US1945001A - Treatment of artificial gas - Google Patents

Description

Patented Jan. 30, 1934 PATENT OFFICE TREATIHENT OF ARTIFICIAL GAS Walter L. Shively, East Orange, N. J., assignor to The Koppers Company of Delaware, a corporation of Delaware No Drawing. .Application January 20, 1931 Serial No. 510,061

7 Claims.

My invention relates to the transmission and distribution of artificial or manufactured gas, such, for example, as coke-oven gas, carburetted water-gas, oil gas and the like, and more particularly to the transportation of such gas at rela tively high pressures and over comparatively long distances for subsequent distribution to consumers at the relatively low pressures normally used in distributing systems such as those supplying communities and the like.

My invention relates also to a problem of increasingly great practical concern, namely the formation and deposition of gummy or resinous material from artificial gas. The exact causes and mechanism underling this problem are still somewhat obscure, but its effects, due probably to changes in distributing systems and gas appliances and the like, are as stated above, of increasing importance at present.

It has been found that under some circumstances there is deposited from gas of the character set forth above, a tacky or resin-like mate- .rial which may even be so pronounced in these characteristics as to resemble varnish.

It further appears that this material often has the unpleasant faculty of depositng in those places where its presence is most harmful. Modern gas distribution systems supply gas to large and ever-increasing numbers of appliances having pilot valves and other devices having extremely small orifices and requiring delicate and prec.se adjustment in order to function successfully.

The amounts of gummy materials actually depositing from the gas may be and, even in troublesome cases, usually are extremely small, but it will be apparent that even minute deposits of material of this character may and do effect a material change of flow conditions through the tiny orifices of pilot valves and the like. Even an amount which could easily be placed upon the head of a common pin can often seriously interfere with the proper functioning of such a device.

Great numbers of such pilot valves are used in communities supplied by gas, and as is well known, it is important for those manufacturing and distributing the gas to insure proper functioning of these'devlces at all times. These, however, repre-v sent but one class of appliances which maybe affected by the deposition of gummy or gum-forming materials.

Aside from the increase in the number and delicacy of such devices and appliances, other factors may increase the difliculty and occurrence of the problem. Gas distribution pressures even in local systems tend to increase and higher gas pressures apparently aggravate the deposition of materials of this character under some circumstances. Ordinarily, however, when gas is made and distributed locally, the problem can be handled satisfactorily in one of several manners.

On the otherv hand, when gas is manufactured at a considerable distance from the community or system to be supplied, the problem is more difflcult and'the usual solutions may prove ineffective. In such instances, the gas is transported through a main built for that purpose at pressures much higher than those necessary, desirable or even permissible in local distribution mains to which the gas is thus deLvered. The high-pressure transportation main may have a length of, for example, fifty miles, although shorter mains, for example ten miles, or longer mains may obviously be required according to the distance between the point of manufacture and thepoint of use. The initial pressures employed vary according to the distance, the s.ze of the main and the amount of gas to be transported, but are inevitably higher than the distribution pressures.

It has been found that deposition of gummy so materials from gas may be especially serious in systems of this character, that is, where the artificial gas is transported at h.gh pressure over relatively long distances prior to its entry into a relatively low-pressure distribution system. The number of stoppages from this cause throughout the latter are believed to be due in part to the high pressure, time of travel, and other conditions of iong-dstance transportation.

It is an object or'm invention to provide a method of transporting artificial gas or of treating such gas during the transportation thereof, whereby such difficulties may be materially reduced or substantially or even completely ellmin ated,' and my invention has for further objects various operative advantages and results, as may appear hereinbelow.

Inorder that my invention may be fully set forth and understood, it is believed to be desirable to now set forth certain facts and theories 1 o regarding the nature of the problem and its solution. I do not, of course, wish to limit my invention in any way to any particular theory, nor is it necessary for me to do so and particularly because the facts with regard to the 105 problem with which my invention is concerned and indeed the materials themselves on account of their nature and the minute quantities involved are difiicult to isolate and determine. But I believe that such facts and theories as will be set 110 forth herein oifer reasonable explanation of the phenomena involved and assist in an understanding of the'solution offered by my invention.

