FYP update no.4
Wednesday, June 10, 2009

As mentioned in our earlier post, the composition of biogas contains 50-75% of methane. This methane can be harvested to produce heat, generate electricity and fuel vehicles.


In our context, we are thinking of applying this system in the third world countries, the methane can be a cost effective solution for cooking and lighting.




Methane has a high calorific value of 35.8MJ/m3. However, to be able to tap on this potential of the methane, it has to be pure. This means that the other components in the biogas will have to be removed.


This is not to say that there are no negative impacts of methane. Methane is odourless and colorless. It will cause suffocation when over inhaled. It is also explosive and should be stored with care. It is also good to note that methane is not very soluble in water and it is denser than air.



The main components of the biogas that needs to be removed are carbon dioxide an hydrogen sulphide (H2S is poisonous)




We used the Buswell equations and calculated that 33.63m3 of biogas will be produced.


Below is the diagram of methane capture system designed by Dr Han:





To add on, relevant calculations have to be peformed before sizing the design of methane capture system.We were stuck with the calculations for the entire 2 weeks. We went to find lecturers like Dr Lee and Mr Wong YT for help.



Most of our researchs direct towards using Henry's Constant for calculation. However, we just could not get the appropriate mass transfer correlations for the calculations.




We then talked about the need to optimize the digester performance through mixing. Mixing will allow more even digestion by the microorganisms and give a unity throughout the digester. By doing so, we prevent the formation of surface scum layer and the deposition of suspended matter at the tank bottom. Initially we thought of using either bubbles or gas to cause turbulence through the tank. This is usually introduced from the tank bottom. There are two possible construction as shown in the slides. We also mentioned about pH Control in the digester during the discussion.



In conclusion we hope that these measures be put in place to ensure a system of higher efficiency and effectiveness.



(Slides to be added)


To add on, we have performed one of the QC tools that we have learnt in the module on Quality Assurance and Statistic. In this case, brainstorming is used to identify the possible ways of improving the digester operation.


For instances,
Possible ways to improve the digester operations:


1. pH probe
  •  Installation of pH probe
  • Addition of lime or sodium bicarbonate
  • Decreasing the waste feed to digester


2. Mixing
  • Installation of mechanical stirrer
  • Gas re-circulation line for mixing


Update: The two proposed ideas were not carried out at last since we could not run our experimental run using the large scale digester. Furthermore, by considering the constraints of the equipment, it may be quite trouble to install the pH probe/stirrer and re-circulation line etc.

Posted byfishy* ><>
at8:52 AM

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