Method and system for production of biochar and energy from moist solid fuels

Abstract

Moist solid fuels can be converted into biochar and thermal energy with a low content of Perfluoroalkyl and polyfluoroalkyl substances (PFAS), volatile organic compounds (VOC's) and NOx by means of a stage-divided system where the conversion process of the solid fuel is in separate stages: drying, pyrolysis, gasification, gas-combustion and energy recovery. The energy recovery stage supply energy to the dryer and excess energy can be used for other purposes.

Description

[0001] METHOD AND SYSTEM FOR PRODUCTION OF BIOCHAR AND ENERGY FROM MOIST SOLID FUELS

[0002] The invention relates inter alia to a method and a system for using moist solid fuels to produce biochar and thermal energy. The biochar produced may have a low content of Perfluoroalkyl and polyfluoroalkyl substances (PFAS), volatile organic compounds (VOC's) and NOx by means of a process divided system where the conversion process of the solid fuel is carried out in: a dryer, a pyrolysis reactor, a gasification reactor, gas combustion reactor and energy recovery. The energy recovery stage supplies energy to the dryer and excess energy can be used for other purposes, such as local and / or district heating and / or process heat in general.

[0003] Reference is made to WO0168789A1 an invention that provides a method for decomposing moist fuel or combustible organic material, said method comprising heating the fuel at separate stages, including a drying stage, a pyrolysis stage to which steam is supplied, an oxidation stage, and a gasification and / or combustion stage, to temperatures causing the fuel to decompose into gaseous and solid components, the fuel at the various stages being at least mainly heated by means of the gases formed by the oxidation, gasification and / or combustion processes.

[0004] Reference is further made to EP1021499A1 an invention that provides a method for gasification of solid carbonaceous material. The gasification is performed in a circulating fluidised bed (CFB) gasifier which comprise a CFB reaction chamber, a particle separator for separation of char-containing particles from the outlet gas of the CFB reaction chamber, and a particle recirculation duct for recirculation of the separated particles to the CFB-reaction chamber. The particle recirculation duct comprises a char reaction chamber for gasification of char contained in the recirculating particles.

[0005] Reference is further made to WO 2007 / 036236 Al an invention that provides a method for recovering heat from hot gas produced in a thermal reactor, by injecting water into the gas at one or more injection zones in such an amount and in such a way that the gas temperature due to water evaporation is reduced to below 400°C, preferably below 300°C, possibly below 150 - 200°C, and the gas dew point becomes at least 60°C, preferably at least 70°C, possibly 80 or 85°C. The gas can then be led through a condensing heat exchanger unit, where at least some of the gas contents of water vapour are condensed, and the condensing heat can be utilized for heating of a stream of fluid, mainly water.

[0006] SUMMARY OF THE INVENTION

[0007] In a first aspect the invention relates to a method of converting, preferably moist, solid carbonaceous material into biochar and thermal energy, the method comprises drying said solid carbonaceous material in a dryer to produce a dried solid carbonaceous material and subsequently pyrolyzing and gasifying said dried solid carbonaceous material in a circulating fluidised bed reactor comprising a pyrolysis reactor and a gasification reactor. The method preferably comprises the steps of:

[0008] • feeding said solid carbonaceous material to said dryer to provide said dried solid carbonaceous material, and

[0009] • feeding said dried solid carbonaceous material to said pyrolysis reactor and pyrolyze said dried solid carbonaceous material to provide a pyrolysed carbonaceous solid material and a product gas comprising particle produced during said pyrolysis,

[0010] • feeding said pyrolysed carbonaceous material to said gasification reactor and gasify said pyrolyzed carbonaceous solid material to provide a gasified carbonaceous material, wherein said gasification is a carried out with addition of an oxygen-containing gasification agent,

[0011] • discharge of said product gas from the pyrolysis reactor, and separating a fraction of said particles from said product gas in a particle separator, such as a cyclone, to provide separated particles, and

[0012] • re-circulating said separated particles to said gasification reactor, wherein

[0013] • preferably, the temperature in said gasification reactor as determined in a fluidized bed of said fluidized bed reactor is below 800°C and higher than the temperature of pyrolysis reactor.

[0014] In preferred embodiments, the temperature in gasification reactor is controlled by controlling the amount of air - or in general oxygen - fed into the gasification reactor. The gasification produces heat by converting at least some of the solid carbon. The pyrolysis requires heat which is received from the gasification due to the use of a circulating fluidised bed reactor. In preferred embodiments, the conversion of carbon is controlled to provide a balance between produced heat in the gasification reactor and the required heat in the pyrolysis reactor to provide pyrolysis. This balance is preferably obtained by controlling the amount of air - or in general oxygen - fed into the gasification reactor. The gasification with oxygen is an exothermic process. By this, the otherwise need for e.g. heat exchangers and / or exchange heat with the surroundings has at least been mitigated.

[0015] The temperature in pyrolysis reactor is typically controlled by the amount of bed material fed from the gasification reactor to the pyrolysis reactor.

[0016] A gasified carbonaceous material as used herein typically refers to a gas comprising CO and / or CO2.

[0017] In a second aspect, the invention relates to a method of converting moist solid carbonaceous material into biochar and thermal energy, the method comprises drying said solid carbonaceous material in a dryer (1) to produce a dried solid carbonaceous material and subsequently pyrolyzing and gasifying said dried solid carbonaceous material in a circulating fluidised bed reactor (25) comprising a pyrolysis reactor and a gasification reactor, the method comprises the steps of:

[0018] • feeding said solid carbonaceous material to said dryer to provide said dried solid carbonaceous material, and

[0019] • feeding said dried solid carbonaceous material to said pyrolysis reactor and pyrolyze said dried solid carbonaceous material to provide a pyrolysed carbonaceous solid material and a product gas comprising particles produced during said pyrolysis,

[0020] • discharge of said product gas from the pyrolysis reactor, and separating a fraction of said particles from said product gas in a particle separator, such as a cyclone, to provide separated particles, and

[0021] • re-circulating said separated particles to said gasification reactor, and

[0022] • gasify said re-circulated separated particles to provide a gasified carbonaceous material, wherein said gasification is a carried out with addition of an oxygen-containing gasification agent, such as air, wherein

[0023] • the temperature in said gasification reactor as determined in a fluidized bed of said fluidized bed reactor is below 800°C and higher than the temperature of pyrolysis reactor.

