STATE EXAM 02_BOILER CONSTRUCTION

State exam

02_Boiler construction

Variant 01

In all marine power plant work one of the greater processes is the formation of steam from feed water. This occurs in the steam boiler, the essential function of which is to provide an efficient flow of heat from the products of combustion to the water and steam. This heat flow is due to conduction from the hot gases and radiation from the flames. The structural features of the steam boiler are such that heat-transfer surfaces are being dispersed throughout the path of gas flow. The simplest structural arrangement consists of one or more steel drums and boiler tubes. Steam boilers have become more complex with the development of power generation. As steam turbines need superheated steam, the steam boiler incorporates a superheater, which is a heat-transfer surface, to form superheated steam from saturated steam. Waterwalls have been added to the unit. They are boiler tubes tied into the water circulation system. The theoretical limit to which flue gas temperature may drop is the temperature of the saturated steam. With higher boiler steam pressures a further extension to the heating surface is made in the form of an economizer. Herein feed water which is lower in temperature than boiler steam, is heated by the flue gases as they leave the boiler surface. The economizer also sets a limit to which the temperature of the flue gases may drop. Further surface in the form of an air heater can be used to reduce the flue gas temperature by warming the air needed for combustion.

The elementary drums and tubes of the steam boiler, when added to in the form of waterwalls, superheater, economizer, air preheater and possibly other heating surfaces give us the steam generating unit. In addition to the heating surface, the steam generating unit includes the furnace, combustion and draft equipment, and a variety of auxiliary equipment for controlling combustion and steam formation. Several accessories for safety and maintenance are also part of the complete unit.

There are two types of boilers in general use: the fire tube and the water tube boiler, with the latter predominating.

Variant 02

One of the most important items of equipment aboard ships, boilers, are used for numerous purposes.

Whether it is steam powered or has a diesel engine as the main form of propulsion, a ship without a boiler is really difficult to imagine; a boiler, in one form or another will be found on a ship. For example if a ship is a steam powered ship, two or more boilers will be provided to produce high temperature, high pressure steam. If a ship is carrying a diesel engine as the main propulsion system, one or two smaller boilers are used for running various ship's machinery and services.

How do Boilers Work?

A basic boiler is a machine with the simplest arrangement of the internal parts. The main job of a boiler is to make high pressure steam. The feed water supplied to the boiler drum utilizes the heat of the energy released by burning the fuel. This energy of the burning fuel is stored in the form of steam with high temperature and pressure. The fuel is burnt in a combustion chamber inside the boiler. To attain high efficiency and complete combustion, air is supplied to this combustion chamber through a separate arrangement. The heat generated in this combustion chamber is transferred to the water from the boiler drum through a large surface area, which enables the highest rate of energy transfer.