In order to maintain a high thermal efficiency of the exhaust gas economizers and avoid excessive soot accumulations periodical soot blowing and cleaning must be carried out.
The goal of cold cracking is to cool and then heat the economizer steel structure. Because the coefficients of expansion of the boiler steel and the hard deposits differ, the deposits come loose during cold cracking. The carbon particles released during the process are burned off when the economizer is heated afterwards. This burn-off must not take place near coastal areas or in congested areas.
The economizer must be cleaned by soot-blowing on approach to the selected port for the cold cracking to be carried out, to minimize the subsequent burn-off.
The correct procedure for cold cracking process is, usually, as follow:
Water washing is recommended to be carried out during dry docking as frequent water washing
causes an external corrosion layer of steel on the economiser tubes, which with regular water washing will eventually cause tube leakage.
Water washing must be carried out when a main engine is stopped, but the economiser should be warm enough for the water to evaporate so that the tubes and fins will not remain moist after washing. Economizer washing must be done with fresh water only and where deposits are highly corrosive or bonded, a soaking spray with a 10% soda ash solution is advisable before washing.
When the water washing has begun, it must be continued until the heating surface is thoroughly washed and all deposits are removed, due to the fact that some types of coatings harden and get very difficult to loosen when they have been saturated and then dried out.
It must be ensured that all the washing water is drained away so that water will not enter the turbochargers. The dirty washing water is collected in a tank which is located beneath the economiser.
The economiser must be dried out immediately after water washing. This is because soot formations produced by the combustion process in the engine contain sulphur compounds. Any residual soot and water will therefore react chemically to form highly corrosive sulphuric acid.
Economizer water washing. Source and credit: Marine Engineer WorkThe water washing is done utilizing a lance water pressure jet, but on some vessels there is a water washing system inbuild into economizer and the system consists of a number of water washing tubes installed on top of the evaporator sections inside the economiser. Each tube is equipped with spraying nozzles designed in such a way that the whole area of the heating surface will be covered.
Water washing must be carried out when the main engine is stopped and the economiser has been cooled down. However, the economiser should be warm enough for the water to evaporate, so that the tubes and fins will not remain moist after washing.
It is important to note that when the heating surfaces are water washed, there is a possibility of generating steam. To avoid a risk of scalding, the operators must remain outside the economiser casing.
The amount of water used for washing depends on the amount and condition of deposits and should be based on experience. The following procedure should be followed:
tart the circulation pumps
and hot water from the separator drums will slowly enter the economiser.If you like my posts, please don’t forget to press Like and Share. You can also Subscribe to this blog and you will be informed every time when a new article is published. Thank you!
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