September, 1923
IND UBTRIAL AND EXGIIVEERING CHEMISTRY
cal improvements in paper-machine construction, but no less due to the uniformity of the ground wood pulp, which is a direct result of scientific control of the grinding process. This illustration of the results of scientific control in the comparatively simple newsprint process indicates what is being done and what can be accomplished in the more complicated operations involved in the manufacture of finer papers. The economic utilization of fibrous raw materials also includes prevention of losses. I n the course of the manufacture of paper there are a number of washing and concentrating processes in which the waste waters inay carry away large amounts of fibers. The reduction or elimination of these losses, which in some mills are very large, is one of the problems of a special committee of the Technical Association of the American Pulp and Paper Industry. So far the work of this committee has consisted in finding out the nature and arnount of these wastes and in informing mills which have neglected this subject how such losses can be determined, and also in investigating the most efficient equipment for recove~y of this material. Most complete recovery has always been obtained by means of settling tanks or basins of various constructions, provided these are of ample capac-
ity, and recently various coagulants have been suggested as a means of accelerating such settling. Another phase of the work of the committee is the utilization of wood room refuse, such as bark and sawdust. These materials are commonly disposed of as power plant fuel, but since their fuel value is very low because of the large amount of moisture they contain, the efficient removal of the greatest possible part of the moisture by means of presses is being studied. I n the discussion of sizing and beating reference was made to the importance of a more exact knowledge of the part which the cellulose fiber, as a colloid, plays in the reactions. I n the other processes, such as cooking, bleaching, dyeing, and the like, the value of a thorough understanding of the nature of cellulose is no less apparent. The establishment of cellulose research institutions in Europe and the United States and, more recently, the formation of a cellulose division of the AMERICAN CHEMICAL SOCIETY,is therefore keenly appreciated by the paper industry. More fundamental data concerning the material of prime importance, cellulose, which mill be the result of further research must necessarily contribute more than anything else toward the development of the paper industry on a sound scientific basis.
Furnace Settings and Refractory Cements By F. J. Wakem JOHNS-MANVILLE, INC., NEWYORK,N. Y .
M
OST inanufacturers underestimate the iinportance
of furnace settings. With economy in view they instal modern equipment and conveniences and then counteract this economy by paying little or no attention to the heart of their production-combustion chambers. A little thought and consideration can in most cases prevent furnace failures, which mean holding up of production, idle labor, and costly repairs. The purpose of furnace settings is to provide a chamber for the most efficient combustion of the fuel used which will in the best manner possible direct the heat to the absorbing surfaces without waste and without the intermingling of excess air. Katurally, the most economical results are obtained when Ihese settings stand up without impaired efficiency under the conditions incidental to their service for the longest possible time. While oil burners, mechanical stokers, and mechanical draft all contribute to increase plant efficiency, they result in more severe furnace conditions. Unless careful thought is given to the subject and the correct precautions taken, modern practice with its forced draft and other devices will result in frequent failures in furnace settings. The design of furnaces varies so greatly with the different types, operating conditions, fuels, etc., that no general statement can be made to apply to all. Each individual case must be treated as a separate problem and the value of experience accepted. It is sufficient to say that the design of a furnace is of the utmost importance, for no manner of brickwork will staiid up under faulty furnace design. The different conditions require fire brick of varied properties; in certain cases, the choice of brick depends upon the heat-resisting quality; in others, resistance to the impinging action of the flame and spawling; while in others. upon the ability to resist the action of clinkers, slagging, and slice bar. Two bricks may show up equaly as well under a heat test of short duration, yet the one after a few weeks of hard ser-
vice will change so that its thermal capacity is lowered, while the other will be practically unaffected. The life of a furnace setting does not depend entirely upon the quality or type of brick used. Failures are often due to the inability of the fire clay or bonding cement used to fulfil its function. The best furnace setting has the proper design, is constructed by careful and experienced workmen, and is made of the best fire brick for the condition, bonded together and protected with a high-grade refractory cement. Aside from the human element or workmanship, failures can generally be traced to one or more of the following causes: plastic deformation, spading, cracking or bulging, clinkering, melting or slagging.
PLASTIC DEFORMATION Plastic deformation or loss in compressive strength due to softening of the brick depends on the heat and load. If only one face or surface of a brick is exposed to the heat, the temperature may be increased to a point far beyond what the brick would stand if the entire brick were surrounded by heat or if even small portions of the other five surfaces were exposed. The reason is that when only one faceorsurface is exposed, the brick conducts the heat from that surface only. Exposure of the four adjacent surfaces of the brick to the face occurs in a furnace setting in which the fire clay or inferior cement bond between the brick has given away. This results froin the melting out of the bond on account of its inability to resist the heat, or from the crumbling and falling away of the bond due to its failure to withstand expansion and contraction. By using a good grade of bonding, refractory cement which will withstand the temperature without melting and which will not disintegrate and fall out of the joint when the brickwork is under stress, the flame can attack the brick on only one face.
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INDUSTRIAL A N D ENG1ATBERIiVGCHEMISTRY MELTING
Ordinarily, the fusion point of a fire brick would appear to 'be its most important characteristic, but in most cases failures will occur from plastic deformation before fusion occurs. The same precautions as used in the case of plastic deformation will help materially to prevent melting of the fire brick. SPAWLING When expansion or shrinkage occurs within a short temperature range, if the change in volume is considerable or the temperature unevenly distributed, then failure by spawling is apt to occur. If more than one surface of the brick is exposed to the heat, especially portions of the four adjacent sides, that part of the brick which is so exposed becomes hotter than the balance of the brick and this causes internal stresses which result in spawling. Bricks adequately protected with a good refractory cement do not take on or give up heat so quickly as exposed brick, so the temperature range of expansion and contraction is increased. Besides, as the heat enters the brick from one face only, the temperature gradient is even and there is less probability of inlernal stress. If spawling occurs or plastic deformation takes place, even though the bricks are bonded together with a suitable refractory cement, additional protection can be had by applying a l/* to '/&xh coating of super-refractory cement to the surface of the combustion chamber. The refractory cement used must have a high melting point, be dense, and have practically no shrinkage. CRACKING AND BULGING Expansion or contraction of fire brick will cause a setting to crack or bulge. When fire clay is used for setting up the brick, attempts are often made to overcome its inability to stay in the joint, by reducing the thickness of bond. This method throws all the stress due to expansion and contraction on the brick itself and causes more severe cracking or bulging. High-grade refractory cements have the necessary amount of elasticity to cushion this strain. SLAGGING The erosive action or slagging of fire brick by molten ash is very prevalent where coals are used, the ash of which softens at a comparatively low temperature. The flames carry particles of molten ash which enter the cracks or pores in the brickwork. This combination of ash and fire brick has a lower melting point than the fire brick itself. The deeper the molten ash enters the brickwork, the more severe will be the action. If the joints of the settings are well protected with a good bond, and the pores and minor cracks in the firebrick filled with a refractory cement applied as a wash coating, this slagging is less likely to occur. CLINKERING
It is practically impossible to prevent clinkering, but it can be retarded if the setting is made as smooth as possible. This can be accomplished by using a good bonding cement and then wash-coating the entire setting with a fine, high temperature cement designed for this purpose. The greatest trouble occurs in removing the clinker. Unless the fire bricks are strongly bonded together, which is not the case when fire clay is used, bricks are apt to be pulled out with the clinker. When parts of fire brick or even whole bricks have been pulled out of the setting with the clinker, the setting can be readily patched with a suitable high temperature cement.
Vol. 15, No. 9
ARCHES A great deal of trouble is experienced with arches where replacement is difficult. Excess expansion or contraction and spawling give the most trouble. Arches bonded with a good refractory which hold the brick in place, cushion the effect of expansion and contraction, and protect the brick from spawling, will give better service. Suspended arches are rather expensive, but they are dependable, and separate bricks which have failed can be replaced with a minimum of time and cost. CEMENTS Whenever possible it is preferable to use a dry, high temperature cement rather than a plastic cement, not only from a standpoint of economy, for plastic cements contain a large percentage of water, but also because of greater satisfaction in the results obtained. Plastic cements contain large quantities of fluxes, such as silicate of soda, which increase shrinkage and lower the fusion point of the cement. A high-grade, machine-mixed, dry, refractory cement will prove most economical. When preparing dry refractory cements for use as a bond between the brick, sufficient water should be added to bring the mixture to the proper mortar consistency, which depends on the porosity of the brick. An excess of water should be avoided, and the mortar should be thoroughly mixed and free from lumps. The mortar should be battered OF troweled on the brick already in place, the brick set on top and tapped uiitil the joint between the brick is about inch thick and cement squeezes out between the edges. Instead of cutting off this cement that squeezes out between the brick, it should be plastered back over the face of the joint and brick so that it protects the edges. In other words a T-joint construction is recommended. When using refractory cements for wash-coating, the cement should be thoroughly mixed with sufficient water to bring it to a thin grout consistency and then applied to the face of the brickwork with a stiff brush or broom. In treating a fire box with a plaster coating of a superrefractory cement to resist spawling, plastic deformation, and melting, all clinkers and loose pieces should be removed, glazed surfaces chipped away, and sufficient notches cut in the wall to provide a key for the cement. The cement should be mixed to a stiff consistency and plastered over the setting to a depth of from l/* to l/z inch, depending on the condition. One refractory cement cannot be a panacea for all ills. Conditions are so varied and requirements of a refractory so diversified that it is necessary to have different cements. with different properties. Guesswork or haphazard treatment of refractory cement problems will mean early failure and expense that could be avoided. It, is safer to realize the importance of using the correct material in the correct manner and call on the refractory manufacturer who has trained engineers available for this service. Hammermill Paper Company Fellowships The Hammermill Paper Company has offered a fellowship t o Yale University for the purpose of developing a research work on cellulose chemistry, The recipient of this fellowship is Tohn I,. Parsons, and he will work under Dr. Hibbert during the coming year. Another fellowship has been granted to the New York State College of Forestry to aid this institution in the development of a course in pulp and paper manufacture. Burton L. Kassing, who graduated this summer, will work for another year under the direction of Professors Wise and Libby on some fundamental work in connection with pulp and paper making.
