Gas-Engines and Producer-Gas Plants Part 10

In recent experiments conducted by the author it was proved that with this governing system ignition still takes place even though the pressure has dropped to 43 pounds per square inch. This system has the merit of rendering it possible to employ ordinary governors of moderate size, since the resistance to be overcome at the point of application of the lever is comparatively small. In the accompanying ill.u.s.tration the Otto Deutz system is ill.u.s.trated.

CHAPTER XI

PRODUCER-GAS

It may here be not amiss to point out the differences between illuminating gas and those gases which are called in English "producer"

gases, and in French "poor" gases, because of their low calorific value.

=Street-Gas.=--This gas, the composition of which varies with different localities, has a calorific value, which is a function of its composition, and which varies from 5,000 to 5,600 calories per cubic meter (19,841 to 24,896 B.T.U. per 35.31 cubic feet) measured at constant pressure and corrected to 0 degrees C. (32 degrees F.) at a pressure of 760 millimeters (29.9 inches of mercury, or atmospheric pressure), not including the latent heat of the water of condensation.

The following table gives the average volumetric composition of illuminating gas in various cities:

____________________________________________________________________ Cities.

______________________________________________ Manches- New London. ter. York. Paris. Berlin.

_____________________ _________ __________ _______ ________ ________ Hydrogen 48 46 40 52 50 Carbon monoxide 4 7 4 6 9 Methane 38 35 37 32 33 Various hydrocarbons 4 6 7 6 5 Carbon dioxide 4 3 2 Nitrogen 5 2 8 4 1 Oxygen 1 ... 1 ... ...

_________ __________ _______ ________ ________ 100 100 100 100 100 _____________________ _________ __________ _______ ________ ________

Furthermore, these const.i.tuents vary within certain limits. This is also true of the calorific value. Experiments made by the author have demonstrated that in the same place at an interval of a few hours, variations of approximately ten per cent. occur.

=Composition of Producer-Gases.=--The average chemical composition of producer-gases varies with the conditions under which they are generated and the nature of the fuel. The following are the proportions of its const.i.tuents expressed volumetrically:

Table Headings-- A: Blast Furnace.

B: Producer.

C: Mond.

D: Mixed (Fichet).

E: Water (Stache).

F: Wood (Riche).

________________________________________________________________________ Gas.

_________________________________________________ A. B. C. D. E. F.

______________________ _______ _______ _______ ________ ________ _______ Nitrogen and oxygen 60 59 42 50 5 1 Carbon monoxide 24 25 11 20 40 29 Carbon dioxide 12 5 16 7 4 11 Hydrocarbons 2 2 2 3 1 15 Hydrogen 2 9 29 20 50 44 _______ _______ _______ ________ ________ _______ 100 100 100 100 100 100 _______ _______ _______ ________ ________ _______ Calorific value in calories. 950 1,100 1,400 1,300 2,400 2,960 Average weight of a cubic meter in kilos 1.30 1.1 1.02 1.05 0.680 0.824 Or of a cubic foot in pounds 0.008 0.007 0.006 0.0068 0.0042 0.0051 ______________________ _______ _______ _______ ________ ________ _______

Blast-furnace gas has been used for generating power by means of gas-engines for about ten years. At the present time it is used in engines of very high power, a discussion of which engines more properly belongs to a work on metallurgy, and has no place, therefore, in a manual such as this.

Producer-gas, in the true sense of the term, is generated in special apparatus either under pressure or by suction in a manner to be described in the following chapters.

Mond gas is produced in generators of the blowing or pressure type from bituminous coal, necessitating the employment of special purifiers and permitting the collection of the by-products of the fractional distillation of the coal. Mond gas plants are, therefore, rather complicated and can be advantageously utilized only for large engines.

More exhaustive information can be obtained from the descriptions published by the builders of Mond gas generators.

