Modern Gasworks Practice

CONTROL OF HORIZONTAL RETORT SETTINGS 143 recluced, with. the result that little fluxing takes place, and ash instead. of clinker is the outcome. Clinker prevents the admission of air, so that local combustion in the fuel-bed takes place. With ash, on the other band, furnace cleaning is a small matter ; and it is possible to find works in which. clinkering of the fires is practically unknown. The remedy for the excessive formation of clinker is simple, and can be directly traced to the mtroduction of adequate grate areas and slow travel of gas ; ■also in some cases to the employment of steam (see p. 68). MAXIMUM COMBUSTION TEMPERATURE The evil of admitting excessive quantities of air should perhaps receive some mention liere ; and it must be borne in mind, that the highest temperature which can be obtained by the combustion of fuel is tliat to which the products are raised on tlieir formation by the heat dispersed. Thus, the larger the volume of gas to be heated the less will the temperature be. It is in this respect that regeneration teils ; for whcn the air is heated before combiistion is allowed to take place, the heat of the air is added to the heat of combustion. Thus the quantity of heat available for raising the temperature of the products is very much greater. With regard to vertical retort furnaces, it may be pointed out tliat in the Glover-Westtype the secondary air is pre-heated by circulating around the coke chamber •constitirtmg the bottom three feet of the retort, and in this way the sensible heat is extracted and turned to useful account. In the Woodall-Du.ckh.am system the coke is discharged more or less cold, but a device has been. made use of by means of which the primary air passes through fireclay tubes adj acent to the base of the retort, thus utilizing heat which. was originally lost. SECONDARY-AIR. DIRECTION In retort settings of nearly every design it is customary to find that the secondary-air channels are arranged round the furnace arcli in such, a manner that when the heated air emerges it meets the gases from the producer practically at right angles. Until recently the advisability of this method has never been questioned, but opinions now appear to be undergomg some change. Dr. Karl Bunte, in a paper read before the German Association at Strassburg some few years ago, pointed out the short-comings of this procedure, and stated that in all the more perfect of modem settings such conditions are obviated. The effect of introducing the secondary air in a strong current at right angles to the producer gases is to give rise to too thorough intermixing of the air and gases, with. the result that short flames are produced. In order to ensure as uniform heating throughout the setting as possible such, short flames should be avoided. To this end the gas and. air streams should meet on almost parallel courses, in which. case admixture of the two is gradual, and flames of larger volume are produced. The majority of existing settings can be readily adapted to meet this requirement. The method of dealing with a typical case is shown in Kg. 51. In this instance the secondary air is conducted in the ordinary way to the apex of the furnace arch. by means of horseshoe channel blocks. As