US 5,285,071 AGrant
Fluid Cell Substance Analysis and Calibration Methods
Issue Date:1994-02-08
•16 Claims
•10 Drawing Sheets
Abstract
A furnace with two hot zones holds multiple analysis tubes. Oxidized gases flow from outlets of the tubes to individual gas cells. The cells are sequentially aligned with an infrared detector, which senses the composition and quantities of the gas components. Each elongated cell is tapered inward toward the center from cell windows at the ends. Volume is reduced from a conventional cell, while permitting maximum interaction of gas with the light beam. Reduced volume and angulation of the cell inlets provide rapid purgings of the cell, providing shorter cycles between detections. For coal and other high molecular weight samples, from 50% to 100% oxygen is introduced to the tubes. Cells are suspended from adjustable holders on a frame which is spaced from a table. The table is moved by a linear motor and a fixed platen. Sides of the table are shielded to prevent electromagnetic and magnetic motor interference with detected results. The gas cells are calibrated for carbon dioxide and water vapor with a mass flow controlled oxidized fuel gas from a single analyzed source of such gas, oxygen and inert gas. Other calibration gases may be included, generated or added in the calibration gas stream.
Metadata
Inventor
- Robert B. LaCount
Application Information
Application Number:US 8495017
Filing Date:1992-03-11
Priority Date:1991-04-29
Art Unit:256
Classifications
IPC:
G01N 2101
Field of Search:
250343;344;345
Patent Drawings (10 sheets)
Description
This invention concerns high molecular weight substance analysis and gas analysis apparatus and methods.
A problem with coal analysis is that exothermic reactions obscure results. Mixing coal with tungsten trioxide as a diluent helps. Low oxygen levels help to retard the exothermic reactions.
Work by the inventor has been centered around a controlled oxidation of coal as the temperature was gradually increased. Six years of studies and over 220 experiments resulted in a method showing some resolution (qualitative analysis) of the sulfur dioxide evolution from coal (diluted with tungsten trioxide) during oxidation with slowly increasing temperature. The results looked promising enough to continue the work. A quantitative system was assembled and continues to function today after well over 500 Runs.
The system works well, but conditions were not good enough to resolve the sulfur dioxide resulting from the pyritic sulfur and the second occurrence of organic sulfur detected from coal. The pyritic sulfur was oxidized just before the higher temperature organic sulfur, and much of the peak overlapped with the organic sulfur peak. That seriously limited the usefulness of that instrument in characterizing the amounts of pyritic and organic sulfur in coal or in providing a potential one step analysis method of the organic, inorganic and total sulfur in coal. Attempts continued to improve the instrument and to find conditions to resolve the sulfur dioxide evolved from oxidation of pyrite and organic sulfur in coal. That finally led to an all out attempt to find better reaction conditions.
A need continues to exist for apparatus for a systematic analysis of coal, particularly for forms of its sulfur content, and to analyze other substances and particularly high molecular weight substances.
Existing gas analysis cells have large volumes. Consequently a large volume of gas must be flowed into and out of a cell before a new significant reading may be taken. Quantities of available gases make purging inconvenient, wasteful and time consuming.
A need exists for analysis cells which may be readily filled, read and purged.
Instrument calibration requires several steps. A need exists for rapid, accurate calibration.
Summary of the Invention
The present invention provides solutions to the long standing needs.
In the present invention, a furnace with two hot zones holds multiple analysis tubes. Each tube has a separable sample-packing section positioned in the first hot zone and a catalyst-packing section positioned in the second hot zone. A mass flow controller is connected to an inlet of each sample packing tube, and gas is supplied to the mass flow controller. Oxygen is supplied through a mass flow controller to each tube to either or both of an inlet of the first tube and an intermediate portion between the tube sections to intermingle with and oxidize the entrained gases evolved from the sample. Oxidation of those gases is completed in the catalyst in each second tube section. A thermocouple within the catalyst pack measures and/or controls the temperature of the second hot zone, which remains substantially fixed. A thermocouple within at least one of the sample packings measures and/or controls the uniform increase of temperature in the first hot zone, reducing the added heat immediately when an exothermic condition is sensed within the sample. Oxidized gases flow from outlets of the tubes to individual gas cells, and the gas flows through and out of the cells. The cells are sequentially periodically aligned with an infrared detector, which senses the composition and quantities of the gas components. Each elongated cell is tapered inward toward the center from cell windows at the end. Each cell contains a volume reduced from a conventional cell, while permitting maximum interaction of gas with the light beam. Reduced volume and angulation of the cell inlets provide rapid purgings of the cell, providing shorter cycles between detections. For coal and other high molecular weight samples, oxygen makes up from 50% to 100% of the gas introduced into the tubes.
This invention provides instruments and analysis equipment for a multi-sample by controlled-atmosphere programmed-temperature oxidation.
Before conception of the invention, a problem existed in determining whether sulfur was present in organic or inorganic compounds, for example in inorganic pyrite, which is iron disulfide. Exothermic reactions obscured results. The inventor experimented with gradually changing the oxygen concentration from 10% in argon to 16% in argon. A slight shift of the pyritic sulfur toward evolution at a higher temperature was noticed under those conditions. Continued increasing of the concentration to 20% and finally to 100% oxygen surprisingly improved results. The 100% oxygen experiment indicated that the pyritic sulfur evolution was moved to higher temperature and was evolved after the higher temperature organic sulfur peak, permitting both peaks to be resolved.
Further work showed that celite or other silica products such as silicic acid, silica gel, and synthetic silicas when used as diluents for the coal resulted in a more highly resolved pyrite evolution peak compared to tungsten trioxide, a previous diluent.
This invention provides use of the higher oxygen concentration ranges (50%-100%) and the use of tungsten trioxide, zirconium dioxide, silicon dioxide products, preferably celite, and other metal oxides as diluents. The invention also provides the use of metal oxides or other catalysts to oxidize organic compounds to oxides of carbon, hydrogen, sulfur and nitrogen. The metal oxides or other catalysts must not interact, absorb and re-emit, the oxide gases produced in the oxidation reaction.
