EP2390409A1

EP2390409A1 - Lignocellulose process

Info

Publication number: EP2390409A1
Application number: EP11167025A
Authority: EP
Inventors: Pasi Petteri Rousu; Juha Rainer Anttila; Keijo Jaakko Einari Hytönen
Original assignee: Chempolis Oy
Current assignee: Chempolis Oy
Priority date: 2010-05-31
Filing date: 2011-05-23
Publication date: 2011-11-30
Also published as: CN102268829A; FI20105613A0; FI20105613A

Abstract

An inlet connection part (108) of an apparatus (106) is connectable to a feed structure (110) for a cooking chemical (104) for cooking lignocellulosic mass. A feed connection part (112) is connectable to a reception connection part (114) of a lignocellulose digester (100) for feeding the cooking chemical (104) and the heat contained therein to the lignocellulose digester (100). At least one heater (116) heats the cooking chemical (104) receivable by the inlet connection part (108) to provide a cooking temperature of the lignocellulose digester (100) without adding an agent heating the cooking chemical (104) to the cooking chemical (104).

Description

Field

The invention relates to a lignocellulose process and, in particular, a cooking step thereof.

Background

Continuous digesters may be used for producing lignocellulosic mass, such as non-wood biomass. In a conventional process, cooking chemical and raw material to be delignified and defibrated are fed to a digester. The raw material comprises plants shredded to pieces of a desired size. The cooking chemical is caustic and it dissolves the lignin of the raw material and thus facilitates the defibration. The cooking chemical may be alkaline or acid. Vapour is also fed from one or more points to the digester to achieve and maintain the correct cooking temperature. The cooking temperature in various processes usually varies between 110°C and 180°C.
This prior art solution is, however, associated with problems. Vapour dilutes the concentration of the cooking chemical, wherefore during the feeding the cooking chemical should have a higher concentration than in the cooking. This, in turn, increases the recovery and concentration costs of the chemical, because a greater amount of chemical must be concentrated and/or the chemical must have a higher concentration than before. Furthermore, since vapour increases the amount of liquid in the cooking, low liquid ratios cannot be used in the digester. In addition, high liquid ratios make the recovery of the chemicals more difficult and increase the recovery costs of the chemicals, because a high liquid ratio increases the quantity of the liquor that must be treated in the recovery.

Brief description

It is an object of the invention to provide an improved lignocellulose process. This is achieved by an apparatus comprising an inlet connection part connectable to a feed structure for a cooking chemical for cooking lignocellulosic mass; a feed connection part connectable to a reception connection part of a lignocellulose digester for feeding the cooking chemical and the heat contained therein to the lignocellulose digester; and at least one heater for heating the cooking chemical receivable by the inlet connection part to provide a cooking temperature of the lignocellulose digester without adding an agent heating the cooking chemical to the cooking chemical.
The invention also relates to a method comprising receiving cooking chemical from a feed structure with an inlet connection part of an apparatus; heating the cooking chemical received via the inlet connection part by means of at least one heater of the apparatus to provide a cooking temperature of a lignocellulose digester without adding an agent heating the cooking chemical to the cooking chemical; and feeding the cooking chemical and the heat contained therein via a feed connection part of the apparatus to the lignocellulose digester.
Preferred embodiments of the invention are disclosed in the dependent claims.
With the lignocellulose process of the invention, the cooking temperature may be controlled without changing the concentration of the cooking chemical.

