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

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SUPPORT SYSTEMS COMMON TO MOST REFINERIES 543

ﬁnished products will include various grades of fuel oil and lube oil. The blending

of the process streams is accomplished either by batch blending in blending tanks or

in-line blending in the pipe line itself.

In-line versus batch blending

In batch blending the components are routed separately into a single receiver tank.

They are mixed in this tank to meet the ﬁnished product speciﬁcation. In the case on

in-line blending the component streams are routed through automatically operated

ﬂow valves to a ﬁnished product tank. With modern computerized control technology

in-line blending is becoming the more common form of blending process. In the case

of gasolines and lube oils in particular in-line blending is extensively the accepted

method. Middle distillates and residuum blending by batch has still some advantage

because there are much fewer components to be handled, although the quantities

involved are usually greater.

The in-line blender operation

An in-line blender is essentially a multiple stream controller with feed-back. The

controller itself is a computer into which the recipe for the blend is keyed. Such

blending recipes have been covered in some detail in Chapter 1 of this Handbook.

The controller automatically starts the pumps for the blend components and moti-

vates the ﬂow control valves on the component lines to meet the required component

quantities. In most cases the component lines join together to form the blended prod-

uct which is then routed to the ﬁnished product tank. A series of on line analyzers

located in the blend run down lines, monitor the ﬁnished product properties and in

turn, reset the controller adjusting the component quantities to meet the end product

speciﬁcation.

The in-line blender design

Most reﬁnery companies have their own proprietary component blending recipes for

their ﬁnished products. These will be in computer program form and usually utilizing

the linear programming techniques described in Chapter 8 of this Handbook. It is this

program software that is installed into the blender controller to activate the respective

component systems. The blender controller acts to start the selected pumps and the

control valves. It also receives data from the on line analyzers located in the product

run down line.

The design of the blending system as a whole is the combined effort of the pro-

cess engineer, the instrument engineer, and the computer specialist. It will be the

duty of the process engineer to develop the blending recipe in terms of component

percentages and quantities to meet a particular product speciﬁcation. The instrument

engineer will ensure that the control valves, pump starting assembly and the on stream

544 CHAPTER 13

analyzers meet the process requirements. A typical list of the instrument engineer’s

responsibilities in this regard are as follows:

The control panel, panel instruments, instrument power supply, annunciators pump

start push buttons, indicating lights, graphic display and all panel wiring

Turbine meters and pre-ampliﬁers

Control valves with positioners

Stream analyzers

Field transmitters (ﬂow, temperature, pressure)

Finally it will be the computer specialist’s duty to translate these requirements into

the software program for the controller computer.

Component tankage

Because the in line blender permits the rapid conversion of the components to ﬁnished

products, the ratio of component to ﬁnished product tankage should be quite large.

For good ﬂexibility this ratio should be 4 or 5 to 1.

The most signiﬁcant process requirement for successful blending is that the properties

of the individual components do not change during the blending operation. Alkylates

and catalytically cracked naphtha vary little unless feed or operation are changed.

Reformates and straight run naphtha however have a greater variability due to changes

in source crude feed quality. These are often stored in separate “running gage”tankage

the quality of the contents of which are tested when full.

Lube oils are a particular problem in component storage, because of the tendency of

the oils to ‘stratify’. That is these oils tend to separate in storage with the heavier

gravity and viscosity portion of the oil sinking to the tank bottom. In most cases

the contents of these tanks are continually mixed using propeller type mixers. Many

companies adopt this system to all heavy component tankage such as gas oils, and

fuel oil product components.

Finished product tankage

Finished product tankage is needed even with the most efﬁcient in line blender. This

is because of required product disposal rates, and product certiﬁcation. However in

many design cases, in-line blending will still only require about one half the product

storage required by batch blending.

Actual requirements of product tankage will usually be dictated by the manner in

which the product is to be shipped from the reﬁnery. The blend rate is usually sized to

blend a day’s production in a certain number of hours. The maximum rate of an eco-

nomically sized blender will usually be too slow to blend into an ocean going tanker.

