EP0019641B1 - Method of processing carbon-water suspensions, resulting from scrubbing the gas produced during the gasification of crude mineral materials - Google Patents

Description

The invention relates to a process for the preparation of suspensions of carbon-containing material and water, which are obtained when the gas is washed out with water, which is formed in the gasification of coal by thickening the suspension, and intimately mixed with a liquid hydrocarbon, the carbon-containing material from the suspension separated by sieving and returned to the starting fuel and admixed with it, while the washing water is again introduced into the washing zone.

Coal dust gasification takes place in the cocurrent of coal with water vapor and oxygen or air in the gasification reactor. The carbon-containing fuels required for this are first finely ground together with water in a wet mill. The finished suspension is then pumped into the reactor, where it is gasified together with the oxygen and possibly water vapor. The reaction takes place very quickly in the flame, so that the average residence time in the reactor is only a few seconds. The final product in this process consists mainly of carbon oxide and hydrogen. In addition, it contains relatively large amounts of entrained carbon-containing solids.

The entrained solid particles are then removed by contacting the synthesis gases with water in conventional washing devices, e.g. Wash coolers, freed from the carried solids. The wash water laden with solids is then fed to a thickener which divides the suspension into solid and wash water, the solid being mixed with the feed material and the wash water being returned to the wash zone. By recycling the solid, the carbon throughput can be brought to approximately 100%.

From DE-A-1 216 259 there is known a process for the preparation of such water-carbon suspensions, according to which the wash water dispersion is first mixed with a gasoline fraction, whereby the coal floats on the water and can thus be separated from the water. Further dewatering is achieved by subsequently mixing the existing petroleum coal suspension with a bunker heating oil and then heating it. This vaporizes the gasoline, which can then be used again for washing out, while the mixture of bunker heating oil and suspended coal is fed back to the gasification reactor.

From DE-A-1 216 259 it is also known to remove at least some of the ash from the gaseous reaction products, since this can increase the usability and the value of the carbon-containing materials recovered later. This ash automatically precipitates in the cooling zone through direct contact with the water and can be removed in the form of sintered material from the bottom of the vessel.

Furthermore, it is known from FR-A-2 343 803 to subject the carbon-containing material to a classification before recycling and only to return the sieve residue to the gasification reactor and to mix it with the feed.

However, it has been shown that these known methods do not significantly increase the economic viability. This is attributed to the fact that, according to previous experience, around half of the fine dust produced during gasification consists of combustible and ash. The ash content of the feedstock will continuously increase due to the continuous recirculation of the solid matter discharged with the synthesis gas. To maintain the pumpability of the feed, additional water must be added, which leads to a deterioration in efficiency. Taking into account the knowledge that the efficiency of the gasification process and thus the economy can be significantly improved by reducing the mineral content in the discharged and returned solid, the invention has set itself the task of developing and proposing a method by means of which the combustible and Incombustible components of the discharged carbonaceous material are separated as much as possible and without too much effort.

According to the invention, this is achieved by thickening the suspension to 200 to 500 g / l, preferably 350 g / l, then mixing it with heating oil as the liquid hydrocarbon and classifying the mixture through a sieve with a mesh size of 0.5 mm , wherein the carbonaceous material is supplied with the sieve residue and with the heating oil. the starting fuel.

Studies have confirmed that the ash content increases with increasing grain fineness, so that the ash content of the total suspension can be significantly reduced by simply separating the finer fractions.

The sieve passage, which contains most of the ash, is then separated from the water and removed from the circuit. The sieve residue, which mainly contains carbon-containing components, is continuously drawn off, hydraulically returned to the gasification reactor and mixed with the feed. Since it is already a water-carbon suspension, prior mixing is not necessary. The suspension can be immediately added to the gasification reactor or else added to the suspension tank. The main advantage of the method according to the invention is that a noticeable reduction in the ash content of the carbon-containing material returned to the process can be achieved with the aid of a classification which is not expensive to use. The process described is neither temperature nor pressure-dependent and can therefore also be carried out without additional process engineering effort. The advantage of the method can also be seen in the fact that A subsequent treatment of the solid discharged with the synthesis gas also makes gasification of ballast-rich carbon-containing minerals economically possible. Without such a treatment, the incombustible content at the inlet of the reactor would otherwise increase very quickly to such an extent that there are hardly enough combustible parts in the feed.

According to the invention, the water-carbon suspension is first thickened to a certain solids content, then intimately mixed with a liquid hydrocarbon and then classified. This causes the carbon-containing parts to be re-wetted, which leads to an agglomeration of the carbon-containing parts, so that during the subsequent classification, the slag-rich solid is discharged with the water through the sieve. It has surprisingly been found that the surface properties of the carbon-containing minerals used do not change even by gasification or partial gasification. The solid washed out of the gas stream is first thickened to a concentration suitable for the crosslinking process in order to minimize the consumption of oil and to make the success of the crosslinking process as cheap as possible. According to the invention, the concentration is 200 to 500 g / l, preferably 350 g / l. The thickener underflow is then mixed intensively with 5 to 20% by weight, preferably 8 to 10% by weight, based on the solids content, with commercially available heating oil. The agglomeration that occurs here relates exclusively to the carbon-containing substances, owing to the surface properties which have already remained the same. In this way it is then easily possible to feed the suspensions of agglomerated carbon-containing parts, slag-rich solid and water to a sieve of 0.5 mm and to feed the sieve residue then obtained back to the reactor and to mix it with the feed. The sieve residue can be mixed in without further pretreatment, because the heating oil still adhering to the solid particles does not hinder the subsequent gasification process, but actually even promotes it. Since this is also a water-carbon suspension, the suspension can also be introduced directly into the gasification reactor. A further improvement is achieved in that comminution is interposed in the method according to the invention. For example, the thickener underflow should be ground to <0.1 1 mm. As a result, the separation effect of the method according to the invention is improved by a more optimal implementation.

Claims (3)

1. Method of processing suspensions of carbonaceous material and water, which are produced by scrubbingthe gas obtained inthe gasification of coal, in which the suspension is thickened, intimately mixed with a liquid hydrocarbon, the carbonaceaus material is separated from the suspension by filtration and returned to, and mixed with, the initial fuel material, while the wash water is again led to the wash zone, characterised in that the suspension is thickened to 200 to 500 g/l, preferably 350 g/l, then mixed with fuel oil as the liquid hydrocarbon, and the mixture is classified over a sieve having a 0.5 mm mesh width, and the classification residue is returned together with accompanying fuel oil as the initial fuel material.

2. Process according to claim 1, characterised in that the tickened suspension is mixed with 5 to 20 weight %, based on the solids content, of fuel oil.

3. Process according to claim 2, characterised in that the tickened suspension is further comminuted, to less than 0.1 mm.