[0024] In a third aspect, the invention relates to a system for drying solid carbonaceous material and subsequently gasification of said solid carbonaceous material in a circulating fluidised bed (CFB) gasification reactor, said system preferably comprising

[0025] • a dryer for drying said carbonaceous material

[0026] • a circulating fluidized bed reactor comprising a pyrolysis reactor and a gasification reactor, said pyrolysis reactor is configured for heating up said carbonaceous material by solids from the gasification reactor;

[0027] • a cyclone for recirculating particles from the pyrolysis reactor to the gasification reactor.

[0028] Preferably, said system is configured to carry out the method according to embodiment of the first aspect to convert moist solid carbonaceous material into gas and char.

[0029] Moist fuel as used herein preferably refers to a moist solid carbonaceous material having a water content. The water content is typically in an amount where at least a fraction of the water content is advantageously to be removed by drying prior to conversion into biochar and thermal energy. Fuel as used herein preferably refers to a solid carbonaceous material.

[0030] In some embodiments, the moist solid fuel comprising dewatered sludge from waste water treatment systems. Such sludge has until now at least to a larger extend been used as fertilizer on farm land, as the sludge contain phosphorus and other fertilizers.

[0031] However in recent years more and more harmful substances have been discovered in such sludge from waste water treatment systems, including heavy metals, leftover medicines and PFAS. Especially PFAS has got a lot of attention and many countries now ban to use sludge from waste water treatment systems as a fertilizer on farm land.

[0032] Preferred embodiments of the present invention can transform dewatered sludge from waste water treatment systems into Energy and a fertilizer containing phosphorus and bio-char.

[0033] In some embodiments, the moist solid fuel comprising dewatered digestate from biogas digestors: The costs of disposing dewatered digestate from biogas digestors is increasing because biogas digestors use more and fiber rich raw materials, such as straw, because the digestors can only convert about half of the organic material into gas.

[0034] More and more biogas systems includes a "gas upgrading" system where CO2 is removed from the biogas. The CO2 removal process require thermal energy.

[0035] The present invention may potentially reduce the cost of disposing dewatered digestate from biogas, utilize the full organic resource, reduce the cost of removing CO2 from the biogas and / or also produce a fertilizer with phosphorus and bio-char which can give a revenue to the biogas system owner.

[0036] In the following, a description of preferred fuels, preferred embodiments of drying, preferred embodiments of pyrolysis and gasification, preferred embodiment of gas combustion, preferred embodiments of gas cooling, preferred embodiments of filtration, preferred embodiments of flue gas condensing, preferred sizes of systems configured to carry out an embodiment of the invention, and typical turn-down ratios for systems configured to carry out an embodiment of the invention. Such preferred embodiments and fuels are nonlimiting to the invention.

[0037] Preferred Fuels

[0038] Solid carbonaceous material to be converted into biochar and thermal energy is also referred to herein as "fuel". In preferred embodiments, fuel may have a high water content such as above 40w / w%, which fuel is difficult to pyrolyze and gasify without drying. Such fuels may be:

[0039] • Dewatered sludge from waste water treatment systems

[0040] • Dewatered sludge from biogas digester

[0041] • Other fuels with high water content

[0042] In preferred embodiments, the fuel may have element sizes below 10cm or even less than 5cm or of even less than 2 cm. Element size typically refers to a unitary body of said fuel.

[0043] In preferred embodiments, the fuel may contain phosphorus, such as containing phosphorus in an amount higher than lg / kg fuel (dry basis). - which can be used as fertilizer if the temperature of the thermal conversion is below 800C. Typically, the fuel contains phosphorus and at least an amount of this phosphor ends up in the ash produced by a preferred method according to the invention. In preferred embodiments, the temperatures during the method is sufficiently low to prevent encapsulation of phosphorus whereby phosphorus is readily available for plants.

[0044] In preferred embodiments, the fuel may contain chlorine and / or potassium. The amount of chlorine may be higher than lg / kg fuel (dry basis) and the amount of potassium may be higher than 4g / kg fuel (dry basis).

[0045] In preferred embodiments, the fuel contains harmful substances such as perfluoroalkyl and polyfluoroalkyl (PFAS), medicinal residues, and / or heavy metals. In preferred embodiments, such harmful substances may be evaporated (typically after being decomposed into non-harmful substances, e.g. water vapor and / or CO2) and / or destroyed and / or captured in a system according to the present invention.

[0046] Preferred embodiments of drying

[0047] In preferred embodiment, drying of moist fuels is typically carried by use of hot air and / or flue gas preferably with a certain amount of O2, typically more than 15%v / v, whereby an exhaust gas from the dryer typically have certain content of O2, normally more than 10%v / v. Alternatively, drying can be carried with minimal content of O2 in the dryer. In such embodiments, thermal energy is added to fuel in the dryer and the water in the fuel evaporates and water vapours leave the dryer with low 02%v / v in the vapour.

[0048] Preferred embodiments of pyrolysis and gasification

[0049] In preferred embodiments, pyrolysis and gasification of solid carbonaceous material is typically done in

[0050] • one or more moving-bed reactors. Such moving-bed reactor(s) may be an updraft (air / gas goes up and fuel down), a downdraft (air and fuel go down) or grate / stoker-based system (moving grate, vibrating grate, stoker) where fuel moves horizontally (often with a slope downwards). and / or

[0051] • one or more fluid-bed reactors. Such fluid-bed reactor(s) may be a bubbling fluid bed (BFB), a circulating fluid bed (CFB) or an entrained flow (EF).

