Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
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734 CHAPTER 16
Table 16.18. Boiling range correction for olefins
Boiling range IBP to
Boiling range correction f FBP
◦
C
1.0 0
0.975 7
0.950 14
0.925 21
0.900 28
0.875 38
0.850 43
0.825 53
0.800 62
0.775 72
0.750 95
0.725 99
0.700 125 or greater
The olefin content of the test sample can be calculated from the bromine number by
the equation
Olefin mass% = f (BM/160)
where
f = Boiling range correction from Table 16.18.
B = Bromine number expressed as grams of bromine per 100 grams of sample.
M = Molecular weight (relative molecular mass of olefin as given in Table 16.19.
Sulfur content by lamp method (D1266)
This test method determines the total sulfur in liquid petroleum products in concentra-
tions of 0.01–0.4 wt%. This method is applicable to all petroleum liquids that can be
burned in a wick lamp. It therefore covers gasoline, kerosene, and naphtha. A blend-
ing procedure can be applied to determine the sulfur content in gas oils and heavier
Table 16.19. Relation of average molecular
weight to 50% boiling point
Average molecular
50% boiling point
◦
C weight
30 72
66 83
93 96
121 110
149 127
177 145
204 164
232 186
QUALITY CONTROL OF PRODUCTS IN PETROLEUM REFINING 735
Figure 16.12. Details of assembled lamp unit.
which can not be burned directly in the wick burner. Figure 16.12 shows the details of
the assembled lamp unit. Figure 16.13 is a schematic diagram of the CO
2
–O
2
supply
manifold and lamp system.
D1266
The sample is burned in a closed system using a suitable lamp (Figure 16.12) and an
artificial atmosphere of 70% carbon dioxide and 30% oxygen to prevent the formation
of nitrogen oxides (Figure 16.13). The oxides of sulfur are absorbed and oxidized to
sulfuric acid by means of a hydrogen peroxide solution. This solution is flushed with
air to remove carbon dioxide. The sulfur as sulfate in the absorbent is determined
by titration of the sulfuric acid with standard sodium hydroxide. The sample size for
direct combustion is 10–15 grams if the predicted sulfur content is below 0.05% for
predicted sulfur content 0.05–0.4% the sample size should be 5–10 g.
The calculation of the sulfur content from the titration is given by the following
equation.
Sulfur Content wt% = 16.03 M × (A/10W )
where
A = milliliters of NaOH titrated
M = molarity of the NaOH solution (Note 1 below)
W = grams of sample burned.
736 CHAPTER 16
Figure 16.13. Schematic diagram of the CO
2
–O
2
supply manifold.
Note 1: The calculation can be simplified by adjusting the molarity of the NaOH
solution to 0.624. Then 1 ml of the solution will be equivalent to 0.001 g of sulfur. In
this case the factor 16.03M in the calculation becomes 1.0.
Octane number research and motor (details of this test are given
in ASTM standards Part 7)
By definition, an octane number is that percentage of isooctane in a blend of isooctane
and normal heptane that exactly matches the knock behavior of the gasoline. Thus,
a 90 octane gasoline matches the knock characteristic of a blend containing 90%
isooctane and 10% n-heptane.
The knock characteristics are determined in the laboratory using a standard single
cylinder test engine equipped with a super sensitive knock meter. The reference fuel
(isooctane and C
7
blend) is run and compared with a second run using the gasoline
sample. Two octane numbers are usually given: the first is the research octane number
(RON) and the second is the motor octane number (MON). The same basic equipment
is used for both octane numbers, but the engine speed is increased for the motor
octane number. The actual octane number obtained in a commercial engine would be
somewhere between the two numbers. The significance of the two octane numbers is
to evaluate the sensitivity of the gasoline to the severity of the operating conditions
in the engine. Invariably the research octane number is higher than the motor octane
number, the difference between them is quoted as the ‘sensitivity’of the gasoline.
QUALITY CONTROL OF PRODUCTS IN PETROLEUM REFINING 737
Conclusion
The specifications and the selected tests given here represent the control measures
used to establish product quality control. Much of the testing described here are
used for plant control while all the tests are necessary to ensure that product quality
of finished products is met. In modern refinery practice much the plant control is
achieved using ‘in line’analyzers tied to control system computers. These computers
automatically adjust plant conditions to meet set product quality criteria. A similar ‘in
line’analysis is used for blending rundown streams for finished products. Invariably,
though, laboratory testing is still used to ‘spot check’plant intermediate product
quality, and laboratory testing is always used as final check on finished product quality.
