Effect of Variation of Fuel Composition on Gas Turbine Off-Design Performance

Transcription

1 Applied Mehanis and Materials Submitted: ISSN: , Vol. 666, pp Aepted: doi: / Online: Trans Teh Publiations, Switzerland Effet of Variation of Fuel Composition on Gas Turbine Off-Design Performane Yesuel Park 1, a, Saemi Park 1,b Joongseong Lee 2,d, Gyungmin Choi 1,e 1 Shool of Mehanial Engineering, Pusan National University, Republi of Korea 2 New Energy Tehnology Researh Center, R&D Division KOGAS, Republi of Korea a ysparkk@pusan.a.kr, b sm.park@pusan.a.kr, d jslee@kogas.or.kr, e hoigm@pusan.a.kr Keywords: off-design analysis, low alorifi value fuel, Heavy duty gas turbine, Modeling, Turbine metal temperature, orretion fator Abstrat. The effets of fuel omposition is investigated in a gas turbine for natural gas. Fuel omposition is divided H/C ratio and heating value. There are three ontrol shemes for gas turbine. In this study, TIT ontrol and TET ontrol is adopted. A full off-design analysis of the gas turbine was performed. Performane harateristis and maximum turbine blade temperature are the main interests. The power output is dereased while heating value of fuel is inreased and H/C ratio of fuel is dereased both ontrol sheme. As heating value of natural gas dereased and H/C ratio of fuel inreased, turbine blade temperature is inreased in TIT ontrol. Otherwise, Blade metal temperature is little influened by H/C ratio of fuel in TET ontrol sheme. Introdution Natural gas ontains methane, heavier hydroarbon and inert omponents whih affet burner performane.[1] For this reason pipeline ompanies and LNG buyers speify allowable ranges of omponents and heating value of fuel. Beause heating value and omposition of LNG is depending on soure and ost of higher heating value fuel is gradually expensive, low alorifi gas fuel will be imported in Korea. Therefore, heating value of LNG imports to Korea is ontinuously dereasing annually relative to domesti natural gas. Beause Gas turbines produe lots of eletri power for its size, it has been used for many aerospae and industrial appliations for many years. For power generation, espeially ombine gas turbine is omposed of topping yle (gas turbine) and bottom yle (steam turbine and HRSG), entire performane ombined gas turbine is influened by performane of gas turbine. The performane of a gas turbine is the result of a omplex interation of different turbo mahines and ombustion system. Fuel omposition affets flame properties inluding heating value, and adiabati flame temperature. In turn, these properties hanges gas turbine primary parameter suh as ompressor inlet mass flow, ompressor pressure ratio, fuel mass flow, and ooling air mass flow. This differene leads the potential to hange net yle power output. To ompensate power loss to operate on a variety of fuel ompositions in power station, entire gas turbine must be analyzed. In addition, gas turbine must be heked operating safely when low alorifi value LNG is used in. Sine gas turbine is sensitive to operating ondition inluding fuel ondition, performane harateristis of gas turbine is affeted by hange of fuel omposition. To analyze performane harateristis of gas turbine, aspen plus v8.0 and aspen dynamis v8.0 is used. All rights reserved. No part of ontents of this paper may be reprodued or transmitted in any form or by any means without the written permission of Trans Teh Publiations, (ID: , Pennsylvania State University, University Park, USA-09/05/16,12:50:41)

2 Applied Mehanis and Materials Vol System modeling Shemati diagram of gas turbine is represented in Fig. 1 with onsidered options. Fig 1. Shemati Diagram of Gas Turbine Table 1. Design speifiations of the gas turbine Item Data Inlet Air temperature (K) Air pressure (Mpa) Air flow (kg/s) Compressor Pressure ratio 15.4 Number of stages 18 Disharge temperature (K) Combustor Fuel Natural gas Fuel lower heating value(kj/kg) Fuel flow 9.76 Pressure loss(%) 4.0 Turbine Turbine inlet temperature (K) Turbine exhaust temperature (K) Exhaust gas flow (kg/s) Performane Power output Thermal effiieny 33 Table 1 shows the major design data of the gas turbine used in this analysis. The power output and effiieny represents frame F gas turbines, espeially the GE PG7241FA. Compressor is modeled using ompressor map. Nozzles and rotors of eah stage exept third rotor are ooled by disharged air from ompressor. The off-design analysis of the turbine is represented by the following hoking ondition. in 1 1 m Tin 2 onstant, where (1) AinPin R 1 Thus, the operating ondition of the gas turbine was determined by mathing the harateristis of the ompressor and the turbine. Therefore, if the ondition is hanges (e.g., a derease in heating value), the mathing between the turbine and the ompressor auses a hange in the working pressure ratio of ompressor thereby affeting the surge margin [3].

3 196 Eletronis, Mehatronis and Automation III Analysis of the variation in turbine blade temperature due to fuel omposition hange is another purpose in this study. A simple thermodynami model was adopted. Tg Tb (2) T T g m m g p, p, g C (3) P T, 0.5, d m m d (4) P, d T Table 2. Fator for Cooling Flow[2] First turbine nozzle Seond turbine nozzle Third turbine nozzle T b,max [K] Pattern Fator Cooling Parameter C Cooling Parameter Φ Table 2 represents ondition of ooling parameter and onsidered options. T b,max is assumed turbine blade temperature. Φ represents the asymptoti ooling effetiveness, the value of whih is 1.0, orresponding to a very high thermal apaity ratio. C represents the tehnology level of the ooling. Table 3. Fuel Composition referene Case 1. Case 2. Case 3. Case 4. CH C 2 H C 3 H NC 4 H IC 4 H C 5 H C 6 H CO CO H H 2 O N Table 3. represents fuel speifiation adopted this paper. Referene is referene fuel of natural gas, ase 1 and ase 2 are primarily omposed of methane, ase 3 is omprised of muh C2+ omponent ompared to referene, and ase 4 is omposed of lots of C2+ omponent. In this study, two ontrol logis are simulated. TIT ontrol is maintained turbine inlet temperature, and TET ontrol is maintained turbine exhaust temperature. Results and Disussion. Fig. 2 represents real and simulation data of power and heat rate orretion fator for various ambient temperature. Maximum error of power is 5% in high temperature beause of ompressor map. If the

4 Applied Mehanis and Materials Vol ompressor map is similar with real ompressor, performane of gas turbine will be well mathed with real data. TIT Control. Performane harateristis of gas turbine using TIT ontrol is simulated. Generally, gas turbine is lassed aording to turbine inlet temperature. Power is inreased while heating value is dereased and H/C ratio is inreased. Fuel flow is varied for onstant TIT with various heating value and omposition of fuel. For example, fuel flow is inreased with low alorifi value fuel, and air flow is dereased due to hoking ondition. Also, fuel flow is different for H/C ratio whih fuel has same heating value. Combustion produts of high H/C ratio of fuel have lots of water ompared to low H/C ratio fuel, so more fuel is required for onstant turbine inlet temperature. Maximum turbine blade temperature is also influened by heating value and H/C ratio. Beause turbine inlet temperature is onstant, maximum turbine blade temperature is more sensitive to H/C ratio in omparison with effet of heating value. Trend of turbine exhaust temperature is similar with maximum turbine temperature. Fig2. Gas Turbine Performane Variation with Ambient Temperature Fig 3. Corretion Fator of Gas Turbine Main Parameter using TIT Control TET ontrol. Turbine exhaust temperature is maintained for performane of bottom yle, generally it is adopted in ombined yle. The performane results are similar to TIT ontrol. Power is inreased while heating value is dereased and H/C ratio is inreased. Turbine inlet temperature and maximum turbine blade temperature is notieable differene. To onstant TET, turbine inlet temperature is varied depending on heating value and H/C ratio. TIT is little hanged for various heating value. Beause inreased or dereased heating value of fuel influenes fuel flow and air flow, very little amount of ooling flow rate is varied by air flow rate. Otherwise, H/C ratio has an effet on ombustion produt, high H/C ratio fuel produe lots of water whih has large speifi heat. Turbine

5 198 Eletronis, Mehatronis and Automation III inlet temperature is sensitive to H/C ratio rather than heating value. Therefore, maximum turbine blade temperature is similar eah other for eah H/C ratio, whih has different turbine inlet temperature with little differene ooling flow. Fig 4. Corretion Fator of Gas Turbine Main Parameter using TET ontrol Summary The effet of natural gas type on the performane of a gas turbine is investigated. In this study, TIT and TET ontrol is adopted. These ontrol sheme is usually adopted in industrial site, espeially TET ontrol is used to maintain performane of bottom yle. Sine the power output has a minimum requirement and is related to profit, and the higher turbine blade temperature ause a large amount of output. However, the maximum metal temperature is assumed to protet turbine blades. The foused parameters are varied with fuel omposition. Referenes [1] D.Straub. D.Ferguson, K.Casleton, G.Rihards : 5th US Combustion Meeting Paper # E06 [2] Young Sik Kim, Jong Jun Lee, Tong Seop Kim, Jeong L. Sohn : submitted to Journal of Energy Conversion and Management (2011) [3] Bryan Li, Mike J. Gross, Thomas P. Shmitt : submitted to Journal of Engineering for Gas Turbines and Power (2011) [4] Mike Segers, P.E, Roy Sanhez, Paul Cannon, Carlos Gutierrez, Bob Binkowski, David Hailey : ISA Power Industry Division 54th Annual I&C Symposium (2011)

6 Eletronis, Mehatronis and Automation III / Effet of Variation of Fuel Composition on Gas Turbine Off-Design Performane /