The technique of the invention can be used to characterize coals, oilshales, carbon deposits on refinery and other catalysts, polymers, soils and other high molecular weight materials. In addition to the sulfur dioxide evolution profiles, the carbon dioxide, water, hydrogen chloride, and nitrogen dioxide profiles are obtained. This allows characterization of the carbon, sulfur, hydrogen, chloride and nitrogen in the material tested and analysis for those elements in the material.
The present invention is suited to resolve the gases evolved from the pyritic and the more oxidatively resistant organic sulfur in the material oxidized. The best conditions are produced in 100% oxygen with a silica product such as celite as a diluent for the material being oxidized. Preferably particle size of solids being oxidized and diluent are about -60 mesh or smaller. Preferably the diluent and the sample substance are well mixed and are uniformly distributed. However, high oxygen concentrations such as 50%-100% oxygen and other diluents such as silicic acid, silica gel, synthetic silicas, tungsten trioxide, zirconium dioxide, and other metal oxides may be used.
The technique is applicable to characterizing many substances, such as for example coals, treated coals, oil shales, polymers, carbon deposits on refinery and other catalysts, soils and other high molecular weight substances. The diluent or a screen may follow the sample. Preferably finely divided quartz wool previously heat treated at about 1100.degree. C. is positioned upstream and downstream of the sample to hold the sample in position. Preferably quartz rods held in place by quartz wool are inserted in any void in the sample and catalyst tubes to reduce internal volume and promote flow-through of the evolved gases.
The invention evolves a material from the sample and oxidizes the evolved material.
When run in the oxidation mode, most of the oxidation occurs in the sample. The second tube and the catalyst complete the oxidation and establish SO.sub.2 -SO.sub.3 equilibrium.
Characterizing the substances under the oxidizing conditions described above is one of the objects of the invention. The evolved gas concentration versus time and/or temperature profiles for carbon dioxide, sulfur dioxide, nitrogen dioxide, hydrogen chloirde, and water are unique. Additionally, analyses for the amount of carbon, sulfur, nitrogen, chloride, and hydrogen in the sample oxidized are obtained by calculations based on the evolved gases.
The instrument can also be used in a pyrolysis mode where an inert gas is passed through the sample and diluent (silica product and/or metal oxides) with gradually increasing temperature. Gases are evolved from the sample and are oxidized by oxygen supplied to the gas stream as it enters the second hot zone. The gases produced carbon dioxide, sulfur dioxide, nitrogen dioxide, hydrogen chloride, and water provide, after analysis, concentration versus time and/or temperature profiles for the pyrolysis gases produced from the substance being tested. Integrating the evolved gas profiles and relating them to the amount of carbon, hydrogen, sulfur, chloride, and nitrogen produced by pyrolysis with time data provides information similar to that of a thermal gravimetric analysis (TGA) experiment, in which samples are weighed as gases evolve. In addition, this provides information on the nature of the elemental composition of the volatile pyrolysis products.
A new multi-tube horizontal split combustion furnace made with two to six or more tubes has been designed and is incorporated into the system. A prototype version contains four combustion tubes and the temperature may be increased or ramped over a wide range of temperatures. However, 2.degree. C. to 10.degree. C., and preferably 3.degree. C. per minute are the preferred rates of increase. The furnace, mass flow controllers for the inlet gases, pressure transducers and regulation system, stepper motor for cell movement, and a number of relays and the whole system may be controlled from one or more micro computers.
The furnace includes a second hot zone with oxidizing tubes, after each of the combustion tubes, containing tungsten trioxide, zirconium dioxide, a metal, or other metal oxide catalysts, heated to approximately 1050.degree. C. The catalysts oxidize any gases that are not already in their highest oxidation state. Additionally, the second hot zone maximizes the sulfur dioxide concentration relative to sulfur trioxide. The second hot zone also assures a constant temperature for the emerging gas. The catalyst preferably does not interact, absorb or re-emit the evolved gases at different temperatures. The catalyst may absorb or emit the evolved gases at the same temperature.
Each combustion train in the new multi-tube furnace is fitted with an oxygen inlet between the two hot zones. That permits the system to be used in a pyrolysis mode, with an inert gas flowing through the system. The pyrolysis gases are all converted to oxides (carbon dioxide, nitrogen dioxide, sulfur dioxide, hydrogen chloride, and water) in the second hot zone. Quantitative pyrolysis experiments, as well as oxidation experiments, can be conducted in any one or all of the combustion trains. The analyses can be completed by analyzing products of the organic compounds and other gases after they pass through the second hot zone using tungsten trioxide, zirconium dioxide, or other metal or metal oxide as an oxidation catalyst. The use of the second hot zone to oxidize the pyrolysis gases simplifies quantitative analysis of the gaseous pyrolysis mixture.
The split tube design allows removal and repacking of the sample tubes. The second hot zone tube is for catalytic conversion and catalyst tubes do not have to be repacked each time a new sample is analyzed.
The thermocouples that control the furnace are located in or outside the combustion tubes and measuring thermocouples are embedded in the samples during the experiment. Employing a measuring thermocouple embedded in the samples ensures accurate sample temperature and controls furnace temperature. This thermocouple, when used as the control thermocouple, provides a more even temperature ramp. The thermocouple can sense an exotherm and call for reduced heating sooner than a thermocouple mounted externally on the combustion tube.
The gases pass through a newly designed gas flow cell for analysis by a fourier transform infrared (FTIR) spectrometer. The gas cell is designed to take full advantage of the elliptical, almost cone-shaped, infrared light beam produced by FTIR spectrometers. The cell contains approximately one-third less gas volume than a conventional cell, and at the same time produces an infrared spectrum of the same intensity as a conventional infrared gas analysis cell of the same length and diameter.
