Algae Harvester and Dehydrator

The goal of the project is to create an energy efficient device that will harvest algae from a photobioreactor, then dehydrate it to a 15% moisture content.

=Problem Definition= Biofuels have become more prevalent as scientists research alternatives to fossil fuels. Common feedstocks for biofuel such as soybean and canola oil have too low biofuel yields to sustain the amount of fuel used today. Algae oil has the potential to have much higher yield, making it a good feedstock option for biofuel. The problem with algae oil is it is difficult and expensive to grow, harvest, and dehydrate the algae so the lipids can be harvested and made into fuel. The goal of the Algae Harvester and Dehydrator project is to make a device that can harvest algae from a high water content, then dehydrate it to a 15% moisture content so it can be made into biofuel.

Background
In the 2018-2019 school year, a team made a photo-bioreactor, (PBR), in which to grow algae. It is a 24.7 gallon cylindrical tank with six tubes for containing lights. It connects to an air pumps which pumps air from the bottom of the tank, allowing for mixing and aeration. Some of the light tubes broken since it was made, which led to damage of the lights. These needed to be remade. An image of these lights with a circuit diagram is on the (Right?).

Specifications
The device has certain requirements we must meet. There are some design specifications that are desired by the client, but not required. We will accommodate the desired specifications if we are able.

Required design specifications:

-The device must retrofit onto the photobioreactor made by a previous senior design team.

-The device must dehydrate the algae to at least a 15% moisture content.

-The device must be as energy efficient as possible.

Desired design specifications

-The device should be able to fit on a table top.

-A continuous flow instead of batch flow is preferred.

-The device should recycle the water back into the photobioreactor.

=Design Considerations= The algae harvester and dehydrator is made of two components, the dewatering system and the dehydrating system. First, the algae is separated from the water and made into a sludge. Then, it is dehydrated to remove as much remaining water as possible to turn it into a powder.

Stage 1: Dewatering Systems
  Our first design, shown on the left, for a dewatering system is a stack of filters going from larger to smaller hole sizes. Since the algae we are working with (Spirulina) is about 10 microns in length, we will be using a 5 micron filter so none of the algae gets through. The filters will lay span the size of the square hole in the center of the system shown in the image. These will stack on top of each other to create a "filter tower" of sorts. The system will use gravity to separate the water from the algae. An issue with this system is potential clogging.   Another design we had for dewatering, shown on the right, is the three stage filter. In the center of the vertical tube is a mechanism with a filter chamber that can move up and down in the system. The cylindrical filter chamber is located on the bottom of the moving mechanism and has two holes, one on each side. One of these holes has a filter covering it and one is open. The filter chamber can rotate so the filter is on the far side when the algae water is pumped in, then it rotates and moves up to the second stage in the dewatering mechanism. This stage blows compressed air through the filtered algae to blow out any excess water. The filter mechanism then rotates again and moves up to the third and final stage. This stage blows compressed air through the filter to blow the algae off of the filter and into a catch basin. This design would be difficult to implement because it is so complicated. It would also use more energy than other designs since it has so many moving parts.

  The design for the sixer filter is shown to the left. Each of the holes on this design is covered by a filter mesh. The way this dewatering system would work is algae water would flow in the thicker tube on the left and would filter through. Compressed air would blow through the smaller tube and push any standing water out through the filter to leave filtered algae sludge. The part of the mechanism with the holes would rotate to allow each hole to have algae water filter through, then have compressed air force any standing water out. The problem with this design is collecting the algae once it has been filtered. The device would need to be taken apart to collect the algae.   The rotary drum filter design is shown to the right. The wall of the drum is made out of a filter screen to allow water to go through, but to keep algae inside. An algae water stream flows perpendicular to the screen on one end of the drum. The drum rotates as the water filters out and causes the algae to tumble inside. This mechanism prevents clogging of the filter screen. The whole drum is set at an angle to cause the tumbling algae to eventually reach the other side of the drum and fall into a catch basin where it will then go to the dehydrator. This filter is the one that was almost chosen for the final design, but it had some issues. A scraping element on the inside would need to be added to scrape algae off of the filter screen and a spiral wall would need to be added to prevent standing water from flowing into the catch basin. These two things could not be implemented together, so this design had to be thrown out.

Stage 2: Dehydrating Systems
''' The design to the right is our design for a vertical cross flow dryer (VCFD) based off of a popcorn maker. This design would use the concept that wet algae has more mass than dry algae. Hot air would blow underneath the algae from the bottom of the dryer. As the algae became more dry, the air blowing from the bottom of the vertical cross flow dryer would blow it out the top to a collection bin. This design would require many complicated equations and calculations, so it was rejected.    ''' To the left are the equations needed to determine the velocity of air needed to push dry particles out of the vertical cross flow dryer. There were too many unknown variables needed to determine this velocity for this design to be feasible. In the above center shows a diagram made of the vertical cross flow dryer to show how dry algae particles would flow out and what variable would need to be determined. ''' Another design for a dehydration system was the rotary drum dryer. This design is very similar to the rotary drum filter, except that it has caps on each end to prevent algae from spilling out the sides. Like the rotary drum filter, the wall of the drum is made of a filter screen to allow moisture to escape. This design was based off of clothes dryers and works in a similar way. Hot air is blown in while the drum rotates to create a tumbling effect to create a more even drying process. One of the caps would have to be removed to collect the algae once it has dried to the desired moisture content.

=Project Learning=

Algae Growth
The algae growing process has proved to be more challenging than we initially anticipated. We thought it would take a couple of weeks for the algae kit we received to grow a sustainable amount of algae for the rest of the project. The first kit we bought did not grow a successful batch of algae. This could have been due to the algae in the kit arriving dead, us not allowing enough time for the algae to acclimate to the new environment, putting too many nutrients into the batch, keeping the algae culture too cold, or a combination of all of these things.

=Final Design= Initially, we had settled on the rotary drum filter and vertical cross flow dryer as the two components of our final design. After a meeting with our instructor, we learned about a filtering technique used in industry that involves the use of a conveyor belt made of filter material. The filter can be easily cleaned and the product can be easily directed to the desired location. The initial rotary drum filter design had two main problems, no way of cleaning the filter and direction of the algae to the dryer. We completely redesigned the filter into a conveyor belt design shown on the ???. In this design, water flows into the top right side of the belt while the belt rotates to the left on a decline. The belt drops the algae sludge into the vertical cross flow dryer, making the harvester to dehydrator portion of the mechanism continuous.

=Validation= Once our design had been decided and built, we made a Design Failure Mode and Effects Analysis (DFMEA) sheet that is shown below. The three most left columns describe the part of the machine that could fail, how it could fail, and what effects failure could have on the whole system. The "sev" or severity column describes the severity of the failure should it happen. A score of 10 is the most severe. The next column shows a potential cause of each failure. The "prob" or probability column rates the probability each cause has to cause the failure. A score of 10 means it is the most likely to happen. The current design controls column describes what measures are already in place in the design to prevent that failure. The "det" detectability column rates how detectable the failure would be. A score of 10 means it is very hard to detect. The RPN column is the total of the severity, probability, and detectability columns multiplied together and shows how much of a risk the potential failure poses. The recommended actions columns describes what can be done to mitigate the failure. We were not able to test for any of the potential failures due to the school shut-down, so the remaining columns are blank.  

=Team Members=

=Additional Documentation=

Project Schedule



Meeting Minutes

https://drive.google.com/open?id=1dLFO-5bWv5WJfnK4vlzzc9MWyAlS_EBG

Presentations