EP1332316B1 - Method for firing an oil firing or gas firing boiler with a dust-like fuel - Google Patents

Description

The invention relates to a method for firing one for the oil or gas firing designed boiler with a dusty, fluidized by means of air fuel.

From US 4 057 021 a burner for the combustion of coal dust is known, from a divergent burner muffle and a subsequent to the largest diameter Acceleration nozzle exists. Combustion air will be the divergent burner muffle on her End smaller diameter supplied via vanes, which the combustion air into a about the axis of the burner muffle rotating flow, so that the combustion air in helical paths at an angle of about 45 ° to the mantlet line of the burner in the direction of the largest diameter of the burner muffle flows due to the nature of Air supply arises in the center of the air intake area a large negative pressure, the result has, that part of the helical air flow in the area of the largest diameter the burner muffle reverses and as return flow in the center of the burner muffle to the air inlet area flowing back. In this return flow is arranged by means of a centric Injection lance, which penetrates the air inlet area of the burner muffle and in the area of largest diameter of Brennerrnuffel ends and carries there a deflection hood, coal dust injected in a fluidized state. The carrier medium for the fluidization of the pulverized coal is an inert gas, in particular combustion exhaust gas. The coal dust is from the backflow carried in the air inlet area. After the first ignition by means of a Ignition lance in the area of the air inlet area burns the coal dust in the helical running flow. The radiant heat emanating from it heats the coal dust in the backflow. Since he is in an inert gas there, he can not immediately burn, but is merely heated and activated. As a result, he spontaneously ignites when he is in the Air inlet area is brought into contact with combustion air.

The document mentions that the atmosphere in the burner towards the to befeuemden Room has an overpressure of 20 mm of WS (about 200 Pa), and that in the burner muffle About 30% to 50% of the calorific energy contained in the pulverized coal is burned. It is further described that the burner instead of a gas or oil burner for firing a boiler can be used and the resulting from the combustion of the coal dust Ashes dry precipitates as the ascheführenden fuel gases in the fired Space-cooled and thereby fall below the ash melting temperature. But this goal can be be achieved only if the boiler has a sufficiently large volume, so that Burn the coal completely and cool the ash below the ash melting point can. About the requirements that an exchange of a gas or oil burner against to allow a pulverized coal burner, however, nothing is mentioned in the document.

• der Feuerraum zum Ausbrand der Öl- oder Gasflamme ausreicht, und
• die Temperatur der Rauchgase im Bereich Austritt Feuerraum / Eintritt Überhitzer (auch Ecktemperatur t_E genannt) meist bei 1.050 bis 1.150°C liegt. Die Ecktemperatur ergibt sich als wirtschaftliches Optimum der Gesamtkosten der Kesselanlage, die sich aus den Kosten für den Feuerungsraum und den Kosten des stromabwärts desselben angeordneten Konvektionsteils ergeben.

Oil or gas fired water tube boiler for generating z. B. steam today are designed so that

• the combustion chamber is sufficient to burn out the oil or gas flame, and
• the temperature of the flue gases in the area outlet combustion chamber / inlet superheater (also called corner temperature t _E ) is usually at 1,050 to 1,150 ° C. The corner temperature results as an economic optimum of the total cost of the boiler plant, resulting from the cost of the firing space and the cost of the downstream arranged convection part.

An oil or gas flame gives its heat in the firebox to 95% to 97% in the form of Radiation off. Up to 3% of the heat is emitted by gas radiation, only 2% heat emission done by convection in the firebox, because the gas flow is slow and stringy.

The need to upgrade existing boiler systems from oil or gas firing to The burning of powdered fuels started in the summer of 2000, when oil and gas prices increased within a short time by more than 100% had risen. The heat price of heavy Heating oil reached about 2.5 times the heat price of steam coal; the gas price follows that Heating oil price usually with a certain time delay.

