SE527127C2 - Process and apparatus for the production of thermal and electrical energy in a pulp mill - Google Patents

Abstract

The invention relates to a process and apparatus for the production of thermal and electric energy in a pulp mill, in particular a sulfate pulp mill, according to which process and waste liquor of the cellulose pulp cooking liquor is concentrated, and this concentrated liquor is burned in the recovery boiler in the presence of biogenic fuels, in which case the thermal energy is recovered from the flue gases from the combustion, and this thermal energy is, when so desired, converted to electric energy. According to the invention, the biogenic fuel used is wood bark or similar waste wood, which is dried to a moisture content below 30%, whereafter it is gasified to fuel gas, which is fed into the recovery boiler. The process according to the invention makes the acquisition of a separate bark boiler in pulp mills completely unnecessary, which significantly lowers the investment costs. The process simplifies the apparatus, its operation and maintenance, and improves energy efficiency.

Description

as a solid in the bark cooker (hereinafter "bark cooker"). Today's sulphate pulp mills also use for energy production sludge recovered from the treatment of debarking circulating water and wastewater, excess sludge from the biological treatment process of wastewater, as well as strong and dilute odor gases, and methanol odor gas, as, in addition to parallel production, to some pine soap, pine oil, birch oil and crude turpentine. Advanced systems are already used, in which excess sludge, strong and dilute odor gases and methanol are burned in the soda recovery boiler.

The heat generated in the soda recovery boiler and in the bark boiler, respectively, is recovered by generating an overheated high-pressure steam in the boiler, which is transferred to a meadow turbine for the production of electricity. The steam leaves the turbine in the form of so-called back-pressure steam, or waste steam, and its heat content is used as process steam in the pulp mill at places where steam is used, or in the production of condensation electricity. If the pulp mill is integrated in a paper mill, excess thermal energy is generally not produced.

A modern sulphate pulp mill produces steam for the turbine plant by burning alkali from the soda recovery boiler to such an extent that the proportion of back-pressure heat and electricity exceeds the heat and electricity consumption of the factory itself, and part of the back-pressure heat must be used for production. an equilibrium situation between energy production and consumption, whereby condensing electricity in a condensing section is supplied to the back-pressure turbine. This means that in order to satisfy its heat and energy needs, the pulp mill does not need a bark boiler, or heat produced therein by means of bark. In this respect, bark is a superfluous fuel for the pulp mill, and a bark boiler is an unnecessary investment. The value of bark sold to outside users is significantly reduced due to the costs incurred in connection with its transport.

However, despite the excess heat production described above, fossil fuels are used in a pulp mill for the regeneration of lime used in the preparation of the cooking liquid; this regeneration is carried out at a temperature above 1000 ° C in the lime kiln (drum kiln).

Dried bark and sawdust were gasified to flue gas (hereinafter generally referred to as "flue gas") as early as the early 1980s, for use as flue gas in the lime kiln to replace the use of fossil fuels.Only a few incinerators were built due to a strong and long-term fall in market prices for crude oil.

The increase in the yield of the boiling, recent modifications of the boiling, the introduction of acid bleaching and the linking of bleaching filtrates within the recycling cycle have reduced the calorific value of the fuel, concentrated liquids, of the soda recovery boiler. At the same time, the control of the conditions, and the emissions from the combustion, have increased in difficulty in step with the increasing boiler size. The increase in the amount of dry matter in the concentrated liquid and new combustion air distribution systems have only partially solved these problems.

From the patent literature, various new possibilities are known for the exploitation of the intra-process biogenic fuels in pulp boiling. Finnish patent no. 102395 shows a method whose principal purpose is to supplement the soda recovery process used today by using the known separate superheat boiling technology, which means that the combustion gas is obtained by gasifying a part of the concentrated liquid. The combustion gas is purified before being fed to the superheater, in order to reduce the alkali level and to prevent soiling of the superheater. The purpose of the method according to the Finnish published patent application no. 82494, is to completely replace the current combustion process with a new refined process, in which the liquid is gasified in a pressurized gasification reactor and the combustion gas is formed from the inorganic material part, and the gas formed from the inorganic material part removed from the gasification reactor. The gas is cooled and purified, and the melt is dissolved so that it can be passed on to the process for preparing alkali boiling liquids. The purified gas is burned to produce steam and electricity in a so-called “gas turbine / gas turbine cycle”. What is meant is thus a process based on pressurized gasification and gas turbine technology.