List of figures

The invention will now be described in greater detail by means of preferred embodiments and with reference to the accompanying drawings, in which:

Figure 1 shows a cooking process, to which fed cooking chemical is heated;
Figure 2 shows a heater with a heat exchanger;
Figure 3 shows a heater, in which a heating fluid has its own pipe in the heat exchanger;
Figure 4 shows a heater with an electric resistor;
Figure 5 shows a heater with a burner;
Figure 6 shows two separate heaters;
Figure 7A illustrates prior art heating of the cooking process and pressure control with vapour,
Figure 7B shows pressure control of a digester without feeding vapour to the digester,
Figure 8A shows a block diagram of a recirculation process;
Figure 8B shows a second block diagram of a recirculation process;
Figure 8C shows a third block diagram of a recirculation process;
Figure 9A illustrates heating of a cooking chemical by mixing it with a flash-evaporated, hot cooking chemical;
Figure 9B illustrates heating of a cooking chemical in a heat exchanger with a flash-evaporated, hot cooking chemical;
Figure 9C illustrates heating of process water in a heat exchanger with a flash-evaporated, hot cooking chemical; and
Figure 10 shows a flow chart of the method.

Description of embodiments

Figure 1 shows process equipment for pulp production. Pulp raw material 102, which may comprise lignocellulose-containing biomass, may be fed to a lignocellulose digester 100. The raw material 102 fed to the digester 100 may be wood-based, non-wood based, or both. Plants may be chopped or cut to pieces of a desired size, such as to chips or the like. The raw material may be biomass, such as grass-stemmed plants.
Grass-stemmed plants generally refer to non-wood based fibre sources, such as straw, grass, reed, bast fibres, leaf fibres, seed hairs. Straw refers to, for instance, corn straw, such as wheat, barley, oat, rye and rice straw. Grass refers to esparto, sabai or lemon grass, for instance. Reed refers to, for example, papyrus, common reed, sugar cane and bamboo. Bast fibre sources include stems of fibre flax or seed flax, kenaf, jute and hemp. Sources of leaf fibres include manilla hemp and sisal. Sources of seed hairs include cotton and cotton linter fibres. In addition, non-wood based fibre sources include reed canary grass, timothy, orchard grass, yellow sweet clover, awnless brome, red fescue, white sweet clover, red clover, goat's rue and medick. In addition, fibre sources for biomass may include different kinds of wood, such as short-fibred hardwood and young thinning wood. Full-grown trees may also be used as fibre sources.
The raw material need not be pre-treated by a wet technique, for instance, thus reducing the amount of water passing to the digester 100, but the plants may be cooked directly as pieces shredded to a size ranging from a few centimetres to tens of centimetres, for example. This applies to reed plants in particular. The raw material may thus be dry when being fed to the digester 100, the dry matter content being 40% to 95%, for instance. Accordingly, the amount of liquid in the digester 100 may be kept small and the liquid ratio may be 1:2 to 1:10, for example.
Cooking chemical 104, which may be alkaline or acid, is also fed to the digester 100. The cooking chemical content in the digester may be 20%, for instance. The temperature in the digester 100 may be 80°C to 200°C, for example. The cooking chemical used in the cooking of biomass may also be a volatile organic solvent, the boiling point of which is below 250°C. An alkaline cooking chemical may comprise, for instance, white liquor, i.e. sodium hydroxide (NaOH) and sodium sulphide (Na₂S), as used in the kraft process. An acid cooking chemical, in turn, may comprise formic acid and/or acetic acid, for example. The cooking chemical may also comprise one or more alcohols. In addition, the cooking chemical 104 may include other substances for delignification, bleaching or other purposes.
The end product of the cooking is pulp, which may be washed and bleached after the cooking. Pulp thus produced may be used, for instance, in the board and paper industry or as a raw material for (bio)ethanol. Also the cooking chemical is recovered from the digester 100 and fed to a separator 130 for recirculation.
In an embodiment, the delignification process may be provided with an apparatus 106 comprising an inlet connection part 108, which may be connected to a feed structure 110 for a cooking chemical for cooking the lignocellulosic mass. The feed structure 110 may be a pipe, through which liquid cooking chemical may be fed to the digester 100. In this case, the inlet connection part 108 of the apparatus 106 may be connected to the feed structure 110 by a threaded connection, a flange connection, one or more separate mechanical connectors or other similar means. The inlet connection part 108 may also be a mere pipe end that has been cut straight and is welded or soldered to the pipe of the feed structure 110.
