FI117479B - Method for producing thermal and electric energy - Google Patents

Description

1 1 7479 '?

A method for generating thermal and electrical energy fcl

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The present invention relates to a process according to the preamble of claim 1 for producing thermal and electrical energy at a pulp mill.

In such a process, the spent liquor from the chemical pulp of the pulp is concentrated to a combustion broth and is incinerated in a recovery boiler for other biogenic fuels. in the presence of substances. The thermal energy from the flue gases from the combustion is recovered, which, if desired, is converted into electrical energy.

The invention also relates to a process according to claim 9 for producing thermal and electrical energy in a sulphate cellulose mill.

15 The modern pulp mill is known to be a major energy producer. The term "pulp mill" as used in the present invention means a chemical pulp mill, e.g. The input and output of feedstock-derived organic material to the fuel is available in all three main forms: solid. as a substance, liquid and gas and as a mixture thereof. Thus, the pulp mill utilizes energy, * * ···. 20 in a pulp digester in a boiler for the recovery of wood dissolved in a cooking liquor (so-called cooking liquor). This recovery boiler is also referred to as the '' recovery boiler '' in connection with the sulphate process. In the case of wood peeling, the 'bark', which is separated from the wood, is in turn burned as a solid in a bark boiler (hereinafter 'bark boiler').

Existing sulphate pulp mills also utilize for energy recovery sludges recovered from the purification of crustal wastewater and wastewater, biological wastewater sludge from the purification of the wastewater, biological and purifying methanol and * ... · as well as crude turpentine.

There are already advanced solutions in which excess sludge, concentrated and dilute odor gases and methanol are burned in a recovery boiler.

. ·:: 30 • * ·. »; * · Λ: The heat generated in the baking boiler and the bark boiler respectively is recovered by developing | * * e,; * high pressure superheated steam in a boiler which is fed to a steam turbine to generate electricity. The steam leaves the turbine in a so-called. back pressure or contact vapor and its heat content 117479 2. ar 'is utilized as process steam in pulp mill consumables or condensing power generation.

If the pulp mill is integrated with the paper mill, there is usually no excess of thermal energy.

A modern sulphate pulp mill produces steam from the recovery boiler from the recovery boiler to the turbine plant to such an extent that the proportion of backpressure heat and electricity exceeds its own heat and power consumption and some backpressure heat has to be produced to achieve a This means that the pulp mill does not need a bark boiler or the heat generated by the bark to meet its heat and electricity needs. In this sense, bark 10 is an excess fuel and bark boiler unnecessary investment for the pulp mill. The value of the shell sold out is significantly reduced by the cost of transportation.

However, in spite of the fuel surplus heat described above, the pulp mill uses fossil fuels for the regeneration of calcite used in cooking liquor at temperatures above 1000 ° C in a lime kiln (drum furnace).

Dried bark and sawdust were gasified as combustion gas (generally referred to as "fuel gas") in the early 1980s to be used as fossil fuel gas in the lime kiln.

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.. · to replace the use of fuels. It was only possible to implement gasification plants * * · · ... * 20 due to the sharp and prolonged decline in crude oil market prices.

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The desired increase in soup yield, recent modifications to the soup, introduction of oxygen bleaching, and incorporation of bleaching filtrates into the recovery cycle have lowered the calorific value of the fuel, combustion liquor, * * * · **. At the same time burning conditions and emissions. . 25 management has become more difficult as the boiler strike increases. Lifting the dry liquor # · · * * · and new combustion air distribution solutions have only partially solved these problems.

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: It is an object of the present invention to eliminate the drawbacks of the prior art to provide a solution particularly suitable for new but also old pulp mills, which allows all the bark and • m ·. ·: Efficient use of other wood-based fuels for energy production.

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The invention is based on the idea that the bark and other wood waste is dried to a dry matter content of more than 70% and the dried bark is gasified to form fuel gas.

A substantial portion of the fuel gas is burned to provide additional heat in the recovery boiler and, if desired, a portion is burned at some other site in the plant where external .v 5 fuels are required, such as in a sulfate mill lime kiln to produce regeneration heat from lime sludge. If, for example, tall oil pitch or tall oil can be used to burn the lime sludge, the combustion gases are completely burned in a recovery boiler.

