PROCESS AND APPARATUS FOR TREATING METHANE-CONTAINING GAS

Abstract

A process for treating methane-containing gas including CO.sub.2 and at least one compound of volatile organic compounds (VOC) wherein the methane-containing gas mixture is compressed, cooled and supplied to an absorption apparatus absorbing liquid VOC reversibly and at least a portion of the VOC is absorbed from the methane-containing gas mixture yielding a methane-containing and VOC- and CO.sub.2-reduced gas mixture and VOC- and CO.sub.2-loaded absorption means. The VOC- and CO.sub.2-loaded absorption means is transported from the absorption apparatus to a desorption apparatus. The methane-containing and VOC-reduced gas mixture is supplied from the absorption apparatus to a separation apparatus for CO.sub.2 removal. A regeneration gas stream includes at least a portion of the CO.sub.2-enriched gas stream which regenerates the VOC- and CO.sub.2-loaded absorption means. The exhaust gas stream discharges from the desorption apparatus and the at least partially regenerated absorption means moves from the desorption apparatus into the absorption apparatus.

Claims

1. A method of processing methane-containing gas, comprising the steps of: a) providing a methane-containing gas mixture comprising 20-60% by volume of CO.sub.2 and at least one compound from the group of volatile organic compounds (VOC), where the at least one VOC is selected from the group consisting of ketones, sulfur-containing hydrocarbons and terpenes, where the VOC concentration in the gas mixture is 10-10 000 ppm; b) compressing and cooling the methane-containing gas mixture from step a); c) feeding the compressed, cooled methane-containing gas mixture to an absorption apparatus, where the absorption apparatus comprises a liquid, reversibly VOC-absorbing absorbent; d) absorbing at least a portion of the VOCs and not more than 5% by volume of the CO.sub.2 by means of the absorbent, giving a methane-containing gas mixture having reduced levels of VOCs and CO.sub.2, and an absorbent laden with VOCs and CO.sub.2; e) feeding the absorbent laden with VOCs and CO.sub.2 from the absorption apparatus to a desorption apparatus; f) feeding the methane-containing gas mixture having reduced levels of VOCs and CO.sub.2 from the absorption apparatus to a separation apparatus comprising a membrane, in which the methane-containing gas mixture having reduced levels of VOCs and CO.sub.2 is separated into a pressure-reduced, CO.sub.2-enriched gas stream and an isobaric, methane-enriched gas stream; g) feeding a regeneration gas stream comprising at least a portion of the CO.sub.2-enriched gas stream from step f) to the desorption apparatus for regeneration of the absorbent laden with VOCs and CO.sub.2 to obtain an offgas stream comprising CO.sub.2 and the VOCs and an at least partly regenerated absorbent; h) removing the offgas stream from the desorption apparatus and recycling the at least partly regenerated absorbent from the desorption apparatus into the absorption apparatus.

2. The method as claimed in claim 1, wherein in step h), the offgas stream is fed to a regenerative postcombustion apparatus for oxidation.

3. The method as claimed in claim 1, wherein at least steps c) to h) are effected continuously.

4. The method as claimed in claim 1, wherein, in step c), 2 to 10 liters of absorbent per Bm.sup.3 of methane-containing gas mixture from step b) is used in the absorption apparatus.

5. The method as claimed in claim 1, wherein, in step g), 1 to 3 liters of VOC-laden absorbent from step d) is regenerated with 1 Bm.sup.3 of CO.sub.2-enriched gas from step f) in the desorption apparatus.

6. The method as claimed in claim 1, wherein the VOC-absorbing absorbent has a boiling point of more than 250 C. at 1013.25 mbar and comprises a compound selected from the group consisting of polyethylene glycol (PEG), mineral oil, esters or combinations thereof.

7. The method as claimed in claim 1, wherein the VOC-absorbing absorbent comprises a compound of the formula (I):
R.sub.1O(CH.sub.2CH.sub.2O).sub.nR.sub.2,I) where n=3 to 11 and R.sub.1 and R.sub.2 are independently selected linear C.sub.1-C.sub.10 alkyls.

