WO1998021526A1

WO1998021526A1 - Method and heat boiler for optimized combustion

Info

Publication number: WO1998021526A1
Application number: PCT/SE1997/001902
Authority: WO
Inventors: Jan Ericson; Sven Bernhardsson
Original assignee: Jan Ericson; Sven Bernhardsson
Priority date: 1996-11-13
Filing date: 1997-11-12
Publication date: 1998-05-22
Also published as: SE510235C2; EP0986721A1; SE9604138L; SE9604138D0

Abstract

The invention relates to a method of accomplishing, in a heating boiler (100) for heating houses and intended for the combustion of fossil fuels and/or renewable fuels, an optimized combustion and an effectual decrease of the temperature of the combustion gases generated when burning the fuel in a burner (2) introduced into a combustion room (1) of the heating boiler, whereby the combustion room (1) is manufactured from a highly alloyed temperature and corrosion resistant material, the combustion gases through a flue duct (6) are brought from the combustion room to a condenser (7) in which the combustion gases are forced to condense, i.e. they are cooled to a temperature below the dew point, the condenser (7) and the flue duct (6) are likewise manufactured from a highly alloyed, temperature and corrosion resistant material and the cooled combustion gases from the condenser are directly, i.e. without the use of a chimney, brought to the atmosphere by using a fan (9) which is governed by at least one sensor (10) to ensure an excess of air in the combustion process. The invention also relates to a heating boiler.

Description

Method and heat boiler for optimized combustion.

Subject of invention:

This invention concerns in general the combustion of renewable fuels and fossil fuels, preferably for heating purposes, and relates more specificallt to a specific method for accomplishing optimized combustion and a drastic lowering of the temperature of the combustion gases and to a heating boiler for this purpose, and of the kind described in the preambles of claims 1 and 7 respectively.

The background of the invention

At present some 750.000 houses in Sweden are heated using direct electric heating and with expected increasing energy costs, the heating costs of those houses will increase drastically. If, with the technique of today, and for said houses, one would switch to heating sources using fossil fuels, renewable or not, the investment costs for the chimney, the heating boiler, the hot water distribution system and the installation jointly become very high.

In addition thereto increasing energy costs, not only for electrical energy but also for fossil fuel combustion, the forthcoming shutdowns of nuclear power plants, the stopped development of hydro power as well as the political ambitions to decrease the carbon dioxide emissions, result in a demand for heating boilers which are suitable for the combustion of renewable fuels as well as of fossil fuels with a high degree of efficiency and emitting clean combustion gases.

Other problems in this context are e.g. that in many older houses, the chimney with increasing age has developed such a bad condition that the risk for fire has increased quite a lot and that the cost for the repair of such a chimney is quite high, that the heating boilers presently available on the market have a traditional, "heavy" and complicated design and are perceived as requiring too much space and that the cooling of the combustion gases is so inefficient, that a traditional chimney is required. The object of the invention

The fundamental object of the present invention is therefore to develop a method as well as a heating boiler of the kind mentioned above, which eliminate or at least minimize the above indicated problems and which satisfies the above discussed present demands as well as the anticipated future demands.

The above stated object is, according to the invention, accomplished by using a specific method and heating boiler respectively as mentioned above, displaying the characteristics defined in the characteristic parts of claims 1 and 7 respectively.

The dependent subclaims describe further advantageous developments of the fundamental ideas of the invention.

Short description of the drawing

The invention and its specific characteristics and advantages are closer described below in connection to an embodiment thereof given solely for the purpose of exemplifying the invention and very schematically illustrated in the enclosed drawing, which in a schematic cross-section thereof illustrates the design of a heating boiler according to the invention.

Detailed description of the invention

As shown by the drawing, the heating boiler 100 according to the invention, consists of a combustion room 1, which is made as an inner tube or shell with a circular cross section, manufactured in a high temperature and corrosion resistant material, preferably a stainless steel with a scaling temperature above about 600°C ; for heating boilers with higher effects, the scaling temperature should be higher than 850°C. The combustion room 1 can be surrounded by an outer shell or tube 5 manufactured from stainless steel and forming a gap 5a in relation to the inner tube 1 , whereby the space formed by the gap between the tubes is used for the circulation of water or air, with the purpose to cool the combustion room as well as to produce hot water or hot air, and by an isolated outer casing 5b. In the combustion room, a burner 2 is introduced either perpendicular to but preferably tangential to the axial direction of the tube 1. The purpose of the latter is to achieve a turbulent flow of the combustion gases, thereby gaining an improved heat transfer to the water- or air-filled space 5a between the inner and outer shell 1 and 5 respectively and to increase the retention time for ash particles, thereby increasing the separation of these ash particles.

To further improve the heat transfer and ash particle separation, the combustion room 1 may also be equipped with a spiral formed guide plate 3, indicated in the drawing, and an ash separator 4, both manufactured in a high temperature material as per above, i.e. preferably a stainless steel with a scaling temperature more than about 850°C for heating boilers with a smaller effect and around 950°C for larger heating boilers. The spiral formed plate 3 has such a width that it covers about half the diameter of the combustion room, as measured through the cross section thereof. The ash separator 4 is located at the upper end of the combustion room and has the shape of a cone, preferably a truncated cone, with its smaller cross section turned to the inner part of the combustion room. The total cross sectional area for combustion gases to pass through the ash separator is at least twice the cross sectional area of the condenser 7 described below.

The hot combustion gases are transferred from the combustion room 1 to a condenser 7 through a flue duct 6 made of stainless steel or a high temperature material as per above, with a scaling temperature of more than about 700°C for smaller heating boilers and more than about 800°C for larger heating boilers. The condenser 7 which cools the combustion gases to a temperature less than 60°C is manufactured from a stainless steel which on one hand has a scaling temperature higher than 700°C and on the other hand has a wet corrosion resistance suited to resist the condense from the fuel giving the most corrosive conditions. The condenser can also be manufactured from acid proof material.

As the name indicates, the condenser 7 has the task of condensing the combustion gases, not only cooling them i.e. the dew point must be reached, which is also important for the efficiency of the condenser, because without condensation the effectiveness of the condenser drastically decreases.

For the condenser 7, a welded lamella heat exchanger with a high heat transfer efficiency is used. Preferably the lamellas are profiled. This is the ultimate design selection, since a plate heat exchanger with rubber sealing can not withstand the high temperatures. That also goes for soldered or brazed plate- and lamella heat exchangers, which soldering or brazing also can corrode. Tubular heat exchangers do technically resist the operating conditions but are too expensive.

The condense from the condenser 7 is separated in a condense separator 8, which is equipped with a plate labyrinth and which can also be cooled to further lower the combustion gas temperature and decrease the moisture. The combustion gas condensation has, for the function of the heating boiler, quite decisive effects. One is that the efficiency of the heating boiler increases, which is of great importance to both the house owner and the environment, and secondly the need for a chimney is eliminated, which greatly reduces the total installation cost. Furthermore the emission of environmentally polluting combustion gases diminishes.

The strong convective effect of the chimney is here replaced by a strong fan 9 with a net effect, corrected for the flow resistance in the outgoing tube 1 1, which is at least as large as the effect of the fan in the burner 2 used. It is a necessary condition for the function of the heating boiler, that the combustion takes place with a proper excess of air. To control that excess air is prevailing, the heating boiler is equipped with a probe 10, for direct or indirect measurement of the oxygen potential, e.g. a lamda sensor.

To be able to always ensure optimized combustion conditions, e.g. at a temperature of about 900°C to 1000°C which gives a minimum amount of NOx, preferably a temperature sensor (not shown in drawing), a pressure sensor (not shown) as well as a governing system (likewise not shown) are also used, whereby said governing system, dependent on the values measured by the sensors, continuously controls the fan 9 and possibly the burner 2 to create optimized conditions for the combustion. At future requirements for environmental marking the governing system can be locked or sealed to eliminate the risk for manipulation.

The fundamental advantages with this invention are achieved through a combination of the features characterizing the invention, such as the condensation of the combustion gases, the highly alloyed construction material and the direct, that is without a chimney, discharge of the combustion gases to the atmosphere, by means of a fan being governed through a sensor to ensuring excess of air during the combustion process.

