Combustion and Bagasse From meeting with Dr. Jenkins 12/4/08

Stoichiometry for Bagasse For complete combustion - with no excess air C3.86 H6.3 O (O N2) yielding 3.86CO H2O N2 One mole of bagasse requires moles of oxygen (in air) to produce 3.86 moles CO2 & 3.15 moles of H2O ---- some moles of N2 enter and exit the combustor. If you have excess air (say 40%) then the has to be increased by 40%.

Why this analysis is important  To analyze how much excess air, we must know what is exiting the chimney.  This analysis will help us determine the efficiency of the oven and give us test results to compare designs based on efficiency of heating the pans and efficiency of fuel use.

Excess Air The theoretical amount of air need for combustion (determined by stoichiometry) is not enough to burn the fuel entirely. Excess air is the estimated ADDITIONAL amount of air needed for complete combustion. Medium (Fuel Type)% Excess Air Natural Gas Coal Bagasse

But Remember… Adding more molecules of oxygen means that more heat is used to warm up these molecules and less is available to heat the pan. Something to think about: A design that allows us to monitor the amount of air flowing into the oven.

Mixing  Reactions will only occur when 0 2 meets the surface of the fuel.  It is much more likely for the fuel to burn completely if there is good mixing.  Obviously a solid does not mix well, but if a fuel such as bagasse was cut into smaller pieces there would be more surface area for the air to have contact with.  In this case the fuel would burn hotter but also quicker.

Just the Right Amount  Less heat will be available to boil off water in the pan.  There is a better chance that the fuel will have been completely used.  Smoke will be produced and particulates will enter the air.  Toxic CO will be released. Too Much AirNot Enough Air

SO HOW DOES THIS RELATE??

For the OVEN  We need a very sealed oven that has controllable valves to allow certain amounts of air into certain parts of the oven  Places of excess air need to be located  Air needs to be distributed

Why Distribute O 2 ??  O 2 shouldn’t all go to one area  Its almost impossible for a solid to combust completely the first time through  If we distribute the air, especially towards the top of the flame, the particulates can be given a second chance to combust

Keep in Mind!  Smoke indicates incomplete combustion  Air is being concentrated to one area underneath the flame and allowing for initial combustion, but not any further combustion  When tires are burned and a huge amount of smoke is emitted, the reaction is happening fast releasing a great amount of heat, but the smoke indicates a huge portion of the fuel is going to waste (NOT EFFICIENT) Air Pollution = UNHEALTHY FOR PEOPLE AND ENVIRONMENT

Idea!  Jenkins spoke of an industrial oven that has a reflective surface that radiates heat back to the coals  This could be placed toward the back of the oven, reflecting back to the fuel source ???

About the Bagasse  The moisture in the Bagasse requires more energy for combustion  We should create a system to dry the bagasse and measure the moisture content  Jenkins suggested: 1. Air dry for a long time and weigh 2. Grind up and put into oven around 110* 3. Take out, let cool and weigh again *when it is taken out of the oven there should theoretically be no moisture in the bagasse, we can compare that to sun-dried bagasse