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MAN TURBO

TURBOMACHINERY FOR

AMMONIA PLANTS

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The ammonia synthesis process has allowed the chemical industry since

the beginning of this century to supply agricultural producers with sufficient

quantities of nitrogen-containing fertilizers.

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TURBOMACHINERY FOR AMMONIA PLANTS

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Ammonia, NH3, has thus become the most important starting

material for the fertilizer industry.

Whilst NH3 today is principally used as an intermediate in a

number of chemical processes, e.g., in the production of nitric

acid, it is also employed as a refrigerant in cooling cycles, oras a nitrogen source when nitriding high alloy steels.

Two elements are needed for the synthetic production of

ammonia:

hydrogen

nitrogen.

Sources of hydrogen are natural gas, naphtha, refinery gases,

and even coal, whereas nitrogen is available in sufficient quanti-

ties in the atmosphere. Ammonia is produced by combining

nitrogen and hydrogen at high pressures and temperatures.

At the heart of an ammonia plant is the turbomachinery, i.e.,

compressors to raise the pressure of the process media

process air, synthesis gas and ammonia together with thecompressor drivers, which are normally steam turbines.

A natural-gas compressor is also necessary when the pressure

of the natural gas supply is below the pressure level required

for the process.

The large variety of turbomachinery required in ammonia plants

is reason enough for plant designers and operators to co-oper-

ate with a partner capable of supplying all the turbomachines

compressors as well as turbines to allow optimisation of the

machinery with the process requirements (and vice versa).

Supply from one source means, apart from clearly defined

responsibilities, that coordination is much simpler and develop-

ment of the contract runs more smoothly.

There are good reasons to choose MAN TURBO as the partner

for the supply of this equipment:

Experience

MAN TURBO stands for compressor and turbine supplies

since 1904 with the first turbomachines for ammonia plantsbuilt by MAN TURBO in the early fifties.

With the supply of many thousands of MAN TURBO process

compressor and turbine casings, including 130 turbomachinery

trains installed in 60 ammonia plants worldwide (plant capaci-

ties range from 400 to 2000 t/day), the companys experience

and reliability is fully proven in the field.

Versatility

As a supplier of axial and centrifugal compressors as well

as steam turbines, gas turbines and tail-gas expanders,

MAN TURBO has the most comprehensive turbomachinery

programme in the world.

Besides turbomachines for ammonia plants, MAN TURBO

supplies compressors and turbines for a large number of

processes, including the production of nitric acid and urea.

Quality and Economy

The high quality of MAN TURBO turbomachines is based on:

intensive research and development activities,

modern CAD, calculation and manufacturing techniques,

high-speed balancing and overspeed testing equipment,

as well as

high-capacity mechanical and thermodynamic testing facilities.

The availability of a wide range of impeller designs (open/closed

design, cylindrical/twisted blades, etc.) and the possibility of

varying blade inlet and outlet angles, impeller diameters or

widths, allow optimum rating for the particular duty points

specified.

In this way the highest possible efficiencies from MAN TURBO

products are guaranteed.

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When using natural gas, the

most important source of

hydrogen, as a feedstock,

the steam-reforming process

is applied.

In the primary reformer, H2 is

cracked from natural gas with

the aid of steam.

This hydrogen is then com-

bined with nitrogen which

has itself been produced in

the secondary reformer from

compressed process air,

to form the synthesis gas

required for ammonia

production.

In the synthesis-gas circuit,

ammonia is condensed withthe aid of an NH3 refrigeration

cycle and led to a storage

tank (via a separation system)

prior to further processing or

distribution.

THE PROCESS

Steam-Reform Process

ST

ST C C

C

Natural gas

Reformer gas

Steam

Primary

Reformer

Gas treatment:

- CO conversion

- CO2 scrubbing

- Methanation

Natural gas compressor

Syngas compressor

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C ST

STC

NH3

Process air

Syngas

Refrigeration cycle

Ammonia

synthesis

Secondary

Reformer

Process air compressor

Ammonia compresso r

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Single-shaft compressor

The basic concept pursued by MAN TURBO for single-shaft

compressors in process-air service provides separate instead

of integrated coolers; this yields advantages in cooler design

regarding type, materials, specification, and water separation.

This concept is characterised by the following features:

Two casingsThree to four coolers, which can be designed to meet all

specified requirements

High efficiency thanks to cooling below the dew point without

danger to the machine, as properly sized water separators

can be used

A gearbox between the two casings allows higher speeds

in the HP section and thus provides a solution enhancing

efficiency and reducing costs.

Multi-shaft integrally geared compressor

As an alternative to the single-shaft compressor, MAN TURBO

has developed the process service version of the multi-shaft

integrally geared compressor with six stages and three pinion

shafts. The design of this machine employs the same standard

design modules that MAN TURBO developed for their integrally

geared compressor with two pinion shafts (i.e. three to four

stages).

The first four stages of the three-shaft process machine are pro-

vided with impellers of the open three-D type, whilst the fifth and

sixth stages have closed impellers.

Direct drive by steam or gas turbine via a fourth pinion shaft (i.e.

without an additional gearbox) is provided.

Where the driver is an electric motor, drive is effected via the

bull-gear shaft similar to the two-shaft machine.

Depending on the desired process air outlet temperature, three-

or four-cooler options are available for MAN TURBO multi-shaft

integrally geared compressors.

Advantages:

High efficiency thanks to optimum speed selection for all

stages and cooling below the dew point

No limitation with respect to cooler rating

Virtually free selection of the driving speed so that also a gas

turbine driver can be used without a problem.

AIR COMPRESSOR

The air compressor takes atmospheric air and delivers it to the secondary

reformer at a pressure of approx. 35-40 bar, before separation of the nitro-

gen. MAN TURBO has built about 60 such compressors for this applicationusing different design concepts.

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The ammonia compressor is part of a refrigeration cycle used

for condensing the gaseous ammonia from the synthesis gas.

Depending on the number of refrigeration stages, this machine

consists of several stage groups and is built with one, two or

three casings. The discharge pressure is approx. 17 bar.

The compressor is a single-shaft machine with up to eight

impellers per casing (horizontally split). Ammonia sidestream

feeding at various refrigeration stages can take place outside

the compressor, in the piping system, or in order to avoid

pressure loss by direct admission to the return channel

between two compressor impellers.

The necessary cooling between the stage groups is achieved

either by evaporation of liquid ammonia or by water-cooled shell

and tube exchangers.

The impellers and internal stator parts are of similar design as for

the single-shaft air compressor. The casing is generally made ofnodular cast iron, because of the high pressure load, or of cast

steel, if required by the customer.

It is essential that any escape of ammonia from the compressor

is prevented, even the smallest of quantities, therefore casing

shaft seals require particular attention.

In most cases a tandem dry gas seal or a double mechanical

seal design is chosen. This also performs the function of a

standstill seal after a shutdown of the machine set.

AMMONIA COMPRESSOR

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Single-shaft compressor

The function of this machine is to raise the pressure of the natu-

ral gas to around 45 bar as required at the inlet of the primary

reformer.

As natural gas is available at different pressures at the various

sites of installation, the natural-gas compressors can be built

with varying numbers of stages and casings.

Depending on the required pressure, the cast steel casing can

either be designed with a horizontal or vertical joint.

In rating and designing the impellers, the gas analysis has to be

taken into account. If the H2S content of the gas exceeds the

limits set out in the NACE rules, the impeller heat treatment is to

be restricted in order to avoid stress corrosion cracking to

an allowable stress of 90,000 psi (621 N/mm2

).

Shaft sealing at the casing is achieved by a tandem dry gas seal

as the prefered solution.

NATURAL GAS COMPRESSOR

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Multi-shaft integrally geared compressor

Integrally geared compressors have been utilized for natural gas

many years. Where these turbocompressors are employed in the

fertilizer industry, it is appropriate to have the two stage com-

pressor driven by an electric motor, with natural gas compressedfrom 24 to 45 bar.

For extending the operating range and the part load behaviour

of the compressor, in the first stage inlet guide vane assemblies

can be provided for controlling the natural gas mass flow and

pressure required.

The whole unit is designed as a single lift skid comprising the

compressor, electric driver, lube oil system as well as dry gas

seal panel and the rack with the local instruments. This arrange-

ment allows a fully pre-assembled compressor package com-

pletely piped and wired up to the junction boxes.

