JP2518892B2 - Structure of fluidized bed boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a flow for combusting wastewater sludge and the like discharged from a paper manufacturing plant, which produces harmful components such as hydrogen chloride gas or chlorine gas by combustion with coal. In a floor boiler, the present invention relates to a technique that does not corrode a high-temperature heat transfer tube even when ash containing unburned components of a fuel that generates the above-mentioned harmful components by combustion is recovered and burned.

[Prior Art] Industrial waste such as papermaking wastewater sludge generated from a paper mill is usually incinerated, but the water content
It was difficult to incinerate because it was as high as 60-70%. recent years,
A fluidized bed boiler that burns sludge and coal together has been planned for both incineration of sludge and effective heat utilization. A fluidized-bed boiler whose main purpose is to incinerate sludge can maintain and suppress the temperature in the bed only by the latent heat of vaporization of water in the sludge, without securing a heat collection tube in the bed, but a certain amount of evaporation is secured. When it is necessary to do so, it is necessary to insert an evaporation pipe or a superheater pipe into the layer to collect heat.

On the other hand, many papermaking sludges contain Cl,
Hydrogen chloride gas (HCl) and chlorine gas (Cl ₂ ) generated by combustion
The corrosion that occurs in the high temperature metal part of the combustor is well known as high temperature corrosion due to chlorine, and there is a failure in some refuse incinerators that generate high temperature steam. Since the high temperature corrosion phenomenon due to chlorine may occur at locations where the metal temperature is 400 ° C or higher, the steam superheater has not been conventionally installed as a corrosion prevention measure, or even if a steam superheater is installed The steam temperature was kept at about 300 ° C or lower so that the tube wall temperature of the superheater was 400 ° C or lower.

Also, as another conventional technique for preventing high temperature corrosion of metal,
Separately, a furnace that burns fuel that generates hydrogen chloride gas or chlorine gas (hereinafter also referred to as sludge and other fuels) and a furnace that superheats the generated saturated steam are placed separately.
It has been practiced to burn coal, heavy oil, or the like that does not cause high-temperature corrosion as fuel in a furnace equipped with a superheater.

FIG. 2 is a diagram showing an example of a first conventional technique, in which steam generated by burning fuel such as sludge is heated by a superheater inserted in a flue of a boiler for burning coal or heavy oil. It is a system diagram of a case. In FIG. 2, 51 is a combustion furnace for fuel such as sludge, 52 is an exhaust heat boiler, 53 is a coal or heavy oil combustion boiler, 54 is low temperature steam, 55 is high temperature steam, 56 is a steam superheater, 57 is sludge, etc. Is a fuel supply port, and 58 is a burner.

The fuel such as sludge sent from the fuel supply port 57 is combusted in the combustion furnace 51, and the generated high temperature gas is discharged into the exhaust heat boiler 52.
Flows into. The exhaust heat boiler 52 is configured by a low-temperature heat transfer surface such as a economizer or an evaporation pipe, and usually does not have a steam superheater, but in the case of having a steam superheater,
The steam temperature is suppressed to a low temperature of about 300 ° C or lower so that the tube wall temperature of the superheater does not exceed 400 ° C.

On the other hand, a boiler 53 for burning coal, heavy oil, or the like is installed separately from the combustion furnace 51, and the flue portion of the boiler 53 is a steam for superheating low-temperature steam generated in the exhaust heat boiler 52. The superheater 56 is inserted. Since the combustion gas in contact with the steam superheater 56 is a combustion gas such as coal or heavy oil, the steam temperature exceeds 300 ° C, and even if the wall temperature of the superheater pipe exceeds 400 ° C, the superheater pipe will be affected by chlorine. Will not be corroded.

FIG. 3 is a diagram showing an example of the second conventional technique, which is described in Mitsubishi Heavy Industries Technical Report Vol.17, No. 6, and burns a fuel such as sludge and a fuel such as bark. It is a system diagram when a boiler and a boiler which uses heavy oil as fuel are installed separately, and each wind flue system and steam system are engaged effectively. In FIG. 3, 61 is a fluidized incinerator for burning fuel such as sludge, 62 is a stoker boiler for burning fuel such as bark, 63 is a heavy oil burning boiler, 64 is a turbine, 65 is a stoker, 66 is a high temperature air duct, 67 and 68 are forced air blowers, 69 is an induced air blower, 70 is an electrostatic precipitator, 71 is a desulfurizer, 72 is a chimney,
73 is fuel such as sludge, 74 is fuel such as bark, 75 is a filter press, and 76 and 77 are air preheaters.

Fuel 74 such as bark is put into the combustion chamber of the stoker boiler 62 and burns on the stoker 65. The high-temperature gas generated by combustion exchanges heat while passing through the heat transfer section of the stoker boiler 62 to generate saturated steam, and lowers the temperature of the gas itself, and the air preheater 76, 77 pushes the fan 67, After the heat is exchanged with the combustion air of the stoker boiler 62 and the fluidized incinerator 61 that are pressure-fed from the 68 to further lower the temperature, dust is removed by the electrostatic precipitator 70 and sulfides are reduced by the desulfurization device 71. Emitted from the chimney 72 into the atmosphere.

On the other hand, fuel 73 such as sludge injected into the fluidized incinerator 61
Is pressure-fed from the forced air blower 68, heat-exchanges with the exhaust gas of the stoker boiler 62, and is burned in a fluidized state by the temperature-raised air to generate a high-temperature combustion gas. The generated hot gas is sent to the heat transfer section of the stoker boiler 62 and
Heat is exchanged in the heat transfer part of the stoker boiler 62 together with the combustion gas of fuel such as bark that has burned on the 65, and saturated steam is generated and then discharged.

The combustion gas generated from the fluidized incinerator 61 contains hydrogen chloride gas, chlorine gas, etc., but the heat transfer part of the stoker boiler 62 does not have a metal temperature exceeding 400 ° C. No corrosion will occur.

Saturated steam generated by the combustion gas of the fuel 74 such as bark in the stoker boiler 62 and the high-temperature gas sent from the fluidized incinerator 61 is installed in the heavy oil combustion boiler 63 together with the saturated steam generated in the heavy oil combustion boiler 63. To the turbine 64 after being superheated to high-temperature steam with high utilization heat efficiency.

[Problems to be Solved by the Invention] As described above, also in the above-mentioned conventional technique, the combustion heat is generated without burning hot fuel that generates hydrogen chloride gas or chlorine gas to cause hot corrosion. It was possible to use it efficiently. However, all of the above-mentioned conventional techniques have a problem that a plurality of furnaces or ducts are required and the equipment cost is increased, so that in recent years, the fluidized bed portion has a cell for burning a fuel containing chlorine, and chlorine. A structure is used in which a fuel containing no hydrogen is partitioned into a cell for burning, and a cell for burning a fuel containing chlorine is not provided with a heat transfer tube having a high temperature.

However, even with these techniques, sufficient analysis has not been performed yet on the collection and circulation of particles scattered from the fluidized bed furnace due to the gas flow.

The present invention has been made in view of such a current situation,
It is an object of the present invention to provide a structure that collects particles containing unburned substances scattered from a fluidized bed with a gas flow and burns them without causing high temperature corrosion by a simple structure.

[Means for Solving the Problems] The above object is achieved by the structure of the fluidized bed boiler described in the claims. That is, the fluidized bed portion of a fluidized bed boiler that burns different types of fuel, the cell that burns the fuel that produces hydrogen chloride gas or chlorine gas by combustion, and the hydrogen chloride gas or chlorine gas that produces by combustion It is classified as a cell that burns fuel that does not generate fuel, and a superheater tube whose wall temperature exceeds 400 ° C is installed in the layer of the cell that burns fuel that does not generate hydrogen chloride gas or chlorine gas. A tube wall temperature of 400 is present in the layers of the cell or in the passages in contact with the combustion gas
In a fluidized bed boiler that does not have a superheater pipe that exceeds ℃, the unburned ash feed position during unburned ash recirculation is other than the cell that has the superheater pipe that has a wall temperature of 400 ℃ or more. It is the structure of the fluidized bed boiler which is in the cell of.

Hereinafter, the operation and the like of the present invention will be described based on Examples.

[Embodiment] FIG. 1 shows an embodiment of the present invention. A system for recirculating unburned ash is based on a fluidized bed boiler that combusts waste sludge containing chlorine discharged from a paper mill. It is a figure which shows the system of each part containing a road. In FIG. 1, 1 is a boiler body, 2 is a coal burning cell, 3 is a sludge combustion cell, 4
Is a first superheater, 5 is an evaporation pipe, 6 is a economizer, 7 is a second superheater, 8 is an evaporation pipe, 9 is a partition, 10 is a sludge inlet, 11 is a coal inlet, 12 is low temperature superheated steam , 13 is high temperature superheated steam, 14
Is an air preheater, 15 is a dust collector, 16 is a forced air blower, 17 is an ejector, and 18 is an unburned ash recirculation pipe.

Sludge containing 60 to 70% of water, which is discharged from the paper manufacturing plant, is thrown into the sludge combustion cell 3 from the sludge feeding port 10 attached to the boiler body 1. On the other hand, coal is injected from the coal injection port 11 onto the coal burning cell 2. A partition wall 9 is formed in the fluidized bed portion between the coal burning cell 2 and the sludge combustion cell 3 to prevent mixing of fuels or combustion products, but the upper empty column portion of each cell. Is a free-flowing structure, the combustion gas generated in the sludge combustion cell 3 is mixed with the coal combustion gas generated in the coal burning cell 2, rises in the combustion chamber of the boiler body 1, and is installed in the convection heat transfer section. After being discharged from the boiler main body 1 through the first superheater 4, the evaporation pipe 5, the economizer 6 and the like, the air preheater 14 exchanges heat with the combustion air, and then the dust collector 15 removes dust. It is released into the atmosphere.

