JPS6239937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the photometric analysis of hydrogen sulfide in alkanolamines, and in particular to the detection of background photometric absorptions caused by impurities in the amine stream, for example, in order to be able to accurately measure the concentration of hydrogen sulfide. The present invention relates to a method and apparatus for measuring and compensating for.

Amine absorption methods for removing hydrogen sulfide from refinery "sour" gas are well known. The mechanism for removing hydrogen sulfide is understood and involves the combination of hydrogen sulfide with alkanolamines. Typically, a "lean" amine, that is, an amine with available sites for binding hydrogen sulfide, is introduced near the top of the countercurrent absorber or absorber, while the sour gas stream is It is introduced near the bottom of the absorber. Inside the absorber, a chemical reaction takes place in which hydrogen sulfide is combined with alkanolamines. The resulting bound amine, the so-called "rich" amine, is then pumped to the inlet of a stripping column, ie a distillation column. In the distillation column, high temperatures provided by high pressure steam are used to remove hydrogen sulfide from the bound amine. After cooling, the stripped amine is sent to an absorption tower to complete the cycle.

The amine absorption desulfurization method was described in a paper titled "Continuous Photometric Analysis for Measurement and Control in Sulfur Recovery Operations" presented by RSSaltzman at the Texas A&M University Process Industries Equipment Symposium in January 1977. ing.

For various economic reasons, the amount and cost of energy utilized to generate the high pressure steam used in distillation columns has been the focus of energy conservation efforts. If energy cost and availability considerations were not more important, steam could be used to reduce the hydrogen sulfide concentration in the absorber to a level below that required for efficient absorption. The typical practice was to use However, as the cost of energy increases, this practice is no longer economical. It is therefore important to provide some indication of the level of hydrogen sulfide remaining in the effluent from the distillation column, so that the efficiency of the distillation column can be optimized in terms of energy consumption.

For this purpose, it is known to utilize photometric analysis equipment to obtain an indication of the amount of hydrogen sulfide remaining in the effluent of a distillation column. One such device is described in the article cited above and is sold by DuPont as the "400 Photometric Analyzer." Such devices rely on the strong ultraviolet absorption of the alkanolamine-hydrogen sulfide bond to measure the concentration of hydrogen sulfide in the distillation column effluent. In general, two problems have been observed with accurate measurement of hydrogen sulfide concentrations.

The first problem concerns the acute temperature sensitivity of the amine-hydrogen sulfide bond absorption. At higher temperatures, greater UV absorption occurs. Therefore, in order to ensure that the sample of effluent from the distillation column introduced into the sample cell of the photometric analyzer is maintained at a predetermined constant temperature, a monitoring passage upstream of the photometric analyzer must be It was necessary to provide a stabilizing heat exchanger. It has been found that by this measure the effect of temperature on the UV absorption of the amine-hydrogen sulfide bond is minimized.

A further problem concerns the effect of recycled impurities in the amine loop. When amines are repeatedly recycled, dust, corrosion inhibitors, or other contaminants produced by chemical breakdown can be generated to form such impurities.
Such impurities act as absorbers of ultraviolet radiation at the same wavelengths that are absorbed by amine-hydrogen sulfide bonds. Therefore, the measurement of the concentration of hydrogen sulfide in the effluent from the distillation column becomes inaccurate. This unnecessarily increases steam usage and at the same time increases energy consumption. Increased consumption of energy under these circumstances is not economically justified and is therefore disadvantageous. It should be noted that the apparatus described in the article was applied in a specially controlled manner in which impurities in the stream were maintained at low levels and the temperature of the sample was precisely regulated.

To measure the concentration of hydrogen sulfide in a stream,
It is also known to introduce a stream sample containing a hydrogen sulfide-amine conjugate into a vessel and then introduce a predetermined amount of hydrogen chloride into the vessel. Hydrogen chloride is replaced with hydrogen sulfide and hydrogen sulfide is measured to obtain an indication of the concentration of hydrogen sulfide in the sample.

