
to 1300C (1796F to 2372F).
In the temperature range where CuO is suitable,
ammonia may be inJected into the contactor to catalytically
reduce NOX. The f~lters remove particulate material or
aerosols generated by this process. In the temperature
range of about 400C to 700C (752~F to 1292F), cyuranic
acid (as developed by Sandia National Labs), or other reduc-
tants, may be in~ected into the fluid-bed filter contactor
to reduce NOX; the filters capture the solid reaction products.
At higher temperatures, 850C to 1100C (1562~ to 2nl2F),
ammonia in~ected into the fluld-bed filter contactor reduces
'~O via the Exxon noncatalytic process.
The followin~ Table I shows the various configura-
tions and para~eters Or filter contactors which may be used
in the practice o~ this invention.
TAB~E I
Confi~urations and Parameters
of Fluid-Red Filter ~ontactors
Fluid-bed re~imes:
3 - bubbling with coarse sorbent ~articles (~300 mi~rons
.012-inch) shown in Fig. 3,
- fully fluidized bed,
- semi-fluidized bed,
- hi~hly turbulent to dilute with small sorbent
~articles (~40 microns .016-inch) shown in Fig. 4,
- fully fluidiæed bed,
- semi-fluidized bed,
- entrained with very fine sorbent particles ~20
microns .0008-inch) shown ln Fig. 5
~4 Vessel orientation:
- vertical upward gas flow wlth bubblin~ and turbu-~
lent beds,
- vertical upward, downward or horizontal gas flow
with entrained beds.
- . : ~ . `. ', ': .
~: ~ . . , . :
,
2a$~
9 56,682
Filter element orientation:
- vertical,
- horizontal.
Filter element parameters:
- length, 1 M - 1-1/2 M (3.28'-4.92'),
- diameter~ 7.62 cm - 10.16 cm (3"-4"),
- type (candle, bags, cross-flow),
- spaclng and packing arrangement, 2 di~meters,
- material, thiclcness and perm.eability, 0.5 cm (0.2"),
- filter cleaninr technique, abrasive by particles,
- ~ilter element manifold design, tub~ sheL-t.
~ed para~.eters-
- sup~rficial gas velocity, 1 r1/sec (3.2~'/sec),
- b~d depth, 2-3 ~l,
- sorbent part~cle size distribution, ~o.64 cm (0.25"),
- gas distributor desi~n, pipes,
- ash and bed particle withdrawal design, pipe into
dense area of bed.
The bubbling-bed filter contactor 46 shown in Fig.
3 includ~s a container 48, subdivided by a horizontal tube
sheet 50 into an upper chamber or plenum 52 and a lower
chamber 54. Ceramic filters 51 are suspended vertically
from the tube sheet 50. The filters 51 are sealed through
the tube sheet openin~ into plenum 52. rielow th~ filters 51
there is a screen or gas dlstributor 53. The holes in the
distributor should be dimensioned to preclude plugging. It
may also be neccessary to cool the distributor 53. Sorbents
are supplied to the chamber 54 through conductor 55. The
combustion products are conducted upwardly into the contactor
41 through the opening 57 and distributed in the chamber 54
by the distributor 53, producing a bubbling fluid-bed 59
between the distributor 53 and the tube sheet 50. Partlculate
si e of the sorbents and the fluidizing velocity of the pro-
ducts of combustion are selected so that the bed is a bubb-
ling bed. The sorbents react with the gas-produclng parti-
culate which is absorbed by the filters 51, resulting in
clean gas which passes out through the opening 61. The ash
is removed from the top part of bed 59 through conductor 63
and spent sorbent is removed from the lower part.o.f the bed
throu~h conductor 65. Typically, the bed 59 has a relatively
low depth, typically 1 to 2 meters (3.28-6.56 ft.).
.. .
