Feed Water and Cooling Water.
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The Importance of Cleanliness: its Effects on the Efficiency of Steam Boilers and Petrol-engine Water Coolers.
By Geo, W. Watson, M.I.Meeh.E., M.I.A.E.
My recently-completed annual inspections of a large number of vehicles and tractors owned by members of the Commercial Motor Users Association have convinced me that the importance of cleanliness, as regards the interior surfaces of boilers, radiators, cylinder•jackets, water tanks, etc., is not yet fully appreciated by owners. Many drivers are most scrupulous in their attentions to these matters, but at the present time, when so many vehicles are in the hands of men without much .experience, a few notes on the causes, effects and prevention of scale may not be out of place.
The causes of scale formation are practically the same both in a boiler and a radiator, the difference in the effects being only one of degree. It is proposed, therefore, to take the case of a steam wagon or tractor boiler first, and later to apply the facts as they relate to the cylinder jackets and radiator of a petrol-engined vehicle.
The Perfect Boiler.
Apart from the design of a steam boiler, the important considerations for the efficient generation of steam are : first the nature of the fuel, and second the general cleanliness of the boiler, so that there shall be no available waste in transferring the heat of the fire to the water. Both these are matters which are entirely in the hands of the owner and driver, and no matter how good the design and construction of a boiler may be, if it is badly fired with an unsuitable fuel, and its inner surfaces kept in a filthy and scaly condition, the fuel cost per ton-mile of work performed will be abnormally high, even if the price per ton of the fuel used is exceptionally low. Then there is another point to be taken into consideration, apart from efficiency, and that is the cost of boiler repairs, which are invariably higher if a boiler is kept in a dirty condition.
One pound of coal is capable of producing a definite quantity of heat under given conditions, and we generally speak of any particular quantity of coal as having a value of so many British thermal units. One B.T. TJ represents the quantity of heat that is required to increase the temperature of 1 lb. of water by 1 degree Fahr. when the water is at its maximum density, which, for all practical purposes may be taken as between 39 degrees and 40 degrees Fahr. A perfect boiler would utilize every single unit of heat which is given out by coal, but the perfect boiler has not yet been, and probably nevtr will be, made, as a certain amount of heat always escapes up the funnel in the form of hot gases, a further quantity is lost by radiation from the firebox, and the remainder is given up to heating the water and converting it into steam.
The Need for Clean Bailers,
The size of a wagon or tractor boiler must necessarily be as small as possible, in order to keep the tare weight of the vehicle within the limit set by the Heavy Motor Car Order, and for this reason it is not possible to allow water spaces so wide as will be found on large land boilers, but by frequent washing to clear away all the deposit left by dirty or unsuitable water before it has time to harden, a small boiler may always be kept in good steaming condition. The use of a good boiler fluid may help to prevent hard deposits being formed, but such a fluid should not be used carelessly or indiscriminately; advice should be taken on this point before use, as so much depends upon the class of water which is being principally used. Drivers should never be allowed to shirk the boilerwashing part of their duties, and owners must do their part by giving the wagon a regular half-day in the shed for this purpose. It is not sufficient to admit clean water at the filling plug, and let it run out at one of the muclholes, or through the blow-off eock, but all the mud covers should be removed at each wash-out, so that a cleaning brush or stirring rod can be passed along each side of the firebox to stir up the deposit., and, make sure that it is all washed away. The hand-hole, or manhole, and any other cleaning holes that may be provided, should also be opened to make sure of a clean job. At the same time that the boiler is washed out, the feedwater tanks should also be thoroughly cleansed., as it is not much good having a clean boiler if it is to be fed again from a dirty tank.
• The Causes of Seale.
Let us now consider the causes of scale and deposits in boilers. I do not profess to be an analytical chemist, but from practical observations and experience I am satisfied that when a boiler is fed with water containing solid matter, especially hardening salts in solution, a coating is formed on the plates and tubes, which, unless removed, will have the effect of decreasing the boiler's efficiency, as explained later, as well as being a source of danger due to local overheating of the metal. According to the findings of analytical chemists, this scale or deposit may be caused by various ingredients present in the water, of which a few examples are here given. Calcium carbonate, popularly called chalk, is absorbed from the strata through which waters flow, by the agency of the dissolved carbonic acid, which combines with the carbonate of the chalk and forms bicarbonate of calcium, which is soluble, and is the actual state in which the chalk is present in water. When the water is heated this bicarbonate loses the carbonic acid gas and reverts to carbonate of calcium, which, being insoluble, is deposited, and is the explanation of the temporary hardness of waters. This explanation applies also to bicarbonates of magnesium which occur in some waters.
