WO2008113309A1 - Method for the wet-chemical transformation of biomass by hydrothermal carbonization - Google Patents

Abstract

The present invention relates to a method for the conversion of biomass into solid matter having higher energy density, particularly into coal, humus or peat. Using said method, organic matter is reduced in water from the biomass by forming a suspension and part of the suspension to be converted is heated to a reaction temperature and is converted under elevated pressure by hydrothermal carbonization into the solid matter having higher energy density. The method is characterized in that the conversion takes place in a reaction volume that is below the surface of the earth. The method ensures consistency of product quality and greater economic efficiency of the process.

Description

 Process for wet-chemical conversion of biomass by hydrothermal carbonation

Technical Field The present invention relates to a process for the conversion of biomass into higher energy density solids, in particular coal, humus or peat, in which organic matter from the biomass is slurried to form a suspension in water and at least one part of the suspension to be converted heated to a reaction temperature and converted at elevated pressure by hydrothermal carbonation in the solids of higher energy density. The organic substances may, for example, be plant parts, other biomass or organic waste.

PRIOR ART The conversion of biomass into products which have a higher mass-specific energy content in comparison with the biomass used, such as, for example, oil, gas or coal, is becoming increasingly important.

Known methods include the production of gas and / or oil and carbon at high temperatures, for example by pyrolysis, gasification or charring. In this context, many catalysts are used, the reaction accelerate and positively influence the product composition.

More recently, wet-chemical processes such as hydrothermal carbonation are being discussed for the recovery of products that have a higher mass-specific energy content compared to the biomass used. Here, plant parts or other organic substances are crushed, slurried in water and usually added with at least one conversion-supporting substance, for example with acid and / or an additional organic or inorganic catalyst. The suspension is filled in a reactor and the reactor is closed. After that, the

Suspension heated to a temperature between 170 ⁰ C and 250 ⁰ C. Since the reactor is closed, due to the partial pressure of water vapor, the pressure increases with increasing temperature. Depending on the temperature, the pressure increases to values of 10 * 10 ⁵ to 20 * 10 ⁵ Pa (10 to 20 bar) or higher. In the course of the hydrothermal carbonation reaction, hydrogen and oxygen in the form of water are split off from the carbohydrates contained in the biomass in several stages, whereby energy is released. The longer the reaction lasts, the more water is already split off and the energy density of the products continues to increase. Among other things, it produces solids such as peat, humus, lignite, hard coal or other substances that have a significantly higher mass-specific energy content compared to the biomass used. Depending on the concentration and structure of the ingredients, especially the carbohydrates (eg sugar, starch, celluloses, hemi-celluloses or others), in various raw materials, different plants and parts of plants, residues from food production, sewage sludge or other biogenic materials and waste, the Reaction faster or slower. Depending on the properties and the concentration of the biogenic raw materials used, more or less heat is released per unit of time

Temperature and pressure in the reactor increase faster or slower and different absolute values of pressure and temperature are achieved. In the course of the reaction, as less and less biogenic material is available for the reaction, the reaction slows down considerably. The temperature drops again until the reaction comes to a halt after a certain time due to too low a temperature. This may result in incomplete conversion of the material used, which may require a reaction time of several hours to several days or more. However, reheating the reactor from the outside to extend the reaction times requires an additional energy input, which can make the carbonization uneconomical.

The coupling of temperature and pressure in this reaction and the different reaction rates of different raw materials used mean that the temperature and pressure profiles during the reaction, depending on the composition and concentration of the biomass in the input stream of the hydro- thermal carbonation are very different. The products thus obtained can therefore differ greatly in their composition. As a result, the products may not be of consistent quality and high yields, which may render the hydrothermal carbonization uneconomical.

The object of the present invention is to provide a process for the conversion of biomass into higher energy density solids by hydrothermal carbonation, with which a more uniform quality of the products is achieved and the efficiency of the process is increased.

Presentation of the invention

The object is achieved by the method according to patent claim 1. Advantageous embodiments of the method are the subject of the dependent claims or can be found in the following description and the embodiment.

