JPS62196522A - Heat recovery method from fluidized bed and its equipment - Google Patents

Abstract

PURPOSE:To be able to recover heat efficiently by a method wherein fluidized solids are moved with revolution in a fluidized bed and heat is recovered from the part of the fluidized where a small amount of air is blown off so as not to disturb the revolving movement and fuel is supplied to the place near the upper surface of the fluidized bed or the part where a large number of air is blown off. CONSTITUTION:At the neighborhood of a fluidized bed installed at the upper part of a wind box 9 heat transfer pipe groups 16 are arranged and the intervals of the groups 16 between the right and left sides in the horizontal direction are sufficiently widened and at their upper and lower parts sufficiently wide paths are formed so as not to obstruct or resist the movement of fluidized solids. Air 2 is sent to the box 9 in such an extent that granular solids are able to be fluidized but not brought in a violent fluidized condition and air amount in excess of two times that sent to the center is sent to wind boxes 8, 10. Fuel is charged from a hopper 20 into an incinerator and an air to fuel ratio in the incinerator is kept properly. By the air 2, blow-up velocity is small at the upper part of the box 9 to lower the granular solids and at the right and left boxes 8, 10, blow-up velocity is large to raise the granular solids. After combustible wastes and fuel are charged from a fuel charge hole 22, they are moved to the center of a blow-off surface 3 and sink together with the fluidized medium and move along a revolving stream in the incinerator and are completely burnt by large excess air ratio and violent fluidization.

Description

[Detailed description of the invention] [Industrial application field] The present invention is applicable to industries such as municipal waste, sewage sludge, raw sludge, oil distillation residue, various combustible processing waste, oil-impregnated sludge, tank sludge, and waste activated carbon. Waste, peat, coal washing sludge,
The present invention relates to a method and an apparatus for burning or incinerating coal in a fluidized bed and recovering its heat using liquid, mud, or solid materials such as coal, including even coal preparation residue, as fuel.

[Conventional technology]

Conventionally, heat recovery technology using a fluidized bed has become widely used because it provides high thermal conductivity, allows the use of a wide range of fuels, and allows for compact equipment. Ta.

By the way, in conventional fluidized beds, the air or other oxygen-containing blown gas for fluidization has a substantially uniform flow rate per unit area over the entire fluidized bed, and the fuel is also blown into the fluidized bed by spreaders, jets, etc. The heat was distributed uniformly over the entire surface of the bed, and a heat transfer surface for heat recovery was also provided over the entire surface of the fluidized bed.

[Problem that the invention seeks to solve]

Therefore, in the conventional technology, solid fuel is produced by reducing the particle size to the same size as, or slightly larger than, granular solids of 1 to 31, which are called fluidized media such as limestone and silica sand. However, the gas blown from the bottom cannot flow and settles and remains at the bottom, causing poor flow and clinker formation. In addition, it is necessary to disperse the supply of liquid or muddy substances, and even then, unless the amount of input is kept to a small amount, there is a risk that they will accumulate at the bottom and cause poor flow, causing combustion to stop.

In addition, the movement of particulate solids such as the fluidized medium, fuel solids, and combustion residue within the fluidized bed is intense only in the vertical direction as the blown gas rises, and there is almost no movement in the horizontal direction, resulting in uneven fuel supply. When this happens, clinker is produced in areas where there is an excess amount, and where there is less clinker, a drop in temperature causes poor combustion.

For this reason, as the area of the hearth becomes larger, the supply mechanism becomes more complicated in order to feed the fuel in a distributed and uniform manner, and even this is not sufficient.

