Tham khảo tài liệu 'intro to marine engineering 2e episode 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 80 Boilers Furnace wall construction The problems associated with furnace refractory materials particularly on vertical walls have resulted in two water-wall arrangements without exposed refractory. These are known as tangent tube and monowair or membrane wall . In the tangent tube arrangement closely pitched tubes are backed by refractory insulation and the boiler casing Figure a . In the monowall or membrane wall arrangement the tubes have a steel strip welded between them to form a completely gas-tight enclosure Figure b . Only a layer of insulation and cleading is required on the outside of this construction. a Tangent tube arrangement b Monowall arrangement Figure Furnace wall construction The monowall construction eliminates the problems of refractory and expanded joints. However in the event of tube failure a welded repair must be carried out. Alternatively the tube can be plugged at either end but refractory material must be placed over the failed tube to protect the insulation behind it. With tangent tube construction a failed tube can be plugged and the boiler operated normally without further attention. Boilers 8 ỉ Firetube boilers rhe firetube boiler is usually chosen for low-pressure steam production on vessels requiring steam for auxiliary purposes. Operation is simple and feedwater of medium quality may be employed. The name tank boiler is sometimes used for firetube boilers because of their large water capacity. The terms smoke tube and donkey boiler are also in use. Package boilers Most firetube boilers are now supplied as a completely packaged unit. This will include the oil burner fuel pump forced-draught fan feed pumps and automatic controls for the system. The boiler will be fitted with all the appropriate boiler mountings. A single-furnace three-pass design is shown in Figure . The first pass is through the partly corrugated furnace and into the cylindrical wetback combustion chamber. The second pass is back over the furnace .
