The present invention relates to a method for optimising the operation of a gas generator, wherein the gas generator has a housing part at the upper end of which are means for supplying fuel, the fuel descending by the force of gravity onto a grate, at a point above the grate being formed a combustion zone, in connection with which are arranged means for supplying gasification gas to it. The invention further relates to a gas generator comprising a housing part at the upper end of which are means for supplying fuel, the fuel descending by the force of gravity onto a grate, at a point above the grate being formed a combustion zone, in connection with which are arranged means for supplying gasification gas to it. In this connection, gasification gas refers to gas containing oxygen. In gas generators, the fuel generally descends by the force of gravity from the upper part of the generator onto the grate. The layer of carbon forming above the grate forms a reduction zone, and above it is located the actual combustion zone into which gasification gas is supplied. Above the combustion zone is formed a pyrolysis zone, where dry distillation of the fuel takes place. The product gases formed are conducted through the grate into a discharge pipe.

Various factors affect the optimal operation of a gas generator, including the supply of gasification gas to the combustion zone, the through-flow of the product gases formed, the supply of fuel, ash removal from the grate, the prevention of the entry of not completely burnt fuel through the grate, for example, when using different fuel particle sizes, the prevention/minimisation of the clogging of the grate and the fixing of a possible clogging situation. The aim of the present invention is to provide a solution by means of which the operation of the gas generator can be optimised by adjusting the properties of the generator affecting these different factors. To achieve this aim, the method according to the invention is characterised in that in the method is used a grate comprised of two concentrically arranged first and second grate parts, of which grate parts at least one grate part can be turned around an axis of rotation passing through a joint centre, and which grate parts can be moved in the direction of the said axis of rotation towards each other, into their mutually interlocking position, and away from each other, into a position partly or completely out of the said interlocking position, and that in the method, the said grate parts are moved with respect to one another and/or jointly to regulate the flow of gases through the grate and/or the removal of ash from the grate and/or to prevent the entry of not completely burnt fuel through the grate. Preferred embodiments of the invention are disclosed in dependent claims 2 to 7.

The gas generator according to the invention is in turn characterised in that the grate of the gas generator is comprised of two concentrically arranged first and second grate parts, of which grate parts at least one grate part can be turned around an axis of rotation passing through a joint centre, and which grate parts can be moved in the direction of the said axis of rotation towards each other, into their mutually interlocking position, and away from each other, into a position partly or completely out of the said interlocking position. Preferred embodiments of the gas generator according to the invention are disclosed in dependent claims 8 to 11.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic view in principle of an embodiment of the gas generator according to the invention in cross-section, and Figures 2A, 2B show an embodiment of the grate used in the gas generator according to the invention as a cross-sectional view in the inter- locking position of the grate parts and similarly in their separated position.

The embodiment of the gas generator according to Figure 1 comprises a housing part 30, inside which is a fuel compartment 14, which preferably has straight walls or widens slightly downwards. The fuel supply arrangement is at the upper end of the housing and it comprises a feeder pipe 12 for fuel, such as wood chips or other biofuel, in connection with which pipe is arranged an upper closing apparatus 20, 21, 22 and a lower closing apparatus 20', 21', 22'. The closing apparatus comprises a pipe closing part 21, 21', a rotating motor 22, 22' of the closing device, and a wiper means 20, 20'. The said closing apparatuses define between them a closable fuel supply space 24, in which are arranged inert gas supply means. The gasifier in itself operates by overpressure, which is why the fuel supply space 24 is pressurised with inert gas before opening the lower closing apparatus and allowing the fuel to enter the fuel compartment 14 inside the housing. Inert gas is used to prevent the effect of the air brought along by the fuel on the combustion process. The closing part 21, 21' is preferably arranged to move along a circular track, 360° about its axis of rotation 23, to bring the closing part from a position completely closing the supply space 24 to a position releasing the passage of fuel into the fuel compartment 14, and back to the position closing the supply space. This turning by 360° keeps the closing part clean better as it is cleaned during its turning movement. It is, however, conceivable to carry out the turning of the closing part about its axis of rotation by a reciprocating turning movement within, for example, an angular range from 0 to 180°.

