iPaper - Page 2

dark oily film contaminates the boiler water level glasses inside. If so, do not blow down the boiler from the bottom; just surface blow several times. If you bottom blow the boiler, it will become totally covered in oil. The boiler should be shut down and released from pressure and the venting valve opened. Afterwards, the boiler can be drained slowly until water stops flowing from the loosened, upper manhole door before opening up the manhole for inspection. The oil will now only cover the boiler in the normal water level range and can be manually removed. Hot or cold water high-pressure jet equipment together with oil dispersive additives would be efficient for removal of the oil. In case the boiler is completely oily inside, the cleaning work could be turned over to a cleaning company specialised in such work. First damage control action (ship) A careful examination and hydrotest of all suspected heating coils, heaters or whatever is leaking in the steam/condensate system. Be aware that even when one leakage is found, there could be several more remaining. When it is assured that no more leakage can be found, the piping system, coils and heaters have to be cleaned of all remaining oil. The oil-fired boiler must not be started up again until an oil-free feedwater supply is guaranteed. Temperature of furnace wall with sediments on water side If the waterside of a furnace wall is fouled with e.g. carbonate, silica, or oil film, the temperature of the furnace wall increases due to added thermal resistance. Preventive action The feedwater/hotwell/cascade tanks have to have filters installed, filled with lofa sponges, coconut fibres or similar, which effectively take up small amounts of oil. The filter inserts have to be exchanged regularly according to demand. The cascade tank can easily be equipped with a continually measuring oil detecting device which monitors if oil is present in the condensate. By locating the sensor in the cascade tank, it can be assured that oil is detected before it enters the feedwater section, which means that no part of the feedwater is being contaminated. Aalborg Industries can supply standardised equipment fulfilling the above specifications. A more comprehensive system for preventing oil from entering the boiler would be to transmit a signal to an air- or electrically operated three-way valve switching over the condensate flow to the bilge until the oil source is pinpointed and eliminated. An investment in such equipment pays off quickly because it prevents the boiler from serious damage by burnt down tubes and furnace room plates. Water 170°C 7 bar(g) Furnace 1200°C Three examples are made to illustrate the increase in temperature of the furnace wall when the waterside of the furnace is fouled with sediments of 2 mm carbonate, 0.5 mm silica, or 0.5 mm oil film: No sediment a0 [W/(m2 x K)] l 1 [W/(m x K)] l 2 [W/(m x K)] a3 [W/(m2 x K)] S1 [mm] S2 [mm] atotal[W/(m2 x K)] Q [kW/m2] T0 [°C] T1 [°C] T2 [°C] 10,000 38 145 20 133 137 2 mm carbonate 10,000 1.72 38 145 2 20 115 119 181.9 0.5 mm silica 10,000 0.172 38 145 0.5 20 95.8 98.7 179.9 0.5 mm oil film 10,000 0.10 38 145 0.5 20 79.9 82.3 178.2 184 256 320 382 467 519 590 633 In conclusion, the maximum temperature of the furnace wall is increased from 256°C to 633°C with an oil film of just 0.5 mm. Furthermore, the transferred heat is reduced from 137 kW/m to just 82.3 kW/m , a reduction of 40%. 2 2 Aalborg Solutions is published by the Aalborg Industries After Sales and deals with operation of steam and heating equipment. Ideas and suggestions for topics are most welcome. Aalborg Industries A/S · Gasvaerksvej 24 · P.O. Box 844 · 9100 Aalborg · Denmark Phone: +45 9930 4000 · Telefax: +45 9810 2233 · E-mail: repair-marine@aalborg-industries.dk For world-wide After Sales addresses, ect., please check http://www.aalborg-industries.com Your Preferred Partner

Page 1 ...