Since the cell contains one-third less volume than a conventional gas cell, the clearing time is about one-third shorter. The cell tapers inward from the ends to the middle. This design shows some interesting flow patterns which might cause the clearing time of the cell to vary as a function of the angle of a directed flow inlet gas stream. At certain inlet angles the cell clearing time is significantly less relative to a non-directed inlet flow. These same inlet angle experiments were also carried out on a non-tapered gas cell that was identical to the above cell, except for the taper and cell volume. The cell clearing time was again found to be a function of the angle of the inlet gas stream. Thus, the directed flow modification is an important feature that also can be incorporated into conventional gas cells.
The properties of smaller volume and shorter clearing time due to the smaller volume and the directed flow make the tapered cell desirable for a wide variety of infrared gas cell applications.
The cell body can be fabricated from glass, steel, or a variety of polymeric materials in any length that will fit in a FTIR cell compartment. Any type of infrared window material (NaCl, CaF.sub.2, KBr, BaF.sub.2, CsI, CsBr, KRS-5, ZnSe, AgCl, Intran-2 or fused silica) may be attached through any conventional state-of-the-art techniques, such as a screw cap with seals threaded onto glass, metal, or plastics or to plastic threaded material snapped around the cell; metal or plastic rims (one behind a flange on the cell) screwed together with the window and seals between the rims.
The cell inlet and outlet can be fitted with simple tubulations at angles from 0.degree. to 360.degree. relative a long axis of the cell for flow through applications. Tubulation on an inside of a cell inlet can be directed at the best angle to give minimum clearing time. Septa for injection of gases directly into the cell, stopcock closures, or different fittings attach a variety of plastic or metal tubing to the cell.
The cell can be heated by a simple heat tape, by a controlled, enclosed heater mounted as an integral part of the cell, or by a number of other state-of-the-art heating methods.
The cell can be fabricated for use at medium or high pressures.
"Beam conforming cells" have been designed for older infrared instruments in which the beam emerged from the instrument in a rectangular shape. However, those differ significantly from the functional shape of the present cell.
A multi-cell holder has been designed to position one of four gas cells in the spectrometer beam for analysis normally every 15 seconds. A longer or shorter analysis timing sequence may be used. A stepper motor with a worm drive train moves the cell holder plate on command from a timer or a computer command. The movable cell holder may be adapted to any infrared instrument currently manufactured.
A mass flow controlled gas mixture is introduced to the combustion tubes. The pressure in the system is measured with a pressure transducer. A pressure regulation system on this instrument is used to keep the pressure in each gas cell constant.
The information obtained from the new instrumental system includes pyrolysis data on the amount of carbon, hydrogen, sulfur, chloride, and nitrogen lost as the temperature of the sample is increased. That information is useful from the single or multi-tube furnace system. The evolved gas information is integrated to provide information similar to that obtained from thermal gravimetric analysis. In thermal gravimetric analysis (TGA) the sample is placed on a sensitive balance and is heated. The weight loss is measured as a function of temperature. In the present pyrolysis technique, the evolved gases are quantitatively measured and integrated over time to provide information on the amount of sample lost with time. The profiles resemble those produced in a TGA experiment, except that instead of mass the elemental composition of the carbon, hydrogen, nitrogen chloride, and sulfur lost by oxidation or pyrolysis is obtained.
A description of the present pyrolysis technique is a controlled-atmosphere programmed-temperature oxidation evolved gas analysis (CAPTO-EGA).
A preferred furnace has first and second hot zones. Multiple tubes extend between the first zone and the second zone. A catalyst is positioned in the tubes in the second zone. Sample-diluent mixtures are packed in parts of the tubes in the first zone. Gas flows into the inlets of the tubes in the first zone and flows through the samples, entraining pyrolysis gases from the samples. An oxygen source connected to the gas introduction means flows oxygen into the tubes for oxidizing the pyrolysis gases before and as the gases flow through the catalyst in the second hot zone. Outlets of the tubes are connected to gas analyzer cells for supplying oxidized pyrolysis gas to the cells, and exhaust lines connected to the cells for flowing gas out from the analysis cells.
A preferred gas supply is an oxygen source. A mass flow controller is connected to the oxygen source. A pressure transducer is connected between the mass flow controller and the tube for measuring pressure as the mass flow controller supplies oxygen to the inlet of a tube.
Plural mass flow controllers and plural transducers are each connected in parallel between an oxygen tank and distinct tubes.
Another embodiment has a source of inert gas and inert gas mass flow controllers connected to the inlets of the combustion tubes for supplying inert gas alone or in combination with oxygen to the combustion tubes.
Plural inert gas mass flow controllers are each connected in parallel between the source of inert gas and the inlets of the tubes.
Preferably the tubes are horizontal tubes, and the furnace is divided by a vertical wall into two heated zones.
In a preferred embodiment, an oxygen relay is connected to each mass flow controller and to an intermediate portion of a tube for supplying oxygen to an intermediate portion of the tube and to pyrolysis gases from the sample before the gases pass into the catalyst.
Preferably one relay is connected to each mass flow controller for receiving oxygen therefrom. A first oxygen supply line is connected between each relay and each pressure transducer connected to the inlet of each tube. A second supply line is connected between each relay and an intermediate portion of each tube for supplying oxygen to each tube between the sample and the catalyst.
Sample thermocouples extend through inlets of each tube into the sample packed in the tube for measuring and/or controlling furnace temperature in the first hot zone.
Catalyst thermocouples are inserted through outlets of the tubes into catalysts within the tubes for measuring and/or controlling temperature in the second hot zone of the furnace.
Plural cells are each connected to a tube extending from an outlet of the combustion tube.
In a preferred form of the invention, the gas analyzer cells are aligned parallel and are mounted on a table. A motor moves the table transversely. An infrared light beam source projects an infrared light beam through the cells. A detector aligned with the source on an opposite side of the table receives light projected through the cells. The motor moves each cell into alignment and out of alignment with the infrared light beam in a predetermined sequential relationship.
Each cell has a tapered body which is relatively wide at the top, relatively narrow in the middle, and relatively wide at the bottom. A cell window forms the top of the cell, and a second cell window forms a bottom of the cell. A cell inlet is connected to a wall of the cell near the upper cell window, and a cell outlet is connected to a wall of the cell near the lower cell window. The inlet and outlet are directly across from one another or any angle to each other.
The tapered cell body is preferably a truncated, generally conical upper cell wall and a truncated, generally conical lower cell wall joined medially in a small waist portion.
The preferred gas inlet is a tube which extends through the upper cell wall at an angle of from about 0.degree. to about 30.degree. from the cell window. Preferably the inlet has an open end which points upwardly or toward the near end of the cell at about 0.degree. to 60.degree. to a vertical direction. An angle of up to about 90.degree. is useful; about 0.degree. to 30.degree. is preferred.
The inlet tube is aligned with the cell wall between a tangential and a radial position for swirling and purging gas from within the cell.
Gas is flowed angularly into a top of a cell and downward through a converging upper portion of the cell, and subsequently downward through a diverging lower portion of the cell and out through the cell outlet at the bottom of the cell.
In a preferred embodiment, the combustion tubes have removable first combustion sections which separate from the second catalyst sections. The combustion sections may be withdrawn and repacked with sample material.
The preferred method of quantitatively analyzing multiple samples includes packing samples in first tube sections and packing a catalyst in second tube sections. The first and second tube sections are placed in horizontal communicating alignment in a furnace having a first hot zone which receives the first tube sections, and a second hot zone which receives the second tube sections. The first hot zone is heated with a gradually increasing temperature, and heating the second hot zone is held at a constant elevated temperature. Gas is introduced into an inlet of each tube. Preferably the gas contains at least 50% oxygen. Heated resultant pyrolysis gases from the sample are entrained within the first tube section, while partially oxidizing the entrained gases. Oxygen may be supplied to the tubes between the sample and catalyst and mixing oxygen with the entrained pyrolysis gases, the gases are heated and oxidized in the heated catalyst within the second tube sections, completing oxidation of the gases. Gases flow out of outlets of the second tube sections and into inlets in plural gas cells connected separately to the outlets of the second catalyst-holding tube sections. Gas flows through the gas cells and is released gas from the gas cells under pressure regulation. The cells are selectively moved into alignment with an infrared beam, and influence on the infrared beam by gas within the cells is sensed with an electronic detector. Other detectors may be used, for example a Raman spectrograph. Non dispersive infrared detectors, mass spectrometry or gas chromatography may be used in lieu of the gas cell analysis for the detection of products. Temperature within the first hot zone is raised at a slow rate of increase, and sequentially positioning the cells within the infrared light beam and detector during the increase in temperature in the first hot zone determines oxidized pyrolysis gases released from the samples and entrained and oxidized, and thereby determines content of the sample.
Preferably the increasing temperature in the first hot zone comprises increasing temperature at a rate of about 2.degree. C. to 10.degree. C. or about 3.degree. C. per minute, while supplying an inert gas with the oxygen to an inlet of each first tube. The rate is chosen so that the products are released at different times and so that exothermic reactions are controlled or avoided.
Cells are preferably suspended from adjustable elements on a frame connected to a table which is moved by a self-contained shielded linear motor.
Calibration is provided by releasing an analyzed mixture of a hydrocarbon fuel gas, oxygen and an inert gas, completely oxidizing the mixture in a heated catalyst and using mass flow controlled resultant gases.
These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings.
Brief Description of the Drawings
FIG. 1 is an overall system schematic drawing.
FIG. 2 shows a preferred gas cell.
FIG. 3 shows further details of a preferred gas cell.
FIG. 4 is a top view of a preferred furnace.
FIG. 5 is a front elevation of the furnace shown in FIG. 4.
FIG. 6 is a side elevation of the furnace shown in FIGS. 4 and 5.
FIG. 7 is a perspective view of one furnace section.
FIG. 8 is an end elevation of an end fitting used to hold tube sections in the furnace.
FIG. 9 is a cross-sectional elevation of the end fitting shown in FIG. 8.
FIG. 10 is a detail of the end fitting shown in FIG. 8.
FIG. 11 is a detail of a tube interconnection fitting.
FIG. 12 is a detail of the fitting shown in FIG. 11.
FIG. 13 is a graph of SO.sub.2 peaks produced from 10% O.sub.2 experiments .
FIG. 14 is a graph of SO.sub.2 peaks from 100% O.sub.2.
FIG. 15 is a schematic perspective view of a cell positioning table and alignment mechanism.
FIG. 16 is a detail of a cell end mounting.
FIG. 17 is a perspective schematic representation of a liquid cell on a movable tube.
FIG. 18 is a perspective schematic representation of a turret cell positioning device.
Detailed Description of the Drawings
Referring to FIG. 1, a sample analysis system of the present invention is generally referred to by the numeral 1. The system has a furnace 3, which holds horizontal tubes 5, in this case four. The furnace is divided into two hot zones 7 and 9. Tubes 5 are divided into sections 11 and 13. First sections 11 hold a sample 15. Second sections 13 hold a catalyst 17. The hot zones are divided by an insulated wall 19, which includes plural tube connectors 21, as will later be described. Each tube section 11 has an inlet 23, on which is provided a gas supply connector 25. Gas is supplied through separate supply tubes 27 and/or oxygen is supplied through supply tubes 29 to separate inlets 23 of the tubes.
When an inert gas is used, an inert gas such as argon from a source 31 is supplied on line 33, which is connected to individual mass flow controllers 35, each of which is connected to a line 27, and each line 27 is connected to one inlet 23 of a sample tube 11. When oxygen is used to the exclusion of, or in addition to, the inert gas, oxygen is supplied from a source 37 through individual mass flow controllers 39 to the oxygen supply line 29 and the input connection 25 on the inlet 23 of each of the sample tubes.
All or part of the oxygen may be supplied through a relay 31 to a supply line 33, which is connected to an individual supply port 35 between the tubes. In a preferred embodiment, all oxygen is introduced either through the inlets 25 or through the supply ports 35. Oxygen is intermingled with evolved and entrained gases 37, and the oxygen 39 fully oxidizes the entrained pyrolysis or partially oxidized gaseous products 37 in the catalyst 17 within each tube. The oxidized gases flow out through the outlet 41 of each tube 5, and through a conduit 43 to an inlet 45 of a gas cell. The gases then flow out through an outlet 47 to an exhaust 49.
