U.S. patent application number 13/187819 was filed with the patent office on 2013-01-24 for advisory controls of desalter system.
The applicant listed for this patent is Arjun Bhattacharyya, Richard Stephen Hutte, Manish Joshi, Vijaysai Prasad, Jayaprakash Sandhala Radhakrishnan, Jeffrey Allen Zurlo. Invention is credited to Arjun Bhattacharyya, Richard Stephen Hutte, Manish Joshi, Vijaysai Prasad, Jayaprakash Sandhala Radhakrishnan, Jeffrey Allen Zurlo.
Application Number | 20130024026 13/187819 |
Document ID | / |
Family ID | 47044732 |
Filed Date | 2013-01-24 |
United States Patent
Application |
20130024026 |
Kind Code |
A1 |
Prasad; Vijaysai ; et
al. |
January 24, 2013 |
ADVISORY CONTROLS OF DESALTER SYSTEM
Abstract
The present invention concerns a method of providing advisory
controls for a desalter system. The method allows a user to
continuously monitor performance of the desalter system, to
continuously monitor position of the emulsion band (or rag layer),
to control the emulsion band using demulsifiers, and to recommend
to users how to maintain optimal pressure drop at the mix valve of
the desalter system. This is achieved by using a first principles
based model combined with an ultra-sound sensor. The ultra-sound
sensor measures the position, quality and size of the emulsion
band. The first principles based model takes into account the
geometry of the desalter system, physical properties of the crude
oil and water, as well as the operating conditions. Thus, the
method provides users with sensing of an emulsion layer through
ultrasound measurements and also gives recommendations on
appropriate corrective actions to be initiated during upsets.
Inventors: |
Prasad; Vijaysai;
(Bangalore, IN) ; Radhakrishnan; Jayaprakash
Sandhala; (Bangalore, IN) ; Zurlo; Jeffrey Allen;
(The Woodlands, TX) ; Hutte; Richard Stephen;
(Boulder, CO) ; Bhattacharyya; Arjun; (Bangalore,
IN) ; Joshi; Manish; (Bangalore, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Prasad; Vijaysai
Radhakrishnan; Jayaprakash Sandhala
Zurlo; Jeffrey Allen
Hutte; Richard Stephen
Bhattacharyya; Arjun
Joshi; Manish |
Bangalore
Bangalore
The Woodlands
Boulder
Bangalore
Bangalore |
TX
CO |
IN
IN
US
US
IN
IN |
|
|
Family ID: |
47044732 |
Appl. No.: |
13/187819 |
Filed: |
July 21, 2011 |
Current U.S.
Class: |
700/272 |
Current CPC
Class: |
G01F 23/2962 20130101;
B01D 17/04 20130101; C10G 33/08 20130101; C10G 33/04 20130101; B01D
17/12 20130101; C10G 2300/80 20130101; C10G 31/08 20130101 |
Class at
Publication: |
700/272 |
International
Class: |
G05B 21/02 20060101
G05B021/02 |
Claims
1. A method of providing advisory controls for a desalter system,
comprising: processing a crude oil blend in an oil refinery,
wherein the crude oil blend creates an emulsion band; utilizing a
desalter system to desalt the crude oil blend; continuously
monitoring performance of the desalter system; continuously
monitoring position of the emulsion band; controlling the emulsion
band using chemicals; and providing recommendations for maintaining
optimal pressure drop at a mix valve of the desalter system.
2. The method of claim 1, wherein the emulsion band comprises crude
oil and water, positioned as a distinct layer between a water and
crude oil interface.
3. The method of claim 2, wherein the emulsion band is dynamic in
position and size.
4. The method of claim 3, wherein the chemicals used to control the
emulsion band are demulsifiers.
5. The method of claim 4, wherein the demulsifiers comprise
oxyalkylated amines, alkylaryl sulfonic acid and salts thereof,
oxyalkylated phenolic resins, polymeric amines, glycol resin
esters, polyoxyalkylated glycol esters, fatty acid esters,
oxyalkylated polyols, low molecular weight oxyalkylated resins,
bisphenol glycol ethers and esters and polyoxyalkylene glycols.
