FI20185713A1 - A system and a method for hydrothermal carbonization of feedstock - Google Patents

Abstract

The invention relates to a system for hydrothermal carbonization of feedstock that contains carbon. The system comprises a carbonization reactor arrangement (100) configured to receive the feedstock, which contains carbon, carbonize the feedstock hydrothermally, and let out hydrothermally carbonized feedstock. The system comprises a dewatering apparatus (510) that is configured to produce dewatered carbonized material. The dewatering apparatus (510) is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C. In addition, use of such a dewatering apparatus (510) to dewater carbonized feedstock. Furthermore, a method, in which the carbonized feedstock is dewatered mechanically at a temperature of at least 80 °C.

Description

A system and a method for hydrothermal carbonization of feedstock

Technical field

The invention relates to systems and a methods for hydrothermal carbonization of feedstock. The feedstock comprises material that contains carbon. Examples of feedstocks include biomass and peat.

Background

Hydrothermal carbonization of carbon-containing feedstock is known from various sources, including EP2396392. The process requires a lot of heat, i.e. energy. In prior art, various heat exchangers are used to recover heat from the process. However, heat exchangers that recover heat from the feedstock, 15 which is typically a reasonably viscous slurry, are large and expensive. This imposes certain limits on the throughput of the process as limited also by the maximum investment allowed.

Summary

In order to increase the throughput of the process without increasing the investments costs, it is proposed to reduce the number of heat exchangers in the system and corresponding process and/or to reduce the amount of moisture of the processed material. To this end, two solutions have been 25 found.

According to a first aspect of the invention, it has been noticed that the feedstock can be pre-heated before the hydrothermal carbonization with steam obtained from a primary flash reactor, which is arranged downstream of the 30 hydrothermal carbonization. Using steam from a primary flash reactor, the processed material will be reasonably dry already before a subsequent drier. Thus, a smaller drier suffices. Moreover, in case the feedstock is pre-heated before the hydrothermal carbonization by directly contacting it with steam obtained from a primary flash reactor, use of a heat exchanger for the purpose 35 can be avoided.

According to a second aspect of the invention, in prior art, the carbonized feedstock may be dried. However, before drying, the carbonized feedstock is typically cooled by a heat exchanger, because the dryers of prior art typically do not withstand a high temperature. It has noticed that by using a dewatering 5 apparatus that is suitable for mechanically dewatering the feedstock at a temperature of at least 100 °C, the carbonized feedstock needs not to be cooled before dewatering. Examples of such a dewatering apparatus include a screw press and a centrifuge. Moreover, since the dewatered carbonized feedstock remains hot, it spontaneously dries also after the dewatering 10 apparatus. The invention is more specifically disclosed in the appended claims.

Preferably, the feedstock is pre-heated before the hydrothermal carbonization with steam obtained from a primary flash reactor, and a dewatering apparatus 15 suitable for mechanically dewatering the feedstock at a temperature of at least 100 °C is used to dewater the carbonized feedstock.

Brief description of the drawings

20185713 prh 29 -08- 2018

Some embodiments are shown in the following figures, in which

Fig. 1a shows in a principal view a system and method for hydrothermal carbonization of feedstock, the system comprising a primary flash reactor, wherein feedstock is arranged to be contacted with steam in a primary pre-heating vessel,

Fig. 1b shows in a principal view a system and method for hydrothermal carbonization of feedstock, the system comprising a primary flash reactor, wherein a primary pre-heating vessel forms a heat exchanger, in which feedstock is arranged to be heated with steam, Fig. 2 shows in a principal view a system and method for hydrothermal carbonization of feedstock the system,

Fig. 3 shows in a principal view a system and method for hydrothermal carbonization of feedstock, the system comprising primary and secondary flash reactors,

Fig. 4 shows in a principal view a system and method for hydrothermal carbonization of feedstock the system,

Fig. 5

Fig. 6

Fig. 7a

Fig. 7b

Fig. 8

Fig. 9

Fig. 10 shows in a principal view a system and method for hydrothermal carbonization of feedstock the system, shows in a principal view a system and method for hydrothermal carbonization of feedstock, the system comprising primary, secondary, and tertiary flash reactors, shows in a principal view a system and a method for hydrothermal carbonization of feedstock, shows in a principal view a system and a method for hydrothermal carbonization of feedstock, shows in a principal view a screw press of a dewatering apparatus, shows in a principal view a screw press of a dewatering apparatus, and shows in a principal view a screw press of a dewatering apparatus.

Detailed description

20185713 prh 29 -08- 2018

The present invention concerns a system and process for the conversion of a feedstock comprising natural raw materials (biomaterials) into materials with increased carbon content. The process includes a pressurized hydrothermal 20 treatment step of the feedstock. Preferably, the feedstock has a carbon content of more than 40 wt %, preferably up to 60 wt %, as measured from the dry matter of the feedstock before the aforementioned pressurized hydrothermal treatment step.

The feedstock material(s) may include components having high carbon contents, such as carbohydrates, preferably cellulose, hemicellulose, lignin, tannins and betulin, preferably in particulate form, e.g. with particle sizes of less than 1 cm. Particularly these feedstock materials may include materials having high contents of lignin, hydrolysis lignin or lignan, such as materials 30 obtained from side-streams of the manufacture of paper, board, biofuel or brewery products, such as pulp obtained from a pulping factory, more preferably from chemical pulp, such as black liquor, or hydrolysis lignin obtained from the manufacture of 2nd generation biofuels or lignan extracts from breweries.

20185713 prh 29 -08- 2018

The feedstock may contain or consist of such starting materials. In case the raw materials comprise larger solid structures (with particle sizes of at least 1 cm), such as peat, coal, or wooden raw materials, preferably selected from bark, branches, needles and twigs, these generally require some processing, 5 e.g. by grinding, to obtain the feedstock for use in the pre-heating step as well as in the hydrothermal treatment step

The feedstock may be formed of processed materials such as dissolved or colloidal materials, or as pulp, for example in the form of black liquor, including 10 among others water, which pulp can be further processed to separate the above mentioned starting materials from the excess water and further components, for example by precipitation, sieving or filtration, to provide a fraction containing the components having high carbon content for use as the starting materials of the hydrothermal treatment step, or the dissolved or 15 colloidal materials, dissolved or dispersed for example in water or an alcohol, such as ethanol, or a mixture thereof, can be used as such, optionally after homogenization, to enable forming a carbon product having a larger content of nanostructured carbon and primary particles on a sub-micron scale.

A system as detailed below may be used to run the process. When the system is operated, a method for treating feedstock that contains carbon is carried out. In an embodiment of the method, the feedstock comprises at least one of the materials as detailed above. In an embodiment of the method, the feedstock, which contains carbon, comprises at least one of

- wood material, such as sawdust, wood chip, bark etc.,

- lignin,

- lignocellulosic materials, such as cellulose, hemicellulose and/or lignin, or processed lignocellulosic materials, such as black liquor,

- peat,

- coal,

- waste material, such as waste of animal and/or fish industry, municipal waste, industrial waste or by-products, agricultural waste or byproducts, waste or byproducts of wood-processing industry, waste or by-products of food industry.