The fuel gas produced by the process of the invention can be used to increase the values of superheated steam produced by the recovery boiler 10,

facilities to improve power supply. It is advantageous to carry out this procedure in order to avoid corrosion problems in the recovery space in a separate superheated boiler, which may also operate in a so-called. front housing for the recovery boiler. In this case, the exhaust gases from the superheating boiler are led to a recovery boiler for heat recovery. It is also possible to superheat the vapor 15 produced in full with the combustion gases produced in the separate combustion of the fuel gas. After the superheaters, the exhaust gases from the separate combustion in the superheater or in the front of the recovery boiler are fed to the evaporation section of the recovery boiler.

More particularly, the process according to the invention is essentially characterized by the characteristics of f ♦ · jyft 20 as set forth in the characterizing part of claim 1.

·; · 5 ♦ m 1 * :; The process for operating the sulphate plant according to the invention for the production of thermal and electrical energy is, in turn, characterized by what is stated in the characterizing part of claim 9 · · · · · ··· 1 '.

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The invention provides considerable advantages. The invention is particularly applicable to the sulfate process, f * · * ", but may also be applied to the soda process, sulfite process, polysulfide process, and various organosolve processes. The invention and its advantages will be described in more detail, particularly with respect to the , but similar benefits can be achieved in other commercial processes. "% · 1 2 · · • ·

This method completely eliminates the need for a separate bark boiler in new pulp mills, which significantly reduces investment costs. The method simplifies i, sir 4 117479 hardware, its operation and maintenance, and improves energy efficiency. The new sulphate plant requires 10 to 20% higher thermal energy production capacity in the recovery boiler.

In old pulp mills, the method can be implemented in connection with major renovations.

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Because the present process is characterized by the fact that the pulp mill uses fossil fuels only during mill shutdown, start-up and malfunction situations, so-called "fouling" remains. greenhouse gas emissions from fossil fuels are extremely low even though energy and cost efficiency are greatly improved.

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The wood raw material, and thus the bark, carries foreign substances harmful to the pulp process, such as silicon, aluminum, chlorine and potassium, which can be enriched in the lye cycle. The gasification technology whereby the ash is recovered, the purification of the fuel gas and the combustion in the furnace and / or recovery boiler provide a good opportunity to limit the entry of the above contaminants into the process.

The dried bark can be used as such for energy production at the pulp mill or e.g.

when used (crushing, grinding, etc.), whereby the final moisture target may be higher (25-35%).

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In addition to the wood residues * * produced at the pulp mill, the scope of the invention is wood-based or equivalent fuels purchased from an external wood production chain or separate fuel production. Peat suitable for processing as described above is also suitable.

• ·! * * · · • · i • · * •; f ·; · Purchasing a bark boiler for a pulp mill costs $ 20-30 million depending on the size of the mill. eu-: ·· roa. It requires operation and maintenance personnel and operating and maintenance materials to function.

30 * · ί / .ί According to the method, the additional investment required for the gasification-based pulp mill is about> half of the bark boiler investment. The cost of operating and maintaining the boiler will not increase as a result of the change. Drying of the shell does not require a separate user 117479 5 municipalities. Drying and gasification equipment maintenance costs are well below the cost of the bark boiler.

The effect of the process according to the method on the environmental load depends on the conditions under which the solution is applied. The greatest improvement is obtained by replacing the heavy fuel oil in the lime kiln with fuel gas (about 45%) and burning the remainder in a recovery boiler (about 55%). In a modern pulp mill, this means about a year.

20,000 tons of fuel gas replacement. This corresponds to about 17,500 tonnes less harmful carbon dioxide emissions per year, and about 12,500 tonnes replacing natural gas in 10 years. It is also important to achieve better control of combustion in the recovery boiler due to the increased thermal output, which, in turn, contributes to reducing interference emissions and increasing the unit size for economic efficiency.