In the process of converting biomass to higher energy and carbon solids, such as coal, humus or peat, organic matter from the biomass is slurried to form a suspension in water. In a preferred embodiment is in the water a

Conversion supportive substance or is added to the water or the suspension. The material that supports the conversion may be for example, an acid and / or an organic or inorganic substance which accelerates the reaction. The biomass may be, for example, organic waste, plant parts, wood, algae or other organic carbonaceous products. At least one part of the suspension to be converted is heated to a reaction temperature and converted at elevated pressure by means of hydrothermal carbonization into the solids of higher energy density. The method is characterized in that the conversion is carried out in a reaction volume which is located below the surface of the earth.

Preferably, the reaction volume to

Buffering of liberated heat of reaction in a radius corresponding to at least 4 times the mean diameter of the reaction volume, surrounded by a mass of compact liquid and / or solid material which is greater than eight times the mass of the suspension in the reaction volume. Above this mass, a good homogenization of the product properties is already observed.

In the proposed method finds the

Reaction thus below the earth's surface instead. Earth's surface is understood to be the boundary layer between the solid earth crust or the waters on the one side and the atmosphere on the other side. In the process below the earth's surface with a sufficient amount of compact, liquid and / or solid material around the reaction volume around even with fluctuating biomass concentration and Compound energy-rich and carbon-rich products are produced, which have a much more uniform composition, than products which are prepared in the known manner in a reactor above the surface.

By shifting the reaction space below the earth's surface with the surrounding material, such as. Rock, sand, water or soil, this material can be a large part of the reaction in the

In the beginning stage, released energy in the form of heat absorb. By taking place with the surrounding mass heat exchange, the temperature in the reaction volume or reaction mixture increases more slowly and not as far as in a reactor above the

Earth surface, the pressure also does not vary so much. As a result, the reaction does not start so quickly and more evenly at the beginning. When the concentration of convertible biomass constituents decreases over time, the temperature falls within

Reaction volume, on the other hand, does not decrease as quickly as in the case of the previous known process control. Rather, the surrounding material then slowly releases the stored heat back to the reaction volume. The reaction volume thus remains much longer warm and the reaction can be continued without additional heating of the suspension over many hours or even days, until even different raw materials are converted to comparable products with higher energy density. Preferably that stands

Reaction volume here at least in places in direct contact with the surrounding compact material. A further advantage of the proposed method is that new biomass can be supplied by the return of heat from the surrounding material into the reaction volume even after removal of the products and can be reacted without external heating or at least without strong additional heating. This allows in many cases the carbonization of several batches in a row without external supply of heat. Basically, the method thus allows both a continuous supply of biomass and a batch operation. As a result, the throughput in the process of the invention can be varied very greatly due to the heat buffering of the surrounding soil or water, without sacrificing the uniformity of the product quality.

The process must be carried out in an area below the earth's surface in which a sufficient mass of surrounding material is available for the thermal buffering. Preferably, the material should in this case be constructed so compact that it has a total mass in the vicinity of four times the mean diameter of the reaction volume, which corresponds to at least eight times the mass contained in the reaction volume. Based on a cylindrical reaction volume of a diameter D and a height H, this means that a cylindrical volume with the same height and four times the diameter minus the cylindrical reaction volume should contain at least eight times the mass of the reaction volume filled with the suspension contains in order to achieve a particularly good heat buffering for the proposed method.

The surrounding material, such as soil, loam, sand or water, is able to at least partially compensate for and absorb the pressure resulting from the reaction due to the pressure prevailing below the earth's surface. A reactor used for the hydrothermal carbonization can therefore be made significantly thinner walled for use under the earth's surface than when used above the earth's surface. This saves additional costs. In a particularly simple reactor design, this reactor may, for example, consist of steel, which in concrete or reinforced concrete in a cavity under the

Earth's surface is embedded. Due to the concrete cover there is a very good heat transfer into the surrounding material. The wall of this reactor can be made very thin-walled.

Furthermore, the wall of the cavity can be used as a reactor wall. If necessary, this cavity can be additionally lined with waterproof materials. Such a lining can also be achieved by synthetic additives in the water. An automatic seal by the reaction products of the process, such as. Carbon particles, may u.U. take place opposite the surrounding rock.