Chapter 17
Economics
17.1 Refinery planning, economics
and handling new projects
D.S.J. Jones
This chapter is divided into three parts. The first deals with the planning of a refinery’s
operation, which includes its optimized crude runs, product slate, and any process
expansion or debottlenecking that may be required to meet this optimized operation.
The second part deals with the process economic evaluation of a proposed new refinery
or new facilities within an existing refinery. The third part is a brief description and
discussion of a refining company’s participation in the execution of an approved
engineering and construction project.
This second part of the chapter is closely related to the first part in so far that process
studies and the ultimate selection of any process or processing route is based on the
approved marketing strategy for the refining company. This in turn is based on the
conclusions following the work undertaken in Part 1. The final phase in this refinery
operation is described in Part 3. This outlines the preparation of contracts to third
parties for the installation of new or expanded facilities. It includes the choice of the
type of contract to be solicited and follows with the selection of a suitable engineering
company to execute the work. Finally, it discusses the company’s activities associated
with the execution of the project by contractors and the subsequent commissioning
and acceptance of the completed facilities.
17.1.1 Refinery operation planning
The basic organization of an oil company consists essentially of three main depart-
ments:
1.0 The Supply Department
2.0 The Refining Department
3.0 The Marketing Department
739
740 CHAPTER 17
The function of these three main departments are co-ordinated by a supply de-
partment. This department undertakes this role in accordance with the following
sequence:
1.0 Marketing department informs the supply department with the quantities of prod-
ucts they can sell.
2.0 Supply department, after making adjustments for stock levels, advise the refinery
of the quantity of each product required.
3.0 The refining department advise the supply department of the actual quantities
they can produce and how much crude they will require to do so.
4.0 The supply department arranges with the marine department for the necessary
shipping to:
r
Provide the crude
r
Lift the products
r
Import the quantities that cannot be produced
In the above sequence of events Item 3 is carried out by the planning section of the
refinery department. Their objective is to translate the production requirements given
by the supply department into a workable system, which specifies the actual operation
of each plant to ensure that the final result is the most economical one practicable.
This is termed the ‘Running Plan’for the operation.
Running plans
Running plans are developed and issued on a monthly basis. They usually cover
periods varying from 11 to 18 months ahead. Long term periods are broken down into
quarters, short term (up to 6 months ahead) are broken down into months. The main
uses of the running plan are to provide data for:
r
Keeping the supply department and the company executives informed
r
Provide information for long term chartering of ships
r
Arrangement of import programs
r
Pin point future product quality and equipment difficulties
The running plan is used in a refinery as the basis for an Operating Program. Such a
program is developed in the refinery by converting the plan into a day to day operation
program for each refinery plant. At the end of every month the plant operation for that
month is summarized and compiled into an Operations Summary which compares
the actual plant operation with the program. Usually the refinery organization will
include a planning department and the production of the both the Operating Program
and the subsequent summary is their responsibility.
ECONOMICS 741
The rules of planning
Before looking at the development of running plans in some detail it is necessary
to understand some fundamental rules. These are listed below and are the “Planning
Data”:
r
Equipment Availability
r
Plant Performance
r
Service Factors
r
Product Quality
r
Planning Properties
r
Blending Properties
r
Crude Availability
r
Crude Quality
r
Tankage and Lines Availability
r
Economic Rules
Most of these rules are self explanatory, but notes on a few of those items, which are
not so apparent, are as follows:
Plant performance
This is an important requirement in planning the refinery daily and long term oper-
ation. The exact operating capability of the various refinery plants must be known.
Such data that is essential are:
r
Yields under any operating condition and any feed quality
r
Product quality under any operating condition and feed quality
r
Maximum and minimum plant throughput
r
Fuel consumption
Blending properties
Most finished products leaving the refinery are blends of one or more basic process
streams. For example all gasoline products will be blends of straight run naphtha’s
and some high octane streams from a cracking unit and/or streams from a catalytic
reformer. Full description and discussion on blending and blended products are given
in Chapter 1 of this Handbook. In planning the refinery’s day to day operation these
blending techniques and, when applicable, blending indices are used.