A state-of-the-art pulp mill (600,000 Adt / d) produces 35-40 MW of electricity at its equilibrium production and use of heat above its own needs. If about 55% of the aforementioned gas is fed into a recovery boiler for incineration and the increasing steam is fed into the condensate section of the turbine, the electrical surplus will increase by about 10 MW and even more when using a separate superheated boiler. Therefore, according to the invention, it is advantageous to introduce at least about 40% of the gas into a ** recovery boiler.

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BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be explored in more detail with reference to the accompanying drawings.

Figure 1 shows a process diagram of the first embodiment of the invention. Figure 2 shows a detailed process diagram of the gasification process of the invention.

As noted above, the recovery boiler is not only a steam boiler but also a pulp mill · *: a key chemical reactor that has traditionally limited its use. other materi- ·· ♦ • · i? ***** as a fireplace for black liquor. The 3 i, *: 30 impurities entering the chemical cycle with the fuel are harmful for the regeneration of cooking chemicals. In addition to its purity, the furnace fuel • · requires a sufficiently hot flame.

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According to the present invention there is provided a process whereby bark and other wood waste produced at the mill is efficiently utilized in energy production. According to the invention, the bark and other wood waste produced at the mill is dried with flue gases and / or steam to less than 30% humidity, gasified and cleaned to meet the purity requirements of the application. The gas is introduced into a chemical recovery boiler for cellulose soup, where it is co-incinerated with the digestate from the cooking liquor.

Preferably, the shell or bark residue is dried to less than 20 wt% moisture, after which it is gasified and at least 40 vol% of the gas thus produced is fed to a recovery boiler.

10 The ash is removed from the combustion gas before being fed to the recovery boiler. f

The heat generated by the combustion gas can be used, for example, for superheating the steam of the recovery boiler in a superheating space separate from the recovery gases of the recovery boiler.

The wood waste used in the invention is bark waste, bark sludge, fibrous sludge, sorting knot or fiber object, or biological waste water treatment sludge or logging residue, separately harvested wood from the forest, wood residues from wood processing or other combustible wood.

·· * •> • · '· »· · ··· · ·, 20 In addition to mechanical dewatering, bark and other wood waste always requires heat drying, * · * before gasification. The final moisture content required depends on the combustion temperature of the fuel gas -f and other flame characteristics. Burning in a lime kiln and • · • · *. *: In a separate superheater, the flame requires a high temperature and good radiation properties, whereby the preferred final moisture after drying is less than 20%, typically between 10 and 4 25 15%. Other uses of fuel gas do not require quite as stringent a moisture requirement. * · · ”Waste heat is available at the cellulose mill, eg from the flue gases of a recovery boiler.

»» "** Surplus heat in the form of tap and / or backpressure vapor ·· ί '·· is also available for drying, if the drying technology would require it, eg for additional drying.

* ·· * · * · · 30 In the process of the method, the water content of the casing is reduced from 60 t / s to 30%, in particular to 20% or less (e.g. about 15%) prior to gasification. Drying the casing can significantly improve its importance in terms of calorific value of the fuel, as shown in the following calculation: 7 117479

With a humidity of 60%, the casing has an effective calorific value of about 15.40 MJ / kg, cal., 2.50 kg of fuel. When the humidity of the casing is reduced to 15%, its effective calorific value rises to 18.86 MJ / kg, incl. 1.18 kg of fuel.

5 During drying, the amount of water is reduced by about 1.32 kg / kg ka. and the effective calorific value of the shell is improved by 22.5%.

Drying thus represents an increase of more than 20% in the calorific value of the moist fuel. The loss of flue gases from combustion is reduced and the combustion efficiency is improved.

10 Also, the boiler structures are reduced compared to a shell boiler. Calorific value and combustion; Improved efficiency increases the production of energy from biofuels and reduces greenhouse gas emissions.

According to a preferred embodiment, the steam used for drying the solid fuel is 15 vapors at a pressure level of 0.1 to 100 bar (a) or preferably at a pressure level of 0.4 to 20 bar, preferably 2 ... 14 bar.

For the drying of solid fuel, the residual heat at the pulp mill can also be used as energy. in various warm waters and in the expansion henna.

