Local Industry.

Progress, Volume VI, Issue 5, 1 March 1911, Page 572

Local Industry.

(By Ernest G. Osborn, Aslibvu'ton.)

An Economical Process.

Gas Firing a Lime-Kiln. New Installation at Mount Somers. Few people realise how large an amount of fuel and money is wasted annually equivalent to many millions of pounds—by the use of unsatisfactory arrangements in furnaces, fire-boxes, and kilns, by which a large proportion of the heating power of the fuels is lost instead of being utilised. The prevention of smoke, and its conversion by combustion into useful heat, is a problem which has reached great importance during recent years, and its solution, or attempted solution, has placed on the market inventions which endeavour to secure the complete burning of the gases contained in smoke. There are thousands of tons of good fuel going to waste every day from the huge smoke stacks of the manufacturing towns of the world, and owners of factories are beginning to realise the calorific value of the gases that daily go to waste. The Smoke Problem. The smoke problem is readily solved in most instances by the use of what are known as gas-producers in place of direct firing, though it is noticeable how . slow some firms are in taking advantage of this method of overcoming their difficulties. One of the most successful gas-producers yet placed on the market, especially adapted for use in limekilns, is that invented by Ernest Sehmatolla, the German engineer whose research work in gaseous engineering has made him world-famous. After years of unsuccessful attempts, he has invented a gas-producer which fulfils all that the man at the limekiln requires. One of his furnaces was recently installed at the Mount Somers limekiln, and so far it has given excellent results. The writer, when visiting the kilns, was struck with the simplicity of the Schmatolla process for converting the crude limestone into quicklime. The Old and Tedious Process. The output of quicklime under the old process was from three to four tons daily, while the new kiln produces ten tons of the purest quicklime every twenty-four hours. Formerly it was the rule to fill the kiln in layers of coal and limestone placed alternately, to set fire to the bottom of the pile, and to leave the kiln to burn almost how it pleased. The amount of coal used was more than double that used by the new kiln. The smoke from the former kiln rolled down in great volumes to the valley below, and being mixed with the gases set free from the limestone, was obnoxious in the extreme. As was inevitably the case by placing the coal in contact with the limestone in the old kiln, the quicklime produced was very impure, being mixed with an inconvenient

percentage of coal dust and . ashes. The heat produced in the former furnace was just about one-half of that produced by the Schmatolla gas-firing method, and the consequence was that a large quantity v? the limestone was only partially converted into quicklime. The New Process. To understand the working of the Sehmatolla gas-producer, it is necessary to be able to explain the action of burning coal. When fresh fuel is thrown into an ordinary fire the gases contained' in it escape suddenly, and as there is seldom enough air provided to complete the combustion of these suddenly evolved gases, the greater part of them escaped unburnt! Smoke is mainly composed of hydro-car-bons of ■ high calorific value, and in the old kiln they were allowed to escape. On the other hand, if the evolution of these can be regulated and spread over a longer period of time, the combustion is rendered more perfect, and the amount of smoke produced is greatly diminished. Unfortunately, with an ordinary furnace or fire-box, it is impossible to thus regulate the evolution, and the gases perforce escape as smoke. With a properly constructed gas-pro-ducer, however, the evolution of the gases is perfectly regular, and is quite independent of the stoking, so that the fuel delivered to the furnace is practically complete in combustion. The principle of Sehmatolla's producer is—by a very gradual heat— expel the gases from the coal, and to cause them to be burnt in a part of the furnace independent of the part where the stoking is done. If the supply of gases from the one part is well regulated, complete' combustion is assured in the other part. Once the fuel has _ entered the stoking doors, every particle of it is used for heating purposes, whereas under the old arrangement 50 per cent, of the best of the heating power of the fuel was lost. How the Smoke is Consumed. In order that the smoke escaping from the first heating of the fuel may be completely burnt, it is led by a series of layers of coal through three separate "zones" of glowing fuel. In passing through the first layer of red-hot ashes, the most easily combustible of the gases in the smoke are consumed, while the second and third deal with those gases less easily burnt. By the time the gases reach the top layer, they have been broken up into their respective constituents, and one of the most valuable of these is carbon monoxide. The flame of this gas is one of the hottest known, and this gas forms one of the best of the calorific agents in the furnace. It produces a great heat—just that heat suitable for burning limestone. The Gas-producer. The gas producer is of square section, and the stoking is done through a number of small charging holes on the surface.

The advantage in having a number of charging vents lies in the fact that one large hole would allow a sudden escape of gas from the furnace every time it was opened. Each hole is fitted with a movable cap, on top of which rests a coal bucket. Removing the caps allows the Coal to drop into the furnace below. A regular heat is produced in the furnace by stoking regularly, and keeping each layer of fresh fuel to a certain depth. It it most necessary to introduce a good air supply into the furnace, or the complete combustion of the gases will not take place. An air blast is generally used in the Schmatolla kiln, and this method has worked successfully at Mount Somers. The Old and the New. Mr. Malcolm Lean, the manager of the Mount Somers kiln, told the writer that the now method of burning the lime was in every way more satisfactory than the former method. In the first place, there was the increased output, and secondly the saving in the coal consumption. They were the two greatest improvements. Then there was the cleanliness of the Schmatolla method, and its production of purer lime. The installation of this type of limekiln is the third which has been made in the Dominion. The other two are at Dunback, Otago. where they are working satisfactorily. •