The product composition can also be made uniform as the pressure increases above the pressure corresponding to the reaction temperature becomes. Due to the additional application of a pressure in the reaction volume, the pressure also increases during the entire reaction and then decreases again, but the percentage relative pressure fluctuations are smaller. It is particularly advantageous if the pressure in the reaction volume is kept constant or at least largely constant by technical measures. These measures decouple temperature and pressure from each other. The operator of the hydrothermal carbonation is thus able to choose the pressure according to the composition of the input so that the homogenization of the product quality is improved. When applying an additional pressure not only the composition of the final product can be made uniform. Rather, depending on the input material, the yield of solid products with high energy density can be increased by the increased pressure, so that the process can be operated even more economically. The operator has with the additional pressure build-up a valuable

Depending on the requirements and composition of the input material, a targeted change and thus an optimization of the product quality or the yield is possible.

The additional pressure build-up, in addition to various other mechanical methods z. B. also be achieved in that the reaction volume is displaced sufficiently deep into the soil. The location of the reaction volume is chosen so deep that a water column located above the reaction volume, which is needed for the supply and removal of the suspension, a hydrostatic pressure in the reaction volume which is higher than the equilibrium pressure which would be set at the reaction temperature in a gas-tight reactor filled with the suspension. When constructing such a hydrostatic pressure, it is also very easy to maintain a constant pressure. It only has to be ensured that a liquid inlet or outlet is possible on the surface of the water column. This can, for example. Through openings or by using non-sealing pumps such as.

Centrifugal pumps are possible. With a temperature increase in the reaction volume, liquid can then escape at the surface and the pressure in the reaction volume remains largely constant. The water column is used as a pressure buffer. The reaction conditions are thereby made uniform and the solids yield can be additionally increased.

Particular advantages arise when the reaction volume is formed with a greater width than height. Thus, in hydrostatic pressure generation, an approximately equal pressure is generated at all points in the reaction volume, whereby the homogenization of the reaction conditions is additionally supported. This formation of the reaction volume can be achieved by introducing into horizontally extending shafts, for example. Kohleschächte.

In a particularly advantageous embodiment for generating the hydrostatic pressure, a height difference of at least 100 m is selected between the upper fill level and the reaction volume. In order to In the reaction volume due to the water column located above it, a pressure of more than 10 * 10 ⁵ Pa (10 bar). Larger differences in height of 200 m or more allow the setting of higher pressures, which can be very advantageous depending on the requirement.

In a very advantageous embodiment, the reactor is designed such that the inlet and outlet openings are arranged at the same height or at least, compared to the total reactor height, at a similar height, so that a hydrostatic pressure difference between the openings does not account for 10% of the pressure exceeds. The pumps used then do not have to overcome high pressure differences and can thus be made very simple and inexpensive.

In addition to the use of a rigid reactor, it is also possible to design the outer wall of the reactor flexible, so that it conforms to the inner wall of the cavity or at least serves only as a barrier to the surrounding rock or water. It is also particularly advantageous to use thin sheets or metal foils which have a high temperature resistance in comparison to other materials.

An advantage of the pressure build-up by the hydrostatic pressure in the reactor is that the pressure increases evenly with increasing depth. The

Reaction does not start abruptly and spontaneously but slowly and evenly with increasing pressure and temperature. By varying the funding speed and the relative borehole diameter in the case of a borehole as a cavity, the residence time can be set specifically and thus adapted to the respective raw material. It is useful to have cooling water connections at regular intervals over the height and volume of the reactor to introduce cold water and slow down the reaction when needed. This can be used to avoid overheating of the reaction and to use the heated water energetically. This process can also be done via to be installed in the reactor heat exchanger.

When setting long residence times in the reactor, it may happen that the flow rate must be throttled to such an extent that the particles in the suspension sediment faster than the suspension flows. To avoid blockages in the reactor different strategies are useful.

Thus, mixing elements, flow plates, static mixers, stirrers or other flow-influencing devices can be incorporated into the reactor to limit the sedimentation of solids. Particularly advantageous gases such as compressed air can be introduced into the reactor, which cause a mixing. It is also possible to achieve gas formation by partial evaporation of the water in the suspension. The turbulences that arise in this case lead to a good mixing and to avoid blockages. Targeted evaporation of some of the water can also be used to deflate the reactor after completion of the reaction. This can be done by pumping in the inlet or outlet befindlichem

Water is carried out a pressure reduction in the reaction volume and a spontaneous evaporation in the reaction chamber can be achieved. By this evaporation process, which is similar to a boiling delay, so much mass is transported out of the reaction space in a very short time that due to the very high flow velocities occurring sedimented or deposited solids and deposits are conveyed to the surface.