1) Die Staubflamme erfordert gegenüber einer Öl- oder Gasflamme das 2- bis 3-fache Ausbrennvolumen. Wenn das Feuerraumvolumen für Gas- oder Ölbefeuenrng bemessen ist, reicht es somit für den Ausbrand von Staub nicht aus. Bei gleicher Feuerungsteistung wie bei Öl oder Gas würde sich der Ausbrand des Staubes bis weit in die nachgeschalteten Einheiten hinein, wie beispielsweise den Überhitzer, hinziehen und dort starke Verschlackung und Korrosion verursachen. Es besteht also als erstes Problem, den Ausbrand des Staubes um 100 oder 200% zu beschleunigen.

2) Bei den für Öl- oder Gasfeuerung üblichen Ecktemperaturen von 1.050 bis 1.150°C würde es bei Verbrennung von Kohlenstaub im Feuerraum und Überhitzer zu starker Schlakkenbildung kommen. Daher muß die Ecktemperatur t_E abgesenkt werden, und zwar in Abhängigkeit vom verwendeten Brennstoff:

a) für Steinkohle gibt das Ruhrkohle-Handbuch (7. Auflage, 1987, Seite 160, Kapitel 3.4 "Ascheschmelzverhalten") den zulässigen t_E-Wert mit maximal 950°C an;

b) für Braunkohle gibt das Rheinbraun-Datenblatt vom März 1987 zum Ascheschmelzverhalten an: "Sinter-Temperatur ≥ 900°C".

Eigene Untersuchungen der Anmelderin mit Braunkohle ergaben:

• t_E = 940°C ... starke Verschlackung
• t_E = 920°C ... Beginn der Verschlackung
• t_E = 880 bis 900°C ...keine Verschlackung. Die Zahlenangaben decken sich also mit den im Rheinbraun-Datenblatt angegebenen Werten.

Das zweite Problem besteht also darin, Maßnahmen zu ergreifen, die zu einer Absenkung der Ecktemperatur von 1.050 bis 1.150°C auf ca. 900°C führen.

3) Senkt man die Ecktemperatur t_E wie vorstehend ab, verkleinert sich das Temperaturgefälle vom Rauchgas (Temperatur t_E) zur Überhitzerrohrwand (meist 550 bis 600°C) von

• bisher z. B. 1.100°C - 600°C = 500°C
• auf jetzt z. B. 900°C - 600°C = 300°C,

also auf etwa 60% der bisherigen Temperaturdifferenz. Entsprechend verringert sich die Dampfüberhitzung, was nicht zulässig ist, wenn dem Kessel beispielsweise eine Turbine nachgeschaltet ist. Als drittes Problem ergibt sich daher, die Überhitzerteistung trotz verringerter Ecktemperatur wieder auf den alten Wert zu erhöhen, der sich bei Befeuerung mit Öl oder Gas ergeben würde.

A simple replacement of the oil or gas burners with pulverized coal burners does not lead to the goal for the following three reasons:

1) The dust flame requires 2 to 3 times the burnout volume compared to an oil or gas flame. Thus, when the firebox volume is sized for gas or oil firing, it is not sufficient to burn off dust. With the same firing rate as with oil or gas, the burn-out of the dust would drag far into the downstream units, such as the superheater, causing severe slagging and corrosion. So the first problem is to accelerate the burnout of the dust by 100 or 200%.

2) At the usual corner temperatures of 1,050 to 1,150 ° C for oil or gas firing, heavy coal formation would occur when pulverized coal is burned in the furnace and superheater. Therefore, the corner temperature t _E must be lowered, depending on the fuel used:

a) for hard coal, the Ruhr coal manual (7th edition, 1987, page 160, chapter 3.4 "ash melting behavior") indicates the permissible t _E value with a maximum of 950 ° C;

b) for lignite, the Rheinbraun data sheet dated March 1987 on ash melting behavior indicates: "sintering temperature ≥ 900 ° C".

