1. Schematics of a Typical
Natural Gas FlowlineThis 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

2. 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

3.  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

4.  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

5.  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.

6. 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.

7. FIGURE 1: BLOCK DIAGRAM OF FLOW THROUGH STATION
FIGURE 2: SCHEMATIC OF A TYPICAL GAS PLANT