WO2007081296A1

WO2007081296A1 - Downdraft/updraft gasifier for syngas production from solid waste

Info

Publication number: WO2007081296A1
Application number: PCT/TR2006/000001
Authority: WO
Inventors: Omer Salman; Coskun Mancuhan; Nilufer Selen Onal; Mustafa Tolay
Original assignee: GEP YESIL ENERJI URETIM TEKNOLOJILERI Ltd STI
Current assignee: GEP YESIL ENERJI URETIM TEKNOLOJILERI Ltd STI
Priority date: 2006-01-16
Filing date: 2006-01-16
Publication date: 2007-07-19
Anticipated expiration: 2008-07-16

Abstract

The present invention relates to a new type gasifier (1) which can run by downdraft or updraft to produce syngas from sorted / unsorted municipal solid wastes (MSW), refuse-derived fuel (RDF), industrial wastes including waste water treatment plant sludge, leather industry residues, agricultural wastes and biomass comprises a bottleneck zone (2), a drying zone (3), a pyrolysis zone (4), a reduction and oxidation zone (5), an ash section (6), a safety valve (10), a rotary valve (8), a vibrator (9) and several igniters (7).

Description

DOWNDRAFT/UPDRAFT GASIFIER FOR SYNGAS PRODUCTION

FROM SOLID WASTE

TECHNICAL FIELD

The present invention relates to a new type gasifier which can run by downdraft or updraft to produce syngas from sorted / unsorted municipal solid wastes (MSW), refuse-derived fuel (RDF), industrial wastes including waste water treatment plant sludge, leather industry residues, agricultural wastes and biomass.

The present invention more particularly, relates to a new type gasifier which can run by updraft or downdraft for minimization of municipal solid wastes (MSW), refuse- derived fuel (RDF) and biomass. The gasifier within the context of the present invention comprises a bottleneck zone, a drying zone, a pyrolysis zone, a reduction and oxidation zone, an ash section, a safety valve, a rotary valve, a vibrator and several igniters.

BACKGROUND OF THE INVENTION

Gasification is the thermochemical conversion of solid material into a gas which can be used to produce electricity by means of a conventional steam-cycle (ie the gas is burned to produce steam in a boiler, to drive a steam turbine) or by direct use in a gas turbine or internal combustion engine. This process offers a number of important advantages over the more conventional combustion process: gas has much better burning properties than solids, it is easier to control and it produces less particulate emissions and gaseous pollutants. Power plant based on gasification rather than combustion also have higher overall conversion efficiencies.

There are hundreds of gasifiers in the patent literature. From the point of view of the tar produced by each type produces the gasifier groups are as follows: updraft, downdraft and fluidized bed.

Updraft reactors are useful for producing gases to be burned at temperature 1000⁰C, but the high tar level up to 10-20% makes them difficult to clean for other purposes. The tar level is intermediate between updraft and downdraft, typically 1-5% in fluidized bed reactors. The low tar levels of downdraft reactors make them more suitable for uses requiring clean gas, which contain 0.1% tar.

In updraft (counterflow) gasification the preheated air or oxygen and if it is necessary the steam contacts charcoal on a grate, generating gas temperatures of 1000- 1400⁰C. This hot gas rises through the down coming biomass, pyrolizing it at successively lower temperatures and eventually drying it. All of the types of tar occur in the final gas, with primary tars dominating, typically at a level of 10-20%.

The pyrolysis happen much faster and rapid pyrolysis produce more tar in raw gas in the updraft gas producers. Updraft gas producers have poor loading capability and they are not suitable for running engine.

In downdraft (coflow) gasification air or oxygen and fuel enter the reaction zone from the top of the reactor and burn most of the tars to pyrolyze the fuel, in a process called "flaming pyrolysis". The flame temperatures are 1000-1400⁰C, but the flame occurs in the interstices of the pyrolizing particles whose temperatures are 500- 700⁰C, so that about 0.1 % of the primary tars are converted to secondary tars and the rest are burned to supply the energy for pyrolysis and char gasification. Very few of the compounds found in downdraft gasification are found in updraft reactors and vice-versa.

