JP6180983B2 - Combustion apparatus, operation method of combustion apparatus, and ash circulation system - Google Patents

Description

  The present invention relates to a combustion apparatus, a method for operating the combustion apparatus, and an ash circulation system.

2. Description of the Related Art Conventionally, a combustion apparatus is known that includes a furnace that burns fuel, and a heat exchanger that is connected to the furnace and exchanges heat with combustion gas from the furnace. In recent years, biomass and waste are used as furnace fuel from the viewpoint of CO ₂ reduction and waste heat utilization. In such biomass fuel and waste fuel, the fuel contains alkali metals such as chlorine, Na, and K, and heavy metals such as lead and zinc. Therefore, combustion in a furnace generates a low melting point compound (about 300 ° C.) such as KCl, NaCl, ZnCl _{2 and} the low melting point compound reaches the heat exchanger together with the fly ash and adheres to the heat transfer tube. To do. Here, when the temperature of the heat transfer surface of the heat transfer tube is higher than the melting point of the low melting point compound (for example, 400 to 500 ° C.), the low melting point compound becomes a molten salt, and airflow obstruction due to ash adhesion to the heat transfer tube. In addition, the heat transfer tube corrodes.

  Therefore, in Patent Document 1 below, coal combustion ash (fly ash) is supplied to the furnace, thereby reducing the concentration of the low melting point compound and reducing the contact area with the heat transfer tube. An apparatus that suppresses airflow obstruction due to ash adhesion and corrosion of heat transfer tubes is disclosed.

Japanese Patent No. 4448053

  However, in the apparatus described in the above publication, there is a problem in that running costs are required because it is necessary to constantly procure coal combustion ash for suppressing corrosion of heat transfer tubes from outside the system.

  Then, an object of this invention is to provide the combustion apparatus which can suppress the corrosion of the heat exchanger tube of a heat exchanger, the operating method of an combustion apparatus, and an ash circulation system, reducing running cost.

A combustion apparatus according to the present invention is a combustion apparatus including a furnace and a heat exchanger, wherein a cleaning unit that cleans fly ash generated in the furnace and passed through the heat exchanger, and moisture from the fly ash that is cleaned by the cleaning unit. A dewatering unit, and a supply line for supplying fly ash dehydrated in the dewatering unit to the furnace. The dewatering unit includes a dewatering unit that dehydrates the fly ash, and a fly ash dehydrated in the dewatering unit. And a drying section for drying .

Further, the operating method of the combustion apparatus according to the present invention includes a cleaning process for cleaning fly ash generated in the furnace and passing through the heat exchanger in the operating method of the combustion apparatus including the furnace and the heat exchanger, and a cleaning process. A dewatering step for dewatering the washed fly ash, and a supply step for supplying the fly ash dehydrated in the water removal step to the furnace. And a drying step of drying the fly ash dehydrated in the dehydration step .

Further, the ash circulation system according to the present invention is a ash circulation system of a combustion apparatus equipped with a furnace and a heat exchanger, a washing unit for washing fly ash generated in the furnace and passing through the heat exchanger, and a washing unit. A dewatering unit that removes moisture from the discharged fly ash, and a supply line that supplies the fly ash dehydrated by the dewatering unit to a furnace. The dewatering unit includes a dehydration unit that dehydrates the fly ash, and a dehydration unit. And a drying section for drying the fly ash dehydrated in the section .

According to such a combustion device, a method for operating the combustion device, and an ash circulation system, the fly ash generated in the furnace and passed through the heat exchanger is washed, so that water-soluble chlorine, Na, K, and the like are dissolved in water. Alkali metals, water-soluble heavy metals, that is, water-soluble corrosive elements are separated from fly ash. The washed fly ash is dewatered to remove the water-soluble corrosive elements separated from the fly ash, and the fly ash from which the corrosive elements have been removed is supplied to the furnace. When the ash from which the corrosive elements have been removed is supplied to the furnace, the low melting point compound generated by the combustion of the furnace adheres to the supplied ash and the adhesion of the low melting point compound to the heat transfer tube is suppressed. The concentration of corrosive elements is reduced by dilution by increasing the amount of ash as a whole. As a result, corrosion of the heat transfer tube can be suppressed. Since the fly ash that suppresses the corrosion of the heat transfer tube is procured and reused in the system, the running cost can be reduced. That is, corrosion of the heat transfer tube can be suppressed while reducing running cost. And when water is removed, the dehydrated fly ash is further dried, so that moisture is further removed from the fly ash before being supplied to the furnace, and the low melting point compound tends to adhere to the supplied ash. Thus, the effect of suppressing the adhesion of the low melting point compound to the heat transfer tube can be further enhanced.