[0052] In preferred embodiments, water vapours can be added to the gasification reactor, which will reduce the temperature in the gasification reactor. The water vapours may come from various sources such as the dryer.

[0053] In preferred embodiments, the temperatures in gasification reactor(s) are typically above 800°C, but it may be advantageous to operate the gasification reactors at temperatures below 800°C to prevent encapsulation of phosphorus, rendering phosphorus with a higher availability to plants and / or less agglomeration of ash. The temperatures in the gasification reactor(s) is typically a temperature of the bed material, which may be sand.

[0054] Heavy metals may evaporate from the fuel in pyrolysis and gasification reactors due to the high temperatures. Examples on such heavy metals which may be present in the fuel are arsenic (As), Cadmium (Cd), Mercury (Hg) and Zinc (Zn). These heavy metals typically constitutes the majority of heavy metal content in waste and / or biomass used as fuel. Moving parts in the reactor and in the hot stages

[0055] In many existing pyrolysis and gasification systems the fuel is moved inside the reactor by mechanical means. Typically, these mechanical means are made of high-grade steel, which is both costly and also needs replacement. In contrast to this, transport of fuel is preferred embodiments of the invention provided by gravity and / or a gas flow. For instance, is transport of material from the gasification reactor to the pyrolysis reactor, and transport of material from the pyrolysis reactor to the gasification reactor assisted by the gas flow from the gasification reactor to the pyrolysis reactor.

[0056] Preferred embodiments of gas combustion

[0057] Gas produced by pyrolysis and gasification, such as in pyrolysis reactor and gasification reactor may be burned or they can be utilized for production of chemicals.

[0058] In embodiments, where the gases are burned, the gases are burned at temperatures in the range of 800-1200°C with a retention time in the range of 1- 3 seconds, which typically allows for harm full longer molecules such as PFAS and VOC to have a tendency to or even essentially be destroyed and decomposed into harmless molecules such as CO2 and H2O. Destruction of such harmful longer molecules may be improved by increasing the turbulence intensity of the gasses during combustion, such as in the gas combustion reactor.

[0059] During drying of fuel, substances such as PFAS e.g. contained in sludge and smelly substances e.g. of digestate, evaporate and are contained in a water vapour produced by drying. By feeding at least a fraction of the produced water vapour to the gas combustion reactor 6 and / or to the gasification reactor 4, such substances are likely to decompose into non-harmful and / or non-smelly substances. During combustion NOx can be produced.

[0060] Preferred embodiments of gas cooling

[0061] Hot flue gas produced by gas combustion may be cooled in a gas cooler 7 and the thermal energy in the gas can thus be transferred into another media such as thermal oil, steam or water. This thermal energy can be transferred to a dryer and / or be used for other purposes, such as local and / or district heating or process heat.

[0062] During cooling of the gas, heavy metals may condensate on particles. NOx can be removed or reduced before and during gas cooling. Such NOx removal or removal may be carried out by selectively non-catalytic reduction (SNCR) and / or selectively catalytic reduction (SCR).

[0063] Preferred embodiments of filtration

[0064] In preferred embodiments, particles and / or harmful substances, such as heavy metals may be removed from the flue gas in a filter. Such a filter may a baghouse filter, an electrostatic filter, other filter or combinations thereof.

[0065] Preferred embodiments of flue gas condensing

[0066] In preferred embodiments, flue gas produced by gas combustion may be cooled, preferably in a condenser, to below its water dew point, whereby water vapours contained in the flue gas condensate to produce a condensate. Such a condensation releases thermal energy which may be recovered into district heating or other purposes.

[0067] Preferred size and turn-down ratio of systems

[0068] In preferred embodiments, systems comprising drying, pyrolysis and gasification are preferable made in sizes of in the range of 1-100 MW thermal input, where thermal input refers to the amount of energy input to the system by the fuel.

[0069] A typical turn-down ratio for such systems is about 1:2 or 1: 3.

[0070] Preferred embodiments of the invention may involve both chemical reactions and exchange of energy. The term "Media" is preferably used for one or more substances that are part of one or more chemical reactions and / or exchange energy. "Media" can be both solid, liquid or gaseous phase.

[0071] BRIEF DESCRIPTION OF THE FIGURES

[0072] The present invention and in particular preferred embodiments thereof will now be described in more detail with regard to the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0073] Fig. 1 schematically illustrates components of a preferred embodiment of a system for production of biochar and energy. In Fig. 1, material flows are indicated by arrows.

[0074] Fig. 2A and B schematically illustrate the energy balance of a 7 MW system (thermal input) using 100% dewatered biogas digestate as fuel with cases for maximum heat output, Fig. 2A, and maximum carbon in biochar, Fig. 2B. The system is configured as disclosed in Fig. 1 although some system elements have been left to render the figures clearer. In Fig. 2A and 2b, the numerals indicated in squares are the reference symbols otherwise used herein. As an example, "Pyrolysis" is in Fig. 2A indicated by reference symbols to involve: pyrolysis reactor 2, cyclone 3, gasification reactor 4, secondary cyclone 5, and circulating fluid bed reactor 25 the latter being the combination of pyrolysis reactor 2 and gasification reactor 4.