Furthermore, since the combustion section and the heat recovery section are located in the same location, lowering the combustion load lowers the temperature of the fluidized bed, making it impossible to maintain the temperature necessary for good combustion. Even if the temperature does not drop to the point where combustion is no longer possible, when the temperature of the fluidized bed decreases, the amount of combustion within the fluidized bed decreases, and the fuel is not completely combusted in the freeboard section, which is the combustion space above the fluidized bed, and leaves the combustion zone. This increases the amount of unburned materials in the fly ash. Conversely, when the combustion load is increased, the lateral mixing is less, and as a result of non-uniform feeding, the temperature of the fluidized bed is partially heated and clinker is formed, or the amount that cannot be combusted in the fluidized bed is increased. As a result, unburned substances will be entrained in the exhaust gas. In addition, to disperse the input fuel and prevent sedimentation,
Operation may be difficult unless a certain amount or more of blown gas is blown into a state of intense fluidity, and in this case, the fluidity is often more intense than necessary, leading to a drastic increase in wear on the heat transfer surface.

Therefore, there is a limit to fluctuations in combustion load, and even then, it is possible to collect unburned materials from the after-combustion chamber or exhaust gas using a high-temperature cyclone and return them to the fluidized bed, or to install a separate combustion furnace for collected ash. It is generally necessary to take measures such as these, and it is difficult to avoid clinker trouble and severe wear on the heat transfer surface.

Furthermore, as mentioned above, there are many problems such as the need to crush the fuel into small pieces, and with conventional technology, the advantages of fluidized bed heat recovery include in-bed desulfurization, complete combustion, and large heat exchange with a small heat transfer surface. However, it has been difficult to put into practical use highly responsive combustion amount control.

[Means for solving problems]

The present invention solves the above-mentioned conventional problems, and the present invention has been made in Japanese Patent Application No. 56-1052 (No.
24608), Japanese Patent Application No. 60-60149, and Japanese Patent Application No. 60-60893, etc., the fuel does not need to be finely pulverized, the fuel can be easily inputted, and the Tallinn To provide a method and device for recovering heat from a fluidized bed, which can perform a considerable partial load without causing car trouble or poor fluidization, reduce wear on heat transfer surfaces, and efficiently recover heat. The purpose is to

The feature of the present invention is to vary the flow rate per unit area of the blowing surface of the blowing gas containing oxygen into the bottom of the furnace to form a fluidized bed on the blowing surface, and to In areas where the flow rate of the blown gas is relatively high, the fluidized solids rise as a whole, and in areas where the flow rate is relatively low, the fluidized solids as a whole fall, and in the upper layer of the fluidized bed, the flow rate of the blown gas decreases from the area where the flow rate is relatively high. In the lower layer of the fluidized bed, the fluidized solid rotates in the fluidized bed from a region where the flow rate of the blown gas is relatively low to a region where the flow rate of the blown gas is relatively low. A fluidized bed configured to recover heat from within the bed so as not to impede the swirling movement of the fluidized solid, and to supply fuel to a portion near the upper surface of the fluidized bed or to a portion where the flow rate of the blown gas is relatively large. A method for recovering heat from heat sources and equipment for carrying out the method.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In the first illustrated example, the inner bottom of the furnace 1 is provided with a blowing surface 3 for dispersing and blowing oxygen-containing blowing gas, for example, air 2, and the blowing surface 3 has both side edges lower than the center. It slopes in an almost symmetrical chevron-shaped cross-section (roof-like), and a noncombustible material outlet 4 is provided near the lowest part of both edges, which is connected to a noncombustible material discharge device 6 via a vertical chute 5. The incombustible material discharge device 6 is further connected to a classification device 7. Air 2 is supplied to a wind box 8 formed below the blowing surface 3.
．． 9. The flow rate per unit area of the air 2 from the wind boxes 8 and 10 on both sides of the air is dispersed upward from the air blowing surface 3 through the blowing surface 3. ) is sufficiently fluidized to form a fluidized bed, but the flow rate of air 2 from the central wind box 9 is selected to be smaller than the former;
The air 2 to 9.10 is regulated by an air volume regulating mechanism such as a flow rate regulating valve 11.

Further, above the wind boxes 8 and 10 on both side edges, reflective walls 12 are provided that partially block the upward flow path of the air 2 blown in and reflect the air 2 toward the center of the furnace 1. In addition to the air 2 that also serves as fluidizing gas, there is an inlet 1 for secondary combustion air 13 on the side wall of the furnace 1 at a higher position than the fluidized bed to be formed, or on the wall of the boiler 15 in contact with the combustion zone.
4 and 14' are provided, and an exhaust gas boiler 15 is integrally provided in the exhaust gas passage to directly recover heat from the exhaust gas from the combustion area of the furnace 1 and its upper space.