··· f. . According to the invention, the whole amount of bark of the pulp mill is dried to low humidity, typically *: * to less than 20%, especially to less than 15%. The heat output from the bark as gas is ·· ♦ * ** * at a modern pulp mill of about 80 MWh / h.

The gas from the dried bark is suitable for combustion as a hot gas combustion in 25 lime kilns and in a recovery boiler. i.

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According to a preferred embodiment, the drying is carried out using gases having a temperature of 200 ° C, preferably 180 ° C or less, to prevent volatile organic compound emissions ··· * * * ··· *. The drying may be carried out in two or more steps, where it is preferred, * ·; In particular, the first step is carried out using flue gases or vapors with temperatures below 200 ° C. In this case, the drainage gases can be combined with the artisanal boiler exhaust gases. The final temperature of the flue gas in the recovery boiler is currently at 160 ° C and the amount of flue gas is high enough to dry the amount of bark generated at the factory> 117479 8 '- • ft1 ·. Indeed, for the drying of solid fuel, the heat remaining after the actual heat recovery of the flue gas generated in the furnace is commonly used by contacting the flue gas with the solid fuel to be dried.

The first drying step aims to remove at least 50% of the moisture of the material to be treated. Preferably, the material has a moisture content of up to 40% by weight, most preferably 30% by weight, after the first step. The second step (s) may be carried out under conditions similar to the first step or at a higher temperature, since the amount of exhaust gas exiting the second drying step, possibly containing VOCs, is advantageous for any purification. f

The material resulting from the drying can be brought to a suitable grain / particle size before gasification, which varies according to the equipment solution used for gasification. The size of the material is also affected by the drying technology used in the process, since it is essential that the bark or the like wood debris is so finely divided that drying results in the aforementioned dry matter contents. Preferably, the wood material is sized from 0.1 to 100 mm.

During gasification, the dried wood material (bark / wood waste) is heated to form combustible gases. The gasification is carried out in a manner known per se, typically in the presence of oxygen, in the presence of a solid heat transfer medium, for example in the presence of a solid heat transfer medium.

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, * {'sessa. Appliance solutions for gasification will be further explored in connection with the description of the figures: *: ** ·.

• A significant portion, preferably the major part of the formed combustion gases, is burned in a recovery boiler (recovery boiler) to produce superheated steam. Part of the gas formed 1 * · -ϋ • * ·> S '"can be led to a lime kiln as a fuel with sufficient calorific value to replace | * ** · j- ·; ·' oil and natural gas. The gas can also be used elsewhere in the mill integration ··; '·· as a substitute for fossil fuel s ♦ * ·! ...:. J1 * x: \ j 30 The heat produced by gasification by combustion gas is also suitable for superheating the recovery boiler steam: (pressure and temperature) can be increased, and the efficiency of power generation can be increased closer to present than the current superheated boiler • '5i; / il' - 'y 9 117479';: f without limiting the superheat corrosion conditions now critical. for the on-site recovery of bark and other organic matter separated from the wood at the mill based on the solid fuel boiler shell.

The factory concept is simplifying and becoming more economical to both acquire and use. In addition, the plant's use of fossil fuels can be decisively reduced.

Figure 1 is a schematic diagram of a preferred embodiment of the process of the invention.

Reference numeral 2 then denotes the mechanical treatment of the wood raw material 1 arriving at the pulp mill. peeling and chipping of owls. The chips 3 and the bark and the corresponding non-cooking parts of the raw material 4 (wood waste such as branches) are separately treated, whereby the chips are normally fed to the mill fiber line 5. The bark 4 is fed to the gasification 6. At least a part, preferably at least 10% (by volume of gas 15), preferably at least 40%, particularly preferably at least 50%, to a sludge boiler 7, to which is also fed a biological sludge from waste water treatment 8. The gases are incinerated in the soda boiler to produce superheated steam 9. Part of the gas produced can be fed to the lime kiln 10 with sufficient calorific value as fuel ***: to replace oil and natural gas. In addition, the fuel gas can be used elsewhere in the factory * * · 'ι §ϊ 20 tetrate (eg auxiliary boiler) as a replacement for fossil fuel. · .; • «· * · · * ·“: The heat produced by gasification by the combustion gas is also suitable for superheating of the recovery boiler vapor in a superheated space separate from the flue gases of the recovery boiler.