The apparatus 106 also comprises a feed connection part 112, which may be connected to a reception connection part 114 of the lignocellulose digester 100 for feeding the cooking chemical and the heat contained therein to the lignocellulose digester 100. The reception connection part 114 may be a part of the feed structure 110 for a cooking chemical, a part of the digester 100, or a separate part attached to the digester 100. Accordingly, the feed connection part 112, which may be a pipe, may be connected to the reception connection part 114 of the digester by a threaded connection, a flange connection, one or more separate mechanical connectors or other similar means. The feed connection part 112 may also be a mere pipe end that has been cut straight and is welded or soldered to the pipe of the reception connection part 114.
The apparatus 100 further comprises a heater 116, which heats the cooking chemical 104 that can be received by the inlet connection part 108 to provide a cooking temperature of the lignocellulose digester 100 without adding an agent heating the cooking chemical 104 to the cooking chemical 104.
The cooking chemical 104 may be fed to one or more locations in the digester 100. In an embodiment, the cooking chemical 104 is fed to only one location in the digester 100, in which case the digester 100 has only one reception connection part 114, which is close to a reception point 132 for the raw material 102 or in the immediate vicinity thereof.
In an embodiment, flow of the cooking chemical 104 through the apparatus 106 to the digester 100 may be measured and controlled. Measurement can be carried out with a flow meter 140 before the cooking chemical 104 is heated in the apparatus 106, whereby the cooking chemical 104 may be completely liquid and have a temperature of 40°C to 60°C, for example. The flow meter 140 may be, for instance, a magnetic flow meter, which is inexpensive and can measure flow of a non-vaporized liquid. The flow meter 140 may comprise a flow controller, or a flow controller may be located in some other part of the process. The flow controller may be a valve, and a flow through the valve may be changed.
In an embodiment, the apparatus may comprise a thermometer 120 and a controller 122, which may receive the temperature of the heated cooking chemical 104 measured by the thermometer 120. The controller 122 may control the heating efficiency of the heater 116 for the temperature and cooking temperature of the cooking chemical 104.
In an embodiment shown in Figure 2, the heater 116 may comprise a heat exchanger, in which heat is transferred from, for example, a hot fluid 200 to the cooking chemical 104 by means of conduction and/or thermal radiation. The heat exchanger may be a tube heat exchanger and/or a plate heat exchanger. Fluid refers to the liquid or gaseous state of a substance. Arrows represent the flow direction of the fluid 200. Accordingly, the cooking chemical 104 that is hotter than the fluid 200 may release some of its heat to the fluid 200. The heater 116 does not apply convection for transferring heat, but the mixing of the cooking chemical 104 and the fluid 200 with one another is prevented by means of at least one wall 202 made of a solid material, for instance, such that the cooking chemical 104 flows in a pipe 204 surrounded by the fluid.
Figure 3 shows an alternative embodiment where also the fluid 200 controlling the temperature of the cooking chemical 104 may be in its own pipe 300. The fluid pipe 300 may be in contact with the pipe 204 of the cooking chemical 104. The walls 202 of the conduits 204 and 300, however, prevent the mixing of the fluid 200 and the cooking chemical 104 with one another.
In an embodiment, the fluid 200 used in the heat exchange may be, for instance, vapour having a temperature of 80°C to 200°C. Vapour may be produced in some other step of the process, for instance. The fluid may also be a cooking chemical (cf. Figure 9B).
When the temperature of the heated cooking chemical 104 is controlled in the embodiments of Figures 2 and 3, it is, for instance, possible to change the flow rate of the hot fluid 200. The flow of the fluid 200 may be changed, for instance, by widening or narrowing a valve 210 by means of the controller 122. If the flow of the fluid 200 in the apparatus 106 is slowed down by decreasing the flow through the valve 210, the cooking chemical 104 heats less. Accordingly, if the flow rate of the fluid 200 is raised by increasing the flow through the valve 210, the cooking chemical 104 heats more. It is known per se to change the flow rate of a liquid or a gas, and it is not described in greater detail herein.
