Modern Gasworks Practice

REFRACTORIES FOR GASWORKS PURPOSES 217 plastic clay, are generally befrter than others. A dense brick that would not absorb the oil should apparently be more satisfactory ; but such bricks do not generally resist spalling action. The fireclay linings of the connections between the <1 ifferp.nl-, shells are often nearly cut away by the abrasive action of coke particles in the gaseous current, and by the slagging action of the ash. It is believed that many failures attributed to the refractory material have really been due to the use of improper cements. The average mason likes cement which works easily under the trowel; and there is a tendency to add plastic clay, or some similar material, to the more refractory cements. The use of such material reduces the refractory qualities of the cement, and the resulting jointing material fuses. This deterioration may even extend to the bricks. In general, better results .are obtained 011 construction work by using a cement consisting chiefly of ground material similar in quality to the grog in the bricks, and a minimum amount of material of lower fusibility. In using silica shapes, cementing material is often ■omitted—the bricks or shapes being separated by corrugated cardboard of such thickness that at the proper temperature the expansion will form a sufficiently tight joint. Salt Corrosion The corrosion of refractories by salt is a problem which mainly concerns the coke-oven engineer. In gasworks the coal carbonized is comparatively dry, wliereas for coking purposes the coal is invariably washed before use. The saline matter in coals consists principally of sodium and potassium chlorides and sulphates, and the process of washing, instead of removing these compounds, may, if the washing water is not frequently changed, actually add to the original amount in the coal owing to the high proportion of dissolved salts which the circulated water contains. W. J. Rees 1 has given the folio wing figures in connection with the water used in •coal washeries :— Water in Circulation in Wash-ery Sodium chloride ....... 1-529 grammes per litre. Sodium sulphate ...... 0-524 Potassium sulphate ...... 0'062 Calcium sulphate ...... 0-168 Magnesium sulphate ...... 0-264 Calcium carbonate ...... 0-057 Magnesium carbonate ...... 0-041 Proportion of Salt in Coal Sodium chloride Sod um sulphate (<z) Unwashed slack. , . . 0-37 per cent. 0’19 per cent. (&) Washed slack .... 0-18 „ 0-08 In the above instance it is evident that the saline compounds have been partly removed by the washing process. The rate of flow of the water through the washery is of importance, as the concentration of salts will be reduced as the rate is increased. 1 Froc. Ceramic Society, XVIII, p. 432.