Best practice no 22

Typically, thermal efficiency reflects how well the boiler vessel transfers heat. This concept usually excludes radiation and convection losses. Combustion efficiency implies only the burner's ability to burn the fuel without the presence of carbon monoxide or unburned hydrocarbons. Boiler efficiency may not mean anything, although if we relate this efficiency to the energy supplied to the boiler in relation to the energy it delivers converted into steam, we can consider this fuel to steam ratio as a true efficiency ratio.

The efficiency of a boiler has been defined as the ratio of heat delivered through steam generation, divided by the heat supplied by the combustion process.

The total heat generated in a combustion process is not completely transferred to the generation of steam due to the natural losses that the boilers or steam generators have in the design, these losses are due to:

• Losses due to radiation and convectio n

• Losses due to waste of hot gases in the chimne y

• Losses due to high temperature condensate drain s

• Losses due to humidity in the steam generate d

These losses have a very significant impact on total efficiency, so it is worth doing a detailed analysis of each of them.

Losses are generally due to the construction design of the boiler or steam generator, so a general description of the design features will be given.

PACKAGE BOILERS

The concept of package boilers has been around the world for around 70 years. In them, all components are designed and installed on a single platform, in such a way that the only connections required for their operation are the installations of: water, electrical energy. , fuel, steam and condensate and chimney for the discharge of combustion gases.

The package boiler is compact, usually requires little space and is assembled complete with burner, fan, insulation, refractories, controls, auxiliary pump and preheater electrically and mechanically interconnected. This gives the owner the simplicity of a single source of responsibility for warranties, repairs and maintenance.

During the Second World War, a new type of package boiler was introduced to the marine industry (Scotch Boiler), which is now widely known in the industry as the Drum Boiler.

TUBE BOILER:

These boilers are built by a cylindrical vessel, with a central burner called "Morrison Tube", the combustion gases pass inside the tubes, called smoke tubes, the water and steam are found on the outside of the tubes. and the burner, contained by the main body. Essentially a flue tube boiler is constructed similarly to a shell and tube heat exchanger.

One of the inherent characteristics of this boiler is the large volume of water it contains; this allows it to respond to load variations with minimal changes in steam pressure.

The ideal design for this type of exchangers is the spherical shape, however, it is not practical, so a cylindrical shape is used.

In a cylindrical body, transverse forces are easily absorbed by the structure, however, longitudinal forces limit the construction of said boilers.

Longitudinal stresses tend to cause lateral failure. These forces are proportional to the pressure and diameter of the container, the thickness of the plate becomes increasingly larger as they try to absorb these efforts, so the pressure limit that these equipment can reach is a maximum of 300 psig. . (21 kg/cm²g).

FOR-IM-024

REVISION DEL FORMATO: C

FECHA DE EFECTIVIDAD DEL FORMATO:10/03/2022