HACCP Oil Refining

ICheaP10 8-11 May 2011 - Florence, Italy

Hazards assessment of

vegetable oil storage and

processing plants

G. Landucci1, B. Nucci2, M. Pierini1, G. Pannocchia1, L. Pelagagge2, C. Nicolella1*

UNIVERSITA DI PISAICheaP10 8-11 May 2011 - Florence, Italy

* [email protected]

mailto:[email protected]


Introduction (1)

The major part of the global vegetable oil production

derives from extraction processes

The process is based on the selective oil extraction

usually carried out with a volatile organic solvent,

typically hexane. After separation from solvent the oil

phase is processed in chemical refining

The vegetable crude oil usually presents a low content

of residual solvent

• SAFETY ISSUES

• PROCESS ISSUES


Introduction (2)

Source Year Country Location Operation Fatalities Injuries Abstract

(A) 1975 The Netherlands harbour/port/dock Maintenance (cleaning) >1

during cleaning of a tank on tanker

after unloading cocosoil, some hexane

vapours caused at least 1 casualty

(A) 1976 The Netherlands factory Processing 4

wear of pumpseal caused hexane

release under the space of building,

ignition, explosion and 4 casualties

(A) 1977 Germany factory Processing fire in extractor of soya factory

(A) 1979 The Netherlands Inland navigation Maintenance 1 vapour cloud explosion on vessel in

locks caused fire and 1 casualty

(A) 1980 Denmark Factory Processing 27

hexane release at extraction plant for

soya bean caused evacuation of the

plant & after switch off (un)loaded

power supply line an explosion

occurred causing 27 casualties

(A) 1983 Argentina storage/depot Storage 1 >1

a fire in an elevator ignited gas from

sunflower pellets in silo setting of an

explosion causing more than 2

casualties

(A) 1983 Germany Factory Processing 2 11 explosion and fire at oil extraction plant

(A) 1984 The Netherlands Factory Processing 2

while working in the cooker without

the required permit flash fire injured 2

workers

(A) 1991 Japan Factory Maintenance >8

A combustible gas-air mixture was

generated in an extractor by residual

hexane content. Ventilation was not

sufficient. Explosion occurred due to

static electricity when the repair work

started in the extractor.

(A) 1994 USA factory-yard Processing (application) 11 hexane leak caused heavy fire

(B) 2006 Italy Factory (refinery) Maintenance (storage) 4 - Welding operation inside a pomace oil

tank

(C) 2007 Spain Factory (refinery) Maintenance (storage) 1 1 Welding operation inside a pomace oil

tank

Accidents involving veg. oil –

hexane (FACTS, TNO 2007)


Introduction (3)

Spoleto, 2006

A catastrophic accident occurred in a vegetable oil refinery in

Italy in 2006.

During maintenance operations, an explosion occurred in a

pomace olive oil- storage tank, causing 4 fatalities among

personnel and damaging the surrounding equipment.

The cause of the explosion was the accidental ignition of the

residual solvent vapour during welding operations

An accident with similar features occurred in Spain only few

months later

The residual solvent may accumulate in the vapour

phase, mixing with air and forming flammable

mixtures which could result in the confined

explosion of the storage vessel in presence of

ignition.


Introduction (4)

Loss of efficiency in high

temperature vacuum

operations (such as the

drying and bleaching).


Aims of the work:

Development of an approach able to

quantitatively evaluate the hazards due to the

residual solvent

Safety issues related to storage – formation of

flammable mixtures inside the tanks

Processing of vegetable oils – determination of

residual solvent accumulation among refining

process


Methodological approach

Estimation of liquid

phase composition

Thermodynamic model

for the estimation of

vapor phase

composition

Model validation

against available

experimental data

1

2

3

Definition and

evaluation of case-

studies

4a

Determination of

hazard indexes5a

Safety issues in storage tanks

Definition of critical

sections for hexane

accumulation

4b

Control and restoring

measures5b

Safety issues in oil refining


Model set up (1)

Liquid phase characterization:

• Triglycerides mixture

(depending on oil type and

origin)

• Free fatty acids (0.5-1 up to few

percent)

• Residual solvent

Schematization:

one reference triglyceride, namely LLP (constituted by two Linoleic

groups and one Palmitic group)

one free fatty acid, namely oleic acid

Thecnical hexane assumed a reference solvent and assimilated as pure

n-hexane

Crude vegetable oil inside the

storage tank


Model set up (2)

A well mixed air-hexane vapour phase is assumed in the top space of the vessel, due to open vent on the tank roof.

Stratification is not considered in the present work, which assesses possible formation of flammable mixtures, without accounting for possible sources of ignition and the consequent effects following the ignition

The analysis is referred to normal operation, the presence of oil sludge (sediment solids) is not considered in model.


Model set up (3)

Equilibrium relationship: c

SAT

i

SAT

iiii NiTPTxPy ,1

Where: 1

iy : molar fraction of the i-th component in vapour phase; 2

P : operative pressure (Pa); 3

i : activity coefficient of the i-th component; 4

ix : molar fraction of the i-th component in liquid phase; 5

SAT

i : fugacity coefficient of the pure i-th component; 6

SAT

iP : vapour pressure of the pure i-th component; 7

T : operative temperature (K) 8

cN : total number of components. 9

A modified version of the UNIFAC (UNIversal Functional

Activity Coefficient) model was used to assess the activity

coefficient


Model validation

In order to test the validity of the model, a comparison with available experimental data was carried out.

