PETONE GASWORKS.

Hutt News, Volume 11, Issue 12, 18 August 1937, Page 2

PETONE GASWORKS.

START OF FOUNDATIONS. Work is proceeding on the foundations for the vertical chamber oven retorts at the Petone and Lower Hutt Gas Lighting Board's works at Petone, which will give the Hutt Valley, whicli has the fifth largest gas unundertaking in the country, the most up-to-date gas manufacturing plant in New Zealand. There is only one other retort plant of the vertical type—that at Auckland —which has been designed from several types. The cost of the Petone plant is about £30,000. Approximately £3000 will be absorbed in foundation work which is under the direction of Australian experts. ■ The foundations are actually being laid on that part of the gasworks property which was once a stop-bank of the Hutt River. At 12 to 14 feet deep the excavators have got solid shells. Indications are that there is a tidal flat 12 feet down. A remarkable feature which is being encountered during the foundation work is that despite the site being at least a mile from the seashore the pumps cannot keep pace with the volume of water at from half-tide until the flood. When the tide turns and passes the half, the pumps once again are able to deal with the volume of water which is encountered eight feet down. Where Gas Comes From. The interesting process of gas manufacture was described by the gasworks manager, Mr Duncan Macpherson. Coal is heated in retorts, of which at present 72 of the horizontal type are used. These will be replaced in due course by the eight new vertical retorts. The . gases given off in heating pass through a central hydraulic main to the gasholder in the course of which passage the gases are purified. The first process the gases undergo is that of tar extraction. They next pass through a condenser for cooling. A livesey washer washes the ammonia out of the gases. A rotary washer then breaks up and takes all the balance of tarry particles and ammonia water and the gases then pass to purifiers, where they are cleansed of sulphuretted hydrogen by means of oxide of iron.

The last-mentioned is a most interesting chemical process. Iron oxide forms a loose chemical compound with the sulphuretted hydrogen. The oxide is later revivified by exposing it to the atmosphere, from which oxygen is taken and the sulphur set free. The iron oxide can then be used again till the accumulation of precipitated sulphur becomes too great. This occurs at about the proportion of one-thii'd. The iron oxide itself undergoes 110 chemical change other than becoming impregnated with sulphur. Sulphuretted hydrogen is a strong-smelling invisible gas. The residuals of gas manufacture are coke and tar. There were 122,000 cubic feet of gas used in the Hutt Valley last year, and already this month more than 11,000,000 cubic feet have been consumed. All this was manufactured at Petone in the way described. After undergoing all the 'processes the purified gas passes into the gasometers or gasholders, those mammoth tank affairs by which the general public identifies a gas works. There arc two at Petone; one frame-guided for Lower Hutt, which has a capacity oi 110,000 cubic feet fully inflated, and one, spiral-guided, for Petone, which has a capacity of 250,000 cubic feet. Each is in three sections. The bottom is for water. The two upper sections contain the gas, and they rise or fall according to the quantity of gas inside. In warm weather when the gas is expanded by the heat they rise without the addition of gas. Five degrees rise in temperature will increase the volume of gas by ;;ne per cent. New Retorts Described. There will be 100 tons of concrete used in the foundation bed and superstructure for the new retorts. Piers 14 feet deep, five feet wide and four feet thick are being constructed, and the whole will be joined together by an earthquake-resisting reinforced panel wall. The horizontal retorts at present in use each take a charge of coal of two and a half hundredweight, and are handled. The eight vertical chamber oven retorts to be installed will each lake two tons. They will be fed automatically from above by measure from the feeding hoppers, which will be filled by the operation of a lever. The doors of the vertical retorts each weigh two tons, and will be worked by hydraulic lever. The doors of the present retorts are handopened and shut in much the same manner as a kitchen oven. The dirt and grime of hand or mechanical scoop feeding of retorts will be eliminated when the new retorts are in operation, and they will produce a better type of coke.