104 MODERN GASWORKS PRACTICE
(3) The air and producer gas should not come together too closely, and should not meet at right angles. The effect of meeting in this way is that too tliorough mixing takes place, and short flames of small volume are the result (see Fig. 53).
(4) The shape of the nostrils is of importance ; they should be tapered in section
(Fig. 51), the smaller width being at the top. In tliis way any lumps or dust falling from above will drop through the nostril in-stead of lodging in it.
(5) The secondary air on both sides of the setting should be under dual control at least, or preferably the supply to eacli nostril should be capable of regu-lation. It is frequently found that the air has a tendency to rush towards the centre nostrils of the furnace arch, this gi ving rise to irregulär distribution of heat and duil mouth-pieces.
(6) The “ nostrils ” should be kept low in comparison with.
Fig. 51.—Deflboting Secondary Air so that Fubnace Gases meet in a Parallel Dibection. Dottbd Line shows usual position of Channel Block.
the bottom retorts. If they are above tlie base of the lowest row of retorts, the latter will be insufficiently heated.
(7) For settings containing two vertical rows of retorts the direction of discharge of the producer gas should be vertical (Figs. 52 and 53). For three rows the “ nostrils ” should point outwards. In this way more effective distribution of heat is assured, whilst the centre retort is not subjected to a direct cutting heat. In some settings in which three vertical rows of retorts are em-ployed, twin combustion chambers are constructed. In this way the central retortis more effectively
protected than is the case when a Fig. 52. Fig. 53.
single chamber is used.
(8) Retorts are far less liable to “ local heating ” when set in tiers of twos. Thus if a setting of eight is decided upon it is preferable to set the retorts in two vertical rows of four rather than in two rows of three and one row of two. In addition, the former arrangement gives a greater yield per square foot of ground. area. The chief objection is that if hånd charging is in vogue a platform will have tobeused for tlie top tier.