Available data ONLY at high hexane concentration (Extraction studies)

The only available data for diluted solutions are reported by Smith & Wechter (J. of the American Oil Chemists’ Society 28, 381-382, 1951).

RSC = 1.32%

RSC = 1.08%

RSC = 0.85%

RSC = 0.62%

RSC = 0.41%

RSC = 0.20%

0

5

10

15

20

25

30

15 30 45 60 75 90 105 120

Temperature (°C)

He

xa

ne

pa

rtia

l p

res

su

re (

kP

a)

Model estimates

Experimental values

Extrapolation

Temperature (°C)


Analysis of vegetable oil storage (1)

The model was applied to the analysis of an industrial storage plant.

The refinery processes sunflower, olive, peanut and corn oil with a maximum residual solvent content RSC of 0.1% by weight

Higher RSC values were taken into account (e.g., 0.38% and 0.75% by weight).

The tank farm is equipped with a heating system which prevents the vessel cooling to temperatures lower than about 18°C in presence of cold weather.

For temperatures higher than 18°C the operative temperature can be assumed equal to the average ambient temperature.

Typical weather conditions of the zone of the oil refinery were considered in the study

•Vegetable oil refinery of SALOV

S.p.A., located in Massarosa (Italy)

•The tank farm of the plant

comprises 28 vessels with volumes

ranging between 85 and 750 m3,

with a total capacity of about 8500

tons.


Analysis of vegetable oil storage (2)

Estimation of

vapor pressure in

the tank

according to

external meteo

conditions

Possibility of

having flammable

mixtures for high

RSC


Analysis of vegetable oil refining (1)

Typical refining process conditions: purification of a sunflower oil assuming a free fatty acid content (FFAC) of 4 %wt. to be reduced up to 0.04 %wt.

Equipment: R: reactor; P: pump; CS: centrifugal separator; E: heat exchanger; S: flash separator;

EJ : steam ejector; F: filter; C: column. Material streams : S_MP: medium pressure steam; S_LP:

low pressure steam; EA: earths & activated carbons; W: water; SH: sodium hydroxide; HP:

phosphoric acid; FO: feedstock oil; SW: soaps & waxes; SE: spent earths; FFA: free fatty acids;

RO: refined oil.


Analysis of vegetable oil refining (2)

Process

section

Operative

temperature

( C)

Operative

pressure

(mbar)

Process description

Neutralization 20 1000 Adding sodium hydroxide to reach an

intermediate grade of acidity

Degumming 20 1000 adding phosphoric acid and subsequently

oil is sent to centrifugal separation to split

the oil fraction from the solid waste.

Washing 90 1000 The oil is washed with water

Dehydration 90 50 Oil is dehydrated in a flash separator under

vacuum conditions

Discoloration 95 60 Adding bleaching earth and activated

carbon in a stirred vessel under vacuum

conditions, then oil filtered

Deodorization 230 2 “physical” neutralization with water steam at

high temperature under vacuum conditions.

The FFAC is stripped and condensed in a

direct contact condenser, while steam with

non condensable vapor are sent to the

ejectors section.


Simulation of vegetable oil refining (1)

Process simulations were performed using HYSYS V7.1

(by ASPEN Tech, Cambridge MA) simulation software.

• The crude vegetable oil, including FFAC and hexane,

was schematized according to the described

thermodynamic model

• A residual hexane content of 0.1%wt. was considered

as process input.

• The aim of the process simulation was to “trace” the

hexane flow through each part of the process, with

particular attention to units working at high

temperature and low pressure, in which hexane

vaporization is favoured (thus issuing safety

problems in shut down and maintenance operations)


Simulation of vegetable oil refining (2)

Sankey diagram identifying the critical nodes in which the accumulation of hexane is predicted

The analysis evidenced the need to focus on the operative problems related to dehydration, discoloration and deodorization

The vacuum conditions are kept in these units by steam

ejectors. The steam ejector model was set up on the basis of

actual plant field data, based on typical operative conditions


Sensitivity analysis

Determine the effect of the variation of a process variable to the refining process performance.

Increasing content of hexane in feedstock oil was analyzed (up to 0.5%)

Effect on the ejector system aimed at keeping low pressures in high temperature units.

The process performance was analyzed through the dehydration efficiency

0,000 0,001 0,002 0,003 0,004 0,0050,70

0,75

0,80

0,85

0,90

0,95

1,00

Dehydra

tion

effic

ency

Hexane weight fraction (w/w)

Potential decrease of 30% in process efficiency related to ejectors, thus evidencing the criticality of the residual solvent content in input feedstock.


Conclusions

A quantitative methodology for the evaluation of residual

volatile solvent content effect on storage and processing of

edible extracted oils.

A thermodynamic model was implemented and validated in

order to reproduce the liquid-vapor equilibrium of crude

vegetable oil - residual solvent system.

Application to industrial case studies:

• Identification of potential hazards due to formation of flammable

mixtures inside the storage tanks

• The critical nodes of solvent accumulation were identified among

the process, evaluating the influence on the global efficiency.

Acknowledgments

This research has received funding from Regione Toscana

(Bando Unico R&S n.2009DUA/526090469/1)


Thank you….

Maintenance operations on a

crude vegetable oil tank

HACCP Oil Refining

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