US3184952A - Method and apparatus for determining coke strength - Google Patents

Description

y 25, 1955 K. K. HUMPHREYS 3,184,952

METHOD AND APPARATUS FOR DETERMINING COKE STRENGTH Filed July 14, 1961 &

KENNETH If. HUMPHREYS [I By United States Patent 0 Jersey Filed July 14, 1961, Ser. No. 124,072 4 Claims. (Cl. 73-42) The present invention relates to a novel method and apparatus for testing particulate matter at normal or elevated temperatures. More particularly, it relates to a method and apparatus for determining the strength of solid metallurgical fuels under conditions similar to those occurring in a blast furnace.

In the blast-furnace process material charged to the furnace is called the burden and includes principally iron ore, flux, coke and scrap. Metallurgical coke and other fuels, such as charcoal and coal, are commonly used as (1) sources of heat and reducing gas, (2) for maintaining burden permeability and (3) for supporting the weight of the other burden materials during their descent through the furnace shaft. These fuels, therefore, must be capable of maintaining their integrity until they are consumed by combustion and other chemical reactions or by solution in the metal pool at the base of the furnace.

As the solid fuel particles reach the tuyere zone of a blast furnace, they are subjected at high temperatures to extremely turbulent motion imparted by the hot blast air entering from the tuyeres to create so-called blast furnace raceways. If the particles are not of sufficient strength at these temperatures to withstand this motion, they will become degraded and thus no longer effective for providing the required support for the furnace burden. Hence, the burden movement becomes erratic by sticking or hanging, thereby upsetting furnace operation. This also results in small fuel particles collecting in the void spaces within the burden above the raceways to reduce its permeability, thereby increasing the pressure drop through the burden and decreasing the amount of air which can be blown through the burden. This renders the furnace difiicult to control and thus causes inefficient operation and decreased production. Hence, it is important that only solid fuels having sufficient physical strength at elevated temperatures be charged to a blast furnace.

It is, therefore, an object of my invention to provide a method and apparatus for determining the physical strength of solid metallurgical fuels under conditions similar to those existing in a blast furnace.

A more specific object of my invention is to provide means for heating'a sample of solid fuel to a temperature equal to that existing in the tuyere zone of a blast furnace and then subjecting the heated material to degrading action similar to that occurring within this zone.

Methods have been proposed for testing and predicting the strength of coke and other solid fuels to avoid charging fuel of inferior strength to the blast furnace. These tests generally consist of abrading, e.g., ASTM Tumbler Test for Coke, Designation D294-50; impacting, e.g., ASTM Drop Shatter Test for Coke, Designation D141- 48; or otherwise subjecting coke samples to degrading forces. A relative-strength index is then reported, usually as the Weight percent of original coke passing or being caught on a sieve of some arbitrary size.

These tests have the following common limitations:

(1) They are not conducted at temperatures representative of those experienced in the lower portion of a blastfurnace stack where mechanical stresses are greatest and where temperature effects are most pronounced. At these temperatures, coke is supporting its maximum Weight load and in addition is subjected to violent motion "ice and severe impact and abrasive forces caused by turbulence in the coke bed because of the high-velocity air jets issuing from the tuyeres.

(2) The rate of momentum transfer between coke particles in existing tests is not comparable to that in a blastfurnace tuyere zone. The air jets in this area, having velocities greater than 200 feet/second, impart a much larger kinetic energy to the particles than that imparted to them by existing tests.

(3) Because they are conducted at ambient temperatures rather than at blast-furnace operating temperatures, cokestrength indices obtained from existing low-temperature tests do not necessarily predict coke strength in the blast furnace. Coke is a heterogenous mixture of many materials and does not necessarily retain its low-temperature strength characteristics at elevated temperatures. Cokes possessing equal strengths at ambient temperatures often very Widely in strength at elevated temperatures.

(4) Because they do not exert a degrading force on coke atthe same temperatures and by a similar mechanism as that occurring in the blast furnace, existing test indices frequently do not correlate with blast-furnace performance. Coke having high strength according to some existing tests, frequently degrades excessively in the blast furnace.

