Distillation Blending and Cutpoint Temperature Optimization (DBCTO) in Scheduling Operations

Brenno C. Menezes

Postdoctoral Fellow

Technological Research Institute

São Paulo, SP, Brazil

Jeffrey D. Kelly

CTO and Co-Founder

IndustrIALgorithms

Toronto, ON, Canada

Ignacio E. Grossmann

R. R. Dean Professor

Carnegie Mellon University

Pittsburgh, PA, US

Lincoln F. L. Moro

Senior Consultant

PETROBRAS

São Paulo, SP, Brazil

October 6th, New Orleans, LA, United States

AI L

2015 [Q&A and Technology Forum]PD -15-08

Objectives

• To improve efficiency, effectiveness and

economy of mixing/blending, reacting/converting

and separating/fractionating inside the oil-

refinery.

• To integrate blending of several streams’

distillation curves with also shifting or adjusting

cutpoints of distilled streams (i.e., initial and/or

final boiling-points, IBP and FBP) in order to

manipulate their TBP curves in an either off- or

on-line environment (Kelly et al, 2014).


Perfect/Ideal/Sharp

Separation

Distillation Curves

From Other

Units

From CDU

Kerosene

Light Diesel

ATR

C1C2

C3C4

N

K

LD

HD

Naphtha

Heavy DieselCrude

CDU

Temperature

Yie

ld (

%)

N

K

LD

HD

N K LD HD ATRFeed


• Li, Hui, Li, A. Integrating CDU, FCC and Blending

Models into Refinery Planning. Comput. Chem.

Eng. 2005.

• Alattas, Grossmann, Palou-Rivera, Integration of

Nonlinear Crude Distillation Unit Models in Refinery

Planning Optimization. Ind. Eng. Chem. Res. 2011.

• Mahalec, Sanchez, Inferential Monitoring and

Optimization of Crude Separation Units via Hybrid

Models. Comput. Chem. Eng. 2012.

• Ali, Yusoff, Determination of Optimal Cut Point

Temperatures at Crude Distillation Unit using

Taguchi Method, Int. J. Eng. & Tech., 2012.


• Cutpoint temperatures (IBP and FBP) are strong

functions of both the light and heavy draw flows

and temperatures for the distillates leaving the

column, tower or side-strippers.

• Other causal factors or process variables

affecting cutpoint temperatures include draw tray

technology, location, efficiency and pressure,

pump-around flows (intermediate refluxes), duty

and return temperature as well as stripping steam

flow which all influence and contribute to the

column’s internal vapor and liquid traffic defining its

separation/fractionation operation.


• Four (4) principles for Nelson (1945) (cf. Kaes,

2009):

‒The yield of a given product or fraction is

primarily a function of the composition of

the feed mixture, not the degree of

separation.

‒The number of trays only slightly alters the

boiling range of the products as defined by

ASTM initial and final boiling points.


• Four (4) principles for Nelson (1945) (cf. Kaes,

2009):

‒The initial boiling point of side draw products is

always low, and must be corrected by either

steam stripping or reprocessing (refluxing).

‒The final boiling point of a side draw

product is primarily controlled by opening

or closing the draw valve to change the

yield.


T01 T05 T10 T30 T50 T70 T90 T95 T99

Temperature

Yie

ld (

%) Back-end:

Front-end:

New Temperature: NT

Old Temperature: OTNew Yield: YNT


Yie

ld (

%) Back-end:

Front-end:

Temperature (⁰F)

T99: 230→214

T01: 91→85


Yie

ld (

%) Back-end:

Front-end:

95.87%

-1.45%

Temperature (⁰F)

T99: 230→214

T01: 91→85


Yie

ld (

%)

Temperature (⁰F)

Difference in Yield: DYNT DYNT99

DYNT01


DBCTO

• Conservative and adaptive TBP cutpoint method

to marginally/incrementally adjust/shift distillate

yields when “non-sharp” (non-ideal, imperfect)

separation exists i.e., without an “infinite” number

of stages and/or reflux.

