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T ransactions of The American Society of Mechanical Engineers Published on the tenth of every month, except M arch, June, September, and December OFFICERS OF THE SOCIETY: W i l l i a m A . H a n l e y , President W . D . E n n is , Treasurer C . E . D a v ie s , Secretary C O M M IT T E E ON P U B L I C A T IO N S : C . B . P e c k , Chairman F . L . B r a d l e y A . R . S t e v e n s o n , J r . C. R. SoDERBERG E. J. K a TES G e o r g e A. St e t s o n , Editor A D V IS O R Y M E M BE R S OF THE C O M M IT T E E ON P U B L IC A T IO N S I W . L. D u d l e y , S e a t t l e , W a s h . N . C. E b a u g h , G a i n e s v i l l e , F l a . O. B. S c h ie r , 2 n d , N ew Y o r k , N. Y . Junior Members C . C. K ir b y , N e w Y o r k , N . Y . F r a n k l i n H. F o w l e r , J r . , C a l d w e l l , N . J . Published m onthly by T he American Society o f M echanical Engineers. Publication office at 20th and N ortham pton Streets, Easton, Pa. T he editorial department located at the headquarters o f the Society, 29 W est Thirty-N inth Street, N ew Y ork, N . Y . Cable address, “Dynam ic,” N ew York. Price $ 1.50 a copy, $ 1 2 .0 0 a year; to m em bers and affiliates, $ 1.0 0 a copy, $ 7 .5 0 a year. Changes o f address must be received at Society headquarters two weeks before they are to be effective on the m ailing list. P lease send old as w ell as new address.. . . By-Law: T he Society shall not be responsible for statements or opinio n s advanced in papers or .... printed in its publications (B 13, Par. 4). . . Entered as second-class matter March 2, 1928, at the P ost Office at Easton, Pa., under the Act o f A ugust 2 4, 1 912. . . . Copyrighted, 1941, by T he American Society o f M echanical Engineers.
Significance of Coal-A sh Fusing T em p eratu re in the Light of R ecent F urnace Studies By E. G. BAILEY,' NEW YORK, N. Y., a n d F. G. ELY,8 NEW YORK, N. Y. This paper reviews recent data relating to the fusing temperature of coal ash as well as of ash and slag from pulverized-coal-fired furnaces of both slag-tap and dryash-removal types. The highly oxidizing conditions in parts of both types of furnaces and the effect upon the slag-and-ash formation cause questions to be raised regarding the greatest usefulness of the present A.S.T.M. standard fusing-temperature method on a reducing a t mosphere alone. Previous work of the Bureau of Mines is confirmed in showing that the form of the iron, whether ferrous or ferric, is of increasing importance with increased iron content. The paper also gives data showing the appreciably higher percentage of iron in the furnace ash and slag over the iron content in the coal ash burned. This increase applies to both dry-ash and slag-tap types of furnaces. More research is needed in both plant and laboratory. THE extended use of coal-ash fusing temperature in connection with the classification, evaluation, and purchase of coal, since Dr. Fieldner and his associates (l)s published previous knowledge will be helpful in planning further work by the complete results of their extensive studies on the subject, others and coordinating it all through the proper agencies toward speaks well for the thoroughness with which that work was done. a reconsideration of the methods of fusing-temperature determination and their use in comparing coal of different kinds and the From time to time, a few questions of doubt have been raised regarding the accuracy with which it represents the relative performance of different coals in different furnaces and stokers, but results from its combustion. it has withstood the test of 22 years of most extended and of increasingly trustworthy use. The data presented in this paper do not detract in the slightest degree from the work done by Dr. Fieldner, but rather emphasize the increasing usefulness of some parts of his work which have been overlooked, or have lain dormant until changed methods of burning coal have brought about a realization of the limitations of the abbreviated data which are so often the only determinations now made and available on a given coal. Many analyses give only the softening temperature. For stoker and fuel-bed combustion, there is general agreement that the softening temperature in a reducing atmosphere, as prescribed by the A.S.T.M. method, is most useful and the initial deformation and fluid point are of little importance in so far as the clinker formation is concerned. With the advent of pulverized-coal-fired furnaces of the slagtap type, there was renewed interest in the fluid temperature of the ash and much work has been done by Sherman, Nicholls, Taylor, and Reid under the direction of the Bureau of Mines (2). A portion of it was carried out in association with an A.S.M.E. Research Committee on the removal of ash as molten slag. Much 1 Vice-President, The Babcock & Wilcox Company; President, Bailey Meter Company. Mem. A.S.M.E. 2 Analytical Engineer, The Babcock & Wilcox Company. * Numbers in parentheses refer to the Bibliography at the end of the paper. Contributed by the Fuels Division and presented at the Annual Meeting, New York, N. Y., December 2-6, 1940, of The A m e r i c a n S o c i e t y o f M e c h a n i c a l E n g i n e e r s . N o t e : Statements and opinions advanced i n papers a r e to be understood as individual expressions of their authors and not those of the Society. data were collected from furnaces, primarily from slag as tapped and with some from fly ash. A thorough study was also made of fluxes; the latest work being concentrated on the viscosity of the molten ash from several different coals. Both Fieldner and Nicholls recognized the importance of the form in which iron existed in ash, as affecting its fusing temperature, and the influence of the atmosphere in the laboratory furnace upon the results. The A.S.T.M. method is based upon a reducing atmosphere, hence, resulting in the iron being largely in the ferrous (FeO) form in the cone as tested. Nicholls studied slag samples and ran fusing-temperature determinations in a neutral atmosphere of nitrogen in an effort to learn what was the fusing-temperature range of the slag as it existed in the furnace. Much of these previous data will be reviewed in further detail by plotting them for comparison with later work given in this paper. The great importance of iron in the ash and slag has become more fully realized as a result of continued field and laboratory work relating to the rate of heat absorption in furnaces and boilers, as shown in two papers by one of the authors (3). It is believed that a brief survey of this work and a comparison of it with the S l a g C h a r a c t e r i s t i c s Data relating to the characteristics of slag from different parts of a two-stage slag-tap furnace are shown in Fig. 1. The coal fired has 13.6 per cent iron (as Fe) in the ash. The ash as usually analyzed would show this as 19.4 per cent Fea0 8 but, since it may exist in slag in the forms of FeO and Fe2Oa, it has been considered to be less confusing to give all percentages as Fe, designating how much is in the different oxide forms, or more simply to show the percentage of Fe which is oxidized to FejOa, the remainder being FeO, with possibly a very small amount of metallic iron, Fe. The slag collected in the furnace at A , B, and C, is materially higher in iron content than is the original coal ash. This segregation is largely due to the pyrites in the coal being coarser and heavier, thereby falling into the slag bed. Also the ash particles higher in iron content are likely to be more sticky and, therefore, adhere more readily to any surface contacted. The oxidation of the iron is least in the slag tapped, that is, only 19 per cent of its iron is in the form of Fe2Os, and 81 per cent in the form of FeO. It should be remembered that the iron oxides are not separate and free, but combined with the other ingredients as complicated silicates. Their properties and fluxing action, however, are affected by the form of the iron oxides entering into these silicate compounds. The ash collected in the boiler-tube bank has about the same iron content as the ash in the original coal, and the farther on it proceeds in the gas stream the higher is the percentage of oxidation. The total travel from the burners to the tube bank is about 60 ft. The fusing-temperature ranges of the slag and ash samples, collected from different parts of the furnace, have been determined in the laboratory, both in a reducing atmosphere by the A.S.T.M.
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