[0075] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0076] The present invention provides a method and a system for thermal conversion of moist solid fuels, such as

[0077] • Dewatered sludge from waste water treatment systems or industry

[0078] • Dewatered digestate from biogas digesters

[0079] • Other fuels with high water content

[0080] In the preferred embodiment shown in Fig. 1, the system comprises:

[0081] • a dryer 1 in which the moist fuel is heated by energy from the gas cooler 7. This heating produces water vapors which are used for the gasification in the gasification reactor 4 and / or used in the gas combustion reactor 6;

[0082] • a pyrolysis reactor 2 in which the dried fuel is heated to preferably 400- 700C by use of hot bed material. The hot bed material is residual produced in a gasification reactor 4, which residue is fed into the pyrolysis reactor 2; • a first particle separator, in Fig. 1 a cyclone 3, in which larger particles produced during pyrolysis are separated off and lead to the gasification reactor 4;

[0083] • a gasification reactor 4 preferably operating at temperatures in the range of 650-850C in which particulate material from the pyrolysis is gasified and where water vapor from the dryer 1 may be supplied. Water vapor typically forms part of a gas having content of N2 and O2 as the water vapor typically is mixed with atmospheric air;

[0084] • a second particle separator, in Fig. 1 a secondary cyclone 5, in which particles are separated off from the gas;

[0085] • a gas combustion reactor 6 in which gases from the pyrolysis and gasification are combusted at preferably 900-1200C. In embodiments where water vapor from the dryer 1 is supplied to the combustion reactor 6, which will reduce the temperature in the gas combustion reactor. In case of high load of water vapor from the dryer the temperature may be remained between 900-1200 e.g. by a burner using a liquid or gaseous fuel.

[0086] • optionally a De-NOx system such as a SNCR system (19) (selective non- catalytic reduction) may receive the flue gas produced by combustion, and reduce the NOx content in the flue gas, and deliver the flue gas at least partly freed from NOx to a gas cooler 7;

[0087] • a gas cooler 7 in which the hot flue gas is cooled and the thermal energy is recovered to thermal oil, steam or hot water;

[0088] • optionally, a particle filter 8, which filters the cooled flue gas;

[0089] • optionally, a flue gas condenser 15 in which the flue gas is further cooled to below dew point of water to produce a condensate.

[0090] The invention is applicable in combination with various types of moist solid fuels. In preferred embodiments, the fuel has an average water content is above 40v / v%.

[0091] In some embodiments, the moist solid fuel is sludge from waste water treatment systems, and the sludge is transformed into thermal energy and a fertilizer containing phosphorus and bio-char. In the dryer 1 moist solid fuel is heated by the thermal energy from cooling the flue gas in the gas cooler 7. For instance thermal oil, steam or hot water may be used as a thermal energy carrying medium. The dryer 1 operates typically at temperatures between 80-350°C, preferably between 120-220°C. This temperature is a temperature measured inside the dryer 1, and the fuel leaving the dryer has typically a temperature being lower than the operating temperature of the dryer 1. Most of the water contained in the fuel evaporate so moisture water content in the fuel after the dryer 1 typically will be below 20% water. Also other substances may evaporate for instance some of the PFAS, odors, etc. so the vapors can advantageously be further treated.

[0092] In embodiment shown in Fig. 1, the water vapors are led to the gasification reactor 4 and / or to the gas combustion reactor 6.

[0093] In preferred embodiments, pyrolysis, particle separation and gasification may be carried out in

[0094] • a circulating fluidised bed (CFB) gasification reactor 4 which comprise a CFB reaction chamber,

[0095] • a particle separator 3 for separation of particles, which typically contain char, from an outlet gas of the CFB reaction chamber, and

[0096] • a particle recirculation duct for recirculation of the separated particles to the CFB-reaction chamber. The particle recirculation duct comprises a char reaction chamber for gasification of char contained in the recirculating particles.

[0097] Water vapours from the dryer may be added to the gasification reactor 4 for reducing the temperature in the gasification reactor 4, which at least potentially prevents sintering of ash and allow for conversion of more char into gas. Preferred embodiments of the invention provide the flexibility of adjusting the fraction of water vapours produced in the dryer 1 and led to the gasification reactor and thereby achieving either high carbon conversion and high production of heat from gas cooler or high carbon content in the fertiliser product.

[0098] The temperatures in the pyrolysis reactor 2 is preferably between 400-700°C.

[0099] These temperatures are provided as solid materials and gas from the gasification reactor are led to the pyrolysis reactor. It is noted that the temperature is the temperature inside the pyrolysis reactor 2, and that the temperature of the material being pyrolyzed typically is lower than a maximum temperature inside the pyrolysis reaction 2.

[0100] The temperatures in gasification reactor 4 is preferably between 650-850C. These temperatures are provide as oxygen is led to the gasification reactor 4 and the oxidation and gasification of char increase the temperature. Also steam and / or flue gas can be added to the gasification reactor 4. The temperature of the material being gasified is typically lower than the maximum temperature inside the gasification reactor 4.

[0101] In the pyrolysis and gasification reactors 2, 4 the solids from the dryer typically decompose into a solid component containing char and ash and a gaseous component containing organic components including tars, methane, CO, CO2, H2 and H2O etc. Remaining PFAS in the solid component (which is not evaporated in the dryer) typically evaporates in the pyrolysis and gasification reactors 2, 4. It is an advantage of preferred embodiments, that long chained, complex PFAS compounds are reduced to short chained, simpler PFAS compounds or even to non-PFAS compounds in the pyrolysis reactor 2. This makes it easier to destroy, such as fully destroy all PFAS compounds in the gas combustion reactor 6.

[0102] Solid particles are moved inside the pyrolysis and gasification reactors 2, 4 preferably without any mechanical means but by using air, steam, flue gas, nitrogen or a combination hereof as fluidization media.

[0103] Silica sand or other types of bed material can be added batchwise or continuously to the pyrolysis or gasification reactors 2, 4 to replenish the bed levels or to adjust chemical or physical properties of the bed material.

[0104] A typical gas composition after the pyrolysis and gasification reactors may be: H2O 46%, H2 7%, CH4 4%, CO 6%, CO2 8%, N2 30%, and the energy content in the gas is typically in the range of 4-5 MJ / kg (including contribution due to that the gas is 650°C warm). In the gas combustion reactor 6 the gases from the pyrolysis and gasification reactors 2, 4 are combusted at 900-1200°C at a retention time of 1-3 seconds. Further, water vapors from the dryer, containing e.g. PFAS, and / orsmelly substances etc. may be co-combusted.