Figure 4 shows an embodiment, in which the heater 116 may receive electric energy. The heater 116 may convert the electric energy into heat energy by means of one or more electric resistors 400, for instance, which become hotter in accordance with the growing intensity of electric current that is fed through them. The electric resistor 400 may be outside the cooking chemical pipe 204 or the electric resistor 400 may also be inside the cooking chemical pipe and thus in direct contact with the cooking chemical 104.
When the temperature of the heated cooking chemical 104 is controlled in the embodiment of Figure 4, it is possible to control, for instance, the intensity of the electric current flowing through the electric resistor 400. When the intensity of the electric current flowing through the electric resistor 400 decreases, the heating efficiency directed at the cooking chemical 104 decreases and the cooking chemical 104 heats less. When the intensity of the electric current flowing through the electric resistor 400 increases, the heating efficiency directed at the cooking chemical 104 increases and the cooking chemical 104 heats more.
The intensity of the electric current flowing through the electric resistor 400 may be diminished by, for instance, decreasing the voltage over the electric resistor 400. Accordingly, the intensity of the electric current flowing through the electric resistor 400 may be increased by, for instance, increasing the voltage over the electric resistor 400. It is also possible to change the resistance value of the electric resistor 400. If the resistance value of the electric resistor 400 is lowered, the intensity of the electric current flowing through the electric resistor 400 increases. If, on the other hand, the resistance value of the electric resistor is raised, the intensity of the electric current flowing through the electric resistor 400 decreases.
Figure 5 shows an embodiment, in which the heater 116 may be a fuel burner 500. When fuel is burnt in the burner 500, heat is generated, which may be used for heating the cooking chemical 104. The fuel may be a solid material, a liquid or a gas. The fuel may also be oil, petrol, ethanol or gas, for example. The fuel may also be black liquor, for instance, which may be produced in a kraft process. Fuel combustion in the burner 500 may be optimised by controlling the amount of air.
When the temperature of the heated cooking chemical 104 is controlled in the embodiment of Figure 5, it is possible to control, for instance, the amount of burnt fuel. The controller 122 may control the amount of fuel to be fed to the burner 500 by means of a valve 510. The more fuel per time unit is fed for burning, the warmer the cooking chemical 104 becomes.
The process equipment may also comprise a separator 130 connected to the digester 100 and the cooking chemical feed structure 110 or the inlet connection part 108 for recirculating the cooking chemical. The separator 130 receives cooking chemical used in the digester 100, purifies the used cooking chemical by, for instance, filtering the fibres and fines away from the used cooking chemical. Part of the cooking chemical may have undergone a chemical reaction in the digester 100, wherefore the used cooking chemical may also be purified chemically by regenerating the chemically reacted part of the chemical back to the original cooking chemical or transferring the chemically reacted cooking chemical to be removed from the recirculation. The purified cooking chemical may be recirculated by feeding it to the heating device 106.
Figure 6 shows a solution in which the apparatus 106 comprises two heaters 600, 602. Usually there may be more than two heaters 600, 602. A transfer pipe 604 for a cooking chemical between the heaters 600, 602 may be, for instance, similar to the feed structure 110. Each heater 600, 602, in turn, may be similar to the heater 116 of Figures 2 to 5, and each one of them may be connected with the thermometer 120 and the controller 122.
In an embodiment, the apparatus comprises two heaters 600, 602, the first heater 600 heating the cooking chemical 104 to a boiling point and the second heater 602 vaporizing the cooking chemical 104 partly or completely. An inefficient heat transfer may thus be avoided. When heating and vaporization are performed in separate heaters 600, 602, each heater 600, 602 may be designed in such a manner that the flow rate of the cooking chemical is suitable for efficient heat transfer. By means of efficient heat transfer, it is possible to reduce the size of the heaters.
Figure 7A illustrates pressure control of the digester 100 in a prior art process, and Figure 7B illustrates pressure control of the digester 100 in a solution where the temperature of the digester 100 is controlled by means of the cooking chemical. In the prior art solution, heated vapour, for instance, may be fed through a valve 700 to the digester 100 in order to increase or maintain the cooking temperature. However, the pressure of the digester 100 cannot rise higher than the pressure of the saturated vapour used for heating. The digester 100 may comprise a valve 702, which releases vapour at a pressure higher than a predetermined pressure out of the digester 100, if the aim is that the pressure of the digester 100 is lower than the pressure of the saturated vapour. The vapour fed to the digester 100 also dilutes the cooking chemical. Thus, the prior art solution is associated with a problem of controlling the concentration, amount and pressure of the cooking chemical.
Figure 7B shows a solution where vapour is not fed to the digester 100. When a predetermined amount of raw material is fed to the digester 100, the heated cooking chemical may be dosed in a desired manner with respect to the raw material. The pressure in the digester 100 may be controlled by the valve 702, which releases gas at a pressure higher than a predetermined pressure out of the digester 100. The predetermined pressure generated by the valve 702 may also be controlled or it may be preset as a fixed value. Thus, controlling the concentration and amount of the cooking chemical does not depend on the pressure in the digester 100, but they may be controlled separately. In addition, the temperature of the cooking in the digester 100 may be controlled independently of the pressure. The pressure of the digester 100 is not restricted to the pressure of the heating vapour either (since no separate heating vapour is used), but the pressure of the digester 100 may be set freely as desired.
Figure 8A shows a more extensive block diagram of the process and the separator 130 in more detail. The delignified pulp mass may be transferred from the digester 100 to a washing and bleaching process 800, after which the pulp mass may be used for the production of board, paper or (bio)ethanol, for example. The separator 130, which may receive cooking chemical from the digester 100, may comprise a regeneration part 802, where the cooking chemical may be distilled, for example, after which the cooking chemical purified by distillation may be returned back to the digester 100 through the apparatus 106.
In an embodiment, no heating energy is needed for distillation, but at least part of the hot cooking chemical may evaporate to the separator 130 during stripping following the blowing after the cooking and during the resulting pressure drop, whereby the cooking chemical is pure due to the evaporation and can be recirculated directly back to the apparatus 106.
After the distillation, concentrated combustible substances may remain in the regeneration part 802, which may be separated from, for instance, hemicellulose in a separation part 804. Combustible substances, such as lignin, may be burnt after the separation in the burner 500 of the heater 116, for instance, which is shown by a broken line between the separation part 804 and the apparatus 106.
The combustible substances may also be burnt in some burner 806 belonging or not belonging to the process equipment, and the heat produced therein may be used for generating vapour, for instance. Vapour thus produced may be used in the heater 116 serving as a heat exchanger to heat the cooking chemical.
Alternatively or in addition, heat generated in the burning of combustible substances may be used for generating electricity. Electricity thus produced may be supplied to the heater's 116 electric resistor 400, which may heat the cooking chemical 104.
From the lignin separator 804, cooking chemical may be returned to the apparatus 106 to be recirculated back to the digester 100 (continuous line).
Figure 8B shows an embodiment, which illustrates the processing steps of Figure 8A in greater detail. From the digester 100, the cooked mass may proceed to a flash evaporation part 820, where the pressure drops abruptly to a normal atmospheric pressure. Since the temperature in the digester 100 has been higher than the boiling temperature of the cooking chemical at normal atmospheric pressure, the cooking chemical evaporates immediately and the evaporated cooking chemical may be transferred to the apparatus 106 and, from there, further to the digester 100. After the flash evaporation, the cooked mass may proceed to an acid washing part 822, where the cooked mass is washed with an acid. The acid may be an organic acid and it may be at least partly the same as the cooking chemical. The liquid substance of the acid washing may be transferred to an evaporator 826, which heats the liquid substance, whereby the cooking chemical evaporates and can be separated and transferred to the apparatus 106. Organic matter, such as lignin, may be treated as described in connection with Figure 8A. After the acid washing, the cooked mass may be transferred to a water washing part 824, where the mass is washed with water. From this part, the liquid substances may be transferred to a distillation part 828, where the different substances may be separated from one another. From the distillation part 828, the cooking chemical is transferred to the apparatus 106 after the separation.