Own investigations of the applicant with lignite showed:

• t _E = 940 ° C ... strong slagging
• t _E = 920 ° C ... start of slagging
• t _E = 880 to 900 ° C ... no slagging. The figures thus coincide with the values given in the Rheinbraun data sheet.

The second problem is therefore to take measures that lead to a lowering of the corner temperature of 1,050 to 1,150 ° C to about 900 ° C.

3) If one lowers the corner temperature t _E as above, the temperature gradient decreases from the flue gas (temperature t _E ) to the superheater tube wall (usually 550 to 600 ° C) of

• previously z. B. 1100 ° C - 600 ° C = 500 ° C.
• on now z. Eg 900 ° C - 600 ° C = 300 ° C,

So about 60% of the previous temperature difference. Accordingly, the steam superheat is reduced, which is not permissible if, for example, a turbine is connected downstream of the boiler. The third problem is therefore to increase the overheating performance despite reduced corner temperature back to the old value that would result if fired with oil or gas.

1) Für die Befeuerung mit staubförmigem Brennstoff ist nach dem Stand der Technik eine Vergrößerung des Feuerraums notwendig.

2) Zur Absenkung der Ecktemperatur muß gemäß Stand der Technik die Heizfläche im Feuerraum vergrößert werden.

3) Will man trotz abgesenkter Ecktemperatur die Überhitzerteistung beibehalten, muß gemäß Stand der Technik der Überhitzer vergrößert werden.

Conventional solutions to solve the three problems mentioned above; would lead to a very large construction effort:

1) For the firing with pulverulent fuel according to the prior art, an enlargement of the firebox is necessary.

2) To lower the corner temperature must be increased according to the prior art, the heating surface in the furnace.

3) If you want to maintain the superheater performance despite lowered corner temperature, according to the prior art, the superheater must be increased.

The invention has for its object to provide a method of the type mentioned, without changing the existing boiler dimensions in one for a corner temperature run from 1050 to 1150 ° C designed boiler.

This object is achieved with a method for firing one for oil or gas firing designed boiler, in which a dust-like, fluidized by means of air fuel, fed to a combustor in which at least 30% of the fuel is burned, the pressure in the combustor being 1000 Pa above the pressure in the boiler's furnace, a burning air / fuel mixture resulting from the combustion to a Flame jet at a speed of 100 to 120 m / s is accelerated into a furnace the boiler is blown, and the flame jet is directed into the firebox so that results in a fast circulation of flue gases.

The invention solves the complex, consisting of three individual problems task by a only measure. This consists of the previous, down the firebox horizontally attached To replace oil or gas burners with combustors in the area of the firebox ceiling or are arranged on this and preferably fire downwards, so that the Flammstrahl as large a propagation volume in the furnace is available and slag formation on firebox walls is avoided.

Combustors are to be understood as small-sized, very heavy-duty special combs, in which at least 30% preferably 60% of the fuel heat to be implemented, and which terminate in a flame acceleration nozzle having a flame jet of at least 40 m / s, preferably produce 120 m / s speed. The residual fuel burns in the flame jet out. The flame jet of a combustor has such a high speed that the Flue gases in the combustion chamber are put into intense motion by the flame jet, in addition to the heat transfer from the flame to the furnace walls by radiation generates a heat transfer by convection and so to a lowering of the corner temperature leads.

So it depends on the appropriate choice of the device with which the dust-like fuel burned and their place of attachment.

The invention will be described below with reference to a schematically shown in Figure 1 Oil or gas boiler, which is converted to the firing with coal dust, explained in more detail.

In the drawing can be seen a limited by water pipes O combustion chamber 1 with a Superheater 2 and a flue gas outlet 3. Downstream there are secondary heating surfaces 4. All water pipes O and heating surfaces are up with a boiler drum. 5 and connected to a water collector 6 at the bottom. Dashed is the place in the lower area 7, on which an oil or gas burner was previously flanged.

