Fahim M.A., Sahhaf T.A., Elkilani A.S. Fundamentals of Petroleum Refining

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The bitumen feed (API ¼ 11) has the following elemental analysis:

80% C; 14% H and 6% S

The maximum allowable density is 1000 lb/ft

and can be correlated

with an elemental residue content as follows:

r ¼ 1033  13:69 H wt% þ 13:85 S wt%

Determine whether the produced hydrogen is enough to remove the

sulphur in the feed

13.5. The following flowsheet shows the role of the IGCC process in the

refinery. The residue flow rate is 32 ton/h with API 6. Air is used at a

rate of 10,000 kmol/h. Steam enters at gauge pressure of 2 bar.

Hydrogen is produced at a rate of 150,000 m

/h. Flue gas flow rate

is 300,000 m

/h with the following analysis: NO

50 mg/m

,SO

10 mg/m

CO 30 mg/m

particulates 10 mg/m

. Calculate the

amount of steam that enters the IGCC unit.

Solvent

192 ton/hr

DAO

IGCC

1700 °C

Hydroconversion

SDA

250 °F

121 °C

Residue

32 ton/hr

Asphalt

Air

75 °C

Steam

Power

466MW

150,000 m3/hr

Flue gas

300,000 m3/hr

REFERENCES

Ancheyta, J., and Speight, J. G. (2007). ‘‘Hydroprocessing of Heavy Oil and Residue.’’

Taylor and Francis, New York.

Furimsky, E. (1999). Gasification in petroleum refinery of 21st century. Oil Gas Sci. Technol.

Rev. IFP 54(5), 597–618.

Gillis, D. B. (1998). ‘‘What is New in Solvent Deasphalting?’’ UOP & Foster Wheeler

Team- UOP LLC, Fred Van Tine - Foster Wheeler USA Corporation.

Maples, R. E. (1993). ‘‘Petroleum Refining Process Economics.’’ PennWell Books, Tulsa,

USA.

Marzin, R., et al., (1998), ‘‘The aquaconversion process, a new approach to residue proces-

sing,’’ NPRA annual meeting, March 15–17, San Antonio.

Morel F., and Peries J. ‘‘Residue Hydroconversion’’ Chapter 13, In Conversion Processes’’

Petroleum Refining, Vol. 3, Leprince P., ed. TECHNIP, France.

354 Chapter 13

Nelson, S. R., and Goodman, R. G. (1985). ‘‘ROSE: The Energy Efficient Bottom of the

Barrel Alternative’’ Spring AIChE meeting, Houston.

Pereria, P., Marzia, R., McGrath, M., and Thompson, G. (2005), ‘‘How to extend existing

heavy oil resources through aquaconversion technology, Huston Congress Technical

Paper.

Phillips, G., and Liu, F. (2002). Advances in residue upgrading technologies offer refiners

cost-effective options for zero fuel oil production. Foster Wheeler Energy Limited,

European Refining Technology Conference, Paris, November.

Rana, M. S., Samano, V., Ancheyta, J., and Diaz, J. A. I. (2007). A review of recent advances

on process technologies for upgrading of heavy oils and residue. Fuel 86, 1216–1231.

Scheffer, B., Rochscklager, K., de Boks, F. (1997). ‘‘The shell residue hydroconversion process,’’

Development and achivement. ACS meeting San Francisco, April 13–17, 347-350.

Scheffer, B., Rozema, W., Ro

bschla

ger, K. W., and Bu

hrman, F. A. (1998). ‘‘Residue

hydroconversion processes – New Options Shell Global Solutions.’’ Shell Netherlands

Refinery, Pernis Country.

UNISIM Design Suite R370, Honeywell Process Solutions, Calgary, Alberta, Canada.

Zhao, S. Q. et al. (2001). Aeta Petro Sinica. Pet. Refining Process. Sect . 17(1), 47–55.

Residue Upgrading 355

CHAPTER FOURTEEN

Safety in Petroleum Refineries

14.1. Introduction

Safety is of extreme importance in all petroleum refineries. Every

employee is involved in developing the regulations and procedures for work

safety. In this way, anyone who works in the refinery is part of the safety system

and will always be sure to work safely and help others work safely.

All routine jobs in the refinery should conform to high safety standards. No

work can be carried out without a permit. This is in order to ensure that

personnel always know where work is being done and, therefore, they can

prevent jobs from overlapping. Whenever workers are in the refinery site, they

have to wear safety clothing known as personal protective equipment (PPE).