- . . . . ~ ,. .,:
- :, ~ :~. :: , . . ,, ,. . :.,;
,. .: ,: ,
.: ~ :... : ,
2 ~
10 56,682
The bed mixing is relatively gentle. There ls
segregation of the smaller and llghter ash particles which
results in effective separation which allows the reinJection
Or t~e fine sorbent particles in th~ gas.
The turbulent contactor 71 includes a container 73
having an opening 75 at the bottom and sealed at the top 77.
Chambers 79 are sealed through the side wall of the contain-
er 73. Generally, horlzontal filters ~1 are sealed in
oppositely arrayed columns through the chambers 79 openin~
into the chambers. The chambers79 are sealed at the bottom
and open at the top. Sorbents are in~ected into the contain-
er 73 through conductor 83. The combustion products are
in~ected throu~h opening 75 producing opposite vertical beds
85. Ash is removed from the regions at the top through con-
ductor 87 and spent sorbent from the region at the bottom
through conductor 89. The clean gas is filtered into cham-
bers 79 and is emitted from the open tops 90 of the chambers.
The turbulent reactor 71 generally operates at
higher fluidizing velocities and with smaller bed particles
than are used in the bubbling réactor 46. ~as and sollds
rnixing in the bed are more vigorous, and the bed has lower
density than in the bubblin~ reactor 46~ resulting in the
use of deeper beds.
There are two types each of bubblin~ or turbulent
fluid-beds. In one, a "fully" fluidized bed, one where
surficient ~as velocity exists at the up~er bed surface to
maintain fluidization of the particles at the upper bed
surface, is produced by placing some filter surface above
the bed as in .`~lewby so that all the gases are not removed
3 within the béd. In the other type, a "semi-fluidized" bed,
where all the gas ~s removed lnternall~ to the bed and the
top portlon Or the bed is nonfluldized, is produced by sub-
merging all of the filter in the bed as in Degnen. This
latter type is still free to expand, in contrast to the
sèmi-fluidized beds dlscussed ln the open literature that have
rlgid filter caps placed on top of the bed. In-bo~h cases,
a very smalI-freeboard region is re~uired above the bed com-
pared to thè large freeboard reglon normally needl~d above
- .
. . : , :
" :: . . ~
' . ': ` ' ': . ,i,
2~68~1
11 56,~2
fluidized beds, 3 to 5 meters, (9.84 to 16.40 ~t.) in most
commercial ~luid-beds. The large rreeboard region in prlor-
art beds is demanded because some particles in the bed are
driven to substantial height.
The entrained contactor 91 lncludes a container
93 having an openin~ 95 at the top and taperlng at the
bottom to form a hopper 97 throu~h which ash and spent sor-
bent are removed. The sorbents and reductants are in~ected
at the top through conductor 99 and the combustion products
are transmitted downwardly through opening 95. An elongated
chamber 101 is sealed through the wall of container 93 and
sup~orts a row of horizontal ceramic filters 103, The fll-
ters are sealed through the wall of the chamber 101 and are
in communication of the chamber~ The filters extend sub-
stantially across the container 93. The chaMber is closed
at the top and open at the bottom.
The combustion products are introduced at a velo-
city such as to produce a vertical entrained bed 105. The
pollutants react with the sorbents and reductants, producing
solids, ~hich adhere to the surface of the filters and are
removed and are dischar~,ed throu~h hopper 97, and atmospheric
~ases which together with the clean gas pass throu~h the
filters 103 and are vented through the open end 107 of the
chamber 101. The sorbent particulate in the entrained con-
?5 tactor which are agitated in the bed are not effective to
scour the adhered cake from the filters 103. Cleanin~ ~ulses
fro~. source 109 are necessar~ to dislodge the cake from the
filters 103. Since the sorbent particles are small, the
reactlons producing the cleanin~ are rapid, and the gas
3 velocities are very high compared to the velocities in the
bubblin~ and turbulent reactors. Since se,~regatlon of ash
and sorbent does not occur in the entrained reactor as it
does in the bubblin~ and turbulent reactors, the sorbents are
once through.