8. The method as claimed in claim 1, wherein the VOC has a vapor pressure of at least 0.1 mbar at 20 C. and/or a boiling point of at most 240 C. at 1013.25 mbar.

9. The method as claimed in claim 1, wherein the at least one VOC is selected from the group consisting of acetone, 2-butanone, 3-methyl-2-butanone, 2-pentanone, 3-pentanone, 3,3-dimethyl-2-butanone, 2-methyl-3-pentanone, 4-methyl-2-pentanone, 3-methyl-2-pentanone, 3-hexanone, 2-hexanone, 5-methyl-3-hexanone, 3-methyl-2-hexanone, 2-heptanone, 4-octanone, 3-octanone, 2-octanone, 2,9-decanedione, -thujene, -pinene, camphene, sabinene, -pinene, myrcene, 3-carene, thujanone, thujopsene, thymol, -terpinene, -caryophyllene, 1,4-cineol, eucalyptol, fenchone, -terpinene, terpinolene, limonene, tricyclene, linalool, menthone, nopinone, p-menthan-2-one, p-menthan-2-ol, camphor, carvomenthone, 3,3-dimethyl-2-bornanone, carbonyl sulfide, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, carbon disulfide, 2-propanethiol, 2-methyl-2-propanethiol, 1-propanethiol, thiophene, 2-butanethiol, isobutyl mercaptan, methyl allyl sulfide, methyl propyl sulfide, butanethiol, dimethyl disulfide, 2-methylthiophene, 3-methylthiophene, tetrahydrothiophene, 1-pentanethiol, thiophenol, dimethyl trisulfide, diisopropyl disulfide, dimethyl tetrasulfide, methyl propyl disulfide and methyl isopropyl disulfide.

10. The method as claimed in claim 1, wherein the methane-containing gas mixture is compressed in step b) to 6 to 24 bar (g).

11. The method as claimed in claim 1, the methane-containing gas mixture (103) is cooled in step b) to 0 C. to 20 C.

12. The method as claimed in claim 1, wherein the VOC-laden absorbent from step d), before being transported into the desorption apparatus, is heated to 30 C. to 90 C.

13. The method as claimed in claim 1, wherein the regenerated absorbent from step g), before being recycled into the absorption apparatus is cooled.

14. The method as claimed in claim 1, wherein, in step c), the liquid, reversibly VOC-absorbing absorbent is fed to the absorption apparatus at a volume flow rate of at least 7.8 kg/Bm.sup.3 of gas mixture.

15. (canceled)

Description

[0066] The invention is elucidated in detail hereinafter with reference to the working examples described and appended. The figures show, in purely schematic form:

[0067] FIG. 1 a schematic diagram of a preferred embodiment of the method of the invention for purification of methane-containing gas;

[0068] FIG. 2 the construction of an in silico simulation model;

[0069] FIG. 3 a step diagram for the VOC methyl mercaptan;

[0070] FIG. 4 a step diagram for the VOC dimethyl sulfide;

[0071] FIG. 5 a step diagram for the VOC acetone;

[0072] FIG. 6 a step diagram for the VOC 2-butanone;

[0073] FIG. 7 a step diagram for the VOC 1-propanol;

[0074] FIG. 8 a step diagram for the VOC toluene;

[0075] FIG. 9 a step diagram for the VOC limonene;

[0076] FIG. 10 a diagram of measured VOC concentrations in plants that produce biogas from renewable raw materials; and

[0077] FIG. 11 a diagram of measured VOC concentrations in plants that produce biogas from waste;

[0078] FIG. 12 the construction of an in silico simulation model.

[0079] In the preferred embodiment of the method of the invention which is shown in schematic form in FIG. 1, in a first step, a methane-containing gas mixture from a gas source 101 is provided. The gas mixture 103 comprises CO.sub.2 and at least one compound from the group of volatile organic compounds (VOCs). The methane-containing gas mixture 103 is compressed in a compressor 105 to 14-18 bar (g) and then cooled in a cooling apparatus 107 to 2-10 C.

[0080] Subsequently, the methane-containing gas mixture 103 is fed to an absorption apparatus 109. The methane-containing gas mixture 103 is introduced here at a lower end 111 of the absorption apparatus 109 and rises upward to an upper end 113 of the absorption apparatus 109.

