US 2971830 A
Description (OCR text may contain errors)
Feb. 14, 1961 Tosl-uo KAWAI EIAL 2,971,830
METHOD OF GASIFYING PULVERIZED COAL IN VORTEX FLOW Filed June 18, 1958 3 Sheets-Sheet 1 FIG.
1961 TOSHIO KAWAl EIAL 2,971,830
METHOD OF GASIFYING PULVERIZED COAL IN VORTEX FLOW Filed June 18, 1958 3 Sheets-Sheet 2 w wE Feb. 1961 TOSHIO KAWAI ETAL 2, 7
METHOD OF GASIFYING PULVERIZED COAL IN VORTEX FLOW Filed June 18, 1958 3 Sheets-Sheet 3 m wE Q Q E m United States Patent METHOD OF GASIFYING PULVERIZED COAL IN VORTEX FLOW Toshio Kawai, Toshio Taniyama, Hideo Yoshida, Yoshiichi Karato, Tetsuya Oorui, and Koichi Yasuhara, Niihama-shi, and Teruyoshi Usamoto, Akita-shi, Japan, assignors to Sumitomo Chemical Company, Ltd., Higashi-ku, Osaka, Japan Filed June 18, 1958, Ser. No. 742,807 3 Claims. (Cl. 48-206) This invention relates to the vortex flow type method for gasifying pulverized coal by suspending it in high temperature gas by means of steam, oxygen, or air.
Various methods have been known for gasifying pulverized coal by fioating or suspending it in a gaseous medium at high temperature. Those methods may be classified into two categories: one wherein the particles of pulverized coal are floated completely downstream with the flow of gaseous medium, and the other, the so-called fluidized bed type, wherein such coal particles are floated or suspended in the gaseous medium so that they remain for a considerable time in the gasification reaction zone. In any of the known methods, there is a definite relation between the terminal velocities with which the particles of pulverized coal are capable of floating in the gaseous fluid and the velocity of the latter in the gasification reaction zone, said relation restricting the gasifying temperature as well as the gasification capacity.
According to the present invention, the method for gasifying pulverized coal is applicable for the range covering the gasifying temperature 'and volume permitted for the foregoing two types, providing a highly efficient method entirely different from the known methods.
in the method proposed by this invention, pulverized coal is floated or suspended in helically'ascending stream of air or oxygen mixed with steam. To this end, pulverized coal mixed homogeneously with the flux mainly composed of iron or ferrous compounds, together with air or oxygen and additional steam, is injected helically downward in a direction tangential to a surface coaxial with the cylindrical gasifying furnace so as to make them impinge on the bottom of the furnace and impart vortex motion to the particles of pulverized coal and liquid slag deposited thereon, the latter being removed therefrom while keeping a gaseous atmosphere in the vicinity of said bottom as an oxidizer for iron by adjusting the amount of said additional steam. Furthermore, the inner diameter of the gasifying furnace is abruptly reduced at its top so as to form a dead space in the region surrounded by the outer surface of the convergent flow of the ascending vortex stream leading to an orifice, and ceiling and side walls of the furnace, a part of the particles of pulverized coal being separated into the same from said stream for further gasification.
In embodiments of this invention, steam may be ejected from an orifice concentric with the opening of a pipe transporting pulverized coal entrained on a stream of oxygen or air, which is sucked by jet energy of the flow of steam. Pulverized coal, oxygen (or air), and steam are then made into a homogeneous mixture in a mixing chamber, to be injected into the gasification chamber in the aforementioned direction. The pipe for transporting pulverized coal and oxygen (or air), is constructed so as to be mounted or dismounted with ease.
The mixing chamber is water-cooled. The liquid slag deposited on the bottom of the furnace is removed continuously via a drain hole opening at the center of the t bottom of furnace, and, while falling from the hole, the slag is suddenly cooled and reduced to fine pieces by jets of water injected from a quenching chamber.