(5) In addition, existing tests are time-consuming and difiicult to perform. Large samples must be tested and a number of duplicate tests must be performed to obtain consistent strength indicates for a given coke or other solid fuel.

The deficiencies enumerated above are substantially eliminated by the use of my invention. A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawing illustrating the present preferred practice. The single figure of the drawing is a diagrammatic representation of apparatus for carrying out the method of my invention. The apparatus as there shown may be considered as two interconnected conduits or pipes. In the one conduit, the sample of screened particles isheated to simulate an operating temperature. The heated sample is then transferred to the other conduit and entrained in a horizontally-moving high-velocity gas stream. The entrained sample is then impinged tangentially against an inner wall of a circular obstruction and is thereby abraded in a rotary motion to simulate an operating condition. Preferably, the entrained sample travels in a horizontal conduit between the areas of entrainment and impingement.

Referring now in detail to the drawing, a sample of the screened particles 10 to be tested, is admitted to conduit or pipe 12 through a capped opening 14. The particles are then pushed to the position shown, in a tubetype furnace -16 by a pusher having a heat-resisting head 18 that preferably fits snugly in conduit 12. The head,

acting as a piston, is carried on a reciprocable, heat-resisting rod 20, preferably of stainless steel. The rod passes through a packing gland 22 in conduit 12. Furnace 16 which may be gas-fired or electrically heated, here comprises a refractory tube 24 partially surrounded by insulation 26,.the portion thereof in open chamber 28 being heated by a series of electrical heating elements 30. Spring-loaded flanges 32 permit expansion and contraction of tube 24, as an integral part of conduit 12, the remainder thereof being heat resistant pipe, preferably of stainless steel.

During heating of sample 10, nitrogen or any other suitable inert gas may be introduced to conduit 12 through a pipe '34 to prevent combustion of sample 10. When the sample has been heated to the preferred temperature, rod 20 is advanced, the sample being pushed along conduit 12 and dropped on a reciprocable, quick-opening abrasionof the entrained'sample.

valve 36, which is thereafter opened to transfer. the

sample from conduit 12 to conduit 38. Conduit 12 may be straight, permitting rod 2% to push the sample into conduit 38 and directly into the gas stream.

A rapidly-moving stream of air or inert gas, supplied. by blower 40, is passed through .conduit 38 to entrain the" particles of sample 19 and to impart to them kinetic energy substantially equal in magnitude to that which they would receive inthetuye-re zone of a blast furnace. The.

out-let cf blower 49 is connected to a conduit 42 having therein a device to measure gas-flow rate, 'for example, an orifice plate 44 with taps on either side thereof connected to a differential pressure gage46. A by-pa-ss gate valve 48-, with a manually or automatically controlled opening permits adjusting the gas flow in conduit 42 and thereafter in conduit 38 to which it is connected.

Conduit 38 is connected tangentially to and near the open top of an abrasion andimpact cylinder 50, supported on a stand 52. Cylinder 50 serves as an obstruction or abrasion means which will permit the particles of sample to strike or impinge against the inner wall and rotate about the perimeter'of cylinder 50 and to proceed therearound in a rotary-motion abrasion to simulate the abrasive action which my studies have indicated as being comparable to that taking place in the raceways at the tuyere zone of a blast furnace. The motion of the sample be comes slower as the energy of motion dissipates and the sample particles settle to the bottom of the cylinder. The separated gas flows upward from the open top of the cylinder, which may be covered by a screen 54 to prevent A conical or sample may be returned to the apparatus for further test ing. 7

A specific example of the practice of the invention, giving quantities involved, is set forth below. 7 Theexample has as an object the determination of the suitability of coke for use in an experimental blast furnace by simulating known operating conditions: 1) a tuyere-zone temperature of about 3200 F., .and (2) an i air-blast linea'rvelocity of about 440 feetper second in The latter creates a high-speed. rotary motion of entrained solid particles, approximately the nose of the 'tuyeres'.

in a circular cross-section having about an 18" diameter, wherein the particles .:abrade against each other and against less-agitated solid burden particles.

