[Professor of Mechanical Engineering, Case School of Applied Science.]
Official reports show that the coal placed on the market amounts
annually to between 450,000,000 and 500,000,000 short tons in the
United States alone. These figures, however, are somewhat misleading
as they do not in any way show the tremendous wastes that are going on
due to our present methods of mining and restrictions in qualities of
coal that can be transported and placed on the market at a reasonable
profit. Careful investigation has shown that the coal wasted or left
in the mines in such form as to be inaccessible to future generations
amounts each year to practically 100 per cent of that placed on the
market, or in other words, at the present time some 450,000,000 tons
are annually lost as far as commercial value is concerned.
If this condition is allowed to continue it is estimated by the United
States Geological Survey that our available supply of bituminous coal
will be exhausted within the next two hundred years.
A realization of the seriousness of this situation has led to a
careful and systematic study of the present lack of efficiency in the
utilization of fuels for both power and metallurgical purposes, to
investigations into more efficient use of the present marketable
grades of fuel, and to a consideration of methods of using the
so-called low-grade fuels, lignites and peats.
The United States Geological Survey has for several years been
investigating the economic value of coals and lignites as gas-producer
fuel. This work, begun with tests of coal and lignite at the 353
coal-testing plant erected at the Louisiana Purchase Exposition, St.
Louis, Mo., in 1904, was continued at St. Louis and at Norfolk, Va.,
and is now being carried on by the Survey at the fuel-testing plant in
Pittsburg, Pa. The tests were undertaken because it was evidently
desirable to determine the value of the gas producer as a means of
increasing efficiency in the use of the coal supplies of the United
States. The early tests proved decidedly encouraging, demonstrating
that many coals now wasted or not mined because they are not
satisfactory fuel for steam-power plants can, by conversion into
producer-gas, be made to do from two to three times as much work as
can be done by the best grades of steam coal burned in a boiler plant.
In consequence, the making of producer-gas tests and the study of the
processes that take place within the gas producer now form an
essential part of the fuel investigations conducted at the Pittsburg
plant under the provisions made by Congress for the analyzing and
testing of mineral fuels.
Rapid Development of the Gas Engine.
It was not until late in the nineteenth century that the gas engine
came into common use, and although many types have been devised within
the last twenty or thirty years it is only within eight or nine years
that large gas engines have been constructed. This development started
eleven or twelve years ago in Germany, Belgium, and England, but
marked progress has been limited to the last eight years.
For a long time the natural fuel of these internal-combustion engines
was city gas, but this was too expensive except for engines of small
capacity. It was seldom found economical to operate units of more than
75 horsepower with this fuel. Cheap gas was essential for the
development of the gas engine, but the early attempts to produce cheap
gas were somewhat discouraging, and for a time it seemed very 354
unlikely that the gas engine would encroach to any extent on the field
occupied by the steam engine. The theoretical possibilities of the
internal-combustion engine operating with cheap fuel promised so much,
however, that the practical difficulties were rapidly overcome, with
the result that the internal-combustion engine has become a serious
rival of the steam engine in many of its applications.
The development of the large gas engine within the last few years has
been exceedingly rapid. It was only ten years ago that a
600-horsepower engine exhibited at the Paris Exposition was regarded
as a wonder, but today four-cycle, twin-tandem, double-acting engines
of 2,000 to 3,500 horsepower can be found in nearly all up-to-date
steel plants, and there are installations in this country containing
several units rated at 5,400 horsepower each.
Development of the Gas Producer for Power Purposes.
The rapid advance of the large gas engine was made possible by
improvements in the production of cheap gas directly from fuel by
means of the gas producer. An early form of producer introduced in
Europe, and now in general use both abroad and in the United States,
is known as the suction producer, a name suggested by the fact that
the engine develops its charge of gas in the producer by means of its
own suction stroke. Although many producers of this type are now used,
most of them are small, seldom exceeding 200 horsepower. A serious
limitation to the utility of the suction producer has been the fact
that, owing to the manner of generating the gas, no tarry fuels could
be used, a restriction that prevented the use of bituminous coals,
lignites, peats, and other like fuels. The fuels in most common use
for producers of this type are charcoal, coke, and anthracite coal,
although attempts are being made so to construct plants that they can
be operated with bituminous or tarry coals.
To meet the demand for the concentration of power in large units, 355
instead of operating a large number of separate installations of small
power capacity, the pressure producer was devised. This producer
develops its gas under a slight pressure due to the introduction of an
air and steam blast, and the gas is stored in a holder until it is
required by the engine. As the gas may thus be stored before passing
to the engine, and as its generation does not depend on the suction
stroke of the engine, tar and other impurities may be removed from it
by suitable devices, and the use of bituminous coal, lignite, and peat
thus permitted.
