No. 177.

The Metal Markets

PAGE 229

Tar and Ammonia Products ...... 229
The Liverpool Mineral Market.... 230
West of Scotland Chemicals........ 230
The Tyne Chemical Report........ 230
Gazette Notices
New Companies.

Patent List

Imports

Exports

Prices Current

Notices.

...... 230 ........ 230 ..... 231 ..... 231 ...... 233 236

Advertisements intended for insertion in the current week's issue, should reach the office by Wednesday morning at the latest.

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Vol. VII.

THE MANCHESTER TECHNICAL LABORATORY. LECTURES ON SCIENTIFIC SUBJECTS OF POPULAR INTEREST.

ON Tuesday evening last the first lecture of the series was

given by Mr. George E. Davis, the subject being"Manufacturing Smoke."

The chair was taken by A. E. Fletcher, Esq., Her Majesty's Chief Inspector of Alkali Works, and there was a good attendance of gentlemen interested in the subject of Smoke Prevention.

In opening the proceedings the Chairman said that the excessive manufacture of smoke was a physical and moral evil which was largely felt in great industrial centres. Not only did the smoke destroy their property, deface their buildings, and cause injurious waste, but it had a pernicious effect upon society. It separated the classes by making the places where smoke was manufactured uncomfortable to live in, so that people who could afford it spent their evenings and week ends in the country, leaving behind them amongst the smoke those who had not the means of escaping from it. So the classes were divided and separated, and those who should be the leaders and helpers in social as well as manufacturing matters were driven into the country by the influence of smoke. The Chairman then called upon Mr. Davis to deliver his lecture on:

MANUFACTURING SMOKE.

Mr. Davis said:-Mr. Chairman and gentlemen, it has been suggested to me that it is not quite clear what is intended to be meant by the title of our lecture to-night.

One querist has humorously asked whether we intend to treat of smoke-manufacturing or manufacturing smoke; but a little reflection will convince any one that the subject will be practically unaltered whether we consider the attribute as adjective or participle.

To treat the word "manufacturing" as a participle would be like " carrying coals to Newcastle." Everyone knows how to manufacture smoke. The operation is carried on too well now-a-days to require description, and therefore it is well that we should consider the doubtful word as an adjective and study the title in this light.

For purposes of discussion, smoke may be conveniently divided into two categories, manufacturing and domestic, when it will be found that each class requires treatment from its own special standpoint, and that the remedies proposed for the one will not deal satisfactorily with the other. This is then a very good reason for separating domestic smoke, from that produced in manufacturing processes.

In dealing with manufacturing smoke it will suffice to notice that produced from coal and coke; smoke is of course capable of being produced from other substances, and especially from liquid fuel, but the employment of this combustible is by no means general at present, so that "sufficient for the day is the evil thereof."

The combustion of coal as a theoretical study is no doubt very well understood in many quarters, but judging from the large number of senseless and absurd patents that are taken out from time to time, there are evidences that the theoretical

study of combustion is often sorely neglected. One would think, that whether coal was cheap or dear, the user of it would endeavour to utilize the utmost amount of heat it is capable of giving out, but in practice we find this is not so, and in most coal burning departments the utmost waste and extravagance prevails.

Most coal users know fully well that the ordinary quality of steam raising coal will theoretically evaporate from 12 to 14 lbs. of water per lb. of fuel reckoned from 212 degrees ahrenheit, yet it is very rare that one meets with an evapora. tive efficiency of more than 7 lbs., even with boilers of good construction and setting.

It is also well known that in several exhibitions, well-known boilers, such as those of Messrs. Galloway, have evaporated as much as 11.8 lbs. of water from 212 F. per lb. of fuel, yet, when these same boilers are employed in ordinary practice, a much smaller duty is obtained. It is our object this evening to show how this comes about, but first of all it is necessary to show how, in ordinary combustion, smoke is produced, its composition, and the deleterious nature of its constituent or component parts.

Combustible substances ignite and burn at very varying temperatures. If I take some petroleum spirit, you will see that the mere application for an instant of a naked flame causes immediate ignition.

1. (Experiment on petroleum spirit.)

If, however, we treat ordinary paraffin oil in the same way, the liquid will actually extinguish the flame of the taper, instead of taking fire, as in the case of the petroleum spirit.

2. (Experiment with paraffin oil.)

If I now heat the paraffin oil, ignition takes place more easily, as you will see.

3. (Experiment by heating the oil.)

We may next endeavour to ignite a mixture of these two liquids when you will observe that the high inflammability of the one aids the apparent indifference of the other.

4. (Experiment on mixed liquids.)

You will also have observed, no doubt, that the paraffin oil did not burn with such a smoky flame as the petroleum spirit, and if I now show you the combustion of a liquid containing more carbon, such as benzene obtained from the dry distillation of coal, you will find that the flame is even more smoky than that of the petroleum spirit.

5. (The combustion of benzene.)

Solids generally, especially those of a semi-mineral nature, require considerably higher temperatures to start the ignition, and this is easily demonstrated by the application of heat to anthracite and graphite.

In the instances I have already shown you, viz :-The ignition of several liquids, the formation of smoke can be readily avoided by the proper regulation of the air supply, and the maintenance of the temperature of combustion. It would be rather difficult without the aid of expensive apparatus to show you this in a satisfactory manner, but by using ordinary coal gas, it can be readily exhibited.

8. (Bunsen's burner and Wanzer lamp.)

It will thus be seen that even with the most readily com. bustible substances, at least two conditions are necessary to avoid the production of smoke. The first is to ensure a proper adjustment of the combustible body and air, while the second is to maintain the flame temperature until the combustion has been completed.

These instructions appear very simple, but the carrying of them out on the large scale is by no means such an elementary problem as at first sight appears. We have principally to deal with the combustion of coal and that often not of the best quality. We will try the application of heat to it.

9. (Ignition of Coal by Bunsen and Batswing). The first application of heat to coal results in the volatilisation of the more volatile products, leaving behind the more fixed portion, or what is generally termed coke. This is what takes place when coal is thrown on a red-hot fire, either in a factory furnace or in a domestic fire-place, forming pulsations so to speak, in the combustion process, the emission of smoke being coincident with the commencement of each pulsation.

Roughly, but quite near enough for all practical purposes, -one third of the component parts of coal may be taken as being volatile under the application of a moderate degree of heat, and two-thirds remain fixed and only burn and pass off as gaseous products with the air supply properly maintained.

Now it is well known that when ordinary fuel is charged into a red-hot furnace, the distillation process occupies but a few minutes, and in that few minutes one-third of the weight of the coal charged in is driven off, while the air supply is tolerably constant, in fact, the large gaseous volume suddenly generated by the distillation of the coal must certainly check the in-flow of air at a moment when more is required.

Moreover, the gaseous portion of coal requires considerably more air for complete combustion per unit of weight than does the fixed portion. An example will perhaps illustrate the matter more clearly:

An ordinary 30 by 7 Lancashire boiler is usually made to burn rather more than 40 tons of coal per week of 132 hours; this amounts to 690 lbs. per hour, or 23 lbs. per square foot of grate area per hour reckoning 30 square feet as the area of the grates.

Working under good practical conditions, 220 cubic feet of air will be consumed per lb. of coal, so that every hour will see brought into the fire-places 690 × 220=151,800 cubic feet of air, which is 12,650 cubic feet every five minutes. We will suppose now that the fireman fires the furnaces every half-hour, and that he does-what I have very often seen done-viz., fire both furnaces of the boiler together. In this case 3 cwts. of coal will have to be thrown on each furnace every half-hour. Of this three hundredweights we have already seen that one-third is volatile and quickly driven off as combustible gas. It may be stated as being accurate enough for all practical purposes that this one-third will be evolved in five minutes, and that the residual twothirds burn off in the remaining twenty-five. Approximately then, one hundredweight of the gaseous portion is supplied with 12,650 cubic feet of air, and the two hundredweights of fixed fuel with 63,250 cubic feet. This calculated per pound of fuel is 113 cubic feet per pound for the gaseous portion, and 282 cubic feet for the fixed.

I am now speaking of an ordinary boiler, fired by hand and looked after in the best manner, and not overworked; the evil becomes much intensified when more than 40 tons of coal per week is burned under a single boiler. The gaseous portion of the fuel requires far more air per unit of weight than the fixed, yet in practice the reverse is actually obtained. This weak point has been observed and partially corrected by several inventors.

It is not my intention this evening to act as an advertising agent for those enterprising men who have endeavoured to solve the smoke problem. Most of them have been invited to attend here this evening, and to exhibit models or drawings or appliances of any special kind they may have designed for lessening or preventing smoke, and no doubt they will be able to explain to you such special apparatus much better than I can do.