Lower investment costs and reduced civil engineering costs

resulting from smaller facility dimensions have opened theapplication for integrally geared turbomachines.

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Large quantities of heat are released in the process, which is

used for the generation of steam. The steam is partly employed

in cracking the natural gas and partly expanded in the steam

turbines driving the compressors.

MAN TURBO builds condensing and back-pressure steamturbines of the reaction type with and without extraction/side-

stream admission using a modular design system.

The MAN TURBO modular system

For the most important sub-assemblies of MAN TURBO steam

turbines, such as the bearing housings, control-valve/nozzle

casing, control-stage casing and exhaust casing, as well as for

the connecting elements, a modular system of geometrically

graded component sizes has been developed. Combining thevarious modules in an optimal manner permits the flexible

adaptation of the machine to the specific duty.

To ensure that the blading is free from vibration resonance

throughout the speed range, a thick cylindrical, drop-shaped

profile with an integral shroud segment was developed for the

rotor blades in the reaction part of the turbine. This is a very

rugged profile; it can be used within a wide stagger angle and

blade spacing range. The availability of this range of blading in

different chord lengths allows the staging to be optimised to

ensure trouble-free operation under all operating conditions.

The tapered/twisted rotor blades of the final stages and the

tapered non-twisted stator blades are again selected from a

standard blade range. The rotors are forged from the solid andthe fully bladed rotor is balanced at full operating speed under

vacuum conditions in several planes.

STEAM TURBINE

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A complex machine train makes very great demands on the

control and protection systems in terms of quality and flexibility.

Such systems must consider the requirements of the process

and provide all functions from start-up to emergency shutdown

of the machine train and process. MAN TURBO has developedelectronic control and protection systems.

Anti-surge control (turbolog ASC)

In the performance characteristic of a turbocompressor the

surge line is the dividing line between ranges of stable and

unstable operation. Reduction of the volume flow rate beyond

this line causes separation of flow from the blading, causing the

gas to flow periodically from the discharge to the suction end

of the compressor a phenomenon referred to as compressor

surging. The resultant extreme load reversals and temperature

fluctuations in the gas-handling components of the machine

must be avoided. This is the task of the antisurge control, a

system which, by controlled opening of the blow-off or bypass

valves, always keeps the compressor flow rate in the stable

range of the performance characteristic. Specially developedby MAN TURBO for this purpose is the electronic control and

protection system called turbolog ASC, which is available on

Simatic S7 hardware as MAN TURBO standard.

This system incorporates components which greatly improve the

dynamic response of the controller and thus allow the distance

between the blow-off line and the surge line to be minimized;

surging is safely prevented under all operating conditions.

In addition to anti-surge control, an independent surge detector

is provided on MAN TURBO compressors. During surging the

mass flow rate temporarily drops to zero and the temperature

suddenly rises. Both values are measured by the surge detection

system, and if one of them passes a limiting level the blow-off

valves are opened and, where necessary, the machine train isshut down.

Speed control (turbolog STMFC)

To allow the speed of the train and thereby the pressures and

flow rates in the process to be controlled and the machine train

to be protected against overspeed, MAN TURBO has developed

the turbine control and protection system turbolog based onSimatic S7 hardware.

This system provides control far superior to the requirements of

NEMA specification SM 23, class D. Depending on the specific

requirements, it is designed for any of the following functions:

turbine speed control

speed-controlled starting of the turbine from standstill

combined control of speed and extraction pressures limited to

controlled extraction turbines

back-pressure control

inlet pressure control

power output control.

Overspeed detection unit

The most important safety device of a steam turbine is a fullytestabel overspeed trip system. Applicable rules (API, German

VGB) require, that the overspeed detection unit is independent

from the speed governor. MAN TURBO provides a triple modular

redundant (TMR) overspeed trip system (Braun).

CONTROL AND SAFETY EQUIPMENT

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To meet today's demands for high quality, economic production

and short delivery, advanced workshops qualified to the latest

standards are required.

