Steam turbine technology has advanced significantly since it was first developed by Sir Charles Parson in 1884 . The concept of impulse steam turbines was first demonstrated by Karl Gustaf Patrik de Laval in 1887. A pressure compounded steam turbine based on in de laval principle was developed by Auguste Rateau in 1896. Westinghouse was one of the earliest licensee for manufacturing steam turbines obtained from Sir Charles Parson and became one of the earliest Original Equipment Manufacturers (OEM) in power generation and transmission.
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
Often, service companies are faced with the challenge of redesigning existing pumps that have failed in the field with extremely quick turnaround times. While there are quick-fix methods to return these pumps into operation, other more complex problems may require taking a step back and analyzing how this particular pump could be redesigned based on its current operation. These engineering upgrades could solve recurring issues with failure modes of a certain machine, and they could also solve new capacity demands that are imposed by a customer based on their system’s upstream or downstream changes. While efficiency increases could be beneficial to the overall system, many times it is more important to solve capacity requirements and increase the life of the pump by decreasing the Net Positive Suction Head Required (NPSHr).
In this blog post, we will investigate how to move an existing centrifugal pump through the AxSTREAM platform in order to solve engineering challenges seen on common OEM pump upgrades. With the use of AxSTREAM’s integrated platform and reverse engineering module, many of the CAE tasks that are common in an analysis such as this one can be realized in record speed. The first step of the reverse engineering process occurs in obtaining the necessary geometrical information for the desired pump. Through AxSLICE, the user can take an STL, IGES, CURVE file, or a generated cloud of points and properly transform this 3D profile into a workable geometry inside the AxSTREAM platform. In a matter of minutes, the user can outline the hub and shroud and transform a blank 3D profile into a profile defined by a series of segments. Seen in Figure 1, the centrifugal pump is now defined by a hub, shroud, and intermediate section.
Steam turbines are designed to have long, useful lives of 20 to 50 years. Often, many parts of steam turbine are custom designed for each particular application, however, standardized components are also used. It is therefore inherently possible to effectively redesign a steam turbine several times during its useful life while keeping the basic structure (foot print, bearing span , casing etc) of these turbines unchanged! Indeed this is also true for many turbomachines. These redesigns are usually referred to as rerates and upgrades, depending on the reasons for doing them. The need for changes to hardware in an existing turbine may be required for (a) efficiency upgrades, (b) reliability upgrade (including life extension), (c) rerating due to a change in process (Process HMDB, use in combined cycle etc), and (d) modification for a use different from that of its original design. Typical changes include hardware components such as buckets/blades, control system, thrust bearing , journal bearing , brush and laby seals, nozzle/diaphragm , casing modification, exhaust end condensing bucket valves, tip seals and coatings.
Performance and Efficiency Upgrade The basic power and/or speed requirements of a steam turbine may change after commissioning for various reasons. The most common reason is an increase (or decrease) in the power required by the driven machine due to a plant expansion or de-bottlenecking. Other reasons include a search for increased efficiency, a change in the plant steam balance, or a change in steam pressure or temperature. Because steam turbines are periodically refurbished, an opportunity exists to update the design for the current operating environment. Turbine OEM’s , services companies and end users often face a challenge of undertaking engineering work within the very tight time frame available for maintenance. The AxSTREAM® software suite provides users with an automated capability of rerate, upgrade and modifications for performance and efficiency objectives. A summary of such features highlighting the capabilities is presented below:
Axial and mixed flow fans have been in high demand for a number of years. The application of these machines span many different industries including HVAC, automotive, appliance, military equipment, and much more. Like many other types of turbomachinery, changing industry standards and market trends have resulted in fierce rivalry to compete on lifespan, efficiency, environmental and user friendliness, and overall quality. With this in mind, it goes without saying that companies are looking for tools needed to develop highly efficient equipment while minimizing noise as quiet fans are typically more desirable which results in higher demand and marketability.
Turbomachinery is a core subject in many engineering curriculums. However, many graduates joining the oil and gas industry are designated as rotating equipment engineers. Though turbomachinery and rotating equipment are used synonymously, all turbomachinery are rotating equipment but not vice versa. Turbinis in Latin implies spin or whirl, and a natural question that arises is – what are the factors that differentiate turbomachinery? In a general sense the term, “rotating” covers the majority equipment used in the industry be it in the upstream, mid-stream or the downstream segment. Yet top rotating equipment specialist in the industry are seen spending their prime time or often being associated with certain unique and specific types of critical rotating machines – the turbomachines.
