Training programe

In the design of an industrial facility, engineers
develop process flow sheets, set up project specifications
and design or select equipment. The design drafters use
the information supplied by engineers and equipment
vendors and applies the knowledge and experience
gained in the office and field to design and layout the
facility.
In the design and layout of an industrial complex,
thousands of piping drawings are needed to provide
detailed information to the craftsmen who will construct
the facility. Facility design and layout must meet the customer’s
expectations as well as comply with safety codes,
government standards, client specifications, budget, and
start-up date. The piping group has the main responsibility for the
design and layout of the facility. Drafters and designers
must coordinate their efforts with the civil, structural,
electrical, and instrumentation groups throughout the
design process. The piping group must provide each
design group the necessary information needed to complete
their part of the project and have the complete set of
plan and construction drawings finished on time. During
this time, it may be necessary for designers to visit the
plant construction site to establish tie-ins or verify information
necessary to complete the design.

Plant layout design plays an important part in the design and engineering phases of nay industrial facility.

The Plant Layout Designer is skilled primarily in the development of equipment arrangements and piping layouts for process industries. Process facilities must be designed and engineered within extremely short schedules while adhering to maintenance, safety, and quality standards; moreover, the design must take constructability, economics, and operations into account. Although the tools to achieve these goals are changing from pencil and paper to computer graphics terminals, the responsibilities of the plant layout designer remains the same.

The Plant Layout Designer must develop layout documents during the conceptual and study phases of a project. The skills needed include:

· Common sense and the ability to reason.

· Knowledge of what a particular plant is designed to do

· A general understanding of how process equipment is maintained and operated

· The ability to generate a safe, comprehensive layout within a specified time and with consideration toward constructability and cost effectiveness

· Creativity

· Sufficient experience to avoid reinventing the wheel

· Knowledge of the principal roles of other design and engineering groups and the ability to use input from these other disciplines

· The ability to resolve unclear or questionable data

· Willingness to compromise in the best interest of the project

· The ability to generate clear and concise documents

· The ability to defend designs when challenged

Principal Functions

The principal functions of the plant layout designer include the conceptual and preliminary development of process unit plot plans, sometimes referred to as equipment arrangements; the routing of major above and below grade piping systems, and the layout of equipment and its associated infrastructure.

Project Input Data

Although there is a vast amount of input data throughout the life of a project, the data basically falls into three distinct categories.

1. Project design data – is supplied by the client or project engineering

2. Vendor data – pertains to equipment and specialty bulk items

3. Internally generated engineering data

Abbreviations

AG Above ground

ANSI American National Standards Institute

ASME American Society of Mechanical Engineers

BBP Bottom of BasePlate

BL Battery Limit

£ Centreline

EL Elevation

IRI Industrial Risk Insurers

N North

OD Outside Diameter

Diameter

NFPA National Fire Protection Association

NPSH Net Positive Suction Head

OSHA Operational Safety and Health Act

PFD Process Flow Diagram

P&ID Piping and Instrumentation Diagram

TL Tangent Line

TOS Top Of Steel

TYP Typical

UG UnderGround

Codes and Standards

ANSI/ASME B31-3 Chemical Plant and Petroleum Refinery Piping

ANSI/ASME B31-4 Petroleum Piping

ANSI/ASME B31-8 Gas Transmission Pipeline

NFPA 30 Tank Storage

NFPA 58 Liquified Petroleum Gas Storage and Handling

NFPA 59A Liquefied Natural Gas Storage and Handling

OSHA 1910-24 Fixed Stairs

OSHA 1910-27 Fixed Ladders

Terminology

Process Flow Diagram : This document schematically shows all major equipment items within a plant and how they are linked together by piping, ducts and conveyors. It shows equipment numbers, flow rates, and operating pressures and temperatures and is used to prepare the mechanical flow diagrams. It is also used to prepare conceptual and preliminary plot plans.

Equipment List : An itemized accounting list by class of all equipment to be used on a project, this document gives the equipment item numbers and the descriptions and is generally furnished by the client or project engineering.