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As will become clear, the feedstock may further comprise water and/or humidity. In addition, in various phases of the method, steam is added to the feedstock.

Referring first to Figs. 1 a and 1 b, and to the first aspect of the invention, Figs. 1a and 1b show systems for hydrothermal carbonization of feedstock that contains carbon. The system comprises a carbonization reactor arrangement 100 configured to receive, carbonize, and let out the feedstock. The carbonization reactor arrangement 100 may comprise multiple carbonization 10 reactors 110, 120, 130, as shown e.g. in Fig. 5. Such a reactor is known from prior art. In prior art, the feedstock is only pre-mixed with water in a vessel (similar to the vessel 630 of Fig. 7b) before introducing it to carbonization.

The systems of Figs. 1a to 6 further comprise a primary pre-heating vessel 15 210. The primary pre-heating vessel 210 comprises a primary inlet arrangement 212 for receiving the feedstock, which contains carbon, and steam for pre-heating the feedstock. The purpose of the primary pre-heating vessel 210 is to pre-heat the feedstock before the reactor arrangement 100 with steam. In Fig. 1a, the feedstock and the steam are intermixed, whereby 20 heating takes place by direct heat transfer. In Fig. 1b, the primary pre-heating vessel 210 forms a heat exchanger, and the feedstock is heated with the steam, while the steam passes through the pre-heating vessel 210 without contacting the feedstock, and heats the feedstock indirectly.

A first function of the steam that is fed to the pre-heating vessel 210 is to preheat the feedstock before carbonization so as to save energy at the carbonization, i.e. in the carbonization reactor arrangement 100. A second function of the steam is to decrease the viscosity of the feedstock so that it can more easily be conveyed, e.g. pumped, to the carbonization reactor 30 arrangement 100. It has also been surprisingly found that heating it itself reduces the viscosity to a great extent.

Referring to Fig. 1a, in an embodiment, the primary pre-heating vessel 210 comprises an outlet 214 for letting out the pre-heated feedstock with the steam. 35 The feedstock may be some kind of slurry or substantially dry. However, preheating with steam reduces the dry-matter content in such a way that the

20185713 prh 29 -08- 2018 feedstock within the primary pre-heating vessel 210 is typically relatively viscous slurry. Moisturizing the feedstock by the steam has synergy with heating also in that both the increased temperature and the increased moisture content reduce the viscosity.

Referring to Fig. 1b, in an embodiment, the primary pre-heating vessel 210 comprises an outlet 214 for letting out the pre-heated feedstock. The feedstock may be some kind of slurry or substantially dry.

Irrespective of the type of primary pre-heating vessel 210 used, for subsequent process steps, and to avoid excessive drying, the moisture content within the primary pre-heating vessel 210 should not be too high. The inlet arrangement 212 may comprise separate inlets for the feedstock and the steam, as indicated in Figs. 1a and 1b, or, provided that direct heat transfer is used, the 15 steam and the feedstock may be let in to the primary pre-heating vessel 210 via the same inlet, as shown in Fig. 4.

As for the viscosity, it was found that when the feedstock consisted of peat, the viscosity of the feedstock dropped from 94 Pa s to 17 Pa s when the 20 feedstock was pre-heated from 20 °C to 90 °C. It is suspected that the viscosity will drop to an even smaller value, if the temperature is further increased. It is also noted that because of the saturation pressure of water, there is a large pressure difference between the primary pre-heating vessel 210 and the carbonization reactor arrangement 100. Typically the pressures may be on the 25 order of 15 bar(a) and 36 bar(a) in the primary pre-heating vessel 210 and the carbonization reactor arrangement 100, respectively. This emphasizes the problems related to pumping of the feedstock into the carbonization reactor arrangement 100.

The feedstock is fed to a pre-heating vessel (210, 220, 230) such as the primary pre-heating vessel 210 through a suitable channel 610. The feedstock is pumped from the primary pre-heating vessel 210 to the carbonization reactor arrangement 100 using a pump 105, as indicated in Figs. 1 and 4.

Since the feedstock is pre-heated in the primary pre-heating vessel 210, the carbonization reactor arrangement 100 is configured to receive the pre-heated

20185713 prh 29 -08- 2018 feedstock, carbonize the pre-heated feedstock hydrothermally, and let out hydrothermally carbonized feedstock. In case direct heat transfer is used in the primary pre-heating vessel 210, the carbonization reactor arrangement 100 is configured to receive the pre-heated feedstock and the steam used to heat the feedstock. The carbonization reactor arrangement 100 is configured to carbonize the pre-heated feedstock hydrothermally, whereby the system comprises a carbonization steam pipeline 440 for conveying steam into the carbonization reactor arrangement 100. Temperature and pressure requirements for the carbonization reactor arrangement are detailed below. These requirements apply also for the carbonization steam pipeline 440. An inlet of the carbonization steam pipeline 440 is arranged downstream from the a pump 105 in order to not to convey the carbonization steam to the primary pre-heating vessel 210.

The system further comprises a primary flash reactor 310. The primary flash reactor 310 comprises an inlet 312 for receiving the carbonized feedstock at a first primary pressure, a first primary outlet 314 for letting out steam, and a second primary outlet 318 for letting out the carbonized feedstock at a second primary pressure, which is lower than the first primary pressure. Such a flash reactor may be called a separator, as its main function is to separate vapor from biomass. By letting out steam from the primary flash reactor 310, the pressure decreases, whereby some of the water evaporates, which cools down the carbonized feedstock within the primary flash reactor 310.

A gist of the first aspect of the invention is to use the steam obtained from the primary flash reactor 310 to pre-heat the feedstock in the primary pre-heating vessel 210. As indicated above, the processed material is dried in the primary flash reactor 310 (and also a subsequent flash reactor 320, 330, if used). Therefore, having a flash reactor has the beneficial effect that less water will be conveyed to the subsequent drying phases. Moreover utilizing the steam of the flash reactor improves the efficiency of the process. In order to utilize the heat of the steam, the system comprises a primary pipeline 410 for conveying steam from the first primary outlet 314 of the primary flash reactor 310 to the primary pre-heating vessel 210. Moreover, the system comprises a primary limiting element 316 configured to limit a flow in the primary pipeline 410. The primary limiting element 316 may comprise a choke configured to maintain a

20185713 prh 29 -08- 2018 proper pressure within the primary flash reactor 310 in normal use. In the alternative or in addition, the primary limiting element 316 may comprise a valve. By controlling the valve, the pressure within the primary flash reactor 310 may be controlled. As well known, the water of the feedstock in the primary 5 flash reactor is typically in saturated state, whereby the pressure therein determines the temperature therein by the well-known saturation pressure of water as function of temperature.

When the system is used, a method for treating feedstock that contains carbon 10 is performed. The method comprises receiving the feedstock, which contains carbon. The feedstock is initially received in a pre-heating vessel 210, 220, 230 (see Figs. 4 and 6), or in a mixing tank 630 (Fig. 7b). The feedstock is finally received in the primary pre-heating vessel 210, optionally via the other pre-heating vessels 220, 230.

The method further comprises pre-heating the feedstock with primary steam received from a primary flash phase (e.g. the primary flash reactor 310), to produce pre-heated feedstock. As indicated above and in Fig. 1a, an embodiment of the method comprises pre-heating the feedstock at least by 20 contacting the feedstock with primary steam received from a primary flash phase. As indicated above and in Fig. 1b, an embodiment of the method comprises pre-heating the feedstock with primary steam received from a primary flash phase in a heat exchanger. The feedstock may be pre-heated in the primary pre-heating vessel 210, which may act as or comprise a heat 25 exchanger. As will be indicated below, the feedstock may be pre-heated also with secondary steam received from a secondary flash phase. As will be indicated below, the feedstock may be pre-heated also with tertiary steam received from a tertiary flash phase.

The method further comprises carbonizing the pre-heated feedstock hydrothermally, to produce hydrothermally carbonized feedstock. As known, hydrothermal carbonization takes place at a temperature of e.g. from 200 °C to 250 °C and in a pressure of from 16 bar(a) to 40 bar(a); preferably at a temperature from 220 °C to 240 °C and in a pressure of from 25 bar(a) to 35 35 bar(a). Herein and below the unit bar(a) refers to absolute pressure, as opposed to e.g. an overpressure relative to atmospheric.

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Typically, the water of the feedstock is saturated in the hydrothermal carbonization. In an embodiment, the feedstock is carbonized using carbonization steam. Correspondingly, an embodiment comprises receiving carbonization steam, preferably saturated steam, at a pressure of from 16 5 bar(a) to 40 bar(a), such as from 25 bar(a) to 35 bar(a), and using said carbonization steam to carbonize the pre-heated feedstock hydrothermally. As indicated above, the carbonization steam is conveyed to the carbonization reactor arrangement 100 through the carbonization steam pipeline 440. Therefore, in an embodiment, the carbonization steam pipeline 440 is 10 configured to withstand a pressure difference of at least 35 bar at a temperature of at least 240 °C. Preferably, the carbonization steam pipeline 440 is configured to withstand a pressure difference of at least 40 bar at a temperature of at least 250 °C. The carbonization steam pipeline 440 may comprise metal having a melting point of more than 300 °C, e.g. aluminum or 15 steel.

The method comprises cooling the carbonized feedstock in the primary flash reactor 310 (i.e. primary flash phase) by lowering pressure, thereby generating primary steam. The pressure may be lowered by letting out the primary steam 20 through the primary limiting element 316. The method further comprises using at least some of the primary steam in the pre-heating of the feedstock.

Preferably, the feedstock is pre-heated to a reasonably high temperature already in the primary pre-heating vessel 210. In an embodiment, the 25 feedstock is pre-heated before the carbonization to a temperature of from 160 °C to 200 °C, such as from 160°C to 180 °C. As indicated above, the feedstock is pre-heated with the primary steam received from the primary flash phase (i.e. reactor 310). Since the steam is typically saturated, these ranges correspond to pressures of from 6 bar(a) to 16 bar(a); or from 6 bar(a) to 30 10 bar(a), respectively.

As indicated above, preferably the feedstock is pre-heated in such a way that the viscosity of the feedstock decreases to a level that is suitable for transferring the feedstock to the carbonization (i.e. carbonization reactor 35 arrangement 100). An embodiment comprises pre-heating the feedstock before the carbonization in such a way that a viscosity of the feedstock is at

20185713 prh 29 -08- 2018 most 100 Pa s, preferably at most 50 Pa s, at the temperature of the feedstock at that point as measured with a shear rate of 1001/s. As indicated above, the temperature at that point is preferably from 160 °C to 200 °C.

It has also been noticed that since already the pre-heating alone often decreases the viscosity to a suitable level, preferably, the moisture content is not significantly increased in the pre-heating.

In order not to moisten the feedstock too much, there are at least two options.

First, in case indirect heat transfer (i.e. a heat exchanger) is used to heat the feedstock, as in the embodiment of Fig. 1b, the pre-heating does not increase the moisture content at all. Second, in case direct heat transfer is used, not too much steam from the flash phase (or phases) should be used. Therefore, as indicated in Figs. 1a, 4, and 7, in an embodiment the primary pipeline 410 15 comprises a primary branch 412 for not conveying the primary steam only to the primary pre-heating vessel 210. Correspondingly, an embodiment of the method comprises using steam obtained from a flash reactor, such as the primary flash reactor 310, the secondary flash reactor 320, and/or the third flash reactor 330, also for another purpose than pre-heating the feedstock. An 20 example of the other purpose is drying, such as drying the feedstock. In an embodiment, steam obtained from a flash reactor (310, 320, 330) is used for drying material. As indicated above, in addition steam obtained from a flash reactor (the same or another flash reactor) is used for pre-heating the feedstock. In an embodiment the primary pipeline 410 comprises a primary 25 branch 412 for conveying the primary steam to a drier.

This has the beneficial effect that the dewatering and drying of the carbonized feedstock will require less energy. In addition, since the amount of steam is reduced, the amount of feedstock in the carbonization reactor arrangement 30 100 is reduced, whereby a carbonization reactor can be used for a greater throughput. For example, if, in a reference case, a feedstock is only diluted to a suitable viscosity by adding water, the dry matter content may be as low as 15 wt% in the carbonization reactor. However, when, as a result of pre-heating, the dry matter content of the feedstock in the carbonization reactor can be 35 increased to 20wt%, the throughput of the process, in terms of dry matter, increases by one third. For example, if the capacity of the carbonization reactor

20185713 prh 29 -08- 2018 arrangement 100 is a hundred units, with a dry matter content of 15 %, only 15 units of dry matter can be processed by the carbonization reactor. In contrast, if the dry matter content can be raised to 20 wt%, 20 units of dry matter can be processed by the carbonization reactor. This bears evidence of 5 significant savings obtainable by the aforementioned pre-heating.

As indicated above, the primary steam is conveyed in the primary pipeline 410. Because of these temperatures and pressures, in an embodiment, the primary pipeline 410 is configured to withstand a pressure difference of at least 15 bar 10 at a temperature of at least 200 °C. The primary pipeline 410 may comprise metal having a melting point of more than 250 °C, e.g. aluminum or steel. In general, the steam in the primary pipeline 410 may be somewhat hotter that the temperature, to which the feedstock is pre-heated in the primary preheating vessel 210.

After cooling the carbonized feedstock at least in the primary flash reactor 310, the carbonized feedstock may be dewatered e.g. in a dewatering apparatus 500. The dewatering apparatus 500 may comprise a such a dewatering apparatus 510 that is suitable for to dewatering material mechanically at a 20 temperature of at least 100 °C and/or a secondary dryer 515, such as a filter 515. Thus, an embodiment of the system comprises a dewatering apparatus 500 configured to receive the carbonized feedstock from a flash reactor, such as the primary flash reactor 310, a secondary flash reactor 320 or a tertiary flash reactor 330, at a first moisture content; and to dewater the carbonized 25 feedstock to produce dewatered carbonized material with a second moisture content that is lower that the first moisture content. In a preferred embodiment, the dewatering apparatus 500 comprises a dewatering apparatus 510 that is suitable for dewatering material mechanically at a temperature of at least 100 °C, such as a screw press 505, as will be described in a greater detail later.

Referring now to Fig. 2, in an explanatory system, the dewatering apparatus 500 comprises only a secondary dryer 515, such as a conventional filter 515. However, conventional filters 515 typically cannot withstand high temperatures. Typically, the temperature of the carbonized feedstock need to 35 be lowered below 70 °C before filtering. Therefore, the explanatory system of Fig. 2 comprises a heat exchanger 620 configured to cool the feedstock before

20185713 prh 29 -08- 2018 the dewatering apparatus 500. As indicated in prior art, a heat exchanger may be integrated with a conveyor. Typically, such a heat exchanger 620 is configured to recover heat to a liquid, such a water, since this is much more efficient than cooling by air.

Referring now to Fig. 3, a preferably embodiment comprises two and only two subsequent flash reactors 310, 320. However, with reference to Fig. 6, also more flash reactors can be used in cascade. As indicated in Fig. 3, an embodiment of the system further comprises a secondary pre-heating vessel 10 220. In a similar manner as the primary pre-heating vessel 210, the secondary pre-heating vessel 220 may be configured to mix the feedstock with steam, are the secondary pre-heating vessel 220 may forms or comprise a heat exchanger for heating the feedstock indirectly with secondary steam. For these reasons, the secondary pre-heating vessel 220 comprises a secondary inlet 15 arrangement 222 for receiving the feedstock, which contains carbon, and steam for pre-heating the feedstock. The secondary pre-heating vessel 220 further comprises an outlet 224 for letting out at least the pre-heated feedstock to the primary pre-heating vessel 210. In case direct heat transfer takes place in the secondary pre-heating vessel 220, also steam is let out from the outlet 20 224 to the primary pre-heating vessel 210. The secondary inlet arrangement

222 may comprise different inlets for the secondary steam and the feedstock at least if indirect heat transfer is utilized, or they may be fed to the secondary pre-heating vessel 220 through only one inlet e.g. in a manner similar to that shown in Fig. 4 for the first inlet arrangement 212 in case direct heat transfer 25 is utilized.

The embodiment of Fig. 3 further comprises a secondary flash reactor 320. The secondary flash reactor 320 comprises an inlet 322 for receiving the carbonized feedstock from the primary flash reactor 310 at a first secondary 30 pressure, a first secondary outlet 324 for letting out steam, and an outlet 328 for letting out the carbonized feedstock at a second secondary pressure, which is lower than the first secondary pressure.

The embodiment of Fig. 3 further comprises a secondary pipeline 420 for 35 conveying steam from the secondary flash reactor 320 to the secondary preheating vessel 220. Preferably the secondary pipeline 420 comprises a

20185713 prh 29 -08- 2018 secondary branch 422 for conveying some of the secondary steam to another process than the pre-heating. This has the beneficial effect that the feedstock is not moistened too much in the pre-heating, as discussed above. In an embodiment the secondary pipeline 420 comprises a secondary branch 422 5 for conveying the secondary steam to a drier.

In use, the secondary pre-heating vessel 220 may be operated in a substantially atmospheric pressure. Therefore, the system may be free from a device configured to limit the flow of the steam from the secondary flash reactor 10 320 to the secondary pre-heating vessel 220. However, another choke or another valve (not shown in Fig. 3) may be used to control the flow of steam within the secondary pipeline 420.

A corresponding method comprises (i) receiving the feedstock from the 15 primary flash phase, (ii) cooling the carbonized feedstock by further lowering pressure, thereby generating secondary steam, and (iii) pre-heating the feedstock with the secondary steam. The feedstock may be heated by contacting it with the secondary steam. The feedstock may be heated in a heat exchanger by using the heat of the secondary steam. As indicated in Fig. 3, 20 the method comprises pre-heating the feedstock with the secondary steam and further pre-heating the feedstock with the primary steam. As indicated in Fig. 3, the primary steam is generated in a primary flash phase, e.g. in the primary flash reactor 310; and the secondary steam is generated in a secondary flash phase, e.g. in the secondary flash reactor 320. Moreover, the 25 carbonized feedstock is first cooled in the primary flash phase and thereafter further cooled in the secondary flash phase. Preferably direct heat transfer is used in both the primary phase (i.e. primary pre-heating vessel 210) and the secondary phase (i.e. secondary pre-heating vessel 220), since typically heat exchangers suitable for the purpose are relatively expensive.

In an embodiment, the feedstock is heated to at most 120 °C with the secondary steam, e.g. in the secondary pre-heating vessel 220. In a preferably embodiment, the feedstock is heated to a temperature of from 80 °C to 110 °C, such as 90 °C to 100 °C with the secondary steam, e.g. in the secondary 35 pre-heating vessel 220.

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The embodiments of Figs. 1a to 3 have the beneficial effects:

- Pre-heating the feedstock decreases the viscosity of the feedstock, whereby smaller and cheaper pumps can be used to pump the feedstock into to carbonization reactor arrangement 100,

- as the viscosity is reduced mainly (or only) by heating, moisture content of the feedstock remains low, whereby throughput is increased,

- use of high-pressure steam for the carbonization is reduced, since the feedstock is preheated with steam having a lower pressure than that needed in the carbonization, and

- the flash phase (or phases) dry the processed material, whereby dewatering to sufficient level needs less energy.

Moreover, having two flash phases and pre-heating phases, as in Fig. 3, has the following particularly beneficial effects:

- suitably hot steam for the primary pre-heating is obtainable from the primary flash reactor 310 (i.e. primary flash phase), since the pressure in the primary flash reactor 310 can be kept higher, when also the secondary flash reactor is used,

- the carbonized feedstock may be released from the secondary flash phase (e.g. the outlet 328 of the secondary flash reactor 320) in a substantially atmospheric pressure, which simplifies the components of the system after the flash phases,

- the carbonized feedstock may be released from the secondary flash phase (e.g. the outlet 328 of the secondary flash reactor 320) in a temperature of approximately only 100 °C (e.g. from 100 °C to 120 °C), which also simplifies the components of the system after the flash phases,

- also the heat of the low pressure steam obtained from the secondary flash phase (e.g. secondary flash reactor 320) is utilized in the process, and

- the secondary pipeline 420 needs not to be very resistant to heat, pressure, or corrosion.

As for the last point, in an embodiment, the secondary pipeline 420 is 35 configured to withstand a pressure difference of at least 1 bar at a temperature of at least 120 °C.