My desire is to set forth, in as clear a manner as I possibly can, the broad principles which underlie the problem, so that smoke producers may not spend their capital unprofit ably when they endeavour to make a change.

Returning now to our remarks upon air supply, the extra requirements of air at the period when coal is newly charged onto the fires has long been catered for by many inventors. Every one who has written or spoken on the smoke question has for many years quoted Mr. C. Wye Williams, and the Parkes split bridge. The air bridge has been adapted to

many boilers, but after a few days use they are generally inefficient, having in a short space of time become choked up with ashes and flue dust. Moreover, in the hand-fired boiler the extra air is only needed when the volatile products are being so rapidly evolved from the coal; at other times, excess of air is decidedly injurious. It may be urged that most of these air bridges have dampers to open or close them; this is granted, but all I have seen without exception were, when examined, so clogged with flue dust, as to be im. movable either one way or the other.

Appliances to admit air to the furnace for so many minutes after firing, self-closing after that period, have been devised by several inventors, and are at work in a few mills to my knowledge; that is to say, they are fitted to the furnace doors, more than this I would not care to vouch for.

The official report of the London Smoke Abatement Exhibition, of 1882, contains descriptions of several appliances devised to give more air at the time immediately after firing. Hollow bridges, hollow bars, superheating chambers, and balanced doors, all provided to give more air.

What I wish to point out now is that too much air may be given.

In a well fired boiler, stoking by hand, the excess oxygen should not exceed 6.5% by volume in the products of combustion, when the sample of gas is taken over a long period, say two hours; whereas, in a boiler flue I once examined, the furnaces to which were fitted with split bridges and selfclosing louvre doors, the excess oxygen amounted to 13.2%, showing a great loss of heat by the chimney.

It needs specially to be observed that those inventors who have laboured to introduce excess air to the furnaces during the period immediately after firing were under normal and well defined conditions working in the right direction.

Those conditions were hand firing, and burning say 13 lbs. of coal per square foot of grate surface per hour; but 40 tons of coal per week means 23 lbs. per square foot of grate surface per hour when applied to an ordinary Lancashire steam boiler, and now-a-days a combustion of 36 lbs. per square foot of grate surface per hour is by no means un

common.

The first limit of coal consumption is very seldom exceeded in the tests made at Smoke Abatement Exhibitions, and hence their uselessness. A very indifferent stoker can prevent visible-smoke when burning coal at the rate of 13 lbs. per square foot of grate surface per hour; it becomes much more difficult at 23 lbs, while at 36 lbs. smoke prevention is almost impossible even with the aid of all the legion of smoke preventing appliances, save mechanical stokers.

The method of testing coals at the Smoke Abatement Exhibition, of 1882, will show us what the engineer of that exhibition imagined to be the proper rate of combustion: on page 141 of that report, the Welsh steam coals were burned at the rate of 8.68 lbs. per square foot of grate area per hour; Nixon's navigation coal, 11.82 lbs.; Northumberland steam coal, 16.73 lbs. and 20.87 lbs.; and artificial fuel, 11.26 lbs.

Complete combustion can only take place when the combustion temperature is maintained; any influence which tends to lower the temperature, within certain limits, tends also to retard combustion. Time is also a material element, so that when the firing is excessive the partly burned gases are hurried out of the hot fireplace and brought into contact with the comparatively cool boiler-plates, thus causing smoke. In an ordinary boiler, burning 23 lbs. of coal per square foot of grate surface per hour, the furnaces have each but a capacity of 21 cubic feet, and as this quantity of air is admitted every second of time, the high pressure of the opera. tion goes without saying.

But the air enters say at a temperature of 70° F. and before it leaves the furnace, or thereabouts, has become expanded to at least four times its original volume, so that not only has the temperature of 2000° F. to be attained in the fourth part of a second, but the space in the furnace above the grate bars must be filled and emptied four times in each second. I have never seen the problem put in this way before, and it will furnish all coal consumers with much food for reflection, and it will also serve to impress upon inventors the necessity of the time element, as against the admission of air only.

Having now shown the necessity of time and the maintenance of the temperature of combustion as applied to hand firing, we may turn our attention to other means that have been designed to overcome some of the difficulties I have already pointed out.

It will naturally have occured to you at this stage to enquire whether the distillation of the coal into one-third gas and two-thirds fixed coke could not be carried on simultaneously with the combustion of both of them, in fixed and regular quantities, so as to avoid the pulsations already spoken of as smoke-pulsations, and to avoid also the irregularity of the air supply, so detrimental to perfect combustion.

