WO2008107727A2

WO2008107727A2 - Three-stage gasifier, fixed bed, which has buffer zone of gaseous flow between pyrolysis zone and combustion zone

Info

Publication number: WO2008107727A2
Application number: PCT/GR2008/000017
Authority: WO
Inventors: Lampros Elefsiniotis
Original assignee: Lampros Elefsiniotis
Priority date: 2007-03-06
Filing date: 2008-03-04
Publication date: 2008-09-12
Also published as: EP2126008A2; WO2008107727A3

Abstract

At the upper place of the gasifier exists the first stage which is the pyrolysis zone (1) and it is a countercurrent reactor. At the middle place exists the second stage which is the combustion zone (2). At the bottom place exists the third stage which is the gasification zone (3) and it is a cocurrent reactor. Figure 1 shows the normal operation of the buffer zone (20) and figure 2 shows the reversed operation of the buffer zone (20). The three-stage gasifier is characterized from the fact that the passage from the normal operation of the buffer zone (20) to the reversed operation of the buffer zone (20) and vice versa is achieved only by proper rotation settings of the pumps (BPA), (BCA), (BPG), (BGO), so creating a new model of gaseous flow management between the three stages of the gasifier. This model can achieve the simultaneous combination of the following advantages: -Industrial scale safe operation ability, by using fuel with big possible variations in humidity and/or composition. -The producer gas is free of harmful components (tars, dioxins). -The gasifier does not expose its moving mechanical parts at temperatures above 750°C. -There is not any moving seal mechanism between the stages of the gasifier.

Description

Three-stage gasifier, fixed bed, which has buffer zone of gaseous flow between pyrolysis zone and combustion zone

The invention refers to three-stage gasifier, fixed bed, which has buffer zone of gaseous 5 flow between pyrolysis zone and combustion zone, which is used for solid carbonaceous materials gasification.

The gasification is a thermochemical process that converts solid fuels into combustible gases. The successive proceedings which take place during the process are: 10 -Pyrolysis(>230°C). The humidity of the solid fuel is converted to vapor. The volatile components of the fuel are converted to gases, consisted mostly from tar and/or polycyclic aromatic hydrocarbons(C_nH_m), carbon dioxide(CO₂), carbon monoxide(CO), methane(CH₄) and hydrogen(H₂). The solid residues are charcoal and ash.

-Gasification(>700°C). The glowing charcoal(C) is affected by vapor(H₂O) and oxygen(0₂). 15 It is converted to gases, mostly hydrogen(H₂), carbon monoxide(CO) and carbon dioxide(CO₂).

The mostly used reactors are fixed bed (cocurrent or countercurrent) and fluidized bed

(simple, circulating or pressurized).

The fixed bed reactors are relatively simple fabrications and they are proper for small and 20 medium scale power, but the fluidized bed reactors are complex fabrications and they are applied for power >20MW.

At the countercurrent gasifier the air moves up-draught, having opposite direction from the fuel, namely enters directly to the hearth and is gradually converted to hot gas, which

25 departs after the drying zone of the reactor. The upper layer of the fuel absorbs the heat of the gas and is dried effectively, thus the countercurrent gasifier presents stable operation using high humidity and/or uneven composition fuel, so gives high coefficient for the gasification performance. Unfortunately, the tars which are produced at the pyrolysis zone are not cracked, thus the countercurrent gasifier gives gas with high concision of tars (30-

30 150 g/Nm³) referring to not trained gas.

At the cocurrent gasifier the air moves down-draught, having the same direction with the fuel, namely enters directly to the hearth but does not passes through the drying zone. The drying and the pyrolysis are mainly achieved from the radiation of the hearth. The tars which are produced at the pyrolysis zone are cracked effectively, because they pass

35 through the high temperature (1100-1200⁰C) field of the hearth and secondary they pass through the medium temperature (700-750⁰C) field of reduction zone. Thus, the cocurrent gasifier gives gas with low concision of tars (0.025-0.100 g/Nm³) referring to not trained gas. This gas, after cooling and particle separation is proper for use into internal combustion engines. Unfortunately, the low thermal exchange between hearth and drying

40 zone causes unstable operation by using high humidity and/or uneven composition fuel. They are trials in the past for multistage gasification, by placing pyrolysis of fuel as first stage, by placing combustion of pyrolysis gases as second stage and by placing charcoal gasification as the third stage of the process, in order to have combination of advantages of the two above types of gasifiers. The separation of the stages encounters problems of gaseous flow management which become from the high temperatures and/or from the possible defect of moving seal mechanisms.