The pressure producer was closely followed in the course of
development by the down-draft producer, which fixes the tar as a
permanent gas and therefore completely uses the volatile hydrocarbons
in bituminous coal, lignite, and peat.
A few scattered producer-gas plants were installed for power purposes
in the United States before 1900, but the application of this type of
power in any general sense has been developed since that date. During
the first few years of this period of development anthracite coal,
coke, and charcoal were used almost exclusively, although occasionally
pressure and down-draft plants ventured to use a well-tried bituminous
coal known to be especially free from sulphur and caking difficulties
and low in both ash and tar making compounds. The rapid development of
the anthracite plant was to be expected, but it remained for the
United States Geological Survey in its testing plants at St. Louis and
Norfolk to demonstrate the possibility of using in such plants
practically all grades of fuel of any commercial value, without
reference to the amount of sulphur or tarry matter which they contain.
Figures 1 and 2 illustrate the very rapid increase in the number of
installations and in the total horsepower of the plants operating with
bituminous coal and lignite since the beginning of these 356
investigations by the Geological Survey in 1904.
Owing to the fact that the dates of installation of many plants are
not ascertainable, it is impossible to present the exact growth either
in number of installations or in horsepower. The relative rate is,
however, approximately shown by Figures 1 and 2, the data for which
were secured from 375 installations. The points for the year 1909 are
estimated from the returns for the first five months. These points
have been checked by two or three methods and indicate only the normal
increase established by the rate of development before the business
depression of 1908. It is probable that the actual figures for the
entire year may exceed those indicated.
Relative Results of Steam and Producer-Gas Tests.
In considering the relation between the economic results of plants of
the two types under discussion, namely steam and producer-gas, the
fact should be remembered that today, in the ordinary manufacturing
plant operated by steam power, less than 5 per cent of the total
energy in the fuel consumed is available for useful work at the
machine.
In this connection it is of interest and value to glance at the
possibilities of the best-designed and most skilfully operated
commercial plant now in use. The data concerning the steam plant
selected for this determination are derived from a table prepared by
Mr. Stott, superintendent of motive power, Interborough Rapid Transit
Company, New York City, which, as Mr. Stott says, shows “the losses
found in a year’s operation of what is probably one of the most
efficient plants in existence today, and, therefore, typical of the
present state of the art.”
[Illustration: Figure 1.--Annual increase in number of producer-gas 357
power plants in the United States.]
[Illustration: Figure 2.--Annual increase in the total horsepower of 358
producer-gas power plants in the United States.]
Average losses in steam plant of the Interborough Company in 359
converting 1 pound of coal, containing 12,500 British thermal units,
into electricity.
======================================+==========+==========
| British |
| thermal | Per cent.
| units. |
--------------------------------------+----------+----------
Loss by friction | 138 | 1.1
Loss in exhaust | 7,513 | 60.1
Loss in pipes and auxiliaries | 275 | 2.2
Loss in boiler | 1,000 | 8.0
Loss in stack | 1,987 | 15.9
Loss in ashes | 300 | 2.4
+----------+----------
Total losses | 11,213 | 89.7
Energy utilized | 1,287 | 10.3
+----------+----------
| 12,500 | 100.0
--------------------------------------+----------+----------
Mr. Stott further presents a table showing the thermal efficiency of
producer-gas plants, concerning which he says:
The following heat balance is believed to represent the best results
obtained in Europe and the United States up to date in the formation
and utilization of producer gas.
Average losses in a producer-gas plant in the conversion of 1 pound of
coal, containing 12,500 British thermal units, into electricity.
======================================+==========+==========
| British |
| thermal | Per cent.
| units. |
--------------------------------------+----------+----------
Loss in gas producer and auxiliaries | 2,500 | 20.0
Loss in cooling water in jackets | 2,375 | 19.0
Loss in exhaust gases | 3,750 | 30.0
Loss in engine friction | 813 | 6.5
Loss in electric generator | 62 | .5
+----------+----------
Total losses | 9,500 | 76.0
Converted into electric energy | 3,000 | 24.0
+----------+----------
| 12,500 | 100.0
--------------------------------------+----------+----------
The thermal efficiency of such plants, as given by different writers,
runs as high as 33, 36, and 38.5 per cent, and for some plants figures
as extravagant as “above 40” are boldly published. Although the
present aim has been to give the figures for a producer-gas plant that
may compare favorably with those of the steam plant of the
Interborough Company, an effort has been made to keep well within
obtainable efficiencies. Attention is also directed to the fact that 360
the producer-gas plant considered should be large enough to compare
favorably with the steam plant. This precludes comparisons with
suction plants, which are relatively small but give higher
proportional efficiencies than the larger pressure and down-draft
plants, for these require more or less auxiliary apparatus.