To increase the flow velocity in the reactor, the flow cross sections can be reduced so far that a critical flow velocity is exceeded. It is also possible to run a cascade in galleries underground

Rührreaktoren to build and surrounded by soil, rock or water, which are flowed through in series. In this form, they are very inexpensive to manufacture and allow a quick flow.

Clogging of the reactor can also be avoided if the flow direction is reversed at regular intervals and thus a type of pulsation is achieved, which is superimposed on a constant flow velocity. This pulsation leads to turbulence in the reactor and thus prevents deposits very efficiently. To avoid impurities in the reaction space as far as possible, it is advantageous to free the suspension of impurities such as stones, metal, glass or similar inorganic materials before the reaction with the aid of a mechanical device. This may be gravitational separation, such as a clarifier in sewage treatment plants, or a hydrocyclone or other method known in the art for separating solids from suspensions.

Furthermore, particles that are prone to sedimentation can be selectively removed from the reactor. To this end, devices may be introduced into the reactor which will batch or continuously convey sedimented solids from the reactor with prior art aggregates (e.g., conveyors, scrapers, chains, screws, pumps). These solids can be fractionated outside the reactor, so that coarse organic materials can be returned to the reaction space after a corresponding comminution.

It may be desirable to remove gases or vapors which arise due to the pressure drop in the upward flowed through part of the reactor from the reactor. This can be achieved by a perforation of the reactor wall, for example in the upstream part of the reactor. These holes may be provided to the environment or to the downstream portion of the reactor. This ensures pressure equalization. As a derivative of the gas You can also use rugged or karst rock formations.

If a rapid escape of the gases or liquid volume due to temperature-density differences (geyser effect) are avoided, appropriate pressure valves or check valves are attached, close when exceeding a defined pressure or a defined flow rate, thereby causing a pressure increase in the short term and the End the degassing process. This targeted convection currents can be prevented.

In a particularly simple embodiment, the reactor consists only of a cavity present in deeper rock layers, wherein the feed of the reaction mixture is conveyed through a feed line to a depth sufficient for the reaction. Particularly advantageous is e.g. the use of old production shafts from mining, shut down tunnels or other underground structures. Here, the existing lining of the shafts or tunnels can be used as a "reactor wall" and the entire volume of the shaft as a reactor In addition to a lining of the shaft with watertight materials, a

Sealing of the system can be achieved by additives in the water or the system seals itself by the reaction products such as coal particles against the surrounding rock itself.

When using holes in the ground, an inlet or outlet must be provided in the lower part of the reactor. Through an inlet or outlet channel in the lower portion of the shaft or hole, the cross-sectional area and flow rate can be variably adjusted, an upward flow is set over the entire remaining shaft cross-section. The area ratio of upflowed reactor space and upflowed reactor part can be up to 99.99% depending on the requirement of 0.01%. Heat exchangers for cooling or heating, which can be arranged in the shaft, are used for temperature and reaction control and thus the

Ensuring the product quality as well as the energy dissipation and thus the energetic use outside the reactor.

It may also be desirable to recycle the product stream from depth deeper into a location similar to geothermal energy than at the point of raw material injection. For example, horizontally extending coal shafts, formerly used as underground mining areas and now shut down, can be used as reaction volumes. In this way, the raw material suspension can be introduced into shafts via outlying areas, and all input streams from the production well can be conveyed centrally from deep within, or vice versa. Thus, existing wells can be used almost completely as "reactors" for the production of biogenic fuels, thus providing tens of thousands of cubic meters of volume as a reactor so that very high throughputs can be achieved despite the long residence time of the reaction underground caverns filled with gas or water, caverns, caves, karstic and use porous rock formations or tunnels filled with water as reactors. One skilled in the geology field will be able to identify suitable cavities that can be stowed with water and used as reactors for the described process.

Particularly advantageous here will always be the use of geothermal energy at greater depths for reaction support. It may also be useful to co-use residual deposits of coal or oil. Here, it is possible, parallel to the reaction of the biomass from oil deposits that have already become uneconomical for production, to promote the remaining reserves so to speak as a by-product. For example, the volume of the deposit can be used as a reactor and any remaining deposits of fossil raw materials can be meaningfully recycled. Due to the high reaction temperature, oils in the rocks become fluid, so that the residual deposits can be extracted from the deep very efficiently.

