cdu enhance energy efficiency

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Enhancing energy efficiency in the CDU

Crude distillation is proba-

bly the oldest process inany renery congura-

tion. In the early days ofrening, black oil in simple

batch stills was used toproduce lighting oil (kerosene)as the main product, besideasphalts to meet the needs ofthe times. Following the devel-opment of the internalcombustion engine, the needfor improved fractionation led

to the use of simple fractiona-tion columns. Demand forincreased throughputs andhigher quality productsresulted in the development ofcontinuous fractionation units.

A simple crude distillationunit constructed in earliertimes included a basic heatexchanger train in whichgenerally hot atmospheric resi-

due was used for preheating,as well as a furnace and acolumn which would not haveany pumparound ows. Theonly aim was to meet productdemands and produce higherquality products. Lowering theenergy consumption of the unitwould not be considered animportant issue in a time ofabundant and low-cost crude.

Revisiting your crude distillation unit may expose hidden potential for majorenergy savings

OSMAN KUBILAY KARAN and CANSU INER

TpraKirikkale Refinery

www.digitalrefining.com/article/1001126 PTQ Q2 2015 1

Over the course of time,energy saving has become oneof the most essential topics inthe oil industry because ofenvironmental considerationsand high production costs due

to uctuations in the price ofproducts. Some studies such asthe pinch method, developedat the end of the 1970s andextended to heat and powersystems, were accepted amongstandard applications forrenery projects relatedto energy savings after the1980s.

In reneries, crude distilla-

tion units (CDUs) are thelargest energy consumers,utilising around 20% of a ren-erys total energy consumption,depending on congurationand type of crude processed.

Tpra Kirikkale Renery isa medium-sized renery with acapacity of 5 million t/y which

began operating in 1986 with aRomanian designed CDU. It isa conversion renery whoseother units were developed tomeet local product demandsfor Turkey. It may be consid-ered a typical example ofits type and was a perfect

30

35

25

20

15

10

5

Energyconsumption,

%C

DU

0

2008 2009 2010 2011 2012

32.6

21.5

16.5

24.0

19.2

Figure 1 Energy consumption in Kirikkale Refinerys CDU as a percentage oftotal consumption by all process units
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avoid plugging by the dirtyfuel oil utilised in the 1980s. A

project was developed toreduce the diameter to 2in andto increase the number of airpreheater tubes in order toincrease the heat transfer areain the air preheaters. In thisway, furnace efciency wasincreased by transferring moreheat to the air fed to the burn-ers. This modication resultedin an increase in heat surface

area of 283 m2 in both furnaceA and furnace B. By changingthe heat surface area, the stackgas temperature decreased byalmost 40C and fuel consump-tion in the furnaces decreased

by 150-200 kg/h.This decrease in fuel oil

consumption corresponds to1.7 Gcal/h of energy savingsper furnace and a reduction

candidate for an energy ef-ciency programme begun

in 2006 after the privatisationof Turkish PetroleumReneries.

As the cost of energy becamea major item, KirikkaleRenery researched a widevariety of opportunities for theCDU as well as other parts ofthe renery to maintain theproductivity of the plant.Many projects were evaluated

according to their economicbenets and many of themwere applied to the site

between 2008-2014. Followingcompletion of the newprojects, a dramatic decrease inenergy consumption in theCDU was achieved (see Figure1). This article describessome of these energy savingprojects.

Kirikkale refinerys CDUKirikkale Renery was designed

to process 5 million t/y of 36API Kirkuk crude. The unitdesign is a daily 18 000 m3 ofcrude oil. A simple ow schemeis shown in Figure 2.

