Field of the Invention

This invention relates to gasification methods for converting chemical energy of various solid, preferably organic, fuels into chemical energy of producer gas and gasifier devices for processing such conversion.

Background of the Invention

Gasification is a conventional process that converts organic or fossil-fuel-based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is typically achieved by reacting the material at high temperatures without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is often referred to as syngas (from synthesis gas) or producer gas.

Various methods for gasification of solid fuel and gasifier devices ("gasifiers") therefor are known in the art, including the following: One such gasifier known in the art, designed for gasification of solid fuel, preferably of organic origin, e.g. wood, includes an elongated vertical hollow inner casing designed to be loaded with fuel and a gas-tight outer casing designed to remove combustion products. The bottom of the casing includes a grid and an ash-bin underneath. Inside the outer casing, a bottom part of the inner casing is designed as a double cone or cylindrical extension. The extension has openings spread along the perimeter for supplying gaseous pyrolysis products into the aforementioned channel that surrounds the inner casing with fuel and is equipped with openings to withdraw heated gas (See patent application DE 3411822 Al, published on October 03, 1985). Another conventional gasifier is described in patent application DE 102007017859 Al, published on October 23, 2008, and includes a chamber for a direct gasification process in the upper part and a crude gas suction chamber directed downwards to unload combustion products through a means of withdrawal. A means of oxidizer supply comprises nozzles coupled to the both chambers on the one side and having an oxidizer supply source on the other.

Also known is a method for gasification of solid fuel comprising thermal processing of a fuel layer in a vertical shaft-type apparatus with air being supplied through a fuel layer ignited from the side opposite to air supply (a reverse gasification process). A fuel layer is thermally processed in two steps successively. The first step involves pyrolysis of solid fuel, while carbon residue remained after pyrolysis is gasified at the second step so that mass ratio of air consumed at the first step and at the second step is within 0.03 ... 0.3 (See Patent UA 41146 U published on May 12, 2009).

The prior art further discloses a method and a device for gasification of a combustible material described in Application DE 10010358 Al published on September 27, 2001. In the said method, pyrolysis takes place in the first reactor at temperature one and gaseous pyrolysis products are supplied from the first reactor to the second one for a further reaction at temperature two, which is above the first one, to achieve partial oxidation of pyrolysis products by supplying oxygen. Pyrolysis takes place in the first reactor without oxygen, and heat energy is introduced into the first reactor by supplying a portion of gaseous reaction products from the second reactor. Temperature one is below the ash melting point, preferably between 600 and 900 degrees Celsius. Temperature two lies in the range of decomposition of long hydrocarbon chains, preferably above 1,000 degrees Celsius. Pyrolysis in the first reactor and/or reaction in the second reactor is/are running in the fluidized state.

The prior art also discloses a method for gasification of condensed and solid fuel for energy production and a gasifier for realization thereof as described in Patent RU 2 520450 C2 with the patent application published on April 20, 2014. The method for generation of pyrolysis-tar-free fuel gas during gasification of condensed fuel comprises fuel supply through a means of loading located in a top part of the gasifier and loading of a solid non-combustible material through a separate means of loading which positions the material in the countercurrent of gaseous products. Oxygen-containing gas is then supplied to a bottom part of the gasifier where pyrolysis and fuel combustion takes places in counterflow gas. Solid residue remained after combustion is unloaded from the bottom part of the gasifier. Gaseous products from the top part of the gasifier are removed from a layer of a solid non-combustible material not mixed with fuel. Gaseous products of pyrolysis and drying are withdrawn from a layer of fuel and are then supplied to a combustion zone located below the zone where fuel and solid non-combustible material are mixed. The gasifier used for realization of the method is designed as a multiple- hearth furnace, a shaft reactor, or a drum.

The prior art also discloses a method for thermal processing of solid waste and a gasifier for realization thereof as described in Patent RU 2 476 770 C2 with the application published on September 27, 2012. According to the said method, solid waste is processed by loading waste into a gasification chamber followed by heating, drying, pyrolysis and combustion with subsequent formation of processed products such as pyrolysis gas and solid residue and removal of processed products from the gasification chamber. Heating, drying, and pyrolysis are run at an absolute pressure between 0.08 and 0.095 MPa. The entire pyrolysis gas so obtained is used as fuel by burning it in a post-combustion chamber. Heat is supplied to waste directly through the upper end surface formed by waste and/or across the entire lateral surface of waste followed by gasification with an agent such as hot combustion products and/or air. Heated combustion products are obtained by burning the fuel-air mixture formed with fuel and air from external sources. Prior to combustion, pyrolysis gas is ejected in the post-combustion chamber by supplying an active jet of air and/or combustion products of the fuel-air mixture being formed from external fuel and air sources.

