Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D19/00—Degasification of liquids
  • B01D19/0005—Degasification of liquids with one or more auxiliary substances
  • B01D19/001—Degasification of liquids with one or more auxiliary substances by bubbling steam through the liquid
  • B01D19/0015—Degasification of liquids with one or more auxiliary substances by bubbling steam through the liquid in contact columns containing plates, grids or other filling elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
  • B01D3/14—Fractional distillation or use of a fractionation or rectification column
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/20—Treatment of water, waste water, or sewage by degassing, i.e. liberation of dissolved gases
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
  • C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Definitions

• This invention relates generally to processes involving heat and mass transfer applications.
• the invention relates to the segregation of operating zones in a heat / mass transfer apparatus, such as a distillation column, to effect efficient separations, heat and product recovery with or without chemical reactions.
• a heat / mass transfer apparatus such as a distillation column
• Two applications illustrating the concept of staged heat and mass transfers are given.
• One relates to applying the segregation concept on wastewater treatment to improve corrosive vapor handling.
• the other relates to recovering both heat and condensate by retrofitting a steam boiler deaerator steam vent with an economizer.
• U.S. Pat. No. 5,476,525 proposed the use of a bare piece of pipe extending two feet from the deaerator to effect heat loss by natural convection. A the ⁇ nostatic steam trap is mounted at the end of this extended pipe to let out steam that is contaminated with gases like oxygen. Obviously, this method offers some condensate recovery and is better than the common "straight venting" method. It is far from efficient.
• U.S. Pat. No. 5,728,200 by the same inventor presented two other methods to recapture the vented steam.
• One method is to contact feed water and return condensate directly with the vent stream, thereby partly condensing the steam into condensate and recovering heat content as well as the condensate.
• the other method is to "bubble" the vent stream through a pool of feed water to capture the same. While the inventor has tried to improve on his previous invention, these proposed methods still have major drawbacks.
• the one stage spray arrangements provides no efforts of separation. In fact, a portion of the gases removed by the deaeration process is recaptured and recycled back into the feed water, increasing the overall deaerator load.
• This invention will demonstrate applications of staged heat and mass transfer concept to provide solutions to the above challenges.
• the present invention focuses on overcoming the difficulties in analyzing the common process of integrated heat and mass transfer by separate zones analysis.
• the present invention takes the approach of built-in design flexibility so that the resulting apparatus and control method can cover a wide range of operating scenarios.
• Fig. 1 shows internal spray quench in wastewater treatment, prior art.
• Fig. 2 shows simplified conceptual staged heat and mass transfer zones
• Fig. 3 shows preferred arrangement of wastewater stripper overhead.
• Fig. 4 shows preferred arrangement of deaerator vent economizer.
• the summary of this invention is the application of the concept of staged heat transfer and mass transfer zones to effect efficient separations, heat and product recovery.
• Two applications following the concept of staged heat and mass transfers are given.
• the first one relates to wastewater stripper overhead and improvements in sour gas handling.
• the second one relates to recovering both heat and condensate from a steam boiler deaerator steam vent by retrofitting the vent with an economizer.
• This invention relates to applying the concept of segregating heat transfer zone and mass transfer zone to facilitate process analysis and to improve process control robustness.
• staged heat and mass transfer zone two typical scenarios are given below.
• This invention focuses on applying the above concept to segregate heat transfer and mass transfer zones so that each zone's function and effectiveness can be identified and possible improvements made.
• the following is a General Example of zone segregation
• Fig. 2 shows a countercurrent stripping of sub-cooled condensate by a vapor stream, containing condensable components, using a packed column arrangement 500.
• Two zones are shown. They are symbolically separated by a boundary (imaginary or physical) into a heat transfer zone 400 above and mass transfer zone 300 below. For clarity, stream numbers are changed to reflect the transitional boundary between the two zone's. Vapor stream 25 changed to vapor stream 35 and liquid stream 150 changed to liquid stream 160 after crossing the boundary.
• Liquid stream 160 containing soluble components like dissolved gases, exiting from the heat transfer zone 400, is in countercurrent contact with vapor stream 25 at mass transfer zone 300. Soluble components, such as dissolved gases, in liquid stream 160 are transferred to vapor stream 25, utilizing mass transfer gradient between the two streams, along mass transfer zone 300 before exiting as liquid stream effluent 170. Likewise, some condensable components in vapor stream 25 are also transferred to liquid stream 160 depending on the dew point of the vapor stream 25.
