Transactions

476 TRANSACTIONS OF TH E A.S.M.E. AUGUST, 1941
J. E. T o b e y . 1’ Ash has always been the chief mischief-maker
in the burning of coal on both stokers and pulverizers. Troubles
from the other properties of coal have gradually been solved.
While splendid progress has been made with ash, this has been
partially offset by new critical conditions arising from the increase
in boiler pressures and temperatures. The authors have
forged another great link in the chain of priceless contributions
Mr. Bailey has made in the solution of combustion problems.
As indicated in the paper, the major importance of iron in ash
and slag must be recognized and provisions made to do more exhaustive
research on the problem in both plant and laboratory.
Recent work by Bailey and Nicholls on ash properties furnish an
excellent springboard from which to launch a comprehensive research
program. It is believed that the interested technical
groups should immediately set in motion the necessary machinery
to carry through such a program.
A u t h o r s ’ C l o s u r e
The authors wish to express their thanks for the several
discussions offered on this paper and for thp active interest shown
in further investigation of the behavior and influence of ash and
slag. They acknowledge the many limitations in the data presented
on a subject of such complexity and agree with Dr. Fieldner
that, for ultimate solution, the problem must be resolved into
its fundamentals. This will require the efforts of many investigators
along different but coordinated lines.
The work of the Bureau of Mines on slag viscosities with relation
to the phase of tapping, and of Gould, Brunjes, and others,
as cited10 by Mr. Julsrud, in regard to the effects of separable constituents
of the ash at its source, are examples of great importance.
In the meantime, much practical value may be gained
from a more complete recognition of such over-all gross characteristics
as can be determined from simple established tests, and from
a study of their relation to conditions existing in the operating
boiler furnace.
Prof. Estep has brought out one point which we wish to clarify
at once by stating that all of the authors’ slag samples, referred
to in the paper, were taken from furnace or boiler heating surfaces
and not from the thermal probe. A great many probe
samples have of course been obtained, and have yielded data of
rather special interest but, in the present discussion, the data are
restricted to furnace or tube-bank samples. In procuring the
samples, care was taken to prevent contamination, by using stainless-steel
tools that were cooled intermittently by dipping them
in water. The condition of these tools over extended periods of
use indicates a negligible deterioration.
Laboratory fusion tests were made with standard-cone specimens
heated in a gas-fired muffle furnace. For the “reducing
condition,” A.S.T.M. specifications were followed, by which a
reducing atmosphere was maintained through the use of an excess
of fuel gas, as evidenced by yellowish flame extending from the
opening in the cover of the furnace for a distance of 6 to 7 in.
The “oxidizing condition” was produced in the same furnace by
using an excess of combustion air, controlled by means of orifices
installed in the gas and air,lines supplying the burner. Orsat
analyses of gases within the cone chamber have shown the
following composition:
C 02, o 2, CO,
per cent per cent per cent
Reducing condition........... 8 .2 to I 0 0 2 to 4.8
Oxidizing condition........... 10.0 to 11 1.6 to 2.8 0
The final state of oxidation of the fused-cone sample, as checked
*• Vice-President in Charge of Engineering, Appalachian Coals,
Inc., Cincinnati, Ohio. Mem. A.S.M.E.
in one case, after being specially mounted on a platinum plaque,
was found to be:
Fusing temperatures
Total Reducing Oxidizing
Ferric iron atmos­ atmospercent­
(as Fe), phere, phere,
age per cent deg F deg F
2000 2380
Original slag sample... 60.4 25.3 2110 2490
2360 2610
Fused in reducing atmosphere
at 2360 F 4.6
Fused in oxidizing atmosphere
at 2610 F 73.0
It is realized that some variation in test-furnace control, and
its influence upon the final state of the sample, may add materially
to the scattering of points in Figs. 5 and 6 of the paper, in addition
to the effects of undetermined fluxes such as lime and magnesia,
as mentioned by Mr. Nicholls. Dr. Fieldner’s suggestion of establishing
an A.S.T.M. standardized procedure for tests in the
oxidizing condition is appropriate and is greatly needed.
The rather startling comparisons cited by Mr. Powell, in Table
2 of his discussion, may find a partial explanation in the early investigations
of Dr. Fieldner, reference (1), where atmospheres of
CO and C 02 (and H2 and H20) were used in various proportions.
Higher softening temperatures were observed for the 100 per
cent CO or the 100 per cent C 02 atmospheres than for intermediate
proportions of mixture, and this was attributed, respectively,
to a predominance of metallic iron, ferric iron, and ferrous
iron, as shown by final analysis of the samples.
The comparison of Mr. Powell’s samples C and D, and of these
with samples A and B is not at all clear, and it would be interesting
to know the further composition of the ash, and whether these
results are confirmed by duplicate test. It has been pointed out
by Reid20 that extremely low concentrations of oxygen, in an
otherwise neutral atmosphere of unpurified nitrogen are nearly
as effective as air in oxidizing molten slag. It may be possible
that sample C would be found as high in ferric percentage as
sample D, but there is still no apparent explanation for their relation
to samples A and B.
By a somewhat opposite process, the softening temperatures of
different ash samples, mentioned by Mr. Sherman, would tend to
be similar to one another in spite of initially different ferric percentages,
because of the reducing action of the test furnace when
ran according to A.S.T.M. specifications.
We are in complete agreement with Mr. Nicholls’ recommendation
of using the term “ferric percentage” instead of the authors’
“per cent oxidation,” for reasons which he mentions. This term
becomes practical as an inverse index of the fluxing power, on the
consideration that the content of metallic iron is usually negligible.
We believe, however, that the expression for total iron content,
and percentages of its oxide forms, is more readily grasped in
terms of elemental Fe.
In the determination of iron forms, it is important that analysis
methods be developed for identifying all forms individually.
Digesting in HC1, or in H2S04 and HF solutions has in some cases
failed to dissolve more than 30 per cent of the total iron in the
slag and, if the state of the undissolved portion is accepted, by
difference, as being FesOs the resulting value of ferric percentage
may be considerably misleading.
In the paper, the presentation of data from laboratory work
stressed the contrast between oxidizing and reducing atmospheres
because that was the only controllable change in test procedure.
It was not intended to imply that the atmosphere was the only
20 “Control of Forms of Iron in the Determination of Fusion Temperatures
of Coal Ash,” by W. T. Reid, Industrial and Engineering
Chemistry, Analytical edition, vol. 7, 1935, pp. 335-338.