当前位置:文档之家› Absorption-Line Probes of Gas and Dust in Galactic Superwinds

Absorption-Line Probes of Gas and Dust in Galactic Superwinds

Absorption-Line Probes of Gas and Dust in Galactic Superwinds
Absorption-Line Probes of Gas and Dust in Galactic Superwinds

a r X i v :a s t r o -p h /0002526v 1 29 F e

b 2000

.

Absorption-Line Probes of Gas and Dust in Galactic Superwinds

Timothy M.Heckman 1

Department of Physics and Astronomy,Johns Hopkins University,Homewood Campus,

3400North Charles Street,Baltimore,MD 21218

Matthew D.Lehnert 1

Max-Plank-Institut f¨u r extraterrestrische Physik,Postfach 1603,D-85740Garching,

Germany

David K.Strickland

Department of Physics and Astronomy,Johns Hopkins University,Homewood Campus,

3400North Charles Street,Baltimore,MD 21218

and

Lee Armus 1

SIRTF Science Center,310-6,Caltech,Pasadena,CA 91125

1.Visiting astronomers,Kitt Peak National Observatory and Cerro Tololo Interamerican Observatory,NOAO,operated by AURA,Inc.under cooperative agreement with the National Science Foundation.

ABSTRACT

We have obtained moderate resolution(R=a few thousand)spectra of

the NaIλλ5890,5896(NaD)absorption-line in a sample of32far-IR-bright

starburst galaxies.In18cases,the NaD line in the nucleus is produced primarily

by interstellar gas,while cool stars contribute signi?cantly in the others.In12

of the18“interstellar-dominated”cases the NaD line is blueshifted by over100

km s?1relative to the galaxy systemic velocity(the“out?ow sources”),while no

case shows a net redshift of more than100km s?1.The absorption-line pro?les

in these out?ow sources span the range from near the galaxy systemic velocity to

a maximum blueshift of~400to600km s?1.The out?ow sources are galaxies

systematically viewed more nearly face-on than the others.We therefore argue

that the absorbing material consists of ambient interstellar material that has

been entrained and accelerated along the minor axis of the galaxy by a hot

starburst-driven superwind.The NaD lines are optically-thick,but indirect

arguments imply total Hydrogen column densities of N H~few×1021cm?2. This implies that the superwind is expelling matter at a rate comparable to the

star-formation rate.This out?owing material is evidently very dusty:we?nd a

strong correlation between the depth of the NaD pro?le and the line-of-sight

reddening.Typical implied values are E(B?V)=0.3to1over regions

several-to-ten kpc in size.We brie?y consider some of the potential implications

of these observations.The estimated terminal velocities of superwinds inferred

from the present data and extant X-ray data are typically400to800km s?1,are

independent of the galaxy rotation speed,and are comparable to(substantially

exceed)the escape velocities for L?(dwarf)galaxies.The resulting selective

loss of metals from shallower potential wells can establish the mass-metallicity

relation in spheroids,produce the observed metallicity in the intra-cluster

medium,and enrich a general IGM to of-order10?1solar metallicity.If the

out?owing dust grains can survive their journey into the IGM,their e?ect on

observations of cosmologically-distant objects would be signi?cant.

Subject headings:galaxies:starburst–galaxies:nuclei–galaxies:active–galaxies:ISM–galaxies:kinematics and dynamics–galaxies:halos–galaxies: intergalactic medium–galaxies:evolution–infrared:galaxies–ISM:dust, extinction

1.Introduction

By now,it is well-established that galactic-scale out?ows of gas(sometimes called

‘superwinds’)are a ubiquitous phenomenon in the most actively star-forming galaxies

in the local universe(Heckman,Lehnert,&Armus1993;Dahlem1997;Bland-Hawthorn 1995).They are powered by the energy deposited in the interstellar medium by massive stars via supernovae and stellar winds.Over the history of the universe,out?ows like these may have polluted the intergalactic medium with metals(e.g.Giroux&Shull1997)and dust(Alton,Davis,&Bianchi1999;Aguirre1999a,b),heated and polluted the intracluster medium(e.g.Gibson,Loewenstein,&Mushotzky1997;Ponman,Cannon,&Navarro1999), and may have established the mass-metallicity relation and radial metallicity gradients in galactic spheroids(e.g.Carollo&Danziger1994).However,the astrophysical relevance of superwinds can not be reliably assessed without?rst understanding their physical, dynamical,and chemical properties.To date,most of the pertinent information has come from observations of the X-ray emission produced by the hot gas(e.g.Dahlem,Weaver, &Heckman1998)or the optical line-emission produced by the warm gas(e.g.Lehnert& Heckman1996a).

In the present paper,we take a complementary approach,and discuss an extensive body of new data that probes the out?owing gas via its interstellar absorption-lines.This technique has some important advantages.First,since the gas is seen in absorption against the background starlight,there is no possible ambiguity as to the sign(inwards or outwards) of any radial?ow that is detected.Second,the strength of the absorption will be related to the column density of the gas.In contrast,the X-ray or optical surface-brightness of the emitting gas is proportional to the emission-measure.Thus,the absorption-lines more fully probe the whole range of gas densities in the out?ow,rather than being strongly weighted in favor of the densest material(which may contain relatively little mass).Finally,provided that suitably-bright background sources can be found,interstellar absorption-lines can be used to study out?ows in high-redshift galaxies where the associated X-ray or optical emission may be undetectably faint.This promise has already been realized in the case of the’Lyman Dropout’galaxies,where the kinematic signature of out?ows is clear in their rest-frame UV spectra(Franx et al1997;Pettini et al1998,1999).

A few pioneering studies have already detected interstellar absorption-lines from superwinds in local starburst galaxies.Phillips(1993)discussed spatially-resolved optical spectroscopy of the NaI“D”doublet in NGC1808,showing that an out?ow of gas at velocities of up to700km s?1could be traced over a region several kpc in size,coincident with a region of extra-planar dust plumes.Several recent papers(Lequeux et al.1995; Heckman&Leitherer1997;Sahu&Blades1997;Kunth et al.1998;Gonzalez-Delgado et al

1998a)have detected blueshifted interstellar absorption-lines in HST and HUT UV spectra of a handful of starburst galaxies,implying out?ows of metal-bearing gas at velocities of 102to103km s?1.

Most of the strong resonance lines of cosmically-abundant ions are found in the UV (e.g.Morton1991;Savage&Sembach1996),and so must be studied with HST or F USE in local starbursts.In the present program,we have instead exploited the relatively greater sensitivity and availability of ground-based telescopes at visible wavelengths to study a large sample of starbursts/superwinds using the NaI doublet atλλ5890,5896?A.In a few cases,we have also observed the KIλλ7665,7699?A doublet,since it probes gas with nearly the same ionization state as NaI,but is more likely to be optically thin(the K abundance is down from Na by a factor of15,while the two doublets have similar oscillator strengths). The ionization potentials of NaI and KI are only5.1eV and4.3eV respectively,so these species should primarily probe the HI and H2ISM phases.Observations in vacuum-UV will be required to study the hotter and more highly ionized gas in absorption.

2.The Data

2.1.Sample Selection

Table1lists the salient properties of the32objects in our sample.These objects have been drawn from the larger samples of infrared-selected galaxies studied by Armus, Heckman,&Miley(1989-hereafter AHM)and by Lehnert&Heckman(1995-hereafter LH95).The speci?c selection criteria used in these in two programs are described in detail in these references.Brie?y,AHM selected on the basis of far-IR?ux and very warm far-IR color-temperatures.LH95selected on the basis of far-IR?ux,moderately warm far-IR color-temperatures,and high galaxy inclination(disk galaxies seen within~30?of edge-on). The AHM and LH95samples overlap in galaxy properties,but the former preferentially selects more powerful and more distant objects.

AHM measured the equivalent widths of the NaD lines in their sample using

low-resolution spectra.The galaxies from AHM were selected for the present program on the basis of the brightness of their nucleus at~5900?A and the equivalent width of NaD. The galaxies from LH95had no prior measures of the NaD line,and were selected based primarily on their proximity and availability at the time of the observations.

Of the32objects,only3are classi?ed as bona?de AGN of the basis of their optical spectra:the type2Seyferts NGC7582and Mrk273and the highly peculiar AGN IRAS11119+3257.No published classi?cation exists for IRAS10502-1843.The remaining

objects are optically classi?ed as HIInuclei or LINER′s,and are presumed to be primarily powered by dusty starbursts(Lutz,Veilleux,&Genzel1999).Even in the Seyfert galaxies NGC7582and Mrk273,optical spectra show the presence of a young stellar population

in the nucleus(Schmitt,Storchi-Bergmann,&Cid-Fernadez1999;Gonalzez-Delgado, Heckman,&Leitherer2000).Thus,with the possible exception of IRAS11119+3257and IRAS10502-1843,the objects in our sample all contain powerful starbursts that can drive superwinds.

2.2.Observations

The observations were undertaken during the period from1988through1994using three di?erent facilities:the4-meter Blanco Telescope with the Cassegrain Spectrograph at CT IO,the4-meter Mayall Telescope with the RC Spectrograph at KP NO,and

the2.5-meter Dupont Telescope with the Modular Spectrograph at the Las Campanas Observatory.Various spectrograph con?gurations were used at each observatory,the details of which are listed in Table2.The spectral resolution used to study the NaD lines ranged from55to170km s?1.While low by the standards of interstellar absorption-line studies, the resolution was good enough to cleanly resolve the NaD lines in most cases(deconvolved line widths of100to600km s?1-see below).

2.3.Data Reduction&Analysis

The spectra were all processed using the standard LONGSLIT package in IRAF.All the data were bias-subtracted using the overscan region of the chip and then?at-?elded using observations of either a quartz-lamp-illuminated screen inside the dome or of a quartz lamp inside the spectrograph.The spectra were then recti?ed using observations of bright stars to determine and remove the distortion perpendicular to the dispersion direction and observations of a HeNeAr arc lamp to determine the two-dimensional dispersion solution. The zero-points in the wavelength scale were veri?ed by measuring the wavelengths of strong night-sky emission-lines.Corrections to the heliocentric reference-frame were computed for the spectra.The spectra were then sky-subtracted by interactively?tting a low-order polynomial along the spatial direction,column-by-column.For a few of the galaxies we obtained relatively low-dispersion spectra that will be used to measure the reddening(Balmer decrement and continuum color).These data were?ux-calibrated using observations of spectrophotometric standard stars,and otherwise were reduced in the same way as the other data.

The spectra were analyzed using the interactive SPLOT spectral?tting package in IRAF.In all cases,a one-dimensional‘nuclear’spectrum was extracted,covering a region with a size set by the slit width and summed over3to5pixels in the spatial direction (typically2by3arcsec).The corresponding linear size of the projected aperture is generally a few hundred to a few thousand parsecs in these galaxies(median diameter700pc).This is a reasonable match to the typical sizes of powerful starbursts like these(e.g.Meurer

et al1997;Lehnert&Heckman1996b).Prior to further analysis,each1-D spectrum was normalized to unit intensity by?tting it with,and then dividing it by,a low-order polynomial.These nuclear spectra are shown in Figure1.Similar one-dimensional spectra for o?-nuclear regions were extracted over the spatial region with adequate signal-to-noise in the continuum for each galaxy.The primary focus of the present paper is on the nuclear spectra,but we will describe the results obtained in the o?-nuclear bins when these are particularly illuminating or interesting.