According to a preferred embodiment of the invention (see Fig. 2), a bark drier 11,13 and a carburettor 14 are dimensioned for the pulp mill, dimensioned over the entire batch, whereby the bark is; * the drying process uses hot gases from the pulp mill, such as flue gases, in particular hot gas from a steam boiler at temperatures below 200 ° C, or steam. • · · Direct contact flue gas drying can be used for drying.

: 30 e · ί, '. Ϊ The slag can be dried in one or more, e.g. two steps, whereby in the first step 11, when the shell is still wet, flue gases and bedding are used. The second drying step may be carried out at a higher temperature. Drying the shell to> 117479,10 to a solids content of about 60 to 80% by weight. Thereafter, the shell may be subjected to pre-treatment 12, such as grinding. In the second stage of drying 13, steam and, for example, fluidized bed drying are used. In both steps, it is advantageous to maintain a low drying temperature to achieve a low emission level. Generally, about 150-170 ° C is a sufficient temperature.

After drying the second stage, the solids content is above 80%, preferably from about 82% to about 90%.

The drying of the second stage may also be carried out at a higher temperature, e.g. 250-400 ° C.

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After drying, the shell and the corresponding solid waste are gasified 14. Typically, the gasification temperature is about 700-1000 ° C, preferably about 750-900 ° C. For gasification, fluidized bed boilers may be used, which may have e.g. a bubbling bed or a circulating bed. Gas. ·: R, product gas, mainly containing carbon monoxide Derived from scrubbing of gas 15 15. The crude ash contains contaminants such as aluminum and the silicon enrichment of the lime and slurry cycle can be prevented by scrubbing the crust and separating the ash from the gas.

The need for gas purification varies according to its application. In addition to the fly ash, tar and ammonia must be removed from the gas used in the recovery boiler 16, »20. Part of the gas (used in practice is about 401% by volume) is introduced into the lime kiln 17 so that the purification of the gas does not have to be as effective in maintaining the flame properties. The need for purification * * is mainly towards ammonia when ΝΟχ emissions need to be limited.

»· • · *; A substantial part of the combustion gases, preferably at least 55% by volume, is introduced into the recovery boiler.

Preferably, the combustion chamber of the recovery boiler is then divided in two directions in the flue gas flow direction.

* · · '·· & • * m Ji * ". * The first part of which burns the gaseous fuel, whereof the * * ·' 'V heat is now used to a considerable extent for the superheating of the steam, and the second part the combustion liquor, where the heat released is primarily used for evaporation of boiler water.

• * · 30. ! ϊ The gas from the gasification 14 can be used not only as a combustion gas for the recovery boiler and the lime kiln, but also elsewhere, such as oil boiler 18, pulp drying 19 and other * such as heating needs. It can also be sold off-site, generally at sites where its use replaces the use of fossil fuels (district heating, paper mill use). In Fig. 2, reference numerals 21 and 22 denote the starting material containers (heaps) and reference numerals 23 and 24 the silos of the dried material. '

Reference numeral 21 denotes the fuel storage depot, and reference numeral 22 denotes the bunker material 5. If desired, the starting material may be pretreated 25. This applies to material coming from the outside or from the peelings, which is subjected to suitable mechanical treatment, for example by using peeling equipment, to make the material suitable for drying and gasification. After the first drying step, the resulting material can be collected in a silo 23 from where it is sold off-site.

"Gas treatment" means, for example, purification of the gas (VOC) from a second gasification step 13.: 15 7

The production of combustion gas, in particular from the bark, has been described above. The invention can also be applied to other types of solid wood waste, such as bark sludge, fiber slurry, sorting branch or fiber object or biological sewage sludge slurry. The biogenic fuel to be gasified may also be logging residue from the forest and / or • 20 firewood and / or surplus wood from the forest and / or other 1 /? , 1 {1 wood suitable for combustion.