• Mass transfer zone 300 operates like a stripping zone with the liquid steam 160 and vapor stream 25 at thermal equilibrium with each other.
• Vapor stream 25 turns into vapor stream 35 after crossing the boundary, enters heat transfer zone 400 where it is put to countercurrent contact with liquid stream 150.
• heat transfer zone 400 latent heat in vapor stream 35 is exchanged for sensible heat in liquid stream 150, raising the temperature of liquid stream 150 as it moves down the heat transfer zone 400.
• Heat transfer zone 400 operates like a quenching zone. At steady state, material balance will result in an equilibrium concentration of acid gases dissolved in the liquid phase across the heat transfer zone 400. This acid gases concentration in turn forces the acid gases to be removed via the vent stream 45. Because of the quenching effect, vapor stream's 35 flow rate decreases as it moves to the top and exits as the concentrated vapor stream 45. Liquid stream's 150 flow rate increases as it moves down.
• This quenching zone operates like a direct contact heat exchanger having temperature gradient (delta T), area (A) for heat transfer and some form of heat transfer coefficient (U).
• delta T temperature gradient
• A area
• U heat transfer coefficient
• Q rate of heat transfer
• zone G In an overhead wastewater treatment application as shown in Fig. 3, two more operating zones is now added to the General Example, zone G, given above.
• the first zone reduces the excess steam to allow proper processing of the off gas through zone G, as described in the General Example above.
• Process vapor is concentrated after passing through zone G and vented to downstream processing units as described above.
• the second zone cleans up the quenching medium to protect the pump and the inline cooler from dissolved acid gases.
• the pretreatment zone 200 primarily functions as heat transfer zone and the vapor stream 15 and the quench liquid stream 40 operate cocurrently. This arrangement offers the advantage of lower pressure drop as the vapor volume in vapor stream 15 is continuously being reduced when it comes in contact with the quench liquid stream 40. Even at very high column loading as dictated by process requirement, flooding is hardly a consideration, unlike countercurrent arrangement. Pressure drop across and capacity through the pretreatment zone 200 are not major concerns. However, the temperature at the pretreatment zone 200 outlet is very important. This temperature is controlled to a target such that the majority of the excess steam in the exiting process vapor stream 25 is condensed and yet the off gases are not appreciably dissolved in the exiting liquid effluent stream 50. This stream 50 is to be cleaned up in the cleanup zone 100 below.
• the pretreatment zone 200 essentially prepares the process vapor stream 15 for zone G processing. Since the process vapor 25 is a substantially reduced feed vapor stream 15 after passing through the pretreatment zone 200, flooding through zone G can be positively prevented. Through zone G, the H2S vapor passes through while the steam content is further condensed and recovered as described above.
• Quench effluent streams 50, 170 from both the pretreatment zone 200 and zone G, 500 respectively, are processed by the cleanup zone 100.
• the cleanup zone 100 functions as a stripping zone.
• the vapor stream 5 and liquid streams 50, 172 are countercurrent to one another as shown.
• the vapor stream 5 contains low concentration of acid gases because steam is present in excess. Therefore, this vapor stream can be used to process the circulating quench water 20 as long as adequate stages are provided. Excess condensate 10, which is quite clean, overflows downward. This setup eliminates process condensate reprocessing as suggested by prior art.
• the circulating pump 700 takes the process condensate 20 from cleanup zone 100 and cools it through air finned cooler 800. Part of the cooled process condensate 30 is diverted as pretreatment quench flow 40 through control valve 101 and enters pretreatment zone 200. The balance of the cooled process condensate 30 passes through control valve 102, further cooled by cooling water heat exchanger 900, and enters zone G 500 as quench stream 150. Liquid stream 170 from zone G 500 can be partly removed as a slipstream 171 for further processing or fed to cleanup zone 100 as liquid feed stream 172.
• the above arrangement allows full operation flexibility because the pretreatment zone 200 is provided to protect zone G 500 from flooding.
• the heat balance control loop varies quench water circulation rate by adjusting control valve 101 to maintain exit temperature of vapor stream 25. As the off gas load changes, the quench flow 140 cooling duty in zone G 500 will adjust to maintain the heat and mass transfer zones boundary's temperature target.
