tailieunhanh - Marine Machinery 7 E Part 6

Tham khảo tài liệu 'marine machinery 7 e part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Mr Oí . Tanker and gas carrier cargo pumps and systems 191 Because of the sulphur dioxide absorbed by the sea water its pH value is changed from around about 7 to about as it passes through the scrubber -hence the selection of polypropylene for the tray tunnel caps and demister mattress. The tower itself is lined with ebonite rubber. Other designs of scrubber used at sea include the impingement and agglomerating type such as the Peabody circular tower Figure . In this type the incoming flue gas is first wetted by sea-water sprayers and then passes upwards through a venturi slot stage which agglomerates the solid particles. The gas then rises through slots in a series of trays. Above the slots are a number of baffle plates. The trays are covered in water introduced at the top of the tower in much the same way as in the tunnel cap tower previously described. A mesh type demister is arranged at the top of the tower. Fans The fans used in the inert gas system must be capable of providing a throughput equivalent to about times the maximum cargo pumping rate since the tanks must be kept supplied with inert gas during cargo discharge. At full output the fans must be capable of delivering at an over-pressure of 192 Tanker and gas carrier cargo pumps and systems Ó7Ơ- 1000 mm . which with pipeline losses equates to a static pressure at the fan of up to 1000 mm . Both electric motor-driven and steam turbine driven fans are used and 11 IS usual to provide one running and one stand-by unit. These are normally both 100 duty units although some installations with a 100 duty and a 50 duty fan have been used. Because of the corrosive nature of the gas the tan materials must be carefully selected. Fan impellers of stainless steel or nickel-aluminium bronze are frequently used and the mild steel casings are internally coated with for example coal tar epoxy. Some problems have been encountered with bearing failures on inert gas fans and these have frequently been .