METHOD AND SYSTEM FOR HOMOGENIZING THE DELIVERY OF FUELS IN A GASIFIER FOR GENERATING SYNGAS

Abstract

A method and a system for uniformization and regulation of the solid fuels pneumatically conveyed using dense-stream conveying, into a gasifier for the production of synthesis gas, is supposed to be configured in such a manner that clearly homogenized feed of the coal to the burner is made possible, whereby the short-term fluctuations are minimized and thus the gasification quality is improved, and regulation of the amounts of coal to the burner is structured to be more effective. This is achieved in that the fine-grain to dust-type fuel is first conveyed out of a feed container positioned below the burner level, to a level above the burner level, and subsequently homogenized in a line that is directed downward toward the burner.

Description

The invention is directed at a method for uniformization and regulation of the solid fuels pneumatically conveyed using dense-stream conveying, into a gasifier for the production of synthesis gas.

Regulated feed of fuel dust in an entrained-flow gasifier is described, for example, in DE 10 2005 047 583 A. In this connection, it is known to react the fuel using the burners that are built into the vertical gasifier wall and are essentially oriented horizontally, whereby the fuel, composed of finely distributed or dust-type (<0.5 mm) fuel particles, for example coke, petro-coke, biological waste, and other fuels, is reacted with gasification agents that contain oxygen, under elevated pressure, at temperatures above the slag melting point.

A device and a method for pneumatic conveying of bulk materials, using the dense-stream method, are known from WO 2006/015702 A1.

In the implementation of pressurized gasification processes, a carbonaceous fuel is reacted with a gas that contains oxygen, whereby the gas that contains oxygen is fed in the sub-stoichiometric ratio, so that a product gas that contains hydrogen and carbon monoxide is obtained. In order to achieve a high rate of reaction of the fuel and a high degree of efficiency, the fuel/oxygen ratio must be adjusted within a narrow range.

In pressurized gasification, burners having coaxial channels are generally used, whereby mixing of the media being fed in takes place not in the burner, but only in the gasifier. An example of a burner used in a pressurized gasification system is presented in detail in EP 0 437 698 A1, for example. Supply of the burners with fuel usually takes place from a feed container that stands slightly above gasifier pressure, by means of dense-stream conveying. In this connection, pneumatic conveying is referred to as dense-stream conveying, whereby the carrier gas transports the fuel particles not as individual particles, but rather in the form of dense fillings or plugs that fill the entire pipe cross-section. In general, dense-stream conveying deliveries possess speeds of 4 to 6 m/s, whereby the high solids charge of the gas stream nevertheless leads to a high transport amount. Dense-stream conveying is very gentle on the material and, above all, is not very susceptible to break-down with regard to sticky or damp transport material.

The quality of gasification is decisively influenced by the uniformity of the coal feed to the burner. While variations over longer time intervals (for example due to planned regulation measures or due to a change in the coal used, etc.) are determined by means of measurement technology and taken into consideration, very short-term fluctuations in the feed quality (feed density and velocity) cannot be compensated.

Since dense-stream conveying involves a fluidized gas/solid mixture, in the broadest sense, here, too, the fluctuations in density and velocity that are typical for a fluidized bed can be observed. These can only be influenced by means of indirect measures, such as the configuration of the feed into the feed line. For this purpose, it is furthermore known that settling phenomena of the solid can occur in long horizontal sections of the feed line, and this is usually minimized by means of the feed of additional gas. Further homogenization is achieved when the line leads upward once again.

Because of the space requirements and the system-specific setup, the situation usually is that the feed container that supplies the burners by way of a feed line is situated “at the bottom” in the system structure, while the burners are situated at a clearly higher level, because of the vertical method of construction of the gasifier. Setup of the feed container “at the bottom” is cost-advantageous, particularly if the required fuel transport into the feed container is based on gravity flow and therefore has to be positioned above the feed container.

Until now, the line placement of the feed line to the burners went from “the bottom” to “the top” at burner level, and there was led horizontally to the connector taps of the burner, in most cases, from where the coal went into the burner.

It is the task of the present invention to configure a method as described initially in such a manner that clearly homogenized feed of the coal to the burner is made possible, whereby the short-term fluctuations are minimized, and thus the gasification quality is improved, and regulation of the amounts of coal to the burner is structured more effectively.

This task is accomplished, according to the invention, with a method of the type mentioned initially, in that the fine-grain to dust-type fuel is first conveyed out of a feed container positioned below the burner level, to a level above the burner level, and subsequently homogenized in a line that is directed downward toward the burner.

It has been shown that uniformity of the fuel/gas mixture transported in the dense stream is achieved by means of the method of operation according to the invention, which uniformity is clearly better than conveying through lines that run horizontally. Because of the homogenization in the drop line ahead of the burner, the fuel particles are accelerated by gravity, whereby gas bubbles that might be contained in the mixture are filled with fuel as the mixture drops.

Embodiments are evident from the dependent claims. In this connection, it can be provided that the homogenization takes place in a line that is directed downward, whose length corresponds to at least five times the line diameter.

It has proven to be practical if the fuel is homogenized in a drop line that is passed out of an elbow, whereby the drop line is oriented at angles <20°, preferably at 0° from the vertical.

However, the range in which the drop line can be adjusted relative to the vertical can also be selected to be different from what is claimed here, depending on the material that is being used; the decisive factor is the homogenization in the drop pipe.

Another practical embodiment according to the invention consists in that gas is fed into the fuel stream, to regulate the fuel throughput, whereby mixing is undertaken just before or in the burner.

Dilution is brought about by adding auxiliary gas into the fuel stream being conveyed as a dense stream, in other words the conveying density is reduced. While the velocity of the diluted fuel is increased, the influence of the reduced density nevertheless predominates, whereby the throughput is reduced.

EXAMPLE

10 kg/s fuel having a density of 400 kg/m³ and a velocity of 5 m/s are conveyed through a burner into the gasifier, using dense-stream conveying. Because of friction and upward conveying, a pressure loss of 100 kPa occurs in the pipeline. In the burner, a pressure loss of 20 kPa occurs due to friction and further acceleration of the suspension. In order to reduce the throughput, auxiliary gas is fed into the fuel line directly ahead of the burner, thereby almost doubling the volume stream. The pressure loss in the fuel channel of the burner is also doubled as a result. Since the fuel channel is only 2 m long, it is filled with the diluted fuel after only 0.2 s. The fuel throughput is already reduced after this short period of time.

The example shows that very rapid adaptation of the fuel throughput is possible. However, the regulation range is restricted by the required amount of gas and the fuel velocity in the burner, which is restricted due to erosion. With this method, the fuel throughput can be changed by +/−10% in a typical application.

The invention will be explained in greater detail below, using the drawing as an example. This shows, in

FIG. 1 a schematic layer diagram, as well as in

FIG. 2 an enlarged detail in the area of a burner, not shown in greater detail, in an indicated gasifier wall.

FIG. 1 shows the dense-stream conveying 2a and 2b out of the feed container 1 into the burners 4a, 4b of the gasifier 3. The exit of the feed container is lower than the burners, so that the fuel should be conveyed horizontally and upward. However, in order to achieve a homogeneous fuel suspension, the fuel is first passed to above burner level, and then, after deflection, homogenized in a drop line having a length of 3 m, for example. Just ahead of the burner, the lines are deflected, in order to feed the fuel into the burners horizontally, and auxiliary gas 11a, 11b is fed into the line. Also, a gas 5a, 5b that contains oxygen and a moderation gas 6a, 6b are fed into the burner, and these influence the gasification parameters.

Alternatively, the auxiliary gas 11a, 11b can be fed directly into the burner or into the fuel channel of the burner.

FIG. 2 shows an alternative embodiment of the method. Dense-stream conveying 2 is passed into the vertical drop line in an arc. Ahead of the burner tap 12, which is oriented vertically, an auxiliary gas 11 or part of the moderation gas 6, for example CO₂, is fed into the gas introduction device 10, in order to reduce the conveying density and the fuel stream.

Claims

1: Method for uniformization and regulation of the solid fuels pneumatically conveyed using dense-stream conveying, into a gasifier for the production of synthesis gas,

whereby

the fine-grain to dust-type fuel is first conveyed out of a feed container positioned below the burner level, to a level above the burner level, and subsequently homogenized in a line that is directed downward toward the burner, wherein gas is fed into the fuel stream, to regulate the fuel throughput, whereby mixing is undertaken just before or in the burner, and wherein for temperature regulation, in particular, at least a part of the gas used in the gasifier (moderation gas) is introduced into the conveyed fuel.

2: Method according to claim 1, wherein

the homogenization takes place in a line that is directed downward, the length of which line corresponds to at least five times the line diameter.

3: Method according to claim 1, wherein

the fuel is homogenized in a drop line that is passed out of an elbow, whereby the drop line is oriented at angles <20°, preferably at 0° from the vertical.

4-5. (canceled)

6: Method according to claim 1, wherein

additional gas, such as nitrogen, carbon dioxide, steam, other inert gases or mixtures of them, is used.

7: Method according to claim 6, wherein

the additional gas is introduced by way of a pipe tap, in the immediate vicinity of the burner.

8: System for uniformization and regulation of the solid fuels pneumatically conveyed using dense-stream conveying, into a gasifier (3) for the production of synthesis gas, particularly for carrying out the method according to claim 1, further comprising dense-stream conveying lines (2, 2a, 2b) from a feed container (1) to the burners (4, 4a, 4b) of the gasifier (3), whereby the end region of the dense-stream conveying line (2) is positioned perpendicular ahead of the burner (4), in each instance.

9: System according to claim 8, wherein

the length of the perpendicular dense-stream line section corresponds to at least five times the dense-stream line diameter.