Also known is a system designed for full conversion of crude hydrocarbons into syngas and slag as described in Eurasian application EA 201001377 Al published on April 29, 2011. The system includes a primary chamber for removal of volatile compounds from crude hydrocarbons, wherein the primary chamber gas (outgoing gas) is generated, and a secondary chamber for further conversion of processed crude hydrocarbons into secondary chamber gas (syngas) and residual substance, a gas re-formulation zone for the treatment of gas obtained in one or more chambers, and a melting chamber wherein the residual substance converts into a glassy state. The primary chamber provides a possibility for direct or indirect supplying additives required for adjusting the carbon content in a raw material. The system also includes a means of control to monitor various stages of the process in the gasification system and arranges them so as to ensure efficient and complete conversion of crude hydrocarbons into syngas. One significant disadvantage of various gasification techniques and devices described above is a relatively high percentage of "dirty" producer gas, i.e. producer gas having relatively high concentration of tar-yielding impurities, such as heavy hydrocarbons, in its composition. This disadvantage is particularly notable when high-moisture and ash-rich fuel is gasified, due to operation of a gasifier using the direct gasification process and/or inability to operate a gasifier using the reverse gasification process with wet fuel.

Summary of the Invention

The object of the invention is to propose a method for gasification of solid fuel and the gasifier for realization thereof with improved efficiency of the gasification process, reduced oxidizer consumption for the gasification process and improved stability of the producer gas so obtained by changing the sequence of thermochemical reactions with subsequent impact on both the quantitative and the qualitative characteristics of gas so generated. An additional object is to improve purity of producer gas and to generate producer gas essentially free from tar- yielding heavy hydrocarbons. Another object is to develop a method and a gasifier for realization thereof where high-moisture and ash-rich fuel may be used without prior processing. Yet another object is to achieve environmentally friendly disposal of chemicals in any (solid, liquid or gaseous) state, including hazardous waste etc., by thermal decomposition.

Accordingly, in one aspect of the invention, a method for gasification of solid fuel in a gasifier comprises a casing defining a cavity and having a fuel compartment, a reverse gasification zone and a direct gasification zone disposed therein, the method comprises a. loading of solid fuel into the fuel compartment,

b. supplying solid fuel and oxidizer into the reverse gasification zone, c. supplying carbon particles obtained in the reverse gasification zone to the direct gasification zone,

d. supplying oxidizer to the direct gasification zone, thereby generating a producer gas,

e. removing the producer gas from the direct gasification zone, and f. mixing the producer gas with solid fuel supplied to the reverse gasification zone, wherein an adsorption filtration zone is formed between the reverse gasification zone and the direct gasification zone, and the mixture of solid fuel and producer gas is then supplied to the reverse gasification zone and the producer gas generated in the reverse gasification zone is then removed for disposal through the adsorption filtration zone. In one embodiment, an annular space substantially free from filling with solid fuel may be formed in the reverse gasification zone.

According to another embodiment of the method, a moisture content in the solid fuel may be predefined to adjust at least one of a. the amount of fuel to be supplied to the reverse gasification zone b. the amount of oxidizer supplied to the reverse gasification zone, and c. the amount of oxidizer supplied to the direct gasification zone. According to yet another embodiment of the method, depending on the predefined moisture content, the ratio of oxidizer supplied to the reverse gasification zone to that of the direct gasification zone may be changed within the predetermined limits to achieve substantially complete combustion of producer gas and its volatile particles in the reverse gasification zone.

According to yet another embodiment of the method, in the process of formation of the adsorption filtration zone, fuel obtained after the reverse gasification zone may be cooled to a temperature that does not exceed a condensation temperature of tars in the fuel coming out of the reverse gasification zone. According to yet another embodiment of the method, a zone between the adsorption filtration zone and the direct gasification zone may be hermetically sealed.

According to yet another embodiment of the method, rarefaction may be achieved in the cavity of the gasifier. According to yet another embodiment of the method, rarefaction may be achieved by removing the producer gas for disposal.

According to yet another embodiment of the method, the fuel compartment of the gasifier may be loaded with solid fuel by mixing pre-milled fuel with a low ash melting point and solid fuel in the fuel compartment. According to yet another embodiment of the method, solid fuel may be subject to further loosening in the fuel compartment. According to yet another embodiment of the method, when producer gas withdrawn from the direct gasification zone may be mixed with solid fuel in the reverse gasification zone, at least one chemical substance is added for further thermal decomposition. Generally, in another aspect, the invention relates to a combined solid fuel gasifier, particularly suitable for realization of the method described above. The combined solid fuel gasifier comprises a casing with a cavity, and further comprising, disposed within the cavity, a. a fuel compartment with at least one means for supplying fuel and a fuel- metering device, b. a second gas generator compartment with the reverse gasification process equipped with a means for supplying oxidizer and a mixing compartment in the upper part, c. a first gas generator compartment with the direct gasification process being equipped with the means for supplying oxidizer, d. an ash collection and removal compartment, and e. an adsorption filtration compartment located between the first gas generator compartment and the second gas generator compartment, the first gas generator compartment and the second gas generator compartment being coupled to one another in parallel using at least one means of producer gas withdrawal from the first gas generator compartment to the mixing unit of the second gas generator compartment, and the adsorption filtration compartment being equipped with a means of removal of producer gas for disposal. According to one embodiment of the gasifier, the gasifier further may comprise a sealing means located between the adsorption filtration compartment and the first generator compartment.