As shown in FIG. 2, each cell 51 has tapered upper and lower body portions 53, which taper uniformly inward from the cell windows 55 and 57 to a narrow central throat portion 59.
Because the cell is tapered, it reduces volume while still allowing maximum interaction of gas with the light beam within the cell.
As shown in FIG. 1, each cell 51 is mounted on a movable table 61, which is driven by a motor 63 to position each cell sequentially and at timed intervals in alignment with an infrared light beam schematically indicated at 67. A spectrograph receiver schematically shown at 65 receives the light which interacts with the gas within the cell 51 and indicates the gas content and quantities of gas within the cell. The preferred form of a gas detector is a Fourier transform infrared detector (FTIR), of which the electronics and the interferometer are generally indicated in the box 66 attached to the light beam source 67 and the detector 65.
The entire table 61 is enclosed in a heated compartment 69 to maintain the cells at constant temperature.
In a preferred embodiment of the invention, a thermocouple 71 is embedded centrally in the sample 15 to measure and/or control heat in zone 1 through a processor 73. Heat in the first hot zone 7 is reduced, for example, when thermocouple 71 senses an exothermic reaction within the sample. The processor programs and controls heat in the first and second hot zones 7 and 9, and receives information from the thermocouple 75 which is mounted in each catalyst pack. The processor also controls the mass flow controllers 35 and 39 and relay 31, and receives inputs from pressure transducer 76, which is connected to the gas inlet 26. Processor 73 also receives information from pressure transducer 78 and controls pressure regulation valve 79. The processor also controls the timing and operation of motor 63, which moves the cells into and out of alignment with the FTIR detector.
As shown in FIG. 3, the narrow waist 59 of tube 51 supported by glass rods 81, which may be attached to the walls of the upper and lower sections 53.
The sodium chloride, zinc selenide or calcium fluoride windows 55 and 57 are bonded to the two bodies or are attached by brackets, which are not shown. O-rings 83 seal the cell ends in the enclosure.
Inlets and outlets may be formed as tubes extending from the cells. As shown, inlet 45 and outlet 47 are made of similar structures. A 5/16" or other hole is made in the end of each section 53. A base 85 is bonded in the opening, and a male connector 87 extends outward therefrom. A 1/8" tube 89 is inserted through a 1/8" O-ring, and a cap 91 is threaded onto the connector 87. Glass tabulations extending from the cells may also be used as inlets and outlets.
In a preferred form of the furnace 3, as shown in FIGS. 4-7, a base 93 forms a support for the furnace. The furnace is formed with separate sections 7 and 9, which are separately heated by heaters 95 and 97.
The furnace sections have identical construction. Each has a box 101 covered by a cover 103, which is held tight by clamps 105. Handles 107 are used to lift the cover around hinges 109. Lower heaters 99 are identical to the upper heaters. The sections 7 and 9 are separated by bracket 115, which supports a central tube connector 117 with an oxygen fitting 119. Tubes are removable from the furnace sections by opening the covers 103 and pulling the T-handles 121 or a lever attached and releasing the tubes, whereupon tube sections such as sample tube sections 11 may be removed and replaced.
FIG. 6 shows the side elevation of the furnace box 101 with openings 123 for receiving the tubes, and internal small openings 125 which extend through the central mounts 117. The bases 93 are shown as identical brackets connected to the lower furnace boxes by thumb screws 127.
As shown in the details of FIGS. 8, 9 and 10, the identical end brackets 111 and 113 are formed with rectangular support bodies 131, having drilled and tapped openings 133 for mounting the bases 135 of the blocks 131 on the cantilevered supports 109 shown in FIG. 5.
The blocks have bores 137 which receive springs 139 and sliding barrels 141. A retainer 143 traps spring 139 in the bore 137. A fitting 145 prevents movement of the barrel 141 outward from the bore. The barrel is supplied with a T-handle 121, or attached lever which is connected to shaft 147. Shaft 147 is connected by threads 148 to an end of the barrel 141. A lock nut 149 threaded on the shaft 147 secures the shaft-barrel connection. Gas tube 151 has a threaded connection 153 with the barrel. An opening 155 in tube 151 communicates with the lumen 157 of the sliding barrel 141.
As shown in FIG. 9 and the detail in FIG. 10, each table 141 has a tube end receiver 161 with a chamfered opening 163 leading to a cylindrical wall 165 to receive a tube end in a slip-fit. A compressible neoprene or other suitable material O-ring 167 rests against radial wall 169 to seal the end of an inserted tube against the wall. To remove or insert a tube, handle 121 or attached lever is grasped and pulled, pulling shaft 147 and barrel 141 to the left, as shown in FIG. 9, whereupon the tube end 23 or 41 may be slid outward from the cylindrical wall 165.
As shown in FIG. 11, the central fitting 117 has opposite tube end receivers 161, which is shown in FIG. 12 to be similar to the receiver 161 shown in FIG. 10. The fitting 117 has two drilled and tapped bolt-receiving openings 133 for attaching the fitting. Oxygen-admitting channel 171 connects with opening 125, which passes between receivers 161 to admit oxygen to the gas flowing through opening 125.
In a preferred embodiment of the invention, the furnace is made of stainless steel sheet material lined with high temperature insulation. The tubes are stainless steel tubes, or more desirably, heat resistant glass, ceramic, or quartz tubes.
The preferred gas cell is made of stainless steel or, more desirably, heat-resistant glass, polymeric materials, quartz or ceramic. A preferred cell is about 18 or 20 cm long and has internal diameters of about 25 mm at the ends and 8 mm at the center.
A metal deposited upon the internal walls of the tapered gas cell body makes these surfaces highly reflective and increases the signal sent to the FTIR detector through an empty gas cell compared to the signal obtained through a gas cell without metal disposition on the internal cell walls.