Energy efficiency projects forthe CDUChange in diameter of airpreheater tubesAs the regulations for emis-

sions from industrial plantshave tightened in the last 20years, so the quality of the fueloil burned in CDU furnaceshas improved with reducedlevels of sulphur and otherimpurities such as heavymetals. It was found that thetwo crude charge furnaces airpreheater tubes were designedwith a large diameter (3in) to

B-1101 A:F

D-1101OVHD

C-1103Splitter

C-1104Debutaniser

G-1104 A/B

C-1101Atmosphericdistillation column

C-1102Stripper

G-1111 A/B

G-1103 A/B

G-1113 A/B

G-1112 A/B

G-1114 A/B

E-1110

E-1122

E-1110

G-1106 A/B

G-1107 A/B

G-1108 A/B

G-1109 A/B

G-1110 A/B

G-1102 A/B

G-1101A1B1

G-1101A2B2

E-1113

E-1111

E-1109

E-1112

D 1102 D 1103E-1119

F-1102

E-1118

Naphtha reflux

B-1106 A:D

G-1105 A/B

Kerosene reflux

Gas ammonia

Neut amin

GasAmmonia

G-1126 G-1116

G-1120G-1121

D-1111D-1108

G-1117 A/BG-1128 A/BG-1129 A/BG-1130 A/BG-1116 A/B

T-1114Neut amin

T-1100De-emulsifier

T-1122Caustic

D-1104Desalter

SP Naphtha

Kerosene

Light diesel

E-1104 A/BE-1109

Sour gas

Sour LPG

LSRN (1)

LSRN (2)

LSRN (3)

HSRN (1)

HSRN (2)

Kerosene (1)

Kerosene (2)

Light diesel

Heavy diesel

Atmosphericresidue (1)

Diesel, kero.or HSRN


Light/heavydiesel

E-1120

E-1107 A:HE-1105 A:BE-1106 A:D

E-1107 A:H

G-1122

Crude oilFrom T4101 to T4105

E-1101 A:FE-1102 A/BE-1103 A/BE-1104 A/BE-1105 A/B

24 in

12 in

Heavy diesel

E-1102 A/B

E-1103 A/B

E-1115

Outlet destinations

Sour gas to D-1701; gas treat unit U-1700

Sour LPG to C-1703; LPG treat unit U-1700

LSRN (1) to hydrogen unit U-1850LSRN (2) to isom. unit U-1150

LSRN (3) to T-4208, T-4209, T-4214A, T-4214B

HSRN (1) to naphtha hydrotreat unit U-1400

HSRN (2) to T-4201, T-4202, T-4203, T-4210

Kerosene (1) to asphalt blending T-4609

Kerosene (2) to T-4213

Light diesel to asphalt blending T-4610

Light/heavy diesel to T-4309, T-4310, T-4312

Heavy diesel to T-4205, T-4206

Diesel, kero. or HSRN to diesel/kero desulph.

unit U-1600

Atmospheric residue (1) to T-4501 to T-4508

Atmospheric residue (2) vacuum unit U-1200

Corrosion inhibitor

T-1105Corr. Inh.

F-1101 A/B

Figure 2 Original flow diagram of the Kirikkale CDU
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in emissions of about 22 000t/y.

Optimisation of naphtha andkerosene pumparoundsThe CDUs main column hastwo pumparounds the kero-

sene pumparound and thenaphtha pumparound thatare used to preheat crude oil

before and after the desalter byremoving heat from thecolumn. The amounts andtemperatures of the pumpa-round ows are crucial andshould be optimised accordingto crude charge ow and typesince they affect the inlettemperature of the desalter andfurnaces and hence are a keyparameter for fuel consump-tion in the heater. Designvalues of the kerosene andnaphtha pumparound ratioswere 1.09 and 0.885, respec-tively. An optimisation studyfor the pumparound owsagainst crude ow were carriedout to increase heat transferthrough the rst and second

preheat trains, to achieveenergy savings in the furnaces.In particular, vapour-liquid equilibrium in thecolumn and product specica-tions were taken into account.After a simulation study, thenaphtha and kerosene pumpa-round ratios were increased to1.32 and 1.42; the crude owand inlet temperature of the

desalter and furnaces alsoincreased by 6.2C and 7.8C,respectively. Energy savingswere about 1.9 Gcal/h in thefurnaces.