According to another embodiment of the gasifier, the gasifier further may comprise a rarefaction means inside the cavity coupled to the means for removing the producer gas for disposal.

According to yet another embodiment of the gasifier, the second gas generator compartment may comprise an inner annular space.

According to yet another embodiment, the gasifier further may comprise a means for determining moisture content before or inside the fuel compartment, coupled to a means for adjusting the amount of oxidizer being supplied to the first gas generator compartment and to the second gas generator compartment.

According to yet another embodiment, the second gas generator compartment may be equipped with a means for supplying additional substances to the mixing compartment.

According to yet another embodiment, the fuel compartment may comprise at least two means for supplying fuel coupled in parallel with the fuel compartment.

According to yet another embodiment, each means for supplying fuel may comprise an auger to supply fuel to a fuel-metering device. According to yet another embodiment, the fuel-metering device may comprise at least one drive. The gasifier may further include a means for loosening solid fuel located inside the fuel compartment and coupled to the drive of the fuel-metering device.

Brief Description of the Drawings

The following figures are intended to help with the understanding of the invention and illustrate and explain its main principles and the essence of the operation, not to limit its scope or spirit. Non-limiting and non-exhaustive aspects and embodiments thereof are described with reference to the following Figures in which:

Fig. 1 shows a general view of the gasifier, according to some embodiments of the invention;

Fig. 2 is a schematic sectional view of the gasifier of Fig. 1; and

Fig. 3 is a schematic sectional view of the gasifier loaded with solid fuel and the movement of combustion products (even lines) and pyrolysis gases (wavy lines).

Detailed Description of the Preferred Embodiments of the Invention

The gasifier disclosed herein contemplates converting chemical energy of various solid organic fuels into chemical energy of producer gas and thereby efficiently control the gasification process by determining the sequence of thermochemical reactions which, in turn, affect the quantitative and the qualitative parameters of gas being so generated. The studies completed by the inventor show that when the method claimed was used, the composition of producer gas was stable and contained only a mixture of CO within 28 ... 32%, H ₂ within 20 ... 24% and N ₂ within 46 ... 48%. The result so achieved, i.e. generation of pure producer gas essentially free from harmful tar-yielding components by gasification of fuel with oxidizer (e.g. air), may be conditioned upon the following.

Similar to conventional approaches, gasification process is maintained by supplying oxidizer to both gas generator compartments. The series-parallel operation of gas generator compartments being parts of the gas generator helps to run the following thermochemical reactions simultaneously:

- oxidation reactions (intensive combustion),

- oxidative pyrolysis,

- steam conversion, and

- reducing reaction.

In the method realized with the gasifier disclosed herein, the second gas generator compartment (with the reverse gasification process) receives primary fuel having moisture content W ^p , e.g. not more than 50%, and ash content A ^p not more than 40%, while the first gas generator compartment (with the direct gasification process) receives fuel "undergasified" in the second gas generator compartment.

Positioning of both gas generator compartments - the one with the reverse gasification process followed by the other with the direct gasification process, and positioning of all other compartments in the sequence described above exactly at their designated sites helps to carry out the gasification process in accordance with the technique which ensures simultaneous running of the said thermochemical reactions. The studies completed by the inventor with the said technique using the combined gasifier described above demonstrate a possibility for gasification of various fuels which quality is deemed insufficient for gasification and, as such, are unattainable employing solid fuel devices known in the art. These benefits are achieved due to several factors.

First, primary fuel is gasified stepwise in a closed cycle (including recycling) through parallel (synchronous) operation of both gas generator compartments of the gasifier. In such gasification of fuel, the efficiency of the technological process may be further achieved by a hardware and software tool for automatic control of the gasification process. In this case, the software unit of such tool contains software modules designed for gasification of a particular type of fuel, i.e. a solid fuel with certain parameters. Data for the operation of such modules are obtained for each type of fuel individually based on statistical data in the process of industrial testing of the gasifier with different fuels. An important point is that entire producer gas so generated is produced only by the second gas generator compartment (with the reverse gasification process) that significantly simplifies the quality control of produced gas.

