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

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ECONOMICS 825

working on the plant is often coupled with the requirements of insurance underwriters

and, in the case of a major mishap, its legal signiﬁcance.

The section should contain at least the following sub sections:

Emergency shutdown

Emergency action by personnel

Plan showing location of ﬁre ﬁghting equipment

Emergency telephone numbers (by client)

Location and setting of pressure relief valves

The contractor’s process engineer is primarily concerned with the writing of the

emergency shutdown procedures. In most process unit this follows the same basic

principles, which are:

1.0 If there is a ﬁred heater either as a feed pre-heater or reboiler, shut down the

burners immediately and introduce steam into the ﬁrebox.

2.0 Again, in the case of ﬁred heaters, take out the fresh feed and recycle products

through the coil until the coil is cool enough not to be damaged. Use vendor data

to ﬁx this temperature.

3.0 Cool down fractionating towers by increasing reﬂux ﬂow and wherever possible

reducing return temperatures.

4.0 In the case of reactors, remove the feed stream immediately and purge with inert

gas such as nitrogen. In the case of reactors in exothermal service and where there

is a coolant, increase the coolant duty.

5.0 Divert all product streams to slop, but maintain any cooling cycle until safe

conditions are reached.

6.0 De-pressure all pressure vessels to ﬂare or to atmosphere at a safe location. Note:

The process engineer must make sure that there exists a de-pressuring system on

all these vessels and that they are clearly shown on the MFD.

7.0 As soon as conditions allow, introduce purge steam into all vessels, towers, and,

where applicable, reactors. In some cases steam would be injurious to catalysts in

reactors, under these circumstances the reactors should be purged with inert gas.

8.0 If the emergency is the result of a ﬁre in a heater ﬁrebox due to a fractured coil,

shutdown the burners and take out the feed immediately. Introduce snufﬁng

steam into the ﬁrebox, and do not recycle product or introduce steam into the

fractured coil.

As in the case of start-up and normal shutdown procedures the same kind of detail

covering the basic actions given above would be written for the emergency shutdown.

Again the MFD would be used as the reference document.

Appendices

The appendices to the manual should contain as much data as possible to assist the

operator of the plant in the safe operation of the plant. As a minimum it should contain:

826 CHAPTER 17

The “As Built Revision”of the MFD

An up to date equipment list

Equipment manufacturers operating instructions and data

A list of hazardous materials used in the process, with a summary of recommended

handling procedures

Plant commissioning

Process engineers from the contractor’s organization are often called upon to assist

in supervising plant commissioning. Process engineers from the client’s organization

are invariably called to supervise the commissioning. This task begins at the point

where the contractor’s ﬁeld organization has completed all their installation activities

and have handed the units over to the client’s“care, custody and control”. At this

point all contractor’s debris has been removed, pressure testing has been completed,

and the unit has been reassembled after the initial ﬂushing out.

The commissioning activities fall into the following sequence of events:

Pre energizing activities

Energizing the plant

Conditioning equipment, calibrating instruments, and setting relief valves

Final check out, and closing up all vessels

Preparation for “start up”

Start-up

Lining out

Performance test runs and guarantee test run

Much of this work is carried out by the future operators of the plant to enhance their

familiarity with the process, and as mentioned earlier, the team is supervised and the

activities planned by the responsible process engineer(s). Further description of the

major commissioning activities now follow:

Pre-energizing activities

When the plant is handed over by the contractor to the client no hazardous material

such as fuel oil, fuel gas or permanent electrical power has been introduced into the

plant area. Obviously before much of the work to check out and condition equipment

utility services must be established, and this will be the objective of this phase of the

work. Normally while the plant is in this “safe”condition many client companies take

advantage of this to carry out their ﬁnal physical check of the plant on a line by line,

item by item basis.

Although the contractor has ﬂushed the plant out before hand over a further and more

thorough ﬂush out is advisable before start-up. This is done at this “safe plant”stage

when utility lines and underground lines can also be ﬂushed out. If the plant is a unit in

ECONOMICS 827

an existing complex oily or chemical drains would at this point be blocked off from the

complex’s main drain systems. Immediately prior to the plant being energized these

drain systems must be unplugged and checked that they are free of any obstruction.

Energizing the plant

As soon as the responsible process engineer is satisﬁed that all pre energizing activities

are complete he will instruct that the utility systems be commissioned. Normally this

starts with the introduction of permanent power and the checking out of the circuits by

the electrical technicians. When this has been completed to the responsible process

engineer’s satisfaction, instructions for commissioning the steam, condensate, and

fuel systems will follow. Note: the water system is usually commissioned before the

ﬁnal ﬂush out and the system used for this ﬂushing activity.

The commissioning of the fuel systems indicates that the plant is now a ‘Hazardous

Area’and all regulations pertaining to this type of area comes into effect.

