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!

How much more can I get with what I have?

Gas turbines are continuing their trend in becoming more efficient with each generation. However, the rate at which their efficiency increases is not significant enough to match more and more constraining environmental goals and regulations. New technologies like combined cycles therefore need to be used to increase cycle-specific power (more power produced without burning additional fuel).

The first generation of combined cycles featured a bottoming steam cycle that uses the heat from the gas turbine exhausts to boil off water in order to power a turbine and generate power. This traditional approach has been around since about 1970 and nowadays allows obtaining an additional 20% in cycle thermal efficiency (40% in simple gas turbine cycle configuration vs. 60% as a combined gas-steam cycle).

Figure 1: General efficiency increases over time for simple and combined cycle gas turbines
Figure 1: General efficiency increases over time for simple and combined cycle gas turbines
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
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

While this traditional approach is definitely effective, it does have some drawbacks; the equipment usually takes a significant amount of 3D space, there is always the risk of corrosion and substantial structural damage when working with 2-phase fluids, and so on. This, therefore, allows for different technologies to emerge, like supercritical CO2 cycles.

A supercritical fluid is a fluid that is used above its critical pressure and temperature and therefore behaves as neither a liquid nor a gas but as a different state (high density vs gas, absence of surface tensions, etc.). As a working fluid, supercritical CO2 has numerous advantages over some other fluids, including a high safety usage, non-flammability/toxicity, high density, inexpensiveness and absence of 2-phase fluid.

 

Figure 3: Example of difference in power density between supercritical carbon dioxide (left) and steam (right) for a 10 MW power turbine
Figure 3: Example of difference in power density between supercritical carbon dioxide (left) and steam (right) for a 10 MW power turbine

Moreover, steam turbines are usually difficultly scalable to small capacities which mean that they are mostly used in a bottoming cycle configuration for high power gas turbines. On the other hand supercritical CO2 (Rankine) cycles can be used for smaller machines as well as the bigger units while featuring an efficiency comparable to the one of a typical Rankine cycle and estimated lower installation, operation and maintenance costs.

Figure 4 Cycle efficiency comparison of advanced power cycles (source: A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors. Dostal, V., 2004
Figure 4 Cycle efficiency comparison of advanced power cycles (source: A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors. Dostal, V., 2004

The paper I presented at the ASME Power & Energy 2015 compares different configurations of SCO2 bottoming cycles for an arbitrary case for different boundary conditions before applying the selected cycle to a wide range of existing gas turbine units. This allowed determining how much additional power could be generated without needing to burn additional fuel and the results were far from insignificant! For the machines studied the potential for power increase ranges from 15% to 40% of the gas turbine unit power. Want to know how much more power you can get with your existing machines? Contact us to get a quote for a feasibility study before designing the waste heat recovery system yourself or with our help.

Innovative Boost of Larger Internal Combustion Engines

The last few decades have brought with them a dramatic increase in the development and use of turbochargers in automobiles, trains, boats, ships, and aircrafts. There are several reasons for this growth, including rising demand for fuel efficiency, stricter regulations on emissions, and advancements in turbomachinery design. Turbochargers are appearing more and more and are replacing superchargers.

turbocharger
Turbocharger

 

Turbochargers are not the only turbomachinery technology growing in popularity in the marine, automobile, and railroad industries. Organic Rankine Cycles are being applied to take advantage of the exhaust gas energy and boost engine power output. ORCs, a system for Waste Heat Recovery, improve the overall efficiency of the vehicle, train, or boat, and reduce specific emissions.

As the size of the engines we consider increases, there is more heat available to recuperate, and more potential WHR systems to use. For instance, we can consider different combinations of these systems with both non-turbocharged and turbocharged engines. We are able to design and compare engine boost system combinations, with and without a turbocharger, with and without a blowdown turbine, and with and without a WHR system, at the cycle and turbine design levels.

In our upcoming webinar, we will do just that. We will design different combinations for larger ICEs and compare the results. This webinar will also cover introductions to these systems and application examples for supplementary power production systems in the automotive and marine industries.

We hope you can attend! Register by following the link below.

Register

 

Throwback Thursday Webinar – Green Energy and ORC

It’s #ThrowbackThursday and we’re sharing one of our past webinars called “Green Energy – Turbomachinery for Organic Rankine Cycles.”iStock_000015544357Medium

Growing global demand for energy coupled with environmental concerns from the prevalence of fossil fuel usage has created a strong demand for new sources of clean energy. This demand has inspired scientists and engineers to search for and propose new solutions to generate greener, cleaner energy. One of the new methodologies which has been proposed is generating electricity from low temperature heat sources, the Organic Rankine Cycle being among the most widely used. Such popularity encouraged innovation in the area, and inspiring various design modifications in conjunction with low temperature heat sources and with a wide range of power rates. Continue reading “Throwback Thursday Webinar – Green Energy and ORC”

Should You Be Implementing the Organic Rankine Cycle?

To have a successful application of an ORC system, the availability of an adequate heat source is crucial. In principal every heat-generating process, such as burning fossil fuel, can be taken as a heat source for ORC.

However, the aim is to improve energy efficiency and sustainability of new or existing applications with the focus on waste heat and renewable energy sources.

Three sectors have been identified as potential sources for the application of ORC power generation: Continue reading “Should You Be Implementing the Organic Rankine Cycle?”

Waste Heat Sources + Trends

Waste Heat losses and Work Potential from Selected Processes
Waste Heat losses and Work Potential from Selected Processes

You might be able to name a few sources of waste heat, but do you know what distributes the largest content?

Waste heat losses arise both from equipment inefficiencies and from thermodynamic limitations on equipment and processes. Continue reading “Waste Heat Sources + Trends”

Working Fluid in Organic Rankine Cycles

orcfluid
ORC Fluid

The choice of the working fluid for any given application is a key issue and should be done based on specific applications to achieve maximal efficiency. For working fluids in ORC, a green energy alternative, there are some requirements to keep in mind:

•Thermodynamic performance
Low pump consumption and high critical point

•Positive or isentropic saturation vapor curve
Avoid wetness in flow path, i.e. avoid damages of flow path elements

•High vapor density
Decrease sizes of equipment (expander and condenser)

•Acceptable pressures
High pressures usually lead to higher investment cost and increasing complexity

•High stability temperature
Prevent from chemical deterioration and decomposition at high temperatures

•Low environmental impact and safety level
•Good availability and low cost Continue reading “Working Fluid in Organic Rankine Cycles”

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