Linear MPC Operating Far From Design Condition: Assessment Derived From Experiments

2020 ◽  
Author(s):  
Iacopo Rossi ◽  
Mario Luigi Ferrari ◽  
Alberto Traverso
Keyword(s):  
Real Time ◽  
Gas Turbine ◽  
Linear Process ◽  
Control Technique ◽  
Target System ◽  
Inlet Temperature ◽  
Test Rig ◽  
Real Time Mode ◽  
Embedded Model ◽  
The Impact

Abstract Model Predictive Control (MPC) is a well-known control architecture that has encountered an enormous variety of applications since the very beginning until current days. The pros and cons of such control technique are very well known and both of them rely on the embedded model, which is used to determine the control trajectory. Still, the discrepancy between embedded model and real operative conditions can affect the control response due to uncertainties in measurement chain, noise and so on. Still, it is hardly available in literature what would happen in case the plant is operating far from the design condition of the model. This is of particular interest once a linear MPC is governing a non-linear process where the linearization of the target plant must be processed to tune the MPC itself. This paper analyses experimental results from a fuel cell gas turbine hybrid system, namely SOFC/GT emulator test rig, where a linearized MPC was adopted to control stack inlet temperature. The test rig is constituted by a modified Turbec T100 micro gas turbine where a volume of 4 m3 is interposed between compressor and turbine. This emulates the impact of the SOFC on the GT. The system is connected in real-time mode to a model, which runs in parallel and reads what is going on the plant side and simulates the behavior of the associated SOFC stack. The MPC controller governs the plant according to the stack inlet temperature computed by the model in real-time mode. This MPC must be considered as a supervisor of the system, as the gas turbine was still equipped with its original control system. The plant was subject to an on-purpose strong degradation -operated via a constant venting of air from compressor to ambient. This operation strongly influenced the performance of the system, which were no longer able to operate at a level of temperature and power for which the controller was designed for. Still, a ramping down in power and back up was performed and the MPC showed performance which were in agreement with the design performance. Such surprisingly good result is explained with the complexity of the embedded model, which was derived from a completely physical model of the target system and constituted by more than 200 states.

Fuel Cell Temperature Control With a Pre-Combustor in SOFC Gas Turbine Hybrids During Load Changes

2016 ◽  
Author(s):  
Valentina Zaccaria ◽  
Zachary Branum ◽  
David Tucker
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Real Time ◽  
Gas Turbine ◽  
Thermal Stresses ◽  
Inlet Temperature ◽  
System Efficiency ◽  
Temperature Deviation ◽  
Conservation Of Energy ◽  
The Impact

The use of high temperature fuel cells, such as Solid Oxide Fuel Cells (SOFCs), for power generation, is considered a very efficient and clean solution to conservation of energy resources. Especially when the SOFC is coupled with a gas turbine, the global system efficiency can go beyond 70% on natural gas LHV. However, the durability of the ceramic material and the system operability can be significantly penalized by thermal stresses due to temperature fluctuations and non-even temperature distributions. Thermal management of the cell during load following is therefore very critical. The purpose of this work was to develop and test a pre-combustor model for real-time applications in hardware-based simulations, and to implement a control strategy in order to keep cathode inlet temperature as constant as possible during different operative conditions of the system. The real-time model of the pre-combustor was incorporated into the existing SOFC model and tested in a hybrid system facility, where a physical gas turbine and hardware components were coupled with a cyber-physical fuel cell for flexible, accurate, and cost-reduced simulations. The control of the fuel flow to the pre-combustor was proven to be very effective in maintaining a constant cathode inlet temperature during a step change in fuel cell load. After imposing a 20 A load variation to the fuel cell, the controller managed to keep the temperature deviation from the nominal value below 0.3% (2 K). Temperature gradients along the cell were maintained below 10 K/cm. An efficiency analysis was performed in order to evaluate the impact of the pre-combustor on the overall system efficiency.

Fuel Cell Temperature Control With a Precombustor in SOFC Gas Turbine Hybrids During Load Changes

2017 ◽  
Vol 14 (3) ◽  
Author(s):  
Valentina Zaccaria ◽  
Zachary Branum ◽  
David Tucker
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Real Time ◽  
Gas Turbine ◽  
Maximum Temperature ◽  
Inlet Temperature ◽  
System Efficiency ◽  
Temperature Deviation ◽  
Conservation Of Energy ◽  
The Impact

