SE501249C2 - Methods and apparatus for the thermal gasification of solid biofuels in two stages - Google Patents

Abstract

Gasification of biofuels to a fuel gas with a high calorific value is taking place in at least two steps. One step is carried out in counter-current with the pre-pyrolysis for release of carbon dioxide. A second step with complete gasification is carried out in co-current. The gasifier, which can be called the counter-current/co-current gasifier, is supplied with a second counter-current section (3) for pre-pyrolysis with conduits (8 and 9) for supply and removal, respectively, of gas and a co-current section (5) for final gasification with a conduit (10) for gasification air and a conduit (11) for removal of fuel gas.

Description

15 20 25 30 IN.) 501 249 A third purpose is to create conditions for a higher total system efficiency through the possibility of interaction between the carburettor and the other components in the complete process system.

The invention relates to a method and device for thermal gasification of solid biofuels in at least two stages, characterized in that one stage consists of prepyrolysis with carbon dioxide evolution in countercurrent and that a second stage consists of final gasification at high temperature in cocurrent. The invention will now be described in more detail with the drawing. Figure 1 and Figure 2. Figure 1 describes the principle. Figure 2 indicates a specific embodiment.

The new carburettor can be described as a two-stage carburettor, or in some embodiments as a multi-stage carburettor, alternatively as a countercurrent co-current carburettor. The latter designation clarifies the inventive concept. The prepyrolysis with preferential emission of carbon dioxide takes place in countercurrent, while the final gasification is carried out in cocurrent, much like in an ordinary cocurrent carburettor of the Imbert type.

The decomposed solid biofuel is fed from the storage tank (1) via the feed device (2) to the countercurrent part (3). After the pre-pyrolysis has been completed, the fuel is fed on via the transfer part (4) to the co-current part (5). The ashtray stand is received by the ash collector (6) and then discharged via the ash dispenser (7).

The prepyrolysis is preferably carried out by means of hot flue gases with a high carbon dioxide content and a low oxygen content which is fed in via the line (8). Exiting pyrolysis gas containing carbon dioxide, water vapor, light compounds such as methanol, acetone, etc.

("Holzgeist") and traces of tar compounds are diverted via the line (9). Preheated gasification air is supplied to the gasification section via the line (10). Formed fuel gas is finally discharged via the line (11). 10 15 20 25 30 501 249 The countercurrent cocurrent carburettor combines the advantages of the known countercurrent carburetors and cocurrent carburetors. Thanks to the preferential release of carbon dioxide in the pre-pyrolysis stage, the fuel value of the fuel gas is significantly increased. The tar content of the fuel gas becomes even lower than with a conventional co-current carburettor due to the departure of tar in the pre-pyrolysis step.

The multi-step principle provides great freedom for process combinations with different consumers of the fuel gas, e.g. a fuel cell power plant, gas turbines or a diesel engine, through the possibilities that four process gas flows provide instead of two as with the conventional carburetors. Exhaust from a diesel engine can e.g. be used for the prepyrolysis step. With the help of so-called pinch technology, process systems can be optimized for maximum overall efficiency.

The technical design of the countercurrent cocurrent carburettor does not present any difficulties for those skilled in the art. Constructive grips applied in today's co-current and counter-current carburetors can be used directly. The current state of the art is well documented in, among other things, the Swedish so-called gengasboken ("Gengas", published by IVA, 1950) - The transfer part (4) can be designed in many different ways depending on the nature of the fuel in question.This part can also be dispensed with according to the example below.Thanks to the relatively low temperature, known lock constructions, feed screws The gas pressure in the supply lines (8) and (10) is regulated so that the pressure difference between the two input gas streams is minimized to avoid gas leakage between the co-current and counter-current parts.

The reaction conditions can be varied within raw limits depending on the nature of the biofuel and other factors. The pre-pyrolysis step is carried out to a final temperature in the range 250 ° C to 400 ° C, preferably 270-300 ° C. At 300 ° C, many biofuels, especially wood fuels, initiate exothermic pyrolysis reactions, so that the temperature rises to about 400 ° C under adiabatic conditions. shows a maximum of 501 249 UI 10 15 20 25 30 pa up to 900 C depending on the detailed design of the reduction zone (see gengas book).

In some cases, both steps can be divided into additional steps, e.g. by supplying steam in the hottest part of the downstream stage or supplying various kinds of available exhaust gas at suitable levels in the countercurrent stage, e.g. for pre-drying.

Figure 2 shows a specific embodiment of the new carburettor intended for wire fuel chips and thermal effects on some MW.

The cross section is rectangular with the mat 600 x 1200 except in the slightly displaced gasification zone. The height is about 6 meters.

The designations are the same as in Figure 1. This embodiment has no special transfer part (4) shown in Figure 1. The gas flows are controlled in the stable with the floats (13) and (15) which are arranged in, or after, the respective gas process system (12). and (14) for further treatment of prepyrolysis gas and industry gas, respectively. Arch formations in the industry column are eliminated by a stirrer (16) with arms (17). The rudder (16) is driven around intermittently with the motor (18).

The carburettor in Figure 2 is apparently as structured as a co-current carburettor according to the current state of the art - if it were not for the connections (8) and (9), which transform the carburettor into a counter-current co-current carburetor according to the invention.

The technical effect of the invention can be easily verified by the fact that the carburettor can also be run as a pure co-current carburettor or counter-current carburetor. Laboratory experiments have shown the characteristic increase of the industry value by the invention by about ten percentage points through reduced carbon dioxide content and reduced nitrogen gas content due to reduced need for gasification air.

Claims (1)

Requirement 1 Method for thermal gasification of solid biofuels in at least two stages characterized in that one stage (3) consists of prepyrolysis with carbon dioxide emissions in countercurrent and that a second stage consists of final gasification at high temperature in cocurrent. Requirement 2 Carburettor for thermal gasification of solid biofuels in at least two stages characterized in that it is equipped with a countercurrent part (3) for prepyrolysis with lines (8) and (9) for supply, resp. gas discharge and a co-current part (S) for final gasification with a line (10) for gasification air and a line (ll) for the discharge of fuel gas.