PRODUCTION OF HIGH QUALITY AQUEOUS ACID UPON THE REFORMATION OF HALOGENATED ORGANIC MATERIALS

Abstract: Methods and apparatus for the production of high quality aqueous acid in the reformation of halogenated organic materials, the methods and apparatus including quenching a gaseous stream from a reactor; separating a gaseous stream from a quenched gaseous stream to form a first washed gaseous stream; atomizing the first washed gaseous stream with a scrubber liquid; separating a gaseous stream from the atomized gaseous stream to form a second washed gaseous stream; and absorbing a portion of the second washed gaseous stream to produce a raw aqueous acid.

Description: PRODUCTION OF HIGH QUALITY AQUEOUS ACID UPON THE REFORMATION OF HALOGENATED ORGANIC MATERIALS The invention relates to gasification processes for halogenated materials, and more particularly, to methods and apparatus for producing high quality aqueous acid from gasification products. Related inventions include a prior patent application for a Method and Apparatus for the Production of One or More Useful Products from Lesser Value Halogenated Materials, PCT international application PCT/US/98/26298, published 1 July 1999, international publication number WO 99/32937. The PCT application discloses processes and apparatus for converting a feed that is substantially comprised of halogenated materials, especially byproduct and waste chlorinated hydrocarbons as they are produced from a variety of chemical manufacturing processes, to one or more "higher value products" via a partial oxidation reforming step in a gasification reactor. During the gasification of halogenated feeds, there is invariably a certain amount of metal salts present in the feeds. These metal salts could be corrosion products from the processes where the halogenated materials were produced, or spent catalysts, etc. Also, within the gasification process itself, corrosion occurs producing additional metal salts (if metals were used to contain the process). Wear of the refractory, generally an alumina based material, can also cause metal salt generation. Additionally, metal salts can also be introduced in process water used for pump purges and feed towers or other vessels, for example. This invention relates to the efficient and effective removal of these salts, typically metal halides and metal oxides, from the products of the gasification process so that a high quality acid product, such as hydrogen chloride (HO), can be produced cost effectively. More particularly, it has been found that the processes of quenching hot gases containing hydrogen halides using a weir quench (or other similar gas/liquid contacting devices) followed by a venturi scrubber (to remove particulate matter such as carbonaceous soot) effectively capture metal salts and largely prevent their entrainment in any subsequent absorption section of the plant, resulting in a cost effective high quality acid product. The invention described in the '865 patent, U.S. 5,174,865 Stultz, et al. "Process for Purifying Crude Hydrochloric Acid", teaches cleaning up metal laden HC1 after the HC1 has been absorbed. The process disclosed in Stultz requires double or triple effect evaporation, and is highly energy intensive. The instant invention takes advantage of a process design for a halogenated material gasification process to clean up gasifier outlet gases prior to absorption of the hydrogen halides. The design of the instant invention reduces capital and makes for a simpler process. The invention includes methods and apparatus for producing high quality aqueous acid from a gasification process for halogenated materials. The methods include in one embodiment quenching a synthesis gas from a reactor (RGS - Figure 3 A) with a first liquid (LSI - Figure 3 A) , the gas containing hydrogen halide(s). The method includes separating a first washed gaseous stream (WGSl - Figure 3 A) containing hydrogen halide(s) from the quenched syngas stream (QGS - Figure 3A). The method includes atomizing the first gaseous stream with a second liquid (LS2 - Figure 3 A) and separating a second washed gaseous stream (WGS2 — Figure 3 A) containing hydrogen halide(s) from the atomized stream (AGS - Figure 3 A). The method includes absorbing hydrogen halide from the second washed gaseous stream into an aqueous solvent to produce a raw aqueous acid. The apparatus includes a reactor in fluid communication with a quench, preferably a weir quench. The quench is in fluid communication with a vapor/liquid separator drum. A venturi scrubber is in fluid communication with a gaseous stream from an upper portion of the quench drum. The scrubber is in fluid communication with a scrubber drum. An absorber is in fluid communication with a gaseous stream from an upper portion of the scrubber drum. A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which: Figure 1 illustrates in block diagram form a preferred embodiment for a gasification process for halogenated materials. Figure 2 illustrates a preferred embodiment for a gasifier in a gasification process for halogenated materials. Figures 3 A and 3B illustrate a