[0081] The words top and bottom relate to the orientation of the respective apparatuses which is shown in the figures.

[0082] Moreover, the absorption apparatus 109 is supplied with a liquid absorbent 117 via a first connecting conduit 115 that opens into the absorption apparatus 109 in the region of the upper end 113. This liquid absorbent 117 flows in droplet form from the upper end 113 to the lower end 111 of the absorption apparatus 109, and comes into contact with the opposing flow of methane-containing gas mixture 103. Contact of the absorbent 117 with the methane-containing gas mixture 103 results in reversible binding of the VOCs present in the gas mixture in the absorbent 117, as a result of which a methane-containing gas mixture 119 having reduced VOC levels is obtained at the upper end 113 of the absorption apparatus 109, while a VOC-laden absorbent 121 collects at the lower end 111 of the absorption apparatus 109. The methane-containing gas mixture 119 having reduced VOC levels is conveyed via a second connecting conduit 123 proceeding from the upper end 113 of the absorption apparatus 109 to a separation apparatus 125. The VOC-laden absorbent 121 is pumped via a third connecting conduit 127 from the lower end 111 of the absorption apparatus 109 by means of a pump (not shown) to a heat exchanger apparatus 129, and heated to 50-70 C. therein. Subsequently, the VOC-laden absorbent 121 is pumped further to an upper end 133 of a desorption apparatus 135 and fed to the desorption apparatus 135. In the separation apparatus 125, the methane-containing gas mixture 119 having reduced VOC levels is separated into a pressure-reduced, CO.sub.2-enriched gas stream 137 (pressure 0.5 to +0.5 bar (g)) and an isobaric, methane-enriched gas stream 139 (pressure 14-18 bar (g)). The CO.sub.2-enriched gas stream 137 is then introduced via a fourth connecting conduit 143 at a lower end 141 of the desorption apparatus 135 and rises to the upper end 133 of the desorption apparatus 135. While the liquid, VOC-laden absorbent 121 is flowing in droplet form from the upper end 133 to the lower end 141 of the desorption apparatus 135, it comes into contact with an opposing flow of CO.sub.2-enriched gas stream 137. As a result of the heating of the liquid, VOC-laden absorbent 121, the bound VOCs are reversibly released and flow together with the CO.sub.2-enriched gas stream 137 to the upper end 133 of the desorption apparatus 135. This gives rise to a purified absorbent 145 that collect at the lower end 141 of the desorption apparatus 135. A fifth connecting conduit 147 conveys the purified absorbent 145 by means of a pump (not shown) to the heat exchanger apparatus 129, where it is cooled to 2-10 C. and then pumped via the feed conduit 115 to the upper end 113 of the absorption apparatus 109. The heat exchanger apparatus 129 may comprise multiple separate heat exchangers 131, 131, 131. At the upper end 133 of the desorption apparatus 135, a CO.sub.2- and VOC-enriched gas stream 149 is removed and sent to a regenerative postcombustion apparatus 151 in order to reduce environmental pollution by the method.

[0083] For utilization of methane-containing gases as natural gas substitute, sulfur-containing components in the product gas have to be lowered below a limit of 6 mg/m.sup.3 sulfur equivalent. The limit is set out, for example, in Rulebook G260 from the DVGW [German Technical and Scientific Association for Gas and Water].

[0084] For other VOCs, for example, limits are applicable for the utilization of gas permeation membranes. In that case, it is necessary for the total VOC concentration to be below 10 ppm, in order, for example, to satisfy the utilization conditions of Evonik (manufacturer of gas permeation membranes).

[0085] A further reason for discussions about limitation of VOCs in biogas are extraneous odors that can be caused by the VOCs.