A similar solution is shown in the Finnish published patent application no. 91172 which relates to a process in which liquid is thermally decomposed in a pressurized reactor at such a low temperature that no melt is formed. The process uses flue gas obtained from black liquor in a gas turbine; the thermal energy contained in its exhaust gases is utilized in a flue gas boiler, whereby part of the flue gas can also be used for the production of high-pressure steam. The exhaust gases from the flue gas boiler are transferred to a fuel dryer, where, for example, bark is dried which is then gasified under pressure. The gas can be used to superheat the steam (immediate overheating). The purified gases are combined with gases from the thermal decomposition of black liquor and then transferred to the gas turbine. This case also concerns a process based on pressurized gasification which replaces the currently used soda recovery boiling process.

A third gas turbine process is shown in the Finnish published patent application no. 84516. The purpose of this known process is to change the ratio of heat production to electrical production in a sulphate pulp mill so that the sulphate pulp process becomes self-sufficient in electricity, without producing more steam than its own needs. It is proposed that only a steam demand corresponding to the heat consumption of the plant is run through the steam turbine at the pulp mill, and that excess steam is used, preferably in its entirety, as injection steam in the gas turbine in order to increase its efficiency. (51 FO \\ 'l ... x PO ä! The gas turbine process mentioned above is not easy to implement in practice, as it is in practice impossible to continue the Tomiinson process with gasification of black liquor due to difficulties associated with pressurized gasification and due to the high financial risks associated with the introduction of new technology, even in an intermediate area.

An object of the present invention is to eliminate the disadvantages associated with the state of the art, and to provide, especially for new but also for older, pulp mills, a suitable alternative which makes it possible to exploit all the bark and others, from wood derived, fuels produced in the factory and, if necessary, sourced from outside for efficient use in energy production.

The invention is based on the idea that bark and other waste wood are dried to a dry material content of over 70%, and that the dried bark is gasified in the form of flue gas. A significant proportion of the flue gas is burned to produce additional heat in the recovery boiler, and if desired, a part is burned in another unit of the factory that needs extra fuel, such as the lime kiln at a sulphate factory to produce lime sludge burning recovery heat. If it is possible to use, for example, tall oil pitch or tall oil for lime reburning, the flue gases are burned in their entirety in the soda recovery boiler.

The flue gas produced by the process according to the invention can be used to increase the values of the superheated steam produced by the recovery boiler, so that they approach them in today's power plant boilers, in order thus to improve the return on electricity. To avoid corrosion problems in the recovery boiler, it is preferable to perform this step in a separate superheater, which can also function as a so-called antechamber of the recovery boiler. In this case, the exhaust gases are transferred from the superheater to the recovery boiler to recover heat. It is also possible to carry out the overheating of the steam produced in its entirety using the combustion gases produced by the separate flue gas combustion. The exhaust gases from the separate combustion carried out in the superheater, or in the antechamber of the recovery boiler, are transferred after the overheating to the condensing part of the recovery boiler.

The object of the invention is thus not to replace the existing soda recovery boiler process (Tomlin's process), as is the case in the previously mentioned references, but a biogenic fuel is gasified and burned in direct contact with the combustion of concentrated liquid according to Tomlin's process in a soda recovery. - ningspanna. Preferably, bark is dried using the combustion gases of the soda recovery boiler. In this case, for drying, for example, a drying unit made of a multi-stage cascade dryer is used. The outlet end of this unit is connected to a carburettor which produces a flue gas which can - possibly after purification - be fed into the recovery boiler.

In particular, the process according to the invention is characterized mainly by what appears from the characterizing part of claim 1.

The process according to the invention for using a sulphate plant for the production of thermal and electrical energy is characterized for its part by what appears from the characterized part of claim 9.

The apparatus according to the invention is characterized by what appears from the characterizing part of claim 19.