Given the relatively low resolution of our spectra,the likelihood that the observed NaD line pro?le contains many unresolved and/or blended kinematic sub-components,and the saturated nature of the NaD lines,we have chosen to parameterize the lines as simply as possible.Thus,for each extracted spectrum,we have?t the NaD doublet with a single pair of Gaussians,constrained to have the same line width and a wavelength separation appropriate to the redshifted doublet.In a few objects,the adjacent HeIλ5876nebular emission-line was strong and broad enough to slightly contaminate the blue half of the NaDλ5890pro?le.For these cases,we?rst?t and subtracted the HeI emission line.Only the parameters of the stronger member of KI doublet at7665?A were measured.The weaker member at7699?A was detected,with a strength consistent with the doublet being optically-thin(i.e.an equivalent width ratio of~2:1).

We have not attempted a rigorous determination of the measurement uncertainties associated with these data.The relatively high signal-to-noise in the nuclear spectra (typically better than30:1per pixel)means that the uncertainties in the measured quantities will be dominated in most cases by systematic e?ects due to the contamination of the NaD line by weaker stellar photospheric features(whose ubiquity likewise makes it di?cult to determine the true continuum level to use in the line-?tting)and by the mismatch in pro?le shape between the actual data and the single Gaussian component used to?t each member of the doublet(see section3.2below).The most straightforward way to estimate the measurement uncertainties is to compare the measurements for the11galaxies in the sample for which we have more than one independent spectrum(taken at a di?erent position angle).We have done so,and the results are reported in the Notes to Table3.

3.Results

3.1.The Stellar vs.Interstellar Contribution

Before using the NaD line to diagnose conditions in the starburst galaxies,it is

imperative to establish that the line is primarily interstellar in origin in these galaxies.

The NaD line is strong in the spectra of cool stars,reaching a peak strength in the range

from K3through M0(see Jacoby,Hunter,&Christian1984).These stellar types can

make a signi?cant contribution to the optical spectrum of a starburst galaxy.First,the

oldest underlying population in the galaxy bulge will have a dominant contribution from K

-type giants(indeed the NaD line is one of the strongest stellar absorption-lines in optical

spectra of early-type galaxies and bulges-e.g.Heckman1980;Bica et al1991).Second,

for starbursts with ages greater than about10Myr,cool supergiants make a signi?cant

contribution to the optical and near-IR light(Bruzual&Charlot1993;Leitherer et al1999).

We have therefore tried to estimate empirically what fraction of the measured equivalent

width of the NaD doublet is contributed by late-type stars in our sample galaxies.To do so,

we have considered other absorption-lines that are conspicuous in the spectra of late-type

stars and galactic nuclei,but which arise from highly-excited states and are therefore of

purely stellar origin(i.e.they are not resonance lines like NaD).The best-studied example

is the MgI b-band at5174?A.The strength of this line is well-correlated with the strength of

the NaD line in spectra of the nuclei of normal galaxies(Bica et al1991;Heckman1980)

and in stars(Jacoby,Hunter,&Christian1984).We have used the latter two data sets to

determine a best-?t to the correlation:W NaD~0.75W Mg?b.The measured strength of Mg?b in our galaxies(from AHM,Veilleux et al1995,or our own unpublished spectra)was

then used to predict the equivalent width of the stellar contribution to the observed NaD

line.We have also compared our data to spectra of K giant stars obtained during the same

observing runs listed in Table2.Rather than measuring the strengths of a few particular

stellar features,we have used the entire ensemble of features in the range between about

5750and6450?A to estimate by-eye the fractional stellar contribution to the NaD line.

The agreement between these two methods is generally satisfactory(the predicted NaD

stellar equivalent widths agree on-average to~0.1dex).Heckman&Lehnert(2000)have

measured the fraction of the red continuum contributed by cool stars for the seven nuclei in

the present sample having the highest quality detection of the interstellar component of the

NaD line.They?nd that this fraction is20to30%,consistent with the rough estimates

reported here.

As listed in Table3,the estimated stellar contribution to the observed NaD line in

our sample galaxies ranges from negligible(<10%)to substantial(>70%),with hints of

a bimodal distribution.Thus,rather than attempting a very uncertain direct correction for the e?ects of the stellar contribution,we have taken the simpler approach of dividing our sample into two bins:the strong-stellar-contamination objects(‘SSC’)in which stars produce≥40%of the measured NaD equivalent-width,and the interstellar-dominated objects(‘ISD’)in which the stellar contribution is≤30%.In the discussion to follow,we will see that the NaD lines in the two sub-samples have signi?cantly di?erent properties, which can be readily understood as re?ecting the relative importance of the stellar and interstellar components.

3.2.Kinematics

The most robust indicator of an out?ow is the presence of interstellar absorption-lines that are signi?cantly blueshifted with respect the the systemic velocity of the galaxy(v sys). Thus,we have?rst compiled the best available measures of v sys for our galaxies The velocities of the nuclear emission-lines are potentially a?ected by radial gas?ows and are not always reliable indicators of v sys(Mirabel&Sanders1988;Lehnert&Heckman1996a). We have therefore determined v sys from(in order of preference)spatially-resolved galactic rotation curves,global mm-wave CO line pro?les,nuclear stellar velocities,global HIλ21cm emission-line pro?les,and optical nuclear emission-line velocities(only used for4objects). See Table1for details and the estimated uncertainties.

The results are shown in Figure2.For the ISD subsample there is strong trend for the centroid of the NaD feature to be blueshifted with respect to v sys.Speci?cally,11of the18ISD nuclei have NaD blueshifts?v greater than100km s?1(hereafter the‘out?ow sources’).In addition,while the nuclear NaD absorption-line in NGC1808lies close to v sys, the galaxy exhibits strongly blueshifted absorption over a several-kpc-scale region along its minor axis(Phillips1993).We therefore include it as a12th member of the out?ow sample.The net blueshifts in the ISD nuclei are in the range?v~100to300km s?1, (with the exception of IRAS11119+3257).1In contrast to these large blueshifts,no net redshifts greater than100km s?1are observed in the ISD sample.Moreover,none of the 14members of the SSC sample show a net NaD blueshift or redshift that is greater than

70km s?1.This is consistent with expectations that the velocity of the nuclear stellar NaD

component will be very close to v sys.

The NaD linewidths in the ISD and SSC subsamples are also signi?cantly di?erent

(Figure3).The lines are relatively narrow in the SSC subsample(W~100to300km

s?1,with a median of180km s?1),and much broader in the ISD nuclei(W~150to

600km s?1,with a median of425km s?1).The lines are especially broad(typically

400to600km s?1)in the out?ow sources.As shown in Figure4,the net blueshift in

these sources is typically about half the line width(?v~1/2W).The peculiar AGN

IRAS11119+3257,with W<

the redmost absorption occurs close to v sys.This is strongly suggestive of a?ow in which

matter is injected at roughly zero velocity and then accelerates outward.The approximate

implied terminal velocity of the?ow is then v term~?v+0.5W,which ranges from220to 1450km s?1in our sample(Table4).This picture is quite di?erent from the standard one

of a simple expanding‘superbubble’in which the absorption is due to a thin layer of cooled

post-shock gas,and for which W<

It is instructive to compare the observed velocities in the absorbing material to the

velocities expected from purely gravitational forces in the starburst galaxy.This is shown

in Figure5,where we plot W vs.the galaxy rotation speed(v rot-see Table1for details).

This?gure has several interesting implications.First,neither the sample as-a-whole nor

any of the above subsamples show any correlation between the velocity dispersion in the

absorbing material and the galaxy rotation speed.This suggests that gravity does not play

a dominant role in determining the dynamics of the absorbing gas.

Figure5also shows that the NaD lines are surprisingly narrow in the SSC sources

compared with expectations for either stars or gas in the bulge of the starburst‘host’

galaxy.The lines are exceptionally narrow if they are stellar in origin,since in this case

the observed line broadening(W obs)will be produced by both the intrinsic stellar line broadening(W?)and that produced by galactic dynamics(W gal):W gal=

normal galaxies of the same rotation speed and Hubble type(typically Sa to Sc),while the

implied values for W gal would be even more discrepant(see above).Put another way,based

on the Hubble types and the galaxy absolute magnitudes(M B~-19to-21)for the SSC subsample,the Faber-Jackson relation for normal galactic bulges would predict typical

values of W gal~200to300km s?1(e.g.Nelson&Whittle1996),while the observed widths are typically only140to200km s?1,even without a correction for the line broadening due to W?.

The nebular emission lines are also narrow in the SSC nuclei,as has been shown to be

more generally true for starbursts by Weedman(1983).In this case,Lehnert&Heckman

(1996b)showed that the narrowness of the nuclear emission-lines could be understood

because the ionized gas was rotationally supported and did not fairly sample the galaxy

rotation curve(it lies within the region of the galaxy with solid-body rotation).If this

explanation applies to the NaD lines in the SSC nuclei,it implies that a signi?cant fraction

of the stellar contribution comes from a dynamically-cold(disk/starburst)component

rather than from the bulge.

Finally,Figure5shows that the NaD linewidths are relatively large in the out?ow

sources(W~1to3v rot).As we have argued above,the kinematic properties of the NaD

pro?les suggest that gas is‘loaded’into the out?ow at v~v sys and is then accelerated up

to some terminal velocity that corresponds to the most-blueshifted part of the NaD line

pro?le.We plot v term vs.v rot in Figure6,from which it is clear that v term is signi?cantly

larger than v rot,but is uncorrelated with it.This suggests that the out?ows may be able

to selectively escape the shallower galactic potential wells,as we will discuss in section4.2

below.

Neither the SSC nor the ISD subsamples show a signi?cant correlation between the

widths of the NaD absorption-line and the Hαemission-line.In particular,the out?ow

sources with very broad(400to600km s?1)NaD absorption-lines have Hαemission-line

widths ranging from145km s?1(NGC7552)to1500km s?1(IRAS11119+3257).This

presumably means that the dynamics of the more tenuous out?owing absorbing gas is

largely decoupled from that of the dense(high emission-measure)gas that provides most of

the nuclear line-emission.

As described above,we have?t the pro?le of the NaD doublet with a single pair of

Gaussians constrained to have the same widths and a?xed separation.Inspection of Figure

1clearly shows that the observed pro?les of many of the ISD sample are more complex

than this.The ISD pro?les generally have a larger kurtosis than a Gaussian(i.e.narrower

core and broader wings)and are sometimes asymmetric with a weak blueward wing on the

λ5890pro?le(e.g.NGC1808,IRAS10565+2448,IRAS11119+3257,NGC6240),and/or

de?nite substructure(e.g.NGC1614,NGC3256,IRAS11119+3257).Observations at higher spectral resolution should prove instructive.

3.3.The Roles of Luminosity and Geometry

Of the32galaxies in our sample,14show relatively weak interstellar NaD absorption-lines(the SSC sample,in which the stellar contribution to the line is strong),6have predominantly interstellar NaD lines lying close to the systemic velocity of the galaxy, and12have interstellar lines that are blueshifted by more than100km s?1relative to

v sys.These12out?ow sources di?er systematically from the other objects in two striking respects:they are more luminous starbursts and they are preferentially located in galaxies seen relatively face-on.

Speci?cally,64%(9/14)of the galaxies with L IR>1011L⊙show out?ows,compared to only28%(5/18)of the less luminous galaxies.The mean values for logL IR are11.44±0.18 and10.86±0.13for the out?ow and other sources respectively,a di?erence that is signi?cant at the2.6σlevel.The relationship to galaxy inclination is stronger:69%(11/16)of the galaxies with a ratio of semi-major to semi-minor axes a/b≤2.0show out?ows,while this is true for only6%(1/16)of the?atter(more highly inclined)galaxies.The mean values for log(a/b)are0.20±0.03and0.42±0.03for the out?ow and other sources respectively,a di?erence that is signi?cant at the4.6σlevel.