Crude availability
With most major oil refining companies the company’s central supply department
issues the availability of crude slates (quantities and crude source) when they issue
742 CHAPTER 17
the requirement data. In most cases the respective refining company has contract for
the purchase of a few specific crudes and their quantities. Of these basic crude slates
one or two of the crude oils may be increased or decreased if necessary. These are
called marginal crude oils. Most often there are two types of crude oils in the slate
which are marginal. One of these marginal crude oils would be used if more crude
than is shown on the slate is required. The other would be backed out of the slate if the
entire projected slate was not required. Thus marginal crude oils play an important
part in the economic running plans for a refinery operation.
Economic rules
Using the planning rules, it is possible to devise an infinite number of schemes that
would meet the majority of the market requirements. Only one such scheme however
would be the most profitable. It is the most profitable plan or scheme that has to
be determined and implemented, and to do this it is necessary to follow some basic
economic rules. These rules may be developed with answers to the following typical
questions:
1.0 If all requirements cannot be met, in which priority order should the various
products be placed?
2.0 Is it profitable to run the refinery to meet just a fuel oil product requirement. That
is not to produce waxy distillates at all?
3.0 What is the optimum octane number severity operation for the reforming and/or
cracking units to meet gasoline requirements?
4.0 Which is the cheapest middle distillates to import if this becomes necessary to
meet a product slate?
5.0 Is it economical to utilize a surplus unit capacity to produce feed to another? For
example to use surplus deasphalting capacity to produce feed for the catalytic
cracker.
6.0 Does it pay to divert straight run naphtha to refinery fuel in a situation where
naphtha outlet is limiting?
The following table is a simplified example of the use of these economic rules to
determine the changing of fuel oil ‘length’in a middle distillate outlet limiting situ-
ation. The only units considered here are the crude distillation unit (atmospheric and
vacuum), cat reformer unit, and the cat cracker (FCCU). Being a middle distillate out-
let limiting there will be spare capacity in the units considered, and all requirements
are met except for fuel oil. The economic rule in this case is that the most profitable
plan will be when the crude and fuel oil are at a minimum while still meeting the
requirements of the other products in the slate.
ECONOMICS 743
Developing the running plan
In most refining companies with more than one refinery installation running plans
are developed in the company’s corporate offices. In this way access to the required
data (such as crude availability, product slate etc.) are readily available to the planner.
Normally running plans are published on a monthly basis. Again normally these plans
cover a period of 18 months. The early part of the period, say the first six months, will
be studied on a monthly basis, and the remainder on a quarterly basis.
The use and purpose of the refinery running plans
The running plans are designed to provide corporate management with data with
respect to the following:
1. The anticipated pattern of production i.e. the surpluses and the deficits that are
likely to occur.
2. The likely operations of the refineries in the company. This covers crude runs and
refinery throughputs.
3. Any inadequacies in refining capacities to meet projected profit margins. This may
form the basis for refinery expansion program. (This is dealt with in a separate
item of this section of the chapter).
4. Indication as to where and when extra business can be accommodated in the
company’s operating plan.
5. The basis for financial forecasting and estimates of profit and loss.
The planning schemes
The content of the running plan will conform to the rules of planning listed and
discussed earlier. The development of all running plans begin with schematic diagrams
giving as many options as possible of the routes by which a required product slate
can be achieved from a particular crude availability slate. The mechanism to arrive
at this is not unlike the process configuration study described in Chapter 2 of this
Encyclopedia. In the case of the plan schemes however the objective is to fit the
process streams to a fixed refinery configuration in order to meet a product slate. In
these schemes excess products are corrected by either reducing crude throughput or
using the stream as blend stock or feed to other unit(s). Deficits in the product slate
may be solved by importing the necessary product components to complete a scheme.
An example of a typical planning scheme to meet middle distillates (Jet Fuel in this
case) and specialties (White Spirit in this case) is given as Figure 17.1.1.
Several of such schemes may be developed to meet this particular product slate criteria.
Each of these will be subject to an economic analysis, and this may extend to one or
more of the company’s several refineries. These economic analyses are made using
Figure 17.1.1.
An example of a planning scheme diagram.