14.2. Hazards in Refinery Units

14.2.1. Crude Oil Pre-treatment

Hydrogen sulphide, hydrogen chloride and salts in the desalter are the main

causes of corrosion in the unit. Corrosion is the source of leakage of oil and

evaporated hydrocarbons. Low boiling point hydrocarbon leaks can possi-

bly lead to fires and explosions in the unit. Scheduled maintenance is

required to prevent salt fouling and corrosion.

14.2.2. Crude Oil Distillation

Low boiling point hydrocarbons may leak from improper connections

between furnace, heat exchangers and distillation column. When the

hydrocarbon leaks find any source of ignition, a fire and/or an explosion

may occur. Thermal cracking is the source of coke formation which may

block lines and connections leading to over-pressurising and sometimes unit

failure and consequent shut down. Coke formation can be prevented by

controlling the temperature and pressure. Relief valves should be provided

and regularly inspected for over-pressure.

Fundamentals of Petroleum Refining

2010 Elsevier B.V.

357

Sour crude distillation, especially at a high temperature of 232



(450



F), causes severe corrosion. Anti-corrosive chemicals and sufficient

wash water are injected to avoid corrosion.

14.2.3. Catalytic Reforming

Catalyst handling and loading should be based on standard operating proce-

dure so as not to crush the catalyst leading to fine particulates that may either

escape into the atmosphere or be deposited in the reformer lines and

connections. Hydrogen chloride and ammonium chloride may form in

the unit pre-heater which can lead to fouling and corrosion. Scheduled

maintenance is required to prevent corrosion and ensure the temperature is

controlled to avoid hot spots in the reactor.

14.2.4. Thermal Cracking

When sour crude is processed in the delayed coking unit, procedures must

be carried out carefully to prevent corrosion, since the unit is working at

high temperatures between 232 and 482



C (450



and 900



F). Above

482



C (900



F) steam is injected to prevent coke formation in the lines.

Scheduled maintenance is required to ensure that the temperature control

units are working properly. Hydrogen sulphide corrosion may occur in the

furnace, coking drums and reactors. Water jets used for coke removal from

the coke drum should be drained properly and completely to avoid explo-

sion when fresh coke forms again during operation.

14.2.5. Hydrotreating and Hydrocracking

Catalyst handling and loading must be carried out with care so that fine

particles from crushed catalyst are not produced. Fine particulates may result

in a dust explosion. Since hydrogen sulphide is present regular maintenance

is required to avoid corrosion. A high operating temperature leads to coke

formation on the catalyst; therefore, care should be taken during the catalyst

regeneration process to avoid fire and explosion.

14.2.6. Fluid Catalytic Cracking

Catalyst handling and loading should be based on the standard operating

procedure to prevent catalyst dust explosion. Oil coating the spent catalyst

should be stripped out in the stripper section of the reactor before sending it

to the regenerator. If not removed, the presence of this oil will cause

explosion during contact with air in the regenerator. Hydrocyclones must

be carefully operated, otherwise catalyst fines will be carried out over to the

distillation column. These fines will be concentrated in the decant oil.

358 Chapter 14

14.2.7. Alkylation

In the alkylation unit, two systems are used, either sulphuric acid or hydro-

fluoric acid, which are both considered hazardous chemicals. Material

handling with extreme care is required especially the hydrofluoric acid

during cleaning processes in which water is used. Improper contact of the

acid with water may lead to an explosion. A concentrated acid is used with

small amounts of water to avoid corrosion. Acid effluent must be neutralised

before it is sent to the sewers.

14.2.8. Hydrogen Production

Scheduled maintenance is required to prevent corrosion and ensure that

temperature and pressure are controlled. This must be done in order to avoid

hot spots in the reactor. Low boiling point hydrocarbons released from a leak

may lead to a fire and/or an explosion. Inspections for piping and connec-

tions should be done regularly to assure hydrogen production quality.

14.3. Safety Programs and Regulations

Regulatory agencies such as the Occupational Safety and Health

Administration (OSHA) (OSHA, 2004) and the Chemical Safety and Haz-

ard Investigation Board (CSIB) in the United States set safety regulations

and accident investigation procedures to ensure work safety in industrial

environments. Refining processes have special safety requirements due to

the handling of crude oil and flammable hydrocarbons. Recently, every

refinery began making its own safety programs based on its processing

scheme, environmental regulations and manpower.

14.4. Accidents and Loss Prevention Measures

All accidents and near misses, which are unplanned events that do not

result in injury, should be reported. Statistical analyses based on the reported

accident data improve regulations and procedures to save lives and property

by reducing and eliminating accidents in industry. The benchmarking

indicators for accident reporting (Ball, 1991) are: lost time accident (LTA)

rate, recordable accident rate, LTA severity rate and days lost per LTA.

