Applications of Centrifugal Pumps

Centrifugal Pumps are the most popular and commonly used type of pump for the transfer of any type of fluid. The volumetric flow rate range of centrifugal pumps can vary from several tens of ml/hour to  one hundred thousand m3/hour , while the pressure can be normal pressure to nearly 20MPa; and the liquid temperature can be as low as -200℃ or as high as 800℃. The fluid being transferred can be water (clean or sewage), oil, acid or alkali, suspension or liquid metal, etc. Therefore, centrifugal pumps are used across numerous industries:

  1. In the oil and gas or chemical industries, converting crude oil to products requires a complex process. Pumps play an important role in transferring these liquids, providing the required pressure and flow rate for chemical reactions. Sometimes, pumps are used to adjust temperature in certain parts of the system.
  2. In agriculture, centrifugal pumps are used in the majority of irrigation machinery. Agriculture pumps make up half of the total amount of centrifugal pumps being used today.
  3. In mining and metallurgy industries, centrifugal pumps are the most widely used equipment, for draining, and cooling of water supplies, etc.
  4. For power generation, the nuclear power plants need large amounts of primary, and secondary system pumps, while the thermal power plants also need boiler feed pumps, condensate pumps, loop pumps and as well as ash pumps.
  5. In military applications, the adjusting of airplane wings and rudders, turning of turret on ships and tanks, the up and down of submarines, all rely on pumps for hydraulic fluids.
  6. In shipbuilding, there are more than 100 different types of pumps in one typical ocean ship.
  7. Other applications include municipal water supplies and drainage; water supplies of locomotives; lubricating and cooling of machining equipment; bleach and dye transfer of textile industry; and milk and beverage pumping and sugar refining in the food industry.

 

Centrifugal pumps can be classified based on the number of impellers in the pump:

A single-stage pump, with only one impeller, is commonly used for high flow and low to moderate total dynamic head, as in Figure 1.

Single Stage Centrifugal Pump
Figure 1. Single Stage Centrifugal Pump

A multi-stage pump has two or more impellers working in a series to achieve higher total dynamic head.
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Can a sales team select the right turbomachinery for a client without bothering the engineering team?

This might seem like a strange question, but we get ask this a lot. The question takes the form of: Can the sales side do a proper preliminary design and select the optimal machine (turbine/compressor/pump)?  Is it possible for the design and application task to be integrated in a way allowing the application team the autonomy to make decisions without going back to the engineering team every time they get an inquiry? After realizing how large of a pain point this is for our clients, we decided to solve this problem for a major turbine manufacturer in Asia and in the process, provided a time-saving solution to maximize the returns for all the stakeholders.

The challenge came with the different competencies of the sales and design team. The sales/application teams are not necessarily experts in design while designers cannot double as application engineers to meet the sales requirements.

In our efforts to solve this issue, we worked with this turbine manufacturer. We listed all of their current processes, limitation, requirements, constraints, and etc. to explore the many possible ways to resolve this pain point. In the end, there were two solutions; (1) Develop custom selection software, or (2) Leverage the AxSTREAM® platform using AxSTREAM ION™.

    1. Developing Custom Selection Software: Developing a custom selection software specific to the manufacturer where their application team can choose the optimal turbine based on expected customer needs. Developing such a custom system requires bringing together the expertise of different teams from turbomachinery (such as aero-thermal and structural) to software developer, testing, etc. Developing such a one-off system also takes considerable time at considerable cost. This approach could solve the current problem, but with rapidly changing technologies and market requirements, this is not a viable long-term solution.
    2. Leverage the AxSTREAM® Platform using AxSTREAM ION™: We evaluated the limitation and possibilities of utilizing our turbomachinery design platform AxSTREAM® to meet the requirement of sales/application engineering team for today’s needs and in the future. We found the organization had a greater advantage using this existing platform rather than investing in the short-term solution of developing a custom selection software. Many of the building blocks required for customization are already available to use via an interface a non-technical sales person could easily use. This platform was utilized for meeting the requirement of this turbine manufacturer saving time and cost while resolving a large pain-point for the organization.

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Demystifying S1-S2 Optimization in Turbomachinery

  1. Historically turbomachinery development began with empirical rules postulated by early pioneers. With the need for jet engine for aircraft propulsion, dimensionless analysis became popular, followed by the 1 D mean line design and 2D meridional methods. Today 2D meridional methods with 3D blade to blade CFD/FEA methods are a necessity as efficiency and reliability requirements are further pushed.

 

  1. One key aspect of 2D meridional design is S1-S2 optimization, which is a time consuming, laborious task and hence subject to human errors. S1-S2 optimization is a task of reviewing, adjusting and optimizing the flow path in the Tangential (S1 or blade-to-blade or pitchwise) and the Meridional (S2 or span wise) planes. The main purpose is to:
  • Fit the flow path to specific meridional dimensional constraints
  • Adjust blade-to-blade parameters while taking into account structural constraints.