In order to accurately measure the concentration of hydrogen sulfide in a stream, it is important and advantageous to compensate for the varying background yield caused by the concentration of various impurities in the recycled amine.

The present invention generates a reference level signal indicative of ultraviolet absorption of impurities and is applied to "zero out" or otherwise eliminate changes in the output of a photometric analysis cell, thereby reducing the flow. to be able to measure the concentration of hydrogen sulfide in
A method and apparatus for photometric analysis of streams containing combined hydrogen sulfide-amines and ultraviolet absorbing impurities.

According to the invention, at least a predetermined amount of bound hydrogen sulfide-amine and a UV-absorbing impurity
A first sample of the stream as effluent from the distillation column containing a concentration, ie, a reference sample, is introduced into a vessel having a predetermined volume. Within the vessel, substantially all of the hydrogen sulfide in the first sample is removed, thereby reducing the concentration of hydrogen sulfide to a second concentration that is lower than the first concentration. The hydrogen sulfide is removed by subjecting the reference sample to predetermined temperature and pressure conditions for a predetermined time interval. The first or reference sample is then photometrically analyzed and the absorbance of the first sample generates a signal indicative of the ultraviolet absorption of any impurities therein and any remaining hydrogen sulfide. This signal provides the basis for carrying out a photometric analysis of a second sample of the distillation column effluent. The difference between the signal indicative of ultraviolet absorption of the second sample and the reference signal is functionally related to the concentration of hydrogen sulfide in the second sample.

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings.

Throughout the following detailed description, like reference numerals in all figures of the accompanying drawings indicate like elements.

Referring to Figure 1, a typical amine absorption method is used to remove hydrogen sulfide contained in so-called "sour" gases produced in natural gas purification plants, refineries, chemical plants, and other industrial processes. A schematic diagram of one of the most commonly used methods is shown. The sour gas is sent to the inlet of a countercurrent absorption column 12 in which it is sulfurized via absorption with monoethanolamine (MEA), diethanolamine (DEA) or a combination of these two or other alkanolamines. Hydrogen is removed. At the outlet of the absorption column 12, the hydrogen sulfide-free gas, the so-called "sweet" gas, is sent to a storage reservoir for further use. Chemically, hydrogen sulfide and other acid gases (eg, carbon dioxide) bind to amine groups, although the bonding forces are weak. Other gases in the stream are essentially insoluble in the amine-water solution and are purged from absorption column 12.

As shown in FIG. 1, countercurrent absorption column 12 receives a charge of stripped amine and water solution that is "lean" or recirculated via conduit or pipeline 14 from pump 16. The chemical combination that occurs in absorption column 12 results in a "rich" solution containing hydrogen sulfide-amine combinations. This solution is removed from the lower part of absorption column 12 via pipeline 18 and pumped by pump 20 via pipeline 20 to the inlet of distillation (stripping) column 24. Within the distillation column 24, the alkanolamine is heated by steam supplied from a high temperature, high pressure steam source, indicated schematically at 26.
The action of heat strips the amine of hydrogen sulfide. Hydrogen sulfide gas is distilled into column 2
4 and conveyed to any suitable sulfur recovery device, such as a device operating with a classical Claus reaction. Water and recycle, ie, stripped amine effluent solution, is conducted to which make-up amine from the amine storage sump can be added from distillation column 24. The recycled amine solution is then cooled by a cooler 30 and passed through a pipeline 32 to a recirculation pump 1 for reintroduction into the absorption column.
6 to complete the amine loop.

The effluent from distillation column 24 includes at least a predetermined first concentration of hydrogen sulfide bound to the amine in the amine-water effluent solution. This predetermined first concentration of hydrogen sulfide is typically about 1200 to 1800 wt.
In the PPM range. As briefly mentioned above, the effluent or stripped amine is added at a location downstream of the distillation column 24 to control the consumption of energy used to generate the steam introduced into the distillation column 24. It is important to monitor the solution. Suitable monitoring stations can be arranged in the output pipeline 28, the coolant discharge pipeline 32 and the absorption tower introduction pipeline 14. The effluent of the distillation column 24 was tested to ensure that the distillation column 24 at all selected locations was effectively and economically removing hydrogen sulfide from the lithium amine solution to a concentration that could be efficiently utilized by the absorption column 12. It is important to monitor This monitoring may be difficult as some alkanolamines (to which no hydrogen sulfide is attached) have background UV absorption. Moreover, repeatedly circulating the amine solution through the amine loop causes an accumulation of impurities therein that absorb ultraviolet radiation. These impurities may include dust, corrosion inhibitors, or other contaminants produced by chemical destruction or by corrosion. These impurities, regardless of their origin, can produce some degree of incidental background UV absorption that, if not compensated for, will cause errors in the analysis of the distillation column 24 effluent. .

The present invention provides an apparatus and method for compensating for the optical absorption of any impurities and amines that tend to make the photometric analysis of the effluent from distillation column 24 inaccurate. As can be seen from FIG.
The photometric analysis equipment indicated at 4 includes a photometric analysis device 36 (shown in more detail in FIG. 3) adapted to measure the concentration of hydrogen sulfide in the effluent drawn from a predetermined location in the amine loop. There is. The photometric analyzer 36 includes a device 38 for removing hydrogen sulfide from a sample of the effluent to a second concentration lower than a predetermined first concentration before introducing the sample to the photometric analyzer 36.
are combined. The hydrogen sulfide in the sample is removed from the predetermined first column present in the effluent from the distillation column 24.
By removing until a second, lower concentration is reached and then photometrically analyzing the sample, an indication of the ultraviolet absorption of the impurities and (if present) remaining hydrogen sulfide can be derived. This instruction provides a basis for correcting for the effect of ultraviolet absorption caused by such impurities and (if present) by residual hydrogen sulfide when analyzing a second sample to determine its hydrogen sulfide content. It is useful because it serves as a line, or reference.

As can be seen from FIG. 3, a photometric analyzer 36 used in connection with the present invention includes a sample cell 40 and a source of ultraviolet radiation, such as a radiation lamp 44, mounted within a source housing 46. Contains. UV radiation source housing 46
Opposed is a photometer housing 48 containing a translucent mirror 52. Mirror 52 directs a portion of the ultraviolet radiation passing through sample cell 40 to first optical filter 6.
0 and the first measurement channel photocell 62 .
It serves as a beam splitter element for directing along optical path 58. Beam splitter 52 directs the remaining portion of the ultraviolet radiation passing through sample cell 40 along a second optical path 64 that includes a second optical filter 66 and a second reference channel phototube 68 . Optical filters 60 and 66 are provided to pass only radiation having selected spectral components. The radiation incident on phototubes 62 and 68 controls the flow of current generated by the phototubes. respective photocells 62 and 6
The signal generated by 8 represents the optical absorption of the sample within cell 40 at the selected wavelength of ultraviolet radiation. These signals are related to the concentration of the substance within the cell 40 by Beer's law. Accordingly, in accordance with well-known photometric analysis techniques, suitable electronic components, such as logarithmic amplifiers 72 and 74, are provided to functionally relate the concentration of ultraviolet radiation absorbing material within cell 40. An electrical signal output can be generated on output line 76. A detailed description of the photometric analysis device described above is given in US Pat. No. 3,306,156. The technical content of US Pat. No. 3,306,156 is incorporated herein by reference.