Secondly, the claimed method allows us to gasify second-grade high-moisture and ash-rich fuels due to the use and the design of the second gas generator compartment with the reverse gasification process. This is achieved because primary fuel is not gasified in this compartment in a conventional way - by partial or complete oxidation. Instead, "dirty" producer gas obtained in the first gas generator compartment is supplied to the mixing compartment of the second gas generator compartment wherein "dirty" producer gas is mixed with the primary fuel being supplied through the fuel compartment using a means of fuel supply so to obtain the enriched mixture which is then supplied to the oxidation zone (intensive combustion) of the second gas generator compartment The amount of oxidizer (e.g. air) being supplied to the oxidation zone of the second gas generator compartment is restricted to the amount required to achieve complete combustion of "dirty" producer gas and volatile particles originating from such gas. The oxidation (combustion) process itself takes place both in the annular space of the second gas generator compartment that is not filled with fuel and between particles of primary fuel deep in a fuel layer in the second gas generator compartment. Thus, "dirty" producer gas and volatile particles present in fuel are completely combusted and are converted into common combustion products (flue gases): C0 ₂ , H ₂ 0, and NO _x . Further, being exposed to high temperatures under restricted amount of oxidizer, particles of primary fuel are converted into a homogeneous mixture of hot carbon particles and ash, more specifically, fresh char that forms a reducing layer. The annular space in the second gas generator compartment is necessary to improve the kindling and combustion of solid fuel during the process of thermal conversion by replacing a number of burners arranged along the perimeter of the casing of the second gas generator compartment with the annular space which is to be filled with oxidizer and wherein oxidation (combustion) of solid fuel takes place. The resulting process of burning "dirty" producer gas and volatile particles of primary fuel help to increase the initial capacity (thickness) of the reducing layer by 10 ... 15 times compared with that of the known gasifiers, in particular those known in the art. The improved capacity of the reduction zone of the second gas generator compartment increases the efficiency of fuel combustion as a final stage of the entire gasifier operation. The reduction zone ultimately shapes the composition of the producer gas being obtained by thermochemical reactions listed in Table 1.

Table 1: Thermochemical reactions and the related thermal effects

These reducing reactions are endothermic, i.e. the reactions which require heat extraction, so the capacity (thickness) of the reduction zone is crucial, especially for gasification of high-moisture fuel. In the gasifiers known in the prior art, excess moisture suppresses or stops the gasification process unlike the present invention whereunder moisture becomes the main source of hydrogen.

Third, a nitrogen oxide (NOJ formed in the process of oxidation of nitrogen, a primary fuel element, and nitrogen supplied to the fuel oxidation (combustion) zones in both gas generator compartments together with oxidizer, may be fully reduced to molecular nitrogen N ₂ . Even at the temperature of 1,000 K the equilibrium constant of the reaction 2 NO + C = N ₂ + C0 ₂ is quite high and is 6.86 x 10 ²⁸ , i.e. the reaction equilibrium is significantly shifted to the right, so the content of NO in equilibrium with carbon will be 10 ¹³ g/m ³ for the reaction at a temperature of 1,000 K.

Additionally, CO and H ₂ are active reducing agents so that NO _x being a producer gas element will be completely reduced to molecular nitrogen N ₂ from hot char after the reduction zone. Fourth, the entire amount of char reacted in the high-temperature reduction zone may be converted into a filler for the adsorption filtration compartment, which is constantly reducing by gasification of the original fresh fuel. For this purpose, char is cooled to a temperature that may not exceed the condensation temperature of tars originating from fuel and found in the oxidation zone and reduction zone forming the adsorption-filtration zone.

The formation of such zone helps to obtain a kind of an inner "gas mask" in the gasifier to pass through entire producer gas generated by the gasifier. The constantly renewable content of such "gas mask" functions not only as a powerful filter but also as a highly effective adsorber. In addition, the adsorbing "gas mask" essentially completely cleans producer gas from all hazardous and toxic contaminants formed during the process of thermal decomposition of various chemicals which got into fuel accidentally or for the purposes of disposal.

Therefore, producer gas generated using the method disclosed and claimed herein has a very high degree of purity from any chemical additives. After withdrawal from the gasifier, producer gas may be insignificantly contaminated with solid particles coming from a layer of char when producer gas came out of that layer and got into a gas accumulation tank of the second gas generator compartment. Gas may be cleaned from such particles and its excessive moisture may be reduced after removal of producer gas for disposal.

Further, the approach disclosed herein helps improve the stability of the chemical composition of producer gas during gasification of various solid fuels, regardless of the characteristics of such fuel (CO + H ₂ + N ₂ ). In addition, the ratio of producer gas elements is maintained automatically to ensure heat-generating capacity at a stable low level Q _H ^P ~ 1,500 kcal/nm ³ . The share of each component per 1.0 Nm ³ of producer gas (%) depends directly on both the amount of fuel, air and water (moisture) supplied to the gasifier and the temperature in the reaction zones of both gas generator compartments. For example, the higher is the fuel moisture content, the higher is the content of hydrogen (H ₂ ) in producer gas. Even given the fact that excess moisture is an undesirable (internal and external) ballast for any type of fuel to be combusted or gasified by means of gasifiers known in the art, wet fuel improves performance of the gasifier claimed herein and helps to ensure stability of the composition of producer gas so generated. The optimal moisture content of primary fuel is W ^p ¾50%. Thus, primary fuel requires further moisturizing in some cases. However, fuel with moisture of W ^p >50 is still suitable for gasification and, to achieve its efficient combustion, fuel and oxidizer (air) consumption is increased in an automatic mode which is provided by a hardware and software tool for automatic control of the gasification process comprising software modules with individual gasification parameters for each type of fuel. The studies have shown that Wp<60 % is the threshold moisture for the proposed gasifier.