At the document DE 895 362 C (BASF AG), the gaseous flow management between the stages becomes from the recirculation of pyrolysis gases through the pumps (8) and (12) at figures 1 and 2. This specific type of gasifier appears the following disadvantages:

-The fixed bed of the pyrolysis reactor (2) seats on some type of moving grate for the removal of charcoal. The flue gas from the combustion of pyrolysis gases applies quite high temperature on the moving grate and therefore the charcoal removal system shall appear often damages. -The fixed bed of the gasification reactor (4) seats on some type of moving grate for the removal of ash. When we insert pyrolysis gases together with air at the position (16), the mixture ignites. Thus the ash removal grate shall appear often damages because of thermal burden. -The gasification chamber (4) is a countercurrent reactor. The pieces of the charcoal fall from the bottom of the pyrolysis reactor (2) and lay on the top of the gasification bed (4). They contain harmful volatile residues (tars, dioxins) due to pyrolysis imperfections. Those volatiles are evaporated without thermal cracking. The producer gas shall have significant amount of harmful components.

At the document WO 02/46332/ A2 (LUTEREK etc), the material lock chamber (68) at figures 7and 12 and 15 manages the gaseous flow between the stages. The main and very serious disadvantage of this layout is that in blockage case of the gates (69) and (70) of the material lock chamber (68), the uncontrollable commixture of gas and air will create explosive gas-air mixture into the reactor.

From the site http://www.mek.dtu.dk we know Viking Gasifier. This is a three stage, laboratory scale gasifier without problems of gaseous flow management. At this, the fuel is imported to the pyrolysis chamber and there, using external heating at the wall of the chamber, takes place thermochemical separation between charcoal and volatiles-vapor. The fragments of the fuel pass through a high temperature air intake zone and when this mixture passes this zone, large fractions of tars and dioxins are burned and/or cracked. After this, the gasification takes place at the glowing charcoal bed. Apart from its advantages and good performance, Viking Gasifier cannot operate at industrial scale. The external heating at the wall of the pyrolysis chamber eliminates the problems of gaseous flow management, but simultaneously limits dramatically the power records of the plant. As above mentioned, the multistage gasifiers have separate stages for pyrolysis, combustion of pyrolysis gases and gasification of charcoal. Quite enough stage and method possible combinations can compose a multistage gasifier, giving the corresponding advantages and/or disadvantages. The present device aims to work at the gaseous flow management between pyrolysis, combustion of pyrolysis gases and gasification of charcoal in order to create a fixed bed gasifier which shall combine the following characteristics:

-Industrial scale safe operation ability, by using fuel with big possible variations in humidity and/or composition. -The producer gas shall be free of harmful components (tars, dioxins).

-The gasifier shall not expose its moving mechanical parts at temperatures above 750⁰C.

-There will not be any moving seal mechanism between the stages of the gasifier.

According to the invention, this is achieved by a three-stage gasifier, fixed bed, which has buffer zone of gaseous flow between pyrolysis zone and combustion zone.

This gasifier is composed from three separate stages, which make pyrolysis (first stage), combustion of pyrolysis gases (second stage) and gasification of charcoal (third stage). The above stages are placed at vertical position, without mechanical separation between them. The pieces of charcoal, which fall from the bottom of pyrolysis bed, form the gasification fixed bed.

The combustion air of the pyrolysis zone moves up-draught, in reverse direction from the pyrolysis gases combustion flue gas, which moves down-draught. We separate the gaseous flow by placing buffer zone between pyrolysis zone and gasification zone. The inlet of the combustion air of the pyrolysis zone is placed at the upper place of the buffer zone and the expansion of the pyrolysis gases combustion flue gas at the lower place.

The flow of the preheated air, which enters at the upper place of the buffer zone, is divided in two streams, by using the proper rotation settings at the pumps of the gasifier. The up- draught stream of the preheated air is cooling the pyrolysis charcoal removing grate and feeds the pyrolysis bed. The down-draught stream of the preheated air feeds the gasification bed.