A feedback controller 78 is interconnected with amplifiers 72 and 74 to provide a system for targeting and measuring the signal on output line 76. This feedback control device 7
8 indicates that the effluent reference sample (generated in the manner described herein) is connected to the cell in order to adjust the output signal on output line 76 to a predetermined reference value corresponding to the optical absorption of the effluent reference sample. 40 is also responsive to the signal generated by amplifier 74 during the period of time it resides within 40. All hydrogen sulfide in the reference sample is removed, leaving only effects caused by impurities in the reference sample. Feedback control device 7
8 suitably adjusts the signal produced on output line 76 to a reference value corresponding to the signal produced by these impurities, thereby eliminating its influence on subsequent analysis. In yet another embodiment of the invention, as shown in FIG. 3, the concentration of hydrogen sulfide in the reference sample is reduced to a predetermined concentration that is lower than the concentration of hydrogen sulfide in the effluent stream. It will be done. Therefore, the signal generated when a reference sample is present in sample cell 40 exhibits the effects of both hydrogen sulfide and low concentrations of impurities. In this case, the feedback control device 78
The signal on output line 76 is suitably adjusted to a reference value that corresponds only to the portion of the signal caused by impurities in the reference sample and the portion caused by the low concentration of remaining uncompensated hydrogen sulfide. Leave only. In this way, the effects of impurities during subsequent analyzes of other samples can be eliminated.

Referring again to FIG. 2, a sample taken from any predetermined location within the amine loop is introduced into the photometric analysis instrument 34 of the present invention through an inlet pipeline 80 in which an inlet isolation valve 82 is located. The sample passes through a filter element 84 and is drawn through another isolation valve 86 into a temperature controlled oven 88 . The portion of the sample that is not drawn into the temperature controlled oven 88 is conveyed via a return line and then via a flow meter and valve 91 to a return line to the effluent outlet. A shutoff valve 92 is connected to a water source so that the photometric analysis machine 34 can be cleaned if desired.

The sample is introduced into a temperature controlled oven 88 that includes a heat exchanger 94 . A temperature controlled oven 88 is provided for the purpose of adjusting the temperature of the sample to a selected temperature, thereby eliminating changes in light absorption caused by the temperature sensitivity of the hydrogen sulfide-amine bond. . The warm air introduced through the inlet vent 95 flows into the oven 8.
8. Constant temperature (±2.0℃ of selected temperature)
temperature of the sample in heat exchanger 94 to the selected temperature. The sample cell 40 is itself located inside the oven 88 . At the outlet of heat exchanger 94 , the heated sample is passed to sample cell 40 via sample cell isolation valve 96 and then via sample cell introduction pipeline 98 . The sample cell discharge pipeline 100 at the outlet of the sample cell 40 is connected to a return line via a flow meter and valve 102. If desired, a bubble trap 106 can be provided upstream of the sample cell isolation valve 96. bubble trap 10
The outlet of 6 is connected by pipeline 108 to the return line via a flow meter and valve 110.

According to the invention, the device 38 for removing hydrogen sulfide from a sample of effluent includes a sample isolation valve 112 connected to the sample cell introduction pipeline 98 at a T-connection. A container 116 is connected to the outlet of the sample cutoff valve 112 . Container 11
6 can be of any suitable type and is preferably made of corrosion resistant material. For purposes of clarity herein, vessel 116 is physically located within a temperature controlled furnace 88. The outlet of the container 116 is connected to the reflux column 1.
It is connected to a vacuum exhaust line 120 via 18. The pressure conditions within vessel 116 are controlled via vacuum evacuation line 120, which is operatively controlled by aspirator 122. Gauge 1
24 allows the pressure level inside the container 116 to be monitored and maintained within predetermined limits.

During operation, photometric analysis equipment 34 is connected to selected locations within the amine loop. As previously discussed, the effluent from distillation column 24 includes a first predetermined concentration of hydrogen sulfide. In order to compensate for absorption effects caused by impurities present in the amine loop, a first sample or reference sample of the effluent solution drawn into the photometric analysis device 34 is connected to the isolation valve 11.
It is collected by temporarily opening 2. A first or reference sample of heated solution is removed from container 116 by the action of the vacuum in evacuation line 120.
be sucked into. If it is desired to continue analyzing the remainder of the sample while the effects of impurities are being compensated for, isolation valve 112 is closed while isolation valve 96 remains open. Isolation valve 96 can also be closed if it is desired to keep analysis of the remainder of the sample suspended while the effects of impurities are compensated for.