Mr. Stott seems ready to accept a thermal efficiency of 24 per cent
for the best producer-gas plants for comparison with 10.3 per cent
efficiency for his steam plant, but a careful study of the problem has
led to a more conservative estimate for the producer-gas plant,
namely, 21.5 per cent.
The tables just given show the comparative efficiencies reached in
plants of the best type, both steam and producer-gas, but these are
seldom realized in common practice. The results obtained in the
government plant at St. Louis are probably more nearly representative
of the ordinary type of apparatus. These results are as follows:
Relative economies of steam and gas power plants at St Louis in the
conversion of 1 pound of coal, containing 12,500 British thermal
units, into electricity.
==================================+====================+====================
| Steam Power. | Gas Power.
+---------+----------+---------+----------
| British | | British |
| thermal | Per cent.| thermal | Per cent.
| units. | | units. |
----------------------------------+---------+----------+---------+----------
Losses in exhaust, friction, etc. | 11,892 | 95.14 | 10,812 | 86.5
Converted into electric energy | 608 | 4.86 | 1,688 | 13.5
+--------------------+---------+----------
| 12,500 | 100.00 | 12,500 | 100.0
----------------------------------+---------+----------+---------+----------
The ratios of the total fuel per brake-horsepower hour required by the
steam plant and producer-gas plant, under full load, not counting
stand-by losses, are presented below as derived from 75 coals, 6
lignites, and 1 peat (Florida).
The curves in Figure 3 show graphically the great economy secured with
the producer-gas plant. The figures for the producer-gas tests 361
include not only the coal consumed in the gas producer, but also the
coal used in the auxiliary boiler for generating the steam necessary
for the pressure blast--that is, the figures given include the total
coal required by the producer-gas plant.
Ratios of fuel used in steam and gas plants.
Average ratio, coal as fired per brake-horsepower hour under
boiler to coal as fired per brake-horsepower hour in producer 2.7
Maximum ratio, coal as fired per brake-horsepower hour under
boiler to coal as fired per brake-horsepower hour in producer 3.7
Minimum ratio, coal as fired per brake-horsepower hour under
boiler to coal as fired per brake-horsepower hour in producer 1.8
Average ratio, lignite and subbituminous coal as fired per
brake-horsepower hour under boiler to lignite as fired per
brake-horsepower hour in producer 2.7
Maximum ratio, lignite and subbituminous coal as fired per
brake-horsepower hour under boiler to lignite as fired per
brake-horsepower hour in producer 2.9
Minimum ratio, lignite and subbituminous coal as fired per
brake-horsepower hour under boiler to lignite as fired per
brake-horsepower hour in producer 2.2
Average ratio, peat as fired per brake-horsepower hour under
boiler to peat as fired per brake-horsepower hour in producer 2.3
In considering the possible increase in efficiency of the steam tests
with a compound engine, as compared with the simple engine used, the
fact should not be overlooked that a corresponding increase in the
efficiency of the producer-gas tests may be brought about under
corresponding favorable conditions. Not only is the producer passing
through a transitional period, but the gas engine must still be
regarded in the same light. In the larger sizes the vertical
single-acting engine is being replaced by the horizontal double-acting
engine. Other changes and improvements are constantly being made which
tend to increase the efficiency of the gas engine, as compounding and
tripling the expansions have already increased the efficiency of the
steam engine.
As has already been stated, the gas engine used in the tests here
reported is of a type that is rapidly becoming obsolete for this size,
namely, the vertical, three-cylinder, single-acting.
A brief consideration of these points will lead at once to the 362
conclusions that a comparison of the producer-gas plant and steam
plant used in these tests is very favorable to the former, and that
any increase in efficiency in the steam tests that might result from
using a compound engine can be offset by the introduction of a gas
engine of more modern type and a producer plant designed to handle the
special kinds of fuel used.
[Illustration: Figure 3.--Comparative service of coals and lignites in
gas-producer and steam-boiler plants.]