preferred embodiment for a quench and a particulate removal process for producing aqueous acids and synthesis gases from reformed halogenated materials. Figures 4A and 4B illustrate a preferred embodiment for an absorber and an aqueous acid clean up process for producing high quality acid and synthesis gases from the gasification of halogenated materials. A preferred embodiment of a gasification process for halogenated materials, in general, is discussed first, for background purposes. The preferred embodiment of the process is comprised of five major processing areas, illustrated in the block flow diagram of Figure 1: 1) Gasifier 200 2) Quench 300 3) Particulate Removal and Recovery 350 4) Aqueous HC1 Recovery and Clean-up 400, 450 5) Syngas Finishing 700 The units of the preferred embodiment of the process will be discussed to place the instant invention in perspective. In the preferred embodiment, the feed will be assumed to be RCl's, or chlorinated organics. The gasifier area 200 of a preferred embodiment, as more particularly illustrated in Figures 2 A and 2B and discussed in more detail below, consists of two reaction vessels, R- 200 and R-210, and their ancillary equipment for the principal purpose of reforming the halogenated material, typically RCl's. (Halogenated material may frequently be referred to herein as RCl's, a typical form.) The RCl's in the form of liquid stream 144 are preferably atomized into a primary reactor R-200, preferably with pure oxygen 291 and steam 298. In a harsh gasification environment the RC1 components are partially oxidized and converted to a synthesis gas (syngas) comprised primarily of carbon monoxide, to hydrogen chloride and hydrogen, and lesser amounts of water vapor and carbon dioxide, as well as trace elements including carbon (as soot). The syngas preferably flows into a secondary reactor R-210, which has been provided to allow all reactions to proceed to completion, thus yielding very high conversion efficiencies for all halogenated species and minimizing undesirable side products. To continue through the rest of the process system of the block flow diagram of Figure 1, hot gases from the reactor area 200 are cooled in a quench area 300 by direct contact with a circulating aqueous stream, preferably by intimate mixing in a weir quench vessel. The mixture then preferably flows to a vapor-liquid separator from which quenched gas passes overhead and a bottoms liquid is cooled and recycled to the weir quench. At least a slip stream of the bottoms liquid is preferably flowed to a filter unit, discussed below, to remove entrained solids. Filtrate from the filter unit is preferably recycled to the quench. Particulates in the syngas passing overhead from the quench vapor-liquid separator, consisting essentially of soot, are preferably scrubbed from the gas stream in an atomizer or scrubber, preferably a wet venturi scrubber. The scrubber liquid is preferably operated on a circulating loop, with blowdown liquid from this scrub system being combined with the slipstream from the quench liquid recycling system and directed to a particle recovery stage 350. In the particle recovery stage, the blowdown and slipstream liquids are preferably flowed to a filter unit, more preferably a continuous candle filter unit. In the filter unit according to a first embodiment a primary filter first removes solids from the process streams and discharges the solids as a concentrated slurry. The concentrated slurry is preferably forwarded to a secondary filter where it is filtered and dewatered to a wet cake which is discharged, such as to a RC1 feed tank for recycle to the gasifier, or to an appropriate disposal system. Alternatively and preferably, the filter unit uses a single filter producing a dry cake, as for example in Figure 3B wherein the quench liquor slipstream 330 is fed directly to FL-350. To return to the quench unit 300, particulate free syngas from the vapor-liquid separator scrubber is next preferably introduced to an HCl absorption column 400. Noncondensible syngas components pass through the absorber overheads and on to a syngas finishing area 700. HCl in the syngas is absorbed to a concentrated aqueous acid bottoms stream of about 35 wt percent HCl in the HCl absorption column 400. This is a high quality aqueous acid stream and is preferably filtered and passed through an adsorption bed 450 to remove final traces of particulates and extremely minute amounts of organics, yielding a high quality aqueous HCl product suitable for sales or internal use. A caustic scrubber, gas superheater, carbon bed adsorber, and syngas flare system can make up syngas finishing unit 700. The caustic scrubber, or syngas finishing column, uses cell effluent in the lower section of the column to absorb final traces of HCl and C12 from the syngas stream. Water can be used in the upper section of the column as a final wash of the product syngas. If the customer is unable to take the syngas, it can be flared to a dedicated flare system. The spent solution from the column bottoms can flow to an appropriate wastewater treatment system or is otherwise disposed