US2493498A

US2493498A - Heating method and apparatus

Info

Publication number: US2493498A
Application number: US705660A
Authority: US
Inventors: Norman E Peery
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1946-10-25
Filing date: 1946-10-25
Publication date: 1950-01-03
Anticipated expiration: 1967-01-03

Description

Jan. 3, 1950 Filed 001:. 25'; 1946 N. EQPEERY HEATING METHOD AND APPARATUS Z-Sheets-Sheet 1 Jams, 1950 N. E'. PEERY HEATING METHOD AND APPARATUS Filed Oct; 25 1946 2 She'ets-Sheet 2 Figlll lnvzn+or= Norman E. Peer-g 5g his AHorneg= g%&l:

Patented Jan. 3, 1950 Norman E. Pecry, San Francisco, Calif., assignor to Shell Development Company, San Francisco,

Calll., a corporation of Delaware Application October 25, 1946, Serial No. 705,660

12 Claims. I

This invention relates to an improved method for heating various materials, by indirect heat exchange with hot combustion gases, and apparatus therefor.

its variations are the most common, the Bonecourtsystem shou1d.be mentioned. In this sys- "tem, a homogeneous explosive mixture of gas and air in the proper ratio for complete com- 2 ing up through a stationary bed of granules of incandescent refractory. A particularly large proportion of the potential energy is thereby converted into radiant energy. This system is par- An object of the invention is to provide a 5 ticularly advantageous where very high tempermethod and apparatus for heating by indirect aturesihlgher than those readily obtainable by heat exchange with combustion gases whereby the more common method) are desired. Due to the temperature throughout the heating zone is the large proportion of radiant energy there is exceptionally uniform and easily and accurately a great tendency to develop localized zones of controllable. Another object of the invention is very high temperature. Also, the system is not to provide a method and apparatus for heatsuitable for operation at the relatively low teming whereby heat transfer is greatly increased peratures (for instance below 1000 F.) usually through conduction. 'An object of the invention desired for chemical conversions. is to provide a method and appara us for heat- In the system of the present invention, exing which s Particularly advantageous in ceptionally uniform temperatures throughout 'y Out chemical reactions and Conversions the entire heating zone are obtained. The temwherein a uniform and controlled temperature perature may furthermore be easily and throughout a definite reaction space is desire curately controlled. Also uniform, controlled In the usual method 0f heatmg by mdn'ect heating at relatively low temperatures, for inheat exchange with combustion gases-the stance below 1000 F., as well as higher temperterial to be heated is placed in or passed through atures, may be ff ted These advantages or a Sultable enclosed chamber usually a coil or points of superiority are attained by effecting the tube, and the combustion gases from a surroundcombustion, a fuel gas within the body of an mg or adjacent combustion zone are caused to 2 agitated finely divided solid heat carrier which pass Over and about Said chamber and exchange 5 in turn exchanges heat indirectly with the maheat therewith. The simplest case is the steam terial to be heated Thus in the present boiler. In this system, large variations in temhem, the combustion zone is fined with a Perature in the a large stantially static bed of finely divided inert solid; part of the heat transfer is by radiation and fuel gas and an oxygen-containing gas are mconsequently there is a great. tendency to jected into the body of the finely divided solid 3 9 hot spots These conditlons are very under combustion conditions at such a rate as to esirable in all cases where a uniform controlled t th fi 1 di 1 1 u temperature is desired as for example when a am 6 Hey v ded 9 en y tated fluidized or pseudo-liquid condition.

carrying out chemical conversions. In order to, f t t n u adapt this simple system to chemical conver- 3 1 e pr-ocess, he inven w I be sions, numerous modifications and variations, .desmbe1 nd explained. more detail in have been made in attempts to overcome these "F -g u! the descmptwn the apparatus disadvantages. One of the most successful of; F rF 11 attached drawmg; In the these is the so-called Petro-Chem Iso-Flow.g r -=terest=of clearness the apparatus illustrated in 'nace now in wide use. In this type of furnace, the Fu s f seml'dmgram' however, the heat transfer rate is very low: Also, I ti l i amplified form- 9 the temperatures are still not asu'niform as would. 5- em ,none t s el framework and be desired. This is especially the case where "a Porting structure i Tube which chemical conversion is being carried out which Ties the d to be is Shown as a single is either appreciably exothermic or endothermic, 9 e s in P t the ppa a us Of since 11; is extremely m t if t impossible will contamseveral tubes with separate inlets to adjust and compensate for variations in the and outletsquantity and position of the liberated or absorbed. I 1 81:? i fei ifinal View Of the section heat of reaction. ica n gure a While ,the above-mentioned simple system and 5 Fi ure II is a P an vi w of the Section IIII 0 indicated in Figure I;

Figure'IH is a plan view of the section III-1m indicated in Figure I. 1

Referring to the drawing, 1 is a furnace or bustion is caused to burn without flame by passhousing structure having inner walls of refractory material, built-to define a combustion zone ;may be introduced. as a mixturewhich may or 2. and; so-called-disengaging zone I. may not be preheated. In general, however, pre- The combustion zone, as indicated heating is advantageous.

