Gas Enginee vs Gas Turbine

7/27/2019 Gas Enginee vs Gas Turbine

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Gas Engine Vs. Gas Turbine driver

09 March 2012 WRTSIL POWER PLANTS1 Wrtsil

Specific case study for PM3 Compressor Station project


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Background

Meeting held between Wrtsil and PV Gas on 21st February 2012. Meeting was based on earlierdiscussions focused on comparing driver (and compression) techniques for PV Gas project for PM3gas booster compressor station, which belongs to Ca Mau GPP project.

At the meeting was shown common level comparison between different driver (Gas Engine and GasTurbine & compressor techniques (Centrifugal Vs Reciprocating). Presentations were also shared with

PV Gas later on.

As a result of the meeting PV Gas shared FEED design material with Wrtsil. In that material GasTurbine was chosen for a driver without any exact conclusion supporting the decision even thoughsome of the disadvantages of Gas Turbine driver where clearly shown, for example, poor efficiency at


full and part load (page 9/10 of doc 104012-10-CA-001).

Based on the material and discussion, it was agreed that Wrtsil will give an Proposal with clearscope of supply for the project via MICO (EPC contractor) with Gas Engine + Centrifugal compressor,therefore the modifications to current design will be as minimal as possible.

The other major goal discussed during the meeting was that Wrtsil will provide case specificcomparison with the benefits of using Gas Engine instead of Gas Turbine as a driver of centrifugal

compressor in this project.


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Framework for comparison

To evaluate the cost of compression for PM3 Gas Compression project, Wrtsil conducted a life-cyclefeasibility evaluation on different alternatives Wrtsil 20V34SG Gas Engine driven centrifugal compressor ( 1 unit) Gas Turbine driven centrifugal compressor ( 1 unit)Later on comes also additional evaluation for Wrtsil 20V34SG Gas Engine driven reciprocating compressor

The gas turbine performance on part load was evaluated using available Gas Turbine data. Speedcontrol performance was evaluated based on attachment Siemens SGT400 curves, which describescommon GT efficiency drop when speed is changed

Issues related to taxes, duties, insurance costs etc. are for the purpose of this study left out

09 March 2012 WDFS/ Saara Kujala3 Wrtsil

Gas analysis, max flow & inlet/outlet pressures are those what Wrtsil has received from PV Gas

Even though all efforts deemed reasonable have been taken to ensure the validity

of the figures for Gas Turbines, no guarantees can be given with respect to this


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Typical weather in Ca Mau

For evaluation, info from FEED design document + weather conditions in Vietnam have been used According to following table was assumed 27.5 Celsius & 85% RH with 100m altitude for annual

average



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Efficiency

One of the key advantage of Gas Engine compared against GasTurbine is extremely higher efficiency, on not only full load butalso more importantly on part load

In compression driver size class of 9-10 MW, typically the netefficiency that can be achieved at site ISO conditions is near 46 %at 100% load with Wrtsil Gas Engines

State of the art Gas Turbine efficiencies in the same ran e at full


load at ISO conditions are more near 33-35%, and suffer a lot athigher ambient temperatures and also at part load

Taking into account site conditions and the aging of the turbines(2%), means that they are heavily oversized for the duty, what

they are designed to


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Gas Turbine ambient derating Vs speed and load control

As known Gas Turbines arecontrolled with air inlettemperature therefore it is also

clear that straight after whentemperature goes up from ISOconditions, the de-rating will start

Gas Turbine ISO @ 15C, sea level,atturbinecoupling,MW


Gas Engine ISO @ 25C , 100m,30% RH

Poweroutput

Power turbine speed, rpm

Specific heat input, KJ/Kwh

Engine inlet temperature ,C


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Common assumptions

Gas price (LHV) = 8.5 USD/MMBtuGas LHV = 36 600 kJ/Nm3

Evaluation span = 20 - 25 years

Driving hours = 8200 hour/year

Site conditions:

Temperature annual average = 27.5 Celsius


Altitude = 100mRelative Humidity = 85%


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Compression power demand at given values

COMPRESSOR POWER DEMANDS WITH DIFFERENT POINTSA A27.5 B C C27.5 D E E27.5 F G G27.5 H

Disch P, barG 86.23 86.23 86.23 86.23 86.23 86.23 61.3 61.3 61.3 61.3 61.3 61.3

Inlet P, barG 31.92 31.92 31.92 43.89 43.89 43.89 31.92 31.92 31.92 43.89 43.89 43.89