It is advantageous for the water used for the suspension to be completely or partially recirculated for the complete utilization of raw materials. For this purpose, it is necessary to separate the desired reaction product, such as coal particles from the suspension and remaining substrates, unreacted raw materials and reaction products such as phenols or other secondary products to promote together with new crushed biogenic raw material back into the reaction space. The skilled person is aware that a concentration of minerals or unreactable Shares must be avoided. This can be done by a correspondingly dimensioned bleed current.

For the separation of the carbon particles also provide procedural approaches such as secondary clarifier, decanters, filter presses or Brikettieranlagen.

Another way to implement this invention is seen in the submarine region. Here, for example, simple thin-walled pipelines can be routed as reactors into great depths into the sea. However, it may also be advantageous to introduce the reaction mixture directly into deep layers of lakes or into deep ocean layers and thus whole areas of the sea, such as e.g. Coastal areas with great depth of sea to be used as reactors. In this case it is particularly advantageous to resort to areas in the ocean which are particularly hot due to volcanic activity, such as e.g. some regions in the Pacific. The upward flow of hot submarine sources may then be used to promote the reaction products, e.g. the coal be used.

The described method brings additional advantages when operated in combination with geothermal energy. Thus, energy is added to the reaction mixture in warmer areas in the soil, the reaction mixture is additionally heated and the reaction is thus accelerated. The additional energy released can then be used in the prior art by dissipating the heat or by transformation into electricity or hydrogen. The carbon-rich reaction products are in many cases present as finely dispersed nanospheres. This fact can be used to promote solid energy very beneficial. Thus, after the exit of the energy carrier suspension from the reactor, first a mechanical separation of the solids from the liquid takes place, for example by centrifugal separation processes. The liquid fraction containing the amino acids and minerals from the organic raw material can be used as fertilizer directly or after concentration by partial separation of the water. The nanoparticulate solids, which consist predominantly of carbon, are again mixed with water and adjusted to a dry matter content of 40 to 60% by mass. Thus, an energy density of up to 18 gigajoules per tonne can be set in the suspension, which corresponds to about half the energy density of crude oil. A transport of the nanoparticulate

Energy carriers over long distances are extremely economical in this form by pipelines known in the art.

Viscosity plays a crucial role in avoiding sedimentation effects and separating the coal from the liquid phase. To avoid too rapid sedimentation of the biogenic raw materials, the viscosity of the suspension in the feed of the reactor should be at least 20 mPas

(measured in the rotational viscometer at a shear rate of 10 / s). In the course of the reactor, for improved separation of the particulate solids, the liquid phase should not exceed values of 5 mPas.

To adjust the viscosity in the feed, various methods are available to the person skilled in the art. Thus, the targeted use of different biomasses, biomass with defined carbohydrates (cellulose, starch, oligosaccharides or monosaccharides), their degree of comminution, concentration and over the duration of the carbohydrates increased viscosity can be adjusted. The parameters described and the choice of raw materials are to be varied in such a way that after the reaction the liquid phase has a correspondingly low viscosity due to the degradation and the conversion of the biomass.

In a further advantageous embodiment of the method according to the invention, the promotion of biomass or reaction suspension takes place in depth in vessels or containers such as containers, barrels, baskets, sacks, cylindrical or cuboid vessels made of different materials or in similar spatially defined volumes in the interior of the under Earth attached reactor.

Due to the high heat capacity of the soil and the liquid in the reactor, the containers or vessels are sufficiently heated in the reactor, so that the reaction can take place inside the container, without discharging the biomass from the containers.

By this measure can be avoided very efficiently that particles from the suspension on the ground sediment the reactor and can no longer be discharged from this. In the described embodiment of the closed or semi-open container, it is also possible to adjust the particle size variable or to dispense with a fine comminution before carrying out the reaction. Thus, larger particles such as pieces of wood can be conveyed into the reactor. This allows carbon particles with several cm edge length to be obtained, which can facilitate the separation of the water from the coal after completion of the reaction.

When carrying out the process in containers, it is important to ensure pressure equalization with the surrounding water. So must through openings or

Ensure that valves in the containers that depending on the depth of the pressure in the reactor can be transferred to the interior of the container.

