Self-Evaluation #2

For the second blogging time frame I believe that I have improved my blogging.  I have posted 9 additional posts and received 12 comments.  I have commented back to others who have commented on my posts very frequently.  I have also followed several other blogs that are interesting to me and commented on their posts.  When I have came across articles or news that seems helpful to others and their blog topics I have found ways to comment on existing posts they have and let them know what I have found on their topic.  I have posted on a variety of different topics within the waste to energy field.  I have used all types of media including pictures, videos, and hyperlinks.  I have moved away from deficit model posts and presented some interesting posts.  I have brought up important issues and problems in the waste to energy field and gotten some good comments on these posts.  I have also connected this class with my senior design class to help me find and received recommomendationsAfter looking at my "Stats" I have received over 410 page views from viewers in 9 different countries.  I have commented on other blogs in the waste to energy field and received some recommendations from one of these blogs to make mine better.  The blog I received recommendations from was from a Renewable Energy Advisor working in India.  Some things I still need to work on include increasing my number or posts and incorporating other experts in the industry.  Overall I feel that I have improved my blog this period and deserve a high B to low A. 

Spring Break 4-Wheeler Jumping

Here is how me and some friends from back home spent Spring Break. YFZ 450 jumping the John Deere 280 skid steer used to build the jump.

Senior design and complications with anaerobic digesters: temperature

Not only is agitation of the sludge an important aspect of anaerobic digesters, temperature is even more important. The sharp temperature fluctuations here in Colorado cause issues with the living organisms.  The optimal temperature for these organisms is 85 F to 95 F.  This is much higher than the average temperature here in Colorado for more than 3/4 of the year.  Only parts of June, July, and August have these high enough temperatures.  To combat this issue our team has determined that a temperature control system must be used.  Using the high temperatures of the products from the gasifier we should be able to use heat integration.  Heat integration is the process of using heat generated in process units to heat other streams in the process.  This same idea can be used to cool certain streams that need to be cooled as well.  This heat integration can be achieved with a immersed piping coil that allows for heat transfer to flow from the hot gases from the gasifier to the sludge being digested.  Again, this adds more equipment to the once simple digester that has already had a mechanical agitator added. 

One way that digesters existing on their own can stay within this optimal temperature range is by burning some of the gas that hey produce. Several ways of heating digesters are available internal and external.  Internal processes leave the sludge in the tank, while external processes move the sludge outside of the tank.  The sludge can be pumped through a heat exchanger, where heat will be transferred to the sludge via a heating fluid such as water.  Types of heat exchangers that can be used include tube-in-tube and shell and tube exchangers.  A boiler uses some of the produced biogas to heat water that is used to heat the sludge.  In a tube-in-tube configuration the water flows in the annulus area counter current to the flow of sludge in the center tube.  The diagram below shows this in more detail.

Shell and tube heat exchangers are similar where the sludge flows in a bank of tubes while heated water flows over the tubes.  The diagram below shows this configuration.  Again a boiler uses produced biogas to heat the water.

A second way of controlling the temperature of a digester without moving and pumping the sludge is by pumping the hot water into tubes within the digester.  This system will not have as good of heat transfer but will keep the sludge from being pumped around.  I feel that this system would be the best due to the fact that pumping the sludge around can put severe stresses on the organisms and may cause them to go dormant or even kill them.  I am not sure of the pumps that would be used or if there are pumps that can be used that reduce this stress.

Senior design and complications with anaerobic digesters: agitation

I chose my topic of waste to energy at the beginning of the semester having a interest in the industry and technology. Later I was able to pick from four senior design topics for my Chemical and Biochemical major, one including a gasification of waste streams to energy.  One stipulation of the project was to integrate a biochemical process with the thermochemical process of gasification to obtain energy from the waste feed stocks.  My group has been looking at the possibility of implementing an anaerobic digester and gasifier to obtain energy from multiple waste feed stocks.  Feed stocks include farm wastes (cow manure), plastics, and woody biomass.  The process will have two feed prep areas where the biodegradables will be fed to the anaerobic digester and the non-biodegradables will be fed to the gasifier.  The left over sludge from the anaerobic digester will then be dried and added to the gasifier to obtain the full amount of energy possible.

After looking into these processes several issues have come up with anaerobic digesters.  Agitation is first.  The time that it takes for the feed stocks to be digested into CH4 and CO2 varies greatly from digester to digester.  One important aspect of this time is agitation.  If the sludge is agitated and well mixed the digestion takes place at a faster rate.  This complicates a simple anaerobic digester from a simple air tight vessel to a vessel with moving parts.  Mechanical agitators can be used to achieve this, but cost more money and expertise on operating the digester.  Because there are living organisms within this sludge, to much agitation can also be harmful to the organisms.  Walking this fine line of how much agitation is needed to speed the process up is making things more complicated.  We hope to find this information soon so that we can begin sizing and pricing the agitation that is needed.  Any suggestions from other processes that people know about in any industry would be greatly appreciated.

Waste to energy close to home

After looking all over the web to try to find waste to energy plants, turns out I was looking to hard.  This weekend I found out a feedlot (Teague Diversified) from my home town has been operating an anaerobic digester to produce electricity for several years now.  After talking with my father about my Science Communication class I am currently in and my blog on waste to energy, he informed me about this certain feedlot and the process they implemented several years ago to produce electricity from cow manure.  

After talking to my father about the technology for a while we got to looking on the internet and came across an article that provided more details on the Teague Diversified biogas generation process.  The information is a little out dated, from Aug. 2005, but provided good information about the basic inputs and outputs of the process.

The feedlot which feeds around 20,000 to 25,000 head of cattle had used the wastes produced to make compost.  After noticing all of the fumes coming off of the piles of compost the owner decided to look into anaerobic digestion to capture and use this energy. The above ground digesters that were installed cut the processing time of around 20 days to 5 days to take raw cow manure mixed with water to a natural gas like product biogas.  The feed goes in with a concentration of solids around 12 to 15 and leaves with a 4 to 6 percent concentration of solids.

One good thing about the process that was implemented is that it can be added onto down the road. Teague has plans to build and operate up to 12 of these above ground digesters, each capable of producing 1 to 2 MW of electricity.  With a total input of just 500 kW, they can expect to produce up to 8 MW of electricity.  They have set up an agreement with the local power provider, Morgan County REA, where they will buy the generated electricity at a rate of 3 to 4 cents per kWh produced.  If the system is to reach the production of 8MW a sub station will have to be built.  

I hope to talk with the owner of Teague Diversified here in the near future to get more information and updates on the process.  Stay tuned as I plan this should open up many great opportunities and be a great resource for information on the waste to energy process.  The picture below is showing the construction of one of the digesters being installed at Teauge Diversified.