155 1 100 10 Excess air 716 100 716 0016 558 6020 10 Theoretical O 2 by volume

155 1 100 10 excess air 716 100 716 0016 558 6020 10

This preview shows page 19 - 22 out of 26 pages.

× 15.5 % 1 100 10 Excess air = × 7.16 100 7.16 0.016 5.58 60.20 = × + + +
Image of page 19

Subscribe to view the full document.

= 10% Theoretical O 2 % by volume 1. Fuels and Combustion Optimizing Excess Air and Combustion For complete combustion of every one kg of fuel oil 14.1 kg of air is needed. In practice, mixing is never perfect, a certain amount of excess air is needed to complete combustion and ensure that release of the entire heat contained in fuel oil. If too much air than what is required for completing combustion were allowed to enter, additional heat would be lost in heating the surplus air to the chimney temperature. This would result in increased stack losses. Less air would lead to the incomplete combustion and smoke. Hence, there is an optimum excess air level for each type of fuel. Control of Air and Analysis of Flue Gas Thus in actual practice, the amount of combustion air required will be much higher than optimally needed. Therefore some of the air gets heated in the furnace boiler and leaves through the stack without participating in the combustion Chemical analysis of the gases is an objective method that helps in achieving finer air control. By measuring carbon dioxide (CO 2 ) or oxygen (O 2 ) in flue gases by continuous recording instruments or Orsat apparatus or portable fyrite, the excess air level as well as stack losses can be estimated with the graph as shown in Figure 1.2 and Figure 1.3. The excess air to be supplied depends on the type of fuel and the firing system. For optimum combustion of fuel oil, the CO 2 or O 2 in flue gases should be maintained at 14 -15% in case of CO 2 and 2-3% in case of O 2 . 20 Bureau of Energy Efficiency Figure 1.2 Relation Between CO 2 and Excess Air for Fuel Oil 7.16 100 72.956 = × 5.58 100 100 7.5% 72.956 x = × =
Image of page 20
1. Fuels and Combustion 21 Bureau of Energy Efficiency Oil Firing Burners The burner is the principal device for the firing of fuel. The primary function of burner is to atomise fuel to millions of small droplets so that the surface area of the fuel is increased enabling intimate contact with oxygen in air. The finer the fuel droplets are atomised, more readily will the particles come in contact with the oxygen in the air and burn. Normally, atomisation is carried out by primary air and completion of combustion is ensured by secondary air. Burners for fuel oil can be classified on the basis of the technique to prepare the fuel for burning i.e. atomisation. Figure 1.4 shows a simplified burner head. The air is brought into the head by means of a forced draft blower or fan. The fuel is metered into the head through a series of valves. In order to get proper combustion, the air molecules must be thoroughly mixed with the fuel molecules before they actually burn. The air in the center is the primary air used for atomization and the one surrounding is the secondary air which ensures complete combustion.
Image of page 21

Subscribe to view the full document.

Image of page 22
  • Spring '17
  • Jerome Ramos

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes