Rotary dosing device

A rotary dosing device for use in analytical instrumentation quickly transfers a sequence of precise molar quantities of gas from a primary stream into a secondary stream. The device has a rotating chamber with dosing ports that cycle through three states: fill, equilibrate, and transfer. The device cycles in an overlapping manner such that as one dose volume fills with gas from the primary stream, another equilibrates at a known pressure and temperature, and another transfers its contents to the secondary stream. The device initiates its operation so that the first transfer in a sequence is a properly filled and equilibrated dose from the primary stream. Rather than cycling a single dose volume through the three states multiple times, the overlapping operation of the rotary doser enables multiple precise molar quantities of gas to be transferred in one-third the time.

BACKGROUND OF THE INVENTION

The present invention relates to a dosing device for transferring precise molar quantities of gas and particularly a dosing device for use in an elemental analyzer.

The determination of elements, such as carbon, hydrogen, and nitrogen, in an organic material is desirable for numerous reasons. In recent years, the food market has become interested in determining the amount of protein in a sample, which can be determined by the nitrogen content. Thus, the determination of nitrogen is important in providing useful information to the nutritional market. The carbon-to-hydrogen ratio is desirable in the characterization of coal and coke samples, as are the carbon, hydrogen, and nitrogen ratios in a variety of other organic materials. Thus, elemental analyzers have been in use for these and other applications for some time.

In present elemental analyzers, a combustion or reduction furnace may be provided for combusting or reducing a sample material such that the combustion gases produced thereby may be analyzed. One such analyzer system is described in U.S. Pat. No. 7,070,738, assigned to the present assignee, the disclosure of which is incorporated herein by reference. U.S. Pat. Nos. 7,497,991; 4,622,009; 6,291,802; and 6,270,727 also disclose components of a combustion system. The disclosures of the '991, '009, '802, and '727 patents are also incorporated herein by reference.

Dosing devices have been used in more than one application. In one application, a gas doser is used to transfer a precise quantity of a known calibrant from a primary stream to a secondary stream as part of the calibration of a detection system in the secondary stream. Some designs have a single dose size for one-point calibration; others have two or more dose sizes for multi-point calibration.

In another application, the primary gas consists of at least a portion of the combustion gases evolving from the burn of a sample; gases that have been collected and equilibrated using a molar transfer device. The dosing device transfers a small representative aliquot from the primary gas stream to the secondary stream for further processing and analysis. Reagents in the secondary stream are consumed by processing the aliquot, so the dose size is made as small as possible to minimize the cost of analysis. However, the dose must be large enough for the instrument to achieve the specified detection limits for the most demanding applications. There may be one or more dose sizes so that the operator can select the size most suitable to the analysis needs. In one instrument having two dose sizes, the ratio of the two dose volumes is about 3:1, and the two doses transfer approximately 1/500 and 1/1500 the volume gas collected in the primary stream.

Dosing devices that transfer a repeatable quantity of gas from a primary stream into a secondary stream are common. The device is placed in a constant temperature environment, or a means is provided to accurately measure the device temperature. A valving means cycles a dose volume typically through three states: fill, equilibrate, and transfer. The equilibration state is important as it allows the primary gas contained in the fixed volume to stabilize at a desired temperature and pressure. By knowing the doser volume, temperature, and pressure the precise molar quantity of gas is known. If two or more dose volumes are used, additional valving means is necessary to select between the dose sizes.

For high precision dosing, the valving paths must have low dead-volumes, and the device should actuate multiple valves simultaneously. If two-way valves are used to accomplish the transfer of gas, a bank of eight such valves is needed and there would likely be substantial dead volume. Alternately, four three-way valves can provide the same operation with lower dead volume but require an additional two-way valve to disable the primary stream for equilibration. If multiple dose sizes exist, only one dose volume is used at any time.

One such design uses a stem valve whose construction essentially has multiple three-way valves situated on the same stem. The stem is moved between two positions actuating all valves simultaneously between two states: fill and transfer. For two dose sizes, another similar stem valve is used to select one or the other. The valve body has eight external ports that extend to the internal stem chamber. Multiple O-rings are installed on the stem and the O-rings must pass by the ports when the stem is actuated so the ports must have smooth edges so they do not slice the O-rings. The stem diameter is made as small as possible to minimize dead volumes, making it challenging to manufacture. The external and internal connections create multiple potential leak points making it difficult to trouble-shoot the valve.

SUMMARY OF THE INVENTION

The disclosed invention solves the problem of quickly transferring a sequence of precise molar quantities of gas from a primary stream into a secondary stream with a simple device that is easy to manufacture and operate, has essentially zero dead-volume, and fewer leak points. The rotary dosing device comprises a rotating chamber, a valve body, two end caps, two end seals, and a motor. The rotating chamber has at least two internal dosing ports, which serve as the dose volumes. As the cylinder is rotated, the dose volumes are cycled through two or three states: fill, equilibrate (optional), and transfer. The device cycles in an overlapping manner such that as one dose volume fills with gas from the primary stream, another equilibrates at a known pressure and temperature, and another transfers its contents to the secondary stream.

The rotating chamber can be actuated multiple times during a single analysis to dose a variable but precise quantity of primary gas into the secondary stream. For example, the doser can be actuated a single time for one analysis, and three times for the next analysis to generate data for two points on a calibration curve. Multiple doses can also provide flexibility in a combustion application allowing the operator to more closely match the aliquot quantity with the analysis requirements.

An aspect of the present invention is to provide a rotary dosing device comprising a valve body and a rotating cylindrical chamber contained in the valve body. The rotating cylindrical chamber having an axial length and comprising: a first dosing port extending through the rotating cylindrical chamber, and a second dosing port extending through the rotating cylindrical chamber. The rotary dosing device further comprising: a primary upstream port for receiving a primary gas stream and introducing the primary gas stream into one of the first and second dosing ports of the rotating cylindrical chamber; a secondary upstream port for receiving a secondary gas stream and introducing the secondary gas stream into one of the first and second dosing ports of the rotating cylindrical chamber; a primary downstream port for receiving a remaining portion of the primary gas stream from one of the first and second dosing ports of the rotating cylindrical chamber; a secondary downstream port for receiving the secondary gas stream from one of the first and second dosing ports of the rotating cylindrical chamber; and a motor for rotating the rotating cylindrical chamber so that each of the first and second dosing ports sequentially aligns with the primary upstream and downstream ports for filling with the primary gas stream and the secondary upstream and downstream ports for transferring the gas to the secondary gas stream.

Another aspect is to provide a method of transferring a precise quantity of a known calibrant from a primary stream to a secondary stream to calibrate a detection system in the secondary stream. The method comprises using the rotary dosing device described herein whereby the known calibrant is introduced to the primary upstream port and a dose of the calibrant is transferred to the secondary stream via the secondary downstream port.

Another aspect is to provide a method of transferring a precise quantity of a small representative aliquot from a primary gas stream including to a secondary stream for further processing and analysis, the primary gas stream including at least a portion of combustion gases evolving from a burn of a sample to be analyzed. The method comprises using the rotary dosing device described herein whereby the primary gas stream is introduced to the primary upstream port and a precise quantity of the aliquot is transferred to the secondary stream via the secondary downstream port.

