characteristics of heavy residue pyrolysis: a systematic approach to the design of fouling...

8/9/2019 CHARACTERISTICS OF HEAVY RESIDUE PYROLYSIS: A SYSTEMATIC APPROACH TO THE DESIGN OF FOULING MITIGATION STRATEGIES USING CHEM…

http://slidepdf.com/reader/full/characteristics-of-heavy-residue-pyrolysis-a-systematic-approach-to-the-design 1/4

CHARACTERISTICS OF HEAVY RESIDUE

PYROLYSIS: A SYSTEMATIC APPROACH TO THE

DESIGN OF FOULING MITIGATION STRATEGIES

USING CHEMICAL ADDITIVES

Christopher Russell 1* and Ron Sharpe2

1 Nalco Energy Services Research and Development, Refinery

Process, 7705 Highway 90-A, Sugar Land, Texas, 77478, USA;2 Nalco Energy Services, Downstream Technical Consulting, Block102, Cadland Road, Hardley, Hythe, Southampton, SO45 3NP, UK

* [email protected]

Introduction

Over the last decade, there has been a marked shift in the

provenance of refinery crude slates due to diminishing reserves of socalled conventional petroleum. The trend toward relatively heavierand sour crudes includes an increase in the occurrence of opportunitycrude blends, which present distinct problems to refiners, such as

increased occurrences of fouling and corrosion. Acquisition offeedstock blends is usually accompanied by bulk compositionalanalysis, for example, asphaltene, sulfur, and metals content, sooperators may attempt to plan refining strategy and infer potential

processing issues. Unfortunately, such analysis is not alwaysindicative or conclusive, and refinery processes may often suffer,resulting in lower conversion and in serious cases, unforeseen shut-down and an outright ban on certain crude blend constituents. The

bottom of the barrel upgrading facilities are often amongst the mosteffected, especially those reliant on thermal conversion, such asvisbreaking and coking, where rampant fouling and deposition mayoccur. The work presented here concerns such thermal conversion

processes, with particular emphasis on fired heater process side performance. Here, we describe a pyrolysis technique for examiningthe potential fouling issues for various feeds, both those consideredconventional and opportunity, and introduce a novel method for

providing a relative ranking system, or index, which considers therates of surface and bulk coke formation together with intrinsicstability parameter changes with process severity. The data provides a

unique insight into cracking behavior and has permitted thedevelopment of a systematic approach to the selection of antifoulantadditives to assist unit engineers achieve operational targets, such asextended run-length and increased conversion, and, more efficient

decoking procedures, both on-line and off-line.

ExperimentalResidual Stability Analysis (RSA) Small aliquots of feed and

pyrolysis residue samples were made up into two toluene dilutions(75 % vol and 25 % vol) before being titrated with i-octane. Theoptically detected flocculation point (decrease in transmittance) wasthen used to calculate stability values for the sample. In essence, the

method is a modification to ASTM D 7157-05, as only two dilutionsare required for determination of stability values, which results infaster sample turn-around time.

Laser Particle Size Analysis A determination of bulk liquid

toluene insolubles was obtained using a standard particle counter.Samples of feed and pyrolysis residue were first diluted in toluene to0.1 % vol prior to flow through the counter. The machine provides a

numbered distribution over a set particle size range. With furthermanipulation, an approximate particle volume was calculated byassuming a spherical particle shape.

Pyrolysis Apparatus and Procedure The pyrolysis apparatusused in this study is a modified high temperature – high pressure

batch autoclave reactor. The main features include constant pressureoperation, distillation of cracked products, additive injection into

reactor during pyrolysis, and quantification of surface deposit viastainless steel micro-reactor inserts. A detailed description of thetechnique is described by Russell et al. (2010)1.

Results and Discussion

Feedstock Characterisation Instances of process foulingexcursions in the furnace tubes of thermal conversion units such as

visbreakers and cokers have been linked to certain characteristics offeed blends, such as sodium content and other inorganic constituents.However, evidence from the field is somewhat anecdotal, and bulkanalytical results are sometimes misleading. Furthermore, laboratorydata on fouling tendency that includes a measure of surface and bulk

coke formation is notoriously hard to find. The lack of a suitable feedcharacterisation method that indicates fouling tendency has led unitoperators and service providers alike to be occasionally caught offguard when processing opportunity crude blends, and even

misdiagnose problems and prescribe ineffective treatment programs.A characterisation method was therefore developed by Nalco that

permits full examination of stability parameter changes and foulant

evolution with increasing severity, and thus some relative ranking offeed fouling tendency. Although the reasons behind the variation in

fouling tendency are in the early stages of proprietary development,the ranking system allows for a systematic design of antifoulantadditive mitigation strategies. The characterisation provides data overa full profile covering a wide range of thermal severities, represented

by a single data point i.e. each data point represents a single batch

pyrolysis experiment. The method of course has drawbacks, such aslack of dynamic flow, however, this is more than compensated for byhigh sheer stirring, and the generation of representative tar product ateach severity that is of a quantity that allows a full range of test work.

The novel aspect of the apparatus is the inclusion of a convenientmethod for the accurate and precise measurement of surfacedeposition during pyrolysis.

Nalco’s service package for visbreaker management includes theinstallation and operation of vistar stability and solids monitoring

equipment. Nalco has developed the equipment within the research

and development department, and it consists of a laser particlecounter for the assessment of toluene insoluble particulates, and aResidual Stability Analyzer (RSA). The RSA is based on the concept

outlined in ASTM D 7157-05, and provides a measure of intrinsicstability (S ), oil solvency power (So) and asphaltene solubility (Sa).

The S value is primarily used for unit monitoring, and may bedirectly correlated to other stability monitoring methods such as the Pvalue. The other stability parameters, So and Sa, may be examined intandem to provide some indication of the formation of insoluble

asphaltene or coke precursor like material. The concept is outlined byWiehe (2008)

2. Essentially, when the solvency power of the oil

surrounding the asphaltenes becomes less than the asphalteneinsolubility, there is the potential for insoluble foulant formation,

especially on hot surfaces. The severity at which this occurs isdifferent for every feed blend, two examples of which are displayed

in figures 1 and 2. Here feed blend A reveals the potential fordestabilized foulant formation at a thermal severity of 27 thermal

severity minutes (TSM), whereas feed B reveals this threshold to beat 35.7 TSM. The data alone indicates feed A to have relatively morefouling potential than feed B. However, as mentioned above, there issome evidence that the concentration of certain feed constituents,

(e.g. inorganic particulates), can have a dramatic effect on fouling potential at process temperatures. It is important, therefore, toemphasize that the stability testing here is performed at ambienttemperature, whereas under process conditions, the point of

Prepr. Pap.-Am. Chem. Soc., Div. Energy Fuels Chem. 2012 , 57(2), 1017

Proceedings Published 2012 by the American Chemical Society



inst

anal par mg

cok dep

peri

Fig

Fig

InarotheThe

foreacfoulsol

of r negldepsom

andStauni

be t

alsoho

ability may wel

ytical detectionmeters. The pri/ g pyrolysis p

e (toluene insolosit (also tolueod in this study

re 1. Full char

re 2. Full char

igure 1, the and 5 TSM, wh by a rapid, cat three stages of

every feed, wit feed: The Indant precursor bility via side-c

esins, and chaigible generati

osition first bece extent on bot

its relative attr e is representeue for each feee prevailing co

characterizedever, catalytic

l be at a relati

limits may alsomary y-axis inroduct, with fil

ubles), and fille insolubles). Tis denoted by a

acterisation of f

acterisation of f

pearance of dch is followedstrophic, perio

surface coke for

h durations anction Period itransformation

hain cleavage,

ges in maltenon and deposimes significant the chemical

ction to foulant by a gradual r d. Over this stake formation m

by rate and orowth plays a

ely lower seve

play a part in cigures 1 and 2led squares de

d diamonds rehe duration of talytical detecti

eed blend A.

eed blend B.

etectable surfac by an initial pe

of depositionmation is a com

rates at eachthought to rep (e.g. decreaondensation an

e solvency) init. The pointthough must al

and physical nat

or foulant precate of depositioge, catalytic gr chanism. The S

set severity.ever-diminishi

rity. Furthermo

alculating stabilrepresents cokeoting bulk liq

resenting surf he coke inductin limits.

e coke occursiod of depositit around 14 TSmon characteris

tage differentresent a periode in asphalte dehydrogenati

tially resultingat which surf o be dependenture of the surf

ursors. The Init. The rate is alwth is thoughtignificant Stage

t these severitg role, as foul

re,

tyinid

ceon

atn,.