[0086] FIG. 2 shows an in silico simulation model of a preferred embodiment of the method of the invention. The simulation model comprises an absorption apparatus 201 and a desorption apparatus 203. The absorbentPEG hereenters the absorption apparatus 201 as a liquid 205. The absorbent leaves the absorption apparatus 201 as a VOC-laden liquid 207 and is heated in a heat exchanger 209. The heated, VOC-laden absorbent 211 thus obtained is conveyed from the heat exchanger 209 to a further heat exchanger 213 and heated further therein. The heat exchanger 213 is supplied here with external heat 215. A significantly heated, VOC-laden absorbent 217 leaves the heat exchanger 213 and is expanded in a control valve 219. The heated, expanded, VOC-laden absorbent 221 enters the desorption apparatus 203, where it releases the VOCs. The largely regenerated, heated, expanded absorbent 223 is compressed by a pump 225 and transported further to the heat exchanger 209 as compressed, heated, largely regenerated absorbent 227. In the heat exchanger 209, it releases some of its heat to the VOC-laden absorbent 207. The cooler, compressed, largely regenerated absorbent 229 is then transported to a further heat exchanger 231 and cooled further therein. For this purpose, the heat exchanger 231 is supplied with external cooling 233. The cooled, compressed, largely regenerated absorbent 205 enters the absorption apparatus 201 again and thus completes the absorbent circuit. A compressed biogas 235 to be cleaned is cooled by means of external cooling 239 in a heat exchanger 237 and then freed of condensate in a condensate separator 241. A resulting cooled, compressed biogas 243 is fed to the absorption apparatus 201, where it comes into contact with the cooled, compressed, largely regenerated absorbent 205 and releases its VOCs to the absorbent 205. A cleaned biogas 245 exits from the absorption apparatus 201 and can then be used for further processes 247. A regeneration gas 249, for example a lean gas from biogas processing 251, is fed to a heat exchanger 253 and heated therein. A heated regeneration gas 255 enters the desorption apparatus 203 and releases the VOC therein from the heated, expanded, VOC-laden absorbent 221. A VOC-laden regeneration gas 257 then exits from the desorption apparatus 203 and releases its heat to the regeneration gas 249 in the heat exchanger 253. A cooled, VOC-laden regeneration gas 259 is conveyed by means of a suction blower 261 to an aftertreatment unit 263.

[0087] In the above-described computer simulation, by means of Henry's law, the solubility of a particular VOC in the absorbent, PEG here, was simulated. In a first step, the equilibrium line where the gas phase and the liquid phase are at equilibrium is simulated; the slope of the equilibrium line corresponds to the Henry coefficient of the compound at the respective temperature. In a second step, the mass balance line that results from the mass balance of the VOC in the absorption apparatus is simulated. The starting point of the mass balance lines is at the VOC concentration at the upper end of the absorption apparatus (cleaned biogas 245) and the concentration of the liquid phase at the upper end of the absorption apparatus (regenerated PEG 205). The end point of the mass balance line is found from the gas phase concentration at the lower end of the absorption apparatus (VOC-laden biogas 243) and the concentration of the liquid phase at the lower end of the absorption apparatus (VOC-laden PEG 207). The start and end points of the mass balance lines are connected by a straight line (mass balance line). This is only applicable under the assumption that the temperature in the absorption apparatus is constant. In the case of a temperature gradient, both the mass balance line and the equilibrium line would be shown as a mass balance curve and an equilibrium curve. A step construction can be drawn between the mass balance lines and the equilibrium lines. Each step represents one theoretical plate of the column. The number of steps is a measure of the required height of the absorption apparatus. In an absorption, the mass balance line is always above the equilibrium line. If the mass balance line is below the equilibrium line, the operation is a desorption.

[0088] FIG. 3a shows an analogous step diagram for the VOC methyl mercaptan (CAS 74-93-1) and PEG as absorbent in the absorption apparatus. The mass balance line (dashed line) is arranged above the equilibrium line (dashed-and-dotted line), and the step construction (solid line) is shown in between.

[0089] FIG. 3b shows a step diagram analogous to the above-described step diagram for the VOC methyl mercaptan (CAS 74-93-1) and PEG as absorbent in the desorption apparatus. The equilibrium line (dashed-and-dotted line) is arranged above the mass balance line (dashed line), and the step construction (solid line) is shown in between. It is apparent from FIG. 3a that a step construction is unviable for methyl mercaptan since a large residue of methyl mercaptan remains in the cleaned biogas if the stream of absorbent was too small (in the simulation model). It is apparent from FIG. 3b that the absorbent is regenerated virtually completely in the desorption apparatus to free it of methyl mercaptan.