The effect may be maximized (maximum reflective interaction of the infrared light beam through the gases being analyzed) by positioning a tapered gas cell, which is already aligned in the infrared beam, at a certain point between the entrance and exit windows of the infrared instrument cell compartment, or by slightly misaligning the cell and beam to promote reflection. The effect provides an increase in the interaction of the infrared light beam with a given concentration of gas, and should be of general utility as a gas cell for detecting somewhat lower concentrations of gases compared to a tapered gas cell without metal deposition on the internal cell walls.
FIG. 13 shows the sulfur dioxide evolution profile resulting from a coal sample thoroughly mixed with tungsten trioxide as diluent and oxidized under the previous TODS conditions of about 100 ml/min. of 10% oxygen in Argon and a linear increase in temperature of 3.degree. C./min. Note that the peak produced from pyrite in the coal appears between the two major peaks produced from the organic sulfur in the coal and is not well resolved from either peak.
FIG. 14 shows the sulfur dioxide evolution profile resulting from a coal sample thoroughly mixed with celite and oxidized with about 100 ml/min. of 100% oxygen and a linear increase in temperature of 3.degree. C./min. Note that the peak produced from pyrite in the coal appears after the second major peak produced from organic sulfur in coal. Also note that the separation between the pyritic peak and the peak resulting from the second major occurrence of organic sulfur in coal are significantly improved, permitting quantitative estimation of the various types of sulfur in coal.
Table 1 shows sulfur dioxide evolution peaks observed from coal and other substances to a specific structural feature.
Example 1
A finely divided, dry, representative sample (50-200 mg with a particle size of -60 Mesh or smaller) is weighed and thoroughly dispersed in approximately 0.6 g of celite and redried for one hour in vacuum at 105.degree. C. The samples are positioned in the combustion tubes between small wads of quartz wool that has been heat treated at 1100.degree. C. for one hour. Any voids in the combustion or catalyst tubes are reduced by positioning quartz rods in the tubes. These rods are also held in place using heat treated quartz wool. The tubes are positioned horizontally in the furnace and measuring and/or control thermocouples are embedded into the sample and catalyst pack. A flow of approximately 100 ml/min. of 100% oxygen is directed through each tube in the first hot zone of the furnace and the FTIR, cell positioner, and data system are set up for data collection. The temperature of the second tube containing the catalyst is quickly raised to at least 1050.degree. C. A linear temperature ramp of 3.degree. C./min. is established in the first hot zone and data collection is initiated. The run is allowed to continue for approximately 5.5 hours until a temperature of at least 1050.degree. C. is obtained. All calculations and graphic hardcopy are completed using the FTIR data system and printer/plotter. Each of the sample tubes in the first hot zone can be used as described above, or any one or more can be used simultaneously to analyze in the pyrolysis mode described below. Any tube in the first and second furnace hot zones can be ramped with a similar or different temperature program. Additionally, the gas flow and pressure control for any of the four sample trains can be the same or dissimilar. The complete operation of the system, including temperature control and monitoring, gas flow, pressure control and monitoring, gas cell positioning unit, and data acquisition, may be under the control of one or more microcomputers.
Example 2
Sample preparation, dilution with celite, and insertion into the combustion tube is completed as described above. Alternatively, for pyrolysis studies the undiluted sample can be placed in a small ceramic, quartz, or metal boat and inserted into the combustion tube. The thermocouple is positioned close to the sample as the combustion tube is inserted into the furnace. The second tube containing the catalyst is positioned in the second hot zone and the temperature raised quickly to at least 1050.degree. C. An inert gas flow, normally 50 ml/min. of Argon or helium, is established in the tubes in the first furnace hot zone and normally, a flow of 50 ml/min. of oxygen is established at the inlet of the second tube to continuously oxidize material lost from the sample as the first tube is exposed to a linear temperature increase, normally of 2.degree.-10.degree. C./min. The data system and gas cell positioner are powered up and the temperature ramp and data collection are initiated. A run is allowed to continue for approximately 5.5 hours until a temperature of 1050.degree. C. is attained (temperature ramp and final temperature required varies with the sample and may be shorter or longer).
A nonvolatile residue may remain in the first hot zone after the highest pyrolysis temperature desired has been attained. The system may be used in the oxidative mode described above to obtain further characterization of any residue. The furnace may be cooled to room temperature and the same sample tube exposed to an oxygen flow (100 ml/min.) directed into the first furnace hot zone as the temperature is increased in a linear ramp of 2.degree.-10.degree. C./min. or more, depending on the amount and type of residue remaining. The gas cells, cell positioner, and data system are all used as described above to complete the characterization of the residue.
The preferred cell positioning device used to move the cell is of general applicability. Multiple cell applications using cell movement devices are common for ultraviolet-visible spectrometers but have never, as far as is known, been applied to infrared spectrometers, due to interferences and vibration. Multiple cell applications for infrared spectrometers center around use of mirrors to move the light through several stationary cells.
The movement device described above uses a stepping motor driven linear or rail screw positioning table. The preferred embodiment uses a commercially available linear motor to move the cells. The movement is the same. The inventors have adapted the linear motor used to move the cells by adding metal shielding to eliminate electromagnetic and magnetic interferences to the spectrometer detector and have reduced vibration by mounting the movement device about 1/16" above the cell compartment so that it does not physically touch the spectrometer. That produces a small, neat package, with the movement mechanism motor and table all being in the cell compartment. The motor for the first linear or rail screw positioning table hangs off the back of the cell compartment. That was somewhat more bulky. However, since the motor was out of the cell compartment it did not have to be shielded. Either or both the linear or rail screw positioning table and the linear motor may be used in a final product.
The cells and cell movement devices work well and may be applied to liquid flow systems as well as to gas flow cell systems. One simply installs conventional or customized liquid flow cells on the table and uses the table and control to operate the system in conjunction with the infrared spectrometer.
This invention provides the new multiple sample furnace, the new cell compartment and the new directed flow, hour glass, gas cell and analytical results based on use of the cell.
