Method and device for separating methane and carbon dioxide from biogas
A method for separating methane and carbon dioxide from biogas and a device are intended for purifying biogas, wherein carbon dioxide is separated off from the biogas. The method is distinguished by an energetically favorable mode of operation. The biogas is passed under atmospheric pressure and standard temperature into an absorption column. While the biogas ascends through a packed bed, which has a surface area of 600 to 1200 m 2 /m 3 , and at a space velocity of 5 to 40 Nm 3 /m 3 h, carbon dioxide present in the biogas is bound in a wash liquid by chemosorption. The purified methane gas is taken off at the top of the absorption column at a defined flow velocity. Carbon dioxide bound in the wash liquid is removed by desorption at a relatively high pressure of 2 to 30 bar and a temperature of at least 120° C. Biogas may be separated into methane and CO 2 .
1. A method of separating methane and carbon dioxide from biogas, which comprises the steps of:
scrubbing in an absorption column in which the biogas ascends through a packed bed in counter flow to a wash liquid which is fed in and binds the carbon dioxide and hydrogen sulphide, and for subsequent regeneration of the wash liquid;
conducting the biogas into the absorption column under atmospheric pressure and standard temperature, wherein the carbon dioxide present in the biogas is bound in the wash liquid by chemosorption as the biogas ascends through the packed bed;
separating off the methane gas at a top of the absorption column at a defined flow velocity;
subsequently removing the carbon dioxide still bound in the wash liquid by desorption at a relatively high pressure of 2 to 30 bar and a temperature of at least 120° C.; and
measuring a CO 2 concentration in the methane gas and a flow velocity of the removed methane gas, and thus the contact time, is set according to a value measured.
2. The method according to claim 1 , which further comprises flowing the biogas in the absorption column through the packed bed having a surface area of 600 to 1200 m 2 /m 3 and a space velocity of 5 up to 40 Nm 3 /m 3 h.
3. The method according to claim 1 , which further comprises setting a flow velocity of the biogas based on an available column cross-section at 0.01 to 0.1 m/s.
4. The method according to claim 1 , which further comprises providing an amine solution as the wash liquid.
5. The method according to claim 4 , which further comprises adjusting a contact time of the scrubbing in response to an amine concentration of the wash liquid.
6. The method according to claim 1 , which further comprises keeping a water balance of the wash liquid constant by setting a biogas temperature and a temperature of the wash liquid circulated in a circuit.
7. The method according to claim 1 , wherein the desorption takes place at a pressure of 8 to 20 bar.
8. The method according to claim 1 , wherein the desorption takes place at temperatures of up to 180° C.
9. The method according to claim 1 , which further comprises using one of steam and thermal oil as a heat exchanger medium for the desorption.
10. The method according to claim 1 , which further comprises removing proportions of NH 3 , COS, H 2 S and SO 2 present in the biogas before the biogas is fed into the absorption column.
11. The method according to claim 1 , further comprising the step of setting a contact time of the scrubbing to be at least 40 seconds.
12. The method according to claim 1 , which further comprises adjusting a contact time of the scrubbing in response to an amine concentration of the wash liquid.
13. The method according to claim 11 , which further comprises feeding in the biogas and the wash liquid at a same temperature.
14. The method according to claim 11 , which further comprises setting the contact time for scrubbing from 50 to 400 seconds.