METHOD FOR THE COMBINED RESIDUE GASIFICATION OF LIQUID AND SOLID FUELS

Abstract

A process for joint entrained-bed gasification of ash-containing solid fuels and liquid fuels which are fed separately of each other to the coal gasification reactor via several burners, said burners having a concentric firing angle of greater than 0 degree such that soot formation is reduced and the conversion efficiency is increased, and the solid is conveyed to the gasification reactor together with an inert gas, and at least part of the ash-containing solid fuel contains fine coal particles which originate from coal mining and are not suited for fixed-bed gasification, and the liquid ash-containing fuel contains residues from a fixed-bed gasification.

Description

The invention relates to a process for the simultaneous gasification of solid fuels and ash-containing liquid fuels under pressure, the solid fuel and the liquid fuel being fed separately of each other to the gasification reactor and the ash content of both fuels being discharged from the reactor as molten slag at a temperature above 1500° C.

STATE OF THE ART

Since many years different gasifier types have been known for the gasification of solid carbonaceous fuels under pressure. The best known processes are fixed-bed, fluidised-bed and entrained-bed gasification. Before the 80s gasification project designs had almost exclusively been based on the fixed-bed gasification process whereas today's units are usually designed as entrained-bed gasifiers. Most of the installed fixed-bed gasifiers are still in operation today.

In comparison to today's entrained-bed gasification processes the fixed-bed gasification has some disadvantages, such as increased water and space requirement and the more complex gas and water treatment. Furthermore, in fixed-bed gasification, tar oils with fine-grained ash particles are obtained as liquid residue product. These residues may in addition contain phenols, fatty acids, heavy metals, ammonia and other impurities. Therefore, the residues must be treated in a complex way. Furthermore, in coal mining large amounts of fine coal particles are obtained (approx. 20-30% of the total amount of coal). This fine coal dust cannot be used for fixed-bed gasification at all or only after complex treatment. In most cases, however, these residues are not useful in the generation of syngas and are passed to a simple combustion unit.

As mentioned in DE 42 26 034 B4 and DE 43 17 319 C1, the liquid residues from the fixed-bed gasification are passed as slurry to the entrained-bed gasification. A technical solution for the gasification of residues in the entrained-bed gasification is not mentioned. An optional utilisation of fine coal particles obtained from coal mining is not mentioned either.

The abstract of DE 42 26 015 C1 mentions the direct process coupling of fixed-bed gasification and oil gasification. However, the oil gasification is only rated for liquid hydrocarbons of a very low concentration of solids or ash, well below one percent by weight. The liquid residues of the fixed-bed gasification, however, contain up to 10% solid particles. The gasification temperatures in the oil gasification are considerably below those of an entrained-bed gasification of coal. This means that any ash particles contained in the fuel continue to be separated as ash and must be disposed of in a complex way. Temperatures above 1400° C., preferably above 1500° C., are required for a separation of the ash particles contained in the residues in molten state from the fixed-bed gasification. The bricklining of the oil gasification unit and the downstream syngas cooling units are not designed for such temperatures.

Thus, only the coal gasification process is suited for a gasification of the residues including the withdrawal of the molten slag. As mentioned in DE 38 20 013 A1, there are coal gasification processes using either a bricklined or a cooled reactor. As explained in DE 38 20 013 A1, a gasifier equipped with a bricklined reactor is also not suited for the gasification of dust-containing tar residues because the forming liquid slag infiltrates and destroys the refractory masonry of the reactors, in particular, in the case of high concentrations of heavy metals or alkali metals in the residues.

Therefore, it is suggested in DE 38 20 013 A1 to degas the dust-containing tar residues in a gasifier equipped with a cooled reactor vessel, the tar residues being fed—independently of the burner—to the reactor together with the steam, i.e. not in a burner having its own oxygen supply. In this process, however, the input of liquid residues is very limited. In addition, in this process, a considerably lower conversion efficiency is to be expected because there is no intensive mixing of the tar residues and the oxygen.

A further disadvantage of the processes described in DE 42 26 034 C1 and DE 43 17 319 B4 is the limited ash concentration in the fuel. The solid fuel is fed to the gasifier as a fuel/water mixture. The supplied water and the ash content must be brought to the required gasifier temperature with the aid of the energy released in fuel gasification. With high ash contents, however, the energy released by gasification is no longer sufficient to maintain the gasifier temperature. As, however, high-ash coal is used in particular in fixed-bed gasification, the combination of an entrained-bed gasification with coal/water supply is very limited.

In addition, the problem of a possible soot formation in the gasification of liquid hydrocarbons is not mentioned in none of the patents. As the downstream plant sections of the coal gasification are not rated for a higher soot load, an increased soot formation would result in considerable problems in these plant sections.

Objectives

It is therefore the target and objective of the invention to flexibly use the ash-containing liquid residues from a fixed-bed gasification and the fine coal particles which cannot be used in a fixed-bed gasification jointly in an entrained-bed gasification and to simultaneously minimise soot formation.

The invention achieves the objective by a process according to the features of the first claim.

The dependent claims disclose an advantageous embodiment of the claims.