Since, as stated above, the inner diameter of the cylindrical furnace in this invention is abruptly reduced at the top thereof in order to form a dead space where the remaining particles of pulverized coal are to be gasified, it is several times larger than that of the orifice opening on the top of the furnace. Consequently, the gaseous stream generated within the furnace is further contracted after passing through the orifice, and forms a stagnant region within the discharge pipe connected thereto. That part ofthe discharge pipe adjacent the stagnant region is most vulnerable to formation of clinker. To cope with this, cooling medium may be injected directly into that part'ofthe discharge pipe. Thus, according to the method of this invention, the paths of particles of pulverized coal and gasifying medium in the reaction zone are lengthened and consequently it becomes possible to give them suiiicient residence time for gasification. This makes it possible to use pulverized coal with a particle size distribution over wider range than .previously possible, as well as to obtain a higher conversion ratio of carbon, and higher gasification capacity and efliciency than in the casev of various known methods. Moreover, the slag can be drained from the furnace continuously and steadily, and, after rapid cooling, solidification, and fracture, can be conveyed away with ease which prevents clinkering at the inner wall of the furnace or blockading of the discharge pipe. Furthermore, the reactants are made into a homogeneous mixture prior to injection into the gasifying furnace so as to protect the wall of the furnace from damage. In addition, the apparatus according to this invention enables removal of obstacles formed in the vicinity of the nozzle opening into the furnace and the repairing of damage due to blockading of the feeder pipe by fuel to be carried out during gasification operations.
In the accompanying drawings illustrating an embodiment of this invention:
Fig. 1 is a vertical cross-sectional view of the apparatus of the invention,
Fig. 2 is a diagrammatic view of the cross-section indicated by line a-a' of Fig. 1.
Fig. 3 is a vertical cross-sectional view of the gas discharge pipe mounted on the top of the furnace,
' Fig. 4 is a diagrammatic view of the cross-section indicated by line b-b of Fig. 3, and
Fig. 5 is a vertical cross-sectional view of the reactant injector.
The optimum particle size distribution of the pulverized coal to be used is assumed as follows (in weight per- .Centage): Inclusion of particles with their diameters ranging from 1,500 microns (as the maximum) to 500 microns, less than 30 percent; with their diameters less than microns, less than 20 percent, and; the average diameter, taken for the whole on the basis of weight, somewhere around 350 microns. Pulverized coal having such particle size distribution is made to form a homogeneous mixture with the so-called flux (an agent intended to fluidify the slag to be produced), is and entrained on a stream of oxygen and supplied through a transporting tube 3 leading to a nozzle 2, as shown in Figs. 1 and 5, and is brought together with steam injected through a pipe 4 to a mixing chamber 13, and is then injected into the vertical cylindrical furnace 1 downward in a direction tangential to a cylindrical sur face coaxial with the furnace. As shown in Figs. 1 and 2, a plurality of nozzles 2 for the injection of reactant is installed on the peripheral wall of the furnace. ,The arrows in Fig. 2 indicate the directions in which the reactant is injected. The nozzle 2 is shown in detail in 1 Wan Fig. 5, wherein the mixture of pulverized coal and oxygen is transported by a pipe 3 surrounded by a watercooling jacket 14, at a fiow velocity of 30 m./sec., accelerated to 110 m./sec. by a convergent section 15, and, through a straight pipe 16 surrounded by the flow of steam, is ejected at the end of the pipe 16 and mixed with it in the mixing chamber 13, and is injected into the reaction furnace from the opening of the mixing chamber 13, also surrounded by the watercooling jacket, at a velocity of 120 m./ sec.
The steam is first introduced to the pipe 4 protected by suitable heat insulating material and brought to the steam induction chamber 18 which leads the fiow of steam to ring type injection hole 17 for injecting steam around the straight pipe 16 having its opening at the entrance of mixing chamber 13 installed within the watercooling jacket 14 mounted near the opening of the burner. This induction chamber 18 is covered with heat insulating material with its surface protected by the watercooling jacket 14. The steam is injected into the mixing chamber 13 from the ring type hole 17 at a velocity of 240 m./sec., and, after sucking and mixing with the mixed flow of pulverized coal and oxygen, is injected into the furnace at 120 m./sec., as stated above.
