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What is a good practice of the exhaust gas economizer water washing?

26 Jun '17, 09:46

June 26, 2017, 9:46 a.m.
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Exhaust gas economizer water washing is a very important routine carried out on board vessels and must be conducted in strict accordance with equipment Maker's and ship Manager's recommendations. It is the most effective method of removing soot accumulated. However, too frequent water washing will result in the promotion of corrosion of tubes and tube plates. When carrying out water washing, keep in mind the following points:

1) Water washing must be carried out periodically at suitable intervals, depending on the degree of soot accumulation or increased draft loss. The most effective approach is to carry out water washing when the value of draft loss rises to 1.5 to 2.0 times the initial value of the non-fouled draft loss value.

2) Confirm before opening the manhole that the inside of the exhaust gas economizer has cooled to 150°C or lower, because fires can be triggered from a sudden inflow of fresh air through the manhole.

3) Prepare a fire fighting hose near the exhaust gas economizer and behind the funnel to allow rapid response to a soot fire.

4) Soot must be completely removed. Pay special attention to the partition inside the exhaust gas economizer, where wet soot is likely to accumulate.

5) Water washing is more effective when the interior of the heating tube is still warm, after stopping the circulating pump. Ideally, the circulating pump should be kept running during the early stages of water washing.

6) Water washing can be performed more effectively by dividing the process into several stages, with fixed intervals.

7) The surface of the heating tube can be forcibly dried by running the circulating pump after water washing, enabling the soot to be peeled off more effectively. It is, however, necessary to first reduce the boiler steam pressure, because the heating tube surface will reach the soot ignition temperature when the boiler steam pressure is 2.0 MPa or higher.

8) Soot remaining on the heating tube surface after completion of water washing will tend to peel off when the heating tube surface has dried and the circulating pump started. Any soot that peels off will accumulate in the exhaust gas economizer bottom. Therefore, confirm without fail that all the soot has been thoroughly removed before starting the main engine.

9) When starting the main engine just after water washing, pay close attention to the exhaust gas side of the exhaust gas economizer and exhaust pipe line. Especially, pay attention during the increase of main engine revolutions from “slow ahead” to “half ahead” etc. After water washing, the ignition temperature of any remaining wet soot is lower, and the soot ignites easily. The ignition temperature of soot is usually around 350 - 450°C. However, after water washing, it is possible for the ignition temperature to drop to around 250°C.

10) To discharge any residual soot after water washing, carry out soot blow as soon as possible after starting the main engine.

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26 Jun '17, 09:55

June 26, 2017, 9:55 a.m.
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