Question

a) Sketch and describe in detail a simple single pass composite boiler.

b) Explain its operation and state two advantages.

c) Sketch a biological sewage treatment plant, label it and explain its operation.

d) State five conditions under which oily water can be discharged overboard

Answer 1

A operation -

The Cochran boiler whose working pressure is normally of the order of 7 bar is available in various types and arrangements, some of which are:

Simple pass composite boilers, i.e., one pass of the exhaust gases and two uptakes, one for the oil fired system and one for exhaust system. Double pass composite boilers, i.e., two passes for the exhaust gases and two uptakes, one for the oil fired system and one for the exhaust system. Double pass exhaust gas, no oil fired furnace and a single uptake. Double pass alternatively fired, two passes from the furnace for either exhaust gases or oil fired system with one common uptake.

The material used is good quality low carbon boiler steel plate. The furnace is pressed out of a single plate and is seamless.

Advantages -

• Low floor area required for the boiler installation.
• Low initialization cost.
• It is easy to operate.
• Less manpower requirement for the operation.
• It is easy to transport from one place to another

operation -

The basic principle of the working of a biological treatment plant is decomposition of the raw sewage. This process is done by aerating the sewage chamber with fresh air. The aerobic bacteria survive on this fresh air and decompose the raw sewage which can be disposed of in the sea. Air is a very important criterion in the functioning of the biological sewage plant because if air is not present, it will lead to the growth of anaerobic bacteria, which produces toxic gasses that are hazardous to health. Also, after decomposition of the sewage with anaerobic bacteria, a dark black liquid causes discolouration of water which is not accepted for discharging. Thus in a biological sewage treatment plant, the main aim is to maintain the flow of fresh air.

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