Significant advantages are achieved with the invention. The invention is particularly applicable to the sulphate process, but can also be applied to the soda process, the sulphite process, the polysulphide process and various organosolv processes. The invention and its advantages are described in more detail, especially in terms of the sulphate process, but corresponding advantages can also be obtained in other commercial processes.

Ef-É? 127 l of new pulp mills make the process of purchasing a separate bark boiler completely unnecessary; which significantly reduces investment costs. The process simplifies the equipment, its operation and maintenance, and improves energy efficiency. A new sulphate pulp mill needs a 10 - 20% higher thermal energy production capacity in the soda recovery boiler. In older pulp mills, the process can be implemented in connection with major basic repairs.

Since the present process is characterized by the fact that fossil fuels in a pulp mill are only used in connection with closure, start-up and in disturbance situations at the factory, the carbon dioxide emissions come from fossil sources, which have a degrading effect on the atmosphere and cause the so-called greenhouse effect. remain very low, despite significant improvements in energy efficiency and cost-effectiveness.

Foreign substances harmful to the pulp process, such as silicone, aluminum, chlorine and potassium, which can be concentrated in the alkali cycle, are removed with the wood material and thus also with the bark. A gasification technology in which the ash can be separated, and the purification and combustion of the flue gas in the lime kiln and / or soda recovery boiler provide a good opportunity to limit the entry of the previously mentioned harmful substances into the process.

Dried bark can be used in the energy production of the pulp mill as such, for example treated (crushed, ground, etc.), and then the target final moisture content can be higher (25 - 35%). The use includes older bark cookers and the lime kiln, as well as the soda recovery boiler, if the separation of harmful foreign substances from the alkali cycle can be implemented.

The field of application of the invention covers, in addition to waste firewood fuel produced at a pulp mill, fuel originating from wood, or corresponds to fuel obtained from a wood production chain outside the factory, or separate fuel production.

Peat treated in the manner described above is also suitable for use as fuel. The acquisition of a bark boiler for a pulp mill costs, depending on the size of the plant, EUR 20-30 million.

It requires personnel for handling and maintenance, as well as materials for its use and maintenance in order to function.

The additional investment required for a pulp mill according to the process, based on gasification, will be about half of the investment in a bark boiler. Handling and maintenance costs for the soda recovery boiler will not increase as a result of the change. The handling of the drying of the bark does not require any special staff. The costs for maintenance of the drying and gasification apparatus will be clearly lower than the corresponding costs for the bark cooker.

The effect of the process according to the invention on the load on the environment depends on the conditions to which the system is applied.

The greatest improvement is obtained if the heavy fuel oil in the lime kiln is replaced, in accordance with the process, with flue gas (approximately 45%) and the rest is burned in the soda recovery burner (approximately 55%). In a modern pulp mill, this means that approximately 20,000 tonnes are replaced with flue gas annually. On an annual basis, this means approximately 17,500 tonnes less harmful carbon dioxide emissions, and if natural gas is replaced, it means approximately 12,500 tonnes per year. Significant is also the improvement in the control of the combustion in the soda recovery boiler, compared to before, which is achieved thanks to the increased heat effect, which in turn makes it possible to reduce harmful emissions, and on the other hand to increase the size of the unit. ket improves the economy.

A modern pulp mill (600,000 Adtld) produces at an equilibrium state of heat production and operation, 35 - 40 MW 527 127 electricity in addition to its own needs. If approximately 55% of the above gas is transferred to the soda recovery boiler for combustion and the increasing steam is transferred to the condensing part of the turbine, the excess electricity will increase by approximately 10 MW, and even more if a separate superheater is used. According to the invention, it is therefore advantageous to transfer at least approximately 40% of the gas to the recovery boiler.

The above invention will be discussed below by means of a detailed description with reference to the accompanying drawings.

Figure 1 shows an overview diagram of the first embodiment of the invention, and Figure 2 shows the detailed process flow diagram for the gasification process of the invention.

As noted above, the soda recovery boiler, together with the steam boiler, is an important chemical reactor for the operation of the pulp mill; this has conventionally limited its use as a site for combustible materials, other than black liquor.