It appears probable from what is shown of the formation in and deposition from artificial gas of gummy materials that the gummy materials actually deposited are not present in the gas as originally produced in readily detectable quantities, but that they are subsequently produced or derived from other substances originally pres ent in the gas, harmless in themselves, but potentially gum-forming".

Under certain conditions, however, these in itially harmless substances in the gas are converted into gummy materials. Just what type of chemical or physical action takes place in this conversion is difficult to determine, and is not known with certainty. It may be that some form of polymerization takes place, resulting in the formation of substances of increased boiling point and resinous character. Ir it may be that a weathering or oxidation takes place that is possibly analogous to the weathering of the vehicle of a linseed oil paint. Or both of these actions or some action of more obscure nature may be involved.

Substances such as coumarone, indene and styrene are frequently spoken of as gum-forming constituents of artificial gas, and these substances as well as those derived from unsaturated organic compounds containing conjugated double bonds, such for example as butadiene, or cyclic unsaturated compounds such as cyclobutadiene and its homologues, have actually been found to be present in gummy deposits of the character indicated. But whether or not these materials themselves, or some polymerized or oxidized products thereof, or even materials less intimately related thereto, constitute the principal immediate sources of the deposits, cannot definitely be stated. It is to be kept in mind that the deposits themselves may consist of very complex, resinous mixtures composed in part of materials which may be harmless in themselves and present only incidentally.

According to one hypothesis, known as the oil mist theory, compression and cooling of the gas, or the treatment of the gas with certain oils, or all of these, may result in the presence in the gas of a fine mist or fog of oil particles. This oil mist, which would probably be harmless or even beneficial in itself, may exert a scrubbing action upon the gas, dissolving from the gas small amounts of gum-forming materials impossible or very diflicilt to remove in any other way. These materials in solution may then be converted into gums or gummy materials and be deposited as such in the mains, services or appliances.

According to another hypothesis, it may be that polymerization or oxidation of the potentially gum-forming constituents present in the gas converts these constituents, originally present in a gaseous or vapor state, to solid or semi-solid materials of higher molecular weight and low vapor pressure. By reason of the very low vaport pressures of such polymerized materials, it requires only minute quantities of the same to saturate the gas with respect thereto. The gas may thus become saturated or super-saturated with respect to the polymerized materials very quickly and some of the same may precipitate in the form of a fine suspensoid composed of particles of a varnish-like consistency, some or all of which are deposited from the gas.

The initial gaseous or vaporous substances present in the gas would undoubtedly be present in relatively large amounts, as compared with the amount of the polymerized products required to saturate the gas, and the polymerization or oxidation would go on continuously and progressively during the transmission of the gas. Accordingly precipitation as above described would also go on continuously and progressively and a troublesome concentration of suspended gummyor resinous material would be continuously maintained in the gas in spite of the deposition of particles from the gas. This hypothesis or theory would account for the observed deposition of gummy material throughout the entire system.

I have observed that excessive dehydration of gas may result in an increase in the difiiculties encountered with regard to the formation and deposition of gummy materials from the gas. Such increased difficulties are not ordinarily encountered to a marked extent where the gas is dried merely to such extent as to prevent the deposition of moisture and not to such extent as to reduce the humidity of the gas to a point far below the saturation point at the temperatures encountered.

When the gas is transported over relatively long distances prior to entry into a local distributing system, it is customary to compress the gas initially to a relatively high pressure. The gas is usually cooled after compression and enters the transportation main at said high pressure and saturated with moisture.

Further cooling of the gas, and possibly the presence of moisture as a mist or fog in the gas,

may maintain the gas at its saturation point with respect to water for some distance along the main, but eventually the natural reduction in gas pressure due to the friction losses or backpressure of the main reduces the relative humidity of the gas to a -point considerably below its saturation point. For example, in a transportation main 50 miles long, the initial gauge pressure being about 25 pounds per square inch, the final gauge pressure at the other end of the main may be only 5 pounds per square inch and the gas at that point only about 20 percent saturated with respect to water vapor.

When the gas then enters a local distribution system, its pressure may be still further reduced, for example, to about 10" water column, and, its relative humidity may thereupon be still further lowered. Under such conditions, gum troubles may become serious.

I have observed that rehydration of the gas after it enters the distribution system from the transportation main, while undoubtedly beneficial so far as general distribution efficiency is concerned, in preventing an unduly dry condition, may not, in an instance such as described, prove effective in eliminating or evenmaterially reducing the deposition of gummy materials.