The buffer zone allows the charcoal which is produced at the first stage to pass and fall without stoppage into the third stage.

The down-draught stream of the preheated air, when pass through the buffer zone, acts as an isolation curtain between first and second stage.

When we treat very wet and/or poor thermally fuel, the pyrolysis zone cannot work effectively. In this case we reverse the flow into the buffer zone, in order that part of the flue gas to feed the pyrolysis bed with heat. Also, when we feed the gasifier with extremely very wet fuel, we provide to the combustion torch additional external supply of gas fuel (natural gas or propane), in order to have enough power for the heating of the huge percentage of vapor which exists into the pyrolysis gases. The three-stage gasifier, fixed bed, which has buffer zone of gaseous flow between pyrolysis zone and combustion zone, according to the present invention, appears combination of the following advantages: -The hot gases, which are derived from the hearth of the countercurrent reactor, pass through the new incoming fuel. From the measurements of the physical parameters at the discharge of the pyrolysis gases we have an immediate image of the composition and/or the humidity of the new incoming fuel, thus the automatic control and the safe operation of the pyrolysis bed are easily achieved by setting the air and/or fuel feed. Thereby settled quantities of charcoal and gases are supplied to the next process stages, thus it is easy to control all the gasification process.

-The pyrolysis gas pump collects the most of the harmful volatiles (tars, dioxins) derived from the pyrolysis zone. Crossing the flame of the burning torch, those harmful volatiles are burned and/or cracked. The pieces of the charcoal, which fall from the first stage, contain also harmful volatile residues (tars, dioxins) due to pyrolysis imperfections. Acting as an additional cleaning stage, the glowing charcoal bed reduces and/or cracks the harmful residues derived from pyrolysis and combustion. So, at the end of the process, we have gas and ash free of harmful residues.

-All the moving mechanical parts of the gasifier are exposed at temperatures below 750⁰C, where the common materials of construction present very good thermal durability. Thus the gasifier shall have very good performance against service and/or blockage problems. -There does not exists any moving seal mechanism between the stages of the gasifier, so the risk for the possible presence of explosive gas-air mixture due to seal defect is minimized.

Figure 1 shows the normal operation of the three-stage gasifier, fixed bed, which has buffer zone of gaseous flow between pyrolysis zone and combustion zone. At the upper place is the first stage which is the pyrolysis zone (1), at the middle place is the second stage which is the combustion zone (2) and at the bottom place is the third stage which is the gasification zone (3). The pyrolysis zone (1) is a countercurrent reactor, fixed bed. At the pyrolysis zone (1) is imported, through the material feeding system (4), the under process fuel and which is held from the grate (5). At the input (6), through the pump (BPA) and the heat exchanger (EPA), is offered preheated air (~400°C). By proper rotation settings of the pumps (BPA), (BCA), (BPG), (BGO), the preheated air (-400⁰C) is divided in two streams. The up-draught stream (13) is cooling the grate (5) and feeds the pyrolysis bed (1).

The down-draught stream (14) pass through the buffer zone, acts as an isolation curtain between pyrolysis zone (1) and combustion zone (2), pass through the combustion zone (2) and feeds the gasification bed (15). The up-draught stream (13) creates the following layers into the pyrolysis zone (1): -Burning Hearth (7). It is achieved partial combustion of the charcoal, which gives the energy for the reactions at the above stacks of material. The rest charcoal and the ash are detached by moving the grate (5), they fall downwards, they pass through the buffer zone

(20), they pass through the combustion zone (2) and they create the fixed bed (15) of the gasification zone (3).

-Reduction Layer (8). Part of the hot carbon dioxide (CO₂), which is produced from the hearth (7), reduces part of the charcoal to carbon monoxide (CO).

-Distillation Layer (9). The volatiles of the fuel are separated through a complicated sequence of pyrolytic reactions, which are described by the general form: C_xH_yO_z → X₁C + X₂CO + X₃CO₂ + X₄CH₄ + χ₅C_nH_m + X₆H₂+ X₇H₂O

The solid fragment (charcoal, ash) falls to the reduction zone (8) while the hot gases rise through the new incoming fuel (10) and they dry it.