Foreign substances that enter the chemical cycle together with the fuel are harmful to the recycling of the boiling chemicals. In addition to being clean, the fuel for the lime kiln must also have a sufficiently warm flame.

According to the present invention, a process is provided in which the bark, and other waste wood produced in the factory, can be used efficiently for energy production. According to the invention, bark and other waste wood produced in the factory are dried by means of combustion gases and / or steam to a moisture content below 30 ° / °, and gasified and purified to meet the purity requirements for the intended use. The gas is transferred to the recovery unit for the chemicals from the pulp boiling, where it is burned together with concentrated liquid obtained from the waste liquid from the boiling.

Preferably, the bark, or bark residues, are dried to a moisture content of less than 20% by weight, after which it is gasified, and at least 40% by volume of the gas thus produced is fed to the recovery boiler. Ash is separated from the flue gas before the gas is fed into the recovery boiler.

The heat produced using flue gas can, for example, be used to superheat the steam from the soda recovery unit in an overheating chamber separated from the flue gases of the soda recovery boiler.

The waste wood used in the invention is bark waste, bark-containing sludge, fiber sludge, twigs or fibers not approved for classification, or excess sludge from biological waste water treatment or deforestation waste, firewood harvested separately from the forest, excess wood from woodworking, or other wood materials suitable for incineration.

Bark and other waste wood always require, in addition to mechanical dewatering, drying with heat before gasification. The desired final moisture content depends on the combustion temperature obtained with flue gas, and on other properties of the flame. Combustion in a lime kiln and a separate superheater requires the flame to have a high temperature and good radiation properties, in which case a preferred final moisture content after drying is less than 20%, typically 10-15%. The requirement for moisture content is not quite as strict in other applications with flue gas. For drying, a pulp plant has access to waste heat from, for example, flue gases from the soda recovery boiler. For drying, there is also excess heat available, in the form of waste steam and / or back-pressure steam, if the drying technology should require it, for example for further drying. In the process according to the invention, the water content of the bark before gasification is reduced from 60% to 30%, in particular to 20%, or lower than this (for example to approximately 15%).

By drying the bark, its importance can be significantly increased in the form of the caloric value of the fuel, which is clear from the following calculation; When the moisture content of the bark is 60%, its effective caloric value is approximately 15.40 MJ / kg, dry matter, 2.50 kg of fuel. When the moisture content of the bark has been reduced to 15%, its effective calorific value has increased to a value of 18.86 MJ / kg, dry material, in this case it is 1.18 kg of fuel.

During drying, the amount of water decreases by approximately 1.32 kg / kg dry matter, and the effective calorific value of the bark is improved by 22.5%.

Thus, drying gives an increase in the calorific value by more than 20% in moist fuel. The losses of flue gases formed in connection with combustion are reduced, and the efficiency of combustion is improved. The cooking structures also decrease compared to those of a bark cooker. The improvement in caloric value and the efficiency of combustion increase energy production with biofuels and reduce the amount of greenhouse gases.

According to a preferred embodiment, steam is used as energy in the drying of solid fuel at a pressure level of 0.01 ... 10O bar (a), or, however, preferably at a pressure level which is in the distribution pressure of the waste steam or back-pressure steam network at a level of 0.4 ... 20 bar, preferably 2 ... 14 bar. It is also possible, as energy for the drying of solid fuel, to use excess energy from, for example, various hot water and expansion vapors in the pulp mill.

According to the invention, the entire amount of bark at the pulp mill is dried to a low moisture content, typically to a moisture content below 20%, in particular below 15%. The thermal effect obtained from the bark in this case is in the form of gas approximately 80MWh / h in a modern pulp mill. '527 177 12 The gas obtained from dried bark is suitable for incineration as such as hot gas combustion in the lime kiln or soda ash recovery boiler.

According to a preferred embodiment, the drying is carried out using gases having a temperature of 200 ° C, preferably 180 ° C or lower, in order to prevent the emission of harmful organic compounds. The drying can be carried out in two or more steps, in which case it is preferable to carry out in particular the first step using flue gases or steam having a temperature below 200 ° C. In this case, the exhaust gases from the drying can be combined with the exhaust gases from the recovery boiler. The final temperature of the flue gases from the soda recovery boiler is currently at a level of 160 ° C, and the amount of flue gas is so large that it is sufficient to dry the amount of bark produced in the factory. For drying the solid fuel, the remaining heat after the actual heat recovery of the flue gas formed in the combustion chamber is usually used by bringing the flue gas into direct contact with the solid fuel to be dried. In the first drying step, the purpose is to remove at least 50% of the moisture content of the material being treated. Preferably, the moisture content of the material is a maximum of 40% by weight, most preferably 30% by weight, after the first step. The second step (additional steps) can be performed under conditions similar to those of the first step, or at a higher temperature, since the amount of exhaust gas from the second drying step, possibly containing VOC, is suitable for possible purification.

The material obtained from the drying can, before gasification, be brought to a suitable granular / particle size, which varies depending on the choices of the apparatus used for the gasification. The material size also depends on the drying technique used in the process, since it is important that the bark, or corresponding waste wood, is so finely decomposed that the above-mentioned dry material content is achieved by drying.

Suitably the wood material is brought to a size of 0.1 - 100 mm.

During gasification, the dried wood material (bark / waste wood) is heated so that they form combustion gases. The gasification is carried out in a known manner, in particular in understoichiometric conditions with respect to oxygen, for example in the presence of a solid heat-conducting material in a fluidized bed. Suitable appliance alternatives for the gasification are discussed in more detail in connection with the description of the figures.

Based on what has been mentioned previously, the apparatus used according to the invention for producing from wood bark comprises a biogenic fuel to be fed into the recovery boiler of the pulp mill, the apparatus being connected to the feed unit of the recovery boiler, which comprises a combination of a bark drying unit having feedstock for the bark to be dried and outlet means for the dried bark, and a dry bark gasifier for the production of flue gas from the bark, the apparatus having feedstock for the bark and flue gas outlet means. The feed means of the carburettor are connected to the outlet means of the drying unit, and the gas outlet means are connected to the feed unit of the recovery boiler to feed the gas produced by gasification into the boiler. In this context, the word “connected” means that the device is in direct or indirect contact with the subsequent or previous device. There may be separate treatment units between the devices as is obvious from the following. 'Feed' and 'outlet' are usually pipes or units or similar means by which the material and products to be treated can be transferred to the apparatus or removed therefrom. In the drying unit or in its individual dryers, for example, flue gases and / or steam as described above are used for drying.

Multi-stage drying and its benefits were discussed above. Preferably, the drying unit actually comprises at least two separate dryers arranged as a cascade dryer, the outlet means of subsequent dryers in the series being connected to the feed means of the carburettor. In such an apparatus installation it is possible to provide a pre-treatment unit for treating the bark obtained from the first dryer, before it is fed into the second dryer. In this case, the pre-treatment unit has a feed unit or feed pipe which is connected to the outlet means of the first dryer, and an outlet unit which is connected to the feed means of the second dryer. Such a pre-treatment unit preferably comprises a grinder.

The first and second dryers may be different bed dryers, including fluid bed dryers. As a carburettor, it is especially preferable to have a fluid bed boiler having a bubbling or rotating bed. It is especially preferred that the outlet means of the carburettor is connected to a gas purification unit for separating impurities from the flue gas before it is fed into the recovery boiler.

A significant part, preferably all, of the gases formed are burned in the recovery boiler (soda recovery boiler) to produce superheated steam. Some of the gas formed, which has a sufficiently large fuel value, can be transferred to the lime kiln as fuel to replace oil and natural gas. The flue gas can also be used elsewhere in the integrated plant as a fuel that replaces fossil fuels.

By means of the invention, the energy coefficient of the current soda recovery boiler process is developed by using bark obtained from debarking wood and using both already known drying and gasification technologies and gas treatment technology. The concept of a boiler (no bark boiler) is thus a key purpose, especially when a new pulp mill is being considered. This presupposes drying and gasification of the entire amount of bark; this is possible especially when using direct flue gas drying by means of flue gases from the soda recovery boiler. 527 127 Heat produced with flue gases, produced by gasification, is thus suitable for overheating of soda recovery boiler vapor in an overheating chamber separated from the flue gases of the soda recovery boiler. In this case, the values (pressure and temperature) of the superheated steam of the recovery boiler can be increased, and the efficiency of the electricity production can be improved from current values to values closer to those of the superheated steam in current power plant boilers, without being limited by overheating unit corrosion conditions. critical. The pulp mill will not need a separate bark boiler, based on the use of solid fuel, to be able to exploit bark and other organic material separated from the wood in the factory. The factory concept will be simplified, and it will also be more economical to both procure and operate. In addition, the use of fossil fuels in the factory can definitely be reduced. Part of the superheating can be carried out, for example, by means of a technique known per se in a separate superheater by utilizing production gas obtained from bark by gasification. This enables an increase in the speed of production of countercurrent electricity by means of bark.

Figure 1 points out the principle of the process flow of a preferred embodiment of the process according to the invention.

Reference number 2 in this case indicates the mechanical treatment of the wood raw material 1 arriving at the factory, the treatment comprising debarking and chipping of logs. The chip waste 3 and the bark and other raw material parts 4 (waste wood, such as branches) not suitable for cooking are treated separately, the chip waste is fed in a conventional manner to the fiber line 5 at the factory.

The bark 4 is fed to gasification 6. At least a part of the gas, preferably at least 10% (of the gas volume), suitably at least 40%, particularly preferably at least 50%, is fed into the soda recovery boiler 7, to which the biosludge 8, obtained from the treatment of waste water, is also fed. The gases are burned in the soda recovery boiler together with concentrated waste liquid to produce superheated steam 9. Some of the formed 16 gas, which has a sufficient fuel value, can be transferred to the lime kiln 10 as fuel to replace oil and natural gas.

The flue gas can also be used in other places in the integrated factory (for example in an additional boiler) as a fuel to replace fossil fuel.

The heat produced with flue gas, produced by gasification, is also suitable for the overheating of the soda ash boiler gas in an overheating chamber separate from the flow gases of the soda recovery boiler.

According to a preferred embodiment of the invention (see Figure 2), a bark boiler 11, 13 and a carburettor 14 are built at the pulp mill, which are dimensioned for the entire amount of bark, the bark being dried using the hot gases of the pulp mill, such as flue gases, in particular flue gases from the soda ash recovery boiler with a temperature below 200 ° C, or steam. Flue gas drying based on direct contact can also be used for drying.

The bark can be dried in one or more steps, for example two as shown in Figure 2, and in that case used in the first step 11, where the bark is still wet, flue gases and bed drying. The second drying step can be performed at a higher temperature. The bark is dried to a dry material content of approximately 60 - 80% by weight.

Thereafter, the bark may be subjected to a pretreatment 12, such as feeding. In the second drying step 13 steam and, for example, fluid bed drying are used. In both steps, it is preferable to maintain a low drying temperature to achieve a low level of excretion. In general, approximately 150 - 170 ° C is a sufficient temperature. After the second drying step, the content of dry material is over 80%, preferably approximately 82-90%.

The second drying step can also be performed at a higher temperature, for example 250 - 400 ° C.

FÖ? 497 17 After drying, bark and corresponding solid waste material 14 are gasified. Normally, the gasification temperature is approximately 700 - 1000 ° C, preferably approximately 750 - 900 ° C. For gasification, it is possible to use fluid bed boilers that have, for example, a bubbling or rotating bed. The production gas obtained from the gasification, which mainly contains carbon monoxide, is transferred to gas purification 15. The bark ash contains foreign substances such as aluminum and silicon whose concentration in lime and the alkali cycle can be prevented by gasifying the bark and separating the ash from the gas.

The need for purification of the gas varies depending on what it is to be used for. In addition to fly ash, tar and ammonia must also be removed from the gas to be used in the soda recovery boiler 16. A portion (in practice approximately 40% by volume) is transferred to the lime kiln 17, whereby the purification of the gas need not be so efficient in order to maintain the sludge properties. The treatment needed is mainly focused on ammonia when NOX emissions are to be limited.

A substantial portion of the flue gases, most suitably at least 55% by volume, is transferred to the soda recovery boiler. Preferably, in this case, the combustion chamber of the soda recovery boiler is divided in the flow direction of the combustion gases into two parts, in the first of these combustion fuels carried there in gaseous state, the heat produced therefrom being substantially used for superheating the steam, and in the second the concentrated liquid, whereby the heat produced therefrom is essentially used for evaporating the boiling water.

The gas obtained from the carburettor 14 can be used not only as a flue gas for the soda recovery boiler and the lime kiln, but also in other places, for example in the oil vessel 18 for the drying 19 of the pulp, and in other environments, for example for heating purposes. It can also be sold outside the factory, generally for purposes where it replaces the use of fossil fuels (direct heat use in a paper mill). In Figure 2, the reference numbers 21 and 22 indicate the initial material content (bark piles) and the reference numbers 23 and 24 indicate the silo for dried material. Reference number 21 indicates storage for purchased fuel and number 22 a container for material coming from the debarking plant. When desired, the starting material can be pretreated 25. This applies to material 25 coming from or from the debarking plant, which material is subjected to a suitable mechanical treatment, for example by means of the apparatus of the debarking plant, to make the material suitable for drying and gasification. .

The material obtained from the first drying step can be collected in a silo 23, from which it is placed outside the factory.

By "treating the gases" is meant, for example, the purification of the gas (VOC) obtained from the second gasification step 13.

In the foregoing, the production of flue gas, in particular from gas, has been described. The invention can also be applied to solid wood materials of other kinds, such as bark-containing sludge, fiber sludge, branches or fibers not suitable for classification, or excess sludge from biological wastewater treatment. The biogenic fuel to be gasified may also consist of log residues collected from the forest and / or fuel wood harvested separately from the forest and / or surplus wood from wood processes and / or other wood materials suitable for incineration.

Claims (27)

10 15 20 25 30 35 REQUIREMENTS A process for the production of thermal and electrical energy in a pulp mill, according to which process waste liquid from the cellulose pulp cooking liquid is concentrated, and the concentrated liquid is burned in the recovery boiler in the presence of biogenic fuel, wherein the thermal energy of the flue gases recovered from the combustion optionally converted to electrical energy, characterized in that the biogenic fuel used is bark or other similar waste wood that is dried to a moisture content of less than 30%, after which it is gasified to produce a flue gas which is fed into the recovery boiler. The process according to claim 1, characterized in that the bark or bark residues are dried to a moisture content of less than 20%, after which it is gasified, and at at least 40% by volume of the gas thus produced is fed into the recovery boiler. The process according to claim 1 or 2, characterized in that ash is separated from the flue gas before it is fed into the recovery boiler. The process according to any one of the preceding claims, characterized in that the heat produced using the flue gas is used to superheat the recovery boiler steam in a superheating chamber separate from the flue gases of the recovery boiler. The process according to any one of the preceding claims, characterized in that the waste wood is bark waste, bark-containing sludge, fiber sludge, branches, or fibers not approved for classification, or excess sludge from biological waste water treatment, or deforestation waste, wood harvested separately from the forest, excess wood from woodworking, or other wood material suitable for firing. The process according to any one of the preceding claims, characterized in that gases having a temperature below 200 ° C are used for drying the bark or corresponding waste wood. 10 15 20 25 30 35 527 127 20 The process according to claim 6, characterized in that steam or flue gases with a temperature lower than 180 ° C are used. The process according to any one of claims 1-5, characterized in that steam having a pressure of 0.1 ... 100 bar, preferably 2 ... 14 bar, is used as energy for the drying of the solid fuel. A process for producing thermal or electrical energy in a sulphate pulp mill, according to which process: - the wood material used for pulp production is partially boiled in the cooking liquid to separate the fibers from each other, - the cooked wood material is extracted as black lye from the fibrous material, - black the liquor is concentrated by evaporation, and - the concentrated liquid is incinerated in the soda ash recovery boiler to recover the boiling chemicals and to produce heat and electricity by means of biogenic fuels, characterized in that - the solid biogenic fuel is converted to gaseous form, - the ash formed is separated, and a significant part of the gas is burned in the same boiler, equipped with heat recovery, as the concentrated liquid. The process according to claim 9, characterized in that the biogenic fuel to be gasified is wood and / or wood bark and / or sludge containing bark and / or fiber sludge and / or branches or fibers not approved for classification and / or excess sludge from bio- logical wastewater treatment. The process according to claim 9 or 10, characterized in that the biological fuel to be gasified is deforestation waste collected from the forest and / or wood harvested separately from the forest and / or excess wood from woodworking and / or other wood materials suitable for burning. . 10 15 20 25 30 35 I ._ \ - 127 21 The process according to claim 9, characterized in that the biological fuel to be gasified is peat. The process according to claim 9, characterized in that the solid fuel to be transferred in gaseous form is dried before gasification to a moisture content of 5 ... 40%, preferably 10 ... 15%. The process according to claim 9, characterized in that the solid fuel is dried with heat remaining after the actual heat recovery of the flue gas formed in the combustion chamber, by bringing the flue gas into direct contact with the solid fuel to be dried. The process according to claim 9, characterized in that the solid fuel is dried by means of energy from steam at a pressure level of 0.1 ... 100 bar or, preferably at a pressure level which is the distribution pressure of the factory waste steam or back pressure steam system, preferably at a level of 2 ... 14 bar. The process according to claim 9, characterized in that the solid fuel is dried using the energy in the excess heat present in the pulp mill in, for example, various hot water or expansion vapors. The process according to claim 9, characterized in that the combustion chamber is, in the direction of the flow of flue gases, divided into two parts, wherein in the first of these the fuel which has been converted to gaseous form is burned, the heat production therefrom being used to a substantial degree for overheating of the steam, and in the second part the concentrated liquid is burned, whereby the heat released therefrom is used primarily for evaporating the boiling water. The process according to any one of claims 9 to 17, characterized in that a part of the solid biogenic fuel, which has been transferred in gaseous form, is burned, after the separation of ash, in the lime kiln and / or other units where its use replaces the use of fossil fuels. 10 15 20 25 30 35 An apparatus for producing from wood bark a biogenic flue gas which is fed into the recovery boiler of a pulp mill, the apparatus being connected to the feed unit of the recovery boiler, characterized in that it comprises as a combination - a bark drying unit (11, 13) which has feedstock for the bark to be dried and outlet means for the bark which has been dried, and - a dry bark carburettor (14) for producing flue gas from the bark, the apparatus having feedstock for bark and outlet means for flue gas, the feedstock of the carburettor being connected to the outlet means of the drying unit and the gas emitter are connected to the feeding unit of the recovery boiler to feed into the boiler the gas produced from the bark by gasification. The apparatus according to claim 19, characterized in that the drying unit (11, 13) comprises at least two separate dryers, which are arranged as a cascade dryer, the outlet means of the subsequent dryer in series being connected to the feed means of the carburettor. The apparatus according to claim 20, characterized in that a pre-treatment unit (12) is arranged between the first and the second dryer for treating the bark obtained from the first dryer before it is fed into the second dryer, the pre-treatment unit has a feed unit connected to the outlet means of the first dryer and an outlet unit connected to the feed means of the second dryer. The apparatus according to claim 21, characterized in that the pre-treatment unit (12) comprises a grinder. The apparatus according to any one of claims 19 to 22, characterized in that the flue gases and / or the steam are used for drying in at least one of the dryers. 10 15 527 1.97 23 The apparatus according to any one of claims 20 to 23, characterized in that the first dryer (11) comprises a bed dryer. The apparatus according to any one of claims 20 to 24, characterized in that the second dryer (13) comprises a fluidized bed dryer. The apparatus according to any one of claims 19 to 25, characterized in that the carburettor (14) is a fluidized bed cooker having a bubbling or rotating bed. The apparatus according to any one of claims 19 to 26, characterized in that the outlet means of the carburettor is connected to a gas purification unit for separating impurities from the flue gas before it is fed into the recovery boiler.