Membrane process for producing carbon dioxide

A process for separating carbon dioxide from a raw gas stream containing carbon dioxide in an amount, on a dry basis, in the range of about 8 percent to about 85 per cent, comprising:

• STEP 1 passing the raw gas stream through a direct contact cooler and removing sulfur dioxide, oxides of nitrogen, and particulate matter;
• STEP 2 cooling the gas by passing the gas through a recycle heat exchanger and a heat exchanger;
• STEP 3 dewatering the cooled gas by passing it through a water knockout;
• STEP 4 pressurizing the gas and cooling the gas to a temperature sufficient to prevent water from condensing upon subsequent compression;
• STEP 5 compressing the gas;
• STEP 6 cooling the gas by a heat exchanger and thereafter deep cooling the cooled gas by a refrigerant heat exchanger to a temperature sufficient to achieve a relative humidity at the first membrane in the range of about 40 per cent to about 50 per cent;
• STEP 7 removing water from the gas stream by passing the cooled gas stream through a second knockout;
• STEP 8 passing the gas stream from the second knock-out through the recycle heat exchanger of step 2;
• STEP 9 removing aerosols and liquids in a coalescing filter, then removing oil and sulfur compounds in an adsorption filter, and removing particulate passing from the absorbent filter;
• STEP 10 mixing gas from the particulate filter with recycle gases received from one or more membranes implemented in one or more subsequent process steps;
• STEP 11 passing the mixed gases to a first membrane, separating the gas stream into a nonpermeate stream and a permeate stream, discharging the non permeate stream, and passing the permeate stream to a compressor;
• STEP 12 cooling the gas from the compressor and removing contaminants from the cooled gas in a second coalescing filter, second adsorption filter, and a second particulate filter;
• STEP 13 passing the cooled gas from the particulate filter to a second membrane, separating the gas stream into a nonpermeate stream and a permeate stream;
• STEP 14 pressurizing and cooling the nonpermeate stream from the second membrane and recycling it to the inlet of the first membrane;
• STEP 15 cooling the permeate stream from the second membrane and mixing it with a recycle vapor stream from carbon dioxide storage;
• STEP 16 pressurizing the cool permeate and recycle stream;
• STEP 17 cooling and removing water from the stream of step 16;
• STEP 18 dehydrating the stream in a desiccant dryer;
• STEP 19 cooling the desiccated gas stream by passing it through first and second recycle gas-gas heat exchanges;
• STEP 20 passing the cooled, desiccated gas stream through a primary condenser and into and through a distillation column in counter current flow to stripping vapors and carbon dioxide passing upwardly through the distillation column;
• STEP 21 condensing the gas of step 20, passing the gas from the condenser through a sump and discharging an effluent recycle stream from the top of the sump and a reflux stream from the bottom of the sump;
• STEP 22 passing the reflux stream into an upper portion of the distillation column;
• STEP 23 passing the effluent recycle stream through the second and then the first recycle gas-gas heat exchanges;
• STEP 24 splitting the effluent recycle stream and passing one portion to the desiccant filter for regeneration;
• STEP 25 passing liquid carbon dioxide from the bottom of the distillation column into a reboiler;
• STEP 26 generating stripping vapors in the reboiler and passing them into a lower portion of the distillation column;
• STEP 27 discharging liquid carbon dioxide from one or both of the reboiler and distillation column, cooling the discharge to a temperature below the bubble point, and delivering the cooled liquid carbon dioxide into an insulated storage tank;
• and
• STEP 28 recovering vapors from the storage tank and recycling them to the inlet of the first membrane.

A process for recovering a target gas from a gas stream containing two or more gases, comprising:

• providing a feed stream containing a mixture of at least a target gas and at least one other gas;
• delivering the feed stream through a first membrane separator within a first pressure range;
• directing a first discharge stream containing a higher purity of the target gas than the feed stream from the first membrane separator to a second membrane separator within a second pressure range;
• recovering from the second membrane separator a second discharge stream containing a relatively higher purity of the target gas than the first discharge stream entering the second membrane separator;
• and
• substantially maintaining the pressure differential between the feed stream and a discharge stream exiting the first membrane at a level substantially less than the pressure differential between the first discharge stream entering the second membrane and a discharge stream exiting the second membrane.

A process for recovering a target gas from a gas stream containing two or more gases, comprising:

• providing a feed stream containing a mixture of at least a target gas and at least on other gas;
• delivering the feed stream through a first membrane separator within a first pressure range;
• directing a first permeate stream containing a higher purity of the target gas than the feed stream from the first membrane separator to a second membrane separator within a second pressure range;
• recovering from the second membrane separator a second permeate stream containing a relatively higher purity of the target gas than the first permeate stream;
• and
• substantially maintaining the pressure differential between the feed stream and the non-permeate stream exiting the first membrane at a level substantially less than the pressure differential between first permeate stream entering the second membrane and the non-permeate stream exiting the second membrane.