The inventive solution provides a process for the recovery of syngas by the gasification of ash-containing liquid residues from a fixed-bed gasification at a pressure of 0.3 to 8.0 MPa and a temperature above 1400° C. using oxygen-containing gaseous gasification agents in a cooled reactor,

in which

• • the ash-containing liquid fuel is fed to the reactor together with an ash-containing solid fuel, and
  • the liquid and the solid fuel are fed separately to the reactor via several burners, and
  • the liquid and the solid fuel are fed to the reactor secantly to the circumference of the reactor at a firing angle above 0°, and
  • the ash-containing solid fuel, dispersed in a supplied gas, is fed to the reactor, and
  • the ash-containing solid fuel constitutes at least part of the portion of fine coal particles from coal mining which cannot be used for fixed-bed gasification.

Normally, coal lumps from coal mining are gasified in a fixed-bed gasification. Fine coal particles below 5 mm cannot be gasified in the fixed-bed gasification and must be gasified in a different way or disposed of. The fixed-bed gasification additionally yields a mixture of condensates as residue, said mixture containing mainly phenols, fatty acids, ammonia, tar oils and medium-heavy oils as well as ash-containing and carbonaceous solid particles. The residue must be treated in a complex way such that it can be passed to further use if required or be disposed of.

Thus, economic operation of a fixed-bed gasification requires a flexible use of the solid and liquid residues obtained from fixed-bed gasification. For this, an entrained-bed gasification with cooled reactor and a separate supply of the ash-containing liquid and solid fuels, the latter being conveyed in a transport gas, is an ideal solution. In an optional embodiment the transport gas consists of 100% or less nitrogen or carbon dioxide or a combination of both gases.

The cooled reactor can be operated at temperatures above 1400° C., preferably above 1500° C. such that the ash-containing fuel particles0 can be discharged as granulated slag. The slag requires no further treatment because possible impurities are not washed out in contrast to the ash in the fixed-bed gasification. Moreover, the cooled reactor is resistant to any impurities contained in the fuels, e.g. heavy metals.

The separate supply of the solid and liquid fuels facilitates the optimum use of the fuels. Typically, the carbonaceous solid fuel is a coal of a fine grain size, preferably below 5 mm, which cannot be used in a fixed-bed gasification. Therefore, the fine coal particles from coal mining which are not suitable for fixed-bed gasification can advantageously be used for being conveyed in a transport gas since a diameter below 0.1 mm is required for conveying the coal in a transport gas. This reduces the normal expenditure by coal grinding. Moreover, the separate supply of the solid fuel facilitates a compensation of possible variances in quality or quantity of the liquid fuel. Moreover, additional coal may be mixed to the solid fuel to increase the overall performance.

On the other hand, a burner which largely reduces soot formation may be used for the ash-containing liquid fuel. Such a burner is described in EP 00 95 103 A1. This burner consists of three tubes arranged concentrically which form a central supply tube and two enclosing annular gaps, the liquid fuel being supplied via the central annular gap formed by the inner and the outer tube. The oxygen or oxygen-containing gas is supplied via the supply tube and the outer annular gap. In a typical embodiment the burner system consists of three concentric tubes with conically tapered end finely distributing the escaping fuel upon exit. This increases the conversion efficiency and thus reduces soot formation to a minimum. The burner system can be equipped with a cooling chamber in the area of the burner outlet.

The carbonaceous solid fuel is preferably conveyed via two burner systems facing each other and, staggered by 90 degrees in relation to these in the horizontal, the ash-containing liquid fuel is also supplied via two burner systems facing each other. Of course, the burner systems may also be provided in any other number and thus also be staggered by an angle greater or smaller than 90 degrees. Burner planes arranged in parallel are also feasible for performance adaptation.

A further reduction of soot formation is achieved by all burners having a firing angle greater than 0 degree and preferably 3-6 degrees, a swirl thus being created inside the reactor. This increases, on the one hand both the residence time and the conversion efficiency, the firing angle being the angle between the discharge direction of the fuel and the horizontal connection line between the burner nozzle and the axis of symmetry of the reactor. The discharge direction of the fuel may also be inclined towards the horizontal if necessary. On the other hand, the separation of the molten slag and of the non-converted carbon particles towards the reactor wall is intensified. There, the non-converted carbon particles are further converted or retained in the slag.

It is also possible to provide several horizontal planes for the burners. Hence, the burner systems can be distributed over one or several horizontal planes. Normally, the firing angle relative to the horizontal plane is 0 degree. However, it is also possible that the firing angle relative to the horizontal plane is greater than 0 degree.

EMBODIMENT EXAMPLES

The following example is to explain the invention. The embodiment example is shown in FIGS. 1 to 3 and detailed in the following sections. FIG. 1 shows an inventive process of a fixed-bed and an entrained-bed gasification. FIG. 2 shows the lateral and vertical view of a gasifier including burners for solid and liquid fuels. FIG. 3 shows a burner suited for running the inventive process. The drawings only show embodiment examples of the invention, the invention not being restricted to these embodiment examples.

In a preferred embodiment, the residues of a fixed-bed gasification are conveyed to an entrained-bed gasifier. Here, the residues are a liquid tar/fine coal mixture obtained as residue from the fixed-bed gasification and non-usable fine coal particles from coal mining.

Every hour 400 t/h of coal are extracted from a coal mine (1), FIG. 1. Of these, approx. 280 t/h of lumpy coal (1a) are suited for fixed-bed gasification (2). Synthesis gas (2a) is produced in the fixed-bed gasification (2). The remaining fine coal (1b) has a diameter lower 5 mm and cannot be used for fixed-bed gasification (2). The remaining 120 t/h of fine coal (1b) are conveyed to the entrained-bed gasification (3) and there converted to synthesis gas (3a). In addition, the fixed-bed gasification (2) yields approx. 95 t/h of fine-coal-containing tar oils to be further conveyed (2b) to the entrained-bed gasification (3). The solid carbon content of the tar oils is approx. 5%. The amount of energy of 95 t/h of the residue product roughly corresponds to 25% of the amount of energy supplied to the fixed-bed gasification via the 280 t/h of lumpy coal.

Thus, the total amount of synthesis gas produced can be increased by the described combination of fixed-bed and entrained-bed gasification from 270,000 Nm³/h to 490,000 Nm³/h.

In the preferred embodiment, FIG. 2, the residues from the fixed-bed gasification and the fine coal are fed separately via four burners to the gasification reactor (4) of the entrained-bed gasifier. Two burners are provided for the solid fuel (5a,5c) and two burners for the liquid fuel (5b,5d). All burners (5a-d) are in a horizontal plane, two burners each facing each other. The burners are designed in such a manner that the fuel escapes from the burners (10) secantly to the circumference of the reactor, the firing angle (9) between the discharge direction of the fuel (11) and the connection line between the burner nozzle and the axis of symmetry of the reactor being greater than 0 degree, preferably 3-6 degrees.

FIG. 3 shows the preferred burner for the gasification of the tar oils of fine coal content. This burner consists of three tubes arranged concentrically (6,7,8) which form a central supply tube (6) and two enclosing annular gaps (7,8), the liquid fuel being supplied via the central supply tube (6). The fuel is supplied via the annular gap (7). The oxygen-containing gas is supplied via outer supply tube (8). The three tubes have a conically tapered end finely distributing the escaping fuel upon exit. This increases the conversion efficiency and reduces soot formation to a minimum.

LIST OF REFERENCES USED

• 1 Coal mine
• 1a Lumpy coal
• 1b Fine coal
• 2 Fixed-bed gasification
• 2a Synthesis gas
• 3 Entrained-bed gasification
• 3a Synthesis gas
• 4 Gasification reactor
• 5a-d Burners
• 6 Central supply tube
• 7 Annular gap
• 8 Outer supply tube
• 9 Firing angle
• 10 Transversal discharge
• 11 Radial discharge

Claims

1. Process for the recovery of syngas by the gasification of ash-containing liquid residues from a fixed-bed gasification at a pressure of 0.3 to 8.0 MPa and a temperature above 1400° C. using oxygen-containing gaseous gasification agents in a cooled reactor,

characterised in that

the ash-containing liquid fuel is fed to the reactor together with an ash-containing solid fuel, and

the liquid and the solid fuel are fed to the reactor separately via several burner systems, and

the liquid and the solid fuel are fed to the reactor secantly to the circumference of the reactor at a firing angle above 0°, and

the ash-containing solid fuel, dispersed in a carrier gas is fed to the reactor, and

the ash-containing solid fuel constitutes at least part of the portion of fine coal particles from coal mining which cannot be used for fixed-bed gasification.

2. Process according to claim 1, characterised in that the residue product from the fixed-bed gasification contains hydrocarbons, in particular tars, but also phenols, fatty acids and ammonia.

3. Process according to claim 1, characterised in that carbonaceous solid fuel is a coal of a fine grain size, preferably below 5 mm, which cannot be used in a fixed-bed gasification.

4. Process according to claim 1, characterised in that the burner system for the supply of the ash-containing liquid fuel consists of three tubes arranged concentrically, oxygen or an oxygen-containing gas being conveyed through the inner and the outer tube of the burner system and the ash-containing liquid fuel being conveyed through the central annular gap formed by the inner and the outer tube.

5. Process according to claim 4, characterised in that the burner system including the three tubes concentrically arranged has a conically tapered end and is equipped with a cooling chamber in the area of the burner outlets.

6. Process according to claim 1, characterised in that the carbonaceous fuel is supplied via two or more burner systems facing each other and, staggered by 90 degrees in relation to these in the horizontal, the ash-containing liquid fuel is supplied via two or more burner systems facing each other.

7. Process according to claim 1, characterised in that the burner systems are distributed over one or several horizontal planes.

8. Process according to claim 1, characterised in that the firing angle between the discharge direction of the fuel and the connection line between the burner nozzle and the axis of symmetry of the reactor is 3-6.

9. Process according to claim 1, characterised in that the firing angle opposite the horizontal plane is greater than 0 degree.

10. Process according to claim 9, characterised in that the transport gas consists of 100% or less of nitrogen or carbon dioxide or a combination of both gases.