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Referring to Figs. 1a, 1b, and 3, preferably the system comprises a condenser 190 that is configured to receive some gaseous substance, including at least steam, from an upper part of the carbonization reactor arrangement 100. The gaseous substance may be released from the carbonization reactor 5 arrangement 100 in order to control the pressure and/or temperature within the carbonization reactor arrangement 100. Typically, the temperature and pressure correspond to water vapor saturation point. Moreover, the carbonization reactions are exothermic, whereby the temperature may tend to increase. Correspondingly also pressure may increase. By releasing some 10 gaseous substance, the pressure and temperature can be lowered; e.g.

brought back to or kept at the designed operating point. In addition to steam, some other off-gases may be conveyed to the condenser 190 from the carbonization reactor arrangement 100. However, the feedstock is not conveyed to the condenser 190. Thus, in an embodiment, only a gaseous 15 substance or gaseous substances are conveyed to the condenser 190. In the condenser 190, gaseous substances may be cooled down to separate off-gas from steam, by condensing the steam to water, e.g. pressurized water. The water and its heat may be utilized in the process by feeding it back to a preheating vessel, such as the primary pre-heating vessel 210, the secondary pre20 heating vessel 220, or the tertiary pre-heating vessel 230. In Figs. 1a, 1b, and 3, the condensed water is conveyed to the primary pre-heating vessel 210 through a pipeline 192. Since the water is typically reasonably hot and pressurized, preferably, the water from the condenser 190 and its heat is utilized by feeding it back to the primary pre-heating vessel 210. 25 Correspondingly, in an embodiment of a method the pre-heated feedstock is carbonized hydrothermally in the carbonization reactor arrangement 100. Moreover, some gaseous substance including steam is conveyed from the carbonization reactor arrangement 100 to the condenser 190, and at least some of the steam is condensed to water in the condenser 190. Finally, the 30 water obtained by said condensing is utilized to pre-heat the feedstock before the carbonization. For example, the water obtained by said condensing may be conveyed to a pre-heating vessel (210, 220, 230).

Figures 4 to 6 illustrate further embodiments. As indicated in Fig. 4, therein the 35 primary inlet arrangement 212 of the primary pre-heating vessel 210 comprises only one inlet. The same inlet is used to let in both the feedstock

20185713 prh 29 -08- 2018 and the primary steam. The same principle can be applied in the embodiments of Fig. 1a, 2, 3, 5, and 6, too; but not in the embodiment of Fig. 1b. Moreover, the secondary inlet arrangement 222 of the secondary pre-heating vessel 220 may, in a similar manner, comprise only one inlet, e.g. in the embodiments of 5 Figs. 3, 4, and 6.

As indicated in Fig. 5, the a carbonization reactor arrangement 100 may comprise more than one carbonization reactors, such as two or at least two carbonization reactors 110, 120, 130. As an example, Fig. 5 shows a 10 carbonization reactor arrangement 100 comprising a first carbonization reactor 110, a second carbonization reactor 120, and a third carbonization reactor 130. Even if not shown, a condenser 190 (see Figs. 2 and 3) may be used in connection with a carbonization reactor arrangement 100 comprising more than one carbonization reactors. The carbonization reactor arrangement 100 15 of any one of the embodiments of Figs. 1a, 1b, 2, 3, 4, or 6 may comprise one, at least one, two, at least two, three, or at least three carbonization reactors.

As indicated in Fig. 6, the system may further comprise a tertiary pre-heating vessel 230 and a tertiary flash reactor 330 connected to the tertiary pre-heating 20 vessel 230 with a tertiary pipeline 430. Such a solution may be energetically favorable, since each pre-heating vessel may be used to heat the feedstock only a little, whereby the heat of the steam may be utilized more effectively. However, using more than two pre-heating vessels and flash reactors may increase the investment costs. It has been found, that in most cases, an 25 optimal number of flash reactors and pre-heating vessels is two, is indicated in Figs. 3 and 4. In case a tertiary pipeline 430 is used as indicated above, preferably the tertiary pipeline 430 comprises a tertiary branch 432 for not conveying some of the tertiary steam to another process than the pre-heating. This has the beneficial effect that the feedstock is not moistened too much in 30 the pre-heating, as discussed above. In an embodiment the tertiary pipeline 430 comprises a tertiary branch 432 for conveying the tertiary steam to a drier.

As indicated in Fig. 6, a vacuum pump 332 may be used to decrease the pressure in a flash reactor (310, 320, 330), such as the third flash reactor 330 35 below atmospheric pressure. In this way, boiling of the feedstock may be effected at a temperature below 100 °C. Thus, the temperature of the

20185713 prh 29 -08- 2018 feedstock may be decreased to a level tolerable by a conventional dewatering apparatus 500. For example, if a pressure of 300 mbar(a) is maintained by the vacuum pump 332 in a flash reactor (310, 320, 330), the water of the feedstock will boil at a temperature of 69 °C, which may be tolerable by a conventional 5 dewatering apparatus 500. A vacuum pump 332 needs not be used, even if more than two flash reactor are used. The tertiary steam and/or water obtainable from the tertiary flash reactor 330 (optionally via the vacuum pump 332) needs not to be conveyed to a pre-heating vessel 230. Thus, a system may comprise a tertiary flash reactor 330 even if it does not comprise the 10 tertiary pre-heating vessel 230 of Fig. 6.

Referring now to Figs. 7a to 10 and to the second aspect of the invention, preferably the processed material is dewatered after the flash phases using such a dewatering apparatus 510 that is suitable for dewatering the carbonized 15 feedstock mechanically at a temperature of at least 100 °C. Examples of such dewatering apparatuses include a screw press 505 and a centrifuge. A dewatering apparatus arrangement 500 may comprise both a screw press and a centrifuge, or only one of a screw press 505 and a centrifuge. Fig. 8 shows a screw press 505, which is an example of such a heat resistant dewatering 20 apparatus 510. Presence of such a heat resistant dewatering apparatus 510 also illustrated in Figs. 1 and 3 to 7b. As indicated above, when using only a conventional filter 515, as in Fig. 2, to dewater the carbonized feedstock, a heat exchanger 620 and/or a vacuum pump 332 may be needed to cool the carbonized feedstock. However, it has been found that such a dewatering 25 apparatus 510 that is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C withstands higher temperatures, and, therefore, a heat exchanger 620 is not needed when the carbonized feedstock is dewatered using at least a heat resistant dewatering apparatus 510. This idea may be used in connection with conventional 30 carbonization systems. The dewatering apparatus 510 (such as screw press 505 or centrifuge) is also suitable for dewatering material (e.g. the carbonized feedstock) mechanically, i.e. without evaporation induced by heating. Clearly, some of the humidity may be evaporated, but the within the drier, the material is not heated for the purpose of drying the material. In this way, in an 35 embodiment, the dewatering apparatus 510 does not comprise a heater configured to heat the carbonized feedstock. In addition, in an embodiment,

20185713 prh 29 -08- 2018 the dewatering apparatus 510 is configured such that at most 25 % or at most 10 % of the water removed by the dewatering apparatus 510 is configured to be removed by evaporation of the water.