Another aspect of the present invention is to provide a rotary dosing device comprising: a valve body; and a rotating cylindrical chamber contained in the valve body. The rotating cylindrical chamber having an axial length and comprising: an upstream end face and a downstream end face on an opposite side of the rotating cylindrical chamber; a first dosing port extending from the upstream end face to the downstream end face, a second dosing port extending from the upstream end face to the downstream end face, and a third dosing port extending from the upstream end face to the downstream end face. The rotary dosing device further comprising: a primary upstream port for receiving a primary gas stream and introducing the primary gas stream into one of the first, second, and third dosing ports of the rotating cylindrical chamber; a secondary upstream port for receiving a secondary gas stream and introducing the secondary gas stream into one of the first, second, and third dosing ports of the rotating cylindrical chamber; a primary downstream port for receiving a remaining portion of the primary gas stream from one of the first, second, and third dosing ports of the rotating cylindrical chamber; a secondary downstream port for receiving the secondary gas stream from one of the first, second, and third dosing ports of the rotating cylindrical chamber; an equilibrate port; and a motor for rotating the rotating cylindrical chamber so that each of the first, second, and third dosing ports sequentially aligns with the primary upstream and downstream ports for filling with the primary gas stream, the equilibrate port for equilibrating the gas from the primary gas stream, and the secondary upstream and downstream ports for transferring the gas to the secondary gas stream.

These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring initially toFIG.1, there is shown a rotary dosing device10having a rotating cylindrical chamber20, a valve body30, an upstream end cap40, a downstream end cap50, an upstream end seal60, a downstream end seal70, and a motor80. As best shown inFIG.7A, five gas paths connect to the device10: a primary upstream path A, a primary downstream path B, a secondary upstream path C, a secondary downstream path D, and a downstream equilibration path E.

As best shown inFIG.4, the rotating cylindrical chamber20has flat end faces21and22perpendicular to the cylinder's axis of rotation including an upstream end face21and a downstream end face22. In the example shown, three equal-volume dosing ports24,26, and28extend the length of the chamber20to both end faces21and22and serve as the internal dose volumes of the device10. It should be noted, however, that the dosing ports24,26, and28may have different volumes to allow different sized doses from each port. As shown inFIG.5, the dosing ports24,26, and28are located at a fixed radius R1from the center of the end faces21and22, and arranged 120° from each other. Although three dosing ports24,26, and28are shown in the disclosed example, only two dosing ports are needed and additional dosing ports may be provided. Such additional dosing ports could be provided for various reasons. For example, if additional equilibration time is desired, there may be additional dosing ports and additional equilibrate positions provided between the fill and transfer positions. There could also be additional ports and positions simply to await filling. Although the dosing ports24,26, and28are shown as extending parallel to the axis of the rotating cylindrical chamber20, the dosing ports may extend at an angle to this axis or may enter and/or exit the chamber20on the curved sidewalls of the chamber20.

Referring back toFIG.1, the valve body30has a large cylindrical bore to receive the rotating cylindrical chamber20and bearings (not shown) to constrain the chamber20radially while allowing it to rotate freely. The upstream cap40and the downstream cap50fasten to the valve body30and axially retain the rotating cylindrical chamber20.

The upstream end seal60is located between the upstream end cap40and the upstream end face21. The downstream end seal70is located between the downstream end cap50and the downstream end face22. As best shown inFIG.2, the seals60and70are preferably composed of two materials: an elastomer material62,72that is in contact with the caps40and50; and a low-friction material63,73such as PTFE or other that is in contact with the rotational end faces21,22of the chamber20. The elastomer material62,72provides a spring force to keep the low-friction sealing surface pressed against the end faces21and22. The seals60and70are retained in the caps40and50so that they do not rotate when the chamber20rotates.

As viewed from the upstream cap40looking at the upstream seal60and the upstream end face21(FIG.5), six positions are defined referenced to the chamber's axis of rotation. These positions are arranged 60° apart, all at radius R1; the selection of the 0° position is arbitrary. The six positions are labeled 1-6 in a clockwise fashion.FIG.6shows the positions on the downstream seal70looking from the upstream end.