The abovementioned corner temperature t _{E of} the flue gases prevails in the area emerging from the combustion chamber 1 / inlet to the superheater 2 and is in modern boilers at 1050 to 1150 ° C.

To change the firing of the illustrated water tube boiler to coal dust firing the oil or gas burner 7 is removed or shut down. Instead, at the head, i. above arranged on the boiler, a combustor 8, which fires downwards from above. A combustor 8 exists from an arbitrarily shaped combustion chamber 9, in which at least 30% of the fuel heat be reacted, and a subsequent to the combustion chamber 9 Flammbeschleunigungsdüse 10, which produces a flame jet 11 having a velocity of about 100 m / s has The water pipes O are from the flame jet 11 and by the combustion heated flue gases.

The combustor 8 is designed in the present case that in it about 50% of the fuel heat be implemented. The remaining 50% burn in the flame jet.

The combustor 8 is attached to the boiler in such a way; that the injected into the firebox Flame jet generated therein the fastest possible circulation of the flue gases

The operation of the illustrated device will now be explained. The dusty fuel, for example Carbon dust is supplied to the combustor 8 in a fluidized state. Be in it at least 30%, preferably 50% of the fuel burned at a pressure of 1,000 Pa is higher than the pressure in the combustion chamber 1. The burning air / fuel mixture is in the Flammbeschleunigungsdüse 10 to at least 40 m / s, preferably 100 m / s flame jet velocity accelerated. The pulse generated by the flame jet in the combustion chamber generates there a strong flue gas circulation, compared to the buoyancy forces of the hot flue gases negligible are. Only the flame jet 11 determines the flow pattern in the furnace 1.

In the flame jet, the remaining fuel heat burns out. If this burnout percentage per Quantity of heat has twice the space required, as before the oil or gas flame, enough designed for oil or gas firing combustion chamber thus for the coal dust firing. The The first problem mentioned above is solved.

• Der Rauchgasinhait des Feuerraums 1 ist ca. 28 kg.
• Bei 90 m/s Flammstrahlgeschwindigkeit hat der Combustor einen Impuls oder Strahlschub von ca. 1,66 kN, oder 170 kg.

Also, the second-mentioned problem is solved. This can be seen by looking at the figures from a typical industrial water tube boiler:
Boiler output 40 t / h, total burner output 38 MW.

• The Rauchgasinhait the firebox 1 is about 28 kg.
• At 90 m / s flame jet speed, the combustor has a pulse or jet thrust of about 1.66 kN, or 170 kg.

The impulse of 170 kg is large compared to the amount of flue gas of 28 kg and thus determines the speed of the flue gases in the combustion chamber 1. This is the upward speed on the rear wall 12 of the firebox about 50 m / s.

The flue gases run in the furnace 1 several times before they leave it through the superheater 2 and the outlet 3. In this way, in addition to the flame and gas radiation heat transfer by convection is generated, the corner temperature t _E of z. B. 1,100 ° C to 900 ° C lowers.

This also solves the second problem.

Shortly before the superheater 2, the flue gas velocity is still 30 to 40 m / s. Thus, the flow is highly turbulent, while previously in the oil or gas burners 7, the rising Flame gases only with 6 to 10 m / s at the superheater 2 arrived.

Since the heat transfer coefficient α is approximately at the 0.7th power of the velocity: α ~ V 0.7 the heat transfer coefficient of the flue gases in the superheater rises accordingly. The reduced by the cooler flue gases (t _E = 900 ° C instead of the former 1100 ° C) temperature gradient between flue gas and superheater is more than offset by the increased heat transfer coefficient α.

This also solves the problem mentioned in the third place.