Piping and Instrumentation Diagrams : These documents schematically show all process, utility, and auxiliary equipment as well as piping, valving, speciality items, instrumentation and insulation and heat tracing requirements.

Piping Specification: This document lists the type of materials to be used for pipes, valves and fittings for each commodity in the plant.

Line run: This is the physical route a pipe takes between any two points as set by the plant layout designer.

Planning Study or layout drawing: This is an orthographic piping plan. This drawing shows all equipment in a given area to scale and includes major process and utility piping systems, significant valving and instruments.

Heat tracing: Equipments, instruments and piping systems require extremely applied heat. This heat may be applied by electrical tracing leads attached to the item or line or through a small bore pipe or tubing that carries steam or other heating media.

Inline: Refers to a component that is placed either inside or between a pair of flanges as opposed to one attached to a piece of pipe or equipment.

Header Block valves: These valves isolate branch lines that are not usually provided with permanent access for plant operations personnel.

Header: This line is the primary source of a commodity used by numerous pieces of equipment or service points in a plant.

Branch: The individual piping leads between headers and users

Maintenance: Equipment and its components require routine maintenance for continued reliability and safe operation. A plant layout designer must provide unobstructed space for service equipment and personnel to access and remove components without removing unrelated equipment and piping.

Operation : Valves, instruments and many types of equipment require frequent attention for operation. These items must be accessible without impairing the safety of personnel.

Safety: The layout of any facility must enable plant personnel to exit a potentially hazardous area without injury.

Cost effective: A cost effective design is the result of a balanced consideration of initial cost, safety and the long term effects of a design in operations and maintenance.

Gravity Flow: When pockets must be avoided in a given piping system, the line is labeled ‘gravity flow’ on the piping and instrumentation diagram.

Open systems: An open system is one in which the contents of a line are discharged and not recovered.

Closed systems; A closed system is one in which the contents of a relief systems or steam trap condensates are recovered.

Flexibility: Every piping arrangement must be sufficiently flexible to allow each line to thermally expand or contract without overstressing the pipe or equipment.

Pipe Supports: The steel members attached to a pipe to hold it in place during operation. Some typical pipe supports are a) Pipe Shoes b) Spring Supports c) Trunnions and dummy legs d) Brackets.

Constructibility : Spending additional time and effort during the engineering phase of a project is often justified if it reduces initial construction staff time or decreases the potential for costly rework on piping layouts.

PLANT LAYOUT SPECIFICATION

Specification means the constraints under which a component should be designed and manufactured.

Specifications encourage uniformity and improve quality. Ignorance or failure to comply with the guidelines set could affect the quality of the design.

Components of a Specification

Modifications: Any revisions, exceptions, or addenda to the specifications should be highlighted in the project documentation.

Terms

Operator Access – the space required between components or pairs of components to permit walking, operating valves, viewing instruments, climbing ladders or stairs and safely exiting the unit in an emergency.

Maintenance Access – the space required to service equipment in place or remove the unit equipment or portions of equipment for off-site repair.

Equipment Arrangement : General plant arrangement must be consistent with prevailing atmospheric and site conditions as well as with local codes and regulations. Equipment must be grouped within common process areas to suit independent operation and shutdown. Equipment within process and off-site areas must be arranged to accommodate operational and maintenance access and to meet safety requirements.

The plot plan is one of the key documents produced during the engineering phase in any processing facility. It is used to locate equipment and supporting infrastructure and to establish the sequence of major engineering and construction activities. Plot plans are used by almost every engineering group within a project task force from estimating and scheduling through construction. Standardization of plot plans is difficult, however a few basic rules are applied.

Plot plans developed with three dimensional CAD modeling have the advantage of producing multiple plans, elevations, and isometric views with no additional effort.

Plot plans are used for

Piping Design: The plot plan is used to produce equipment arrangement studies that facilitate the interconnection of above and below ground process and utility piping systems and to estimate piping material quantities.

