US1881528A - Coking gas oven - Google Patents

Description

L C. HAMLINK COKING GAS OVEN Oct. 11, 1932.

Filed April 28, 1927 5 Sheets-Sheet l L. C. HAMLINK COKING GAS OVEN Oct. 11, 1932.

Filed April 28, 1927 5 Sheets-Sheet 2 F' RON 7' WASTE GAS l.. c. HAMLINK 1,881,528

COKIN@ GAS OVEN Filed April 28, 192? 5 Sheets-Sheet 3 CMST//V @HAMM/Zn Oct. 11, 1932.

NSE 11m m n,

Oct. 1l, 1932. l.. c. HAMLINK 1,881,528

COKIN@ GAS OVEN Filed April 28. 1927 5 sheets-Sheet 4 L. c. HAMLINK 1,881,528

COKING GAS OVEN Filed April 28. 1927 5 sheets-Sheet 5 L L h .11,v

Oct. l1, 1932.

Patented Oct. 11, 1932 Unirse STA TESPATENT, ermee i LAZNBY C. AIJLENK, OF CLEVELAND HEGfI-ITS, OHIO, ASSIGNOR TO THE GAS V- CHNEZRY COVANY,'OF CLEVELAND, OHIOQA. CORPORATON OF OHIO COKIN@ GAS VOVEN Application 1ed`Apri1 ,28,

My invention relates to coking gas-ovens and particularly to that class of apparatus in which a plurality of parallel retorts is employed, each of the sides of which is associated with a heating unit for supplying the re- Ygases of combustion; together quired heat tothe coal in the retorts for maliing the desired gas product and ley-product coke which heating units each includes regenerators for conserving the heat of the with valve mechanisms for controlling the flow of the fuel-gas, the flow of the air for supporting the combustion of the latter and the flow of the gases of combustion', whereby the direc- :tion of flow of the latterfthrough the units may be reversed and the heat of the regenerai tors applied to such air. Also in this type of apparatus, two waste-gas andtwo fuel-gas flues are employed, which, by means of vthe lvalve mechanism, are alternately rendered of au operative, the fuel-gas flues or conduits being connected with a source of fuel-gas supply. rlhat is, the valve mechanism may be so manipulated that fuel-gas first passes through 29" 'one fuel-gas flue or conduit, then with air passes through the heating unit in one direction and is burned in v'such unit. of combustion then pass out through the one waste-gas ilue. Or the valve mechanism may be so manipulated as to cause the fuel-gas to i'irst pass through the other fuel-gas flue or conduit, thenV with air through the heating unit in the opposite direction and burned in said unit, the gases of combustion then passing out through the other waste-gas flue.

Apparatus of this type is generally referred to as a by-product gas-oven since comme 1cially usable gas is the product of main value and eolie is a by-product. Heretofore in apparatus of this type communication between the fuel-gas flues and each heating unit has been controlled by two separate valves. There were, in consequence, twice as many of these valves as there were heating units and the element of expense was such that these valves had to be constructed from materials and in a manner such that they were not capable of withstanding a temperature of over approXimately 7 O0o F. without injury.

The gases j 1927. Serial No. 187,243.

without first cooling the gas, inasmuch as'the ypreducer-gas would enter the apparatus at a ytemperature of about 12000 F., or over, and rwould eventually impair or destroy the controlling valves above referred to. Such cooling action, however, resulted in a loss of thermal etliciency, as will be understood by those skilled in the art, and required the presence in the apparatus of a regenerator for reheating this gas in order to produce the proper llgame temperature in the combustion chamers.

rllhe general object of the present invention is to increase the eiieiency of coking gasovens of the above-described type, one of the 'Y specific objects being to provide a structure in which the producer-gas source may be connected directly with the apparatus, that is, without subjecting the fuel-gas to a cooling operation before it passes into the heating units, and thereby enabling me to take advantage to the fullest extent possible of the economic value of the sensible heat in such producer-gas.

The said invention consists in character-g istics of structure and combinations of parts hereinafter fully described and particularly pointed out in the claims.

In the annexed drawings:

Figure 1 represents a plan of a coking gasoven of the above-described type and embodying my invention.

Fig. 2 represents a front elevation.

Fig. 3 represents a vertical longitudinal broken section on an enlarged scale, taken upon the planes indicated by line IIL-III,

Fig. 1, and'viewed in the direction indicated by the arrows.