While'the mixing chamber 13 and steam induction chamber 18 are constructed as combined elements fixed to each other, the transporting pipe 3-15-16 is connected with the induction chamber 18 in such manner as to make it detachable from the latter. That is, the transporting pipe is mounted loosely inside a sleeve 19 fixed to the induction chamber 18 and loosely supported near its one end within a hole in the wall of the induction chamber 18, said end being inserted in the entrance of mixing chamber 13. Thus the gas pressure within the sleeve 19 is the same as that within the steam induction chamber, and the steam-tightness with respect to the outside atmosphere is maintained by a gasket 20a fixing the transporting pipe 3 to the sleeve 19. As a means for supporting the transporting pipe 3 at a fixed position, a gate valve 20b is installed in front of the sleeve 19, and the gasket 26b to keep the air tightness between the fixed tube and atmosphere is fixed thereto at a distance longer than the length of the straight part 16 of the pipe. Thus it is possible to replace the transporting tube while in operation without any leakage of steam and gas from the furnace. For this procedure, the transporting pipe 3 is pulled out halfway from the sleeve after closing its inlet while maintaining steamtightness with gasket 20a, and is then drawn out completely after closing the gate valve 2%. By reversing the procedure, the transporting pipe can be attached during operation.
With the reactant injected through such nozzles in a downward oblique direction, gasification begins. Corn paratively roug still unreacted carbon particles and the melted slag flowing down the side wall of the furnace and depositing on the bottom of furnace are stirred and imparted whirling movements directly by the kinetic energy of the injected jet streams. This serves to hold the rough carbon particles in agitated and suspended state for furthering gasification, as well as resulting in homogenization of the slag deposited on the bottom of furnace. In addition, by imparting a whirling motion to the carbon particles and gasifying medium near the bottom of the furnace, thereby shifting them nearer to the side wall of the furnace, the loss of carbon through the overflow drain in the center of the bottom of furnace can be prevented.
In the present invention, the slag tapping temperature is lowered by the addition of flux, and, to this end, iron or substances mainly composed of ferrous compounds,- such as pyrite cinder, may be used. In g the optimum gasification temperature, at which the highest gasification efiiciency is obtained, in the suspension and entrainment process for gasification of pulverized coal mixed together rnto a homogeneous composition.
ing the suspension and entrainment process, gasification was often carried out, for the necessity of tapping ash} at certain temperature considerably deviating from the optimum value, at the expense of gasifying efiiciency.
It has been found that, if, in the case of coal containing more than 30 percent of Si0 in its ash, substances mainly composed of iron or ferrous compounds are added to pulverized coal in such manner that the weight ratio of FeO gradient to SiO in the outgoing melted ash is made to exceed V2, the produced ash will have a melting point at approximately 1200:50" C., and relatively low' viscosity permitting its easy removal from the furnace In the entrainment and suspension process of this in.- vention, the stream of gas generated in the furnace iswhirled to impart a vortex motion to the particles of. coal and flux; Thus a greater part of the ash and fluxv separated from generated gas by centrifugal force is thrown onto the surface of side wall where the ash becomes melted through the effect of flux, the ash then flowing down along the side wall to form a liquid deposit on the furnace bottom where the ash and the end product of the flux, presumably FeO, are stirred and Accordingly, the resident time of the flux in upper part of the furnace is very short, while the melted slag stays at the bottom for a considerable time. It is essential that the iron in the fiux is maintained in the form of ferrous monoxide (FeO); unlike in an iron refinery, it should not be reduced to iron itself. In the present method, if the ferrous compounds are to be turned into or maintained in the form of FeO, the amount of steam. to be added will have to be adjusted to regulate the so-called water gas reaction," so as to preserve an oxidizing atmosphere for iron in the vicinity of the bottom of the furnace by making the ratio of carbon dioxide to carbon monoxide (CO /CO) more than 0.35, and, that of steam to hydrogen (H O/Hz), more than 0.8, in the generated gas. Thus, While retaining the highest possible gasifying efiiciency, the slag can be drained easily in melted state.
