Post by thread:] stoichiometric values for a wood gasifying furna

{Quote hidden}>-----Original Message----- >From: Lee McLaren [spam_OUTlmclarenTakeThisOuTTASNET.NET] >Sent: 06 May 2004 09:18 >To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU >Subject: [OT:] stoichiometric values for a wood gasifying furnace > > >I know this sounds WAY off topic but there is a PIC (or 3) in >this honest! > >I am designing and building a gasifying wood furnace, part of >the design requires the introduction of air after the wood has >been turned into a gas so that the gas burns completely. I am >going to use a butterfly valve moved by a servo to control the >air mix but need to measure the fuel / air ratio to ensure >that the mix is correct. I have been doing some research I >would like to confirm or correct my conclusions. > >Conclusions: >I need to adjust my air / fuel mixture to stoichiometric for >clean efficient burning (without eating the firebox!). >Stoichiometric for a wood furnace will read the same value on >a automotive 'Exhaust Gas Oxygen sensor' as it would for >Stoichiometric for a correctly tuned car. > >I expect when things are working correctly that the furnace >will burn with a blue flame but I need to build the controller >to mix the air correctly. I have found some interesting >information on wide band sensors but I need a ball park to >know if even these are going to work. I am trying to use a >standard automotive exhaust gas oxygen sensor with careful >consideration to where it is installed so it does not melt. >They are a lot cheaper than the alternative. > >Please be gentle, I know a lot more about electronics than I >do about wood gasification. A standard oxygen sensor has a very non linear output that is only good for indicating too much oxygen, or not enough oxygen as you probably know. The sesnor should be mounted as close to the source of the exhaust gasses as possible, both to heat the sensor to working temperature and reduce lag. I don't know what the typical exhaust gas temperature of your furnace would be, but I suspect lower than the EGT of a typical gas/petrol powered engine. Typicaly an oxygen sensor needs to beheated to at least 300 degrees C (600F) to start operating, and normal operating temperature is closer to 750-800 degrees C (around 1400F). You will have to derive a control scheme based on the lag of the exhaust gasses reaching the sensor, and also on the lag of the furnaces response to opening or closing the butterly valve. The output of the sensor will probably just need to be integrated, I suspect that any propotional term will cause problems given the non-linearity of the sensor. You will also need to be able to operate the system in an open loop mode until the sensor is heated up and operating properly, although I don't know what the best method of detecting this point would be. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to postmasterKILLspambookham.com. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Thanks for that Mike, the furnace temperature will be between 1000C and 1200C the further addition of air causes the furnace to burn very hot and hence the efficiency and low emissions. I was hoping to try and maintain the mid point on the low bandwidth sensor but understand that it has very little range, I expect it wont hurt if it hunts slowly from too rich to too lean as long as I don't go too far in lean direction at least. For start-up I was going to move slowly to a set point which will err on the side of rich until I get to a predetermined temp and then try to do some smart things. I have some of the MAX6675's on order to monitor the exhaust temp. I am going to use a PC for the controller with a number of PIC USB devices to control servos and monitor temp and fuel/air mix. There will be separate fail safes as well as I don't wont to overheat 700l of water! I will be aiming for a 90C running temp when it is working. regards Lee McLaren {Original Message removed}

This is a very intersting project. I hope you tell us on the list about your results. I for one is very interested. Regards /Ake -----Ursprungligt meddelande----- Från: pic microcontroller discussion list [.....PICLISTKILLspam.....MITVMA.MIT.EDU]För Lee McLaren Skickat: den 6 maj 2004 12:15 Till: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU Ämne: Re: ] stoichiometric values for a wood gasifying furnace Thanks for that Mike, the furnace temperature will be between 1000C and 1200C the further addition of air causes the furnace to burn very hot and hence the efficiency and low emissions. I was hoping to try and maintain the mid point on the low bandwidth sensor but understand that it has very little range, I expect it wont hurt if it hunts slowly from too rich to too lean as long as I don't go too far in lean direction at least. For start-up I was going to move slowly to a set point which will err on the side of rich until I get to a predetermined temp and then try to do some smart things. I have some of the MAX6675's on order to monitor the exhaust temp. I am going to use a PC for the controller with a number of PIC USB devices to control servos and monitor temp and fuel/air mix. There will be separate fail safes as well as I don't wont to overheat 700l of water! I will be aiming for a 90C running temp when it is working. regards Lee McLaren {Original Message removed}

>-----Original Message----- >From: Lee McLaren [lmclarenspam_OUTTASNET.NET] >Sent: 06 May 2004 11:15 >To: @spam@PICLISTKILLspamMITVMA.MIT.EDU >Subject: Re: ] stoichiometric values for a wood gasifying furnace > > >Thanks for that Mike, the furnace temperature will be between >1000C and 1200C the further addition of air causes the furnace >to burn very hot and hence the efficiency and low emissions. > >I was hoping to try and maintain the mid point on the low >bandwidth sensor but understand that it has very little range, >I expect it wont hurt if it hunts slowly from too rich to too >lean as long as I don't go too far in lean direction at least. > That's exactly how it operates when used in an automotive application. The slope around stoichiometric is so steep that holding stoich perfectly is pretty much impossible. >For start-up I was going to move slowly to a set point which >will err on the side of rich until I get to a predetermined >temp and then try to do some smart things. I have some of the >MAX6675's on order to monitor the exhaust temp. > As long as you can always guarantee a rich mixture at start up then this should work. With EGT and EGO sensors, you should be able to do some fairly smart control algorithms. >I am going to use a PC for the controller with a number of PIC >USB devices to control servos and monitor temp and fuel/air >mix. There will be separate fail safes as well as I don't wont >to overheat 700l of water! I will be aiming for a 90C running >temp when it is working. > Good luck, sounds like an interesting project. Let us know how it goes! Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to KILLspampostmasterKILLspambookham.com. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Hi, After proper gaz/air ration, proper burning is a combination of 3 factors, its called the 3T. It consist of Temperature / Time / Turbulence. IMHO you must have 10% excess air to make sure the combustible is all consumed. The air entrance should be in a vortex so you will have a better mix. This is to say that 3 circular entrance points is better than a single bigger one. I have seen lower excess air but the 3 T where pretty darn good. Pierre Desrochers ----- Original Message ----- From: "John Ferrell" <TakeThisOuTjohnferrellEraseMEspam_OUTEARTHLINK.NET> To: <RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU> Sent: Thursday, May 06, 2004 12:41 PM Subject: Re: ] stoichiometric values for a wood gasifying furnace > A friend of mine applied a thermostat control on his Franklin style stove > with an ordinary wall thermostat and a solenoid controlled flapper valve. > The mechanics of a flapper are easiers to deal with than a butterfly. If you {Quote hidden}> really need the proportional control, that is another story... > > John Ferrell > http://DixieNC.US > > ----- Original Message ----- > From: "Michael Rigby-Jones" <Michael.Rigby-JonesEraseME.....BOOKHAM.COM> > To: <EraseMEPICLISTMITVMA.MIT.EDU> > Sent: Thursday, May 06, 2004 4:34 AM > Subject: Re: ] stoichiometric values for a wood gasifying furnace > > > > >{Original Message removed}