I and -I[I,"is rectangular in plan. While this The space 3 immediatelyabove-the level of therectangular-plan of the combustion zone ism-Ir 5 'fl elydivided inert solid is called the disengaging ticularly suitableinmost cases, the apparatus zone. This zone is preferably of. larger horizontal is not limited .v his respect. Thus, by suitable cross-section than the combustion zone. It is rearrangement of the pipes, etc.-, combustion preferably at least 3 ft, m t; t may be zonesof any desired horizontal section such as somewhat less in some cases: where the finely circular, oval, square, etci. may be used- The; Iii-divided solid material is particularly dense and co'mbustion zone is substantially completely filled the disengaging-zone is larger in horizontal crosswith'a finely divided inert solid as will be 'desection'than the combustion zone. The hot com- 'scribedin more detail below. The combustion busti on gases leave .the disengaging space by zonewhe'remre extends r ubstantially'the means oiconduits l6 and II. This hot gas bottom up to the level of the 'fl'nely divided solid usually carries in suspensions. minor amount of the finely'divide'd solid from'the combustion zone.

(see'Fig'ure I). Asuitable ,tube 4 designed to 1 v I It is therefore preferably passed to a means for carry 'thedluid to be heated, nd preferably of heat resistant alloy, is suitably supported (by the nacovery of this solid. Thus,this gas is passed means not shown) within the combustion zone. to"cyclone separators l8 and I9. The gas, subm the apparatus illustrated, the tube 4 runs stantially free of suspended. solids, is then disler'igthwise and horizontal excep for the return c a d V a l ne 120, blower II and line 22. It bends. In most cases when a fluid reactant or is often necessary to recycle a portion of thi reactants are tobe heated, horizontal tubes'are hot gas to the combustion zone. For this purpose quite suitable. lin such cases where the tube the apparatus .is preferably-provided with suitable or tubes contain a solid fixed'catalyst, it isde-j '25 inlettubes such as tube 23 feeding from manifold sirable that the tube be placed at-an angle of line ,24."'The desired portion. of the gases to be at least from the horizontal. The projecting thu r cl d is ppliedito manifold 24 by line ends of tube 4 and the outer surface of the I "and blower 2| v In some cas s it will be found furnace may be insulated-(not shown). In such desirable fortemp'erature control to cool the gas cases where there are a' plurality of tubes or a 3o om what. {Thismay be accomplished by injectcoil such as illustrated, suflicient'space should; ing water or steam into the fluidized powder or be provided between the tubes or turns of the a into the disengaging space.

Nozzles

28 and 29 0011- to allow circulation of the, fluidized so1id.- are. provld J r hi P rpose. When injecting I is desirable to place the tubes or t n of the steam or' water into the fluidized powder the space. In the apparatus illustrated, the fuel gas coil in the combustion zone so that a space equal cooling efiect is more pronounced; however, by to'one tube diameter or somewhat more is proinjecting' it into the disengaging zone the gas vided between the individual tubes'orturns. The velocity in the oombustion zone isnot affected.

most suitable diameter-and number of the'tubes Also, if desired, suitable heat exchange equipment.

or "coils will vary with the'temperature and heat 1 or a waste heatboiler or the like may be used to transfer requirements. The-spacing and the ratio"4 0. recover additional heat from the combustion of tube heating surface to volume willlbe adjusted gases priorto discharging them.

in am! particular case according to known en Finely divided solid collected by the cyclone gineering' principles to provide-therequirements separators may befedto manifold line 24 by of heat transfer and residence time of the parlines 26 and 21., This material is then blown ticular operation contemplated; v 4 back into the combustion zone by the recycled Thefuel for ,theapparatus is fuel gas such as gas. a water gas, producer gas or natural gas. This gas The apparatus is also provided with one or is supplied by line and is introduced into the more separate bu'rners for fuel gas, oil, or any combustion zone near the bottom by means of other fuel located in the disengaging space. In two parallel

