WO2000067020A1 - Spent acid strength measurement method - Google Patents
Spent acid strength measurement method Download PDFInfo
- Publication number
- WO2000067020A1 WO2000067020A1 PCT/US2000/011171 US0011171W WO0067020A1 WO 2000067020 A1 WO2000067020 A1 WO 2000067020A1 US 0011171 W US0011171 W US 0011171W WO 0067020 A1 WO0067020 A1 WO 0067020A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- acid
- spent acid
- spent
- acid strength
- vibration frequency
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/26—Oils; viscous liquids; paints; inks
- G01N33/28—Oils, i.e. hydrocarbon liquids
Definitions
- the invention relates to a method for measuring spent acid strength, and more particularly to a method for correcting acid concentration values calculated from in situ measurements taken by a vibration frequency mass flowmeter positioned on a spent acid flow line in an acid alkylation system.
- a recently developed and very successful in situ technique for monitoring spent acid strength is through the use of a vibration frequency mass flowmeter positioned on a spent acid flow line. After installation and calibration, the device continuously 2 monitors the process fluid temperature, flow rate, and vibration frequency of the flow line. All else being constant, changes in vibration frequency are caused by density changes in the process fluid. Thus, after adjusting for temperature, the vibration frequency changes are used to provide continuous, real-time assessment of acid strength.
- the invention relates to a method for correcting for the acid strength values calculated from drifting vibration measurements taken from a spent acid line by a vibration frequency mass flowmeter.
- the invention involves determining the differential between the acid strength value calculated from in situ measurements taken by a vibration frequency mass flowmeter on a spent acid line and a laboratory- determined strength of a spent acid sample taken substantially contemporaneously with the in situ measurements. Subsequent acid strength values calculated from subsequent in situ measurements are biased from about 1% to 100% of the differential.
- the invention involves determining the differential between the acid strength value calculated from in situ measurements taken by a vibration frequency mass flowmeter on a spent acid line and a laboratory- determined strength of a spent acid sample taken substantially contemporaneously with the in situ measurements. Subsequent acid strength values calculated from subsequent in situ measurements are biased from about 1% to 100% of the differential.
- the vibration frequency mass flowmeter can be a single device or combination of devices capable of measuring change in the vibration frequency of the spent acid flow tube, as well as the flow rate and temperature of the spent acid.
- An example of such a device is the Elite Coriolis mass flowmeter manufactured by Micromotion Company.
- the device may be installed on any "spent acid line,” defined as any line through which spent acid flows, including an intermediate acid stream line, a recycle line and/or a spent acid line to storage.
- Vibration changes in the spent acid line and the fluid flow rate are measured by the device, which are used to calculate the density of the spent acid.
- the spent acid temperature measured by the device is used to correlate the calculated density with an acid concentration, which is then converted to a percentage acid strength.
- the acid strength is then biased by a correction factor based on the difference between the lab- evaluated acid strength and that calculated from the output of the vibration frequency mass flowmeter at the time the lab sample is obtained. 4
- the type of acid catalyst and the nature of the alkylation reaction it catalyzes are not particularly limited, so long as a drift from laboratory-evaluated acid strength values occurs in the acid strength values calculated from the in situ measurements.
- the frequency of the lab-to-in situ comparisons and the magnitude of the biasing will vary depending upon how quickly hydrocarbons accumulate on the spent acid line and the extent to which the deposits affect tube vibration.
- Experience with specific alkylation reactions and commercial units will allow those of ordinary skill in the art to optimize the biasing method of the invention for individual applications. Nevertheless, we have found that the method can be effective when lab-to-in situ comparisons are conducted only once a day.
Abstract
A method for correcting for the acid strength values calculated from drifting vibration measurements taken from a spent acid line by a vibration frequency mass flowmeter. The invention involves determining the differential between the acid strength value calculated from in situ measurements taken by a vibration frequency mass flowmeter on a spent acid line and a laboratory-determined strength of a spent acid sample taken substantially contemporaneously with the in situ measurements. Subsequent acid strength values calculated from subsequent in situ measurements are biased from about 1 % to 100 % of the differential.
