DE3729408A1 - DIFFUSION METHOD FOR CONTINUOUSLY CONVERTING A LIGHT-PERMEENTING GAS TO A HEAVY-PERMEABLE GAS UNDER HOEHEREM PRESSURE - Google Patents

Description

The invention relates to a diffusion method for continuous Admixing a slightly permeating gas to a higher pressure present heavier permeating gas.

In chemical engineering there is often the need for a small amount of gas available under low pressure, continuous To meter in a larger amount of gas, which is under a higher pressure stands.

As is known, this is a suitable compressor for the under low pressure gas zuzumischende used.

This is expensive both in terms of investment and operating costs.

It was therefore the task of modifying the process so that no Compressor is needed.

As far as the zuzumischenden gas is hydrogen or another easily permeated by diffusion membranes gas and as far as the is difficult to permeate by admixture to be conditioned gas and as far as suitable pressure conditions are present, this task becomes According to the invention solved that of the mentioned types of gas flowed through spaces via a suitable diffusion membrane - in the form of a Diffusion cell - be contacted with each other.

Further features of the invention are the subject of the dependent claims.

Below is a description of the inventive method.

The drawing shows a diffusion cell with the corresponding Flow rates.

A gas G ₁ with the pressure p ₁ is continuously a second gas G ₂ with the pressure p ₂ < p ₁ be admixed.

This is achieved without the use of a compressor by applying a suitable diffusion membrane, if the following conditions are met:

• 1. The partial pressure p _{2.1 of} the gas G ₂, which is to prevail after the mixture in the gas G ₁, must be lower by a sufficient amount than the pressure p ₂, with which the gas G ₂ is available.
• 2. The permeability of the diffusion membrane for the gas G ₂ must be greater than the permeability to the gas G ₁ in a sufficient ratio.

If these conditions are fulfilled, then the admixture can be carried out according to the Drawing shown method.

Due to the presence in the gas G ₂, less readily permeating impurities and the back diffusion of components from gas G ₁ in the gas G ₂ a more or less large proportion of the gas G to be withdrawn from the system ₂.

Gas G ₁ enters through the nozzle 1 E in the diffusion cell D with the diffusion membrane M and leaves it with the admixed proportion Δ G _{2.1 of} the gas G ₂ and reduced by the gas G ₂ diffused fraction Δ G _1.2 by the nozzle 1 A.

Gas G ₂ enters through the nozzle 2 E in the diffusion cell and leaves it, reduced by the gas G ₁ ₁ over-diffused portion Δ G _2.1 and increased by the back of gas G ₁ in gas G ₂ back-diffused portion Δ G _1.2 through the nozzle 2 A as residual gas.

Gas G ₁ flows through the diffusion cell unregulated and suffers only a minimal pressure drop, the height of which depends on the construction of the diffusion cell.

The influx of gas G ₂ to the diffusion cell is controlled by a flow control member; the outflow of the residual gas stream can be determined by a fixed choke.

However, to minimize the amount of residual gas, it can also be regulated become.

example

A plant for the production of hydrogen from natural gas after the Steam reforming process should use a natural gas volume of 1000 kmol / h, for hydrogenating desulfurization, a hydrogen amount of 100 kmol / h is to be mixed.  

The pressure of the natural gas at the point of admixture amounts to plabs = 40 bar, that of the available hydrogen (purity 99 vol.%, Remainder: methane) p _2abs = 20 bar.

The hydrogen partial pressure in the conditioned for hydrodesulfurization natural gas after admixture is p _2.1 = 4 bar.

The diffusion cell is flowed through in countercurrent. This makes it possible to obtain in the residual gas, a hydrogen concentration of about 20% corresponding to a partial pressure of p _2A = 3 to 4 bar (depending on the pressure in the diffusion cell). From the natural gas, a proportion of 1% (essentially methane) diffuses to the hydrogen side.

The residual gas therefore contains the following quantities:

Methane from backdiffusion 10 kmol / h Methane from hydrogen (1.0%) 1.04 kmol / h Hydrogen 20%  2.75 kmol / h 13.79 kmol / h

The amount of water to be used is thus

the quantity of natural gas to be used

1000 + 10 = 1010 kmol / h.

The residual amount of 13.79 kmol / h will be combined with natural gas and others Residual gases from the process used to underfire the reformer furnace; their calorific value thus remains in the process.

Claims (10)

1. A diffusion method for the continuous admixing of a slightly permeating gas, for example hydrogen, to a heavier present under higher pressure permeable gas, characterized in that the flowed through by said gas species spaces via a suitable diffusion membrane - in the form of a diffusion cell - are interconnected , 2. Diffusion method according to claim 1, characterized in that a Part of the gas used for dosing to discharge Impurities and back-diffused proportions from the zu conditioning gas is withdrawn from the diffusion cell. 3. Diffusion method according to claims 1 and 2, characterized that the gases in the diffusion cell in countercurrent to each other become. 4. Diffusion method according to claims 1 and 3, characterized that the residual gas deduction is controlled after the analysis of the residual gas. 5. Diffusion method according to claims 1 and 3, characterized that the residual gas take-off after the analysis of the conditioned gas is regulated. 6. Diffusion process according to claims 1 to 3 and 5, characterized characterized in that the inflow of zuzumischendem gas with constant Pressure occurs and the amount to be admixed by throttling the Residual gas flow is regulated. 7. Diffusion method according to claims 1 and 6, characterized that the lighter permeating gas as a component in a mixture is present. 8. Diffusion method according to claims 1 and 7, characterized that a commercial apparatus is used, which is for the Recovery of hydrogen from purge gas of an ammonia synthesis was developed.   9. Diffusion method according to claims 1 and 6, characterized that hydrogen is used for the hydrogenating desulfurization of natural gas in the is metered under higher pressure natural gas. 10. Diffusion process according to claims 1 to 6 and 8, characterized characterized in that the metered hydrogen, in whole or in part, the by reforming the conditioned and then hydrogenating Desulfurized natural gas produced in the following plant product represents.