perforated pipes

8 and 9. Other Figures-I and, II this is indicated by the single equivalent means may be provided. Air or other burner 5 Supplied w s and air y lines 6 gas containing suiiicient oxygen for the combusn tion of the fuel gas is supplied by blower Ill and I In Operation the fin ly vid d inert solid ma line H and is introduced into the combustion rial filling the combustion zone is maintained zone, preferably at. a plurality of points, by the ina so-calledfluidized or pseudo liquid state havperforated section of pipe I l at the bottom of ing a density of at least 20 lbs/cubic foot. This the combustion zone. It is found desirable-to I pseudo liquid completely fills the combustion p e a the P t0 intl'dducing it intdthe zone, exhibiting a more or less definite upper combustion-zone; This is accompl i the level, as indicated. The pseudo liquid is in vio-- apparatusillustrated by passi s he l l O lent agitation; if a small amount of lampblack is coil I2 which 15 connected to the pe rated s added it is seen to be evenly dispersed throughout 9 1 by line in h case the. thezone in a few'seconds. In order to permit required for preheatmg is obtained from the the attainment of this pseudo liquid condition wi 19118, "i s n 5 a m t ftheli'n tsol id should be sufilciently finely divided is desi ne 9 givelmm'e uniform combustion least v most of it passes a 40-mesh U S zather than $0 n j of high Stand dlsieveL Larger particles may be present emperatures. If higher temperatures are. d in t1 ith um sired, the preheating of the air and/or fuel gas g s elem quamity shouldbeefl'ected outsideof the combustion-zone; 6 er 9 .r tame Partlcles as f instance Separate preheater. nrpyby havingdiameters between about 20 microns and p1 acing the preheating coils in therdiisefiglggmg are suitable. In spite of the violent agitationin the combustion zone, it is found that I ere is little eroding of the particles in the system and consequently little carry-over of the -and air are independently introduced into/the combustion zone, the air only being preheated It is tobe understood that the fuel gas and air material to the cyclone separators. In some cases, in fact, the cyclone separators may be disthus increasing the range, of application and facilitating the control of the apparatus.

The composition of the inert solid may vary and is preferably chosen in accordance with the particular case. Ingeneral, the more important desired properties of the solid material are (1) It-should be capable of withstanding the temperatures prevailing in the combustion zone without fusing or sticking.

(2) It should have a high coefficient of heat conductivity.

(3) It should not be consumed or destroyed by the combustion. v I

Thus, when relatively low temperatures are to prevail in the combustion zone a material having a high coefficient of heat conductivity, such as metal powder, powdered metal oxides (for instance, iron oxide), and the like, is preferably chosen. Such material may have a relatively low fusion point. When higher temperature is to prevail in the combustion zone a more refractory material such as silicon, silica, alumina, zirconia or the like is chosen, even though such materials generally do not have particularly good coefficients of heat transfer.

Some further particulars regarding the process and apparatus of the invention arebest made evident by a description of an operation. Since the process of the invention is particularly advantageous for carrying out chemical conversions of a highly exothermic or endothermic nature at relatively low temperatures, a process of this type is chosen to illustrate the operation. Thus, the operation of the process will be described in connection with the dehydrogenation of methylcyclohexane to toluene with a tungsten sulfide-nickel sulfide catalyst. For this endothermic conversion a series of tubes connected to common headers instead of the single tube 4 is preferred. Also, since the tubes are substantially filled with a bed of the cataylst pellets, the tubes are preferably inclined rather than horizontal. These variations however have no bearing upon the functioning and control of the heating'system described.

The finely divided solid may be, for example, particles of zirconia chiefly from about 100 microns to about 500 microns in diameter. There are thirty-two 3-inch alloy reaction tubes, 24 feet long, in the combustion zone. The apparatus has a heat adsorption capacity of about 10 mm. B. t. u. per hour and a thermal efliciency of about 65%, excluding the power drives for the blowers.

In starting the apparatus valve 30 is throttled, valve 3| is opened and blower 2| is started. The amount of air circulated is adjusted by means of the valves and/or the blower to bring the powder into the desired fluidized state. Burner i is started. When the temperature of the finely divided solid reaches about 600 F. or somewhat higher, blower i0 is started and natural gas is introduced via line II." The total introduction of gas into'the combustion zone is regulated to give a superficial gas velocity of about 2 feet per second. The finely divided zirconia is then in an agitated fluidized state having a density of about -40-lbs./cubic foot. When the temperature in the combustion zone reaches the desired temperature, for instance 1200" F., burner 5 is shut off, valve 30 is adjusted and methylcyclohexane is passed through the reaction tubes. The temperature is then controlled by control of the natural gas and air supplied to the combustion zone. The density and agitation of the powder may be adjusted by adjusting the amount of gas recycled. The gas which is not recycled is discharged via line 22.

A small amount of the cyclone separator. This is re-introduced into the combustion zone by means of the recycled gas as described.