[0090] FIGS. 4a and 4b show, analogously to the above-described step diagrams, a step diagram for the VOC dimethyl sulfide (CAS 75-18-3) and PEG as absorbent in the absorption apparatus (FIG. 4a) and in the desorption apparatus (FIG. 4b). It is apparent from FIG. 4a that a multitude of steps is needed for cleaning of the biogas and a residue of dimethyl sulfide nevertheless remains in the biogas. It is apparent from FIG. 4b that the absorbent is regenerated virtually completely in the desorption apparatus to free it of dimethyl sulfide.

[0091] FIGS. 5a and 5b, analogously to the step diagrams described above, show exactly such step diagrams for the VOC acetone (CAS 67-64-1) and PEG as absorbent in the absorption apparatus (FIG. 5a) and in the desorption apparatus (FIG. 5b). It is apparent from FIG. 5a that a multitude of steps is needed for cleaning of the biogas and a very small residue of acetone nevertheless remains in the biogas. It is apparent from FIG. 5b that the absorbent is regenerated virtually completely in the desorption apparatus to free it of acetone.

[0092] FIGS. 6a and 6b, analogously to the step diagrams described above, show exactly such step diagrams for the VOC 2-butanone (CAS 78-93-3) and PEG as absorbent in the absorption apparatus (FIG. 6a) and in the desorption apparatus (FIG. 6b). It is apparent from FIG. 6a that only a few steps are needed for cleaning of the biogas and no residue of 2-butanone remains in the biogas. It is apparent from FIG. 6b that the absorbent is regenerated in the desorption apparatus to free it of 2-butanone by means of a multitude of steps, but a small portion of 2-butanone remains in the regenerated absorbent.

[0093] FIGS. 7a and 7b show, analogously to the above-described diagrams, step diagrams for the VOC 1-propanol (CAS 71-23-8) and PEG as absorbent in the absorption apparatus (FIG. 7a) and in the desorption apparatus (FIG. 7b). It is apparent from FIG. 7a that only a few steps are needed for cleaning of the biogas, and a very small residue of 1-propanol remains in the biogas. It is apparent from FIG. 7b that, in spite of a multitude of steps, the absorbent is not fully regenerated in the desorption apparatus to free it of 1-propanol.

[0094] FIGS. 8a and 8b show step diagrams created analogously to the above-described diagrams for the VOC toluene (CAS 108-88-3) and PEG as absorbent in the absorption apparatus (FIG. 8a) and in the desorption apparatus (FIG. 8b). It is apparent from FIG. 8a that only a few steps are needed for cleaning of the biogas, but a residue of toluene remains in the biogas since it was incompletely regenerated. It is apparent from FIG. 8b that, in spite of a multitude of steps, the absorbent is not fully regenerated in the desorption apparatus to free it of toluene. Since the mass balance line and the equilibrium line run parallel, complete regeneration is impossible.

[0095] FIGS. 9a and 9b show analogously created step diagrams for the VOC limonene (CAS 7705-14-8) and PEG as absorbent in the absorption apparatus (FIG. 9a) and in the desorption apparatus (FIG. 9b). It is apparent from FIG. 9a that only a few steps are needed for cleaning of the biogas, but a residue of limonene remains in the biogas since it was incompletely regenerated. It is apparent from FIG. 9b that, in spite of a multitude of steps, the absorbent is not fully regenerated in the desorption apparatus to free it of limonene since the mass flow of the absorbent is too high (in the simulation model).

[0096] On the basis of the simulation according to FIGS. 2 to 9, it can be stated that VOCs having a boiling point between 35 C. and 100 C. can be virtually fully released from the biogas in the absorption apparatus and virtually fully released from the absorbent in the desorption apparatus. VOCs having a boiling point higher than 100 C. are virtually fully removed from the biogas. However, the regeneration of the absorbent is incomplete. VOCs having a boiling point of less than 35 C. are incompletely removed from the biogas. The gas constituents CO.sub.2 and methane remain almost entirely in the gas phase.