The use of high temperature fuel cells, such as solid oxide fuel cells (SOFCs), for power generation is considered a very efficient and clean solution for conservation of energy resources. When the SOFC is coupled with a gas turbine, the global system efficiency can go beyond 70% on natural gas lower heating value (LHV). However, durability of the ceramic material and system operability can be significantly penalized by thermal stresses due to temperature fluctuations and noneven temperature distributions. Thermal management of the cell during load following is therefore essential. The purpose of this work is to develop and test a precombustor model for real-time applications in hardware-based simulations, and to implement a control strategy to keep constant cathode inlet temperature during different operative conditions. The real-time model of the precombustor was incorporated into the existing SOFC model and tested in a hybrid system facility, where a physical gas turbine and hardware components were coupled with a cyber-physical fuel cell for flexible, accurate, and cost-reduced simulations. The control of the fuel flow to the precombustor was proven to be effective in maintaining a constant cathode inlet temperature during a step change in fuel cell load. With a 20 A load variation, the maximum temperature deviation from the nominal value was below 0.3% (3 K). Temperature gradients along the cell were maintained below 10 K/cm. An efficiency analysis was performed in order to evaluate the impact of the precombustor on the overall system efficiency.

A New Calculation Approach to the Energy Balance of a Gas Turbine Including a Study of the Impact of the Uncertainty of Measured Parameters

2005 ◽  
Author(s):  
Helmer G. Andersen ◽  
Pen-Chung Chen
Keyword(s):  
Energy Balance ◽  
Gas Turbine ◽  
Control Volume ◽  
Ambient Air ◽  
Energy Balance Equation ◽  
Inlet Temperature ◽  
Exhaust Gas ◽  
Gas Composition ◽  
Intake Flow ◽  
The Impact

Computing the solution to the energy balance around a gas turbine in order to calculate the intake mass flow and the turbine inlet temperature requires several iterations. This makes hand calculations very difficult and, depending on the software used, even causes significant calculation times on PCs. While this may not seem all that important considering the power of today’s personal computers, the approach described in this paper presents a new way of looking at the gas turbine process and the resulting simplifications in the calculations. This paper offers a new approach to compute the energy balance around a gas turbine. The energy balance requires that all energy flows going into and out of the control volume be accounted for. The difficulty of the energy balance equation around a gas turbine lies in the fact that the exhaust gas composition is unknown as long as the intake flow is unknown. Thus, a composition needs to be assumed when computing the exhaust gas enthalpy. This allows the calculation of the intake flow, which in turn provides a new exhaust gas composition, and so forth. By viewing the exhaust gas as a flow consisting of ambient air and combusted fuel, the described iteration can be avoided. The study presents the formulation of the energy balance applying this approach and looks at the accuracy of the result as a function of the inaccuracy of the input parameters. Furthermore, solutions of the energy balance are presented for various process scenarios, and the impact of the uncertainty of key process parameter is analyzed.

Modelling the Effect of External Flue Gas Recirculation on NOx and CO Emissions in a Premixed Gas Turbine Combustor With Chemical Reactor Networks

2018 ◽  
Author(s):  
V. Prakash ◽  
J. Steimes ◽  
D. J. E. M. Roekaerts ◽  
S. A. Klein
Keyword(s):  
Gas Turbine ◽  
Flue Gas ◽  
Recirculation Zone ◽  
Chemical Reactor ◽  
Inlet Temperature ◽  
Part Load ◽  
Flue Gas Recirculation ◽  
Reactor Networks ◽  
Gas Recirculation ◽  
The Impact

The increasing amount of renewable energy and emission norms challenge gas turbine power plants to operate at part-load with high efficiency, while reducing NOx and CO emissions. A novel solution to this dilemma is external Flue Gas Recirculation (FGR), in which flue gases are recirculated to the gas turbine inlet, increasing compressor inlet temperature and enabling higher part load efficiencies. FGR also alters the oxidizer composition, potentially leading to reduced NOx levels. This paper presents a kinetic model using chemical reactor networks in a lean premixed combustor to study the impact of FGR on emissions. The flame zone is split in two perfectly stirred reactors modelling the flame front and the recirculation zone. The flame reactor is determined based on a chemical time scale approach, accounting for different reaction kinetics due to FGR oxidizers. The recirculation zone is determined through empirical correlations. It is followed by a plug flow reactor. This method requires less details of the flow field, has been validated with literature data and is generally applicable for modelling premixed flames. Results show that due to less O2 concentration, NOx formation is inhibited down to 10–40% and CO levels are escalated up to 50%, for identical flame temperatures. Increasing combustor pressure leads to a rise in NOx due to thermal effects beyond 1800 K, and a drop in CO levels, due to the reduced chemical dissociation of CO2. Wet FGR reduces NOx by 5–10% and increases CO by 10–20%.

scholarly journals A Real-Time Degradation Model for Hardware in the Loop Simulation of Fuel Cell Gas Turbine Hybrid Systems