-Drying Layer (10). The humidity of the fuel is converted to vapor, which departs together with the rest gases. The pyrolysis gases (PG) derived from the layers of hearth (7), reduction (8), distillation (9) and drying (10) is a mixture from CO, CO₂, CH₄, C_nH_m, H₂, H₂O και N₂.

The pyrolysis gases (PG) are sucked through the pyrolysis gas pump (BPG) and in cascade, through the pyrolysis gas duct (11), they are imported into the torch (12).

From the measurements of physical parameters of the pyrolysis gases (PG) at the duct (11) we achieve the automatic control of the pyrolysis zone (1) by setting the feed of the pump (BPG) and/or fuel feed (4).

At the torch (12), through the pump (BCA) and the heat exchanger (ECA), is offered preheated air (~550°C). The torch (12) blends the pyrolysis gases (PG) with the preheated air (~550°C) and creates flame 1100⁰C- 1200⁰C. The flue gas (16) expands into the space of the combustion zone (2) and trends down-draught, in order to come together with the gasification bed (15).

The most of the tars and the dioxins which exist into the pyrolysis gases (PG), when they cross the flame of the torch (12), are burned and/or cracked. The combustion of pyrolysis gases (PG) produces steam, which is component of the gasification reactions and releases heat, which is energy source for the reactions of the gasification bed (15).

The gasification zone (3) is a cocurrent reactor, fixed bed. The pieces of charcoal, which fall from the pyrolysis zone (1), form the gasification fixed bed (15). The gasification bed (15) of the cocurrent reactor (3) seats on the ash discharge system (17). The water which is evaporated in drying layer (10), the steam which is produced in combustion zone (2) and the down-draught air stream (14) participate together with charcoal in the gasification reactions.

The gasification bed (15) operates with temperature shift from 1100°C-1200⁰C (upper side) to 700°C-750°C (lower side), due to the endothermic gasification reactions. Thus, the mechanical parts of the ash discharge system (17) are not under significant thermal burden. In the gasification bed (15) are prevailing the reactions:

C + H₂O → CO + H₂

CO + H₂O → CO₂ + H₂

2C + O₂ → 2CO Acting also as an additional cleaning stage, the glowing charcoal bed (15) reduces and/or cracks the harmful residues derived from pyrolysis (1) and combustion (2).

The producer gas discharges from the output of the gasification zone (18), passes through the heat exchangers (ECA) and (EPA), passes through particle cleaning and cooling gear

(19), passes through the producer gas pump (BGO) and it is delivered for use. The final producer gas has low conciseness in tars (0.025g/Nm³) and it is rich in H₂ and CO.

This is proper for use into internal combustion engines.

When we treat very wet and/or poor thermally fuel, the pyrolysis zone cannot produce sufficient quantities of charcoal and combustible pyrolysis gases. In this case we reverse the flow into the buffer zone, in order that part of the flue gas to feed the pyrolysis bed by heat.

In figure 2 we show (using equivalent symbols and descriptions with figure 1) the reversed operation of the buffer zone, which is achieved by modification of the normal operation, in order to gasify very wet and/or poor thermally fuel. The pyrolysis zone (1), the combustion zone (2), the gasification zone (3), material feeding system (4) and the grate (5) are as they have been described in normal operation.

During the reversed operation of the buffer zone (20), by proper rotation settings of the air pumps (F1), (F2), (F3), (F4), the flue gas from the torch (12) is divided in two streams. The up-draught stream (22) passes through the buffer zone (20) and enforces additional heat to the pyrolysis bed (1). The down-draught stream (23) feeds the gasification bed (15).

At the input (6), through the air pump (BPA) and the heat exchanger (EPA), preheated air

(~400°C) is offered and trends up-draught (24), cools the grate (5) and enters into the pyrolysis zone (1).

The up-draught flue gas stream (22) and the up-draught air stream (24) create the following layers into the pyrolysis zone (1):

-Burning Hearth (7). It is achieved partial combustion of the charcoal which, together with the up-draught air stream (24), gives the energy for the reactions at the above stacks of material. For the rest, see description at normal operation.

-Reduction Layer (8). See description at normal operation. -Distillation Layer (9). See description at normal operation.

-Drying Layer (10). See description at normal operation.

The pyrolysis gases (PG), the pyrolysis gas pump (BPG), the pyrolysis gas duct (11) and the torch (12) are as they have been described in normal operation.

The automatic control of the pyrolysis zone (1) is like in normal operation. At the torch (12), through the pump (BCA) and the heat exchanger (ECA), is offered preheated air (-550⁰C). The torch (12) blends the pyrolysis gases (PG) with the preheated air (-550⁰C) and creates flame 1100°C-1200⁰C. As above mentioned the flue gas of the torch expands into the space of the combustion zone (2) and is divided in up-draught stream (22) and down-draught stream (23).

The gasification zone (3), the gasification fixed bed (15) and the ash discharge system (17) are as they have been described in normal operation.

The water which is evaporated in drying layer (10) and the steam which is produced in combustion zone (2) participate together with charcoal in the gasification reactions. In the gasification bed (15) are prevailing the reactions: C + H₂O → CO + H₂ CO + H₂O → CO₂ + H₂

The output of the gasification zone (18), the heat exchangers (ECA) and (EPA), the particle cleaning and cooling gear (19) and the producer gas pump (BGO) are as they have been described in normal operation.

When we feed the gasifier with extremely very wet fuel, we provide to the combustion torch additional external supply of gas fuel (natural gas or propane), in order to have enough power for the heating of the huge percentage of vapor which exists into the pyrolysis gases.

In figure 2 we show the emergency operation of the invention, which is achieved by modification of the reversed operation, in order to gasify extremely very wet fuel. In this case we provide to the combustion torch (12) additional external supply (21) of gas fuel (natural gas or propane), in order to have enough power for heating at 1100°C-1200⁰C the huge quantity of vapor which is evaporated in the drying layer (10) and exists into the pyrolysis gases (PG).

The emergency operation of the invention gasifies extremely very wet fuel. Also, by the same way, the system makes cold startup.

The document PCT/GR2007/000017 (Elefsiniotis Lampros) is priority document of the present invention. There, at half page of text, the concept of this invention is presented as reverse engineering of the document OBI 20060100143.

The document PCT/GR2007/000017 contains figure 3 and claim 4, which have date of application the 06 March 2007 and are the concept of the present invention. At the document PCT/GR2007/000017 the recommended support of the concept of the present invention does not exists. So, in order to support correctly the concept of the invention, the present document is submitted.

Claims

1. Three-stage gasifier, fixed bed, which has buffer zone (20) of gaseous flow between pyrolysis zone (1) and combustion zone (2). At the upper place of the gasifier exists the first stage which is the pyrolysis zone (1) and it is a countercurrent reactor. At the middle place exists the second stage which is the combustion zone (2). At the bottom place exists the third stage which is the gasification zone (3) and it is a cocurrent reactor. The preheated air (~400°C) is offered at the input (6), through the pump (BPA) and the heat exchanger (EPA). At the pyrolysis zone (1) is imported, through the material feeding system (4), the under process fuel and which is held from the grate (5). The pyrolysis zone (1) is divided at the burning hearth (7), the reduction layer (8), the distillation layer (9) and the drying layer (10). The pyrolysis gases (PG) are sucked through the pyrolysis gas pump (BPG) and through the pyrolysis gas duct (11) they are imported into the torch (12). At the torch (12), through the pump (BCA) and the heat exchanger (ECA), is offered preheated air (~550°C). The torch (12) blends the pyrolysis gases (PG) with the preheated air (-550⁰C) and creates flame 1100°C-1200⁰C. The flue gas of the torch (12) expands into the space of the combustion zone (2).

The gasification zone (3) receives the pieces of charcoal, which fall from the pyrolysis zone (1) and form the gasification fixed bed (15). The gasification bed (15) seats on the ash discharge system (17).

The producer gas discharges from the output of the gasification zone (18), passes through the heat exchangers (ECA) and (EPA), passes through particle cleaning and cooling gear (19), passes through the producer gas pump (BGO) and it is delivered for use. The three-stage gasifier, who has layout described from the above paragraphs of the present claim, is characterized from the fact that the gaseous flow management of the buffer zone (20), which is achieved by proper rotation settings of the pumps (BPA)₁ (BCA), (BPG), (BGO), allows the charcoal which is produced at the pyrolysis zone (1) to pass and fall without stoppage into the gasification bed (15) and that simultaneously the separation of the stages is available without any moving seal mechanism between the stages.

2. Three-stage gasifier, according to claim 1 , further characterized by the fact that the gasifier does not expose its moving mechanical parts at temperatures above 750⁰C because at the input (6) is offered air (~400°C) which cools the grate (5) and simultaneously the gasification bed (15) protects the ash discharge system (17) from the high temperature of the combustion zone (2).

3. Three-stage gasifier, according to claim 1 , further characterized by the fact that it has two steps of thermal cracking for the harmful residues (tars, dioxins). First step is the flame of the torch (12) and second step is the glowing charcoal bed (15), which is a cocurrent reactor.

4. Use of the three-stage gasifier of the claim 1 for the gasification of dry and/or medium wet fuel. This is the normal operation of the buffer zone (20), easily understandable when you see figure 1.

By proper rotation settings of the pumps (BPA), (BCA), (BPG), (BGO), the preheated air (~400°C) which is offered at the input (6), through the pump (BPA) and the heat exchanger (EPA), is divided in two streams. The up-draught stream (13) is cooling the grate (5) and feeds the pyrolysis bed (1). The down-draught stream (14) passes through the buffer zone, passes through the combustion zone (2) and feeds the gasification bed (15). The flue gas (16) of the torch (12) expands into the space of the combustion zone (2), is directed to the gasification bed (15) and releases heat, which is energy source for the gasification reactions.

The water which is evaporated in drying layer (10), the steam which is produced in combustion zone (2) and the down-draught air stream (14) participate together with charcoal in the gasification reactions. The three-stage gasifier, whose the normal operation of the buffer zone (20) is described from the above paragraphs of the present claim, is characterized from the fact that the buffer zone (20) allows the charcoal which is produced at the pyrolysis zone (1) to pass and fall without stoppage into the gasification bed (15) and that simultaneously the down- draught stream (14) which is created by proper rotation settings of the pumps (BPA), (BCA), (BPG), (BGO), when passing through the buffer zone (20), acts as an isolation curtain between pyrolysis zone (1) and combustion zone (2).

5. Use of the three-stage gasifier of the claim 1 for the gasification of very wet and/or poor thermally fuel. This is the reversed operation of the buffer zone (20), easily understandable when you see figure 2.

At the input (6), through the air pump (BPA) and the heat exchanger (EPA), preheated air (~400°C) is offered and moves up-draught (24), cools the grate (5) and enters into the pyrolysis zone (1). By proper rotation settings of the air pumps (BPA), (BCA), (BPG), (BGO), the flue gas from the torch (12) is divided in two streams. The up-draught stream (22) passes through the buffer zone (20) and enforces additional heat to the pyrolysis bed (1). The down-draught stream (23) is directed to the gasification bed (15) and releases heat, which is energy source for the gasification reactions. The water which is evaporated in drying layer (10) and the steam which is produced in combustion zone (2) participate together with charcoal in the gasification reactions.

The three-stage gasifier, whose the reversed operation of the buffer zone (20) is described from the above paragraphs of the present claim, is characterized from the fact that when we treat very wet and/or poor thermally fuel ,the buffer zone (20) allows the charcoal which is produced at the pyrolysis zone (1) to pass and fall without stoppage into the gasification bed (15) and that simultaneously the up-draught flue gas stream (22), which is created by proper rotation settings of the pumps (BPA), (BCA), (BPG), (BGO), passes through the buffer zone (20) and enforces additional heat to the pyrolysis bed (1).

6. Use of the three-stage gasifier, according to the claim 5, for the gasification of extremely wet fuel, in which the reversed operation of the buffer zone (20) is modified to emergency operation and which is characterized from the fact that it can treat extremely wet fuel by offering to the combustion torch (12) additional external supply (21) of gas fuel (natural gas or propane), in order to have enough power for heating at 1100°C-1200°C the huge quantity of vapor which exists into the pyrolysis gases (PG).

7. Use of the three-stage gasifier, according to the claims 4 and 5, which is characterized from the fact that the passage from the normal operation of the buffer zone (20) to the reversed operation of the buffer zone (20) and vice versa is achieved only by proper rotation settings of the pumps (BPA), (BCA), (BPG), (BGO), so creating a new model of gaseous flow management between the three stages of the gasifier. This model can handle big possible variations in humidity and/or composition of the fuel.