Sulphate of calcium, popularly called gypsum, is very slightly .soluble in water at ordinary temperatures, except in the presence of certain other salts which tend to increase its solubility. In hot water this substance is almost insoluble, hence it is deposited when the water is heated after a certain degree of concentration is reached, or, at times, under increased pressures, and unless it is counteracted the deposit consisting of this sulphate of calcium is hard, more or less compact, and greatly retards the transmission of heat through the boiler plates ; hence the importance of minimizing the degree of concentration of the water in a boiler, this being done by emptying the boiler at frequent intervals and refilling it with a fresh supply of the feed-water. Sulphates and nitrates of magnesium are also sometimes found in feed-waters, and these are objectionable in a steam boiler only wen the amount of chlorides is high 'and the proportion of carbonates low, in which case these salts undergo decomposition in the boiler and react with the chlorides, producing hydrochloric acid, which, like acids generally, is destructive to the metal of the boiler. Chloride of magnesium, usually indicative of the B31 presence of sea or tidal water, acts in the same way as the compounds mentioned, but produces the acid directly by its own decomposition. Hence this is a very undesirable constituent of feed-waters.
Sodium chloride., commonly kcalled salt, has no action on the boiler, but tends to cause priming, and, as explained, acts by decomposition when magnesia is present.
Sulphate of sodium is present in many, if not all, waters, but is quite inert, and only a,dds to the fixed solids.
Different Results Call for Different Treatment.
From the varioua data ascertained from analytical chemists, it will be found that the analytical results with any sample can be classified under one or other systematic group headings. R will be admitted that such a classification must be made in the case of any. proposed effectual remedy ; therefore, notwithstanding the general similarity of the salts in feed-waters, the quantities and proportions vary, so that the scale resulting from the evaporation of different waters varies in structure, appearance, and percentage composition. Chalky waters give a -white or yellowish-white, somewhat brittle, scale.
Ferruginous, or iron, Watars usually give hard scale of a compact granitic character ; when broken, the fractured surface is red or black. • Silicated waters give gritty, brittle scale, very hard in the presence of iron oxide.
Carboniferous waters usually yield a comparatively soft deposit of a black, sooty character,
A composition could be supplied which would, more or less rapidly, have the desired effect of causing the disappearance of existing scale, but as it is only acids that will cligsolve scale, it follows that a composition claiming -to do this must be unsuitable in a boiler, and no engineer, knowing the connection between the presence of acid and the dissolving of scale, would care to use such a preparation.
The Effects of Scale.
If a boiler is regularly and thoroughly washed, as advocated, the formation of scale will be prevented, or, at any rate, minimized. A very little scale will soon decrease the efficiency of a boiler very
seriously ; for instance, scale only in, thick will reduce a boiler's efficiency by about 10 per cent., and if it is allowed to increase to in., a,s often found in steam-wagon boilers„ there is a heat loss amounting
to 18 per cent. Even taking-the scale at ala which is quite commonly found, its presence means that at least 10 per cent. more fuel must be burnt for each ton-mile of work performed. This is a point that the owner should consider, and if it is put to the driver that the presence of that amount of scale means extra work for him for shovelling on the coal, there should be no difficulty in convincing the man that his best plan is to make a clean job Of his boiler on the shed .day, in preference to, putting in an extra 10 per cent, of stoking throughout the Kest of the week.
The Prevention of Scale.
As previously stated, scale can only be dissolved by the action of acids, but as such a courae has most damaging effects, its use cannot be considered. If scale has already formed in a boiler as much of it as possible should be caret idly scraped or chipped away. " Prevention is better than cure," however, and it is preferable to take steps for preventing, or ,minimizmg, the formation of scale. There are two ways of effecting this : either by removing the scale-forming salts from the water before it enters the boiler,, or bv,treating the water inside the boiler with something which will act upon these salts in the manner r don ire d.