2015 ◽  
Author(s):  
Valentina Zaccaria ◽  
Alberto Traverso ◽  
David Tucker
Keyword(s):  
Fuel Cell ◽  
Real Time ◽  
Gas Turbine ◽  
Hybrid Systems ◽  
Current Density ◽  
Gas Turbines ◽  
Hardware In The Loop ◽  
Fuel Utilization ◽  
Time Operation ◽  
The Impact

The theoretical efficiencies of gas turbine fuel cell hybrid systems make them an ideal technology for the future. Hybrid systems focus on maximizing the utilization of existing energy technologies by combining them. However, one pervasive limitation that prevents the commercialization of such systems is the relatively short lifetime of fuel cells, which is due in part to several degradation mechanisms. In order to improve the lifetime of hybrid systems and to examine long-term stability, a study was conducted to analyze the effects of electrochemical degradation in a solid oxide fuel cell (SOFC) model. The SOFC model was developed for hardware-in-the-loop simulation with the constraint of real-time operation for coupling with turbomachinery and other system components. To minimize the computational burden, algebraic functions were fit to empirical relationships between degradation and key process variables: current density, fuel utilization, and temperature. Previous simulations showed that the coupling of gas turbines and SOFCs could reduce the impact of degradation as a result of lower fuel utilization and more flexible current demands. To improve the analytical capability of the model, degradation was incorporated on a distributed basis to identify localized effects and more accurately assess potential failure mechanisms. For syngas fueled systems, the results showed that current density shifted to underutilized sections of the fuel cell as degradation progressed. Over-all, the time to failure was increased, but the temperature difference along cell was increased to unacceptable levels, which could not be determined from the previous approach.

Status of the Automotive Ceramic Gas Turbine Development Program: Year Five Progress

1996 ◽  
Author(s):  
Tsubura Nisiyama ◽  
Norio Nakazawa ◽  
Masafumi Sasaki ◽  
Masumi Iwai ◽  
Haruo Katagiri ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Development Program ◽  
Ceramic Materials ◽  
Inlet Temperature ◽  
Test Rig ◽  
Target Values ◽  
Ceramic Components ◽  
Combined Test ◽  
And Performance ◽  
The Individual

Petroleum Energy Center of Japan has been carrying out a 7-year development program to prove the potential of an automotive ceramic gas turbine for five years with the support of the Ministry of International Trade and Industry. The ceramic gas turbine now under development is a regenerative single shaft engine. The output is 100kW, and the turbine inlet temperature (TIT) is 1350°C. All the ceramic components are now entering the 1350°C TIT test phase after completing 1200°C TIT evaluation tests, including durability tests, in various types of test rigs. The compressor-turbine combined test rig and the full assembly test rig which is the same as an actual engine and incorporates all the components are now going through 1200°C TIT function and performance evaluation tests. In the near future, we are planning to increase the TIT to 1350°C. In consideration of the current level of high-temperature, long-term strength available from the ceramic materials, we decided to change the rated speed to 100,000 rpm because the initial rated speed of 110,000 rpm, if unchanged, involves considerable risks. Then we reviewed mainly the designs of the compressor and turbine and revised the target values of the individual components to match the specifications that satisfy the target performance of the engine.

Experimental Investigation of the Performance of a Micro Gas Turbine Fueled With Mixtures of Natural Gas and Biogas

2013 ◽  
Author(s):  
Homam Nikpey ◽  
Mohsen Assadi ◽  
Peter Breuhaus
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Co2 Emissions ◽  
Fuel Mixture ◽  
Combined Heat And Power ◽  
Test Rig ◽  
Heating Value ◽  
Micro Gas Turbine ◽  
Fuel Mixtures ◽  
The Impact

Previously published studies have addressed modifications to the engines when operating with biogas, i.e. a low heating value (LHV) fuel. This study focuses on mapping out the possible biogas share in a fuel mixture of biogas and natural gas in micro combined heat and power (CHP) installations without any engine modifications. This contributes to a reduction in CO2 emissions from existing CHP installations and makes it possible to avoid a costly upgrade of biogas to the natural gas quality as well as engine modifications. Moreover, this approach allows the use of natural gas as a “fallback” solution in the case of eventual variations of the biogas composition and or shortage of biogas, providing improved availability. In this study, the performance of a commercial 100kW micro gas turbine (MGT) is experimentally evaluated when fed by varying mixtures of natural gas and biogas. The MGT is equipped with additional instrumentation, and a gas mixing station is used to supply the demanded fuel mixtures from zero biogas to maximum possible level by diluting natural gas with CO2. A typical biogas composition with 0.6 CH4 and 0.4 CO2 (in mole fraction) was used as reference, and corresponding biogas content in the supplied mixtures was computed. The performance changes due to increased biogas share were studied and compared with the purely natural gas fired engine. This paper presents the test rig setup used for the experimental activities and reports results, demonstrating the impact of burning a mixture of biogas and natural gas on the performance of the MGT. Comparing with when only natural gas was fired in the engine, the electrical efficiency was almost unchanged and no significant changes in operating parameters were observed. It was also shown that burning a mixture of natural gas and biogas contributes to a significant reduction in CO2 emissions from the plant.

Through Flow Calculations for Convective Cooling Turbines

2014 ◽  
Author(s):  
Li Haibo ◽  
Chunwei Gu
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Calculation Method ◽  
Conjugate Heat Transfer ◽  
High Efficiency ◽  
Thermodynamic Efficiency ◽  
Inlet Temperature ◽  
Flow Calculation ◽  
Through Flow ◽  
The Impact

Conjugate heat transfer is a key feature of modern gas turbine, as cooling technology is widely applied to improve the turbine inlet temperature for high efficiency. Impact of conjugate heat transfer on heat loads and thermodynamic efficiency is a key issue in gas turbine design. This paper presented a through flow calculation method to predict the impact of heat transfer on the design process of a convective cooled turbine. A cooling model was applied in the through flow calculations to predict the coolant requirements, as well as a one-dimensional mixing model to evaluate some key parameters such as pressure losses, deviation angles and velocity triangles because of the injection cooling air. Numerical simulations were performed for verification of the method and investigation on conjugate heat transfer within the blades. By comparing these two calculations, it is shown that the through flow calculation method is a useful tool for the blade design of convective cooled turbines because of its simplicity and flexibility.

Off-Design Performance Investigation of a Low Calorific Value Gas Fired Generic-Type Single-Shaft Gas Turbine

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Raik C. Orbay ◽  
Magnus Genrup ◽  
Pontus Eriksson ◽  
Jens Klingmann
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Pressure Ratio ◽  
Calorific Value ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Flammability Limits ◽  
Generic Type ◽  
Wobbe Index ◽  
The Impact

When low calorific value gases are fired, the performance and stability of gas turbines may deteriorate due to a large amount of inertballast and changes in working fluid properties. Since it is rather rare to have custom-built gas turbines for low lower heating value (LHV) operation, the engine will be forced to operate outside its design envelope. This, in turn, poses limitations to usable fuel choices. Typical restraints are decrease in Wobbe index and surge and flutter margins for turbomachinery. In this study, an advanced performance deck has been used to quantify the impact of firing low-LHV gases in a generic-type recuperated as well as unrecuperated gas turbine. A single-shaft gas turbine characterized by a compressor and an expander map is considered. Emphasis has been put on predicting the off-design behavior. The combustor is discussed and related to previous experiments that include investigation of flammability limits, Wobbe index, flame position, etc. The computations show that at constant turbine inlet temperature, the shaft power and the pressure ratio will increase; however, the surge margin will decrease. Possible design changes in the component level are also discussed. Aerodynamic issues (and necessary modifications) that can pose severe limitations on the gas turbine compressor and turbine sections are discussed. Typical methods for axial turbine capacity adjustment are presented and discussed.

scholarly journals Status of the Automotive Ceramic Gas Turbine Development Program: Year 3 Progress

1994 ◽  
Author(s):  
Takane Itoh ◽  
Hidetomo Kimura
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Performance Test ◽  
Development Program ◽  
Turbine Rotor ◽  
Maximum Speed ◽  
Inlet Temperature ◽  
Test Rig ◽  
Thermal Test ◽  
The Individual

Under the ongoing seven-year program, designated “Research and Development of Automotive Ceramic Gas Turbine Engine (CGT Program)”, started in June 1990. Japan Automobile Research Institute. Inc. (JARI) is continuing to address the issues of developing and demonstrating the advantageous potentials of ceramic gas turbines for automotive use. This program has been conducted by the Petroleum Energy Center (PEC) with the financial support of MITI. The basic engine is a 100 kW, single-shaft regenerative engine having a turbine inlet temperature of 1350°C and a rotor speed of 110,000 rpm. In the third year of this program, the experimental evaluation of the individual engine components and various assembly tests in a static thermal test rig were continued. Exhaust emissions were also measured in a performance test rig for an initially designed pre-mixed, pre-vaporized lean (PPL) combustor. A maximum speed of 130,700 rpm was obtained during hot spin tests of delivered ceramic turbine rotors, which was almost the same level as during cold spin tests. A dynamic thermal test including a centrifugal compressor, a ceramic radial turbine rotor and all the ceramic stationary hot parts was initiated.

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