SUPPORT SYSTEMS COMMON TO MOST REFINERIES 545

Thus, product tankage and loading pumps are needed to supplement the blender. Con-

versely, the minimum rate of a blender will usually be too fast to blend directly into

a road tanker. In some cases however this is done by limited volume transfer pumps

taking suction directly from component tankage.

Road and rail loading facilities

The extent of product shipping facilities required in a chemical or petroleum complex

depends on the size of the complex, the local market, the number of different products

to be shipped and the market to be supplied. Normally the shipping facilities installed

in most plants is sufﬁcient to cater for normal product handling and the ﬂexibility

required for seasonal demands. The capacity of these facilities will almost invariably

exceed the plant’s total production.

The most common method of shipping product is by road or rail in suitably designed

tanker cars. In the case of large complexes located on coastal or river side sites shipping

by barge or ships carry the bulk of the plant products. This section however will deal

only with dispatch by road and rail.

Loading rates

Loading rates for road and rail tankers vary from as low as 150 GPM to as high as

1,000 GPM, but most terminals load at rates between 300 to 550 GPM. Road tankers

have capacities from 1300 to 6500 gals and one tractor can haul two 6500 gals tanks.

The number of loading arms required for each product to be loaded varies with:

Truck size

Number of loading hours per day

Number of loading days per week

Time for positioning, hook up, and depositioning of the truck.

Figure 13.12 gives the number of arms or spouts required for loading a 3,500 gal

truck under various conditions.

The conditions shown in Figure 13.12 is for ﬁlling at a rate of 300 GPM (bottom

curve) and for 500 GPM (top curve). The loading time is taken as the ﬁlling time per

tank truck plus 10 minutes. Thus loading time is:

Tank truck capacity gals

GPM

+ 10 minutes

Tank car capacity is taken as 3,500 Gallons. Thus for the lower curve loading time

is 22 minutes per car, and for the upper curve 17 minutes per car. Assuming that a

single product is loaded over 4 hr in an 8 hr day 5 days a week then number of trucks

546 CHAPTER 13

Figure 13.12. Number of loading arms for quantity shipment.

required per Barrel/Day is:

B/D × 42 × 5days× 8 hr/day

3500 gals/truck × 20 hr loading per week

= 0.024 trucks per Barrel/Day.

Then for 1000 B/D number of trucks per working day = 0.024 × 1000

= 24 Trucks/day of 4 hr ﬁlling.

Time to load trucks at 300 GPM ﬁlling rate = 24 ×22 minutes = 528 minutes.

To complete loading in 4 hrs the number of arms required =

528

240

= 2.2

Continuing with this calculation for several more shipping capacities and for ﬁlling

rates of 300 and 500 GPM produces the data given in Figure 13.12.

Loading equipment

Figure 13.13 is a schematic drawing for a typical road or rail loading facility.

The loading pumps which are located close to the product storage tanks take suction

from these tanks. The loading pumps are high capacity, low head type with ﬂat

head/capacity characteristic. They operate at between 35 and 45 psi differential head.

SUPPORT SYSTEMS COMMON TO MOST REFINERIES 547

Figure 13.13. Schematic diagram of a loading facility.

These pumps discharge through an air eliminator drum into the loading header. Several

loading arm assemblies are connected to the loading header. Each of these assemblies

include a remote operated block valve followed by a desurger (optional), then a

strainer located before the loading meter. The product ﬂows from the meter into a

swivel jointed loading arm and nozzle. Tank trucks and rail cars are loaded through

their top hatches into which the nozzles of the loading arm ﬁt.

Air eliminators are used to disengage air and other vapors which would interfere with

the accuracy of the meters. Disengaging of the vapors is accomplished at about 3 psig.

Should there not be sufﬁcient static head at the disengaging vessel a back pressure

valve must be provided to obtain this pressure. The meters are positive displacement

type and desurgers are installed to decrease hydraulic shock resulting from quick

shutoff.

Loading facilities arrangement

Figures 13.14 and 13.15 show the arrangement of loading facilities for truck and

railcar, respectively.

The dimensions shown on the diagram are applicable to one world area and may not

be applicable to other localities. The equipment and its arrangement shown in the

diagrams however are standard for most of these facilities.