Further, near the middle of the height of the fluidized bed formed above the wind box 9, a group of heat transfer tubes 16 are arranged horizontally or slightly inclined in a grid pattern. The horizontal distance between the left and right sides must be at least sufficiently wider than the diameter of the bulky non-combustible material to be charged into the furnace 1, so that the heat exchanger tube group 16 does not block its movement, and the heat exchanger tube group 16
It is necessary to provide sufficiently wide passages above and below the heat exchanger tube group 16 so that the passages do not block or create resistance to the movement of the fluidized solid in the upper and lower portions of the fluidized bed. The heat transfer tube group 16 is also configured to perform forced circulation by drawing out canned water from below the water surface of the air-water drum 17 shared with the exhaust gas boiler 15 using a circulation pump 18 and returning it to the air-water drum 17 through the heat transfer tube group 16. It has become. Reference numeral 19 indicates a lower header of the exhaust gas boiler 15.

A hopper 20 and a supply device 2 are placed above the blowing surface 3.
In the first illustrated example, a fuel inlet 22 connected to the fuel inlet 1 is provided, and in the first illustrated example, it is provided in the vicinity of right above the high part of the blowing surface 3.

To explain its operation, the granular solids on the blowing surface 3 are fluidized in the wind box 9 at the high central part of the blowing surface 3, but not to the extent that it becomes a violent fluid state. ,
Air 2 is sent at a flow rate of about 1 to 3 times the flow start speed Gmf, and the air 2 is sent to the left and right wind boxes 8° 10 so that the flow rate per unit area is more than twice that of the center. here,
Fuel is introduced into the furnace 1 from the fuel inlet 22 via the hopper 20 and the supply device 21 according to the required amount of steam, and the air-fuel ratio in the fluidized bed is maintained appropriately accordingly.
If the air volume from the central wind box 9 is close to Gmf, only the air volume from the left and right wind boxes 8 and 10 is adjusted, but if the air volume from the central wind box 9 is considerably higher than Gmf, the air volume is adjusted. Adjust the total amount of flowing air before branching out.

In this way, due to the blown air 2, the granular solids show a downward flow because the overall blowing speed is low above the central wind box 9, and the blowing speed is high above the left and right wind boxes 8.10. The granular solid flows upward from the reflection wall 1.
The air 2 blown up by the action of 2 is accelerated along the reflecting wall 12 and moves large granular solids toward the center in a blown-off manner. That is, the entire mixture is thoroughly mixed while rotating as shown by the arrow in FIG.

Therefore, low-grade coal, peat, coal washing sludge, coal cleaning residue containing a large amount of incombustibles, sludge, municipal waste, and other combustible wastes generated during various production and treatment processes and other liquid, muddy, or solid fuels are When fuel is injected onto the surface of the fluidized bed from the fuel inlet 22, it is not buried in the fluidized bed but is brought to the center of the high side of the blowing surface 3 due to the swirling flow of the fluidized medium that moves or is blown from the left and right. Then, as it sinks with the fluidized medium in a buried manner, it is supplied with heat and a small amount of combustion air, breaks up, and partially burns while dispersing and moving within the fluidized bed along the swirling flow.
At the portion where the amount of blown air is large, complete combustion occurs due to the large excess air ratio and intense flow.

Therefore, even if the fuel is a lump of fuel having a relatively large diameter, or even if the fuel is partially injected all at once, it can be burned without any problem.

In addition, fine incineration ash among the ash content of the fuel is blown up,
The incineration residue flies away from the top of the fluidized bed along with the combustion exhaust gas, but the rest is blown away by the swirling flow and reaches the left and right incombustible material extraction ports 4, but the incineration residue has a diameter close to that of the fluidized medium or has a ventilation resistance similar to that of the fluidized medium. It becomes assimilated with the medium. Therefore, the incombustibles remaining together with the fluidized medium are extracted by the incombustible material discharging device 6, and the incombustibles with a diameter equal to or smaller than that of the fluidized medium are returned to the furnace 1 by the classification bag W7. Discharge the material out of the system. Note that these removals of incombustibles are unnecessary if the incombustibles contained in the fuel are smaller than the fluidized medium, and the
does not necessarily have to be inclined.

