9 DETERMINATION OF FLUE GAS DENSITY.

THE INFLUENCE LINE.

(Paper by Prof. H. PAYNE.)

The PRESIDENT said he was sorry Prof. Payne was not present. It was a disadvantage to take the discussion of thé paper if the author was not present. If members had no

objection he would postpone the discussion until next meeting.

PAPERS.

A METHOD OF DETERMINING THE DENSITY OF FLUE GASES.

By JAS. ALEX. SMITH. (Past President.)

FOREWORD:

Engineers, whether power, metallurgical or manufacturing, can always ascertain the density of the gases within their province, either by chemical analysis or precision weighing. But it is not always essential to know the chemical composi-tion; or the composition may be deducible with sufficient accu-racy if the density is known. Then methods of a simpler or more direct character have a use, particularly when it is de-sired to study cause and effect concurrently, and without any appreciable intervening interval during which the cause might vary.

The purpose of this paper is to describe a mode of de-termining gas density by gauge reading. So far as the writer is aware, the method is new.

GENERAL PRINCIPLES:

The basic theorem is that the densities of gases and their pressures per unit area of base are directly proportional when the gas-columns are of equal height.

92 VICTORIAN INSTITUTE OF ENGINEERS.

Hence, if a column of air in a vertical tube of known height is displaced by a given gas, the barometric and thermo-metric conditions remaining constant, the densities are in the simple ratio:—

P

when.—D = Density of the given gas referred to air taken as unity—

P = Known air pressure due to column height, and—P' = Difference (±) of pressure due to gaseous dis-

placement.

PRESSURE MEASUREMENT:

Assume that an accuracy within one per cent. of the total air pressure due to the vertical or column height is required; in other words, that a pressure due to the air in a column the one-hundredth of the height of the column in the given case must be evaluated. This order of minuteness of magnitude at once contraindicates mechanism subject to friction, and indicates the use of "frictionless" liquid gauges.

Postulating that, without the introduction of undesirable complications, .02 inch is-the smallest significant difference of level of such a gauge, then the relation of that minimum gauge space to the minimum correlated gas-tube height (h) is given by the equation:—

h= .02 inch X I00 x . .. .. .. .. .. . • .. .. (2). when x is the specific gravity of the gauge-liquid referred to. air as unity. Therefore water, which is about 772 times heavier than air, if used in a simple syphon gauge, and under the conditions postulated, requires a complementary gas-tube not less than, .02 inches x Ioo x 772 = 1,544 inches, = about 13o feet in height. Conversely, if the height (h) in inches be given, then the maximum specific gravity of the possible gauge-liquid (air, as before, being taken as unity) is-determined by the formula,-

X=---2-- .. Any convenient value may be assigned to h. Let, then, the

vertical height of the gas-column be Ioo inches. Then x =

D P±Pf

= .. (I)

DETERMINATION OF FLUE GAS DENSITY. 93

specific gravity 50. That is, for such a tube height, a liquid iS indicated not more than 5o times heavier than air, or.

772 = 15.44 times lighter than water.

50 No such light liquid is known; but its equivalent may be

attained if two immiscible liquids are caused to partially equilibrate each other in such a manner that the difference <which may be made as small as desired) of the specific gravi-ties becomes the measure of the equivalent specific gravity of the liquid system as a whole.

A gauge on the differential principle, capable of readily dealing with gas pressures of the small magnitude in ques-tion, has already been described by the author in the "Pro-ceedings" for November, 1909, Vol. X., p. 155, under the title, "A Simple, Sensitive, Two-Liquid Differential Gauge for Measuring Small Pressures."*

GAS-TUBE:

The gas-tube is very simple. In the example before the meeting, it consists of a piece of /a inch wrought-iron gas-barrel Ioo inches in vertical height. At the bottom two stop-cocks permit alternative connection to a gas-source or to a gauge. To check diffusion the passage through the latter cock should be reduced to a pin-hole. At the top, a third cock, opening into the air, permits the tube to be gas-flushed and filled, and when the main passage is closed, continues the connection by a minute by-pass large enough to preclude any possible barometric difference of pressure between the gas inside and the air outside the tube, yet so small that diffusion is negligibly slow. The surface of the liquid in the gauge cistern, and the bottom of the gas-tube must be approximately at the same level.

"CALIBRATION: If the gauge constants are unknown, a simple, compre-

hensive calibration covering all the factors can be effected thus:—All parts being filled with air, adjust the gauge to zero.

''Also reprinted in " ENGINEERING " London, 1910, Vol. XC., p. 144, and elsewhere.

VICTORIAN INSTITUTE OF ENGINEERS. 94

DIAGRAM OF GAS-DENSITY APPARATUS.

Scale, 3 full size.

A—Gas-tube. B—Inlet gas cock. C—Gauge cock. D—Outlet gas cock. E—Differential -gauge.

Note.—The barometric equalising vent (at D) is not shown. It con-sists of a piece of clockmaker's "bushing wire," one inch long and -uinch bore.

DETERMINATION OF FLUE GAS DENSITY. 95

Then displace the air in the tube with any easily generated or procured gas of known density, for instance CO2 , the specific gravity of which is 1.524. Then the pressure upon unit of base of ioo inches vertical of CO2 is equal to the pressure of too x 1.524 = 152.4 inches of air. There-fore, the consequent liquid displacement due to the displace-ment of the air by gas is equivalent to that which would be caused by an air pressure of 152.4– 100.0= 52.4 inches. The scale can be graduated or interpreted accordingly.

CORRECTIONS: When relativity only is required, corrections may be dis-

pensed with. The case of the immediate effect of draft volume variation upon chimney-gas density is an example.

But if absolute readings are required, and if the barometric and thermometric conditions differ from those which may have been assigned in respect to P (formula I), and upon which the value of the gauge divisions is computed, then a corrected value P" must be substituted for observed P' in formula (I); then.—

P,.-(461+t) 29.92xP' – (461+t')xP' ...

461x b 15.41xb

when. —I = observed temperature on Fahr's scale—b = observed barometric . pressure in inches -

P'= observed pressure due to gas displacement, and--P".= corrected value of observed displacement pres-

sure.

Strictly, a further correction should be made to compen-sate for the variation in the gas system volume, due to the movement of the liquid in the gauge. Usually, however, this amount is so small that it may be neglected in practice.

SCALES:

The actual graduations may be in any convenient term, i.e.—density or specific gravity, percentages, or direct evalua-tions of the major object of the test.

VARIANTS:

(i.): The mode is equally applicable in the case of density change due to chemical reaction other than com-bustion.

(4)

96 VICTORIAN INSTITUTE OF ENGINEERS.

(ü.): In the case of inconveniently high tubes, all adjustments may be brought within operative reach by construct-ing the tube as an inverted n , providing that the minute equalising vent must then be placed at the vertex, and must remain permanently open.

(iii.): A gas tube within a chimney and extending to its full height, affords a means of ascertaining the density of the chimney gases at the mean temperature within the whole stack. From this may be deduced the potential ascensional power of the gases, a result not given by the ordinary draught gauges, which show the utilised value only.

(iv.): Obviously portability can be attained by constructing the tube in screwed sections.

(v.): Photographic continuous records can be attained by the use of any of the well known devices. This implies a constant passage of gas, therefore precautions must be taken against the vitiation of the results by the introduction of extraneous pressure head, either by periodically cutting off the gas supply, or by making the inlet very small in comparison with a relatively large outlet permanently open. Neces-sarily there will be a lag in the records in respect to time.

DISCUSSION.

The PRESIDENT said they were indebted to Mr. Smith again for a valuable contribution to the "Proceedings." Mr. Smith had described a very ingenious instrument, and one that should be of considerable use in many of their under-takings. It ought to find a place in.the boiler house, where a dose study of flue gases was required. He thought Mr. Smith would be pleased to further explain the apparatus at the close of the meeting. In the meantime they could ask any ques-tions they desired.

Mr. J. T. N. ANDERSON asked if it was not a fact that Mr. Smith was the first designer of that apparatus?

