Method and system for production of a hot burnable gas based on solid fuels

The invention relates inter alia to a method and a system for producing hot burnable gas with a low content of NOx, dust and tar as well as clean ash with a low carbon content by means of a stage-divided thermal reactor. In the stage- divided thermal reactor the conversion process of the solid fuel takes place in separate vertical stages (from below and up) : ash burn-out, char oxidation and gasification, pyrolysis, drying and a partial oxidation stage wherein a part of the gas from the gasifier is oxidized. The stages: ash burn-out, char oxidation and gasification, pyrolysis and drying comprise part of an updraft gasifier. The partial oxidation stage functions both as:

• a tar reduction stage, and

• a NOx reduction stage, and

· as heat source for drying and pyrolysis of the top layer of the updraft

gasifier.

BACKGROUND OF THE INVENTION

Production of hot burnable gases during thermal conversion of fuel is well known. In literature such a process is often named "thermal gasification". The hot burnable gas is often named "producer gas" or "gasification gas". The hot burnable gas can be used for several purpose e.g. for combustion for production of hot water, steam or heating thermal oil, or it can be cooled and cleaned and used as gas in a gas engine or gas turbine, or it can be synthesized into liquid products, or it can be distributed to end users further away.

Reference is made to WO/2010/022741, which relates to a thermal reactor in which solid fuel can be converted into a clean hot flue gas with a low content of volatile organic compounds (VOC's), NOx and dust, and clean ash with a low carbon content by means of a stage-divided thermal reactor, where the conversion process of the solid fuel is in separate vertical stages (from below and up) : ash burn-out, char oxidation and gasification, pyrolysis, drying, and a gas combustion stage where gas from the gasifier is combusted. and WO 01/68789 Al : A staged gasification process and system for thermal gasification of special waste fractions and biomass, e.g. wood, comprising a drier in which the fuel is dried upon contact with superheated steam. The dried fuel is fed into a pyrolysis unit to which superheated steam is also supplied. The volatile tar, containing components produced in the pyrolysis unit, is passed to an oxidation zone in which an oxidation agent is added so as to cause a partial oxidation, whereby the content of tar is substantially reduced. The solid fuel components from the pyrolysis unit may be fed into a gasification unit to which hot gases from the oxidation zone are supplied. In the gasification unit the solid fuel components are gasified or converted to carbon. The gas produced in the gasification unit may be burnt in a combustion unit, such as a combustion engine. Thus, a gasification process is obtained for gasification of biomass and waste with a high energy efficiency, low tar content of the gasification gas and with moderate risk of slagging for a wide spectrum of fuels, including fuels with a large content of moisture and

WO 2008/004070 Al : A method of controlling an apparatus for generating electric power and apparatus for use in said method, the apparatus comprising : a gasifier for biomass material, such as waste, wood chips, straw, etc.. Said gasifier being of the shaft and updraft fixed bed type, which from the top is charged with the raw material for gasification and into the bottom of which gasifying agent is introduced, and a gas engine driving an electrical generator for producing electrical power, said gas engine being driven by the fuel gas from the gasifier. By supplying the produced fuel gas directly from the gasifier to the gas engine and controlling the production of the fuel gas in the gasifier in order to maintain a constant electrical output power, the necessity of using a gas holder between the gasifier and the gas engine is avoided and

Page 5 and 15 of the report "Formation, Decomposition and Cracking of Biomass Tars in Gasification", 2005 with ISBN number: 87-7475-326-6 and page 8-12 of the report: "Biomass gasification - State of the art description, December 2007", deliverable 8, of the project "Guideline for safe and eco-friendly biomass gasification"

Thermal reactors

Solid fuel is usually converted into a burnable gas (gasification) or into a flue gas (combustion) in a moving bed or a fluid-bed reactor.

Moving-bed reactors are typically divided into following categories: updraft (air/gas goes up and fuel down); downdraft (air and fuel go down) or

grate/stoker-based system (moving grate, vibrating grate, stoker) where fuel moves horizontally (often with a slope downwards).

Fluid-bed reactors are typically divided into the following categories: bubbling fluid bed (BFB), circulating fluid bed (CFB) or entrained flow (EF).

Most reactors are originally designed for conversion of coal. Fresh solid fuel such as biomass or waste has very different properties compared to coal. Especially the content of volatiles and water is much higher in biomass and waste. In coal, the volatile content is normally below 30%, whereas for biomass and waste the volatile content is normally above 65% (dry ash free weight basis). Further, the content of water in fresh biomass and waste is often above 20%, and even often above 50%, so drying of the fuel is often a very important issue in biomass and waste reactors. Further, the content and the composition of the ash can be very different for coal and biomass/waste. Also the content of alkali metals (Na, Ka), Chlorine, Potassium, Silica etc. may be much higher, and ash melting points of biomass and waste are known to be much lower than in coal.

Therefore, standard "coal reactors" are not optimal for conversion of biomass and waste. Feeding systems and means of transporting the fuel

Feeding systems are normally screw or push type or pneumatic "spreader stoker" feeders. In grate systems, the fuel is transported by the grate. In most cases, combustion air is led through the grate. These systems may have several problems including hot spots on the grate, uneven air distributions, ash/char falling through the grate, controlling the stages on the grate etc. In fluid-bed systems, the fuel is mixed with the bed material. The fluid-bed systems may have problems with separating the bed material from the ash, and with separating the different process steps as fluid beds are normally well-stirred reactors. Updraft gasifiers are not often used, as the amount of tars (longer gaseous molecules that condensate while cooled) is very high. Updraft gasifiers were earlier used for production of town gas, but these sites have caused

environmental problems due to the tars. Lately updraft gasifiers have been used also for gas-engine operation with extensive tar removal systems, such as described in WO 2008/004070 Al and for full combustion of solid fuels as in WO/2010/022741.

Updraft gasification technology is known as a simple and robust technology. In updraft gasifiers, there is a simple feeding and transporting mechanism, both into the reactor and out of the reactor, where the ash can be removed in a cold state. When the ash layer is in the bottom of the reactor, the gasification agent

(air/steam) is added. It is well known that updraft gasifiers convert the fuel very well and that there is very little carbon in the ash.

However, the updraft gasification technology has some disadvantages such as · The produced gas has a high content of tars, which are difficult to clean up when syngas production is the aim of the gasifier

• A high bed, of 3 meters or more, a lot of space is needed for drying due to the top of the bed being cold (below 300C).

• Scaling up is normally difficult as the different zones in the ash layer cannot be controlled separately. In systems such as WO 01/68789 Al one or several of the process reactions are physically separated from the others. This can have some process advantages, but it also has the disadvantages that the reactors become: · Larger

• More expensive to built

• More expensive to maintain.