• Uses ASTM D86 cutpoint temperatures that are

not as suitable as TBP temperatures given that

they over-predict the initial boiling-point (IBP) and

under-predict the final boiling-point (FBP) – but,

they are quicker to measure in the lab and field!


DBCTO

From Other

Units

From CDU

Temperature (⁰F)

Yie

ld (

%)

ASTM D86

TBP

Inter-conversion

Evaporation

Curves

Interpolation

Ideal Blending

Evaporation

Curve

Multiple

Components

Final

Product

ASTM D86

Interpolation

Inter-conversion

TBP


Cutpoints.+Process Variables

• Step1: Collect and Convert ASTM D86

laboratory or field analyzer historical data to TBP

temperatures using API TDB 3A1.1.

• Step2: Collate process variable data properly

synchronized with ASTM D86 laboratory or field

data.

• Step3: Regress selected TBP cutpoint

temperature (typically 90%, 95% or 99%) with

causal process variables previously mentioned

such as draw flow, temperature, pressure, steam,

pump-around duty, etc.


Curves Interpolation

What if I need T85%?

Use the interpolated

curve to extract any point


Example

• Maximize flow of DC1 and DC2 ($0.9 for DC1 and

$1.0 DC2) with lower and upper bounds of 0.0 and

100.0 each (for fixed DC3 and DC4 at 1). The ASTM

D86 specifications for their blend are D10 ≤ 470, 540

≤ D90 ≤ 630 and D99 ≤ 680. Only DC1 is an CDU stream.

DC1 DC2 DC3 DC4

1% 305.2 (353) 322.2 (367) 327.0 (385) 302.4 (368)

10% 432.9 (466) 447.1 (476) 405.2 (435) 369.7 (407)

30% 521.6 (523) 507.1 (509) 457.1 (462) 441.0 (449)

50% 565.3 (551) 549.5 (536) 503.3 (492) 513.8 (502)

70% 606.4 (581) 598.4 (573) 551.1 (528) 574.3 (550)

90% 668.3 (635) 666.1 (634) 605.8 (574) 625.4 (592)

99% 715.7 (672) 757.7 (689) 647.0 (608) 655.2 (620)

Table. Inter-Converted TBP (ASTM D86) Temperatures in Degrees F.


Example

Figure. ASTM D86 distillation curves, including the final blend, which

is determined by the blended TBP interconversion to ASTM D86.

The new and

optimized TBP curve

for DC1 given its

front and back-end

shifts is now:

[(1.053%,312.8),

(10.015%,432.9),

(31.188%,521.6),

(52.361%,565.3),

(73.534%,606.4),

(94.707%,668.3),

(98.995%,689.3)]

Yie

ld (

%)

Temperature

For DC3 and DC4 fixed at 1,

DC1 takes a new profile to match D90 of

the blend.


CDU and Blender integration

DBCTO in Scheduling Oper.

FCC

DHT

NHT

KHT

REF

DC

B

L

E

N

SRFCC

Fuel gas

LPG

Naphtha

Gasoline

Kerosene

Diesel

Diluent

Fuel oil

Asphalt

Crude-Oil

ManagementCrude-to-Fuel Transformation Fuel Blending

and Distribution

VDU

Menezes et al. (2015)

CDU and Blender integration


Summary

• Use TBP temperatures instead of ASTM D86.

• Fit a regression model i.e., MLR, PCR, PLS or DR

(Dynamic Regression), of how causal process

variables affect the selected TBP cutpoint

temperature (at 90%, 95% or 99%) and not the

distillate yield explicitly.


Novelty


Impact in the Industry

• Integration of the distillation unit and fuel blending

using IBP and FBP (cutpoints) of the streams.

• Based on daily experimental data run gathered in the

field (ASTM D86) instead of blending indices

correlations.

• Reduce losses by off-spec fuels.

• Reduce the blender RTO efforts to get on-spec fuels.

Distillation Blending and Cutpoint Temperature Optimization (DBCTO) in Scheduling Operations

Engineering

Transcript of Distillation Blending and Cutpoint Temperature Optimization (DBCTO) in Scheduling Operations