In some cases it is desirable to inject steam or

water byinjection nozzles

28 and 29. This is often the case where a low-temperature highly exothermic process is being carried out. In such cases the-flows of gaseous fuel and air are low and the amount of recycle gas is quite large. The

under such pressure is provided.

combustion may then be improved by increasing the flows of gaseous fuel and air, decreasing the recycle gas flow, and cooling the recycle gas by the injection of steam or water.

The illustrated apparatus is intended for operation at substantially atmospheric pressure. The combustion takes place under positive pressure, however, due to the "hydraulic head of the powder in pseudo liquid state. It will be appreciated, however, that the process of the invention is also applicable for operation in which the combustion zone is maintained under a higher pressure it an apparatus capable of operation Operation under a positive pressure has some advantages. However the greatly increased cost of the apparatus designed to operate under high pressure makes the use of such pressure unattractive for at least most cases.

The inventionclaimed is:

1. An apparatus of the class described comprising a furnace'structure having inner walls of refractory material defining a lower combustion zone and an upper disengaging zone, a bed of fluidized powdered inert refractory solid substantially filling said combustion zone, a coil or tubeiwithin said combustion zone provided with external connections for passing a fluid to be heated therethrough, an ancillary burner above said combustion zone in said disengaging zone, a conduit for combustion products connecting said disengaging zone with a dust separator, a; conduit for gases provided with a blower'connecting the gas outlet of said separator with said combustion zone near the bottom thereofi and means for injecting a gaseous fuel and oxygen into said combustion zone near the bottom thereof.

'2. An apparatus of the class described comprising a furnace structure having inner walls of refractory material defining a lower combustion zirconia powder collects ina conduit for combustion products connecting said disengaging zone with a dust, separator, a conduit for gases provided with a blower connecting the gas outlet of said separator with said combustionzone near the bottom thereof and means for separately injecting a gaseous fuel and oxygen into said combustion zone near the bottom thereof. v 3. An apparatus of the class described comprising a furnace structure having inner walls of refractory material defining a lower combustion zone and an upper disengaging zone, a bed of fluidized refractory inert powder consisting of particles of spheroidal shape between about 20 microns and 50 microns in diameter substantially filling said combustion zone. a coil or tube within said combustion zone provided with external con- -nections for passing an ancillary fluid to be heated therethrough, a burner above said combustion zone in said disengaging zone. a conduit for combustion products connecting said disengaging zone with a dust separator, a conduit for gases provided with a blower connecting the gas outlet of separator with said combustion zone 11 the bottom thereof and means for iniecting a-gaseous fuel'and oxygen into said combustion zone near the bottom thereof.

' 4. An apparatus according to claim 1 further provided with means for preheating'gases, communicating with said means for injecting fuel gas and air' into said powdered solid near the bottom of said combustion zone.

5; An apparatus according to claim 1 further provided with means for returning solid particles collected in said separating means to the com-' bustion zone.

inert and non-combustibleweiractory' powders I consist essentially of rounded particlesof. zir conia.

10. Method according to claim 8 in which the density of said inert'and non-combustible refractory powder in pseudo -liquid condition is at least. pounds per cubic foot.

11. The method of heating by indirect heat exchange with hot combustion gases material to be chemically reacted which comprises passing said material in indirect heat exchange relationship through a combustion zone, maintaining said 6. The method of heating by- 'indirect heat exchange with hot combustion gases material to be chemically-reacted which comprises passing said material in indirect heat exchange relationship through a combustion zone, maintaining said combustion zone filled witha substantially static bed of an inert and non-combustible refractory powder, andsupplying a gaseous fuel andan oxygen-containing gas within said powder under combustion conditionsat such a rate as to maintain said powder in a-pseudo-liquid condition whereby the materialbeing heated is brought to a suitable uniform reaction temperature.

7. Method according to claim 6 in which-the inert and non-combustible refractory powder consists essentially'of particles within th range of from about 20 microns to about 500 microns.

8. Method according to claim 6 in which the inert and non-combustible refractory powder consists essentially'of substantially spherical par ticles.

9. Method acco claim '6 in which the temperature.

combustion zone filled with a substantially static bed of an inert and non-combustible refractory powder. supplying a gaseous fuel'and a gas containing free oxygen within said powder under combustion conditions at such a rate as to main chemically reacted which comprises passing said material in indirect heat exchange relationship through a combustion zone, maintaining said combustion zone filled with a substantially static bed of an inert and non-combustible refractory powder, supplying a gaseous fuel and an oxygencontaining gas within the-body of said powder under combustion conditions'at such a rate as to maintain said powder in a pseudo-liquid condition, and controlling the temperature in said combustion zone by the addition of regulated quantities of steam whereby the material being heated is brought to a suitable uniform reaction Y NORMAN E. PEERY.

1 REFERENCES CITED Y The following references are oi record in' the 9. t s. Patent: