JPS63159589A - Apparatus for burning alkali pulp waste liquid - 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 [Industrial Field of Application] The present invention relates to an alkaline pulp cooking waste liquid combustion apparatus for recovering soda and heat by burning the alkaline pulp cooking waste liquid.

[Conventional technology]

The traditional pulp manufacturing method is kraft pulp, but
The kraft pulping method is difficult to completely eliminate pollution such as bad odors, and from an economic perspective, heavy oil is consumed in the lime kiln, and the resulting white liquor concentration is low.
Due to limitations on the steam conditions of the recovery boiler installed in the Shikamo combustion equipment, efficiency improvements in terms of heat utilization at pulp mills are almost reaching their limits. The direct causticization method overcomes this limit and is free from odor pollution, surpasses the kraft pulping method in terms of efficiency and economy, and has the potential to produce pulp comparable in quality to kraft pulp, so it is being researched in various fields. Development is underway.

A configuration diagram of a circulating fluidized bed combustion apparatus for carrying out this conventional direct causticizing method is shown in FIG.

An air dispersion plate a is installed in the lower part, and an alkaline pulp cooking waste liquid (hereinafter abbreviated as black liquor) inlet C and an iron oxide particle inlet C are installed in the upper side wall of the air dispersion plate A, and the lower end thereof A circulating fluidized unburnt bed furnace body e, which is provided with an air inlet d and an air inlet d.
The upper end is connected to the cyclone fVc via piping. The upper end of the cyclone f is connected to the flue gas outlet g, and the lower end is connected to the transfer pipe.The transfer pipe has one side connected to the air distribution plate a of the circulating fluidized bed combustion furnace main body. The particle inlet IK connected to the upper position and the other branch to the piping leading to the product outlet j. Black liquor and iron oxide particles are transferred to the respective black liquor inlet and iron oxide particle inlet C. The air is introduced into the circulating fluidized bed combustion furnace main body 8, and is supplied from the air inlet d at the bottom of the furnace to the air distribution plate a#/
c, the black liquor is burned inside the high-temperature circulating fluidized bed combustion furnace main body e by the dispersed air supplied, and at the same time, the alkali in the black liquor is captured by iron oxide, and some of it reacts and becomes a reaction product. Produces sodium ferrate. Reacted and unreacted iron oxide particles are discharged from the circulating fluidized bed combustion furnace body e along with the combustion gas,
The particles are collected by the cyclone f) and returned to the circulating fluidized bed combustion furnace main body e through the particle inlet 1 through the circulation system. Some of the particles from the particle circulation system are taken out of the system through the product outlet j. That is, in this type of combustion furnace, the combustion of black liquor, the capture of alkali in the black liquor on the surface of iron oxide particles, and the reaction between the captured alkali and iron oxide are the two main processes.
The capture and reaction takes place in the circulating fluidized bed combustion furnace body e.

[Problem that the invention seeks to solve]

In the conventional apparatus, the particle size of the iron oxide used is limited due to problems in the combustion of the black liquor, the capture of the alkali, and the reaction between the alkali and the iron oxide (hereinafter referred to as causticizing reaction). In a circulating fluidized bed, the gas flow rate in the combustion furnace is between 5 and 1
The gas velocity in the combustion furnace is as fast as 0 m/8, and the residence time of the gas in the combustion furnace is about 1 to 3 seconds at most. If the iron oxide particles flew out of the combustion furnace together with the combustion gas within this residence time, the causticizing reaction to create ferric acid soda from iron oxide and alkali would be slow and complete, depending on the particle size of the iron oxide. do not. Therefore, the iron oxide particles that flew out of the combustion furnace are recirculated to the combustion furnace, and the particle size of 1 iron oxide particle is 2.
Slightly coarse particles of about 0.00 to 500 microns are used, and the residence time of the iron oxide particles in the high-temperature combustion furnace is lengthened by utilizing the gravitational fall of the particles in the combustion furnace.

As a means of gaining the residence time necessary for the reaction, one device is a device that maintains the particles collected by a cyclone installed at the outlet of the combustion furnace at a high temperature.In other words, iron oxide powder is injected and combusted together with the alkaline pulp cooking waste liquid. Alkaline pulp cooking waste liquid recovery equipped with a fluidized bed combustion furnace that recovers heat and alkaline ferric acid sodium from the alkaline pulp cooking waste liquid, and a cyclone that collects solid powder accompanying combustion waste gas from the fluidized bed combustion furnace. An alkali pulp cooking waste liquid recovery apparatus was proposed, characterized in that a fluidized bed reactor was disposed downstream of the cyclone to maintain a high temperature and high oxygen atmosphere for the solid powder collected by the cyclone (Japanese Patent Application No. 1983). -115347), but it was necessary to maintain a high temperature of 950 to 1000°0 at the cyclone outlet. In other words, in the previously proposed device, it was necessary to maintain the particles collected by the cyclone at a high temperature in a fluidized bed reactor installed downstream of the cyclone to burn unburned carbon and proceed with the reaction.

[Purpose of the invention]

The present invention seeks to provide a black liquor combustion device with a simple structure that can overcome the drawbacks of the conventional and previously proposed devices implementing the direct caustic method and can increase the residence time of iron oxide particles. It is something.

[Means for solving problems]

In order to sufficiently promote the reaction between iron oxide particles and alkali, the black liquor combustion device of the present invention increases the cross-sectional area of the combustion furnace at the top of the circulating fluidized bed combustion furnace main body and reduces the flow rate of combustion gas, thereby reducing the amount of iron oxide in the combustion furnace. By increasing the amount of particles retained, the residence time of the particles in the combustion furnace is increased and the reaction rate is improved.

That is, when the present invention burns the alkaline pulp cooking waste liquid in a soda recovery boiler to recover heat and soda, iron oxide particles are supplied to the combustion furnace together with the alkaline pulp cooking waste liquid, and the alkali in the alkaline pulp cooking waste liquid is recovered. In a circulating fluidized bed combustion furnace used for the so-called direct causticizing method, in which sodium ferrate is taken out of the combustion furnace and caustic soda is recovered by extraction with hot water, the furnace bottom has a high combustion gas flow rate and a small furnace cross-sectional area. This is an alkaline pulp cooking waste liquid combustion apparatus characterized in that the above-mentioned circulating fluidized bed combustion furnace main body with a large furnace cross-sectional area is provided in the upper part.

〔Example〕

A configuration diagram of a circulating fluidized bed combustion apparatus which is an embodiment of the present invention will be explained with reference to FIG.

In Fig. 1, 1 is the circulating fluidized bed combustion furnace main body, 2 is the furnace bottom constituting the lower part of the circulating fluidized bed combustion furnace main body 1, 3 is the air inlet, 4 is the pressure equalization chamber for combustion air, and 5 is the circulating fluidized bed combustion furnace. Air distribution plate at the bottom of the bed combustion furnace 1, 6 is a black liquor inlet, 7 is an iron oxide particle inlet, 8 is a heat exchanger installed at the exchange combustion furnace outlet, 9 is a heat exchanger △ adjacent to the outlet Cyclone, 10 is combustion waste gas outlet, 1
1 is a cooling device for the collected particles collected by the heat exchanger 8 and the cyclone 9; 12 is a transfer pipe that sends the particles collected by the heat exchanger 8 and the cyclone 9 to the cooling device 11; and 13 is a cooling device 11. A connecting pipe 14 for recirculating the particles from the reactor to the furnace bottom 2 of the circulating fluidized bed combustion furnace main body 1 is an outlet for taking out reactive particles from the circulating fluidized bed combustion furnace main body 1.

The black liquor is introduced into the circulating fluidized bed combustion furnace body 1 together with the iron oxide particles through the black liquor inlet 6 and the iron oxide particle inlet lower, respectively, and the air is supplied through the air distribution plate 5 from the air inlet 3 at the bottom of the furnace. The combustion occurs in the high-temperature circulating fluidized bed combustion furnace main body 1 and furnace bottom 2. At the same time, the alkali in the black liquor is captured by iron oxide particles, and some of it reacts to form sodium ferrate. Reacted and unreacted iron oxide particles and a small portion of unburned carbon particles are discharged from the circulating fluidized bed combustion furnace main body 1 together with combustion waste gas, collected by a heat exchanger 8 and a cyclone 9, and transferred to a transfer pipe 12. and falls to the cooling device 11 at the bottom. The particles cooled by the cooling device 11 are supplied to the furnace bottom 2 from the connecting pipe 13. These circulating particles are transferred to the circulating fluidized bed combustion furnace main body 1.
It maintains a uniform temperature and stably burns the waste liquid, and also serves to capture the alkali in the waste liquid into iron oxide particles when the waste liquid is burned. The particles discharged from the reactant particle outlet 14 to the outside of the circulating fluidized bed combustion furnace main body 1 are sent to the next causticizing step.

〔Effect of the invention〕

The following effects can be expected from the apparatus of the present invention.

+1) The residence time of iron oxide particles in the high-temperature combustion furnace can be extended, and the reaction rate of the causticizing reaction can be increased. If the reaction rate can be maintained high, soda carbonate and unreacted iron oxide as impurities will be reduced, resulting in better thermal economy.

(2) Previously proposed invention (Patent application 11534/1986)
Compared to the method of keeping the cyclone-collected particles at a high temperature as in No. 7), the apparatus is simplified because the high-temperature area necessary for the reaction can be limited to the inside of the combustion furnace. In addition, there is no need to maintain the outlet of the circulating fluidized bed combustion furnace at the high temperature required for the reaction, and there is a large margin in combustion conditions, making operation easier.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a circulating fluidized bed combustion furnace which is an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional apparatus.

Claims (1)

[Claims] When the alkaline pulp cooking waste liquid is burned in a soda recovery boiler to recover heat and soda, iron oxide particles are supplied to the combustion furnace together with the alkaline pulp cooking waste liquid, and the alkali in the alkali pulp cooking waste liquid is converted into the above-mentioned sodium ferric acid. In a circulating fluidized bed combustion furnace used for the so-called direct causticizing method, in which caustic soda is recovered by taking it out of the combustion furnace and extracting it with hot water, it has a bottom part with a small furnace cross-sectional area where the combustion gas flow rate is high, and a furnace cross-sectional area in the upper part. An alkaline pulp cooking waste liquid combustion apparatus comprising the circulating fluidized bed combustion furnace main body having a larger size.