Method for producing acetylene and syngas

Abstract

A process for producing acetylene and syngas by partial oxidation of hydrocarbons with oxygen, involving: separately preheating a hydrocarbon and a oxygen-comprising input stream; mixing in a mass flow ratio of the oxygen-comprising to hydrocarbon stream at an oxygen number no more than 0.31; feeding the streams via a burner block to a combustion chamber and therein partially oxidizing the hydrocarbon(s) to a cracking gas; quenching the cracking gas to 80 to 90° C. downstream by injecting an aqueous quench medium to obtain a process water stream-1 and a product gas stream-2; cooling the product gas stream-2 in a cooling column by direct heat exchange with cooling water to obtain a process water stream-2 as bottoms, a product gas stream-2 as uppers, and a sidestream; and depleting the sidestream of soot in an electrofilter to generate therein a process water stream-3 combined with water streams-1/2 to afford the process water stream-4.

Claims

1. A process for producing acetylene and synthesis gas by partial oxidation of one or more hydrocarbons with oxygen, the process comprising: separately preheating a first input stream comprising a hydrocarbon and a second oxygen-comprising input stream; mixing the first and second streams in a mass flow ratio of the second to the first input stream at an oxygen number of not more than 0.31, the oxygen number meaning a ratio of an oxygen amount actually present in the second input stream to the stoichiometrically necessary oxygen amount required for complete combustion of hydrocarbons in the first input stream, to obtain a mixed stream; feeding the mixed stream via a burner block to a combustion chamber in which the hydrocarbons are partially oxidized, thereby obtaining a cracking gas comprising the acetylene and the synthesis gas; quenching the cracking gas to a temperature in a range of from 80 to 90° C. downstream of the combustion chamber by injection of an aqueous quench medium to obtain a first process water stream I.sub.liq and a first product gas stream I.sub.g; cooling the first product gas stream in a cooling column by direct heat exchange with cooling water to obtain a second process water stream II.sub.liq, as a bottom stream, a second product gas stream II.sub.g, as a top stream, and a sidestream; depleting the sidestream of soot in an electrofilter to generate in the electrofilter a third process water stream II.sub.liq, which is combined with the first and second process water streams I.sub.liq and II.sub.liq to afford a fourth process water stream IV.sub.liq, purifying the fourth process water stream IV.sub.liq by partial evaporation in a decompression vessel, wherein the fourth process water stream IV.sub.liq is evaporated in a proportion in a range of from 0.01 to 10 wt. % based on total fourth process water stream weight to obtain a purified fifth process water stream V.sub.liq; withdrawing the purified fifth process water stream V.sub.liq at a bottom of the decompression vessel and passing the purified fifth process water stream V.sub.liq through one or more soot channels comprising surface particle separators to obtain a sixth process water stream VI.sub.liq freed of floating soot; and recycling the sixth process water stream VI.sub.liq into the process.

2. The process of claim 1, wherein the sixth process water stream VI.sub.liq is completely recycled into the process.

3. The process of claim 1, further comprising: dividing up the sixth process water stream VI.sub.liq exiting the soot channels into a first water substream, which is supplied as a seventh process water stream VII.sub.liq to a cooling tower and cooled therein and subsequently recycled into the cooling column, and a second water substream, which is recycled as an eighth process water stream VIII.sub.liq into a quench region below the burner block.

4. The process of claim 1, further comprising: dividing up the sixth process water stream VI.sub.liq exiting the soot channels into a first water substream, which is supplied to a heat exchanger as a seventh process water stream VII.sub.liq and, after cooling, obtaining a cooled substream, the cooled substream being recycled into the cooling column and a remaining substream being discharged into a wastewater, and a second water substream exiting the soot channels, which is recycled into a quench region below the burner block as an eighth process water stream VIII.sub.liq.

5. The process of claim 1, wherein the fourth process water stream IV.sub.liq is evaporated in a proportion in a range of from 0.5 to 5 wt. % based on the total fourth process water stream weight.