Conditioning equipment

Certain new process equipment will require conditioning before being used in the

process. Some of these are:

Reactors: In some processes these will have refractory lining which will need to be

‘Cured’. Curing is the subjection of the refractory to a controlled increasing tem-

perature environment until the curing temperature is reached. The refractory is held

at this temperature for a prescribed period of time, before cooling back to ambient

temperature. The cooling is also undertaken in a controlled fashion. Many reactors

and reactor systems also require drying out. This too is accomplished during this

period using heated air or inert gas and the recycle gas compressor if there is one in

the circuit.

Heaters: All heaters will have refractory lining and these will need to be ‘Cured’as

described above. If the heater contains coils that are to be used in steam generation

service, these coils need to be treated with hot caustic soda to remove all traces of

grease or other undesirable contaminants.

Fractionating columns and vessels generally: These usually need to be dried. This is

usually done at the same time that the associated heaters are being conditioned. The

hot air or inert gas stream passing through the heater coils to protect them during the

refractory curing is routed to the vessels and used for the drying activity.

Piping in sour service: Piping and pots etc in high H

S and hydrogen concentration

service often need to be acid treated to protect them against local corrosion or embat-

tlement under these conditions. This is called ‘Pickling’and is usually accomplished

bysetting up a temporary system. This contains a reservoir for the fresh acid, one or two

828 CHAPTER 17

small skid mounted reciprocating pumps and a receptacle for the used acid. The pumps

deliver the acid through the piping and equipment for a prescribed period of time.

All of these conditioning procedures are provided by the respective equipment man-

ufacturers and would be included as part of the operating manual.

The opportunity is normally taken at this time to calibrate as much instrumentation

as possible. Flow meter oriﬁce plates are installed and, where possible, ﬂow meters

and control valves used in these procedures. Relief valves are set, and this is always

done by the client’s organization, and the settings certiﬁed.

Final check out, and closing up of all vessels

This will be the last opportunity to check such items as the internals of towers, frac-

tionation trays, condition of refractory and other linings, hold up grids, distributors,

and the bottom of the tower bafﬂing system (to and from the re-boiler). A ﬁnal check-

out of the piping layout also needs to be carried out at this point. When satisﬁed that

all is satisfactory the process engineer will authorize the following ﬁnal prestart-up

activities to be completed:

Catalyst loaded into the respective reactors. This is often supervised by the licensor’s

representative. The reactor closed up by installing the correct operating gaskets.

This later point is made because during the prestart-up activities and conditioning

temporary gaskets are used on manways, nozzle connections and the like. These

are replaced by the correctly speciﬁed gaskets for the operating conditions. The

temporary gaskets are never used again and are thrown away.

All towers containing random packing are loaded with the packing and closed up.

Permanent speciﬁed gaskets are used to replace temporary gaskets as described

above.

All other vessels and towers are closed up using the permanent speciﬁed gaskets.

In cases where equipment has been subject to a caustic wash the temporary silica

level gauges used during the wash are replaced by the speciﬁed operational ones.

With the completion of these ﬁnal checks and vessel close up, the plant is now ready

for start-up.

Start-up and lining out

The activities and their sequence for starting up the plant are carried out as described

in the operating manual. In the case of an oil reﬁning plant for example the ﬁrst activity

is to eliminate air from the plant systems. This is done by using water or steam or

inert gas or a combination of all three. The use of steam or water is prohibited for

most reactor system where the catalyst would be irreparably damaged by such contact.

Thus inert gas is circulated using the recycle compressor for this purging. Thus the

recycle compressor is commissioned and will then continue to function until plant

shut down. In the case of the fractionating units of the crude distillation and thermal

ECONOMICS 829

cracking systems, water and steam are used for purging. The water is used to purge

the heaters and tower bottom systems and steam is used for purging the upper sections

of the fractionating towers.

After the purging comes the introduction of the cold feeds. In the case of units that

contain reactors and use hydrogen under pressure a leak testing program is required.

First of all the plant is subject to leak testing at operating pressure using the inert gas.

Then as the inert gas is replaced by hydrogen further leak tests are required. All leaks

must be repaired before start-up of these units can begin.

Where water has been used for purging, the water is replaced by the oil feed. This is

termed the ‘oil squeeze’. The steam is not replaced by anything. It continues to ﬂow

through the tower until after start-up where it may then be replaced by the vapor phase

of fractionation.

Start-up may be deﬁned as beginning when the purge program shows conditions to be

safe to apply heat into the plant. In the case of catalytic plants using a hydrogen stream,

the hydrogen stream is circulated and heated up to its operating temperature ﬁrst. When

the plant operating conditions are on gas circulation the oil feed is introduced and

heated.