DISCUSSION-DETERMINATION OF FLUE GAS DENSITY. 97

Mr. J. A. SMITH said as far as he knew that was so.

The PRESIDENT said the gauge portion had been previously

communicated to the Institute, and had been published in the "Proceedings." It had been reprinted in "Engineering" in Iwo. Undoubtedly the instrument ought to find a field of

usefulness in many directions. It was so extremely sensitive

and devoid of internal friction.

Mr. F. C. LINDBLADE asked if Mr. Smith took any special

precaution against the small dust to be found in the air to be

measured?

Mr. J. A. SMITH said he had not found it necessary to take precautions against dust. The fact that the dust floated indi- cated that it could be considered statically as nearly of the same specific gravity as the gas. Its mass in relation to the mass of the gas was usually negligible. It would not, how-.ever, be difficult to arrange a simple filtering device.

He might point out in respect to another matter that the temperature of the gas tested was the temperature of the ..atmosphere at the time. The gas could be very easily cooled; but that was hardly necessary since the mass of the gas-tube was something like 1,000 times the mass of the contained gas. Thus, even if the gas entered the tube hot, it would cool down

almost instantaneously.

Mr. J. T. N. ANDERSON said he presumed in measuring

hydrogen it would be necessary to employ a longer tube.

Mr. J. A. SMITH said no. Assuming the hydrogen to be 14 times as light as atmospheric air they would get a much

.greater pressure difference than would exist if the gas under test were of nearly the same density as air. It was the pres-

sure difference that was in question.

Mr. A. E. HUGHES asked whether the diffusion would

-introduce sensible errors?

Mr. SMITH said no. Owing to the length of the gas-tube, its small bore, and the small diameter of the diffusion aperture, diffusion was very slow—the error would be of the

order of r per cent. in 20 minutes.

G

98 VICTORIAN INSTITUTE OF ENGINEERS.

Mr. J. C. LANE said that for the testing of flue-gas, the in-strument would be superior to the "Orsat," if Mr. Smith could get away from the ioo-inch tube that hindered its portability.. The "head" was necessary to obtain the gauge effect.

With regard to the other portion of the apparatus—the fl tube—they had recently discovered at the Melbourne City Electric Station a very satisfactory liquid for fixing the line of demarcation that was found when dealing with liquids of a slightly different specific gravity. Ordinary , carbolic acid crystals were used. These when dissolved in water would only take up a certain amount of that liquid. The balance of the water remained clear and floated on the heavier liquid, which was coloured with methyl violet. This was found exceedingly satisfactory and sensitive. It did not mark or discolour the. water column in any way, and there was always a clear line to denote the zero point. What liquids did Mr. Smith use?

Mr. SMITH said various liquids were available. Those in the actual instruments before the meeting were kerosene and methylated alcohol coloured with a "spirit-soluble" analine dye. They were to a small extent soluble in respect to each other. But if they were kept in the same bottle, they quickly became mutually saturated, and liquids sufficiently stable in, specific gravity resulted. There was, after a period of use, an inclination to stain the glass tube in the portion which should be clear. This did not materially affect indica-tions, and new liquid could be quickly substituted, but the liquids mentioned by Mr. Lane would seem to be of very con-siderable promise.

As to the height of the tube, as he had explained in the paper, they might make it in pieces, screwing them together. That gave portability. Otherwise, if a shorter tube.

were used, they must be satisfied with a proportionately greater error than one per cent., or, alternatively, they must make the gauge more sensitive.

The PRESIDENT said they should express to the author their appreciation of his efforts in presenting the result of an' interesting study.

A vote of thanks to the author was then carried.

WMIIr_ VIM rv__ i

DISCUSSION—THE INFLUENCE LINE. 137

Mr. J. T. N. ANDERSON said he presumed the reading of a contribution of that sort did not constitute a discussion on the paper. One could only express gratitude to Prof. Payne for the large amount of work he had put into the paper. It was only fair to Prof. Payne that he should be present when the paper was being discussed. That being so; he would move that the discussion on the paper be postponed. Under the rules a discussion upon a paper lapsed after two meetings un-less by resolution of the meeting.. They were deeply indebted to Prof. Payne for giving them one of the most instructive papers that had been read before the Institute, and the least they could do- was to give the author an opportunity of hearing-the discussion on his paper.