Figure 8C illustrates one more way of recirculating the cooking chemical. In this embodiment, the mass cooked in the digester 100 may proceed to the flash evaporation part 820, from where the cooking chemical is transferred to the apparatus 106 similarly as in Figure 8B. The cooked mass may then proceed to the separation part 830, where cooking chemical may be separated from the mass to the evaporation part 826 by mechanical pressing, for instance. In the evaporation part 826, the cooking chemical, which is an acid, may be separated and transferred to be used in the acid washing part 824. In the evaporation part 826, the dry matter of the mass is separated from the liquid substances and the liquid substances may be transferred to the apparatus 106, from which the liquid substances serving as cooking chemicals are transferred to the digester 100. In this case, the cooking chemical is not necessarily a pure acid.
Figure 9A shows an embodiment, in which the cooking chemical is heated by flash evaporation. After the cooked mass has proceeded to the flash evaporation part 820, the cooking chemical, which is rapidly converted into vapour, may be used for heating the cooking chemical to be fed to the digester by, for instance, mixing the unheated cooking chemical and the cooking chemical vapour from the flash evaporation in the heater 106, which may be a contact condenser, for instance. Consequently, the flash-evaporated cooking chemical condenses and the liquid cooking chemical heats. From the heater 106, the suitably heated cooking chemical may be fed to the digester 100.
Figure 9B shows an alternative embodiment, in which the cooking chemical is heated in two different steps. After the cooked mass has proceeded to the flash evaporation part 820, the cooking chemical, which is rapidly converted into vapour, may be used for heating the cooking chemical to be fed to the digester without mixing the unheated cooking chemical and the cooking chemical vapour from the flash evaporation in the heater 600. In this case, the heater 600 is a heat exchanger as shown in Figure 2 or 3, for example. The heated cooking chemical, which is heated by the vapour from the flash evaporation, and the cooking chemical liquid, which is cooking chemical that has been converted into liquid after the flash evaporation, may be in the same state and at approximately the same temperature when they are transferred to the second heater 602. The cooking chemical suitably heated in the heater 602 may be fed to the digester 100. The heater 602 may operate as illustrated in Figure 6.
In the embodiment according to Figure 9C, the cooking chemical vapour from the flash evaporation part 820 may be used for heating, for instance, process water in a water heater 900, the structure of which may be similar to that of the cooking chemical heaters 106 shown in Figures 2 and 3. During the heating process, the cooking chemical that has cooled to a liquid state may be transferred from the water heater 900 to the heater 106, to which unheated cooking chemical may also be fed. The cooking chemical that has been heated to a suitable temperature in the heater 106 may be fed to the digester 100. Heated process water may be utilised in different processes, such as during heating of the cooking chemical.
Figure 10 shows a flow chart of the method. In step 1000, the inlet connection part 108 of the apparatus 106 receives cooking chemical 104 from the feed structure 110. In step 1002, at least one heater 116 of the apparatus 106 heats the cooking chemical 104 received via the inlet connection part 108 to provide a cooking temperature of the lignocellulose digester 100 without adding an agent heating the cooking chemical 104 to the cooking chemical 104. In step 1004, the cooking chemical 104 and the heat contained therein are fed via the feed connection part 112 of the apparatus 106 to the lignocellulose digester 100.
The temperature of the cooking chemical may be controlled by means of a computer program. For instance, the controller 122 may comprise a processor, memory and a suitable computer program. The controller 122 may also be a part of a larger system controlling the entire process and comprising at least one processor, memory and suitable computer programs.
Although the invention is described above with reference to the examples according to the accompanying drawings, it is clear that the invention is not restricted thereto, but may be modified in various ways within the scope of the accompanying claims.