At the lower end of the fuel compartment is a grate comprised of an upper grate 1 and a lower grate 2. When gasifying material containing solid carbon, the grate of the gasifier has a significant role in the functioning of the pro- cess. The adjustment of the efficiency of the process and carbon conversion, which is directly proportional to the efficiency of gasification, can be substantially influenced by the geometry and movements of the grate. A preferred embodiment of the grate suitable for use in the solution according to the present invention is shown more closely in cross-section in Figures 2A and 2B. The grate is preferably made of annular furnace bars 31, 32, which have the same centre, but a different diameter. The grate rings are preferably disposed in such a way that some of them, for example, every second or third grate ring, are fixed to the upper grate 1 and the other grate rings to the lower grate 2. The grate rings are bound together by a connection piece 33 which penetrates the grate in the direction of the grate surface. There may be one or more connection pieces on each side. In Figure 2A, the upper 1 and lower grate 2 are moved towards one another in the direction of the axis of rotation, whereby the grate rings 31, 32 become interlocked, and in Figure 2B, they are separated from one another. The lower grate 2 is arranged to be rotated by means of a motor 7. The entire grate 1, 2 is preferably arranged to be moved in the direction of the axis of rotation of the lower grate, as shown by arrow 9. In this solution, efficiency of the process can be adjusted by moving the grate 1, 2 in the direction of travel of the fuel by ad- justing, for example, the thickness of the carbon layer in the reduction zone above the grate.

By rotating the lower grate 2 about its axis of rotation, while the upper grate remains in place, is achieved better ash removal, the formation of clogging harmful to the passage of gas is prevented, and the entry of not completely burnt fuel through the grate is prevented. By changing the distance between the grate rings 31, 32 in accordance with arrow 8, the efficiency of the process can be improved and the flow of gas through the grate can be adjusted. Furthermore, the geometry of the grate rings is designed so as to be advan- tageous to the process. The cross-section of a grate ring may be, for example, a triangle, a square, a parallelogram, a trapezium or a circle. The geom- etries of the cross-sections of the rings may in addition vary according to the side of the grate (upper/lower grate) or even by ring in the same grate. Mutually moving grate parts make possible the use of fuels of different granular sizes and the optimisation of the combustion process.

In the embodiment of the gas generator shown in Figure 1, the supply of oxygen to the combustion zone is arranged to take place through both the edge nozzles 4 on the periphery of the housing and the gasification gas nozzles 5 of the central pipe 6. The gasification gas is fed into the combustion chamber through the edge nozzles 4 by means of a blower 11, and through the gasification gas nozzles 5 of the central pipe 6 by means of a blower 15. By means of this gasification gas feeding arrangement is achieved an increase in the surface area of the combustion zone and a steady supply of oxygen into the combustion zone of gasification, which is particularly im- portant in the gasification of biomass, because due to the properties of the fuel, a certain temperature range must be maintained in the combustion zone to achieve successful gasification. By changing the geometry of the nozzle head of the central pipe 6 it is possible to control the flow of the gasification gas into the reactor and at the same time to control the flow of fuel in the reactor. The central pipe 6 with its nozzle head is arranged to be moved in its longitudinal direction and/or transverse direction and/or to be rotated about its longitudinal central axis, whereby the surface area of the _^ fuel in the combustion zone and the conditions in the combustion zone can be adjusted by moving and/or rotating the central pipe 6. The efficiency of the process can be improved in this way. Moving the central pipe prevents arching and should arching take place, arching can also be opened by means of it. The rotating and/or actuating motor of the central pipe 6 is marked by reference numeral 13. In the coflow process, the discharge of product gas takes place from the lower part of the gasifier through outlet 10, and in a counterflow process from the upper part of the gasifier through outlet 3. In a method utilising the gas generator according to the invention, fuel supply takes place with through a space pressurised with inert gas, in which case the fuel supply will not cause disturbances in the combustion process through pressure change and excessive oxygen input. Pressurisation also prevents the product gas from escaping out of the gasifier through the supply space. By moving the grate parts 1, 2 with respect to one another and/or jointly, the flow of gases through the grate and/or ash removal from the grate can be optimised and/or the entry of not completely burnt fuel through the grate can be prevented.