[0105] After the gas combustion reactor 6 a De-NOx system using SNCR system and / or SCR system can be applied to reduce the NOx content of the flue gas.

[0106] The SNCR system and / or SCR system may in preferred embodiments reduce the NOx content to below thresholds given by authorities for emission from a stack.

[0107] The flue gas produced in the gas combustion reactor 6 may be cooled in a gas cooler 7 in which energy is recovered from the hot flue gas to produce steam or to heat up thermal oil or water. The gas cooler 7 may be configured to cool the flue gas to 100°C, although a preferred flue gas temperature after the gas cooler 7 may be between 120-200°C.

[0108] During gas cooling in the gas cooler 7 most of the heavy metals condensates and agglomerate on the particles contained in the gas.

[0109] The flue gas composition after the gas cooler 7 is in preferred embodiments typically: H2O 40%, CO2 7%, N247%, O2 6%.

[0110] Particles contained in the cooled flue gas may be removed in a downstream particle filter 8. Such particle filter 8 may typically be a bag-filter or an electrostatic precipitator (ESP). Beside particles, heavy metals may also be removed from the cooled flue gas by the filter 8. If considered necessary, a bag filter may be used and additives added for further chemical cleaning on the bag surfaces.

[0111] A flue gas condenser 15 may be installed downstream of the filter, or in general downstream of the gas combustion reactor 6. Such flue gas condenser 15 may serve one or more of the following purposes:

[0112] • recover more energy from the flue gas;

[0113] • capture harmful particles which are not captured in the filter; capture water soluble substances; produce condensate typically comprising water that can be used in the process or for other purposes

[0114] As illustrated in Fig. 1, a flue gas condenser 15 may comprise a heat exchanger by which the heat is extracted from the flue gas contained in the flue gas condenser 15.

[0115] Preferred embodiments of the invention may provide a prominent advantage of present invention by that the residue of the gasification is a biochar which may have one or more of the following advantages:

[0116] • the carbon of the biochar is stable and therefore rarely decompose further when exposed to oxygen at temperatures below 100°C, and can therefore be considered a way to make carbon capture;

[0117] • the micropore structure of the carbon rich ash makes the ash hydroscopic which make it suitable for water storage;

[0118] • nutrients from the fuel such as phosphorus and potassium are retained

[0119] • PFAS, medicine residues, heavy metals are typically substantially not present in the biochar.

[0120] In general, ash from the gasification reactor 4 may be an attractive fertilizer to bring out on farm land.

[0121] Moist fuels may be transported to the dryer 1 using e.g. cranes and screw conveyors. Dry fuel may be transported to the pyrolysis reactor 2 using chain- or screw conveyors and a pressure barrier between dryer 1 and pyrolysis reactor 2 may be provided typically with rotary valves.

[0122] An intermediate dry fuel storage (not illustrated) between dryer 1 and pyrolysis reactor 2, some advantages may be achieved, namely that there is no direct dependency between capacity of dryer 1 and heat produced by gas cooler 7. Thereby variations amounts, moisture content, and / or calorific content in fuel may be handled easier. In preferred embodiments, mix moist fuel with dry fuel or provide a bypass around the dry fuel storage gives further flexibility.

[0123] Biochar is preferably taken out from underneath second particle separator (in Fig. 1, the secondary cyclone 5), from a bottom of pyrolysis reactor 2 and / or from gasification reactor 4. Biochar may be taken out using water cooled screws and water may be added to biochar to deactivate the carbon and to reduce dust nuisance. Biochar can be stored in closed containers.

[0124] Preferred embodiments of the system and method are found to be easy to regulate.

[0125] A flow of moist fuel into dryer 1 may be regulated to maintain a certain constant level in a dry silo of e.g. 80%. Flow of dry material into pyrolysis is regulated to achieve the needed heat output for dryer, process heat and other heat demands.

[0126] The water vapour from the dryer 1 may be divided between gasification reactor 4 and gas combustion reactor 6 based on operator's preference (maximum heat output or maximum carbon in biochar) and adjusted to obtain the desired temperature in the combustion reactor 6 e.g. 1000°C. If temperature is too low then a larger fraction of the water vapour may added to the gasification reactor to convert more carbon into gas.

[0127] It is also possible to adjust how much the moist fuel is dried in the dryer 1 or adjust an amount of dried fuel with moist fuel to obtain a certain moisture content in the fuel before it enters the pyrolysis. Typically, if fuel has a high moisture content, more char will be converted into gas in the processing and more energy is released from the biochar. This lowers carbon content in the biochar but makes more energy available in the gas cooler 7.

[0128] Temperature in pyrolysis reactor 2 may be regulated by adjusting the amount of a control gas (e.g. air, steam, flue gas, nitrogen) fed into the e.g. the bottom of the pyrolysis reactor 2. This will expand the bed material (e.g. sand) column and increase the bed material circulation and bring more hot bed material from the gasification reactor 4 to the pyrolysis reactor 2. Temperature in gasification reactor may be regulated by adjusting amount of air fed into e.g. the bottom of the gasification reactor 4. An increased amount of air will react with the carbon and increase the temperature.

[0129] Pressure in the reactors may be controlled by a fan before the stack 23. This fan may be regulated to maintain neutral pressure in the second particle separator 5. This may avoid flow of pyrolysis gas or air into a biochar extraction system. In embodiments where equipment for upgrading syngas is applied, such equipment may be advantageous to operate the pyrolysis reactor 2 at higher pressure.

