CA1310808C - Fluidized bed plant - Google Patents
Fluidized bed plantInfo
- Publication number
- CA1310808C CA1310808C CA000603745A CA603745A CA1310808C CA 1310808 C CA1310808 C CA 1310808C CA 000603745 A CA000603745 A CA 000603745A CA 603745 A CA603745 A CA 603745A CA 1310808 C CA1310808 C CA 1310808C
- Authority
- CA
- Canada
- Prior art keywords
- fluidized bed
- reactor
- bed reactor
- displacer
- secondary gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
- B01J8/24—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
- B01J8/44—Fluidisation grids
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C10/00—Fluidised bed combustion apparatus
- F23C10/18—Details; Accessories
- F23C10/20—Inlets for fluidisation air, e.g. grids; Bottoms
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L9/00—Passages or apertures for delivering secondary air for completing combustion of fuel
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C2206/00—Fluidised bed combustion
- F23C2206/10—Circulating fluidised bed
- F23C2206/101—Entrained or fast fluidised bed
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
- Fluidized-Bed Combustion And Resonant Combustion (AREA)
Abstract
Abstract of the Disclosure A fluidized bed plant system to carry out exothermic processes in a circulating fluidized bed and which consists of a fluidized bed reactor, a solids separator and a recycling path and which includes lines for supplying oxygen-containing primary gases through the bottom of the fluidized bed reactor, lines for supplying oxygen-containing secondary gas on a level which is at least 1 m above the reactor bottom but not in excess of 30% of the height of the reactor, and a fuel line which opens into the fluidized bed reactor between the primary and secondary gas lines. In order to ensure a satisfactory cross-mixing of oxygen-containing secondary gas and fuel, particularly in reactors having large dimensions, the plant comprises one or more displacers which cover 40 to 75% of the bottom surface of the fluidized bed reactor. The height of the displacer is not in excess of one-half of the height of the fluidized bed reactor. The displacer is so arranged that the remaining bottom surface of the fluidized bed reactor constitutes a single coherent surface. The one or more displacers is preferably square or rectangular in cross-section and may be provided with means for feeding oxygen-containing secondary gases and/or means for feeding fuel.
Description
1 31 Q~
Back~round of Invention The present invention is in a circulating fluidized bed system for carrying out exothermic processes. The system consists of a fluidized bed reactor, a solids separator and a recycling line wherein oxygen-containing primary gas is supplie~'~ through lines through the bottom of the fluidized bed reactor and oxygen-containing secondary gas is supplied to the reactor at an elevation o at least 1 meter above the reactor bottom but not in excess of 30% of the height of the reactor. Fuel is introduced into the fluidized bed reactor between the primary and secondary gas inlets. The fluidized bed reactor has a bottom surface area, 40 to 75~ of which is covered by one or more displacers having a height not in excess of one-half of that of the reactor.
Processes and equipment for handling circulating fluidized beds, particularly for combusting carbonaceous materials, have proved most advantageous and for numerous reasons are superior to processes and equipment in which so-called orthodox or conventional fluidized beds are employed.
; The basic prooess for combustion in a circulating fluidized bed is describ:ed in U.S. Patent 4,165,717. In that process the; combustion is in two stages and the heat released by the combustion is extracted by means of cooling t 3t 080~
surfaces disposed in the fluidized bed reactor.
significant advantage of that process is that the combustion process can be adapted to the required output in a technic~lly simple manner by controlling the suspension density, and hence the hea~ transfer to the cooling surfaces, especially in the upper portion of the reactor space.
In the combustion process using a circulating fluidized bed in accordance with U.S. Patent 4,111,158 at least a portion of the heat released by combustion is extracted in a fluidized bed cooler, which succeeds the flui~ized bed reactor. Cooled solids from the cooler are recycled to the fluidized bed reactor to maintain or control the reactor temperature. In that case an adapt~tion to the required output can be achieved by an increase or decrease of the rate at which solids flow through the fluidized bed cooler and then back into the fluidized bed reactor.
While the absve referred to processes have pro~en highly satisfactory, the existing trend towards plant units for progressively larger heat outputs results in certain difficulties in the control of the process because the higher thermal demands require larger reactor dimensions, particularly larger reactor cross-sections. In the larger cross-section uni~s, satisfactory transverse mixing of fuel and the like, and of oxygen-containing secondary gas, +) (thermal), i.e. ~ 3 ~ 0808 throughout the cross-section of the fluidized bed reactor is no longer ensured in the inlet region although such mixing is required for the reaction~ As a result, a considerahle part of the reaction can occur in the upper portion of the reactor space. Also afterburning may occur when the solids and gas have been separated in the solids separator following the reactor. This sequence of events is encountered in plants having combustion heat outputs above about 300 MW ln fluidized bed reactors having reactor areas in excess of about 50 m2.
In a prior proposal for solving the above pro~lem in reactors having a large cross-sectional area 40 to 75~ of the bottom surface area of the fluidized bed reactor was covered by one or more displacers, each displacer having a height not in excess of one-half of the height of the fluidized bed reactor. The geome~ric configuration of the displacer was selected subs~antially as desired. For instance, in a fluidized bed reactor having a circular cross-section the displacer may have the shape of a cylinder or of a-frustum of a cone and the center of the bottom displacer surface may lie ~pproximately on the center of the bottom surface. In a reactor having a rectangular cross-section the displacer may have the shape of a dam, which at its ends may optionaIly adjoin the parallel Wall5 of the reac~or so that the lower portion of the reactor space was effectively divided into two separate chambers.
Two dams may be provided, which may be virtually at right angles to each other and which - if they adjoin the walls of the reactor - would divide the lower part of the reactor space into ~our separate chambers.
