DE3036259C2 - - Google Patents

Description

The invention relates to a method for elimination Process wastewater containing tar acid from the hydrogenation of coal.

Coal hydrogenation is usually the addition of molecular hydrogen to coal under Pressure and understood under divisive conditions, with catalysts generally present.

When the coal is hydrogenated, part of the coal in the Oxygen containing coal to tar acids, i. H. to Phenols, cresols and xylenols implemented. In the Separators split off hydrogenation reactions process wastewater is generated. The very water soluble Phenols, cresols and xylenols go out in these Quench and reaction water existing aqueous phase about.

Another amount of wastewater containing tar acid falls in the addition of water vapor (stripping steam) carried out atmospheric distillation of the in the Hydrogenated coal oil.

The process waste water can because of the tar acid content and also due to a harmful hydrogen sulfide and ammonia content for environmental reasons are readily released into public waters.  

Therefore, it was previously necessary to process waste water after separation of hydrogen sulfide and Ammonia of a phenol recovery plant with a downstream To supply wastewater treatment. First that wastewater purified in this way can have a low residual content derived from phenols. That kind of Treatment of the process waste water requires a considerable amount apparatus and energy expenditure, the the bigger the bigger the one to be cleaned Amount of water.

The invention is therefore based on the object To improve the treatment of process wastewater. The task is solved by a procedure with the characteristic Features of claim 1.

The process wastewater becomes a carbon gasification process fed. When carbon gasification is Water or steam processing agent. According to the invention So the waste water becomes the processing medium water or steam and / or as a substitute for Fresh water and live steam are used. This is particularly advantageous if the carbon in the form of a coal liquid suspension (coal / Water slurry) or hydrogenation residues in the gasification reactor is pumped.

The carbon gasification plant, to which the process waste water from the hydrogenation is fed, is preferably connected to the hydrogenation plant in which the process waste water was obtained. In this network, the gasification plant supplies the hydrogen required for the hydrogenation. An example of the invention is explained below using a method scheme according to FIG. 1.

In the exemplary embodiment, gas flame coal is made of the Ruhr area feedstock for a coal liquefaction plant Plant with a throughput of 5000 t (waf) coal / day.

In a first process step, the coal processed, d. H. it is dried and ground.

The coal pretreated in this way is mashed in a second process step 1 . For mashing 1 of the coal, oil from the hydrogenation process is returned, ie it is mashed with circulated oil. The oil added during mashing 1 is referred to as grinding oil. The rubbing oil serves as a solvent in which it is able to release bound hydrogen to the coal. This leads to the beginning of liquefaction, which can also be referred to as hydration or swelling. The solvent also facilitates the actual hydrogenation 2 of the coal, which takes place with the addition of free hydrogen. This hydrogen comes from a gasification plant, which will be explained below. The hydrogenation stage 2 is followed by various separators. The gaseous, liquid and solid phases are separated from each other in the separators.

A first separation process 3 takes place by cooling and quenching with fresh water. The gaseous phase separates and liquid products separate from the gas. Furthermore, the tar acids formed in the hydrogenation 2 from the oxygen contained in the coal go z. T. here in the aqueous phase consisting of quench and reaction water.

In addition to the aqueous phase, 3 liquid products, gas and solid-containing residue are obtained during the deposition. The resulting gas is partly recycled into the hydrogenation 2 . The remaining part of the resulting gas is fed to a gas scrubber 4 , from which it enters a low-temperature decomposition 5 . In this process stage, heating gas, SNG, LPG and H₂ are produced. The hydrogen is also fed to the hydrogenation 2 .

The liquid products obtained in the separation 3 are distilled atmospherically with the addition of stripping steam. In the atmospheric distillation 6 , a water phase, which contains tar acids, is again formed during cooling. The main product of atmospheric distillation 6 , however, are light oil and medium oil, which are subjected to a hydrogenating stabilization in a process step 7 . In addition to these products, gas is obtained, which reaches the low-temperature decomposition 5 via the gas scrubber 4 . The gas originating from the distillation 6 is worked up in the same way as the gas originating from the deposition 3 .

Finally, solvent is obtained for the mashing 1 in the atmospheric distillation 6 .

The solid-containing residue obtained in quench 3 is topped in a vacuum distillation 8 . This creates on the one hand solvent for mashing 1 and on the other hand a vacuum residue.

The vacuum residue from distillation 8 is gasified in a residue gasification 9 according to the Texaco gasification process. The high-melting residue can contain up to 50% solids. With the residue gasification 9 , according to the invention, in contrast to an otherwise possible waste water treatment by ammonia extraction 10 with subsequent phenol extraction 11 , biological treatment and discharge into public waters, a special use of the waste water shown in dashed lines is also connected. The waste water used in the gasification serves to remove the tar acid, without the otherwise expensive equipment and energy required for the cleaning stage.

According to the invention, the process wastewater obtained in the separation and quenching 3 and in the distillation 6 are optionally fed to the residue gasification 9 and / or a coal gasification 12 with an upstream suspension production 13 . The coal gasification 12 serves to generate the hydrogen required for the hydrogenation 2 and the stabilizing hydrogenation 7 , which may be necessary in addition to the hydrogen from the cycle gas, the low-temperature decomposition and the residue gasification. The gasification 12 , like the residue gasification 9, is a gasification according to the Texaco process. It is an autothermal gasification under pressure. With this gasification, pre-shredded feed material with a grain size of less than 0.1 mm is mixed with water to form a stable, pumpable paste which contains approx. 55-60% solids.

This suspension is a burner at the head of the Reactor supplied and vertically in the downflow in Reactor under increased pressure in the presence gasified by steam and supply of oxygen. The reaction with oxygen gives rise to temperatures of approx. 1400 ° C. The ash is liquid. It Synthesis gas is created that with a carbon turnover of approximately 95% has the following gas analysis:

CO₂15-20% CO45-55% H₂30-40% CH₄ca. 1%

The Texaco process is essential in terms of production of the pumpable slurry, which an entry of the coal or hydrogenation residues with Allowed using a pump.

Fresh water per se would be required for the production of the slurry, which according to the invention is replaced by the waste water from the separation and quenching 3 and the distillation 6 . The fresh water supply to be replaced by the wastewater is shown in dash-dot lines in the suspension production 13 and corresponds to the water vapor supply in the residue gasification 9 also shown in dash-dot lines. The waste water supply to the residue gasification 9 and to the suspension preparation 13 is shown in broken lines.

Specifically, a throughput of 5000 t of gas flame coal / day corresponding to an hourly output of approx. 208 t / h in the hydrogenation approx. 63 t / h water with a tar acid content of approx. 7.4 g / dm³. In atmospheric distillation fall about 4.4 t / h of water with a tar acid content from approx. 1.58 g / dm³.

The amount of residue resulting from vacuum distillation is approx. 74.2 t / h with a solids content of about 40%. To gasify this residue steam addition of approx. 28.9 t / h is necessary. There is a hydrogen deficit caused by the Gasification of about 14.4 t / h coal is covered. For the mashing of this amount of coal is the use of 9.6 t / h of water is necessary. By using it of the process waste water for gasification listed above decreases in the wastewater treatment stages amount of water to be enforced 67.4 t / h to 28.9 t / h. At the same time it decreases the one otherwise required for wastewater disposal considerable equipment and energy expenditure accordingly.

The hydrogen is obtained from the synthesis gas with subsequent conversion and gas scrubbing 14 and fed to the hydrogenation 2 and the stabilization 7 .

From the gasification only wastewater is produced with slight neutralization in public Waters can be discharged.

Claims (3)

1. A process for eliminating tar-containing process waste water from the hydrogenation of coal, characterized in that the waste water is fed to a carbon gasification process. 2. The method according to claim 1, characterized in that that the waste water for treatment a pumpable coal / liquid suspension be used. 3. The method according to claim 1 or 2, characterized characterized that from the resulting Gas hydrogen for the hydrogenation is obtained.