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Claims (18)

1. A process for generating thermal and electrical energy in a pulp mill comprising concentrating the spent liquor from the pulp digestion liquor to a combustion broth and burning it in a recovery boiler in the presence of biofuels, recovering from the or wood waste of this type, which is dried to less than 30% humidity and then gasified to a combustion gas which is fed to a recovery boiler. ΐ 10 Method according to Claim 1, characterized in that the shell or bark residue is dried to less than 20% moisture, after which it is gasified and at least 40% by volume of the gas thus produced is fed to a recovery boiler. ~ 3. A method according to claim 1 or 2, characterized in that the ash is separated from the combustion gas before being fed to the recovery boiler. Method according to one of the preceding claims, characterized in that | * *: The heat generated by the combustion gas is used to enter the steam in the recovery boiler in a superheated space separate from the flue gas boiler. | The method according to any one of the preceding claims, characterized in that the wood is a bark waste, a sludge containing bark, a fiber sludge, a sort of branch or fiber, or * ... * residual sludge or logging residue from biological wastewater treatment, * 25 * firewood, wood residues from wood processing or other wood suitable for incineration. • · ta. * ··· «i« M ·· i * ·· 6. A method according to any one of the preceding claims, characterized in that the ··· * ...! gases having a temperature substantially below 200 ° C are used for drying the wood or similar wood waste. • · • • · ·., V Process according to claim 6, characterized in that steam or flue gas having a temperature below 180 ° C is used. . A 13 1 1 7479 Process according to one of Claims 1 to 5, characterized in that steam is used for drying the solid fuel fuel at a pressure of 0.1 to 100 bar, preferably 2 to 14 bar. 3 5 9. A process for the production of thermal and electrical energy in a sulphate pulp mill comprising: - partially dissolving the wood pulp used for pulp in a digestion solution to separate the fibers; for the production of heat and electricity utilizing biogenic fuels, characterized in that: 15. the solid biogenic fuel is gaseous formed, gy 0 - the ash produced is separated and the f - gas is burned to a significant extent in the same heat recovery boiler as the digestate. ·> ··· * *, ***: 20 Method according to Claim 9, characterized in that the biofuel to be gasified is wood and / or bark and / or bark sludge and / or fiber sludge and / or sorting twig or fiber objects and / or biological sewage sludge surplus sludge- * • • * * * * Tue * * *** ^ «·· • 9" 'Vi ···:...' 11. A method according to claim 9 or 10, characterized in that the biogenic fuel to be gasified is harvested logging residue and / or separately harvested from the forest. or wood processing surplus wood and / or other wood suitable for incineration ·· * ** ». 3 ·. ···. · $ * · «···· ** · •« • · • · · A process according to claim 9, characterized in that the biofuel genetic fuel to be gasified is peat. 14 1 17479. A process according to claim 9, characterized in that the solid fuel to be converted into a gaseous form is dried to a moisture content of V before gasification. 5 to 40%, preferably 10 to 15%. Method according to Claim 9, characterized in that the residual heat after the actual heat recovery of the flue gas generated in the furnace is used for drying the solid fuel by directly contacting the flue gas with the solid fuel to be dried. Method according to Claim 9, characterized in that the energy used for drying the solid fuel is steam at a pressure level of 0.1 to 100 bar, or preferably at a pressure level of 2 to 14 bar at the distribution pressure of the intermediate or back pressure steam network. "' Method according to Claim 9, characterized in that the residual heat at the pulp mill, e.g. in various warm waters and in the expansion henna. A method according to claim 9, characterized in that the furnace is divided in two directions, in the direction of the flow of the gases ..., 20, the first of which is to burn the fuel placed in the gas space, where the heat generated is used to a considerable extent for steam section superheat and in the other part for combustion liquor, the heat released is primarily used for evaporation of boiler water. • · * * »• ·· · * • · e. -.¾ 25 A process according to any one of claims 9 to 17, characterized in that a portion of the solid biogenic fuel in gaseous form is incinerated after ash * * * separation in a lime kiln and / or other locations where its use replaces phospho * * * * ··· the use of hedgehog fuels. ^ • · · • · · * • * · • · * ··. '· * · ♦ • · ♦ • · · ·. • · · · · • · ·? 1: 4 117479 15: s Krav