It has been found that difficulties in the operation of a fluidized bed plant designed with the above displacer may arise if the displacer divides the lower part of the reactor space into separate chambers because in that case the primary air or fluidized gas stream may entrain bed material from one chamber so that the internal circulation of solids always taking place in a fluidized bed reactor wiL-l cause such entrained bed material to enter another chamber or other chambers. Unless an expensive control is provided there will be no reverse or compensating flow of material because ~he flow of the 1uidizing air through the "depleted" chamber will be restricted owing to the different hydrostatic pres~ures over the bottoms of the respective chambers.
S~m~arv of the Inven~ion It is an object of the invention to provide a fluidized bed system which consists of a fluidized bed reactor, a solids separator and a recycling path and serves to carry out exothermic processes in a circulating fluid~2ed bed ': '';
1~1080~
which system ensures a satisfactory and reliable operation without the need for an expensive or elaborate control even when the plant is opera-ted at a high combustion power.
According to the presen-t invention there is provided a fluidized bed system for conducting an exothermic process comprising:
- a fluidized bed reactor, a solids separator and a recycling means;
- means for supplying oxygen-containing primary gases through the bottom oE the fluidized bed reactor;
- means for supplying oxygen-containing secondary gases in an eleva-tion of at leas-t about 1 meter above the reactor bottom but not in excess of 30% of the height of the reactor;
- means for introducing fuel into the fluidized bed reactor between the primary and secondary gas inlets;
- one or more displacer means covering 40 to 75%
of the bottom surface area of the fluidized bed reactor, the remaining bot-tom surface of the fluidized bed reac-tor constituting a single coherent surface, said displacer means having a height not in excess of one-half of the height of the fluidized bed reac-tor.
In order to provide a single coherent surface the one or more displacers is so designed that individual segments oE the reactor bottom communicate with each other.
This can be achieved, e.g., in that a gas-permeable bottom surface is left between the displacer at its largest dimension and the reac-tor wall or - if the displacer extends from wall to wall - the displacer is formed with at least one through passage, which may be open--topped or tunnal-like, so that individual bottom segments are joined to each other. The displacers must not be so designed or positioned such that separate bottom segments and separate fluidizing chambers are formed. The fluidizing gas may optionally flow at a lower velocity through -the connecting surfaces which are left by the displacer or displacers or through the base surfaces whlch define the passage compared to -the velocity of the fluidizing gas flowing through the main surfaces of the grate.
The configuration of -the displacer may substantially be selec-ted as desired. For instance, in a fluidi2ed bed reactor which is circular in cross-section, the displacer : /
~ /
~ /
: /
- 5a -~, ~ 3t 08~8 may consis~ of a cylinder or of a frustum of a cone and the center of the circular bottom surface of the displacer may lie approximately on the center of the bottom surface of the reactor. In a reactor having a rec~angular cross-section the displacer may consist of a dam. Two dams may be provided which extend substantially at right angles to each other.
It is particularly desirable to provide displacers which are square or rectangular in cross-section. Certain departures from the exact geometric figure, e.g., the provision of rounded corners, are permissibleO
The displacer may be made from a refractory material which is conventional in furnace construction.
Alternatively it may be made of membrane walls or finned walls protected by a covering consisting of ram~ed compound on the surface or surfaces exposed to the reactor space. A
coolant may pass through the protected walls. The one or more displacers is firmly affix~d to the reactor and together with the reactor constitute a structural unit.
The material which is capable of an exothermic reaction lS charged throu~h a plurality of charging devices so that individual segments formed in the lower part of the reactor space can be separately supplied.
In accordance with a preferred feature of the invention the one or more displacers is provided with a device for 1~10808 charging fuel. Fuel is charged on a plurality of levels so that an effective distribution o the fuel will be ensured.
In accordance with a further preferred feature of the invention, the displacer is provided with means for supplying oxygen~containing secondary gas. Such means may optionally be arranged on a plurality of levels. In accordance with that feature of the invention the -wY~Y~L~
chamber portions may be supplied with secondary gas through inlets which are provided in the wall of the fluidized bed reactor and in the interior of the reactor so that an optimal admixing of the secondary gas will be ensured.
If secondary gas is supplied through ports provided in the wall of ~he fluidized bed reactor, the uppermost point or surface of the displacer should be disposed above such ports. If secondary gas is supplied on a plurality of superimposed levels the displacer must extend ahove ths level of at least the lower st inlet.
In accordance with another desirable embodiment of the invention, the one or more displacers has a cross-sectional area which decreases from the bottom of the displacer to its top. In that case and in conjunction with the last described embodiment it will be possible to maintain the velocity of flow in the reactor part providea with the displacer within certain limits in spite of the supply of secondary gas.
.. .
1 3 1 0~8 The principle of the circulating fluidized bed which is used in the fluidized bed plant is distinguished in that states of distrihution having no defined boundary layer are provided, contrary to the "orthodox" fluidized bed, in which a dense phase is separated by a distinct density step from the overlying gas space. In the circulating fluidized bed there is no density step between a dense phase and overlying gas space but the solids concentration in the reactor decreases over substantially the height of the reactor.
By means of the Froude and Archimedes numbers the following ranges may be defined for the operating conditions:
0.,1 c 3/~ x ~r2 x ~ ~ lO
a~d 1~ Ar ~ 100 0 - 0 _ --wherel n 3 Ar ,~
,~ x ~,~ 2 r2 U2 ~; x dk , _ ~ _ . ' ' ' ' .
a~d u ~ ralative gas velocit;~ m./~
Ar Archimede~ numb~r Fr 8 Froud~ number ~ ~ . deII~ity of ga~ i~ kg/n~3 3 k 8 den~it;y of ~olid particle il~ kg/m3 d ~3 ~ diam~ter of 3pherical particle irl m ~J ~ kinema~i¢ ~iscosity i~ m2/~
e 8 co~s~ant of grav~tatio~l in mJQ2 The exothermic reaction is carried out at least in two stages with oxygen-containing gases supplied on different levels.