In the case of the noncatalytic units where only fractionation is being carried out heat

may by applied to the oil feed directly. This is done when the oil squeeze is complete

and the water content of the oil ﬂowing out of the plant is at an acceptable level. The

plant conditions are obtained in accordance with the procedures described in the oper-

ating manual by adjusting heat input, reﬂux rates, pressures and respective circulating

rates in the case of the catalytic plants. Up to the point when the operating conditions

have been reached the total products have been routed to slop. They may be returned

later as feed or used in the reﬁnery fuel system. As soon as the plant has reached its

operating conditions product streams are required to be diverted to storage. This is

done however only after the product quality has been conﬁrmed by laboratory tests.

Performance and guarantee test runs

Usually as soon as possible after the plant has been lined out and is in production a

performance test run may be carried out. The purpose of this test run would be to

establish as far as possible the limits of the various systems included in the process.

Normal feedstock would be used and the performance of the plants under various

operating conditions examined. The other objective of this exercise is to familiarize

the operators with the plant control responses to the various changes.

The guarantee test run is a more formal requirement. At the end of the test run carried

out over a ﬁxed period and under speciﬁc conditions, the client will accept the plant

830 CHAPTER 17

completely or require remedial work and further test runs to meet the guarantees.

More details on this test run is given in the next section of this chapter.

An example of a commissioning plan used in the commissioning of a ‘grass roots’re-

ﬁnery on sites facilities is given in Figure 17.1.12. This plan reﬂects the program for the

onsite units and tank farm only. All the utility plants had already been commissioned

and started up before this plan begins. The program was successful and apart from

some minor problems the reﬁnery was brought on stream in the time span predicted.

Process guarantees and the guarantee test run

Among the last activities that a contractor’s process engineer performs on a project is

the preparation of the process guarantees that are usually required by the client, and

the procedure for testing the plant to meet the guarantees. The process guarantees

may begin to be developed as soon as a ﬁrm process has been established and manu-

facturer’s guarantees obtained for the performance of the various manufactured items

of equipment. The process engineer may be required to guarantee the performance

of any plant that he has calculated and speciﬁed equipment, piping, instruments etc

for. He will not be expected to guarantee the performance of any item of plant or

piece of equipment he has not speciﬁcally designed. He will also not be expected to

guarantee any criteria that cannot be measured during a test run. Thus if a process

engineer calculates a fractionating unit to meet a speciﬁed separation, he will be ex-

pected to guarantee that the design will make the separation at the design feed rate and

composition. He will not however be expected to guarantee the performance of in-

dividual items of equipment contained in the unit, and which have been properly

speciﬁed by him. This guarantee is carried by the respective manufacturers who have

designed and fabricated the items.

The process performance is tied also to a guarantee of its efﬁciency. This will be in

terms of a guarantee of the utility consumption in the plant whilst operating on the

design throughput and conditions. Of course the guarantees as written will differ

from process to process but will usually follow a similar pattern or format. This is as

follows:

Description of the feed in terms of throughput, composition, or source (in the case

of crude oil for example).

Design operating conditions and the guarantee of the product speciﬁcation at these

conditions. Alternatively a guarantee of the fractionation or separation performance

of the process in terms of key component separation.

A guarantee of the hydraulic capacity of the process system. This would only be

in the terms that the process system will handle a design quantity per unit time.

Note, this hydraulic guarantee would not normally be combined with the stream

composition speciﬁcation guarantee. This is discussed later.

ECONOMICS 831

Figure 17.1.12. A typical commissioning plan.

832 CHAPTER 17

The utility consumption guarantees. These are usually taken for the total plants in

the new or revamped complex. Rarely are utility guarantees written for individual

units making up the new or revamped complex.

A list of the accepted test procedures that will be used.

The guarantee test run procedures that are written in some detail. Provision is

normally made in them for the contractor’s process engineer to instruct operating

changes to be made as necessary before or during the test run.

Description of the notices to be given in event that:

1. The test run was successful and met all the requirements of the guarantee.

2. The test run was not successful and requires to be run again.

3. Some or all of the guarantee requirements cannot be met and a limited liability

clause is evoked.

The following paragraphs describe and discusses the contents of a performance guar-

antee in more detail than given in the list above.

Description of the design feedstock

Although the plant may have been designed on the basis of handling more than one

feedstock of slightly differing composition, the test run is conducted using one of the

design feedstocks as a parameter. This practice is more common in the oil reﬁning

industry than in the production of chemicals or even petrochemicals. This is so because

most reﬁneries handle crude oil from various sources around the world, and these can

vary considerably in composition. The intermediate products from the various crude

oils therefore can also vary in composition.

The choice and proper deﬁnition of the test run feedstock is absolutely basic in

developing the guarantees and assessing the result of the guarantee test run(s). This

begins by providing a statement of the design feed throughput. This should be as

simple as possible and preferably in the units of measurement used in the client’s

original “Duty Speciﬁcation”. If the measurement units used in the design or the

units of measurement used in the operation of the process differs from that in the

“Duty Speciﬁcation”, then the conversion factors used to convert from one unit of

measurement to the others must be noted here. There must be no ambiguity concerning

this quantity.

