ESSAY COMPETITION.

Hokitika Guardian, 16 May 1924, Page 4

ESSAY COMPETITION.

A VISIT TO TilK GAS WORKS. (15,v Kathleen Kennedy, Pupil Hokitika Convent School). Tli- first compartment we were shown nt the Hokitik'ii Gas Atorks was tho cnmpnrtment in which the coal is stored. The lour stages of coal are petit, lignite, bituminous, which lust produces the best gas, anthracite, which is best foY generating steam, and the last stage, black lead or pure carbon. This coal compartment opened oil' the room in which were the furnaces and retorts. The retorts are semi-cylindrical and built in sets of six. The principle of those retorts is the same as that of an ordinary cooking range, and it the temperature were less, bread and pastry rould la* cooked in them. Knell retort is nine leet long, and when It ibeing filled with coal, flame gushes out from the opening • this is caused by the gas mixing with the oxygen oi the air. Originally retorts were constructed entirely of cast iron, but the iron shrinks ami is Unable to withstand the high temperature, so after much re-

search they were constructed of fireclay. Tu some works the letorts are vertically constructed and these are filled by- hopping machines. Steam is often injected into the retorts through tlie hot coke over the white hot carbon and this produces producer-gas. This gas is mixed with coal gas to the proportion of thirty to sixty per cent. II this producer gas were Used alone it Would he extremely dangerous as there is no perceivable smell and often there would he escapes which would pass unnoticed until too late. Ascension pipes’ are large vertical pipes which lead from the retorts into the hydraulic main, which is half full of water. There is no danger of the main becoming dry as the moisture from the coal is a great asset and occasionally water is pumped into it. 01 course the ascension pipes go up one inch under the water in order that the water may act as a seal and prevent the gas from slipping hack to the retorts. The gas passes from the main into the condensers and at this stage is called foul gas, as it Amlains c.muumia. tar and other impurities; the tar is in the form of minute globules full, of gas. The way of getting rid of the tar is by breaking the globules. Krom the condensers the gas passes into the exhauster which is worked by a gas engine.

This ongiiu? is used to draw the gas from the retorts and tw force it through the other apparatus, 'i here is a part of the machine called the regulator. which allows the exhaust to work the gas over and over again. The gas engine may he left for hours without

anyone near it, while a steam engine requires constant watching, hut, the

gas engine, as weli as any other engine, must not he allowed to pull into the exhaust the carbonic arid which would spoil the gas. The engine uses four strokes to do its work, one to draw the charge in. the second lor compression, the third for the explosion, and the fourth for the exhaust. Krnrti the exhaust engine the gas goes to washers and scrubbers.

The gas bubbles through perforated plates, which process takes away n percentage of ammonia, tar and sulphur. The scrubber consists ol plates one foot apart through which a shower of water Hows. Here the rest of the ammonia is removed. If the ammonia were left in the gas it would eat away the pipes, brass fittings and the meters.

The purifiers are rectangular tanks in which is the purifying matter, red oxide of iron and lime, which is not used now. The tanks lire two in number, the tank in which the oxide is blacker —this is caused hv the sulphur clinging to the iron and treeing the oxygen —is used first and the Iresher tank used last. The purifiers are cleaned periodically ami the iron oxide which is taken out is lett to absorb the oxygon and to drop the sulphur, and when this has been done, can he used again.

The station meter is a large cylindrical tank with a clock to register till the gas made. Leakages are able to he found out by comparing the sum of cubic feet registered hv tf!e consumers’ meters and the iiumlier of cubic feet registered by the station meter. The best meters arc the wet meters which have a quantity oi water in them; the dry meters lose a great, deal of gas. because the bellows which ill them take the place of water in the net meters hceiinio cracked and so allow the gas to ooze through the openings in the leather. r l be consumers meters should bo well looked alter by the Company because il tlu* meters are of poor quality there is u laigei loss of gas to the Company. The gasometer is a large tank which fits into a well of water; the principle of this part of the apparatus is tlio some* ;i> that <>l in* ornpty piacoil invcTjioly in n hasm ol watoi. The gsisoinotor rises as it heroines lull ot’ and falls ns the lias out. There are two pipes loading to tho gasometer. one the inlet pipe or tlie pipe through which the gas enters the gasometer, and the other tlie nutlet pipe through which the gas goes t' l the governor; these pipes go sixteen foot below the water and both pipes rise one foot above the 'surface of tho water in order that tlie water may act as a seal. The gasometer is constructed of old Scotch iron, and is now. after fifty years of use. as good as ever. Iron must lie used in the construction as other base metals would soon he pitted. The gasometer holds twenty-two thousand feet of gas. enough L> l" st the consumers twenty-four hours. The governor is the last of the apparatus and regulates the supply ol ga.s to the consumers. The governor n the means of cutting off the consumer’s supply of gas and il the machine rises too quickly it will disorganise all the meters, lights, and gas heaters of the town.