This techniques provides the advantage that the reaction is "soft", local overheating is avoided and the formation of NX i5 substantially suppressed. The uppermost inlet for oxygen-containinq gas should be sufficiently above the lowermost one to ensure that the oxygen content of the gas supplied at the lower inlet is substantially consumed at the height of the reactor corresponding to the upper inlet.
Under an operating condition when the fluidizing and secondary ga5eg are supp}ied at predetermined volume rates, a given average suspension density is obtained and hence, a certain heat transfer is achieved. The heat ~ransfer to the cooLing surfaces can be increased by increasing the suspension density by an increase of the rate of fluidizing ' _ g _ .
.
+) This e~bodiment has been explained in more detail in U.S. Patent 4 165 717.
gas and optionally o the rate of secondary gas. At a virtually constant combustion temperature the higher heat transfer will permit an extraction of the quantities of heat which are generated at a higher combustion heat output.
Whereas the higher combustion heat output involves a higher oxygen demand, this wil] virtually automatically be met hecause a higher fluidizing gas rate and optionally a higher secondary gas rate is required in order to increase the suspension density. ~) In accordance with another suitable feature of the invention, the fluidized bed system is provided with at least one fluidized bed cooler, which is connected to the reactor via a solids supply line and a solids recycle line.
Hot solids are withdrawn from the circulating fluidized bed and are coolea by direct and indirect heat exchange in a fluidized state, and at least a partial stream of cooled solids is recycled to the circulatin~ fluidized bed.
That embodiment has been explained in more detail in U.S. Patent 4,111,158. In that system the temperature can be kept constant virtually without a change of the operating conditions in the fluldized bed reactor, e.g., without a change of the suspension density and other parameters, merely by a control of the withdrawal of hot solids and a controlled recycling of the cooled solids. In dependence on the output and on the selected reaction temperature the .~
:: :
recycling will be effected at a higher or lower rate. Any desired temperature can be adjusted from those very close to the ignition point to higher temperatures, which may be limited, e.g., by a softening of the reaction residues. The temperature may lie between about 450 and 950C.
Heat is extracted in the fluidized bed cooler under conditions which effect an extxemely high heat transfer, e.g., in a range from 300 to 500 watts~m2 C.
To control the temperature in the fluidized bed reactor, at least a partial stream of cooled solids ls recycled from the fluidized bed cooler. For instance, the required partial stream of cooled solids may be fed directly into the fluidized bed reactor. In addition the exhaust gas may also be cooled by a supply of cooled solids, which may be fed, e.g., to a pneumatic conveyor or to a suspension heat exchanger stage, and such solids may subsequently be separated from the exhaust gas and be recycled to the fluidized bed cooler~ As a result, the heat of the exhaust gas will enter the fluidized bed cooler, too.
It is particularly desirable to supply one partial current of cooled solids directly into the fluidized bed reactor and to supply another partial stream of cooled solids indirectly to the fluidized bed reactor after a cooling of the exhaust gases.
131080~
A recooling of the hot solids from the fluidized bed reactor should be effected by a countercurrent flow of the solids to the cooling fluid in a fluidized bed cooler which has a plurality of cooling chambers which are flown through in succession and contain interconnected cooling registers. In -tha-t case the combustion heat can be absorbed by a relatively small quantity of coolant.
In accordance with another feature of the fluidized bed system that is provided with a fluidized bed cooler, the latter is combined with the fluidized bed reactor in a unit of construction. In that case the fluidized bed reactor and the f]uidized bed cooler comprise a common wall, which is suitably cooled and which has an opening -through which cooled solids can flow in-to the fluidized bed reactor. As has been mentioned hereinbefore the fluidized bed cooler may comprise a plurality of cooling chambers but it may a:Lternatively consis-t of a plurality of units which are pxovided with cooling surfaces and each of which has in common with the fluidized bed reactor a wall having an opening for the Elow of solids and a separate ; solids supply line. Such an arrangement is described in EP-A-206 066 published on december 30, 1986.
The system utilizing the fluidized bed cooler is of wide application particularly because almost any desired heat carrier medium can be heated in the fluidized bed cooler. From a technological aspect the generation of steam in various forms and the heating of heat carrier salts are of special significance.
Within the scope of the invention, air or oxygen-enriched air or commercially pure oxygen may be used asoxygen-containing gases. The output can be increased by carrying ou-t the reaction under pressure, e.g., up to 20 bars.
Basically all materials which are capable of a ., ~ 3 ~ iQ 8 0 ~
self-sus-taining combustion may be used in -the fluidized bed plant in accordance wi-th -the inven-tion. Examples of such materials are coals of all kinds, par-ticularly of inferior quality, such as coal washery refuse, sludge coal, high-sal-t coal, but also brown coal and oil shale. Additional fields of applica-tion include the roasting of various sulfide ores or ore concentrates.
The various fea-tures of novel-ty which characterize the inven-tion are pointed out with particularity in the claims annexed -to and forming a part of this specification.
For a be-tter understanding of the inven-tion, its operating advantages and specific objects obtained by its use, reference should be had -to the accompanying drawings and /
~,////
~' _ , .
,, , -` 1 31 080~
descriptive matter in which there .is illustrated and described a preferred embodiment of the invention.
