Chris, Your volumes are too small for a full-scale continuous plant if my sources of information are correct. I've studied this subject a bit when looking at plant design for a friend ( the 'studied' was via personal communication with a few people in commercial biodiesel and process engineering, and taking a couple of the Iowa State University courses on commercial biodiesel production technology, which were co-taught by a continuous process plant builder, and covered in great detail what circumstances to utilise batch plants and what circumstances to utilise continuous, and hybrids of both) It's really expensive in material and engineering to build such a unit, and it takes a lot of 'tuning' for the process.
Continuous process makes sense when you're very high-volume. We were looking at building a half million gallon per year plant at the time (which is considered extremely small, believe it or not), and the advice we universally got was that we were too small for true continuous to make sense. half a million gallons a year is 1400 gallons per day if you were theoreticaly operating with no down time and running 24/7 (not likely!) , which is about 5000 liters per day in that case- much more than your volumes, and still considered 'too small' for efficient operation. After our research we were not 100% convinced that it could not be done- but a lot of different factors point to batch processing or a hybrid approach even at the scale we were looking at. Part of the reasoning is that a continuous plant should be run 24 hours a day- there is a lot more metal to heat up than in a batch plant, and it causes problems, expense, and time, to heat it up and shut it down every shift like you would do if you could not get enough business or enough feedstock to run it 24 hours a day. There have been half million gallons per year pilot plants built here 'continuous'- but I imagine that they were operating inefficiently, more as a research facility prior to the company installing their fullscale plant. Most of my information is on facilities in the US, not in Europe or elsewhere, and I am not an expert by any means. I got the impression that continuous plants are more the norm over there, and batch is more the norm here in the US. Todd is right, do it in batch-style. But don't do 1000 gallon batches (anybody). It's very difficult to do a good mix in such a big tank. I've heard anecdotally that a few people who have attempted it had trouble getting a good mix during the reaction (and therefore got poor conversion, not meeting standards, which matters if you're commercial, might matter less to you personally if you're homebrew or farm-scale). The plant design engineer I asked about this suggested that 500 gallons is a good limit for a reasonable stirred-tank batch reactor. In my case, 250 or 500 gallon tanks are cheap to find.Get two of them and run them to get your 1000 batches. That being said, there are lots of places in the process where a hybrid batch-continuous approach makes sense. I think washing is one of them- countercurrent washing where biodiesel flows in one direction and water flows in the other. Dewatering is probably better done with flow rather than in pot stills. Mixing catalyst/methanol into oil is in my opinion far, far better done with pumps (and static baffle type mixers if you;re really concerned about big batches) than with a stirred tank (and might eliminate the 'big batch/poor mixing' problem.) Some stagewise approaches like the two-stage base-base processes seem well-geared to semi-continuous operation. Oil pretreatment (ie dewatering and filtration) can be automated as a continuous flow. But for small plants, it seems to me that it is difficult to startup and shutdown the system if it is a true continuous plant, and it also seems to me that it would defeat the purpose of continuous systems if you had to continually adjust it day to day for differing feedstock. Also on Todd's coment on question three: that 'glycerol' that forms in the acid side of the reacion is actually water and methanol with some free fatty acid (methanol is a solvent for ffa) and some of your sulfuric acid and some colorants from the oil (I think this is detailed more in Dr. Jon Van Gerpen's papers on the process, which can be found somewhere on www.me.iastate.edu/biodiesel) . Remove this layer (and recover it's methanol), the water is a big problem, especially for the acid esterification process (water stops the esterification). If what is happening in the acid side is mostly esterification of free fatty acids rather than transesterification of triglycerides, then there should'n't be much glycerol forming. My opinion is also that a hybrid approach would give you more flexibility if something in the process doesn't behave as planned (ie acid side of the reacion not reducing ffa as much as desired and needing to be re-run, problems in washing, etc). mark --- In biofuel@yahoogroups.com, "Appal Energy" <[EMAIL PROTECTED]> wrote: > Chris, > > 10,000 liters is only three days in a 1,000 gallon batch reactor. That > leaves you 27 days each month free for increasing your volume and clientele. > > You might wish to ask yourself a few cost/benefit equation questions. What > is the cost of batch processing verses the need for a > machinist/engineer/boiler mechanic for continual processing? For the small > volumes that you are speaking of, batch processing will get you in with less > up front cost, less maintenance cost and equivalent yields to a pricier CP. > > Question two: Agitate like a som bitch. The greater the of turnover of > reactants the better off the process is. "Not to splash" may be advised > under a less than enclosed environment? > > Question three: Whenever possible separate the small amount of glycerin that > forms during the acid side prior to conducting the base side. > > Todd Swearingen > > ----- Original Message ----- > From: "Chris Albrecht" <[EMAIL PROTECTED]> > To: <biofuel@yahoogroups.com> > Sent: Saturday, October 11, 2003 12:14 PM > Subject: [biofuel] Continuous processing > > > > Good day, Everybody! > > > > I have just concluded a contract whereby I can get 3000Lt of WVO per month > from an international franchise. This will in all probability go up to > 10,000Lt monthly whan my project goes national. Which brings me to a > question: > > > > All the site I have visited about continuous processing, have a lot to say > about the process, but extremely little about how - which is what I'm > looking for. Can anybody please point me in a direction? I have look at > Biox, CTER etc. > > > > My next question: > > Step 8 of the foolproof method says not to splash, but under Equipment > this is said: > > "The pump should take the mixture from near the bottom of the reactor and > return it via the top, to splash down on the surface." > > > > Third one: > > Does the acidified glycerine from Step 18 gets added back to the total > volume of BD? > > > > I am planning on building a semi-continuous batch process plant to start > my production. > > > > Regards > > > > Chris Albrecht > > CAPE TOWN > > South Africa > > > > > > > > [Non-text portions of this message have been removed] > > > > > > > > > > Biofuel at Journey to Forever: > > http://journeytoforever.org/biofuel.html > > > > Biofuels list archives: > > http://archive.nnytech.net/ > > > > Please do NOT send Unsubscribe messages to the list address. > > To unsubscribe, send an email to: > > [EMAIL PROTECTED] > > > ------------------------ Yahoo! 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