The hv-products of coal arc: Coke, aiiniline and azo dyes, ammonia. Lu and sulphur. Many drugs Used by the chemists are extracted from coal tar. The drug nsperine is an extract from carbolic oil.

This essay was awarded 0o marks. THE MANUFACTURE OK GAS. (By Mary Kerridge. I’upil Hokitika Convent School). A fluid is distinguished from a solid by the want of rigidity of its panicles, therefore gas may he defined as a fluid that yields to compression. The manufactured fuels are —coni gas. producer gas and water gas. Coal is is a form of carbon found underground. Trees have been buiicd and by slow combustion have been converted into coal. 'I here are five stages in coal formation—peat, lignite, bituminous, anthracite and black-lead. The most useful is the bituminous coal from which coal-gas is produced. The coal is heated in semi-cylindrical fire-clay retorts, having a length of nine feet. The mouth pieces are cast iron hut if the inside were cast iron they would not stand long on account of the great heat. The principle of the working of the retorts is the same as that of the ordinary cooking range. The fire circulates. Each retort may be charged with three hundred weight of coal and produces on an average two thousand, feet of gas. Tf the re-

takes longer to make and is in smaller quantities. In Hokitika about T 2.000 cubic feet of gas are produced to a ton of ordinary coal. When the coal is baked so that there is no more gas in it, it forms coke, which is carbon. By passing air over white-hot carbon, producer-gas which is a mixture of carbonic monoxide and nitrogen is obtained. Water-gas is produced by passing steam over red-hot carbon, producing a mixture of hydrogen and carbon monoxide.

The gas is conducted by ascension pipes into the hydraulic main which is half full of water. The pipes go into tile hydraulic main for about one inch under the surface of the water which forms a seal to prevent the gas from going hack. From tlie hydraulic main the gas goes into condensers where the till is dropped. This tar is in tlie form of minute globes formed with gas. They must he broken to release the gas. The gas next goes to the exhaust engine which is a rotary pump-. The function of the exhauster is to remove the gas from lliC retorts. To get the required exhaust there is n regulator which allows the exhauster to work gas over again through the by-pass. V ithont the regulator there would lie a hard pull on the retorts and thus draw oil C. 0.2 from the furnace which would upset the whole make of gas. Iho gas engine works in four strokes -fiist, pulls in gas; second, compression; third, explosion; toiirth, exhaust. Krom the exhaust engine the ga-, passes to washers where it bubbles through water. Here the ammonia and sulphuretted hydrogen are extracted. Thence is passes to the scrubber whcie a shower of water absorbs the balance of the ammonia. Krom the scrubbers the gas is removed to purifiers containing hvdrntcd oxide of iron where tlie .sulphur is extracted. When the sulphur comes in contact with oxide of iron it unites to the iroll and liberates the oxygon* There arc always tvvo purifiers around which is a partition of water acting as a seal. The oxide of iron is exchanged according to the percentage of sulphur-in the gas. V lion the oxygen reunites with the oxide ot iron it may lie used again.

The gas now enters a station motor where it is measured before passing into the gas-holder. A governor placed at the outlet of the holder regulates

the pressure of gas to the consumer. The gas holder is like a large cu inverted in a. basin of iron, It is mad

of old Scotch iron, which unlike the model'll iron, does not pit away. It holds about 22,000 ft. of gas. The pipes conducting the gas into the holder go sixteen feet beneath the surface of the earth and come up one foot above tlie surface of the witter in the holdei. When the holder is heavy there is

iiioro pressure on tlie gas. From the tar that is deposited in the condensers is extracted hv Irnetional distillation the liases ol' aniline and az-> dyes, saccharin. pitch, naplitalene and carholie oil. 1 lie ammonia from the washers and scrubbers*is the chief source of ammonia salts. Coaltar products: benzole, naphtha, creosote oils, oreaso oils, diesel en;;ip.e oil. carbolic oil. crcsylie acid, naphthalene, pyridine ,anthracite, sulphate ol ammonia. This essay was awarded !)•'! marks.