DK174439B1 - Plant for gasification of bio-fuel comprises pyrolysis unit from which pyrolysis coke and gas are fed to reactor unit formed by rotary oven - Google Patents

Abstract

A plant (1) for the gasification of bio-fuel (2) comprises a pyrolysis unit (4) from which pyrolysis coke (14) and gas (18) are fed to a reactor unit (11) formed by a rotary oven (16).

Description

DK 174439 B1

The present invention relates to a biofuel gasification plant comprising a pyrolysis process unit, a chamber for partial oxidation of gaseous pyrolysis products, a solid pyrolysis product gasification reactor unit, an ash extraction unit and a gasification outlet unit. The invention further relates to a process for gasification comprising a feed and processing of biofuels, a pyrolysis step, a tar decomposition step performed by partial oxidation of gaseous pyrolysis products, a gasification step for solid pyrolysis product and the gasification is carried out in an oxidation step followed.

In particular, the invention relates to a gasification plant and a method using biofuels in the form of multi-fuels as well as products derived from agricultural cultivation, for example straw from cereal crops.

For several years, there has been a desire to convert as much as possible of regenerable 15 domestically produced fuel, for example biomass for energy purposes. The main argument for this desire is that this reaction is CO2 neutral. That is to say, for example, when biomass is incinerated, no more CO 2 is produced than natural degradation.

20 In Denmark, straw in particular is a product that is desired to be used. Traditional heat production is the most widespread form of use of straw energy. Known technique is used for this, which can keep construction costs down.

Another method could be to utilize straw's energy potential via gasification. By gasification, electrical energy can be produced by means of a gas motor driving a generator. Such a process has the advantage that a higher efficiency can be obtained than in a traditional power-heat production via a steam process. Especially for smaller plant sizes, there is an advantage, as the cost of gasification plants is less than the cost of traditional steam process plants.

30 DK 174439 B1 2

In gasification, two main gasification principles are used, namely countercurrent gasification and co-current gasification. Both principles can include one or more steps.

5 Countercurrent gasification is characterized by a simple construction and a high carbon conversion. Here, a very tar-containing gas is produced. This means that the gas cannot be used for engine operation without efficient cleaning, otherwise the tar will damage the engine.

10 Co-current gasification is distinguished by producing a cleaner gas which can be used relatively easily for engine operation by connecting the gas outlet from a gasification plant with an engine, possibly via a relatively simple system for cleaning and cooling the gas.

The traditional co-current system demands good quality fuel. There is a significant loss of carbon in the form of carbon that remains unreacted in the ash.

Thus, with the known plants and processes of the type described initially, there has been a great sensitivity to the physical properties of the fuel or also the process has led to a more or less polluted gas which requires extensive purification before the gas can be used. as fuel for an engine that can be utilized, for example, in a cogeneration plant.

After gas purification according to the known principle, a residual product is obtained in the form of a tar-containing condensate, which in turn requires extensive purification before it can be discharged to the recipient.

25

Using a step-divided co-stream carburetor, it has been possible to solve some of these problems.

Thus, a two-stage gasification process is known which allows 30 to produce a substantially tar-free gas which requires only a relatively simple particle purification.

DK 174439 B1 3

However, the known two-stage gasification is associated with disadvantages, with coke gasification taking place in a co-current fixed bed reactor. Such a reactor unit has a limited scope, being largely unsuitable for very fine-grained coke. When the reactor bed contains very fine-grained coke, a large pressure drop occurs over the coke bed. This involves a high risk of loss in the form of unreacted coke in the ash of the bearing material. Furthermore, it has so far not been possible to apply the fixed-bed principle in larger plants, and it has thus been difficult to scale the known plants up to power size, which are desirable gasification plants for use in cogeneration.

10 For several years, therefore, in the work of biomass gasification, there has been a desire to provide a gasification plant or process which enables the production of substantially tar-free gas, which completely converts the pyrolysis coke and which has no significant pressure loss in the coke reactor, and also enables the use of different types of biofuels and can be sized for the desired power, preferably within a larger power range.

It is the object of the present invention to provide a plant and a method for gasification of biofuel of the type mentioned in the preamble, which enable these wishes to be fulfilled, thereby minimizing the disadvantages of the known systems.

According to the present invention, this is achieved with a gasification plant of the type mentioned initially, which is characterized in that the reactor comprises a rotary furnace whose inlet is connected to the pyrolysis unit for receiving the partially oxidized product from the pyrolysis and whose outlet is connected to a separates where ash and gas are separated and fed to ash extraction and gas outlet respectively.

The process according to the invention is characterized in that the gasification is carried out during rotation of the solid pyrolysis product while adding gasifier.

With such a plant and method, a known unit is used to feed and process the biofuel as well as a known unit for the pyrolysis process. This application is used in conjunction with a reactor unit provided in the form of a rotary kiln or rotary coke reactor.

At the approach of this reactor unit, a combustion chamber is provided in which a partial oxidation of the gaseous pyrolysis product is made.

The rotary coke reactor has an oxidation zone where the solid pyrolysis product (coke) is converted to gas by means of a gasifier, for example in the form of air, steam and heat as well as a reduction zone where there is a reduction of CO 2 to 10 CO.

Through the movement pattern of the solid pyrolysis product (coke) in the rotary furnace, an increased area of the contact surface between the hot gas and the coke particles will be obtained, which facilitates the conversion process, creating ideal heat and dust transmission conditions. That is, it will be possible to significantly increase the sales efficiency of coke. Furthermore, the continuous rotation, in which the coke is transported partially along the periphery of the rotary kiln followed by a free fall through the gas stream, will cause virtually all coke to be converted, as no coke will be embedded in ash which will prevent coke conversion.

20

With a rotary kiln as a reactor, it becomes possible to adapt to different types of coke, as the sensitivity to fine material becomes very small. Furthermore, it will be possible to influence several parameters for the sizing of the plant. Thus, it will be possible to optimize the reactor by changing the diameter 25 by regulating the coefficient of drop of the coke, for example, by using drivers in the rotary kiln, so that the fall sequence and thus residence time in the reactor can be affected.

Furthermore, it will be possible to influence the velocity of the gas through the reactor and through the outlet section, so that as little as possible flying dust emerges from the reactor. This allows for the generation of a cleaner gas, thereby facilitating the separation of gas fraction and ash fraction.

DK 174439 B1 5

Furthermore, it is possible to vary the rotational speed and inclination angle of the rotary kiln in order to vary the residence time in the reactor and thus the plant's tolerance of a wide range of particle sizes for the coke. The angle of inclination may be between 0 ° and 10 °. In an installation, this angle will preferably be fixed once it is adjusted, but alternatively, the angle of inclination may be adjustable, and it is also possible to make the carriers interchangeable in order to be able to place carriers of different shapes and / or numbers so as to to affect the rotor oven's dimension / power.

10 As the gas in the reactor passes through an almost empty space where there are only the rotating and falling coke particles, in practice there is virtually no pressure loss in the rotating reactor. This simplifies the system and eliminates the risk of creating undesirable gas-discharge currents in the carburettor interior or outside.

15 Based on the various control parameters, rotary kilns can handle different types of biomass from very fine grain to coarse granulated coke. There is only requirement that these granulated materials be able to pass through the pyrolysis unit.

Furthermore, a reactor in the form of a rotary kiln will have an additional option of scaling up, since it can be fed by a greater or smaller number of pyrolysis units.

At the inlet to the reactor, as mentioned, a combustion chamber is provided in which the tar-containing pyrolysis gas is subjected to a partial oxidation by the addition of air and water vapor, so that the gas supplied to the coke reactor is substantially tar-free. Optionally, pure oxygen can be added instead of air. Hereby the gas temperature is increased to a level which will preferably be above 1000 C. The gases are introduced at this temperature into the coke reactor where an effective reaction of coke takes place at temperatures between approx.

1000 ° C and 700 ° C. Thus, unreacted (non-consumed) oxygen and steam are introduced together with the now tar-free pyrolysis product to the rotary coke reactor. Here, a number of oxidation and reduction processes occur, which consume the rest of the oxygen and water vapor while the coke is converted to gas. The gas produced preferably consists of CO, H2, CH4, CO2 and N2.

DK 174439 B1 6

According to a particular embodiment, the plant is characterized in that the inlet of the rotary kiln comprises a vertical shaft connected to a pyrolysis unit located above the rotary kiln, which is separated into two channels where a first channel is arranged below the outlet 5 from the pyro light unit and primarily the solid pyrolysis product leads to the reactor and where another channel is connected to the outlet of the pyrolysis unit and the gaseous pyrolysis product leads to the reactor.

In this embodiment, a particularly simple design is obtained by transferring material 10 in the form of coke and pyrolysis gas from the pyrolysis unit to the reactor. Thus, coke can fall through a separate channel and be guided into the rotary kiln via a deflection plate. The channel for the coke transport may preferably be provided immediately below the outlet of a pyrolysis unit in the form of a auger conveyor, so that gravity brings the coke from the pyrolysis unit into the reactor.

15

The channel for the pyrolysis gas may be arranged parallel to or wholly or partially enclosing the channel for the boiling transport, and does not require significant density requirements due to limited pressure in the reactor. At the bottom of said second duct adjacent to the inlet of the rotary furnace are provided chambers where the partial oxidation of the tar-containing pyrolysis gas takes place, the duct being provided here with a supply of water vapor and air.

By dividing the process in the manner described, it is possible to decompose the tar content of the pyrolysis gas very purposefully, forcing the produced tar through the combustion chamber, where ideal conditions for tar decomposition / decomposition exist.

As the partial oxidation chamber is very well defined, this construction will allow air / oxygen to be added to the pyrolysis gas in a correct position to obtain a partial oxidation of the pyrolysis gas, namely in the reaction zone or reaction chamber provided in direct connection with the rotary furnace inlet.

DK 174439 B1 7

A system according to the invention which is used for gasification of biofuel for use of the product gas in a gas engine is treated with the biofuel as follows.

5 Biofuel is processed to ensure a uniform size, and then conveyed via transport means to the inlet of the pyrolysis unit. It should be noted that the inlet must be gas tight. In the pyrolysis step, thermal conversion takes place in an oxygen-free atmosphere to form coke and volatile constituents in the form of condensable tar, gases and water vapor produced by the process. The amount and composition of the 10 volatiles are dependent on the biomass residence time and pyrolysis temperature in the pyrolysis unit. Pyrolysis of biomasses typically occurs in the temperature range of 200 ° C -

Q

Thus, volatiles are gradually released from the biomass, leaving a solid of coke. Coke quality depends on chemical composition, which in turn depends on pyrolysis temperature as well as ash content in the biomass.

15 In the combustion chamber, partial oxidation occurs as the air is added and a partial combustion of the pyrolysis gas takes place so that the temperature rises at a temperature above 1000 C, for example up to 1100 ° C, so that the tar degrades.

20

This gas flows through the oxidation zone of the rotary kiln where the coke is decomposed.

With the aid of the oven rotation and the carriers inside the oven, a long residence time is obtained with free fall in the gasification medium. Due to the rotation, there is no accumulation of coke and ash, and thus there will be no risk of uncoated coke being embedded in an insulating ash layer which prevents heat and gasifier from converting the coke into a usable product gas.

In the reduction zone there is a reduction of CO 2 in that there is still little coke left for the reduction of CO 2 to CO. Thereby the rest of the coke is traded / consumed.

The outlet of the rotary kiln is connected to a coarse separator which can be relatively simple.

Due to low air flow, the ash will fall to the bottom of a coarse separator located adjacent to the outlet to be removed via an ash outlet at the bottom. A gas outlet for product gas is provided at the top of the coarse separator. After the coarse separator, the product gas can be processed via gas purification and cooling if, for example, it is to be used in an internal combustion engine.

5

Gas purification can be done according to various principles which are well known, for example by tar cleaning by thermal cracking, the mineral dolomite being used as a catalyst.

10 A smoke washer or scrubber where liquid is injected into the gas and where water which cleanses heavy particles is collected and destroyed.

Purification can also be done as particle cleaning in cyclones along with various types of filters. In such a gas processing, the gas in extraction from the coarse separator o 15 may be cooled from a temperature to approx. 300 C or even lower temperature.

The thus purified and filtered product gas can then be fed to an engine, for example gas engine in cogeneration systems. Thus, the gas engine and a generator can produce heat and power respectively. Cooling water in the engine can be used for hot water production 20 and the exhaust gas from the engine can be fed to the pyrolysis unit's heating jacket to utilize some of the thermal energy for the pyrolysis process.

The invention will now be explained in more detail with reference to the accompanying schematic drawing, in which FIG. 1 shows a section through a first embodiment of a plant according to the invention; FIG. 2 shows a partially horizontal section through a board chamber and a cooker shank for the one shown in FIG. 1, FIG. 3 is a sectional view of a rotary kiln for illustrating the carriers; FIG. 4 shows a partial sectional view of a rotary kiln for illustration of material migration, FIG. 5 shows a sketch of another embodiment of a plant according to the invention, and fig. 6 shows a principle diagram of the method according to the invention.

In the following, identical or similar elements in the various figures of the drawing will be denoted by the same reference numeral. Thus, no specific explanation is given for each figure.

Also, only the essential elements included in the system of the invention 10 will be explained. Thus, no explanation will be given of energy supply, control system and measuring equipment included in the plant in order to make this functional. However, in the light of the present disclosure, it will be possible for the person skilled in the art to provide such elements as will render the plant functional.

In FIG. 1 illustrates a plant 1 for gasification of biofuel 2. Biofuel 2 is thus introduced into a gas-tight feed system 3 of a pyrolysis unit 4 comprising a auger conveyor 5 driven by an engine 6 and having an outlet 7. Pyro The light unit 4 is provided with a pipe casing 8 and may supply heat as indicated by the arrow 9 from exhaust gas from an engine. This flow temperature 9 will typically be in the order of 600 C. From the pipe casing 8 there will be a heat emission as well as an exhaust gas outlet, as indicated by arrow 10, the temperature of which can typically be in the order of 350 ° C.

The pyrolysis unit 4 is connected to a reactor unit 11 via a vertically oriented shaft 25 12. The shaft 12 contains a first channel 13, in which pyrolysis coke 14 ffa the outlet 7 of the auger falls directly into an inlet 15 of the rotary furnace 16. The shaft 12 comprises a second channel 17 for pyrolysis gas 18 flowing from the pyrolysis unit 4 to the inlet 15 for the rotary furnace 16. In Figure 2, a section is illustrated illustrating how the second channel 17 approximately partially surrounds the channel 13 for the pyrolysis coke. At the bottom of the second channel 17, a chamber 19 is provided adjacent to the inlet 15. of the rotary kiln 16, which constitutes a zone for the partial oxidation of the gaseous pyrolysis products. In chamber 19, water vapor 21 and air 22 are supplied via one or more supply pipes 20 in a well-defined position for the pyrolysis gas. This is preferably supplied at a temperature between 500 ° C - 600 ° C and a temperature of typically 1100 C. is established in the chamber 19, thus, a thermal decomposition of tar in the pyrolysis gas is effected.

The rotary kiln 16 is driven by motors 23 which are used to drive support rollers 24. This can be done according to a principle known, for example, from cement kilns, drying kilns for green fodder etc. In the inner 25 of the rotary kiln an oxidation zone 25A is provided. and a reduction zone 25B where coke 26 (see Figures 3 and 4) is decomposed as the pyrolysis gas passes from left to right. Thus, in the reactor 16, a series of oxidation and reduction processes take place, which consume the rest of the oxygen and steam while the coke is converted to gas.

The rotary kiln has an outlet 27 which opens into a coarse separator 28. The coarse separator 28 has a wall 29 so that gas does not flow directly to a gas outlet in the form of an outlet 30 for product gas 31. Due to low flow velocity, ash will fall into the bottom 32 of the coarse separator and via a gas-tight lock 33 and a auger conveyor 34 driven by a motor 35 is fed to an outlet 36 for the ash 37.

20

Typical dimensions of the embodiment shown in FIG. 1 can be a diameter of 1.2 meters and a length of 6 meters for the rotary kiln in a plant with a capacity of one MW. In a plant with a capacity of 10 MW the diameter can typically be 3.8 meters and the length can be typically being 18 feet. It will be possible to scale up the plant for services up to 50 25 MW, which is a significant increase over a fixed-rent plant, which typically has a capacity of up to 2-3 MW. In a fixed bed carburetor, there is frequent cooking loss in the order of 10% of the energy input due to incomplete conversion of coke embedded in the ash. In a rotary oven according to the invention, the coke will react completely, which is said to result in an increase in efficiency of 10%.

In the embodiment shown, the rotary kiln is illustrated as being substantially horizontal. However, this may be positioned at an oblique orientation, as illustrated in Figures 4 and 5. The angle may be between 0 and 10.

5 In FIG. 3 and 4 illustrate a cross section and a longitudinal section through a rotary kiln 16, respectively.

It should be noted that the system illustrated in FIG. 4, is constructed according to a different principle than the plant of fig. I, wherein the pyrolysis unit 4 is located concentrically on a center axis 53 through the rotary kiln 16 and in direct extension of the rotary kiln 16 as well as the chamber 19.

In the interior of the rotary furnace are provided 54 which guide the coke 26 along the inner periphery of a web 55 until they reach an upper point where the coke 26 falls to the bottom of the rotary furnace via the web 56.

An angle 57 formed between vertical and a line through the center 53 of the rotary furnace to the tip 58 of the driver 54 is referred to as the drop angle, that is, the angle at which coke no longer follows the periphery of the rotary kiln. It should be noted that the coke, while following the web 55, is accompanied by a slip in the material on the cylindrical wall of the rotary kiln. Thereafter, a roll and, finally, a cascade action is made as the coke 26 descends via the droplet 56.

In FIG. 4 illustrates how coke 26 is inserted through aperture 15 according to a web 59. The coke will then make a zig-zag movement, being lifted up to an upper level 60 where the coke will drop down along the drop line 56. The coke's movement pattern will depend on the selected angle 61 for the oblique orientation of the rotary kiln relative to a horizontal plane 62. By changing the angle 61, it is possible to change the drop distance of the coke 26 through the rotary kiln 16. The coke will then have an initial axial drop distance 63 due to the lift of the carrier 64 of the coke 26. The coke can further be imparted to another axial drop distance 64 due to the coke sliding on the joints. Hereby is obtained the pattern of movement illustrated by dotted lines in FIG. 4. 1 In FIG. 5, an alternative embodiment is illustrated in which the pyrolysis unit 4 is located axially in extension of the rotary kiln 16 in a manner similar to that of FIG. 4. In FIG. 5 is illustrated how a frame 65 supports the rotary furnace 16 and the pyrolysis unit 4 relative to a bottom frame 66. It will be possible to arrange the frame 65 pivotally about a pivot point 67 for adjusting the inclination angle of the rotary kiln 61 and thereby being able to influence the residence time of the coke through the plant for the other elements included in the design principle illustrated in FIG. 5, which corresponds substantially to the elements and units illustrated in FIG. 1. No further explanation will therefore be given to these.

When operating a plant according to the invention, gas velocity occurring through rotary kilns 16 can be between 0.2 and 1 meter per minute. per second, preferably 0.5 meters per second. second.

Hereby, the ash in the rotary furnace under gasification of the coke 26 will only be moderately entrained through the interior of the furnace. This is also essential in order to obtain such a small amount of ash in the outlet 30 in the coarse separator 28.

In FIG. 6, the same reference numerals are used for identical or similar 15 elements. The figure thus illustrates the primary process steps / products included in the process of the invention.

The invention is not limited to the embodiments shown above, since other elements may be used in place of the illustrated ones. Thus, it is possible to replace the auger conveyor with belt conveyors or other conveying means, and it is also possible to provide the pyrolysis unit 4 at a position other than the position above the rotary kiln 16.

It should be noted that the individual units and elements included in the plant must be made with gas seals that withstand the pressure and temperatures used in the plant. However, the sizing of such seals will be within the skill of the art, and no specification thereof is therefore given.

Claims (10)

A biofuel gasification plant comprising a pyrolysis process unit, a chamber for partial oxidation of gaseous pyro light products, a solid pyrolysis product reactor unit for gasification, an ash extraction unit and a gasification gas outlet unit, characterized in that the reactor comprises a rotary furnace whose inlet is connected to the pyrolysis unit for receiving the partially oxidized product from the pyrolysis and whose outlet is connected to a separator where ash and gas are separated and fed to ash outlet and gas outlet respectively. 10 Gasification system according to claim 1, characterized in that the inlet of the rotary furnace comprises a vertical shaft which is connected to a pyrolysis unit located above the rotary furnace and which is separated into two channels where a first channel is arranged below the outlet of the pyrolysis unit and primarily the solid pyrolysis product leads to the reactor and where another channel is connected to the outlet of the pyrolysis unit and the gaseous pyrolysis product leads to the reactor. Gasification system according to claim 2, characterized in that the chamber for partial oxidation is provided in said second channel at entrance to the rotary kiln. 20 Gasification plant according to claim 2 or 3, characterized in that the oxidation zone of the reactor and the reduction zone of the reactor are provided inside the rotary furnace. Gasification plant according to any one of the preceding claims, characterized in that the pyrolysis unit comprises transport means for the biofuel. Gasification plant according to any one of the preceding claims, characterized in that the rotary furnace is provided with solid pyrolysis product carriers. DK 174439 B1 Gasification system according to any one of the preceding claims, characterized in that the rotary furnace is disposed at an angle between 0 ° and 10 ° relative to the horizontal, and that this angle is preferably adjustable. A process for gasification comprising a feed and processing of biofuel, a pyrolysis step, a tar decomposition step carried out by partial oxidation of gaseous pyrolysis products, a gasification step for solid pyrolysis product and the gasification being carried out in an oxidation step followed by a reduction stage, is done while rotating the solid pyrolysis product while adding gasifier. Process according to claim 8, characterized in that the partial oxidation is carried out in a zone provided at the inlet to the rotating process step and the oxidation and reduction are carried out in the rotating zone. 15 Process according to claim 8 or 9, characterized in that gas and ash are separated at the outlet from the rotating zone and fed to gas outlet and ash outlet respectively.