The temperature mode in the oxidation (combustion) zones of both gas generator compartments are also automatically controlled and maintained at the required level in accordance with the software module for gasification of each fuel type and may vary within 600 ... 1,300 °C depending on the ash melting point of primary fuel. The process of adjusting temperature parameters is carried out by changing the fuel- to-oxidizer (air) ratio. The studies of the proposed method and the gasifier showed a possibility of generating producer (air) gas containing ballast nitrogen N ₂ below 50%, in particular with following approximate chemical composition: CO - 28-32 %, H ₂ - 20...24 % and N ₂ - 46...48 %. The amount of nitrogen (N ₂ ) in producer gas depends on the amount of oxidizer (air) supplied to the reaction zones of both gas generators using any means of air supply known in the art, e.g. fans. The design of the proposed gasifier helps to reduce the volumes of oxidizer supplied for gasification by preheating primary fuel supplied through the fuel compartment having a means of fuel supply. Heating is achieved with hot "dirty" gas supplied into the mixing compartment of the second gas generator compartment through the means of producer gas withdrawal (gas pipeline) from the first gas generator compartment. Thus, in the oxidation (combustion) zone of the second gas generator compartment, primary fuel coming from the mixing compartment is already heated and its moisture and volatile particles are partially lost. This helps to partially reduce oxidizer (air) consumption and, consequently, reduce the amount of nitrogen (N ₂ ) in the oxidation (combustion) zone of the second gas generator compartment.

In the first gas generator compartment, nitrogen (N ₂ ) in producer gas is reduced by superadiabatic mode of the filtration combustion process in the reaction zone of this compartment since oxidizer (air) and combustion products move towards the movement of fuel. The effect of superadiabatic heating is achieved by internal heat exchange between gasification products and primary reactants (fuel and air), the intensity of which is provided by the above-described design of the gasifier. At different stages of the gasification process, heat flows are optimized by simple changes in the concentration of reagents - hydrocarbon fuel or oxidizer (air) which directly affect and shape the thermal structure of the combustion wave of the carbohydrate system. The proposed gasifier allows us to completely use the above- described effect of interdependence of the content of reagents to achieve maximum superadiabatic heating during filtration combustion processes in the adsorption filtration zone between the reverse gasification zone and the direct gasification zone. Further, highly toxic chemicals - poisons, herbicides and pesticides, medical wastes, pharmaceutical waste and expired pharmaceutical products - may be disposed of using the gasifier claimed herein. Thermal decomposition of any chemicals in any state is run at a temperature up to 1,300 °C. The thermal decomposition process is environmentally friendly because the gasifier is operated under vacuum in the cavity of the gasifier and simplifies the process of loading chemicals in a solid, liquid and gaseous form through a means of supplying additional materials to the mixing compartment, which may be a backup nozzle located on the lateral surface of the mixing compartment. It should be noted that the internal cavity of the gasifier casing is not operated under pressure, so rarefaction established therein prevents release of carbon monoxide CO, a known human hazard produced during the gasification process, through a casing of the gasifier before it is supplied for re-oxidation, so the operator safety during operation of the gasifier is improved.

Further, sealing of the zone between the adsorption filtration zone and the direct gasification zone with a means of sealing located exactly between the adsorption filtration compartment and the first generator compartment helps to achieve the required level of rarefaction, i.e. traction necessary to ensure a flow of producer gas so obtained from the direct gasification zone to the reverse gasification zone with producer gas being passed through the adsorption filtration zone under the action of a means of rarefaction coupled to the means of removal of producer gas for disposal. In the absence of hermetical sealing in the zone between the adsorption filtration zone and the direct gasification zone, the required rarefaction may not be achieved by increasing the volume of inner cavity of the first gas generator compartment (direct gasification process) and the ash collection and removal compartment

Depending on the chemical composition of substances intended for disposal and primary fuel profile, the ratio of chemicals to primary fuel is determined. This ratio may vary in the following ranges: chemicals are within 0.5 ... 1.5: 10 mass units and the ratio depends entirely on the amount and the quantity of hydrocarbons in primary fuel since hydrocarbons fill the internal "gas mask" of the gasifier with coke and, together with ash, form the strong the adsorption filtration compartment.

Chemicals passing through the high-temperature (oxidation) zone of the second gas generator compartment as decomposition products, together with producer gas, enter the adsorption filtration compartment wherein they are adsorbed with porous coke and are filtered with char in this compartment. Further, cooled char of the adsorption filtration compartment serves as a so-called zone of "quenching" for gaseous products that prevents reverse reactions.