It should be noted that many fuels which give poor results under steam
boilers have been used with great ease and efficiency in the gas
producer, which thus makes it possible to utilize low-grade coals and
lignites that have heretofore been regarded as practically useless. 363
Several of the poorest grades of bituminous coals have shown
remarkable efficiency in the gas producer, and lignites and peat have
been used with great facility, thus opening the way to the
introduction of cheap power into large districts that have thus far
been commercially unimportant owing to lack of industrial
opportunities. Experiments with “bone,” a refuse product in
bituminous-coal mining, have given excellent results, showing an
efficiency in the producer equal to that reached by good steam coal
under boilers. Recent investigations with other low-grade fuels, such
as mine roof slabs, culm, and washery refuse, have also demonstrated
the possibility of using such material to advantage in the producer
under proper commercial conditions.
Number and Class of Plants.
A list of producer-gas power plants recently secured indicates that at
present there are over 500 such plants in operation in the United States,
ranging in size from 15 to 6,000 horsepower.
Figure 4.--Summarized data of producer-gas power plants in United
States.
=========================+=======+==================================+
| | Horsepower. |
|No. of | |
|plants.| |
| +-------+--------+--------+--------+
| | Total.|Average.|Minimum.|Maximum.|
| | | | | |
-------------------------+-------+-------+--------+--------+--------+
Anthracite coal: | | | | | |
Over 500 horsepower | 8 | 7,550| 950 | 600 | 1,500 |
500 horsepower or less | 407 | 40,550| 100 | 15 | 500 |
+-------+-------+--------+--------+--------+
| 415 | 48,100| 116 | 15 | 1,500 |
+=======+=======+========+========+========+
Bituminous coal: | | | | | |
Over 500 horsepower | 20 | 49,000| 2,450 | 750 | 6,000 |
500 horsepower or less | 17 | 5,150| 300 | 35 | 500 |
+-------+-------+--------+--------+--------+
| 37 | 54,150| 1,460 | 35 | 6,000 |
+=======+=======+========+========+========+
Lignite: | | | | | |
Over 500 horsepower | 3 | 7,275| 2,430 | 525 | 3,750 |
500 horsepower or less | 19 | 1,725| 90 | 25 | 250 |
+-------+-------+--------+--------+--------+
| 22 | 9,000| 410 | 25 | 3,750 |
+=======+=======+========+========+========+
All plants | 474 |111,250| 235 | 15 | 6,000 |
-------------------------+-------+-------+--------+--------+--------+
=========================+=======+=======
| | Per
| Per | cent
| cent | of
| of | total
| total | horse-
|number.| power.
-------------------------+-------+-------
Anthracite coal: | |
Over 500 horsepower | ... | ...
500 horsepower or less | ... | ...
+-------+-------
| 88 | 43
+=======+=======
Bituminous coal: | |
Over 500 horsepower | ... | ...
500 horsepower or less | ... | ...
+-------+-------
| 8 | 49
+=======+=======
Lignite: | |
Over 500 horsepower | ... | ...
500 horsepower or less | ... | ...
+-------+-------
| 4 | 8
+=======+=======
All plants | 100 | 100
-------------------------+-------+-------
Data secured from this list are summarized in the table on the 364
previous page according to the type of fuel used, and separately for
all plants above 500 horsepower and for those not exceeding 500
horsepower.
It will be observed from this table that about 88 per cent of the
total number of installations in this country are operating on
anthracite coal (a few using charcoal or coke), and that bituminous
coal and lignite are used in the remaining 12 per cent. Of the total
horsepower approximately 57 per cent is derived from bituminous coal
and lignite and 43 per cent from anthracite coal, charcoal, and coke.
In point of size it will be noted that the bituminous plants average
12½ times the size of the anthracite plants.
In 1906 a large number of these plants were carefully inspected in
order to secure definite information from the owners and operators
regarding the more or less successful operation of such installations.
Similar inspections were made in 1908.
Deductions from Visits of Inspection.
The deductions made from the visits in 1906 were as follows:
1. The plants as a whole are giving remarkable satisfaction
considering the very brief period of development that has passed since
the introduction of this type of power.
2. The most serious difficulty seems to arise from the lack of
competent operators to run the plants rather than from defects or
troubles in the plants themselves.
3. Incompetent salesmen are undoubtedly to blame for serious
misrepresentations and misunderstandings.
4. The neglect shown by some manufacturers in respect to their plants
after they are installed and paid for has not been farsighted, and the
failure of the manufacturers to give the purchasers or operators of 365
plants full information regarding their construction and method of
operating has certainly been detrimental to the business.
At the present time (1910) the following modifications might be
advantageously made to the above statements: