MEMBRANE BIO-REACTOR FOR CONDENSATE CLEANUP

Abstract

The present invention relates to the integration of a membrane bio-reactor in a conventional hydrogen plant to remove ammonia and other organics such as methanol from the process condensate.

Claims

1. A process for cleaning a process condensate from a synthesis gas or hydrogen production plant, comprising: processing a hydrocarbon feedstock in a reactor to produce a synthesis gas and at least one stream of contaminated process condensate; introducing the contaminated process condensate into a membrane bio-reactor integrated with a single steam system of the plant, wherein high levels of organic contaminants and ammonia are removed; and routing a clean process condensate from the membrane bio-reactor to produce an export steam in a single steam system of the synthesis gas or hydrogen production plant, wherein the export steam produced is derived at least in part from said clean process condensate.

2. The process of claim 1, further comprising routing the clean process condensate through a clean water heater thereby reducing the temperature of the contaminated process condensate to a temperature ranging from about 60 F. to about 130 F. prior to introducing it into the membrane bio-reactor.

3. The process of claim 1, wherein a stream of cold contaminated process condensate is mixed with a stream of hot contaminated process condensate forming a contaminated process condensate and routing same to a flash drum and removing about 40 to 80 percent of the carbon dioxide prior to routing the contaminated process condensate to the membrane bio-reactor.

4. The process of claim 3, further comprising routing the contaminated condensate stream from the flash drum to a cold water heater where the clean process condensate is employed to lower the temperature of the contaminated process condensate prior to introducing it into the membrane bio-reactor.

5. The process of claim 1, wherein the synthesis or hydrogen production plant includes a reactor that is a steam methane reformer, an auto-thermal reformer or a partial oxidation unit.

6. The process of claim 1, wherein the membrane bio-reactor operates at pressures ranging from about 10 to 35 psia.

7. The process of claim 1, wherein the clean process condensate stream is routed to a stripping section of a deaerator of the single steam system in the synthesis gas or hydrogen production plant.

8. The process of claim 1, wherein the clean process condensate stream is mixed with make-up water in the clean water tank and routed to a demineralized water heater of the single steam system in the synthesis gas or hydrogen production plant.

9. The process of claim 3, wherein the clean process condensate stream is routed to the clean water heater where it cools the contaminated hot condensate stream and is further routed to a demineralized water heater of the single steam system in the synthesis gas or hydrogen production plant.

10. The process of claim 3, wherein the contaminated hot condensate stream is routed to a trim water cooler prior to mixing with the contaminated cold condensate stream.

11. The process of claim 1, wherein the contaminants removed from the clean condensate stream are selected from the group comprising ammonia, methanol and other organic compounds.

12. The process of claim 1, wherein the export steam is high quality having less than 0.5 ppmw ammonia and less than 10 ppmw methanol.

13. A process for cleaning a process condensate from a synthesis gas or hydrogen production plant, comprising: processing a hydrocarbon feedstock in a reactor to produce a synthesis gas and at least one stream of contaminated process condensate; introducing the contaminated process condensate into a membrane bio-reactor integrated with a single steam system of the plant, wherein high levels of organic contaminants and ammonia are removed; and heating a clean process condensate from the membrane bio-reactor to produce an export steam in a single steam system of the synthesis gas or hydrogen production plant.

14. A process for cleaning a process condensate from a synthesis gas or hydrogen production plant, comprising: processing a hydrocarbon feedstock in a reactor to produce a synthesis gas and at least one stream of contaminated process condensate; introducing the contaminated process condensate into a membrane bio-reactor integrated with a single steam system of the plant, wherein high levels of organic contaminants and ammonia are removed; and routing a clean process condensate from the membrane bio-reactor to one or more process operation units in the single steam system of the synthesis or the hydrogen production plant to produce an export steam.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0023] The objects and advantages of the invention will be better understood from the following detailed description of the preferred embodiments thereof in connection with the accompanying figures wherein like numbers denote same features throughout and wherein:

[0024] FIG. 1 is a process flow diagram of a related art single steam system associated with a hydrogen or syngas production plant;

[0025] FIG. 2 is a process flow diagram of a related art segregated/dual steam system associated with a hydrogen or syngas production plant;

[0026] FIG. 3 is a schematic of an integrated MBR with hydrogen or syngas production plant in accordance with one exemplary embodiment of the invention;

[0027] FIG. 4 illustrates a schematic of an integrated MBR with hydrogen or syngas production plant in accordance with another exemplary embodiment of the invention;

