GB2124651A - Process for the agglomeration of coal slurry - Google Patents

Abstract

A process for the agglomeration of coal slurries in which the coal slurry is agglomerated with fuel oil or tar-oil containing for example 1-10% (preferably 2-4%) of pitch or with raw tar, optionally together with powdered coal and/or a pre- agglomerated coal and preferably with 0.01-1.0% of a surface-active agent, in the presence of steam under pressure (e.g. at an overpressure of at least 0.02 MPa), if desired mixed with air. The agglomerate may then be separated from the waste and its water content reduced.

Description

SPECIFICATION A process for the agglomeration of coal slurry The invention relates to a process for the preparation of an agglomerate possessing good mechanical and firing properties from aqueous coal slurry, by using a binding agent.

Processes are already known by which aqueous coal slurries, which seriously pollute the environment and cause storage problems, are rendered suitable for further processing.

Thus in numerous patent specificatons (U.S.

4,234,320; DE 29 GB 2,024,250 A; DE 2753628; US 4,126,426; RB 874,315) the utilization of coal slurries and more particularly the agglomeration thereof are dealt with.

The first step of any of the mentioned processes is the admixing of the aqueous coal slurry with a so-called binding agent; the latter is usually a liquid hydrocarbon. The admixing can be performed mechanically (e.g. with a propeller mixer), by ultrasonic energy or by a hydrodynamic method wherein liquid phases are contacted at high differences in speed. As result of the admixing the grains stick to the oil emulsified in water and form an agglomerate of a readily filterable size. Generally it is more advantageous if the admixing is performed at higher temperatures.

Some methods (e.g. US patent specification 4,234,320) suggest performing the agglomeration in two steps.

According to US patent specification No.

4,234,320 the aqueous suspension of the solid material is admixed with the hydrocarbon binding agent under turbulent stirring, the formed agglomerate is separated from the water and the non-agglomerated grains, then the agglomerate is put into a mixer containing water the temperature of which is higher than the softening point of the binding agent. In this mixer further binding agent is added, then the thus-obtained higher quality agglomerate is separated by a percussion separator from the hot water, which is recycled into the process.

The process according to the U.S. patent specification No.4,126,426 differs from the previous suggestion mainly in that before agglomeration the coal slurry is separated into two fractions according to the grain size.

The fraction of the smaller grain size (under 0.1 mm) is admixed with a binding agent and agglomerated and separated, and then the fraction of bigger grain size-which can be more easily treated is added after dehydration to the agglomerate. In this case again liquid hydrocarbons are used as binding agent. The process is more effective at higher temperatures.

According to Belgian patent specification No. 874,315 the stirring leading to the agglomeration is performed in a hydrodynamically: the liquid hydrocarbon is admixed to the flowing coal slurry, the agglomeration after stirring and the separation are performed in a filter centrifuge. According to this method it is suitable to prepare an aqueous emulsion of the hydrocarbon before admixing with the coal slurry.

Exact admixing and viscosity data can be found in the British patent specification 2,024,250 where the agglomeration is preceded by flotation to concentrate the dry matter. A great advantage of the process seems to be the low oil consumption.

According to the German patent specificaiton No. 2,753,628 the agglomeration is performed with an aqueous oil emulsion. After the separation the process is repeated with the nonagglomerated waste. An oil of high boiling point is used, and the efficacy is increased by adding surface-active agents. The separation from the waste and the water is performed on a shaking screen, and then the agglomerate is purified by washing away the waste.

On the basis of the above-cited patent specifications the main characteristics of the known processes are as follows: 1. The aqueous coal slurry is admixed with a liquid hydrocarbon as binding agent so that the particles form a filterable agglomerate. The admixing processes vary-mechanical, hydrodynamical and ultrasonic processes are described.

2. The agglomeration is more efficacious if the temperature of the system is higher.

3. The hydrocarbons used are mainly various liquid fractions of crude oil and of carbonaceous distillation products.

4. If necessary, the product is further dried mechanically and/or thermally.

With the known methods the admixing of the coal slurry with the agglomerating substances and the heating of the mixture always demanded two separate process steps whereby the duration of the process and the demand for apparatuses were considerably increased.

