This document provides a description of the components and systems of an ammonia booster compressor, including: 1. The compressor is a positive displacement oil injected screw compressor that compresses gas via meshing rotors. 2. The gas circuit includes an oil separator, gas cooler, and secondary oil separator to reduce oil carryover before the gas exits. 3. The lubrication system uses oil pumps and filters to supply pressurized oil to the compressor and includes components like an oil cooler and pressure control valve.

1. AMMONIA PLANT
TPM STEP-4
AMMONIA BOOSTER COMPRESSOR K-1441/1442
Description of WRVT510 Compressor
The Howden oil injected screw compressor is a positive displacement capacity
controlled oil flooded rotary machine.
Compression is achieved by the meshing of two asymmetric profile steel rotors with
parallel shafts housed in a casing. Each rotor is supported by two plain white metal
bearings fitted adjacent to the compression chamber. The action of the rotor is entirely
rotary. The accurately machined rotors are called male and female. The male (driving)
rotor has four lobes which mesh with six flutes in female (driven) rotor, each rotor
having the same outside diameter.
Compressor lubricating oil is injected into the bearings and rotor space at a pressure
equivalent to discharge pressure plus 2 bars. The bearings therefore also act as shaft seals
within the compressor. The compressor input shaft is fitted with a mechanical seal hence
the compressor is completely sealed from atmosphere.
Rotor end thrust is accommodated by tilting pad thrust bearings. The male rotor which
takes the majority of end thrust is also fitted with a balance piston. One side of the
balance piston is subjected to oil pressure whilst the other is at gas suction pressure. The
balance piston thrust therefore opposes normal rotor end thrust, ensuring that the thrust
bearings are lightly loaded.
GAS System:
Gas is drawn into the compressor via a non return valve and suction strainer. The non
return valve is necessary to prevent the compressor being motored in the reverse
direction when it is stopped with high gas pressure at the discharge. On leaving the
compressor the gas oil mixture enters a combined primary separator / reservoir vessel.
The majority of the oil separates from the gas stream on entering this vessel, due to the
reduction in velocity, the separated oil falling by gravity into the reservoir base.
The gas and entrained oil droplets than pass through a knitted stainless steel wire mesh
separator element mounted in the upper portion of the vessel. Almost al the remaining oil
is collected by impingement on the very fine wire mesh, from which it falls by gravity
into the reservoir base. The gas leaving this separator contains approximately 30 to 50
ppm of oil by weight. The separator / reservoir vessel is also provided with a safety /
relief valve.
The gas then passes through a gas cooler before entering a high efficiency secondary oil
separator. This separator incorporates replaceable high efficiency filter elements which
are 100% effective in the removal pf liquid phase oil. Oil carry over d/s of this separator
is less than 5 ppm by weight.
Separated oil is returned to the compressor through a small pipe fitted with a filter,
orifice and isolating valves. Isolating valves and a thermal relief valves are provided for
the separator. A non return valve is also fitted downstream of the separator.
A gas bypass line with a control valve rated for 10 percent capacity is also provided.
Capacity control from 10% to 0% is achieved via this line. An air operated ball valve is
also included which opens automatically on shut down to equalize the pressure in the
system.
Parts in Gas Circuit:
1. Non Return Valve:
Suction and discharge non return valves are Wafer type with body and seat manufactured
in low temperature steel and disc in alloy steel