The present invention also achieves a better calibration method for water vapor in a gas stream. Normally, one bubbles a gas through water or several different salt/water mixtures if several different concentrations of water vapor are needed. One must set up several bubblers in series to make sure the gas is saturated with water vapor. That method has been used over the years. However, it is time consuming and cumbersome. The present invention uses a gas cylinder containing analyzed mixtures of butane and oxygen in an inert gas such as Argon. Other hydrocarbons such as methane, ethane and propane may be used. The mass flow controlled gas stream is passed through an oven containing an oxidation catalyst, converting the butane quantitatively to carbon dioxide and water. These gases are led directly to the gas cells and serve as a simple, rapid, convenient route to calibrate for both carbon dioxide and water. That allows all of the calibration gases and/or calibration gas precursors to be placed in one cylinder. Water could not have been mixed with sulfur dioxide or nitrogen dioxide in one cylinder, due to reactions between the components in the cylinder. However, hydrocarbons such as butane are compatible with sulphur dioxide and nitrogen dioxide in one cylinder.
One embodiment of the present invention provides multiple sample characterization of coals by controlled-atmosphere programmed-temperature oxidation (CAPTO).
The invention provides the characterization of coals and other high-melting organic solids by use of a new CAPTO apparatus designed for simultaneous analyses of multiple samples. Diluted samples of coals and other high-melting organic solids are subjected simultaneously to an oxidative treatment and a linear increase in temperature and evolve combustion gases intermittently as a function of temperature. For example, distinctive sulfur dioxide evolution patterns are observed among coals of different rank and between raw and treated coals. Plots of concentration vs temperature as well as the total carbon, hydrogen, sulfur, and nitrogen content may be obtained for a number of examples and may be compared to values obtained using ASTM methods.
The new system uses a quad-bore split tube furnace design permitting simultaneous analysis of up to four samples. Each of four first and second hot zones are capable of being heated independently. Temperature ramp, gas flow, and system pressure are all controlled. Software control may be used. A PC-controlled FTIR equipped with multiple gas cells and cell positioner is used as the detector for the system. The instrument is designed for use in an oxidative mode, pyrolysis mode, or any inert gas/oxygen combination.
The gas generating and furnace side may be controlled by a computer system design for a controlled-atmosphere programmed-temperature oxidation (CAPTO) apparatus used in coal characterization.
Current PC software and the hardware interfaces are available for control of a CAPTO apparatus capable of simultaneous analysis of multiple coal samples.
The apparatus includes furnaces with eight independently controlled hot zones. Temperature ramp, gas valves, gas pressure and flow may all be under software control.
The detector is a PC-controlled FTIR spectrometer equipped with multiple gas cells on a stepper-motor positioning table. The apparatus utilizes one direct memory access (DMA) channel, 10 PID control loops, one serial channel, 48 analog and 21 digital input/output lines. A first phase involved installation of a 486 PC-controlled FTIR. Custom application software runs within LabCalc (Galactic Industries, Salem, N.H.), and controls acquisition of spectra over time and temperature. Upon installation of new furnaces and related sensors and controllers, a second 486 PC was used, running custom application software within VIEWDAC (Keithley Asyst, Rochester, N.Y.). A final phase controls the entire apparatus from a single PC.
The invention provides a multiple-cell design for the rapid analysis of several gas steams by fourier-transform infrared spectrometry.
The gas flow cell configuration achieves rapid, simultaneous analysis of multiple gas streams produced from controlled-atmosphere programmed-temperature oxidation (CAPTO). Resolution and quantitative analysis with CAPTO as detected by evolved gases is enhanced by relatively slow rates of temperature increase. Sample throughput for CAPTO can be improved by oxidizing several separate samples simultaneously and monitoring each experiment individually.
A multiple furnace configuration incorporates multiple gas flow cells and a linear positioning device to carry out sequential interrogation of several separate gas streams using a single FTIR spectrometer. The individual gas cells have reduced volume compared to conventional cells of the same overall length and width. Cell clearing time is improved by a combination of beam-conforming envelope and directed gas inlet flow. The use of front surface metal coatings provides for increasing radiant power. The mounted gas cells are positioned in the FTIR sample compartment by a single x or y axis or turret positioning device under computer control. Cell mountings and operational approaches were developed to maintain long-term positional stability (repeatability) and sensitivity. All parameters were compared to a single cell system and results indicate the performance (along with the compact size, and ease of implementation) make the invention preferable to other multiplexing approaches. The invention is widely applicable.
FIG. 15 shows a cell 51 suspended from an adjustment frame 175 with openings 177 for holding several cells. The frame has a rectangular top 179 supported on legs 181 above table 183.
As shown in detail in FIG. 15 and 16, y axis adjustment is provided by threaded rods 185 and wing nuts 187. Rods 185 are welded to upper halves 189 of externally threaded split rings 191. Ends of cells 51 are inserted in the split rings and threaded nuts 193 clamp the rings on the cell ends. Turning wing nuts 187 control y axis adjustment to align the cells between an infrared source and a detector.
Parallel threaded rods 195 are held above the frame top 179 on supports 197. Slides 199 with clevises 201 at the bottoms 203 and top 205 provide adjustment in the x axis. Thumb wheels 207 in the top clevises move the suspenders which comprise the slides and the rods 185 along the openings 177 to adjust the cells in the x direction.
A linear motor 209 beneath the table 183 cooperates with fixed motor platen 211 to smoothly slide the table to sequentially align the cells with the infrared source and detector. Shields 213 along the sides of the table prevent stray electromagnetic radiation and magnetic fields from reaching the detector.
Table 183 may be replaced by a barrel-shaped turret with cells 51 cylindrically aligned for sequential positioning between the source and detector.
FIG. 17 shows one of a number of liquid cells 215 with a liquid inlet 217 and an outlet 219 mounted on the table in place of the gas cells. A cell holder 221 is fixed to the table with adjustable connectors through openings 223. Blocks 225 mounted on a centrally slotted vertical portion of holder 221 adjustably receive a centrally open cell mount 227 on which the cell is fixed. The linear motor moves the liquid cells to sequentially align the cells and the thin liquid films therein with the IR source and the detector.
The cells are made of thin IR transparent materials. Shielding 213 isolates electromagnetic and magnetic fields from the detector.