Civil Engineering: The plot plan is used to develop grading and drainage plans, holding ponds, diked areas, foundation and structural designs and all bulk material estimates.

Electrical Engineering: The plot plan is used to produce area classification drawings, to locate switchgear and the incoming substation and motor control center, to route cables and to estimate bulk materials.

Instrument Engineering: The plot plan is used to locate analyzer houses and cable trays, assist in the location of the main control house, and estimate bulk materials.

Systems Engineering: The plot plan is used to facilitate hydraulic design , line sizing and utility block flow requirements.

Scheduling: The plot plan is used to schedule the orderly completion of engineering activities.

Construction: The plot plan is used to schedule the erection sequence of all the plant equipment, which includes rigging studies for large lifts, constructability reviews, marshaling, and lay-down areas throughout the entire construction phase.

Estimating: The plot plan is used to estimate the overall cost of the plant.

Client use: The plot plan is used for safety, operator, and maintenance reviews and to develop an as-built record of the plant arrangement.

To develop a plot plan, a designer must assemble the following information

1. Equipment list

2. Process flow diagram

3. Block flow diagram

4. Specifications

5. Process design data

6. Equipment sizes

7. Materials of construction

Types of Plot Plans

The grade mounted horizontal inline arrangement: Usually located within a rectangular area, with equipment placed on either side of a central pipe rack serviced by auxiliary roads.

The structure mounted vertical arrangement: has equipment located in a rectangular multilevel steel or concrete structure.

Various requirements dictate the location of equipment and supporting facilities within the conventional operating plant, and many factors must be considered when designer is locating the equipment. They are:

Plant Layout Specification highlights the spacing requirements for equipment and access widths and elevation clearances for operator and maintenance access.

Economic Piping: The major portion of the piping within most process units is used to interconnect equipment and support controls between equipment. To minimize the cost, the equipments must be located in the process sequence and close enough to suit safety needs, access requirements, and piping flexibility.

Process Requirements: Equipments must be located in a specific position to support the plant’s process operation.

Common operation: Equipment that requires continuous operator attention or shares common utility and maintenance facilities should be located in the same area.

Real estate availability:

Equipment sizes: Equipment sizes vary in a process plant and hence care must be taken to ensure that large cumbersome pieces of equipment first and then plan the remainder of the unit around them.

Underground facilities: Depending on soil conditions, the foundations are either piled or spread footings. Instruments, electrical cabling can be located above or below grade along with underground piping, cooling system which the designer need to investigate.

Climatic conditions: Weather conditions influence the location of certain equipments, which may require them to be housed.

Pipe Racks: Most inline plant arrangements are furnished with a central pipe rack system that acts as the main artery of the unit supporting process interconnection feeds, product and utility piping, instrument and electrical cables and sometimes air coolers and drums.

Roads, Access Ways and Paving: For maintenance and safety, the principal access to and from most process units is by auxiliary roads. Clearance according to project specifications should be provided. Most clients require that the equipment areas, the areas beneath the pipe rack and the areas around buildings be paved with concrete for housekeeping.

Buildings: Apart from buildings that house equipment, it is often necessary to position control houses, substations, analyzer houses, and operator shelters within the process unit battery limits.

Equipment spacing for operator and maintenance access, safety, piping flexibility and support and platforming requirements.

Compressor machines are used to increase the pressure of a gas by mechanically reducing its volume within its case. Air is most frequently compressed, but natural gas, oxygen and nitrogen are also compressed. Positive displacement, centrifugal and axial compressors are the three common types used in process facilities and pipeline stations.

Centrifugal and reciprocating compressors and their drives require a variety of auxiliary equipment to support operation.

Lube Oil consoles provide lubricating oil to the compressor bearings. These may be stand alone or be mounted directly on the compressor frame.

Seal oil consoles provide oil to the hydraulic seals located at the outer end of the compressor shaft.

Surface condensers reduce gas or vapor to a liquid by removing the heat.

