At these off-design conditions, the gas turbine efficiency and life deterioration rate can significantly deviate from the design specifications. During a gas turbine’s life, power generation providers may need to perform several overhauls or upgrades for their engines. Thus, the off-design performance after the overhaul can also change. Prediction of gas turbine off-design performance is essential to economic operation of power generation equipment. In the following post, such a system for complex design and off-design performance prediction (AxSTREAM®) is presented. It enables users to predict the gas turbine engine design and off-design performance almost automatically. Each component’s performance such as the turbine, compressor, combustor and secondary flow (cooling) system is directly and simultaneously calculated for every off-design performance request, making it possible to build an off-design performance map including the cooling system. The presented approach provides a wide range of capabilities for optimization of operation modes of industrial gas turbine engines and other complex turbomachinery systems for specific operation conditions (environment, grid demands more).
With AxSTREAM®, people are given several options for their design criteria, which provides flexibility. With that being said, we often get asked what their differences are and here is a brief explanation addressing just that.
The design criteria menu includes power, internal total-to-static efficiency, internal total-to-total efficiency, polytropic efficiency, diagram total-to-static efficiency, and diagram total-to-total efficiency as shown in Figure 1
Power and efficiency are related, but not always the same thing, especially when the boundary conditions are not fixed as design parameters. In AxSTREAM’s Preliminary Design Module, the user can set boundary conditions such as pressure at inlet and outlet, inlet total temperature, etc., as a range instead of a specific value. Along with other parameters, the solver generates hundreds or even thousands of solutions within the range.
The second part of my posts focused on different industries that rely on turbomachinery as we tried to identify the challenges that they face. Being fascinated by the space industry along with the increasing interest of the global market for launching more rockets for different purposes, I started this chapter with the description of a liquid rocket propulsion system and how this can be designed or optimized using the AxSTREAM platform. Moving a step closer to earth, next I focused on the aerospace industry and the necessity for robust aircraft engines that are optimized, highly efficient, and absolutely safe. One of the articles that I enjoyed the most referred to helicopters and the constant threats that could affect the engine performance, the overall operation and the safety of the passengers. Dust, salt and ice are only a few of the elements that could affect the operation of the rotating components of the helicopter engine, which allows us understand how delicate this sophisticated and versatile aircraft is.
As a thermodynamic Brayton cycle, the performance of the gas turbine engine is influenced by the turbine inlet temperature, and the raise of this temperature can lead to better performance and more efficient machines. Current advancements in the development of cooling systems allows most modern gas turbines to operate in temperatures much higher than the material melting point. Of course nothing would have been possible without the parallel development of advanced materials for structural components as well as advances in computing resources and consequently in aerodynamic design, prognostic and health monitoring systems and lifing processes. In particular, as far as the lifing of the machine is concerned, the high pressure (HP) turbine containing the most advanced high temperature alloys and associated processing methods, as well as the combustor which represents the key components that have limited life and tend to strictly dictate the cycles of operation and the allowable time on the wing.
Thermal energy storage can be achieved with widely diverse technologies, including molten salt application. By heating the salt and storing it in insulated containers, users can pump out the salt to release the heat stored when the energy is needed. For example, with solar application the molten salt stores the excess heat that is produced during the day and releases it at night to produce electricity.
To go back to the question, blade tip losses represent a major efficiency penalty in a turbine rotor. These losses are presently controlled by maintaining close tolerances on tip clearances. Tip leakage resulting by gaps between the blade tip and the casing can account for about 1/3 of the total losses in a turbine stage. The reason is mainly the offloading of the tip since the leaking fluid is not exerting a force on the blade, as well as the generation of complicated flow further downstream due to the leakage vortex.
Centrifugal compressors span a number of applications including oil compression systems, gas shift systems, HVAC, refrigeration, and turbochargers. It works by using energy from the flow to raise pressure, using gas to enter the primary suction eye (impeller). As the impeller rotates, the blades on the impeller push the gas outwards from the center to the open end of impeller to form a compression. Compressors are commonly used for combustion air supplies on cooling and drying systems. In HVAC system application, fans produce air movement to the space that is being conditioned. As a key component of an energy cycle, design/performance requirement must be met. While a design can easily be scaled from an existing design through appropriate parameters, a tailored design from scratch to confirm with design requirement for the specific cycle would give a better match and improve overall cycle performance.
There are variants of non-aerodynamic constraints in centrifugal compressor design practice, from frame size to durability and ultimately cost. An optimized impeller design should also ensure that aerodynamic problems associated with the all compressor components are minimized. With all of these (aerodynamic and non-aerodynamic) design constraints, there is no better way to optimize your compressor design than starting from the preliminary step, making sure that your compressor meets your criteria from a one dimensional basis ( a step that is often overlooked in practice).
Over the years, as steam turbine technology advanced, the design principles were based on either impulse type or reaction type with reaction type being more efficient. Though impulse was not as efficient as reaction type, it gained popularity due to lower cost and compact size. With advances in design and optimization methods being employed, the efficiency levels between these two types are not very distant, ranging between 2 – 5% based on the size and application. Read More
One of the main goals in power generation practice is to deliver the lowest possible cost per unit of electricity to meet the growing demand. Often in practice, economic assessment of a power plant is depicted by their levelized cost of energy (LCOE), also known as levelized energy cost (LEC), which is the average price per unit of power delivered to break even with total cost (capital and operating) over the length of its operating lifetime.
Generally, cost factor which contributes to power generation can be categorized into two main groups: capital cost and operating charges. Capital cost (usually consisting of a series of fixed cost factors which do not vary with the level of output) encompasses equipment, rent/land cost, and any other costs associated with the establishment of the power generation plant, up until when it’s ready to operate. This is a critical data point needed for accurate investment decision making. Whereas operating cost (combination of fixed, semi-fixed and variable charges) covers all costs related to daily operational and/or production cost incurred – which should include maintenance, fuel, feed water, etc.