CHAPTER 111
THE HORIZONTAL RETORT BENCH
The practice of laying retorts horizontally is still the most common in this country. In spite of the perfectioa to which. otlier types of carbonizing plant has been brought, the older rncthod is as yet able to h.old its owd, and tliere is little fear that within the present generation it will be universally supplanted. So far as the smaller works are concerned, the horizontal beuch is more convenient, and less costly in the first place ; and, up to the present, vertical installations have been chiefly confined to those works where comparatively large quantities of coal can be håndled with a considerable saving in working expenses.
There are three types of horizontal settings in common use to-day. Tliese are :
1. Direct-fired settings.
2. Semi-gaseous settings.
3. Gaseous-fired settings.
Types 2 and 3, which. are gradually taking the place of the more extravagant direct-fired settings, may again be subdivided as follows ;—
(a) Generator settings.
(b) Regenerator settings.
(c) Those heated by means of outside producers of various types.
Although the initial cost of the gaseous-fired setting is greater than that of the direct-fired setting, the additional outlay is soon redeemed by the saving effeeted in fuel. For this reason even small works are finding it profitable to instal at least the generator principle, and it may be said in general that the direct system should be confined to those works making less th.an 2 or 3 million cubic feet per annum. In such, cases, interest on additional Capital and extra labour entailed in supervision make the gaseous system a doubtful advantage. In the “ direct ” furnace the air passes through the coke in large and often unrestricted quantities, and combines with the carbon to form CO2 direetly. In the gaseous settings the retorts are heated by the exothermic reaction of the combination of CO and oxygen in burning to CO2. The great drawback of the direct furnace is the difficulty of Controlling the air supply, which results in a considerably inereased consumption of fuel, together with irregulär heating of the setting. In faet, in very small works, where the plant is not making gas througliout the whole twenty-four hours, cases have been known where all the coke has been made use of for heating the retorts, and in isolated
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