Modern Gasworks Practice

126 MODERN GASWORKS PRACTICE (3) Bench, reconstructed from furnace-arch. level in old main arches. Time for drying at least two weeks and a half. Four days to bring up to working heats. (4) Entire old benches. Siow fires for four or five days. Thirty-six hours for bringing up to working heats. “ SLOW FIRES ” With regard to picking-up benches from cold, there is a prevailing tendency to hurry the work along, which. no doubt accounts in no inconsiderable way for reducing the life of retorts, etc. The actual period of “slow fires” varies with the condition of the setting as explained above ; that is, whetlier the brickwork is green througliout, or whether the bench has merely been let down for repairs. The procedure adopted for manipulating the various dampers and slides during preliminary heating and picking-up varies in accordance with the taste of the individual ; . but, speaking generally, the folio wing points are those chiefly requiring attention in coimection with. the larger types of regenerator settings. First, with. slow fires it is preferable to isolate the main flue and chiinney during the earlier portions of the period, this being done by closing the main dampers between the regenerators and the flue. An outlet for the warm products of combustion is then made by removing a couple of bricks from the front wall of the setting at a point just beneath the crown of the furnace arch. In this way the waste gases circulate m the setting alone. In addition, of course, it must be remembered that the furnace di.arging hole is left uncovered. With regard to the admission of air to the furnace, most engineers prefer to close the secondary-air ports. The furnace door is left wide open, so that as much warm air as possible may pass through the sp.tting, and carry away the moisture from the brickwork. During this time the fire bars, if of the horizontal type, should be water cooled in. the usual way, and clinkering carried out about twice per week. As regards the retorts, the doors of these should be closed, so as to retain as much heat as possible ; but they should on no account be tightened up with levers, otherwise the expanded air and steam, being unable to escape (the foul-main valve being closed) will force an exit through some weak spot in the joints, thus giving unnecessary trouble when the retorts are charged up. Particular attention should be given to this point when new work througliout is being dealt with. “ FAST FIRES ” « ^^en’ a^ei f°urteen to twenty-one days, the time comes for working up from “ slow ” to medium fires certain precautions are necessary. First, the main flue and chimney are brought into play ; and to this end the setting dampers may be opened to a small extent (usually about one-quarter of their full working amount), and the outlet made in the front wall of the setting must at the same time be sealed by replacmg the bricks which. were removed at the outset In some instances it is usual to open the main dampers to nearly their full working extent for an hour or so, in. order to heat up the shaft sufficiently to ensure its Clearing a good draught. From the point of view of the brickwork, however, this is not to be advised, and the