tic

orofneon

incetoce

ialsotois

esnt

film be

key rolsimilarthe bul

used toInitialleach edeposit

the pre

order oare uni

period

coke aexamplasphaltA, the

a signianalysifeed. Sabove,

where:

Coke; i T

inductiand catwith a

Figure

Arelative/ C, aamena

set of

foulingresidegroupAfrica.

period,

deposit A

above

liquid

comes thicker.

e in increasindepositional rek liquid. There

describe or c, however, the

vent describeded after 5 TSM,

dicted occurre

f these characteque for each f for surface dep

ppears at 20.5e in figure 1.ene formation osurface fouling

icant observatis. Coke formatich information

have been inclu

Nalco Resid FST = stability

p = Induction P

e fouling index

on period, as oastrophically dulk H / C meas

3. Nalco Fouli

expected, samly higher foulin there may bele for insolubil

feeds, and ma

feed of moderaith the conve

of feed blend tThese feeds hand therefore

ion over bulk li

tifoulant Add

ombines stabil

oke formation

Instead, radical

surface foulagime maybe ap are therefore

aracterize a feenduction perioin figure 1. I

followed by bu

ce of insoluble

ristics is not ueed. For instanosit is very sh

TSM, relativeherefore, despi

ccurring at a reltendency is act

n, which is noton rate is also, including theded in a relative

ouling Index =threshold; BC

eriod; k = Rate

is highly weig

ce this is breacevelop. The fourement of the f

g Index with H

ples with a relg tendency than relatively mor ty and coke for

therefore be c

te fouling. Feedtional feed set.ypes whose pr ave a distinctly a strong te

uid coke forma

itive Program

ty parameters t

tendencies for

formation is th

t thickness an plied to the co

any paramete

d’s coke gener duration will bn this case, slk liquid coke a

asphaltenes at

usual, but the r ce, in figure 2,rt, at 0.5 TSM,

ly longer thate the predictiatively lower sally greater for

discernable fro significant cheverity of form fouling index:

{(ST)(BC ip; k = Bulk Coke;

ted to the durat

hed, fouling caling index is peeds in figure 3.

/ C ratio.

tively low H /those with rela

e polynuclearmation. Feed

lassed as a rel

B, on the otherIn fact, Feed

ovenance is Br short surfacedency toward

tion.

Design Theogether with s

he first time t

ught to play a

d hardness. Ae generated ins that may be

ation potential.e compared forrface coke is13 TSM, then

27 TSM. The

elative timingsthe induction

, whereas bulk

for the feedn of insolubleverity for feedfeed B. This is

conventionalracteristic of aation described

(SC ip; k )}SC = Surface

ion of the coke

n quite rapidlylotted together.

C ratio exhibitively higher H

aromatic coresresides in this

atively normal

hand, does not belongs to a

azil and Westcoke induction

surface coke

data presentedrface and bulk

describe feed





sig

betrelais u

depwhisupis u

that

concokicok

and

theres

thefor

preof

theand

Fig

desi

In t

cokithe

pro

oppexhidepfollwit

thro

up tto tto cforden

startuntr

periapp

tem

ificant surface

een 1.4 and 1.ively fast rate.controllable. T

osition is controch there is catarsaturated, andcontrollable. F

run length

ersion may beng unit, which

e formation cou

away from theDepending onspecifically delt in increased r

two. An exampa visbreakerious feed blend

p to 35% of a

leading furnacetreated campai

re 7. Fieldgned antifoulan

he initial untre

ng is so rapid tunit shut downessing can leadAn investigat

ortunity feed us bit Feed Typeosition over fowing run was

continuous

ughout. In this t

o 35% opportue untreated ru

onversion increa prescheduled

oted by the blue

up, there iseated run. Simod of time thaears to be appa

erature (TMT)

coke generation

, where gener t these severiti

he data suggest

lled, or inhibitestrophic depositreaches a thresor a visbreakin

ay be exten

increased withoperates at a sld potentially b

urnace.the objectives osigned furnaceun length or co

le of such a casnit, where fol

, experienced searticularly pro

skin tube tempns.