Fig. 4 represents a transverse section, on said enlarged scale taken u on the )lanes in- K dicated by line IV-IV, Fig. 3, and viewed in the direction indicated by the arrows.

Fig. 5 represents a partial transverse section, on saidv enlarged scale, taken upon the plane indicated by line V-V,Fig.` 3, and

' viewed in the direction indicated by the dicatedby line X-X, Fig. 2, viewed in the direction indicated by the arrows.

Fig. 11 represents a transverse verticalsection otsaid valve mechanism taken upon the` plane indicated by line XlmXl, Fig. 1.

Fig. 12 represents a transverse vertical section taken upon the plane indicated by line XII-XIF Fig. 1, and

13 represents a longitudinal vertical section taken upon the plane indicated by line XIII-XIII, l 1.

In the illustrated embodiment of my i ivention, suitable materials such as briclr, masonry andl steel are employed to form a main battery structure 1, emboc a plurality of' parallel and verticall oven chambers 2 extendingv transversely of the structure 1, as shown in Fi 3, each provided the top with suitable charging openings 3 and covers 4 therefor, andv an oven-gas outlet 5, Fig. 5, all of these outlets being connected to a main takeoif duct 6, for conducting the oven-gas to a suitable gas-holder (not shown) as will be understood.

ln this` main stru ture is also provided a plurality of heating units for heating the two opposite sides ot the oven chambers.`

of these units includes a combustion i. fr 7 and these cb aro-bers alternate longitudinally of the battery, with the oven chambers 2, so that each side of each oven chamber is laterally adjacent to a combustion chamber 7 as shown in Fig. 3.

Each Ycombustion chamber is sub-divided into a plurality ot vertical front heating coni- `vbustion flues 8, and rear heating ilues 3 by vertical walls 82 terminating short of the top of the oven chamber to form a horizontal passagevQ, Figs. 3 and 4;

Beneaththe front part of each combustion chamber and parallel therewith are two Ypassages and 11, and beneath the rear part i Y The bottom of each vertical heating` flue S and18 is provided with an opening 15 or 154 which communicates with two laterally di- 4verging passages or ports, 16 and 1701916.

and 17", whose lower ends respectively com- Vmunicate with the passages 10 and 11, and

10 and 11', 3, 4, and 6. The latter passages are each formed at their sides with ledges 18 and 13, respectively, upon which rest loosely placed damper- bricls 19 and 19, Fig 8, which may be used to vary the extent 01" communication of the passages 16 and 17 and 16 and 17 with the passages 10, 11, 10 and 11 by slidingthem along the ledges 18 and 13, to partially'cover the bottoms of said passages 16 and 17 and 16" and 17 Beneath each combustion chamber 7 are two transversely alined vertical regenerators 20and 20 whose inner ends are separated by a longitudinal wall 21, Figs. 3 and 6, and adV jacent thereto and parallel with these regenerators are two narrow vertical fuel- gas passages 22 and 22" respectively, and also alinevd transversely of, the main battery structure,

Figs; 3., 4 and 9.

lFliese fuel- eas assaoes 22 and 22 are ro.-

vided internally with staybricls 23 for sup-V porting their Walls, as shown in Figs. 3 and 4, and their inner ends are separated from each other by the wall 21. 'Y

The upper end of each front regeneratoi Y 2O is connected with a passage 1l by means of a plurality of vertical passages 24,. correspending in number with the heating lues 3 which are located above the reoeneratorsy 20, Fig. 6; and each of the front fuel-gas passages 22 is, connected with a passage 10, by the saine number oi vertical passages 25, Fig. 4. Similarly the upper end of each rear regenerator 20 is connected with a passagev 11 by means of ai plurality oi' vertical passages 24, cor esponding .in number with ythe heating lues 3 which arelocated above the nregenerators 20', and each of therear fuel-- Ygas passages 22 is connected with a passagel 10 by the saineV number of vertical passages 25". The bottoni ont each of the front regenerators 2O is connected with va common longitudinally extending horizontal waste-gas Hue 26 by means of a vertical passage 27, and the bottom of each of the rear regenerators 20 with a common longitudinally extending horizontal waste-gas flue 28 by means of a vertical passage 29, as shown in Figs. 3 and 6. The degree of vcommunication between the regenerators andthe waste-gas flues 26 and cating with both of the regenerators and 28l may be controlledby .slidable dampergitudinally extending horizontal fuel-gas flue 31 by means of a vertical passage 32, andthe bottom of each rear fuel-gas passage 22" is connected with av common longitudinally extending horizontal fuel-gas flue 33 4by 'means of a vertical passage 34, asshown in Fig. 4. The degree of communicationbetween the fuel- gas passages 22 and 22 andthe fuelgas iues 31 and 33 may be controlled by slidable damper-bricks 35, Figs. 4 and 9.

Below each regenerator and 20 is a horizontal air-supply passage 36 or'36 whose communication with vvthe atmosphere is controlled by a damper 37 or 37 Fig. 6. As has been common practice heretofore, suitable means are provided for simultaneously actuating all of the front dampers 37, and

aoV

similar means for simultaneously actuating all of the rear dampers 37', and which it will hence not be necessaryV to further describe.

AccessA to the damper-bricks controlling communication between the regenerators 20 and 20 and the waste- gas flues 26 and 28 is afforded through the outer ends of the air- passages 36 and 36 and to the damper-bricks controlling communication between the fuel- gas passages 22 and 22 and the fuel- gas flues 31 and 33 through the outer openings 38 and 38 normally closed by doors 39.

Each heating unit therefore consists of two transversely alined vertical regenerators', two transversely alined vertical fuel-gas passages respectively adjacent the regenerators,

a combustion chamber above and communifuel-gas passages, the communication between the regeneratorsand combustion chambers being controllable and the communication between the fuel-gas passages and combustion chambers being likewise controllable.

These heating units also include the air- supply passages 36 and 36 for the regenerators 20 and 20, respectively.

It will be noted from the description and drawings that the direct communication between the fuel- gas flues 31 and 33 and the heating units is permanently open as is also the communication between the said units `and the waste- gas flues 26 and 28, the amount of` opening being controllablevby the damperbricks 35 and 30, respectively as described above.

Each of the fuel- gas flues 31 and 33 is j closed at oneuend of the main battery structure as shown in Fig. 1 at 31a and 33a, and extends beyond the other end of said' structure, the left-hand end thereof Vas illustrated, and access to these latter extending ends is controlled by a reversing valve 40.0f any -my present invention and I have illustrated such a valve as applied to my improved apparatus, in the drawings, Fig. 1, 2, 10,-11,.12 and 13. Y

The left-hand extending ends of the said two fuel-gas iiues terminate under the casing 41 of thevalve 40, Figs. 1 and 12, and communicate with the interior of said casing through vertical passages 31 and 33 respectively, and the top of such casing is connected-with a downcomer pipe 42 which in turn is connected with a Y gas-producer 44 which supplies hot fuel-gas. A dust-catcher 43 may be interposed between the gas-producer and downcomer pipe.

Between the end portions ofthe tw'o fuelgas ues 31 and 33 is an auxiliary waste-gas flue 45 which communicates with the interior o f the casing of the valve by means of a vertical passage and this communication is controlled by a slide-valve 46, Figs. 12 and 13.

The other end of this flue 45 communicates with the stack 47, Fig. 1.

The valve 40 is provided with the movable member 48, Figure 12, which may be shifted to permit communication between the downcomer 42 and either the fuel-gasV iue 31 or the fuel-gas flue 33. In so doing communication is established between the auxiliary flue 45 and that fuel-gas flue which is shut off from communication with the downcomer 42.

Each of the waste- gas flues 26 and 28 is closed at one end of the main battery structure as shown at 26a and 28a, Fig. 1, and

extends beyond the other end of saidV structure, the left-hand end thereof as illustrated.

rl`he extending ends of the two waste- gas flues 26 and 28 terminate under the casing 50, Figure 11, of a valve 49 similar to valve 40, and communicate with the interior of said casing through vertical passages 26 and 28 respectively. The auxiliary waste-gas flue 45 extends two waste-gas flues, Figs. 1 and 11, and communicates with the interior of the casing 50 of reversing valve 49 by means of the vertical passage 45a.

The movable valve-member 51 of the valve 49., may be shifted so as to establish communication between the auxiliary waste-gas passage 45 and either one of the waste- gas iiues 26 and 28 to the exclusion of the other, as will Vbe understood.

Descriptz'zmA of operation,

between the end portions of the lines in Figs. ll and 12, respectively. Under such conditions the rear air-control danipers 37 are given their open position and the front air-control dampers 37,v given their closed position, as shown in Fig. 6.y

Let it also be assumed that the apparatus. has been in previous operation in a inan-V l sages 34 and into and through the rear fuelgaspassages 22. Frein the latter itipasses up throughthe passages 25 to the transverse passages thence to the passages 16 and into the rear heating flues 8 which are above 1 the rear regenerators` 20 and fuel-gasY pas-V 28 sages 22. Y s Y Simultaneously with the above-described direction of travel of the fuelgas, air passes Y into the rear air-passages 36 up through the heated rear regenerators out through the passages 24 and into the transverse passages 11. F rom the latter the heated air passes up through the passages 17 into the rear heating flues 8 into which the fuel-gas is passing. The air and oas therefore become mixed in these heatino' fines 8 and combustion of the D Y i gas is effected therein.

The frases of heatin@` dass out of the rear combustion lues into the passages?) ano over to the heating flucs which are above the" front b regenerators 20. Y

As' Will be noted from Fig. ll, the front waste-gas flue 26 is connected with the auX- '1" Lf i45 lh 'thtle iiiaiy waste gas uo ant ence wi i Le stack. It will also be noted from Fig. 12 th at the front fuel-gas flue 3l is connected with the said auxiliary flue 45, but this connection is limited by the slide-valve 46, the latter being set so as to materially restrict the draft from the fuel-gas flue 3l 'to the stack. Y

The greater portion of the gases ofY coinbustion, therefore, pass from the front coinbustion chambers down through the passages 1'4" connected therewith, through passages 24 and into and through the front regenerators 20, heating thelater. From the regenerators V20, they then. pass through the passages 27 connectel therewith, into the front wastegas flues 26, into valve-member 51, over into the waste-gas fine 45 to the'st'ach. V f

A much smaller quantity of these gases and which is regulatable by the slide-valveV 46, passesL from the front heating flues'S, down through the passages i6 connected therewith throughV assao'es 25 intoandi through the front fuel-gas passages 22, through ythe passages 32, into and through the front fuel-gas flue 3l, into valvelchainber 48, and past the valve 46, through passage 45 (Fior. 13) toauxiliary Waste-gas flue 45 and thence tol the stack, thuspurging the front fuel-gas passages' 22 and the front fuelgas fiile 31'of any air which might khave gained access thereto by leakage or otherwise, and so preventing the formationof an explosivefinixtur'e when the operation is reversed as hereinafter describe Y To reverse'the above-'described operati-on,AV the valves 40 and 49 are operatedto shift their movable members over toV their other positions, rear air dampers 37 are closed and front air dampers 37 vare opened.V Valve 40 will vthen establish connection between the downconier 42 and the front fuel-gas flue 3l and also establishconnection between 'the flue 45 (and hence the stack) and the rear fuel-gas `iue 33'.` Valve 49 willthen establish` connection between the flue 45 (and' hence the stack)V and the rear waste-gas fine quence flow into the vfront fuel-gas flue 31',

up through-the front fuel-gas and into the front heating flues 8.

Air will flow yinto the front air-supply passages 36 up through the heated front regenerators 20 and into the front heatingrflues 8 where it supports Vthe combustion of the fuel-gas. The gases of combustion pass up to and through passages 9'and down ythe-rear heating flues 8. The' greater part of-these' gases then passes through passages 17', then passes through and heats the rear regenerators 20, then passes into and through'the rear Waste gas fine 28, through valve 49 to the stack.` A'sinaller amountof the gases passes through passagesl and purges the rear fuelV gas passages 22" and the rear fuel gas flue 33, as a result of the connection of the rear fuel-gaslue with the stack by the valve 40,`

aswill be understood.

