US2682458A - Gasification of carbonaceous solids - Google Patents

Description

E-JMM Jun 29, 1954 STEAMI FUEL E; GORIN 2,682,458 GASIFICATION OF CARBONACEOUS SOLIDS Filed Feb. 4, 1950 GRUSHER l4 I6 26 f INVENTOR EVERETT GORIN TTORNEY Patented June 29, 1954 2,682,458 GASIFICATION 0F CARBONACEOUS SOLIDS Everett Gorin,

Whitehall, Pa., assignor to Pitts-- burgh Consolidation Coal Gompany,

Pittsburgh,

Pa., a corporation of Pennsylvania ApplicationFebruary 4, l950,'SerialNo. 142,466

2 Claims. 1

This invention relates to the .gasiflcation of carbonaceous solid fuels, and, more particularly, to the manufactureoi carbon monoxide and hydrogen by thereaction of steamiand carbon-in fluidized systems.

It is generally mosteconomicalto use-'asthe solid feed material to a steam-.carbonifiuidiced gasiflcation vessel a carbonaceous material produced by once-throughgrinding without any intermediate classification of the solids. The resulting grind has a rather wide particle size distribution which'xrequires that a'rela'tivelyhigh linear velocity :be employed to provide good fluidization. Under these high velocity conditions, the :solid lines are selectively elutriated from the vessel.

It has been round'that .the .flnes 'cannotxbe eificiently gasified even when .they are returned to the fluidized bed by'means of accyclone. The reason for this is that the fines circulate so rapidly between the bed and the cyclone that their residence time in the bed is very short. As a matter of fact, a considerable portion of the fines must be removed from the cyclone before returning to the system to prevent the fines recirculation rate from building up to an unmanageable figure. This phenomenon causes the loss of carbon through incomplete gasification of the fines.

Another disadvantage of the conventional type of fluidized system is the'difilculty in obtaining a high steam conversion at the high linear velocities required to obtain good fluidity with beds of manageable height. This is true particularly whenopera-ting under pressure since, under these conditions, the mass velocity of steam :put throughthe bed increases more rapidly than the rate of carbon-steam reaction.

The present invention provides for the introduction of carbonaceous solids ground to a wide range of particle sizes into a fluidized bed and for the circulation of steam through the bed under reaction conditions. The necessary heat is preferably supplied by the introduction'of oxygen into the system to eiiectpartial combustion of the solids. The velocity of the fluidizing gases is such as to maintaina condition of good fluidity in the bed with consequent elutriation of a substantialjproportion of solid fines. These fines I have'foundhave a higher average carbon contentthan that of .the bed proper because of their short residence'time .in the bed. The effluent gases (including unreacted steam) and elutriate'd solidflnesfrom this fluidized bed of carbonaceous materialare conwhere the coal is 2 temperature to complete the gasification of solid carbonaceous fines.

This procedure has-the following advantages: 1. Due to the narrower and finer average size consist of the particles entrained from .the lower bed, good fluidity is achieved in the upper bed at the lower velocity with the very substantial decrease in entrainment rate from the upper bed.

2.. Due to the relatively low velocities prevailing in the upper bed, high over-all steam conversions are obtained and 3. Higher over-all carbon efliciency is obtained.

Other objects and advantages of my invention -:1 willbecome apparent-upon reference to the following detailed description and the accompanyingdrawing in which is shown a diagrammatic illustration of a preferred embodiment of my invention.

Referring to the drawing, a. description of the apparatusand its operation for gasifying coal will now be described. It is understood, however, thatzany'carbonaceous solid fuel capable of reacting With-s'team to produce carbon-monoxide and hydrogen may be used.