6. The method of claim 5 further comprising adding the demulsifiers
until point of inflection is reached.
7. The method of claim 1, wherein an ultra-sound sensor is used to
monitor position of the emulsion band.
8. The method of claim 7, wherein the ultra-sound sensor measures
the position, quality or size of the emulsion band.
9. The method of claim 8, wherein a first principles based model is
used to monitor performance of the desalter system.
10. The method of claim 9, wherein the first principles based model
utilizes geometry of the desalter system, physical properties of
crude oil and water, and operating conditions of the desalter
system.
11. The method of claim 10, wherein a Model Predictive Controls
utilizes the first principles based model to control the emulsion
band using chemicals.
12. The method of claim 11, wherein the Model Predictive Control
can utilize performance measurements, salt removal, water removal,
and oil content of brine to adjust model parameters.
13. The method of claim 12, wherein the Model Predictive Controls
doses the chemicals so that the sensed emulsion band is under
control.
14. The method of claim 13, wherein the Model Predictive Controls
provides advisory solutions to users on effect of changing the mix
valve delta pressure drop based on performance of the desalter
system.
15. The method of claim 14, wherein recommendations are provided to
users based on effect variation in wash water flow rate and based
on performance of the desalter system.
16. The method of claim 1, further comprising: processing a new
crude oil blend in the oil refinery; and recalculating the desalter
system based on the new crude oil blend.
17. The method of claim 16, further comprising: determining
effectiveness of chemical treatment; and initiating appropriate
corrective actions during upset conditions.
18. The method of claim 17, wherein the chemical treatment
comprises adding demulsifiers to keep position and size of the
emulsion band under control.
19. The method of claim 18, wherein advisory solutions and
recommendations are provided to users when initiating appropriate
corrective actions during upset conditions.
20. The method of claim 19, wherein the advisory solutions are
provided to users for changing the mix valve delta pressure drop
based on performance of the desalter system.
Description
FIELD OF INVENTION
[0001] The present invention pertains to a method of providing
advisory controls for a desalter system. More particularly, the
method continuously monitors performance of the desalter system,
continuously monitors position of the emulsion band, controls the
emulsion band using chemicals and provides recommendations for
maintaining optimal pressure drop at the mix valve.
BACKGROUND OF THE INVENTION
[0002] Desalting is typically the first operation in oil
refineries. Crude oil that is processed without desalting is
detrimental to the refinery assets, leading to severe corrosion
problems. The desalter system removes the majority of salts in the
crude oil by injecting water into the system. Because of the higher
solubility in water, salts move from the crude oil to the water
phase. Thus, desalter systems are typically large gravity settling
tanks that provide enough residence time for both the water and the
crude oil to settle. Usually density of water is higher than that
of oil hence, water settles at the bottom of the desalter system
and crude oil leaves the unit from the top. Further, the addition
of an electrical grid at the top of desalter systems promotes the
separation of crude oil at the top and the water to settle at the
bottom.
[0003] In ideal operation, the crude oil and water should have a
very thin interface. However, in practice, during the operation, an
emulsion of water in crude oil is formed as a distinct layer
between the water and crude oil. This emulsion band is also called
a rag layer, and can be quite dynamic in position and size.
Typically, these emulsion bands can cause oil refiners to run less
than optimum wash water rates and low mix valve pressure drops,
which reduces its efficiency for salt and sediment removal.
Excessive growth of these emulsion bands can shorten the
operational lifespan of the electrical grids in the desalter
system, thus bringing the entire refinery operations to a halt.
Accordingly, it is not only important to monitor and control the
performance of the desalter system, but also to keep the position
and size of the emulsion band under control.
[0004] Performance of the desalter is characterized based on three
parameters: percentage salt removal in desalted crude oil relative
to that of feed, percentage water removal in desalted crude oil
relative to that of feed, and percentage oil carry over in brine or
desalter water exit stream. Optimal operation of the desalter means
very high values of salt and water removal and close to zero value
for oil carryover in water.
