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Post by fiedia on Feb 2, 2023 8:42:18 GMT -8
Hello,
There are several posts giving optimal temperature for a clean fire:
-’Even the lowest "clean-burning" wood fire temperature is around 600ºC, which is the minimum needed to crack all the off-gassing carbon compounds into CO2.’
-‘bottom of heat riser it comes to around 800C that is no enough to burn CO but everything else is pretty much burned.’
-’Your core only needs to be hot enough to burn creosote and not so hot that you start making nitrous oxide. So you want a core temp of 1100 to 1500’ (Fahrenheit => 600 to 800 Celsius)
Do you have more information (chemistry, experiment results...)? Thanks
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Post by masonryrocketstove on Feb 4, 2023 2:08:51 GMT -8
Hello, There are several posts giving optimal temperature for a clean fire:
-’Even the lowest "clean-burning" wood fire temperature is around 600ºC, which is the minimum needed to crack all the off-gassing carbon compounds into CO2.’
-‘bottom of heat riser it comes to around 800C that is no enough to burn CO but everything else is pretty much burned.’
-’Your core only needs to be hot enough to burn creosote and not so hot that you start making nitrous oxide. So you want a core temp of 1100 to 1500’ (Fahrenheit => 600 to 800 Celsius)
Do you have more information (chemistry, experiment results...)? Thanks
The first two are from US universities giving the basics on clean wood combustion as it's understood within the "fire triangle" of Fuel + Air + Heat = Combustion chemical chain reaction. The first link introduces the concept of primary and secondary combustion stages of solid wood fuel, and the third paper / link goes into a lot more research depth as to why staging the combustion process with primary and secondary air injection is important to reducing particulate matter (ppm), NOx, and CO, etc. Heating with Wood: Principles of Combustion" From Montana State University erc.cals.wisc.edu/woodlandinfo/files/2017/09/mt198405hr.pdf"The process by which gases are released from wood and burned is called primary combustion. Primary combustion begins at about 540° F, continues toward 900° F and results in the release of a large amount of energy. Primary combustion also releases large amounts of unburned combustible gases, including methane and methanol as well as more acid, water vapor and carbon dioxides. These gases, called secondary gases, contain up to 60 percent of the potential heat in the wood. Their combustion is important to achieve high overall combustion efficiency. The secondary gases are not burned near the wood because of lack of oxygen (oxygen is being consumed by primary combustion) or insufficient temperature. The conditions needed to burn secondary gases are sufficient oxygen and temperatures of at least 1100° F." " Using Your Wood Stove Efficiently and Effectively" from PennState University extension.psu.edu/using-your-wood-stove-efficiently-and-effectively" One of the keys to high-efficiency combustion is keeping the combustion zone hot, at least 600°C (1,100°F). If it is colder than that, the wood will tend to "smolder" (hot enough for combustible gases to escape from the wood, but not hot enough for those gases to burn). If you keep the stove hot by using dry wood and refueling the stove before it cools down, you can ensure that your fuel is as completely combusted as possible, minimizing emissions as well as creosote buildup in the flue." " Primary Measures For Low-Emission Residential Wood Combustion – Comparison of Old With Modern Optimised Systems" From the Proceedings of the 17th European Biomass Conference & Exhibition, June 2009, Hamburg, ETA-Renewable Energies (Ed.), Italy www.academia.edu/download/85035171/Paper-Brunner-primary-measures-for-low-emission-wood-combustion-Hamburg-2009.pdf"The combustion process in stoves is characterised by three combustion phases, the ignition phase, the main combustion and the burnout phase (see Fig. 1). At the beginning of a combustion cycle, during the ignition phase, the O2-content of the flue gas decreases while the furnace temperatures increase. As long as the O2- concentrations are too high and the furnace temperatures are too low to achieve appropriate burnout conditions, high CO, OGC and PM emissions are detected. As soon as stable combustion conditions have been reached the main combustion phase begins. This phase is characterised by quite stable O2 concentrations in the flue gas and sufficiently high temperatures in the furnace to provide acceptable burnout conditions. During this phase the CO, OGC and PM emissions are significantly lower than during the ignition phase. At the end of the combustion cycle charcoal burnout takes place, the O2 concentrations in the flue gas start to increase and the furnace temperatures decrease again. Consequently, the burnout quality decreases and the CO emissions increase. The OGC and the PM emissions however stay on a rather low level which is due to the fact, that the main amount of volatiles has been released from the fuel during the ignition and the main combustion phase. The major part of the emissions generated during one combustion cycle is related to the ignition phase. Therefore, optimised stove designs should aim at a very short ignition phase which means, that high flue gas temperatures and low O2-concentrations in the flue gas (around 10 vol% (d.b.)) are reached within short time. During the main combustion phase optimised mixing of the gases released from the wood logs with the combustion air can lead to improved burnout conditions. The implementation of appropriate air staging concepts has shown to be a very efficient measure for emission reduction in stoves. Therefore, the stove should be divided in a main combustion chamber and a subsequent burnout zone. Moreover, a staged combustion air supply should be realised." "The primary combustion air flow which is also used to control the fuel burning rate (load control) should be kept as low as possible. In any case an understoichiometric air ratio should be maintained for the primary combustion air supply. The secondary air is then used to almost completely oxidise the gaseous compounds released from the fuel bed (CO, hydrocarbons). This burnout can be improved by an appropriate mixing of the gases released from the fuel bed with the combustion air as well as by the provision of enough residence time at high temperatures (>800°C) after injection of the secondary combustion air." "As presented in this paper, a considerable number of primary measures for the reduction of CO, OGC and PM emissions from residential biomass combustion systems exist. The most important ones are the implementation of appropriate air staging, the provision of an intensive mixing of the combustion air and the flue gases in the secondary combustion zone, enough residence time in the secondary combustion zone at temperature >800°C as well as furnace geometries and air injection..." |
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Post by martyn on Feb 4, 2023 14:09:10 GMT -8
What about an optimum temperature for secondary air ?
I am thinking there is no one answer as it might depend on the temperature of the fire it would be feeding and possibly many other factors like the size of the chamber but I dont really know what I am talking about!
Very occasionally I have seen blue flashes coming from my secondary air supply tube what is that all about?
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Post by fiedia on Feb 5, 2023 1:05:29 GMT -8
Very interesting information. Unfortunately, I could not open the third link.
So the goal is to reach at least 600°C to get secondary combustion and ideally 800°C to minimize pollution.
I am wondering if there is a max temperature to avoid the release of other pollutants, for example nitrous oxides described by Solomon . |
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Post by Dan (Upstate NY, USA) on Feb 5, 2023 4:10:23 GMT -8
I wonder if nitrous oxides can be reduced with the "dry seam"??!
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Post by josephcrawley on Feb 5, 2023 7:49:50 GMT -8
I wonder if nitrous oxides can be reduced with the "dry seam"??! Heck the dry seam can even burn water. |
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