Coal from a hopper I8 is fed to a crusher [2 ground to arange of particle sizes, preferablyfrom about 325 to about 14 mesh. The finely-divided crushed coal is then fed through'conduit It into another conduit it where it is picked up by steam and conveyed to a fluidizing vessel :8. Additional steam is introduced into the vessel 28 through conduit 2% and is distributed'by aporous plate 2! into the fluidized bed. The oxygen required for heat is introduced through conduits 22 and I'M into conduit'zt. The superficial linear'velocity of the gases circulating through the vessel 18 is regulated so as to establishand maintain a bed of the finely divided coal in afluidized condition. This-linear velocity preferablylies between 0.75 and 3.0 feet per second. The amount of oxygen fed to the vessel is sufiic-ient to elevate the temperature of the bed and maintain it at steam-carbon reaction temperatures preferably in the neighborhood. of

1800 F. The solid residue or ash from the steam carbon reaction is withdrawn through discharge conduit 26 as required to maintain the level of the fluidized bed.

The effluent gases, including unreacted steam, from the fluidized bed in vessel l8 and the elutriated fines are conveyed through conduit 28 which in turn communicates with a manifold conduit 30. The latter is provided with a plurality of feed conduits 32, in which the gases and fines are conducted to a second vessel 34. This vessel is provided with a plurality of cones along its bottom to which the feed conduits 32 are con-- nected. Each of the cone shaped members has grid member 38 disposed therein above the apex of the cone but below the point of introduction of the efliuent gases and fines from vessel l8. Oxygen is introduced into the vessel 3d through a plurality of conduits 38 leading from the oxygen conduit 22. open into the vessel 34 at a point sufiiciently above the grids to insure that all of the oxygen is consumed by reaction with the carbon before it has a chance to mix with the products of vessel l8. Additional steam may be introduced along with the oxygen from a conduit 39 communicating with conduit 22. This may be desirable in those cases where the volume of oxygen is insufficient to fluidize the bed in vessel 3d.

The linear velocity of the gases circulating through vessel 34 is reduced below that maintained in vessel i8 so that the solid fines are carried by the eiiiuent gases are retained in vessel 34 in a fluidized condition. This reduced velocity preferably is between 0.05 and 0.5 feet per second.

The temperature within the vessel 34 is maintained at substantially the same level as that in l8 by means of the oxygen introduced. In view of the lower linear velocity of the fluidizing gases, only a small percentage of fines is elutriated by the effluent gases from the fluidized bed in vessel 34. These may be returned to the bed by means of one or more cyclones, 40. The solid free product is then recovered through conduits 42 which communicate with a common exit line 43. The solid residue or ash is withdrawn through a plurality of discharge conduits 44 communicating with each of the cone shaped members along the bottom of the vessel 34.

In the operation of a system of the above type, it is necessary to maintain a balance between the inventories and linear velocities in the two vessels such that (1) good fluidity is obtained in both vessels; (2) the elutriation rate from the lower vessel is not substantially greater or smaller than that required to supply the carbon requirements to convert the steam passed through the upper bed; and (3) the elutriation rate from the upper vessel is maintained small. The required interrelationship between the several variables may be made less critical by providing for recycle of fines between the upper and lower beds by means of a standpipe 46 disposed to automatically return the surplus fines from the upper to the lower beds.

The exact relationship between liner velocity, size consist and bed inventories will depend on the nature of the solid fuel, its size distribution and the bed temperatures and pressures. It is usually convenient to operate the system in such a manner that from 3060% of the carbon fed to the system is gasified in each of the vessels. This means that approximately one-half of the ash is removed from each vessel. In order to accomplish the same amount of gasification in both The feed conduits 32 4 the upper and lower beds, the carbon inventory in the upper bed must be at least twice that in the lower bed. This is required to compensate for the retardation of the gasification rate by the gasification products.

The outlet velocity from the lower bed may be based on the median particle diameter. The median particle diameter is defined as the diameter of the sieve opening which holds up fifty weight percent of the charge. The outlet velocity from the lower bed is, therefore, generally regulated to lie within the velocity range from 25-150% greater than the terminal velocity for free fall of a particle having this median diameter. The terminal velocity is a function of the particle size, shape, density and gas viscosity and may be readily calculated from established equations. Similarly, the outlet velocity from the upper bed is regulated to lie within the range of 10-75% greater than terminal velocity for free fall of a particle having the median diameter of the upper bed.