of. Gasifier area 200, in a particularly preferred embodiment, as discussed above, consists of two reaction vessels R-200 and R-210 and their ancillary equipment for the principal purpose of fully effective halogenated feed material conversion. For the purpose of the following discussion the halogenated material will be assumed to comprise RCl's, a typical form. The RC1 liquid steam is preferably atomized into a primary reactor R-200 with preferably a pure oxygen stream 291 and a steam stream 298 through a main burner or nozzle BL-200. In the harsh gasification environment the RC1 components are partially oxidized and converted to synthesis gas (syngas) comprised primarily of carbon monoxide, hydrogen, hydrogen chloride, and lesser amounts of water vapor and carbon dioxide. The syngas preferably flows into a secondary reactor R-210 provided to allow all reactions to proceed to completion, thus yielding very high conversion efficiencies for all halogenated species and minimizing undesirable side products. Primary gasifier R-200, in the preferred embodiment illustrated, functions as a down fired, jet stirred reactor, the principal purposes of which are to atomize the liquid fuel, evaporate the liquid fuel, and thoroughly mix the fuel with oxygen, moderator, and hot reaction products. The gasifier operates at approximately 1450°C and 5 bars, gauge (barg) (75 psig). These harsh conditions insure near complete conversion of all halogenated feed components. A very small amount of soot, essentially being carbon, is formed in the gasifiers. Due to the low partial pressure of oxygen in the gasifier, essentially all halogens, including chlorine as shown above, equilibrate to the hydrogen halide. The secondary gasifier R-210 in the preferred embodiment functions to allow the reactions initiated in the primary gasifier to proceed to equilibrium. The secondary gasifier R-210 operates at approximately 1400°C and 5 barg (75 psig). These conditions are simply a function of the conditions established in the primary gasifier, less limited heat loss. The reactions specifically desired in the secondary gasifier reduce or eliminate undesirable byproducts from the primary gasifier. The following represents typical operating performance of the gasifier system with respect to production of species other than the desired CO, H 2 , and HCl: Exit gas CO 2 concentration: 1.0 - 10.0 volume percent Exit gas H 2 O concentration: 1.0 - 10.0 volume percent The following example is provided for background. Example 1 The following feed streams were fed to the gasifier through an appropriate mixing nozzle: Chlorinated organic material: 9037 kg/hr Oxygen (99.5 percent purity): 4419 kg/hr Recycle vapor or moderator: 4540 kg/hr [58.8 wt percent water vapor, 41.2 wt percent hydrogen chloride] The resulting gasification reactions resulted in a synthesis gas stream rich in hydrogen chloride and chamber conditions of approximately 1450°C and 5 bars, gauge (barg). Having reviewed a preferred embodiment of a gasification process for halogenated materials, in general, the preferred embodiments of the instant invention will now be discussed as illustrated in Figures 3A, 3B, 4A and 4B. Gaseous stream 210 containing hydrogen halide(s) from a reactor is cooled in a quench unit 300, typically from approximately 1400°C, to typically approximately 100° C as illustrated in Figures 3 A and 3B. It will be assumed in further discussion of the preferred embodiments herein that the halogenated material feed into the gasifier is a chlorinated organic fuel. Quenching is preferably achieved in a single contacting step where a recirculating, cooled aqueous hydrogen chloride liquid stream 317 is vigorously contacted with a hot gaseous stream 210 from a reactor. This contacting step is preferably carried out in a weir quench Q-310. A weir quench essentially includes a short vertical weir cylinder which penetrates a flat plate. Quench liquor flows into an annular volume created between vessel walls and the centralized cylinder, above the flat plate. The liquor preferably continually overflows the top of the cylinder and flows down the wall of the cylinder. Simultaneously, gas flows down through the cylinder into the region below. This co-flow of liquid and gas, with liquid evaporating as it cools the gas, creates an intimate mixing and cooling of the gas stream. The inventory of liquid around the weir can serve as a reservoir in the event of temporary interruption of liquid flow. Liquid overflowing the weir can operate in one of three manners. In the first manner, low liquid flow could be insufficient to fully wet the ID wall of the weir. In the second and preferred manner, the liquid flow fully wets the weir ID, creating a full liquid curtain in essence, but does not completely fill the cross section of the weir. Gas flow area is still available down the weir diameter. In the third operating manner, liquid flowrate can be so high that back-up of the liquid occurs, to the point that the weir functions as a submersed orifice. The functionality of a weir quench requires that a heat balance be maintained and that the liquid flowrate