[0097] FIG. 10 shows a diagram based on 48 measurements of VOCs in biogas samples, where the biogas was produced from renewable raw material. The concentration of VOCs in the biogas is between 5 and 20 ppm. Individual values are higher. VOCs in biogas from renewable raw materials do not present any problems in further processing.

[0098] FIG. 11 shows a diagram based on 138 measurements of VOCs in biogas samples, where the biogas was produced from waste. The concentration of VOCs in the biogas is between 10 and 250 ppm. Higher concentrations were also achieved in numerous cases. VOCs in biogas from waste frequently present problems in further processing; therefore, controlled removal of the VOCs is necessary.

Experimental Data

[0099] FIG. 12 shows the in silico simulation model of the preferred embodiment of the method of the invention as described in FIG. 2. Various parameters for the biogas, absorbent and the regeneration gas were added to the simulation model in order to show what amount of CO.sub.2 and VOC is absorbed. The simulation model comprises three gas streams at different stages. A compressed methane-containing gas BG1 is fed to a heat exchanger 1201, and leaves it as a cooled compressed methane-containing gas BG2. The methane-containing gas BG2 is fed to an absorption apparatus 1203, wherein the CO.sub.2 and VOC constituents present in the methane-containing gas BG2 are absorbed. A methane-containing gas BG3 having reduced levels of CO.sub.2 and VOCs leaves the absorption apparatus 1203. In the absorption apparatus 1203, the methane-containing gas BG2 comes into contact with a cooled regenerated absorbent AB1. The cooled regenerated absorbent AB1 absorbs CO.sub.2 and VOCs in the absorption apparatus 1203, and leaves the absorption apparatus 1203 as a CO.sub.2- and VOC-laden absorbent AB2. The CO.sub.2- and VOC-laden absorbent AB2 is heated in a heat exchanger 1205 and leaves it as a heated CO.sub.2- and VOC-laden absorbent AB3. The heated CO.sub.2- and VOC-laden absorbent AB3 is heated further in a further heat exchanger 1207 and leaves it as a heated CO.sub.2- and VOC-laden absorbent AB4. The heated CO.sub.2- and VOC-laden absorbent AB4 is fed to a control valve 1209 and expanded, and leaves it as a heated, expanded, CO.sub.2- and VOC-laden absorbent AB5. The heated, expanded, CO.sub.2- and VOC-laden absorbent AB5 is fed to a desorption apparatus 1211.

[0100] A regeneration gas RG1 is heated in a heat exchanger 1213 and leaves it as a heated regeneration gas RG2. The regeneration gas RG1 is a gas stream with CO.sub.2 as its main constituent. The heated regeneration gas RG2 is fed to the desorption apparatus 1211 and comes into contact therein with the heated, expanded, CO.sub.2- and VOC-laden absorbent AB5. The heated regeneration gas RG2 releases CO.sub.2 and VOC from the absorbent AB5 to obtain a CO.sub.2- and VOC-laden regeneration gas RG3 and a largely regenerated, heated, expanded absorbent AB6. The largely regenerated, heated, expanded absorbent AB6 is compressed in a pump 1215 and fed to the heat exchanger 1205 as a compressed, heated, largely regenerated absorbent AB7. In the heat exchanger 1205, the compressed, heated, largely regenerated absorbent AB7 releases its heat to the CO.sub.2- and VOC-laden absorbent AB2 and leaves the heat exchanger 1205 as a cool, compressed, largely regenerated absorbent AB8. The cool, compressed, largely regenerated absorbent AB8 is fed to a heat exchanger 1217 and cooled, and leaves it as a cooled regenerated absorbent AB1. The CO.sub.2- and VOC-laden regeneration gas RG3 is fed to the heat exchanger 1213, releases its heat to the regeneration gas RG1 and leaves the heat exchanger 1213 as a cooled, CO.sub.2- and VOC-laden regeneration gas RG4. The cooled, CO.sub.2- and VOC-laden regeneration gas RG4 is conveyed in a suction blower 1219 as a cooled, CO.sub.2- and VOC-laden regeneration gas RG5 to an aftertreatment unit 1221.

