EP0484993B1 - Process for controlling the start-up of a fluidised bed gasification of solid fuel - Google Patents

Description

The invention relates to a method for regulating the start-up of gasification of solid, fine-grained fuels with oxygen-containing gas and water vapor in the fluidized state in a gasification reactor, which has an outlet duct for product gas at the upper end and an ash outlet in the lower region. The gasification works at a pressure of 1 to 100 bar.

A method of this type is described in U.S. Patent 4,594,967. Here, several sections of the fluidized bed interact in a controllable manner. The start-up is carried out with the help of a heating burner, then oxygen is added to the fuel in a substoichiometric amount until the gasification stage has been reached.

The invention has for its object to start the gasification reactor easily controllable, wherein the reactor can be structurally simple. According to the invention, this is achieved in the process mentioned at the outset by burning an ash and fine-grained fuel-containing solid mixture in the reactor in the heating-up phase with the supply of oxygen-containing gas in the vortex state while supplying oxygen-containing gas and thereby the temperature in the reactor up to about the target temperature of the gasification increased that at the end of the heating phase in a subsequent inerting phase, the supply of oxygen-containing gas is reduced, an inert gas is passed into the reactor, the free oxygen content in the product gas is practically reduced to zero and the temperature is kept practically constant, and that after the Inerting phase passes into the gasification, with oxygen or oxygen-containing gas and possibly water vapor conducts into the reactor, increases the fuel supply and keeps the target gasification temperature in the range from 600 to 1500 ° C, measured in the upper region of the reactor or in the discharge duct, practically constant after a set time and, if the temperature is too low, reduces the supply of solid fuel and if the temperature is too high, the supply of fuel increases. In stationary gasification operation, the temperature does not drop, since otherwise the product gas would contain undesired smoldering products.

In the heating phase, the temperature is gradually increased. In the case of a reactor with brick lining, temperature increases of approximately 40 to 120 ° C. per hour are recommended. If the temperature is too high, the supply of solid fuel is reduced and if the temperature is too low, the supply of solid fuel is increased, because there is an excess of stoichiometric oxygen in the gasification reactor. For economic reasons in particular, it is advantageous to pass air into the reactor as an oxygen-containing gas in the heating phase. For example, when the heating-up phase has ended and the target temperature of the gasification has been reached, the supply of oxygen-containing gas is reduced and, in an inerting phase, an increasing amount of inert gas is introduced into the reactor. The total amount of gas supplied remains mostly constant. This inert gas is usually recycled product gas, nitrogen or carbon dioxide.

If the reactor has been purged sufficiently with inert gas during the inerting phase so that the oxygen content in the product gas disappears, the gasification can begin. Here, a gasifying agent mixture is passed into the reactor, which mainly consists of oxygen (for example also air) and more or less water vapor. At the beginning of the gasification, in the response time, decreasing amounts of inert gas (eg N₂ or CO₂) will be fed to the reactor. At the same time, the reactor is given more fuel and reduces the proportion of ashes fed to zero. If the fuel, eg lignite, itself contains a lot of water, the proportion of water vapor in the gasifying agent mixture can be reduced and possibly omitted entirely. When the gasification has reached the steady state, the temperature is kept constant with a fluctuation range of ± 40 ° C, which is done by regulating the fuel supply.

As an additional measure to regulate the temperature in the reactor, the supply of water vapor can be varied, which is possible both in the heating phase and during inerting and gasification.

Fig. 1

die Vergasungsanlage in schematischer Darstellung,

Fig. 2a

den Temperaturverlauf beim Anfahren und

Fig. 2b

eine Möglichkeit der Einstellung der Brennstoff- und Betriebsmittelzufuhr beim Anfahren.

Design options of the method are explained with the aid of the drawing. It shows:

Fig. 1

the gasification plant in a schematic representation,

Fig. 2a

the temperature curve when starting and

Fig. 2b

a possibility of adjusting the fuel and operating fluid supply when starting.

In the reactor (1) of FIG. 1, solid fuels are gasified in the vortex state, which are fed in by a conveyor (2). Coal, lignite or peat can be used as solid fuels. The fuels or inert material are fed from a storage bunker (3) via a metering device (4), for example a rotary valve. Above the storage bunker (3) there is a container (6) for the fuels to be gasified and a container (7) for inert material, especially ash or sand. To simplify matters, the following explanations speak of the fact that the fuel to be gasified is coal and the inert material is ash.

