DD219953A1 - METHOD FOR CLEANING GASES - Google Patents

Abstract

The invention relates to a process for the adsorptive purification of gases, in particular biogas. The object and the object of the invention are, in addition to the separation of steam, ammonia and sulfur compounds, above all, a separation of the carbon dioxide which is favorable in terms of energy and apparatus. This is achieved according to the invention by the arrangement of silica gel and zeolitic molecular sieves in a certain layer ratio to one another in switchable adsorption apparatuses. Temperature and pressure data for the adsorption and desorption, as well as Spuelgaseinsatz and utilization are set forth.

Description

Field of application of the invention

The invention relates to adsorptive gas separation, in particular the purification of biogases.

Characteristic of the known technical solutions

For biogas purification, a two-stage adsorption process according to the temperature and pressure swing principle is known, as described in "Nickel Topics", VoI 34 (1981), H 1, page 10. Disadvantage of this process is the desorption at reduced pressure in the pressure swing stage Since the provision and application of vacuum energy and equipment

are expensive. , ' ; .

The prior art also includes physically and / or chemically acting gas scrubbers (absorption method) in connection with downstream adsorption for fine cleaning and drying or removal of the components by the detergent or by reactions of the detergent with the components contained in the biogas into the gas have arrived.

Disadvantages of gas scrubbing with downstream adsorptive Feinreiriigung are the high process pressure with optimal driving style of physical gas scrubbing (4 to 10MPa) and the consequent high relaxation losses and the long loading and relaxation times of the temperature change stage and the high energy and investment costs

Regeneration of the detergent. '

In US Pat. No. 3,594,983 it has been proposed to remove carbon dioxide from hydrocarbon-containing gas mixtures, in particular and in small amounts, by adsorption on synthetic zeolites by means of water vapor and hydrogen sulfide. For this purpose, three adsorber units are used for the components to be removed, one of which is in the loading phase, one in the desorption phase by Druckswing and one in the Desbrptionsphase by Temperaturswing. Disadvantage of this solution is the use of vacuum as well as the provision of larger amounts of impurity-free regeneration gases in the temperature swing desorption phase and the high technical and regulatory technical effort for the three Adsorbereinheiten.

Object of the invention

The aim of the invention is to develop an economically favorable process for the adsorptive removal of carbon dioxide of different proportions in methane-containing gases, in particular from biogas. Explanation of the essence of the invention

It is an object of the invention to reduce the state of the art inherent lack of high energy and equipment costs. '

This object is achieved in that biogas, ^N the still contain methane or water vapor, sulfur compounds, traces of ammonia and carbon dioxide, are passed through an adsorber - seen in the flow direction - with a bed entporigen silica gel for binding the water vapor, with a · Charge of zeolitic molecular sieve of the types Ca A and / or Na X for the uptake of the NH ₃ and the sulfur compounds and with a bed of zeolitic molecular sieve of the type Ca A with 68 to 80 mol% Ca ¹¹ 'ions or of the type Na X Absorption of CO _{2 is} filled, wherein for the average bed preferably the Ca A type with 58 to 64 mol% Ca ² 'ions is suitable and the volume ratio of the beds to each other - seen in the flow direction. - 1: 2: 5 amounts to. Further essential features of the invention are an adsorption pressure of only 2 to 4 kPa (U) at an adsorption temperature of 293 to 303 K, wherein compliance with this temperature is made possible by installed in the Adsorbensschüttung internals for indirect cooling. These internals are used in the subsequent desorption process for heating the Adsorbensschüttung. The desorption is carried out in a known manner by raising the temperature and rinsing, but according to the invention with a regeneration temperature of 523 K, with a rinsing time of one third of the heating time in the final phase and with a necessary purge gas of only (at most) the product of Adsorbervolumen and purge gas pressure. In the cooling phase, at most one purge gas is required, which corresponds to the product of the double Adsorbervolumen and the purge gas pressure. This purge gas is returned to the process.

embodiments

One of the possible embodiments is shown below. A gaseous mixture present in a biogas reactor at a pressure of 3 kPa, which is water vapor saturated at 308K and has the following composition 59.8% by volume of CH ₄ ^; , . '' - ..:. ; _: . ^:

40.0 voi .-% CO ₂ ,: -

0.2% by volume HjS \

100 vpm NH ₃

should be cleaned in such a way that no disturbances occur in the cryogenic methane liquefaction, i.e., the following upper limits are required

CO _2. <5övpm. .... '/. '^:; ..

H ₂ Q -S 3vpm

For this purpose, the crude gas is fed into an adsorber of 1.42 m ³ content of a plant consisting of at least two adsorbers whose apparatuses are operated in cyclic permutation in the adsorption and desorption phases. As a result, the biogas first flows through a layer of narrow pore silica gel of the type KE 1 / in which it is dried. It then passes through a layer of zeolitic molecular sieve of the type Ca A with 58 to 64 mol% Ca ²⁺ ions, where the sulfur compounds u. NH _{3 are} withdrawn / and last through a layer of a molecular sieve of the type. Ca A with 68 to 80 mol% Ca ²⁺ ions, wherein the removal of CO ₂ takes place. Indirect cooling of the bed keeps the temperature approximately between 293 and 30.3 K during the adsorption phase. The volume ratio of the layers in the adsorber in the above-mentioned sequence is 1: 2: 5. Shortly before reaching the CO ₂ breakthrough, the cyclic permutation of the adsorption and Desorptionsyorganges takes place within the alternately operated adsorber, which happens at a cycle time of about one hour. The desorption is carried out by raising the temperature to 520 K by indirect heating of the bed and by flushing in countercurrent to the loading flow direction with product gas. The purge phase of the desorption process is limited to the last third of the heating time in order to minimize the loss of product gas which is discharged into the atmosphere laden with impurities. This amount of purge gas is thus only one Adsorbervölumen based on the purge gas pressure, which are at 1.42m ³ and 3kPa (Ü) about 1.46 m ³ i. N. \

The subsequent cooling takes place indirectly; at the same time, it is flushed by means of product gas. This purge gas, which is required in an amount of at most two Adsorbervolumina - based on the Spülgasdruck- is returned to the process. _: . , -;

The following embodiment relates to the adsorptive purification of biogas with reduced CO ₂ content and partially reduced H ₂ S-NH ₃ content, as it appears after a previous water wash. For example, 18Om ³ LN./h of water vapor-saturated crude gas at 303 K and ³ MPa are to be adsorptively purified

Composition, *. .. ·: ·: - ,. '

96.9 vol .-% CH ₄ .....; ' ^: V. ' / ';.; .. ^r ' - ''. "ß .v · ;,

200 vpm H ₂ S + organic aliphatic sulfur compounds:

100 vpm NH ₃ . '. , V:, _: ... " ^: ,., '.'

In order to avoid any disturbances in the subsequent methane liquefaction by corrosive and freezing components, the following upper limits must be observed: COj <50 vpm, NH ₃ < ₃ vpm, H ₂ O <3 vpm

Sulfur compounds <4vpm.

The raw gas is placed in an adsorber of a plant consisting of at least two adsorbers of each i, 85m ³ content whose apparatus are operated in cyclic permutation in the adsorption and desorption phases. Here it first flows through a layer of dense pebble gel der'Type KE 1, in which it is freed from water vapor. Thereafter, it passes through a layer of zeolitic molecular sieve of the type Na X, in which the sulfur compounds and the NH _{3 are} retained. Subsequently, the gas flows through a layer of a molecular sieve of the type Ca A with 68 to 80 mol% Ca ²⁺ -loneni wherein the CO _{2 is} adsorbed. The volume ratio of the layers is according to the aforementioned arrangement 1: 2: 10. In this arrangement, the cycle time is up to the breakthrough of impurities about four hours. The regeneration can be done either in two ways:

- By raising the temperature to 523K and rinsing the bed.

- By pressure reduction of 2.9MPa to 0.1 MPa (all intermediate pressures are conceivable) and temperature increase to 523K and flushing of the bed. , , \:

With each Regenerierungsart sufficient desorption is achieved. For both types, the flushing takes place in countercurrent to the loading flow direction, that product gas is used as purging gas, that the rinsing phase during the desorption is limited to the last third of the heating time and that during the indirect cooling of the bed to be rebonded a continuous rinsing takes place. The total purge gas volume is at most twice the adsorber volume at the purge gas pressure, that is at 3MPa and 1.85m ³ 111m ³ iN; and at 0.1 IVIPa 3.7 m ³ i. N., from which it follows that the Spülgasbedarf depends on the degree of pressure reduction during Regenerierprozeß. Also in this embodiment, the Spülgasänteil the cooling phase is returned to the process. It is understood that during regeneration by means of pressure reduction of the adsorber before its re-loading with product gas is to string again.

Claims (3)

Erfindungsahsprüche: 1. A process for the purification of gases, in particular for the adsorptive separation of water vapor, sulfur compounds, traces of ammonia and carbon dioxide from methane-containing gases, in alternately operated adsorption, which are filled with at least two different - arranged in separate layers - adsorbents, which are used as a bed of internals to Heat exchange can be indirectly cooled or heated and their regeneration by increasing the temperature and purging with product gas in countercurrent to the Beladestromrichtung or by lowering the pressure associated with temperature increase and also flushing, characterized in that - A raw gas with its pressure of 2 to 4kPa (Cl), first a layer of dense-pored silica gel, then a layer of molecular sieve of type Ca A with 58 to 64 mol% Ca ²⁺ ions and / or of the type Na X flows through and then a layer of molecular sieve of the type Ca A with 68 to 80 mol% Ca ²⁺ ions or of the type Na X is conducted, the proportions of the layers on the total charge of an adsorber would behave like 1: 2: 5 - And that at a regeneration temperature of about 523 K, the purging period for the bed limited to the last third of the ' heating and the purge gas volume corresponds to the volume of the adsorber under purge gas pressure, - And that the purge gas in the cooling phase of the desorbiei th adsorber is at most twice the Adsorbervolumen, under purge gas pressure and this amount is returned to the process. 2. The method according to item 1, characterized in that in raw gases with low carbon dioxide content of the adsorption 2 to 4MPa (LJ) and the shares of the layers of the total charge of the adsorber as 1: 2: 10 behave. 3. The method according to the items 1 and 2, characterized in that the adsorption temperature is 293 to 303K