As distinguished from mere rehydration of this character, my invention contemplates the maintenance of the gas during the transportation thereof through a high pressure main at a high relative humidity throughout the entire length thereof. I accomplish this by rehydrating the gas, i. e., introducing moisture thereto, at such intervals and to such extent along the main that the more or less gradual reduction in relative humidity which would otherwise take place due to the natural reduction in pressure along the main is prevented or controlled. I

prefer, for best results, to maintain the gas substantially saturated with moisture, but a minimum relative humidity of 90 percent, or possibly only percent, may prove suificiently effective depending somewhat upon the severity of the tendency to depositgums.

By relative humidity is meant the amount of water vapor which is present in a definite volume of gas at any temperature expressed as a percentage of the amount which would be present in an equal volume of the gas if it were completely saturated with water vapor at the same temperature.

It may appear at first glance that due to the natural expansion and gradualreduction in relative humidity along the main, it would not be possible to maintain the gas at its saturation point unless the points of rehydration were very close to each other. However, in practice I have found that along a main of fair dimensions in tervals of from five to fifteen miles, but preferably ten miles, are suificient, if at such points an excess of moisture, whether in the form of steam or water mist, is introduced. In this manner, an excess of moisture is imparted to the gas which is carried along as a mist or fog until evaporated into the gas. This evaporation tends to maintain the gas at its saturation point.

As some of the moisture added in this manner inevitably precipitates near the point of rehydration, I ordinarily prefer to add at each point two or three times as much moisture as will theoreticallybe required to re-saturate the gas or to carry the gas in a saturated or nearly saturated state to the next point of rehydration, as the case may be.

In general, the points at which moisture is to be admitted to the transportation main in accordance with my invention are located wherever the relative humidity of the gas tends to show a substantial reduction from that desired.

Where. as in the preferred instance, it is desired to maintain the gas saturated or substantially saturated, it is desirable to rehydrate the gas at points where the gas is saturated or substantially saturated, that is, before the natural decrease in pressure reduces the moisture content below the saturation point of the gas.

Where the gas is to be maintained at a minimum humidity below but near its saturation point, as, for example, at ninety percent saturation, the rehydration points may be located at or just prior to points when the relative humidity of the gas would otherwise fall to a figure corresponding to a ninety percent saturation.

In a specific instance, it was desired to accomplish the prevention of gum troubles in a system in which coke-oven gas is manufactured at a distance of approximately forty miles from the distributing mains of a certain community. Approximately 7,500,000 cubic feet of gas (measured at 60 F. and 30" Hg.) are delivered per day into the highpressure line connecting the manufacturing plant and the distributing system. The gas enters the transportation main at a gauge pressure varying from twenty to forty pounds per square inch and at a temperature somewhat higher than the temperature of the main, for example, at about 60 F. when the temperature of the main is about 45 F.

The gas entering the high-pressure main is saturated with moisture, and ordinarily remains in a saturated condition for approximately ten miles, as is evidenced by the appearance of water in the drips along the main for this distance and also by actual dew-point determinations. This is undoubtedly due largely to the cooling of the gas, but also to the evaporation into the gas of moisture carried by the gas as a fog or mist originally present as such in the gas in the main.

Prior to the installation of means for rehydrating the gas along the main in accordance with my invention, the gas ordinarily reached the other end of this forty-mile main at a gauge pressure of from about five to twenty pounzls per square inch, and at a low relative humidity, for example, a relative humidity of to only 25 percent.

Under these conditions, trouble from the formation and deposition of gummy materials was encountered in the transmission line and in the distributing system of the community at the end of the line, and in other communities deriving at least part of their gas supply from intermediate points along the line where the gas had a relative humidity of, for example, only sixty or seventy percent. Numerous expedients were tried, but none prior to the application of my invention offered satisfactory relief from the difficulties encountered.

The gas in the main branches of the distribution system of the community at the end of the above forty-mile main is ordinarily maintained at a pressure corresponding to a water column of about 10", so that the drop in pressure at the point when the gas passed from the transportation main into the distributing mains caused a further and considerable drop in the relative humidity of the gas.

Largely for the reason that the distribution of so dry a gas in distributing mains designed and previously used for the distribution of moist gas causes increased leakage losses, dust troubles, hardening of meter leathers and the like, rehydration of the gas after entering the distributing system was practiced in this instance, but it was observed that this did not put a stop to the dimculties due to gum deposition.

In accordance with my invention, the gas was then rehydrated by the addition of steam at the rate of about one hundred pounds per hour at a single point located approximately ten miles from the manufacturing plant, where the flow of gas was approximately 313,000 cu. ft. per hour, bringing the relative humidity of the gas at the end of the line to approximately eighty percent.

The efiect of this single introduction of steam Was remarkable. A quantitative comparison at one point, for example, showed a deposition of only two milligrams of gummy material per 100 cu. ft. of gas after steam injection was commenced as compared with a deposition of sixteen milligrams per 100 cu. ft. of gas prior to steam injection, other conditions of the tests being similar.

Tests made nearer the point of steam injection indicate a reduction of gum deposition to an even lower amount. Further injection of a like quantity of steam into the gas at a point approximately 5 miles from the community receiving the gas has resulted in complete elimination of suspended gummy material in the gas as it reaches said community.

While, as stated hereinabove, I do not desire to limit my invention to any particular theory, it does appear from observation of the employment of my invention under actual full-scale operating conditions, that if the gas is maintained at a high relative humidity and preferably at or near its saturation point by the injection of excess steam pressure transportation main, the deposition of harmful gummy materials can be satisfactorily prevented or controlled.

This beneficial result may possibly be due to some inhibitive action of moisture in the gas. It may be chemical or catalytic, or mechanical, dependent upon surface contact or a like phenomenon, or may be due to some unknown factor or to a combination of factors. It may result in part from a mechanical scrubbing action of the excess moisture with respect to fine particles of polymerized or oxidized materials. Such theories or conjectures are exceedingly difiicult of proof. The fact remains that the troubles can be largely controlled in an economical, simple and positive manner by the application of my invention.

In systems where the pressure drop to which the gas is subjected upon entering the distribution system from the transportation main is severe, it may be desirable to further rehydrate the gas in the low-pressure distribution system. In most cases, however, this is not necessary, and it is an advantage of my invention that rehydration of the gas according to my invention in the high-pressure transportation main in most cases automatically conditions the gas for low-pressure distribution against too low a moisture content on the one hand and too high a moisture content on the other. Mere conditioning of the gas for low-pressure distribution is not, however, the principal object of my invention, but simply constitutes an added advantage thereof.

It will be obvious, therefore, that my invention is clearly distinguished from the rehydration of natural gas, which has been practiced where this dry gas is introduced into local distributing means previously employed and designed for the distribution of moist artificial gas. Natural gas contains no gum-forming constituents and need not be rehydrated for the prevention of gum troubles.

Rehydration of gas according to the present invention and as now practiced is not necessarily inconsistent with the proven advantages of gas dehydration. The latter is of advantage principally with respect to the low-pressure distribution of gas, and as is well known should not be so conducted as to dry the gas to such an extent that the gas is excessively dry and the distribution system is too rapidly dried out.

Insofar as high-pressure gas transportation is concerned, dehydration is of somewhat less importance. While my present invention contemplates the actual introduction of moisture to the gas. even to a point beyond the saturation point of the gas, it realizes advantages which in many instances far outweigh any disadvantages such as increased corrosion or the like which may re sult from the presence of excess moisture. As will readily be appreciated by those skilled in the art, it is largely a question of balancing advantages and disadvantages, as is true of any gas- -making or handling operation.

inabove to an extent not heretofore possible and with a minimum of difficulty and expense and this is the more surprising since many complicated and expensive methods have heretofore been suggested and tried without success.

It will be obvious to those skilled in the art that my invention is not limited to the specific examples given hereinabove by way of illustration but may be variously practiced and embodied within the scope of the claims hereinafter made.

I claim as my invention:

1. In a method of transporting artificial gas containing gum forming material through a transportation main at pressures materially higher than the pressure at which the gas is subsequently distributed and which involves the deposition of gummy materials in the relatively lowpressure system through which the gas is subsequently distributed the improvement which comprises treating the gas to repress the gum formation therein by introducing moisture into the gas as water or steam in the high pressure line at intervals during its passage through said transportation main and thereby maintaining a sufficiently high relative humidity therein at above throughout its entire travel through said transportation main as to repress gum formation therein.