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The Optimization Challenge in the Development of Turbomachinery

Optimization (or parametric studies) of a twin spool bypass turbofan engine with mixed exhaust and a cooled turbine can be considered one of the most complex problem formulations. For engine selection, determining the thrust specific fuel consumption and specific thrust is necessary against variables such as design limitations (Inlet temp, etc.), design choices (fan pressure ration, etc.) and operating conditions (speed & altitude). The task involves cycle level studies following machine, module, stage and component level optimization. This calls for an integrated environment (IE) and it is desirable to have such an IE operating on a “single” platform.

Historically IE was developed for the design of axial turbines (mainly steam). Later, it was expanded for gas turbines (especially blade cooling calculations) and axial compressors via plug-in modules. The new challenge designers face today is developing mixed flow machinery. An effective system for modern turbomachinery design needs to do the following:

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Steam Heat & Mass Balance Considerations in Refineries

Optimizing the heat and mass flow i.e. steam balance in a plant that has several levels of steam pressures is not a simple task due to the vast array of equipment such as turbines, heat exchanges, steam auxiliaries and accessories used. The steam balance of a refinery plant is further complicated because of use of steam for chemical processes and compression. Depending on processor licensor, technologies and many other traditional factors, it is not uncommon to see steam pressure levels defined in refineries as simply HP & LP or HP,MP & LP or as complex as VHP, HHP, HP, MP and LP.

The traditional approach to designing a steam system is to install steam generators able to generate steam at the maximum pressure and temperature with enough redundancy in capacity as required by the process. Modern steam generators tend to be inclined towards higher pressure steam rather than lower pressure steam – saturated high pressure steam has higher temperature meaning  less exchange surface in heat exchangers and reboilers, high density of high pressure steam requires less bore in the steam mains. Consequently, the usage of high pressure steam represents less capital expenditure. The resultant philosophy is to generate steam at the highest possible temperature and pressure, expand steam from a higher pressure to a lower pressure level through the most efficient means possible and use process at the lowest economically attractive pressure and temperature.

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Rotating Equipment Specialist in the Oil and Gas Industry – A Turbomachinery Professional

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.Oil and Gas

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.

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What Turbomachinery does to Avert Climate Change (Part 2 of 2)

Last week I described two ways which the turbomachinery industry addresses climate change. This week, I explain two more:

  1. Waste Heat Recovery

Even though processes are becoming more and more efficient they are still mostly wasteful (Figure 1).

Figure 5 Typical energy distribution in a system
Figure 1 Typical energy distribution in a system

The excess energy from processes is eventually released into the environment but bringing down the temperature of the exhaust allows multiple things; direct reduction of the global warming potential as well as possibility to utilize this heat to boil a working fluid before running it through a turbine where it can generate some power without requiring burning additional fuel. A well-known example of such a system is the traditional gas-steam cycle that allows turning a 45% efficient gas turbine cycle into a 60% system by utilizing the gas turbine exhaust heat to boil some water in a secondary loop before passing the resulting steam through a different turbine. In the same manner waste heat recovery can be applied with different fluids (including the trending refrigerants like R134a & R245fa, steam and the state-of-the-art supercritical CO2 as shown on Figure 2) and a multitude of applications; internal combustion engines, steel production plants, marine transports, etc.

Figure 6 Example of a simple, recuperated Brayton, supercritical CO2 cycle that uses the exhaust flow of a gas turbine to heat its working fluid
Figure 2 Example of a simple, recuperated Brayton, supercritical CO2 cycle that uses the exhaust flow of a gas turbine to heat its working fluid
  1. Selection of the best working fluid

Whether it’s deciding to design the main energy conversion cycle or its waste heat recovery system one of the critical parameters to pay close attention to is the working fluid selection; good selection of the fluid will often lead to make a compromise between cost/availability, thermodynamic performance (see Figure 3) and environmental friendliness. One must make sure that the performances of the designed cycle with the chosen fluid are high enough and the fluid cheap enough to make the concept financially viable without sacrificing pollution considerations which can prove devastating in case of leaks.

Figure 7 Example of a fluid performance comparison at different temperatures
Figure 3 Example of a fluid performance comparison at different temperatures

The working fluid selection is also performed so that in addition to the environmental footprint being reduced the physical footprint is minimized as well; this is done through the selection of high density fluids (helium, SCO, etc.) which allows for a reduction in component size and therefore cost (as portrayed on Figure 4), – indirectly it also allows for less material being produced which also “saves trees”.