[0130] In preferred embodiments, the system may be produced from materials suitable for the temperatures and chemical composition inside the various reactors. Nonlimiting examples of materials are:

[0131] • dryer 1: Can be made of stainless steel or carbon steel with outside insulation;

[0132] • pyrolysis reactor 2, gasification reactor 4, particle separators 3, 5, such as cyclones 3 and 5, gas combustion reactor 6: These elements typically comprise a vessel which may be made with an inner liner of hard, high- temperature materials such as refractory and an outer gas-tight steel shell. Thermal insulation can be applied inside and / or outside steel shell;

[0133] • gas cooler 7: a gas cooler may be made in a number of sections in the flow direction of the gas to be cooled. For instance, a first section being located immediately downstream the gas combustion reactor 6 may be made of high temperature steel and a downstream second section, preferably being a last section, in which the gas has a lower temperature relatively to the inlet temperature, may be made of carbon steel or stainless steel depending on temperatures and corrosive compounds in flue gas;

[0134] • filter 8: may be made of carbon steel or stainless steel depending on temperature and corrosive compounds in the flue gas;

[0135] • flue gas condenser 15: may be made of fiberglass.

[0136] As described above, preferred embodiments of a system and of a method may offer a number of advantages compared to state-of-the-art technologies. It could therefore be expected that the system will be expensive and complicated. However, the simplicity and the compactness of preferred embodiments may be a main advantage of the invention.

[0137] Typically, the pressure of the system will be atmospheric, but the system can be built for both underpressure and overpressure. Here, underpressure refers to a pressure being lower than the pressure in the surrounding atmosphere, and overpressure to a pressure being higher than the pressure in the surrounding atmosphere. The under and overpressure are typically less than 0.1 bar lower respectively higher than the pressure in the surrounding atmosphere. Such over and underpressures have the advantage that minor leakage(s) in the system either results in that the air is sucked into the system or gas in the system is expelled to the room in which the system is installed.

[0138] In preferred embodiments, an underpressure and overpressure in top of the pyrolysis reactor 2 are typically less than 0.1 bar lower respectively higher than the pressure in the surrounding atmosphere. Overpressure in top of the pyrolysis reactor 2 may in preferred embodiments be up to 40 bars.

[0139] The invention is explained in more detail in the following, referring to the drawings where

[0140] Fig. 1 schematically illustrates how the basic process steps of the system according to the invention interact.

[0141] Fig. 2A and B schematically illustrate the energy balance of a 7 MW system (thermal input) using 100% dewatered biogas digestate as fuel with cases for maximum heat output, Fig. 2A, and maximum carbon in biochar, Fig. 2B. The system is configured as disclosed in Fig. 1 although some system elements have been left to render the figures clearer.

[0142] In Fig. 1, 1 is a drying to which moist fuel is added. The dryer is heated by a warm media 12, which - after being cooled by the dryer - leave the dryer 1 as a cooled media 13 at a colder temperature. The media for drying can be thermal oil, hot water or steam (which condensate) or other. Evaporated water vapours (steam) leave the dryer 1 and dried fuel is led to the pyrolysis reactor 2. The pyrolysis reactor receives char and bed material of 650- 850°C from the gasification reactor 4 and so the fuel is heated to 400-700°C thus being pyrolyzed. Due to high velocity of the gases in the top of the pyrolysis reactor (>2 m / s) will the fuel flow upwards and is led to the first cyclone 3 which separates bed material and larger fuel particles from the gas. The bed material and larger particles are led to the gasification reactor 4. Also water vapor 10 and air and / or flue gas 20 is added to the gasification reactor 4, thus bringing the gasification reactor temperature to 650-850°C.

[0143] The gas from the cyclone 3 is led to secondary cyclone 5, which is designed to capture smaller particles. These smaller particles are captured and collected in receptacle 21.

[0144] After secondary cyclone 5 the gas is led to the gas combustion reactor 6 where also air and steam from the dryer 1 is added. Air is preferably introduced via a separate air inlet 24. The gasses are burned at 900-1100°C in the gas combustion reactor 6. The gas combustion will form NOx which will be reduced by the SNCR system 19 placed downstream of the gas combustion reactor 24. Hereafter, the gases is cooled in the gas cooler 7. The cooling is provided by thermal oil or water which is heated to about 200-300°C; alternatively steam 12 may be produced. The warm thermal oil or water or steam 12 is led to the dryer 1 and returned 13 to the cooler 22 at a temperature of about 150-200°C. Excess energy may be used for district- or process heat 14 in the cooler 22 before the media is returned to the gas cooler 7 at a temperature of about 100-150°C.

[0145] After the gas cooler 7 the flue gas is led to a filter 8 which capture at least some particles contained in the flue gas, which particles are collected as an ash disposal 18.

[0146] After the filter the flue gas is led to the flue gas condenser 15, where the flue gas can be cooled to about 30-60°C thus producing considerable amounts of energy 16 due to flue gas condensation. In the flue gas condenser 15, water vapours contained in the flue gas is condensed. The condensed water is disposed as a water disposal 17. If necessary this water is cleaned in a water filter, typically prior to be disposed.

[0147] The flue gas after being cooled in the condenser is emitted to the atmosphere through the stack 23.

[0148] In Fig. 2, the energy balance of a system, producing hot water and biochar from moist fuel is illustrated.

[0149] The energy balance is an example of a 6,9 MW thermal input system using 100% of dewatered biogas digestate with 30% dry matter. Two cases are considered:

[0150] • Case 1 (see Fig. 2A): Optimized for heat production. Large share of steam from dryer is led to gasification reactor and most carbon is converted to syngas leaving only a small amount of heating value in biofertilizer (0,4 MW). Relevant if heat price is high and biochar price is low.

[0151] • Case 2 (see Fig. 2B): Optimized for biochar. Small share of steam from dryer is led to gasification reactor and only the amount of carbon is converted to syngas which is needed to ensure a thermal balance in the system and for achieving 1000°C in combustion reactor. Relevant if biochar prize is high and heat price is low.