FIG. 18 shows a preferred turret. Bearing blocks 229 are mounted at ends of a fixed table 231. Rotary holders 233 are mounted on axles 235. Ends of cells 51 are mounted in openings 237. A shielded stepper motor 239 drives one or both rotary holders 233 to sequentially align a cell 51 with an infrared light beam 241 and a detector 243. The apparatus is enclosed within a cell compartment 245.
The positioning table may be used with liquid cells for analytical testing of liquids. In that case, thin film liquid cells are plates along which thin films of liquid flow or which are coated by the liquid to be tested. The plates are suspended from a frame mounted above a table. The plates are moved in x and y axis for alignment by threaded rods, thumb wheels and wing nuts. Once aligned, the plate-like cells are moved sequentially into alignment with the source and detector by a linear motor mounted in the table.
The preferred method of calibrating for carbon dioxide and water includes oxidizing fuel gas in a mass flow controlled relationship and flowing the resultant carbon dioxide, water vapor and inert gas to the device being calibrated. One preferred method uses an analyzed mixture of oxygen, an inert gas and a substance containing carbon and hydrogen with or without other elements and oxidizes the substance, using the resultant gases and water vapor as calibration standards.
For example an analyzed mixture of a fuel gas such as butane, oxygen, sulphur dioxide and nitrogen dioxide and an inert gas such as argon can be used from one cylinder to provide a standard calibration mixture for carbon dioxide, water vapor, sulphur dioxide and nitrogen dioxide. Another example uses methylamine, oxygen and an inert gas such as argon as the source of calibration gases of carbon dioxide, water vapor, and nitrogen dioxide in an argon/oxygen mixture.
While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.
Claims
I claim:
1. Gas test cell apparatus comprising plural cells, each connectable to a gas conduit, a frame for mounting the cells, a table for supporting the frame, slides connected to the frame and rods connected to the slides, wherein the cells are aligned parallel to each other and are mounted in holders connected to the rods, a motor mounted within the table and a platen along the table for moving the table transversely, and sequentially aligning the cells with an infrared light beam source for projecting an energy beam through the cells, and a detector aligned with the source for receiving light projected from the source through the cells, the motor and platen cooperating for moving the table and frame and moving each cell into alignment and out of alignment with the infrared light beam source.
2. The apparatus of claim 1, wherein the frame comprises a rectangular frame having parallel spaced elongated openings on parallel sides of the frame, wherein the rods project through the openings and through the slides which are mounted on top of the openings.
3. The apparatus of claim 2, wherein the rods are threaded and wing nuts are connected to the rods for adjusting the position of the rods in the slides.
4. The apparatus of claim 3, further comprising fixed parallel thread rods connected to the frame, and thumb wheels mounted on the fixed rods and connected to the slides for moving the slides along the openings for adjusting the position of the slides and cells with respect to the frame.
5. The apparatus of claim 4, wherein the cells are elongated and the holders comprise split rings having external threads and threaded nuts, the split rings surrounding ends of the cells and the threaded nuts enclosing the split rings and anchoring the cell ends in the split rings.
6. The apparatus of claim 1, further comprising electromagnetic and magnetic shielding positioned along the table for shielding the detector from electromagnetic and magnetic fields created by the motor.
7. A fluid analyzing apparatus comprising a table, a frame connected to the table, suspenders connected to the frame and holders connected to the suspenders for mounting plural fluid cells aligned parallel and spaced from the table, a motor and a fixed platen for moving the table transversely, an infrared light beam source for projecting an infrared light beam through the cells, and a detector aligned with the source for receiving light projected through the cells, the motor and platen cooperating for moving each cell into alignment and out of alignment with the infrared light beam source and detector.
8. The apparatus of claim 7, wherein the supsenders comprise rods and slides.
9. The apparatus of claim 8, wherein the frame comprises a rectangular frame having parallel spaced elongated openings on parallel sides of the frame, wherein the rods project through the openings and through the slides which are mounted on top of the openings.
10. The apparatus of claim 9, wherein the rods are threaded and wing nuts are connected to the rods for adjusting the position of the rods in the slides.
11. The apparatus of claim 8, further comprising fixed parallel thread rods connected to the frame, and thumb wheels mounted on the fixed rods and connected to the slides for moving the slides along the openings for adjusting the position of the slides and cells with respect to the frame.
12. The apparatus of claim 8, wherein the cells are elongated, and the holders comprise split rings having external threads and threaded nuts, the split rings connected to the rods and surrounding ends of the cells and the threaded nuts enclosing the split rings and anchoring the cell ends in the split rings.
13. The apparatus of claim 8, further comprising electromagnetic and magnetic shielding positioned along the table for shielding the detector from electromagnetic and magnetic fields created by the motor.
14. A fluid analyzing apparatus comprising a table, first and second bearing blocks mounted on the table, axles mounted on the bearing blocks, rotary holders mounted on the axles, the holders having circular openings extending through the holders parallel to the axles at spaced intervals in the holders, plural elongated cells, each having spaced first and second ends, the first ends of the cells being mounted in the openings in the first holder, and the second ends of the cells being mounted in the openings of the second holder, a stepping motor mounted on the table and connected to at least one of the holders for rotating the holders and cells in steps, an infrared light beam source for projecting an infrared light beam into a first end of one cell, a detector aligned with the second end of said one cell for receiving light projected from the source through the said one cell, the motor and holders cooperating for moving each cell successively into alignment and out of alignment with the infrared light beam source and detector.
15. The apparatus of claim 14, wherein the cells are arranged in a circle.
16. A fluid analyzing apparatus comprising a table, holders adjustably connected to the table for mounting plural fluid cells, wherein the fluid cells are aligned parallel to each other and spaced from the table, a motor connected to the table and cooperating with a fixed platen for moving the cells on the table sequentially into alignment with an infrared light beam source for projecting an infrared light beam sequentially through the cells, and a detector aligned with the source for receiving light sequentially projected through the cells, the motor and platen cooperating for moving each cell into alignment and out of alignment with the infrared light beam source and detector.
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