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The incoming secondary air enters the recuperators a t atmospheric temperature and leaves them a t a temperature of about 760' C. The retorts themselves are charged or filled with coal a t from IO- to 12-hr. intervals. This means that the internal surfaces of the retort are subjected to a very considerable variation in temperature, due t o their filling with a large quantity of cold material. The retorts are about 23 f t . long and have a t the top a heavy iron casting forming the upper mouthpiece. This involves a rather considerable load per square inch of cross section a t their lower portions, where they are subjected to the highest temperatures, so that, in addition t o their refractory qualities, their resistance to deformation under load must also be considered. I n order to secure the most economical materials under the rather diverse conditions that exist in a modern retort bench, it has been necessary t o use both silica and fire-clay materials. This gives rise to an extremely complicated problem in the design and construction 01 these benches, on account of the different coefficients of expansion of the two classes of material. The average silica material will expand about a / ~ e in. per ft., while the average fire-clay material, under the same temperature, will probably expand about in. Another consideration, especially in heating up the setting for the first time, is the fact that silica develops the greater part of its expansion at 3m'to 350' C. while fire clay expands gradually up to about 1100' C. The bench structure may be looked upon roughly as a rectangular column of silica material, floating on a cast-iron base, NORTON COMPANY WORCESTBR, MASSACHUSETTS which a t the existing temperature has about the same expansion as the fire clay, surrounded by a retaining wall of fire-clay material and enclosed in a heavy steel framework. REFRACTORY PROBLEMS OF THE GAS INDUSTRY These requirements may be more clearly illustrated by a series By W. H. FULWEILBR AND J. H. TAUSSIQ of slides showing a modern vertical setting. There are two general processes in use for the manufacture of Fig. 2 shows the steel framework and lower cast-iron plates inuminating gas. The one, which is known as the coal-gas process, involves the distillation of coal in refractory vessels called which support the retorts and the upper structure of the bench. Fig. 3 shows the combustion chamber where the initial comretorts a t a comparatively high temperature, i. e., 1000' t o 1200' C., and the other, known as the water-gas process, consists in bustion of the producer gas and secondary air takes place. These decomposing steam by passing i t through a highly heated quan- arches are double and are of the highest grade.silica material tity of carboniferous material, i. e., generally, anthracite coal in order to resist the extremely high temperature, and also to or coke and in carbureting this gas with petroleum oil, which support a load which may amount t o 25 Ibs. per sq. in. is injected into heated vessels along with the water gas. Fig. 4 shows the retorts which are of silica and also the recuperators which are of fire-clay material. COAL GAS I n the operation of these recuperators, the heating waste gases We niay take as a typical example of a modern coal-gas installation, a system now coming into general use, which is known pass back and front in their downward travel through the large horizontal flues, while the secondary air. which is being heated, as the vertical retort system. Fig. I giv& a sectional elevation of such an installation. It rises around these flues through the rather small spaces t o be will be noted that there are a number of retorts located in the seen alongside the blocks forming the horizontal flues. Fig. 5 shows the upper portion of a bench nearing completion combustion chamber. These are heated by means of producer gas generated in the producer and burned with a preheated and illustrates how the upper sections of the retorts are connected with the iron castings, forming the upper mouthpiece. supply which is technically known as secondary air. Fig. 6 illustrates the large mass of iron work with the many The products of combustion pass downward through recuperators or heat interchangers, in which the incoming supply joints which connect the upper portion of the retorts to the gascollecting system. of secondary air is preheated to the desired temperature. It will be apparent that the question of expansion, and parProbably a more efficient type of apparatus, and the one being used in the most recent installations, is one in which the ticularly the differential expansion, is one that requires a very considerable amount of thought in both the design and actual producer gas is made in external producers. The coal gas as it passes out a t the tops of the retorts is con- work of construction, since provision must be made for the iron ducted through appropriate piping to the condensing, scrubbing, plates t o move as they expand on the lower framework, and t o follow the expansion of the fire-clay walls so as to keep the reand other purifying apparatus. The temperature in the combustion chamber is 1 4 5 0 ~ torts in line with the iron mouthpiece and to prevent the reto 1550" C., in the lower portion of the retorts, 1350'to 1500' C. mainder of the silica structure being displaced relative to the This temperature gradually decreases throughout the re- fire-brick construction. This is especially important in view of tort chamber and at the top, where the gases enter the recupera- the large number of joints that must be kept tight. tors, is about 850' C. It gradually decreases through the reIt may be said that in the usual type of construction, the cuperators and the gas leaves them a t a temperature between benches are built in stacks of about go f t . in length. Expansion 480' and 530' C. springs are provided on the longitudinal tie members, so that an SUPERIOR REFRACTORIES OF THE FUTURE
For all installations where the cost will justify the expense, the superior refractory of the future will be made of fused alumina, silicon carbide, crystallized sillimanite, fused spinels, sintered magnesia, or other very refractory mineral substances that have been so fused or sintered as to have attained completed cliemical change and have come to a constancy in volume. Which of these refractory substances will be most suitable in a given case will be much more dependent on physical than on chemical conditions, and the desired physical properties can be obtained with much more certainty with such refractories than with such materials as clay, bauxite, or calcined magnesite in which the physical and chemical reactions and alteration have not been carried to stability, i. e., the physical-chemical reactions are only partially completed in the fabricated refractory ware. In the case of the superior refractories under discussion, there need be either no bonding material used, or, t o produce the maximum strength, there need be but a small per cent of very fusible material such as silicate of soda, very fusible clay, or stoneware glaze. A strong, highly refractory article can be thus made of any of these materials, and have any structural characteristic desired. The present-day demands for special superior refractories will be met by very refractory materials which have been fused or sintered t o a physical and chemical constancy; and so fabricated, as here described, as t o have the essential physical and mechanical properties.
THE J O U R N A L OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
expansion of z in. or a total of 4 in. can take place in a length of go ft. Regarding the expansion, vertically, the construction is arranged so that the silica members, which include the retorts and combustion chamber lining, can expand freely from the outer fire-clay brick work, and the connections to the iron work, forming the gas take-offs, are so arranged that this expansion is taken care of by slip joints. CHARACTER OF MATERIAL USED-In the combustion chamber, retorts, and connecting blocks, which are exposed to a temperature of 1550' C., high-grade silica material is used. This will contain over 96 per cent Si02 with about 1 . 5 per cent CaO which acts as a bond. In the recuperators, where the temperatures vary from atmospheric to 850", normal conditions, and I I O O O , maximum, fire-clay material is used, containing 55 per cent SiOz, the remainder being AI208 plus small quantities of CaO, Fez03, etc. On account of the rapid changes in temperature, due to the high conductivity and radiation of the iron work, that occur a t the top and bottom of the retorts, fire clay is used in these sections because of its smaller coefficient of expansion and its ability to resist spalling under these conditions. The outside walls are made of a lower grade fire brick, since they are exposed to moderate temperatures only. The whole bench structure is insulated with a covering of brick made from infusorial earth.
Vol.
11,
No.
12
One bench of nine retorts will require approximately 76 tons of silica material and 108tons of fie-clay material. In spite of the care used in the selection of materials, failures of refractory materials sometimes occur from carelessness in 'operation, if extensive temperatures are generated. Fig. 7 shows the character of the failure of material in the combustion chamber of a vertical bench. Fig. 8 shows failure in the retort chamber of a horizontal bench. In the above examples the material was of fire clay which has now been replaced with silica material. It wi11 be noted that the material has been softened by the excessive temperature. WATSR GAS
Fig. g is a photograph of a model of standard form water-gas apparatus. This consists generally of three steel shells, lined with fire brick and insulating material. The shell to the left is called the generator, and is provided with grate and suitable connections for the introduction of air under pressure and for steam both below the grate and above it, also with a set of connections and reversing vaIves, so that the products of combustion may be taken either from the top of the generator or from the bottom of the generator. These connections connect with the top of the carburetor which is the second vessel. This is also steel, lined with fire brick and with checker brick. The bottom of the carburetor is connected to the bottom of
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In0 2
the superheater, which is similar to the carburetor 111 construction, and is provided with a stack valvr a t the top for the escape of the waste gases and with a connection leading to the -ling and purifying system for the water go5 that iS produced. In operating, the fuel contained in the generator is brought up to a high temperature by means of an air blast introduced beneath the grate Any combustible gase burned by means of an carburetor and a t the botto er, thus enabling the temperature of these vessel When the fuel has reached the proper temperature, the air blast is shut off, the stack valve lowered and the steam IS passed
At the top of the carburetor i t meets a stream of oil which is vaporized upon contact with the hot checker brick and on further contact in the carburetor and superheater is cracked, and transformed into ;1 fired gas, light hydrocarbon vapors, and a small amount of tar. In the water-gas apparatus, we have the effectof high temperatures, abrasion, slagging action, and spalling action. In the generator, the linings are subjected a t the top to the effect of abrasion due to the introduction of the fuel, to the abrasive action of the small particles whirled about by the blast, and also to the effect of tools used in rem0vir.g the clinker.
Fro. 3
PIP. 4
In the combustion zone we have very high temperature due to the preliminary combustion of the fuel, slagging action due to the ash of the fuel, a certain amount of abrasion due to the fuel itself, and, depending upon the character of the fuel used, we may have serious abrasion causcd by the removal of clinker. In the lower portion of the generator the temperatures arc lower, but we have the effects of steam on the up run, the hot gases on the down run, and the effect of tools in rcmoving the clinker, which grndually collects on the grate from which i t is removed a t intervals. through a t high velocity, a i d a certain amount of slagging actmi Jrom the I n the c ture, but nd the crown are exposed to a tem-
Pro. 5
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T E E J O U R N A L OF I N D U S T R I A L Table I show, the analyses of ash of a number of generator fuels, having various melting points. It will be noted that there
1133 1195
29 7 34 0
14 2 21 0
49 9 23 2
development of three distin 01 s tend to build out on Of 'ously reduein:: the working area. Thrs ing down from the top. While this usly deteriorate the lining from the I t of the mechanical abrasion in the barring down is a very destructive factor
PIG 6
perature as high as 1200' during the blasting period and are then deluged with a spray oi cold oil during the gas-making period. This results in an accelerated spalling action on the checker brick, and has required the development of a special test to determine what are suitable brick for this work. CHARACTER OF MATERIALS usI3n-b the selection oi matena s, the two important points, then, are the generator lining and the checker brick
Fro 8
The ashes with t ising temperature fuse to a certain extent an the sides of the linings but to the greater part they come down on the grate forming s compact mass which can be removed without much difficulty. The ashes with a low fusing temperature, and it will be noted these are generally high in iron and rather low in slumina, seri ously attack the linings and in addition come down and fonn on the grate bars a very hard. compact m s s of material that i s exceedingly dSEcult to remove when cold. In extreme cases melt and run through the grat erial in the ash pit
In the selection e not only to consider the relatively high temperature, due to the combustion of fuel, but also the action of the clinker as a slag.