Mr. C. F. LINDELADE seconded. Carried.

Mr. J. S. DETHRIDGE said he would like to add that it should be clear that the reason was that the paper could only be discussed at two meetings. He would like to say how highly the paper was appreciated.

DENSITY OF FLUE GASES.

(Paper by JAS. ALEX, SMITH.)

Mr. J. N. REESON said it was one or two meetings, since they had had the good fortune of listening to Mr. Smith's paper on his apparatus for measuring the density of flue gases. Therefore the paper was not quite so well within their recol-lections as it might have been. He was much struck with the simplicity and novelty of the apparatus, and he thought the Institute was indebted to Mr. Smith for bringing under it notice an apparatus of that kind.

Evidently Mr. Smith's object in designing the apparatus, was to determine the density generally of flue gases contain-ing the usual proportion of carbonic acid gas. They all knew that carbonic acid gas was a heavy gas, thus the instrument would register the variation in the proportion. Although in' good re-generating furnaces one was able to obtain very high efficiency, in ordinary boiler furnaces the efficiency was extremely low, and he was wondering whether an instrument-

138 VICTORIAN INSTITUTE OF ENGINEERS.

.of that kind, which would indicate the difference in density, would be sufficiently accurate to determine the quality of flue gases.

He could not help thinking that an analysis of the flue gases, although it would take more time, would perhaps be a more useful guide. He was not saying anything to disparage the use of Mr. Smith's instrument, but it occurred to him that perhaps an analysis would help them. Mention had been made by one of those taking part in the last discussion as to the use of an instrument of that character in determining the ,constitution of illuminating gases. He thought, in that case, although no doubt the instrument would indicate variations in the constitution, yet the variations were so slight that if the instrument were a recording one, they would generally :see a straight line. He might indicate the variations that would occur in ordinary coal gas. He would take the ordinarily con-:stituted coal gas, as it was understood in Australia. He might mention that the coal gas in Australia was quite a different product from that in Europe, because it was the product of an entirely different coal. Coal gas in Australia was com-posed of:—

COL, .. .. .. 2 per cent. Oxygen .. CH .. .. .. .... 4 C.111 .. .. .. 30 ;,

H. .. .. 43.5 ff

CO... .. .. .. .: Io

It would be seen that if there was a variation of the CO2 — and the COQ was not likely to vary more than 0.2 per cent.—that would have an inconsiderable effect on the gravity of that gas. The gravity of coal gas was about .48. It would be seen that the variation in the proportion of the CO2 would affect the gravity very slightly indeed. It was also ,obvious that the proportion of nitrogen would affect the gravity considerably. But as the nitrogen, for the sake of those who supplied the gas, was kept as low as possible, he feared that an instrument such as that, although it was an extremely nice one, and one that he was interested in from

)f

DISCUSSION--DENSITY OF FLUE GASES. 139

-an academic point of view, from the point of view of .determining the quality of coal gas, he was afraid, would not be of great value.

Mr. Smith had kindly promised to lend him the instrument, and he purposed, to gauge its efficiency. The easier they could make the determining of the constitution of flue gases, -or of any other gases, the better it was for everybody, because the ordinary workman, who had a goed. deal to do with those matters, should have placed in his hands some instrument that he could more or less understand, and it should help him in his work. He was sorry to say that, not only the British workmen, but workmen all over the world, did not always realise that the instruments with which they were supplied were going to help them in their work. If they would only realise that the production of a good flue gas meant less firing, they might bring it home to them that if they paid more atten-tion to their fires, the work would be rendered less arduous than it was. He had again to thank Mr. Smith for his kind-mess in bringing the instrument under their notice.

Mr. J. T. NOBLE ANDERSON asked if Mr. Smith had given thought to the utilisation of the apparatus for other purposes

-than measuring CO. and other gases?