As shown inFIGS.1,2, and7A-7D, a primary upstream port42on the exterior of the upstream cap40connects to the upstream primary path A and a secondary upstream port44connects to the upstream secondary path C. These two ports42and44extend internally to interface with the dosing ports24,26, and28. The primary upstream port42occupies position1, and the secondary upstream port44occupies position5. Upstream grooved paths46and48in the internal surface of the upstream cap40allow the valve to operate in two positions: start-up and normal as described further below. On the upstream cap40, a first upstream grooved path46extends between positions1and2, and the second upstream grooved path48extends between positions4and5.

As shown inFIGS.1,3, and7A-7D, the downstream cap50has three downstream ports51,52, and53. A primary downstream port51connects externally to the primary downstream path B, a secondary downstream port52connects to the secondary downstream path D, and an equilibration downstream port53connects to the equilibration downstream path E. These three downstream ports51,52, and53extend internally to interface with any of the dosing ports24,26, and28. The primary downstream port51occupies position1, the secondary downstream port52occupies position5, and the equilibration port53occupies position3. There are two downstream grooved paths54and55in the internal surface of the downstream cap50: a first downstream grooved path54extends between positions1and2, and a second downstream grooved path55extends between positions4and5. The equilibrate port53may be eliminated if equilibration using a back pressure is not desired.

There are paths in the end seals60and70that align with the ports and grooved paths in the caps40and50.

The end faces21and22are finished so as to inflict minimal wear on the sealing surface they rotate against.

There is a feature82in the center of the downstream end face22having a non-circular shape such that it can be engaged by a similarly shaped mating coupling on a shaft of the motor80to rotate the chamber20. The motor80may be a stepper motor that is fastened to the downstream cap50and a feature on the motor shaft passes through an opening83in the downstream cap50and downstream seal70engages the mating feature82on the chamber face22to rotate the chamber20.

Under normal conditions, the internal dosing ports24,26, and28align with positions1,3, and5on the caps40and50and end seals60and70as shown inFIG.7A: position1is filling, position3is equilibrating, and position5is transferring. In the example shown inFIG.7A, the first dosing port24is aligned in position1in communication with the ports42and51for filling the first dosing port24with gas from the upstream primary gas stream A while excess gas flows to the downstream primary gas stream B, which may be atmosphere exhaust106. The second dosing port26is aligned in position3for communication with equilibrate port53for equilibrating at a particular pressure which may be established by the back-pressure exhaust gas stream E. The third dosing port28is aligned in position5in communication with the ports44and52in order to allow the upstream secondary gas stream C to flow through the third dosing port28into the downstream secondary gas stream D. The chamber20is then rotated 120° per cycle in a clockwise fashion as described further below.

However, for the first transfer, it is not desirable to start out by advancing the chamber20clockwise 120° because the gas in the dosing port that is in the equilibrate position3(the second dosing port26), is unknown so transferring to the secondary gas stream D is undesirable. For this reason, at start-up the chamber20is rotated counter-clockwise 60° to an intermediate position so that its dosing ports24,26, and28align with positions2,4, and6. The grooved channels46,48,54, and55in the end caps40and50and the end seals60and70extend the primary upstream and downstream paths A and B and the secondary upstream and downstream paths C and D to reach the intermediate positions2and4. As shown inFIG.7B, the second dosing port26, which had been in the position3, is now moved so as to be filled in position2; the third dosing port28, which had been in transfer position5, is now still providing a flow path for the secondary gas stream in position4; and the first dosing port24, which had been filling in position1is now backed into a waiting position at position6with its input and output blocked off.