Additionally, an increase inpumparound levels resulted ina decrease in top reux sinceextra heat removal reducedheat losses from the columntop air coolers. As a result of


reducing the amount of topreux, a pump was shut downsince only one pump wasneeded to transfer liquid as topreux and splitter column feed.

Installation of variable speed

driveCrude oil from the desalter issent to the furnaces via G-1102A and B pumps (see Figure 2),one of them (A) with an elec-tric drive while the other has asteam turbine. Now that therate of crude charge changesfrequently in response toeconomic conditions, a 6 kVvariable speed drive wasinstalled in the electric motor.Variable speed drives for thatlevel of voltage are known to

be expensive but a feasibilitystudy showed that the returnon investment was satisfactory.After installation of the varia-

ble speed drive, electricityconsumption decreased bymore than 50% (from 392 kWhto 180 kWh) for the same oper-ating conditions.

Use of antifoulantCrudes with a high asphaltenecontent cause more fouling inthe second preheat train (afterthe desalter) because of itshigher temperature comparedto the rst preheat train.Fouling in a preheat traindirectly affects the chargefurnace inlet temperature and

hence leads to greater fuelconsumption. The loss of inlettemperature is measured as adecay rate of C/day and, byusing an appropriate antifou-lant in the second preheattrain, it was found that thedecay rate reduced to 0.0175C/day from 0.08 C/day. Theeconomic return on use of anti-foulants is satisfactory and

calculated at around $910000/y. Using antifoulant alsoreduces cleaning time for theexchangers as a side benet.

Tempered water system forcooling residues

In the original design of theCDU and VDU at Kirikkalerenery, cooling of atmos-pheric residue to storage wascarried out by air coolers whilevacuum residue run-down wascooled by a tempered watersystem. Cooling with air is notan efcient approach, espe-cially for heavy products, sinceit depends on ambient temper-atures which sometimes cause

bottlenecks on hot summerdays. A project was developedto combine the residue coolingsystems of the CDU and VDUwith tempered water cooling.Installing a combined temperedwater circulation systemremoved the bottleneck in resi-due cooling and the recoveredwaste heat, about 3 Gcal/h,was transferred to crude oil

before the rst preheat train.This also prevented shock

condensation of chlorides andwater in the naphtha pumpa-round in the rst exchangers inthe preheat train (E-1101 A-Din Figure 2) since crude fromstorage is at low temperatures(5-10C) during winter. Thissudden cooling of the naphthapumparound was causing a

corrosion mechanism involvingHCl-water condensation, lead-ing to heat exchanger tubeleakage. This problem with thereliability of the heat exchang-ers was also prevented byincreasing the inlet tempera-ture of E-1101 A-D.

An old shell and tube heatexchanger taken from anunused reformer unit was rated
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by simulation and was retrot-ted to be added to the rstpreheat train so that crude oiltaken from tank is heated withtempered water from the resi-due cooling tempered watersystem. The approaches of Ts

in the current system were alsochecked so as not to cause apinch problem due to over-heat-ing of the crude charge. Onlythe cost of piping and valvesapplied to this project since thewater circulation pumps werefound to be adequate andcontinued to be used with theretrotted old exchanger.

Using crude oil as a heat sinkand transferring waste heat tothe unit charge resulted in anincrease in the desalter andfurnace inlet temperatures andhence fuel savings in thefurnaces. The inlet temperatureof the furnaces increased by4-5C and the economic returnof this project is $900 000/y.Because less fuel is consumed,emissions from the furnacesalso decreased as another bene-

t of the project.