Brief Description of the Drawings Figure 1 illustrates in a top plan view various examples of illustrative confiyurations of displacers which are circular or rectangular in cross-section and may be used in a fluidized bed reactor;
Figure 2 is a perspective view showing the lower portion of the fluidized bed reactor provided with a displacer; and Figure 3 is a longitudinal sectional view showing the :~ fluidized bed reactor.
;~
. escription of_Preferred Embodiment A fluidized bed reactor 1 is diagrammatically indicated : in Figure 2 and its bottom surface is partly covered by at least one prismatic displacer 7 so that there are a : :piuraIity of fluidizing segments 6. :The displa~ers 7 are provided with secondary gas openings:ll in their ~n*~ upper portion.
.
.
~ ~t ~8~
The fluidized bed reactor 1 shown in Figure 3 has a cooling surface 2, which is indicated to consist of a membrane wall~ The lower reactor chamber 8 is divided by a damlike displacer 7 into four segments, namely, two segments which are parallel to the dam, onP segment in front of the dam and one segment behind the dam. An oxygen-containing fluidizing gas is supplied to the lower reactor chamber 8 through a line 5 and a fluidi2ing grate 6, with fuel through lines 3 and with oxygen-containing secondary gas through lines 9. Additional secondary gas is fed through line 10 and the secondary gas openings 11. Additional fuel is fed through lines 3. The gas-solids suspension exits through line 4 passing into a separator, such as a cyclone. The entrained solids in line 4 are separated in the cyclone and recycled to a lower por~ion of the reactor.
.
- Example , Coal was com~usted with air to produce saturated steam.
; The fluidized bed reactor 1 of the fluidized bed plant had a base surface area of 12.5 m x 10.1 m and a height of 30.5 m. Its bottom surface was partly covered by a displacer 7 having a bottom surface area of 8.5 m x 8~1 m in such a manner that four segments were obtained, which were provided with fluidizing grates 6. Two segments having a .
.
~ .. . .. . .
,.. .
1~10808 width of 2 m each extended parallel to the longer wall of the reactor. Two segments having a width of 1 m each were disposed between respective ends of the displacPr 7 and the reactor wall. The displacer 7 had the shape of a prism which had a height of 6.8 m. Each segment was in communication with at least one other segment.
The wall surface of the 1uidized bed reactor 1 was entirely lined with water-cooled membrane walls. The walls of the displacer 7 consisted also of water-cooled membrane walls, which on the side facing the reactor were protected with refractory material.
Coal at the rate of 110,400 kg/h was supplied to the fluidiæed bed reactor 1. The coal had a lower heating value of 15.9 MJ/kg and an average particle diameter of 0.2 mm.
Limestone having approximately the same particle size was introduced into the reactor at a rate of 10,400 kg/h. The feeding of the coal and lîmestone was effected through a total of six lines with the aid of entraining air at 100C
and at a rate of 11,040 sm3/h. The fluidizing gas consisted of 230,00 sm /h of air at a temperature of 260C which was introduced into the reactor through the fluidizing grates 6.
The secondary gas lines 9 and 11 were used to supply additional air at 260C at a total rate of 206,000 sm3/h on three levels respectively disposed 2 m (51,500 sm3~h), 4.6 m (51,500 sm3/h) and 7.3 m ~103,000 sm3/h) above the fluidizing grate 6.
Under the selected operating conditions a temperature of 850C was maintained in the fluidized bed reactor 1.
Saturated steam at 140 bars and at a rate o~ corresponding to a heat output of 102 MW was produced at the cooling surfaces 2 and on the membrane walls of the displacer 7.
It will be understood that the specification and ; examples are illustrative but not limitative of the p:resent invention and that other embodiments within the spirit and scope of the invention will suggest themselves to those skilled in the art.
~: +) (thermal) ~'' ~'
Back~round of Invention The present invention is in a circulating fluidized bed system for carrying out exothermic processes. The system consists of a fluidized bed reactor, a solids separator and a recycling line wherein oxygen-containing primary gas is supplie~'~ through lines through the bottom of the fluidized bed reactor and oxygen-containing secondary gas is supplied to the reactor at an elevation o at least 1 meter above the reactor bottom but not in excess of 30% of the height of the reactor. Fuel is introduced into the fluidized bed reactor between the primary and secondary gas inlets. The fluidized bed reactor has a bottom surface area, 40 to 75~ of which is covered by one or more displacers having a height not in excess of one-half of that of the reactor.
Processes and equipment for handling circulating fluidized beds, particularly for combusting carbonaceous materials, have proved most advantageous and for numerous reasons are superior to processes and equipment in which so-called orthodox or conventional fluidized beds are employed.
; The basic prooess for combustion in a circulating fluidized bed is describ:ed in U.S. Patent 4,165,717. In that process the; combustion is in two stages and the heat released by the combustion is extracted by means of cooling t 3t 080~
surfaces disposed in the fluidized bed reactor.
significant advantage of that process is that the combustion process can be adapted to the required output in a technic~lly simple manner by controlling the suspension density, and hence the hea~ transfer to the cooling surfaces, especially in the upper portion of the reactor space.
In the combustion process using a circulating fluidized bed in accordance with U.S. Patent 4,111,158 at least a portion of the heat released by combustion is extracted in a fluidized bed cooler, which succeeds the flui~ized bed reactor. Cooled solids from the cooler are recycled to the fluidized bed reactor to maintain or control the reactor temperature. In that case an adapt~tion to the required output can be achieved by an increase or decrease of the rate at which solids flow through the fluidized bed cooler and then back into the fluidized bed reactor.