'35 Fi~. 6 shows speci~lc practice of thls invention
in the temperature range be~ore the heat exchanger 19, some-
times referred to as an "economizer", of about 400C to
.
... . .
.
, ~
2 ~
12 56,6~2
550C (752F to 1022F). The lime hydrate 111 (or atmos-
pheric pressure dolomitic hydrate or pressure hydrated
dolomite), a particularly effectlve calcium-bascd sorbent,
is in~ected as fine particles (-325 mesh) to convert simul-
taneously the ~Cl, I~F and Sx into solid particulate and to
filter out and remove this particulate as ash.
The Cu~O4 particulate 113 is in coarse rorm,
typically -0.25-inch (-o.64 cm) and constitutes particulate
which serves as the pseudo-liquid medium of the fluidized-
bed and, in additlon, serves as the catalyst for the reduc-
tion of NOX. ~hese coarse bed particles remain in the
fluidized-bed ~!ith only limited replacement for long-time
oeriods. The calcium hydrate sorbent and flyash are removed
separately from the fluidized-bed by the natural segregation
of these fine particles to the top of the fluidized-bed.
There~is a "drain'1 115 near the top Or the bed through which
the fine particles flow like a liquid.
The followint~ Table II presents the factors that
control the performance of this invention:
TABL~ II
Performance Factors
1. ~he MSW properties and the nature of the
flyash particles produced.
2. The M~t! incinerator and operating conditions,
~5 and the temperature of the combustion products, the compo-
sition of the combustion products, the dust loading, and
the fluctuations in these conditions.
3. For retrofit appllcations, the avallable space.
4. rhe selected design and op~ratin~. conditions
3 of the emissions control device, particularl~ those influ-
encing the preC~sure drop across the fluidized-bed and the
pressure drop across the filter elements.
Ty~i~al operatin~ conditions and vessel size of
the apparatus for practicinÆ this invention ls based on a
gas pressure dro~ throu~h the fluid-bed and filter of about
40 inches (100 cm) of water, a plant size of 50 million
Btu/hr, (V5.275 x 101 Joules/hr), a ceramic candl~ filter
face velocity of 15 ft/min (4.6 M/min) in close-packed verti-
cal or horizontal bundles. The vessel slze is from 2 to 3 ~1
.. ~. , : . :
' ~: ', : '~ . . ' . :
. .
13 56,682
(6,56 to 9.84 ft.) in diameter, and 2 to 4 M (~.56 to 13.12
ft.) in height, respectively, with the CuO or CuSO4 catalyst
o~ mean particle size about 400 mlcrons (.016-inch) ln dia-
meter. The s~perficlal ~as velocities range from 1 to 3
M/s (3.3 to 9.8 ft/sec), respectively, and bed depths of
1 to 2.5 M(3.3 to 9.9 ft.), respectively. The performance
estlmates for a typlcal Fig. 6 system are shown in Table III.
TABLE III
Performance Estimates
1. Partlculate control: ~ 99.9;~.
2, HCl/HF removal: ~ 90% potential.
3. Sx removal:~> 90% potential.
4. Sorbent consumption: Calcium-to-HCl molar
feed ratio of about 1Ø
5. N0x reduction: Satisfy applicable emissions
standards.
6. Am~onia consumption: Stoichiometric ratio
about 1.2:1 ammonia to N0x.
7. Solid waste generation: Similar in nature
but smaller quantity than in other dry, calcium-based or
sodium-based sorbent in~ection schemes.
I~lhile preferred practice of this inYention has
been disclosed herein, many modifications thereof are feas-
ible. This invention is not to be restricted except insofar
as is necessitated by the spirit of the prior art.
.: . . ,
' ' ' , ~ ~
!~ ~ . . . ; ~ '
' . ' ' . ~ , . :: '