After filling the second dosing port26, the chamber20advances clockwise 60° to the original starting position (FIG.7A) to equilibrate the first dose contained in the second dosing port26in position3. After that, the chamber20will advance 120° clockwise per cycle as normal. For example, moving from the position inFIG.7Ato the position shown inFIG.7C, the second dosing port26is advanced from the equilibrate position3to the transfer position5in order to transfer the first dose to the downstream secondary stream D using carrier gas from the upstream secondary stream C, the first dosing port24is moved from the filling position1to the equilibrate position3, and the third dosing port28is moved from the transfer position5to the filling position1. Next, the chamber20will again advance 120° clockwise so that the chamber20rotates from the position inFIG.7Cto that inFIG.7Dwherein the first dosing port24is advanced from the equilibrate position3to the transfer position5in order to transfer the second dose to the downstream secondary gas stream D using carrier gas from a carrier source102via the upstream secondary gas stream C, the third dosing port28is moved from the filling position1to the equilibrate position3, and the second dosing port26is moved from the transfer position5to the filling position1. Next, the chamber20will again advance 120° clockwise so that the chamber20rotates from the position inFIG.7Dto the initial position inFIG.7Awhereby the third dose in the third dosing port28may be transferred to the secondary gas stream D.

The chamber20may continue to rotate and deliver doses to the secondary gas stream D. The number of rotations will depend on the molar dosage desired for the particular analysis. This rotary dosing device10thus allows for selection of any particular dosage that is an increment of a single dosage from one of dosing ports24,26, and28. The rotating chamber20can be actuated multiple times during a single analysis to dose a variable but precise quantity of primary gas into the secondary gas stream. For example, the rotating dosing device10can be actuated a single time for one analysis, and three times for the next analysis to generate data for two points on a calibration curve. Multiple doses can also provide flexibility in a combustion application allowing the operator to more closely match the aliquot quantity with the analysis requirements.

The rotary dosing device10is capable of quickly transferring a sequence of precise molar quantities of gas from the primary gas stream into the secondary gas stream. The rotary dosing device10is a simple device that is easy to manufacture and operate, has essentially zero dead-volume, and fewer leak points.

The rotary dosing device10may be used in a method of transferring a precise quantity of a known calibrant from a primary gas stream to a secondary gas stream to calibrate a detection system in the secondary gas stream. The method comprises using the rotary dosing device10described herein whereby the known calibrant is introduced to the primary upstream port42and a dose of the calibrant is transferred to the secondary gas stream via the secondary downstream port52. A size of the dose of calibrant may be varied to achieve multi-point calibration.

The rotary dosing device10may also be used in a method of transferring a precise quantity of a small representative aliquot from a primary gas stream including to a secondary stream for further processing and analysis, the primary gas stream including at least a portion of combustion gases evolving from a burn of a sample to be analyzed. The method comprises using the rotary dosing device10described herein whereby the primary gas stream is introduced to the primary upstream port42and a precise quantity of the aliquot is transferred to the secondary stream via the secondary downstream port52. A size of the dose of aliquot is variable.

The rotary dosing device10is thus well suited for use in an elemental analyzer, which comprises a sample source100for providing a gas sample into the primary gas stream A received at the primary upstream port42of the rotary dosing device10. The sample source100may be a combustion furnace. Examples of components of suitable combustion furnaces are disclosed in U.S. Pat. Nos. 7,497,991; 4,622,009; 6,291,802; and 6,270,727. The disclosures of the '991, '009, '802, and '727 patents are incorporated herein by reference. The elemental analyzer may also include a carrier source102for providing a carrier gas in the secondary gas stream C received at the secondary upstream port44of the rotary dosing device10. The elemental analyzer may further include at least one analysis cell104for receiving the secondary gas stream D from the secondary downstream port52, and for analyzing the received secondary gas stream D in which the gas sample is introduced by the rotary dosing device10. In addition, the elemental analyzer may include an atmosphere exhaust106for exhausting to atmosphere the primary gas stream B received from primary downstream port51, and a back-pressure exhaust108coupled to equilibrate port53for bringing the dose in the dosing port connected to equilibrate port53to the desired pressure.

It will become apparent to those skilled in the art that, given the teaching of this specification, multiple bidirectional or unidirectional ballasts may be employed to achieve the improved performance of an analyzer. It will also be apparent to those skilled in the art that these and other modifications can be made without departing from the spirit or scope of the invention as defined by the appended claims.