A five pound sample of blast-furnace coke, screened to a size such that its particles are retained on 1"a1id pass through 1 /2" screens, was charged through. opening. 14

to conduit 12 and pushed-into refractory tube 24 in fur nace 16. 1 It was heated to about 3200" F. in an atmos-.

phere of nitrogen, supplied through pipe 34. When the heating was substantially completed,v blower was started, and valve 48 adjusted to provide an air flow of about 440 feet per second in the 3 conduit 38. Pusher rod 20 was thereafter advancedand the heated sample (pushed through conduit 12 until it fell on valve 36. Opening of this valve dropped the sample into conduit .38

where it became entrained in the air stream, being thereafterimpinged tangentially against the circular Wall of an 18" diameter cylinderrStl, to induce a rotary-motion ergy .was "dissipated thus separating them from the air,

As their kinetic en the coke particles dropped and the separat'edair left the cool in nitrogen, pumped 'in through pipe 60. The sample was thereafter collected, rescreened and weighed. A relative measure of-the physicalstrength of the sample maythen bedetermined and reported. as the ratio of the weight of particles retained on a 1 screen after the test to the original weight retained-on :a 1" screen. This ratio is a good index for comparing the relative suitability of'various fuels for use in the blast furnace.- That fuel having the highest ratio being the stronger and therefore the better. fuel. For. example, for 5#'samples, after-test weights of 4.5 and a ratio of indicates an extremely strong coke; 3.8#,"0. 76 ratio, a

moderately strong coke; 2.1#, 0.42 ratio, an extremely weak coke.

I have found that when testing samples according to my invention, the results are reproducible within limits of :3,%. Error caused by combustion of the particles is negligib-le in the short time interval that the samples'are in contact with the air blast. Maximum retention time of the particles in the air stream is 0.1 second or even less whenrsimulating the highest jet velocities'encountered in blast-furnace operation. Cooling of the particles while they are in the blast line is also negligible.

While the above example illustrates a preferred method of operation,--other conditions of operation may be used without departing from the spirit of the invention. The sample may beheated to any temperature existing in the blast-furnace stack to determine the strengthfiofa sample in this area. The heating step may be eliminated to determine the breakage characteristics of the fuel during handling. The impact-abrasion.cylinder 50 may be replaced by a conical or 'funnel shaped means. or by a box or flat plate when determining the resistance ofthe sample to impact forces at ambient or elevated temperatures. The air stream in the air-blast pipe may be heated in addition to heating the sample, to minimize heatlosses therefrom. The invention may also be used to test solid materials other than metallurgical fuels.

Itwill be apparent that apparatus changes may then be made to, effect. the desired result. and 38 need onlybe large enough to conveniently .accommodate the sample particles- The blower should have a capacity to deliver the velocity and volume of gas or air required. The diameter of an impact-abrasion cylinder may be larger or smaller, asrequired'by operating conditions. In actual operation of blast furnaces, it has been determined that the race way diameters at tuyere level will vary between about 12" and 48' The variations depend on factors including blast furnace geometry, air flow rate and size of materials. The impact-abrasion cylinder diameter and fuel test conditions should then be within 'therange of operating conditions. Thisshould also be the case, when testing materials other than blast furnace coke.

Many of the deficiencies in prior-art'coke testing, as beingnon-indicative of blast furnace operating conditions, are substantially,eliminated bythe usefof my invention. In accordance therewith, testing is performed at the temperaturesexisting in the tuyerezone of the blast furnace. In addition, strength indices'may be obtained atanylower temperature level if desired, as a measure of coke strength in the upper regions of vthe'blasbfurnace stack. Similarly testing may be performedv at ambient temperatures to obtain an estimate offuel breakdown duringhandling prior to'charging. Testing is performed at jet and'particle velocitiesequivalent tothose occurring in a blast-furnace tuyere zone; thus the rate of momentum transfer and abrasion occurring .between particles in a blast'furnace' is simulated. In 'thiseway I can determine which fuels should perform well in a blastifurnace and which may adversely affect furnace operation. My-invention does not require thatlarge; coke isamplesgbe tested torobtain The conduits 12 a m u "o consistent results. A single strength determination of a few pounds of coke is usually sufficient. Testing time and the quantities tested are, therefore, minimized. My invention also has the advantage of being capable of adjustment to any desired set of blast-furnace operating conditions. This flexibility permits accurate determination of coke strength at such conditions, and also permits the use of my invention for a wide variety of other strength-testing purposes on a wide range of solid materials.

