Patent Application
20130199920
The invention relates to a device for the thermochemical carbonization and gasification of wet, especially water-containing and/or dry, biomass for producing an energy carrier and/or raw-material carrier by means of a heatable carbonization reactor having a closable inlet, in which the biomass is converted into a solid, pourable or gaseous energy carrier and/or raw-material carrier and is discharged via a closable outlet to a coolable vessel connected to the carbonization reactor for interim storage of the energy carrier and/or raw-material carrier, which is connected to a downstream gasification reactor, in which gas and waste substances, such as ash, are separated from the biomass.
Biomass gasification is generally known. This is understood as a process in which biomass is converted into a product gas or combustible gas by means of a gasifying or oxidizing agent (generally air, oxygen, carbon dioxide or steam) by partial combustion.
Through gasification, the biomass that is in the form of solid fuel can be converted into a gaseous secondary fuel, which can be used more efficiently in various usage options, e.g. production of electricity or as fuel and propellant (combustible gas) or for use as synthesis gas for chemical synthesis. Analogous processes also exist for other solid fuels, especially for the gasification of coal (coal gasification).
The gasification of biomass starts after drying at temperatures of approx. 150° C., with steam and oxygen being evolved first. At higher temperatures, the solid constituents of the biomass are burnt. This gas ignites as soon as secondary air is supplied; the flash point is from 230 to 280° C.
Industrial biomass gasification, is partial combustion by means of a gasifying or oxidizing agent (generally air, oxygen, carbon dioxide or steam) without ignition at temperatures from 700 to 900° C., in which it is not oxidized to carbon dioxide (CO2), as in combustion, but essentially to carbon monoxide (CO). Further components of the resultant gas are hydrogen (H2), carbon dioxide (CO2), methane (CH4), steam (H2O) and a number of trace gases and impurities, depending on the biomass used. A solid residue is left (ash and coke); moreover, some fractions of the product gas may condense out as the temperature is lowered (tar and water).
The combustible product gas can be oxidized further in a downstream process by combustion (combustible gas) or a chemical synthesis (synthesis gas) with release of energy (exothermic process). If the gasification takes place with air, the resultant product gas diluted with nitrogen is often also called lean gas (LCV, low calorific value gas).
Hydrothermal carbonization (for instance: “aqueous carbonization at elevated temperature”) is a chemical process for simple and highly efficient production of lignite, synthesis gas, liquid petroleum precursors and humus from biomass with release of energy. In a few hours, the process technically duplicates the formation of lignite (“coalification”) that occurs in nature in 50 000 to 50 million years.
The currently known working process is as follows: biomass, especially plant material, (for simplicity represented as sugar, with the formula C6H12O6, in the following reaction equation) is heated to 180° C. together with water in an isochoric process in a pressure vessel. The pressure may increase to 2 MPa. During the reaction, oxonium ions are also formed, which lower the pH to pH 5 or lower. In this process, the carbons pass into an aqueous phase and so are lost. This energy is no longer available for the working process. This step can be accelerated by adding a small amount of citric acid. It must be borne in mind that at low values of pH, more carbon passes into the aqueous phase. The reaction taking place is exothermic, i.e. energy is released. After 12 hours, the carbon of the educts has been converted completely: 90 to 99% of the carbon is in the form of solid phase as an aqueous sludge of porous lignite beads (C6H2O) with pore sizes between 8 and 20 nm; the remaining 1 to 10% of the carbon is either dissolved in the aqueous phase or has been converted to carbon dioxide. The reaction equation for the formation of lignite is:
C6H12O6→C6H2O+5 H2O ΔH=−1.105 kJ/mol
The reaction can be terminated in several stages with incomplete water cleavage, obtaining different intermediates. With termination after a few minutes there is formation of liquid intermediates, lipophilic substances, but their manipulation is very difficult on account of their high reactivity. Next, these substances polymerize and peat-like structures form, which after approx. 8 hours are available as intermediates.
Theoretically the reaction could be catalyzed with certain metal particles, but these would very quickly add onto the products and lose their function.
Owing to the exothermic reaction of hydrothermal carbonization, about ⅜ of the calorific value of the biomass based on the dry matter is released (with high content of lignin, resin and/or oil, still at least ¼). With skillful process control it could be possible, by means of this waste heat, to produce dry biocoal from wet biomass and optionally use some of the converted energy for power generation.
The most important aspect is that a simple method is made available for converting atmospheric CO2 indirectly via biomass into a stable, harmless storage form, a carbon sink. Using the method of hydrothermal carbonization, as with other methods of carbonization of biomass, decentralized permanent storage of a large amount of carbon throughout the world would thus be possible. This would be much safer than the liquid or gaseous sequestration of carbon dioxide currently being discussed. With adequate chemical stability of the coal, it could also be used very well for soil improvement.
The artificially produced humus could be utilized for the revegetation of eroded areas. Through this intensified plant growth, additional carbon dioxide could be bound from the atmosphere, so that the final effect would be achievement of a carbon efficiency above 1 or a negative CO2 balance. The resultant coal slurry could be used for combustion or for operating novel types of fuel cells with an efficiency of 60%, which are currently under investigation at Harvard University. For the production of conventional fuels, the carbon/water mixture would first have to be heated strongly, so that so-called synthesis gas, a gas mixture of carbon monoxide and hydrogen, is formed:
C6H2O+5 H2O→6 CO+6 H2
Alternatively the liquid intermediates that form during incomplete reaction of the biomass could be used for producing fuels and plastics.
In addition, the resultant coal slurry could be briquetted and marketed as an environment-friendly—because it is carbon dioxide-neutral—“natural coal”, which, in comparison with the starting biomass, it should be possible by means of separation/filtration/compaction to dry with lower energy consumption and owing to its higher energy content per volume/mass would incur lower transport costs and would require less storage area.
The main problem when producing synthesis gas from biomass is tar formation, which can largely be avoided in a hydrothermal process. However, it is not then apparent why the indirect route via biocoal should be followed for this. Under supercritical conditions, at 400° C. and a pressure of at least 221.2 bar (the critical temperature of water is 374° C.), it should be possible to break down a biomass slurry into CO2 and H2, but this requires a high energy input.
Problems still to be solved are suitable process control, and problems in the collection, transport and storage of the biomass in question. These operations also require energy—this should be less than is released by hydrothermal carbonization.
Finally, every biomass combustion process is preceded by a gasification process, as the biomass itself is not combustible—basically it is only the gases produced from the biomass that are combustible.
In the carbonization of biomass corresponding to the state of the art, such as hydrothermal carbonization HTC in an aqueous or steam environment, additionally water or steam is supplied to the reactor from outside. This means considerable additional costs for construction and operation of the carbonizing plant. Thermal energy is required for providing the water or the steam and for heating the water. Utilization or disposal of the process water after carbonization represents an additional operation, involving considerable technical and financial costs.
In the known processes, gases and vapors are formed. These often represent an additional problem, which must be solved with technical measures and with considerable additional costs.
The problem to be solved by the invention is to obtain more or less all the carbon and gases from the biomass and to produce these simply and economically.
This problem is solved according to the invention by
a) supplying external thermal energy to the carbonization reactor, which is connected operatively to a heating element, in particular is surrounded by a heating jacket, and supplying further thermal energy at least from one plant, especially from the gasification reactor,
b) supplying cooling energy from the second vessel or cooling vessel to the gasification reactor,
c) supplying moisture, especially water, to the second vessel or cooling vessel, to ensure an almost continuous process,
d) from the carbonization reactor and/or the second vessel or cooling vessel, supplying reaction gas to a gas storage tank, wherein the reaction gas is recycled to the gasification reactor.
In this way, carbon, especially coal, for heating and for driving units and moreover also gases are obtained from biomass in a simple, economical and energy-saving manner with equipment that is easy to set up, for use by various consumers, such as gas engines, gas turbines and heating installations.
The method according to the invention preferably uses water-containing biomass, which mainly arises as municipal waste and in many cases must be disposed of at great expense. In this method it is, however, also possible to use other biomass, which does not have to be disposed of as residue.
At least two reactors are used for implementing the method. These are on the one hand the carbonization reactor and on the other hand the gasification reactor.
In contrast, in the method described here, the energy required for evaporation is provided by utilizing heat that is released during cooling of the reactor gas produced.
Owing to the gasification operation, preceded by carbonization of the biomass, reactor gas produced by the method according to the invention is almost completely free from tar or tar-forming constituents. This is in particular also achieved because the manner in which the process is managed means that the volatile, incombustible fractions from the biomass can be lowered from the existing 80% to approx. 30%, cf. Tables 1 and 2. The values for an installation of the prior art are given in Table 1 and for the equipment according to the invention in Table 2.
After it leaves the gasification reactor, the reactor gas is cleaned by dust separation to remove solid particles, e.g. fine dust, and can then be utilized for producing power and heat.
The small proportion of additional water or heating steam means that only very little process water is produced. No additional costs arise for wastewater treatment or wastewater disposal either, as the water supplied is evaporated in the plant.
The plant can be employed on a small industrial scale using gas-engine generator sets with heat utilization for supplying limited local areas of settlements with power and heat and in parallel for the disposal of suitable municipal wastes.
In the method according to the invention, the problem of contamination of the gases and of tar formation is also solved in that there is almost complete internal disposal of critical reaction products in gaseous and vapor form through combustion in the gasification reactor.
This leads to avoidance of CO2, wherein in this case only a small part of the possible energy would be free.
One advantage of hydrothermal carbonization is that the usable plant biomass is not restricted to plants with low moisture contents and the energy obtainable without carbon dioxide emissions is not reduced by the drying steps required or if necessary is directly usable for drying the end products. Thus, even previously barely usable plant material such as clippings and prunings from gardens and from green areas in towns can be used for energy production, at the same time with a saving of carbon dioxide, which otherwise would be formed—together with the even more climate-damaging methane—during bacterial transformation of the biomass. The operation of the complete plant is also energy-saving because almost all the thermal energy released is recycled to the working process.
For this it is advantageous that the moisture-containing biomass received in the carbonization reactor is evaporated at pressures between 5 and 30 bar, preferably at pressures between 15 and 25 bar, especially at pressures of about 20 bar and at temperatures between 200° and 1200° C., preferably between 400° and 800° C., and reaction gas is formed, which is supplied directly or indirectly to the gasification reactor via a line.
It is also advantageous that the gasification reactor operates in a temperature range between 1200° and 1800° C., preferably between 1000° and 1400° C., and during the working process releases thermal energy via a line connecting the gasification reactor and the carbonization reactor.
According to a development of the invention, an additional possibility is that a cyclone separator and/or gas scrubber is connected via a line to the gasification reactor, wherein a heat exchanger can be provided between the cyclone separator and/or gas scrubber, which lowers gas to the working temperature of the heat exchanger between 40° C. and 80° C. or between 50° C. and 60° C. and recycles the resultant abstracted energy to a heating system and/or to the working process of the plant. The thermal energy released from the heat exchanger is supplied via a line to a consumer, such as a heating system.
Furthermore, it is advantageous that the harmful substances or impurities released in the carbonization reactor and/or in the second vessel or buffer tank are destroyed or at least partially destroyed by means of a thermal device or are led away.
It is also advantageous that the device for the thermochemical carbonization and gasification of wet, especially water-containing and/or dry, biomass for producing an energy carrier and/or raw-material carrier by means of a heatable carbonization reactor having a closable inlet, in which the biomass is converted into a solid, pourable or gaseous energy carrier and/or raw-material carrier and is discharged via a closable outlet to a coolable vessel connected to the carbonization reactor for interim storage of the energy carrier and/or raw-material carrier, which is connected to a downstream gasification reactor, in which gas and waste substances, such as ash, are separated from the biomass, is characterized by the following features:
a) the thermochemical carbonization and gasification device or the first vessel of wet, especially water-containing and/or dry, biomass is connected via a closable connection to a second vessel or buffer tank;
b) the first vessel and/or the second vessel or buffer tank are in each case connected via a line to a gas storage tank, especially reaction gas storage tank;
c) the reaction gas storage tank is connected via the line to the gasification reactor;
d) the gasification reactor is connected directly or indirectly to a cleaning device, such as a cyclone separator and/or gas scrubber;
e) the thermal energy obtained or energy released in the gasification reactor is supplied via at least one line for process control of the thermochemical carbonization and gasification device or to the first vessel.
It is advantageous that the gasification reactor is connected via a line to a processing device for treatment and/or further processing of the coal obtained in the gasification reactor.
It is especially important for the present invention that the second vessel and/or the gasification reactor is connected via the line to the processing device for treatment or further processing of the coal obtained in the vessel and/or in the gasification reactor and a spun-bonded fabric or a ribbon fabric is used as carrying layer.
It is also advantageous that saturated steam is obtained in the gasification reactor, which is connected via a line conveying saturated steam to a consumer or to a heating system and/or a steam piston engine.
Moreover, it is advantageous that the gasification reactor is connected via at least one line to a consumer or at least to a gas compressor and/or gas engine.
It is also advantageous that the gasification reactor and/or the second vessel can be cooled by means of a cooling device, or in each case is surrounded by a cooling jacket and the cooling device is fed with cooling water, wherein at least also cooling water from the cooling jacket of the second vessel is supplied via a line to the gasification reactor.
Furthermore, it is advantageous that the method is characterized by the following method steps:
a) the biomass is converted in a carbonization reactor by means of external thermal energy and further thermal energy, which is supplied from the plant to the carbonization reactor, into a solid, pourable or gaseous energy carrier and/or raw-material carrier;
b) the gas formed in the carbonization reactor is received in a reaction gas storage tank;
c) the reaction gas obtained or present in the first and second vessel is supplied directly or indirectly to the gasification reactor;
d) at least a proportion of the energy obtained in the method of thermochemical carbonization and gasification of wet, especially water-containing and/or dry, biomass is recycled to the processing process, especially to the vessel;
e) the coal obtained in the gasification reactor is supplied to a further processing device;
f) the cooling energy fed in the second vessel is supplied simultaneously or subsequently to the cooling jacket of the gasification reactor;
g) the released energy produced in the gasification reactor or the saturated steam is supplied to one or more consumers, such as a heating system, and/or to a steam piston engine.
According to a development of the invention, an additional possibility is that the reaction gas produced in the complete plant or in the first vessel is supplied directly or indirectly to a cyclone separator and/or to a gas scrubber, then to a dehumidifier, or directly or indirectly via a compressor to the consumer.
It is also advantageous that in one or more lines, control valves are provided, which can be turned off or on manually or by a drive device, wherein the drive devices can be controlled via a computer in relation to the working process.
Further advantages and details of the invention are explained in the patent claims and in the description and are shown in the drawings, showing:
At initial start-up of the complete plant, first wood or charcoal is put in a gasification reactor 16 and then the plant is started up. The reaction gas obtained in the gasification reactor 16 is supplied via a line to a heating element 4, which surrounds the carbonization reactor or first vessel 1. As a result, the carbonization is started. The gas received in the heating element 4 is constantly cooled through introduction of biomass. Energy is saved as a result of this working process. The energy loss that arises is supplied to the plant with external energy.
The carbonization reactor or first vessel 1 is connected operatively to a heating element, in particular is surrounded by a heating jacket 4. The carbonization reactor 1 is supplied at least with external thermal energy 60 and in an advantageous, energy-saving manner with further thermal energy at least from the complete plant, especially from a gasification reactor 16, so that in this way the plant can be operated very economically. The biomass can be supplied continuously or batchwise to the vessel 1. A blow-off valve 7 for controlling the pressure of vessel is provided in the upper part of vessel 1. If the biomass is supplied batchwise to vessel 1, then vessel is filled with cold or also warmed biomass and is heated by the heating element, so that the water present in the biomass evaporates. The steam is supplied to a reaction storage tank 21, so that the energy, which is also made available to the gasification reactor 16, can be fully utilized. With further heat supply above approx. 180° C., the chemical reaction starts and largely coal and gaseous reaction products are produced from the biomass.
The reaction gas led away from vessel 1 has a temperature of at least 300-400° C. This is led at least partially via line 28 into the reaction gas storage tank 21 and from there into the gasification reactor 16. In line 28 there is a nonreturn valve 80, so that excess pressure from the reaction gas storage tank 21 cannot escape to vessel 1.
In the reaction gas storage tank 21, the gas is cooled by the cooling device 49, which is connected via a line 51 and 30 to the vessel 9, to a temperature of approx. 80°. A pressure of approx. 2 to 5 bar prevails in vessel 9 and in the reaction gas storage tank 21. The cooling water is conveyed from the reaction gas storage tank 21 via a line 78 to the cooling jacket 52 of the gasification reactor 16. As a result, more saturated steam can be produced. Via line 78, the reaction gas storage tank 21 for the gasification reactor 16 can be emptied completely.
In vessel 16, various measuring points 81 are provided, with the aid of which the temperature in vessel 16 can be controlled.
The gas storage tank 21 has a regulating function and serves for receiving the reaction gases from vessels 1 and 9. The reaction gas from the reaction gas storage tank 21 is burnt with the coal in the gasification reactor 16.
During combustion of the reaction gas and of the coal in the gasification reactor 16, there is formation of synthesis gas, which is then supplied to one or more consumers, such as a gas engine.
After the required reaction temperature is reached, the chemical reaction begins in the biomass and in addition to the biocoal there is also formation of gas, mainly CO2 and steam. This gas-steam mixture is called reaction exhaust gas. The total pressure inside the reactor is found from the sum of the boiling pressure of steam and the partial pressure of the inert gas fraction in vessel 1. The reaction is associated with generation of heat, i.e. an exothermic reaction takes place in the vessel. For limiting the pressure, the carbonization reactor or first vessel 1 has the pressure-regulated or controlled valve 7. After completion of the reaction, the carbonization reactor or first vessel 1 is relieved from pressure by fully opening valve 7, until it can be opened safely and the biocoal can be removed.
In continuous operation, the biomass is supplied to the carbonization reactor or first vessel 1 in small amounts and in short time intervals via a pressurized air lock or a receiving tank 9 from above. In the carbonization reactor 1 there is always high pressure and high temperature of about 16 bar and 200° C. The biomass supplied is heated in the carbonization reactor and the water it contains evaporates at least partially, or even completely, depending on the process time. The reacting biomass passes through the reactor from top to bottom, with continuous stirring. After the reaction process, coal is removed from a second vessel or buffer tank 9, also called a pressurized air lock. To limit the pressure in the vessel, reaction exhaust gas is released continually by the pressure control valve 7 from the carbonization reactor. The pressurized air lock 9 can also be in the form of a buffer tank.
So that sufficient moisture can be made available to the biocoal in vessel 9 during the working process, fresh water is supplied to it via the cooling device 49 and line 51. Furthermore, vessel 9 can be equipped with a stirrer, to ensure better penetration of the biocoal with moisture.
The plant can also be operated cyclically or with varying pressure, with a pressure of approx. 20 bar and a temperature of 200° C. in the carbonization reactor 1. The biocoal present in the second vessel or buffer tank 9 is cooled. For this, the vessel or buffer tank 9 has a cooling jacket 51. The pressure in the buffer tank 9 is also controlled by a pressure-controlled valve 12, depending on how the process is operated.
Depending on how the process is operated, the moisture-containing biomass received in the carbonization reactor 1 can evaporate at pressures between 5 and 30 bar, preferably at pressures between 15 and 25 bar, especially at pressures of about 20 bar and at temperatures between 200° and 1200° C., preferably between 400° and 800° C., and reaction gas can be formed, which is supplied directly or indirectly to the gasification reactor 16 via a line 30.
The gasification reactor 16 according to
At this temperature, the biocoal reaches the middle part 62 of the gasification reactor 16. There, gasification takes place at temperatures above 900° C. The reaction gas that is released from the biocoal reaches temperatures of up to 1800° C. By suitably controlling the reaction process with the aid of a computer by manual control, the temperature of the solids still in the gasification reactor 16 is limited so that the ash does not melt.
As can be seen from
The reactor gas is led via the outlets 68 in a perforated, partially cylindrically or conically expanded, internal wall 69 of the gasification reactor bottom 63 into an annular gap 70 that is formed between an external wall 71 and the internal wall 69 of the gasification reactor bottom 63.
The gasification reactor 16 is also connected directly or indirectly to a cleaning device, such as a cyclone separator 18 and/or gas scrubber 20. From there, the gas is conveyed to a gas compressor 44 and/or to a gas engine 48.
The gasification reactor 16 is also connected via line to the reaction gas storage tank 21 (
In the upper part of the casing 66 of the gasification reactor 16 there are one or more outlets 72 distributed round the circumference, through which the reactor gas is withdrawn from the gasification reactor 16. Lines 73 connected thereto open into one or more dust separators, which are for example in the form of cyclone separators 18 and from which the reactor gas is supplied for further use or is supplied to the consumers, such as the gas engine 48 or gas compressor 44. The ash is discharged at the lower end of the gasification reactor bottom 63 via an outlet 65 and is transported from there by a conveyor to a disposal tank.
In the lower region of the external periphery of the gasifier middle part 62, one or more gas lances or thermally connected melting units 74 are provided, so that reaction exhaust gas 75 from the carbonization reactor 1 and optionally also from the second vessel or buffer tank or the pressurized air lock 9 can be injected into the gasification zone of the gasification reactor 16. As a result, by means of the high temperatures, waste substances still present, such as sulfur and chlorine compounds, are burnt.
The gasification reactor 16 (
The heat taken up by the coolant can be used for evaporation of the cooling water and for superheating the high-pressure steam 76 thus produced.
The gasification reactor 16 can be operated continuously. The biomass is supplied in short time intervals or continuously. The reactor gas and the ash are discharged continuously as volume or mass flows from the gasification reactor 16.
The reactors 1 and 16 described are operated roughly simultaneously.
By arranging the carbonization reactor 1, the buffer tank 9 and the gasification reactor 16 according to
The moisture-containing biomass received in the carbonization reactor 1 evaporates at pressures between 5 and 30 bar, preferably at pressures between 15 and 25 bar, especially at pressures of about 20 bar and at temperatures between 200° and 1200° C., preferably between 400° and 800° C. Reaction gas is also formed, which is supplied directly or indirectly to the gasification reactor 16 via line 30.
Another possibility for construction of the complete device, consisting of vessels 1, 9, 16, is shown in
The biocoal leaving the buffer tank 9 is transported by means of mechanical conveying devices, such as a conveyor belt or worm conveyor 77, into the filling hopper of the adjacent gasification reactor 16, feeding the latter continuously.
A flow chart of the complete plant is shown in
The gasification reactor 16 is connected via a line 34 to a further processing device 36 for treatment and/or further processing of the coal obtained in the gasification reactor 16.
The saturated steam that is formed in the gasification reactor 1 is connected via the saturated steam line 38 to a consumer or to a heating system and/or a steam piston engine 42.
The reaction gas produced in the complete plant or in the first vessel 1 is supplied directly or indirectly to the cyclone separator 18 and/or gas scrubber 20 and then to a dehumidifier 56 or directly or indirectly to a compressor 44 or to the consumer 48.
In one or more lines 26-34, 38, 50, 53, 54, control valves can be provided, which can be turned on or off manually or by a drive device, wherein the drive devices are controlled via a computer in relation to the working process.
Analysis Values from the Prior Art HTC
(hydrothermal carbonization) charcoal
Analysis Values of the Plant and Device According to the Invention
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2011/075023 | 2/14/2011 | WO | 00 | 4/11/2013 |