• die Luft wird dem Combustor 8 mit einem Druck zugeführt, der um 1.000 Pa über dem Druck im Feuerraum 1 liegt;
• im Brennraum 9 des Combustors 8 verbrennt ein Teil des Brennstoffs bei diesem höheren Druck;
• in der Flammbeschleunigungsdüse 10 wird das Druckgefälle vom Brennraum 9 zum Feuerraum 1 in Geschwindigkeit umgesetzt.

The achieved by the inventive measures increase the heat transfer in the furnace 1 is also still energy efficient, as the following consideration shows:

• the air is supplied to the combustor 8 at a pressure which is 1,000 Pa above the pressure in the combustion chamber 1;
• in the combustion chamber 9 of the combustor 8 burns a portion of the fuel at this higher pressure;
• In the flame acceleration nozzle 10, the pressure gradient is converted from the combustion chamber 9 to the combustion chamber 1 in speed.

• auf den Druck des Brennraums 9 verdichtet,
• dann durch Teilverbrennung erwärmt, und
• schließlich auf den Druck im Feuerraum 1 entspannt:

So the air will be:

• compressed to the pressure of the combustion chamber 9,
• then heated by partial combustion, and
• finally relaxed to the pressure in the firebox 1:

This is a heat engine process that releases mechanical work. in the present Case, this work appears as energy increase, i. Acceleration of the Ftammstrahls. So his energy comes mainly from the combustion and has only a small Part are applied by the blower, with which the fluidized fuel in the combustor. 8 is introduced. The power requirement of this air blower is hardly greater than that of a conventional Oil burner.

These economic effects you get not only in the conversion of the invention oil or gas boilers on pulverized coal firing, but especially if you have one Design boiler from the outset as a pulverized coal boiler. Man kann.dann the combustion chamber of in the beginning, just as small as in an oil-fired boiler.

The same considerations apply to other fuel dusts than coal.

Depending on the boiler design, the combustor can fire in any direction, ie downwards, upwards, transverse or oblique. This depends on practical considerations, such as: B. the achievement The fastest possible circulation of the flue gases in the furnace or the bulging of Impurities. It is important that the outgoing from him flame jet sufficient free volume is available to expand into without being on the walls of the caldera meet and there to produce a slag leading ash precipitate. At lying Boilers is the combustor so "across", i. mounted substantially horizontally.

In the illustrated embodiment, the combustor 8 is arranged eccentrically, because this under the conditions of the example gives the highest flue gas circulation speeds. If other conditions require it, the combustor can also be symmetrical to the firebox be arranged, with the circulation speeds are slightly smaller.

With fire chambers of larger dimensions perpendicular to the drawing plane can several Combustors can be arranged side by side as a battery.

It should finally be mentioned that, if necessary, at the boiler in the area of the bottom, where the water collector 6 runs, can set up a fume hood, if highly ashy fuel should be used. However, the applicant's experience has shown that in the case of Most types of coal can be dispensed with such a ash deduction, as the ash than. Fly ash due to the fierce flue gas movement the firebox together with the Flue gas leaves and can be filtered outside the boiler from the flue gases.

Claims (3)

1. A method for fuelling a water tube boiler designated to be fuelled with oil or gas with a fuel comprising a dust fluidised by air, wherein at the same time the temperature at which the flue gases exit the combustion chamber is lowered without affecting the power and the efficiency of the water tube boiler at which the hitherto used oil or gas burners are substituted by combustors which are arranged at the top in the region of the combustion chamber top wall or are arranged on top thereof and in which at least 30% of the fuel is burned at a pressure which is by 1000 Pa higher than the pressure within said combustion chamber, said combustors each firing into the combustion chamber with a flame jet directed downward and having a velocity of about 100 m/s so that the flue gases circulate with high velocity within said combustion chamber and provide a heat transfer onto the walls of the combustion chamber by convection in addition to heat radiation.
2. The method of claim 1 in which the flame jet is directed eccentrically into the combustion chamber.
3. The method of claim 1 or 2 in which 60% of the fuel is burned within the combustor.

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