[0028] FIG. 5 depicts a schematic of an integrated MBR with hydrogen or syngas production plant in accordance with a further exemplary embodiment of the invention;

[0029] FIG. 6 illustrates a schematic of an integrated MBR with hydrogen or syngas production plant in accordance with yet another exemplary embodiment of the invention; and

[0030] FIG. 7 a schematic of an integrated MBR with hydrogen or syngas production plant in accordance with a further exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention provides for the removal of contaminant byproducts in a syngas or hydrogen plant through the various exemplary embodiments where a membrane bio-reactor (MBR) is integrated with the syngas or hydrogen production plant in order to produce a high quality export steam in a single steam plant design. A hydrocarbon feedstock is reacted in a steam reformer, autothermal reformer or partial oxidation reactor to form syngas, which can be further reacted and/or purified to form hydrogen.

[0032] An MBR uses live organisms in the bio-reactor to consume ammonia and organic matter including methanol, ethanol and organic acids such as formic acid and acetic acid for their growth. The MBR process consists of a suspended growth biological reactor integrated with a membrane filtration system. The MBR works on the principle of aerobic digestion. This requires use of air blowers to feed air to the bio-reactor tank. Overflow from the MBR is sent to the membrane separation unit which separates solids (bio-sludge) from the clean water. Bio-sludge, which is about 2% solids, is then recycled back to the bio-reactor. Part of this recycle is continuously discarded. This discard stream is thickened into bio-cakes using a bio-sludge thickening process. MBRs are widely employed in wastewater treatment which contains far more complex contaminants than those present in the process condensate. Several water cleanup companies including GE and Siemens have deployed this technology at numerous waste water treatment sites worldwide.

[0033] In the present invention, the MBR is employed to remove the aforementioned contaminants, and particularly ammonia and methanol from the process condensate in syngas plant. For the purpose of this description, the plant produces hydrogen by reacting natural gas in a steam reformer. However, it will be recognized by those skilled in the art that the hydrogen plant could also be an auto thermal reformer or a partial oxidation reformer based plant.

[0034] With reference to FIG. 3, an exemplary embodiment of the invention is provided where the MBR 310 is integrated with the hydrogen plant water/steam system 300. In this method, hot and cold contaminated condensate streams 301 and 302 are mixed together. The pressure of the mixed condensate stream 303 is dropped from about 200-500 psig to about 0-60 psig and then the mixed contaminated condensate is fed to a flash drum 304. Flash drum 304 operates at a pressure of about 0 psig to 60 psig and removes about 40-80% of the CO.sub.2 present in the mixed contaminated condensate which leaves the flash drum in the vapor stream 305. This vapor stream can be either vented or sent to the flue gas duct of the furnace depending on the environmental regulations. Such integration can substantially reduce consumption of pH adjustment chemicals which are added by the pH chemical injection system to the condensate prior to the treatment in the MBR. Contaminated liquid stream condensate 306 exiting the flash drum 304 would need to be cooled to suit bio-reactor 317 inlet operating temperature. The living organism in the bio-reactor consumes ammonia and organic compounds such as methanol, ethanol and organic acids. To improve efficiency, this can be done by heating the clean water from the clean water tank 400 against the heat from the contaminated liquid condensate stream 306 coming out of the flash drum 304. Heated clean water 314 is then fed to the sequence of process operation units such as the demineralized water heater 307, deaerator 308, boiler feed water pump 309, boiler feed water heater 311, boiler 315, steam drum 312 and steam superheater 313. Steam at the exit of the steam superheater is quite pure, having less than 0.5 ppmw ammonia and less than 10 ppmw methanol and can be directly exported to the customer.

[0035] Typically, the temperature of the stream fed to the MBR as liquid condensate stream 321 can vary in temperature from a range of about 32 F. to 130 F., preferably 50 F. to 130 F. For typical systems, the flow of stream 321 ranges from 50-300 gpm. In typical MBR configurations, the equipment is a sequence of different unit operation and the number of different units shown in FIG. 3 is typically prescribed by the MBR manufacturer. For instance, it may include an equalization tank 350, a pH injection system 315 and a bio-sludge thickening system 316 as prescribed by the MBR manufacturer. The membrane bio-reactor operates at pressures ranging from about 10 to 35 psia.