Unit capacity restriction is a disadvantage for downdraft gas producers. So, multiple units operating in parallel when higher capacity is desired. A lower overall efficiency and difficulties in handling higher moisture and ash content are also the following disadvantages.

Considering the crossdraft gas producer, high exit gas temperature, poor CO2 reduction, high gas velocity are disadvantages. Unlike downdraft and updraft gasifiers, the ash bin, fire and reduction zone in crossdraft gasifiers are separated. These design characteristics limit the type of fuel for operation to low ash fuels such as wood, charcoal and coke. The relatively higher temperature in cross draft gasifier has an obvious effect on gas composition such as high carbon monoxide, and low hydrogen and methane content when dry fuel such as charcoal is used.

In fluidized bed gasifiers preheated air or oxygen and if it is necessary the steam levitate the incoming particles which recirculate through the bed. Some of the oxidation contacts biomass and burns the tars as they are produced as in a downdraft gasifier; some of the oxidant contacts charcoal as in an updraft gasifier.

There are also several patent documents related to the gasifiers. WO 2005047435 discloses a gasifier for the gasification of biomass and waste to produce combustible effluent, comprising: a fuel valve for loading solid fuel into a first oxidation zone; a first throat defining the lower edge of the first oxidation zone; a second throat defining the lower edge of a second oxidation zone; a reduction zone linking the first oxidation zone to the second oxidation zone and; two oppositely located (at the reduction zone) vortex discharge pipes for the combustible effluent wherein in the first oxidation zone the gas flow is in the same direction as fuel flow and in the second oxidation zone the gas flow is in the opposite direction to the fuel flow.

US 4306506 discloses an apparatus for the conversion of solid fuels and solid organic waste materials by high temperature gasification into gaseous fuel called "producer gas". The apparatus comprises a stacked two-section gasifier defining sequentially descending drying, distillation, oxidation and reduction reaction zones through which a column of the solid fuel descends during its conversion to the gaseous fuel. The lower reactor section is of double-shell construction and defines the lower oxidation and reduction reaction zones. Means are provided for drawing air into the oxidation zone for burning reaction with carbonized fuel passing therethrough and for thereafter drawing reaction gases downwardly through the lower reduction zone of the gasifier and then through the annular space defined by the double-shell structure of the lower section in indirect counter-current heat exchange relationship with the fuel column portion in the oxidation and reduction zones. The inner shell element of the lower section is arranged in hanging manner within its associated outer shell element to allow expansion of the double-shell structure under the high temperature conditions experienced by the gasifier without harmful stress build-up in the apparatus. The inner shell element supports within its lower portion two stacked funnel-shaped transition pieces which form a series of throat-like constrictions for supporting the fuel column in the gasifier and which cause localized increase in the velocity of the gases passing downwardly therethrough and leaving the reduction zone of the reactor.

US 4309195 discloses an apparatus for effecting the conversion of solid fuels (including solid organic waste materials having a fuel valve) by high temperature gasification into clean-burning and uniform gaseous fuel called "producer gas." The apparatus comprises a two-section, stacked double-shell gasifier reactor defining sequentially descending, drying, distillation, oxidation and reduction reaction zones through which a continuously fed column of the solid fuel descends during its conversion to a gaseous fuel. Means are provided for drawing process air into the oxidation zone for burning reaction with carbonized fuel passing therethrough and for thereafter drawing reaction gases in downdraft fashion through the lower fuel reduction zone of the gasifier and thence in sequence through the annular space defined by the double-shell structure of the lower section of the gasifer in indirect countercurrent heat exchange relationship with the fuel column portion in the oxidation and reduction zones and through the annular space defined by the double- shell structure of the upper section of the gasifier in indirect co-current heat exchange relationship with the fuel column portion in the drying and distillation zones. The inner shell elements of the two sections of the stacked double-shell reactor structure are arranged in hanging manner within their respective outer shell elements to allow expansion of the double-shell structure under the high temperature conditions experienced by the gasifier without harmful stress build-up in the apparatus.

In order to prevent above mentioned disadvantages, the gasifier is needed which has unique and optimum design, produces less tar and heavy metals, prevents explosion risk and uncontrolled air leakage. Also it must be harmless to the environment and economically viable. 5 I V^ I / I M -- " " ^ - -

BRIEF DESCRIPTION OF THE INVENTION

The main scope of the present invention is to develop a new type gasifier for the sorted / unsorted municipal solid wastes (MSW), refuse-derived fuel (RDF), industrial wastes including waste water treatment plant sludge, leather industry residues, agricultural wastes and biomass minimization.

A different objective of the present invention is to develop a new type gasifier which prevents explosion risk and uncontrolled air leakage.

A further objective of the present invention is to minimize formation of tar and heavy metals.

Another objective of the present invention is to produce of synthesis gas (syngas) or fuel gas under atmospheric or elevated pressure.

Other objective of the present invention is to develop a new type gasifier which is harmless to the environment and economically viable.

In order to achieve the scope, a new type gasifier was developed which can run either updraft or downdraft to produce syngas from municipal solid waste (MSW), refuse-derived fuel (RDF) and biomass. Mentioned gasifier comprises a fuel inlet, a drying zone, a pyrolysis zone, a reduction and oxidation zone, an ash section and igniters, together with necessary equipment for process control.

BRIEF DESCRIPTION OF THE FIGURES

The embodiment and advantages of the present invention shall be made clear with the figure described as following and the present invention is to be evaluated by taking into account such descriptions.

Figurei ; one example of the gasifier of the present invention.

REFERENCE NUMBERS The main components of gasifier (1) to produce syngas from sorted / unsorted municipal solid wastes (MSW), refuse-derived fuel (RDF), industrial wastes including waste water treatment plant sludge, leather industry residues, agricultural wastes and biomass would typically be as follows:

1. Gasifier

2. Bottleneck Zone

3. Drying Zone 3.1. Syngas Zone

3.2. Higher Syngas Outlet Zone

4. Pyrolysis Zone

4.1. Higher Preheated Air or Oxygen Inlet

4.2. Air Nozzles 4.3. Air Chamber

5. Reduction and Oxidation Zone

5.1. Lower Syngas Outlet Zone

5.2. Cooling Air Inlet

5.3. Lower Preheated Air or Oxygen inlet 6. Ash Section

6.1. Ash Grate

6.2. Air Nozzles

6.3. Air Chamber

6.4. Ash Discharger 7. Igniter

8. Rotary Valve

9. Vibrator

10. Safety Valve

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a new type gasifier (1) which can run updraft or downdraft for the sorted / unsorted municipal solid wastes (MSW), refuse-derived fuel (RDF), industrial wastes including waste water treatment plant sludge, leather industry residues, agricultural wastes and biomass minimization.

As is known, syngas production is the process of converting biomass and solid waste into combustible gases (carbon monoxide, methane and hydrogen) that ideally contain all the energy originally present in the solid or liquid carbon-based material (feedstock). In practice energy conversion efficiencies lie between 60% and 90%. It can be broadly defined as the thermochemical conversion of a solid or liquid carbon- based material feedstock into a combustible gaseous product (combustible gas) by the supply of a gas production agent (partial oxidation) under the application heat. Oxidation can be done either by using air or oxygen. If oxygen is used, the resulting gas (syngas) will have a higher calorific value.

The thermochemical conversion changes the chemical structure of the feedstock by means of high temperature. The agent introduced allows the feedstock to be quickly converted into gas by means of different heterogeneous reaction. The combustible gas contains CO₂, CO, H₂, CH₄, H₂O, N₂, and trace amounts of higher hydrocarbons, inert gases present in the gas production agent, various contaminants such as small char particles, ash and tars.

Direct process occurs when an oxidant agent is used to partially oxidize the feedstock. The oxidation reactions supply the energy to keep the temperature of the process up. If the process does not occur with an oxidizing agent, it is called indirect gas production and needs an external energy source. The moisture content in the feedstock which produces steam is the most commonly used indirect process agent, because it is easily produced and increases the hydrogen content of the combustible gas.

This process does produce hydrocarbon liquids, such as tars and oils, limiting the ability to handle fines. In order to limit the amount of fines that are entrained in the product gas, dusty tars, taken out in downstream separation processes, are recycled back to the top of the gasifier (1 ). The dusty tars are believed to "stick" or conglomerate the smaller fragments of the solid waste and biomass together, obtaining the necessary size requirements of the solid waste gasifier (1 ). In order for the process to function correctly there are a number of parameters that need to be maintained within certain limits. These include: particle size distribution, moisture content, ash content, volatile matter content, heating value, bulk density, feedstock composition.

Particle size distribution is important to ensure that the flow of matter through the reactor is uniform and blockage does not occur through agglomeration. It is also necessary to ensure that particle size is not such that heat transfer to the full mass of the feedstock is prevented. The ideal situation is to have a high surface area and a low mass. As the particles get smaller, however, problems of dust formation and pass-out from the gasifier (1 ) can occur.

With regard to moisture content, as it increases the thermal efficiency of conversion decreases. There comes a point at which the amount of heat required for drying becomes excessive and this provides an upper limit to acceptable moisture contents for gasification systems. In practice it is desirable for the moisture content to be between 10% and 20% in the feedstock. Moisture is actually involved in the biomass conversion process, providing the hydrogen molecules for hydrogen gas formation and for very dry feeds may have to be made up with the injection of steam. With

MSW typically having moisture contents of approximately 50% it is necessary for some drying to occur, before the feedstock is fed into the gasifier (1).

The total ash content in the biomass and the chemical composition of the ash are both important. The composition of the ash affects its behavior under the high temperatures of combustion and gas production. For example, melted ash may cause problems in gas producers. Such problems may vary from clogged ash- removal caused by slagging ash to severe operating problems from ash accumulation within the thermal reactor.

Volatile matter refers to the part of the biomass that is released when the biomass is heated. During this heating process the biomass decomposes into volatile gases and solid char. Biomass and solid waste typically have a high volatile matter content (up to 80%) whereas coal, for example, has a volatile matter content of less than 20%. The heating value of differing biomass substrates can vary significantly. Biomass and solid waste, for example, can vary from 10MJ/kg to 20MJ/kg. Bulk density will also vary significantly with the type of waste that is being gasified.

Uniform feedstock composition is preferable as this ensures that product gas composition will remain stable and provide less difficulty for subsequent usage technologies.

According to the present invention, the gasifier (1) gasifies pelletized, refuse-derived fuel (RDF). Gasifier (1 ) is used alternately to feed low-energy gas to drive an internal combustion engine (ICE) with 1 MWe and heat (2 MWth) production capacity.

According to the present invention, the following reactions take place:

1. Manufacture of Synthesis Gas

Biomass (or coal + O₂ -> CO + H₂ (carbon monoxide and hydrogen) 2. Water gas shift adjusts CO/H₂ ratio

CO+H2O < - > CO₂ + H₂ 3. Synthesis with catalyst

CO+2H₂ ^ CH₃OH (methanol)

00+H₂ -> "(CH₂)n" (diesel or gasoline, the Fischer Tropsch reaction) 3H₂ + N₂ -> 2NH₃ (ammonia)

Process relies on chemical processes at elevated temperatures >1000°C. The rotary valve (8) integrated to the system which prevents uncontrolled air leakage, for security purposes and control fuel feed rate. Air inlet from the top of the gasifier (1) from the bottleneck zone (2).

Vibrator (9) is mantled to the gasifier (1) since the feedstock material in the gasifier (1 ) is not at the same level all the time, but there may become small peaks inside. In order to evenly distribute the feedstock vibrations are applied at certain periods.

No slurried form feedstock is fed to the gasifier (1 ), only briquettes are accepted. Gasifier (1) produces syngas which mainly consists of CO, H₂, CO₂, CH₄. Reactant agent for the process to occur is only the air at environmental conditions. The reactor contains air preheater, O₂ supplier and steam generator are activated in case of necessity. Gasifier (1 ) can be operated under the vacuum conditions.

According to the present invention, gasifier (1 ) can be considered under downdraft (coflow) gasification reactor umbrella where the flame temperatures are 1000- 1400⁰C, but the flame occurs in the interstices of the pyrolysing particles whose temperatures are 500-700⁰C, so that about 0.1 % of the primary tars are converted to secondary tars and the rest are burned to supply the energy for pyrolysis and char gasification. Very few of the compounds found in downdraft gasification are found in updraft reactors and vice-versa. Because of low tar production abilities, the downdraft type has been chosen as the design parameter and in addition to that flexible feedstock properties played a major role for the selection of updraft and downdraft design parameters.

The solid waste gasifier (1 ) operates at close to atmospheric pressure at approximately 600⁰C, employing air or O₂ as the process / fluidized agent. The product gas as a result of gasification process is assumed with the below characterization.

Tablei . Gasifier (1) output results (Preferred Gas Quality)

Fuel Feeding

Figurei illustrates one example of the gasifier (1 ) which can run either updraft or downdraft of the present invention. Refuse-derived fuel (RDF) or any other solid waste pellets should have diameter of 20 - 100 mm in order to be properly gasified in the gasifier (1). Feedstock input (RDF pellets) before solid waste gas production is assumed to be the best with the below characterization.

Table 2. Ultimate analysis of RDF pellets and briquettes (% by weight)

Table 3. Proximate analysis of RDF pellets and briquettes (% by weight, daf)

Sample C H N S O (difference)

Pellet (MSW) 48 .80 8. 45 6. 50 1. 85 34.40

Briquette (MSW) 53 .5 7. 90 6. 15 1. 75 30.70

Below itemized solid waste types are some of the materials minimized and used as renewable energy source (fuel) at gasification process.

- Sorted / unsorted municipal solid waste,

- Industrial wastes including waste water treatment plant sludge,

- Leather industry residues,

- Agricultural wastes, etc.

Fuel that is too large or too moist is generally the cause of feed line plugging, although backpressure may also prevent the fuel from moving forward. Measures should be taken to insulate the line and prevent the system from reaching temperatures at which pyrolysis commences. The fuel-feeding systems convey the fuel from storage bins and hoppers to the gasifier (1 ). An ideal feeding system provides smooth and continuous feeding and allows for accurate control of the feed rate by hopper weighing and rotary valve (8). The system should be relatively insensitive to variations of fuel size and must maintain sufficient pressurization to prevent the backflow of gases from the gasifier (1) to the feeding system. Typically, the fuel-feeding system consists of two parts: fuel transport from storage to the gasifier (1 ) and injection into the gasifier (1). Feedstock flow to the gasifier (1) is controlled over the rotary valve (8) and also a safety valve (10) is integrated to the gasifier (1 ).

Particles of fuel 20 to 100mm. in diameter are introduced into the gasifier (1) from the top, while the oxidant agent (air or O₂) enters from the top oxidation zone and bottleneck zone (2). The solid waste gasifier (1 ) can be broken up into zones, which blows out the uncontrolled gas pressure formed as a result of water vaporization and gas formation from volatile organics.

Drying

In the drying zone (3) which is below the bottleneck zone (2), the solid waste is heated and dried while cooling the product gas that is about to leave the gasifier (1 ). This zone may have the temperature up to 400⁰C. The fuePs water evaporates to the vapour phase; which is necessary to produce H₂ in the reaction zone.

In updraft working conditions syngas suction occurs in the syngas zone (3.1 ) of the gasifier (1 ). The hot gas coming upwards from the bottom of the gasifier (1 ) heats up the material inside during its transport.

The syngas is taken out from higher syngas outlet zone (3.2) and transferred into cyclones for gas cleaning. The temperature of syngas at the higher syngas outlet zone (3.2) can be up to maximum 400⁰C. This higher syngas outlet zone (3.2) is active when the process is in updraft mode. Pyrolysis

Briquetted waste is broken down to coke, tar, CH₄, H₂, in the pyrolysis zone (4) which is between 400 - 600⁰C. Tar formation is at highest level. The material is thermally degraded in pyrolysis zone (4) and various types of aromatic hydrocarbons are produced. Depending on the chemical reactions, heavy tars, light tars or water soluble hydrocarbons or aromatic compounds can be produced in this part of the process.

In downdraft working conditions there is only higher preheated air or oxygen inlet (4.1 ) near the reduction and oxidation zone (5) which is working only in the downdraft working conditions.

Depending on the fuel type and the working conditions, air nozzle (4.2) positions can be changed which has an effect on the entrance angle of the air to the gasifier (1 ). This situation increases the efficiency of the process.

The air enters the gasifier (1 ) in the atmospheric temperature and heated up in the air chamber (4.3); where the temperature depends on the pyrolysis zone (4) and on the sucked air flow rate. There the optimum air temperature distribution is evenly realized. Homogenization of appropriate air temperature is realized. This zone prevents the heat loss out from the system.

Reduction and Oxidation

In the bottleneck zone (2) the solid waste gas is between 1000 - 1200⁰C, the H₂O and O₂ in the introduced air or O₂ reacts with coke and output gas is called solid waste gas (SWG) which mainly consists of CO, H_2, CO₂, CH₄, at temperature between 1000 - 1200⁰C. Steam feeding to the reduction and oxidation zone (5) is optional. As the MSW runs through the descendent zone the SWG cools down to 600 - 800⁰C. At the downdraft working conditions the gas sucking to the gasifier (1) is realized downwards and at the updraft working conditions the gas is sucked upwards. SWG is sucked to the cleaning system after it reaches 400 - 600⁰C in the gasifier (1). The syngas is taken out from this lower syngas outlet zone (5.1) and transferred into cyclones for gas cleaning. The temperature of syngas at the lower syngas outlet zone (5.1 ) can be up to maximum 400⁰C. This lower syngas outlet zone (5.1 ) is active when the process is in downdraft mode. As a result of the optimization and development, the minimum possible tar and particle material content in a downdraft gasifier (1 ) is reached within the context of the present invention.

If the system is working under downdraft working conditions, the air chamber (4.3) functions for the cooling of ash section (6).

The temperature of cooling air at the cooling air inlet (5.2) is between 35-7O⁰C. The heated air sucked from this zone during downdraft conditions is used as combustion air in gas burners for the heat economy.

In updraft working conditions, the preheated air for gasification purposes is sucked into the gasifier (1 ) by means of lower preheated air or oxygen inlet (5.3).

Ash Discharging

Depending on the inert material content in the fuel, the gasification process produces ash which has to be extracted from the system by means of ash discharger (6.4) located at the ash section (6). In both up 7 downdraft working conditions the formed ash is extracted in certain quantities from the bottom of the gasifier (1).

Ash grate (6.1) is made out of a special material which is high temperature resistant; so that the syngas in the accumulated ash content in this portion can be sucked easily. The necessary porosity has been realized at the ash material for the easy gas transfer. In addition to that, ash agglomeration and syntherization have been prevented. By having this tailor made ash grate (6.1) the continuous ash and gas flow has been reached. Air nozzles (6.2) located at this portion of the gasifier (1 ) are manually opened. These have to be closed during downdraft running, otherwise the syngas is burnt with the help of the inlet air coming from these air nozzles (6.2) which is not appreciated at all.

If the system is working under downdraft working conditions, the air chamber (6.3) functions for the cooling of ash section (6). The temperature of cooling air is between 35-70⁰C. The heated air sucked from this zone during downdraft conditions is used as combustion air in gas burners for the heat economy.

Gasifier (1 ) ash residues could be used to fertilize the ground (rarely if the feedstock is not agricultural waste), as the concrete material or disposed in a sanitary landfill. Instead, solid residues of gas pre-treatment and air pollution control systems are typically disposed in landfills, because of their high heavy metal concentration level. Sometimes, solid residues can be used in industrial processes, such as cement mills, for a complete integration between gasification and industrial processes.

Table 4. Ash Analysis of Municipal Solid Waste (% Weight)

Once the gasifier (1) is ignited at the selected mode it has to continue in that mode. However, the present gasifier (1 ) is currently putting on efforts on necessary mechanical changes so that it will be possible to change the mode from downdraft to updraft or from updraft to downdraft working conditions during the process, without any interruptions.

Igniters (7) are located in the middle air chamber (6.3) which are used for start up of the process and to heat up the systems. The two igniters (7) on both sides of the gasifier (1) are using propane gas initially and once the system reaches its steady state these are switched off, and from that point on system is ran by its own product syngas. The number of igniters (7) can be increased in case of necessity.

Minimum 3MW energy output (electrical + heat) equivalent syngas makes the system a commercial process.

Claims

1. A solid waste gasifier (1) which produces syngas from sorted / unsorted municipal solid wastes (MSW), refuse-derived fuel (RDF), industrial wastes including waste water treatment plant sludge, leather industry residues, agricultural wastes and biomass comprising a bottleneck zone (2), a drying zone (3), a pyrolysis zone (4), a reduction and oxidation zone (5) and an ash section (6), a vibrator (9) and a rotary valve (8) characterized in that said gasifier (1 ) can be operated either under downdraft or updraft conditions according to needs and once the gasifier (1 ) is ignited at the selected mode it has to continue in that mode and by putting on necessary mechanical changes, the mode from downdraft to updraft or from updraft to downdraft working conditions during the process can be changed without any interruptions.

2. A solid waste gasifier (1) in accordance with claim 1 , wherein the syngas is sucked downwards at the downdraft working conditions and the syngas is sucked upwards at the updraft working conditions.

3. A solid waste gasifier (1) in accordance with claim 1 , wherein said drying zone (3) comprises at least one syngas zone (3.1) in which syngas suction occurs in updraft working conditions and at least one higher syngas outlet zone (3.2) from where the syngas is taken out when the process is in updraft mode.

4. A solid waste gasifier (1) in accordance with claim 1 , wherein said pyrolysis zone (4) comprises at least one higher preheated air or oxygen inlet (4.1 ) which is working only in the downdraft working conditions and air nozzles (4.2) whose positions can be changed depending on the fuel type and the working conditions to influence the entrance angle of the air to the gasifier (1 ) and at least one air chamber (4.3) which functions for the cooling of said ash section (6) when the process is in downdraft mode and in which the gas is heated.

5. A solid waste gasifier (1) in accordance with any of the preceding claims wherein said reduction and oxidation zone (5) comprises at least one lower syngas outlet zone (5.1 ) from where the syngas is taken out when the process is in downdraft mode, at least one cooling air inlet (5.2) and at least one lower preheated air or oxygen inlet (5.3) which provides that the preheated air for gasification purposes is sucked into the gasifier (1 ) when the process is in updraft mode.

6. A solid waste gasifier (1 ) in accordance with any of the preceding claims wherein said ash section (6) comprises an ash grate (6.1 ) which is made out of a high temperature resistant material and said ash grate (6.1) prevents ash agglomeration and syntherization and also provides the continuous ash and gas flow, air nozzles (6.2) whose positions can be changed depending on the fuel type and the working conditions and said air nozzles (6.2) have to be closed during downdraft running, at least one air chamber (6.3) which functions for the cooling of said ash section (6) when the process is in downdraft mode and an ash discharger (6.4).

7. A solid waste gasifier (1 ) in accordance with any of the preceding claims wherein said gasifier (1 ) comprises at least two igniters (7) which are located in the middle air chamber (6.3, 4.3), said igniters (7) are used for start up of the process and to heat up the systems and switched off once the system reaches its steady state.

8. A solid waste gasifier (1) in accordance with any of the preceding claims wherein said gasifier (1) produces dry H₂ in the range of about % 10.0 to about %15.0, dry O₂ in the range of about % 1.0 to about %1.5, dry N₂ in the range of about % 53.0 to about % 65.0, dry CH₄ in the range of about %1.5 to about %2.5, dry CO in the range of about %15.0 to about %20.0, dry CO₂ in the range of about % 9.0 to about %15.0, dry C₂H₂ in the range of about % 0.5 to about

%1.0, dry C₂H₆ in the range of about % 0.5 to about % 1.0, dry GCV in the range of about % 4.5 to about % 6.0 by weight.

9. A solid waste gasifier (1 ) in accordance with any of the preceding claims wherein said gasifier (1) comprises at least one safety valve (10).

10. A solid waste gasifier (1 ) in accordance with any of the preceding claims wherein minimum 3MW energy output (electrical + heat) equivalent syngas makes the system a commercial process.