Dear Marc, People have been getting debris out of water since forever, and so there is an incredible variety of designs. Some intakes work well, many have problems. However, getting a few leaves out of water isn't really such a difficult demand. I have a book out, Microhydro: Clean Power from Water, that mentions the Coanda screen design, which has lots of promise for micro and small hydro and would be worth investigating. (BTW, you can get a signed copy of the book from me at : 401 Arnold Avenue, Victoria BC V8S 3L9($30 Canadian plus $15 Canada international postage and handling) I am excited about it because in many microhydro systems with direct drive and sealed bearings, the intake is the only maintenance required. A more carefree screening system is thus most valuable...
Think of really difficult screening problems like "dewatering coal slurry"... There's a great Home Power magazine article on the Coanda screen in issue #71. You can get it from.www.hydroscreen.com. Cheers, Scotty -----Original Message----- From: Marc de Piolenc [mailto:[EMAIL PROTECTED] Sent: Thursday, April 22, 2004 9:54 PM To: Microhydro List Subject: [microhydro] New (???) trash rack design A couple of weeks ago I was privileged to visit a medium hydro project near Baongon, Bukidnon, owned by one of the independent (i.e. non-NAPOCOR) power producers now emerging here in the Philippines. This was the first hydro project by this company, and was attended with serious troubles which were overcome mainly by grit and perseverance. Their original hydro expert consultant made some poor design decisions which continue to cause operational problems, and a contractor chosen by him managed to drop a generator set weighing 12 tons twenty meters to the turbine-house floor, with predictable material damage and one life lost. The company, instead of abandoning the project, simply fired the consultant, assembled their best people and set them to work acquiring the necessary expertise in-house. The plant has now operated profitably for a little over three years, and the company is considering further projects. There are still problems, however - leaky sluice-gates cost them some power generating capacity, especially during periods of seasonal low water flow, and the trash rack, while adequate most of the year, gets clogged with debris during peak flows, limiting plant capacity at just the time when the plant should be delivering maximum output...and maximum profit. The power company's renewables manager, the plant manager, the civil works contractor and Yours Truly were kicking over possible modifications to the trash rack, since a solution to that problem would produce a very large gain. I brought up the moving trash rack design I had seen somewhere - you know, the one that looks like those toasters you see in restaurants - a series of linked sections driven and guided by sprocket wheels. Then we started counting up moving and wearing parts and got discouraged. The renewables guy came up with a simpler mechanism - a horizontal-axis cylinder. I think they're now looking into that as a retrofit to the plant. The reason I'm writing to the list is that I kept doodling variations of this scheme on my way home and afterward, and came up with something that looks promising to me that I would like to offer for critique. This is not a possible retrofit to the existing plant in Baongon, however, because it requires the penstock to upen upward into the forebay tank instead of the horizonatally oriented opening that now exists. If it is any good, however, I would like to propose it to them for future projects. The idea is to have a vertical axis cylinder whose axis coincides with the centerline of the first, vertical segment of the penstock. The idea here is that water can enter through the full perimeter of the cylinder, making the full surface area usable (the earlier scheme makes only the projected area usable). Of course a scraper has to be provided to raise and remove the debris, and this is provide by a spiral fixture that makes one full turn from the base of the screen cylinder to the top, where a conveyor belt or some other arrangement takes over to dump the debris downstream. I can send a sketch to anybody who is interested and needs something better than my verbal description. Anyway - while I spent some time congratulating myself on my cleverness, in retrospect this seems like a fairly obvious solution, which leads me to suspect that it has flaws that I have so far failed to perceive. Comments by more experienced list members would be welcome! Marc de Piolenc Iligan City, Philippines Does your company feature in the microhydro business directory at http://microhydropower.net/directory ? If not, please register free of charge and be exposed to the microhydro community world wide! NOTE: The advertisements in this email are added by Yahoogroups who provides us with free email group services. The microhydro-group does not endorse products or support the advertisements in any way. More information on micro hydropower at http://microhydropower.net To unsubscribe: send empty message to [EMAIL PROTECTED] Yahoo! Groups Links ------------------------ Yahoo! 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