Condensate pump removes the condensate from the hot well in the surface condenser.

Air blowers deliver fresh air to cool the internally housed electric motors.

Inlet air filters provide clean filtered air for operation of gas turbines.

Waste Heat system take hot exhaust gas from gas turbines and put high outlet temperatures like 400 to 650 deg C to use in various ways.

Compressor suction drum/knockout pot are provided since compressors require dry gas that is free of foreign particles.

Pulsation dampener/volume bottles minimizes the negative effects of vibration on the life of reciprocating compressors and associated piping.

Types of compressor drives are

A) Electric motor

B) Steam Turbine

C) Gas Turbine

General Compressor layout

Inlet Piping: The ASME power test code requires a minimum of three diameters of straight run piping between the elbow and the inlet nozzle. The preferred design is one in which the horizontal run is parallel to the compressor shaft.

Suction Line Strainers: Compressor suction lines must be free of any foreign particles that could damage the internals of the machine. Strainers are installed in the inlet line between the block valve and the compressor inlet nozzle.

Breakout flanges: All lines to a compressor that must be removed for maintenance of the compressor or strainer removal must have a set of flanges in the line in addition to the set at the compressor nozzle.

Miscellaneous Piping Connections should be piped up by one or the other.

Primary Operating Valve Accessibility for the operator from grade or the operating platform around the machine. Valves that are physically out of reach may be made accessible through extension stems or chain operators.

High pressure steam inlet piping on the basis of the compressor outline drawing to locate the neutral axis. Locating the line anchor close to the steel frame enable the designer to generate a layout with a minimum amount of leg, thereby satisfying the stress and flexibility requirements.

Straightening Vanes are provided to smoothen the flow and improve the compressor performance. These vanes must be in ASME or American Gas Association standards.

Reciprocating Compressor Piping should be simple and run as low to grade as possible to facilitate support. Once the piping is completed, it is simulated by electric circuits which identifies potential acoustic or pulsation problems.

Line branches should be located as close to line support as possible. All such connections should be located on top of the piping to minimize any potential liquid carry over.

Drain Piping should be provided on suction and discharge piping to avoid liquid carry over into the cylinders.

Drums are cylindrical hollow steel vessels used in process plants as intermediate containers that receive liquid from distillation and condensing equipment. Drums also collect liquid from vapor circuits and pump it to the other process groups, disposal or product storage. They are also used for chemical and catalyst storage, steam generation and deaeration of boiler feed water.

Types of Drums

Drums are categorized into

a) Horizontally mounted

b) Vertically mounted

Drums are located within a process unit either adjacent to related equipment or as a standalone operation.

Drums are dictated by net positive suction head (NPSH), minimum clearance, common platforming and maintenance and operator access.

The first step in drum layout is setting the height of the drum. To do this the plant layout designer requires the following information

a) Drum dimensions

b) Type of heads

c) Support details

d) NPSH requirements of pump

e) Bottom outlet size

f) Minimum clearances

g) Location

To position nozzle locations the following information are required.

a) Process vessel sketch

b) Instrument vessel sketch

c) Piping and instrument diagrams

d) Plant layout specifications

e) Nozzle summary

f) Insulation requirements

g) Plot plan

Platform Arrangements

Platforms are required at drums for access to valves, instruments, blinds and maintenance access. For tall vertical drums, platforms are usually circular and supported by brackets attached to the shell of the drum.

Piping Arrangements

Piping at drums should be in conjunction with nozzle locations, platform arrangements and drums location to related equipment. Piping should be positioned to facilitate the installation of supports, with sufficient flexibility to absorb any excessive stresses during operation.

Drum Instrumentation

Level, pressure and temperature instruments are used to control the operation of the drum and should be placed in a position for optimum operation and maintenance. Instrument requirements are usually highlighted on an instrument vessel sketch furnished by the instrument engineer.

Maintenance

Maintenance of drums is limited to removal of such exterior components as large relief or control valves for off site repair. Handling of such items can be achieved by means of fixed davits or by mobile equipment.

EXCHANGERS

Heat exchangers are similar to pumps and vessels. The control of heat within any facility is an important part of plant operation. The heat exchanger is used to maintain a heat balance through the addition or removal of heat by exchange with outside sources or between streams of two different operating temperatures.

Coolers cool process streams by transferring heat to cooling water, atmosphere and other media.

Exchanger exchanges heat from a hot to a cold process stream.

Reboiler boils process liquid in tower bottoms usually steam, hot oil, or a hot process steam as the heating medium.

Heater heats a process stream by condensing steam.

Condenser condenses vapor by transferring heat to cooling water, atmospheric air or other media.

Chiller cools a process stream to very low temperatures by evaporating a refrigerant.

Common heat exchangers used in processing facilities are;-

a) Shell and tube exchangers

b) Plate Exchangers

c) Spiral Heat Exchangers

d) Double pipe exchangers

e) Air cooler exchangers

FURNACES

Furnaces, also refered to as heaters, are one of the main pieces of equipment in a process complex. A furnace may raise the temperature of a gas or hydrocarbon liquid to meet specific processing needs or, in the case of pyrolysis and reformer furnaces, cause a chemical or physical change to the medium.

Primary Parts of a Furnace

The radiant section houses rows od horizontal or vertical tubes that carry the product to be heated.

Burners are primarily fired by oil or gas and located in the radiant section.

The convection section located above or downstream from the radiant section houses rows of horizontal tubes that are heated by the hot flue gases.

The stack is usually located above the convection section and carries the flue gases to the atmosphere.

Insulation lines the walled surfaces of the radiant and convection surfaces.

Fuel is fed to the burners located along the furnace floor. It is then ignited by a pilot gas line located in the burner. The combustion air flow is regulated by adjustment of the air registers. For proper operation within a furnace a natural draft must be maintained. As the temperature rises, the hot flue gas rises out of the stack and begins to exert a negative pressure within the radiant and convection sections.

Types of furnaces

A) Box type houses rows of horizontal or vertical tubes in the radiant section

B) Circular type houses tubes mounted vertically or helically in the radiant section.

C) Pyrolysis furnace product tubes are placed in the center of the radiant section because of a relatively short residence time, high heat transfer rate and need for even temperature distribution in the tubes.

D) Reformer furnace, the preheated process fluid flows through catalyst filled tubes, which are usually located in the center of the radiant section.

Pumps can be classified in the two basic types:

- Centrifugal pumps

- Positive displacement pumps

The centrifugal pump produce a head differential and a flow by increasing the velocity of the liquid through the machine with a rotating vane impeller.

The positive displacement pump operates by alternating of filling a cavity and then displacing a given volume of liquid. The positive displacement pump delivers a constant volume of liquid against a varying discharge head.

When to use a Centrifugal Pump (CP) or a Positive Displacement Pump (PDP) is not always a clear choice. The two types of pumps behave very differently. The CP has varying flow depending on pressure or head, where the PDP has more or less a constant flow regardless of pressure.

Another major difference between the pump types is the effect of viscosity on the capacity of the pump.

· The CP losses flow when the viscosity goes up

· The PDP pump actually increases flow.

Higher viscosity liquids fill in the clearances of a PDP causing a higher volumetric efficiency.

The pumps behaves different considering mechanical efficiency as well. Changing the pressure have little or no effect on the volume flow in the PDP, but has a dramatic one in the CP.

Another consideration is Net Positive Suction Head NPSH. In a CP the NPSH varies as a function of flow, determined by pressure. In a PDP NPSH varies as a function of flow determined by speed. The lower the speed of a PDP pump, the lower the NPSH.

A PDP is better suited for high viscosity applications. A CP becomes very inefficient at even modest viscosity.

PDP pumps generally gives more pressure than CP's.

Net Positive Suction Head - NPSH

A definition and an introduction to Net Positive Suction Head - NPSH.

Low pressure at the suction side of a pump can encounter the fluid to start boiling with

• reduced efficiency
• cavitation
• damage

of the pump as a result. Boiling starts when the pressure in the liquid is reduced to the vapor pressure of the fluid at the actual temperature.

To characterize the potential for boiling and cavitation, the difference between the total head on the suction side of the pump - close to the impeller, and the liquid vapor pressure at the actual temperature may be used.

Suction Head

Based on the Energy Equation - the suction head in the fluid close to the impeller can be expressed as the sum of the static and the velocity head:

h_s = p_s / + v_s² / 2 g (1)

where

h_s = suction head close to the impeller

p_s = static pressure in the fluid close to the impeller

= specific weight of the fluid

v_s = velocity of fluid

g = acceleration of gravity

Liquids Vapor Head

The liquids vapor head at the actual temperature can be expressed as:

h_v = p_v / (2)

where

h_v = vapor head

p_v = vapor pressure

Note! The vapor pressure in a fluid depends on temperature. Water, our most common fluid, starts boiling at 20 ^oC if the absolute pressure in the fluid is 2,3 kN/m². For a temperature of 80 ^oC the boiling starts at absolute pressure 47,5 N/m², and of course at 101.3 kN/m² (normal atmosphere) boiling starts at 100 ^oC.

Net Positive Suction Head - NPSH

The Net Positive Suction Head - NPSH - can be expressed as the difference between the Suction Head and the Liquids Vapor Head:

NPSH = h_s - h_v (3)

or

NPSH = p_s / + v_s² / 2 g - p_v / (3b)

Required NPSH - NPSH_r

The required NPSH - NPSH_r - is the NPSH that must be exceeded to avoid vaporization and cavitation in the impellers eye. The NPSH_r is always higher than the theoretical NPSH due to head loss in the suction pipe and the pump casing, and local velocity acceleration and pressure decrease on the impeller surface.

NPSH_r is in general determined experimentally by the pump manufacturer and a part of the pump performance curves documentation.

The required NPSH_r increases with the square of increased capacity.

Available NPSH - NPSH_a

The available NPSH - HPSH_a - is the NPSH available for a particular system and must be determined during design and construction of the system, or determined experimentally on the actual physical system.

The available NPSH_a can be calculated with the Energy Equation. For a common application - where the pump lifts a fluid from an open tank at one level to an other, the energy or head at the surface of the tank is the same as the energy or head before the pump impeller and can be expressed as:

h₀ = h_s + h_l (4)

where

h₀ = head at surface

h_s = head before the impeller

h_l = head loss from the surface to impeller - major and minor loss in the suction pipe

In an open tank the head at surface can be expressed as:

h₀ = p₀ / = p_atm / (4b)

For a closed pressurized tank the absolute static pressure inside the tank must be used.

The head before the impeller can be expressed as:

h_s = p_s / + v_s² / 2 g + h_e (4c)

where

h_e = elevation from surface to pump - positive if pump is above the tank, negative if the pump is below the tank

Transforming (4) with (4b) and (4c):

p_atm / = p_s / + v_s² / 2 g + h_e + h_l (4d)

The head available before the impeller can be expressed as:

p_s / + v_s² / 2 g = p_atm / - h_e - h_l (4e)

or as the available NPSH_a:

NPSH_a = p_atm / - h_e - h_l - p_v / (4f)

Available NPSH_a - the Pump is above the Tank

If the pump is positioned above the tank, the elevation - h_e - is positive and the NPSH_a decreases when the elevation of the pump increases.

At some level the NPSH_a will be reduced to zero and the fluid starts to evaporate.

Available NPSH_a - the Pump is below the Tank

If the pump is positioned below the tank, the elevation - h_e - is negative and the NPSH_a increases when the elevation of the pump decreases (lowering the pump).

It's always possible to increase the NPSH_a by lowering the pump (as long as the major and minor head loss due to a longer pipe don't increase it more). This is important and it is common to lower the pump when pumping fluids close to evaporation temperature.