preferably remains approximately within the second weir flow regime, as described above. This range may be approximately 1900 liters/min (500 gpm) to 5700 liters/min (1500 gpm) for acceptable weir performance. A weir quench would preferably operate at a gasifier system pressure, approximately 5 barg (75 psig). Inlet temperature would be normally approximately 1400°C, and exit temperature normally would be approximately 100°C. Quench liquid flowrate might be approximately 5200 liters/minute ( 1400 gpm) at 60°C. Quench liquor stream 317 supplied to the weir quench is preferably a circulating solution. The two-phase stream 310 that exits the weir quench chamber preferably flows to a vapor-liquid separator, such as drum D-310. Liquid droplets are separated from the vapor stream in the drum, allowing a relatively liquid-free gaseous stream to pass overhead, as a first washed gas stream (WGSl), preferably into a particulate scrubbing system. Collected bottoms liquid from the drum is preferably pumped, as by pump P-310, through a graphite plate and frame heat exchanger E-310 and back to the weir quench as quench liquor. The heat exchanger rejects the heat duty of quenching the gas, typically from about 1400°C to approximately 100°C, which heat duty could entail approximately 37MM kJ hr (35 MMBTU/hr). The circulation rate and exchanger outlet temperature could be varied to achieve desired quench outlet temperatures within the operational constraints of the weir device and within heat exchanger boundaries, which might further be defined by a water balance efficiency and a contaminant removal efficiency. Both pump P-310 and cooler E- 310 could be operated with two units and one as spare. Due to the preferable vigorous gas-liquid contact in the quench, the quench liquid 317 can be very near equilibrium with the gas phase, which might be typically 30 - 32 wt percent HCl. Make-up liquor stream 315 for the quench system can come from a particulate filter unit 350, which is at a high enough HCl concentration to avoid absorbing HCl from the gas and rather let it pass through where it can be captured as saleable acid in the absorber. A weir quench functions effectively as a gas wash for removing at least first order contaminants, due to the weir quench's inherent gas-liquid contact. Both particulate and other trace gas species are removed to a certain extent - with removal efficiency increasing with increasing liquid operating rate. A weir quench coupled with a downstream particulate scrubber VS-320 preferably enables the removal of essentially all aqueous acid soluble impurities from a gas stream so that an aqueous acid produced in a downstream absorber can cost effectively meet the impurities limits of aqueous HCl specifications. The aforementioned impurities are anticipated to include primarily NH 3 , metals, and metal salts. Metal salts that are entrained in gaseous stream WGSl exiting a quench knockout drum, such as a quench drum D-310, are preferably fed to an atomizing scrubber, such as a wet venturi scrubber VS-320. The purpose of the venturi scrubber is to further scrub particulates, mostly soot, from the synthesis gas. A venturi scrubber functions well to additionally remove entrained metal salts. A venturi scrubbing system would typically be anticipated to operate at 90 -110°C and at a syngas system operating pressure, for example, approximately 4.8 barg (70 psig). Normal vapor load is anticipated to be 1 actual cubic meter per second under operating conditions (2100 actual cubic feet/min), requiring approximately 1900 liters/min (500 gpm) aqueous scrubbing (for 30-35 wt percent HCl). Pressure drop across a venturi would typically be 0.7 bars (10 psi). Solids concentration in a circulating scrub liquor LS2, is anticipated to run about 0.5 wt percent. Efficient metal salt and particulate removal prior to acid absorption is desirable to prevent downstream equipment plugging problems and to effectively and efficiently meet syngas particulate specifications. Venturi technology is one of the more efficient technologies for removing very fine solids from a vapor stream. While a gas wash effect of a quench can effectively remove larger solids, as just discussed, the high energy expended through a venturi can improve the capture efficiency for particles of all sizes, in particular as compared to other wet scrubbing devices. In the venturi VS-320, the particles and metal salts penetrate and become trapped in liquid droplets through the fluid acceleration and deceleration created by the venturi. Pressure drop can be optimized to maximize atomization and velocity differentials for particle capture. Pressure drop can, however, drop below a point where atomization of the liquid becomes too fine, creating droplets which are too small to practically separate in a downstream vapor-liquid separator. In preferred embodiments, a three-phase gaseous stream 320 discharges from venturi VS-320, preferably tangentially, into a vapor-liquid separation drum D-320. The tangential entry can create a cyclonic effect, the centrifugal force of which can force the liquid droplets (with captured solids) to