The aim of the invention is to eliminate the deficiencies of the known processes and to economically prepare a fuel with a good heating value and a low ash content.

As a result of our tests we have found a process in which the admixing and the heating can be performed in a single step by the aid of steam introduced into the coal slurry.

The disadvantage of the known processes in using the liquid hydrocarbons for the agglomeration resides in the fact that the product could not be readily handled and generally its heating value was not good.

In the course of our tests it was observed that if to the fuel oil or tar-oil used as binding agent a small quantity (e.g. 110%) of black pitch is added or raw tar is used (which can contain 50% of black pitch), the filterability, mechanical strength and its separability from the waste considerably improve the ash content is reduced and its heating value increases.

Moreover we have found that the effect of the steam is increased to a considerable degree if it is mixed with air because thus the mixing effect is enhanced.

It is advantageous to add a surface-active agent to the coal slurry. Both ionic and non-ionic agents can be used.

It has been found that the addition of a small quantity of powdered coal (e.g. of a low waste content) and/or of the agglomerate obtained as product to the mixture of coal slurry and oil promotes a better separation of the waste from the particles and at the same time improves the mechancial properties of the formed agglomerate.

Accordingly the invention relates to a process for the agglomeration of coal slurries in which the coal slurry agglomerated with fuel oil or tar-oil containing for example, 110% (preferably 24%) of pitch or with raw tar, optionally together with powdered coal and/or a pre-aggiomerated coal and preferably with 0.01-1.0%ofa surfaceactive agent, in the presence of steam under pressure (e.g. at an overpressure of at least 0.02 MPa), if desired mixed with air. The agglomerate may then be separated from the waste and its water content reduced. Percentages herein are by weight.

If the coal slurry processed is one formed in the production of coal suitable for coking the process allows the ash content to be reduced even below 12% and thus the obtained agglomerate can also be made suitable for coking. This fact is very important in the power industry.

The process is generally illustrated by the flow diagram (Figure 1) as follows: The coal slurry containing about 30% of dry matter and about 35 to 40% of waste, related to the dry matter, is led from settling holder 1 with the help of the slurry pump 13 through the heat exchanger 4 into the premixing container 5. In mixer 5 powdered coal and agglomerate can be admixed, if desired, from the reservoirs 3 and 21 respectively. The coal slurry is agglomerated in mixing reactor 6 operated by the (tangential) introduction of steam through valve 16. Raw tar (or fuel oil or tar-oil containing 3% of black pitch) is taken from reservoir 2 through pump 1 2 and preheated in the heat exchanger 4. When an oil is used it may be sprayed into the steam.The agglomerate prepared in mixing reactor 6 and the waste slurry are passed again through the heat exchanger 4, and then led into the countercurrent separator 7, the bottom product of which is an agglomerate of coal formed with oil and the top product is the waste which can be removed as a thin slurry. The agglomerate leaving separator 7 is dehydrated by mechanical separator 9 and forwarded by the transport system 10 for use or storing. The waste leaving the top of separator 7 is admixed in mixer 8 with a flocculating agent from tank 20, and then led to settler 11 from which the settled waste containing about 40% water is transported to a drier by pump 1 5.The water from the overflow of the settler 11, which is nearly free of slurry, is taken through valve 1 9 and pump 14, partly to feed the settling separator 7, and partly for recycling to the coal dresser through valve 17.

The filtrate appearing at filter 9 is led through valve 1 8 into the same water circulation.

The process according to the invention is further illustrated with the help of the following examples.

Example 1 A coal slurry with a dry matter content of 250 g/l and having an incombustible residue of 35% is led through a heat exchanger at a rate of 4 I/minute into an agglomeration mixer. Fuel oil containing 3% of black pitch (light sulfur fuel oil F60/130) is added at a rate of 100 g/minute to the coal slurry preheated to 5060 C. The viscosity of the fuel oilis 5.2 EO at 700C, and the softening point of the pitch dissolved in it is 85950C. The intensive mixing of the coal slurry and the added oil is effected by tangentially introducing direct steam. The oil is sprayed into the steam. The pressure of the steam used for mixing is 0.1 MPa.The agglomerate prepared in the mixer and the waste slurry are led through a heat exchanger into a countercurrent settler, the bottom product of which is the agglomerate of coal formed with oil and the top product of which is the waste removed as thin slurry. The agglomerate leaving the settler is dehydrated by a vacuum filter and transported for use or storage by a transport system. The quantity of the formed agglomerate is 0.95 to 1.0 kg/minute, its composition is as follows: water content 9% solid substance content 80% oil content 11% incombustible residue 17% The waste leaving the settler is admixed in the mixer with a flocculating agent, then let into the settler from which the settled waste with a water content of 40% is taken to a drier.

The quantity of the waste formed is 420-450 g/minute, and its water content is 4042%.

The oil content of the 1 70-1 80 g of dried waste is 1.21.3%, its measured carbon content is 3 4%, and its incombustible resjdue content 8789%. The water from the settler is almost free of slurry and the filtrate obtained at the separator are recycled into the water flow of the system.

Example 2 The process is essentially the same as that described in Example 1 but instead of the fuel oil containing 3% of black pitch the same quantity of tar-oil containing 10% of black pitch is used, and 0.1% of Na-salt of dodecyl-sulfonic acid related to the solid substance content of the coal slurry, is added.

The quantity of the agglomerate formed is 1050 kg, composition is as follows: water content 9.5% solid substance content 80% oil content 1 0.5% incombustible residue 17% The quantity of the waste formed is 450 g, its water content amounts to 43%.

Example 3 The process is essentially identical with that described in Example 1, with the difference that in the premixer a prepared agglomerate is added to the starting coal slurry.

The quantity of the agglomerate added is 60 g/minute, and its composition is as follows: solid substance content 75% oil content 16% water content 8.2% incombustible residue 12.4% The quantity of the agglomerate formed is 1.10 kg/minute, its composition is as follows: water content 9% oil content 16% solid substance content 75% incombustible residue 13.5% Quantity of the barren formed is 480 g, and its water contents amounts to 4344%.

The oil content of the dry matter is 1.3%, and its measured C-content amounts to 4.0%; and the amount of the incombustible residue is 88%.

Example 4 The process is identical with that described in Example 1, with the difference that the starting coal slurry has a lower (25%) ash content, and a centifuge was used for dehydration.

The quantity of the agglomerate formed is 1050 kg, its composition is as follows: water content 10% oil content 10% solid substance content 80% incombustible residue 10% if the starting coal is suitable for the preparation of blast furnace coke, the formed agglomerate, too, is of coking quality.

The quantity of the removed barren is 380 g, and its water content amounts to 41%.

1.2 to 1.3% of its dry substance content is oil and the carbon content of its combustible part amount to 3.5 to 4.0%, and the incombustible residue amounts to 91 to 91.5%.

Claims (11)

Claims

1. A process for the agglomeration of a coal slurry, which comprises agglomerating the coal slurry with a binder in the presence of steam under pressure, said binder being a fuel oil or taroil which contains pitch or being raw tar.

2. A process as claimed in claim 1 in which the binder is a pitch-containnig fuel oil or tar-oil and is mixed with the steam prior to the agglomeration step.

3. A process as claimed in claim 1 or claim 2 in which the steam is mixed with air.

4. A process as claimed in any one of the preceding claims in which the agglomeration is performed in a mixer into which the steam is introduced tangentially.

5. A process as claimed in any one of the preceding claims in which the binder is fuel oil or tar-oil containing 2 to 4% by weight of pitch.

6. A process as claimed in any one of the preceding claims wherein the coal slurry additionally contains powdered coal and/or preagglomerated coal.

7. A process as claimed in any one of the preceding cliams in which the coal slurry contains a surface active agent.

8. A process as claimed in any one of the preceding claims in which the steam is used at an overpressure of at least 0.02 MPa.

9. A process as claimed in any one of the preceding claims in which the agglomerated coal is subsequently separated from nonagglomerated waste and its water content reduced.

10. A process as claimed in any one of the preceding claims in which the coal slurry used is a slurry formed in the production of coking coal.

11. A process as claimed in claim 1 substantially as described herein with reference to the drawing or in any one of the Examples.