As for the reference signs, a dewatering apparatus in general or a dewatering apparatus arrangement in general is denoted by 500, a dewatering apparatus that is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C is denoted by 510, a screw press (which is an example of a dewatering apparatus that is suitable for dewatering the 10 carbonized feedstock mechanically at a temperature of at least 100 °C) is denoted by 505, and a conventional filter (which can not tolerate temperatures greater than about 70 °C) is denoted by 515. The dewatering apparatus arrangement 500 may comprise at least two dewatering apparatuses, as in Fig. 4. In case the dewatering apparatus arrangement 500 consists of only one 15 dewatering apparatus 500, it may be referred to as a dewatering apparatus 500. In an embodiment, the dewatering apparatus 510 that is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C is also configured to dewater the carbonized feedstock mechanically at a temperature of at least 100 °C.

Referring to Figs. 7a and 7b, a system for hydrothermal carbonization of feedstock that contains carbon comprises a carbonization reactor arrangement 100. The carbonization reactor arrangement 100 is configured to receive the feedstock, which contains carbon, carbonize the feedstock hydrothermally, 25 and let out hydrothermally carbonized feedstock. As indicated above, the feedstock may be received through the channel 610 and pumped with a pump

105. The feedstock may be pre-mixed with water, if needed. Carbonization steam may be fed to the carbonization reactor arrangement 100 through a carbonization steam pipeline 440. The system further comprises a dewatering 30 apparatus 500 downstream from the carbonization reactor arrangement 100.

The dewatering apparatus 500 is configured to receive the carbonized feedstock at a first moisture content, and dewater the carbonized feedstock to produce dewatered carbonized material with a second moisture content that is lower that the first moisture content. Moreover, in the embodiments of Figs. 7a 35 and 7b, the dewatering apparatus arrangement 500 comprises a dewatering

20185713 prh 29 -08- 2018 apparatus 510 that is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C, such as a screw press 505.

In this way, the second aspect of the invention relates to a use of a dewatering 5 apparatus 510 that is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C, such as a screw press 505 or a centrifuge, to dewater carbonized feedstock obtained from hydrothermal carbonization of feedstock that contains carbon. In such a use, a method for treating feedstock that contains carbon is performed. An embodiment of the 10 method comprises receiving the feedstock, which contains carbon; and carbonizing the feedstock hydrothermally, to produce hydrothermally carbonized feedstock. The method further comprises dewatering the carbonized feedstock using dewatering apparatus arrangement 500 comprising a dewatering apparatus 510 that is suitable for dewatering the 15 carbonized feedstock mechanically at a temperature of at least 100 °C, such as a screw press 505.

As indicated above, because the dewatering apparatus 510 is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 20 100 °C , the feedstock may be dewatered at a higher temperature than in some other dewatering apparatuses. Therefore, in an embodiment of the method, the carbonized feedstock is dewatered at a temperature of at least 80 °C. More precisely, in an embodiment of the method, the carbonized feedstock is dewatered at a temperature of at least 80 °C using a dewatering apparatus 25 510 that is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C. More preferably, the carbonized feedstock is dewatered at a temperature of at least 85 °C, at least 90 °C, or at least 95 °C, or at least 100 °C using a dewatering apparatus 510 suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C, 30 such as a screw press 505. Correspondingly in an embodiment, the dewatering apparatus 510 suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C is also configured to dewater the carbonized feedstock mechanically at a temperature of at least 85 °C, at least 90 °C, at least 95 °C, or at least 100 °C. The temperature herein refers 35 to the temperature of the feedstock within the dewatering apparatus 510. The dewatering apparatus 510 itself may be located in a cooler environment.

20185713 prh 29 -08- 2018

Typically, a dewatering apparatus 500 (or 510 or 505) cannot withstand the temperature and pressure of the carbonization; such temperatures and pressures are indicated above. At least such a screw press would be expensive and heavy. Therefore, an embodiment of the system further 5 comprises a primary flash reactor 310. The primary flash reactor comprises an inlet 312 for receiving the carbonized feedstock at a first primary pressure, a first primary outlet 314 for letting out steam, and a second primary outlet 318 for letting out the carbonized feedstock at a second primary pressure, which is lower than the first primary pressure. Moreover, the system is configured to 10 convey the carbonized feedstock from the second primary outlet 318 to the dewatering apparatus 500, 510. The system may comprise a primary limiting element 316 configured to limit a flow from the first primary outlet 314. The system may comprise a secondary flash reactor 320. The system may comprise a tertiary flash reactor 330. In this way, in an embodiment, the system 15 comprises one or more flash reactors (310, 320, 330) for letting out steam from the carbonized feedstock, thereby cooling the carbonized feedstock before the dewatering apparatus 500, 510. Correspondingly, an embodiment of the method comprises before the dewatering, lowering a pressure of the hydrothermally carbonized feedstock to produce steam and to cool the 20 hydrothermally carbonized feedstock.

Referring to Figs. 8, 9, and 10, a screw press 505 suitable for dewatering the carbonized feedstock comprises an inlet end 512 and an outlet end 514; and a channel 516, along which the feedstock is arranged to move from the inlet 25 end 512 to the outlet end 514. Moreover, in order to squeeze the carbonized feedstock, the channel 516 tapers towards the outlet 514 end, as indicated in Figs. 8 to 10. Furthermore, to let out water from the screw press 505, a wall (518, 519) of the channel 516 is water permeable. The water permeable wall may be an inner wall 519 or an outer wall 518, or both the inner wall 519 and 30 an the outer 518 wall may be water permeable. Water permeability may be achieved e.g. by perforations. The water permeable wall (518, 519) may be e.g. made from a perforated metal plate.

Also more generally, a dewatering apparatus 510 suitable for dewatering the 35 carbonized feedstock mechanically at a temperature of at least 100 °C comprises an inlet end 512 and an outlet end 514; and a channel 516, along

20185713 prh 29 -08- 2018 which the feedstock is arranged to move from the inlet end 512 to the outlet end 514. For example, in a centrifuge, in the channel 516, the water is separated from the dewatered biomass by centrifugal forces.

In order to convey the feedstock from the inlet end 512 to the outlet end 514, the screw press 505 comprises means for transferring the feedstock from the inlet end 512 to the outlet end 514 along the channel 516, whereby the tapering channel 516 and the water permeable wall (518, 519) are, in combination, configured to squeeze water out of the feedstock. In a preferable embodiment, 10 the means for transferring the feedstock from the inlet end 512 to the outlet end 514 comprises a threaded part (520, 530), i.e. a part having threads 522, configured to transfer the feedstock from the inlet end 512 to the outlet end 514 along the channel 516 upon rotation of the threaded part (520, 530), in particular the threads 522 thereof. In an embodiment, the system comprises 15 an actuator 540, such as a motor, configured to rotate the threaded part (520, 530). The actuator 540 may be e.g. a hydraulic motor, a steam turbine, an electric motor, or a combustion engine.