It is likely that the primary correlation is between an observed out?ow and low galaxy inclination(small a/b).The weaker apparent correlation with L IR is probably induced by the loose anti-correlation in our sample between L IR and a/b.This anti-correlation re?ects our selection of galaxies from both the LH95‘edge-on’galaxy sample(large a/b and moderate L IR)and the AHM‘FIR-warm’sample(broad range in a/b and large L IR).

Taken at face value,the correlation with galaxy inclination implies that there is a high probability(~70%)that an observer located within~60?of the rotation axis of a starburst galaxy will see out?owing gas in absorption.This geometrical constraint is consistent with the observed loosely-collimated out?ows seen in emission along the minor axes of edge-on starburst galaxies(e.g.Dahlem,Weaver,&Heckman1998).

3.4.Column Densities and Optical Depths

The NaD line is clearly optically-thick in these galaxies.The ratio of the equivalent widths of theλ5890andλ5896members of the doublet(R)can be used to estimate the

optical depth(e.g.Spitzer1968).The distribution of R is markedly di?erent in the SSC and ISD subsamples.In the former,there is a very narrow observed range(R~1.1to 1.3).This is consistent with a strong stellar contribution to the NaD line,since R~1.0 to1.3(indicative of large optical depths)is characteristic of cool stars.The range is much broader for the ISD sample,from R=1.1to1.7.This range corresponds to central optical depths in theλ5896line ofτ~20to0.5.

At?rst sight,it might appear odd that the NaD line is optically-thick,yet is not black at line center.This can be seen for the ISD sample in Figure7,where we have plotted R vs.the normalized residual intensity at the center of theλ5890feature:I5890=F5890/F cont (with the respective?uxes measured at line center and in the adjacent continuum).There is a broad range in I5890from0.14(nearly black)to0.7.More tellingly,there is no correlation between R and I5890.This implies that the absorbing gas does not fully cover the background continuum light,and that I5890is determined more by this covering factor(C f) than by the optical depth.A covering factor less than unity is natural in these galaxies. First,the continuum light may arise in part from stars in the galaxy that are located in front of most of the absorbing gas(i.e.this is not the idealized case of a purely foreground absorbing screen:the gas and stars are likely to be mixed).Secondly,the gas is likely to be quite clumpy and inhomogeneous(e.g.Calzetti1997;Gordon,Calzetti,&Witt1997).

In the limit of large optical depth,C f=(1?I5890),but for low or moderate optical depth C f>(1?I5890).For the typical optical depths in this sample,we can approximate C f by(1-I5890).This can be demonstrated quantitatively for those members of the ISD sample in which the NaD lines are well-resolved,narrow enough so that the two doublet members are cleanly separated from one-another(W<300km s?1),and that have high signal-to-noise spectra.These constraints leave us with only three objects:NGC1808, NGC2146,and M82.Following Hamann et al.(1997)and Barlow&Sargent(1997),we have:

C f=(I25896?2I5896+1)/(I5890?2I5896+1)(1)

where I5896is the normalized intensity at the center of theλ5896line.The measured values of C f are0.83,0.84and0.84for NGC1808,NGC2146,and M82respectively,while the corresponding values for(1?I5890)are0.83,0.82,and0.82.

In this circumstance-in which optically-thick gas only partially covers the continuum source-the measured equivalent width of the NaD doublet(EQ)will be insensitive to the NaI column density,and will instead be primarily determined by the product of C f and the line-of-sight velocity dispersion in the gas.We plot the separate dependences of EQ on

I5890and W in Figures8and9respectively for the ISD sample.It is clear from these two

?gures that EQ is determined largely by the covering factor(Figure8),since there is no

correlation between W and EQ(Figure9).

Given that the NaD doublet is moderately optically-thick in these galaxies,it is not

straightforward to estimate a NaI column density(N NaI).We have taken three approaches,

and emphasize that these are designed to give us only a rough(order-of-magnitude)

estimate.Our techniques can potentially underestimate N NaI,because they are insensitive

to any NaI sub-component that is highly optically-thick,yet kinematically quiescent.

The?rst is the classical doublet ratio method(e.g.Spitzer1968),which relates R

directly to the optical depth at line center,and thereby allows the column density to be

deduced from the equivalent width.In the spirit of this analysis,we will not attempt to

measure columns for all the individual cases,but will instead estimate a characteristic

value based on the typical observed parameters.The median value observed in the ISD

sample is R~1.2,implying that the corresponding median optical depth at the center of

the NaDλ5896line isτ5896~4(see Table2.1in Spitzer1968).The median observed value EQ~6?A for the doublet,equation2-41and Table2.1in Spitzer(1968),and the oscillator

strength from Morton(1991),together imply N NaI~1014cm?2.Note that this assumes C f=1,and should be increased by C?1f,or a typical factor of~1.6.

A variant of the doublet-ratio technique can be applied to the three cases discussed

above in which the two members of the NaD doublet are cleanly separated and well-resolved

(NGC1808,NGC2146,and M82).Again,following Hamann et al(1997)we have:

τ5896=ln[C f/(I5896+C f?1)](2) The resulting values forτ5896are2.3,2.1,and1.9for NGC1808,NGC2146,and M82 respectively.These are smaller than the values implied by R by a factor of~2in these cases.The implied values for N NaI are1.0×1014,6×1013,and6×1013cm?2after correction by C?1f.

We have also measured the equivalent width of the KIλ7665line in three of the nuclei

(NGC1614,NGC1808,and NGC3256).Since KI and NaI have very similar ionization

potentials,and since K and Na show similar grain depletion patterns(Savage&Sembach

1996),the expected ratio of the NaI and KI column densities should be15for gas with a

solar Na/K ratio.The measured values for the NaD doublet ratio imply optical depths at

the center of the NaDλ5890line of8,16,and1.6for NGC1614,NGC1808,and NGC3256

respectively.The implied optical depths for the KIλ7665line would then be0.5,1.1,and

https://www.doczj.com/doc/504624030.html,ing the oscillator strength tabulated by Morton(1991),the measured

equivalent widths of the line imply that N KI=3×1012,4×1012,and1.3×1012cm?2

respectively.Assuming N NaI=15N KI,the corresponding NaI columns are4.5×1013,

6×1013,and2×1013cm?2.These values are about a factor of two or three smaller

than would have been deduced for these three cases using the NaD doublet ratio alone.

The value for NGC1808is in good agreement with that derived from Equation2.Under

the circumstances,we regard the agreement between the three methods as satisfactory,

and conclude that the typical value in the ISD sample is logN NaI=13.5to14.A?nal

indirect indication that these NaI column densities are roughly correct comes from the

detections of the“Di?use Interstellar Bands”in the seven highest-quality spectra of the

ISD sample(Heckman&Lehnert2000).The observed strengths of these features agree

with the strengths seen in Galactic sight-lines with logN NaI~13.5to14.

What is the total gas column density associated with the out?ow?To calculate this

directly from the(already uncertain)NaI column requires knowing the metallicity of the

gas,the fractional depletion of Na onto grains(typically a factor of~10in di?use clouds in

the Milky Way)and the potentially substantial ionization correction to account for ionized

Na.Assuming solar Na abundances and a factor of ten correction for depletion onto grains

(e.g Savage&Sembach1996),N NaI=1014cm?2implies a typical value for N H of5×1020

(N Na/N NaI)cm?2.We can also take an empirical approach suggested by the correlation

between N NaI and the total gas column towards stars in our own https://www.doczj.com/doc/504624030.html,ing the data in

Herbig(1993),values for N NaI in the range we estimate(logN NaI~13.5to14)correspond to sight-lines with N H~1.5to4×1021cm?2.Interestingly,this is just the range of values for N H deduced from the amount of reddening along the line-of-sight to these nuclei based

on either the Balmer decrement or the colors of the optical continuum,assuming a normal

Galactic extinction-curve and dust-to gas ratio(section3.5,and see also AHM;Veilleux et

al1995).

These estimates suggest that the ionization correction factor is signi?cant but not

huge(i.e.N Na/N NaI~3to10).Since its ionization potential is only5.1eV,the presence of relatively signi?cant amounts of NaI implies that it is associated with gas having a signi?cant dust optical depth in the near-UV:for a Galactic extinction curve and dust-to-gas ratio,a Hydrogen column density of N H=8×1020cm?2is required to produceτdust=1at 5.1eV(λ~2420?A).

It is instructive to compare the total column densities we infer for the out?ows of a few

×1021cm?2to the column densities in the other components of the ISM in these galaxies. Column densities to the nucleus for the hot X-ray-emitting gas are estimated to be of-order 1021cm?2in superwinds(e.g.Suchkov et al1994;Heckman et al1999;Strickland1998).In the nuclei themselves,the dominant ISM component is molecular,and the inferred columns

range from~1023to1025cm?2(e.g.Sanders&Mirabel1996).

The HIλ21cm line is observed in absorption against the bright nonthermal radio sources in starburst nuclei(e.g.Koribalski1996;Heckman et al1983;Mirabel&Sanders 1988).The implied column densities are typically a few×1021to1022(T spin/100K)cm?2. The absorption is centered close to v sys and spans a velocity range similar to that of the molecular gas.This strongly suggests that this gas is a trace atomic component in the starbursting molecular disk or ring.The kinematics of the gas responsible for theλ21cm absorption are therefore quite distinct from the gas that produces the blueshifted NaD absorption.This has several plausible explanations.First,the out?owing HI is probably too hot(T>103K)to produce strong absorption atλ21cm.Second,the background radio continuum source against which the gas that produces theλ21cm absorption is observed will almost certainly be invisible in the optical:it lies behind a total column density (overwhelmingly H2)of~1023to1025cm?2,corresponding to A V=60to6000!Clearly, such material will not contribute to the observed NaD absorption-lines.

3.5.Dust Associated with the Absorbing Gas

We have argued in section3.4that the NaD lines are are optically thick,and that EQ is set primarily by the covering fraction for the absorbing gas(C f)rather than by the line width(W-see Figures8and9).This inference helps explain the otherwise puzzling correlations found by AHM and Veilleux et al(1995)between EQ and the reddening inferred from either the Balmer decrement or the color of the optical continuum in the nuclear spectra of large samples of starbursts.ForτNaD>>1and C f=1,EQ would be set by W,and so no correlation with the reddening would be expected.If instead EQ is principally determined by the fraction of the starburst that is covered by gas containing NaI(and dust grains),then this correlation is more reasonable.

Veilleux et al(1995)have also shown(via the Balmer decrement)that the region

of signi?cant reddening extends far beyond the nucleus in many far-IR-bright galaxies. Thus,to gain further insight into the relationship between the NaD absorption and dust-reddening,we have mapped out the spatial variation in the depth of the NaD line (I5890)and the reddening in the six galaxies in our ISD sub-sample for which we have the relevant data on the reddening(M82,NGC3256,NGC6240,Mrk273,IRAS03514+1546,and IRAS10565+2448).The size of the region mapped was set by the detectability of the NaD line,and ranges from3to9kpc(except for M82,where the mapped region is only500pc in diameter).In each case,we have corrected the Hαand Hβemission-line?uxes for the e?ects of stellar absorption-lines(using measures of the equivalent widths of the high-order

stellar Balmer absorption-lines in NGC3256and NGC6240and an assumed value of2?A for the other galaxies).We have also corrected the data for foreground reddening using the measured Galactic HI column density and assuming a standard extinction curve.

