Last month we discussed a few basic aspects of wind as a source of clean energy. We showed what wind was, how it forms and where it goes. Then after going on a tangent about the history of turbines, we showed where on the Earth we could recover the highest amount of wind energy and how this potential changes with altitude. Today’s post offer the pros and cons of wind energy while touching upon several topics discussed in the previous post before diving into the optimal where and when.
Getting into the “What”
With an established worldwide potential of more than 400 TW (20 times more than what the entire human population needs) and a clean, renewable source wind is definitely attractive to the current and future generations. In terms of harvesting it, over 99% percent of wind farms in the USA are located in rural areas with 71% of them in low-income counties. Indeed, the more land is available (and the fewer buildings), the higher the possibility and interest to transform this kinetic energy into mechanical work and then most likely electricity.
Where one would see sporadic turbines on the side of the highway, these stand-alone equipment have begun to turn into actual modules (farms) that can work as an overall unit instead of individual ones. This strategy of creating a network of turbines follows the philosophy of “the Whole is Greater than the Sum of its Parts”. What this translates into is that by having 20 (arbitrary number) wind turbines working together to determine the best orientation, pitch, etc. of their blades in such a way that it least negatively impacts the downstream units we can produce more energy than if each of them were live-optimized individually (some interesting A.I. work is going into this). This means that the overall system is more efficient at converting energy and therefore it is more cost effective to provide bulk power to the electrical grid. This is similar to the concept in the post on solar energy comparing PV panels and CSP. Read the full post here.
In terms of power production per wind turbine, the utility-scale ones range from about 100 kW to several MW for the land-based units (Offshore wind turbines are typically larger and produce more power – getting ahead of myself here but check out the figure below for wind potential in Western Europe that clearly showcases coast vs. non-coast data). On the low-power end of the spectrum, we find some below 100 kW for some non-utility applications like powering homes, telecommunications dishes, water pumping, etc. Solar power (PV) is generally regarded as the first choice for homeowners looking to become energy producers themselves, but wind turbines make an excellent alternative in some situations. It would take a wind turbine of about 10 kilowatts and $40,000 to $70,000 to become a net electricity producer. Investments like this typically break even after 10 to 20 years.
Onto the “Where”
One of the elements of wind formation we covered in the last post here was a different in pressure (and therefore temperature). This simplification works rather well at the macro-scale, but as we zoom in closer to the surface we can see that wind flow speeds and patterns vary quite significantly based on more than just the general location of Earth. On top of the altitude we already discussed, factors like vegetation, presence of high-rise buildings or bodies of water come into play.
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:
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.
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.
In mining and metallurgy industries, centrifugal pumps are the most widely used equipment, for draining, and cooling of water supplies, etc.
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.
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.
In shipbuilding, there are more than 100 different types of pumps in one typical ocean ship.
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.
A multi-stage pump has two or more impellers working in a series to achieve higher total dynamic head. Read More
In reciprocating engines, the reciprocating motion of pistons is transformed into a rotating motion of the crankshaft, which is responsible for the drive of a whole engine system. Instantaneous torque excitation due to gas forces after firing on the shaft system have to be investigated to ensure proper functioning. A typical torque function over the crankshaft angle can be seen in Figure 1.
Such a 720°-periodic function can be created in AxSTREAM RotorDynamics™, which provides a transient approach to determine the response torque in the shaft after a respective torque excitation. In this example, a rotor speed of 3000 rpm is considered. With this information, the total time for two crankshaft-revolutions (720°) reads: Read More
Choosing how to start something is often the most challenging part since the rest is usually about moving with the flow (turbomachinery pun intended). So, now that we got that out of the way let’s talk about our next topic after we do a quick flashback on the previous episodes of this Clean Energy series.
In thefirst post in this series, we discussed clean energy as a whole. After describing what it is and what it is not, we pointed out some of the energy sources we would analyze in subsequent articles.
The second post in this series took us on an extraterrestrial journey for two reasons: we looked at solar energy and we also went on a tangent about the rovers operating on planet Mars. I got so many “Likes” on these little droids that I figured I would keep going with them (that or I found a cool article that I’ll be sharing here) for this current post on one of the fastest-growing energy sources in the world: Wind Energy. What’s the link between Mars equipment and wind? See this recent discovery – https://www.space.com/41023-mars-wind-power-landers-experiment.html
The wind we are looking at in today’s post is somewhere in between bovine flatulence and hurricanes in terms of intensity. Wind as we know it is created by air (or any fluid) moving from a zone of high pressure to one of low pressure. This high-to-low concentration migration might sound tricky, but it is easy to understand if you think of cars on a highway. It is more likely that cars stuck in a slow lane on the highway would move on to a lane with less traffic rather than the other way around.
Pressure varies with things like irregularities on the Earth surface, AKA altitude (“in case loss of cabin pressure occurs, oxygen masks will drop […]”), but also with temperature. This means that two people at the same altitude but in areas of different temperatures would experience different pressures. For example, think of standing at the North Pole vs. standing on a Caribbean beach vs. standing on a paddleboard in the Great Lakes. This example of standing at different places demonstrates the uneven heating of the Earth from the sun due to its shape (not flat), its rotation and its tilt, as we introduced in the previous post. But which location is under the most pressure? Colder temperature equals higher pressure. Let me explain with another analogy, (even though this example has nothing to do with pressure, it will help the information stick). When people get stressed, we say they are under pressure. We can imagine somebody above the Arctic Circle is more stressed (cold, where to find food, shelter, etc.) than somebody enjoying a Mai Tai on the beach at an all-inclusive resort in Aruba. So here is your mnemonics; colder equals higher pressure.
Now that we have seen what wind was and the theory behind how it forms, we can start thinking about how to utilize this energy. Today we will talk about the aerodynamic aspect of wind turbines while in a future post we will be focusing on the assessment of such technology as wind power; pros, cons, where, what, etc. Read More
It is very important to have Anti-Icing Systems for ground-based gas turbines located in humid climates (where air relative humidity can be more than 80% and dense fog can cause air temperatures to drop below 5 0C). Such climatic conditions lead to ice formation. This ice can plug the inlet filtration system causing a significant drop in pressure in the inlet system, which in turn leads to performance loss. In extreme cases, there is even a possibility that the ice pieces get ingested into the compressor (first blade stage) which may cause foreign object damage. Ice may also cause the disruption of compressor work because of excessive vibration, or surging by decreasing the inlet flow. The major factors that lead to the ice formation in gas turbines are ambient temperature, humidity and droplet size. So, under the climatic conditions which are prone to ice formation, an anti-icing system is employed which heats the inlet air before entering the compressor. Let us discuss some important aspects of Anti-Icing Systems.
The objective of an Anti-Icing System is to prevent or limit the ice formation in the gas turbine inlet path.
Gas Turbine Anti-Icing Systems (GT-AIS) can be categorized in two groups.
Inlet heating systems
Component heating systems
Inlet heating systems operate by transferring heat from a heat source (exhaust gases can be used) to the cold ambient air at the entrance of the gas turbine. If the temperature of inlet air raises sufficiently by this heat transfer, icing cannot form in the gas turbine intake.
AxCYCLE™ is a tool, which provides the flexibility and convenience to study various parameters and understand the performance of thermodynamic cycles.
Steam turbine seals are parts inserted between moving and stationary components, to reduce and prevent steam leakage and air leaking into the low pressure areas. The leakage can happen through vane, gland, and shaft, etc. To reduce leakage from those parts while guaranteeing smooth operation of a steam turbine, engineers have to design these seals, taking into account not only efficiency, but also mechanical strength, vibration and cost.
As an example, steam turbine flow path seals improve overall efficiency installing various types of shrouds, diaphragms, and end seals which prevent idle leaks of working steam in the cylinders. In steam turbines, labyrinth seals are widely used. Some labyrinth seals are also used with honeycomb inserts. It is believed that the use of such seals makes it possible to achieve a certain gain due to smaller leaks of working fluid and more reliable operation of the system under the conditions in which the rotor’s rotating parts may rub against the stator elements. However, we can only consider it as a successful design if the structures are compliant with the manufacturing capabilities and have good vibration stability.  Furthermore, seal leakage can significantly affect efficiencies. Better seals increase efficiencies but add extra cost to both manufacturing and maintenance, so the design needs to be done with the turbine flow path design. Although modeling the seals in 3D CFD is theoretically possible, the calculation resources and time are extremely demanding.
This important task can be completed very easily with AxSTREAM NETTM. AxSTREAM NETTM provides a flexible method to represent fluid path and solid structure as a set of 1D elements, which can be connected to each other to form a thermal-fluid network. For each fluid path section, the program calculates fluid flow parameters for inlet and outlet cross-sections, like velocity, density, temperature, mass flow rate, etc. Therefore, the leakage from the whole system can be modeled in this network, as shown in Figure 1.
