Fire with the right technology

You fire to fill an energy demand in your house. How hard you load the firing is often determinant to your firing result. To fire with wood without accumulation directly to the effect demand of the house therefore requires a certain technology that not too many can do. To fire to small effect demands is also very difficult. To get a fairly good function you have to make a log fire which means adjusting the wood inserts to the actual heat demand. You can seldom fill up the wood hopper with wood in the evening to with help of the draught regulator have it make the night. Such a firing makes the draught regulator strangles the oxygen to the combustion to prevent a boiling and then the combustion temperature sinks. With this way of firing you have destroyed both the temperature and oxygen supply, and the smoulder firing is a fact. This handling then leads to heavy tar coatings that make the efficiency lower and seriously increase the risk of soot fire and disturbing emissions and could also, in worst case, lead to a fire incident. Then it is up to the owner of a double boiler or an over combustion boiler to watch out for too high flue-gas temperatures. You can to a certain degree lower the flue-gas temperature by lower the flue-gas damper of the boiler so that the boiler is not over loaded compared to what the convection part in the boiler can receive. Dry wood and a good under pressure mean risk for over load and very high flue-gas temperatures.

Below you find explanations listed of the different boilers on the market, to not create confusion of concept.

There are at least four groups of boilers:
1. Simple boilers
2. Combination boilers
3. Double boilers
4. Kitchen boilers

Simple boiler we call a boiler that has a hearth and is adjusted to a type of energy, e.g. oil or pellets.

Combination boilers are all boilers that have one and the same hearth where several different types of energy can be used. Example, wood burning, oil and pellets. Then the same hearth is combined for two or several different types of energy and the boiler is then called combination boiler.

Double boilers are the boilers that have separate hearths for oil/pellets or wood. On these boilers oil/pellet burners can be mounted even if you want to fire with wood.

Kitchen boilers are the water jacketedhearths that are installed in kitchens. These are often complemented with a hob and owen for cooking. These past years these boilers have become very common and today exist with different combustion systems. Boilers can then be devided into separate groups after different combustion principles.

Here they are explained.

Over combustion means that you take out the flue-gases in the upper part of the hearth and thereby ignite the total wood content of the hearth with very high flue-gas temperature as result. By this, the firing cycle becomes as most intense during the first time after the ignition, to gradually more and more decrease this firing principle makes it difficult to during the whole time add the right amount of oxygen to the combustion that therefore destroy stable combustion results.

Under combustion means that you take out the flue gases above the roster, but from the lower part of the hearth. Hereby you ignite only a smaller part of the wood content of the hearth concurrently with the burning of the wood fuel on the bottom of the boiler, new wood falls down into the combustion zone with relatively low flue gas temperature as result if you compare with the over combustion principle. If the hearth is conic with the bigger part upwards, it means that the risk of the wood getting jammed decreases. More modern under combustion boilers have a ceramic isolated after combustion chamber where the gases from the wood get to finish burning before the convection starts.

Reversed combustion basically works like under combustion but with the difference that the primary air is added above the roster surface or ceramic hearth instead of under, and the flue gases are found in the ash space. With this construction, the gases will, in proportion to under combustion get the opposite way to pass down through the roster surface instead of above.

Blue flame combustion is the best technology if you are thinking about choosing wood burning as heat altenative. The principle is quite new within wood combustion and built on an old technology, the wood-gas principle, the technology started in Sweden in the beginning of the 1980's. Briefly the combustion can be explained that you use excess air and the moisture content of the wood, in other words the water steam in the wood, to break down the pyrolysis gases to shorter hydrocarbon chains often boilers with reversed combustion principle are used and complemented with a fan in the boiler that is providing the combustion air both primarily and secondarily. The air feed is constructed in a way that the fan creates a jet effect that sucks down the pyrolysis gases from the wood hopper down to the combustion chamber, hereby both a more stable combustion result and faster combustion process are obtained that give a better control over the end result. The firing - and combustion technology put less pressure on the fireman and are not so sensitive to outer disturbances that natural draught boilers can be. The blue flame technology is distinguished by that the flame is no longer white or yellow and glowing but transparent and blue in the tone. To a person who has not seen a blue flame boiler burn it is easiest to compare the flame to the flame you create when you fire with LP-gas. This combustion principle normally gives the best efficiency and the best environmental result and lowest wood consumption.