32 The majority of steam users prefer to treat the feedwater inside the boiler, the general action of that which is added to the water being to cause the hardening salts dissolved to become at once insoluble. There is an erroneous idea that the occasional use of common soda, is all that is required in a steam boiler, and that its so-called cheapness is in line with its efficiency. The action of soda on the salts in the water is entirely a chemical one, and this is only possible under certain conditions. The use of soda renders steam boilers liable to prime, it affects the joints' and valves, corrodes them and •induces leakage, and it is also subject to variation in quality.
The use of a non-acid boiler compound, such as " is far preferable. This preparation, a viscous' fluid, consists chiefly of a carbon compound which has no action upon iron, steel or other metals, but which has the valuable property of rendering all water impurities innocuous and incapable of forming scale, whilst it also has the effect upon existing scale which may briefly be explained as follows : —It works its way through the interstices of the scale, the rate of this Percolation depending on the porosity and degree of compactness of the same, and when the preparation reaches the underlying plate of the boiler, it there diffuses and insinuates itself behind the incrustation, causing it to crumble and flake, so that when the boiler is opened it can readily be 'removed.
This preparation as a preventive of scale differs from the old style of boiler composition, inasmuch as it absorbs the gaseous carbonic anhydride from the water, forming an intermediate salt which throws the scale-forming salts out of salution, suspending them in the water in a non-crystallizable and powdery state. Incrustation is thus forestalled and prevented. Steam generated from sea water containing " Boilerine " is free from ammonia. Other strong recommendations which .have contributed greatly to its success and widespread adoption are found in the facts that : (a) aia is Mit only a preventive, but also a disuniter of incrustation in boilers' (b) it is absolutely non-volatile, and does not affect the purity of the steam pro. (Weed from water treated with it; (c) it does not –discolour the water in the 'boiler, and it will not cause priming. It is guaranteed free from arsenic, acids and poisonous substances, and, being a good neutralizer of grease and acids, is an enemy to corrosion and pitting. The fact, that the National Physical Laboratory, Bushey House, Teddington (controlled by the Royal Society), have given it a prolonged trial in their engineering department and have continued to use it since 190B, is notable evidence of its. quality, and of its acceptance in the scientificworld.
Water Action in Radiators.
Thus far I have dealt only with steam boilers, but the same set of objections to water impurities apply also to cylinder jackets and radiators (or more correctly .speaking, water-coolers) for petrol-engined vehicles. The circulating water of the average petrol wagon is only drained off when repairs become necessary to the radiator ; very few users appear to realize that, when held in contact with iron or steel, water gradually decomposes, and in consequence the metal suffers corrosion. The corrosive action is increased in proportion to the rising temperature. The heating of the water also causes the lime salts to be deposited in the form of a thick grey slime, which, in time, hardens like stone, adhering to the metal and ultimately choking the passages. The efficiency of a radiator, thereby, is quickly reduced. Considering the complex character of the small passages in a motor-vehicle radiator, the importance of preventing their becoming partly, or wholly, choked will be appreciated. Urileas a suitable preventive be added to the water, the only possible way to keep a radiator up to its ina,ximum efficiency is to run off the water very frequently and wash all passages dear of muddy deposit before it has time to harden.
Once a radiator becomes thickly coated with scale it is almost impossible to remove it; if the scaling action has progressed so far that the engine cannot be run without overheating, it would probably be cheaper in the end to fit a new radiator, or at least a new tube block. Many owners resort to the use of soda, but if any part of the radiator or piping be made of aluminium the effect might be disastrous. In any case, soda would only be partly effective, and if grease were present in the water, as it invariably is in a radiator, the soda would so act upon the grease as to make the deposit adhere more easily to the tubes and walls. Any saponified oil by combining with the lime and magnesia in the water, forms an insoluble curdy deposit such as may be seen sticking to the sides of wash basins; this deposit can only be removed by friction—clean water alone has no effect upon it.
, Aluminium and Soda.