Here, it is preferable that the water content of the slurry containing the fly ash washed by the washing unit is 50 to 60% in the dehydration unit.

  Further, when the washing unit is configured to wash fly ash by water washing, water-soluble chlorine, water-soluble alkali metal, and water-soluble heavy metal can be separated from fly ash at low cost.

  ADVANTAGE OF THE INVENTION According to this invention, corrosion of the heat exchanger tube of a heat exchanger can be suppressed, aiming at reduction of running cost.

It is a schematic block diagram which shows the combustion method to which the operating method and ash circulation system which concern on embodiment of this invention are applied.

  Hereinafter, preferred embodiments of a combustion apparatus, a combustion apparatus operating method, and an ash circulation system according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a combustion apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, a combustion apparatus (combustion facility) 100 includes a furnace 1, a heat exchanging unit 2, a bag filter 3, and a chimney 4 connected in this order, and branches from the bag filter 3, The fly ash tank 5, the water washing unit 6, and the water removal unit 11 are connected in this order, and a line L that connects the water removal unit 11 and the furnace 1 is further provided.

  The furnace 1 is a fluidized bed furnace for burning biomass fuel, waste fuel or the like, and the inside of the furnace is a combustion chamber. In the combustion chamber, for example, a fluidized material such as silica sand is accommodated, and a fluidized bed is formed while the fuel and the fluidized material are fluidized by combustion air to burn the fuel. Biomass fuel, waste fuel, and the like are carried into the system by a truck or the like, temporarily stored in the fuel storage tank 9, and then introduced into the furnace. Moreover, the gas temperature in a furnace is set to 800-1000 degreeC.

  The heat exchanging unit 2 includes a plurality of heat exchangers that exchange heat with the combustion gas generated in the furnace 1 and recover exhaust heat. The heat exchange unit 2 is disposed downstream of the furnace 1 in the flow path of the combustion gas from the upstream side to the downstream side. , The superheater 2a, the economizer 2b, and the air preheater 2c are provided in this order.

  The superheater 2a transfers the heat of the combustion gas to the steam from the steam drum through the heat transfer tube, thereby making the superheated steam. The gas temperature of the superheater 2a is set to 400 to 900 ° C, and the temperature of the heat transfer surface of the heat transfer tube is set to about 500 ° C.

  The economizer 2b preheats the boiler feed water by transferring the heat of the combustion gas to the boiler feed water via the heat transfer pipe. The boiler feed water preheated by the economizer 2b is converted into steam by a steam drum, and the steam is supplied to the superheater 2a.

  The air preheater 2c preheats the air by transferring the heat of the combustion gas to the air via the heat transfer tube. The air preheated by the air preheater 2c is supplied to the furnace 1 as combustion air and also supplied to the drying unit 8 as high-temperature drying air.

  The bag filter 3 collects fly ash that passes through the heat exchanging unit 2 and accompanies the combustion gas. Here, in order to increase the collection efficiency of fly ash, the bag filters 3 are arranged in parallel in two, but may be one.

  The fly ash tank 5 is for storing fly ash collected by the bag filter 3.

  The water washing part 6 carries out the water washing (water washing) of the fly ash from the fly ash tank 5. FIG. In addition, you may provide the tank which stores the slurry containing the fly ash which washed with water suitably as a buffer for temporary storage. Incidentally, as the water washing part 6, the system which carries out water washing | cleaning by throwing fly ash into the tank in which water was stored and stirring can also be employ | adopted.

  The dewatering unit 11 is for removing moisture from the slurry containing fly ash sent from the water washing unit 6, and here includes a dehydrating unit 7 and a drying unit 8 connected in this order.

