ELECTRICITY IN DAIRY FACTORIES.*

New Zealand Journal of Agriculture, Volume XXVII, Issue 5, 20 November 1923, Page 310

ELECTRICITY IN DAIRY FACTORIES.*

C. V owell,

Assoc.A.I.E.E., Grad.I.E.E., London, in the New Zealand

Journal of Science and Technology.

The value of electricity to mankind lies in the three main effects it is capable of producingnamely, (i) magnetic effect, (2) heating effect, (3) chemical effect. •

The first, which is always present when any electric current flows, is the most important of all. Upon it depends the working of all electric bells, telephones, telegraphs, electric motors, and electromagnetic apparatus. Electric motors alone now supply many millions of horse-power. The magnetic, effect produced by an electric current is directly proportional to the current producing —or, in other words, if the current is doubled the magnetic effect is also doubled.

The heating effect, which is second in importance, is also always present whenever an electric current flows, and is also directly proportional to the current producing it. Upon the heating effect depends all electric lighting, heating, cooking, &c., as well as the operation of the electric furnaces used for making calcium carbide, carborundum, and nitrogenous compounds for use in manures and explosives, &c.

Chemical effect : Under suitable conditions an electric current will also produce a chemical effect, which, • like the others, is also directly proportional in amount to the current flowing. ;

In dairy factories the chief uses to which electricity may be applied are the driving of the machinery by electric motors, and the heating of water and milk. Before discussing the various methods of driving dairy-factory machinery by electricity it will be helpful to define the main electrical terms.

The electrical unit of pressure, which is analogous to pounds of pressure per square inch in steam, is the volt. One volt of electrical pressure is a little less than the pressure that would be obtainable from a single-cell battery such as is used for ringing electric bells. The unit of current is the ampere, and is analogous to the volume of steam passing through a steam-pipe. The power supplied to a steamengine depends upon the pressure of steam in the steam-pipe and the volume of steam passing through the steam-pipe. Exactly the same is the case with electricity : the power supplied to an electric motor depends upon the current and the pressure of voltage at which that current is supplied. - ; ■ \-

For power, the unit is the volt-ampere or watt, the power in watts being the product of volts and amperes. As the volt-ampere or watt is a very small amount of electric power, a larger unit is used, known as the kilowatt, which is 1,000 watts. It will be interesting at this stage to note that 746 watts, or about three-quarters of a kilowatt, are equal to 1 horse-power.

With steam working, the amount of energy supplied by a steamengine is measured in horse-power-hours — or, in other words, the

horse-power developed by the engine multiplied by the number of hours it has been working. Similarly, with electric power the amount of energy supplied is measured in kilowatt-hours, or the number of kilowatts being supplied multiplied by the number of hours’ duration of the supply. The kilowatt-hour is commonly known as the Board of Trade unit, and is spoken of merely as the unit of electricity.

The Southland Electric-power Board rates for electric energy, per unit per month, are as follows : For the first 21 units, yd. ; for the second 21 units, 4d. ; for the following 42 units, 2|d. ; for all over 84 units,

It will be seen from this sliding scale of charges that the more electric energy consumed the lower will be the average price per unit. Take, for example, a consumer using 100 units per month : his bill will come to £1 10s., or an average of 3 - 6d. per unit. If he consumes 200 units per month his bill will be £2 2s. 6d., or an average of 2-55d. per unit; and if he consumes 300 units per month his bill will come to £2 15s., or an average of 2-2d. per unit. It is therefore apparent that the greater the use made of electricity the lower will be the cost per unit or per horse-power-hour.

In tests on the driving of separators by electricity and steam which were carried out recently the following methods were employed. The results are valuable, and they go to prove, that dairy factories in Southland' cannot afford to use steam where electricity is available at the above rates. . .

In the steam test half a ton of coal was carefully weighed out and reserved for use during the separating-period. The fire was worked into good condition, and 100 lb. of steam raised on the boiler. This head of steam was maintained approximately constant both before and during the separating-period. As soon as the separators were started the boiler was fired from the half-ton of coal specially reserved. At the end of the separating it was calculated that nearly a quarter of a ton of coal remained. The cost of the coal (Kaitangata) delivered into the bunker is £1 us. per ton, and the quantity of whey separated was 3,000 gallons. Thus the coal-cost of separating 1,000 gallons of whey by steam-power works out at slightly over 2s. yd., or 3-rd. per 100 gallons. It must be noted that the fire and boiler were left at the end of the test in the same condition as at the beginningthat is, with a full head of steam. The quantity of coal burnt in raising steam has not been added in ; if it were, the cost of separating by steam-power would be still higher.

