DE102010026172B4 - Process for preventing deposits of carbonate-rich waters in the flow stream gasification - Google Patents

Abstract

Process for avoiding precipitation of alkaline earth carbonates in pipelines and apparatus of the entrained flow gasification in the recycling of process water, according to which the process water, in particular residual quench water from the quencher (4), a relaxation and dust separation in a process water treatment (15) are subjected, - the water vapor saturated raw gas from the entrained flow gasification reactor (3) in a crude gas scrubber (7) is dedusted, - then for the raw gas in an exothermic crude gas conversion (8) the required CO / H ratio is set, - then from the cooling of the raw gas in a waste heat recovery and cooling ( 9) a CO-rich condensate (16), which is free from alkaline earth, is recovered and the CO-rich condensate (16) in a collecting tank (19) the treated process water (18) after the expansion and dust separation and before a temperature increase the circulating water (12) is added in a circulating water heating (14).

Description

The invention relates to a method which prevents the deposition of alkaline earth carbonates from the quench and wash waters in the entrained flow gasification.

The invention relates to a process for the gasification of solid, liquid or pasty fuels having ashlar-containing ashes, with a free oxygen-containing oxidant under normal and elevated pressure to 10 MPa. Solid fuels are pulverized coal of different rank, petroleum cokes and other grindable solids with a calorific value greater than 7 MJ / kg. By liquid fuels are meant sludge-like oil-solid suspensions or water-solid suspensions, such as coal-water slurries. The ratio of fuel to oxygen-containing gasifiers is selected so that the gasification temperatures are above the melting point of the ash. As a result, the fuel ash is melted into liquid slag, which leaves the gasification space together with the gasification raw gas and is cooled directly by injecting water in a quenching chamber or indirectly by heat removal in a waste heat boiler. Such a gasification device goes out DE 197 18 131 A1 out.

A detailed description of a gasification process can be found in J. Carl u. a., NOELL CONVERSION PROCESS, EF publishing house for energy and environmental technology GmbH, starting from page 32.

During the direct or indirect cooling and subsequent water washing, the high process pressures and temperatures result in the solution of calcium carbonate, which reaches the saturation limit in the condensates and washings produced. This causes the operational problem that calcium carbonate precipitates out of the water during temperature and pressure changes and is deposited on the walls of the pipelines. This occurs particularly aggravating in basic process waters, which have their cause in the ammonia formed during gasification. After the equation HCO ₃ ^- + OH ^- → CO ₃ ^- + H ₂ O In addition, soluble bicarbonate converts into sparingly soluble carbonate. Pipe constrictions to complete blockage are the consequence. Experiments with chemical additives and physical measures, such as the application of magnetic fields, do not lead to an improvement of the situation.

From the DE 10 2007 037 860 A1 For the quenching process of an entrained-flow gasification plant, it is known that an increase in the pH of the circulating water into the alkaline range to values> 6.5 results in an increased deposition of carbonates.

From the DE 10 2008 047 930 A1 is a direct raw gas cooling in the entrained flow gasification known to be minimized in the condensation losses. Here, the raw gas generated during the entrainment gasification is first dedusted and CO-converted. The dedusted and COkonvertierte raw gas is cooled by direct contact with supplementary water. The heated make-up water is fed to the process water circuit for quenching.

The object of the invention is to treat the circulating, calcium carbonate-rich process waters of an entrainment gasification device in such a way that precipitation of calcium carbonate is largely prevented.

The object is achieved by a method having the features of the first claim. The dependent claim is a further advantageous embodiment of the innovation again.

According to the invention, low-lime or -free, CO ₂ -containing waters from the process are added to the lime-rich or lime-saturated wastewaters. This is particularly significant if the fresh water requirement is to be limited by intensive recycling. In addition, by discharging ammonia from the water cycles, the pH is shifted to the acidic region, so that the bicarbonate conversion to carbonate does not take place.

By adding CO ₂ -rich waters, the calcium carbonate is converted into bicarbonate according to the following equation: CaCO ₃ + H ₂ CO ₃ = Ca (HCO ₃ ) ₂ and prevents precipitation of the carbonate from bicarbonate-rich water. Calcium bicarbonate, unlike carbonate, is soluble in water to higher concentrations. If bicarbonate-rich waters are released, carbon dioxide is liberated and the above equation runs from right to left. Then the risk of deposits in piping and apparatus is particularly great.

The carbon dioxide-rich waters are recovered as process-specific condensates, in particular according to the process stages of the raw or clean gas conversion.

The invention will be explained in the following in an embodiment with reference to two figures.

• 1: ein Vergasungsverfahren mit integrierter Rohgaskonvertierung
• 2: ein Vergasungsverfahren mit nachgeschalteter Reingaskonvertierung

Showing:

• 1 : a gasification process with integrated raw gas conversion
• 2 : a gasification process with downstream clean gas conversion

In the figures, like reference numerals designate like elements.

The in 1 represented entrained flow gasification reactor via the lines 1 and 2 dust-like fuel and an O ₂ / steam mixture supplied as a gasifying agent. The reaction takes place in a gasification flame at a pressure of 4 MPa and a temperature of 1600 ° C in the gasification reactor 3 , The hot gasification gas and the fuel ash molten to liquid slag enter the quenching 4 in which by injecting water through the quench nozzles 5 in excess crude gas and slag are cooled, the crude gas at about 210 ° C saturated with water vapor and the slag is granulated. The slag is in a water bath on the slag removal 6 from the quenching 4 removed and removed from the process. The excess quench water passes through the residual quench water line with dust 17 into the process water treatment 15 , The water vapor-saturated raw gas is passed through the crude gas line 11 from the quencher 4 in the raw gas scrubbing 7 transferred. This is operated with treated process water, condensates from the process or fresh water. The temperature in the raw gas scrubber 7 is kept within the range of the quenching temperature if possible. The dust-free, water vapor-saturated crude gas then passes into the crude gas conversion 8th in the reaction CO + H ₂ O = CO ₂ + H ₂ the required for the subsequent further processing CO / H ₂ ratio is set. The raw gas is heated by the exothermic reaction to about 360 ° C and then the waste heat recovery and cooling 9 fed and cooled to about 30 ° C. Subsequently, the raw gas passes 10 for further treatment in subsequent system parts. In waste heat recovery and cooling 9 fall condensates 16 on, which have high CO ₂ contents due to the high CO ₂ partial pressures in the raw gas after the conversion. For example, the following concentrations were found: CO ₃ ^2- / HCO ₃ ^- 853 mg / l HS ^- / S ^2- 31 mg / l pH 5.5

Since the condensates are free of alkaline earths, the carbon dioxide can only be physically dissolved and present as carbonic acid H ₂ CO ₃ , which also proves the low pH.

Residual quench water from the quencher 4 passes over the Restquenchwasserleitung 17 into the process water treatment 15 , in which initially made a two-stage relaxation to about 0.06 MPa, separated in a thickener, the thin phase and from the thick sludge in a filter press, the solid is deposited. The thin phase, together with the filter effluent, is treated as process water 18 the water collection tank 19 fed. By the relaxation of the residual quench water, CO _{2 is} released, the water becomes alkaline and the carbonate deposition increases. For the relaxed and dust-free residual quench water, as treated process water 18 over the water collection tank 19 is returned to the cycle, the following values result: CO ₃ ^2- , HCO ₃ ^- 800 mg / l HS ^- , S ^2- 10 mg / l NH ₄ ⁺ 500 mg / l pH 8th

Since the CaCO3 solubility at these temperatures only at approx _. 15 mg / l, the risk of deposits is very high. By adding the CO ₂ -rich condensate 16 in the collection tank 19 the carbonate-bicarbonate equilibrium is shifted in the direction of the soluble bicarbonate. From the water collection tank 19 this is made from recycled residual quench water 18 , Wash water and condensate 16 formed circulating water 12 via the circulation pump 13 and a circulating water heating 14 the quench nozzles 5 fed again. Of course this can be done in waste heat recovery and cooling 9 accumulating condensate 16 also, at least in part, directly as washing water for raw gas scrubbing 7 be used. In order to limit the coal salts and the ammonia content, a certain part of the circulating water becomes via the water removal 20 discharged and chemically treated. The amount discharged depends on the salt content of the coal.

In many cases, no raw gas, but a clean gas conversion is used, as in 2 shown. Then joins the Rohgaswäsche 7 For example, a desulfurization 21 before the desulfurized raw gas in a clean gas conversion 22 adjusted to the required CO / H ₂ ratio. The condensate 16 falls in this variant in one of the clean gas conversion 22 downstream waste heat recovery and cooling 9 at. The circulation procedure is maintained as described.

LIST OF REFERENCE NUMBERS

1

fuel supply

2

Gasifying agent supply

3

gasification reactor

4

quenching

5

quench nozzles

6

slag removal

7

raw gas scrubbing

8th

crude gas

9

Heat recovery and cooling

10

Raw gas for further treatment

11

Raw gas line from quenching

12

Circulating water for quenching

13

Circulation pump

14

Circulating water heating

15

Process water treatment

16

carbon dioxide-rich condensate

17

Restquenchwasserleitung

18

processed process water

19

Water collection tank

20

drainage

21

desulphurization

22

Clean gas conversion

Claims (2)

Process for avoiding precipitation of alkaline earth carbonates in pipelines and apparatus of entrained flow gasification in the recycling of process waters, according to which - the process waters, in particular quenching water quench (4), a relaxation and dust separation in a process water treatment (15) are subjected, - the water vapor saturated raw gas dedusted from the entrained flow gasification reactor (3) in a crude gas scrubber (7), - then the required CO / H ₂ ratio is set for the crude gas in an exothermic crude gas conversion (8), - then from the cooling of the raw gas in a Abhitzegewinnung and cooling (9) a CO ₂ -rich condensate (16), which is free from alkaline earths, and - the CO ₂ -rich condensate (16) in a collecting tank (19) the treated process water (18) after the expansion and dust separation and before a temperature increase of the circulating water (12) in a Kreislaufwasseraufheizung (14) is set. Method according to Claim 1 characterized in that to limit the salt and ammonia content of the circulating water, a portion of the circulating water via a water outlet (20) is discharged from the circulation.

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