Furthermore, in the heat transfer tube group 16, the internal can water is forcedly circulated, and the external fluidized bed does not form a boundary layer, and there is contact heat transfer with the fluidized bed, so that the granular solids are well stirred. Therefore, a large amount of heat transfer can be expected, and the amount of heat transfer with the exhaust gas is at most several tens of kcaff/
200-300 kca1 for rd h'C
The value is 7%h''c or more.

In the case of natural circulation, it is preferable to tilt it slightly to prevent steam from accumulating on the top surface, but since there is sufficient height up to the air/water drum 17, it is quite possible to provide a circulation amount commensurate with the amount of heat transfer. .

In order to maintain combustion, the temperature of the fluidized bed is 500 to 600°C or higher, preferably 700 to 800°C, but 900 to 10°C.
At temperatures above 00°C, the fluidized bed, such as sand and combustion residue, begins to melt, so the fluidized bed must be cooled. However, this cooling is achieved entirely through heat recovery without the need to inject water into the fluidized bed or increase the amount of air blown into the bed. This has the advantage that the heat transfer area for this purpose is small.

In addition, since combustion takes place in a fluidized bed, increasing the height of the fluidized bed increases the rate of combustion within the fluidized bed and reduces the amount of combustion heat input into the fluidized bed during partial load. It is possible to suppress it.

Based on this and the principles of air volume adjustment and flow condition adjustment described above, partial load operation is easy with the Bokuto method, and partial loads of 50% or more are possible without changing the air ratio and therefore without reducing heat recovery efficiency. It is.

In addition, the change in the strength of the flow state in the heat transfer tube group 16 can always be made weak based on the principle of air volume adjustment described above. Therefore, it is possible to operate under good conditions without causing scaling or wear.

The method of flowing the canned water to the heat transfer tube group 16 in the fluidized bed does not necessarily have to be as shown in the first illustrated example. Needless to say, it can be used in a variety of ways, such as a method of using it as a general purpose, a method of having an air/water header completely independent of the exhaust gas boiler 15, a method of using it as a heat medium boiler or a hot water generator, etc.

However, since the heat transfer tube group 16 in the fluidized bed cannot recover heat from the generated exhaust gas, it is necessary to combine it with the exhaust gas boiler 15 as shown in the first example, or use other heat recovery equipment from the exhaust gas such as an air preheater or an economizer. It is preferable to use it in combination with the fuel to increase the amount of heat recovered from the fuel.

In the above examples, when the wear and heat transfer amount of the heat transfer tube group 16 were measured, the following favorable results were obtained.

Heat transfer tube thinning was hardly observed and scaling A thin layer with unusual scale was formed, but no growth was observed over time and heat transfer amount was 200 to 300 kca12/%h℃ Temperature conditions Canned water temperature, input temperature 10℃ Front and back fluidized bed temperature around 50℃ 780-840'C Heat exchanger tube material 5TB40A Hearth heat load 15 (1-250X 10' kca
14 / g h 'C Furthermore, when the throughput is large and the heat load increases, or the calorific value of the fuel is high and it is necessary to make it large or high load that requires an additional heat transfer area. As shown in FIG.
This problem can be dealt with by providing a group of heat transfer tubes 16 in the upper fluidized bed section and also providing an incombustible material outlet 4 in the bottom center of the furnace 1.

The third illustrated example is a further modification of the second illustrated example, in which a reflecting wall 12 is also provided above the side edge of each blowing surface 3, 3 on the furnace center side for guiding the swirling flow of granular solids. This is an example in which the fuel inlet 22 is not opened at one central location as in the second illustrated example, but is divided and opened above each blowing surface 3.

The fourth illustrated example is an example in which the blowing surface 3 is inclined in one direction, the incombustible material outlet 4 is provided near the smallest part, and the reflecting wall 12 is omitted. It is also possible to arrange the surfaces substantially symmetrically with respect to the furnace center line, provide a common incombustible material outlet 4 in the center, and open solid fuel inlets 22 at the upper portions of both side walls of the furnace 1, respectively.

Note that, as shown in FIGS. 4 and 5, the blowing surface 3 does not necessarily coincide with the bottom surface of the furnace 1, and by blowing in a gas containing oxygen such as air, the fluidized medium flows in the vicinity above the level. The same effect can be obtained using any type of device such as a perforated plate, air diffuser pipe, air diffuser nozzle, etc. Regarding the behavior of incombustibles, fluidized media, fuel, combustion residue, etc. in the fluidized bed, there is no problem in considering this blowing surface as the bottom of the fluidized bed.

There is no movement beneath that surface, and it is filled with a fluid medium and is fixed, meaning that it does not serve as a substantial container.

The operations of the second to fifth illustrated examples are also almost the same as those of the first illustrated example.

〔Effect of the invention〕

As explained above, according to the present invention, there is no need to finely crush the fuel into smaller pieces than a few cranes, and if the combustion rate is not explosive, no crushing or coarse crushing up to about 100+N can cause problems with talin force and poor flow. It can be operated without causing any problems, is capable of a considerable partial load, and can be taken out of the furnace without stopping operation, even if large amounts of incombustible material are mixed in.

In addition, since there are some areas with intense fluidity, it is easy to crush and activate desulfurization agents such as dolomite and limestone, and by first involving solid fuel in the fluidized bed and then burning it, It is possible to suppress explosive combustion and implement NOx countermeasures such as two-stage combustion.
It also has excellent performance from the perspective of pollution prevention.

In addition, wear on the heat transfer surface is significantly reduced, heat transfer reduction due to scaling is prevented, efficient heat recovery is achieved, and high load operation is approximately twice that of conventional fluidized beds. It has many extremely beneficial effects, such as making it possible to

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIG. 1 is a longitudinal cross-sectional view of the entire furnace showing one example, and FIGS. 2 to 5 are longitudinal cross-sectional views of parts of a furnace showing other examples. 1...Furnace, 2...Air, 3...Blowing surface, 4...
Non-combustible material outlet, 5... Vertical chute, 6... Non-combustible material discharge device, 7... Classifier, 8, 9.10... Wind box, 11... Flow rate control valve, 12...・Reflection wall, 13...
・Secondary combustion air, 14.14'...Inlet, 15...
・Exhaust gas boiler, 16... Heat exchanger tube group, 17... Air/water drum, 18... Circulation pump, 19... Lower header,
20... Hopper, 21... Supply device, 22... Fuel input port.

Claims (1)

[Claims] 1. A fluidized bed is formed on the blowing surface by changing the flow rate per unit area of the blowing surface of the blowing gas containing oxygen into the bottom of the furnace, and the flow rate of the blowing gas is changed depending on the part. In areas where the flow rate is relatively high, the fluidized solids rise as a whole, and in areas where the flow rate is relatively low, the fluidized solids as a whole fall, and in the upper layer of the fluidized bed, from the area where the flow rate of the blown gas is relatively high to the area where it is low, Further, in the lower layer of the fluidized bed, the fluidized solid is rotated in the fluidized bed from a portion where the flow rate of the blown gas is relatively low to a portion where the flow rate is high. A fluidized bed characterized in that heat is recovered so as not to impede swirling movement of the fluidized solid, and fuel is supplied near the upper surface of the fluidized bed or to a portion where the flow rate of the blown gas is relatively large. heat recovery method. 2. A blowing surface for blowing gas containing oxygen is provided at the bottom of the furnace, and a flow rate adjustment mechanism is provided to change the flow rate per unit area of the blowing gas on the blowing surface depending on the portion of the blowing surface, and the blowing surface A heat transfer surface for heat recovery is provided above the portion where there is relatively little blown gas so as not to impede the movement of the fluidized solid, and a fuel inlet is provided in the upper part of the furnace wall. Heat recovery device from fluidized bed.