In the ' electric test the A.V. 6 Alfa-Laval separator was driven by an electric motor, by means of Vowelks constant-tension drive. A house-service type of kilowatt-hour meter was installed to measure the quantity of electric'energy consumed. The separator was run up to speed for a consumption of o-88 unit. The speeding-up occupied 28| minutes, the constant-tension apparatus being set for a slow acceleration. ...

Separating was commenced and continued for one hour, during which time approximately 600 gallons of whey were separated for a consumption of 2-59 units, or a total consumption from the commencement of speeding-up of units. Had separating been continued for a longer period the proportion of the energy consumed in speeding-up

to that used in separating would have been less. If we neglect the energy consumed in speeding-up, the consumption of electricity per ioo gallons of whey separated works out at 0-431 unit, or, including the energy consumed in speeding-up, 0-578 unit.

In a second test 200 gallons of whey were pumped into the separator-vat, and it was found that the time occupied in separating this quantity was 18 minutes, and the consumption of electricity 0-72 unit, or 0-36 unit per 100 gallons. This does not include energy used in speeding-up.

In a third test two separators were driven by steam and one by electricity. It is assumed that the one driven electrically separated one - third of the day's total quantity of whey, which was 2,850 gallons., The total consumption of electricity, including speeding-up, was 5-08 units, or 0-53 unit per 100 gallons of whey separated. From the. foregoing test the average consumption of electricity for 100 gallons of whey separated, including speeding-up, works out at 0-554 unit. Taking the last season’s whey at 722,188 gallons, the consumption of electricity for separating during the nine and a half months that the factory was open would have been 4,000 units, which would have cost £33 15s. The consumption of coal chargeable to separating for that period was not less than 6o-i8 tons, costing £93 5s. 6d. The saving in favour of electricity is thus £59 10s. 6d., or 63-8 per cent.

ADDENDA.

On 30th May, towards the close of the season, when the supply of milk had reduced sufficiently to allow all the whey to be skimmed by one separator, the following results were obtained in a steam test using Mataura lignite (which is delivered into the bunker for 14s. pd. per ton) for fuel.

Whey separated, 793 gallons ; fuel consumed, 3| cwt. ; cost, 2s. yd. Cost per 100 gallons of whey separated, 3-pd.

In an electric . test made on 2nd June, when all the whey was skimmed by the same single separator but driven by electricity, the following results were obtained : Whey separated, 922 gallons ; electricity consumed, 4-38 units ; cost (estimated on probable season’s consumption), 8-88d. Consumption per 100 gallons of whey separated, 0-475 unit. Estimated cost per 100 gallons of whey separated, id.

It will be seen that the consumption of electricity in this test, is 0-079 unit per 100 gallons of whey separated less than in previous tests. This is probably due to better adjustment of the driving-apparatus. It will also be seen that the cost by steam was o-8d. higher per 100 gallons of whey separated than in the previous test. This is due to the inherent inefficiency of collective driving, which becomes more apparent when a factory is working at part capacity. In this case only one out of three separators was in operation. The higher cost also suggests that, although the fuel being used was less than half the price of that used in the earlier test, the. increased amount required renders it less economical.

It must be remembered that this is the saving in the fuel bill alone if only the separators were driven electrically. If the rest of the machinery were driven electrically the percentage of saving would

be even greater, owing to the gradually reducing price per unit charged for electricity. Other economies would be effected, such as reduced maintenance of boiler and engine, reduced renewals of belts, reduced consumption of oil, saving of labour in boiler and engine attendance, &c. The very considerable economy effected by the use of electricity is due in no small measure to the efficiency of the constant-tension drive, which has the unique function of maintaining a perfectly uniform turning effort on the pulley of the separator. Even the slight variations which would be produced by sticky or greasy patches on the belt are compensated for.