[0005] Furthermore, operation of the desalter system is difficult
and requires an expert with vast experience to make the right
corrective decision. The crude oil blend in refineries changes
frequently, and when the refineries process a new blend, the
operators need to be able to judge performance of the desalter
system without direct visibility of the emulsion band (rag layer),
to determine effectiveness of the chemical treatment, and to
initiate appropriate corrective actions during upset
conditions.
[0006] Thus, there exists a strong need for a method of providing
advisory controls for a desalter system, which continuously
monitors performance of the desalter system, continuously monitors
position of the emulsion band, controls the emulsion band using
chemicals and provides recommendations for maintaining optimal
pressure drop at the mix valve.
SUMMARY OF THE INVENTION
[0007] In one exemplary embodiment of the invention, a method of
providing advisory controls for a desalter system is disclosed. The
method allows a user to continuously monitor performance of the
desalter system, to continuously monitor position of the emulsion
band (or rag layer), to control the emulsion band using
demulsifiers, and to recommend to users how to maintain optimal
pressure drop at the mix valve. In another embodiment, this is
achieved by using a first principles based model combined with an
ultra-sound sensor. The ultra-sound sensor measures the position,
quality and size of the emulsion band. The first principles based
model takes into account the geometry of the desalter system,
physical properties of the crude oil and water, as well as the
operating conditions.
[0008] Once the ultra-sound sensor measures the emulsion band, a
Model Predictive Controls is utilized to dose the chemicals so that
the sensed emulsion band is under control. Advisory solutions are
then provided to users on the effect of changing the mix valve
pressure drop based on the performance of the desalter system.
Recommendations are also provided to the users based on the effect
variation in wash water flow rate and based on performance of the
desalter system. Thus, the method provides users with sensing of an
emulsion layer through ultrasound measurements and also gives
recommendations on appropriate corrective actions to be initiated
during upsets.
[0009] The present invention and its advantages over the prior art
will become apparent upon reading the following detailed
description and the appended claims with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] These and other aspects of the invention will be understood
from the description and claims herein, taken together with the
drawings showing details of construction and illustrative
embodiments, wherein:
[0011] FIG. 1 is a schematic process diagram showing one embodiment
of the invention;
[0012] FIG. 2 is a schematic process diagram showing the desalter
model framework of the present invention;
[0013] FIG. 3 is a graph depicting the dynamic effect of chemical
dosage of the present invention;
[0014] FIG. 4 is a graph depicting the dynamic effect of mix valve
delta P (pressure) of the present invention; and
[0015] FIG. 5 is a graph depicting a step change in wash water rate
of the present invention.
DETAILED DESCRIPTION
[0016] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as "about", is not limited
to the precise value specified. In at least some instances, the
approximating language may correspond to the precision of an
instrument for measuring the value. Range limitations may be
combined and/or interchanged, and such ranges are identified and
include all the sub-ranges stated herein unless context or language
indicates otherwise. Other than in the operating examples or where
otherwise indicated, all numbers or expressions referring to
quantities of ingredients, reaction conditions and the like, used
in the specification and the claims, are to be understood as
modified in all instances by the term "about".
[0017] "Optional" or "optionally" means that the subsequently
described event or circumstance may or may not occur, or that the
subsequently identified material may or may not be present, and
that the description includes instances where the event or
circumstance occurs or where the material is present, and instances
where the event or circumstance does not occur or the material is
not present.
[0018] As used herein, the terms "comprises", "comprising",
"includes", "including", "has", "having", or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article or apparatus that comprises a
list of elements is not necessarily limited to only those elements,
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus.
[0019] The singular forms "a", "an", and "the" include plural
referents unless the context clearly dictates otherwise.
[0020] Disclosed is an improved method of providing advisory
controls for a desalter system. The method allows a user to
continuously monitor performance of the desalter system, to
continuously monitor position of the emulsion band (or rag layer),
to control the emulsion band using demulsifiers, and to recommend
to users how to maintain optimal mix valve delta pressure (delta P)
drop at the mix valve. In one embodiment, this is achieved by using
a first principles based model combined with an ultra-sound sensor.
The ultra-sound sensor measures the position, quality and size of
the emulsion band. The first principles based model takes into
account the geometry of the desalter system, and physical
properties of the crude oil and water, as well as the operating
conditions.
[0021] The method of providing advisory controls for a desalter
system utilizes the process model and the actual constraints that
arise while controlling the desalter system. Typically, there are
three manipulated variables that control the desalter system. The
variables include the chemical dosing pump that controls the
release of chemicals, such as demulsifiers to control the emulsion
band. The mix valve delta pressure drop that controls the quality
of the emulsion formed depending on the percentage opening of the
valve. And, the wash water rate that controls the performance of
the desalter system (See FIG. 1).
[0022] The proposed method can also utilize online measurements of
performance parameters if available, these include percentage salt
and water removal in desalted crude and oil carry over in desalter
brine, these measurements can be used to estimate or fine tune
model parameters of the controller (See FIG. 1).
[0023] In one embodiment, based on above variables, the method of
providing advisory controls for a desalter system utilizes a Model
Predictive Control to automatically dose the chemicals such that
the sensed emulsion band is under control. Advisory solutions are
then provided to users on the effect of changing the mix valve
delta pressure drop based on the performance of the desalter
system. Recommendations are also provided to the users based on the
effect of variation in wash water flow rate which is based on
performance of the desalter system.
[0024] In operation, the desalter system is difficult to operate
and requires an expert with vast experience to make the right
corrective decision. For example, the crude blend in oil refineries
changes frequently. Thus, when refineries process a new blend
operators must recalculate and adjust chemical dosage, mix valve
pressure drop and wash water rates of the desalter system. However,
monitoring performance can be difficult as users do not have direct
visibility of the desalter system, they also do not know the
effectiveness of the chemical treatment or the appropriate
corrective actions to be initiated during upset conditions. The
proposed method addresses these concerns and allows users to have
sensing of the emulsion layer through ultra-sound measurements and
also gives recommendations on appropriate corrective actions to be
initiated during upsets.
[0025] Ultra-sound measurements are used to monitor position of the
emulsion band. An ultra-sound transmitter and receiver are inserted
at various levels of the desalter system, and the time of flight is
measured. The time of flight is the time it takes for the
ultra-sound to travel through the water from the transmitter to the
receiver. (See US 2006/0211128 A1, Johnson et al.).
[0026] Upset conditions cause the emulsion band to grow, so
operators need to monitor position of the emulsion band. Operators
want the emulsion band to be as small and as thin as possible.
Monitoring of the emulsion band can thus be done via sensing of the
emulsion band through ultra-sound measurements.
[0027] Furthermore, chemical treatment, or the addition of
demulsifiers is a difficult task if done without obtaining feedback
on the performance of the desalter system. Excessive addition of
the demulsifiers tends to stabilize the emulsion, but causes severe
performance issues with the desalter system. Subsequently,
underdoses are always ineffective in breaking the emulsions. Thus,
it is important to add the demulsifiers until the point of
inflection is reached. The point of inflection is determined when
maximum entitlement has been reached. Specifically, the addition of
chemicals improves performance to a certain point. Once this point
is reached, then performance will decrease with the addition of
chemicals. This maximum entitlement point is the point of
inflection.
[0028] Typical demulsifiers used in the chemical treatment of the
emulsion band include, but are not limited to, water soluble
organic salts, sulfonated glycerides, sulfonated oils, acetylated
caster oils, ethoxylated phenol formaldehyde resins, polyols,
polyalkylene oxides, ethoxylated amines, a variety of polyester
materials, and many other commercially available compounds.
Specifically, the demulsifiers can comprise oxyalkylated amines,
alkylaryl sulfonic acid and salts thereof, oxyalkylated phenolic
resins, polymeric amines, glycol resin esters, polyoxyalkylated
glycol esters, fatty acid esters, oxyalkylated polyols, low
molecular weight oxyalkylated resins, bisphenol glycol ethers and
esters and polyoxyalkylene glycols. This enumeration is, of course,
not exhaustive and other demulsifying agents or mixtures thereof
can be used as is known to one skilled in the art.