This brings us to another stage of the enquiry.

If the coal necessary for any required degree of combustion could be dusted on to the white-hot fire in a continuous stream, and in the exact ratio required for complete combustion, everything would go well until the capacity of the furnace for complete combustion is over-stepped. Many inventors have endeavoured to accomplish this and many have succeeded in producing very good specimens of what are now known as mechanical stokers.

There is not time to go into the details of these appliances in the short space of an evening lecture, but as I have already said, the makers of many of these things have been invited to be present to-night, so that no doubt they will be pleased to explain their contrivances to you.

What I have set myself to do, is, to bring before you what are considered by many the strong and weak points of mechanical stokers as applied in practice.

The first remark must be a general one, and the good old engineering maxim, that "no machine is stronger than its weakest part" bears upon it.

Break-downs have sounded the death knell of many a mechanical stoker, and in many instances blame has been cast upon the principle of stoking mechanically, when it ought to have been thrown on the constructive engineer; but experience begets perfection, and the lessons of the past have not been disregarded by the inventor of to-day.

The many mechanical stokers are all of them capable instruments in the hands of an ordinary fireman. They feed in the coal regularly, most of them break up and discharge the clinkers, and all of them when not worked beyond their capacity, give a chimney absolutely free from visible smoke.

If the foregoing statements be true, and it must be admitted they are, why is it that the mechanical stoker is not universally adopted? There are several reasons-the first, that many steam users grudge the extra outlay on the boilers is sadly too true. Secondly, many have been led to expect a large per cent. saving in £. s. d., which has not perhaps been realised, and the knowledge of this has led their friends to hesitate in adopting the invention, but, any. how, the gain is to the public in having a less-contaminated atmosphere, and fewer smoke-begrimed buildings to disgrace our public walks.

I am of opinion that a well-arranged mechanical stoker will always show a better utilisation of heat units from the coal over even the most perfect hand-firing, but cæteris paribus the difference is not always so appreciable as some inventors would have us believe.

The greatest drawback, however, to mechanical stoking is the fluctuating requirements of the steam user.

In mills merely running a steam-engine, mechanical stokers will act admirably, but in the case of bleach-works, papermills, or chemical works and such like establishments, where a small and regular supply is required for several hours together, and then suddenly, and without warning, the whole steam-raising power is brought into requisition, the mechanical stoker is not suited, unless it be specially arranged.

There is no insuperable difficulty in this, but it is a noteworthy fact that these little arrangements are often not thought of inside the works where they are required until suggested by an outsider. In one works in which all the boilers were so well provided with mechanical stokers that one could not tell whether the factory was in operation or not by a mere inspection of the chimney top; the steam

required in large volumes intermittently brought down the pressure in the mains to near 7 lb. per square inch, so that some plant in which I was interested, was brought to a standstill. Some of the workmen began at once to argue against the efficiency of mechanical stokers, not realising the fact that the stokers were blameless; but this was soon put right by detaching a boiler from the set, for high pressure duty, which of course overcame the supposed evil.

A well-proportioned and carefully-fired Lancashire boiler, whether manipulated by hand or by a mechanical stoker, should allow of the transfer of not less than 80 per cent. of the theoretical heat of the coal to the water when an econo. miser is used in connection therewith; the heat lost by the chimney gases should not exceed 10 per cent,, nor should the loss by unburned carbon in the ashes exceed 23 per cent.

As I have many times publicly pointed out, the smoke difficulty lies in a nutshell. If the boilers are carefully hand fired and the coal is burned quietly, say at a rate not exceeding 12 lbs. per square foot of grate surface per hour, and with an air supply produced by a chimney draught equal to 220 cubic feet at 62 F. per lb. of fuel, there will be no visible smoke. As we increase the quantity of coal per unit of time over a given area, so we increase the density of the smoke shade, until, when all restraint is removed, smoke of Stygean blackness is constantly emitted.

The case I have already put before you, in which the steam pressure in the mains became reduced to 7 lbs., is not a matter that could be allowed to happen in every works, and it is doubtful whether it was an economical proceeding in the factory where it was wont to happen. It is, however, not an uncommon occurrence, and is a fault that has been considered by the makers of nearly all the mechanical stokers, so that most of these appliances are now provided with independent firing doors, that when a sudden call is made for a large volume of steam, that call may be met by extra hand firing.