Description
SPENT ACID STRENGTH MEASUREMENT METHOD
FIELD OF THE INVENTION The invention relates to a method for measuring spent acid strength, and more particularly to a method for correcting acid concentration values calculated from in situ measurements taken by a vibration frequency mass flowmeter positioned on a spent acid flow line in an acid alkylation system.
BACKGROUND OF THE INVENTION Commercial acid alkylation units typically react an alkane, commonly isobutane, with an olefin in the presence of an acid catalyst to form an acid- hydrocarbon mixture. The mixture is allowed to settle and the acid is separated from the hydrocarbon products, with a portion of the acid being recycled to the reactor to catalyze additional reactions. Since the concentration and catalytic activity of the recycled ("spent") acid is lower than fresh acid, a continuous alkylation process requires that acid "strength" (a relative value calculated from the acid concentration in the process fluid stream) be regenerated through the addition of fresh acid to the recycled acid.
Accordingly, the largest controllable operating expense for a commercial acid alkylation unit is fresh acid make-up cost. Even for a mid-sized refinery, annual acid costs can run into the millions of dollars. Consequently, the industry is continually searching for ways to improve acid utilization efficiency to reduce operating costs. A recently developed and very successful in situ technique for monitoring spent acid strength is through the use of a vibration frequency mass flowmeter positioned on a spent acid flow line. After installation and calibration, the device continuously
2 monitors the process fluid temperature, flow rate, and vibration frequency of the flow line. All else being constant, changes in vibration frequency are caused by density changes in the process fluid. Thus, after adjusting for temperature, the vibration frequency changes are used to provide continuous, real-time assessment of acid strength. Significantly improved acid utilization efficiency is readily achieved over conventional systems relying on acid strength data from periodic sampling. The clear advantages of this spent acid strength monitoring system notwithstanding, when implemented on a commercial acid alkylation unit we noted a drifting of the calculated acid strength values away from those obtained from laboratory-evaluated acid samples. We found that heavy organic materials in the spent acid stream of the acid alkylation unit deposit on the spent acid lines. The deposits increase the mass of the lines, thereby altering their vibration frequency and distorting the calculated acid strength. As deposits accumulate, the difference between the actual and calculated acid strength widens and the ability to efficiently manage acid make-up accordingly deteriorates.
SUMMARY OF THE INVENTION
Briefly, the invention relates to a method for correcting for the acid strength values calculated from drifting vibration measurements taken from a spent acid line by a vibration frequency mass flowmeter. The invention involves determining the differential between the acid strength value calculated from in situ measurements taken by a vibration frequency mass flowmeter on a spent acid line and a laboratory- determined strength of a spent acid sample taken substantially contemporaneously with the in situ measurements. Subsequent acid strength values calculated from subsequent in situ measurements are biased from about 1% to 100% of the differential.
DETAILED DESCRIPTION OF THE INVENTION As described above, obtaining real-time spent acid strength values for a commercial acid alkylation unit realizes tremendous operating cost savings due to
3 improved acid utilization efficiency. However, we found that over time, acid strength values calculated from data obtained from a vibration frequency mass flowmeter positioned on a spent acid line drift from laboratory-determined values. Heavy hydrocarbons carried by the spent acid deposit on the flow tube interior to increase the mass of the line, skew the vibration frequencies measured by the device and distort the calculated acid strength values.
Our recognition of this problem led to a discovery of an efficient method of compensating for the drift. The method maintains the accuracy of the in situ acid strength measurements without requiring the flow tube to be taken off-line for removal of the heavy organic deposits. Specifically, the invention involves determining the differential between the acid strength value calculated from in situ measurements taken by a vibration frequency mass flowmeter on a spent acid line and a laboratory- determined strength of a spent acid sample taken substantially contemporaneously with the in situ measurements. Subsequent acid strength values calculated from subsequent in situ measurements are biased from about 1% to 100% of the differential.