[0029] Furthermore, the operator advisory system recommends to
operators how to maintain optimal mix valve delta P drop at the mix
valve. Based on feedback options such as emulsion layer position,
crude oil properties and wash water rate, the effect of delta P on
performance is determined and recommendations are provided to the
operator. Further, depending on the maximum entitlement, operators
can make decisions to impact percentage opening of the mix valve as
well.
[0030] As shown in FIG. 1, Model Predictive Controls (MPC)
implementation of the desalter system 100 comprises a dynamic
desalter model, the model is built using the physics of the
desalter and establishes an explicit transfer function between the
chemical addition and performance, and delta P and performance.
Specifically, the MPC allows for manual control of the delta P 102
and automated control of chemical dosing 104 directly in the
desalter device 106. The delta P 102 and chemical dosing 104 are
continuously monitored, providing feedback 108 to the control room
(not shown) for the operators. The feedback options include
emulsion layer position, crude oil properties and wash water rate,
and the MPC implementation utilizes the feedback options to develop
a dynamic desalter model 100. Specifically, the MPC implementation
100 establishes explicit transfer functions between the chemical
addition 104 and performance 110, and the delta P 102 and
performance 110, wherein f(x.sub.1, x.sub.2, . . . x.sub.n), with
x.sub.1=emulsion layer position, x.sub.2=crude oil properties,
x.sub.n=wash water rate and optionally, x.sub.3=Salt removal from
crude, x.sub.4=Water removal from crude, x.sub.5=oil carryover in
brine
[0031] As shown in FIG. 2, a desalter model framework 200 comprises
an input of crude oil 202, which is continuously flowing into the
desalter model 204. Water 206 is then injected into the desalter
model 204, and is controlled by the mix valve delta P 208. The
water 206 mixes with the crude oil 202 in the desalter model 204,
and because of the higher solubility in water, salts move from the
crude oil to the water phase. The desalter model 204 then provides
enough residence time for both the water and the crude oil to
settle. Due to the density differences, water settles at the bottom
of the desalter model 204 and exits via a valve on the bottom 210,
and desalted crude oil leaves the desalter model 204 from the top
212.
[0032] Further, other inputs 214, such as dimensions of the
desalter model, atmospheric pressure, physical properties of the
desalter model, the efficiency limit of the electric field and
chemical dosage, are used to develop the dynamic desalter model.
From these additional inputs 214, the desalter model 204 creates
intermediate outputs 216, such as drop size distribution, and
emulsion layer height and thickness. The drop size distribution is
dependent on the delta P 208, wherein if the mix valve delta P 208
creates low pressure, drop size is smaller and salt removal
efficiency is high, but settling of the water is slower. Whereas,
if the mix valve delta P 208 creates high pressure, drop size is
larger and settling of the water is faster, but salt removal
efficiency is low. These additional outputs 216 are used to develop
a dynamic desalter model for use with the Model Predictive
Controls. For example, the Model Predictive Controls disclose the
following formula used to determine automatic online control of
chemical dosing and advisory control of delta P:
[ .eta. 1 .eta. 2 .eta. n ] = [ f 11 ( x 1 x n ) f 12 ( x 1 x n ) f
21 ( x 1 x n ) f 22 ( x 1 x n ) f n 1 ( x 1 x n ) f n 2 ( x 1 x n )
] [ Chemical Conc . .DELTA. P mix valve ] ##EQU00001##
[0033] .eta..sub.1.fwdarw.Performance Parameters (emulsion layer,
salt concentration, etc.)
[0034] x.sub.1.fwdarw.Measurements (temperature, density,
viscosity, etc.)
[0035] The proposed structure essentially helps to automate
performance through chemical dosing and gives recommendations to
the operator on effect of delta P on performance.
[0036] FIG. 3 depicts a graph showing online control of chemical
dosing. The dashed lines represent the maximum efficiency of the
chemical concentration. The MPC is able to establish explicit
transfer functions between chemical addition and performance.
[0037] FIG. 4 depicts a graph showing predictions/recommendations
for manually controlling the mix valve delta P. The dashed lines
represent the maximum efficiency of mix valve delta P. The MPC is
able to establish explicit transfer functions between delta P and
performance.
[0038] FIG. 5 depicts a graph showing a step change in the wash
water rate. Typically, the wash water rate is at 5%, however at
around 60 seconds, a step change occurred and the wash water was
adjusted accordingly.
[0039] In operation, the desalter model is created using the
physics of the desalter system. The desalter model is used in the
Model Predictive Controls to automate performance through chemical
dosing and to give recommendations to the operator on effect of
delta P on performance. To determine the desalter model, an overall
material balance is calculated:
[0040] The rate of change of rag layer thickness (dh/dt) can be
calculated using mass balance for the desalter system. Rate of
change of rag layer mass=Mass of Fluids In-Mass of Fluids Out. In
addition, Bernoulli's principle equation is used to relate the
pressure head and the velocity heads of the fluids inside the
desalter.
[0041] Further, the emulsion band thickness can be calculated for a
specific crude oil-water mixture from batch settling experiments
using correlation available in the literature. (See S. A. K.
Jeelani and Stanley Hartland, Prediction of Steady State Dispersion
Height from Batch Settling Data, AIChE Journal, 31(5), 711,
(1985)).
[0042] Then, water and crude oil volumes are calculated in the
desalter, using the desalter's actual shape (including the dished
end portions) and the position of the rag layer. The volumes are
expressed as a function of the height of the rag layer.
[0043] The size distribution of the water droplets at the desalter
entrance is a function of various parameters including the crude
oil and water flow rates, fluid properties (viscosity, density, and
surface tension), temperature, pressure drop at the mix valve,
dimensions of the mix valve. The Sauter mean diameter of the water
droplets is calculated using these parameters.
[0044] The overall drop size distribution of water droplets is
determined from the Sauter mean diameter using multiple
correlations. (See Paul D. Berkman and Richard V. Calabrese,
Dispersion of Viscous Liquids by Turbulent Flow in a Static Mixer,
AIChE Journal, 34(4), 602, (1988)).
[0045] The terminal settling velocity of the water droplets in the
oil phase is calculated using Stokes law. It takes into account the
diameter of the particles, viscosity of the continuous phase and
the difference in densities between the two phases. The volume
fraction of the dispersed phase (water) is used to calculate the
hindered settling velocity of the water drops.
[0046] In a desalter, both the demulsifier chemicals and the
electrical field generated by the grid perform one function--to
reduce the repulsive forces between the water droplets, agglomerate
them, leading to coalescence and increase in size of the drops. The
quantitative effect of the chemical dosage and electrical field on
the droplet size is added in the form of empirical correlations.
These effects are incorporated in the form of a `size increase
factor`.
[0047] The individual residence times of the water phase and the
oil phases in the desalter are calculated using the respective flow
rates and the volumes occupied by each phase in the desalter. Based
on the residence time of the phases and the settling velocity of
the drops, a `Critical Drop Diameter` is calculated. This is the
smallest drop size that can settle into the water phase within the
available residence time. Drops smaller than this critical size, do
not settle and are carried over in the oil stream. Based on the
fraction, the water-separation efficiency of the desalter is
calculated.
[0048] Finally, the electrical grid, and the effect of the mix
valve delta P performance and chemical selection and dosage is
determined. Based on these model steps, model results are
calculated to determine predicted drop size distribution, predicted
emulsion band thickness, predictive demulsifier dosage, etc. These
predictions can then be used to create the desalter model. The
desalter model is then used in the Model Predictive Controls to
automate performance through automatic, online chemical dosing and
to give recommendations to the operator on the effect of delta P on
performance.
[0049] While this invention has been described in conjunction with
the specific embodiments described above, it is evident that many
alternatives, combinations, modifications and variations are
apparent to those skilled in the art. Accordingly, the preferred
embodiments of this invention, as set forth above are intended to
be illustrative only, and not in a limiting sense. Various changes
can be made without departing from the spirit and scope of this
invention. Therefore, the technical scope of the present invention
encompasses not only those embodiments described above, but also
all that fall within the scope of the appended claims.
[0050] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
processes. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. These other examples are intended to be within the
scope of the claims if they have structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
* * * * *