Figure 8 Example of difference in power density between supercritical carbon dioxide (left) and steam (right) for a 10 MW power turbine
Figure 4 Example of difference in power density between supercritical carbon dioxide (left) and steam (right) for a 10 MW power turbine

What Turbomachinery does to Avert Climate Change (Part 1 of 2)

Most people complain about climate change, but few take measures to address it. In this article we will see some ways turbomachinery-oriented companies contribute to the well-being of the planet.

  1. Selection and optimization of energy conversion technology (recuperation, proper selection of expander configuration, etc.)

Not all technologies are created equal; where you would use a steam turbine is not necessarily where you would want a gas turbine or an organic Rankine cycle (ORC) instead. Each one of them has its pros and its cons; ORC exist because they do not require as much energy as what is needed for steam cycles, gas turbines have a great power density and an outstanding start-up time (several minutes instead of hours) which makes them great candidates for punctual, unexpected peaks in power demand, etc.

Figure 1 Simple Rankine cycle schematics
Figure 1 Simple Rankine cycle schematics

Now, take the case of a gas, steam or ORC; they all include, in their most basic configuration, a compressing element (compressor or pump), an expander (usually a turbine), a cooling/condensing component and a heating component (boiler, combustion chamber, HRSG, etc.) as one can see on Figure 1 and each of these have an associated efficiency.

This means that their careful design and thorough optimization should be performed in order to maximize the overall performance of the full system. Whether it’s used for power generation or propulsion the result is the same; more power generated for the same amount of heat input (usually the combustion of fuel). However, before starting the full design of the different components the entire system needs to be optimized as well; correct positioning of extractions/inductions, appropriate cooling parameters, use of recuperation/regeneration (see Figure 6), and so on.

Figure 2 Recuperated Rankine cycle
Figure 2 Recuperated Rankine cycle

 

Only when the cycle boundary conditions (and therefore its configuration) are fixed the full design of the components can be performed although some preliminary studies should be undertaken to determine the feasibility of these designs and get an estimation of the components performances. Another goal of such feasibility studies is to determine such things as the estimated dimensions of the components, the configuration of the expander (axial, radial, axi-radial, counter-rotating, etc.) Finally some compromises always need to be done between efficiency improvement and cost of manufacturing, operation and maintenance.

 

 

 

  1. Operation at optimal conditions (design point for overall cycle and each component)
Figure 3 Comparison of efficiency and power rating for axial and radial configurations of turbines
Figure 3 Comparison of efficiency and power rating for axial and radial configurations of turbines

Each energy conversion system whether it is for power generation, propulsion or any other application is designed for a set of operating conditions called a design point. This is where the system will typically be optimum for and where it will be running most of its “on” time. This is why ensuring that the design point (or design points) is accurately defined is critical since operation outside of these defined conditions will lead to additional losses that translate into a lesser power production for the same cost of input energy. Performance prediction of systems at off-design conditions is an essential part of any design task which allows restricting system operation to conditions of high components efficiency. If the pump/compressor is operated at a different mass flow rate its pressure ratio will be different and so will be the efficiency and therefore the amount of power generated by the expander, see Figure 4.

Figure 4 Performance map of a centrifugal compressor showing its efficiency as a function of the mass flow rate for different rotation speeds
Figure 4 Performance map of a centrifugal compressor showing its efficiency as a function of the mass flow rate for different rotation speeds

In our next post, we will continue the discussion of the turbomachinery industry as it relates to climate change. Stay tuned!

Siemens to Acquire Dresser-Rand

desserIt was announced this week that Siemens, a German electronics and engineering company, has made a deal to purchase Dresser-Rand, a US-based oilfield equipment manufacturer. This agreement concludes a bidding war between Siemens and Sulzer, a Swiss pump manufacturer.

siemensThe deal, worth $7.6 billion, will give Siemens direct access to US domestic oil production, a sector currently booming from new extraction techniques like hydraulic fracturing. Houston, Texas is a primary hub for the oil industry and this location is an ideal place for Siemens to enter the growing US market. Siemens has already played a role in the US power industry, mainly with its production of gas turbines. The company is also purchasing Rolls-Royce Holdings PLC’s energy gas turbine and compressor business, including its Houston operations. Continue reading “Siemens to Acquire Dresser-Rand”

Sustainable Turbomachinery

iStock_000015544357MediumThis past Tuesday was the 44th celebrated Earth Day. On Earth Day, more than 100 countries join together to literally stop and smell the roses, appreciate the splendor and beauty of Mother Nature and take extra efforts to be more conscientious for our shared home.

Turbomachinery, though not always the first thing that comes to mind when speaking on the subject of green technology, plays an important role toward our efforts for a more sustainable environment.
Continue reading “Sustainable Turbomachinery”