JPH0257802A - Method of controlling oil combustion on fluidized bed and generation plant executing said method - Google Patents

Abstract

PURPOSE: To obtain a uniform temperature distribution in a bed by supplying oil in the form of water/oil emulsion to the bed. CONSTITUTION: Oil emulsion contains 4-50% of water, 0-2% of emulsifier, and the remainder of oil. When oil fuel is supplied the form of water/oil emulsion to the bottom 11 of a combustor 10, water contained in a fuel drop 2 delays heating and emission of volatile substances. The fuel 2 spreads into the bed 11 and emits volatile substances upon elapsing some time while the water evaporates to blow off the fuel drop 2 to produce a small drop 2a. Consequently, the fuel is dispersed and it is not deposited on the bottom 13 of the combustor 10. Subsequently, solid coke particles 4 are formed, dispersed into the bed 11 and burnt. When the fuel drop is heated in a region 23 around a nozzle, volatile components are volatilized while the water is evaporated and the fuel drop 2 begins to be decomposed. The water disperses the fuel well to enlarge the combustion area 16. Combustion takes place uniformly in the bed and a uniform temperature distribution can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a power plant of the type in which oil is combusted in a fluidized bed of granular material, in order to control the temperature distribution in the bed and thus to control the temperature distribution in the combustion device. This invention relates to a control method that can eliminate thermal stress occurring in structural materials. This method is mainly applied to PFBC power plants where combustion takes place at pressures higher than atmospheric pressure (PFBC is the English name Pressuriz
ed Fluidized Dan ed Ombugtion
(an acronym for pressurized fluidized bed combustion).

The invention also relates to a power plant in which the method of the invention is applied. The present invention primarily relates to a PFBC power plant that burns coal and oil alternately or simultaneously.

[Problem to be Solved by the Invention 1] The combustion of oil in a fluidized bed of granular material involves several technical problems with respect to the temperature distribution in the bed compared to the combustion of coal. . These problems are particularly acute when combustion takes place at pressures above atmospheric, such as in PFBC power plants.

The content of volatile substances in oil droplets is much higher than in coal particles. As a result, combustion occurs more rapidly and more intensively, and burns out before it is sufficiently distributed within the bed paste. The temperature distribution within the bed then becomes uneven. This creates undesirable and harmful thermal stresses in the structural materials in the floor tank, especially in the material of the steam pipes. Larger oil droplets stick together to form droplets and are deposited on the bottom in putty-like slats. This is especially true when burning highly viscous oils such as residual oil from refineries or bunker oil C.

In order to obtain a good temperature distribution both vertically and horizontally, in the case of oil combustion it is necessary to install the oil nozzles close to each other and preferably at two or more levels. is recognized. It makes the plant more complex and expensive. This drawback is particularly great in PFBC power plants that burn both coal and oil.

Means for Solving the Problems 1 According to the invention, a satisfactory temperature distribution is obtained by supplying the oil in the form of a water/oil emulsion. Water slows combustion. A heating zone is formed around the nozzle and a combustion zone is formed outside of it in a larger bed volume.

As the water evaporates, it blows out the fuel and disperses it throughout the floor. A power generation plant to which the method of the present invention is applied includes, in addition to the equipment normally provided in such a plant, a device for producing oil pore suspension and a device for controlling the production.

A suitable oil pore suspension contains 4 to 50% water, 0 to 2% emulsifier, and the balance oil. Appropriate water content is determined depending on the type of oil contained in the fuel.

[Example] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

At time 0 of time scale 1 in FIG. 1, oil droplet 2 leaves the nozzle and the volatile components indicated at 3 exit the oil droplet and burn, forming a coke residue 4. This process only takes place for a few seconds. The coke residue 4 is then combusted. The combustion of coal takes place in a similar way in principle, but since the content of volatile components is lower, the combustion takes place slower and more evenly in a fluidized bed.

2 and 3 show nozzles 5 and 6. FIG. Small oil droplets burn in a small compact combustion zone 7 and large oil droplets burn in a larger combustion zone 8. Especially in the case of small oil droplets, it is very difficult to create the required uniform temperature distribution in the bed.

In FIG. 4, reference numeral 10 denotes a combustion device, which comprises a bed 11 of granular material and a steam pipe 1 for cooling this bed.
2. At the bottom 13 of the combustion device 10, oil nozzles 14 are installed at a relatively large distance from each other, and air nozzles 15 are also provided to supply air for the fluidization of the bed 11 and the combustion of the oil. Due to the high content of volatile components, combustion takes place quickly within the restricted combustion zone 16 and a portion of the combustion may take place within the freeboard 17 of the combustion device 10. Due to the poor distribution of the combustion, the temperature within the bed 11 is not uniform and there are regions of low temperature 18 between the combustion zones 16. Combustion within the freeboard 17 causes the temperature at that location to become very high. Such uneven temperature distribution within combustion device 10 creates harmful thermal stresses in structural components, such as steam tube 12. The curve 19 shown below the combustion device 10 in FIG. 4 shows the temperature change in the horizontal section of the combustion device, and the curve 20 shown to the right of the combustion device shows the temperature change in the vertical section.