Reference has already been made to the possible disastrous effects of soda upon aluminium. A few months ago I had an experiment made to show the wasting effect which common washing soda has upon aluminium alloy such as is used in radiator construction, and the results speak for themselves. For the purpose of this experiment a piece of aliiminium measuring 2K ins, long, by in. wide and in. thick, was taken. This was thoroughly cleaned and washed in sodium hydrate (Na HO), and dilute sulphuric acid (H2 SO4). After drying in an air oven it was cooled and found to weigh 3.6552 grammes. It was then immersed in a bottle containing washing soda, prepared of the strength of 2 lb. to the gallon of London tap water. The water containing the test _piece was then kept boiling for five hours, at the end of which time the aluminium was remove& carefully and thoroughly washed in distilled water, and dried in an air oven at 180 degrees Centigrade. The test piece was then cooled in a dessicator and found to weigh 3.6170 grammes, showing a loss of 0.0382 grammes due to the action of the soda ; this is equivalent to 1.04 per cent, reduction in weight during five hours.
Radiator Cleansers.
Many preparations have been offered which are claimed to be effective in the removal of deposits, but I have not yet found one that doe g not do more damage than the scale itself. If I may again use an old tag " Prevention is better than cure," and it applies to radiators as forcibly as boilers.
I have tried many patented preparations with this object in view., but my experience has been that the best of these is known as Boilerine " radiator tablets. These, presumably, are prepared on the same scientific basis as is their maker's boiler compound. By their use the water in the radiator, and therefore the tubes' is kept clean, the circulation is unimpeded, the radiation is maintained at a maximum, and the risk of choking the channels avoided. Analysis by "The Lancet-" disclosed no corrosive action on metals when used in the quantity directed, which is, of course, based upon the degree of hardness of the water. For London water two tablets to the gallon are sufficient. A soluble combination of the lime salts of the water with the ingredients of the tablet is formed which has negative properties in regard to metal. It is claimed also for this compound that in time it is effective in removing existing scale, for which purpose it is suggested that it be used in the proportion of 50 to 100 tablets per gallon, draining the water out after 100 miles of running and flushing the radiator. with clean water. After a few repetitions of this treatment it is claimed that the scale will practically be removed. Future water used should be treated, to prevent deposit, rust or corrosion, by the addition of one tablet for eaeh seven degrees of hardness. The cost for effective treatment in this way
for a very badly scaled radiator may, however, prove greater than that of a new tube block or complete radiator. For this reason I think it should be considered rather in the light of a preventive of scale, than an economic cure of "a bad case," the action on hardened scale being necessarily slow. Preventive treatment equalizes all waters, whatever the hardness.
Interesting Experiments.
In order to show that these tablets have no action whatever upon aluminium, but to a very large extent reduce, or prevent, the corrosive action of water, a series of comparative tests were made last year by Mr. W. F. Nicholson, B.Sc., of Messrs. Parker and Lester, manufacturing chemists.
The 'first of these tests was with two strips of aluminium, which, after being thoroughly cleansed, dried and weighed in the manner already discussed, were boiled in main water, having 19.4 degrees of hardness, on a. sand bath for ihree hours. The water used for one of the test pieces was untreated and the other treated with tablets at the rate of three tablets to the gallon. The specimens were then placed in bottles in the liquid in which they were boiled, and the bottles sealed. Thirty days later both bottles were opened, and after the specimens had been thoroughly washed and dried, that in the untreated water was found to have last 3.04 per cent, of its weight by corrosion, whilst that immersed in the treatedsolution had lost only 0.076 per cent. , A further test, of a month's duration, with a specimen immersed in a, stronger solution (100 tablets to the gallon) showed that there was absolutely no change in its weight, thus conclusively proving that, even when used of a strength of 20 to 50 times greater than is recommended as means of preventing scale formation, no harmful or metal-corroding action was experienced. The tablet-treated water, as already stated, has no damaging effect upon metal, neither does it have any effect upon rubber. I have made many experiments with these tablets, and each one has strengthened my conviction that they are not only efficacious, but perfectly safe to use. In using any preparation which has the property of retaining foreign matter in solution with the water, it is, of course necessary to empty a radiator about once a fortnight and fill up with fresh clean water ; otherwise the solution would become so concentrated that it would no longer hold the matter in solution, and some would be precipitated.