Although I have disclosed herein the preferred practice and apparatus of my invention, I intend to cover as well as any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

1. A method of testing a charge of particles having a predetermined minimum starting size substantially greater than the size of particles when disintegrated to a powder, to determine their resistance to being abraded to smaller particles, comprising placing a charge of particles of at least said minimum starting size in a horizontally disposed cylinder, applying heat to the cylinder, then, after the charge has been heated to a predetermined temperature, pushing a piston through said cylinder and quickly displacing the charge therefrom with minor abrasion thereto, immediately injecting the charge into an impact chamber in a stream of compressed gas and controlling the force exerted by said gas to abrade the charge therein to a limited degree, but insufficient to effect impact-disintegration thereof to a powder, and finally collecting the abraded charge.

2. A method as defined in claim 1 characterized by the charge being blast furnace coke, all the particles thereof having at least a minimum size usable in a blast furnace, heating said charge to about 3200 F. in an inert atmosphere and entraining said heated particles in an air stream moving at about 440 feet per second.

3. Apparatus for testing a charge of particles having a predetermined minimum starting size substantially greater than the size of particles when disintegrated to a powder, to determine their resistance to being abraded to smaller particles, comprising a cylinder disposed substantially horizontally, a piston reciprocable therein, a heating chamber through which the cylinder extends, an impact chamber having an injector gas-supply pipe connected thereto, a pipe connecting one end of said cylinder to said injector pipe and means connected to said injector pipe adapted to supply thereto a stream of compressed gas having a controlled force to abrade the charge in said impact chamber to a limited degree, but insufiicient to effect impact-disintegration thereof to a powder.

4. Apparatus as defined in claim 3 characterized by said impact chamber comprising a vertical, open-top, funnelshaped receptacle, having a screen over said top and a valve at the bottom thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,242,796 5/41 Stockton 241-17 2,515,542 7/50 Yellott 241-5 X 2,768,938 10/56 Martin 241--S X 2,853,241 9/58 Gindoif et al 241-- X 2,864,560 12/58 Carkeek et a1 241-17 X 2,905,321 9/59 Hitchner 73-12 X 2,983,453 5/61 Bourguet et al. 241-5 X 2,995,026 8/61 Schmidt 7312 FOREIGN PATENTS 1,094,977 12/54 France.

RICHARD C. QUEISSER, Primary Examiner.

ROBERT L. EVANS, Examiner.

Claims (1)

1. A METHOD OF TESTING A CHARGE OF PARTICLES HAVING A PREDETERMINED MINIMUM STARTING SIZE SUBSTANTIALLY GREATER THAN THE SIZE OF PARTICLES WHEN DISINTEGRATED TO A POWDER, TO DETERMINED THEIR RESISTANCE TO BEING ABRADED TO SMALLER PARTICLES, COMPRISING PLACING A CHARGE OF PARTICLES OF AT LEAST SAID MINIMUM STARTING SIZE IN A HORIZONTALLY DISPOSED CYLINDER, APPLYING HEAT TO THE CYLINDER, THEN, AFTER THE CHARGE HAS BEEN HEATED TO A PREDETERMINED TEMPERATURE, PUSHING A PISTON THROUGH SAID CYLINDER AND QUICKLY DISPLACING THE CHARGE THEREFROM WITH MINOR ABRASION THERETO, IMMEDIATELY INJECTING THE CHARGE INTO AN IMPACT CHAMBER IN A STREAM OF COMPRESSED GAS AND CONTROLLING THE FORCE EXERTED BY SAID GAS TO ABRADE THE CHARGE THEREIN TO A LIMITED DEGREE, BUT INSUFFICIENT TO EFFECT IMPACT-DISINTEGRATION THEREOF TO A POWDER, AND FINALLY COLLECTING THE ABRADED CHARGE.

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