Thus, an embodiment of the method comprises conveying the carbonized 20 feedstock from an inlet end 512 of the screw press 505 to an outlet end 514 of the screw press 505 along a channel 516 that is limited by a water permeable wall (518, 519) and has a shape that tapers toward the outlet end 514. Thus, the method comprises squeezing water out of the carbonized feedstock in the channel 516. As indicated above, in an embodiment, the carbonized feedstock 25 is conveyed in the channel 516 by using a threaded part (520, 530), such as a screw 520.

Referring to Fig. 8, in a preferable embodiment, the screw press 505 comprises a tubular shell 530 that limit the channel 516 from outside. Preferably, at least 30 a wall 518 of the tubular shell 530 is water permeable. The tubular shell 530 may comprise perforations, through which water may permeate the tubular shell 530. The screw press 505 further comprises a screw 520 arranged inside the tubular shell 530 and forming an inner wall of the channel 516. In Fig. 8, the screw 520 has a body with conical shape so that the body of the screw 520 35 tapers towards the inlet end 512. The walls 519 of the body of the screw 520 may be water permeable. In this way, the channel 516, which is left in between

20185713 prh 29 -08- 2018 the screw 520 and the tubular shell 530 tapers towards the outlet end 514, as shown in Fig. 8. The screw 520 has threads 522 on its outer surface, whereby the screw 520 is configured to move the feedstock towards the outlet end 514 by rotation of the screw 520. Rotation of the screw is schematically indicate by 5 an arrow on the right hand side of the screw 520. Thus, the screw 520 is a threaded part 520. As indicated above, at least one of the walls 518, 519 (preferably at least the wall 518 of the shell 530) is water permeable.

In an embodiment, the materials of the screw press 505 are heat resistant at 10 least to 100 °C. This has the effect that the carbonized feedstock need not be cooled below the boiling point of water at the atmospheric pressure. Therefore, substantially all the cooling after the carbonization may be performed using one or more flash reactors (310, 320, 330), of which a last one is configured to operate in an atmospheric pressure. In particular, a heat exchanger 620 is not 15 needed for cooling in such a case. Thus, an embodiment comprises at least one flash reactor (310, 320, 330) and the system does not comprise a heat exchanger 620 configured to cool the carbonized feedstock by indirect heat transfer in between a flash reactor (310, 320, 330) and the dewatering apparatus 500. More precisely, in an embodiment, the system does not 20 comprise a heat exchanger 620 configured to cool the carbonized feedstock by indirect heat transfer of heat to a liquid, such as water, in between a flash reactor (310, 320, 330) and the dewatering apparatus 500. Herein indirect heat transfer refers to heat transfer through a wall of a heat exchanger 620. Such a wall is typically made of metal, and may be e.g. a wall of a pipe.

Referring to Fig. 9, in another embodiment, threads 522 are arranged on an inner surface of the tubular shell 530 of a screw press 505. Thus, in this embodiment, the tubular shell 530 forms a threaded part. A wall 518 of the tubular shell 530 may be water permeable. Inside the tubular shell 530, a cone 30 520 that tapers towards the inlet end 512 has been arranged. A wall 519 or a surface 519 of the cone 520 may be water permeable. In between the cone 520 and the tubular shell 530 a channel 516 that tapers towards the outlet end 514 has been arranged. By rotation of the tubular shell 530, the threads 522 thereof convey the feedstock towards the outlet end 514, whereby water is 35 squeezed out from the feedstock. Rotation of the tubular shell 530 is indicated by an arrow on the left hand side of the screw press 505 of Fig. 9. As indicated

20185713 prh 29 -08- 2018 above, at least one of the walls 518, 519 (preferably at least the wall 518 of the shell 530) is water permeable.

Referring to Fig. 10, in another embodiment, threads 522 are arranged on an 5 screw 520. The body of the screw 520 has a substantially constant diameter.

The body of the screw 520 has a wall 519 or a surface 519, which may be water permeable. Moreover, the outer shell 532 has a shape that tapers towards the outlet end 514. In between the outer shell 532 and the screw 520 a channel 516 that tapers towards the outlet end 514 has been arranged. A 10 wall 518 of the outer shell 532 may be water permeable. By rotation of the screw 520, the threads 522 thereof convey the feedstock towards the outlet end 514, whereby water is squeezed out from the feedstock.

In an embodiment, the carbonized feedstock is dewatered with the dewatering 15 apparatus 510 suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C to produce dewatered carbonized material with a dry-matter content of at least 40 % by weight.

As is evident, dewatering apparatus 510 suitable for dewatering the 20 carbonized feedstock mechanically at a temperature of at least 100 °C, such as a screw press 505, may be used in connection with the embodiments of Figs. 1a, 1b, 2, and 3 to 6. However, due to the heat exchanger 620 of Fig. 2, in the alternative, a conventional filter may be used as the dewatering apparatus 500. Thus, an embodiment of the system comprises one or more 25 pre-heating vessels (210, 220, 230) configured to pre-heat the feedstock before the carbonization reactor arrangement 100 by using steam from at least one of the flash reactors (310, 320, 330). Moreover, such an embodiment comprises a pipeline or pipelines (410, 420, 430) for conveying steam from the one or more flash reactors (310, 320, 330) to the one or more pre-heating 30 vessels (210, 220, 230). Therefore, an embodiment comprises using the steam produced the lowering a pressure of the hydrothermally carbonized feedstock (which may take place in a flash reactor) to pre-heat the feedstock, which contains carbon, before carbonizing the feedstock. In other words, the steam produced the lowering a pressure of the hydrothermally carbonized feedstock 35 is used upstream from the carbonizing (e.g. the carbonization reactor arrangement 100) to pre-heat the feedstock, which contains carbon.

20185713 prh 29 -08- 2018

Typically the feedstock cools down to some extent in the dewatering apparatus 510 suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C. Thus, the feedstock may be further dried after the dewatering apparatus 510. For these reasons, an embodiment of the 5 dewatering apparatus arrangement 500 comprises a secondary dryer 515 arranged downstream from the dewatering apparatus 510 suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C. This is indicated e.g. in Fig. 4. The secondary drier 515 may comprise e.g. a filter. Even if not shown, the dewatering apparatus arrangement 500 of 10 Figs. 1a, 1b, 3, 5, 6, 7a, and 7b could comprise a secondary drier 515 downstream from the dewatering apparatus 510 suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C.

