This document discusses using a turboexpander, gearbox, and generator system to generate electric power from a gas pressure reduction station. It explains that a turboexpander's performance depends on inlet flow, pressure, and temperature. Using a gearbox between the turboexpander and generator allows the turboexpander to operate at a higher, more efficient speed than the generator, increasing power output. A case study shows that using a gearbox can increase power generation by 96% compared to direct coupling without a gearbox. The document concludes that while a gearbox increases capital costs, it can improve the revenue from additional power generation.

1. © Rooz Parhizkar
 gastec.au@outlook.com
 0403 003 128
Turboexpander – Gearbox – Generator
for Electric Power Generation
in a Gas Pressure Reduction Station (GPRS)
A Case Study by
Ross Rhyme
ENT-EI-PRS-016-R00

2. © Rooz Parhizkar
 gastec.au@outlook.com
 0403 003 128
Turboexpander – Gearbox – Generator
 ross@enerturbo.com.au
 +61 403 003 128
Turboexpander Performance
• TE Inlet Flow (Q2) determined by process demands;
• Household / industry consumption;
• Fuel consumption in power plants or compressor stations;
• TE Inlet Pressure (P1) determined by gas line;
• TE Discharge Pressure (P2) determined by process demand (same as flow);
• TE Inlet Temperature (T1) determined by minimum allowable gas temperature
(by process or equipment).
• To sum up: Q1↑, P1↑, P2↓ ⇨ POWER↑
Process Parameters Affecting Turboexpander Performance

3. © Rooz Parhizkar
 gastec.au@outlook.com
 0403 003 128
Turboexpander – Gearbox – Generator
 ross@enerturbo.com.au
 +61 403 003 128
Turboexpander Performance
• TE Polytropic Efficiency ~ NS (Specific Speed)
• N: Rotational Shaft Speed
• ∆h: Ideal Enthalpy Reduction
• N is Determined by Driven Equipment Speed
• ∆h is Determined by Turboexpander Number of Stages
For Specified Process Conditions; (Q2,P1,P2)

4. © Rooz Parhizkar
 gastec.au@outlook.com
 0403 003 128
Turboexpander – Gearbox – Generator
 ross@enerturbo.com.au
 +61 403 003 128
A GPRS Utilizing Turboexpander(s)
• Generator Speed (Constant)
• 50 Hz ~ 3000 rpm
• 60 Hz ~ 3600 rpm
• Turboexpander Speed
= Generator Speed
• Directly Coupled
• Lower Efficiency
> Generator Speed
• Coupled via a Reducing Gearbox
• Higher Efficiency
Electric Power Generation Application

5. © Rooz Parhizkar
 gastec.au@outlook.com
 0403 003 128
Turboexpander – Gearbox – Generator
 ross@enerturbo.com.au
 +61 403 003 128
Why Using Gearbox?
• Process Conditions
• P1 = 48 bar
• P2 = 19 bar
• Flow = 6.43 kg/s
A Case Study
Turboexpander Gearbox Generator
Speed
(rpm)
Specific
Speed
Type
Efficiency
(%)
Mechanical
Power
(kW)
Speed
Ratio
Efficiency
(%)
Speed
(rpm)
Efficiency
(%)
Electric
Power
(kW)
31125 40.78 Radial 78.87 671.0 10.4:1 97 3000 97 631.3
3000 3.93 Axial 42 331.6 - - 3000 97 321.7
Using Gearbox ⇨ 96% More POWER!!!

6. © Rooz Parhizkar
 gastec.au@outlook.com
 0403 003 128
Turboexpander – Gearbox – Generator
 ross@enerturbo.com.au
 +61 403 003 128
Why Using Gearbox?
• More power translates to higher income and a gearbox
increases the capital cost: revenue balance should be checked
in an economic analysis;
• Increasing turboexpander speed beyond a limit may require
utilization of magnetic bearings: that again adds to the capital
cost;
• Determining turboexpander speed affects its type (for a
reasonable performance):
• Radial / Axial;
• Impulse / Reaction;
• Full Admission / Partial Admission.
Final Remarks