Here lies the secret of smoke production where there is a mechanical stoker. A boiler furnace already fired to its full capacity is perhaps suddenly made to burn three times as much fuel as when it was working smokeless, and perhaps with the same supply of air by the chimney; but even suppose that an increased ratio of air be supplied it would then mean that the furnace would have to be filled and emptied of its gaseous contents no less than twelve times in every second.

If this extra firing is not done, what is the result? Steam down, kiers idle, and the workmen affected, engaged in those saintly exhortations so characteristic of the workman of to-day.

I would not have you to suppose that the mechanical stoker is the only appliance devised to secure freedom from smoke.

The mechanical stoker cannot properly be called a smoke consumer. It is simply an apparatus to feed the fuel into the furnace in a continuous and scientific manner, and to give easy access to the air supply, by breaking up the clinker, causing it to leave the fire-bars; it allows of an almost perfect regulation of the air supply, so that much larger quantities of coal may be burned on a given grate area without smoke being produced.

There is a range of boilers working in Liverpool to-day fitted with a well-known mechanical stoker, each boiler burning 1,120 lbs. of coal per hour without producing smoke. Why, then, should visible smoke be allowed in our Northern towns?

At this point, some of our steam-using friends may be tempted to enquire respecting the merits of undergrate blowers.

Now it is a well-known fact that less air is required for combustion per lb. of fuel burned when the air is forced into the furnace than when the products of combustion are simply withdrawn by the chimney draught, and it is possible that some day steam users will settle down to the mechanical stoker, combined with an undergrate blower, as the orthodox method of steam raising.

In the Permanent Chemical Exhibition you will see drawing of a system of undergrate blowers of which I happen to know the details of a recent installation.

Up to the date of the change the boiler was fired with ordinary boiler slack at 12s. 6d. per ton, divided in quantity equal to, say, 45x tons, producing y volumes of steam. With the undergrate blowers y volumes of steam are now produced by the combustion of 44x tons of dross, costing 3s. per ton, and with the advantage of a smokeless chimney.

The earliest patent for steam raising, in which the prevention of smoke was considered, was taken out by James Watt in the year 1785-just 105 years ago. Have we made any advance in the matter during these 105 years? When I look round the neighbourhood of all large manufacturing towns and see the clouds of black smoke issuing from the chimneys, when I observe the smoke-begrimed buildings in our city streets, I am tempted to think that if our forefathers were worse off than we are now, the "good old times" must have been rare old times indeed.

We may now turn our attention to another system by means of which coal may be burnt smokelessly, that is, by first converting it into gas.

All of you have heard, no doubt, of water-gas; well, no one would think of firing steam boilers with water-gas, but what is called "producer-gas" may often be, and is, so employed.

Producer-gas is a by-product, so to speak, of water-gas, but it is also produced as a substantive product in the Siemens, Dowson, or Wilson producers. It is very easy to burn this gas without producing smoke, but though some few have stated that there is a pecuniary advantage in using it, yet I believe that this is so only under special conditions, and under special circumstances.

Producer-gas must not be confounded, in any way, with coal-gas as we ordinarily know it. The heating powers of the two are very different and must be duly considered.

One lb. of coal-gas will give out 12,233 units of heat, while a pound of the best producer-gas will give out but 1,000 units.

To put it more plainly, 12 lbs. of producer-gas will not do more heating than 1 lb. of coal-gas, even when the producers and the combustion are well managed, while if they are badly managed, gaseous fuel may become a very expensive luxury indeed.

Producer-gas is, bulk for bulk, nearly twice the weight of coal-gas, so that 6,000 cubic feet of Dowson gas are only equal to 1,000 cubic feet of coal-gas, and if, as stated, Dowson gas can be made for four-pence per 1,000 cubic feet, this is equal to using coal-gas at two shillings.

The tests made at the Smoke Abatement Exhibition of 1882 with this gas, as compared with coal-gas, show a ratio of 4'17 to ro, but I am inclined to the opinion that this is to favourable for general practice.

The industrial application of gaseous fuel seems inclined to receive a fresh impetus through the introduction of Mr. Mond's patented process, in which ammonia is recovered from the products of combustion or rather from the products of the gasification.

We may now turn our attention to the composition of the gaseous products of combustion, from ordinary coal and coke.

The gases from the flues of a carefully-fired Lancashire boiler, not overworked, may be stated as :