Placing the nozzles closer together in the bottom 13 of the combustion device 10 creates a horizontally even temperature distribution within the floor 11. In this case, as shown in FIG. 5, combustion takes place within a restricted height and the combustion zone 16 is low. A temperature gradient as shown by curve 21 is created. tube 1
The combustion gases are cooled in the cooling zone formed by 2. The cold gas delivered from the combustion device reduces the efficiency of the turbine driven by this gas. Vertical temperature gradients create thermal stresses in the structural materials.

Figure 6 shows another problem with oil combustion. If oil splitting is insufficient, that is, if the oil droplets are large, when the oil droplets exit from the nozzle 14, they form a droplet mass 22 and the combustion device 1
It is easy to accumulate on the bottom 13 of 0. In this bottom 13 volatile components are lost, possibly forming coke and forming slag. This slag disturbs the combustion and makes it difficult or impossible for the combustion residual products to exit the combustion device 10. It also prevents or makes restarting difficult or blocks the nozzle.

If the oil fuel is supplied to the bottom 11 of the combustion device 10 in the form of a water/oil emulsion, all of the above-mentioned disadvantages are essentially eliminated. 7 and 8 illustrate the course of events when such fuel is introduced into bed 11. FIG. The moisture contained in the fuel droplets 2 retards the heating and release of volatile substances. Fuel 2 is on floor 11
spread inside. After a certain time, volatile substances are released,
Then, the water evaporates and blows away the fuel droplets 2, causing small droplets 2a
Make it. As a result, the fuel is well dispersed and the combustion device 10
The accumulation of droplets 22 on the bottom 13 of the tank is eliminated. Solid coke particles 4 are formed, diffuse into the bed 11 and burn.

The fuel droplets are heated in the area 23 (FIG. 8) around the nozzle. At the boundaries of the area, the volatile components of the fuel evaporate,
Then, as the moisture evaporates, the fuel droplets 2 begin to decompose. The moisture then diffuses the fuel well and greatly expands the combustion zone 16.

Effects of the Invention J According to the present invention, the combustion zone around and above the fuel nozzle is thus enlarged, and an even combustion distribution, uniform temperature, and gradual temperature gradient are obtained in the in-bed metal body. , and it is also obtained even if the oil nozzles are installed relatively far from each other. It is shown in FIG. The curves 25 and 26 below and to the right of the combustion device 10 show the temperature distribution within the bed 11 in its horizontal and vertical sections. The temperature is almost uniform and the temperature gradient is gentle.

[Brief explanation of the drawing]

FIG. 1 shows the sequence of events of oil droplet combustion. Figures 2 and 3 show the combustion zone in an oil nozzle with small and large oil droplets, respectively. FIG. 4 shows the combustion in the bed and the horizontal and vertical temperature gradients when the nozzles are placed relatively far from each other. FIG. 5 shows the combustion in the bed and the vertical temperature gradient when the nozzles are placed close to each other. Figure 6 shows the problem of oil buildup at the bottom of the bed. FIG. 7 shows the event sequence of combustion of oil pore suspension. FIG. 8 shows combustion around an oil nozzle when combustion is carried out using an oil hole suspension. FIG. 9 shows the combustion in the bed and the temperature gradients in the horizontal and vertical directions when combustion is carried out using an oil pore suspension. 2... Fuel droplet, 2a... Small droplet, 4... Coke particle, 1°... Combustion device, 11... Floor, 12... Steam pipe, 14... Fuel nozzle, 15 ... Air nozzle, 16 ... Combustion area, 17 ... Free board, 2
3...Fuel heating zone, 25...Horizontal temperature gradient,
26...Vertical temperature gradient. Fl(3,6 Fl6.4 Fl(3,5 Fl(3,9)

Claims (4)

[Claims] (1) A method of controlling temperature distribution and preventing oil buildup at the bottom of the bed when oil is combusted in a fluidized bed of granular material, wherein the oil is supplied to the bed as a water/oil emulsion. A method characterized by: (2) Claim 1, wherein the water/oil emulsion contains 5 to 40% water, 2% or less emulsifier, and the balance oil.
Method described. 3. Process according to claim 1, characterized in that the water/oil emulsion is fed to a fluidized bed in which combustion takes place at pressures above atmospheric pressure. (4) In a power generation plant implementing the method according to any one of claims 1 to 3, in addition to the equipment normally provided in such a plant, an emulsion fuel consisting of oil, water and an emulsifier is provided. 1. A power generation plant comprising: a device for producing emulsion; and a device for controlling the composition of the emulsion.