While being gasified in the lower part of the furnace, the particles of coal have their size gradually reduced as they rise suspended and entrained on the helically ascending stream 5 until they approach the top of the furnace. As the vertical component of the velocity of ascending stream, a value which will prevent any carbon particles with diameters of less than 500 microns to 'remain on the bottom of furnace, i.e., 2 to 2.5 m./sec.,
s recommended in the method of this invention. Since, in this method, the inner diameter of the cylindrical furnace 1 is abruptly contacted at its top to form an orifice on the ceiling with nearly flat surface, there is formed a suddenly contracting flow. Thus, carbon still remaining as particles is thrown by centrifugal force into the dead space 10 surrounded by the surface of said contracting flow, the furnace side wall, and ceiling 21 of the furnace, and is gasified during compulsory floating residence therein. The speed of the stream passing through the orifice must be limited to 50 m./sec. ,as the maximum, and this restricts the lower limit of inner diameter of the orifice. The behavior of coal particles in the dead space 10 are as described below. The carbon particles ascending suspended and entrained on the upward vortex stream are cast into the dead space 10 because the centrifugal force acting on them exceeds the viscous resistance olfered by the stream, and are partly gasified by the gasification medium diifusing from the stream and sinking under gravity. They are against en= traiii'H On-themain' stream where the latter moves off the side' wall offurnac'e. Thus, as they circulate in and outside the boundary of dead space, as indicated by dotted line's ll in Fig. l, gasification continues until their size is reduced to a point where equilibrium is reached between the centrifugal force acting on them and the'viscous re-: When their size-is cles,-conversion was not accomplished, even at the final" stage to be performed, in a reaction zone at lower temper'-' atures. According to the present method, therefore, the conversion rate 'of carbon as a whole can be remarkably improved, since sufficient time is given for reaction of those particles compulsorily retained in dead space in such part of reaction zone as is placed under relatively low temperature. Heretofore, increasing the resident time, that is, increasing the eifective reaction volume of the furnace, has been practically limited; in view of the accompanying defects, such as an increase in heat loss to atmosphere, it was not economic to excessively enlarge the furnace. According to the present invention, however, the eifective reaction surface in the reaction zone is increased by compulsorily holding carbon particles in the dead space 10, thereby enabling them to be kept in contact with the gasifying medium for a sufficient time. Moreover, the ash and carbon particles still remaining to be reacted are returned to the bottom of the furnace, and the generated gas is released with a minimum possible inclusion thereof.
However, it is unavoidable that a certain portion of the melted ash goes out of the orifice accompanying the generated gas. When it is. slowly cooled to solidify through a semi-melted state, it is apt to deposit on iron elements, bricks, etc., frequently causing burning damage or blockading of discharge pipe 9 and other elements. As is well known, when a fluid passes through a suddenly changed cross-section in a pipe, there is always formed stagnant zone in its vicinity. This is also the case with the apparatus embodying this invention, wherein the inner diameter of the cylindrical furnace is usually several times larger than that of the discharge pipe 9. Thus, as shown in Fig. 3, a stagnant region 24 is formed within the discharge pipe 9, and that part of the pipe adjacent to this region is most vulnerable to formation of clinker. To cope with this, the discharge pipe 9 mounted downstream of the orifice 22 constructed with bricks is cooled with a coolant, such as water, which, after flowing down through the jacket 23, is sprayed directly into the stagnant region to drive it away, thereby preventing the formation of clinker. This also provides an efficient means for cooling the hot gas stream in the discharge pipe 9. The coolant, which may be either a liquid, such as water, or a gas, such as steam or nitrogen, is injected at a high speed, preferably in such direction as is eflicient for eliminating the stagnant region 24. To this end, it is preferred to make the gas stream component of the jet velocity of the coolant greater than that of the gas stream, and to give a whirling motion to the jets of coolant, as indicated in Fig. 4.
Meanwhile, the liquid slag is drained continuously from hole 6 in the bottom of furnace 1. As shown in Fig. 1, the slag drained from the hole 6 in liquid state is made into small drops by minimizing the contact area of the edge of hole 6 from which they fall off. As they fall through the quenching chamber 7, water 25 is sprayed toward them from the periphery of chamber 7 to cool upward to a space outside the" them'suddenly and fracture the solidified slag to piecesi, The fractured slag fall into water 26in a vessel, and, after'being further cooled and broken up, is carried away by a suitable transporting device 27, such as belt con-' veyor.
To illustrate the nature of this invention, concrete data obtained in an embodiment thereof are given as followsi Referring to accompanying drawings, four nozzles 2' were'mounted at symmetrical positionsalong the inner* weight) of approximately 300 microns and a heating value" of 6,000 kcal./kg., fiux consisting of totaling 2 tons per hour, mxed with pyrite cinder (Composition: SiO
of particles with their size less than 200 mesh representing' 86 %"of'the' whole), totaling 1104 steam flow at 500 C., totaling 738 kg./hr. made toward the bottom of furnace at an angle of 15 downwardto a tangent to a circle 1.5 m. in diameter concentric with the horizontal cross-section of the cylindrical furnace. The injected reactants, after impinging on the furnacebottom, form a rising vortex stream as indicated by stream line 5 in Fig. 1 as they continue gasi fication reaction therein, while melted slag, almost free from rough particles of coal, was drained through a hole 0.2 m. in diameter placed at' the center of furnace bottom, and, after being quenched and fractured by jets of Water in quenching chamber 7 fell into was carried away by belt conveyor 26 at kg./hr. The size of the fractured pieces was limited to only 9 mm. at the maximum, whereas, in case no water injection was made, lump slag with its diameter as large as 8 cm. was occasionally produced on the belt conveyor.
