Pipeline System Operation

Seite 1

Pipeline System Operation

How Centrifugal Pumps Work

Working Principals of Centrifugal Pumps

How to select a Pump and Motor

Pump Cavitation

Pipeline Operations:

Business

Physical

Physical: covers the product movements and pipe cleaning or pigging and integrity management

Products are gathered in central points and then dispatched to various destinations.

--> this is done through scheduling which involves product pumping schedule that is based on:

pipeline capacity

shippers requirements

Controlling of pipeline pressure is important it sets certain operating limits:

MAOP

Maximum discharge pressure to protect piping & equipment

Minimum suction pressure to avoid cavitation

Max/Min pressure at a control point

Max/Min delivery pressure for contractual obligations

Min/Max flows through pumps for efficient pump operation

Maximum power of pumps

Minimum discharge temperature for pipelines in permafrost

Booster Pumps are installed between the tanks and the pump station because tanks don't provide sufficient suction head

Tight Line Operations --> when there are multiple intermediate pump stations and open station pumps directly into the suction side of the pumps at the next station.

the advantages over the previous operation:

tanks are not necessary at the mainline stations

extra operation of pumping into and out of tankage is not required

interfacial mixing is minimized for batch operation

Pressure monitoring and controlling points:

suction set point: suction pressure limits, a lower limit under which the pump will not operate and shut down. An Upper limit needs to be reduced to avoid over pressuring the discharge pressure at the upstream station.

discharge set point: this pressure is to be maintained as a maximum pressure. if pressure is equal to or higher than the discharge set point the pressure regulator is activated to reduce the actual pressure level.

tight line operation--> liquid density and viscosity changes can occur in batching or blending operation

if stations have centrifugal pumps are operating at maximum pressure the flow will decrease and the density and viscosity increase

Sphere:

form of pig that is put in place to separate the two adjacent products.

it can be inserted at the injection point or the running pump stations and received at the delivery point or at running pump stations further along the pipeline

without the pig, interfacial mixing or transmit takes place

this depends on the pipe length and reynolds number

There are rules that outline the handling of transmix:

interface mixture maybe cut into one or the other product, or divided between two adjacent products

Slop--> when the transmix doesn't meet the shippers specifications

if the size of transmix is larger than the specified amount and cannot be blended into other products the company must pay

Batching tracking

monitors the volume of each batch, its origin and its destination, current location and ETA

its tracking begins when the batch is launched and tracked using difference in density or value status or on batch schedule

volumes are updated based on injection and delivery volumes obtained at metering locations

Batch interfaces can be detected by a densitometer or by dye detector.

Pipeline System Design Pipeline system design is concerned with--> line sizing, route selection, equipment sizing and facility location

system operation is concerned with--> steady-state operations at different flow rates, pipeline system/facility start up and shut down. product receipt & delivery flow rate change

Transient state-->

flows in transit from one steady state to the other.

transient solutions provide hydraulically realistic results.

it occurs when the flow is disturbed or changed in the pipeline system

large transients can occur suddenly and in a short time when fluid flow is interrupted

Pressure Surge

change in pressure of the pipeline that occurs abruptly during a change from normal steady state or another transient state flow in the pipe

surges travel at acoustic speed

if pressure is higher than normal operating pressure upsurge

if pressure is lower than normal operation pressure downsurge

Behaviors of surge Wave

if a vale is suddenly closed a sequence of changes in pressure takes place in the pipeline:

Valve:

velocity stops instantaneously and the pressure or head the value increases by the amount of the surge

this results in a slightly enlarged pipe and a density increase in the fluid.

the pressure increase causes a sharp fronted pressure wave to propagate upstream at acoustic speed.

At time L/a seconds:

the wave front reaches the end of the pipe. the velocity becomes zero throughout the pipe, the pressure is the same and the pipe is enlarged and the fluid is compressed

At time 2l/a seconds:

the pressure throughout the pipe has returned to its original value.

the critical period occurs when: the velocity experiences a reversal in direction mirroring the reflection of the pressure wave.

this causes the pressure to decrease from the initial conditions of steady state flow. causing the pipe to shrink and the liquid to expand

At time 3l/a seconds:

the negative wave reaches the reservoir, velocity is zero

At time 4l/a seconds:

the wave returns to the valve and original conditions are restored.

Transients are two types:

Pressure transient : when change in energy occurs

flow transients: change in flow rate caused by change in energy

The main causes of Transient flow:

change in valve settings including opening or closing status change

starting and stopping of pumps

changes in pump speed or head

pipeline rupture or leak

collapse of column separation or trapped air

arrival of batch at interface of pump

Line Packing and Line unpacking

the fluid volume increases or decreases dependent on the line pressure.

packing = high volume

unpacking = low volume

EQUATION of potential surge ( magnitude of surge wave) LECTURE 4A, SLIDE 12

The magnitude of the pressure increases when the pressure surge is traveling upstream, this is due to the fact that the pressure increase at the stoppage point is the sum of the potential surge pressure and the pressure rise due to line packing.

To avoid pipe failure due to transient flow one should take into account

changes to pump operations

power failures

valve operation