The new fabrication shops and test facilities of MAN TURBO'sturbomachinery sector satisfy these requirements in every

respect. High-capacity working facilities have been combined

in fabrication isles for an optimum flow of materials, including

equipment for the machining of casings, blade fabrication,

impeller fabrication, rotor machining, and assembly.

The main machining operations are performed

by CNC machine tools. The machine tools

incorporate the latest technology.

WORKSHOPS

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1 Mater ia ls receiving

2 Diaphra gms

2a Small parts stores

3 Shipment

4 Rotor

4a Materia ls / toolshop

5 Small parts & blade fabrication

6 Cas ing fabrication

6a High-bay warehouse

7 Assembly

8 Balancing

9 Stores

10 Gas turbine service shop

11 Large machinery test stand

12 Development test stands

13 Training Shop

14 Screw compressor service shop

15 Turbomachinery service shop

16 Free-field test stand

17 Gas turbine test stand

18 Piping shop

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MAN TURBO owns and operates different testbeds for turbo-

machinery in order to execute factory acceptance tests. One

test centre for compressors, steam, process-gas and indus-

trial-gas turbines as well as for individual components has

been integrated into the production shops.

Machines/machine trains are completely assembled in the

assembly bay and subsequently transferred to the adjacent test

stand by two 80t cranes.

After erection on the 44 m long steel foundation and connection

to the permanent piping systems (steam, air, water, oil), all kinds

of tests to DIN/VDI/ASME/API can be conducted:

mechanical testing of the individual machines

mechanical testing of a complete machine train

thermodynamic testing with air and other gases in open or

closed loop systems.

The drivers used during testing are either those supplied under a

particular contract or the various test stand drivers which areavailable, i.e.:

an 18 MW condensing steam turbine

one 6.5 MW and two 2.5MW variable-speed motors which

can, if necessary, be coupled ogether.

In 2004 an additional packaging and test centre for large strings

was commissioned.

It is now possible if necessary to work on up to three machine

trains at the same time, on an area of over 4400 square meter.

Modules up to 600 tonnes are by no means an exception.

Two cranes, each capable of lifting 150/180 tonnes, and with a

crane hook height of over 17 metres, will guarantee the neces-

sary flexibilty in the machine assembly and testing in the future.

This test bed includes a cooling water circuit with three cooling

towers, and a 20 MW electrical power supply in addition to the

steam supply (50 bar, 500 C, 55 t/h).

MAN TURBO's Quality System complies with ISO 9001 and is

the basis for the reliability of the company's high-quality products.

The QA division, which reports to the Chairman of the Executive

Board, initiates, coordinates, and monitors all activities affecting

quality, while also issuing, and controlling the compli-ance with,QA Manuals and Procedures, such as:

Design

Material procurement

Production planning

Fabrication

Functional tests

Procedural qualifications

Calibration of gauges and test equipment.

Main points of an inspection plan for a machine train in an

ammonia plant:

Testing of specimens taken from workpieces of machine

components

Ultrasonic examination after rough machining and finish-

machiningMagnetic-particle testing

Dye-penetrant examination

Radiography

Dimensional and visual examination

Heat stability testing

Hydrostatic testing

Overspeed testing

Run-out measurement on rotors

Clearance measurements

TEST FACILITY QUALITY ASSURANCE

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ERECTION AND SERVICE

All erection and service activities for MAN TURBO machine trains

are carried out by MAN TURBO's centralized machinery service

sector.

Service activities ensure the greatest possible availability and

operational reliability of MAN TURBO turbomachinery even aftermany years of operation.

This objective is pursued through

the use of meticulous erection procedures,

thorough commissioning/trial operation,

regular inspection,

preventive maintenance,

fast repairs,

readily available spare parts and intensive advisory services.

The company's service consultancy team further ensures expert

feedback on a regular basis to promote the consistent develop-

ment of MAN TURBO's products and services. The following

provisions have been made to ensure comprehensive service to

our cus-tomers:a close-knit network of representatives in many countries

of the world

service outlets at strategic points

an independent service workshop at the company's

Sterkrade works.

An emergency service is available at Sterkrade outside normal

working hours.

1+2_Test centres in

Oberhausen/Germany

3+4_Control and monitoring

systems of a test st and

1

3 4

2

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440 402-0

440 402-2000