While the absve referred to processes have pro~en highly satisfactory, the existing trend towards plant units for progressively larger heat outputs results in certain difficulties in the control of the process because the higher thermal demands require larger reactor dimensions, particularly larger reactor cross-sections. In the larger cross-section uni~s, satisfactory transverse mixing of fuel and the like, and of oxygen-containing secondary gas, +) (thermal), i.e. ~ 3 ~ 0808 throughout the cross-section of the fluidized bed reactor is no longer ensured in the inlet region although such mixing is required for the reaction~ As a result, a considerahle part of the reaction can occur in the upper portion of the reactor space. Also afterburning may occur when the solids and gas have been separated in the solids separator following the reactor. This sequence of events is encountered in plants having combustion heat outputs above about 300 MW ln fluidized bed reactors having reactor areas in excess of about 50 m2.
In a prior proposal for solving the above pro~lem in reactors having a large cross-sectional area 40 to 75~ of the bottom surface area of the fluidized bed reactor was covered by one or more displacers, each displacer having a height not in excess of one-half of the height of the fluidized bed reactor. The geome~ric configuration of the displacer was selected subs~antially as desired. For instance, in a fluidized bed reactor having a circular cross-section the displacer may have the shape of a cylinder or of a-frustum of a cone and the center of the bottom displacer surface may lie ~pproximately on the center of the bottom surface. In a reactor having a rectangular cross-section the displacer may have the shape of a dam, which at its ends may optionaIly adjoin the parallel Wall5 of the reac~or so that the lower portion of the reactor space was effectively divided into two separate chambers.
Two dams may be provided, which may be virtually at right angles to each other and which - if they adjoin the walls of the reactor - would divide the lower part of the reactor space into ~our separate chambers.
It has been found that difficulties in the operation of a fluidized bed plant designed with the above displacer may arise if the displacer divides the lower part of the reactor space into separate chambers because in that case the primary air or fluidized gas stream may entrain bed material from one chamber so that the internal circulation of solids always taking place in a fluidized bed reactor wiL-l cause such entrained bed material to enter another chamber or other chambers. Unless an expensive control is provided there will be no reverse or compensating flow of material because ~he flow of the 1uidizing air through the "depleted" chamber will be restricted owing to the different hydrostatic pres~ures over the bottoms of the respective chambers.
S~m~arv of the Inven~ion It is an object of the invention to provide a fluidized bed system which consists of a fluidized bed reactor, a solids separator and a recycling path and serves to carry out exothermic processes in a circulating fluid~2ed bed ': '';
1~1080~
which system ensures a satisfactory and reliable operation without the need for an expensive or elaborate control even when the plant is opera-ted at a high combustion power.
According to the presen-t invention there is provided a fluidized bed system for conducting an exothermic process comprising:
- a fluidized bed reactor, a solids separator and a recycling means;
- means for supplying oxygen-containing primary gases through the bottom oE the fluidized bed reactor;
- means for supplying oxygen-containing secondary gases in an eleva-tion of at leas-t about 1 meter above the reactor bottom but not in excess of 30% of the height of the reactor;
- means for introducing fuel into the fluidized bed reactor between the primary and secondary gas inlets;
- one or more displacer means covering 40 to 75%
of the bottom surface area of the fluidized bed reactor, the remaining bot-tom surface of the fluidized bed reac-tor constituting a single coherent surface, said displacer means having a height not in excess of one-half of the height of the fluidized bed reac-tor.
In order to provide a single coherent surface the one or more displacers is so designed that individual segments oE the reactor bottom communicate with each other.
This can be achieved, e.g., in that a gas-permeable bottom surface is left between the displacer at its largest dimension and the reac-tor wall or - if the displacer extends from wall to wall - the displacer is formed with at least one through passage, which may be open--topped or tunnal-like, so that individual bottom segments are joined to each other. The displacers must not be so designed or positioned such that separate bottom segments and separate fluidizing chambers are formed. The fluidizing gas may optionally flow at a lower velocity through -the connecting surfaces which are left by the displacer or displacers or through the base surfaces whlch define the passage compared to -the velocity of the fluidizing gas flowing through the main surfaces of the grate.
The configuration of -the displacer may substantially be selec-ted as desired. For instance, in a fluidi2ed bed reactor which is circular in cross-section, the displacer : /
~ /
~ /
: /
- 5a -~, ~ 3t 08~8 may consis~ of a cylinder or of a frustum of a cone and the center of the circular bottom surface of the displacer may lie approximately on the center of the bottom surface of the reactor. In a reactor having a rec~angular cross-section the displacer may consist of a dam. Two dams may be provided which extend substantially at right angles to each other.
It is particularly desirable to provide displacers which are square or rectangular in cross-section. Certain departures from the exact geometric figure, e.g., the provision of rounded corners, are permissibleO
The displacer may be made from a refractory material which is conventional in furnace construction.
Alternatively it may be made of membrane walls or finned walls protected by a covering consisting of ram~ed compound on the surface or surfaces exposed to the reactor space. A
coolant may pass through the protected walls. The one or more displacers is firmly affix~d to the reactor and together with the reactor constitute a structural unit.
The material which is capable of an exothermic reaction lS charged throu~h a plurality of charging devices so that individual segments formed in the lower part of the reactor space can be separately supplied.
In accordance with a preferred feature of the invention the one or more displacers is provided with a device for 1~10808 charging fuel. Fuel is charged on a plurality of levels so that an effective distribution o the fuel will be ensured.
In accordance with a further preferred feature of the invention, the displacer is provided with means for supplying oxygen~containing secondary gas. Such means may optionally be arranged on a plurality of levels. In accordance with that feature of the invention the -wY~Y~L~
chamber portions may be supplied with secondary gas through inlets which are provided in the wall of the fluidized bed reactor and in the interior of the reactor so that an optimal admixing of the secondary gas will be ensured.
If secondary gas is supplied through ports provided in the wall of ~he fluidized bed reactor, the uppermost point or surface of the displacer should be disposed above such ports. If secondary gas is supplied on a plurality of superimposed levels the displacer must extend ahove ths level of at least the lower st inlet.
In accordance with another desirable embodiment of the invention, the one or more displacers has a cross-sectional area which decreases from the bottom of the displacer to its top. In that case and in conjunction with the last described embodiment it will be possible to maintain the velocity of flow in the reactor part providea with the displacer within certain limits in spite of the supply of secondary gas.
.. .
1 3 1 0~8 The principle of the circulating fluidized bed which is used in the fluidized bed plant is distinguished in that states of distrihution having no defined boundary layer are provided, contrary to the "orthodox" fluidized bed, in which a dense phase is separated by a distinct density step from the overlying gas space. In the circulating fluidized bed there is no density step between a dense phase and overlying gas space but the solids concentration in the reactor decreases over substantially the height of the reactor.
By means of the Froude and Archimedes numbers the following ranges may be defined for the operating conditions:
0.,1 c 3/~ x ~r2 x ~ ~ lO
a~d 1~ Ar ~ 100 0 - 0 _ --wherel n 3 Ar ,~
,~ x ~,~ 2 r2 U2 ~; x dk , _ ~ _ . ' ' ' ' .
a~d u ~ ralative gas velocit;~ m./~
Ar Archimede~ numb~r Fr 8 Froud~ number ~ ~ . deII~ity of ga~ i~ kg/n~3 3 k 8 den~it;y of ~olid particle il~ kg/m3 d ~3 ~ diam~ter of 3pherical particle irl m ~J ~ kinema~i¢ ~iscosity i~ m2/~
e 8 co~s~ant of grav~tatio~l in mJQ2 The exothermic reaction is carried out at least in two stages with oxygen-containing gases supplied on different levels.
This techniques provides the advantage that the reaction is "soft", local overheating is avoided and the formation of NX i5 substantially suppressed. The uppermost inlet for oxygen-containinq gas should be sufficiently above the lowermost one to ensure that the oxygen content of the gas supplied at the lower inlet is substantially consumed at the height of the reactor corresponding to the upper inlet.
Under an operating condition when the fluidizing and secondary ga5eg are supp}ied at predetermined volume rates, a given average suspension density is obtained and hence, a certain heat transfer is achieved. The heat ~ransfer to the cooLing surfaces can be increased by increasing the suspension density by an increase of the rate of fluidizing ' _ g _ .
.
+) This e~bodiment has been explained in more detail in U.S. Patent 4 165 717.
gas and optionally o the rate of secondary gas. At a virtually constant combustion temperature the higher heat transfer will permit an extraction of the quantities of heat which are generated at a higher combustion heat output.
Whereas the higher combustion heat output involves a higher oxygen demand, this wil] virtually automatically be met hecause a higher fluidizing gas rate and optionally a higher secondary gas rate is required in order to increase the suspension density. ~) In accordance with another suitable feature of the invention, the fluidized bed system is provided with at least one fluidized bed cooler, which is connected to the reactor via a solids supply line and a solids recycle line.
Hot solids are withdrawn from the circulating fluidized bed and are coolea by direct and indirect heat exchange in a fluidized state, and at least a partial stream of cooled solids is recycled to the circulatin~ fluidized bed.
That embodiment has been explained in more detail in U.S. Patent 4,111,158. In that system the temperature can be kept constant virtually without a change of the operating conditions in the fluldized bed reactor, e.g., without a change of the suspension density and other parameters, merely by a control of the withdrawal of hot solids and a controlled recycling of the cooled solids. In dependence on the output and on the selected reaction temperature the .~
:: :
recycling will be effected at a higher or lower rate. Any desired temperature can be adjusted from those very close to the ignition point to higher temperatures, which may be limited, e.g., by a softening of the reaction residues. The temperature may lie between about 450 and 950C.
Heat is extracted in the fluidized bed cooler under conditions which effect an extxemely high heat transfer, e.g., in a range from 300 to 500 watts~m2 C.
To control the temperature in the fluidized bed reactor, at least a partial stream of cooled solids ls recycled from the fluidized bed cooler. For instance, the required partial stream of cooled solids may be fed directly into the fluidized bed reactor. In addition the exhaust gas may also be cooled by a supply of cooled solids, which may be fed, e.g., to a pneumatic conveyor or to a suspension heat exchanger stage, and such solids may subsequently be separated from the exhaust gas and be recycled to the fluidized bed cooler~ As a result, the heat of the exhaust gas will enter the fluidized bed cooler, too.
It is particularly desirable to supply one partial current of cooled solids directly into the fluidized bed reactor and to supply another partial stream of cooled solids indirectly to the fluidized bed reactor after a cooling of the exhaust gases.
131080~
A recooling of the hot solids from the fluidized bed reactor should be effected by a countercurrent flow of the solids to the cooling fluid in a fluidized bed cooler which has a plurality of cooling chambers which are flown through in succession and contain interconnected cooling registers. In -tha-t case the combustion heat can be absorbed by a relatively small quantity of coolant.
In accordance with another feature of the fluidized bed system that is provided with a fluidized bed cooler, the latter is combined with the fluidized bed reactor in a unit of construction. In that case the fluidized bed reactor and the f]uidized bed cooler comprise a common wall, which is suitably cooled and which has an opening -through which cooled solids can flow in-to the fluidized bed reactor. As has been mentioned hereinbefore the fluidized bed cooler may comprise a plurality of cooling chambers but it may a:Lternatively consis-t of a plurality of units which are pxovided with cooling surfaces and each of which has in common with the fluidized bed reactor a wall having an opening for the Elow of solids and a separate ; solids supply line. Such an arrangement is described in EP-A-206 066 published on december 30, 1986.
