In conventional gas generators, the throat portion of gasifier vessel has a con- stant cross-sectional area. As to the generation of clean product gas, however, this is not an optimal situation. this is because the gasifier throat should at the maximum capacity demand conditions preferredly be capable of passing a larger volumetric gas flow than in the minimum capacity operating situation.

One prior-art gas generator embodiment is described in FI Pat. No. 60,884.

It is an object of the invention to provide a gas generator facilitating the cross- sectional area of its gasifier throat to be controllable to an optimal combustion value during the gasifier operation. In the invention the variable cross-sectional area is implemented by means of a vertically movable control element, particu- larly a throttle cone. When the throttle cone is in its upper position, the volu- metric gas flow through the gasifier throat is reduced to a value corresponding the minimum capacity of gas generator operation. Respectively, having the throttle cone driven into its preset lower position, a larger volumetric gas flow is allowed to pass unrestrictedly to the reducing layer-of coal thus facilitating the operation of the gas generator at its maximum capacity.

The gas generator in accordance with the invention is particularly characterized in that at the gasifier throat, substantially concentric with the cylindrical gasifier vessel center axis, is adapted an upward tapering control element of the gasifier

throat cross-sectional area.

A preferred embodiment of the gas generator according to the invention is characterized in that the control element is an upward tapering throttle cone adapted movable in the vertical direction.

Another preferred embodiment of the gas generator according to the invention is characterized in that the support shaft of the vertically movable throttle cone is adapted to pass through the gasifier grate.

A still another preferred embodiment. of the gas generator according to the invention is characterized in that the throttle cone support shaft is connected to the gasifier grate such that the rotation of the throttle cone support shaft also causes rotation of the gasifier grate.

Hence, the gasifier of the gas generator according to the invention is made adjustable to cope with the actual gasifier output demand so as to maintain at all times an optimum volumetric gas flow rate and temperature in the gasifier throat, whereby proper conditions are created for the generation of a product gas at maximized quality.

In the following, the invention is examined in more detail with the help of a pre- ferred exemplary embodiment by making reference to the attached drawing showing a vertically sectional view of a gasifier according to the invention suitable for use in a gas generator.

Referring to the diagram, therein is shown designated by reference numeral 1 a gasifier vessel that basically has a straight cylindrical shape with the exception of the gasifier throat 6, wherein the cross-sectional area of the vessel is con- stricted distinctly smaller than elsewhere in the gasifier vessel. The gasifier throat 6 is situated above the gasifier grate 2. In the gasifier is combusted solid

fuel 8. Reference numeral 3 designates a gasifying coal bed and reference numeral 4 designates combustion air injection nozzles that are distributed evenly about the periphery of the gasifier vessel. The gasifier combustion zone 7 operates above the combustion air injection nozzles 4.

In the middle of the gasifier, at the gasifier throat 6 in a position concentric with the vertical center axis of the gasifier is adapted a controllable throttle cone 5 of the gasifier throat. The shape of the throttle cone is made upward tapering.

Advantageously being made of a metallic or ceramic material, the throttle cone is supported by a shaft 9 adapted to extend through the underlying gasifier grate 2. To the support shaft 9 is advantageously connected a hydraulic actuator mechanism that moves the throttle cone 5 in the vertical direction thus accomplishing the control of the open cross-sectional area in the gasifier throat.

In the upper position of the throttle cone, the volumetric flow rate of gas passing via the throat is controlled to a minimum value corresponding to the smallest output of the gas generator. Conversely, in a preset lower position of the throttle cone a larger volumetric flow of gas is permitted unobstructedly to the reducing coal bed thus facilitating maximum output from the gas generator.

According to a preferred embodiment, the gasifier grate 2 can be made rotata- ble, whereby the rotating movement is advantageously accomplished through the rotation of the cone support shaft 9. Such rotating movement of the shaft can be implemented using any appropriate actuator construction well known to a person skilled in the art. Alternatively, the rotating movement can be imposed directly on the grate, whereby the grate in turn rotates the throttle cone.

To a person skilled in the art it is obvious that the invention is not limited to the exemplary embodiment described above, but rather, can be varied within the scope and spirit of the appended claims. For instance, the actuator mechanisms connected to support shaft 9 are not shown inasmuch as suitable implementa- tions of such arrangements may be considered to be readily available.