The vibration frequency mass flowmeter can be a single device or combination of devices capable of measuring change in the vibration frequency of the spent acid flow tube, as well as the flow rate and temperature of the spent acid. An example of such a device is the Elite Coriolis mass flowmeter manufactured by Micromotion Company. The device may be installed on any "spent acid line," defined as any line through which spent acid flows, including an intermediate acid stream line, a recycle line and/or a spent acid line to storage.
Vibration changes in the spent acid line and the fluid flow rate are measured by the device, which are used to calculate the density of the spent acid. The spent acid temperature measured by the device is used to correlate the calculated density with an acid concentration, which is then converted to a percentage acid strength. The acid strength is then biased by a correction factor based on the difference between the lab- evaluated acid strength and that calculated from the output of the vibration frequency mass flowmeter at the time the lab sample is obtained.
4
The type of acid catalyst and the nature of the alkylation reaction it catalyzes are not particularly limited, so long as a drift from laboratory-evaluated acid strength values occurs in the acid strength values calculated from the in situ measurements. The frequency of the lab-to-in situ comparisons and the magnitude of the biasing will vary depending upon how quickly hydrocarbons accumulate on the spent acid line and the extent to which the deposits affect tube vibration. Experience with specific alkylation reactions and commercial units will allow those of ordinary skill in the art to optimize the biasing method of the invention for individual applications. Nevertheless, we have found that the method can be effective when lab-to-in situ comparisons are conducted only once a day.
Though the invention has been described above with reference to specific embodiments, other embodiments of the invention can readily be envisioned by one of ordinary skill in the art in light of this teaching. Modifications, substitutions, changes and/or omissions may be made without departing from the spirit and scope of the invention defined in the appended claims.
Claims
1. A method for correcting acid strength values calculated from in situ measurements taken by a vibration frequency mass flowmeter positioned on a spent acid line in an acid alkylation system, said method comprising: determining the differential between a) an acid strength value calculated from in situ measurements taken by a vibration frequency mass flowmeter positioned on a spent acid line in an acid alkylation system, and b) a laboratory-determined strength of an acid sample drawn substantially contemporaneously with said in situ measurements; biasing subsequent acid strength values calculated from in situ measurements by 1% to 100% of said differential.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US30195699A | 1999-04-29 | 1999-04-29 | |
| US09/301,956 | 1999-04-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2000067020A1 true WO2000067020A1 (en) | 2000-11-09 |
Family
ID=23165643
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/US2000/011171 WO2000067020A1 (en) | 1999-04-29 | 2000-04-26 | Spent acid strength measurement method |
Country Status (1)
| Country | Link |
|---|---|
| WO (1) | WO2000067020A1 (en) |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4473442A (en) * | 1982-02-22 | 1984-09-25 | Phillips Petroleum Company | Acid regenerator control |
| US5407830A (en) * | 1993-12-01 | 1995-04-18 | Mobil Oil Corporation | Control of low inventory alkylation unit |
| US5594180A (en) * | 1994-08-12 | 1997-01-14 | Micro Motion, Inc. | Method and apparatus for fault detection and correction in Coriolis effect mass flowmeters |
-
2000
- 2000-04-26 WO PCT/US2000/011171 patent/WO2000067020A1/en not_active Application Discontinuation
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4473442A (en) * | 1982-02-22 | 1984-09-25 | Phillips Petroleum Company | Acid regenerator control |
| US5407830A (en) * | 1993-12-01 | 1995-04-18 | Mobil Oil Corporation | Control of low inventory alkylation unit |
| US5594180A (en) * | 1994-08-12 | 1997-01-14 | Micro Motion, Inc. | Method and apparatus for fault detection and correction in Coriolis effect mass flowmeters |
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