DE102010026175B4 - Mud recycling in the flash process - Google Patents

Abstract

Process for the expansion and purification of excess quench water in a gasification device that gasifies fuels containing ash at a gasification pressure of, for example, 4 MPa, according to which - the excess quench water is expanded to approximately atmospheric pressure via an expansion valve in a first expansion tank (2), - the liquid phase from the first The expansion tank (2) is fed to a second expansion tank (3) and expanded to a pressure below atmospheric pressure, - the liquid phase from the second expansion tank (3) is fed to a thickener / lamellar clarifier (4) for sludge separation, - the sludge drawn off in the thickener / lamellar clarifier a filter system (5), characterized in that the sludge drawn off in the thickener / lamellar clarifier is divided into a main flow to the filter system (5) and a sludge return (7) to the first expansion tank (2).

Description

The invention relates to a method for the expansion and purification of excess quench water of a ash-containing fuel gasifying gasification.

The excess residual quench water ( 1 ) is brought in the soot water relaxation system in a 2-stage relaxation of the gasification pressure of, for example, 4 MPa to a pressure below the ambient pressure and thereby cooled to about 50-80 ° C. In the first stage, the soot water is expanded to about ambient pressure by means of a control valve. The resulting vapor-liquid mixture is in a separating vessel ( 2 ) separated before the liquid phase in the same way a second flash tank ( 3 ), in which the expansion into the vacuum region (pressure range below atmospheric pressure) takes place. The separated liquid phase is used in the subsequent soot water treatment with flocculant ( 8th ), in the downstream thickener / lamellar clarifier ( 4 ) to promote the solids separation. The solids enriched sludge reaches a dewatering stage ( 5 ). Clear running of the thickener / lamellar clarifier ( 4 ) and the filtrate of the drainage ( 7 ) are used in the gasification process as 6 ) returned.

By the described relaxation passes in addition to the evaporated water content and the bound in the liquid under pressure carbon dioxide (CO ₂ ) in the resulting vapors. Thus, the lime-carbonic acid ratio shifts in the expanded liquid and the pH increases to values above 8. Thus, carbonates are formed and it comes to the formation of firmly adhering deposits and laminations, especially in the first expansion stage ( 2 ). These deposits lead in the course of operating time to block the withdrawal of the liquid phase and thus to interrupt the Rußwasserentspannung.

The above deposits and incrustations can only be removed mechanically. Chemical release by acid (such as HCL) would require the use of expensive acid-resistant materials. For cleaning, the affected Rußwasserentspannungslinie must be taken out of service and switched in the meantime on the so-called bypass, a Rußwasserabkühlung with subsequent relaxation, which can be shared by two or more gasification lines, but not at the same time. After switching off the soot water line and a manual cleaning of the two separation tanks and possibly the affected lines, the Rußwasserentspannung can be put back into operation after appropriate inerting. The bypass system that has since been used must be shut down, rinsed and possibly cleaned manually. All this means a high manual and temporal effort. It should be noted that there is a loss of availability if it comes during use of the soot water bypass to a disturbance in another Rußwasserentspannungslinie.

From the not pre-published DE 10 2009 030 717 A1 is a method for the relaxation of gas and dust laden quench water from the dust gasification known in which the excess quench water is expanded via two flash tank and separated from the expanded gases and water vapor formed. The expanded excess water is fed after a separation of solids in the quench water cycle.

From the DE 10 2008 012 965 A1 is a method for the treatment of resulting in the coal gasification fluid streams is known in which in a mixing zone, a free-falling water film cools the crude gas and a suspension that leads unfavorable fuels and fly ash, discharged and relaxed in several stages to below atmospheric pressure. As a result of the expansion, some of the gases dissolved in the suspension are released with the steam. In order to keep the amount of gas to be disposed small, it is proposed there to largely condense the water vapor.

From the US 5,415,673 For example, a process for producing synthesis gas by partial oxidation in a gasification reactor is known. The black water generated by quench cooling is depressurized in several successive stages of expansion, including a vacuum flash stage, whereby flash vapors are separated. The concentrated black water from the expansion zone is thickened and filtered off a filter cake.

From the DE 10 2008 028 003 A1 a process for the purification of process water, in particular for the continuous purification of process water in the paper industry is known, in which the process water to be purified is first contacted for the degradation of impurities contained in the wastewater in an anaerobic reactor with anaerobic microorganisms, then in a first separation step as a percentage more of the gas (s) contained in the process water is / are separated than from the solids contained in the process water and then in a second separation step, the solids contained in the process water are separated. In one embodiment, separated solid is recycled to the first separation step causing the first separation device, which serves as crystallization nuclei for the solids to be formed from the ions contained in the process water.

The invention is based on the problem for a method for relaxation and purification of excess quench of a ash-containing fuels gasifying gasification device specify how the structure of adherent deposits and laminates of carbonates can be significantly reduced, especially in the first expansion stage in a simple manner.

The problem is solved by the features of claim 1.

The inventive measure a return of a portion of the generated sludge from the solids separation, the thickener / lamellar clarifier in the first flash tank cause the crystallization nuclei contained in the sludge precipitation of the carbonate, whereby the deposits of carbonate on the container wall of the first expansion stage ( 2 ) are reduced accordingly.

The thus from the first relaxation stage ( 2 ) discharged solids also act as nucleation nuclei for the carbonate precipitation in the second expansion stage ( 3 ).

The introduction of additional solids and residual sludges ( 7 ) in the first relaxation stage ( 2 ) has a favorable effect on the solids separation in the thickener / lamellar clarifier (US Pat. 4 ), leading to a reduction in the need for flocculant ( 8th ) leads.

The input of the sludge can also be carried out so that a corresponding energy input into the liquid volume takes place.

By the sludge recycling according to the invention in the first expansion stage ( 2 ), an optional internal sludge return into the thickener / lamellar clarifier ( 4 ) or can be dispensed with altogether.

A retrofitting of already existing plants with the sludge recycling according to the invention in the first expansion stage ( 2 ) is possible without any problems.

Advantageous developments of the invention are specified in the subclaims.

The invention is explained in more detail below as an exemplary embodiment in a scope necessary for understanding with reference to a figure. Showing:

1 a method according to the invention realizing Rußwasser-relaxation system.

The in the thickener / lamellar clarifier ( 4 ) and withdrawn at the bottom of the sludge is withdrawn continuously and after the sludge removal pump ( 9 ) into a main flow to the filter system ( 5 ) and a sludge recycle (Recycle) ( 7 ) divided. This recycled sludge contains a multitude of additional nucleation nuclei that act as an initiator for precipitation of the carbonate in the first separation vessel ( 2 ) be used. Thus, the deposition of the carbonate is no longer predominantly on the container wall of the first expansion stage ( 2 ), but primarily on the introduced crystallization seeds, which are then discharged with the soot water of the first expansion stage. Also in the second relaxation stage ( 3 ) these additional solid particles act as nucleation nuclei for the remaining carbonate precipitate. Furthermore, the sludge recirculation has a beneficial effect on the solids separation in the thickener / lamellar clarifier (US Pat. 4 ), leading to a reduction in the need for flocculants ( 8th ) leads.

LIST OF REFERENCE NUMBERS

1

Restquenchwasser

2

separating vessel

3

expansion tank

4

Thickener / lamella

5

dewatering stage

6

Circulation water

7

Fraction of the filtrate of drainage

8th

Soot water treatment with flocculation aid

9

Sludge removal pump

10

Sludge storage tank

Claims (5)

Process for the expansion and purification of excess quench water of a gasification device, which gasifies ash-containing fuels at a gasification pressure of, for example, 4 MPa, consequently - the excess quench water via a pressure relief valve into a first expansion vessel ( 2 ) is vented to approximately atmospheric pressure, - the liquid phase from the first flash tank ( 2 ) a second expansion tank ( 3 ) and released to a pressure below atmospheric pressure, The liquid phase from the second flash tank ( 3 ) a thickener / lamellar clarifier ( 4 ) is fed to the sludge separation, - the sludge withdrawn in the thickener / lamellar clarifier a filter system ( 5 ) is characterized in that the sludge drawn off in the thickener / lamellar clarifier is divided into a main flow to the filter system ( 5 ) and a mud return ( 7 ) in the first expansion tank ( 2 ). A method according to claim 1, characterized in that the from the second expansion tank ( 3 ) separated liquid phase in the subsequent soot water treatment with flocculant ( 8th ). Method according to one of the preceding claims, characterized in that the part of the sludge to be returned as a partial flow of the continuous sludge removal pump ( 9 ) is removed. Method according to one of the preceding claims, characterized in that in discontinuously operating sludge removal pump ( 9 ) the recirculated sludge from the sludge stack container ( 10 ) is taken. Method according to one of the preceding claims, characterized in that the growing on the crystallization seeds carbonate precipitates are discharged as an additional solid from the first flash tank together with the separated liquid phase.

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