• the secondary cooler 900 can be deleted if the main cooler 800 maintain adequate temperature approach. The combination is for optimizing the dry and wet bulb temperatures and cooling water usage.
• Suitable material of construction for zone G can be fiberglass, high temperature polymer, ceramic packing, other non-corrosive materials or even stainless steel. The rest of the zones are not under severe operating conditions. Those skilled in the art would have no trouble specifying the proper material of construction.
• Dissolved gases, like oxygen, in make up water needs to be removed by a process commonly known as deaeration before the makeup water is suitable for use as boiler feed.
• the steam vent on a deaerator is around half to one percent of the steam generation load.
• a deaerator steam vent apphcation is shown in Fig. 4.
• the same numbering system as used in the General Example is repeated here to reflect the application of the exact same concept.
• the first zone is the mass transfer zone 300. It allows countercurrent contact of steam vent 25 to strip out dissolved gases in the incoming makeup water 160.
• This mass transfer zone 300 operates like a stripper.
• the makeup water 160 is partly deareated and exits this stripping zone 300 as preheated feed flow 170 to deaerator.
• the second zone above 400 allows countercurrent contact of cold makeup water 150 running down to scrub out part of the remaining steam content in the steam vent 35 moving up.
• the non-condensibles are eventually being vented 45 while the incoming cold makeup water 150 is brought to thermal equilibrium with the steam vent 35 at the boundary between the two zones.
• this application is identical to zone G above, either as a stand-alone General Example or as part of the wastewater treatment stripping section application.
• zone G method straight adaptation of zone G method is favored here because of the following specific process criteria:
• vent stream 25 flow rate is relatively constant and seldom needs adjusting.
• the quench flow 150 is only a fraction of the total makeup water flow to the deaerator.
• Suitable elevation can be provided, including proper liquid seal, to allow the economizer effluent to enter a pressurized deaerator receiver tank in stead of an atmospheric deaerator receiver tank.
• Suitable material of construction like fiberglass, high temperature polymer, stainless steel or other non-corrosive materials can be used.
• zone boundary temperature can be conttolled.
• quench flow to the economizer can be controlled such that the temperature at midway measures 75 deg C. It is important to note that this location is not necessarily the boundary location. However, once the temperature is fixed, the zone boundary is more or less determined as well. This way, the vent stream 45 exits to atmosphere with only the equilibrium amounts of saturated water vapor at close to the makeup water temperature.
• the economizer also strips the makeup water of dissolved gases resulting in reduced deaeration load.
• staged heat and mass transfer zone can be added to any existing deaerator vent stream without imposing any restriction on the original venting requirement. It simply makes the deaerator operate so much more efficiently.
• the economizer unit can be sized and elevated sufficiently to allow feed by gravity. Heat and condensate recovery will be the ongoing savings.
• control method employed in this invention can be enhanced by taking advantage of making the zone boundary movable as opposed to a stationary boundary as indicated above.
• the alternate control method is to preset the quench water flow but cycles the flow in an on/off fashion with a timer. This way, the economizer is being purged out periodically with intermittent quench flow.
• the concept of this invention can be extended to retrofitting existing process units as given by the deaerator vent example above. Any quenching process that experiences difficulty in hydraulics or unstable operation can be analyzed by this method of segregating the operating zones into staged heat / mass transfer zones. Boundaries of these zones can be moved to facilitate the finding of a process solution to the problem. Examples can be found in special heat exchange services that can potentially be converted from indirect to direct contact heat exchange services, after taking severity and load into consideration. In the example of acid gas stripping and scrubbing, this invention can be combined with other prior art to incorporate chemical reaction within the zones. Heat and mass transfer zones can then be tailored for pH adjustments, chemical reactions and product removal such as ammonium sulfate.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
• Physical Water Treatments (AREA)
• Degasification And Air Bubble Elimination (AREA)
• Heat Treatment Of Water, Waste Water Or Sewage (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 2001
  • 2001-03-14 EP EP01918621A patent/EP1268024A4/de not_active Withdrawn
  • 2001-03-14 WO PCT/US2001/008023 patent/WO2001072393A1/en not_active Ceased
  • 2001-03-14 CN CN01802865A patent/CN1436092A/zh active Pending
  • 2001-03-14 JP JP2001570350A patent/JP2003527959A/ja active Pending
  • 2001-03-14 CA CA002390067A patent/CA2390067A1/en not_active Abandoned

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