The rate of ash collected within the furnace represented 75 percent of the whole amount produced.
Gasification of carbon included in fine particles is nearly completed at high temperature ranging from 1500 to 1600 C. in which they find themselves immediately after leaving a nozzle. In the case of rough particles, however, they are partly gasified while they are stirred by the injected streams at the furnace bottom, and, when they have their diameters reduced to 500 microns, they are entrained on the ascending vortex stream, and are further gasified while sweeping the side wall of furnace under the centrifugal force created by their rotation. Vertical velocity component of 2 to 2.5 m./sec. is recommended as the optimum value. A discharge pipe 0.5 m. in its diameter was provided on the ceiling wall of furnace, and those carbon particles released to a dead space 1% were compulsoriiy retained in this space until their diameter was reduced to 150 micronsin this case, the minimum separable diameter-circulating in the path indicated by a broken line. Thus, after fully gasified, they were led outside through the discharge pipe 9.
Water cooling conduit pipe 23 was provided at the junction of main body of gasifying furnace 1 and discharge pipe 9, and six spray nozzles for water, steam, etc., were installed. Those nozzles were arranged so as to produce a vortex flow by injecting water sprayed by steam at a rate of 150 kg. per 1,000 N m. of gas under the temperature of 1,300 (3., at a veiocity of 150 m./sec., in a direction tangential to the inner wall of watercooling jacket and at an angle forming 45 C. with the direction of gaseous stream. Thus, by suddenly cooling the melted dusts their deposition to the discharge pipe 9 in a part adjacent to a dead space to be formed around the contracted flow therein was prevented. The temperature of the discharged gas was lowered to 900 (3., and no forma- Injection was a rate of 386 diameter and 3 m. in
totaling 140 kgI/hr'i, and oxygen m. hr., was injected into'the furnace at a velocity of Y m'./sec.' through'the" ejector effect of' water 26, and i tion of clinker in the discharge pipe was noted during long-term operations of 15 months.
The amount of dry gas generated was measured to be 3258 t m.3 /hr., and its composition was identified as follows:
Percent Percent CO 13.4 CH; 0.5 CO 51.1 N 2.9 Hg 31.9 0.2
in this operation, 97.9% of carbon was converted 'into gas, with the eificiency of gasification representing 73.8%.
The composition of gas sampled from the lower part ofdead space 10, with the temperature of gas within the furnace at 1350 C., was found as follows:
001 o 00 n, on. N, m0
Percentageotwetgasnn 11.8 0.2 an; 23.4 0.4 2.5 22.2
1. A method for gasifying pulverized coal by injecting,
in a downward and tangential direction towards a hypothetical horizontal circle and with high velocity into the lower part of a gasification zone having a substantially rectangular vertical section which zone connects with a narrow cylindrical cooling zone at the top and the center thereof, a mixture consisting of pulverized coa1,,flux and a gaseous medium containing molecular oxygen in admixture with steam, causing the mixture to ascend helically in said gasification zone so as to form a vortex-type stream, the flux being selected from the group consisting of metallic iron and pyrite cinder, employing an amount of steam sufiicient to maintain the lower part of the gasification zone as an oxidizing atmosphere so that iron in the flux is in the form of FeO, sharply restricting the vortex type stream at the upper part of the gasification zone and forming a stagnant zone at the upper corners of the rectangular section outside of the restricted stream into which stagnant zone pulverized coal which has not .1 ben gasified is thrown for return to the vortex-type stream,
directing the restricted stream to the cooling zone, and
injecting tangentially a cooling medium at a stagnant region formed at the'lower'part of the cooling zone.
2. A method according to claim 1, wherein the pulverized coal consists of particles having a maximum diameter of about 1500 microns, less than 20% by weight of the total being above 500 microns in diameter, less 1 than 30% by weight being below 'microns and approximately 350 microns being the average particle diameter.
3. A method according to claim 1, wherein the gaseous 1 medium containing oxygen is selected from the group consisting of oxygen and air.