[0152] List of reference symbols used

[0153] 1 Dryer

[0154] 2 Pyrolysis reactor

[0155] 3 Cyclone

[0156] 4 Gasification reactor

[0157] 5 Secondary cyclone

[0158] 6 Gas combustion reactor

[0159] 7 Gas cooler

[0160] 8 Filter

[0161] 9 Pipe

[0162] 10 Pipe

[0163] 11 Pipe

[0164] 12 Warm media

[0165] 13 Cooled media

[0166] 14 District and / or process heat

[0167] 15 Flue gas condenser

[0168] 16 Energy (heated media)

[0169] 17 Water disposal

[0170] 18 Char and ash disposal

[0171] 19 SNCR system (selective non-catalytic reduction system)

[0172] 20 Gasification agent

[0173] 21 Receptacle

[0174] 22 Cooler

[0175] 23 Stack

[0176] 24 Air inlet

[0177] 25 Circulating fluidized bed reactor

[0178] 26 Flow of material and gas from gasification reactor 4 to pyrolysis reactor 2

[0179] 27 Exit gas

Claims

Claims1. A method of converting moist solid carbonaceous material into biochar and thermal energy, the method comprises drying said solid carbonaceous material in a dryer (1) to produce a dried solid carbonaceous material and subsequently pyrolyzing and gasifying said dried solid carbonaceous material in a circulating fluidised bed reactor (25) comprising a pyrolysis reactor (2) and a gasification reactor (4), the method comprises the steps of:• feeding said solid carbonaceous material to said dryer (1) to provide said dried solid carbonaceous material, and• feeding said dried solid carbonaceous material to said pyrolysis reactor (2) and pyrolyze said dried solid carbonaceous material to provide a pyrolysed carbonaceous solid material and a product gas comprising particles produced during said pyrolysis,• discharge of said product gas from the pyrolysis reactor (2), and separating a fraction of said particles from said product gas in a particle separator, such as a cyclone (3), to provide separated particles, and• re-circulating said separated particles to said gasification reactor (4), and• gasify said re-circulated separated particles to provide a gasified carbonaceous material, wherein said gasification is a carried out with addition of an oxygen-containing gasification agent (20), such as air, wherein• the temperature in said gasification reactor (4) as determined in a fluidized bed of said fluidized bed reactor (25) is below 800°C and higher than the temperature of pyrolysis reactor (2).

2. A method according to claim 1, wherein additional solid carbonaceous material is supplied to the pyrolysis reactor (2) and / or to the gasification reactor (4) without having been dried in said dryer (1).

3. A method according to claim 1 or 2 wherein said drying in said dryer (1) is configured to heat said solid carbonaceous material by addition of thermal energy, e.g. by heat conduction and / or heat radiation and / or by using a gas having a low O2 content, to produce an exhaust having a low content of free O2, such as less than 5 %v / v O2 and a high content of water such as 80 %v / v , typically as steam.

4. A method according to any of one of the preceding claims, wherein product gas and / or said gasified carbonaceous material is oxidized in a gas combustion reactor (6) by oxygen (O2) preferably being oxygen contained in atmospheric air, to produce an exit gas (27) exiting said combustion reactor (6), wherein• at least parttime during said oxidation oxygen is fed into said gas combustion reactor (6) through an air inlet (24).

5. A method according to claim 4, wherein the temperature of said oxidation in said gas combustion reactor (6) is controlled by reintroducing a fraction of said exit gas (27) (flue gas) exiting said combustion reactor (6), wherein said fraction is reintroduced in an amount so that the temperature of said oxidation above 800°C, preferably above 800°C and below 1200°C.

6. A method according to claim 4 or 5, wherein said oxidation in said gas combustion reactor (6) is an essential full oxidation in which said exit gas exiting said gas combustion reactor (6) contains free oxygen (O2), or a partial oxidation in which said exit gas has essentially no free oxygen (O2).

7. A method according to any one of the preceding claims, wherein at least a part of water vapour generated by said drying is collected and fed to said gas combustion reactor (6) by one or more pipes (9, 11) fluidicly connecting said dryer (1) and said gas combustion reactor (6).

8. A method according to any one of the preceding claims, wherein at least a part of the water vapour generated by said drying is collected and fed to said gasification reactor (4) by one or more pipes (9, 10) fluidicly connecting said dryer (1) and said gasification reactor (4).

9. A method according to any one of the preceding claims, wherein ash and char produced• in said pyrolyzing reactor (2) during said pyrolysis, and / or• in said gasification reactor (4) during said gasification is extracted from said pyrolyzing reactor (2) and / or said gasification reactor (4) via a bottom of said pyrolyzing reactor (2) and / or a bottom of said gasification reactor (4).

10. A method according to any one of the preceding claims, wherein said particle separator provides a product gas containing ash and char produced• in said pyrolyzing reactor (2) during said pyrolysis, and / or• in said gasification reactor (4) during said gasification wherein said ash and char contained in the particle freed product gas are extracted in a secondary particle separator, such as a secondary cyclone (5).

11. A method according to claim 8 or 9, wherein content of carbon in said extracted ash is at least 5%v / v.

12. A method according to any one of the preceding claims, wherein the ash from the gasification system is cooled and pacified, preferably by humidifying said ash with water.

13. A method according to any one of the preceding claims, when dependant on claim 4 or 5, where said exit gas (27) exiting said gas combustion reactor (6) is cooled in gas cooler (7) and wherein at least a fraction of energy recovered by the gas cooler (7) from said exit gas is to use to heat up water and / or thermal oil and / or produce steam in cooler (22).

14. A method according to claim 13, wherein at least some of said recovered energy is used for drying said solid carbonaceous material in said dryer (1).

15. A method according to any one of the preceding claims 13 or 14, wherein said exit gas after being cooled in said gas cooler (7) exits the gas cooler (7) and is filtered in filter (8), such as a bag house filter or electrostatic filter.