Decomposition products of chemicals adsorbed and filtered with char are then exposed to thermal retreatment in the oxidation (combustion) zone of the first gas generator compartment wherein char is supplied as as-fired fuel. After the thermal retreatment, decomposition products of chemicals are converted into neutral compounds which come in contact with chemical elements of ash or, as individual elements, pass through the ash collection and removal compartment that is cooled together with fuel ash. Ash may be removed by an auger into an external ash collector.

If primary fuel ash contains no chemical elements able to bind and neutralize decomposition products of chemicals intended for disposal, such chemical elements and their compounds are supplied to the gasifier in the necessary quantity together with the chemicals through the second (backup) means of fuel supply, which is coupled in parallel with the fuel compartment together with another means of fuel supply. If such elements are contained in ash in the insufficient quantity, such insufficient quantity is then supplied. In particular, this may include binding and neutralization of chlorine compounds, phosphorus, sulfur and the like.

Materials and substances which may not be used as fuels, or when such use appears to be problematic, may also be disposed of by mixing them to the primary fuel. Such materials and substances may include wastes of cardboard and paper production ("recovered stock"), wastes contaminated with glue from typographies, waste polymer materials subject to recycling, crushed polymer containers used for transportation and storage of poison, toxic or environmental pollutants. Further, waste of fat production, shredded waste of livestock and poultry production, deposition on filters and sludge from treatment facilities at meat and fish processing enterprises etc. may also be used as additives. Fuels with low ash melting point and "sintering" fuels may also be subject to gasification. This can be both straw with an ash melting point of 800 °C and some hard coal grades which sinter (slag) at a temperature within 1,100 ... 1,300 °C. To achieve efficient gasification, such fuels should be pre-milled and mixed with primary fuel at a certain ratio depending on the profile of each fuel. In particular, the use of power-generating coal grades such as D, G, Zh, OS and T as a primary fuel in either gasifier is problematic since coal particles may partially sinter and form so-called "cakes" which completely halt the gasification process and require an emergency stop of the gasifier and complete unloading of fuel. Thus, such coal should be mixed at a certain ratio with fuels able to re-disperse coal particles to prevent regrouping of particles and sintering during gasification. Such solvent fuels may include: brown coal, sludge from the urban sewage, pig manure, chicken manure, sunflower husk, straw, wood chips, waste wood, corn silage and the like.

Primary fuel and additional pre-milled fuel with a low ash melting point are simultaneously supplied to the gasifier through at least two means of fuel supply coupled in parallel to the fuel compartment and are designed, e.g. in the form of nozzles. Both types of fuels are mixed directly in the fuel compartment using a means of solid fuel loosening which has a rotary drive from the fuel-metering device. An auger shaft of such drive may be equipped with blades which mix and loosen fuel in the fuel compartment while the shaft rotates to prevent fuel from compaction and caking. This is especially important for fuels with high moisture content, tar- yielding components, fats and the like.

The efficiency of the method and the gasifier for realization thereof according to this invention is confirmed by the experimental results of gasification of some fuels at the nominal mode of operation of the gasifier claimed herein as given in Table 2.

Explanatory notes to Table 2. The following symbols and legend are used in Table 2.

- W ^p - moisture of primary fuel, %,

- A ^p - ash percentage of primary fuel, %,

- Q ^H _P (mm Hg) - lowest combustion value of as-fired fuel, kcal/kg, - V _{producer gas} - producer gas production, nm ³ /hour,

- M _T ^p - fuel consumption, kg/hour,

- M _T ^p (specific) - specific fuel consumption, kg/nm ³ (based on producer gas),

- Q _H ^P (producer gas) - lowest combustion value of producer gas, kcal/nm ³ , - P _T - thermal capacity of the gasifier operated in the nominal mode, Gcal/hour (MW),

- Q _H ^P _(C H ₎ - lowest combustion value of natural gas accepted for calculations, kcal/nm ³ ,

- K _n - coefficient used to recalculate producer gas to natural gas equivalent, K, - V _CH - capacity based on natural gas equivalent, nm ³ /hour,

- C _T - cost of 1.0 ton of as-fired (primary) fuel (including fuel shipment and preprocessing costs), USD/ton,

- O _e - operational costs (including salary of service staff, power supply costs, propane-butane, feed water, personal protection equipment and the like), USD/hour,

- S _p - total costs, USD/hour,

- η _Γ - gasification efficiency coefficient (conversion efficiency coefficient),

- η _τ -thermal efficiency coefficient of the gasifier.

The key performance indicators of the gasifier according to this invention include the gasification efficiency coefficient η _Γ and thermal efficiency coefficient of the gasifier

The gasification efficiency coefficient η _Γ or conversion efficiency coefficient determines the proportion of chemical energy of fuel converted into gas chemical energy and is calculated using the formula below: η _Γ = Vp _roduC er gas Q _H ^P (producer gas) / Q ^H p (as-fired fuel) M ^T _P .

The thermal efficiency coefficient of the gasifier η _τ determined as a ratio of total useful heat obtained to the aggregate amount of heat introduced to the gasifier:

H _T = (V _r .r. Q _H ^P (producer gas) + Q _{P 0} . M _B ) / (Q ^H _P (as-fired fuel) M _T ^P + Q _B ) _; where Qp _0, is enthalpy of water heated in water (heat-transfer agent) cooling jackets, kcal/kg,

Q _B is enthalpy of oxidizer (air) supplied to the gasifier for fuel gasification, kcal/nm ³ .

M„ is mass (weight) of water (heat-transfer agent) which circulates in a closed loop of the gasifier cooling system. Table 2 shows the results of gasification exemplified by fuels such as chips of various wood, milled peat and brown coal grade B2. As shown in Table 2, the gasifier operated in the nominal mode generates 3,000 nm ³ of producer gas per hour with the lowest combustion value being stable at 1,500 kcal/kg regardless of a fuel type or profile. This is one of the key performance indicators of the gasifier according to the invention especially given the fact that air producer gas is generated. Thus, the studies demonstrate that the generation of producer gas is stable at a relative high level (compared with the known analogs) and does not depend on the use of different solid fuels varying by moisture and ash content, as this is achieved by the above features of the proposed method and the gasifier. Referring now to Fig. 1, in many embodiments, the combined solid fuel gasifier (Fig. 1) includes the casing with the cavity wherein the fuel compartment with at least one means of fuel supply 1, the mixing compartment 2, the second gas generator compartment (with the reverse gasification process) 3, the adsorption filtration compartment 4, the sealing compartment 5, the first gas generator compartment (with the direct gasification process) 6, and the ash collection and removal compartment 7 are located successively. The fuel compartment with at least one means of fuel supply 1 includes a fuel compartment lid 8, a primary fuel inlet nozzle 9, the auger shaft 10, the auger shaft drive 11, the primary fuel auger feeder 12, a case of the primary fuel auger feeder 13, the fuel collector 14, the fuel accumulation tank 15, a fuel low level sensor 16, a fuel top level sensor 17, and the fuel-metering device 18 having a drive. If there are two means of fuel supply coupled in parallel to the fuel compartment 1, the latter comprises the additional auger shaft 19, the additional auger shaft drive 20, the additional fuel auger 21, the case of the additional fuel auger 22 and the additional fuel inlet nozzle 23. The primary fuel inlet nozzle 9 may be designed so that it is coupled with an outlet nozzle of a belt conveyer with scrapers to automate supplying primary fuel.

The fuel compartment 1 is coupled to the mixing compartment 2 with a flange joint 24.

The mixing compartment 2 includes a gas distributor 25, the fuel low level sensor for the mixing compartment 26, the fuel top level sensor for the mixing compartment 27, a means of supplying additional materials to the mixing compartment (backup nozzle) 28 and explosion relief valves 29.

The second gas generator compartment 3 includes an air distributor 30, a means of oxidizer supply 31, a burner 32, and a temperature sensor 33. The second gas generator compartment 3 is coupled to the adsorption filtration compartment 4 with the flange joint 34.

The adsorption filtration compartment 4 includes the gas accumulation tank 35, the producer gas outlet nozzle 36, the nozzle 37 whereon the sensor 38 is positioned through the flange joint 39, and explosion relief valves 40. The sensors 38 are designed to determine the quantitative and qualitative composition of the producer gas so generated and the related temperature parameters before producer gas is withdrawn from the producer gas outlet nozzle 36. Besides sensor location, the flange joint 39 provides access for service staff to the cavity of the adsorption- filtration compartment 4 for servicing.

In this case, the producer gas outlet nozzle 36 is coupled to the means of rarefaction inside the cavity which may be an external fan (not shown on figures).

The sealing compartment 5 includes the casing 41 having the form of a truncated cone, with larger bottom up, coupled to the first gas generator compartment 6 with the flange joint 42. The means of sealing may be any known means, such as a rotary valve (as shown in Figs. 2, 3). The sealing compartment 5 itself with a layer of fuel inside, the fuel being pressurized to move fuel particles in this compartment and form a sealing layer directly from fuel particles, may also be used as the means of sealing. The first gas generator compartment 6 includes the gas accumulation tank 43, a burner 44, a temperature sensor 45 and explosion relief valves 46.

The first gas generator compartment 6 is coupled to the ash collection and removal compartment 7 with the flange joint 47. The ash collection and removal compartment 7 includes the means of oxidizer supply 48, an air distributor 49 and an ash collector 50 equipped with an ash remover auger 51 with the drive 52. The ash collection and removal compartment 7 includes access hatches 53 and 54 to service the inner space. The first generator compartment 6 and the second gas generator compartment 3 are interconnected in parallel with a means of producer gas removal - a gas pipeline 55. The means of producer gas removal 55 is coupled to the second gas generator compartment 3 with the "dirty" producer gas inlet nozzle 56 and to the first gas generator compartment 6 with the "dirty" producer gas outlet nozzle 57. The inner annular space 58 is formed in the casing of the second gas generator compartment 3.