  The dehydration unit 7 dehydrates the slurry containing fly ash sent from the water washing unit 6 by driving a slurry pump P disposed between the dehydration unit 7 and the water washing unit 6. Reduce the rate to 50-60%. As the dewatering unit 7, a press dewatering type belt press dehydrator widely used for sludge treatment is employed here. In addition, since the dehydration part 7 should just make the moisture content of a slurry 50 to 60%, it replaces with a belt press type dehydrator, and uses a press dehydration type screw press type dehydrator or a rotation disk. For example, a dehydrator that performs centrifugal dehydration can be used, or the water can be drained naturally.

  The drying unit 8 dries the dewatered cake containing fly ash from the dewatering unit 7, and here, the moisture content is reduced to 20% or less by the high-temperature air (hot air) supplied from the air preheater 2c through the line L1. Dry so as to be. The high temperature air may be a burner or may be steam. Further, the high-temperature air exhausted from the drying unit 8 is used as combustion air or the like through the line L2.

  The line L is a supply line for supplying fly ash from the drying unit 8 to the furnace 1 through the ash storage tank 10. The ash storage tank 10 adjusts the supply of fly ash to the furnace 1.

  Next, the operation of the combustion apparatus 100 having such a configuration will be described. First, for convenience of explanation, a description will be given from a state where ash is not supplied from the ash storage tank 10 to the furnace 1 through the supply line L (conventional state).

  Biomass fuel, waste fuel, and the like are supplied from the fuel storage tank 9 to the furnace 1 and combusted while flowing together with the fluidizing material in the fluidized bed in the furnace 1. Fly ash generated by the combustion of the furnace 1 is accompanied by the combustion gas and proceeds to the subsequent stage.

  Here, as described above, biomass fuels and waste fuels contain chlorine, alkali metals, and heavy metals in the fuel, and therefore, low melting point compounds of about 300 ° C. due to combustion in the furnace 1. Is generated. A part of the low melting point compound adheres to the fly ash generated by combustion, and is accompanied by the combustion gas together with the fly ash and goes to the subsequent stage. The combustion gas passes through each of the heat exchangers of the superheater 2a, the economizer 2b, and the air preheater 2c of the heat exchanging section 2, thereby exchanging heat with the respective heat transfer tubes and recovering exhaust heat.

  At this time, some of the low melting point compounds adhere to the heat transfer tube and cause corrosion due to the above-described molten salt, but in this embodiment, the corrosion of the heat transfer tube is suppressed by a method described later. .

  The fly ash that does not adhere to the heat transfer tube regardless of whether or not the low melting point compound is attached to the bag filter 3 is collected by the bug filter 3. On the other hand, the combustion gas passes through the bag filter 3 and is discharged from the subsequent chimney 4 to the atmosphere.

  The fly ash collected by the bag filter 3 and the fly ash to which the low melting point compound adheres are stored in the fly ash tank 5, and a desired amount is appropriately cut out as needed and introduced into the water washing unit 6.

  In the water washing unit 6, the fly ash is washed with water, and water-soluble chlorine, water-soluble alkali metal, water-soluble heavy metal, that is, water-soluble corrosive elements are separated from the fly ash. Thus, since the water washing part 6 is the structure which wash | cleans fly ash by water washing, a water-soluble corrosive element can be isolate | separated from fly ash at low cost. The fly ash and the water-soluble corrosive element are introduced into the dehydration unit 7 as a slurry.

  In the dewatering unit 7, the slurry is dewatered, and the water-soluble corrosive elements separated from the fly ash are removed as cleaning waste water. On the other hand, the fly ash from which the corrosive elements have been removed is introduced into the drying unit 8 as a dehydrated cake.

  In the drying unit 8, the dewatered cake is dried, and the fly ash from which moisture has been removed to a predetermined level by the drying is supplied into the furnace 1 via the line L.

  Here, in the superheater 2a at the rear stage of the furnace 1, the temperature of the heat transfer surface of the heat transfer tube is about 500 ° C., which is higher than the melting point (about 300 ° C.) of the low melting point compound generated by the combustion of the furnace 1. Therefore, there is a possibility that the low melting point compound becomes a molten salt in the heat transfer tube of the superheater 2a and the heat transfer tube is corroded.

  However, in this embodiment, as described above, first, the fly ash generated in the furnace 1 is washed (washing process), and by this washing, water-soluble corrosive elements are separated from the fly ash, and then washed. The fly ash was dewatered (water removal process), the water-soluble corrosive element separated from the fly ash was removed by this water removal, and then the fly ash from which the corrosive element was removed was transferred to the furnace 1. Supply (supply process).

