FI85993C - Foerfarande Foer behandling av raosaopa - Google Patents

Description

1 85993

METHOD FOR TREATMENT OF RAW FILM - FÖRFARANDE FÖR BEHANDLING AV RAsAPA

The invention relates to a process for the treatment of crude film formed in an alkaline cellulose process. In particular, the invention relates to a process for treating the so-called crude clay produced in sulphate cooking and derived from wood extracts and for producing combustion gas from the crude clay.

10 In the sulphate pulp mill, it is known to separate soap from waste liquor (black liquor) in connection with the evaporation of the broth (Virkola, N.-E./ Manufacture of wood pulp, part 2, Academy of Technical Sciences, Turku 1983, 1334). In addition to the material derived from wood extracts, the raw soap contains e.g. inorganic substances, especially sodium (e.g. 4-6%) and water (approx. 30%). Crude soap is utilized either by boiling it with sulfuric acid to a so-called crude pine oil, e.g. so-called mixed oil, if part of the bog comes from hardwood, or to burn it in a recovery boiler. Crude pine oil can be sold to a distillery for further refining.

In current processes for bleached sulphate cellulose, both of the above uses are problematic. Tall oil production 25 complicates the mill's sulfur balance and indirectly causes either an increase in sulfur dioxide emissions or costs to reduce SO2 emissions. The use of hardwood sap for the production of tall oil is otherwise uneconomical. The importance of this fact will increase 30 in the future as the share of hardwood pulp in production increases. Combustion of raw clay in a recovery boiler is often not economically justified, as the energy balance of pulp mills is currently in surplus V. In addition, the recovery boiler often forms a bottleneck in 35 processes, resulting in lower cellulose production capacity when burning soap.

2 85993

It is an object of the present invention to obviate the above drawbacks. In particular, it is an object of the invention to develop the treatment of the crude film generated in the alkaline cellulose process so that it can be utilized in the factory process. It is a further object of the invention to provide a treatment for the crude clay so that the sodium contained in the clay is recovered and so that the process does not cause an increase in sulfur dioxide emissions or additional costs to reduce sulfur dioxide emissions.

With respect to the characterizing features of the invention, reference is made to the claims.

The invention is based on the use of a gasification technique to treat a leach 15 formed in an alkaline cellulose process. Gasification technology offers an alternative in an effort to expand the use of low quality solid or liquid fuels. In gasification, the organic matter of the raw material reacts with oxygen and water vapor at a high temperature, e.g. 600-20 1300 ° C, and is converted to fuel gas (Kurkela, E.,

Biomass 18, 1989, 287). The gasification technique has not previously been applied to the treatment of crude clay with a high sodium content.

According to the invention, the crude soap, air and possibly water vapor are fed to a gasification reactor in which ... the organic matter of the flux is converted into combustion gas at a high temperature, in the range of 600 to 1300 ° C. Sodium salts such as sodium carbonate (NaaCOa), sodium sulfide (NaaS) and possibly sulfur gases such as hydrogen sulfide (HaS) are formed from the inorganic material of the filter. In the process, a significant proportion of the sodium salts are separated from the product gas either in the gasification step itself or in a subsequent, still high temperature process step. The product gas is used as fuel for the pulp mill in the pulp mill, and the separated sodium salts are returned to the mill's chemical cycle.

‘It is noteworthy that raw soap cannot be burned 3 85993 as such in a lime kiln due to the high sodium content. Currently, the only technical solution for sodium separation is to boil soap into pine oil. However, the use of crude pine oil as fuel does not make economic sense. During the development of the process according to the invention, a new and surprising finding has been made that by refining the organic organic matter into fuel gas at high temperature it is possible to remove a considerable proportion of sodium compounds from inorganic material, after which the gas can be advantageously used as lime kiln fuel and separated sodium salts can be used. return to the chemical cycle. The use of a honeycomb requires nothing more than the partial removal of sodium compounds from the gas. Sulfur-15 compounds do not cause problems in the lime kiln, nor do small amounts of sodium compounds. In addition, it can be stated that the use of raw clay as fuel for the lime kiln does not complicate the mill's sulfur balance or energy balance. On the contrary, the external fuel purchased for the lime kiln, typically heavy fuel oil, can, thanks to the invention, be largely replaced by lignite.

·, Sodium compounds can be separated from the gas e.g.

in the immediate connection of gasification or e.g. in a separate process step. One way to enhance the separation is to use a temperature close to the melting point of the sodium compound mixture, e.g. about 750 ° C. In this case, the sodium particles agglomerate into larger particles by adhering either to each other or to any reactor bed material. The larger particles obtained can be separated from the gas relatively easily. If necessary, the temperature of the gas can be slightly lowered before the actual separation and the temperature can be e.g. 400 - 1300 * C. Suitable separation devices are, for example, cyclones 35 and filters. Alternatively, the gasification reactor can be designed with a large or larger part. the agglomerated sodium particles do not leave under the gas * 85993 stream and thus remain in the reactor from which it can be removed, e.g. as a melt.

The new method according to the invention is an economically viable way of utilizing raw soap and at the same time offers e.g. the following advantages over current uses. The method utilizes the energy content of the smelter and can replace the purchased fuel without increasing the energy surplus of the recovery boiler. Furthermore, the method does not affect the black liquor capacity of the recovery boiler, which in turn often determines the cellulose production capacity. Furthermore, the method alleviates the sulfur balance problem of the plant. In addition, the economic competitiveness of the method does not depend on the species of wood from which the soap originates.

In the following examples, three ways of implementing the new method are described by way of example. The examples are intended only to illustrate the invention without limiting it in any way.

Example 1 Figure 1 shows a schematic diagram of an application in which sodium compounds are separated in a carburetor and / or its primary cyclone. The crude soap, material stream 1, and air, material stream 2, are fed to a carburetor 10, where they; react with each other at a temperature of 600 to 800 ° C. The gasification air can be enriched with oxygen if desired. The carburetor operating pressure is only slightly higher than normal air pressure. The water vapor required for gasification reactions is obtained from the water contained in the filter. If this amount is not sufficient, water vapor can be fed to the carburetor. The gasification reactor operates on a fluidized bed principle, e.g. a bubbling or circulating bed, and the bed material consists of sodium salts formed during gasification. Some of the salts, stream 3, are continuously removed from the reactor so that the bed mass remains constant. The removed sodium salts 35 are returned to the chemical cycle of the plant, e.g. through the solvent tank of the recovery room or the furnace of the recovery boiler.

: The product gas, substance stream 4, which may contain a small amount of 5 85993 sodium compounds, is fed to a factory lime kiln where it is used as fuel, possibly simultaneously with other fuels. If necessary, the temperature of the gas can be lowered before combustion, for example by transferring heat to the gasification air.

Example 2

The embodiment according to Example 2 differs from the alternative mentioned in Example 1 in that in this case some other solid in addition to the sodium salts is used as the fluidized bed material. The purpose of using the second solid is, for example, to facilitate the control of the fluidized bed or to enable a higher gasification temperature. In this case, some 15 of this additive also enters the sodium salt effluent, Figure 1, stream 3. The relative amount of additive can be influenced e.g. by selecting a salt extraction site. Separation of the additive from the sodium salts is straightforward when the substance is not water soluble. The separation can take place, for example, after a separate dissolution step-20 or if the gas is not returned from the additive. : in a green reactor, eg in a green liquor clarifier.

'Example 3

Figure 2 shows a schematic diagram of an implementation in which sodium salts are separated in a separate process step. The raw soap, material stream 1, and air, material stream 2, · ... are fed to a carburetor 10, where they react with each other at a temperature of 700 to 1200 * C. In terms of pressure and the need for water vapor, the implementation does not differ substantially from Example 1. The reactor operates in the so-called The reaction products (gases and salts) are passed through an intermediate pipe to another circulating bed reactor. 11. The bed material consists of an additive, e.g. sand, and the sodium salts which accumulate in it, or alternatively, e.g., only sodium salts. Suo-:: 35 removal of material, stream 3, and recovery are carried out in the same way as in Example 1 or 2. The product gas, -. stream 4, the temperature must be below the melting point of the sodium salts, so that heat is removed from the reactor if necessary by means of a heat exchanger, e.g. a steam generator, in case the gasification temperature is above the melting point of the sodium salts, some of the sodium salts are recovered , from which the molten phase flows to the bottom of the reactor and further out of the reactor through a suitable bottom opening. Such a hardware solution has previously been used in other substantially different applications (Orjala, 10 M., Ruottu, S. and Huotari, J., VTT Research, no. 607,

State Technical Research Center, Espoo, 1989). The product gas is utilized in a lime kiln as in Examples 1 and 2.

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Claims (10)

A process for treating bar soap formed in an alkaline cellulose process, characterized in that the bar soap is gasified with air at a temperature of 600 - 1300 ° C, that part of the sodium compounds of the soap is separated from the gas obtained. and that the recovered gas is advantageously used as fuel in the blast furnace and the separated sodium compounds are fed back into the chemical circulation. 10 2. A method as claimed in claim 1, characterized in that the bar soap is gasified with water vapor. Process according to Claim 1 or 2, characterized in that the sodium compounds 15 are separated in the gasification stage or at a separation stage thereafter. 4. A process according to any of claims 1-3, characterized in that the sodium particles are agglomerated into larger, easily separable particles in connection with the separation of the sodium compounds. 5. A process according to claim 4, characterized in that the process uses a solid additive in which the sodium compounds are agglomerated. race . * · .. 25 6. A process according to claim 5, characterized in that in the release additive it is not water-soluble, and it is separated from the water-soluble sodium compounds in connection with the clearing of the raw salt liquor or alternatively in connection with a separate leaching phase. Process according to any one of claims 1 to 6, characterized in that the gasification reactor operating in accordance with the liquid bed principle is used in the process. 35 8. A process according to any one of claims 1 to 7, characterized in that the sodium compounds are separated during a process phase coming after the gasification phase, in which a reactor operating according to the floating bed principle is used. 9. A process according to any one of claims 1-8, characterized in that the gasification reactor is used according to the suspension principle. Process according to any of claims 1-9, characterized in that the separated sodium compounds are returned to the chemical circulation, e.g. via the tank 10 of the solvent boiler or the flame oven of the soda boiler.