The method for gasification of solid fuel using the combined solid fuel gasifier described above is illustrated by following example.

First, solid fuel 59 is loaded into the fuel compartment of the gasifier 1 through the primary fuel inlet nozzle 9. When mixed fuel is gasified (various fuels or solid fuel mixed with fuel having other parameters to improve the efficiency of the gasification process as described above), other fuel 60, e.g. pre-milled fuel with a low ash melting point is supplied into the fuel compartment of the gasifier 1 through the additional fuel inlet nozzle 23. With the auger shaft 10, the auger shaft drive 11, the primary fuel auger feeder 12, the additional auger shaft 19, the additional auger shaft drive 20, the additional fuel auger feeder 21, primary fuel 59 and other fuel 60 are supplied through the fuel collector 14 to the fuel accumulation tank 15 where fuels are mixed. Solid fuel is supplied from the fuel accumulation tank 15 to the mixing compartment 2 and then is supplied to the second gas generator compartment 3. The oxidizer 61 (preferably air) is supplied through the means of oxidizer supply 31 to the inner cavity of the second gas generator compartment 3 followed by igniting a mixture of solid fuel and oxidizer by means of the burner 32 and the reverse gasification of the solid fuel so obtained. The annular space 58 in the reverse gasification zone is free from filling with solid fuel to form the ignition and combustion zone in the entire volume of the second gas generator compartment 3. Carbon particles obtained in the reverse gasification zone are then supplied through the adsorption filtration compartment 4 and sealing compartment 5 to the first gas generator compartment 6 into the direct gasification zone. The oxidizer 62 is supplied to the direct gasification zone through the means of oxidizer supply 49.

Fuel and solid gasification products pass by gravity from the upper part to the bottom part of the casing of the gasifier by gravitational force. During the direct gasification process, producer gas 63 is generated and withdrawn from the first gas generator compartment 6 through the pipeline 55 followed by mixing with solid fuel supplied to the second gas generator compartment 3 in the reverse gasification zone and supplying the mixture of solid fuel and producer gas 63 back to the second gasification gas generator compartment 3. Passage of the entire producer gas generated by the gasifier through the adsorption filtration compartment 4 ensures operation of the inner "gas mask" of the gasifier as described above (realization of adsorption and filtration processes) using the gas accumulation tank 35 and the producer gas outlet nozzle 36 followed by withdrawal of producer gas 64 obtained in the reverse gasification zone through the producer gas outlet nozzle 36 by means of rarefaction established in the cavity of the gasifier.

Ash coming from the first gas generator compartment 6 may be removed by the ash removal auger 51 having the drive 52 from the ash collector 50 into the external ash storage tank.

When hazardous chemicals are to be disposed of as described above, such chemicals are supplied in any state through a backup nozzle 28 to the mixing compartment 2 followed by thermal decomposition together with solid fuel.

Fuel moisture may be predefined followed by the adjustment of the amount of fuel to be supplied to the reverse gasification zone and/or the amount of oxidizer to be supplied to the reverse gasification zone and direct gasification zone using the metering device 18.

Further, when the adsorption filtration zone 4 is formed, fuel may be cooled after the reverse gasification zone to the temperature which does not exceed condensation temperature of tar in the fuel coming out the reverse gasification zone. The cooling may be achieved by any known means, in particular, by cylindrical cooling jackets 65 varying in diameter and located inside the adsorption filtration zone 4.

When passed through the fuel accumulation tank 15, the solid fuel is loosened using the means of solid fuel loosening 66 - blades on the fuel auger shaft which are located inside the fuel accumulation tank 15.

The solid fuel and oxidizer supply parameters, moisture and temperature are controlled using the fuel low level sensor 16, the fuel top level sensor 17, the fuel low level sensor for the mixing compartment 26, the fuel top level sensor for the mixing compartment 27, the temperature sensor 33, the sensor 38, the temperature sensor 45, and primary fuel and additional fuel moisture sensors which may be located before the combustion compartment (e.g. on the belt conveyer, not shown on figures) with subsequent transfer of data so obtained to the hardware and software tool for automatic control of the gasification process which, using the above software modules, changes the parameters of supplying primary and/or additional fuel, oxidizer, chemicals etc.

The explosion relief valves 29, 40 and 46 ensure safety of the operation of each element of the gasifier.

Therefore, the method for gasification of solid fuel claimed herein and the gasifier for realization thereof help to improve efficiency of the gasification process, reduce oxidizer consumption for the gasification process and improve stability of the composition of the producer gas so obtained, to improve purity of producer gas free from tar-yielding heavy hydrocarbons without pre-processing and to provide environmentally friendly disposal of chemicals in any (solid, liquid and gaseous) state, in particular hazardous waste etc.

While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

Table 2: Results of gasification of some solid fuels in the gasifier at the nominal operational mode and performance indicators of the gasification method claimed in the invention