_.
their ertremelv neutral character mav move sufficientlv ab vantageous to w a m n t more extensive tsials.
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ki
Two classes of carborundum materials have been worked withthe solid brick and the veneered brick. The solid brick is much stronger mechanicdlly and it3 extra cost @ill probably be compensated for by a longer life. I n the consideration of these materials it must be remembered that they will cost about 30 times as much as the fire-clay materials.
1157
satisfactory, but in general such bricks do not resist the spalling action. Another feature that requires some consideration is the quest i p of abrasive action in the fire-clay linings of the connections between the different shells. These linings are often almost entirely cut away by the abrasive action of the coke particles in the gas steam, and by the slagging action of the ash. CEMENTS
In connection with the general use of refractories, it has been found that great care must be used in the choice of cements, and is believed that frequently failures have been attributed to the refractory material, when, in fact, they may have been due to the use of improper cements. A great deal of experimental work has been done on this subject, and it is believed that we are now being directed to the use of more suitable materials for this purpose. One of the difficulties involved js that the average mason wishes cement which works easily under the trowel. With the more refractory cements, which should be used, there is a tendency to add plastic clay or a similar material to give it this smooth working and it is the use of such material that seriously deteriorates the refractory qualities of cement with the result that the jointing material fuses and this deterioration may even extend t o the brick itself. I n general, better results are obtained on construction work by using a cement composed principally of ground material similar in quality to the grog in the brick and a minimum amount of material of lower fusibility. In using silica shapes where the expansion is high, no cementing material is used in many cases, the brick or shapes being ldid up separate from one another by means of corrugated cardboard, whose thickness is so chosen that when the brick are brought up to the proper temperature it will allow sufficient room for the expansion to take place and thus form a sufficiently tight joint.
FIG. 9
LABORATORY TESTS
With all of these neutral materials, the adhesion of the slags to the sides is eliminated, along with any corrosive action which might take place, and this also results in a decrease in the time required for cleaning the sets, as the barring down with high fusing ashes is eliminated. The use of water-cooled iron surfaces, which have been very successfully adopted in producer work, is being seriously considered for a t least a small portion of the zone, where the greatest corrosive effect is observed. In connection with the checker brick it has been found by the use of the so-called “dipping test” that certain classes of brick are very much more efficient in resisting the spalling action, due to the alternate heating and cooling, than others. These may be described generally as bricks of the flint-clay type with rather coarse grog and a minimum amount of plastic clay. A dense brick that would not absorb the oil should apparently be more
The complexity of requirements has led to the use of a number of laboratory tests, to insure that material as received will be of suitable character for the use intended. These tests are generally those which have been adopted by the American Society for Testing Materials and need not be described here, They include tests for the resistance t o deformation under the load a t high temperature, for slagging action, fusibility, and spalling action. I n connection with the resistance to deformation under load an automatic device is used which determines the expansion of the specimen a t various temperatures and under different loads. This is a very important matter, as the expansion should be accurately known in order that the proper allowances for it may be made in the design and construction of bench work. UNITEDGAS IMPROVBMBNT COMPANY
319_ARc~STREET, PBILADELPHIA, PA.
FOREIGN INDUSTRIAL NEWS 1
B y A. MCMILLAN, 24 Westend Park St.,Glasgow, Scotland
THERMALENE Thermalene, discovered by Karl Wolf, of Zurich, is an intimate mixture of acetylene and vaporized oils and is claimed to have important advantages over other gases for producing high temperatures. The generating mixture is supplied in tin cans, the largest of the four commercial sizes now prepared yielding zoo cu. f t . of gas. Each tin can is packed with alternate 1a.yers of calcium carbide and crude oil mixed with sawdust. The addition of water, slaking the carbide, sets up the
generative action, vaporizing the oil. The acetylene and oil gas thus generated, cooled and purified, combine in the pipes. Thermalene is somewhat heavier than air and has a specific heat a little over l/s that of acetylene, and a t room temperature is liquefied by a pressure of from 1500 to 1600 lbs. per sq. in. A notable peculiarity is a soft, sweet, inoffensive odor. I n welding, sparks are thrown off. It can be used at relatively low pressure, produces no corrosive or poisonous effects, and is not liable t o cause explosions.