the walls where they can coalesce and gravity drain to the bottoms. A radial vane demister followed by a chevron vane demister, or other suitable demisting devices, (not shown) may be placed in the upper half of the separator drum to maximize liquid droplet removal from the gas stream. Optimally, an essentially particle free gaseous stream WGS2 flows on to the acid, or HCl, absorption system. A bottoms liquid stream 322 from a scrub vapor-liquid separator D-320, actually a very dilute slurry, is preferably pumped directly back to the inlet of the venturi scrubber. Most (for example, 80 percent) of the scrub liquid is preferably atomized directly to the center of the venturi throat via a pressure atomization nozzle. Remaining liquid can be introduced via several tangential nozzles to create a swirling film of liquid which wets the walls of the venturi into the throat. For effective scrubbing efficiency, liquid to gas ratios are best maintained at or near 33 liters of scrub liquor per actual cubic meter of gas (0.25 gallons/actual cubic foot of gas). Due to the vigorous gas liquid contact in the venturi, the scrub liquid is very near equilibrium with the gas phase. That is, it is typically 30-32 wt percent HCl. Make-up liquor stream 406 for the scrub system can come from absorber system bottoms, which should be at a high enough HCl concentration to avoid absorbing HCl from the gas and rather let it pass through where it can be captured as saleable acid in the absorber. A continuous blowdown stream 325 to a particulate recovery unit 350, or filter unit, can be used to control the solids and metal salt concentration in this circulating scrub liquid. This blowdown also serves to control the aqueous chemistry, limiting salt and metal concentrations to acceptable levels. Thus, a venturi scrubber also functions as a gas wash for removing contaminants due to its inherent gas-liquid contact. Again, both particulate and other trace gas species are removed to a certain extent. The venturi scrubber, coupled with the upstream weir quench, can optimally remove essentially all aqueous acid soluble impurities from a gas stream so that aqueous acid produced in a downstream absorber T-410 can each effectively meet the impurities limits of aqueous HCl specifications. Again, these impurities include primarily NH 3 , metal and metal salts. Greater than 99.5 percent of the HCl in raw syngas from a venturi can be absorbed in an HCl absorption tower, such as tower T-410 of Figure 4 A. Typically HCl might be approximately 25 percent of the inlet syngas gaseous stream 321, and can preferably be removed to roughly 0.05 percent in a syngas overhead product stream 418. After bulk removal of HCl in bottom liquid stream 410 in an absorber, the remaining syngas gaseous stream 418 can pass to a syngas finishing area for final removal of trace components to produce a saleable or useable product. Aqueous hydrogen chloride liquid stream 410 flows through an absorber bottoms cooler E-420 and preferably flows as stream 421 to an activated carbon bed system 450 (Figure 4B). A prefilter FL-450 for the carbon bed T-460 system may remove particulate matter which may have been captured in the acid through the absorber system. Carbon beds can serve as a guard against very small amounts of semivolatile and heavier organic compounds in the product acid. Organic species which might have broken through a reactor and into the absorber are adsorbed to the carbon surface, and thus removed from the acid stream. An after filter FL-460 can remove final traces of solids which may break through carbon bed discharge screens. Two carbon beds T-460, illustrated in Figure 4B, are preferably operated singly, with the second bed as a spare. Near the end of the carbon adsorption capacity they may be operated in series to fully expend the useful life of a "spent" bed. A bed can then be taken out of service for a new charge of activated carbon. The beds can also be operated in parallel if necessary due to high differential pressure. High differential pressure could be the result of temporary high flow conditions or from bed pluggage. Normal passage drop through a single bed might be approximately 0.7 bars (10 psi) at normal flowrates. Product acid stream 460, which is suitable for sales or other internal use HCl , can be stored in vat V-480. From there it can be pumped, as stream 481, to a site distribution header. Some degassing of an aqueous acid will occur in vat V-480. The drop in pressure to this atmospheric tank liberates noncondensibles absorbed from the syngas in the HCl absorber. These gases 482 can be vented to a vent blower knockout drum to be forwarded on to an Outside Block Limits vent treatment system. The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, and materials, as well as in the details of the illustrated system may be made without departing from the spirit of the invention. The invention is claimed using terminology that depends upon a historic presumption that recitation of a single element covers one or more such elements, recitation of two elements covers two or more such elements and so forth.

