JP2684816B2 - Recovery method of lime in papermaking cleaning sludge - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for recovering and regenerating lime in papermaking cleaning sludge, and more particularly to a method for recovering and regenerating lime that can reduce the usage rate of expensive fuel such as heavy oil.

[Prior Art] In the regeneration process, as is well known, the blow liquor from the digester is separated into a valve and a black liquor. The separated black liquor is subjected to various treatments to obtain green liquor, and this green liquor is separated into a clear liquid and dregs by a clarifier. Then, this clarified liquid is put into a slaker together with quick lime to dissolve the quick lime [Ca
O + H ₂ O → Ca (OH) ₂ ] and causticization of green liquor [Na ₂ CO ₃ + Ca
(OH) ₂ → 2NaOH + CaCO ₃ ]. This reaction continues in the causticizing tank. Since the white liquor (diluted stock solution) thus obtained contains sludge (CaCO ₃ ), the belt filter separates the sludge from the white liquor, and the white liquor is sent to the cooking process. Collect as a liquid. The cleaning sludge as the cleaning residue is Ca
Since it is mainly composed of CO ₃ , it is dried with a newly supplemented limestone grain, and then 1000-1250 in a rotary kiln.
It is calcined at a temperature of ℃ [CaCO ₃ → CaO + CO ₂ ] and recovered as reclaimed quicklime for causticizing. This rotary kiln is fueled by heavy oil.

[Problems to be Solved by the Invention] As described above, heavy oil is used as a fuel in the rotary kiln for recovering the lime component in the cleaning sludge, resulting in a high fuel cost.

It is widely practiced to use combustible waste substances as auxiliary fuel. Therefore, it is conceivable to use the pulp sludge discharged from the paper manufacturing process as an auxiliary fuel for calcination of lime in the rotary kiln.

However, burning pulp sludge produces ash, so the sodium compounds contained in cleaning sludge and pulp sludge melt during calcination of lime and stick to this ash to form a large lump, which prevents the prescribed firing. Alternatively, the molten sodium compound adheres to the furnace wall together with the ash, damages the furnace wall, or thickly deposits the ash (ash) to close the furnace. For this reason, conventionally, pulp sludge cannot be used as an auxiliary fuel for calcination of lime, and a large amount of expensive heavy oil has been used.

[Means for Solving the Problem] The method for recovering and regenerating lime in papermaking cleaning sludge digestion according to the present invention is to incinerate pulp sludge in a first furnace at a temperature of 800 ° C. or lower while The papermaking cleaning sludge mainly composed of calcium carbonate is charged and heated, and the calcium carbonate particles of the heated papermaking cleaning sludge are burned in a second furnace at a temperature of 850 ° C. or higher and recovered as quicklime particles. It is a feature.

[Operation] According to the method of the present invention, calcium carbonate can be fired using pulp sludge as an auxiliary fuel. That is, in the method of the present invention, the pulp sludge is incinerated at a temperature of 800 ° C. or lower in the first furnace, and the cleaning sludge mainly containing calcium carbonate is first charged and heated therein to be preheated. If the cleaning sludge is heated during incineration at a low temperature of 800 ° C or lower, the sodium compounds contained in the cleaning sludge and pulp sludge do not melt, and even if incinerated ash of pulp sludge is generated. It will not stick to it and adhere to the furnace wall or tube wall. The heated calcium carbonate particles are then heated in the second furnace to 85
Baking at a high temperature of 0 ° C or higher. At this time, this second
Since no ash is generated in the furnace of No. 2, even when the sodium compound is melted during this high temperature firing, there is no problem that the sodium compound sticks to the ash and inhibits firing, and that the ash does not adhere to the furnace wall or pipe wall.

Thus, according to the present invention, it becomes possible to calcine calcium carbonate using pulp sludge as an auxiliary fuel and recover it as quicklime.

In the present invention, the incineration temperature in the first furnace is 800 ° C or lower,
Particularly, about 700 to 800 ° C is suitable. The firing temperature in the second furnace is preferably 850 ° C. or higher, especially about 850 to 950 ° C.

Embodiment An embodiment will be described below with reference to the drawings.

FIG. 1 is a system diagram of a lime recovery and regeneration apparatus suitable for carrying out the method according to the embodiment of the present invention. The reference numeral 10 is a fluidized furnace, and in the order from the lower side, the quick lime cooling unit 1, the calcination unit 2,
An air preheating unit 3, a pulp sludge incineration unit 4, and a drying unit 5 are provided in multiple stages.

The quicklime cooling unit 1 is divided into two upper and lower chambers by a dispersion plate 11, and air is introduced into a lower air chamber 12 from a feed fan 13. A fluidized bed 14 of quick lime (CaO) is formed in the fluid chamber 1a above the dispersion plate 11.

The firing section 2 is divided into two chambers, an upper chamber and a lower chamber, by a dispersion plate 15, and a combustion chamber 17 having a burner 16 is provided below the dispersion plate 15. The combustion chamber 17 and the flow chamber 1a are partitioned by a partition wall 1b. The burner facing the fluidized bed is on the upper side of the dispersion plate 15.
There is a firing chamber 19 equipped with 18 and calcium carbonate (Ca
A fluidized bed 20 of CO ₃ ) is formed.

The air preheating section 3 has a plate 22 having an opening 21 on the lower side thereof.
It is partitioned from the firing section 2. The upper side is partitioned from the pulp sludge incinerator 4 by a plate 24 having an opening 23. An air preheater (heat exchanger) 25 is installed between the plates 22 and 24. Air (a temperature of about 20 ° C. in this embodiment) is introduced into the air preheater 25 from a feed fan 26, and the air heated in the air preheater 25 is supplied to the combustion chamber 17 through a pipe 27.

The pulp sludge incineration section 4 has the dispersion plates 28 and 29 arranged in two stages. A combustion chamber 31 having a burner 30 is provided below the lower dispersion plate 28. The upper side of the dispersion plate 28 is a pulp sludge incineration chamber 33 in which a fluidized bed 32 is formed. Pulp sludge (having a water content of about 50% in this embodiment) is introduced into the incinerator 33 from a supply line 54.

A gas temperature control chamber 34 is provided on the upper side of the upper dispersion plate 29, and a heat transfer tube 36 is arranged so as to be immersed in a fluidized bed 35 made of a fluid medium such as sand. Water is introduced into the heat transfer tube 36 to collect steam. A plate 38 having an opening 37 is provided above the gas temperature control chamber 34.

The drying section 5 has a drying chamber 40 defined by a dispersion plate 39, and in the drying chamber 40, a fluidized bed 41 of washing sludge mainly composed of calcium carbonate for drying is formed.

The drying chamber 40 and the incineration chamber 33 are connected by a pipe 42, and the incineration chamber 33
The firing chamber 19 and the firing chamber 19 are connected by a pipe 43. Furthermore, the firing room
19 and the cooling chamber 1a are connected by a pipe 44.

The cleaning sludge as the raw material sludge mainly containing calcium carbonate (CaCO ₃ ) is introduced into the mixer 46 through the supply line 45, and is mixed with the large-sized one of the collected products of the cyclone 47 in the mixer 46. It This mixture is introduced into a cage mill 49 via a supply line 48, and is supplied from the cage mill 49 to the cyclone 47 via a supply line 50. A solid component is collected in the cyclone 47, and a small component having a diameter of about 1 mm is introduced into the drying chamber 40 via the supply line 51. The gas separated by the cyclone 47 is sent to the waste heat recovery device and the gas processing chamber via the pipe 52 and the fan 53.

The raw material (cleaning sludge) supplied from the supply line 51 into the drying chamber 40 is fluidized and dried in the fluidized bed 41. The dried product is sent to the incineration chamber 33 through the pipe 42 and is preheated in the fluidized bed 32 to about 700 to 800 ° C. Pulp sludge is introduced into the incineration chamber 33 via a supply line 54 and a fluidized bed is provided.
It is dried and incinerated at about 750 ℃ in 32.

The particles of calcium carbonate in the cleaning sludge preheated in the incineration chamber 33 are put into the firing chamber 19 via the pipe 43 and fired in the fluidized bed 20. The temperature of this fluidized bed 20 is
In this embodiment, the temperature is set to about 900 ° C., and it is decomposed into carbon dioxide (CO ₂ ) of calcium carbonate (CaCO ₃ ) and quick lime (CaO). At this time, since no combustion ash is generated in the firing chamber 19, even if the sodium compound (NaOH) adhering to the calcium carbonate is dissolved, it does not hinder the firing. The produced quick lime is put into the cooling chamber 1a via the pipe 44,
The fluidized bed 14 is cooled by contact with air. The cooled quicklime is recovered via the take-out line 55. The temperature at the time of recovery is about 345 ° C.

 The flow of gas will be described next.

The air introduced from the feed fan 13 into the air chamber 12 passes through the dispersion plate 11 to form a fluidized bed 14, and the fluidized bed 14
Heat exchanges with quick lime inside to cool the quick lime. Air heated by this heat exchange (about 345 ° C in this embodiment)
Is introduced into the combustion chamber 31 via the pipe 56.

A burner 30 is provided in the combustion chamber 31, and the introduced air is used as combustion air for the burner 30. The combustion gas generated in the combustion chamber 31 has a temperature of about 530 ° C. in this embodiment, and passes through the dispersion plate 28 to form the fluidized bed 32.

In the fluidized bed 32, pulp sludge is injected as an auxiliary fuel as described above, and the temperature of the fluidized bed due to the combustion of the pulp sludge is about 750 ° C., which is higher than the temperature of the gas passing through the dispersion plate 28. At this incineration temperature of about 750 ° C, the sodium compounds contained in the washing sludge and the pulp sludge do not melt, and even if combustion ash of the pulp sludge is generated, the fusion of the sodium compound with the melt does not occur, Ash does not adhere to the furnace wall of the fluidized furnace or the inner surface of the pipe due to melting of the sodium compound.

The combustion gas at about 750 ° C. that has passed through the fluidized bed 32 then passes through the dispersion plate 29 to form the fluidized bed 35.

The fluidized bed 35 is for preventing a temperature rise due to afterburning of gas blown up from the combustion chamber 33. That is, a part of the combustible components in the pulp sludge cannot be completely burned in the fluidized bed 32, but is post-burned (afterburning) in the freeboard portion on the upper side of the fluidized bed 32 or in the gas temperature control chamber 34, and the gas temperature rises. try to. As described above, when the gas temperature becomes excessively high, the sodium compound melts and sticks to the ash, so that the fluidized bed 35 is formed in the temperature control chamber 34 and the gas temperature is set to about 750 ° C. by the heat transfer tube 36. To maintain.

The gas at about 750 ° C. that has passed through the fluidized bed 35 then passes through the dispersion plate 39 to form the fluidized bed 41. The gas that has escaped from the fluidized bed 41 has dropped to about 350 ° C., and this gas is sent to the cage mill 49 via the duct 58. In the cage mill 49, this gas is used for drying the raw material, and the raw material and gas are sent from the supply line 50 to the cyclone 47 and separated into solid and gas. As described above, this gas component is discharged through the pipe 52.

As is clear from the above description, in this embodiment, the combustion chamber 33 is used as the first furnace for incinerating the pulp sludge, and the calcining section 2 is heated in the first furnace and preheated in the cleaning sludge. It is used as a second furnace for firing calcium carbonate particles at temperatures above 850 ° C. And
Since pulp sludge is used as an auxiliary fuel,
The amount of heavy oil supplied to the burners 16, 18, 30 is much smaller than that of the conventional example.

Next, the collection results of the present invention example and the conventional example will be shown. The cleaning sludge supplied from the supply line 45 has a water content of 20.
%, The balance being substantially of CaCO ₃ .

As is apparent from the above table, the amount of heavy oil used is significantly reduced by the method of the present invention.

[Advantages of the Invention] As described above, according to the method of the present invention, it is possible to reduce the amount of fuel such as heavy oil used and to reduce the fuel cost. In addition, ash accumulation in the furnace and damage to refractories are also prevented.
Further, according to the method of the present invention, the pulp sludge incineration facility and the limestone regenerating facility can be integrated.

[Brief description of the drawings]

 FIG. 1 is a system diagram of a lime recovery and regeneration device. 1 ... Quick lime cooling part, 2 ... Firing part, 3 ... Air preheating part, 4 ... Pulp sludge incineration part, 5 ... Drying part, 10 ... Fluidized furnace, 11,15,28,29,39 ... … Dispersion plate, 16,18,30 …… Heavy oil burner.

Claims (1)

(57) [Claims] 1. A pulp making sludge is incinerated at a temperature of 800.degree. C. or lower in a first furnace, and a papermaking cleaning sludge mainly containing calcium carbonate is put into the first furnace and heated. Calcium carbonate particles from papermaking cleaning sludge
A method for recovering and regenerating lime in papermaking cleaning sludge, which comprises calcination in a second furnace at a temperature of 850 ° C. or higher to recover as quicklime particles.