Figure10shows that not only do the extra-nuclear data points for these six galaxies de?ne a good correlation between the amount of reddening and the depth of the NaD line along a given line-of-sight through the starburst and its out?ow,they de?ne the same correlation as that de?ned by the ensemble of all the ISD nuclei in our sample.The nuclear and o?-nuclear points are pretty well-mixed in Figure10,although there is some tendency for the nuclear lines-of-sight to have the larger values of reddening and deeper NaD absorption-lines.The correlation of I5890is better with the color of the stellar continuum than with the Balmer decrement.This is reasonable because the NaD line is observed in absorption against the background stellar continuum(rather than against the emission-line gas)and because the Balmer decrement is likely to be signi?cantly a?ected by dust directly associated with the emission-line gas itself(in addition to the dust in the foreground material responsible for the NaD absorption).

The observed Balmer decrements imply extinctions of A V~1to5for a standard Galactic extinction curve.Similar values are implied by the continuum colors:a typical starburst is predicted(in the absence of reddening)to have a color of log[C65/C48]~

-0.3(Leitherer&Heckman1995),while the observed colors in Figure10range from

log[C65/C48]~-0.2to+0.3(corresponding to A V=0.7to4.2).Note also that in both Figure10a and10b,the extrapolation of the correlation to I5890=1.0(no absorption,

C f=0)has an x-intercept at the intrinsic values expected for an unreddened starburst (log[C65/C48]~-0.3and log[Hα/Hβ]=0.46).

In summary,the data imply that over regions with sizes of several or many kpc,the out?ows contain inhomogeneous highly dusty material.For a standard Galactic extinction law and dust-to-gas ratio,the typical implied HI columns are a few×1021cm?2.These HI column densities agree well with the estimates in section3.4above based upon the NaI column density.

3.6.Sizes,Masses,and Energies

We have measured the size of the region over which signi?cantly blueshifted NaD absorption is detected(?v>100km s?1)for the12out?ow sources.The sizes are listed in Table4,and range from1to10kpc in diameter.They must be regarded as lower limits (since the background starlight usually becomes too faint to detect the absorption at larger

radii).Tracing the full extent of the absorbing material farther out into the galactic halos will probably require observing suitably bright background QSO’s(see Norman et al1996).

These lower limits to the size of absorbing region can be used to estimate the (minimum)mass and kinetic energy in the out?ow.That is,for a region with a surface area A,a column density N H,and an out?ow velocity?v:

M>5×108(A/10kpc2)(N H/3×1021cm?2)M⊙(3)

E>2×1056(A/10kpc2)(N H/3×1021cm?2)(?v/200km/s)erg(4)

We have scaled these relations using values for A,N H,and?v that are typical,and have assumed an equal contribution to M and E from the front(observed)and back sides of the out?ow.

If we adopt a simple model of a constant-velocity,mass-conserving superwind?owing into a solid angle?w,extending to arbitrarily large radii from some minimum radius(r?-taken to be the radius of the starburst within which the?ow originates),we obtain:

˙M~60(r

?/kpc)(N H/3×1021cm?2)(?v/200km/s)(?

w

/4π)M⊙/yr(5)

˙E~8×1041(r

?/kpc)(N H/3×1021cm?2)(?v/200km/s)3(?

w

/4π)erg/s(6)

The statistics of the ISD subsample in the present paper imply that out?ows are commonly observed in absorption in IR-selected starbursts(12/18cases).On the other hand,many of the out?ow galaxies in the present sample were selected from AHM on the basis of the strength of their NaD line(objects above the~70th percentile in EQ). If the presence of observable blueshifted absorption is determined by viewing angle(see section3.3),this suggests that?w/4πlies in the range~0.2to0.6(consistent with the weakly-collimated bipolar out?ows seen in well-studied superwinds).

To put the above estimates into context,we can consider the rate at which mass and energy are returned by massive stars.The median bolometric luminosity of the12out?ow galaxies in our sample is L bol~2×1011L⊙.The implied median rates of mass and kinetic energy returned from supernovae and stellar winds are roughly˙M ret=5M⊙per year and ˙E

ret

=1043erg s?1respectively(e.g.Leitherer&Heckman1995).Since(˙M/˙M ret)~

3to10,the absorption-line gas in the out?ow must be primarily ambient gas that has

been loaded into the?ow.This inference agrees with similar conclusions about the hot

X-ray-emitting gas in superwinds(section4.2below,and see e.g.Strickland1998;Suchkov et al1996;Heckman et al1999).Since(˙E/˙E ret)<10%,the absorbing gas does not carry the bulk of the energy supplied by the starburst.Most of this energy probably resides in the form of the thermal and kinetic energy of the much hotter(T>105.5K)X-ray-emitting gas.

A bolometric luminosity of2×1011L⊙corresponds to a star-formation rate of about 12M⊙per year(for a Salpeter IMF extending from1to100M⊙).Thus,the out?ow rates estimated from the NaD lines are comparable to the star-formation rate:the feedback from massive stars drives the ejection of as much gas as is being converted into stars.Similar inferences for starbursts have been made using the X-ray and optical emission-line data

(e.g.Suchkov et al1996;Heckman et al1999;Della Ceca et al1996,1999;Martin1999).

4.Discussion&Implications

4.1.The Origin&Dynamics of the Absorbing Material

As discussed above,the red-most part of absorption-line pro?le in the out?ow objects is close to v sys,suggesting that absorbing material is injected from quiescent material at or near v sys,and is then accelerated up to some terminal velocity as it?ows outward.This is physically plausible,as the hot(X-ray emitting)out?owing gas interacts hydrodynamically with colder denser material that is located either inside the starburst,or in the inner portions of the galactic halo(see for example Hartquist,Dyson,&Williams1997;Suchkov et al1994;Strickland1998).

Let us assume that a cloud of gas with a column density N,originally located a distance r0from the starburst,is accelerated by a constant-velocity superwind that carries an outward momentum?ux˙p into a solid angle?w.Ignoring the e?ects of gravity for the moment,the clump’s terminal velocity will be(Strel’nitskii&Sunyaev1973):

v term=420(˙p/7×1034dynes)1/2(?w/1.6π)?1/2(r0/kpc)?1/2(N/3×1021cm?2)?1/2km/s(7) In this expression,we have used the momentum?ux supplied by stellar winds and supernovae(Leitherer&Heckman1995)in a starburst having a bolometric luminosity equal to the median value for the out?ow sample(2×1011L⊙)and have adopted the estimates in section3above for N and?w.Starbursts with this luminosity have typical estimated

radii of roughly1kpc(see for example Heckman,Armus,&Miley1990;Meurer et al1997).

From these elementary considerations,we conclude that the observed terminal velocities

(typically400to600km s?1)are easily accommodated.

Equation7also predicts that the out?ow speeds will be larger in more luminous

starbursts.This trend is mitigated to some degree by the fact that more powerful

starbursts tend to be larger.Lehnert&Heckman(1996b)and Meurer et al(1997)argue

that starbursts have a maximum characteristic surface-brightness,which then implies

˙p∝L bol∝r2.Together with Equation7,this implies that such‘maximum starbursts’will have v term∝L1/4bol(although the clouds can not be accelerated to velocities larger than that of the?ow that accelerates them!).Our sample shows no convincing evidence of a trend for

larger v term in the more luminous systems,but this sample covers a rather small range in

starburst luminosity.It will be instructive to extend this study to dwarf starbursts with

L bol<109L⊙.

Assume now that the cloud immersed in the out?ow is subjected to a gravitational

force imposed by an isothermal galaxy potential whose depth corresponds to a circular

rotation speed v rot.In order that the outwardly-directed force due to the superwind exceed

the inwardly-directed force of gravity,the value for the cloud column density must satisfy

the condition:

N<7×1021(˙p/7×1034)(?w/1.6π)?1(r/kpc)?1(v rot/200km/s)?2cm?2(8) Thus,the typical column densities estimated for the out?ows(~few×1021cm?2)lie near the upper bound for material that will?ow out(rather than falling in).This may not be a coincidence:given a range of cloud column densities,the blueshifted absorption-line will be dominated by the largest-column-density clouds that can be expelled.Alternatively, the observed column densities may simply arise because N H~2×1021cm?2corresponds to a dust optical depth of unity in the continuum at the wavelength of the NaD doublet(for a standard Galactic dust-gas ratio).That is,continuum-emitting regions in these nuclei lying behind sight-lines with much higher columns are invisible in optical light and sources behind sight-lines with much lower columns contain little NaI.It would be interesting to test Equation8by measuring values of N for out?ows in‘low-intensity’starbursts(small ˙p/r)and starbursts occurring in dwarf galaxies(small v rot).

4.2.Insights from Numerical Simulations

The above elementary considerations give some simple physical insights into the origin

and dynamics of the absorbing material.More detailed insight comes from hydrodynamical

simulations of starburst-driven superwinds(e.g.Tomisaka&Bregman1993,Suchkov et

al1994,Strickland1998,Tenorio-Tagle&Munoz-Tunon1998).In these simulations the

coolest densest gas that has been hydrodynamically disturbed by the starburst is associated

with the swept-up shell of ISM that propagates laterally in the plane of the galaxy,and

fragments of the cap of the original superbubble shell now being carried vertically out of

the disk by faster,more tenuous,wind material.

Shear between the hot shocked starburst ejecta and the cool dense shell in the disk of

the galaxy leads to entrainment and stripping of cool dense gas into the wind?owing out

of the disk(through Kelvin-Helmholtz instabilities,and presumably additional interchange

processes such as thermal conduction and turbulent mixing layers that can not be included

in current simulations).Dense gas already in the wind interior,for example the superbubble

shell fragments,is accelerated outward via the ram pressure of the wind.

This process can be seen in Figure11,in which the outward trajectories of four typical

entrained clouds are traced over an interval of1.5Myr from a2-D hydrodynamic simulation

of M82’s galactic wind(Strickland1998).This is based on the thick-disk ISM distribution

of Tomisaka&Bregman(1993).In this model a mass of108M⊙is turned into stars in an

instantaneous burst(Salpeter IMF over the mass range1to100M⊙).At a time7Myr

after the burst,the resulting wind has properties that are a reasonable match to M82.By

this time,supernovae and stellar winds have returned1.3×107M⊙and6×1056ergs to

the ISM.

Within|z|≤1.5kpc of the disk there is M=1.9×108M⊙of gas cooler than

T=3×105K.The majority of this gas is at the minimum temperature allowed in these

simulations of T~6×104K.This material occupies a projected area of~2kpc2,so the

average hydrogen column density of this gas is N H~9×1021cm?2.This cool gas has a broad range of velocities,from v~10–103km s?1,with a mode of~60km s?1(which

is associated with the slow expansion of the outer shock in the plane of the galaxy).The

associated kinetic energy is1.3×1055ergs.