Saturated steam generated by absorbing heat in the radiant part of the boiler body 1, the economizer 6 in the convection heat transfer part, the evaporation pipe 5, the evaporation pipe 8 constructed in the fluidized bed of the coal burning cell 2 and the like is first generated by the boiler. It is sent from the drum to the first superheater 4 constructed in the convection heat transfer section and superheated. At that time, the temperature of the superheated steam is maintained at about 300 ° C or lower so that the wall temperature of the superheater pipe does not exceed 400 ° C.

The steam superheated in the first superheater 4 is further burned in the coal firing cell 2
Is sent to the second superheater 7 installed in the fluidized bed and is superheated, and becomes high-temperature steam with good heat utilization efficiency and is sent to the outside of the boiler system. At that time, since the combustion gas that comes into contact with the first superheater 4 is a mixed gas of sludge combustion gas and coal combustion gas, chlorine high temperature corrosion due to hydrogen chloride gas or chlorine gas contained in the sludge combustion gas. The steam temperature is set so that the tube wall temperature of the first superheater 4 does not exceed 400 ° C.

Further, in the second superheater 7 constructed in the fluidized bed of the coal-only burning cell 2, the coal-only burning cell 2 and the sludge combustion cell 3 are blocked by the partition wall 9 in the fluidized bed portion, and are generated by the burning of sludge. Since there is no possibility that hydrogen chloride gas, chlorine gas, or the like will flow into the fluidized bed of the coal burning cell 2, even if the steam temperature in the second superheater 7 is set to a sufficiently high value, high temperature due to chlorine will be generated in the superheater pipe. No corrosion will occur.

Particles (fly ash, fly ash) that are scattered from the fluidized bed furnace due to the gas flow are usually called unburned ash when they contain unburned substances, in order to increase boiler efficiency. It is necessary to collect the unburnt ash and circulate it into the boiler furnace for combustion.

However, when burning sludge containing chlorine,
Calcium contained in unburned ash containing hydrogen chloride generated from sludge
It has the property of adsorbing at low temperature and repeating the operation of separating at high temperature. Therefore, the total amount of unburned ash recovered by the air preheater 14 or the dust collector 15 is sludged by the ejector 17 and the unburned ash recirculation pipe 18 without a heat transfer pipe whose wall temperature exceeds 400 ° C in the layer. By sending it into the combustion cell 3, the combustion of unburned components is completed and the boiler efficiency is increased, and the heat transfer tubes such as the second superheater tube constructed in the fluidized bed of the coal combustion cell 2 are made of chlorine. Can be prevented from being corroded by.

[Advantages of the Invention] The invention of the present application, which is configured as described above, causes high-temperature steam with high utilization heat efficiency to be generated in a single-body boiler, and a measure for reducing unburned components is solved to solve the problem of high-temperature corrosion. Therefore, it is possible to carry out the recycling method, and it is possible to increase the boiler efficiency and reduce the equipment cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a system of a fluidized bed boiler capable of circulating combustion of unburned components without causing high temperature corrosion due to chlorine, which is an embodiment of the present invention. 2 to 3 are examples of conventional techniques. 1 ... Boiler body, 2 ... Coal burning cell, 3 ... Sludge combustion cell, 4 ... First superheater, 5,8 ... Evaporation tube, 6 ...
... coal saver, 7 ... second superheater, 9 ... division wall, 10 ... sludge input port, 11 ... coal input port, 12 ... low temperature superheated steam,
13 …… High temperature superheated steam, 14 …… Air preheater, 15 …… Dust collector, 16 …… Push blower, 17 …… Ejector, 18 …… Unburned ash recirculation pipe, 51 …… Sludge and other fuel Combustion furnace, 52 …… Exhaust heat boiler, 53 …… Coal or heavy oil combustion boiler, 54 ……
Low temperature steam, 55 …… High temperature steam, 56 …… Steam superheater, 57 ……
Fuel supply port for sludge, 58 ... Burner, 61 ... Fluidized incinerator for burning fuel such as sludge, 62 ... Stoker boiler for burning fuel such as bark, 63 ... Heavy oil combustion boiler,
64 …… Turbine, 65 …… Stalker, 66 …… High temperature air duct, 67, 68 …… Push blower, 69 …… Induction blower, 70 ……
Electrostatic precipitator, 71-desulfurization device, 72-chimney, 73-fuel such as sludge, 74-fuel such as bark, 75-filter press, 76,77-air preheater.

Claims (1)

(57) [Claims] 1. A fluidized bed portion of a fluidized bed boiler that burns a plurality of different fuels, a cell that burns fuel that generates hydrogen chloride gas, chlorine gas, or the like by combustion, and a hydrogen chloride gas or chlorine gas that burns. It is divided into a cell that burns fuel that does not generate, etc., and a superheater tube whose tube wall temperature exceeds 400 ° C. is installed in the layer of the cell that burns fuel that does not generate hydrogen chloride gas or chlorine gas. In a fluidized-bed boiler that does not have a superheater tube with a wall temperature exceeding 400 ° C in the layers of cells other than the cells or in the passages that come into contact with combustion gas, inflow of unburned ash during unburned ash recirculation A structure of a fluidized bed boiler characterized in that the position is in a cell other than the cell in which the superheater tube having a tube wall temperature exceeding 400 ° C is installed.