The proposed design with a construction of high temperature materials and stainless steels and with the efficient condensation of the combustion gases, furthermore makes it possible to load the heating boiler according to the invention with a high effects per volume unit. As an example, a heating boiler designed according to the invention for use at the effect level of 10- 20 kW has a volume of only 0.25 m³. This means that the heating boiler according to this embodiment of the invention can be manufactured to a low cost despite the fact that the cost per unit of weight of the material used is rather high. Simultaneously, the reliability, due to absence of corrosion, is very high even when thin walled material is used. The fact that no part of the heating boiler is exposed to higher pressure than given by the highest pump distance for the hot water, simplifies the construction and lowers its costs .

One, from many aspects, optimized structure is achieved by designing the heating boiler such that the components included therein, in their shape and capacity, are carefully balanced to each other.

In one embodiment as illustrated in the drawing, the heating boiler can, in the tube 11 leading from the fan 9, be equipped with a damper 12, which through a branched tube 13 transfers a controllable part of the combustion gases back to the burner 2 for reuse, while the remaining part of the combustion gases is used in a heat exchanger 14 for preheating the fresh combustion air supplied to the burner. To summarize it shall be explained that in a suitable practical embodiment the invention concerns a heating boiler with an effect of up to a maximum of about 500 kW, suitable for the combustion of renewable fuels or fossil fuels, which is manufactured from stainless steel and high temperature materials and which can be exposed to high effect loads and may thus be designed very compact, still having a long service life and having a high degree of efficiency. Through a tangentially positioned burner, a controlled flow of the combustion gases and an ash separator in the combustion room, the fly ash is separated before it reaches the condenser. The condenser consists of a compact and efficient, welded lamella heat exchanger which very strongly cools the combustion gases. In this way the degree of efficiency strongly increases and the need for a chimney is eliminated. The condense is separated in a condense separator and the cooled combustion gases or a portion thereof are then discharged from the house by means of a fan. At least one sensor governs the combustion process so that the combustion always occurs with an excess of air. No part of the heating boiler is pressurized to a pressure higher than the discharge head to the highest located radiator in the house.

In this way a heating boiler is developed, which satisfies the environmental requirements set today and in the near future, and which at the same time meets the demand from housing owners for a compact, reliable heating boiler which can be installed to a low total cost and in a limited space.

Even if the invention has been described with reference to specific embodiments thereof, it should be obvious that it also includes such modifications and changes which are obvious to a person skilled in this field. The extent of the invention will therefore only be limited to the enclosed patent claims.

Claims

PATENT CLAIMS

1. Method of accomplishing, in a heating boiler (100) for heating houses and intended for the combustion of fossil fuels and/or renewable fuels, an optimized combustion and an effectual decrease of the temperature of the combustion gases generated when burning the fuel in a burner (2) introduced into a combustion room (1) of the heating boiler, characterized in that the combustion room (1) is manufactured from a highly alloyed temperature and corrosion resistant material, in that the combustion gases through a flue duct (6) are brought from the combustion room to a condenser (7) in which the combustion gases are forced to condense, i.e. they are cooled to a temperature below the dew point, in that the condenser (7) and the flue duct (6) are likewise manufactured from a highly alloyed, temperature and corrosion resistant material and in that the cooled combustion gases from the condenser are directly, i.e. without the use of a chimney, brought to the atmosphere by using a fan (9) which is governed by at least one sensor (10) to ensure an excess of air in the combustion process.

2. Method according to claim 1, characterized in that the combustion temperature in a first step is lowered through contact with the combustion room (1) which is cooled by a circulating fluid, and that the retention time of the combustion gases in the combustion room (1) is prolonged through giving the combustion gases a turbulent flow in contact with the cooled inner wall of the combustion room to increase the heat transfer to the circulating fluid and to increase the retention time for the fly ash and thereby improve the efficiency of the separation of said ash from the combustion gases in the combustion room.

3. Method according to claims 1 or 2, characterized in that the combustion room (1) is designed with a circular cross section and in that the burner (2) is positioned tangentially in relation to the combustion room, whereby the combustion gases are given the turbulent flow in the shape of a circular movement in the combustion room, and in that the turbulent, circular movement of the combustion gases in the combustion room (1) is supported by a spiral shaped guide plate (3) arranged on the inner wall of the combustion room, and said plate being manufactured from a highly alloyed temperature- and corrosion resistant material.

4. Method according to one or some of claims 1-3, characterized in that no part of the heating boiler (100) is pressurized to a higher pressure than that corresponding to the highest located radiator in the house/houses.