  For this reason, the low melting point compound produced by the combustion of the furnace 1 adheres to the supply ash and the adhesion of the low melting point compound to the heat transfer tube is suppressed, and the corrosive element is formed by dilution due to the increase in the amount of ash as a whole. The concentration of is reduced. As a result, corrosion of the heat transfer tube can be suppressed. Since the fly ash that suppresses the corrosion of the heat transfer tube is procured and reused in the system, the running cost can be reduced.

  That is, according to this embodiment, corrosion of the heat transfer tube can be suppressed while reducing running cost.

  Further, in the present embodiment, since the drying unit 8 that dries the fly ash dehydrated by the dehydration unit 7 is provided, the moisture is further removed from the fly ash before being supplied to the furnace 1. The low melting point compound easily adheres to the ash, and the effect of suppressing the adhesion of the low melting point compound to the heat transfer tube can be further enhanced.

  The surplus fly ash generated in the system by reusing the fly ash can be appropriately discharged out of the system from the fly ash tank 5.

  As described above, the present invention has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment. For example, the above embodiment includes the superheater 2a because corrosion is particularly likely to occur. Although the application to the combustion apparatus is described, any combustion apparatus having a heat exchanger in which the temperature of the heat transfer surface of the heat transfer tube is higher than the melting point of the low melting point compound can be applied.

  Moreover, in the said embodiment, although water-soluble corrosive element is isolate | separated from fly ash by the water washing of the water washing part 6, if a water-soluble corrosive element can be isolate | separated from fly ash, it will depend on a solution. It may be washed.

  Moreover, in addition to the method of procuring fly ash in the system and reusing it, it is also possible to use a method of procuring coal combustion ash from outside the system as in the prior art.

  Moreover, the water removal part 11 can also be set as the structure provided with at least one of the dehydration part 7 and the drying part 8. FIG.

  Moreover, in the said embodiment, although the furnace is made into the fluidized-bed furnace, it can apply also to the circulating fluidized-bed furnace which has a cyclone, Furthermore, with respect to other furnaces, such as an incinerator, a melting furnace, and a gasification furnace. Even applicable.

  DESCRIPTION OF SYMBOLS 1 ... Furnace, 2 ... Heat exchange part, 2a, 2b, 2c ... Heat exchanger, 6 ... Water washing part (washing part), 7 ... Dehydration part, 8 ... Drying part, 11 ... Dewatering part, 100 ... Combustion apparatus , L ... supply line.

Claims (5)

In a combustion apparatus equipped with a furnace and a heat exchanger,
A cleaning unit for cleaning fly ash generated in the furnace and passed through the heat exchanger;
A dewatering unit for removing moisture from the fly ash washed by the washing unit;
A supply line for supplying the fly ash dewatered by the water removal unit to the furnace ,
The dewatering unit includes a dehydrating unit that dehydrates the fly ash, and a drying unit that dries the fly ash dehydrated by the dehydrating unit. The combustion apparatus according to claim 1, wherein the dehydrating unit sets a water content of the slurry containing the fly ash cleaned by the cleaning unit to 50 to 60%.   The combustion apparatus according to claim 1, wherein the cleaning unit cleans the fly ash by water cleaning. In an operation method of a combustion apparatus provided with a furnace and a heat exchanger,
A cleaning process for cleaning fly ash generated in the furnace and passing through the heat exchanger;
A water removal step for removing the fly ash washed in the washing step;
A supply step of supplying the fly ash removed in the water removal step to the furnace ,
The method of operating a combustion apparatus , wherein the dewatering step includes a dehydration step of dehydrating the fly ash and a drying step of drying the fly ash dehydrated in the dehydration step . In an ash circulation system of a combustion apparatus equipped with a furnace and a heat exchanger,
A cleaning unit for cleaning fly ash generated in the furnace and passed through the heat exchanger;
A dewatering unit for removing moisture from the fly ash washed by the washing unit;
A supply line for supplying the fly ash dewatered by the water removal unit to the furnace ,
The ash circulation system , wherein the dewatering unit includes a dehydrating unit for dehydrating the fly ash and a drying unit for drying the fly ash dehydrated by the dehydrating unit .

Images