The second item of importance in this section is the composition of the design feed-

stock. Where possible this should be a breakdown in the quantity of each component

in either weight or molar terms. Occasionally volume composition may be used, how-

ever, the composition and the units it is quoted must be able to be measured using

accepted normal test equipment and/or reagents.

ECONOMICS 833

When it is not possible to give the feed composition as described above other accept-

able criteria for establishing the feed quality may be used. For example in deﬁning the

quality or composition of a crude oil or the products of crude oil distillation boiling

points and boiling curves are used (See “Elements of Petroleum Processing” also by

the author

). Again however these characteristics of the feedstock must be measurable

by accepted means. The test methods to be used in evaluating the guarantee test run

results are listed in this document. This item is discussed later.

Test run conditions and the guarantee of product quality

Following the description covering the design feedstock comes the heart of the perfor-

mance guarantee—the guarantee of the end product. This guarantee however is always

tied to the feedstock and to the conditions that the plant is operated on to meet the

product speciﬁcation. Where there is a catalytic or any other type of reactor involved

in the process this guarantee may extend to cover the yield of product promised by

the contractor or the licensor.

The pertinent process conditions to obtain the guarantee with respect to the end

product is deﬁned here. Obviously these conditions will reﬂect the basic parameters

used in the design of the facility. The process engineer developing the guarantee

document however must be sure that the conditions described here are pertinent to

meeting the end product speciﬁcations and yield. Over or incomplete deﬁnition of the

process conditions may lead to ambiguity and conﬂict in operating the plant under

test run conditions.

The product speciﬁcation, and its yield under certain circumstances should reﬂect

exactly those given in the client’s“Duty Speciﬁcation”. Yields and or product quality

which have been left open or to be conﬁrmed by a licensor’s pilot plant tests, during

the compiling of the “Duty Speciﬁcation”must be included here. These should be

qualiﬁed however with reference to the client’s acceptance of them and his approval

for their use in the plant design. They become part of the client’s licensor agreement.

The contractor may then develop the remaining process guarantees on the design

carried out by him based on this approved licensor data.

Performance of the plant may also be judged by the performance of some engineering

principle used in the design. For example in oil reﬁning the performance of some of

the complex fractionators used (e.g., the atmospheric crude distillation unit) is most

often deﬁned in terms of fractionating efﬁciency. This is measured by the difference

in the ASTM distillation temperature reading between a 95 vol% recovery of a light

product and the 5 vol% reading of the adjacent heavier product. The test used to

determine these readings is the accepted ASTM distillation test carried out routinely

Published by John Wiley & Sons Ltd.

834 CHAPTER 17

in all reﬁneries. The measure of these test temperatures indicates how much of the

lighter product is contained in the heavier one and vice versa. This of course is also a

measure of the respective products composition and the contaminants they contain.

The hydraulic guarantee

Although this is tied to the plant design and its ability to handle the feed and product

streams as stated earlier it is guaranteed separately to the performance guarantee

described above. This is so because very often it is not possible for a contractor

to guarantee the quantity of product that the plant will make. An example of this

is again seen in the oil industry. When a contractor’s process engineer designs the

unlicensed units of an oil reﬁnery he does so using the design crude’s assay data. All

the product yields and composition therefore are based on the assay data which the

contractor could not have developed—he is therefore not expected to guarantee it.

From his design calculation however he has sized the various systems in terms of

piping instruments and of course speciﬁed the various pumps. He is expected to

guarantee these based on the design ﬂows he has used. Thus, the hydraulic guarantee

should start with the following statement:

“When the unit is operated on the design feedstock and at the design feed rate the

following systems shall be capable of handling:

Stream One 450 gpm measured at 60

◦

Stream Two 600 gpm measured at 60

◦

Utility consumption guarantees

Normally contractors offer utility guarantees as a summation of the cost of all utilities

consumed by the process. These are also determined as a summary of the utilities

consumed by all the plants considered in the test run. The utility guarantee ﬁgure is

developed from the utility balances compiled during the process design. Much of these

ﬁgures are based on manufacturers guaranteed equipment efﬁciencies for electric

motors and turbines. Others are based on the process heat and material balances The

calculated utility consumption for each utility is multiplied by the respective utility

unit cost as provided by the client in his “Duty Speciﬁcation”. The utility guarantee

ﬁgure is then quoted as the sum of all these cost items as a single cost ﬁgure.

In preparing the utility guarantee the following should appear in the statement of the

guarantee:

Unit cost of each utility

Expected normal consumption of each utility

Either the guaranteed total daily cost of all the utilities as one ﬁgure (This would

include a contingency factor agreed to by the client.)