Part 32

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.

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.