548 CHAPTER 13

Figure 13.14. Tank truck loading facility.

In truck loading the meters and strainers are located at the loading station. The con-

nection of the loading arm is made by an operator actually standing on the car itself.

In the case of the truck loading facilities the loading arm is operated from an adjacent

platform. As in the case of the truck loading the meter and strainer together with the

on/off valve is located on the loading site.

Figure 13.15. Rail car loading facility.

SUPPORT SYSTEMS COMMON TO MOST REFINERIES 549

Jetty and dock facilities

Tankers and barges are loaded and unloaded at jetties or docks. In almost all circum-

stances these facilities for handling petroleum products are separate from those used

for general cargo. Very often tankers, particularly the modern ‘Super’tankers are

loaded and unloaded by submarine pipelines at deep water anchorage. This section

of the chapter however deals only with onshore docking facilities.

Jetty size, access, and location

Tanker sizes range from small coastal vessels of 10,000 bbl capacity to super tankers

in excess of 250,000 bbl capacity. The more common tanker size is one of 140,000 bbl

capacity and this size tanker is labeled a T2. This tanker is usually used for product

carrying. It can carry as much as three different product parcels at the same time. The

larger tankers are usually used for crude oil transportation.

Ideally the jetty size should be sufﬁcient to cater for both these size tankers, and

usually at least one of each size at the same time. In some reﬁneries which have

jetty facilities these usually include barge loading items also. The barge loading

may however be located on remote docking facilities from the larger sea going

tankers.

The location of the jetty itself must consider the following:

There is sufﬁcient deep water to cater for the larger crude carrying tanker

It is located as close as possible to the reﬁnery’s tank farm

It is in an area that has a good approach road and park

There is sufﬁcient room for a product/crude pipe-way

There is sufﬁcient waterway in which to maneuver and handle tanker docking

A fully loaded T2 tanker has a maximum draft of 30 ft. The larger crude carrying

tanker would have a maximum draft around 45 ft. It is important to minimize rundown

pipe lengths to and from the jetty loading area and the reﬁnery tank farm. The ﬁrst

is the piping cost factor and the second is that often the pumping characteristics may

have a negative static head during the pumping program.

A good onshore jetty approach road is mandatory for the operation of the jetty. This

is required for safety reasons and the easy approach way for emergency vehicles

(such as ﬁre engines and ambulances). The approach road is also required for the

transportation of the operating staff, ship’s crew, and the ships chandler vehicles.

Usually this approach road is dedicated for jetty use and will be quite independent of

any adjacent reﬁnery road.

550 CHAPTER 13

There must be room on shore and on the jetty itself for the loading and unloading pipe

way(s). This can be quite extensive depending on the reﬁnery size and the number of

products that are exported. There are several options for the location and size of this

pipe way conﬁguration. On the jetty itself it maybe carried on overhanging supports

on both sides of the jetty pier or it can be supported by an independent pipe rack

adjacent to the jetty pier (much more expensive however), and this pipe rack could be

multitiered. On shore the pipe way can be located along the roadway at ground level

or elevated with two or more tiers. It could also be elevated and run above the roadway.

This does however restrict access by limiting vehicle height using the roadway.

Finally the location of the jetty must allow sufﬁcient waterway room for tankers to

be berthed properly. Tankers arriving from the open sea must have room so that tugs

can handle and turn the ship around to face open sea before tying up at the jetty.

A layout plan of a typical tanker jetty is shown below as Figure 13.16.

Equipment

The equipment required for tanker loading include pumps, hose or ﬂexible loading

pipe, and handling cranes or structures. The loading pumps are located at the tank

farm. These are centrifugal type with discharge pressures in excess of 100 psig. This

is dependant on rundown pipe lengths, but pressure drop through the loading hoses

or ﬂexible loading pipes are within 10–25 psig. Also, and as mentioned earlier there

is often a static head loss to the deck manifold of an empty tanker.

When a rubber hose is used, it is supported by a dockside derrick plus the tanker boom.

