IDDS 2011 - My Project (Part 2)

After figuring out what kind of oil we were looking at, the next challenge was figuring out how we would actually extract the oil.

It seems that the most common method for extracting the oil currently involves grinding the seeds into powder and then putting it in boiling water. The oil can be skimmed off the top. Unfortunately, we were not able to observe this process firsthand or find accurate data on the yield through this process. Still, we wanted to explore other methods to see if they would improve on this process.

I was really excited about the prospect of solvent extraction--that is, using chemicals that can separate the oil from the seedcake. I was interested since it seemed like there was a lot of scope for designing a low-cost system that could use solvents to produce oil. The advantage is that once the oil has been separated from the solvent (usually hexane, but there are other compounds that can be used), the solvent can be reused over and over, while the oil that comes out is very high quality. Unfortunately, the solvents tend to be fairly expensive (it's not a recurring expense, but it still was going to set the price of our system higher than we wanted) and also somewhat dangerous (part of the process requires heating the system, and if that isn't done carefully, the solvents are highly flammable and can cause a lot of damage) and it is also one of the slowest methods for extracting oil. I was pretty disappointed when I had to concede that the system just wasn't viable.

We also built a hydraulic jack press, which used a car jack and a plunger to apply pressure to a chamber filled with moringa seeds. The system had a lot of advantages in that it was safe, easy to use and understand, produced very clean oil and could be built easily in most major towns. We played with a few different designs based on what we had seen with screw presses (very useful for palm and coconut since the oil flows out so well) and ram presses (uses a massive piston to deliver the huge amounts of force necessary to extract the oil from the seeds), but ultimately the press was leaving too much oil behind in the seeds, so we knew we would need a more efficient press.

A three ton car jack brings the plunger down to crush the seeds. There are small slits in the cup so that oil can flow out and collect in the plastic container.

We finally built a small screw expeller, which I was very skeptical about from the start. I had worked with a screw expeller called the Piteba in 2008 and found the machine frustrating to use and too inconsistent in its performance. Other people had reported more satisfactory experiences than mine, but I decided to spend more time building the jack press above. However, I had to say that it was highly impressive that they were able to produce a screw auger with variable pitch without computerized machinery. The auger was also slightly bigger than the Piteba design and much less expensive. We were able to tweak some elements in the design to improve the performance and by final presentations we were pretty proud of our final prototype.

Our locally produced auger. The diameter is 1.5 inches. You can see how the seeds are compressed as it moves down the channel in order to make it easier to extract the oil. Photo credit - Ben Chapman

As the user turns the crank, the seedcake comes out the end, while the oil comes out the slit and can be collected in the cup. It is necessary to heat the chamber to improve the yield. In our final design, we had a better looking funnel, heater and oil collection tray. Photo credit - Dennis Obwona

Introduction
My Project (Part 1)
My Project (Part 2)
Other Work
Delivering Content
My Team
Language
Where We Stayed
Suame Magazine
New Longoro
Maker Faire
Food
Potluck
Ramadan
Transportation
Accra