data depictingt additive packa

ated run (deno

hat conversionor decoking aftto significant loion into the

ing the techniq behavior i.e. s

rmation of instarted using thhigh tempera

reated run the f

ity crude, and c, therefore ther

ase. In fact, the, larger scale,data points in f

a dramatic dif lar to the labo coke surfaceent. After arou

begins to rise,

is markedly in

tion and deposies, the generatios that surface c

, up to a point oion. Perhaps thold beyond whi unit, the labora

ed with stabl

little change toignificantly hig shifted into th

f unit engineers,heater antifoulversion, or an

e history is dislowing goodvere fouling wilematic opport

erature is displ

the performage to visbreaker

ted by data in

is reduced afterer 100 days. Suss of revenue.fouling chara

es described aowing a high t

olubles in thetwo stage pass

ure coke su

eed compositio

onversion targee was not an agtarget was to mturn around. Tigure 7. Over th

erence betweeatory studies,deposition is r nd 60 days or

but at a signif

creased to a sta

tion proceeds an of coke mater ke formation a

r severity, beyo system becom

ch coke formatitory data sugge

e conversion,

run length. Foer severity, m

e coke drum its

the applicationant package mcceptable ratio

layed in figureesults with thh the introductinity crude. He

yed for untreat

ce of laboratfurnace.

red), heater tu

only 60 days ach interruptions

teristics of t

ove revealed itndency to surf bulk phase. Tivation procedu pressant dosa

was similar, w

t remained simigressive approaaintain run lenhe treated rune initial days af

the treated an increase to tlatively inhibito, the tube me

icantly lower r

ge

aialnd

ndesonsts

or

ast

elf

ofayof

7,eironre,

ed

ry

be

ndin

is

tocehere,ge

th

archthiser

ndheedtal

te

than u

conver shut dooperati

designelengthrefiner

T

approa

involviimpactcoke fo

Conclu

Adevelo

tendencand atechniqfeeds

surfacethe obstreatme

informa high passiva

as ther negate

proced particul

laboratonset ooperatoIndeed,

heaterindicat

by at le

Refere(1) R

24(2) W

C

(3) SSPa

der untreated

ion is reducedwn date. Howeg comparabl

d antifoulant tr by 70 days, or

operators aree data prese

h to the desig

g precise andon fired heater rmation and de

sions

laboratory pyed by Nalco t

y of heavy resmeasure of bue offers a mnd those feeds

fouling over berved differencnt programs

tion on foulingaffinity fortion is a key ta

is some feed by the deve

re, which alsoar high temp

ry conditions,f significant srs may be ablethe program d

n a visbreaker,d that the treatast 70 %.

cesssell, C. A., Cr , 5483.iehe, I. A. ProcC Press, Taylo

arpe, R., Russelrface passivatiotent 8,092,618

onditions. At

slightly to facilver, over the p to untreated

eatment packag70 %. This isery satisfied witted here dem

n of antifoulan

nique laborato performance bosition.

rolysis apparat characterize a

due feeds by clk liquid andthod to distinthat exhibit a

lk liquid phases is currently uhave been sp

tendency, andurface foulingtic, although sc

type specificity.lopment of axhibits a usefulerature coke

the treatment prface coke for to extend run

escribed above

where the leadiment package e

zier, S., Sharpe

ss chemistry ofr and Francis Gr

l, C. A., Crozien technique for2, January 10,

run length of

itate operationriod when the

conditions, t

e succeeded ina significant inh.onstrates how

additive treat

y work can hay effectively re

us and procend relatively r

ombining stabilsurface coke f uish betweenrelatively grea

coke formation.nder investigatiecially design

hether or not t. In such instreening in the r

. The variationnew two sta

synergistic relasuppressant m

ogram effectivation, and su

length or increwas applied to

g skin tube mextended visbre

, R. Energy and

petroleum macr oup: Florida, 20

, S. (Nalco Co.,reduction of fo012

170 days, the

to the targetedvisbreaker washe laboratory

increasing runcrease that the

a systematic

ent programs

e a significantducing surface

ure has beennk the fouling

ity parameters,ormation. Theormal foulinger affinity for

The reason foron. Antifoulanted using the

e feed exhibitsances, surfaceig is necessary

was somewhatge passivationtionship with aaterial. Under

ely inhibits thegests that unitse conversion.a real furnace

tal temperatureker run length

Fuels, 2010 ,

omolecules,08

USA).ling. US



characteristics of heavy residue pyrolysis: a systematic approach to the design of fouling...

Documents