The system utilizing the fluidized bed cooler is of wide application particularly because almost any desired heat carrier medium can be heated in the fluidized bed cooler. From a technological aspect the generation of steam in various forms and the heating of heat carrier salts are of special significance.
Within the scope of the invention, air or oxygen-enriched air or commercially pure oxygen may be used asoxygen-containing gases. The output can be increased by carrying ou-t the reaction under pressure, e.g., up to 20 bars.
Basically all materials which are capable of a ., ~ 3 ~ iQ 8 0 ~
self-sus-taining combustion may be used in -the fluidized bed plant in accordance wi-th -the inven-tion. Examples of such materials are coals of all kinds, par-ticularly of inferior quality, such as coal washery refuse, sludge coal, high-sal-t coal, but also brown coal and oil shale. Additional fields of applica-tion include the roasting of various sulfide ores or ore concentrates.
The various fea-tures of novel-ty which characterize the inven-tion are pointed out with particularity in the claims annexed -to and forming a part of this specification.
For a be-tter understanding of the inven-tion, its operating advantages and specific objects obtained by its use, reference should be had -to the accompanying drawings and /
~,////
~' _ , .
,, , -` 1 31 080~
descriptive matter in which there .is illustrated and described a preferred embodiment of the invention.
Brief Description of the Drawings Figure 1 illustrates in a top plan view various examples of illustrative confiyurations of displacers which are circular or rectangular in cross-section and may be used in a fluidized bed reactor;
Figure 2 is a perspective view showing the lower portion of the fluidized bed reactor provided with a displacer; and Figure 3 is a longitudinal sectional view showing the :~ fluidized bed reactor.
;~
. escription of_Preferred Embodiment A fluidized bed reactor 1 is diagrammatically indicated : in Figure 2 and its bottom surface is partly covered by at least one prismatic displacer 7 so that there are a : :piuraIity of fluidizing segments 6. :The displa~ers 7 are provided with secondary gas openings:ll in their ~n*~ upper portion.
.
.
~ ~t ~8~
The fluidized bed reactor 1 shown in Figure 3 has a cooling surface 2, which is indicated to consist of a membrane wall~ The lower reactor chamber 8 is divided by a damlike displacer 7 into four segments, namely, two segments which are parallel to the dam, onP segment in front of the dam and one segment behind the dam. An oxygen-containing fluidizing gas is supplied to the lower reactor chamber 8 through a line 5 and a fluidi2ing grate 6, with fuel through lines 3 and with oxygen-containing secondary gas through lines 9. Additional secondary gas is fed through line 10 and the secondary gas openings 11. Additional fuel is fed through lines 3. The gas-solids suspension exits through line 4 passing into a separator, such as a cyclone. The entrained solids in line 4 are separated in the cyclone and recycled to a lower por~ion of the reactor.
.
- Example , Coal was com~usted with air to produce saturated steam.
; The fluidized bed reactor 1 of the fluidized bed plant had a base surface area of 12.5 m x 10.1 m and a height of 30.5 m. Its bottom surface was partly covered by a displacer 7 having a bottom surface area of 8.5 m x 8~1 m in such a manner that four segments were obtained, which were provided with fluidizing grates 6. Two segments having a .
.
~ .. . .. . .
,.. .
1~10808 width of 2 m each extended parallel to the longer wall of the reactor. Two segments having a width of 1 m each were disposed between respective ends of the displacPr 7 and the reactor wall. The displacer 7 had the shape of a prism which had a height of 6.8 m. Each segment was in communication with at least one other segment.
The wall surface of the 1uidized bed reactor 1 was entirely lined with water-cooled membrane walls. The walls of the displacer 7 consisted also of water-cooled membrane walls, which on the side facing the reactor were protected with refractory material.
Coal at the rate of 110,400 kg/h was supplied to the fluidiæed bed reactor 1. The coal had a lower heating value of 15.9 MJ/kg and an average particle diameter of 0.2 mm.
Limestone having approximately the same particle size was introduced into the reactor at a rate of 10,400 kg/h. The feeding of the coal and lîmestone was effected through a total of six lines with the aid of entraining air at 100C
and at a rate of 11,040 sm3/h. The fluidizing gas consisted of 230,00 sm /h of air at a temperature of 260C which was introduced into the reactor through the fluidizing grates 6.
The secondary gas lines 9 and 11 were used to supply additional air at 260C at a total rate of 206,000 sm3/h on three levels respectively disposed 2 m (51,500 sm3~h), 4.6 m (51,500 sm3/h) and 7.3 m ~103,000 sm3/h) above the fluidizing grate 6.
Under the selected operating conditions a temperature of 850C was maintained in the fluidized bed reactor 1.
Saturated steam at 140 bars and at a rate o~ corresponding to a heat output of 102 MW was produced at the cooling surfaces 2 and on the membrane walls of the displacer 7.
It will be understood that the specification and ; examples are illustrative but not limitative of the p:resent invention and that other embodiments within the spirit and scope of the invention will suggest themselves to those skilled in the art.