Mixed gas is generated in apparatus arranged so that the retort is kept at a high temperature, thereby producing a gas richer in hydrogen than that made by producers. It should be observed that in practice the generators at present used yield a producer-gas, the calorific value of which fluctuates between 1,000 and 1,400 calories per cubic meter (3,968 to 5,158 B.T.U. per 35.31 cubic feet); and the composition varies accordingly, in the manner that has already been indicated in the tables for producer-gas and mixed gas. There is no necessity, therefore, for drawing a distinction between these two qualities of gas.

Water-gas should theoretically be composed of 50 per cent. carbon monoxide and 50 per cent. hydrogen, resulting from the decomposition of steam by incandescent coal. In practice, however, it contains a little nitrogen and carbon dioxide. The gas is obtained from generators in which air is alternately blown in to fan the fire and then steam to produce gas. Water-gas is employed in soldering on account of its reducing properties and of the high temperature of its flame. The great quant.i.ty of carbon monoxide which it contains renders it very poisonous and exceedingly dangerous, because it is generated under pressure. From the economical standpoint, its generation is more expensive than that of producer-gas, for which reason its employment in gas-engines is hardly of much value.

Wood-gas, the composition of which has already been given, is generated in apparatus of the Riche type, the principle of which consists in heating a cast retort charged with any kind of fuel, namely wood, and vertically mounted on a masonry base.

This apparatus should be of particular interest to the proprietors of sawmills, furniture factories, and the like, since it offers a means of using the waste products of their plants.

The relatively high proportion of carbon monoxide in producer-gas is objectionable from a hygienic standpoint, so much so, indeed, that it has attracted the attention of manufacturers. Carbon monoxide, the specific gravity of which is 0.967, is a gas peculiarly poisonous and dangerous. It cannot be breathed without baneful effects, and is even more dangerous than carbonic-acid gas, which eventually causes asphyxiation by reducing the quant.i.ty of oxygen in the air. For this reason, it is necessary to take the utmost precaution in efficiently and continuously ventilating the rooms in which the gas-generators and their accessories are installed. This suggestion should be followed, above all, when the apparatus in question are installed in cellars and bas.e.m.e.nts. As a further precaution, where the plant is rather large a workman should not be allowed to enter the generator room alone.

Blowing-generators, or those in which the gas is produced under pressure, are more dangerous than suction-generators. In the former a leaky joint may cause the vitiation of the surrounding air as the producer-gas escapes; in the suction apparatus the same fault simply causes more air to be drawn in.

Dr. Melotte recommends the following procedure in cases of carbon monoxide asphyxiation:

CARBON MONOXIDE ASPHYXIATION

Cases of poisoning by carbon monoxide are both frequent and dangerous.

The gas is extremely poisonous, and all the more dangerous because it is odorless, colorless and tasteless. When it comes into contact with the blood, it forms a combination so stable that it is reacted upon by the oxygen of the air only with difficulty. It follows, therefore, that with each respiration of air charged with carbon monoxide, a certain quant.i.ty of blood is poisoned. In consequence of this, there is a possibility of poisoning in open air.

=Symptoms.=--The symptoms observed will vary with the manner in which the blood has been poisoned. There are two ways in which this poisoning can occur. The one depends upon whether the atmosphere contains an excess of carbon monoxide; the other whether the air breathed contains only traces of the gas.

=Gradual, Rapid Asphyxiation.=--At first a vague sickness is felt, rapidly followed by violent headaches, vertigo, anxiety, oppression, dimness of vision, beating of the pulse at the temples, hallucinations, and an irresistible desire to sleep. If at this stage the patient has a sufficient idea of danger to prompt him to open a window or door, he will escape death.

In the second stage, the victim's legs are paralyzed, but he can still move his arms and his head. The mind still preserves its clearness, and in a measure a.s.sists the further process of asphyxiation because of its impotency. Then follow coma and death.

=Slow, Chronic Asphyxiation.=--Slow, chronic asphyxiation is not infrequent. Its symptoms are often difficult to detect. Poisoning is manifested by weakness, cephalalgia, vomiting, pallor, general anemia, la.s.situde, and local paralysis. If any of these symptoms appear in the men who work in the vicinity of the producers, immediate steps should be taken to prevent the possibility of carbon monoxide asphyxiation.

FIRST AID IN CASES OF CARBON MONOXIDE POISONING

It has already been stated that the oxygen of the air has no oxidizing effect upon blood contaminated by carbon monoxide. Only a liberal current of pure oxygen can oxidize the combination formed and render hematosis possible. This liberal current can be obtained from an oxygen tank of the portable variety, provided with a tube carrying at its free end a mask which is held over the mouth and the nostrils. The absorption of gas takes place by artificial respiration, which is effected in several ways. The most practical of these are the Sylvester and Pacini methods.

=Sylvester Method.=--The patient is laid on his back. His arms are raised over his head and then brought back on each side of the body.

This operation is repeated fifteen times per minute approximately. The method is very frequently employed and is excellent in its results.

=The Pacini Method.=--Four fingers are placed in the pit of the arm, with the thumb on the shoulder. The shoulder is then alternately raised and lowered, producing a marked expansion of the chest. This method is the more effective of the two. The movements described are repeated fifteen to twenty times each minute very rhythmically.

One or the other of these two methods of treatment should be immediately applied in serious cases. Certain preliminary precautions should be taken in all cases, however. The patient should be carried to a well-ventilated and moderately heated room, stripped of his clothes, and warmed by water-bottles and heated linen. Reflex action should be excited, the peripheral nervous system stimulated in order to contract the heart and the respiratory muscles, and the precordial region cauterized. In addition to this treatment, the region of the diaphragm should be rubbed and pinched, the skin rubbed, cold showers given, flagellations administered, urtications (whipping with nettles) undertaken, the skin and the mucous membranes excited, the mucous membrane of the nose and of the pharynx t.i.tillated with a feather dipped in ammonia, alcohol, vinegar, or lemon juice. Rhythmic traction of the tongue is effective when carried out as follows: The tongue is seized with a forceps and kept extended by means of a coa.r.s.e thread. It is then pulled out from the mouth sharply and allowed to reenter after each traction. These movements should be rhythmic and should be repeated fifteen to twenty times a minute.

All these efforts should be continued for several hours. When the patient has finally been revived, he should be placed in a warm bed.

Stimulants such as wine, coffee, and the like should be administered. If the head should be congested, local blood-letting should be resorted to and four or six leeches applied behind the ears. It should be borne in mind that the various steps enumerated are to be taken pending the arrival of a physician.

IMPURITIES OF THE GASES

Most of the coal used in generating producer-gas contains sulphur.

Sulphuretted hydrogen is thus produced, which mixes with the gas and imparts to it its characteristic odor. In some gas-generators, purifiers are employed in which sawdust mixed with iron salts is utilized, with the result that a combination is formed with the sulphuretted hydrogen, thereby removing it from the producer-gas. In other forms of generators a more summary method of purification is adopted, so that traces of sulphuretted hydrogen still remain. Since this gas attacks copper, the employment of this metal is not advisable for the following apparatus: Generator (openings, c.o.c.k for testing the gas); piping (gas-pressure c.o.c.ks, drain and pet c.o.c.ks); engine (gas-admission c.o.c.k, lubricating joint in the cylinder, valves and c.o.c.ks of the compressed-air starting-pipe).

The distillation of coal in generators results in the formation of ammonia gas. This also has a corrosive action on copper and its alloys; but owing to its great solubility, it is eliminated by the waters of the "scrubber" and does not reach the engine.

PRODUCTION AND CONSUMPTION

The quant.i.ty of gas produced in most generators varies from 6.4 to 8.2 pounds per cubic foot of raw coal burnt in the generator. The engine consumes per horse-power per hour 70 to 115 cubic feet of gas, depending upon its richness.