GRC Transactions, Vol. 39, 2015

Evaluation of Inflow Radial Turbo Expander Field Performance for a 25 MW Geothermal Organic Rankine Cycle Train

Reza Agahi and Felix Mohr Atlas Copco Gas and Process

Keywords Inflow radial turbine, turboexpander, Organic Rankine Cycle (ORC), isentropic efficiency, variable inlet guide vanes, brine, power plant design, Turkey, Pamukuren

Abstract

The first phase of a geothermal Organic Rankine Cycle (ORC) power plant was commissioned in October, 2013. The electrical power production capacity of this plant will be in excess of 100 MW when phases two and three are com- pleted in 2015. This geothermal ORC power plant was optimized with normal butane as the working fluid using an inflow radial turbine. The first phase, with nominal power of 45 MW consisted of two power trains. Each power train has a nominal capacity of 22.5 MW electrical power output. In this paper we present the geothermal resource design conditions, the thermodynamic issues for the choice of working fluid, field performance of the inflow radial turbine and comparison with the expected performance.

Introduction The Pamukuren geothermal ORC power plant is located in Aydin province in Turkey. The order for phases I and II of this power plant was awarded to a consortium consisting of a turbine supplier, an engineering provider and air cooled condenser supplier. The plant was configured in multiple Table 1. Geothermal Resource data. trains. Each power train was designed with Brine Steam NCG’s Reinjection two parallel stages of inflow radial turbines Flow Temperature Flow NCG’s Flow Temperature mounted on an integral gearbox driving a single synchronous generator. The design 1,400 t/h 161 °C 55 t/h CO2 22 t/h 80 °C called for electrical output capacity of each train to be nominally 22.5 MW. Table 2. Turbo Expander Stage Gas Dynamics Performance. Table 1 depicts the original brine con- ditions for the ORC plant design. Inlet Inlet Outlet Outlet n-Butane Gen. Turbine Ambient Pres. Temp. Press. Temp. Flow Power Exp. Normal butane was chosen as the work- Temp Bara °C Bara °C Kg/h KW Eff % ing fluid based on the the available geothermal resource data and characteristics of an inflow Winter (5 °C) 25.00 125.00 4.00 57.70 594,000 11,550 82.5 radial turbine. Figure 1 shows T-s Diagram for n-butane. Table 2 depicts gas dynamic perfor- Design (18 °C) 25.00 125.00 2.90 54.70 594,000 10,250 87.0 mance of each expander stage. Figure 2 depicts Summer (35 °C) 25.00 125.00 5.10 70.70 594,000 8,550 84.0 the Process Flow Diagram PFD for the ORC.

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Figure 1. T-s Diagram for the ORC with n-Butane.

Field Performance Evaluation Methodology

3 Turbo expander-generator field performance B evaluation can be based on an expander discharge temperature or the generated electrical power. The for- C mer methodology is applicable to processes where the B main function of the expander is to produce cryogenic

refrigeration. The latter approach is applied where an 2 4 A expander is utilized for energy recovery. 1 D D In this discussion we consider the power ef- 5 ficiency for field performance evaluation.

C

3 D 4

B 5 2 A 1

Figure 2. PFD for the ORC Process.

Operational Data and Field Table 3. Operational Resource Data. Performance, December 2013 Brine Steam + Reinjection Train Flow Temperature NCG Flow NCG’s Temperature The plant was commissioned in I 1,129 t/h 164 °C 91.00 m3/h 2.5 % CO2 74 °C September 2013 and synchronized with II - - - - - the electrical grid in October 2013. Table 3 depicts the actual resource data for the Table 4. Turbo Expander Stage Gas Dynamics Performance. power trains which I recorded in the first Train/Exp/ month of operation. Table 4 shows the Ambient Inlet Inlet Outlet Outlet Gen. Oper. Exp. gas dynamics performance for the turbo 10.0 Press. Temp Press. Temp. Flow Power Eff. (1) Eff. (2) expanders for these power trains. °C Bara °C Bara °C Kg/h KW % % Table 4 shows the calculated ex- I / 1 25.00 128.90 3.70 63.80 - - - pander efficiencies using the generated I / 2 24.70 132.40 4.30 60.00 - - - electrical power method. The calculated I - - - - 1,141,500 9,080 87.00 86.00 field performance efficiency is in line with (1)Based on Generator Power and Calculated Gas Power expected. (2)The expected efficiency with head coefficient and flow coefficient corrections

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Table 5. Operational Resource Data. Another round of field perfor- Steam + Reinjection mance evaluation was conducted for Temperature NCG Flow Temperature train II in November 2013. Table 5 Train Brine Flow t/h °C m3/h NCG’s °C shows geothermal resource data. Table I - - - - - 6 depicts the gas dynamics perfor- II 1,200 167 95.00 2.5% CO2 76 mance for train II. Calibration of instruments and Table 6. Turbo Expander Stage Gas Dynamics Performance. fine tuning of the ORC process were carried out for several weeks after the Train/Exp/ Inlet Outlet Gas Exp. Eff. Ambient 3.0 Press. Inlet Press. Outlet Power Oper. (2) power plant was synchronized °C Bara Temp °C Bara Temp. °C Flow Kg/h KW Eff. (1) % % II / 1 25.30 133.60 3.20 59.70 - - - Operational Data and Field II / 2 25.80 136.90 3.20 64.20 - - - Performance, in 2014 II - - - - 998,400 19,030 80.00 79.00 The following tables depict the (1)Based on Generator Power and Calculated Gas Power (2)The expected efficiency with head coefficient and flow coefficient corrections Pamukuren plant performance during 2014. The data utilized is based on Table 7. Turbo Expander Stage Gas Dynamics Performance. days of operation where the ambient temperature was close to the original Train/Exp/ Inlet Outlet Outlet Gen Exp. Ambient 6.90 Press. Inlet Press. Temp. Flow Power Eff. (1) Eff. (2) design parameters. °C Bara Temp °C Bara °C Kg/h KW % % As shown the actual plant I / 1 25.00 136.60 2.30 69.50 - - - - performance exceeds the design ex- I / 2 24.70 134.30 2.80 67.30 - - - - pectations and the expander isentropic I 572,400 18,920 85.00 84.50 efficiency is also consistently better than expected. II / 1 24.90 130.40 2.70 58.40 - 16,590 - - Finally, it is interesting to note II / 2 24.80 129.00 2.80 59.90 - - - - that the Pamukuren power plant II 511,600 16,590 88.00 83.50 performed better than the other geo- (1) Based on Generator Power and Calculated Gas Power thermal ORC plant in the same region (2)The expected efficiency with head coefficient and flow coefficient corrections during hot and humid summer days. Table 8. Turbo Expander Stage Gas Dynamics Performance. Train/Exp/ Inlet Inlet Outlet Outlet Gen Exp. References Ambient 19.70 Press. Temp Press. Temp. Power Eff. (1) Eff. (2) °C Bara °C Bara °C Flow Kg/h KW % % Bloch, Heinz , Soares, C. 2001, Turboexpanders I / 1 25.08 131.02 3.10 68.24 - - - - and Process Applications, Gulf Profes- sional Publishing. I / 2 24.02 133.51 2.99 66.32 - - - - I 568,400 18,180 90.00 86.50 II / 1 25.00 129.28 3.15 61.67 - - - - Hoyer, Dan, Kitz, K. Gallup, D. 1991, Salton Sea Unit 2, Innovation and Successes, II / 2 24.73 131.89 3.19 64.50 - - - - Geothermal Resource Council Transac- II 540,200 18,840 86.00 85.70 tions, Vol. 15. (1)Based on Generator Power and Calculated Gas Power (2)The expected efficiency with head coefficient and flow coefficient corrections Ben Holt & Richard G. Campbell, 1984, The Mammoth Geothermal Project, Geo-Heat Center Quarterly Bulletin, Vol. 8 No. 4. Table 9. Turbo Expander Stage Gas Dynamics Performance. Train/Exp/ Inlet Inlet Outlet Outlet Gen Exp. (1) (2) Agahi, Reza, Allen M. 1997, Geothermal En- Ambient 30.5 Press. Temp Press. Temp. Flow Power Eff. Eff. ergy Using Turboexpanders, Geothermal °C Bara °C Bara °C Kg/h KW % % Power in Asia 1997 Conference, 24-28 I / 1 24.96 130.85 4.29 84.00 - - - - February, Bali, Indonesia (1997).. I / 2 24.88 132.64 4.23 84.00 - - - - I 546,400 13,790 84.00 81.40 Agahi, Reza, Spadacini, C, 2010, Comparison II / 1 24.97 129.40 3.83 70.28 - - - - between Variable and Fixed Geometry Turbine in Geothermal Power Plants, II / 2 24.89 131.48 3.77 69.80 - - - - Proceedings World Geothermal Congress, II 449,700 11’770 71.00 68.10 Bali, Indonesia, April 25-29. (1)Based on Generator Power and Calculated Gas Power (2)The expected efficiency with head coefficient and flow coefficient corrections

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