Compressor
Designs for Minimum Power & Highest Efficiencies
Compressor selection by Pro-M is mechanically and
aerodynamically optimised. It represents the minimum compression
power and the highest efficiency you can achieve in practice for the
specified process conditions.
Compressor Power,
Driver Power & Driver Rating
Process engineers
need to know the power required to compress the gas. If it is driven
by electrical motor, the motor size must be determined. For gas
turbine drivers, an error of 10% in power estimation can cause a
major re-design later in the project and may even effect project
economics because a larger more expensive gas turbine may be
required.
Pro-M provides accurate and realistic compression
powers, taking into account practical issues such as mechanical
losses, internal leakage, balance piston leakage etc. All of these
parameters affect the actual compressor power. Gear losses are added
when a gearbox is installed between the driver and the compressor.
A 10% power margin is added to arrive at the driver rating
to allow for fouling and loss of efficiency which is common in
centrifugal compressors.
Capital Cost Savings With
Smaller Driver Size
By identifying minimum
compression power, Pro-M also helps to reduce the driver size and
save on the associated capital cost. For example, gas turbine
drivers are particularly expensive and a 10% reduction in compressor
power could allow a smaller gas turbine frame and lead to savings of
$ 0.25-0.5 million for one train.
Reduced Fuel
Consumption & Reduced Operating Costs
Gas
compression dominates the power consumption of a gas processing
plant. Where fuel is imported and costed, savings in compression
power will result in substantial savings in plant operating costs.
Calculation of Actual Efficiency
Until now changing process conditions did not show
any performance benefit because compressor efficiency was specified
by the user and fixed at an estimated value. Since Pro-M calculates
efficiency for you, it allows you to interact with process design
and see its impact on compressor efficiency and power.
Further Efficiency Gains Through Process Design
When designing a compression system to suit a set
of process conditions, the solution is limited to the compressor
wheel options that are commercially available. In effect the
selected design will be the one that most closely matches the
process conditions. In many instances, efficiencies can be further
improved by adjusting process conditions to bring them in line with
the closest commercially available compressor design. This will
produce a solution that is truly optimised. Pro-M allows such
iteration and fine-tuning of the process conditions to improve
compressor efficiencies, leading to further reductions in power
consumption.
MSE provide training courses in compressor
design and optimisation. Details can be found on the MSE website at
www.mse.co.uk
Interaction Between Process Design & Compressor
Performance
If after an initial analysis you find
that the compressor performance is not what you wanted you can
re-run with different processes conditions. For example, if the
driver power is too large and you want to employ a smaller driver,
you can modify your process conditions i.e. reduce flow or reduce
pressure ratio and re-run Pro-M until you can find the driver rating
of your choice.
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Redesign of Existing Plant To Suit New Process
Conditions
If you are modifying an existing plant
you can also use Pro-M to find the optimum compressor geometry for
the new process conditions and view the corresponding efficiencies
and compression powers.
Compressor Selection Within
Practical Limits
The speed and impeller diameter
combination derived by Pro-M gives the highest aerodynamic
efficiency while keeping the design within realistic design limits
for the selection of a centrifugal compressor. Pro-M takes into
account practical and manufacturing constraints such as maximum
shaft speeds, impeller diameters and tip speeds. It also limits the
number of impellers in order to achieve acceptable vibration
characteristics.
In short Pro-M offers an optimised design
of a centrifugal compressor, which you can buy from most compressor
manufacturers.
Encapsulation of Mechanical Design
Data
Pro-M encapsulates the mechanical design
limits of centrifugal compressor proven technology. The design
methodology used by Pro-M embodies the same principles used by
compressor manufacturers.
Reduced Gas
Turbine Emissions
Typical gas turbine thermal
efficiencies for mechanical drivers vary between 28 - 38 %. Assuming
an average thermal efficiency of 33%, a gas turbine will consume 3
kW (10236 Btu/hr) of fuel to deliver 1 kW of net power to the
compressor. Thus to deliver an output of 50,000 kW of compressor
power the engine will consume 150,000 kW (512 x 106 Btu/hr) of
energy in the form of fuel burned.
A 10% saving in power by
compressor optimisation with Pro-M will lead to 5,000 kW reduction
in compressor power and 15,000 kW (51.2 x 106 Btu/hr) of less fuel
burned. This will reduce emissions significantly.
Smaller Cooler
Size & Cooling Medium Flows
Higher compressor efficiencies derived by
Pro-M can result in lower discharge temperatures which reduce
aftercooler duty and size, as well as cooling medium flows.
Process Design
Leading to Viable Compressor Designs
Pro-M converts the process data into parameters
which are used for compressor design. If a process design gives rise
to an impractical compressor design Pro-M will warn you that the
process conditions you have selected are not within practical limits
for the selection of a centrifugal compressor. You can then alter
the process conditions and try again until you reach viable
compressor geometry. This ensures that the process conditions you
specify will lead to a viable and practical machine for your process
plant.
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