5. Method according to one or some of claims 1-4, characterized in that a part of the combustion gases conducted away by the fan (9) is transferred back to the burner (2) for reuse and/or that fresh air supplied to the burner (2) is preheated by the combustion gases.

6. Method according to claims 1-5, characterized in that the components of the heating boiler (100) are carefully balanced to each other with regard to shape and capacity and that the combustion is governed by a control system which dependent upon values detected by a lamda sensor and/or a temperature sensor and/or a pressure sensor governs the fan (9) and possibly the burner (2).

7. Heating boiler (100) for the combustion of fossil fuel and/or renewable fuels for the heating of houses, with a combustion room (1) with a burner (2) introduced into it, characterized by a standing condenser (7), connected to the combustion room through a flue duct (6) for condensing the combustion gases, i.e. for cooling said gases to a temperature below the dew point, and in that the combustion room (1), the flue duct (6) and the condenser (7) are manufactured from highly alloyed temperature and corrosion resistant materials, and a fan (9) connected downstream from the condenser for directly, that is without a chimney, bringing the cooled gases to the atmosphere, and by at least one sensor (10) for the direct or indirect measurement of the oxygen potential, said sensor being connected for governing the fan (9) to ensure excess of air in the combustion process.

8. Heating boiler according to claim 7, characterized in that the inner wall of the combustion room (1) is made out of a tube manufactured from stainless steel with a scaling temperature of more than about 600°C, at larger effects more than 850°C, in that the flue duct (6) is manufactured from stainless steel with a scaling temperature exceeding some 700°C, at larger effects exceeding 800°C and in that the condenser (7) is manufactured from a stainless steel with a scaling temperature exceeding some 700°C and also having a wet corrosion resistance adapted to the fuel causing the most corrosive condense.

9. Heating boiler according to claim 7 or 8, characterized in that the condenser (7) is a welded lamella heat exchanger with a high heat transfer rate and with profiled lamellas and by a condense separator (8), comprising a plate labyrinth, for the separation of the condense from the condenser.

10. Heating boiler according to claim 7, 8 or 9, characterized in that the combustion room (1) has a circular cross section and an inner- and outer shell (1 and 5 respectively) with a space (5a) formed inbetween for the circulation of a cooling fluid and in that the burner is positioned tangentially in relation to the combustion room causing the combustion gases to perform a turbulent circular movement in the combustion room.

11. Heating boiler according to claim 10, characterized by a spiral shaped guide plate (3) arranged on the inner wall of the combustion room, to support the circular movement of the combustion gases in the combustion room, in that the spiral shaped guide plate is manufactured from a highly alloyed temperature- and corrosion resistant material, in particular stainless steel with a scaling temperature exceeding some 850°C, at larger effects exceeding some 950°C, and preferably having such a width, that it with its turns covers substantially half the diameter of the combustion room (1).

12. Heating boiler according to claim 11, characterized in that in connection to one end of the combustion room (1) an ash separator (4) is arranged, having the shape of a cone, preferably a truncated cone, turned in towards the combustion room, in that the ash separator has a total flow area for combustion gases which is at least twice as large as that of the condenser (7) and in that the ash separator is likewise manufactured from a highly alloyed temperature and corrosion resistant material, in particular stainless steel with a scaling temperature exceeding some 850°C, at larger effects exceeding some 950°C.

13. Heating boiler according to any or some of claims 7-12, characterized by a damper (12) in a tube (11) coming from the fan (9), for returning, through a branched tube (13), a portion of the combustion gases to the burner (2) for reuse and/or by a heat exchanger (14) in contact with the outgoing tube (13) for preheating fresh air supplied to the burner (2).

14. Heating boiler according to any or some of claims 7- 3, characterized in that the fan (9) has a net effect, corrected for the flow resistance in the outgoing tube (13), which at least corresponds to the effect of a fan provided in the burner (2).

15. Heating boiler according to any or some of claims 7-14, characterized in that the outer wall (5) of the combustion room (1) is made out of stainless steel, and that in the space (5a) formed between the outer and inner walls, water or alternatively air is circulated for heating purposes.

16. Heating boiler according to any or some of claims 7-15, characterized in that with regard to shape and capacity the components included in the heating boiler (100) are carefully balanced to each other and by a governing system for continuously regulating the fan (9) and possibly the burner (2) dependent upon values detected by a lamda sensor, and/or a temperature sensor and/or a pressure sensor.