Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing

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1066 CHAPTER 18

APPENDICES

Figure 18.A.1. LMTD correction factors.

PROCESS EQUIPMENT IN PETROLEUM REFINING 1067

Figure 18.A.2. Heat of combustion of fuel oils.

1068 CHAPTER 18

Figure 18.A.3. Heat of combustion of fuel gasses.

PROCESS EQUIPMENT IN PETROLEUM REFINING 1069

Table 18.A.1. Values for coefﬁcient C.

1070 CHAPTER 18

Table 18.A.2. Some common heat transfer coefﬁcients Uo.

Fluid being cooled Fluid being heated

(BTU/h.f

◦

Exchangers

s and lighter Water 75–110

s and lighter LPG 75

Naphtha Naphtha 75

Naphtha Water 80–100

BPT 450 (kero) Hy oil (crude) 70–75

Gas oils Crude 40–50

Gas oils Water 40–70

Light fuel oil Crude 20–30

Waxy distillates Hy oils 30–40

Slurries Waxy distillate 40

MEA or DEA Water 140

MEA or DEA MEA or DEA 120–130

Water Water 180–200

Air Water 20–30

Lt HC vapour H

-rich stream 35–40

Lt HC vapour Naphtha 38

Condensers

Full-range naphtha Water 70–80

Amine stripper O/heads Water 100

s and lighter Water 90

Reformer efﬂuent (Lt HC) Water 65

Table 18.A.3. Standard exchanger tube sheet data.

External

= o.d. of BWG l = thickness d

=i.d. of Internal area surface per foot

tubing (in.) gauge (ft) tubing (in.) (in.

) length (ft

)

10 0.0112 0.482 0.1822 0.1963

12 0.00908 0.532 0.223 0.1963

14 0.00691 0.584 0.268 0.1963

16 0.00542 0.620 0.302 0.1963

18 0.00408 0.652 0.334 0.1963

1 8 0.0137 0.670 0.355 0.2618

1 10 0.0112 0.732 0.421 0.2618

1 12 0.00908 0.782 0.479 0.2618

1 14 0.00691 0.834 0.546 0.2618

1 16 0.00542 0.870 0.594 0.2618

1 18 0.00408 0.902 0.639 0.2618

10 0.0112 1.232 1.192 0.3927

12 0.00908 1.282 1.291 0.3927

14 0.00691 1.334 1.397 0.3927

16 0.00542 1.37 1.474 0.3927

Chapter 19

A dictionary of terms and expressions

D.S.J. Jones and P.R. Pujad´o

Abel ﬂash points

This is a test procedure for determining the ﬂash point of light distillate such as

kerosene. The ﬂash points determined by this method will be in the range of 85–120

◦

The apparatus consists of a water bath with a heating source into which is suspended

a cup containing the material to be tested. The water bath is heated and retained at a

ﬁxed temperature. The temperature of the sample being tested in the cup is measured

by a thermometer. The lid of the cup contains a shutter and a small gas burner from

which a ﬂame of determined length exits. The rate of temperature rise of the test

material is noted and at predetermined temperatures the shutter is opened and the

burner ﬂame exposed to the space above the test liquid in the cup. The temperature

at which a ﬂame is observed crossing the surface of the oil sample when the burner

is dipped into the cup is the ﬂash point. The ASTM name and number for this test is

D56-01 Standard Test Method for Flash Point by Tag Closed Tester.

Absorption units

Absorption units usually consist of a trayed or packed tower in which a gas stream is

contacted with a lean solvent in a counter current ﬂow. Usually the gas stream enters

below the bottom tray or packed bed and rises up the tower meeting the solvent liquid

stream which enters the tower above the top tray or packed bed ﬂowing down the tower.

Undesirable material in the gas stream is selectively absorbed into the liquid stream.

This liquid stream then enters a stripping column (usually a Steam Stripper), where

the absorbed material is stripped off and leaves as an overhead product. The stripped

solvent stream is then rerouted to the absorber tower to complete the cycle. These

processes are used in petroleum reﬁning to remove heavy hydrocarbons from a light

1072 CHAPTER 19

Figure 19.A.1. A schematic of a typical absorption unit.

gas stream. More commonly this type of unit is used in gas treating for the removal

of H

S from a gas stream (see Chapter 10 of this book). A schematic ﬂowsheet of an

absorption (gas treating unit) is shown as Figure 19.A.1.

Anhydrous hydro ﬂuoric acid

Anhydrous hydroﬂuoric acid (AHF) is a colorless, mobile liquid that boils at 67

◦

at atmospheric pressure, and therefore requires pressure containers. The acid is also

hygroscopic therefore its vapor combines with the moisture of air to form “fumes”.

This tendency to fume provides users with a built-in detector of leaks in AHF storage

and transfer equipment. On the other hand, care is needed to avoid accidental spillage

of water into tanks containing AHF. Dilution is accompanied by a high release of heat.

Hydroﬂuoric acid is very corrosive. It attacks glass, concrete, and some metals—

especially cast iron and alloys that contain silica (e.g., Bessemer steels). The acid also

attacks such organic materials such as leather, natural rubber, and wood, but does not

promote their combustion (see Chapter 15 for details).

Air condensers and coolers

Air cooling of process streams or condensing of process vapors is more widely used in

the process industry than cooling or condensing by exchange with cooling water. The

A DICTIONARY OF TERMS AND EXPRESSIONS 1073

Figure 19.A.2. A forced air ﬂow arrangement.

use of individual air coolers for process streams using modern design techniques has

economized in plant area required. It has also made obsolete those large cooling towers

and ponds associated with product cooling. This item in Chapter 18 describes air

coolers in general and outlines a method to estimate surface area, motor horsepower,

and plant area required by the unit.