Some installations employ a combination of hose and pipe or ﬂexible assemblies

of pipe and swivel joints supported by structures. Automatic adjustment for tide

and tanker draft is incorporated in this equipment. Hose and various assemblies are

available in sizes from 2 to 12 inches diameter with the 8 and 10 inch most frequently

used for products.

Barges are usually loaded through hoses supported by dockside derricks or, in some

cases by derricks on the barges. To conserve space barges are frequently moored two

or three abreast with the loading hose being manhandled across the in board barges

to the outboard barge. This hose is accordingly limited in size to a 6 inch diameter

weighing about 8 lb/ft.

Loading rates

Tanker piping and pumping systems are designed for relatively high rates. The un-

loading pumps for the T2 tanker size can handle up to 8,000 bph. Super tankers

unloading crude have pumps that can handle quantities of 22,000 bph or more. A

SUPPORT SYSTEMS COMMON TO MOST REFINERIES 551

PGII

FUTURE WATER

EFFLUENT

TREATING

S132

METERING

MARINE

SUB STA

B 88, by tiaden

D76

S140

S139

S131

S130

S136

B2007

S141

S142

S143

CRUDE

PIPE TRACK

REFINERY ROAD

SERVICE ROAD

PIPE TRACK

FUTURE

CLARIFICATION

BASIN

SETTLING

POND

A 3708

262000

STORM WATER

HOLDING POND

AD 3711

FUTURE AERATED

LAGOON

Figure 13.16. A typical tanker jetty layout.

desirable product loading rate for each product is 8,000–10,000 bph and it is general

practice to load two products simultaneously. Loading rates for barges are usually

limited to 2,000 bph. Barges have capacities ranging from 600 to 2,000 bbl. Barges

are ﬂat bottomed shallow draft vessels used to transport products short distances in

canals, harbors, or inland waterways.

Quantities loaded aboard tankers are measured by metering storage tanks and tanker

compartments. Products loaded into barges are measured by metering. Meters are

located on the dock near the hose connections. These metering facilities include

strainers, and ﬂow controllers.

552 CHAPTER 13

Other features

Some of the other features that are considered in the establishing of jetty facilities are:

Ship ballast handling

Tanker mooring facilities

Slop and spill collection facilities

Lighting and communication facilities

Ship ballast water is handled using specially allocated on shore tanks to collect the

water which will of course be contaminated. This contamination will be the petroleum

product residue remaining in the ships tanks after product unloading. Ships arriving

at the reﬁnery jetty under ballast are usually the smaller product tankers. These are

the vessels that will load at the reﬁnery with the ﬁnished products for shipment. The

ballast water is pumped from the ships tanks to the onshore ballast water tankage by

the ships pumps. From the ballast water tanks the content is drained off to the reﬁnery’s

efﬂuent treating facilities. The hydrocarbon contaminants are removed from the water

in the treating plant and routed to the reﬁneries slop system to ﬁnally enter the reﬁnery

processes. The treated efﬂuent water is drained back to the sea.

The length of the jetty’s loading/unloading wharf where the ships are moored are sized

to accommodate two or more tankers of ﬁxed length (say two T2’s). The allocated

space for these vessels must conform to standard conditions usually established by the

particular Port Authority Regulations. One of these regulations which sets the length

of the wharf is that the space between moored vessels should be such that the stern

and aft mooring lines of adjacent vessels measured at an angle of 45

◦

to the center

line of the vessels do not overlap.

Slop and spill facilities around loading or unloading vessels at the wharf may be

contained by a temporary boom installed around the vessel during these operations.

Any spillage is contained by the boom and is subsequently disposed of by the same

route as the ballast water.

Jetty lighting is based on the main reﬁnery lighting code and practice. This means

that all access ways and roads will have general street lighting. Areas where personnel

are employed on a 24 hr basis will be ﬂood lit between the hours of sun set and sun

rise. This lighting will be supplemented by the ships lighting facilities as required

for loading/unloading activities and for ship berthing and departure. Ship to onshore

communication by means of telephone. radio, and company computer systems are

activated as soon as the ship has been berthed.

Waste disposal facilities

All process plants including oil reﬁneries produce large quantities of toxic and/or

ﬂammable material during periods of plant upset or emergencies. A properly designed