JPS58132195A - Black liquor burning boiler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler device for burning black liquor and recovering 1JaOH, and particularly to the structure of an existing black liquor combustion boiler modified into a black liquor combustion boiler using a direct caustic soda recovery method.

In the pulp manufacturing process at a paper mill, chemicals such as NaOH are used to separate the wood components cellulose (fiber) and lignin (resin) and extract only the cellulose. A solution containing a mixture of dissolved lignin and Na components after the cooking process is discharged as a waste liquid called black liquor. Conventionally, a method has been practiced in which heat is recovered by burning this black liquor, and at the same time NaOH is recovered and reused.

FIG. 1 is a system diagram showing a conventional black liquor combustion and NaOH recovery method.

However, in the process shown in Figure 1, the aa(oH)2 used for NaOH recovery is obtained by heating the OacO3 produced in the causticizing process 4 and adding its condensate to produce slaked lime (ca(OH)2).
) has to go through a complicated process of producing it, resulting in problems such as increased equipment costs and increased energy consumption.

That is, in the calcination step 5, a calcination device usually called a lime kiln is used, and a direct causticization method is proposed in which energy such as petroleum is added to black liquor and combusted. First, the method proposed by the inventor will be explained with reference to FIG. Lignin is separated from the wood chips using NaOH in the cooking process 1, and the black liquor containing lignin and Na components is added with Fe203 as iron oxide powder in the combustion process 2, so that the following reaction occurs.

2NaOH+ 002 →Na2003...
・(1) Na2003+Fe2O3→2Na? e02
+CO2 (2) Of these, NaFe02 is hydrolyzed in the next dissolution step 7 and NaOH is recovered.

2NaFeO2+ H2O2NaOH+ Fe2O3−
(In other words, in the direct causticization method, NaOH can be recovered by performing the reactions (1), (2), and (3), and the Fe2O3 used for this recovery can be separated and recycled for reuse. can.

What should be noted when implementing the above method is that NaFeO
Three types of 2, αβγ, have been confirmed based on its crystal structure, and it has been confirmed that production of β-NaFeO2 is preferable in order to effectively carry out the hydrolysis shown in reaction formula (3). To react and generate this β-NaFeO2, N
The ambient temperature of the mixture of a2co3 and Fe2o3 was set to 800
~1ooo'c.

This β-NaFθ0 reaction product is Na as a combustion residue.
It was also confirmed through experiments that this reaction was caused by the fact that 2003 and Fe2O3 were deposited on the bottom of the furnace and the ambient temperature was maintained at 800-1000°C.

Therefore, it is necessary to take these points into consideration when converting an existing black liquor combustion boiler into a boiler suitable for the direct causticizing method.

This invention is intended to facilitate modification by providing a protrusion in the furnace to form a throat portion, dividing the furnace into upper and lower halves, and making the lower furnace have a fluidized bed portion.

In short, this invention provides a furnace of a black liquor combustion boiler with a protrusion protruding from the wall surface to form a throat part, forms an upper furnace and a lower furnace via this throat part, and connects the bottom of the lower furnace with combustion residue. A black liquor combustion boiler is characterized in that it is formed in a fluidized bed section, and is equipped with a device for supplying part of the combustion exhaust gas and air to the furnace and controlling the temperature of the fluidized bed.

First, in the reaction shown in the above-mentioned formula (2), the softening point and melting point of the ash mainly composed of 1 JaFeo□ produced by black liquor combustion are shown in the following table.

Note that the stock solution here means a black liquor that does not contain Fe203.

Table 1 In the above cases, the molar ratio of Fe and Na, more specifically the molar ratio of Fe203 and Na2 Cj 03 (or Fe/Na), must be 1 or more for the reaction, and in the black liquor combustion process, the formula NaF generated based on (2)
The softening point of e02 is l・10 when the molar ratio is 1 in the table above.
0℃, and if it is below this, even if the molar ratio is increased, N
aFeO2 does not soften and becomes powdery, and furthermore, 80
If the temperature is controlled within the range of 0°C to 1000°C, the generated NaF
It has been confirmed through experiments that the crystal structure of eO2 is mostly β-type.

Further, assuming that black liquor having an Fθ7Na ratio of 1 or more is burnt, in order to suitably hang β-NaFeO3, it is necessary to maintain the temperature of the deposited portion at the above-mentioned 800 to 1000°C. Considering the conditions for this, it is clear that it is necessary to take measures to prevent temperature rise due to burner flame radiation and to maintain the temperature of the deposition portion between 800 and 1000°C.

Next, the structure of a black liquor combustion boiler according to the present invention will be explained. Of course, the structure proposed by this invention can be easily adopted in a newly constructed black liquor combustion boiler, but it is particularly suitable for modifying a multi-stage black liquor combustion boiler to a black liquor combustion boiler structure that is directly applied to causticizing means. It is important to note that it shows the structure.

Figure 3 shows a conventional Tomlinson-type black liquor combustion boiler 101.
The black liquor sprayed from the burner 102 adheres to the wood pipe wall, dries, falls off, forms charpet 103 and burns, and the smelt mainly composed of Na2003 flows from the outlet 104 and NaOH is It is recovered through a process.

Combustion air is supplied into the furnace from a primary air wind box 105 and a secondary air wind box 106 through nozzles 105a and 106a, which are openings provided in the furnace wall.

A wood tube 107 with studs is connected to a connecting member 108 made of an elongated steel plate to form the bottom plate of the furnace.

In this invention, a fourth
As shown in the figure, a protrusion 109 formed by a water tube is formed in an upper furnace 111 and a lower furnace 112, and a throat portion 110 serving as a gas passage is provided between the upper and lower furnaces. A partial cross-section of the bottom water pipe of the existing black liquor combustion boiler is as shown in FIG. 5, but when remodeling, as shown in FIG.
will be established. In addition, there is a pressure gas chamber 11 under the bottom ice wall.
4a, 114b', and ``114c.If necessary, part of the wind box 105, 106 is left as a wind box 115, and an air supply/glue 115a is provided in the space above the accumulation of combustion residue in the lower furnace 112. The nozzle 105 booster 7 ann 119 in FIG. 3 sucks and recirculates high-temperature exhaust gas through the pipe 118 and supplies it to the pressure gas chambers 114a, 114b, 114c to form a fluidized bed section 120 of combustion residue. If necessary, air for temperature reduction is supplied through a pipe line 121 connected to the pipe line 118.

A second embodiment of the present invention will be explained with reference to FIG. 7 including a control system.

The furnace of boiler 201 that burns black liquor has a part of the ice wall tube (
For example, every other row of tubes) are made to protrude into the furnace, and this protruding tube group forms a throat portion 202 to divide the furnace into an upper furnace 203a.

Black liquor and iron oxide powder are mixed in a storage tank 204, and the mixed liquid (hereinafter simply referred to as fuel) is supplied to a burner 206 via a pipe 205a and a pump 205. Combustion air from the blower 207 passes through the damper 8a and the pipe 8 to the burner 206.
is supplied to the wind box.

Fuel combustion residue (mixture of Na2003 and Fe2O3)
falls onto the upper slope of the protrusion 9 of the ice wall tube. Since this upper surface is formed with an angle α (for example, 50 degrees) that is greater than the angle of repose of the powdery residue with respect to the horizontal, the powdery material slides on the upper slope of this protrusion 9 and passes through the throat 202 to the lower furnace. The inner G falls and becomes the deposit part 10. This deposit is sent to the cooling bag @11 connected to the bottom outlet 10a, cooled, and supplied to the belt conveyor 11. The weight is measured by a weighing device 12 and then sent to a dissolution tank 13. The cooling device 11 shown in the drawings is of a screw type having an outer water-cooled cylinder and an inner water-cooled barrel.

Instead of this screw type, a fluidized bed type cooler may be used, and a cooling pipe may be provided inside the fluidized bed type cooler to use water cooling.

Due to the formation of the protruding portion 9, the deposition portion 10 becomes a nokuna 20.
This prevents the temperature of the upper surface of the deposited portion from rising excessively and causing melting when the deposited portion receives radiant heat.

On the other hand, since the deposits are cooled by the water cooling pipe on the bottom wall of the furnace, the temperature of the deposits is lowered and no adhesion occurs, which is good, but on the other hand, this is not preferable from the viewpoint of the aforementioned formation of β-NaFθ02.

For this reason, it is necessary to supply the necessary thermal acid and to supply a high temperature gas to the deposition section in order to impregnate the deposition section with gas and fluidize it so that it can be easily discharged. For this purpose, it is preferable to provide an exhaust gas extraction port 14 at a location with a suitable gas flow downstream of the combustion gas, for example, downstream of the evaporator tube group, and to extract high-temperature gas therefrom and supply it from the bottom of the furnace via a pipe 15.

A pressure gas chamber 16 is provided at the bottom of the furnace, and a heat insulating material 17 is provided on the inner surface. The high temperature gas is connected to the connecting member 10 shown in FIG.
The deposit is fluidized by ejecting it from the nozzle 113 provided at 8,
And keep the humidity of the layer at 800-1000℃ and β-NaF
Maintain conditions suitable for the generation of e02. A plurality of air supply ports 24 are provided in the space above the deposit to help control the temperature rise of the deposit.

Recirculating such high-temperature combustion gas and supplying it to the pressure gas chamber is also effective in reducing nitrogen oxides (NOx) in the exhaust gas.

The amount of pressure gas supplied for recirculation, the amount of air supplied from the pipe line 24, and the amount of air supplied from the nozzle 24 are mainly controlled to maintain the temperature within the fluidized bed of the deposit at 800-1000°C. This is what is done.

The signal is transmitted to the fluidized bed temperature sensor 21. Mixed gas temperature sensor 20. Humidity detector in the space above the deposition section 25. The humidity signal from the temperature sensor 22 of the recirculated combustion gas is sent to a control box 23 that stores and issues command signals, and the amount of exhaust gas and air that is recirculated is controlled by the command signals from the control box that receives these temperature signals. be done.

If necessary, in order to blow off deposits on the upper surface of the protrusion 9, a plurality of nozzles 26 are provided along the upper surface of the protrusion 9 to eject pressurized air. is supplied to these nozzles 26.

By carrying out this invention, the production rate of β-NaFe02 can be increased and the efficiency of NaOH recovery can be made significantly higher.

[Brief explanation of drawings]

Figure 1 shows NaO containing combustion in a conventional black liquor combustion boiler.
Fig. 2 is a process diagram of direct causticization by combustion of a mixture of Fe2O3 and black liquor, Fig. 3 is a sectional view of a conventional black liquor combustion boiler, and Fig. 4 is an embodiment of the present invention. Figure 5 is a cross-sectional view of a modified black liquor combustion boiler, Figure 5 is a cross-sectional view of the conventional wood tube at the bottom of the furnace, Figure 6 is a cross-sectional view of the furnace bottom modified to a perforated plate, and Figure 7 is the control system. FIG. 3 is a cross-sectional view of a second embodiment of the present invention, including a second embodiment of the present invention. 201... Black liquor combustion boiler 202...
...Throat part 203a ... Upper furnace 203b ... Lower furnace 10 ... Deposition part 9 ... Protrusion part 14 ... Exhaust gas Extraction port 20...Mixed gas temperature detector 21...
...Fluidized bed temperature sensor 22 ...Recirculating combustion gas temperature sensor 23 ...Control box 25 ...Temperature detection in the space above the deposition section Vessel 2
6... Nozzle 108... Connection member 113... Nozzle

Claims (1)

[Claims] 1. The furnace of the black liquor combustion boiler is provided with a protrusion protruding from the wall surface to form a throat portion, an upper furnace and a lower furnace are formed via this throat portion, and the bottom of the lower furnace A black liquor combustion boiler, characterized in that a fluidized bed section made of combustion residue is formed, and a device is provided for supplying combustion exhaust gas and air to a lower furnace and controlling the temperature of this fluidized bed. 2. Against the horizontal surface of the upper furnace side slope of the protrusion 3.
2. A black liquor combustion boiler according to claim 1, wherein the angle of inclination is greater than the angle of repose of combustion residue. 3. The black liquor combustion boiler according to claim 1 or 2, characterized in that a combustion residue blowing device is provided along the slope on the side of the upper furnace. A temperature sensor for recirculating combustion gas, a temperature sensor for detecting the temperature of the mixed gas, and a temperature sensor for detecting the temperature of the deposition section. A humidity detector detects the spatial humidity of the lower furnace, and a control box is installed to receive signals from the humidity detector.
Claims characterized in that a command signal circuit is provided for controlling the recirculation exhaust gas position, the amount of air mixed therewith, and the amount of air supplied to the space above the deposition section based on a command signal from the control box. The black liquor combustion boiler according to any one of items 1 to 3.