Accident frequency rates are calculated on the basis of number of

accidents per 100,000 working hours. The typical LTA rate is 0.3. An

LTA value of 0.3 means 0.3 injuries per 100,000 h. The average time at

work in refineries is 2000 h per year (50 work weeks/year  40 h/week).

Safety in Petroleum Refineries 359

For example, if a refinery has 1000 employees, the working hours will be

2 million (1000 employee  2000 h), and with a LTA rate of 0.3, this gives

6 accidents per year in this refinery based on OSHA’s LTA.

OSHA’s incidence rate (2004) is based on the number of incidents per

100 workers years (2000 h/year). Therefore, OSHA incidence rate is based

on 200,000 h of all workers exposed to hazards, either based on injuries

(equation 14.1) or based on lost workdays (equation 14.2):

OSHA incidence rate

based on injuries



number of injuries 200000

total hours worked by all employees

ð14:1Þ

OSHA incidence rate

based on lost workdays



number of lost workdays 200000

total hours worked by all employees

ð14:2Þ

The OSHA incidence rate provides information on all types of work related

accidents.

Example E14.1

A reﬁnery has 1500 full-time employees. In a particular year, this plant had 28

reportable lost-time injuries that resulted in 175 lost workdays. Compute the

OSHA incidence rate based on injuries and lost workdays.

Solution:

Since total working hours for all employees is 1500  2000,

OSHA incidence rate

based on injuries



28  200000

1500  2000

¼ 1:87

OSHA incidence rate

based lost workdays



175  200000

1500  2000

¼ 11:67

14.5. Risk Management and Risk Assessment

High risk is addressed in refineries because of the handling of hazard-

ous and flammable materials such as hydrocarbons and processing chemicals.

Risk assists in terms of frequency of occurrence and consequences as follows

(Maher and Sharp, 1996):

Risk ¼ðFrequencyÞðConsequenceÞð14:3Þ

Accident probability and worst case scenarios are typical key issues in calcu-

lating the risk. Process failure is based on equipment failure probabilities.

360 Chapter 14

The probability of a failure in a process depends on the time of usage and the

demand on a control unit, the maintenance time period, and device specifica-

tions. Table 14.1 lists failure rates for some selected process components. The

probability P that the component will fail during the time interval (t), knowing

the average failure rate (m)is

P ¼ 1  e

mt

ð14:4Þ

Process components interact in two way; first, process failure can occur

when components fail in parallel, which means that all components in

parallel must fail together to lead to process failure. The gate is an AND

in the parallel components. Second, process failure occurs when some

components fail. The gate here is OR. For the first type the failure rate is

process

¼ P

 P

... ð14:5Þ

For the second type, the formula is

process

ð14:6Þ

The total reliability R of a process is the probability that components in a

process will not fail and can be calculated as

R ¼ 1  P ¼ e

mt

ð14:7Þ

Example E14.2

In the reformer unit, a reacto r works at high pressure and temperature. The

reactor contains two control units (see the attached ﬁgure). The ﬁrst unit

consists of a high pressure alarm to alert the operator in case of any emergency

Table 14.1 Failure rate data for commonly used process components (Crowl

and Louvar, 2002; Lees, 1986)

Instrument

Failures/

year Instrument

Failures/

year

Controller 0.29 Level measurement (solids) 6.86

Control valve 0.60 Pressure Switch 0.14

Flow measurement (ﬂuids) 1.14 pH-meter 5.88

Flow measurement (solids) 3.75 Pressure relief valve 0.022

Flow switch 1.12 Pressure switch 0.14

Gas-liquid chromatograph 30.6 Solenoid valve 0.42

Hand valve 0.13 Stirrer motor 0.044

Indicator lamp (alarm) 0.044 Strip chart recorder 0.22

Level measurement

(liquids)

1.70 Thermocouple

measurement

0.52

Valve positioned 0.44 Thermometer measurement 0.027

Safety in Petroleum Refineries 361

increase in pressure and a pressure relief switch. The second control unit consists

of pressure controller connected to a solenoid valve to close the feed supply to

the reactor. Estimate the probabilities of process failure due to high pressure.

Pressure

Control

Pressure

Switch

Alarm

Solenoid

Valve

Reactor

Feed

Solution:

Failure rate for each component is selected from Table 14.1. The probability P is

then calculated using equation (14.4). An increase in pressure occurs when both

(AND) the alarm and the shut down system fails in supplying feed. Failure in the

alarm unit is in a series (OR) with a pressure switch and assuming t = 1 year.

Therefore,

alarm

¼ð1  e

0:14

Þþð1  e

0:044

Þ¼0:1736

shutdown

¼ð1  e

0:29

Þþð1  e

0:42

Þ¼0:5946

The probability of process failure is

process

¼ðP

alarm

ÞðP

shutdown

Þ¼ð0:1736Þð0: 5946Þ¼0:103=year

This means that failure may occur once every 9.7 years (1/0.103 = 9.7).