It willv be noted from the above const-rnc! tioii,'that by providing valve mechanism for controlling the influx of fuel-gas into the fuel-gas flues 3l and 33and for controlling the efflux of the gases of combustion fromv the waste- gas fines 26 and 28, all of theV direct connections between the fuel-gas fines and heatingunits, and betweeny the heating units and the wastegas fines may be left perinanently open, after being set `as desired byf means of the damper-bricks 35 andV 30,-re speotively, thus eliminating theV necessity of providing separate valves,` for controlling ac-V cess to and discharge from said units. A valve-mechanism for complete control Vand. capable of eeoting the 'necessary reversal', is therefore provided, which is greatly simplilied jas compared with the previous practice, andlwhich may therefore; be made heat- Yresisting to any required degree without passages 22 ioo iis

ist

mamas wise, and Yenter the Vfuel-gas passages and combustion chambers ata high degree of temperature, usually-about 1300O F. Y

It will also be Seencfrom the above-described construction that the damper-bricks l9and 19vby being 4placed intermediately of the bottom of the combustion chambers and tops of the fuel gas passages 2:2, Q2 and the regenerators 20 -'and 2l are out of the direct influence of the destructive action of the high heat generated in the combustion chambers during combustion, thus tending to prolong the life of these bricks and are also in a position in whichfthey are readily accessible for adjustment. f Y

`.By eliminating the multiplicity of controlling'valves heretofore employed and as heretofore described, both the fuel-gas liues and'waste-gas iiues may be placed beneath the apparatus, and incorporated in the masonryffundation structure as shown.

It will be further'noted that inasmuch as the fuel-gas need not be reheated, a regenerator for heating such gas is not required. This make it possible to make the fuel-gas passages 22 and22 vnarrow and the regenerators 20. and 20 wide, as shown in Figure 3, thus providing a greater regenerator surface for the airL than has heretofore been possible in by-product gas ovens using producer-gas as fuel. At the same time, the total regenerator surface is reduced ascompared to that heretofore required,`thus resulting in economy of construction.

What claim is:

l. In a coke oven battery, a series of alternate coking chambers and combustion chambers for heating the same arranged side by side in a row, a regenerator unit below each of said combustionchambers, eachof the regenerator-units comprising two regenerators and each of the regenerators of each of said units communicating with the combustion chamber above the unit, two fuel-gas flues extending along said battery and communieating with eachof said combustion chambers and an air inlet for each ofsaid regenerators and means for controlling same; a single reversing valve for controlling lall of the fuel-gas flow into both of said fuel-gas flues; two waste-gas lues extending along said battery, the one communicating with one of the regenerators of each of said units and the other waste-gas flue with the .other regenerator of the same unit; vand means for controllingthe out-flow from said waste-gas iues.

2. A coke oven battery comprising a series of alternate coking chambers and combustion chambersfor heating the coking chambersarranged side by side in a row; a regenerator unit associated with each combustion chamber, each regenerator unit including two regenerators each of whichhas communication with its associated combustion chamber and each regenerator having an air inlet means for-controlling the air inlets ;two fuel conduits` extending lalong the battery and having communication with all the combustion chambers; two waste-gas flues extending along said battery and communicat-A c ing with the regenerator units; an outlet flue for waste gases adapted to communicate with said waste-gas flues a single reversing valve associated with thefuel conduits andv adapted to control the flow of fuel from a source of supply alternately through said conduits to all the combustion chambers; and valve mechanism associated with the waste-gas iues and adapted to control the flow of wastegas from' said two waste-gasflues to the outy ling the air inlets; a waste-gas flue system including two waste-gas flues extending along the battery, one of said flues communicating with the front regenerators and the second flue communicating with the rear regenerators, 4an outlet-Hue adapted to communi.- cate with said `waste-gas flue, and asingle reversing valve associated with said fiues and adapted to place said waste-gas fines alternately in communication with the out-let flue and a fuel-gas conduit system including two conduits extending along the battery, one conduit having communication with the front portions of the combustion chambers and thesecond conduit having communication with the rear portions of the combustion chambers, and means associated with said conduits and adapted to control the How of fuel Igas through the conduits to the combustion chambers. y

4. A coke oven battery comprising a series of alternate coking chambers and combustion chambers for heating the same arranged side by side in a row; a regenerator unit below each of said combustion chambers, each of the regenerator units comprising two regenerators each of which communicates with the co-mbustion chamber above the unit; an

air inlet for each of said regenerators; means for controlling the air inlets; two vfuel-gas conduits extending along said battery and communicating with each of said combustion chambers; a single reversing valve for con-- trolling the fuel-gas iow alternately into said fuel-gas conduits; two waste-gas ilues extending along` said battery and. communicating with the two regenerators of each of ioo lee