Water content in the fuel

Normally, a thermal reactor is made for either fuel with high water content (= low heating value) or for fuel with low water content (= higher heating value).

However, end users often prefer a unit that can convert a broad range of fuels.

WO 2007/036236 Al describe a solution to this problem : If the combustion unit is designed for wet fuels and receives a dry fuel then the lack of water in the fuel can be compensated for by adding water to the fuel or into the thermal reactor, so the drying zone doesn't become too hot, thus resulting in NOx formation and/or overheating materials. Tars and Partial oxidation of tars

When a solid fuel is heated to 200-600°C gaseous hydrocarbons (tar) will be produced.

These tars can lead to plugging or break down of the subsequent processes such as heat exchangers, filters, engines, turbines or fuel cells. According to

"Formation, Decomposition and Cracking of Biomass Tars in Gasification",

Fjellerup et. Al, 2005, it can therefore "be necessary to remove or crack the tars.

3

The allowable tar levels are about 50.5 and 1 mg/Nm for gas engines, gas turbines and fuel cells, respectively. There is though a large uncertainty

concerning these values. "

Cracking of tars can be done by partial oxidization : Oxygen (0 ₂ ) reacts with the condensable tar molecules and decompose the tar molecules into small gaseous molecules, that are not condensable. With partial oxidation at temperatures around 600-900°C and with an air ratio above 0.2 the tar content of the gas can be reduced 90 - 95% or more, maybe even 98-99 %. Partial oxidation is especially efficient at temperatures of 800-900°C.

Typical amount of Tar from an updraft gasifier - without partial oxidation - is about 5-10 g/Nm3 gas.

Dust

One of the major technical problems in converting solid fuels into energy in a technically robust and environmentally friendly way is to remove the load of dust produced in the thermal reactor.

In most types of thermal reactors the dust level out of the thermal reactor is more than 500 mg/Nm3. Therefore, extensive filtering is normally necessary. Only very few types of reactors (for instance updraft gasifiers) have a dust level below 100 mg/Nm3. Such reactors may not need filtering.

NOx

NOx is causing acid rain and there are therefore strict limitations on NOx levels from thermal reactors.

Fuel NOx is formed from the nitrogen in the fuel when oxygen is added to the fuel and the fuel is heated and chemical reactions occur.

Thermal NOx is formed in the gas combustion stage and is mainly dependent on the temperature. The higher the temperature is, the higher NOx formation, but also the higher the oxygen content is, the more NOx is formed. The NOx formation is moderate when the temperature is below 1100°C, but NOx formation accelerates when the temperature gets above 1100°C.

NOx level from state of art thermal reactors are 200 mg NOx/m3 or above.

Reduction of NOx by thermal oxidation

According to the Final Report from the ERA-NET Bioenergy Project FutureBioTec: "Future low emission biomass combustion systems", October 2012, the NOx level in gases can be reduced if the gases are in reduced atmosphere (No or very little content of 02). Especially, if the temperature is between 600-900°C and the retention time is 1 second or longer, the NOx reduction is considerable.

NOx can also be reduced for instance by Selective catalytic reduction (SCR) or Selective non-catalytic reduction (SNCR).

The SCR process use a catalyst to convert NOx into diatomic nitrogen, N ₂ , and water, H ₂ 0. The SNCR method is used to reduce NOx emissions in thermal plants using solid fuels such as biomass, waste and coal. The process involves injecting either ammonia or urea into the hot flue gas where the temperature is between 750°C and 1100°C to react with the nitrogen oxides formed in the combustion process. The resulting product of the chemical redox reaction is nitrogen (N ₂ ), carbon dioxide (C0 ₂ ), and water (H ₂ 0).

Oxygen content in flue gas

An important parameter for combustion plants is the oxygen content in the flue gas. The lower the oxygen content, the better.

There are several advantages to low-excess oxygen including :

• Lower amount of flue gas and therefore:

- lower loss of energy in flue gas in the stack

- lower investment cost and energy consumption for air blowers and flue gas blower

- smaller and cheaper components downstream of the thermal reactor

• Higher steam ratio in the flue gas and therefore better radiation properties

• Higher water dew point in the flue gas and therefore higher energy

efficiency in a condensation cooler.

Typically, the excess air is more than 5%, such as 7% (dry basis), which corresponds to a lambda (stoichiometric ratio) of 1.3 or more. Steam content in flue gas

There are several advantages of a high steam content in the flue gas. These advantages include, but are not limited to:

• Radiation properties improved

· Recovery of heat in condensing unit improved

• Soot formation prevented

• Limitation of temperature and hence NOx formation. Air distribution

In typical gasification and combustion plants, air is distributed to many of the stages:

• The drying stage

• The pyrolysis stage

• The gasification/oxidation stage

· The ash burn-out stage

• The gas combustion stage, and here often in several stages (secondary and tertiary stages).

Steam and oxygen content in the combustion air

Normally untreated air is used for combustion, but the properties of the air can be improved by adding steam and/or oxygen to the air.

Steam in the primary air (for the solid biomass) results in lower temperatures in the oxidation zone, which prevent slagging of the ash and improves the

gasification reactions (H20 + C -> CO + H2).

Steam in the secondary air (gas combustion) reduces temperatures in the gas combustion section, thus reducing NOx. Further steam prevents soot formation. A high content of oxygen in the air results in a lower mass flow, thus reducing the size of the plant.

Carbon content in the ash

In grate and fluid-bed systems, the carbon content of the ash is often 10% or more. This leads to an efficiency and environmental problem : The carbon contains valuable energy, which is not utilised, and it also contains environmentally unfriendly substances, such as PAH (Polycyclic aromatic hydrocarbons).

Further, it is often a technical problem that ash sinters at 700-900°C depending on the ash components. To prevent ash sintering in fluid beds and grate systems, the char content is often high, such as 10% or above.

Further, in grate systems, unburned fuel with high char content often falls through the grate; hence the char content in the bottom ash will increase.

Ash removal system

In grate systems and in fluid-bed systems, the ash removal systems are costly and complicated, as the ash removal system is operating at temperatures above 300 C.

In fluid-bed systems, ash and sand are mixed, so after ash/sand removal, the sand needs to be separated from the ash.

Ash-removal systems of updraft gasifiers can be made simple, as the temperature in the ash removal system is below 300 C.

Moving parts in the reactor and in the hot stages

In grate systems, the fuel is moved from the inlet to the ash outlet by a grate. Typically, this grate is made of high-grade steel, which is both costly and also needs replacement. Normally, a part of the grate is replaced at least every year, and costs related to downtime, materials and labour may be very high.