Example E14.3

Consider a control valve (CV), a tank (T) and two pumps (Pump1 and Pump2)

in the following conﬁguration.

CV T

Pump1

Pump2

Flow in

Flow out

Assume that Pump2 is a full capacity spare for Pump1. Pump2 is only needed

when Pump1 fails and cannot perform its function. Determine the reliability

within the system.

Data: the failure rate of Pump1 and Pump2 are 0.91 and 0.81, respectively. Tank

failure rate is 0.99 and control valve failure rate is 0.9.

362 Chapter 14

Solution:

From the ﬂow diagram Pump1 and Pump2 are in parallel (AND) and other

components are in series (OR):

The reliability rate for pump 2 per year is:

R ¼ e

mt

¼ expð0:81Þ¼0:4448

Other reliability rates can be calculated similarly.

The reliability of the system is

R ¼ R

þ R

þðR

Pump1

 R

Pump2

R ¼ 0:4065 þ 0:3715 þð0:4448  0:4025Þ¼0:95

This means that the system is reliable and safe 95% of the operating time during

the one year period.

14.6. Fire and Explosions

Accidental vapour cloud explosion hazards are of great concern to the

refining and chemical processing industry, and a number of catastrophic

explosion accidents have had significant consequences in terms of death,

injury, property damage, loss of profit, and environmental impact.

Fuel-air explosives (FAE) disperse a cloud of fuel which is ignited by a

source to produce an explosion. The main destructive force of FAE is high

over-pressure. For fuel vapour cloud explosion, there is a minimum ratio of

fuel vapour to air below which ignition will not occur. Also there is a

maximum ratio of fuel vapour to air, at which ignition will not occur. These

limits are the lower (LEL) and upper explosive limits (UEL). For gasoline

vapour, the typical explosive range is from 1.3 to 6.0 mol% vapour to air,

and for methane, this range is 5–15 mol%. Flammability limits are related to

explosive limits since most explosions are followed by fire. The mass and

type of material released contribute to the potential damage from a vapour

cloud explosion.

Example E14.4

A mixture of propane in air containing 4.03 mol% C

is the feed to a

combustion furnace. If there is a problem in the furnace, a stream of pure air

(dilution air) is added to the fuel mixture prior to the furnace inlet to make sure

that ignitio n is impossible. If propane ﬂows at a rate of 150 mol/s in the original

fuel gas mixture, what is the minimum molar ﬂow rate of the dilution air

needed?

The LFL of propane in air is 2.05 mol% C

and the UFL is 11.4 mol%

Safety in Petroleum Refineries 363

Solution:

Suppose that n

is the fuel gas ﬂow rate

Propane feed rate: 0.0403n

= 150 then n

= 3722 mol/s

The product fuel must contain at least 2.05 mol % propane (LFL) to avoid

ignition

If n

is the ﬂow rate of the product gas, then

Propane balance: 150 = 0.0205n

then n

= 7317 mol/s

Air ﬂow rate = 7317 – 3722 = 3595 mol/s

The minimum air ﬂow rate is 3595 mol/s.

Flammability limits for vapours are determined in a mixture with air using

the following Le Chatelier equation:

LFL

mix

=LFL

ð14:8Þ

where LFL

is the lower flammability limit for component i (vol%) and y

is the

mole fraction of component i. The same formula can be used for the UFL

mix

Example E14.5

What are the LFL and UFL of a hydrocarbon gas mixture composed of 2 vol%

methane, 0.4 vol% ethane and 0.5 vol% propane and the balance is air?

The following table contains the LFL and UFL for each component in the

mixture.

LFL (vol%) UFL (vol%) Vol%

Methane 5.3 15 2

Ethane 3.0 12.5 0.4

Propane 2.2 9.5 0.5

Air 97.1

Solution:

Normalise the hydrocarbon vol% and assume an ideal gas mixture. The mol%

for the three hydrocarbons is calculated to be 68.96 mol% methane, 13.8 mol%

ethane and 17.24 mol%. The LFL can be calculated using equation (14.8):

LFL

mix

0:6896=5:3 þ 0:1380=3:0 þ 0:1724=2:2

¼ 3:93%

Similarly, UFL

mix

= 13.305%

Since the mixture contains 2.9 vol%, and the LFL

mix

is 3.93%, it is not ﬂamma -

ble. For the mixture of hydrocarbons to be ﬂammable, the vol% of the mixture

in air must be in the range 3.93–13.305%.

364 Chapter 14