Method and device for separating a gas mixture by means of pressure swing adsorption

1. Method for separating a gas mixture according to a pressure swing adsorption process (PSA process), comprising the steps of:

separating the gas mixture by adsorbing at least one gas component in an adsorbent mass provided in each vessel of a plurality of vessels, wherein each vessel has at least one inlet and one outlet; and

storing off-gas from said process into an off-gas vessel,

wherein in each of said plurality of vessels the following steps are conducted,

(i) admitting the gas mixture for a specified period into a first vessel via an inlet of said vessel, and releasing a separated product gas via an outlet of said vessel, to be followed by admitting the gas mixture into a second vessel while continuing the release of product gas from the first vessel, to be followed by

(ii) releasing purge gas from the first vessel via its outlet,

(iii) releasing off-gas from the first vessel via its inlet and admitting at least part of the off-gas into the off-gas vessel,

(iv) admitting purge gas into the first vessel via its outlet, and releasing off-gas from said vessel via its inlet,

(v) admitting a separated product gas into the first vessel until the pressure in the first vessel has reached a predetermined value, after which admitting of the gas mixture into the first vessel begins, and the steps are to be repeated beginning with the step (i), wherein during at least one of the steps (iii) and (iv) at least part of the off-gas from the first vessel is released directly to an off-gas consuming device, characterized by

(a) connecting, in a first state in which pi>po+Δ and pi>pb, each of the plurality of vessels directly to both the off-gas consuming device and the off-gas storage vessel,

(b) connecting, in a second state in which pb<pi<po+Δ, each of the plurality of vessels directly to only the off-gas consuming device, and

(c) connecting, in a third state in which pi<pb and po>pb, the off-gas storage vessel to the off-gas consuming device, wherein

pi represents the value of the pressure at the inlet of the respective one of the plurality of vessels,

po represents the value of the pressure in the storage vessel,

pb represents a pressure having a predetermined value, and

Δ represents a predetermined pressure difference.

2. Method as claimed in claim 1 , wherein the gas mixture comprises hydrogen gas and the product gas is hydrogen.

3. Method as claimed in claim 1 , wherein the off-gas consuming device comprises a burner.

4. Apparatus for separating a gas mixture according to a pressure swing adsorption process (PSA process), comprising a plurality of vessels, wherein each vessel has at least one inlet and one outlet, an adsorbent mass is provided in each of said vessels for adsorbing at least one gas component, and the inlet of each of said vessels is connected to a storage vessel for an off-gas, wherein the inlet of each of said plurality of vessels and the storage vessel are further connected to an off-gas consuming device, and wherein control and connection means are provided for

(a) in a first state, in which pi>po+Δ and pi>pb, directly connecting each of the plurality of vessels to both the off-gas consuming device and the off-gas storage vessel,

(b) in a second state, in which pb<pi<po+Δ, directly connecting each of the plurality of vessels to only the off-gas consuming device, and

(c) in a third state, in which pi<pb and po>pb, connecting the off-gas storage vessel to the off-gas consuming device, wherein

pi represents the value of the pressure at the inlet,

po represents the value of the pressure in the storage vessel,

pb represents a pressure having a predetermined value, and

Δrepresents a predetermined pressure difference.

5. Apparatus as claimed in claim 4 , wherein each inlet is connected to the off-gas consuming device by a common conduit having a first control device, which is provided with a bypass conduit having a check valve, a branch conduit connected to the off-gas storage vessel and a second control device.

6. Apparatus as claimed in claim 5 , wherein the first control device is a pressure reducing device and the second control device is a pressure reducing device.

7. Apparatus as claimed in claim 5 , wherein the first control device is a control valve and the second control device is a control valve.

8. Apparatus as claimed in claim 5 , wherein the first control device is a control valve and the second control device is a pressure regulator.

9. Apparatus as claimed in claim 8 , wherein the pressure regulator comprises a pressure reducer valve and a control valve.

10. Apparatus as claimed in claim 4 , wherein each inlet is connected to the off-gas consuming device by a common conduit which is provided with a first control device and with a bypass conduit extending between the inlets and said first control device and having a check valve, a branch connected to the off-gas storage vessel and a second control device.

11. Apparatus as claimed in claim 4 , wherein each inlet is connected to the off-gas consuming device by a common conduit, the common conduit being connected to the off-gas storage vessel via a branch conduit in which a first pressure sensor, a valve and a second pressure sensor are provided.

12. Apparatus as claimed in claim 4 , wherein each inlet is connected to the off-gas consuming device by a common conduit which has a first control device, which is provided with a by-pass conduit which leads through the off-gas vessel and has a check valve and a second control device.

13. Apparatus as claimed in claim 4 , wherein the plurality of vessels includes at least two vessels.

14. Apparatus as claimed in claim 4 , wherein the plurality of vessels includes four vessels.

15. Apparatus as claimed in claim 4 , wherein the off-gas consuming device includes a burner.