CS197877B1 - Process for preparing pure hydrogen from coke-oven gas - Google Patents

Description

( ⁵⁴ ) Process for producing pure hydrogen from coke oven gas

The present invention relates to a process for producing very pure hydrogen by washing coke oven gas with liquid methane.

A closed nitrogen-methane cycle with a compressor is used to pump the cold from the desorption / rain / column to the required temperature level.

Starting material for production of very pure hydrogen / min. 95 7. mol. H is a coke oven gas which is precalculated before it enters the apparatus in a manner commonly used. Pre-purified coke oven gas / Known composition in% mol .: 52/2 H ₂ # 7,0 N ₂ ; 8.6 CO, 0.9 O ₂ > 28.7 CH 2; 2.6 C ₂ H 2 / passes through a system of low-temperature exchangers in which the admixture is gradually condensed. The gas, partially de-admixed, enters the absorption column, where it is purged with liquid methane, which removes hydrogen from any undesirable constituents, especially 0 ₂ , CO, N ₂ > Nitrogen cycle with a compressor ensured evaporation of the components O ₂ , CO, N ₂ from methane. Pure methane is then cooled with liquid nitrogen, which is produced after throttling in a closed circuit.

A disadvantage of the nitrogen circuit (or circuit with another pure substance) used is that the nitrogen must be compressed in a relatively large amount and at a relatively high pressure. The closed circuit pressure is given by the condensation pressure of nitrogen at the desorption column boiling temperature, increased by the necessary minimum temperature difference necessary for heat exchange.

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197 877

The aforementioned drawbacks are not a process for producing pure hydrogen from coke oven gas by liquid methane scrubbing, wherein the scrubbing liquid methane is regenerated by desorption of the absorbed impurities and cooling in a closed circuit by using nitrogen and methane sweep to cool the de-absorbed liquid methane. 80: 20 to 20: 80.

An advantage of the process according to the invention is the reduction of the necessary condensation pressure. By reducing the condensation pressure, there is a substantial saving in compression work and the resulting energy savings. The scrubbing methane was then cooled to the same temperature as liquid nitrogen. Evaporation of the steam-capped nitrogen-methane mixture occurs in an exchanger that is designed to efficiently utilize the cold by flowing methane. The property of the mixture is used to boil within a certain temperature interval. By using the mixture in the circuit, the cooling capacity is increased over pure nitrogen.

An exemplary embodiment of the invention is shown schematically in the accompanying drawings. Fig. 1 shows the closed cycle of the cold cycle absorption and desorption column apparatus for transferring the cold using a reciprocating compressor; and Fig. 2 shows a schematic representation of the coke gas line cooling rates and heating lines of both cycles at the cold end of the Q-t diagram. .

As can be seen from FIG. 1, the coke oven gas KP passes through a heat exchanger where it is cooled to a temperature of about 103 K through the individual cold fluids flowing through the conduits 16, 18. After separation of the heavy components in the separator T, it enters the absorption column 2 where it is washed with supercooled liquid methane. Liquid methane scrubs unwanted 0g, CO, Ng components from the raw hydrogen and is throttled from the bottom of column 2 of the desorption column 2. Before entering the de-sorption column 2, the contaminated methane is stripped of the lighter components by boiling. The methane is then compressed by pump 2 to column 2 pressure (e.g. 2 NPa) and is subcooled in heat exchangers 11 and 12. The methane subcooling is largely ensured by a closed cycle which pumps the cold from the bottom of the column 6 to the heat exchangers 12. According to the invention, the working medium in the cycle is a mixture of nitrogen and methane in a suitable ratio (in the particular case in moles). X 60 Ng and 40 CH 2, which preferably replaces the nitrogen circuit. The compressor 13 compresses the Ng-CH3 mixture to a pg / 2.1 HPa pressure. After passing through the water cooler 14 and the oil absorber 15, the working medium enters the heat exchanger 6 and fed to the column of the column 2, where it takes over a substantial part of the cold. After cooling in heat exchanger 10 is a mixture of Ng - CH ^ throttled to the pressure p ₁ / 0.15 NPA / and formed parokapaUnné protlproudně mixture is cooled in heat exchanger 12 pure methane. The heat exchanger 12 is designed to provide a two-phase evaporation throughout the heat exchanger bundle.

When a closed cycle is used to pump cold as a working medium instead of nitrogen in a nitrogen-methane mixture in a suitable ratio, which varies according to the specific task, the required amount and the required pressure Pg in the closed circuit are changed. Figure 2 schematically shows the heating lines of both cycles at the cold end of the β - * t diagram. Reducing ΔΤ from AT ₁ to TTg and correspondingly reduced axargia loss by irreversible heat exchange leads to reduced compression work using Ng - CH *

The curve 17 corresponds to the heating line with the nitrogen cycle, the curve 18 corresponds to the heating line with the N ₂ + CH ₂ mixture and the curve 19 corresponds to the cooling c of the coke oven gas line. This results in energy savings. A further advantage of the invention is that when designing higher power units, a closed-cycle turbo-compressor could be used instead of a piston compressor, which further simplifies the device.

Claims (1)

SUBJECT OF THE INVENTION Process for producing pure hydrogen from coke oven gas by liquid methane scrubbing, wherein the scrubbing liquid methane regenerates the desorption of absorbed impurities and cooling in a closed circuit, characterized in that a nitrogen / methane mixture of 80:20 to 20:80 is used to cool the desorbed liquid methane. .