[0036] In the operation of the MBR 310, the equalization tank 350 is used to suppress fluctuations in a portion of the liquid stream condensate's flow, temperature and contaminant levels. pH chemical injection system 315 is employed to raise the pH of the mixed condensate from about 6 to 10. The bio-reactor 317 has biomass specifically grown to consume ammonia and organic compounds. This reactor is aerated by ambient air to supply oxygen to biomass. Biomass sludge from bio-reactor 317 is sent to a membrane 318 to separate biomass from clean water. Concentrated biomass sludge from the membrane is recycled back to the bio-reactor 317. The process also has a biomass blowdown to maintain biomass concentration in the bio-reactor. Vent from the bio-reactor is directly sent to the atmosphere or routed to the flue gas duct of the furnace in order to meet the environmental regulations. Bio sludge blowdown from the bio reactor 317 is fed to the bio sludge thickening process which thickens the sludge to make solid cakes, which can then be sent to the landfill. Alternatively, bio sludge can be routed to the flue gas duct of the furnace where it is incinerated at high temperature. Without being limited to a particular theory, it is believed that bio-reactor 317 consumes ammonia and organic compounds like methanol, ethanol and organic acids from the liquid condensate stream 321 entering equalization tank 350. The bio-sludge inside the bioreactor 317 contains living organisms (i.e., solids) and clean condensate (i.e., liquid). The clean condensate stream 320 is routed to the clean water tank 400, where it can be combined with clean make-up water in this embodiment.

[0037] In another exemplary embodiment, and as shown in FIG. 4, instead of sending the clean condensate 320 to the clean water tank 400, it is sent directly to the clean water heater 410 upstream of the MBR 310. Subsequent to heating in the clean water heater 410, clean condensate 314 is sent to the stripping section 420 of the deaerator 308. This type of configuration reduces the load on the clean water tank pump (not shown) and the demin water heater 307 thus potentially enabling additional operating cost savings.

[0038] With reference to FIG. 5, another exemplary embodiment is depicted where the hot condensate stream 301 is cooled by clean water 322 from the clean water tank 400 prior to mixing with the cold condensate stream 302. The mixed contaminated condensate stream 303 is routed into the flash drum 304. This configuration maximizes heating of the clean water stream 322 from the clean water tank 400 and thus reduces the load on the demineralized water heater 307 in the single steam train/system 501.

[0039] Turning to FIG. 6, the configuration of the integration is similar to that of FIG. 4, except for the hot condensate stream 301 is cooled by clean condensate 320 prior to mixing with the cold condensate stream 302. This configuration maximizes heating of the clean condensate stream and thus reduces the load on the demineralized water heater 307.

[0040] As depicted in FIG. 7, another system integration of an MBR 310 with hydrogen or syngas production plant 300 is provided. It has same configuration as shown in FIG. 5 except hot condensate stream 301 is cooled in a trim water cooler 701. This type of configuration may be used when no heat sink is available to take advantage of the low grade heat in the hot condensate stream 301. The trim cooler, for instances, utilizes water received from a cooling tower (not shown) to reduce the temperature of hot condensate stream 301, such that the the mixed condensate stream 303 is at a temperature suitable for MBR 310.

[0041] The following Comparative Example, provides the advantages of the present invention.

Comparative Example

[0042] Process simulations were carried out for the base case in accordance with the embodiment of the related art shown in FIG. 1 and one method of integrating MBR with SMR based hydrogen production plant as shown in the embodiment ofFIG. 3 in the present invention. Table 2 shows the comparison between the two cases. Based on the comparison, MBR integration is capable of reducing the ammonia and methanol in export steam to very low levels in order to meet the high quality export steam specifications.

TABLE-US-00002 TABLE 2 Comparison Between Related Art and One Configuration of Present Invention Base Case MBR Case Unit (FIG. 1) (FIG. 3) Hydrogen Production MMSCFD 118 118 Cold Condensate Flow GPM 66 67 Hot Condensate Flow GPM 181 180 Ammonia in Cold ppmw 1088 1098 Condensate Methanol in Cold ppmw 985 976 Condensate Ammonia in Hot ppmw 698 691 Condensate Methanol in Hot ppmw 142 140 Condensate Ammonia in Export Steam ppmw 210 <0.5 Methanol in Export Steam ppmw 96 <10

[0043] Thus, as can be seen in the present invention the ammonia and methanol contaminants are reduced to below 0.5 and 10 ppmw, respectively, as compared to the base case.

[0044] While the invention has been described in detail with reference to specific embodiments thereof, it will become apparent to one skilled in the art that various changes and modifications can be made, and equivalents employed, without departing from the scope of the appended claims.