Within vessel 116, a majority of the hydrogen sulfide bound to the amine within the first or reference sample within the vessel is removed, thus leaving a second concentration of hydrogen sulfide lower than the predetermined first concentration. remains in the reference sample in container 116. The second concentration is the first
The second concentration of hydrogen sulfide in the reference sample in container 116 is preferably in the range of 400-800 ppm by weight, although it only needs to be lower than the concentration. The concentration of hydrogen sulfide in container 116 is reduced by applying a predetermined temperature and predetermined pressure condition to the sample in container 116 for a predetermined period of time.

The first or reference sample portion inside container 116 is heated to a temperature in the range of 60°C to 80°C, preferably 70°C, for a period of time in the range of 30 to 90 minutes, preferably in the range of 50 to 60 minutes. at 0.105Kg/ ^cm2
(1.5psia) to 0.14Kg/ ^cm2 (2.0psia),
Hydrogen sulfide from the reference sample in vessel ¹¹⁶ is preferably maintained at an absolute pressure of 2.0 psia to a concentration lower than the first concentration of hydrogen sulfide in the effluent of distillation column 24. It turned out to be removed. However, if the absolute pressure is 0.35
Kg/cm ² (5 psia) to 0.49 Kg/cm ² (7 psia), the temperature is preferably in the range 90°C to 110°C, most preferably 100°C, and the time interval is 3 hours (180 minutes) to 4
hours (240 minutes). Operating at higher temperatures makes the device less temperature sensitive. In addition, air aspirators can be used to obtain even higher absolute pressures. Preferably, the source of heat applied to the sample in container 116 is derived from a temperature controlled oven 88. However, due to the temperature sensitivity of the measurement, for example, the temperature of the sample cell 40 is controlled by a thermistor in order to compensate for the change in the absorbance of the alkanolamine-hydrogen sulfide bond with changes in temperature and improve the accuracy of the analysis. It may be necessary to measure.

At the end of the hydrogen sulfide removal period, isolation valve 112 is opened and isolation valve 96 is closed, thereby directing the first reference sample to sample cell 40 via sample cell introduction pipeline 98. In sample cell 40, the ultraviolet absorption of impurities and residual hydrogen sulfide in the first reference sample is measured and a signal representative of the measurement is generated. This signal is used by the feedback controller 78 to appropriately adjust or zero the output line 76, thereby compensating for the absorption of ultraviolet light due to any impurities and residual hydrogen sulfide in the manner previously described. be able to. The isolation valve 112 is then closed and a second sample of the effluent is taken. However, this second sample
Since the effluent is directly introduced into the sample cell 40 via the sample cell introduction pipeline 98, the ultraviolet absorption of the effluent can be measured. however,
The effect on UV absorption by impurities in the effluent is taken into account since it was previously nulled by the first or reference sample. Therefore, the concentration of hydrogen sulfide in the second sample derived by Beer's law can be obtained more accurately.

The photometric analysis instrument 34 can be used periodically to manually nullify the effects of impurities generated in the amine loop. For example, an arbitrary period (for example, once every hour) can be selected depending on the changing process conditions. However, firmware that controls the operation of the photometric analysis instrument 34 according to the invention, such as automatically controlling the opening and closing of various valve elements within the apparatus and controlling the application of the appropriate temperature, pressure and time parameters used in accordance with the invention, It should be understood that automatic control can be achieved using a microprocessor device based on .

Numerous modifications can be made by those skilled in the art with the benefit of the teachings of the present invention. Although some of these modifications have been described above, all such modifications are to be construed as falling within the contemplation of the invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a typical amine absorption method illustrating the environment in which the present invention may be used; FIG. ) Schematic diagram of the apparatus for generating a reference signal indicative of the ultraviolet absorption of
The figure is a more detailed schematic diagram of the photometric analysis device used in the apparatus of FIG. 12...Absorption tower, 14...Pipeline, 16...Pump, 18...Pipeline, 20...Pump, 22
...pipeline, 24...distillation column, 28...effluent pipeline, 32...pipeline, 34...photometric analysis instrument, 36...photometric analysis device, 38...hydrogen sulfide removal device, 40...sample cell, 80...introduction pipeline , 88... oven, 94... heat exchanger, 98
... Sample cell introduction pipeline, 100... Sample cell discharge pipeline, 116... Container, 120... Vacuum exhaust line.

Claims (1)

[Claims] 1. (a) Isolating a first sample or reference sample of a stream containing a hydrogen sulfide-amine combination and an _ultraviolet radiation absorbing impurity having a predetermined first concentration of hydrogen sulfide; and (a ₂ ) said isolated first
(b) exposing a sample or reference sample to a predetermined pressure lower than atmospheric pressure at a predetermined temperature for a predetermined time interval to remove hydrogen sulfide from the first sample or reference sample to a predetermined second concentration; (c) ultraviolet absorption photometric analysis of a reference sample to generate a reference signal indicative of ultraviolet absorption of hydrogen sulfide and impurities remaining in said first or reference sample; and (c) a second sample in said stream. photometrically analyzing a sample of hydrogen sulfide to generate a signal indicative of the concentration of hydrogen sulfide and ultraviolet absorbing impurities in the second sample, and comparing the signal with the reference signal. A method for ultraviolet absorption photometric analysis of the concentration of hydrogen sulfide in a stream of hydrogen-amine combinations and ultraviolet radiation-absorbing impurities. 2 The predetermined pressure is 0.105Kg/cm ² in absolute pressure.
2. A method according to claim ¹ , characterized in that the temperature range is between 1.5 psia and 2.0 psia. 3 The predetermined pressure is 0.14Kg/cm ² in absolute pressure.
(2.0 psia). 4. The method according to any one of claims 1 to 3, characterized in that the predetermined temperature is in the range of 60°C to 80°C. 5. The method according to claim 4, wherein the predetermined temperature is 70°C. 6. Method according to any one of claims 1 to 4, characterized in that the predetermined time interval is in the range of 30 minutes to 90 minutes. 7. A method according to claim 6, characterized in that the predetermined time interval is in the range of 50 to 60 minutes. 8 The predetermined pressure is 0.35Kg/cm ² in absolute pressure.
A method according to claim 1, characterized in that the temperature is within the range of (5.0 psia) to 0.49 Kg/cm ² (7.0 psia). 9. A method according to claim 8, characterized in that the predetermined temperature is in the range of 90°C to 110°C. 10. The method according to claim 9, characterized in that the predetermined temperature is 100°C. 11. A method according to claim 1, 8, 9 or 10, characterized in that the predetermined time interval is in the range of 3 to 4 hours. 12 a container for receiving therein a reference sample of a stream containing a hydrogen sulfide-amine conjugate and an ultraviolet radiation absorbing impurity having a predetermined first concentration of hydrogen sulfide; and having the reference sample absorbed into said container. and a suction device for maintaining the reference sample at a predetermined pressure lower than atmospheric pressure for a predetermined time interval, and applying heat to the reference sample at a predetermined temperature while the reference sample is in the container. A device for preparing a first sample by removing hydrogen sulfide from the reference sample to a predetermined second concentration, an ultraviolet radiation source, and a second sample taken from the first sample and the flow are introduced. and an ultraviolet absorption photometric analyzer with a sample cell for measuring the ultraviolet absorbance of the stream containing hydrogen sulfide-amine combinations and ultraviolet radiation absorbing impurities. A device that photometrically analyzes the concentration of hydrogen sulfide in water.