6. The process of claim 1, wherein the partial evaporation is carried out by decompression into vacuum.

7. The process of claim 1, wherein the partial evaporation is carried out by decompression into a vacuum in a range of from 50 to 900 mbar a.

8. The process of claim 1, wherein the partial evaporation is carried out by decompression into a vacuum in a range of from 200 to 600 mbar a.

9. The process of claim 1, wherein the partial evaporation is carried out by adiabatic decompression.

10. The process of claim 1, wherein the partial evaporation is assisted by heating.

11. The process of claim 10, wherein the heating is carried out by direct steam injection.

12. The process of claim 1, wherein the first input stream comprises natural gas.

Description

(1) In the drawing:

(2) FIG. 1 shows a schematic representation of a preferred inventive plant comprising a cooling tower and

(3) FIG. 2 shows a schematic representation of a further preferred plant for performing the inventive process without a cooling tower.

(4) The plant shown in FIG. 1 is supplied with a hydrocarbon-comprising gas stream (1) and an oxygen-comprising gas stream (2), these are preheated separately via preheaters V1 and V2, mixed in a mixing means (M), supplied via a burner block (B) to a combustion chamber (F) and subsequently quenched by injection of an aqueous quench medium in a quench region (Q) to obtain a process water stream I.sub.liq and a product gas stream I.sub.g.

(5) The product gas stream I.sub.g is cooled by direct heat exchange with cooling water in a cooling column (K) to obtain a process water stream II.sub.liq as the bottom stream, a product gas stream II.sub.g as the top stream and a sidestream II.sub.lat. The sidestream II.sub.lat is supplied to an electrofilter (E) and therein depleted of soot to form a process water stream III.sub.liq. At the top of the electrofilter, the purified gas is discharged and supplied to the cooling column. If required (startup of the plant, disruptions), a stream of the sidestream II.sub.lat exiting the cooling column may be sent to a cracking gas flare. The process water streams I.sub.liq, II.sub.liq and III.sub.liq are combined to afford process water stream IV.sub.liq sent to a single-stage decompression vessel (F) and partially evaporated therein to obtain a purified process water stream V.sub.liq. This purified process water stream V.sub.liq is passed through the soot channels (R) comprising surface particle separators to separate the floating soot. At the top of the decompression vessel, the generated flash vapor and inert constituents are withdrawn and sent to a vacuum plant. The process water stream VI.sub.liq exiting the soot channels is divided up and a substream of this process water stream VI.sub.liq is supplied as process water stream VII.sub.liq to a cooling tower (T) and cooled therein and subsequently recycled into the cooling column (K). A substream of this recycled process water stream is supplied to the upper region of the electrofilter as a washing stream to clean the wires. The second substream of the process water stream VI.sub.liq is recycled as process water stream VIII.sub.liq into the quench region below the burner block.

(6) The further preferred embodiment shown in FIG. 2 shows a largely analogous plant but with the exception that a heat exchanger (W) is provided in place of the cooling tower (T). The process water stream VI.sub.liq exiting the soot channels is divided up and a substream of this process water stream VI.sub.liq is supplied to a heat exchanger (W) as process water stream VII.sub.liq and, after cooling, a substream of this cooled process water stream is recycled into the cooling column (K) and the remaining substream is discharged into the wastewater and the second substream of the process water stream VI.sub.liq exiting the soot channels is recycled into the quench region below the burner block as process water stream VIII.sub.liq.

WORKING EXAMPLES

Comparative Example

(7) Without process water purification, the open soot channels and the exhaust air from the cooling tower in a plant corresponding to the schematic diagram in FIG. 1 give rise to the following emissions specifically for 1 t of acetylene:

(8) TABLE-US-00001 Open water quench emissions Soot Cooling channels tower Total kg/t Ac kg/t Ac kg/t Ac CO 0.303 0.486 0.789 CH4 5.69E−02 1.05E−01 0.162 C2H6 7.66E−03 1.47E−02 0.022 C2H4 7.00E−03 2.85E−02 0.036 C2H2 1.66E−01 5.31E+00 5.475 PROPENE 5.30E−04 1.91E−03 0.002 PROPADIENE 1.01E−03 3.65E−03 0.005 PROPYNE 2.40E−03 8.59E−02 0.088 BUTENYNE 1.73E−03 3.93E−02 0.041 BUTADIENE 7.58E−03 7.05E−01 0.712 BENZENE 2.40E−03 1.36E−01 0.138 NAPHTHALENE 5.69E−04 1.09E−02 0.011

INVENTIVE EXAMPLES

(9) The process water purification efficiency is a function of the flash vapor amount as shown in the following table:

(10) To this end, the process water is decompressed from 87.3° C. and 1.013 bar absolute to pressures between 200 mbar absolute and 800 mbar absolute. This partially evaporates the process water in a proportion of 0.0038% to 4.94% by weight. % teilverdampft. This results in the following depletions of dissolved gases as a function of the decompression pressure.

(11) TABLE-US-00002 Depletion by flashing according to pressure (open water quench) Exit 87.3 85.7 75.8 60.1 temperature [° C.] Entry 87.4 87.4 87.2 87.1 temperature [° C.] Entry pressure 1.013 1.013 1.013 1.013 [bar(absolute)] Exit pressure 800 600 400 200 [mbar(absolute)] Flash vapor 0.0038% 0.3108% 2.14% 4.94% amount based on feed [%] Depletion Depletion Depletion Depletion CO 87.7% 99.9% 99.99% 100.00% Methane 84.8% 99.8% 99.98% 100.00% Ethane 83.9% 99.8% 99.98% 100.00% Ethylene 63.1% 99.4% 99.94% 99.98% Acetylene 14.2% 93.5% 99.31% 99.84% Propene 66.8% 99.5% 99.95% 99.99% Propadiene 66.8% 99.5% 99.95% 99.99% Propyne 12.8% 92.7% 99.15% 99.77% Butenyne 19.1% 95.4% 99.47% 99.86% Butadiene  5.2% 82.4% 97.42% 99.14% Benzene  8.4% 88.9% 98.66% 99.62% Naphthalene 22.1% 96.1% 99.56% 99.88%

(12) It is clearly apparent that depletion has strong dependence on decompression pressure. Carrying out an inventive, for example single-stage, decompression of the process water upstream of the cooling tower results in only the following emissions to the environment:

(13) The process water enters the single-stage flash stage at 87.4° C. and is decompressed to 400 mbar absolute.

(14) The stream cools from 87.4° C. to 75.8° C. and 2.14% of flash vapor based on the feed are formed. The table additionally shows the depletion in percent effected by the purification step.

(15) TABLE-US-00003 Open water quench with flash emissions Cooling tower Depletion kg/t in % CO 1.05E−04 99.9866% Methane 2.87E−05 99.9823% Ethane 4.29E−06 99.9808% Ethylene 2.29E−05 99.9356% Acetylene 3.80E−02 99.3053% Propene 1.31E−06 99.9462% Propadiene 2.50E−06 99.9463% Propyne 7.54E−04 99.1462% Butenyne 2.17E−04 99.4727% Butadiene 1.84E−02 97.4207% Benzene 1.84E−03 98.6649% Naphthalene 5.10E−05 99.5561%

(16) Due to the high depletion rate, the cooling tower may be substituted by a closed heat exchanger without the process being subjected to intolerable accumulations of polymerizable components, in particular of higher acetylenes and naphthalene.

(17) TABLE-US-00004 Secondary components in the process water Closed water quench Closed water quench Without flash [ppmw] With flash [ppmw] CO 2.367 0.001 Methane 0.511 0.000 Ethane 0.071 0.000 Ethylene 0.139 0.000 Acetylene 25.812 0.186 Propene 0.009 0.000 Propadiene 0.018 0.000 Propyne 0.417 0.004 Butenyne 0.191 0.001 Butadiene 3.410 0.089 Benzene 0.018 0.009 Naphthalene 0.053 0.000