At higher distances above the disk there is much less cool gas.For gas above|z|=1.5

kpc the mass of cool gas,associated primarily with the fragments of superbubble shell cap,

is M=1.5×107M⊙.For a projected area of~8.5kpc2,the average column density is

N H~1.6×1020cm?2.This cool gas high above the plane typically has higher velocities than the gas within the plane of the galaxy,the distribution of mass with velocity being

50万吨年煤气化生产工艺

咸阳职业技术学院生化工程系毕业论文(设计) 50wt/年煤气化工艺设计 1.引言 煤是由古代植物转变而来的大分子有机化合物。我国煤炭储量丰富,分布面广,品种齐全。据中国第二次煤田预测资料,埋深在1000m以浅的煤炭总资源量为2.6万亿t。其中大别山—秦岭—昆仑山一线以北地区资源量约2.45万亿t,占全国总资源量的94%;其余的广大地区仅占6%左右。其中新疆、内蒙古、山西和陕西等四省区占全国资源总量的81.3%,东北三省占 1.6%,华东七省占2.8%,江南九省占1.6%。 煤气化是煤炭的一个热化学加工过程,它是以煤或煤焦原料,以氧气(空气或富氧)、水蒸气或氢气等作气化剂,在高温条件下通过化学反应将煤或煤焦中的可燃部分转化为可燃性的气体的过程。气化时所得的可燃性气体称为煤气,所用的设备称为煤气发生炉。 煤气化技术开发较早,在20世纪20年代,世界上就有了常压固定层煤气发生炉。20世纪30年代至50年代,用于煤气化的加压固定床鲁奇炉、常压温克勒沸腾炉和常压气流床K-T炉先后实现了工业化,这批煤气化炉型一般称为第一代煤气化技术。第二代煤气化技术开发始于20世纪60年代,由于当时国际上石油和天然气资源开采及利用于制取合成气技术进步很快,大大降低了制造合成

气的投资和生产成本,导致世界上制取合成气的原料转向了天然气和石油为主,使煤气化新技术开发的进程受阻,20世纪70年代全球出现石油危机后,又促进了煤气化新技术开发工作的进程,到20世纪80年代,开发的煤气化新技术,有的实现了工业化,有的完成了示范厂的试验,具有代表性的炉型有德士古加压水煤浆气化炉、熔渣鲁奇炉、高温温克勒炉(ETIW)及干粉煤加压气化炉等。 近年来国外煤气化技术的开发和发展,有倾向于以煤粉和水煤浆为原料、以高温高压操作的气流床和流化床炉型为主的趋势。 2.煤气化过程 2.1煤气化的定义 煤与氧气或(富氧空气)发生不完全燃烧反应,生成一氧化碳和氢气的过程称为煤气化。煤气化按气化剂可分为水蒸气气化、空气(富氧空气)气化、空气—水蒸气气化和氢气气化;按操作压力分为:常压气化和加压气化。由于加压气化具有生产强度高,对燃气输配和后续化学加工具有明显的经济性等优点。所以近代气化技术十分注重加压气化技术的开发。目前,将气化压力在P>2MPa 情况下的气化,统称为加压气化技术;按残渣排出形式可分为固态排渣和液态排渣。气化残渣以固体形态排出气化炉外的称固态排渣。气化残渣以液态方式排出经急冷后变成熔渣排出气化炉外的称液态排渣;按加热方式、原料粒度、汽化程度等还有多种分类方法。常用的是按气化炉内煤料与气化剂的接触方式区分,主要有固定床气化、流化床气化、气流床气化和熔浴床床气化。 2.2 主要反应 煤的气化包括煤的热解和煤的气化反应两部分。煤在加热时会发生一系列的物理变化和化学变化。气化炉中的气化反应,是一个十分复杂的体系,这里所讨论的气化反应主要是指煤中的碳与气化剂中的氧气、水蒸汽和氢气的反应,也包括碳与反应产物之间进行的反应。 习惯上将气化反应分为三种类型:碳—氧之间的反应、水蒸汽分解反应和甲烷生产反应。 2.2.1碳—氧间的反应 碳与氧之间的反应有: C+O2=CO2(1)

煤气化工艺流程

煤气化工艺流程 1、主要产品生产工艺煤气化是以煤炭为主要原料的综合性大型化工企业,主要工艺围绕着煤的洁净气化、综合利用,形成了以城市煤气为主线联产甲醇的工艺主线。 主要产品城市煤气和甲醇。城市燃气是城市公用事业的一项重要基础设施,是城市现代化的重要标志之一,用煤气代替煤炭是提高燃料热能利用率,减少煤烟型大气污染,改善大气质量行之有效的方法之一,同时也方便群众生活,节约时间,提高整个城市的社会效率和经济效益。作为一项环保工程,(其一期工程)每年还可减少向大气排放烟尘万吨、二氧化硫万吨、一氧化碳万吨,对改善河南西部地区城市大气质量将起到重要作用。 甲醇是一种重要的基本有机化工原料,除用作溶剂外,还可用于制造甲醛、醋酸、氯甲烷、甲胺、硫酸二甲酯、对苯二甲酸二甲酯、丙烯酸甲酯等一系列有机化工产品,此外,还可掺入汽油或代替汽油作为动力燃料,或进一步合成汽油,在燃料方面的应用,甲醇是一种易燃液体,燃烧性能良好,抗爆性能好,被称为新一代燃料。甲醇掺烧汽油,在国外一般向汽油中掺混甲醇5?15勉高汽油的辛烷值,避免了添加四乙基酮对大气的污染。 河南省煤气(集团)有限责任公司义马气化厂围绕义马至洛阳、洛阳至郑州煤气管线及豫西地区工业及居民用气需求输出清洁能源,对循环经济建设,把煤化工打造成河南省支柱产业起到重要作用。 2、工艺总流程简介: 原煤经破碎、筛分后,将其中5?50mm级块煤送入鲁奇加压气化炉,在炉内与氧气和水蒸气反应生成粗煤气,粗煤气经冷却后,进入低温甲醇洗净化装置,除去煤气中的CO2和H2S净化后的煤气分为两大部分,一部分去甲醇合成系统,合成气再经压缩机加压至,进入甲醇反应器生成粗甲醇,粗甲醇再送入甲醇精馏系统,制得精甲醇产品存入贮罐;另一部分去净煤气变换装置。合成甲醇尾气及变换气混合后,与剩余部分出低温甲醇洗净煤气混合后,进入煤气冷却干燥装置,将露点降至-25 C后,作为合格城市煤气经长输管线送往各用气城市。生产过程中产生的煤气水进入煤气水分离装置,分离出其中的焦油、中油。分离后煤气水去酚回收和氨回收,回收酚氨后的煤气水经污水生化处理装置处理,达标后排放。低温甲醇洗净化装置排出的H2S到硫回收装置回收硫。空分

煤化工产业概况及其发展趋势

煤化工产业概况及其发 展趋势 集团标准化办公室:[VV986T-J682P28-JP266L8-68PNN]

我国煤化工产业概况及其发展趋势 煤化学加工包括煤的焦化、气化和液化。主要用于冶金行业的煤炭焦化和用于制取合成氨的煤炭气化是传统的煤化工产业,随着社会经济的不断发展,它们将进一步得到发展,同时以获得洁净能源为主要目的的煤炭液化、煤基代用液体燃料、煤气化—发电等煤化工或煤化工能源技术也越来越引起关注,并将成为新型煤化工产业化发展的主要方向。发展新型煤化工产业对煤炭行业产业结构的调整及其综合发展具有重要意义。 1 煤化工产业发展概况 1. 1 煤炭焦化 焦化工业是发展最成熟,最具代表性的煤化工产业,也是冶金工业高炉炼铁、机械工业铸造最主要的辅助产业。目前,全世界的焦炭产量大约为~亿t/a,直接消耗原料精煤约亿t/a 。受世界钢铁产量调整、高炉喷吹技术发展、环境保护以及生产成本增高等原因影响,工业发达国家的机械化炼焦能力处于收缩状态,焦炭国际贸易目前为2500万t/ a。 目前,我国焦炭产量约亿t/a,居世界第一,直接消耗原料煤占全国煤炭消费总量的14%。 全国有各类机械化焦炉约750座以上,年设计炼焦能力约9000万 t/a,其中炭化室高度为4m~5.5m以上的大、中型焦炉产量约占80%。中国大容积焦炉(炭化室高≧6m)已实现国产化,煤气净化技术已达世界先进水平,干熄焦、地面烟尘处理站、污水处理等已进入实用化阶段,焦炭质量显着提高,其主要化工产品的精制技术已达到或接近世界先进水平。 焦炭成为我国的主要出口产品之一,出口量逐年上升,2000年达到1500t/a,已成为全球最大的焦炭出口国。 从20世纪80年代起,煤炭行业的炼焦生产得到逐步发展,其中有的建成向城市或矿区输送人工煤气为主要目的的工厂,有的以焦炭为主要产品。煤炭行业焦化生产普遍存在的问题是:焦炉炉型小、以中小型焦炉为主,受矿区产煤品种限制、焦炭质量调整提高难度较大,采用干法熄焦、烟尘集中处理等新技术少,大多数企业技术进步及现代化管理与其他行业同类工厂相比有较大差距。 1.2 煤气化及其合成技术 1.2.1 煤气化 煤气化技术是煤化工产业化发展最重要的单元技术。全世界现有商业化运行的大规模气化炉414台,额定产气量446×106Nm3/d,前10名的气化厂使用鲁奇、德士古、壳牌3种炉型,原料是煤、渣油、天然气,产品是F-T合成油、电或甲醇等。 煤气化技术在我国被广泛应用于化工、冶金、机械、建材等工业行业和生产城市煤气的企业,各种气化炉大约有9000多台,其中以固定床气化炉为主。近20年来,我国引进的加压鲁奇炉、德士古水煤浆气化炉,主要用于生产合成氨、甲醇或城市煤气。

煤气化技术的现状及发展趋势分析

煤气化技术是现代煤化工的基础,是通过煤直接液化制取油品或在高温下气化制得合成气,再以合成气为原料制取甲醇、合成油、天然气等一级产品及以甲醇为原料制得乙烯、丙烯等二级化工产品的核心技术。作为煤化工产业链中的“龙头”装置,煤气化装置具有投入大、可靠性要求高、对整个产业链经济效益影响大等特点。目前国内外气化技术众多,各种技术都有其特点和特定的适用场合,它们的工业化应用程度及可靠性不同,选择与煤种及下游产品相适宜的煤气化工艺技术是煤化工产业发展中的重要决策。 工业上以煤为原料生产合成气的历史已有百余年。根据发展进程分析,煤气化技术可分为三代。第一代气化技术为固定床、移动床气化技术,多以块煤和小颗粒煤为原料制取合成气,装置规模、原料、能耗及环保的局限性较大;第二代气化技术是现阶段最具有代表性的改进型流化床和气流床技术,其特征是连续进料及高温液态排渣;第三代气化技术尚处于小试或中试阶段,如煤的催化气化、煤的加氢气化、煤的地下气化、煤的等离子体气化、煤的太阳能气化和煤的核能余热气化等。 本文综述了近年来国内外煤气化技术开发及应用的进展情况,论述了固定床、流化床、气流床及煤催化气化等煤气化技术的现状及发展趋势。 1.国内外煤气化技术的发展现状 在世界能源储量中,煤炭约占79%,石油与天然气约占12%。煤炭利用技术的研究和开发是能源战略的重要内容之一。世界煤化工的发展经历了起步阶段、发展阶段、停滞阶段和复兴阶段。20世纪初,煤炭炼焦工业的兴起标志着世界煤化工发展的起步。此后世界煤化工迅速发展,直到20世纪中叶,煤一直是世界有机化学工业的主要原料。随着石油化学工业的兴起与发展,煤在化工原料中所占的比例不断下降并逐渐被石油和天然气替代,世界煤化工技术及产业的发展一度停滞。直到20世纪70年代末,由于石油价格大幅攀升,影响了世界石油化学工业的发展,同时煤化工在煤气化、煤液化等方面取得了显著的进展。特别是20世纪90年代后,世界石油价格长期在高位运行,且呈现不断上升趋势,这就更加促进了煤化工技术的发展,煤化工重新受到了人们的重视。 中国的煤气化工艺由老式的UGI炉块煤间歇气化迅速向世界最先进的粉煤加压气化工艺过渡,同时国内自主创新的新型煤气化技术也得到快速发展。据初步统计,采用国内外先进大型洁净煤气化技术已投产和正在建设的装置有80多套,50%以上的煤气化装置已投产运行,其中采用水煤浆气化技术的装置包括GE煤气化27套(已投产16套),四喷嘴33套(已投产13套),分级气化、多元料浆气化等多套;采用干煤粉气化技术的装置包括Shell煤气化18套(已投产11套)、GSP2套,还有正在工业化示范的LurgiBGL技术、航天粉煤加压气化(HT-L)技术、单喷嘴干粉气化技术和两段式干煤粉加压气化(TPRI)技术等。