The preferred linear velocity employed depends to some extent on the nature of the particle size distribution as well as on the median particle diameter. The size distribution of most grinds obeys the Rosin Rammler equation fairly well.

where R. is the cumulative weight percent of particles having a diameter greater than as; and b and n are constants characteristic of the particular grind employed.

A number of commercial grinds of a typical char produced by the low temperature distillation of coal with the corresponding values of b, n, median particle diameter and suitable range of outlet linear velocities to employ in the lower gasification bed of a two vessel system are given in the table below.

Table I Sieve Opening R Mesh X=microns Grind #1 Grind #2 Grind #3 Grind#4 00195 .000894 .00180 n l, 04 1. l8 1. 10 Median Par 10 D meter,

Microns 200 130 144 104 Terminal Velocity of Median Particle, ft./sec 1. 9 0. 6 0.75 0.4 Linear Velocity Range in Lower Bed 2.3-4.0 1.0l.5 1.0-1.9 0.5-1.0

The above figures apply to the gasification of low temperature char with oxygen-steam mix-- tures at atmospheric pressure and 1800 F. It is to be understood that velocity figures cited will vary with the operating conditions i. e. the velocities increase as the density of the fuel increases and decrease as the pressure increases.

The linear velocity to be employed in the lower bed is a function of the value of n as well as the median particle diameter. The velocity employed should fall in the upper part of the range specified above when n is low 1. e. less than 1.1 and in the lower part of the range when n is high 1. e. greater than 1.1.

The fineness of the grind that it is best to employ depends on the operating pressure and temperatures. Fine grinds having median particle diameters less than 125 microns are preferably employed when operating at pressures in excess of 100 p. s. i. or at temperatures below 1750 P. On the other hand, when one operates at pressures below 100 p. s. i. or at temperatures above 1750 F., it is best to employ grinds having median particle diameters in excess of 125 microns in order to obtain full advantage of high capacities as allowed by the kinetics of the gasification reaction. It should be pointed out that in those cases where the size range of the solids fed to the first reaction zone is a very wide one, it may be desirable to employ more than one additional reaction zone, with each successive zone containing progressively narrower size ranges of progressively smaller particles, with corrrespondingly lower velocities of the fiuidizing gases.

The operation of the two bed system is summarized in a typical case of a feed comprising a low temperature char in the table below.

gases including said unreacted steam in contact with said solid fines in said second reaction zone under steam-carbon reacting conditions and at a linear velocity which is less than that of the gas passing through said first reaction zone but which is sufficiently high to establish and maintain a turbulent dense solids phase superimposed by a dilute solids phase, maintaining the carbon inventory in said second reaction zone at least twice that in the first reaction zone, and recovering the gaseous products from said second reaction zone.

2. The method of gasifying a carbonaceous solid fuel which comprises feeding said solid fuel in a finely divided state that includes a range of particle sizes to a gasification reaction zone, passing steam in contact with said solids fuel in said reaction zone under steam-carbon reacting conditions and at a linear velocity sufiiciently high to establish and maintain a turbulent dense solids phase superimposed by a dilute solids phase, discharging ash from said reaction zone as required to maintain the level of said dense solids Table II Linear Vel.,' Steam F. P. S. Bed Bed Conv., Bed Feed Depth, Temp, Percent of it. F. Initial Initial Final Chg.

Lower Char-Oxygen 1.1 1. 5 8.0 1, 800 Upper Elutriated Fines Product 0. 2 0.3 4. 0 1,800 85 Gas from Lower Bed Oxygen.

SIZE RANGE (WT. PERCENT IN TYLER SCREEN) 14 28 35 65 100 200 325 Pan Char Feed 0. 2 4. l 5. 4 20. 4 .0 22. 2 13. 3 19.3 Lower Bed- 0. 4 7. 1 14.4 39. 2 l7. 6 16.7 3. 4 1.2 Upper Bed 1. 2 ll. 2 32.1 31. 8 23. 7

The entrainment rate was of the order of 0.01 lb./s. c. if. from the upper bed as compared with an entrainment rate of 0.07 lb./s. c. f. from the lower bed.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of gasifying a carbonaceous solid fuel which comprises feeding said solid fuel in a finely divided state that includes a range of particle sizes to a gasification reaction zone, passing steam in contact with said solids fuel in said reaction zone under steamcarbon reacting conditions and at a linear velocity sufiiciently high to establish and maintain a turbulent dense solids phase superimposed by a dilute solids phase, discharging ash from said reaction zone as required to maintain the level of said dense solids phase, withdrawing the eflluent gases including unreacted steam together with entrained solid fines from said dilute solids phase and conducting same to a second and separate gasification reaction zone, passing said eilluent phase, withdrawing the effluent gases including unreacted steam together with entrained solid fines from said dilute solids phase and conducting same to a second and separate gasification reaction zone, passing said efiluent gases including said unreacted steam in contact with said solid fines in said second reaction zone under steamcarbon reacting conditions and at a linear velocity which is less than that of the gas passing through said first reaction zone but which is sufiiciently high to establish and maintain a turbulent dense solids phase superimposed by. a dilute solids phase, maintaining the carbon inventory in said second reaction zone at least twice that in the first reaction zone, returning the fines in excess of a predetermined level in said second reaction zone to the dense phase in said first reaction zone, and recovering the gase- 0115 products from said second reaction zone.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,027,290 Smith May 21, 1912 1,687,118 Winkler Oct. 9, 1928 1,898,967 Schneider et al. Feb. 21, 1933 1,913,968 Winkler June 13, 1933 2,509,866 Hemminger May 30, 1950 2,619,415 Hemminger Nov. 25, 1952

Claims (1)

1. THE METHOD OF GASIFYING A CARBONACEOUS SOLID FUEL WHICH COMPRISES FEEDING SAID SOLID FUEL IN A FINELY DIVIDED STATE THAT INCLUDES A RANGE OF PARTICLE SIZES TO A GASIFICATION REACTION ZONE, PASSING STEAM IN CONTACT WITH SAID SOLIDS FUEL IN SAID REACTION ZONE UNDER STEAMCARBON REACTING CONDITIONS AND AT A LINEAR VELOCITY SUFFICIENTLY HIGH TO ESTABLISH AND MAINTAIN A TURBULENT DENSE SOLIDS PHASE SUPERIMPOSED BY A DILUTE SOLIDS PHASE, DISCHARGING ASH FROM SAID REACTION ZONE AS REQUIRED TO MAINTAIN THE LEVEL OF SAID DENSE SOLIDS PHASE, WITHDRAWING THE EFFLUENT GASES INCLUDING UNREACTED STEAM TOGETHER WITH ENTRAINED SOLID FINES FROM SAID DILUTE SOLIDS PHASE AND CONDUCTING SAME TO A SECOND AND SEPARATE GASIFICATION REACTION ZONE, PASSING SAID EFFLUENT GASES INCLUDING SAID UNREACTED STEAM IN CONTACT WITH SAID SOLID FINES IN SAID SECOND REACTION ZONE UNDER STEAM-CARBON REACTING CONDITIONS AND AT A LINEAR VELOCITY WHICH IS LESS THAN THAT OF THE GAS PASSING THROUGH SAID FIRST REACTION ZONE BUTWHICH IS SUFFICIENTLY HIGH TO ESTABLISH AND MAINTAIN A TURBULENT DENSE SOLIDS PHASE SUPERIMPOSED BY A DILUTE SOLIDS PHASE, MAINTAINING THE CARBON INVENTORY IN SAID SECOND REACTION ZONE AT LEAST TWICE THAT IN THE FIRST REACTION ZONE, AND RECOVERING THE GASEOUS PRODUCTS FROM SAID SECOND REACTION ZONE.

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