16. A method according to any one of the preceding claims 13-15, wherein said exit gas after being cooled in said gas cooler (7), is cooled further in a flue gas condenser (15) where energy released by condensation is recovered and a further cleaning of said exit gas (27) may be carried out.

17. A system for converting moist solid carbonaceous material into biochar and thermal energy, the system comprising:• a dryer (1) configured to dry said solid carbonaceous material to produce a dried solid carbonaceous material,• a circulating fluidised bed reactor (25) arranged to received said dried solid carbonaceous material from said dryer (1), the circulating fluidised bed reactor (25) comprising: o a pyrolysis reactor (2) configured to pyrolyze said dried solid carbonaceous material to provide a pyrolysed carbonaceous solid material and a product gas comprising particles produced during said pyrolysis, and; o a gasification reactor (4) comprising an oxygen-containing gasification agent, such as air, inlet, said gasification reactor (4) being configured to gasify said pyrolyzed solid carbonaceous material and / or said particles to provide a gasified carbonaceous material, and;• a particle separator, such as a cyclone (3), arranged in fluidic communication with said pyrolysis reactor (2) and said gasification reactor (4), said particle separator arranged to receive said product gas from said pyrolysis reactor (2) and separate a fraction of said particles from said product gas, and to feed said fraction of particles to said gasification reactor, wherein said system is adapted to control a temperature in said gasification reactor (4) as determined in a fluidized bed of said fluidized bed reactor (25) to be below 800°C and higher than the temperature of said pyrolysis reactor (2).

18. A system according to claim 17, wherein said system is configured to supply additional solid carbonaceous material to said pyrolysis reactor (2) and / or to the gasification reactor (4), wherein said additional solid carbonaceous material have not been dried in said dryer (1).

19. A system according to claim 17 or 18 wherein said dryer (1) is configured to heat said solid carbonaceous material by addition of thermal energy, e.g. by heat conduction and / or heat radiation and / or by a gas having a low O2 content, toproduce an exhaust having a low content of free O2, such as less than 5 %v / v O2 and a high content of water such as 80 %v / v, typically as steam.

20. A system according to any of one of the preceding claims 17-19, further comprising a gas combustion reactor (6) comprising an air inlet (24), where the gas combustion chamber (6) is configured to oxidise said gasified carbonaceous material by oxygen (O2), preferably being oxygen contained in atmospheric air, said oxygen (O2) fed into said gas combustion reactor (6) through the air inlet (24) at least parttime during said oxidation, to produce an exit gas (27) exiting said combustion reactor (6).

21. A system according to claim 20, wherein the system is configured to control the temperature of said gas combustion reactor (6) during oxidation by being configured to reintroduce of a fraction of said exit gas (27) (flue gas) exiting said combustion reactor (6), wherein said fraction is reintroduced in an amount so that the temperature of said oxidation is above 800°C, preferably above 800°C and below 1200°C.

22. A system according to claim 20 or 21, wherein the system is configured to provide said oxidation in said gas combustion reactor (6) as an essential full oxidation in which said exit gas exiting said gas combustion reactor (6) contains free oxygen (O2), or a partial oxidation in which said exit gas has essentially no free oxygen (O2).

23. A system according to any one of the preceding claims 17-22, further comprising one or more pipes (9, 11) fluidicly connecting said dryer (1) and said gas combustion reactor (6), said pipes (9, 11) being configured to collect at least a part of water vapour generated by said dryer (1) and to feed said part of water vapour to said gas combustion reactor (6).

24. A system according to any one of the preceding claims 17-23, further comprising one or more pipes (9, 10) fluidicly connecting said dryer (1) and said gasification reactor (4), said pipes (9, 10) configured to collect at least a part of water vapour generated by said dryer (1) and to feed said part of water vapour to said gasification reactor (4).

25. A system according to any one of the preceding claims 17-24, wherein said pyrolyzing reactor (2), and / or said gasification reactor (4) comprises extraction means, such as screws and / or rotary valves, arranged at the bottom thereof, said extraction means being configured for extracting ash and char produced during pyrolysis and / or gasification from said pyrolyzing reactor (2) and / or said gasification reactor (4) respectively.

26. A system according to any one of the preceding claims 17-25, further comprising a secondary particle separator, such as a secondary cyclone (5), wherein said secondary particle separator is configured to extract ash and char contained in a particle freed product gas output from said particle separator, said ash and char being a product of pyrolysis in said pyrolyzing reactor (2) and / or gasification in said gasification reactor (4).

27. A system according to claim 24 or 25, wherein the system is configured to provide a content of carbon in said extracted ash as at least 5%v / v.

28. A system according to any one of the preceding claims 17-27, wherein the system is configured to cool and pacify ash from the gasification system, preferably by humidifying said ash with water.

29. A system according to any one of the preceding claims 17-28, when dependant on claim 20 or 21, said system further comprising a cooler (22) and a gas cooler (7), where said gas cooler (7) is configured to cool said exit gas (27) exiting said gas combustion reactor (6), and to heat up water and / or thermal oil and / or produce steam in said cooler (22) by use of at least a fraction of energy recovered by said gas cooler (7) from said exit gas.

30. A system according to claim 29, wherein the system is configured to use at least some of said energy recovered by said gas cooler (7) for drying said solid carbonaceous material in said dryer (1).

31. A system according to any one of the preceding claims 29 or 30, further comprising a filter (8), such as a bag house filter or electrostatic filter, configuredto filter said exit gas (27) after said exit gas has been cooled in said gas cooler (7).

32. A system according to any one of the preceding claims 29-31, further comprising a flue gas condenser (15) configured to further cool said exit gas (27) which has been cooled in said gas cooler (7) and to allow for recovery of energy released by condensation and a further cleaning of said exit gas (27).

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