2. 2. Suction Strainer
Suction strainer casing is a pressure vessel designed for the full system pressure in low
temperature steel. The strainer element is made from one sheet of 60 mesh corrugated
stainless steel gauze sandwiched between the two sheets of 20 mesh corrugated stainless
steel gauze formed into a cylinder. The element fits inside a support drum made from 2
mm thick stainless steel perforated plate with approx. 50 % open area. The gas flow
through the element is from inside to outside.
3. Primary Separator / Reservoir
This unit has a dual function; it acts as a primary oil separator and also as an oil reservoir
for the lubricating system. The vessel is manufactured in carbon steel and upper and the
upper portion of the vessel contains a combined baffle and knitted wire pack separator
element.
4. Gas cooler
The gas cooler is a shell and tube unit and is designed to cool the full compressor gas
throughput to 38 deg C.
5. Secondary oil Separator
The secondary oil separator is a high efficiency unit designed to reduce oil carry over to
less than 5 ppm by weight. The unit contains coalescer elements which should be
changed when the differential pressure across the unit reached 0.5 Kg/Cm2. The
separated oil returns to the compressor via a connection designed for this purpose.
6. Isolating valves
Secondary separator isolating valves are reduced bore ball valves with carbon steel body
and stainless steel ball and stem.
7. Safety / relief valve
A safety / relief rated for the full compressor throughput is mounted on the primary
separator. It is a cross by style JOS valve with a carbon steel body and is set to relieve at
25 Kg/Cm2g. the secondary separator is fitted with a ¾” X 1” thermal relief valve set at
25 Kg/Cm2g.
8. Gas bypass valve
This is a fisher control type 667-GL globe valve with carbon steel body and stainless
steel trim. The valve has a type 667 pneumatic actuator and a type 3582 positioner. The
valve is rated to pass 10 % of the compressor throughput. When capacity control
between 0 to 10 % is required, the valve operates automatically, maintaining a constant
preset compressor suction pressure by bypassing excess gas from compressor discharge
to suction.
9. Gas pressure equalizing valve
This is an air operated full bore ball valve with carbon steel body and stainless steel ball
and stem. When the compressor stops, a solenoid valve in the air supply line opens and
air is allowed to the valve actuator, opening the valve fully and thereby equalizing the
pressure in the system
LUBRICATION SYSTEM
The compressor package incorporates a force feed lubrication system. Electric motor
driven oil pumps draw lubricating oil from the reservoir vessel, which is at compressor
discharge pressure and passes though a micro filter and the clean, cooled oil then enters
the oil manifold from which connections feed the oil to the compressor services.
Manifold oil pressure is maintained at a positive differential above compressor discharge
pressure by having the oil pump flow rated higher than the compressor requirement, and
bypassing the excess through a control valve, back to the reservoir. The correct oil
temperature to the compressor is maintained by having a temperature control valve
mounted at the cooler inlet and another in a cooler bypass line. These valves operate
from a common controller which senses manifold temperature.
A solenoid valve is fitted in a return line from the manifold to the oil reservoir. Solenoid
valves are also fitted in oil drain line from the compressor to the reservoir. These valves

3. prevent the compressor fill up with oil on startup and also enable oil to be circulated
before the compressor is started. Interlock ensures that the compressor can not be started
until these valves are closed.
Parts in Lubrication System:
1. Oil pumps:
The oil pumps gear type driven by electric motor. Pumps have steel casing complying
with API 614
2. Oil Cooler:
The oil cooler is a two pass water cooled shell and tube unit. It has a carbon steel shell
and stainless steel tubes and tube sheet.
3. Oil Filter:
The oil filter is a duplex unit with changeover valve which allows either one cartridge or
the other to be in use. Elements are replaceable glass fiber type with an absolute
filtration of 25 micron.
4. Differential Pressure Control Valve:
This is a fisher controls type V500 ball valve with carbon steel body and stainless steel
trim. The valve has a type 1052 actuator and a type 3610J positioner. Oil / gas
differential pressure is sensed by a differential pressure transmitter and communicated to
a controller which controls the differential with this valve.
5. Oil temperature control valves
These are fisher control type V500 ball valves with carbon steel body and stainless steel
trim. Valves have a type 1052 actuator and type 3610J positioner. Valves are controlled
by a Foxboro pneumatic temperature controller type 43 AP to maintain the manifold
temp. at 40 deg C.
6. Oil pressure relief valves:
To ensure that the oil / gas differential pressure does not exceed a safe limit, a relief
valve is fitted at the discharge of each pump. Valves are set at 6.7 kg/Cm2 differential
and are capable of passing the full pump capacity.
7. Pump Non return Valves
Non return valves are fitted at the discharge of each pump. These are wafer type with
steel body, disc and seat.
8. Oil Heater:
The heater is a 6 KW FPFR unit complete with integral thermostat set at 30 deg C.
9. Oil Level Switch:
The oil level switch is a ZR 2132 RO4 chamber type. It is set to switch off the heater if
the oil level falls close to exposing the heater element.
Capacity Control:
Capacity control is achieved by means of a sliding valve which is an integral part of the
compressor and a gas bypass valve. The slide valve is operated by a piston within a
hydraulic cylinder which is mounted on the compressor. To move the slide valve, oil
from the lubrication system is fed , via solenoid valve, to one side or other of the piston
which is connected to the slide valve. Slide valve movement alters the point on the rotor
length at which compression begins, allowing capacity to be controlled from 100% down
to10 % with approximately proportionate power saving. Capacity from 10 % to 0 % is
controlled by the gas bypass system.
The slide valves are controlled manually by ON Load / OFF Load push buttons mounted
on the local panel. If the system demand is so that the compressor is operating at 10 %
capacity, it is detected by a 10 % limit switch mounted on the compressor hydraulic
cylinder.