In some updraft gasifiers, there is a large stirrer in the top to even out the fuel. Shapes

Fluid-bed reactors and updraft gasifiers are typically round, whereas grate systems are typically rectangular.

The round shape in typical updraft gasifiers results in a maximum size of about 10 MW thermal. A typical key figure of updraft gasifiers is 1 MW/m2 of char gasification reactor. At 7 MW, the diameter is then more than 3 m and, due to the grate design, the flow may become uneven if the plant is much bigger. Therefore, it is recognized that app. 10MW is the maximum input of round updraft gasifiers. Size of plants

Combustion plants are made in very small scale, such as stoves of 5 kW and even below, or in very large scale, such as coal-fired power plants, which can be several hundred MW.

Turn-down ratio

A typical turn-down ratio of grate systems and fluid beds is about 1 : 2, whereas updraft gasifiers may have a turn-down ratio of 1 : 10 or even 1 : 20.

SUMMARY OF THE INVENTION

The present invention provides an improved method and an improved system or installation for gasification of biomass and waste. Various aspects, features and embodiments of the invention will be presented in the following .

Thermal reactors

The present invention may be viewed as using the updraft gasification principle followed by a partial oxidation stage. An updraft gasifier utilizes gravity to move solid matter between process stages. Thus, directional wording such as up and down and top and bottom is to be interpreted in the normal way with respect to gravity. In the updraft gasifier the fuel is fed into the top of the fuel bed and converted into a burnable gas in the following successive stages (from top and down) : a drying stage, a pyrolysis stage, a char gasification and an oxidation stage and an ash burn out stage. Above the updraft gasifier oxygen is added to the gas from the updraft gasifier and so the tars from the updraft gasifier are cracked (by partial oxidation) into non-condensable gases, and heat from exothermal reactions of the partial oxidation is transferred to the top layer of fuel in the updraft gasifier, which hereby effectively dries and pyrolyses the fuel.

Thus, the present invention provides, in a first aspect, a method for converting a solid carbonaceous fuel into burnable gas and ash, said method preferably comprises stages, where the fuel may be heated to temperatures causing the fuel to decompose into gaseous and solid components, and a partial oxidation stage, where the gaseous components produced are partially oxidised, the stages taking place inside a thermal reactor and preferably comprises:

- a drying stage,

a pyrolysis stage, in which the fuel is pyrolysed without addition of oxygen,

a gasification and oxidation stage, in which char is converted to gas an ash burn-out stage to which oxygen is supplied, and

- a partial oxidation stage to which oxygen is supplied,

wherein

the fuel at the pyrolysis stage is heated by means of the gases formed in the gasification and oxidation stage and the partial oxidation stage, the drying stage, the pyrolysis stage, the gasification and oxidation stage and the ash burn-out stage form an updraft gasifier and are carried out in an updraft moving bed reactor,

and

the partial oxidation stage takes place above the pyrolysis stage, where the gases from the updraft gasifier are partially oxidized, and heat from the partial oxidation is transferred to the top layer of fuel in the updraft gasifier.

Preferably, the stages are not provided by mechanical dividing elements, such as horizontal wall elements. In the present context "stage" is preferably used to designate a specific region or zone within a chamber, which chamber being defined by wall elements. In addition, a stage is preferably defined as a region or zone in which a given process is taken place. In the present content, the stages comprised in the updraft gasifier (e.g. drying, pyrolysis, char gasification and partial oxidation, ash burn out) are separate stages in the sense that the different processing of the fuel are carried out in separate stages. In addition, the stages are successive in the sense that fuel goes directly from one stage to another. Each of the stages may also be characterized as being coherent, typically in the sense that the stage is a zone in which a particular process is taken place. The partial oxidation stage is also a stage that is separate from the other stages and where processes involving gas from the updraft gasifier take place.

By gases from the updraft gasifier are partially oxidized preferably means that the gases from the updraft gasifier are burned to provide a partial oxidation of the gases. As presented herein, burned is preferably not considered to be a complete oxidation.

In some preferred embodiments of the method according to the invention, the partial oxidation stage may be closer than 4 m to the top of the solid fuel or even closer than 2 m to the top of the solid fuel.

In some preferred embodiments of the method according to the invention, the temperature in the partial oxidation stage may be between 550 - 950°C, preferably between 750 - 900°C.

In some preferred embodiments of the method according to the invention, the gas leaving the thermal reactor (gas produced in the reactor) may have a heating value of 2-5 MJ/Nm ³ , wherein the heating value may be controlled at least by the water content of the carbonaceous fuel.

In some preferred embodiments of the method according to the invention, the tar content of the gas from the updraft gasifier may be reduced by 90 - 99% in the partial oxidation stage preferably by controlling the oxygen injected into the partial oxidation.

In some preferred embodiments of the method according to the invention, gas from the partial oxidation stage may be cooled preferably either within the thermal reactor or downstream from the thermal reactor.

In some preferred embodiments of the method according to the invention, the oxygen required for the partial oxidation in the partial oxidation stage may be supplied as air, oxygen enriched air or pure oxygen. In some preferred embodiments of the method according to the invention, the oxygen injected into the partial oxidation stage may be injected horizontally or in a direction pointing downwards. In some preferred embodiments of the method according to the invention, the partial oxidation stage may be followed by a gas combustion stage such that the gases from the updraft gasifier pass through the partial oxidation stage before they go into the gas combustion stage, where gas from the gasifier is combusted. In some preferred embodiments of the method according to the invention, the gas combustion stage may be downstream from the thermal reactor.

In some preferred embodiments of the method according to the invention, the gas combustion stage may be inside the thermal reactor.

In some preferred embodiments of the method according to the invention, the gas combustion stage may be supplied with air and/or flue gas.

In some preferred embodiments of the method according to the invention, the gas combustion stage may be followed by an SNCR stage such that the gases from the updraft gasifier pass through the partial oxidation stage and the gas

combustion stage before they go into the SNCR stage within which urea or ammonia is injected and reacts with the NOx compounds in the gases. In some preferred embodiments of the method according to the invention, the gas from the updraft gasifier may be converted into liquid fuel in a gas synthesis stage.

In some preferred embodiments of the method according to the invention, the partial oxidation may be provided to have a retention time of the gas in the partial oxidation stage of more than 1 second, such as more than 2 seconds and provide a temperature in the partial oxidation stage between 500-1000°C, such as between 600-900°C thereby producing NOx content in the gas leaving the thermal reactor below 200 mg/Nm3, such as below 150 or even below 100 mg/Nm3. In some preferred embodiments of the method according to the invention, oxygen, such as air, may be introduced into the partial oxidation stage in an amount assuring partial oxidation and may be intimately mixed with the gases produced in the pyrolysis stage, the temperature in partial oxidation stage may be between 500-1000°C, such as between 600-900°C and the retention time in the partial oxidation stage may be more than 1 seconds, such as more than 2 seconds, thereby preferably providing a tar content in the gas leaving the thermal reactor below 0.5 g/Nm ³ , such as below 0.1 g/Nm ³ , or even below 0.05 g/Nm ³ . In some preferred embodiments of the method according to the invention, the flow of gas upwardly through the top layer solid fuel may be controlled so as to keep the amount of dust, below 500 mg/Nm3, such as below 100 or event below 50 mg/Nm3 in the gas leaving the thermal reactor (1). In some preferred embodiments of the method according to the invention, method is controlled, preferably be controlling, inter alia, the amount of in-feed of carbonaceous fuel into the reactor, so that the retention time in the ash burn-out stage (6) is at least one hour, such as at least two hours, such as at least 4 hours, thereby providing a carbon content in the ash after burn-out less than 10%, such as less than 5%, such as less than 1%, or even less than 0.5% based on weight.

In a second aspect, the invention relates to a system for converting a solid carbonaceous fuel into burnable gas and ash said system preferably comprising a thermal reactor, said thermal reactor comprising stages for conversion of solid carbonaceous fuel into a burnable gas, said stages being separate process stages preferably comprising :

an ash burn-out stage,

a char gasification and oxidation stage,

a pyrolysis stage, and

- a partial oxidation stage,

said thermal reactor may further comprise means adapted to controlling the oxygen amount to be led to the ash burn-out stage and the partial oxidation stage so that the gases produced may be converted into burnable gas with low emissions (NOx, CO) and with low excess oxygen content and preferably high steam content, and where further said partial oxidation stage may be providing heat to the pyrolysis and drying stages by radiation and convection.

In some preferred embodiment of the system according to the invention, the system may comprise a reactor wall of the thermal reactor preferably extending from fuel inlet to ash outlet in a horizontal or sloping direction so that fuel moves towards the ash outlet by gravitational force.

In some preferred embodiment of the system according to the invention, system may further comprise means, such as one or more nozzles, to inject oxygen into the partial oxidation stage, preferably horizontally or in a direction pointing downwards.

In some preferred embodiment of the system according to the invention, the system may further comprise a gas combustion stage in the thermal reactor where gas from the gasifier may be combusted.

In some preferred embodiment of the system according to the invention, the system may further comprise an SNCR stage.

In some preferred embodiment of the system according to the invention, the system may further comprise means, such as one or more nozzles, to inject urea or ammonia into the SNCR stage. In some preferred embodiment of the system according to the invention, the system may further comprise a gas synthesis stage, wherein gas from other process stages may be converted into liquid fuel.

In the following, preferred embodiments of different items preferably forming part of the invention are further detailed.

Transporting systems

The fuel is transported into the thermal reactor, preferably by screws, pushers, spreader stokers or other transporting means. Preferably, the gasifier does not need any transporting mechanism inside the reactor besides the ash removal system.

Description of the stages in the updraft gasifier = the solid part

(from top to bottom):

Fresh fuel is transported into the reactors drying stage. In the drying stage, the water in the fuel evaporates. Fuels may have a very little water content, such as a few %, or fuels may have high water content, such as 60% (weight basis) or higher. At atmospheric pressure, drying happens when the fuel is heated to e.g. 100°C. The higher the temperature is, the faster is the drying process. The energy for the drying process comes from two internal processes:

• Heat from the partial oxidation above, primarily transferred by radiation and convection

· Heat from the char gasification below, primarily transferred by convection.

As the drying stage is effectively heated to a high temperature, such as 400°C or even 600°C or above, the drying reaction time in this reactor is short: Fuels with a high moisture content above 40% water, can dry in around 1 hour while dryer fuel can dry much faster such as below 5 minutes, thus resulting in a very compact drying stage.

When the fuel is dried and further heated, further de-volatilization occurs in the pyrolysis stage. In the pyrolysis stage, the solid organic fuel is heated to a temperature between app. 300° and 900° C and decomposed into a solid component containing char and ash and a gaseous component containing organic components including tars, methane, CO, C02, H2 and H20 etc.

The energy for the pyrolysis process comes primarily from two other internal processes:

• Heat from the partial oxidation above, primarily transferred by radiation and convection

• Heat from the char gasification below, primarily transferred by convection. As the pyrolysis stage is effectively heated to a high temperature, such as 400°C or even 700°C or above, such as 500°C or even 700°C or above , the pyrolysis reaction time according to this invention is very short, such as below 1 hour or such as below 5 minutes, thus resulting in a very compact pyrolysis stage.

Compact drying and pyrolysis stages result in a plant with reduced building height and reduced material costs.

In the char oxidation and gasification stage, the solid component produced in the pyrolysis stage is converted into a burnable gas and a carbon-rich ash.

Gasification reactions (mainly C02+C -> 2 CO and H20 + C -> CO + H2) are endothermal (energy consuming). Gasification agent is the gas produced by the oxidation. The temperature in the gasification and oxidation stage is between 600°C-1100°C. In literature, "gasification" is often named "reduction".

In the oxidation stage, the carbon that is not gasified in the gasification stage is oxidized/burned by use of oxygen. Besides oxygen, also steam and nitrogen can be added as dry air, moisturized air, and steam can also be let to the oxidation stage. The temperature in the oxidation stage is between 700-1100°C. The ash layer.

Below the char oxidation and gasification stage is the ash layer. The oxidation agent (air) and possibly steam are let into the ash layer. The temperature of air/steam is low, such as below 300°C or even below 100°C. Hereby, inert ash is cooled, resulting in a cold ash, such as below 300°C, or even below 200°C.

The ash can be removed by an ash removal system, such as ash screws or other means.

Description of the partial oxidation part (above the solid part)

The updraft gasifier produces a combustible gas containing H20, H2, CO, C02, CH4 and higher hydrocarbons. A typical gas composition just above the bed when a fuel with 50% water content used is:

H20: 41%, H2: 12%, CH4: 2%, CO: 18%, C02: 4%, N2: 21%, higher

hydrocarbons (Tars) : 2% (% by volume). The gases are then partially oxidised in the partial oxidation stage. If air is used and if the temperature of the partial oxidation is 800C, then an excess air ratio is about 0.45 (air added/air necessary for complete combustion) and an

approximate gas composition after partial oxidation is:

H20: 33%, H2: 11%, CH4: 0%, CO: 4%, C02: 13%, N2: 39%, higher

hydrocarbons (Tars) : 0%

During the partial oxidation the relative amount of higher hydrocarbons (tars) is reduced, maybe even to zero. Other processes take place as well in the partial oxidation stage such as the partial oxidation of methane: 2CH4 + 02→ 2CO + 4H2,

The partial oxidation process is carried out near the bed surface, such as 4 metres or below, and hereby the top of the bed is heated by the partial oxidation stage mainly by radiation, but also somewhat by convection.

Cooling the partial oxidation stage

It can be an advantage to keep the flame in the partial oxidation below 950C or even below 800C, as a lower temperature will reduce NOx and soot formation.

The heat transfer from the partial oxidation to the updraft gasifier bed results in a colder flame, and hereby is the NOx and soot level low.

There are several ways to keep the temperature of the partial oxidation stage at the right temperature:

• The amount of oxygen can be regulated : More oxygen will increase the temperature and vice versa.

• Water can be injected into the thermal reactor via nozzles and the

evaporative energy of the water will cool the partial oxidation stage.

• cooling items can be inserted such as steam super heater or other types of superheaters i.e. helium based superheaters for use in Stirling engines. Dust

While other technologies, such as grates, have a high speed of air/gas (more than 10 m/s) through the solid fuel such other reactors have a dust level out of the thermal reactor of more than 500 mg/Nm3 at full load.

In preferred embodiments of the current invention is used an updraft gasifier where the speed of gas through the top layer of the solid fuel is below 2 m/s or even below 1 m/s, which result in a very low-dust gas leaving the updraft gasifier.

Position of the nozzles for partial oxidation

The nozzles can be placed in a uniform height or in various heights, and

preferably the nozzles point horizontally or even a bit downwards, e.g. in an angle of 0-20 degrees in such a way and in such a height that heat transfer to the bed below is optimized. But the nozzles shall, or may, not point into the fuel layer, as this will increase dust emissions.

All in all may the dust level of current invention be very low: such as below 100 mg/Nm3 or even below 50 mg/Nm3.

Preferably, the walls of the thermal reactor are shaped in such a way that there is some back mixing/recirculation of the flue gas which will improve NOx reduction and tar reduction. Also the walls can be placed in an angle so that radiation from the hot walls to the top layer of the fuel is increased.

Moisturized air can be used for the partial oxidation as moisturized air reduce soot and NOx formation, and increase overall efficiency when condensing of the gas is used.

The nozzles are designed to give the right mixing of air and gasification gas.

Typically, the nozzle speed (speed of gas out from the nozzle) will, or could, be between 20-40 m/s at full load.

The temperature in the partial oxidation stage is typically between 550-950°C. Water content in fuel

A gasification unit according to the present invention can use a wide spectrum of fuels, such as wet fuels with a low heating value or dry fuels with a high heating value. This is possible by adjusting the amount of air used for partial oxidation. The temperature of the partial oxidation stage can easily be adjusted by changing the amount of air/oxygen for the partial oxidation. Fuel with a low moisture content (= high heating value) needs little air, while fuel high moisture content needs more air to keep the same temperature in the partial oxidation zone.

It is further possible to increase the temperature by using oxygen enriched air or to reduce the temperature by sprinkling water (such as a condensate) into the partial oxidation zone.

A water sprinkling system further has the advantages that:

• NOx formation is prevented with lowered temperature

· Soot production is lowered with lowered temperature and increased steam content

• Radiation properties are increased with higher steam content

• Condensation energy to be recovered for heat production in low- temperature condenser is increased with the amount of water evaporated in the thermal reactor.

A system that adds water to the system can ensure a very stable temperature, independently of the fuel heating value in the thermal reactor, and hereby stable and low emissions.

Use of the product gas

The gas produced according to the invention can be used to several purposes:

• The gas can be combusted in a combustion chamber and the hot flue gas can heat up water, thermal oil, steam or the like

· The gas can be cooled and cleaned and used in internal combustion

engines, gas turbines or fuel cells or the like

• The gas can be converted into liquid fuel by condensing and/or synthesis.

• The gas can be cleaned and cooled and distributed to end users through gas-pipes. NOx

Low NOx content in the produced gas is, or may be, an important feature of the present invention. Fuel-NOx is formed when there is an over stoichiometric air-fuel ratio in the fuel. In the present invention, there is very limited or even no excess air in the char oxidation stage as the present invention uses the updraft gasification principle. Thermal-NOx is formed when temperatures are high, such as over 1100C. As preferred temperatures are 800-950C, very small amounts of thermal NOx are produced.

Further: as described earlier (ref. Final Report from the ERA-NET Bioenergy Project FutureBioTec) can the NOx level in gases be reduced if the gases are in reduced atmosphere (No or very little content of 02). Especially, if the

temperature is between 600-900°C and the retention time is 1 second or longer, the NOx reduction is considerable.

A main chemical reaction path for reducing NOx, is that CO react with NOx and form free N2 at temperature between 600-900C.

As the partial oxidation gas has a considerable amount of CO, is a result of above that the present invention may result in a gas with a very low NOx such as below 200 mg/Nm3, or even below 150 mg/Nm or even below 100 mg/Nm3. Preferred embodiments of controlling to accomplish the above, may be

summarized as the retention time is typically provided by the size of the thermal reactor, and the temperature is controlled by the amount of oxygen/air introduced into the partial oxidation stage, since more oxygen/air provides a higher temperature.

To ensure a very low NOx formation, a SNCR method can be used, for instance, urea can be injected. Tar content in product gas

A main advantage in the present invention is that the content of tars is limited. As previously described is the typical amount of tar from an updraft gasifier in the range of 5-10 g/Nm3. According to preferred embodiments of the present invention - with a partial oxidation stage after an updraft gasifier - will the tar amount be reduced at least 90% (to 0,5-1 g/Nm3), and possibly even as low as below 0,2 g/Nm3 (tar reduction of 96-98%).

Such very low tar level is achieved due to good (intimately) mixing, the right amount of oxygen (to provide a partial oxidation), sufficient retention time (such as more than 1 seconds, such as more two seconds) and temperature of partial oxidation stage such as between 500-1000°C, such as between 600-900°C.

There are several advantages of the low tar content in the air including :

· Simpler, cheaper and more robust gas cleaning, if gas needs to be cooled and cleaned.

• Cleaner condensate if the gas cooling system produces a condensate. Air distribution

The combination of low tar content, low NOx, low dust in the gas and clean ash is, or may be, a very unique feature for the present invention. This is realized as the necessary air for complete combustion is used for two processes only:

• Char conversion (primary air)

• Partial oxidation (secondary air) while drying and pyrolysis are driven by energy from radiation from the partial oxidation and convection from the hot gas in the char gasifier.

Hereby, each active oxygen molecule is used either for burning out de-volatilized char or for oxidizing gas components, such as the tars.

Carbon content in the ash

In the present invention, an updraft gasification principle is used for converting char into burnable gas and ash. In an updraft gasifier, according to preferred embodiments of the invention, the retention time of the final carbon burn-out in the ash burn-out stage may be several hours which is much more than in for instance in grate furnaces, which have a retention time of about 10 minutes in the final carbon burn-out stage. This results in a high char burn-out, thus a low carbon content in the ash, in the present invention : The carbon content in the ash is, or may be, less than 10%, or even below 5% or 1%.

To reduce sintering, moisturized air can be used, or steam can be added in the bottom of the thermal reactor. Ash removal system

Another main advantage of the invention is, or may be, the simplicity of removing the ash. In grate systems and in fluid-bed systems, the ash removal systems are costly and complicated, whereas according to this invention the ash removal system is technically easy to embody and cheap.

In the present invention, the ash can easily be removed by a round grate system or simply by one or several screws.

Standard screws remove materials from one end, so if screws are used they must have, or may have, a special design so the ash is removed in an even layer.

No (or limited) moving part in the reactor and in the hot stages

A major advantage of the present invention is that there is no moving parts placed in warm stages, such as the drying, pyrolysis, char oxidation and char gasification stages. Ideally, the system consists of the following moving parts:

· Feeder (below 100°C)

• Ash screw (ash is below 300°C)

• Air blower (below 100°C).

However, for some types of plants according to the present invention and/or types of fuels, it may be an advantage to have one or several stirrers/pushers to move biomass/ash from one reaction stage to the other. Note: for some plants according to the present invention, it might be an advantage to have one or several thermocouples or other sensors that for lifetime reasons are moved into the hot stages during longer or shorter periods. Shapes

The thermal reactor is divided into stages in the vertical direction. The various stages include (from below and up) :

• Ash burn-out

· Char oxidation and gasification

• Pyrolysis

• Drying

• Partial oxidation. The partial oxidation stage functions both as tar reduction and heat source for the top layer of the updraft gasifier.

According to the invention, the stages can be partly horizontally divided, i.e. the drying section could be close to the feeder, and the pyrolysis stage could be horizontally away from the feeder. Such a shape will keep pyrolysis gases away from the feeder, and it will keep the feeder section cool (such as below 200°C).

The height of the thermal reactor may differ from a few metres for small plants to more than 8 metres, such as more than 10 metres for large plants.

In the horizontal plane, the thermal reactor is preferably round or rectangular.

The solid bed as well as the partial oxidation stage may have different dimensions For instance, the bottom part of the thermal reactor may have one diameter, and higher up in the drying/pyrolysis region, it may be wider, and above in the partial oxidation stage, the thermal reactor may be even wider.

Downstream

A plant may comprise components or stages, which are located outside of the thermal reactor and such that the gasses produced in the thermal reactor pass through those components or stages subsequently, i.e. after leaving the thermal reactor. Such components or stages are said to be located downstream from the thermal reactor. Size of plants

Typically, these types of plants will be between 1-50 MW thermal input, but they may be both smaller and larger. A typical design parameter is, or may be, that there shall be about lm2/MW fuel input in the gasification section and about 1-2 seconds retention time in the partial oxidation stage; the retention time may be determined as the volume of the partial oxidation stage divided by the volume flow through the partial oxidation stage.

Turn down ratio

Another important feature of the present invention is the high turn-down ratio. Depending on the design and fuel, the invention can be used to design thermal reactors with a turn-down ratio of 1 : 10 or even below e.g. 1 :20.

Easy to regulate

Another important feature is that the system is, or may be, also very easy to regulate. Bed height

It is desirable to have an even bed height. Therefore, a registration system of the bed height may preferably be installed and the registration system may preferably interact with the feeding system. The bed height can be registered by sensors such as radar, ultrasonic or gamma measurements. The bed height will, or may be, typically be between 1-3 meters.

Ash removal

In the bottom of the gasifier, the ash is removed, and oxygen (air) is injected into the ash layer. The ash removal system is activated when the ash is with a minimum of ash, as only by then is the temperature of the ash low. When the ash layer contains char, the char will oxidize, and the ash will be warm. When the char is fully burned, the ash will be cold. Thus, temperature measurements right above the oxygen (air) inlet can indicate if the char is fully burned and then activate the ash removal system. Oxygen for gasification and for partial oxidation

The stoichiometric ratio for the thermal reactor is app. 0.5-0.9. A typical gas composition is: H20: 33%, H2: 11%, CH4: 0%, CO: 4%, C02: 13%, N2: 39%, higher hydrocarbons (Tars) : 0-1% (by volume).

Typically the heating value of gas produced in the thermal reactor will, or may, be between 2-5 MJ/Nm3 (higher heating value at 25C). The main influence of the heating value is the water content of the fuel. The drier the fuel is, the higher the heating value is.

The oxygen supply for the partial oxidation may preferably be controlled by a temperature sensor and/or by a sensor that measures CO and/or H2 content.

The updraft gasifier stage operates, or may operate, with a stoichiometric ratio of 0.2-0.25, so about 20-40% of the oxygen is led to the ash burn-out stage and the rest to the partial oxidation stage.

Water for temperature control

As described previously, water can be used for temperature control of the gas combustion stage.

Cheap, simple and compact

As described above, the system offers a number of advantages compared to state-of-the-art gasification technologies. It could therefore be expected that the system will be expensive and complicated. However, the simplicity and the compactness of the system is a main advantage of the invention.

Pressure of system

Typically, the pressure of the system will be atmospheric, but the system can be built for both underpressure and overpressure.

Materials

Typically, a system will be built of high-temperature materials such as bricks and insulation blocs inside, followed by insulation and a steel vessel. BRIEF DESCRIPTION OF THE FIGURES

The invention, and in particular preferred embodiments thereof, is presented in more details in the following, referring to the drawings where: Fig. 1 schematically illustrates how the basic process steps of the thermal reactor according to the invention interact.

Fig. 2 schematically illustrates an energy plant producing heat and power. Fig. 3 shows an energy-mass balance of the energy plant illustrated in Figure 2.

Fig. 4 shows the flow lines of the air added to the partial oxidation reactor 13, and to the combustion chamber in the plant illustrated in Figures 2 and 3. Fig. 5 shows the velocity lines in the partial oxidation reactor and in the

combustion chamber in the plant illustrated in Figure 2 and 3.

Fig. 6 shows a schematic diagram of the updraft ash system and the updraft gasification part illustrated in Figures 2, 3, 7, 8 and 9; in fig. 6, upper part, the view is illustrated in a side view to show the interior of the thermal reactor, the lower part of fig. 6 is illustrates the ash screws as seen in an end view.

Fig. 7 shows schematically a thermal reactor with an updraft gasifier and a partial oxidation zone, and downstream from the thermal reactor: a zone for gas combustion and a boiler.

Fig. 8 shows the system depicted in fig. 7 in use,

Fig. 9 illustrates another embodiment of an energy plant producing heat and power,

Fig. 10a and 10b shows temperature distribution and flow velocities during use of a thermal reactor according to a preferred embodiment of the present invention, DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION In Fig. 1, 1 is a unit or reactor to which fuel and oxygen is added and a burnable gas with low dust and low tar content is produced (in fig. l, the gray-shaded box framing : Drying, Pyrolysis, Char gasification and oxidation, Ash burn-out and Ash Layer is only for illustrating the updraft gasification stages) :

Conversion of fuel to gas in updraft gasifier

The fuel is converted thermally by addition of air (and/or oxygen). Thus, a burnable gas, 14, with a low dust and a low tar content is produced in the thermal reactor 1. The fuel added to unit 1 is solid, e.g. biomass, waste or coal.

The fuel is fed by a feeder 2, and converted to a gas in the bottom of the reactor, which is an updraft gasification process, comprising drying process 3, pyrolysis process 4, char gasification and oxidation process 5, ash burn out process 6, an ash layer 7, an ash removal system 8, one or several gasification agents 9 and one of several sensors SI.

Gasification agents, 9.

The gasification agents 9, can be 02, C02 and/or H20 or a mix hereof. A preferred mix is moisturized air, with 0.2 kg H20 per kg dry air. Another preferred mix is recirculated flue gas that is mixed with fresh air, so the mix has an 02 content of 10-13%. The temperature of the gasification agent is preferably between 80-150C.

SI and the ash removal system, 8.

SI is the sensor that activates the ash removal system. SI is preferably one or several temperature sensors that register the temperature of the ash layer. The setpoint of SI is preferably between 80-120C. When the temperatures are below the setpoint, the ash layer is thick, SI registers a low temperature, and some ash can be removed by the ash removal system 8. When ash is removed the solid stages above will move downwards due to gravity, including the ash burnout stage, which has a temperature of 300-800 C. Following this, the temperature sensor SI will register a higher temperature and the ash removal system will stop and await further ash removal until the temperature is again below the setpoint. The ash can be removed by several types of ash removal systems including screws. When screws are used they preferably must have, or may have, a special design so ash is removed in an even layer - see also fig. 6, fig. 7 and fig. 8.

Size of the updraft gasifier

The cross sectiona area of the updraft gasification part is approximately 1 m2/MW thermal input of fuel. The height of the updraft gasification bed is about 1-3 m.

Gas composition, gas speed and dust emission from updraft gasifier.

The gas composition of the updraft gasification part depend on the fuel. A typical gas composition using biomass with 50% moisture is :

H20: 41%, H2: 12%, CH4: 2%, CO: 18%, C02: 4%, N2: 21%, higher

hydrocarbons (Tars) : 2% (% by volume).

The cross sectional area of the updraft gasification part is approximately 1 m2/MW thermal input of fuel.

The gas production of the updraft gasification part at full load is about 0.15-0.2 kg/s/MW, which equals 0.15-0.2 kg/s/m2 which equals a gas speed of app. 0.3- 0.4 m3/s. Due to this very low gas speed through the updraft gasifier, very little dust (below 100mg/Nm3) is carried on to the partial oxidation process.

Partial oxidation, 10.

Above the updraft gasifier fuel bed is the partial oxidation stage 10: Oxygen, 13, is added to the gas (e.g. by introducing air), and the gas is hereby partially oxidized and the temperature of the gas is increased due to exothermic reactions of the gas with oxygen. Also the gas composition is changing as the tars

(hydrocarbons with many carbon atoms) are decomposed into smaller

hydrocarbons. The temperature of the partial oxidation stage is preferably between 750C-950C. If air is used an approximate gas composition after partial oxidation is, or may be: H20 33%, H2 11%, CH4 0%, CO 4%, C02 13%, N2 39%, higher hydrocarbons (Tars) 0% The inlet of the oxygen for the partial oxidation process is placed above the inlet of the fuel for the updraft gasifier. Preferably the inlet for the oxygen is 1-4 m above the inlet of the fuel. The partial oxidation is carried out above the top of the fuel bed, and here the partial oxidation also functions as an extra heat source for the drying and pyrolysis stages, and the fuel bed in the updraft gasifier can be as low as 1-3 m in height. Control of partial oxidation, S2

The temperature and gas composition of the partial oxidation stage can be controlled and optimized in various ways, depending on the purpose of the plant: One or several sensors S2 can measure temperature and/or gas components such as e.g. CO, H2, CH4, C02, H20, NOx.

The exit temperature can be controlled by the amount of oxygen added and/or amount of water, 12, added : More oxygen increases the temperature, whereas more water decreases the temperature.

The gas composition can also be adjusted by the amount of oxygen and/or amount of water added.

The amount of NOx can further be reduced by injection of urea, 12, or other SNCR catalyst. Feeding system 2 and control of bed height S3

The feeding of the fuel is adjusted according to the thermal output of the plant and the bed height of the updraft gasifier.

The Sensor S3 measures the bed height. The sensor S3 is preferably a radar, but it can also be other systems such as ultrasonic, IR camera, etc. When the bed height is too large less fuel is feed into the gasifier, and eventually more gasification agent 9 is added, and vice versa. Gas cooler 11

In connection with, or after the partial oxidation stage 10, the gas can be cooled in one or several gas coolers 11, which can be integrated in the thermal reactor 1 or in following stages. Hereby a colder gas, 15, is produced. Thus, the gas cooler(s) 11 are typically considered optional, not mandatory in connection with the present invention.

In Fig. 2, an energy plant, producing heat and power, is schematically illustrated. In fig. 2, the items with reference numerals A00-AFR-A07, F00-F09 and W00-W12 are explained in fig. 3. Further, OCR CYCLE in fig. 2 refers to Organic Rankine Cycle.

A06 is the air for the updraft gasifier which is first preheated by the gasification reactor then, moisturized in the "Gasification Humidifier". Hereafter it is named A07. The air is then heated in drawing by external heat jacket of the "gas combustion". Hereafter it is named A07 and this moisturized and dry air is then lead to the blower (the arrow) and pushed into the air inlet of the gasifier. It is noted, that this process involving the Gasification Humidifier may be considered optionally.

It is illustrated how the updraft gasification section is supplied with solid fuel 2 on the top, moisturized and preheated air 9 in the bottom and how ash is removed from the bottom 8. It is also illustrated that moisturized and preheated air 13 (A04) is partially oxidizing the gases produced in the updraft gasifier, and that water 12 (Wll) is supplied to the partial oxidation stage. The water is in this case quench water and carrying particles collected in the quench to the thermal reactor.

The produced gas 14, may be lead to a combustion chamber where the gas is combusted to a flue gas consisting of N2, C02, H20 and 02.

Due to the under stoichiometric conditions in the reactor 1, the content of NOx in the produced gas is very low (Below 150 mg/Nm3).

Due to the design of the combustion chamber the CO content after the

combustion chamber is very low (below 10 mg/Nm3). Due to the low velocity of the gas leaving the updraft gasifier the dust content is very low (below 100 mg/Nm3)

The flue gas from the combustion chamber may be cooled in several stages:

Firstly the flue gas is cooled in thermal oil heat exchangers in the ORC cycle which is producing electricity and heating. Secondly the flue gas is cooled in the Quench and in the Flue gas scrubber. The Quench function as cooler before the flue gas- scrubber and as particle removal system. The flue gas scrubber function both as a cooler of the flue gas and as a heater of the condensate water. The energy of the hot water produced in the Flue gas scrubber is transferred to the district heating water through the heat exchanger "Scrubber heat recovery".

The gasification air used in the updraft gasifier is moisturized in the Gasification Humidifier, and subsequently heated and dried before it is lead to the updraft gasifier.

The air used for the partial oxidation and for the gas combustion chamber is moisturized in the Combustion Humidifier, and subsequently heated and dried before it is lead to the reactor 1, and to the combustion chamber.

The produced condensate is filtered in a filter before excess condensate water is lead to the sewer system or used as process water somewhere else.

It should be noted that this system only has one stream of solid particles, namely the bottom ash 8, of the updraft gasifier.

Water and particles collected in the Quench is used to moisturize the bottom ash.

Fig. 3 shows an energy-mass balance of the energy plant illustrated in Figure 2. The Energy-mass balance is based on 2500 kg/hour of biomass with ~1% ash and 30% water. This is equivalent to approximately 8.697 MW thermal input to the plant (Based on Lower heating value of the fuel).

It is seen that the gas leaving the reactor 1 (=F01), has a temperature of 900C and a gas composition of app. 26.8% H20, 0% 02, 40.3% N2, 12.3% C02, 7.8% CO, 12.8% H2 and 0% CH4. It is also seen that the plant produces ~1430 kW power and ~7921 kW heat resulting in an overall efficiency of ~107%. The high efficiency (above 100%) is possible due to the fact the energy input is measured as low heating value, and the flue gas condensation system converts the water vapours in the flue gas into energy in terms of hot water.

Fig. 4 shows the flow lines of the air added to the partial oxidation stage 10 and to the combustion chamber 16 in the plant illustrated in Figures 2 and 3.

It is seen that the air speed (at the oxygen/air injection 13) is approximately 25 m/s in the inlet in the reactor. Fig. 4 also illustrates by numeral 17, openings used for oxygen and/or air into the gas combustion stage.

Fig. 5 shows the velocity lines in the partial oxidation reactor and in the

combustion chamber in the plant illustrated in Figure 2 and 3, and Figure 7, 8 and 9. It is seen that the velocity at the top of the updraft gasifier is below 1 m/s which results in very little transport of dust upwards.

Fig. 6 shows a schematic diagram of the updraft ash system and the updraft gasification part illustrated in Figures 2 and 3. Six air nozzles 9 are placed between each of the seven ash screws 8, so there is a total of thirty-six air nozzles in the ash layer.

The size of the reactor is: Width : 3 m, depth : 3 m, which results in 9 m2. As the fuel input in the reactor is app 8.7 MW the specific load approximates 1 MW/m2.

Each air nozzle supplies 0.25 m2 of ash-layer with air.

Three thermo-couples, SI, are placed in the ash layer between each ash screw to monitor the temperature of the ash layer. So in total there are eighteen

thermocouples.

It is seen that the shaft of the screws is conical. This is to ensure that ash is removed in an even layer. It is seen that the screws have an angle of app. 25 degrees downwards from the feed to the ash system. This is to ensure an even height of the fuel layer, as the fuel in the top will approximately have such angle. See also figure 4 and 5. It is seen that the gasification reactor has refractory lining in a least two qualities. The inner lining has high temperature and chemical resistance while the outer lining has good insulation properties.

Fig. 7 shows schematically a thermal reactor with an updraft gasifier and a partial oxidation zone, and downstream from the thermal reactor: a zone for gas combustion and a boiler (thermal oil heater). Fig. 8 shows the system depicted in fig. 7 in use,

Fig. 9 illustrates another embodiment of an energy plant producing heat and power. An explanation as to the reference numerals A00-AFR-A07, F00-F09 and W00-W12 can be found in fig. 3. The basic operations of the plant shown in fig. 9 is as illustrated in fig. 3, and fig. 9 can be viewed as a more complete illustration of the plant shown in fig. 3. Fig 10a shows temperature distribution within a thermal reactor according to the preferred embodiment illustrated in fig. 8. Please observe that the vertical and horizontal planes in which the temperatures are shown, are not physical planes but imaginary planes at which the temperatures are determined. Fig. 10b shows the flow lines of the air added to the partial oxidation stage 10 and to the combustion chamber 16 and of the gases therein of the preferred embodiment illustrated in fig. 8.

With reference to fig.s 4, 5 and 10, please observe, that the lower part of the thermal reactor is not illustrated, and the lower boundary in the illustration of the thermal reactor is the top of the bed. The thermal reactor may be as illustrated in fig.s 7 and 8. Please observe that dimensions given in the drawings are not to be construed as limiting for the scope of the invention, since they refer to a preferred

embodiment. Herein oxygen/air is preferably used for referencing air, such as atmospheric air, oxygen enriched air and/or pure oxygen

List of reference symbols used : 1 Thermal reactor ("unit" is also used herein interchangeably with thermal reactor)

2 Feeder

3 Drying stage

4 Pyrolysis stage

5 Char gasification and oxidation stage

6 Ash burn-out stage

7 Ash layer

8 Ash removal system

9 Gasification agent(s)

10 Partial Oxidation stage

11 Gas cooler

12 Water and/or urea injection

13 Oxygen/air injection

14 Burnable gas

15 Colder gas

16 Gas combustion stage

17 Oxygen/air injection into the gas combustion stage