~: +) (thermal) ~'' ~'
Claims (11)
1. A fluidized bed system for conducting an exothermic process comprising:
a fluidized bed reactor, a solids separator and a recycling means;
means for supplying oxygen-containing primary gases through the bottom of the fluidized bed reactor;
means for supplying oxygen-containing secondary gases in an elevation of at least about 1 meter above the reactor bottom but not in excess of 30% of the height of the reactor;
means for introducing fuel into the fluidized bed reactor between the primary and secondary gas inlets;
one or more displacer means covering 40 to 75% of the bottom surface area of the fluidized bed reactor, the remaining bottom surface of the fluidized bed reactor constituting a single coherent surface, said displacer means having a height not in excess of one-half of the height of the fluidized bed reactor.
a fluidized bed reactor, a solids separator and a recycling means;
means for supplying oxygen-containing primary gases through the bottom of the fluidized bed reactor;
means for supplying oxygen-containing secondary gases in an elevation of at least about 1 meter above the reactor bottom but not in excess of 30% of the height of the reactor;
means for introducing fuel into the fluidized bed reactor between the primary and secondary gas inlets;
one or more displacer means covering 40 to 75% of the bottom surface area of the fluidized bed reactor, the remaining bottom surface of the fluidized bed reactor constituting a single coherent surface, said displacer means having a height not in excess of one-half of the height of the fluidized bed reactor.
2. The fluidized bed system of claim 1 wherein the one or more displacers is square or rectangular in cross-section.
3. The fluidized bed system of claim 1 wherein the one or more displacers is provided with fuel supply means.
4. The fluidized bed system of claim 3 wherein the fuel supply means is disposed on a plurality of levels.
5. The fluidized bed system of claim 1 wherein the one or more displacers is provided with the means to supply oxygen-containing secondary gases.
6. The fluidized bed system of claim 5 wherein the secondary gas supply means is disposed on a plurality of levels.
7. The fluidized bed system of claim 1 wherein the one or more displacers has an upwardly decreasing cross-sectional area.
8. The fluidized bed system of claim 1 wherein cooling surfaces are disposed in the free space of the fluidized bed reactor above the secondary gas inlet or on the wall of the fluidized bed reactor.
9. The fluidized bed system of claim 1 wherein cooling surfaces are disposed in the free space of the fluidized bed reactor on the wall of the fluidized bed reactor.
10. The fluidized bed system of claim 1 further comprising at least one fluidized bed cooler connected to the reactor via a solids supply line and a solids recycle line.
11. The fluidized bed system of claim 1, wherein cooling surfaces are disposed in the free space of the fluidized bed reactor above the secondary gas inlet and on the wall of the fluidized bed reactor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3821509.8 | 1988-06-25 | ||
| DE3821509 | 1988-06-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1310808C true CA1310808C (en) | 1992-12-01 |
Family
ID=6357257
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000603745A Expired - Lifetime CA1310808C (en) | 1988-06-25 | 1989-06-23 | Fluidized bed plant |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0349030A1 (en) |
| JP (1) | JP2785041B2 (en) |
| AU (1) | AU615310B2 (en) |
| CA (1) | CA1310808C (en) |
| DD (1) | DD289586A5 (en) |
| FI (1) | FI92955C (en) |
| IN (1) | IN170802B (en) |
| PL (1) | PL161384B1 (en) |
| ZA (1) | ZA894791B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2757930B1 (en) * | 1997-01-02 | 1999-02-26 | Gec Alsthom Stein Ind | IMPROVED SOLE LFC BOILER FIREPLACE |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1052367B (en) * | 1956-10-10 | 1959-03-12 | Du Pont | Device for carrying out catalytic reactions in a fluidized bed |
| DE2539546C3 (en) * | 1975-09-05 | 1985-10-24 | Metallgesellschaft Ag, 6000 Frankfurt | Process for incinerating carbonaceous materials |
| DE2624302C2 (en) * | 1976-05-31 | 1987-04-23 | Metallgesellschaft Ag, 6000 Frankfurt | Methods for carrying out exothermic processes |
| JPS61217616A (en) * | 1985-03-25 | 1986-09-27 | Ebara Corp | Fluidized bed heat reaction furnace |
| JPS61217617A (en) * | 1985-03-25 | 1986-09-27 | Ebara Corp | Fluidized bed reaction furnace and operating method therefor |
| DE3706538A1 (en) * | 1987-02-28 | 1988-09-08 | Metallgesellschaft Ag | Fluidized bed system |
-
1988
- 1988-08-23 IN IN708/CAL/88A patent/IN170802B/en unknown
-
1989
- 1989-04-18 PL PL1989278938A patent/PL161384B1/en unknown
- 1989-04-26 FI FI891981A patent/FI92955C/en not_active IP Right Cessation
- 1989-06-01 DD DD89329152A patent/DD289586A5/en not_active IP Right Cessation
- 1989-06-13 EP EP89201524A patent/EP0349030A1/en not_active Withdrawn
- 1989-06-23 CA CA000603745A patent/CA1310808C/en not_active Expired - Lifetime
- 1989-06-23 AU AU36764/89A patent/AU615310B2/en not_active Expired
- 1989-06-23 ZA ZA894791A patent/ZA894791B/en unknown
- 1989-06-26 JP JP1163619A patent/JP2785041B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| FI891981A0 (en) | 1989-04-26 |
| DD289586A5 (en) | 1991-05-02 |
| EP0349030A1 (en) | 1990-01-03 |
| ZA894791B (en) | 1991-02-27 |
| AU615310B2 (en) | 1991-09-26 |
| AU3676489A (en) | 1990-01-04 |
| PL161384B1 (en) | 1993-06-30 |
| FI92955C (en) | 1995-01-25 |
| FI92955B (en) | 1994-10-14 |
| JP2785041B2 (en) | 1998-08-13 |
| JPH0248033A (en) | 1990-02-16 |
| PL278938A1 (en) | 1989-12-27 |
| IN170802B (en) | 1992-05-23 |
| FI891981A (en) | 1989-12-26 |
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