|Title of Invention||
"A DEVICE USEFUL FOR EVALUATING CORROSION INHIBITORS USED FOR CORROSION CONTROL OF OVERHEAD DISTILLATION UNITS"
|Abstract||A device useful for evaluating corrosion inhibitors used for corrosion control of overhead distillation units, which comprises a distillation flask having means for thermo regulated heating, the said distillation flask being provided with temperature probe and stirrer, the said distillation flask being connected to a graduated receptacle provided with means for condensing distillate vapors, the said graduated receptacle being provided at its top and bottom with corrosion monitoring probes and temperature probes .|
|Full Text||This invention relates to a device useful for evaluating corrosion inhibitors used for the corrosion control of overhead distillation units. The device of the present invention can be used to evaluate the effectiveness of corrosion inhibitors that are used to control overhead corrosion in the refinery distillation units.
Literature survey indicates absence of any laboratory standard tests to evaluate the corrosion of refinery distillation units. Overhead corrosion studies have been carried out either by simple laboratory techniques by using on stream coupons or pilot plant simulation. A tube and shell glass model condenser was designed in the laboratory in order to investigate the corrosion control (J. M. Slaiman, H. J. Nassouri, Proceedings 8th International Congress on Metallic Corrosion, Vol. 2, DECHEMA, Germany, 1533 (1981)). Conventional weight loss method was used to monitor the corrosion rate in this set-up. Recently, simulated corrosion tests have been used for the development of new corrosion inhibitor to reduce corrosion in crude tower overhead (Shaorn Tang, Zeli Jiang, Quigbin Mao, Oil & Gas Journal, 92 (38), 68 (1994)). The tests described were of simple immersion type, using classical weight loss and LPR technique with purely aqueous medium containing hydrochloric acid and hydrogen sulphide in ppm levels.
A simulator had been used for the determination of the rate of overhead corrosion of a distillation column in petroleum
refining (NALCO Chemical Company, Japanese Patent No. Kokai Tokkyo Koho Hei 2- 302495 (12-13), December 14, 1990; Chemical Abstract 114:105574r (1991)). The device described has a fractional distillation tower and this tower simulates the corrosion activity on the inner surface of the condensation and/or heat exchanging equipment in the oil refinery set-up where the tower in fact is connected to the condensation and/or heat exchanging equipment through overhead steam line. It has an overhead corrosion simulator with a water box which is provided with U-shaped inclined corrosion simulation device. This U-shaped corrosion simulation device is connected to the overhead steam line. Moreover, the said U-shape tube contains the buffer walls which form multiple number of cells in series and these cells are further equipped with the provision for connecting the corrosion probe and temperature probe. Each probe gets so adjusted that it comes in contact with the steam phase and the liquid phase. The corrosion probe and the temperature probe can determine the corrosion rate at different temperatures in the liquid phase as well as gaseous phase in each cell that form the inclined U-shape tube type corrosion simulation equipment. The said cell works in such a manner that the measurement of branching out steam from the process flow gas which undergoes condensation, is repeated incrementally in accordance with the temperature range, lower than even what the temperature is at the inlet. In
addition, sample line is provided in each cell of the inclined U-shape corrosion simulation equipment to take samples for analysis of chlorides, pH , salt content or their mixture. This corrosion simulation equipment is fixed inside the actual oil refinery processing units.
This corrosion simulator has the following major 1 imitations:
1) The device is complex and can be used only in any oil
refining processing units. Hence, any new corrosion control
measures like proper selection of (from a series of commercially
available) corrosion inhibitors cannot be studied in an oil
2) The effect of variation of corrosion rate with the
variation of two phase (aqueous/hydrocarbon) liquid media cannot
be quantitatively studied, and hence,
3) the effect of different types of corrosion inhibitors in
a two phase system, when compared to that of a single aqueous
phase alone cannot be quantitatively studied.
The main objective of the present invention is to provide a device useful for evaluating corrosion inhibitors used for the corrosion control of overhead distillation units which obviates the above noted drawbacks. Another objective is to carry out comparative evaluation of corrosion inhibitors which are used in the control of overhead corrosion in refinery distillation units to enable to select and use the most suitable corrosion
Inhibitor. Yet another objective of the present invention is to provide a device which can be used to monitor the corrosion in the liquid phase or in the vapour phase or in teh condensation zone where the condensate impinges the corrosion monitoring devices like Electrical Resistance probe or Electrochemical (EC) Corrosion Monitoring probe (K.D. Effird, R. J. Jasinski, Corrosion 45 (1989), 65).
In figure 1 of the drawings accompanying this specification a schematic diagram of an embodiment of the present invention is shown.
Accordingly, the present invention provides a A device useful for evaluating corrosion inhibitors used for corrosion control of overhead distillation units, which comprises a distillation flask (1) having means for thermo regulated heating, the said distillation flask (1) being provided with temperature probe (2) and stirrer (5,6), the said distillation flask being connected to a graduated receptacle (3) provided with means (4) for condensing distillate vapors, the said graduated receptacle (3) being provided at its top and bottom with corrosion monitoring probes (7) and temperature probes (2).
The means for thermo regulated heating used may be such as an external heating jacket.
The means used for condensing distillate vapours may be such as water cooled condensers.
The corrosion monitoring probes used may be such as an
electrical resistance probe, electrochemical corrosion probe.
The temperature probes used may be such as a thermocouple.
The present invention consists of a device for evaluation of corrosion control of overhead refinery distillation units. A definite quantity of the liquid (single phase or two phase) is taken in a distillation flask (1) of say one liter capacity which is heated by a thermoregulated heating jacket (not shown in the figure). The temperature of the liquid in the distillation flask, the condensing vapour and the liquid condensate is measured by temperature probes (2). The liquid in the distillation flask is heated and the distillate vapours are condensed into a graduated receiver (3) by means of water cooled condensers (4) which are located at the top and bottom part of the receiver (3). The liquid in the distillation flask is continuously stirred during the distillation by means of a stirring device which consists of a shaft with teflon blades (5) and a prime mover (6). The corrosion rates of the condensing vapourphase and the liquid condensate in the graduated receiver (3) are monitored by devices like Electrical Resistance probe or Electrochemical Corrosion probes (7) near the region wherein the distillate vapours impinge while condensing over one of the probes just above the graduated receiver (3) and another probe (7) inside the condensed liquid at the bottom of the receiver. The corrosion rate as well as the temperature at the condensing vapour phase and inside the liquid condensate are continuously
monitored while the liquid is being distilled.
The following examples are given by way of illustration and should not be construed to limit the scope of the present invention.
Using the device an embodiment of which is as shown in the figure-1 of the drawing,the corrosion tests were carried out under different conditions whose details are given below:-
This experiment which was carried out in the present device had brought out the difference between the corrosion rate while distilling a purely aqueous system with the corrosion rate while distilling two phase hydrocarbon-aqueous system. In the former experiment, dilute hydrochloric acid with pH 4.0 was taken in the distillation flask 1 and the distillation was carried out. The temperature as well as the corrosion rate at the condensing vapour region (top of the receiver 3) were monitored at different intervals of time during distillation. In another identical experiment, toluene-aqueous hydrochloric acid having a pH value of 4.2 was taken in the distillation flask and the distillation was carried out. This two phase medium gave a constant boiling azeotropic mixture whose boiling point was 84.1oC as monitored by the temperature probe. In addition, this two phase medium gave a constant distillate composition containing 13.5 wt% water which was periodically checked from the liquid condensate collected in
the graduated receiver 3. The present laboratory distillation
device was specifically suited for such types of azeotropic
disti1lation.The corrosion rates at different intervals of time
were monitored and the results of these two sets of experiments
are given in Table-1. The corrosion rate vs time data indicate
Corrosion Rate Data in the condensing vapour region while distilling single phase/two phase liquids as feeds in the laboratory distillation device.
* Average data from triplicate experiments.
that there is consistently high corrosion rate while distilling
purely aqueous hydrochloric acid when compared to the corrosion
rate data obtained while distilling two phase medium containing
hydrochloric acid under identical pH values.
The present set of experiments highlighted the need for the presence of both hydrocarbon and aqueous phase for the actual evaluation of corrosion inhibitors that are used in the control of overhead corrosion of refinery distillation units. The results of the evaluation of two typical acid corrosion inhibitors namely, propargyl alcohol and ethynylcyclohexylamine in a single phase,dilute aqueous hydrochloric acid of pH 4.2 using the present laboratory distillation device are given in Table-2.
Table-2. Corrosion Rate Data for the Distillation of a single phase aqueous hydrochloric acid using the Laboratory Device.
* Average data from triplicate experiment.
The results of the evaluation of the same inhibitors in two phase (Toluene-aqueous hydrochloric acid) using the present laboratory distillation device are given in Table-3. Evaluation of corrosion
Corrosion Rate Data for the Distillation of two phase liquids (Toluene-aqueous HCl of pH 4.2) using the Laboratory Device.
* Average value from quadraplicate experiments.
inhibitors meant for controlling the corrosion of overhead
columns of any refinery distillation units requires the presence
of two phase media. This can be seen by comparing the data of Table-2 and Table-3, wherein the former contains the data corresponding to single phase aqueous acid media and the latter contains the data for the two phase media. Moreover, simple immersion tests cannot bring out the effectiveness of inhibitors for controlling the corrosion of overhead refinery distillation units. This was confirmed by the corrosion rate data which were generated by simple immersion of the corrosion probe in a continuously stirred two phase media at a constant temperature. The corrosion rate data corresponding to this immersion test are given in Table-4.
Corrosion Rate Data from a Simple Immersion Test in continuously stirred two phase media at 50+0.loC in the absence and presence of corrosion inhibitors.
* Average data of eight experiments.
Comparison of the data from this table with those of the data in Table-3 clearly brings out the real effectiveness of these inhibitors in controlling the corrosion of overhead distillation units when the inhibitor evaluation was carried out using the laboratory device.
1. A device useful for evaluating corrosion inhibitors used for corrosion control of overhead distillation units, which comprises a distillation flask (1) having means for thermo regulated heating, the said distillation flask (1) being provided with temperature probe (2) and stirrer (5,6), the said distillation flask being connected to a graduated receptacle (3) provided with means (4) for condensing distillate vapors, the said graduated receptacle (3) being provided at its top and bottom with corrosion monitoring probes (7) and temperature probes (2).
2. A device a claimed in claims 1 wherein the means for thermo regulated heating used is an external heating jacket.
3. A device as claimed in claims 1 & 2 wherein the means used for condensing distillate vapors is water cooled condensers.
4. A device as claimed in claims 1-3 wherein the monitoring probes used is an electrical resistance probe, electrochemical corrosion probe.
5. A device as claimed in claims 1-4 wherein the temperature probes used is thermocouple.
6. A device useful for evaluating corrosion inhibitors used for corrosion control of overhead distillation units substantially as herein described with reference to the examples and drawings accompanying this specification.
|Indian Patent Application Number||1863/DEL/1997|
|PG Journal Number||36/2004|
|Date of Filing||04-Jul-1997|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI- 110 001, INDIA|
|PCT International Classification Number||C23F 13/22|
|PCT International Application Number||N/A|
|PCT International Filing date|