In the lower area, the reactor (1) has a distribution chamber (9) for gases and / or water vapor which flow in through the line (10). These fluids enter the reactor (1) through a grate (11). A branch line (12) with a valve (13) enables the metered supply of these fluids simultaneously into an area above the grate (11).

In the stationary gasification state, a circulating fluidized bed forms in the reactor (1), a mixture of product gas and solids passing through the exhaust duct (15) into a cyclone (16) and being separated there. The product gas flows through line (17) to a waste heat boiler (18) and is available in line (19) for further use. Since the product gas is rich in the components H₂ and CO, it can e.g. be processed into synthesis gas.

Solids separated in the cyclone (16) flow back to the reactor (1) in line (20). Ash with a low residual carbon content enters the ash chamber (23) through a pipe (22) which is guided centrally through the distribution chamber (9) and is periodically drawn off through the line (24).

A water vapor line (26), an oxygen line (27), an air line (28) and an inert gas line (29) are connected to the collecting line (10). Each of these lines (26) to (29) has a control valve (30) and a measuring device (31) for determining the amount flowing through. The control valves (30) are actuated by a control unit (35) via signal lines (32); the quantity flowing through the respective line is communicated to the control unit (35) by a signal line (33) from the measuring device (31). A temperature measuring device (34) detects the temperature in the exhaust duct (15) and this information passes through the signal line (36) into the control unit (35). From here, the temperature is regulated by semi-automatic or fully automatic control in a manner to be described. The supply of coal to the reactor (1) is regulated via the control line (37). Details of the possibilities of how this regulation takes place are explained with the aid of FIGS. 2a and 2b.

In Fig. 2a the vertical axis (T) indicates the temperature (e.g. in ° C), the horizontal axis (t) is the same for Figs. 2a and 2b the time axis (values e.g. in hours). The vertical axis (M) of Fig. 2b relates to quantities (e.g. in kg / h) of substances which are fed to the reactor (1) as a function of time. The solid line (a) represents the course of the air supply through line (28), line (b) belongs to the inert gas supplied through line (29), the dash-dotted line (c) belongs to the coal feed and the dotted line (d ) belongs to the water vapor that flows through line (26).

For the first heating, ash is placed in the reactor (1), swirled with hot air and later a start-up burner (40) is started. Gaseous or liquid fuel, for example natural gas or heating oil, is fed to this burner (40) through line (41) and air is fed in through line (42). As a result, the temperature measured in the measuring device (34) gradually increases until, at time (A), coal is fed from the bunker (3) in a metered amount via the cellular wheel sluice (4) to the reactor (1). In the heating phase now starting with the supply of coal, the coal swirled by the air supply burns with excess oxygen in the reactor, as a result of which the temperature is further increased. The start-up burner (40) can be switched off and the proportion of ash supplied is almost zero. If the temperature rise is too steep, the supply of coal to the reactor is reduced and then increased if the temperature rise is below the desired course remains. To correct an excessively high temperature, water vapor can also be passed into the reactor. The setpoint temperature can be specified in the control unit (35) by manual control or by automatic calculation.

The temperature rise in the heating phase continues until the setpoint of the gasification temperature is reached or slightly exceeded. In Fig. 2a this is the time (B). The inerting phase now begins to make the oxygen content in the product gas disappear. For this purpose, the supply of air through line (28) to the reactor (1) is reduced at constant temperature and at the same time the amount of inert gas is increased. It is ensured that the total amount of air and inert gas remains approximately constant. In FIG. 2a, the time (C) denotes the point at which the oxygen content in the product gas has decreased to 0 and the inerting phase has ended. An analyzer, not shown, determines the oxygen content in the product gas of the channel (15).

Now the gasification operation can be started. To do this, a start phase called the response time is required, which lies between points (C) and (D). Here, the supply of coal and oxygen-containing gas is increased, while gradually turning off the supply of inert gas. Finally, increasing amounts of water vapor can be led into the gasification, cf. the dotted line (d) in Fig. 2b. These regulations can be made automatically or by hand. At the same time, it is ensured that the temperature either remains practically constant or only drops a little during the setting time and then remains constant, cf. the lines (m) and (n) in Fig. 2a.

In the stationary gasification operation, which begins at time (D), the reactor (1) is ideally provided with constant amounts of coal, water vapor and oxygen (for example in the form of air) supplied, for example, 1 kg of water vapor is used per Nm³ of oxygen. If lignite or peat is gasified, which is very watery, the supply of water vapor can be reduced or possibly completely eliminated.

In gasification operation, the temperature is regulated by regulating the coal supply via the cellular wheel sluice (4), the reactor (1) being given more coal if the temperature is too high and less coal if the temperature is too low. It is advisable to keep the temperature constant during the gasification with a fluctuation range of ± 40 ° C and preferably ± 30 ° C.

example

In a plant corresponding to the drawing, 21318 kg of coal are gasified per hour. The reactor (1) has a diameter of 2.5 m and a height above the grate (11) of 15 m. The coal to be gasified is a coal mixture with a lower calorific value of 5579 kcal / kg, a water content of 24% by weight and an ash content of 8.3% by weight. The coal has the following elementary analysis (water and ash free):

The combustion and gasification takes place without technically pure oxygen only with air, nitrogen and water vapor. The supply of secondary air through line (12) is dispensed with.

For the first heating up to about 350 ° C, hot air of 420 ° C is fed into the reactor, which contains up to 1000 kg of ash in increasing quantities. Then the burner (40) also comes into operation, to which an increasing amount of up to 361 kg / h of heating oil is fed. After 8 hours of heating, the temperature in channel (15) reaches 600 ° C., at which coal is fed into the reactor; this corresponds to point (A) in FIGS. 2a and 2b. The table below shows the amounts of coal and operating materials (in kg / h) fed to the reactor at various times, together with the temperatures in channel (15). Points (A) to (D) relate to FIGS. 2a and 2b, and the time course of the amounts of substance that are fed to the reactor can also be seen in FIG. 2b.

The gas composition in channel (15) at different times is:

CH₄

   2,5 Vol.-%

H₂

   14,7 Vol.-%

CO

   20,8 Vol.-%

CO₂

   7,0 Vol.-%

N₂

   48,8 Vol.-%

H₂O

   6,2 Vol.-%

At time (D), ie at the start of stationary gasification operations, a product gas with the following composition is generated:

CH₄

2.5 vol%

H₂

14.7 vol%

CO

20.8 vol%

CO₂

7.0 vol%

N₂

48.8 vol%

H₂O

6.2 vol%

To regulate the temperature in the range between times (A) and (B) while 38767 Nm³ / h combustion air is being used, it must be taken into account that when the temperature is increased or decreased by 10 ° C compared to the setpoint, the coal supply by 20 kg / h must be reduced or increased in order to return to the setpoint. During the stationary gasification at a target temperature of 920 ° C, a coal quantity of 21318 kg / h and an air quantity of 38767 kg / h, if the temperature changes by 10 ° C, the coal supply has to be changed by 150 kg / h to get the To reach the target temperature.

Claims (6)

1. A process of controlling the starting up of the gasification of fine-grained solid fuels, which are treated in a fluidized state with oxygen-containing gas and water vapor in a gasifying reactor, which is provided at its top end with a duct for discharging product gas and at its bottom portion with means for withdrawing ash, characterized in that during the heating-up phase preceding the gasification a mixture of solids comprising ash and fine-grained fuels is combusted in a fluidized state in the reactor with a supply of oxygen-containing gas to provide a hyperstoichiometric supply of oxygen and the temperature in the reactor is thus increased approximately to the temperature desired for the gasification, the heating-up phase is immediately succeeded by an inertizing phase, in which the supply rate of oxygen-containing gas is decreased and an inert gas is supplied to the reactor and the content of free oxygen in the product gas is decreased virtually to zero whereas the temperature is maintained virtually constant, and the inertizing phase is succeeded by the gasification, in wnich oxygen or oxygen-containing gas and optionally steam are fed to the reactor, the fuel supply rate is increased and the temperature desired for the gasification, which when measured in the top portion of the reactor or in the discharge duct lies in the range from 600 to 1500°C, is maintained virtually constant after a time for temperature adjustment, and in which the supply rate of solid fuel is decreased when the temperature is too low and the supply rate of fuel is increased when the temperature is too high.
2. A process according to claim 1, characterized in that the temperature is gradually increased during the heating-up phase, in which the supply rate of solid fuel is decreased when the temperature is too high and the supply of solid fuel is increased when the temperature is too low.
3. A process according to claim 1, characterized in that the temperature is maintained constant within a fluctuation range of ±40°C during the gasification after the adjusting time.
4. A process according to claim 1, characterized in that air as an oxygen-containing gas is fed to the reactor in the heating-up phase.
5. A process according to claim 1, characterized in that carbon dioxide or product gas is used as an inert gas during the inertizing phase.
6. A process according to claim 1 or any of the following claims, characterized in that the total rate of oxygen-containing gas and inert gas is maintained virtually constant during the inertizing phase.

Images