Referring to Figs. 7b, 3, and 2, the water that is obtained from the dewatering 15 apparatus 500 as a result of dewatering the carbonized feedstock may be recycled back to the process. In particular, as indicated in Figs. 7b and 3, the water that is obtained from the dewatering apparatus 510 suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C may be recycled back to the process. Preferably, the water is recycled 20 to a point upstream from the carbonization reactor arrangement 100. As an example, in Fig. 3, the water that is obtained from the dewatering apparatus 510 is recycled upstream of both the pre-heating vessels 210, 220. The water is conveyed through the pipeline 632 to the channel 610, where it becomes mixed with the feedstock, and becomes fed into the secondary pre-heating 25 vessel 220. As another example, the system of Fig. 7b comprises a mixing tank 630, from which the feedstock is fed to the carbonization reactor arrangement 100 via the channel 610. Such a mixing tank could be used in connection with the embodiments of Figs. 1, 3, 4, 5, or 7, whereby the feedstock would be fed from the mixing tank 630 to a pre-heating vessel 210, 30 220, 230, preferably to that pre-heating vessel that is arranged most upstream.

The mixing tank 630 is configured to receive dry or substantially dry feedstock through the channel 605. The mixing tank 630 is configured to receive water from the dewatering apparatus 510 through the pipeline 632. In the mixing tank 630, the feedstock is moistened to properly decrease the viscosity of the 35 feedstock. Also water from other sources can be used to moisten the feedstock in the mixing tank 630. With reference to Fig. 7b, in an embodiment, the system comprises a pipeline 632 configured to convey water from the dewatering apparatus 510 to a point upstream from the carbonization reactor arrangement 100. Correspondingly, in an embodiment of the method, water obtained from the dewatering apparatus 510 is recycled back to the process, upstream from 5 the carbonizing (i.e. upstream from the carbonization reactor arrangement 100). With reference to Figs. 2 and 3, in an embodiment, the system comprises a pipeline 632 configured to convey water from the dewatering apparatus 500, 510 to a point upstream from the primary pre-heating vessel 210. Correspondingly, in an embodiment of the method, water obtained from the 10 dewatering apparatus 500, 510 is recycled back to the process, upstream from the pre-heating (i.e. upstream from the primary pre-heating vessel 210 or the pre-heating vessel 220, 230 that is arranged most upstream).

Claims (15)

1. Claims:

   1. A system for hydrothermal carbonization of feedstock that contains carbon, the system comprising

   5 - a carbonization reactor arrangement (100) configured to • receive the feedstock, which contains carbon • carbonize the feedstock hydrothermally, and • let out hydrothermally carbonized feedstock, and

   - a dewatering apparatus (510) that is configured to receive the carbonized 10 feedstock having a first moisture content and to produce dewatered carbonized material having a second moisture content that is lower than the first moisture content, wherein

   - the dewatering apparatus (510) is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C.
2. 2. The system of claim 1, wherein the dewatering apparatus (510) comprises a screw press (505) comprising

   - an inlet end (512) and an outlet end (514),

   - a channel (516), along which the feedstock is arranged to move from the inlet 20 end (512) to the outlet end (514), wherein • the channel (516) tapers towards the outlet (514) end and • a wall (518, 519) of the channel (516) is water permeable, and

   - means for transferring the feedstock from the inlet end (512) to the outlet end (514) along the channel (516), whereby the tapering channel (516) and the

   25 water permeable wall (518, 519) are configured to squeeze water out of the feedstock.
3. 3. The system of claim 2, wherein the screw press (505) comprises

   - a threaded part (520, 530) having threads (522), the threaded part (520, 530) 30 configured to transfer the feedstock from the inlet end (512) to the outlet end (514) along the channel (516) upon rotation and

   - an actuator (540) configured to rotate the threaded part (520, 530).
4. 4. The system of any of the claims 1 to 3, wherein the dewatering apparatus

   35 (510) comprises a centrifuge.

   20185713 prh 29 -08- 2018
5. 5. The system of any of the claims 1 to 4 comprising

   - a pipeline (632) configured to convey water from the dewatering apparatus (510) to a point upstream from the carbonization reactor arrangement (100).

   5
6. 6. The system of any of the claims 1 to 5, comprising

   - one or more flash reactors (310, 320, 330) for letting out steam from the carbonized feedstock, thereby cooling the carbonized feedstock, wherein

   - the dewatering apparatus (510) is arranged downstream from the one or more flash reactors (310, 320, 330).
7. 7. The system of the claim 6, comprising

   - one or more pre-heating vessels (210, 220, 230) configured to pre-heat the feedstock before the carbonization reactor arrangement (100) by using steam obtainable from at least one of the flash reactors (310, 320, 330), and

   15 - a pipeline or pipelines (410, 420, 430) for conveying steam from the one or more flash reactors (310, 320, 330) to the one or more pre-heating vessels (210, 220, 230).
8. 8. Use of a dewatering apparatus (510) suitable for dewatering material 20 mechanically at a temperature of at least 100 °C to dewater carbonized feedstock obtained from hydrothermal carbonization of feedstock that contains carbon.
9. 9. A method for treating feedstock that contains carbon, the method comprising

   25 - receiving the feedstock, which contains carbon,

   - carbonizing the feedstock hydrothermally to produce carbonized feedstock, and

   - dewatering the carbonized feedstock mechanically at a temperature of at least 80 °C.
10. 10. The method of claim 9, comprising

    - dewatering the carbonized feedstock with a dewatering apparatus (510) that is suitable for dewatering the carbonized feedstock mechanically at a temperature of at least 100 °C, such as a screw press (505).

    20185713 prh 29 -08- 2018
11. 11. The method of the claim 10, wherein

    - the dewatering apparatus (510) comprises a screw press (505), the method comprising

    - conveying the carbonized feedstock from an inlet end (512) of the screw 5 press (505) to an outlet end (514) of the screw press (505) along a channel (516) that • is limited by water permeable wall (518, 519) and • has a shape that tapers toward the outlet end (514), thereby

    - squeezing water out of the carbonized feedstock in the channel (516);

    10 preferably,

    - the carbonized feedstock is conveyed in the channel (516) by rotating a threaded part (520, 530), such as a screw (520).
12. 12. The method of the claim 10 or 11, comprising

    15 - recycling water obtained from the dewatering apparatus (510, 505) back to the process, upstream from the carbonizing.
13. 13. The method of any of the claims 9 to 12, comprising

    - before the dewatering, lowering a pressure of the hydrothermally carbonized 20 feedstock to produce steam and to cool the hydrothermally carbonized feedstock.
14. 14. The method of claim 13, comprising

    - using said steam to pre-heat the feedstock, which contains carbon, before 25 carbonizing the feedstock.
15. 15. The method of any of the claims 9 to 14, wherein the feedstock has a carbon content of more than 40 wt % as measured from the dry matter of the feedstock;

    30 for example, the feedstock comprises at least one of

    - wood material, such as sawdust, wood chip, or bark;

    - lignin;

    - lignocellulosic materials, such as cellulose, hemicellulose and/or lignin, or processed lignocellulosic materials, such as black liquor;

    35 - peat;

    - coal;

    - waste material, such as waste of animal and/or fish industry, municipal waste, industrial waste or by-products, agricultural waste or byproducts, waste or byproducts of wood-processing industry, waste or by-products of food industry.