It may also be advantageous to allow a liquid exchange from the container with the surrounding liquid through suitable openings in the containers. In this case, the heat transfer is improved into the interior of the container and also allows the transition of liquid reaction products and non-suspended fine particles from the containers in the surrounding liquid and thus in other containers. Thus, despite a very efficient avoidance of sedimentation effects and blockages in the reactor, an exchange of the temperature, of

Liquid and reaction products between the containers, resulting in a faster response and to a homogenization of the product composition leads.

The promotion of the containers through the reaction space can be carried out in a displacement promotion, similar to the procedure in the case of tower heaters in the food industry, which are used for heating cans. Each container pushes the next container in the tubular reaction space on. It is also possible to use conveyors for containers of the prior art, such as e.g. Chain conveyors, screws, cables or other devices for transporting vessels through pipelines. The transport of the containers through the shaft or reaction cavities can also be carried out in a similar way to other transport

Mining devices by cables or in a kind of "underwater railroad" done on rails.

It is possible to generate spatially defined reaction volumes by

Reactor areas are separated by locks, sheets or other internals or that so-called. Pigging, which cause a substantial sealing of the reactor cross-section and are moved with the flow are used as partitions between individual reactor sections. Due to this multi-chamber design of the reaction space, different process conditions such as temperatures can be set in each segment, which facilitates process control. Brief description of the drawings

The proposed method will be briefly explained again with reference to an embodiment in conjunction with the drawings. Hereby show:

1 shows an example of the arrangement of the reaction volume below the earth's surface; and

Fig. 2 is a schematic representation of the process flow in the proposed

Method.

Ways to carry out the invention

Figure 1 shows schematically an example of an embodiment of a reactor for carrying out the present method, which is introduced in this example in a shaft 1 below the earth's surface. The shaft 1 is located at a depth of 200 m. The reactor 2 has an inlet 3 to the reaction volume, which in this case occupies the entire volume of the horizontally arranged reactor. The slurried biomass is pumped via this feed 3 in the reaction volume. The reaction products are pumped back up via the outlet 4. The wall of the reactor 2 can be made relatively thin, since the hydrostatically generated in this case pressure is absorbed by the surrounding soil 5. The reactor 2 is surrounded in a radius of soil 5, which corresponds to at least four times the diameter D of the reaction volume. There are no major cavities in this perimeter, so that the total mass in a volume occupied by the material in that perimeter is at least eightfold Mass of the reaction mixture in the reaction volume corresponds. The slurried biomass is first introduced into the reactor 2 at a temperature of about 80 ^° C. Due to the very violent exothermic reaction in the reaction volume at the beginning of the process, the suspension heats up to over 200 ⁰ C. The heat absorption and storage due to the large mass of the surrounding material means that there is no rapid overheating. In a later stage of the reaction, in which much less heat is generated, the reaction temperature is achieved by the heat given off by the surrounding material, so that the reaction can be maintained without external supply of energy over a longer period of time.

Figure 2 shows schematically the process flow again in a flow chart. The delivered from a farm biomass 6, which may be in a dry or wet state, is first crushed in a crushing and suspension step 7 and slurried in water. As additives, acids, organic or inorganic catalysts can be used. After heating the resulting suspension to about 80 ⁰ C, this is with a suitable pump in the deep shaft reactor 8, as shown schematically, for example, in Figure 1, promoted. In the reaction volume of this reactor, the exothermic reaction takes place, whereby in the first period of the process, a hot suspension of about 200 ⁰ C is discharged from the reactor containing water and carbon particles. The heat of this suspension is used in a conversion step 9 to electrical To generate energy. In a separation step 10, the separation of water and coal, so that finally pure coal 11 is available for energy production. The coal can be used, for example, as a raw material for liquid hydrocarbon-rich fuels. In which

Separation step 10, a fraction of water with dissolved minerals and amino acids is obtained. The minerals and amino acids are separated in step 12 and transported as fertilizer 13 back to the field. The water is reused in the crushing and suspension step 7.