Additional pumparound flowIn the original ow scheme,two pumparound ows (naph-tha and kerosene) were usedfor transferring heat from thecolumn to the crude owing tothe furnace (see Figure 2). Aftera process study, an opportunitywas discovered to install a new

pumparound ow whichutilises heavy gas oil drawfrom the column. It provided aheat duty of about 14.8 Gcal/hand was used for the reboilerrequirement of the splittercolumn bottom. Because of thisadditional free heat source, thereboiler red heater (F-1102 inFigure 2) was removed after anew shell and tube exchanger

was installed. Overall fuelconsumption reduced by 16.3Gcal/h and a CO

2equivalent

saving of 43 617 t/y wasrealised.

Change in furnace air blowers

The renery CDUs chargefurnaces originally had six airblowers which required 400 kWeach. Since they in excess ofrequirement in the 1980s, onlyone is utilised with a bypassline for two furnaces. Sharingair from one blower with a

bypass line caused an air distri-bution imbalance between thetwo furnaces, with a resultingdecrease in furnace efcienciesand unreliable operation.

The renerys combustiondivision developed a projectfor furnace efciencies inwhich the capacity of the air

blowers was to be decreasedwith the installation of new

blowers and a variable speeddrive tted to the air blowersmotors, adjusting fan speedsaccording to oxygen demand

in the furnaces determined viaonline oxygen analysers in thestacks.

The saving in electricity iscalculated to be 3.2 millionkWh/y, with expected fuelsavings of 11.3 million kWh/year. Installation work is ongo-ing and start-up of the projectis planned for the second quar-ter of 2015.

Preheat train optimisation andpreflash drumA heat integration study wasstarted in 2014 utilising pinchanalysis of the current owscheme of the CDU, with theaim of nding out whetherthere is an opportunity todecrease hot-cold approachesand add a preash drum.

Using the SuperTarget tool(from KBC), an optimisationstudy of the preheat trains wascarried out. Among manyscenarios given by the model,the Hv. diesel vs crude heatexchanger (E-1104 AB in Figure2

) is to be relocated after thedesalter and a new heavy gasoil pumparound heatexchanger will be added to thesecond preheat train. Apreash drum will also beplaced before the charge heaterto separate crude vapourswhich will be sent directly tothe kerosene zone of the atmos-pheric distillation column.Bottom liquid will be sent tothe furnace. After the preashdrum, crude oil will also beheated in another new heatexchanger with atmosphericresiduum before entering thefurnace. By changing the owscheme and adding new equip-ments, fuel consumption of thered heaters is calculated to

be reduced by nearly 16 Gcal/hand the economic return of the

project will be $6.9 million/y.Because of the high equipmentcost, a preash column was notselected, so two preash drumswill be placed to guarantee noentrainment by heavier prod-ucts inside the column.

Detailed engineering of theproject is continuing andstart-up will probably be in2016.

ConclusionThe rening industry faces achallenging situation when itcannot control its biggest costitem, crude prices, and manyreners have to be at theirttest to survive by cuttingoperational costs by evaluatinghidden opportunities forenergy savings in an increas-

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ingly competitive globalbusiness environment.

Successful and cost-effectiveinvestments for energy ef-ciency technologies andpractices will meet the chal-lenge of both maintaining thehigh quality of products whilereducing production costs.

Starting in 2008, TpraKirikkale Renery developedan initiative for prioritisingenergy saving projects, not

only for the CDU but also forother process units and utilities(see Figure 3). The CDUprocesses all of the crude oilcharged to the renery. It is amajor energy user and theopportunities for energy ef-ciency it contains vary fromheat integration, waste heatrecovery, lower use of utilitiesand improving fractionation,


Osman Kubilay Karan is CDU, VDU,

Amine and Sulphur Recovery Units

Process Superintendent with TpraKirikkale Refinery. He holds a bachelors

degree in chemical engineering from

Middle East Technical University, Ankara,

Turkey and is a certified Energy Supervisor

for industrial plants.

Email: [email protected]

Cansu Iner is CDU, VDU, Amine and

Sulphur Recovery Units Process Chief

Engineer with TpraKirikkale Refinery.

She holds a bachelors degree in

chemical engineering and a masters in

industrial engineering for engineeringmanagement, both from Middle East

Technical University, Ankara,Turkey.