煤气化工艺流程

精心整理 煤气化工艺流程 1、主要产品生产工艺 煤气化是以煤炭为主要原料的综合性大型化工企业,主要工艺围绕着煤的洁净气化、综合利用,形成了以城市煤气为主线联产甲醇的工艺主线。 主要产品城市煤气和甲醇。城市燃气是城市公用事业的一项重要基础设施,是城市现代化的重要标志之一,用煤气代替煤炭是提高燃料热能利用率,减少煤烟型大气污染,改善大气质量行之 化碳 15%提 作用。 2 。净化 装置。合成甲醇尾气及变换气混合后,与剩余部分出低温甲醇洗净煤气混合后,进入煤气冷却干燥装置,将露点降至-25℃后,作为合格城市煤气经长输管线送往各用气城市。生产过程中产生的煤气水进入煤气水分离装置,分离出其中的焦油、中油。分离后煤气水去酚回收和氨回收,回收酚氨后的煤气水经污水生化处理装置处理,达标后排放。低温甲醇洗净化装置排出的H2S到硫回收装置回收硫。空分装置提供气化用氧气和全厂公用氮气。仪表空压站为全厂仪表提供合格的仪表空气。 小于5mm粉煤,作为锅炉燃料,送至锅炉装置生产蒸汽,产出的蒸汽一部分供工艺装置用汽

,一部分供发电站发电。 3、主要装置工艺流程 3.1备煤装置工艺流程简述 备煤工艺流程分为三个系统: (1)原煤破碎筛分贮存系统,汽运原煤至受煤坑经1#、2#、3#皮带转载至筛分楼、经节肢筛、破碎机、驰张筛加工后,6~50mm块煤由7#皮带运至块煤仓,小于6mm末煤经6#、11#皮带近至末煤仓。 缓 可 能周期性地加至气化炉中。 当煤锁法兰温度超过350℃时,气化炉将联锁停车,这种情况仅发生在供煤短缺时。在供煤短缺时,气化炉应在煤锁法兰温度到停车温度之前手动停车。 气化炉:鲁奇加压气化炉可归入移动床气化炉,并配有旋转炉篦排灰装置。气化炉为双层压力容器,内表层为水夹套,外表面为承压壁,在正常情况下,外表面设计压力为3600KPa(g),内夹套与气化炉之间压差只有50KPa(g)。 在正常操作下,中压锅炉给水冷却气化炉壁,并产生中压饱和蒸汽经夹套蒸汽气液分离器1

煤化工工艺流程

煤化工工艺流程 典型的焦化厂一般有备煤车间、炼焦车间、回收车间、焦油加工车间、苯加工车间、脱硫车间和废水处理车间等。 焦化厂生产工艺流程 1.备煤与洗煤 原煤一般含有较高的灰分和硫分,洗选加工的目的是降低煤的灰分,使混杂在煤中的矸石、煤矸共生的夹矸煤与煤炭按照其相对密度、外形及物理性状方面的差异加以分离,同时,降低原煤中的无机硫含量,以满足不同用户对煤炭质量的指标要求。 由于洗煤厂动力设备繁多,控制过程复杂,用分散型控制系统DCS改造传统洗煤工艺,这对于提高洗煤过程的自动化,减轻工人的劳动强度,提高产品产量和质量以及安全生产都具有重要意义。

洗煤厂工艺流程图 控制方案 洗煤厂电机顺序启动/停止控制流程框图 联锁/解锁方案:在运行解锁状态下,允许对每台设备进行单独启动或停止;当设置为联锁状态时,按下启动按纽,设备顺序启动,后一设备的启动以前一设备的启动为条件(设备间的延时启动时间可设置),如果前一设备未启动成功,后一设备不能启动,按停止键,则设备顺序停止,在运行过程中,如果其中一台设备故障停止,例如设备2停止,则系统会把设备3和设备4停止,但设备1保持运行。

2.焦炉与冷鼓 以100万吨/年-144孔-双炉-4集气管-1个大回流炼焦装置为例,其工艺流程简介如下:

100万吨/年焦炉_冷鼓工艺流程图 控制方案 典型的炼焦过程可分为焦炉和冷鼓两个工段。这两个工段既有分工又相互联系,两者在地理位置上也距离较远,为了避免仪表的长距离走线,设置一个冷鼓远程站及给水远程站,以使仪表线能现场就近进入DCS控制柜,更重要的是,在集气管压力调节中,两个站之间有着重要的联锁及其排队关系,这样的网络结构形式便于可以实现复杂的控制算法。

煤气化工艺流程

煤气化工艺流程 1、主要产品生产工艺 煤气化是以煤炭为主要原料的综合性大型化工企业,主要工艺围绕着煤的洁净气化、综合利用,形成了以城市煤气为主线联产甲醇的工艺主线。 主要产品城市煤气和甲醇。城市燃气是城市公用事业的一项重要基础设施,是城市现代化的重要标志之一,用煤气代替煤炭是提高燃料热能利用率,减少煤烟型大气污染,改善大气质量行之有效的方法之一,同时也方便群众生活,节约时间,提高整个城市的社会效率和经济效益。作为一项环保工程,(其一期工程)每年还可减少向大气排放烟尘1.86万吨、二氧化硫3.05万吨、一氧化碳0.46万吨,对改善河南西部地区城市大气质量将起到重要作用。 甲醇是一种重要的基本有机化工原料,除用作溶剂外,还可用于制造甲醛、醋酸、氯甲烷、甲胺、硫酸二甲酯、对苯二甲酸二甲酯、丙烯酸甲酯等一系列有机化工产品,此外,还可掺入汽油或代替汽油作为动力燃料,或进一步合成汽油,在燃料方面的应用,甲醇是一种易燃液体,燃烧性能良好,抗爆性能好,被称为新一代燃料。甲醇掺烧汽油,在国外一般向汽油中掺混甲醇5~15%提高汽油的辛烷值,避免了添加四乙基酮对大气的污染。 河南省煤气(集团)有限责任公司义马气化厂围绕义马至洛阳、洛阳至郑州煤气管线及豫西地区工业及居民用气需求输出清洁能源,对循环经济建设,把煤化工打造成河南省支柱产业起到重要作用。 2、工艺总流程简介: 原煤经破碎、筛分后,将其中5~50mm级块煤送入鲁奇加压气化炉,在炉内与氧气和水蒸气反应生成粗煤气,粗煤气经冷却后,进入低温甲醇洗净化装置

,除去煤气中的CO2和H2S。净化后的煤气分为两大部分,一部分去甲醇合成系统,合成气再经压缩机加压至5.3MPa,进入甲醇反应器生成粗甲醇,粗甲醇再送入甲醇精馏系统,制得精甲醇产品存入贮罐;另一部分去净煤气变换装置。合成甲醇尾气及变换气混合后,与剩余部分出低温甲醇洗净煤气混合后,进入煤气冷却干燥装置,将露点降至-25℃后,作为合格城市煤气经长输管线送往各用气城市。生产过程中产生的煤气水进入煤气水分离装置,分离出其中的焦油、中油。分离后煤气水去酚回收和氨回收,回收酚氨后的煤气水经污水生化处理装置处理,达标后排放。低温甲醇洗净化装置排出的H2S到硫回收装置回收硫。空分装置提供气化用氧气和全厂公用氮气。仪表空压站为全厂仪表提供合格的仪表空气。 小于5mm粉煤,作为锅炉燃料,送至锅炉装置生产蒸汽,产出的蒸汽一部分供工艺装置用汽,一部分供发电站发电。 3、主要装置工艺流程 3.1备煤装置工艺流程简述 备煤工艺流程分为三个系统: (1)原煤破碎筛分贮存系统,汽运原煤至受煤坑经1#、2#、3#皮带转载至筛分楼、经节肢筛、破碎机、驰张筛加工后,6~50mm块煤由7#皮带运至块煤仓,小于6mm末煤经6#、11#皮带近至末煤仓。 (2)最终筛分系统:块煤仓内块煤经8#、9#皮带运至最终筛分楼驰张筛进行检查性筛分。大于6mm块煤经10#皮带送至200#煤斗,筛下小于6mm末煤经14#皮带送至缓冲仓。 (3)电厂上煤系统:末煤仓内末煤经12#、13#皮带转至5#点后经16#皮

(能源化工行业)我国煤化工产业概况及其发展方向

(能源化工行业)我国煤化工产业概况及其发展方向

我国煤化工产业概况及其发展趋势 煤化学加工包括煤的焦化、气化和液化。主要用于冶金行业的煤炭焦化和用于制取合成氨的煤炭气化是传统的煤化工产业,随着社会经济的不断发展,它们将进壹步得到发展,同时以获得洁净能源为主要目的的煤炭液化、煤基代用液体燃料、煤气化—发电等煤化工或煤化工能源技术也越来越引起关注,且将成为新型煤化工产业化发展的主要方向。发展新型煤化工产业对煤炭行业产业结构的调整及其综合发展具有重要意义。 1煤化工产业发展概况 1.1煤炭焦化 焦化工业是发展最成熟,最具代表性的煤化工产业,也是冶金工业高炉炼铁、机械工业铸造最主要的辅助产业。目前,全世界的焦炭产量大约为3.2~3.4亿t/a,直接消耗原料精煤约4.5亿t/a。受世界钢铁产量调整、高炉喷吹技术发展、环境保护以及生产成本增高等原因影响,工业发达国家的机械化炼焦能力处于收缩状态,焦炭国际贸易目前为2500万t/a。 目前,我国焦炭产量约1.2亿t/a,居世界第壹,直接消耗原料煤占全国煤炭消费总量的14%。全国有各类机械化焦炉约750座之上,年设计炼焦能力约9000万t/a,其中炭化室高度为4m~5.5m之上的大、中型焦炉产量约占80%。中国大容积焦炉(炭化室高≧6m)已实现国产化,煤气净化技术已达世界先进水平,干熄焦、地面烟尘处理站、污水处理等已进入实用化阶段,焦炭质量显著提高,其主要化工产品的精制技术已达到或接近世界先进水平。 焦炭成为我国的主要出口产品之壹,出口量逐年上升,2000年达到1500t/a,已成为全球最大的焦炭出口国。 从20世纪80年代起,煤炭行业的炼焦生产得到逐步发展,其中有的建成向城市或矿区输送人工煤气为主要目的的工厂,有的以焦炭为主要产品。煤炭行业焦化生产普遍存在的问题是:焦炉炉型小、以中小型焦炉为主,受矿区产煤品种限制、焦炭质量调整提高难度较大,采用干法熄焦、烟尘集中处理等新技术少,大多数企业技术进步及现代化管理和其他行业同类工厂相比有较大差距。 1.2煤气化及其合成技术 1.2.1煤气化 煤气化技术是煤化工产业化发展最重要的单元技术。全世界现有商业化运行的大规模气化炉414台,额定产气量446×106Nm3/d,前10名的气化厂使用鲁奇、德士古、壳牌3种炉型,原料是煤、渣油、天然气,产品是F-T合成油、电或甲醇等。 煤气化技术在我国被广泛应用于化工、冶金、机械、建材等工业行业和生产城市煤气的企业,各种气化炉大约有9000多台,其中以固定床气化炉为主。近20年来,我国引进的加压鲁奇炉、德士古水煤浆气化炉,主要用于生产合成氨、甲醇或城市煤气。 煤气化技术的发展和作用引起国内煤炭行业的关注。“九五”期间,兖矿集团和国内高校、科研机构合作,开发完成了22t/d多喷嘴水煤浆气化炉中试装置,且进行了考核试验。 结果表明:有效气体成分达83%,碳转化率>98%,分别比相同条件下的德士古生产装置高1.5%~2%、2%~3%;比煤耗、比氧耗均低于德士古7%。该成果标志我国自主开发的先进气化技术取得突破性进展。 1.2.2煤气化合成氨 以煤为原料、采用煤气化—合成氨技术是我国化肥生产的主要方式,目前我国有800多家中小型化肥厂采用水煤气工艺,共计约4000台气化炉,每年消费原料煤(或焦炭)4000多万t,合成氨产量约占全国产量的60%。化肥用气化炉的炉型以UGI型和前苏联的Д型为主,直径由2.2m至3.6m不等,该类炉型老化、技术落后。加压鲁奇炉、德士古炉是近年来引进用于合成氨生产的主要炉型。

煤气化制甲醇工艺流程

煤气化制甲醇工艺流程 1 煤制甲醇工艺 气化 a)煤浆制备 由煤运系统送来的原料煤干基(<25mm)或焦送至煤贮斗,经称重给料机控制输送量送入棒磨机,加入一定量的水,物料在棒磨机中进行湿法磨煤。为了控制煤浆粘度及保持煤浆的稳定性加入添加剂,为了调整煤浆的PH值,加入碱液。出棒磨机的煤浆浓度约65%,排入磨煤机出口槽,经出口槽泵加压后送至气化工段煤浆槽。煤浆制备首先要将煤焦磨细,再制备成约65%的煤浆。磨煤采用湿法,可防止粉尘飞扬,环境好。用于煤浆气化的磨机现在有两种,棒磨机与球磨机;棒磨机与球磨机相比,棒磨机磨出的煤浆粒度均匀,筛下物少。煤浆制备能力需和气化炉相匹配,本项目拟选用三台棒磨机,单台磨机处理干煤量43~ 53t/h,可满足60万t/a甲醇的需要。 为了降低煤浆粘度,使煤浆具有良好的流动性,需加入添加剂,初步选择木质磺酸类添加剂。 煤浆气化需调整浆的PH值在6~8,可用稀氨水或碱液,稀氨水易挥发出氨,氨气对人体有害,污染空气,故本项目拟采用碱液调整煤浆的PH值,碱液初步采用42%的浓度。 为了节约水源,净化排出的含少量甲醇的废水及甲醇精馏废水均可作为磨浆水。 b)气化 在本工段,煤浆与氧进行部分氧化反应制得粗合成气。 煤浆由煤浆槽经煤浆加压泵加压后连同空分送来的高压氧通过烧咀进入气化炉,在气化炉中煤浆与氧发生如下主要反应: CmHnSr+m/2O2—→mCO+(n/2-r)H2+rH2S CO+H2O—→H2+CO2 反应在6.5MPa(G)、1350~1400℃下进行。 气化反应在气化炉反应段瞬间完成,生成CO、H2、CO2、H2O和少量CH4、H2S等气体。 离开气化炉反应段的热气体和熔渣进入激冷室水浴,被水淬冷后温度降低并被水蒸汽饱和后出气化炉;气体经文丘里洗涤器、碳洗塔洗涤除尘冷却后送至变换工段。 气化炉反应中生成的熔渣进入激冷室水浴后被分离出来,排入锁斗,定时排入渣池,由扒渣机捞出后装车外运。 气化炉及碳洗塔等排出的洗涤水(称为黑水)送往灰水处理。 c)灰水处理 本工段将气化来的黑水进行渣水分离,处理后的水循环使用。 从气化炉和碳洗塔排出的高温黑水分别进入各自的高压闪蒸器,经高压闪蒸浓缩后的黑水混合,经低压、两级真空闪蒸被浓缩后进入澄清槽,水中加入絮凝剂使其加速沉淀。澄清槽底部的细渣浆经泵抽出送往过滤机给料槽,经由过滤机给料泵加压后送至真空过滤机脱水,渣饼由汽车拉出厂外。 闪蒸出的高压气体经过灰水加热器回收热量之后,通过气液分离器分离掉冷凝液,然后进入变换工段汽提塔。 闪蒸出的低压气体直接送至洗涤塔给料槽,澄清槽上部清水溢流至灰水槽,由灰水泵分别送至洗涤塔给料槽、气化锁斗、磨煤水槽,少量灰水作为废水排往废水处理。 洗涤塔给料槽的水经给料泵加压后与高压闪蒸器排出的高温气体换热后送碳洗塔循环

国内煤气化技术评述与展望

2012年 第15期 广 东 化 工 第39卷 总第239期 https://www.doczj.com/doc/504624030.html, · 59 · 国内煤气化技术评述与展望 付长亮 (河南化工职业学院,河南 郑州 450042) [摘 要]依据煤气化技术的常用分类标准和评价指标,分析研究了国内所用的煤气化技术的优势与不足。综合考虑原料广泛性、技术先进性、投资成本等因素,认为航天炉干粉煤气化技术具有适应的煤种多、气化效率高、生产能力大、碳转化率高、投资省、操作费用低等优势,在未来的煤化工产品生产中将会得到普遍的应用。 [关键词]煤气化技术;评述;展望 [中图分类号]TQ [文献标识码]A [文章编号]1007-1865(2012)15-0059-02 Review and Prospects of Domestic Coal Gasification Technology Fu Changliang (Henan V ocational College of Chemical Technology, Zhenzhou 450042, China) Abstract: According to common classification standard and evaluation index, advantages and disadvantages of domestic coal gasification technology were analyzed and studied. Considering comprehensively the raw material extensive, technology advanced and investment cost, it was thought that HT-L dry powder coal gasification had the vast potential for future development, because of the more quantity of coal type used, higher gasification efficiency, larger production capacity, higher carbon conversion, lower investment cost. Keywords: coal gasification technology ;review ;prospects 1 煤气化及其评价指标 煤气化指在高温下煤和气化剂作用生成煤气的过程。可简单表示如下: +???→高温 煤气化剂煤气 其中的气化剂主要指空气、纯氧和水蒸汽。煤气化所制得的煤气是一种可燃性气体,主要成分为CO 、H 2、CO 2和CH 4,可作为清洁能源和多种化工产品的原料。因此,煤气化技术在煤化工中处于非常重要的地位。 煤气化反应主要在气化炉(或称煤气发生炉、煤气炉)内进行。不同的煤气化技术主要区别在于所用的气化炉的形式不同。 通常,对煤气化技术的评价主要从气化效率、冷煤气效率、碳转化率和有效气体产率四个方面进行。气化效率衡量原料(煤和气化剂)的热值转化为可利用热量(煤气的热值和产生蒸汽的热值)的情况,是最常用的评价指标,标志着煤气化技术的能耗高低。冷煤气效率衡量原料的热值转化为煤气热值的情况,是制得煤气量多少及质量高低的标志。碳转化率衡量煤中有多少碳转化进入到煤气中,是煤利用率高低的标志。有效气体产率衡指单位煤耗能产出多少有效气体(CO+H 2),是对煤气化技术生产有价值成分效果好坏的评价。这四个指标不完全独立,从不同的方面反映了煤气化技术中人们最关注的问题。 2 煤气化技术的分类 煤气化的分类方法较多,但最常用的分类方法是按煤与气化剂在气化炉内运动状态来分。此法,将煤气化技术分为如下几种。 2.1 固定床气化 固定床气化也称移动床气化,一般以块煤或煤焦为原料。煤由气化炉顶加入,气化剂由炉底送入。流动气体的上升力不致使固体颗粒的相对位置发生变化,即固体颗粒处于相对固定状态。气化炉内各反应层高度亦基本上维持不变。因而称为固定床气化。另外,从宏观角度看,由于煤从炉顶加入,含有残炭的灰渣自炉底排出,气化过程中,煤粒在气化炉内逐渐并缓慢往下移动,因而又称为移动床气化。目前,国内采用此方法的煤气化技术主要有固定床间歇气化法和加压鲁奇气化法。 2.2 流化床气化 流化床煤气化法以小颗粒煤为气化原料,这些细粒煤在自下而上的气化剂的作用下,保持着连续不断和无秩序的沸腾和悬浮状态运动,迅速地进行着混和和热交换,其结果导致整个床层温度和组成的均一。目前,国内属于此方法的煤气化技术主要有恩德粉煤气化技术和ICC 灰融聚气化法。 2.3 气流床气化 气流床气化是一种并流式气化。气化剂(氧与蒸汽)与煤粉一同进入气化炉,在1500~1900 ℃高温下,将煤部分氧化成CO 、H 2、CO 2等气体,残渣以熔渣形式排出气化炉。也可将煤粉制成 煤浆,用泵送入气化炉。在气化炉内,煤炭细粉粒与气化剂经特殊喷嘴进入反应室,会在瞬间着火,发生火焰反应,同时处于不充分的氧化条件下。因此,其热解、燃烧以及吸热的气化反应,几乎是同时发生的。随气流的运动,未反应的气化剂、热解挥发物及燃烧产物裹挟着煤焦粒子高速运动,运动过程中进行着煤焦颗粒的气化反应。这种运动形态,相当于流态化技术领域里对固体颗粒的“气流输送”,习惯上称为气流床气化。属于此类方法的煤气化技术较多,国内主要有壳牌干粉煤气化法、德士古水煤浆气化法、GSP 干粉煤气化法、航天炉干粉煤气化等[1-3]。 3 国内主要煤气化技术评述 3.1 固定床间歇式气化 块状无烟煤或焦炭在气化炉内形成固定床。在常压下,空气和水蒸汽交替通过气化炉。通空气时,产生吹风气,主要为了积累能量,提高炉温。通水蒸汽时,利用吹风阶段积累的能量,生产水煤气。空气煤气和水煤气以适当比例混合,制得合格原料气。 该技术是20世纪30年代开发成功的。优点为投资少、操作简单。缺点为气化效率低、对原料要求高、能耗高、单炉生产能力小。间歇制气过程中,大量吹风气排空。每吨合成氨吹风气放空多达5000 m 3。放空气体中含CO 、CO 2、H 2、H 2S 、SO 2、NO x 及粉灰。煤气冷却洗涤塔排出的污水含有焦油、酚类及氰化物,对环境污染严重。我国中小化肥厂有900余家,多数采用该技术生产合成原料气。随着能源和环境的政策要求越来越高,不久的将来,会逐步被新的煤气化技术所取代。 3.2 鲁奇加压连续气化 20世纪30年代,由德国鲁奇公司开发。在高温、高压下,用纯氧和水蒸汽,连续通过由煤形成的固定床。氧和煤反应放出的热量,正好能供应水蒸汽和煤反应所需要的热量,从而维持了热量平衡,炉温恒定,制气过程连续。 鲁奇加压气化法生产的煤气中除含CO 和H 2外, 含CH 4高达10 %~12 %,可作为城市煤气、人工天然气、合成气使用。相比较于固定床间歇气化,其优点是炉子生产能大幅提高,煤种要求适当放宽。其缺点是气化炉结构复杂,炉内设有破粘机、煤分布器和炉篦等转动设备,制造和维修费用大,入炉仍需要是块煤,出炉煤气中含焦油、酚等,污水处理和煤气净化工艺复杂。 3.3 恩德粉煤气化技术 恩德粉煤气化技术利用粉煤(<10 mm)和气化剂在气化炉内形成沸腾流化床,在高温下完成煤气化反应,生产需要的煤气。 由于所用的原料为粉煤,煤种的适应性比块煤有所放宽,原料成本也得到大幅度降低。得益于流化床的传质、传热效果大大优于固定床,恩德粉煤气化炉的生产能力比固定床间歇制气有较大幅度的提高。由于操作温度不高,导致气化效率和碳转化率都不高,且存在废水、废渣处理困难等问题。此技术多用于替代固定床间歇制气工艺[4-6]。 [收稿日期] 2012-07-21 [作者简介] 付长亮(1968-),男,河南荥阳人,硕士,高级讲师,主要从事化工工艺的教学与研究。