In a classical sense, turbomachines are devices in which energy is added into or taken out from a continuously ﬂowing ﬂuid by the dynamic action of one or more moving blade rows. By this definition propellers, wind turbines and unshrouded fans are also turbomachines but they require a separate treatment. The subject of ﬂuid mechanics, aerodynamics, thermodynamics and material mechanics of turbomachinery when limited to machines enclosed by a closely ﬁtting casing or shroud through which a measurable quantity of ﬂuid passing in unit time makes the practical linkage to rotating equipment – those which absorb power to increase the ﬂuid pressure or head (fans, compressors and pumps) and those that produce power by expanding ﬂuid to a lower pressure or head (hydraulic, steam and gas turbines). Further classification into axial, radial and mixed type (based on flow contour), and impulse & reaction (based on principle of energy transfer) is common. It is the large range of service requirement that leads to different type of pump (or compressor) and turbine in service.
The demands of the plant construction and energy sector after a shorter response time for questions upon newly defined operating points of a turbomachine train are one of the biggest challenges in the service business. This becomes particularly obvious if the future points can only be realized by redesigning the flow-relevant components. Often, it is necessary to have more time to check the dynamic behavior of the train, than in the development of the appropriate revamp measures for the core machine itself.
In addition to the different utilization rates of the affected departments, the causes of the delays often lie in the lack of interface quality between the design/ calculation and train integration team. On top of that, a certain amount of time will be required by manufacturers of the critical components such as gearboxes or drives to perform a lateral check. This lateral check is not only mandatory, in case of a component modification such as changing the transmission ratio or upgrading the drive, but it is also necessary if the coupling between the train components must be changed to ensure torsional stability.
When deciding on a new product line, manufacturers of turbomachines and their engineering teams must often decide whether to rescale a product that they already manufacture or to begin a full design process for a completely new machine. For example, a producer of 5 MW axial turbines wants to start manufacturing 10 MW turbines, does it make sense to create a brand new design from scratch or to simply scale up the 5 MW turbine they already produce to a similar 10 MW version? To answer this question, many considerations have to be taken into account, the general answer however is, that it is almost always a better idea to start a new design.
Improved Design Technology
Many manufacturers wrongly believe that by simply scaling their current product that they will save not only on design costs, but that they can leverage their existing manufacturing capabilities to stamp out a similar product. What is not factored in however is the progress of design technology and theory since their original machine was first conceptualized. The result from a simple scaling process will simply be a less optimized and efficient machine for any use as compared to a new configuration using the latest in design software. Increasing software sophistication and computing power are constantly pushing the boundaries of efficiency while minimizing operating costs. Simply put, your competitors will have designed a superior product compared to yours.
AxSTREAM 3D Blade Design Software
When was your current machine designed? Many older machines were created using materials that by today’s standards are simply not capable of operating at the extreme conditions (mostly temperatures) required today to attain the energy efficiency requirements set up by ever increasing regulations. Depending on materials used, the optimal blading structure, bearings, etc. geometries would be significantly unique. If one were to simply scale up their current product, they would either be using old materials or have inefficiently designed machine components for a different material. In either case, their scaled machine will be inferior to a configuration that was conceptualized and optimized from scratch.
Another very significant aspect of machine resizing is that it is not a straight forward process; if you want to double your power generation in a turbine for example you are not going to be doubling the blade size or mean diameter, for example, even when considering the same boundary conditions (inlet pressure and temperature, as well as, outlet pressure, rotation speed, and so on). For each specific set of conditions, fluid, rotation speed, mass flow rate, etc. a unique flow occurs inside the different blades. Changing one parameter will lead to changes in the flow and therefore result in inefficiencies, as it is what happens in off-design conditions (the machine is not operating at its maximum performance). This is why flow similarity parameters become relevant.
Machine Purpose and Type
One of the obvious questions to ask is, what is the purpose of my new machine and how much larger (or smaller) will I need it to be? If the new machine is intended for use with a completely different fluid, a new design will be optimal as different fluids interact in unique ways with varied rotor and stator configurations.
The machine type that you are considering is also critical to the decision. Different turbomachines do not scale in similar fashion with increase in size. For instance, radial turbines are usually not as efficient as axial turbines when one starts to approach the 2 MW range. In this instance the ideal solution is for a complete redesign since a smaller scale version that the manufacturer may have had would not be configured to operate at higher power ranges efficiently.