Throttled inlet P 39.76 38.6 38.32

Inlet T c 38 27.5 25 38 27.5 25 38 27.5 25 38 27.5 25

Rpm 10625 10369 10307 8524 8297 8242 9086 8834 8774 7438 7438 7438

Kw 9617 9220 9125 6140 5860 5792 6135 5853 5786 3946 4016 4032

Polytropic eff % 84.77 84.71 84.84 84.73 83.25 83.62 82.37 83.16

Power Demand are clearly under 10MW in most driving points

Therefore Wrtsil 20V34SG engine is optimal choice with 10MW ISO output, only point A has to be

later confirmed Gas Turbines de-rate heavily with given values, possible choices for Gas Turbines could be:

Solar Titan130, 15MW ISO Output or Siemens SGT400 with 13.5MW ISO Output


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Comparison fuel consumption per hour

DRIVER EFFICIENCY AND FUEL CONSUMPTION GAS LHV = 36600 kJ/Nm3

A27.5 C27.5 E27.5 G27.5WRTSILPOWER NEED * [kW] 9408 5980 5972 4098

SPEED [RPM] 732 586 624 525

EFFICIENCY [%] 44.31 43.66 43.34 43.13

FUEL CONSUMPTION [Nm3/h] 2088 1347 1355 935

GAS TURBINEPOWER NEED [kW] 9220 5860 5853 4016

SPEED [RPM] 8230 6585 7011 5903

EFFICIENCY [%] 30.62 25.01 26.13 21.67

FUEL CONSUMPTION [Nm3/h] 2962 2305 2203 1823

*Gearbox losses included for Wrtsil


Wrtsil solutions efficiency is almost flat

Gas turbine efficiency will drop heavily

Wrtsil cannot guarantee anything else than ownvalues. Anyhow, for Gas Turbine efficiency calculationshas been used common tools and info from themanufacturers


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Yearly Fuel costs

CASE A27.5 = stage 2 CASE E27.5 = stage 1

Fuel gas Cost Fuel gas Cost

[Nm3/year] [USD] [Nm3/year] [USD]

Wrtsil 20V34SG 17 125 010 4 964 540 11 113 892 3 221 917

Gas Turbine (e.g. Solar Titan130) 24 286 280 7 040 593 18 066 515 5 237 483

Assumed 8200hour/year, so Gas Turbine & Gas Engine & Compressor and auxiliary maintence is clearly reduced from hours.

Gas price assumed to be 8.5 USD/MMBtu

2.07 Million USD/YearSavings by Wrtsil

solution2.01 Million USD/Year


In stage 1 using of Wrtsil solution saves at 27.5 C gas inlet/ambient conditions atleast over 2 Million USD annually!

In stage two the difference is in same level but cumulative numbers bigger. Loading

is better in this case.

At higher temperature, efficiency difference will be higher and will increase theWrtsil solutions fuel savings.

PAYBACK time of Wrtsil solution is very low


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OPEX costs for 20 years, without fuel Costs

Operation costs of Gas Engine Vs. Gas Turbine driven plants are in in similar levels

More starts & stops, would cause decreasing of time between maintenance for Gas Turbines.However, not for Gas Engines.

Figure shows normal cumulative cost in both cases. More specific and detailed comparision canbe carried out, if needed



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N+1 Solution

More number of independent gas compression units would provide more flexibility in operation andmaintenance. While one of the unit is under shutdown (scheduled or un-scheduled) the rest of the

lant is available.


N+1 approach is widely used in Oil & Gas sector, because usually the throughput is the most importantfactor for pipeline owners. Standby solution improves the over all availability and reliability of the plant

Going for N+1 solution would mean even more savings in fuel gas cost because plant could be driven

with highest possible efficiency all the time.

Optimum solution for this particular project could be (2 working + 1 Stand by), which PV Gas may like toexplore dependind on their priorities


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Conclusions

There is a potential to save approx 35 to 40 Million USD over the project life Cycleby using Wartsila solutions as compared to Gas Turbine

There is major advantage in net efficiency on long term basis for Gas Engine driven

compressor and a huge potential to save on fuel

Running of Centrifugal Compressor with Gas Enginewould mean a very short payback time for PVGas


Standby unit solution (e.g 2+1) is adviced byWrtsil for this and similar projects

Wartsila recommends to

verify and take a closer lookat using Reciprocatingcompressors for this orsimilar projects in future.

Documents

Gas Enginee vs Gas Turbine