煤气化技术的现状和发展趋势

煤气化技术的现状和发展趋势 1、水煤浆加压气化 1.1 德士古水煤浆加压气化工艺(TGP) 美国Texaco 公司在渣油部分氧化技术基础上开发了水煤浆气化技术,TGP 工艺采用水煤浆进料,制成质量分数为60%~65%的水煤浆,在气流床中加压气化,水煤浆和氧气在高温高压下反应生成合成气,液态排渣。气化压力在2.7~6.5MPa,提高气化压力,可降低装置投入,有利于降低能耗;气化温度在1 300~1 400℃,煤气中有效气体(CO+H2)的体积分数达到80%,冷煤气效率为70%~76%,设备成熟,大部分已能国产化。世界上德士古气化炉单炉最大投煤量为2 000t/d。德士古煤气化过程对环境污染影响较小。 根据气化后工序加工不同产品的要求,加压水煤浆气化有三种工艺流程:激冷流程、废锅流程和废锅激冷联合流程。对于合成氨生产多采用激冷流程,这样气化炉出来的粗煤气,直接用水激冷,被激冷后的粗煤气含有较多水蒸汽,可直接送入变换系统而不需再补加蒸汽,因无废锅投资较少。如产品气用作燃气透平循环联合发电工程时,则多采用废锅流程,副产高压蒸汽用于蒸汽透平发电机组。如产品气用作羟基合成气并生产甲醇时,仅需要对粗煤气进行部分变换,通常采用废锅和激冷联合流程,亦称半废锅流程,即从气化炉出来粗煤气经辐射废锅冷却到700℃左右,然后用水激冷到所需要的温度,使粗煤气显热产生的蒸汽能满足后工序部分变换的要求。 1.2 新型(多喷嘴对置式)水煤浆加压气化 新型(多喷嘴对置式)水煤浆加压气化技术是最先进煤气化技术之一,是在德士古水煤浆加压气化法的基础上发展起来的。2000 年,华东理工大学、鲁南化肥厂(水煤浆工程国家中心的依托单位)、中国天辰化学工程公司共同承担的新型(多喷嘴对置)水煤浆气化炉中试工程,经过三方共同努力,于7 月在鲁化建成投料开车成功,通过国家主管部门的鉴定及验收。2001 年2 月10 日获得专利授权。新型气化炉以操作灵活稳定,各项工艺指标优于德士古气化工艺指标引起国家科技部的高度重视和积极支持,主要指标体现为:有效气成分(CO+H2)的体积分数为~83%,比相同条件下的ChevronTexaco 生产装置高1.5~2.0 个百分点;碳转化率>98%,比ChevronTexaco 高2~3 个百分点;比煤耗、比氧耗均比ChevronTexaco 降低7%。 新型水煤浆气化炉装置具有开车方便、操作灵活、投煤负荷增减自如的特点,同时综合能耗比德士古水煤浆气化低约7%。其中第一套装置日投料750t 能力新型多喷嘴对置水煤浆加压气化炉于2004 年12 月在山东华鲁恒升化学有限公司建成投料成功,运行良好。另一套装置两台日投煤1 150t 的气化炉也在兖矿国泰化工有限公司于2005 年7 月建成投料成功,并于2005 年10 月正式投产,2006 年已达到并超过设计能力,目前运行状况良好。该技术在国内已获得有效推广,并已出口至美国。 2、干粉煤加压气化工艺 2.1 壳牌干粉煤加压气化工艺(SCGP) Shell 公司于1972 年开始在壳牌公司阿姆斯特丹研究院(KSLA)进行煤气化研究,1978 年第一套中试装置在德国汉堡郊区哈尔堡炼油厂建成并投入运行,1987 年在美国休斯顿迪尔·帕克炼油厂建成日投煤量250~400t 的示范装置,1993年在荷兰的德姆克勒(Demkolec)电厂建成投煤量2 000t/d 的大型煤气化装置,用于联合循环发电(IGCC),称作SCGP 工业生产装置。装置开工率最高达73%。该套装置的成功投运表明SCGP 气化技术是先进可行的。 Shell 气化炉为立式圆筒形气化炉,炉膛周围安装有由沸水冷却管组成的膜式水冷壁,其内壁衬有耐热涂层,气化时熔融灰渣在水冷壁内壁涂层上形成液膜,沿壁顺流而下进行分

现代煤气化技术发展趋势及应用综述_汪寿建

2016年第35卷第3期CHEMICAL INDUSTRY AND ENGINEERING PROGRESS ·653· 化工进展 现代煤气化技术发展趋势及应用综述 汪寿建 (中国化学工程集团公司,北京 100007) 摘要:现代煤气化技术是现代煤化工装置中的重要一环,涉及整个煤化工装置的正常运行。本文分别介绍了中国市场各种现代煤气化工艺应用现状,叙述汇总了其工艺特点、应用参数、市场数据等。包括第一类气流床加压气化工艺,又可分为干法煤粉加压气化工艺和湿法水煤浆加压气化工艺。干法气化代表性工艺包括Shell炉干煤粉气化、GSP炉干煤粉气化、HT-LZ航天炉干煤粉气化、五环炉(宁煤炉)干煤粉气化、二段加压气流床粉煤气化、科林炉(CCG)干煤粉气化、东方炉干煤粉气化。湿法气化代表性工艺包括 GE水煤浆加压气化、四喷嘴水煤浆加压气化、多元料浆加压气化、熔渣-非熔渣分级加压气化(改进型为清华炉)、E-gas(Destec)水煤浆气化。第二类流化床粉煤加压气化工艺,主要有代表性工艺包括U-gas灰熔聚流化床粉煤气化、SES褐煤流化床气化、灰熔聚常压气化(CAGG)。第三类固定床碎煤加压气化,主要有代表性工艺包括鲁奇褐煤加压气化、碎煤移动床加压气化和BGL碎煤加压气化等。文章指出应认识到煤气化技术的重要性,把引进国外先进煤气化技术理念与具有自主知识产权的现代煤化工气化技术有机结合起来。 关键词:煤气化;市场应用;气化特点;参数数据分析 中图分类号:TQ 536.1 文献标志码:A 文章编号:1000–6613(2016)03–0653–12 DOI:10.16085/j.issn.1000-6613.2016.03.001 Development and applicatin of modern coal gasification technology WANG Shoujian (China National Chemical Engineering Group Corporation,Beijing100007,China)Abstract:Modern coal gasification technology is an important part of modern coal chemical industrial plants,involving stable operation of the entire coal plant. This paper introduces application of modern coal gasification technologies in China,summarizes characteristics of gasification processes,application parameters,market data,etc. The first class gasification technology is entrained-bed gasification process,which can be divided into dry pulverized coal pressurized gasification and wet coal-water slurry pressurized gasification. The typical dry pulverized coal pressurized gasification technologies include Shell Gasifier,GSP Gasifier,HT-LZ Gasifier,WHG (Ning Mei) Gasifier,Two-stage Gasifier,CHOREN CCG Gasifier,SE Gasifier. The typical wet coal-water slurry pressurized gasification technologies include GE (Texaco) Gasifier,coal-water slurry gasifier with opposed multi-burners,Multi-component Slurry Gasifier,Non-slag/slag Gasifier (modified as Tsinghua Gasifier),E-gas (Destec) Gasifier. The second class gasification technology is fluidized-bed coal gasification process. The typical fluidized-bed coal gasification technologies include U-gas Gasifier,SES Lignite Gasifier,CAGG Gasifier. The third class gasification technology is fixed-bed coal gasification process. The typical fixed-bed coal gasification technologies include Lurgi Lignite 收稿日期:2015-09-14;修改稿日期:2015-12-17。 作者:汪寿建(1956—),男,教授级高级工程师,中国化学工程集团公司总工程师,长期从事化工、煤化工工程设计、开发及技术管理工作。E-mail wangsj@https://www.doczj.com/doc/504624030.html,。

煤气化工艺资料

煤化工是以煤为原料,经过化学加工使煤转化为气体,液体,固体燃料以及化学品的过程,生产出各种化工产品的工业。 煤化工包括煤的一次化学加工、二次化学加工和深度化学加工。煤的气化、液化、焦化,煤的合成气化工、焦油化工和电石乙炔化工等,都属于煤化工的范围。而煤的气化、液化、焦化(干馏)又是煤化工中非常重要的三种加工方式。 煤的气化、液化和焦化概要流程图 一.煤炭气化

煤炭气化是指煤在特定的设备内,在一定温度及压力下使煤中有机质与气化剂(如蒸汽/空气或氧气等)发生一系列化学反应,将固体煤转化为含有CO、H2、CH4等可燃气体和CO2、N2等非可燃气体的过程。 煤的气化的一般流程图 煤炭气化包含一系列物理、化学变化。而化学变化是煤炭气化的主要方式,主要的化学反应有: 1、水蒸气转化反应C+H2O=CO+H2 2、水煤气变换反应CO+ H2O =CO2+H2 3、部分氧化反应C+0.5 O2=CO 4、完全氧化(燃烧)反应C+O2=CO2 5、甲烷化反应CO+2H2=CH4 6、Boudouard反应C+CO2=2CO 其中1、6为放热反应,2、3、4、5为吸热反应。 煤炭气化时,必须具备三个条件,即气化炉、气化剂、供给热量,三者缺一不可。 煤炭气化按气化炉内煤料与气化剂的接触方式区分,主要有: 1) 固定床气化:在气化过程中,煤由气化炉顶部加入,气化剂由气化炉底部加入,煤料与气化剂逆流接触,相对于气体的上升速度而言,煤料下降速度很慢,甚至可视为固定不动,因此称之为固定床气化;而实际上,煤料在气化过程中是以很慢的速度向下移动的,比

较准确的称其为移动床气化。 2) 流化床气化:它是以粒度为0-10mm的小颗粒煤为气化原料,在气化炉内使其悬浮分散在垂直上升的气流中,煤粒在沸腾状态进行气化反应,从而使得煤料层内温度均一,易于控制,提高气化效率。 3) 气流床气化。它是一种并流气化,用气化剂将粒度为100um以下的煤粉带入气化炉内,也可将煤粉先制成水煤浆,然后用泵打入气化炉内。煤料在高于其灰熔点的温度下与气化剂发生燃烧反应和气化反应,灰渣以液态形式排出气化炉。 4) 熔浴床气化。它是将粉煤和气化剂以切线方向高速喷入一温度较高且高度稳定的熔池内,把一部分动能传给熔渣,使池内熔融物做螺旋状的旋转运动并气化。目前此气化工艺已不再发展。 以上均为地面气化,还有地下气化工艺。 根据采用的气化剂和煤气成分的不同,可以把煤气分为四类:1.以空气作为气化剂的空气煤气;2.以空气及蒸汽作为气化剂的混合煤气,也被称为发生炉煤气;3.以水蒸气和氧气作为气化剂的水煤气;4.以蒸汽及空气作为气化剂的半水煤气,也可是空气煤气和水煤气的混合气。 几种重要的煤气化技术及其技术性能比较 1.Lurgi炉固定床加压气化法对煤质要求较高,只能用弱粘结块煤,冷煤气效率最高,气化强度高,粗煤气中甲烷含量较高,但净化系统复杂,焦油、污水等处理困难。 鲁奇煤气化工艺流程图

相关主题
相关文档 最新文档