The PRESIDENT suggested to Mr. Smith that it would be of great interest to the members if he could demonstrate the use of his apparatus at some installation where boiler gases were used. He would be glad to afford Mr. Smith an oppor-tunity to give a practical demonstration at the City Electric .Supply Works.

Mr. J. A. SMITH said he would do so with pleasure. And he would be pleased to lend the apparatus to anyone who •chose to make such tests, provided that they would under-take to make the results public. His apparatus, such as it was, and anything he knew, were at the disposal of any member who seriously wished to use them.

Mr. C. F. LINDBLADE said he had brought to the meeting a somewhat similar instrument, which he had used in a totally different sphere. It was used more as a thermometer. It was

140 VICTORIAN INSTITUTE OF ENGINEERS.

based on an instrument Mr. Smith had described several years ago in the Proceedings of the Institute. The gauge was some-what similar to Mr. Smith's present instrument, only that the-scale magnification was not so great. The purpose for which it was used was testing electrical cable joints. A closed annular gas vessel was . slipped over the cable. The gas in. the vessel was connected to the gauge by a flexible rubber tube. Any thermal variation in the gas was thus translated into pressure. Then, if the annulus was slowly moved along, the cable and over a joint, the perfection or otherwise of a. mode of jointing would at once be indicated by the order of the temperature—or pressure—rise in relation to the other portions of the current carrying cable. He had treated many joints, and found it as accurate as many of the elaborate-electrical testing instruments in use.

The PRESIDENT asked if Mr. Lindblade depended on the-resistance of the area at different parts of the section.

Mr. LINDBLADE said he did. He said that exceedingly small currents could be measured by passing them through thiii wire inserted in a "Thermos" flask. The flask was closed, except by a connection to the differential gauge. The thermal insulation was thus very high, and, as before, the heat effecf was measured as a pressure. He then gave a short demon-stration of the use of the instrument. It was shown that a.

variation of r deg. F. gave a scale reading of about 3i inches.

Mr. C. J. LANE said he had previously mentioned that he used a liquid that answered very well. He had brought a small sample along, that might be of interest to members. It was carbolic acid crystals dissolved in water. The specific gravity of the liquid, at 6o deg. F., was 1.05. It would not take up any more water at that temperature, but as the tem-perature rose, it would absorb slightly more water until at about 16o deg. Fahr. it would all become the same colour. However, the temperature error did riot add any inaccuracy to the instrument, because, when necessary, the zero level could be adjusted. If they were working at ioo deg. they could adjust the zero level to that temperature. Assuming-

DISCUSSION-DENSITY OF FLUE GASES. 141

io change in conditions took place during the reading, the instrument would be perfectly accurate.

The PRESIDENT called on Mr. J. A. Smith to reply.

Mr. J. A. SMITH said, with regard to the first part of the .discussion, a number of questions were put, and remarks made, and these were answered at the time. He need not .further refer to them.

With regard to the discussion that night—in answer to .Mr. Reeson, he thought he had made it clear that there was no intention of suggesting the abolition of the method of

.analysis. Nothing could give a more definite or absolute result than chemical analysis. But he felt that it was not .always convenient; and sometimes an analysis was not re- -quired, then his instrument, though not intended to supplant any instrument in use, gave an additional method. It had a _particular utility where it was advisable to get the result -before conditions could change. The volume of air through the furnace might alter, and they would require to know the immediate effect. The method in respect to chemical com-position was qualitative rather than quantitative, but in respect to the simpler mixture of flue gases it was largely quantitative also. The case of the complex gas to which Mr. Reeson had referred was clearly a case to which the instrument would not be applied. The components differed so greatly, and their permutations might be so numerous in the case Mr. Reeson .

:.had referred to, that the instrument would not be applicable at all.

The instrument was applicable, not only to flue gases, but to other gases in manufacturing processes, where the gaseous mixture was relatively simple. Another means of -obtaining a more accurate result, if it were necessary, was to increase the length of the tube. But, as it was, one could get an accuracy within I per cent. In Mr. Reeson's practice, he presumed, it was necessary to know with precision the volume or mass of each of the gases present. In many other cases in engineering, it was not necessary. What the engineer

was seeking for was, generally, the amount of CO2. Nothing •else greatly concerned him. It was not likely, for instance, -there was unconsumed hydrogen passing away.

