The subject of the present invention is a closed firewood-burning fireplace-type furnace, which in addition to the commonly-known operation as a standard fireplace, also provides long-term operation (up to 12 hours) at low nominal power (up to 3,5 kW).

The first mode of operation is that of the standard, commonly-known fireplace, where the wood fuel is loaded into a primary chamber. During the burning process, a larger amount of firewood bums simultaneously; therefore, the burning time is shorter and burning power greater. The second mode of operation by means of corresponding regulation and the feeding of wood fuel from a reservoir provides an essentially longer burning time at a lower burning power. Construction and regulation of the furnace enables very clean combustion and consequently, low smoke emission and high energy efficiency, despite the fact that the burning power is lower. In both operational modes, the user may continuously observe burning wood logs through a glass.

The technical problem solved by the subject invention is the construction of a fireplace- type furnace, which enables long-term burning, preferably up to 12 hours, with constant low power up to 3,5 kW, very clean combustion and high energy efficiency.

State of the art

There are no known solutions that would enable long-term burning with constant low burning power, clean combustion and high efficiency.

A known solution that enables longer burning or has an integrated firewood reservoir is described in a patent application US 4335702. This solution enables longer burning, due to the firewood reservoir, where wood logs are placed in a horizontal position. However, it does not allow burning under 3,5 kW, since too large an amount of firewood would be burning simultaneously. The user is also deprived from observing the flame, which also represents an aesthetic aspect of the furnace use. The second known solution is patent application US 4355587, which also enables a longer burning time and includes a firewood reservoir. This solution is very unpractical, since it requires a lot of space. It differs from the previously described solution in that the wood logs are placed one above the other in an inclined tube, which can cause disturbances of wood log dosage into the combustion chamber. Another setback of this furnace is that the flame is not visible to the user.

In most of the proposed solutions, the burning power is adjusted merely by the quantity of firewood fed into the burning process, where fresh air is normally fed into the combustion chamber from below, which means that the quality of combustion is thereby changing.

It is commonly believed that in order to achieve smoke emissions within the limits provided by standards, higher burning power is required. None of the proposed solutions enable a lower burning power, where despite lower burning power, low smoke emissions in the environment are achieved, as required by currently valid standards.

The subject invention solves the described technical problem by introducing a new construction of a permanent burning fireplace-type furnace, where the wood logs are placed in such manner that only a part of one wood log is present in the combustion zone (one of all loaded into the furnace), which enables controlled burning with low power and very clean combustion.

Description of the invention

The invention will be described in more detail in the following embodiment and presented in the attached drawing.

Figure 1: Longitudinal cross section of fireplace-type furnace

The permanent burning fireplace-type furnace according to subject invention consists of a reservoir, preheating channel, a primary and a secondary combustion chamber and a smoke channel.

The fuel reservoir 1 is a vertically disposed tube, mainly functioning as fuel 2 storage. The preferred type of fuel 2 is firewood placed in the reservoir 1 in a vertical direction. In the lower section, the reservoir 1 continues into the primary chamber 6.

Besides fuel 2 storage, the reservoir 1 also prepares fuel 2 for combustion. In the upper part of the reservoir 1 , the fuel 2 is preheated and in the lower part of the reservoir , where the reservoir 1 is connected with the primary chamber 6, the fuel begins to gasify. Gasification of preheated and partially gasified fuel 2 is completed in the primary chamber 6. Generated gases inflame and combust in the secondary chamber 9.

The fuel 2 is fed into the primary chamber automatically, based on its own weight. In this manner, uniform and long-term burning is achieved, without intervention to the furnace. A part of the generated heat 10 from the primary chamber 6 and from the secondary chamber 9 maintains the preheating process and gasification of the fuel 2 in the reservoir 1.

Air 3 is fed only into the primary chamber 6. Therefore, burning of the fuel 2 in the reservoir 1 is prevented. In such a manner, the lack of oxygen required for burning in the reservoir 1 is achieved. The air 3 is fed through the inlet 5, which is positioned on the point of connection of the reservoir 1 and primary chamber 6, guiding the air 3 directly towards the wood log.

The air 3 is preheated in the preheating channel 4, which is positioned beside the reservoir 1 and extends from one to two thirds of the reservoir 1 height, before being fed into the primary chamber 6.

The air 3 enters the preheating channel 4 from the outer bottom side, travels through the outer part up to the top of the preheating channel 4 and turns down through the inner part to the inlet 5, where it enters the primary chamber 6. The ratio between the height of the primary chamber 6 and the diameter of the reservoir 1 is between 0,8 and 2,5. The air 3 is preheated to ensure the highest possible temperature in the primary chamber 6 and the secondary chamber 9.

The entire periphery of the primary chamber 6 and of the secondary chamber 9 is surrounded with thermo accumulating elements, composed of two layers of different materials. The inner layer 8 is made of ceramics, which is harder and wear resistant, and functions as a thermo accumulator. The outer layer 7 is made of vermiculite and functions as a thermal insulator. In such a manner, a stable temperature in the primary chamber 6 and in the secondary chamber 9 is secured and thereby stable furnace operation as well.

Above the secondary chamber 9 at the entrance into the smoke channel 12, a catalyst 11 is provided, which takes care of the complete oxidation of non-combusted gases and diminishes the amount of harmful emissions into the environment, which is a priority for reducing CO emissions into the atmosphere.