Co2 separation device in gas and its membrane separation method and method for controlling membrane separation of co2 separation device in gas

A CO2 separation device in gas, comprising:

• a source gas introduction line configured to introduce source gas containing CO2,
• a first membrane separator connected to an end of the source gas introduction line and configured to membrane-separate CO2 from the source gas;
• a first permeable gas discharge line configured to discharge first permeable gas permeated by membrane separation of the first membrane separator to be collected as collected CO2;
• a first non-permeable gas discharge line configured to discharge first non-permeable gas not permeated by membrane separation of the first membrane separator;
• a second membrane separator provided at a downstream side of the first membrane separator and configured to membrane-separate CO2 from first non-permeable gas;
• a second permeable gas discharge line configured to discharge second permeable gas permeated by membrane separation of the second membrane separator to be collected as collected CO2;
• a return line of second permeable gas branched from a part of the second permeable gas discharge line and configured to return the second permeable gas to a source gas side or a first non-permeable gas side;
• and
• a CO2 concentration meter provided in the first permeable gas discharge line and configured to measure CO2 concentration in the first permeable gas;
• wherein
• the second permeable gas is recycled to the source gas side in the case where the CO2 concentration in the first permeable gas is 90 mol % or less.

A CO2 separation device in gas, comprising:

• a source gas introduction line configured to introduce source gas containing CO2,
• a first membrane separator connected to an end of the source gas introduction line and configured to membrane-separate CO2 from the source gas;
• a first permeable gas discharge line configured to discharge first permeable gas permeated by membrane separation of the first membrane separator to be collected as collected CO2;
• a first non-permeable gas discharge line configured to discharge first non-permeable gas not permeated by membrane separation of the first membrane separator;
• a second membrane separator provided at a downstream side of the first membrane separator and configured to membrane-separate CO2 from first non-permeable gas;
• a second permeable gas discharge line configured to discharge second permeable gas permeated by membrane separation of the second membrane separator to be collected as collected CO2;
• a return line of second permeable gas branched from a part of the second permeable gas discharge line and configured to return the second permeable gas to a source gas side or a first non-permeable gas side;
• and
• a CO2 concentration meter provided in the source gas introduction line and configured to measure CO2 concentration in the source gas;
• wherein
• the second permeable gas is recycled to the source gas side in the case where the CO2 concentration in the source gas is 20 mol % or less.

A method of membrane separation in a CO2 separation device in gas comprising:

• serially providing membrane separators including separation membrane for selectively separating CO2 from source gas containing CO2 in two stages;
• discharging first permeable gas permeated by membrane separation of the first membrane separator to be collected as collected CO2 and second permeable gas permeated by membrane separation of the second membrane separator to be collected as collected CO2;
• obtaining CO2 concentration in the source gas or the first permeable gas after membrane separation by the first membrane separator when first non-permeable gas not permeated by membrane separation of the first membrane separator in the first stage is membrane-separated by the second membrane separator in the second stage;
• and
• recycling the second permeable gas after membrane separation by the second membrane separator to a source gas side in the case where the obtained CO2 concentration in the first permeable gas is 90 mol % or less, or the obtained CO2 concentration in the source gas is 20 mol % or less.

A method for controlling membrane separation in the CO2 separation device in gas, comprising:

• serially providing first and second membrane separators including separation membrane for selectively separating CO2 from source gas containing CO2 in two stages, and providing a third membrane separator for pre-processing in a bypass line that bypasses a source gas introduction line at an upstream of the first membrane separator;
• obtaining CO2 concentration in the source gas when first non-permeable gas not permeated by membrane separation of the first membrane separator in the first stage is membrane-separated by the second membrane separator in the second stage;
• and
• membrane-separating CO2 in the source gas by the third membrane separator for pre-processing, setting the CO2 concentration of third non-permeable gas not permeated by the third membrane separator to 30 mol % or less and introducing the third non-permeable gas having the CO2 concentration of 30 mol % or less to the first membrane separator to selectively separate CO2.