This brings out an important point in the electrification of dairy factories. Had a large motor been installed in the engine-room little or no saving would have been effected. A little consideration will make this clear. The electricity used at Wyndham is generated in Invercargill by steam-power and then transmitted a distance of twentyseven miles. If the steam-engine is merely replaced by an electric motor of equal power its operation at Wyndham would necessitate the consumption of an amount of coal at Invercargill power-station nearly equal to that required by the present steam-engine, the only economy it would be possible to effect being due to the higher efficiency of the steam plant at Invercargill power-station as compared with the efficiency of the small steam-engine and boiler at the factory.

It is only -by careful and scientific installation of motors of the correct power and specially designed for the particular machine they are to drive that the maximum economy may be obtained. Collective driving by electricitythat is, driving the whole factory by one large motoris comparatively inefficient, although it still has to be used in the case of steam-power. Individual drive — that is, one motor for each machine or group drive, in which case two or more similar machines are grouped together and driven by one motor the more efficient method of applying electric-motor drive. Each method has its advantages and disadvantages, and these have. to be carefully considered with relation to the cost of installation of each method.

Individual drive has the advantage of allowing of direct coupling to the driven machine, or where belting is necessary it is reduced to a minimum : this reduces maintenance and running costs in belt-renewals and oil. A further advantage is that a 'motor of the exact power required to drive the machine may be used. It also enables the motor to operate at higher efficiency, for the reason that electric motors, in common with other prime movers, operate most efficiently at or near their full load. Another advantage of individual drive is that the driven machines, together with their motors, may be made selfcontained units. This is of great advantage where there is a possibility of the plant having to be moved or reduced in size, or where part only of the plant is required at the beginning or towards the end of the season.

One disadvantage of individual drive is that the capital cost of several small motors is greater than that of a few of larger size, giving the same . total horse - power. Another disadvantage becomes of importance when the machines to be driven require only little power. This is due to the fact that small electric motors have an inherent

lower efficiency than large ones. It is on account of these two disadvantages that the group method is used. To obtain the maximum economy with group drive, only similar machines, or machines with similar operating characteristics, should be grouped together. Of +hese machines only those which start up and shut down at the same time should be included in one group.

The chief advantage of group drive is that fewer motors are required, which reduces capital cost; also, the motors used are larger, and therefore more efficient. Machines which occupy a large floorspace relative to the power required by them should not be grouped, as the loss of power in belts and shafting more than offsets the increased efficiency of the motor ; also, the capital cost of the belts, shafting, plummer-blocks, &c., more than offsets the reduced price per horsepower of the larger-sized motors.

Electricity for heating purposes in dairy factories does not show up to the same advantage as for power. In fact, in Southland, with its abundance of lignite easily mined, electricity for heating purposes on a large scale cannot compete. The reason is that £i worth of coal contains vastly more heat-units than £i worth of electricity. Smallsize electrical - heating apparatus, such as electric kettles, are now made with the very high efficiency of 80 to 90 per cent., which enables electricity to compete favourably with such inefficient appliances as a cast-iron kettle heated on an ordinary fire. When, however, the more efficient system of heating by high-pressure steam is used, generated by an efficient steam boiler, the cost of heating by steam is considerably lower than by electricity. It. must be remembered, however, that for heating small quantities of liquid electricity is probably the next cheapest source of energy, and also possesses the great advantage of being ready for use at any time of day or night, and may be automatically regulated.

At the present time the tendency in pasteurizing is to increase the speed with which the temperature of the milk is raised and lowered. Electricity would be capable of giving a higher temperature surface than steam, and therefore could be used more efficiently than steam in a flash pasteurizer. Another use of electricity in pasteurizing or sterilizing is at present being experimented with. It consists • of exposing the milk to the action of the ultra-violet rays emitted by the mercury vapour electric lamps. These rays are chemically active, and produce an effect similar to sunburn if allowed to impinge upon the skin. Sunlight is one of the best sterilizing agents, and this artificial sunlight has a similar effect.

In conclusion, I suggest that the great advantages which may be derived by using electricity to operate dairy factories behoves all dairy companies within the electrically reticulated area to give earnest consideration to the electrification of their factories. There are thus great possibilities of future development in the application of electricity to dairying.

Registration of Nurseries. — In the year 1922-23 560 nurseries were registered and inspected by the Department, and certificates issued, an increase of thirtyfive as compared with the previous year; A>6o was collected in registration fees.

* Paper read before the Southland Dairy-factory Managers’ Association, at Wyndham, 1st March, 1923.