POUR POINT OF LIQUIDS
Pour Point: The pour point of a liquid is the lowest temperature at which it will flow under prescribed conditions. It is a rough indication, but an important one in pipeline design and operation.
Vapor Pressure: Vapor pressure is an important physical property of hydrocarbon liquids subjected to vaporization.
Flash point: fuel’s flash point is the lowest temperature a which the hydrocarbon liquid’s vapor can ignite momentarily (flash) when exposed to a flame.
What are the main reasons to know those properties?
In pour points, once temperatures of hydrocarbon liquids fall below their respective pour points, these liquids start to show non-Newtonian behavior and therefore conventional pipeline design and operation will have to be modified to be effective. Whereas, in Vapor pressure, at normal pipeline operating pressure and temperature, crude oils remain liquid, but LPG and NGL can vaporize because their vapor pressures are high.
Q1) A) What are the main facilities and systems required for liquid pipelines?
Ans àThe main facilities that are involved in liquid pipelines are Mainline pumping facilities (including prime movers, station controls and others), Pipeline inspection devices (scraper traps, pigging stations), Delivery/custody transfer meter stations, and Product quality control and sampling, and Storage facilities (tankage/caverns). And for the main systems are Protection or corrosion control systems, Supervisory Control and Data Acquisition (SCADA) systems, Leak detection systems, and Communication systems.
Discuss the types of pipeline exist in oil industry.
There are two types of liquid transmission pipelines: single product which is transporting a petroleum product in a single stream such as crude oil. And multi-products pipelines which is transporting generally multiples of hydrocarbon liquids in a batch form.
What is difference between single vs. multiple product pipeline?
In single products pipeline, transporting a petroleum product in a single stream includes low vapor pressure fluids for example crude oil, bitumen, water, and many others along with refined products, and high vapor pressure fluids such as condensate, propane, and more. In contrast, multiple products pipelines consist of number of products (low and high vapor pressure) in a batch form.
Q1) b)
What is pressure surge and control point?
Pressure surge: large transients are often called a pressure surge, which is a change in pressure in the pipeline that occurs abruptly during a change from either a normal steady state or another transient state flow in the pipe.
Control point: The control point is a point in a pipeline section where the pipeline pressure drops below the vapor pressure or exceeds the maximum allowable operating pressure.
What are considerations to do surge control?
The main purpose of transient control or surge control is to protect the pipeline system by reducing the magnitude of surges to the allowable strength limits of pipe, valves, and pumping and other equipment. Approximately, there are two ways of managing surges: Direct control of the surges and Extra protection of the pipeline and equipment
Q2) a) Describe the pressure operating limits to be properly taken into account in design and operational analysis?
The control of pipeline pressure is crucial to ensure safe, reliable, and economical operations.
The pressure limits include:
- Maximum allowable operating pressure (MAOP) for safety
- Maximum discharge pressure at pump stations to protect station piping and equipment
- Minimum suction pressure at pump stations to avoid cavitation
- Minimum or maximum pressure at a control point
- Minimum and maximum delivery pressures to satisfy the contractual obligations and protect equipment
- Minimum and maximum flows through pumps for efficient
- Maximum power of pumps to operate below the pumping power limit
- Minimum discharge temperature for heavy crude
- Maximum discharge temperature for pipelines in permafrost
Q2) b) Discuss the main causes of transients in pipelines?
The main causes of transients in a pipeline are:
- Change in valve settings including open or close status change
- Starting or stopping of pumps
- Changes in pump speed or head
- Pipeline rupture or large leak
- Collapse of column separation or trapped air
- Arrival of a batch interface at the pump
What could be main reasons for pipeline failures?
Many pipeline failures, particularly for liquid pipelines, occur because improper provisions are made to manage transient related problems such as pump trip, and many other.
Q2) c) What are the main properties of liquid pipeline that should be known for pipeline operations?
pipeline operations involve transporting products from the lifting points to the delivery points; lifting products into the pipeline and delivering the received products to the designated delivery points. The receiving and delivery points may be tank farms, refineries or another pipeline.
Q3) a) Discuss the typical studies required for oil terminal design and what are the regulations that affect the terminal design?
The Regulations governing Aboveground Storage Tanks (AST) are to address sources of pollution that may result from ASTs operation. In case of potential leakage new ASTs are required to meet acceptable design and installation criteria Regulations also require that all ASTs be equipped with normal and emergency venting system. Such as Burchfield Oil Depot in the UK in 2005
Why Bund wall is required for storage tanks?
bunds are generally designed to contain any spills from the tank or tank piping. This is the reason why they are required for storage tanks.
Q3) b) What is the typical data required for tank design?
Data required to undertake a tank design should include the following:
・ Design Code
・ Tank Location
・ Nominal capacity of tank and tank diameter and/or height restrictions;
・ Internal tank pressure
・ Rate of filling and emptying tank
・ Design and Operating pressure
・ Design and Operating Temperature
・ Density of Liquid and Design Density
・ Prevailing wind direction and maximum Wind Speed and Pressure
・ Corrosion Allowance (shell/bottom and roof)
Q4) a)
The purpose of a measurement system is to determine a numerical value that corresponds to the variable being measured. Measurements are required for producers, customers/shippers and transportation companies for custody transfer or change in ownership or responsibility as well as pipeline system monitoring and control. Also, measurements may be required if petroleum products move across national boundaries.
Q4) b) Discuss the following tank calibration methods
The tank calibration method:
- Manual Tank Strapping Method (MTSM): Tanks must only be calibrated after they have been filled at least once with a liquid of density equal to or greater than that of the liquid which they will hold when in use. The hydrostatic test applied to new tanks will satisfy this requirement in most cases
- Optical Reference Line Method (ORLM): The Optical Reference Line Method is an alternative method for determining tank diameter using an optical device. This method still requires manual strapping of a reference circumferential measurement. This reference strapping of the first ring, 20% below the top horizontal weld seam, forms the datum. Deviations in diameter are then measured using the optical equipment.
iii. Electro-Optical Distance Ranging Method (EODRM): This method of calibration of tank shell dimensions uses internal measurement procedures. The instrument consists of an electro-optical distance-ranging device capable of precision angular measurement and a laser beam emitter that may be part of the instrument. Distances and slope angles are measured at a predetermined number of target points around the internal circumference of the tank.
Q.5: (a) Discuss the following regasification options for LNG plant?
- Intermediate Fluid Vaporizers (IFV): The IFV is characterized by its unique concept of three heat exchangers and the use of intermediate fluid. Thanks to the use of intermediate fluid, the IFV is not subject to freezing and has a wider temperature range of the heating medium.
LNG is first introduced into the heat-transfer tube of the E2. Next, the LNG exchanges heat with intermediate fluid gas above the E1 shell and is almost entirely vaporized and then transferred to the shell side of the E3 via an interconnecting line. Here, the LNG exchanges heat with seawater that flows inside of heat-transfer tube and is warmed up to be delivered as gas at a normal temperature.
- Open Rack Vaporizers (ORV): The open rack type LNG vaporizer (ORV) uses seawater as its heat source and is a typical higher flow LNG vaporizer. The seawater enters the top of the vaporizer and is runs over the aluminum tubes. The LNG flows up and is converts from a liquid into a gas. The benefit of using heat from the seawater is that this energy is for free and there is no further CO2 emission for degasifying the LNG. The water is gathered in the basin at the bottom of the vaporizer tubes before being returned to the sea.
iii. Submerged combustion vaporizers (SCV): An SCV has a structure in which an underwater burner, burning fuel-gas, generates heat to vaporize LNG. It comprises a tank, an underwater burner, a bun dle of heat-transfer tubes, combustion-air fan and fuel-supply control device. Both the bundle of heat-transfer tubes, which are a heat exchanging portion, and the underwater burner, a heat source, are submerged in the sea.
6) a)
A SCADA system is designed to assist pipeline operators in the operation of the pipeline system using real-time and historical information.
DCS systems were developed to automate process control systems. A DCS is to process a high number of transactions at a high speed in order to implement multiple real-time closed loop control.
6) b)
Centrifugal pumps add kinetic energy to the liquid by increasing the liquid flow velocity, while positive displacement pumps add energy periodically to the liquid by the direct application of a force to movable volumes of liquid. And Centrifugal pumps is used more because they have prevalent application in liquid hydrocarbon pipeline transmission systems as they are capable of handling variable heads and flow rates.