Email: [email protected]

though to other, smaller meas-ures resulting in large gains.

During such studies, it wasseen that many possible energysaving opportunities generallyrequire short payback timesranging between two years andas little as a few months.

Reners monitoring suchopportunities for savings willrst need a benchmark of theirCDU and other units to iden-tify areas for improvements,

and then an energy strategyand management programmeto locate and apply theimprovements according totheir economic priorities. Evenwhen such programmes arecompleted, there is a need tocontinue monitoring keyperformance indicators anddiscover further opportunitiesfor savings.

C-1103Splitter

B-1101 A:F

D-1101OVHD

Unstabilised naphthafrom DHP (U-1650)

G-1104 A/B

C-1101Atmosphericdistillation column

C-1102Stripper

G-1111 A/B

G-1103 A/B G-1112 A/B

G-1114 A/BE-1131 A/B

E-1110

E-1121E-1122

E-1110

E-1114

E-1118

No flow

E-1127

G-1106 A/B

G-1107 A/B

G-1108 A/B

G-1109 A/B

G-1131 A/B

G-1110 A/B

G-1102 A/B

G-1101A1B1

G-1101A2B2

E-1123

E-1124

E-1113

E-1111

E-1109

E-1112

D 1102 D 1103E-1119E-1118

Optimisation ofnaphtha and kerosenepumparound

Naphtha reflux

B-1106 A:D

G-1105 A/B

Air blowers

Kerosene reflux

Gas ammonia

Neut amin

Corrosion inhibitor

GasAmmonia

G-1126 G-1116

G-1120G-1121

D-1111D-1108

G-1117 A/BG-1128 A/BG-1129 A/BG-1130 A/BG-1116 A/B

T-1114Neut amin T-1105Corr. Inh.

T-1100De-emulsifier

T-1137Anti-foulant

T-1122Caustic

D-1104Desalter

Pre-flash drum ~ongoing project

Modification ofair blowers ~ongoing project Variable speed

drive ~ completed

Injection ofanti-fouling~ completed

Tempered watersystem project~ completed

Air preheatmodification~ completed

SP Naphtha

Kerosene

Light diesel

E-1125E-1104 A/BE-1109

Sour gas

Sour LPG

LSRN (1)

LSRN (2)

LSRN (3)

HSRN (1)

HSRN (2)

Kerosene (1)

Kerosene (2)

Light diesel

Heavy diesel



Light/heavydiesel

E-1120

E-1107 A:HE-1105 A:B

E-1106 A:DE-1107 A:H

G-1118G-1119

G-1122

D-1138

Crude oilFrom T4101 to T4105

E-1129 A/D

E-1130E-1101 A:FE-1102 A/BE-1103 A/BE-1104 A/BE-1105 A/B

24 in

12 in

Heavy diesel

New heavy diesel project ~ completed

E-1102 A/B

E-1103 A/B

E-1115

Outlet destinations

Sour gas to D-1701; gas treat unit U-1700

Sour LPG to C-1703; LPG treat unit U-1700

LSRN (1) to hydrogen unit U-1850LSRN (2) to isom. unit U-1150

LSRN (3) to T-4208, T-4209, T-4214A, T-4214B

HSRN (1) to naphtha hydrotreat unit U-1400

HSRN (2) to T-4201, T-4202, T-4203, T-4210

Kerosene (1) to asphalt blending T-4609

Kerosene (2) to T-4213

Light diesel to asphalt blending T-4610

Heavy diesel to T-4205, T-4206

Atmospheric residue (1) to T-4501 to T-4508

Atmospheric residue (2) vacuum unit U-1200

G-1113 C/D

C-1104Debutaniser

F-1101 A/B

Figure 3 Current flow diagram of the CDU indicating changes after 2008

LINKS

More articles from the following

categories:

Corrosion / Fouling Control

Crude Vacuum Units

Mass Transfer & Separation
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