Claims: WHAT IS CLAIMED IS: 1. A method for producing high quality aqueous acid from a gasification process for halogenated materials, comprising: quenching a gaseous stream containing hydrogen halide from a reactor with a quench liquid to form a quenched gaseous stream; separating a gaseous stream containing hydrogen halide from the quenched gaseous stream to form a first washed gaseous stream; atomizing a scrubber liquid with the first washed gaseous stream to form an atomized gaseous stream; separating a gaseous stream containing hydrogen halide from the atomized gaseous stream to form a second washed gaseous stream; and absorbing hydrogen halide from at least a portion of the second washed gaseous stream into an aqueous solvent to produce a raw aqueous acid. 2. The method of claim 1 that includes filtering the raw aqueous acid through a carbon bed filter. 3. The method of claim 1 that includes separating at least a portion of the quench liquid from the quenched gaseous stream and recirculating at least a portion of the separated quench liquid to the quenching step. 4. The method of claim 1 that includes separating at least a portion of the scrubber liquid from the atomized gaseous stream and recirculating at least a portion of the separated scrubber liquid to the atomizing step. 5. The method of claim 1 wherein the first separating of a gaseous stream includes separating an overhead gas. 6. The method of claim 1 wherein quenching includes flowing the gaseous stream from a reactor through a weir quench structured to provide mixing and evaporative cooling of the gaseous stream. 7. The method of claim 1 wherein the atomizing is performed in a venturi device. 8. The method of claim 1 wherein the quench liquid includes a hydrogen halide solution. 9. The method of claim 1 wherein the scrubber liquid includes a hydrogen halide solution. 10. The method of claim 1 wherein the first separating of a gaseous stream takes place at a temperature of at least approximately 80°C and at a pressure of at least approximately 4 barg. 11. The method of claim 1 wherein the second separating of a gaseous stream takes place at a temperature of at least approximately 70°C and at a pressure of at least approximately 3.5 barg. 12. Apparatus for producing high quality aqueous acid from a gasification process for halogenated materials, comprising: a reactor in fluid communication with a source of halogenated materials and oxygen; a quench in fluid communication with a gaseous stream produced by the reactor; a drum in fluid communication with a gaseous stream produced by the quench; a venturi scrubber in fluid communication with a gaseous stream from top portions of the quench drum; a scrubber drum in fluid communication with an atomized gaseous stream produced by the venturi scrubber; and an absorber in fluid communication with a gaseous stream from a top portion of the scrubber drum. 13. The apparatus of claim 12 that includes a carbon bed filter in fluid communication with a bottoms liquid drawn from the absorber. 14. The apparatus of claim 12 that includes lines for recycling a bottoms liquid from the quench drum to the quench vessel. 15. The apparatus of claim 12 that includes lines for recycling bottoms liquid from the venturi scrubber drum to the venturi scrubber. 16. The apparatus of claim 12 wherein the quench is a weir quench.

Inventors: JEWELL DENNIS W, SALINAS LEOPOLDO III, SEIDEL KIMBERLY K, JEWELL, DENNIS, W., SALINAS, LEOPOLDO, III, SEIDEL, KIMBERLY, K.
Applicants: DOW CHEMICAL CO, JEWELL DENNIS W, SALINAS LEOPOLDO III, SEIDEL KIMBERLY K, JEWELL, DENNIS, W., SALINAS, LEOPOLDO, III, SEIDEL, KIMBERLY, K., THE DOW CHEMICAL COMPANY
Application year: 2001
Main classification: C01B7
IPC codes: C01B7