As in the case for shell and tube exchangers there are many excellent computer

programs that can be used for the design of air coolers. The method given in Chapter 18

for such calculation may be used in the absence of a computer program or for a good

estimate of a unit. The method also emphasizes the importance of the data supplied

to manufacturers for the correct speciﬁcation of the units.

Figures 19.A.2 and 19.A.3 show the two types of air coolers used in the process

industry. Both units consist of a bank of tubes through which the ﬂuid to be cooled or

condensed ﬂows. Air is passed around the tubes either by a fan located below the tubes

Figure 19.A.3. An induced air ﬂow arrangement.

1074 CHAPTER 19

(Figure 19.A.2) forcing air through the tube bank or a fan located above the tube bank

drawing air through the tube bank (Figure 19.A.3). The ﬁrst arrangement is called

‘Forced draft’and the second ‘Induced draft’.

Air in both cases is motivated by a fan or fans driven by an electric motor or a

steam turbine or in some cases a gas turbine. The fan and prime driver are normally

connected by a ‘V’belt or by a shaft and gear box. Electric motor drives are by far

the most common prime drivers for air coolers.

The units may installed on a structure at grade or as is often the case on a structure

above an elevated pipe rack. Most air coolers in condensing service are elevate above

pipe racks to allow free ﬂow of condensate into a receiving drum.

Air systems

All chemical and petroleum plants require a supply of compressed air to operate the

plant and for plant maintenance. There are usually two separate systems and these

are:

Plant air system

Instrument air system

Plant air is generally supplied by a simple compressor with an after cooler. Very

often when plant air is required only for maintenance this is furnished by a mobile

compressor connected to a distribution piping system. Air for catalyst regeneration and

the like is normally supplied by the regular gas compressor on the unit. Instrument air

should always be a separate supply system. Compressed air for instrument operation

must be free of oil and dry for the proper function of the instruments it supplies. This

is a requirement which is not necessary for most plant air usage. A reliable source

of clean dry instrument air is an essential requirement for plant operation. Failure of

this system means a complete shut down of the plant.

Figure 13.36 in Chapter 13 of this Handbook shows a typical instrument air supply

system. Atmospheric air is introduced into the suction of one of two compressors via

an air ﬁlter. The compressors are usually reciprocating or screw type non-lubricating.

Centrifugal type compressors have been used for this service when the demand for

instrument air is very high. The air compressors discharge the air at the required

pressure (usually above 45 psig) into an air cooler before the air enters one of two

dryers. One of the compressors is in operation while the other is on standby. The

operating compressor is usually motor driven with a discharge pressure operated

on/off start up switch. The standby compressor is turbine (or diesel engine) driven

with an automatic start up on low/low discharge pressure switch.

A DICTIONARY OF TERMS AND EXPRESSIONS 1075

The cooled compressed air leaves the cooler to enter the dryers. There are two dryer

vessels each containing a bed of desiccant material. This material is either silica

gel (the most common), alumina, or in special cases zeolite (molecular sieve). One

of the two dryers is in operation with the compressed air ﬂowing through it to be

dried and to enter the instrument air receiver. The desiccant in the other dryer is

being simultaneously regenerated. Regeneration of the desiccant bed is effected by

passing through the bed a stream of heated air and venting the stream to atmosphere.

This heated stream removes the water from the desiccant to restore its hygroscopic

properties. At the end of this heating cycle cooled air is reintroduced to cool down

the bed to its operating temperature. When cool, the unit is then shut in ready to be

switched into operation for the ﬁrst dryer to start its regeneration cycle. The various

operating and regeneration phases are automatically obtained by a series of solenoid

valves operated by a sequence timer switch control. These dryers (often including the

compressor and receiver items) are packaged units supplied, skid mounted, and ready

for operation.

The instrument air receiver vessel is a pressure vessel containing a crinkled wire

mesh screen (CWMS) before the outlet nozzle. It is high-pressure protected by a

pressure control valve venting to atmosphere, and of course is also protected by a

pressure safety valve. The air leaves the top of this vessel to enter the instrument air

distribution system servicing all the plants in the complex.

Alkylation

Alkylation as utilized in the petroleum industry was developed independently by UOP,

Shell, the Anglo Iranian Company, and Texaco in 1932–1936. Motor fuel alkylation

in the petroleum reﬁning industry refers to the acid catalyzed conversion of C

–C

oleﬁns with isobutane into highly branched C

–C

isoparafﬁns collectively called

alkylate, a valuable gasoline blending component. A major constituent of alkylate is

2,2,4-trimethyl pentane which is deﬁned as 100 on the octane scale.

Alkylation reactions are catalyzed by liquid and solid acids, including H

, AlCl

–

HCl, HF, HF–BF

–HSO

F (ﬂuorosulfuric acid), triﬂuoromethane sulfonic

acid chlorided Pt alumina, BF

on alumina, zeolites, and ion exchange resins. How-

ever, the catalysts and associated processes commercialized during World War II

for aviation gasoline, were HF alkylation and sulfuric acid alkylation. These are the

process met with in most of today’s reﬁneries (see Chapter 9 for a fuller historical

description).

The chemistry of the alkylation process is quite complex and is given in some detail

in Chapter 9 of this Handbook. Brieﬂy it can be summarized by the following reaction

stages: