Schematics of a Typical Natural Gas Flowline This document contains a brief synopsis on the equipment I was introduced to during

my industrial training experience at the natural gas plant station of Nigerian Gas

Company Limited situated at Papalanto, Ogun State powering the Olorunsogo II Power

Plant and a brief description of the plant in general using schematic diagrams and

pictures.

Contents 1.0 INTRODUCTION:....................................................................................................................... 2

1.1 Plant’s Equipment: .................................................................................................................... 2

Vertical Scrubbers ............................................................................................................... 2

Monitor and Active Control Valves .................................................................................... 2

Slam – Shut Valves, ............................................................................................................. 3

Non–Return Valves, ........................................................................................................... 3

Pressure Reducing Skids ...................................................................................................... 3

A Boiler .............................................................................................................................. 4

A Gas Chromatograph ........................................................................................................ 5

Heat exchangers ................................................................................................................. 5

A Pig Launching and Receiving Trap. .................................................................................. 5

Relief valves. ...................................................................................................................... 5

1.2 Station Description: .................................................................................................................. 6

1.0 INTRODUCTION: Natural gas from underground reservoirs flows out of the gas wells under pressure to the gathering

stations. At the gathering stations the gas pressure is reduced and the heavier gases are removed

leaving mainly natural gas. The gas is then piped from the gathering stations to reduction and

metering stations (R&M stations) hundreds of kilometers away. The R&M station connects the gas

users to the pipeline. The primary function of the R&M station is to treat the gas, reduce the pressure

to the customers’ needs and accurately measure the flow in order to provide reliable data for billing

gas customers.

1.1 Plant’s Equipment: Some of the equipments worked with in my station include:

Vertical Scrubbers

Monitor and Active Control Valves

Vertical scrubbers have

filters installed in them. The

unit operations taking place

include filtration and

cyclonic separation of

entrained solids and liquids.

Active and monitor

regulating valves were

used to keep the gas

pressure within the set

point

Slam – Shut Valves,

Non–Return Valves,

Pressure Reducing Skids

Relief

valves

Boiler

Active and monitor

regulating valves

PRS

expansion

The reduction in

gas pressure takes

place here at the

PRS

The non – return valve

helps safeguard the

station by allowing gas

passage in one direction

only

The slam – shut is a

final control element

which operates as a

Fail – Close final

protector in the gas

plant

Actuator

A Boiler Certain industries requiring gas supply at medium pressures.

The boiler heats up raw water in the flow line, converts it to low pressure steam and

sends it via the return line to the heat exchanger.

It contains some isolation valves, non – return valves, gas solenoid valves, electro –

hydraulic safety shut – off valves, heat pump suctions, heat pump discharge isolation

valves, heating pumps, a dosing pot, boiler packages and chimneys, pressurization units,

display units, expansion vessel heating system isolation valve, mains cold water

incoming stopcock, pressurization unit mains cold service valve, just to sum it up.

Boiler chimney for

effluent gas spewing Dosing pot for chemical

charging and analysis

BOILER’S SIX CHIMNEYS (outside

view)

Pressurization unit Water flow – in and

Return lines

Display unit showing the PU and twin

heating pumps

A Gas Chromatograph

Heat exchangers The high pressure steam leaving the boiler is fed to the heat exchangers which are

recuperative shell and tube heat exchangers heating the gas by indirect contact of the

steam with the gas. This heat translates into increasing the pressure of the gas.

Not all plants make use of their heat exchanges. The customer’s need determines this.

A Pig Launching and Receiving Trap.

Relief valves. These are used in venting excess gas from the line especially in the occurrence of back

pressure gas from the customer.

Pipeline pigging is a common practice in oil and

gas companies, it is carried out during pipeline

pre-commissioning as well as during operation in

order to ensure pipeline fitness-for –purpose, and

maintain integrity.

1.2 Station Description: The Reduction and Metering station is physically located at Olorunsogo, Papalanto, in Ogun state.

The primary customer is the Power Holding Company of Nigeria, Olorunsogo.

For the following description, refer to the figures below.

Natural gas enters the station at the A Pig Launching and Receiving Trap. It is associated

in the sense that it contains condensates (a great enemy to the station, that contains

higher carbon alkanes such as propane, butane and even entrained water) and travels

through the Vertical Scrubbers where the gas is conditioned by filtering the gas to strip

the condensates and solids such as shale entrained in it. The gas, after leaving the

Filter/Scrubbers passes through the heat exchangers where it is heated prior to the

pressure reduction section (the gas cools approximately one °F per bar when the

pressure is reduced assuming adiabatic expansion; heating is provided to offset this

temperature drop). After heating, the gas is passed through the Pressure Reducing Skids

where the pipeline pressure is reduced to a pre-defined pressure for customer usage.

Thereafter, the gas flows through the metering section where the physical parameters

(static pressure, differential pressure and temperature) of the gas are measured and

recorded by the Barton mechanical chart recorders (one for each metering train). The

physical parameters are also measured and stored by the redundant flow computer

systems. A Gas Chromatograph is used to determine the gas composition, specific

gravity and calorific value. The flow computer systems include smart instruments to

collect the physical parameters. The flow computers then use the physical parameters

and information from the gas chromatography to calculate the volumetric flow and

calorific value of the gas. The gas is then piped to the end user.

FIGURE 1: BLOCK DIAGRAM OF FLOW THROUGH STATION

FIGURE 2: SCHEMATIC OF A TYPICAL GAS PLANT