2. In a method of transporting artificial gas containing gum forming material through a transportation main at pressures materially higher than the pressure at which the gas is subsequently distributed and which involves the deposition of gummy materials in the relatively low-pressure system through which the gas is subsequently distributed, the improvement which comprises treating the gas to repress gum forma-' tion therein by introducing water into said gas during its travel through the high pressure line of said transportation mains at such intervals and in such amounts and in such manner as to maintain the relative humidity of the gas at a point and at above 80% at least close to its saturation point throughout its entire travel through said transportation main to repress gum formation therein.

3. In a method of transporting artificial gas containing gum forming material through a transportation main at pressures materially higher than the pressure at which the gas is subsequently distributed and which involves the deposition of gummy materials in the relatively low-pressure system through which the gas is subsequently distributed, the improvement which comprises treating the gas to repress the gum formation therein by introducing moisture into the gas as water or steam in the high pressure line at intervals during its passage through the high pressure line of said transportation main to maintain the gas at least 80% saturated with respect to water vapor to repress gum formation therein.

4. In a method of transporting artificial gas containing gum forming material through a transportation main at pressures materially higher than the pressure at which the gas is subsequently distributed and which involves the deposition of gummy materials in the relatively low-pressure system through which the gas is subsequently distributed, the improvement which comprises treating the gas to repress gum formation therein by introducing water to said gas during its travel through the high pressure line of said transportation mains at such intervals and in such amounts and manner as to humidify and maintain it 'at' and thereby compensate for the decrease in relative humidity due to the natural reduction in pressure along the main and to maintain the gas substantially saturated with water vapor to repress gum formation therein.

5. In a method of transporting artificial gas containing gum forming material through a transportation main at pressures materially higher than the pressure at which the gas is subsequently distributed and which involves the deposition of gummy materials in the relatively low-pressure system through which the gas is subsequentlydistributed, the improvement which comprises treating the gas to repress gum formation therein by introducing water to said gas in the high pressure side main when the latter, by reason of the natural fall of pressure along said transportation main, tends to fall below its saturation point, in' such .manner and amount as to maintain it at a relative humidity above 80% and thereby not only to saturate the gas but also to provide an excess or moisture in the form of a mist carried by the gas and capable of evaporating into the gas to compensate for the lowering of the relative humidity of the gas which would otherwise occur by reason of further natural decrease in gas pressure along said transportation main to repress gum formation therein.

6. In a method of transporting artificial gas containing gum forming material through a transportation main at pressures materially higher than the pressure at which the gas is i subsequently distributed and which involves the deposition of gummy materials in therelatively low-pressure system through which the gas is subsequently distributed, the improvement which comprises treating the gas to repress gum formation therein by introducing water in the form of. steam to said gas when the the natural fall of pressure along said transpora relative humidity above portation main of said transportationv latter, by reason ct tation main, tends to fall below its saturation point, in such amount as not only to saturate the gas but also to provide an excess of moisture in the form of a mist carried by the gas and capable of evaporating into the gas to compensate for the lowering of the relative humidity of the gas which would otherwise take place by reason of further natural decrease in gas pressure along said transportation main, and again introducing water in the form of steam to said gas whenever the gas tends to fall below its saturation point, whereby the relative humidity of the gas is maintained at least close to the saturation point during the course of travel of the gas through said transformation does not proceed at such rate as to be objectionable.

.7. In a methodiot transporting artificial gas containing gum forming material through a transportation main at higher than the pressure at which the gas is subsequently distributed and which involvesthe deposition of gummy materials during the subse quent distribution of the gas at relatively low pressures, the improvement. which comprises treating the gas to repress gum formation therein by introducing the gas during its passage through the high pressure linegof said transportation main to maintain the gas at a high relative humidity at above 80% throughout its entire passage through said main, and introducing additional water in the form of a fine spray to said gas subsequent to its passage from said relatively high pressure transportation main into and a relatively low pressure distribution system in amount sufficient to maintain the gas at a high relative humidity during its passage through said distribution system while insufllcient to cause a permanent deposition of moisture from said gas throu'ghout said distribution system to repress gu formation therein.

WALTER L. SHIVELY.

at which saturation point gum pressures materially;