[0101] Table 1 below shows parameters for the simulation model with the absorbent PEG1843. This absorbent absorbs only 2.5 kg/h of methane (0.4%), while 36.6 kg/h of CO.sub.2 (3.6%) and more than 98% of the VOCs (dimethyl sulfide (DMS), acetone, 2-butanone and terpene) are absorbed. It should be noted here that VOCs having low boiling point such as DMS (boiling point 37 C.), having moderate boiling point such as acetone (boiling point 56 C.) and 2-butanone (boiling point 79.6 C.), and having high boiling point such as terpenes (boiling point 140-230 C.) are absorbed.

[0102] This is apparent from the differences in mass between BG2 and BG3. The 36.6 kg/h of CO.sub.2 and the VOCs are released from the methane-containing gas BG2 to the absorbent AB1, which is apparent in the increase in CO.sub.2 and VOC concentrations from AB1 to AB5. The VOC- and CO.sub.2-laden absorbent then passes the 36.6 kg/h of CO.sub.2 and VOC onward to the regeneration gas RG1, which is apparent in the increase in CO.sub.2 and VOC concentrations from RG1 to RG3.

TABLE-US-00001 TABLE 1 BG2 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 1585 1540 732 777 645 689 Volume flow rate [m.sup.3/h] 83.9 82.3 365.8 435.7 0.693 0.774 Temperature [ C.] 8 8 20 55 8 57 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg/h] 1022.0 985.4 730.0 766.6 0.14 36.76 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.03 Acetone [kg/h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg/h] 0.42 0.00 0.00 0.42 0.03 0.44 Terpenes [kg/h] 3.95 0.06 0.00 3.88 44.51 48.40 H2O [kg/h] 0.69 0.00 0.00 0.69 0.03 0.70 PEG [kg/h] 0.00 0.00 0.00 0.06 600.00 600.00

[0103] Tables 2 to 4 show similar parameter configurations to table 1 and differ from table 1 merely in that the temperature of the regeneration gases RG1 and RG3 and of the absorbent AB5 and the mass flow rate of RG1, RG3, AB1 and AB5 was varied.

[0104] Tables 5 to 8 show the same parameter configurations as tables 1 to 4; the only change in the simulation model was of the absorbent from PEG1843 (tables 1-4) to PEG300 (tables 5-8).

TABLE-US-00002 TABLE 2 BG2 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 1585 1541 732 776 846 890 Volume flow rate [m.sup.3/h] 83.9 82.3 365.8 389.1 0.910 0.969 Temperature [ C.] 8 8 20 20 8 22 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg/h] 1022.0 985.5 730.0 766.5 0.22 36.76 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.04 Acetone [kg/h] 0.34 0.00 0.00 0.33 0.01 0.35 2-Butanone [kg/h] 0.42 0.002 0.00 0.40 0.22 0.62 Terpenes [kg/h] 3.95 0.35 0.00 3.60 245.54 249.14 H2O [kg/h] 0.69 0.03 0.00 0.66 0.36 1.01 PEG [kg/h] 0.00 0.00 0.00 0.00 600.00 600.00

TABLE-US-00003 TABLE 3 BG2 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 1585 1540 732 777 638 682 Volume flow rate [m.sup.3/h] 83.9 82.3 403.3 435.7 0.686 0.767 Temperature [ C.] 8 8 50 55 8 57 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg/h] 1022.0 985.4 730.0 766.7 0.10 36.76 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.03 Acetone [kg/h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg/h] 0.42 0.00 0.00 0.42 0.01 0.42 Terpenes [kg/h] 3.95 0.05 0.00 3.89 37.64 41.54 H2O [kg/h] 0.69 0.00 0.00 0.69 0.00 0.68 PEG [kg/h] 0.00 0.00 0.00 0.06 600.00 600.0

TABLE-US-00004 TABLE 4 BG2 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 1585 1540 732 777 638 682 Volume flow rate [m.sup.3/h] 83.9 82.3 365.8 399.8 0.685 0.766 Temperature [ C.] 8 8 20 27.96098 8 57 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg/h] 1022.0 985.4 730.0 766.7 0.09 36.76 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.03 Acetone [kg/h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg/h] 0.42 0.00 0.00 0.42 0.00 0.42 Terpenes [kg/h] 3.95 0.05 0.00 3.89 37.55 41.45 H2O [kg/h] 0.69 0.00 0.00 0.69 0.00 0.68 PEG [kg/h] 0.00 0.00 0.00 0.00 600.00 600.00

TABLE-US-00005 TABLE 5 B62 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 1585 1542 732 775 646 689 Volume flow rate [m.sup.3/h] 83.9 82.5 365.8 433.7 0.612 0.689 Temperature [ C.] 8 8 20 55 8 57 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 556.3 2.1 3.3 0.00 1.17 CO2 [kg/h] 1022.0 985.3 730.0 766.7 0.14 36.86 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.03 Acetone [kg/h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg/h] 0.42 0.00 0.00 0.42 0.03 0.45 Terpenes [kg/h] 3.95 0.07 0.00 3.88 45.31 49.20 H2O [kg/h] 0.69 0.01 0.00 0.69 0.24 1.17 PEG [kg/h] 0.00 0.00 0.00 0.00 600.00 600.00

TABLE-US-00006 TABLE 6 BG2 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 15.85 1542 732 775 848 890 Volume flow rate [m.sup.3/h] 83.9 82.5 365.8 387.3 0.803 0.856 Temperature [ C.] 8 00 20 20 8 22 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 556.3 2.1 3.3 0.00 1.17 CO2 [kg/h] 1022.0 985.4 730.0 766.6 0.22 36.86 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.04 Acetone [kg/h] 0.34 0.01 0.00 0.33 0.04 0.37 2-Butanone [kg/h] 0.42 0.02 0.00 0.40 0.26 0.66 Terpenes [kg/h] 3.95 0.35 0.00 3.60 245.54 249.14 H2O [kg/h] 0.69 0.05 0.00 0.64 1.52 2.15 PEG [kg/h] 0.00 0.00 0.00 0.02 600.00 600.00

TABLE-US-00007 TABLE 7 BG2 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 1585 1542 732 776 638 681 Volume flow rate [m.sup.3/h] 83.9 82.4 403.3 433.9 0.604 0.681 Temperature [ C.] 8 8 50 55 8 57 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 556.3 2.1 3.3 0.00 1.17 CO2 [kg/h] 1022.0 985.3 730.0 766.8 0.10 36.86 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.03 Acetone [kg/h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg/h] 0.42 0.00 0.00 0,42 0.01 0.43 Terpenes [kg/h] 3.95 0.05 0.00 3.89 37.64 41.54 H2O [kg/h] 0.69 0.00 0.00 0.69 0.06 0.73 PEG [kg/h] 0.00 0.00 0.00 0.37 600.00 600.00

TABLE-US-00008 TABLE 8 Mass flow rate BG2 BG3 RG1 RG5 AB1 AB5 Mass flow rate [kg/h] 1585 1540 732 777 638 682 Volume flow rate [m.sup.3/h] 83.9 82.3 365.8 399.8 0.604 0.682 Temperature [ C.] 8 8 20 28 8 57 Pressure [bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg/h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg/h] 1022.0 985.4 730.0 766.7 0.09 36.76 DMS [kg/h] 0.04 0.00 0.00 0.03 0.00 0.03 Acetone [kg/h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg/h] 0.42 0.00 0.00 0.42 0.00 0.42 Terpenes [kg/h] 3.95 0.05 0.00 3.89 37.55 41.45 H2O [kg/h] 0.69 0.00 0.00 0.69 0.00 0.68 PEG [kg/h] 0.00 0.00 0.00 0.05 600.00 600.00

[0105] In all parameter configurations in the simulation model, it is clear that only about 3.6% by volume of the CO.sub.2 present in BG1 is absorbed by the absorbent. It should be noted that, in tables 2 and 6, the concentration of the terpenes in AB1 and AB5 is higher than in tables 1, 3-5 and 7-8. In all parameter configurations, the terpenes were not fully removable from the absorbent (see AB1). It is nevertheless surprisingly possible to largely remove the terpenes present in the methane-containing biogas BG2 therefrom; see BG3.