The steam turbine is one of the most important power generating equipment items in use. Around half of the electricity generated worldwide comes from steam turbines. Steam turbines can be fueled by coal, nuclear energy, petroleum or natural gas, alternatively by biomass, solar energy or geothermal energy. Thus a large amount of fuel can be saved and CO2 emissions significantly reduced by optimizing key components of these widely used machines.
An important goal in steam turbine technology is to improve efficiency. The continuous flow of steam conditions is one of the commonly accepted efficiency contributor for steam power plants. The chart below shows expected improvement in thermal efficiency for USC double-reheat fossil-fuel power units compared to common supercritical-pressure ones, according to Hitachi.
Due to technological advancements in the aerospace industry, air transportation has become the primary means of travelling. This begs the question of “what are the key factors that could push the industry to the next level and allow for higher performance, low cost and low carbon emission flights?”
For a low carbon aviation to be achieved, a lot of effort is currently put on the aircraft-propulsion integration. Low-pressure-ratio fans are one of the concepts that is being studied in this regard. The lower the pressure across the propulsive element the more the exhaust velocities will decrease and therefore the higher the propulsive efficiency will be. However, a constant level of thrust would require an increase of the fan area, which could lead to an increase of the total weight of the configuration and ultimately cancel the efficiency benefits of the concept. Read More
Nowadays the scientific community is strongly concerned about problems of efficiency increase and emissions reduction in power generation, ship, and vehicle drives such as internal combustion engines (ICE). A system utilizing waste heat recovery (WHR) is an effective solution for the aforementioned problems.
ORC (meaning organic Rankine cycle, not the scary monsters from Lord of the Rings) is one WHR solution which delivers additional power from the turbine/engine exhaust gas/steam energy. ORC systems operate on hydrocarbon-based fluids which effectively avoid the typical disadvantages associated with water-based steam turbine systems while bringing the advantage of better performance at part load and in non-continuous operation. ORC systems, capable of utilizing low temperature heat sources of 100-200°C, can be designed in compact and modular packages which require very little maintenance.
The design criteria of an ORC system and its components includes finding the maximum possible heat recovery from the available high and low temperature waste heat flows of a turbine or ICE to produce the maximum amount of additional power while decreasing the load on the turbine’s cooling system, under certain restrictions like geometry and cost.
The first step is to design the thermodynamic cycle configuration. Figure 1 is a flow diagram of a dual loop supercritical organic Rankine cycle (SORC) with separate turbines and given design parameters of the components, generated with AxCYCLE™ software, developed by SoftInWay. The cycle consists of 6 heat exchangers, 2 turbines (HPT and LPT), 2 pumps (HPP and LPP) and the condenser. Both turbines operate with the same backpressure – 1.3 bars. The flows of the working fluid (R245fa in this case) are mixed at the condenser inlet and split at its outlet. The temperature – entropy diagram for the presented cycle is shown on Figure 2. The process 1-2-3-4-5-1 corresponds to the high pressure loop operation and the process 10-20-30-40-10 is for the low pressure loop operation. All these can be easily manipulated and obtained with user-friendly interface of AxCYCLE™.
In terms of component design, ORC turbines can be of axial, radial inflow and radial outflow configurations. The type of turbine you should select depends on the application. To delve further into the topic, check out SoftInWay’s webinar on “Radial Inflow versus Outflow Turbines – Comparison, Advantages and Applicability” here – http://learn.softinway.com/Webinar/Watch/102 Read More
We as human kind have always aimed at achieving something better, something bigger. This led to the research on gas turbines, which was mainly inspired due to the immediate requirement in the aerospace and power generation industry, to also look beyond the scope of aeronautics.
Today gas turbine technology is often used when dealing with aerospace and power generation industries, but believe it or not, gas turbine technology has been used in ground transportation too; notably locomotives.
The Early Applications
After the first world war, several countries had the expertise and the finances to invest in achieving the technological edge in the new post war era. The gas turbine technology was one such technological endeavor, and by the mid-20th century the gas turbine could be found in several applications. Birth of gas turbine locomotives can be credited to two distinct characteristics of these locomotives versus the contemporary diesel locomotives. First, there are fewer moving parts in a gas turbine, decreasing the need for lubrication. This can also potentially reduce the maintenance costs. Second, the power-to-weight ratio is much higher for such locomotives which makes a turbine of a given power output physically smaller than an equally powerful piston engine, allowing a locomotive to be powerful enough without being too bulky.