6 'reagisce i heating units including combustion chambers, a frontv series and a rear series of regenerators communicating with spaced portions lof the combustion chambers and hav-` ing valved air inlets, and the coking and combustion chambers being disposed side by side inL a row and in alternate relation to each other; a gas flue system comprising two waste-gas flues extending along the battery, one flue communicating with the front series of regenerators and the second flue communicating with the rear series of regenerators, an outlet-flue adapted to communicate with said waste-gas flues, a reversing valve adapted to place said two waste-gas flues in communication with said outlet-flue, two fuel-gas conduits extending along the battery, one of said conduits having communication with one portion of each combustion chamber and the second conduit having communication-with j f another portion of each combustion chamber,

a valve associated with. said conduits, and a passage extending from the last-mentioned Valve to the outlet-flue, said last-mentioned valve being `adapted to connect one of the fuel-gas conduits-with a source of fuel-gas and to connect the other conduit with said passage. Y

6. A coke oven battery comprising a series of alternate coking chambers and combust. tion chambers for heating the same arranged side by side in a row; a regenerator unit belowe'ach combustion chamber, said unit including a front regenerator communicating with the Vfront portion of the combustion chamber directly above and a rear regenera-tor communicating with the rear portion of the same combustion chamber; valved air inlets for said regenerators; a waste-gas flue system including two waste-gas iues extending along the battery,.one flue communicating with all the front regenerators and the second Hue communicating with all the rear regenerators, an outlet-flue adapted to communicate with said waste-gas flues, anda reu versing valve interposed between the two waste-gas fines and the outlet-flue and adapted to place either of said two waste-gas flues in communication with the outlet-nue; and a fuel-gas conduit system including two fuelgas conduits 4extending along the battery,

one conduit having communication with the front Vport-ion of each combustion chamber and the second conduithaving communication with the rear portion of each combustion chamber, and a valve mechanism'associ- 65- ated with said conduits and communicating duits with a source-0f fuel-gas and the otherf conduit with the outlet-flue.

7 In a coke oven battery, a series of col;- ing units each comprising a coking chamber and a combustion chamber side by side vfor heating the same, said units being positioned in a row so that thecoking chambers alter-V nate with the combustion chambers; a series of auxiliary units below the coking units, each auxiliary unit corresponding to acoking unit and including two regenerators and a fuel passage adjacent thereto, each regenerator being substantially wider than .the fuel passage adjacent thereto, and the width of each auxiliary unit being substantially the same as the width. of the corresponding coking unit.; conduits connecting each combustion chamber to the two regenerators and the fuel passage of the corresponding auxiliary unit; two fuel conduits extending along the battery, some ofthe fuel passages communicating with one of said fuel conduits and the balance of the fuel passages communicating with the other fuel conduit; and a Vsingle reversing valve for controlling the flow of fuel through said fuel conduits to all of the fuel'passages.

8. A coke ovenrbattery comprising a series of colring units positioned side by side.

in a row, eachV coking unit consisting of a coking chamber and a combustion chamber contacting therewith and the units being'po; sitioned so that the coking chambers alternate withthe combustion chambers; a series of auxiliary units positioned side Yby side in a row below the front portions of the coking units, each auxiliary unitbeing operatively associated with one of the combustion chambers and including a regenerator and a fuel-gas passage adjacent thereto, each regenerator being substantially wider than the fuel-gas passage adjacent thereto and the combined width of one regenerator and its adjacent fuel-gas passage being substantially the same as the combined width of' the corresponding coking and combustion chambers associated therewith; a second series of similar auxiliary units similarly positioned below the rear portions of the 'coking units; air inlets for the regenerators; means for controlling the Viniiow of air through said inlets; a wastegas iue system including two waste-gas iues extending along the auxiliary units, one flue communicating with the regenerators of one series of auxiliary units and the second flue communicating with the regenerators of the other series of auxiliary units, an outlet-flue adapted to communicate -with said wastegas flues, and a reversing Valve adapted to place the two waste-gas flues alternately in communication with the outlet-flue; and a fuel-gas feeding system including two fueliro gas conduits extending along the auxiliary units, one conduit communicating with the ueLgas passages of one series of auxiliary units and the second conduit co1n1nunicating with the fuel-gas passages of the other

Images