I42 VICTORIAN INSTITUTE OF ENGINEERS.

It had been asked by Mr. Anderson if the principle had beenT applied to other purposes than ascertaining the density of gases. Mr. Lindblade had supplied an illustration in the-measuring of electrical resistance. He recognised Mr. Lind-blade's instrument as a well-constructed modification of one he had brought before the Institute in 1909.*. Mr. Lindblade-had improved it in a number of directions, and had applied it to purposes that seemed to give great promise. The accuracy obtained by its use as a thermometer was very great. When first he used it as a thermometer it was because he had' failed to get the results he sought by the use of resistance-thermometers of precision. He made one on the pressure principle, in which he could recognise definitely a change of one-thousandth of one degree Fahrenheit. It was essentially the same as the one described in the 1909 paper, except that the-range was longer, and it was more sensitive. Another adapta-tion of it was in barometric work, when one limb of the gauge-was connected to a constant-temperature control gas reservoir. He had used it in that direction for meteorological work, It responded to the slightest variation of the barometer in a very marked degree. There were many other purposes. He had not used it for purposes of stress on pieces of machinery in-motion, as suggested by Mr. Anderson, but possibly it could be used for that purpose.

Mr. Lindblade had done excellent work, and along the lines upon which he was working there were other fields of practical application. For instance, the equivalent of the ammeter was interesting. In the early days of electrical' research, a recognised method of testing an electric current was to cause it to flow through a wire passing through the-bulb of an air thermometer. Then the electric energy trans lated into thermal effect was measured by the movement of a. simple liquid in a vertical tube. The method adopted by Mr. Lindblade was more sensitive.

As to Mr. Lane's method, it possessed considerable ad-vantages; but he did not think he could agree with Mr. Lane in one point—that temperature did not alter the accuracy of the liquid. Temperature altered the solubility of the *"The Differential Pressure Gauge in Engineering Thermometry," by

Jas. Alex: Smith, Proceedings of the Victorian Institute of Tngineering, Vo. X., p. ¶96, agog.

DISCUSSION--ROAD CONSTRUCTION. 143

salt. It was, therefore, not sufficient to bring the instrument-to zero, since they would be dealing with liquids, the difference of the specific gravities of which varied in an unknown ratio, according to the temperature. For ordinary constant tem-peratures the liquid Mr. Lane had introduced was of great promise.

As to the President's remarks—his instruments were at the disposal of anyone who proposed seriously to test their actual installation, and he trusted those who did test such-installation would give the Institute the benefit of their work.

ROAD CONSTRUCTION TO STAND MODERN TRAFFIC. (Paper by J. T. NOBLE ANDERSON.)

The PRESIDENT said it had been his intention to have-asked a few well-known road engineers to favour them with their presence, but the matter was overlooked at the last moment. He would be pleased to receive a motion that the discussion be postponed until next meeting, so that a more useful discussion might be ensured.

Mr. J. N. REESON moved that the discussion be postponed.:

Mr. H. E. GROVE seconded. Carried.

MODERN METHODS OF EARTH EXCAVATION. (Paper by C. CATANI.)

Mr. J. T. N. ANDERSON said Mr. Catani had just suffered° a very severe loss, in that his son had been killed in action.

Mr. JAS. ALEX. SMITH said he had just received a letter from Mr. Catani, requesting that, if possible, the discussion.. be postponed.

The discussion was postponed accordingly.

Mr. J. T. N. ANDERSON moved an expression of condol-ence with Mr. Catani on the occasion of the loss of his Son-at the front.

Mr. J. N. REESON seconded. Carried.

Library Digitised Collections

Author/s:

Smith, James Alexander

Title:

A method of determining the density of flue gases (Paper & Discussion)

Date:

1917

Persistent Link:

http://hdl.handle.net/11343/24592

File Description:

A method of determining the density of flue gases (Paper & Discussion)