LIST OF REFERENCE NUMBERS

I shaft 2 reactor

3 inlet

4 expiration

5 surrounding soil

6 biomass 7 crushing and suspension step

8 reactor

9 conversion into electrical energy

10 separation step

II Coal 12 Separation of minerals and amino acids from water

13 fertilizer

Claims

claims 1. A process for the conversion of biomass into solids of higher energy density, especially in coal, humus or peat, are slurried in the organic matter from the biomass to form a suspension in water and at least heated to be converted part of the suspension to a reaction temperature and is converted at elevated pressure by hydrothermal carbonization in the solids of higher energy density, characterized in that the conversion is carried out in a reaction volume, which is located below the surface of the earth. 2. The method according to claim 1, characterized in that the reaction volume for buffering released heat of reaction in a radius corresponding to at least a 4 times the mean diameter of the reaction volume is surrounded by a mass of compact liquid and / or solid material, the larger is eight times the mass contained in the reaction volume. 3. The method according to claim 1 or 2, characterized in that the conversion is carried out at a process pressure which is higher than an equilibrium pressure, which varies in the reaction Set temperature in a filled with the suspension gas-tight reactor. 4. The method according to claim 3, characterized in that the process pressure is generated hydrostatically by introducing the part of the suspension to be converted into a volume range of a filled with water or the suspension to an upper level volume, wherein between the upper level and the reaction volume forming volume range is a height difference of at least 100 m. 5. The method according to any one of claims 1 to 4, characterized in that a cavity in the soil is used for the reaction volume, in particular a borehole or a shaft or shaft system, which is filled with water or the suspension. 6. The method according to any one of claims 1 to 4, characterized in that an area below the water surface of a sea or a lake is used for the reaction volume. 7. The method according to any one of claims 5 or 6, characterized in that at least one reactor is introduced into the cavity, the sea or the lake and filled with water or the suspension. 8. The method according to claim 7, characterized in that the reactor is formed with a flexible outer wall. 9. The method according to claim 7 or 8, characterized in that the reactor is introduced into a horizontal or inclined shaft and surrounded with water having a hydrostatic pressure with which a wall of the reactor is at least partially relieved of pressure in the reactor. 10. The method according to any one of claims 7 to 9, characterized in that the reactor is formed at least partially perforated to allow passage of gases. 11. The method according to any one of claims 5 to 10, characterized in that the reactor or cavity at different heights via cooling water supply lines controlled cold water is supplied to slow down the conversion in order to avoid overheating. 12. The method according to any one of claims 1 to 11, characterized in that the part to be converted of the suspension is pumped in a pumping direction through the reaction volume, wherein by repeated short-term reversal of the pumping direction, a pulsating flow of the part to be converted by the suspension the reaction volume is generated. 13. The method according to any one of claims 1 to 12, characterized in that turbulence in the reaction volume are generated in order to counteract a sedimentation of solids in the reaction volume. 14. The method according to any one of claims 1 to 13, characterized in that by circulating the suspension or by pumping used for cooling water or another cooling medium dissipated heat is used to generate electrical energy. 15. The method according to any one of claims 1 to 14, characterized in that cavities or locations are used for the conversion, in which geothermal contributes to increasing the temperature of the suspension to be converted. 16. The method according to any one of claims 1 to 15, characterized in that a cycle is formed, in which the solids of higher energy density separated after conversion from the suspension and a portion of the suspension is fed again to the reaction region. 17. The method according to any one of claims 1 to 16, characterized in that prior to introduction of the suspension in the Reaction volume heavy substances are separated from the suspension. 18. The method according to any one of claims 1 to 17, characterized in that in the water at least one conversion-supporting substance is contained or that at least one conversion-supporting substance is added to the water or the suspension. 19. The method according to any one of claims 1 to 18, characterized in that the viscosity of the reaction volume supplied to the suspension is adjusted so that it is at least 20 mPas. 20. The method according to any one of claims 1 to 19, characterized in that the viscosity of the reaction volume supplied suspension is adjusted so that a withdrawn from the reaction volume liquid phase does not exceed a viscosity of 5 mPas. 21. The method according to any one of claims 1 to 20, characterized in that the supply of the suspension to be converted takes place in containers which allow a transfer of a pressure exerted on the containers pressure on their contents, wherein the suspension to be converted remains during the conversion in the container , 22. Use of the solids of higher energy density produced by the method according to any one of claims 1 to 21 as a fuel or as a starting material for fuels, in particular for hydrocarbon-rich liquid fuels or fuels.