Claims

An apparatus, characterized in that the apparatus (106) comprises
an inlet connection part (108), which is connectable to a feed structure (110) for a cooking chemical (104) for cooking lignocellulosic mass;
a feed connection part (112), which is connectable to a reception connection part (114) of a lignocellulose digester (100) for feeding the cooking chemical (104) and the heat contained therein to the lignocellulose digester (100); and
at least one heater (116) for heating the cooking chemical (104) receivable by the inlet connection part (108) to provide a cooking temperature of the lignocellulose digester (100) without adding an agent heating the cooking chemical (104) to the cooking chemical (104).
Process equipment, characterized in that the equipment comprises a lignocellulose digester (100), a feed structure (110) for a cooking chemical (104) and, connected to the digester (100), an apparatus (106) as claimed in claim 1; and
the lignocellulose digester (100) is arranged to receive from the apparatus (100) lignocellulosic mass and cooking chemical (104) coming from the feed structure (110) and heated to provide a cooking temperature for producing pulp.
Equipment as claimed in claim 2, characterized in that the equipment comprises the feed structure (110) for a cooking chemical and a separator (130) connected to the digester (100) and the cooking chemical feed structure (110) or an inlet connection part (108) for recirculating the cooking chemical in such a manner that the separator (130) is arranged to receive used cooking chemical from the digester (100), to purify the used cooking chemical, and to feed the purified cooking chemical to the apparatus (106).
An apparatus as claimed in claim 1, characterized in that the apparatus comprises a thermometer (120) and a controller (122); and the controller (122) is arranged to receive the temperature of the heated cooking chemical (104) measured by the thermometer (120) and to control the heating efficiency of the heater (116) for the temperature and cooking temperature of the cooking chemical (104).
An apparatus as claimed in claim 1, characterized in that the heater (116) comprises a heat exchanger (300), which is arranged to heat the cooking chemical (104) with vapour.
An apparatus as claimed in claim 1, characterized in that the heater (116) comprises an electric heater (400), which is arranged to heat the cooking chemical (104).
An apparatus as claimed in claim 1, characterized in that the heater (116) comprises a burner (500), which is arranged to heat the cooking chemical (104).
A method, characterized by the method comprising receiving (1000) cooking chemical (104) from a feed structure (110) with an inlet connection part (108) of an apparatus (106);
heating (1002) the cooking chemical (104) received via the inlet connection part (108) by means of at least one heater (116) of the apparatus (106) to provide a cooking temperature of the lignocellulose digester (100) without adding an agent heating the cooking chemical (104) to the cooking chemical (104); and
feeding (1004) the cooking chemical (104) and the heat contained therein via a feed connection part (112) of the apparatus (106) to the lignocellulose digester (100).
A method as claimed in claim 8, characterized by receiving used cooking chemical from the digester (100) at a separator (130), purifying the used cooking chemical, and feeding the purified cooking chemical to the apparatus (106).
A method as claimed in claim 8, characterized by measuring the temperature of the cooking chemical (104) by means of a thermometer (120) and controlling by means of a controller (122) the heating efficiency of a heater (116) for the temperature and cooking temperature of the cooking chemical (104).
A method as claimed in claim 8, characterized by heating the cooking chemical (104) with vapour of a heat exchanger (300).
A method as claimed in claim 8, characterized by heating the cooking chemical (104) by means of an electric heater (400).
A method as claimed in claim 8, characterized by heating the cooking chemical (104) by means of a burner (500).