Geothermal power market has been showing sustainable growth globally, with many installations in developing countries. As people turn to renewable sources while demand for energy is experiencing rapid growth, geothermal is found to be a reliable energy source and current development is calculated to increase global capacity by over 25%. Geothermal power plants can usually be divided into several types of cycles, including binary, flash, double flash and more. Flash power plants are found to be the most common forms of geothermal power plant and specifically, we are going to talk about the double flash cycle.
A flash system produces high pressure dry steam to move the turbine, generating electricity after going through a flash separator. A double flash system uses two flashes separating systems in order to generate more steam from the geothermal liquid and increase cycle output. The cycle starts with high temperature fluid extracted from a geothermal source to a high pressure separator (HPS) for flashing. The HPS produces a saturated steam that enters the high pressure turbine and the remaining brine is directed into a secondary low pressure separator (LPS). Reducing the flashing pressure increases the mixture quality in the LPS, which results in higher steam production. Low pressure saturated steam is mixed with the steam flow exhausted from the high pressure turbine and the resulting steam flow is directed to the low pressure turbine and produces more electricity. Steam that is exhausted from the low pressure turbine will then be compressed and injected back to the ground. In a flash system, separator pressure has a significant effect on the amount of power generated from the system – and the flashing pressures also influence double flash cycle significantly. In order to optimize one design, the value of parameters versus cost of operations should be taken into account.
Power generation and energy sectors happen to be very politically volatile. With our new leader in the USA taking control, we are expecting a shift in technology trends. The topic of bringing more coal fired power plants back to the equation has been brought up quite often, coming after Trump’s skeptical statement regarding global warming and climate-change. To follow that statement, Donald Trump pledged to lift restriction on US agencies funding new coal plants in other parts of the world. In addition, Australia’s minister also has been arguing regarding adding new coal power plants into the mix. As world’s largest coal exporter, it should economically make sense for Australia to forego with the plan.
There are three major categories that typically determine whether a technology would be suitable to be implemented: cost to public, reliability of supply and environmental impact. The old coal power generator is found to be less reliable as well as less environmentally friendly. Consequently, a new technology must be used to provide “cleaner” energy from coal. Southern Company has become one of the first private sectors using new technology to produce energy from coal. The technology is said to be generating electricity while at the same time capturing carbon dioxide from coal. Maybe if this technology is implemented, we will come back to coal.
As technology has evolved, so has the refrigeration industry. What were once holes in the ground filled with ice and snow have transformed into the modern high-efficiency compression machinery we have become so familiar with today. However, as common as these devices have become, the design process remains a challenge. This is where a combination of scientific knowledge, experience and creative initiative comes into play. While there are, of course, several variations in terms of the application of each design step, the guidelines presented here could be applied not only to refrigeration compressors, but also to compressors used in many other processes and industries.
There are a number of steps to consider throughout the compressor design process, and each step has to relate back to the original design concept. Experience has shown that having a starting concept and an end goal in mind is imperative. Namely, before you can begin the process, you need to know where you are starting and where you want to end up. With this in mind, before we can even get started with preliminary design, blade profiling and analysis of computational fluid dynamics (CFD), it is important to take out a piece of paper and start brainstorming. Consideration of the different refrigeration technologies (cycles), is always a great place to start, so we can ensure we will design the best compressor for the application. The cycle will directly impact the rest of the compressor design decisions, so this is not a step that can be bypassed. This article’s discussion begins with cyclic compression.
In modern days, power generation planners are faced with the challenge of pushing out the most energy from fuel while at the same time minimizing cost and emission.However, finite fuel also generates mass concerns regarding the reserve left to be used in nature. Consequently, people are continuously looking for an economical and highly efficient solution.
To this date, combined cycle gas turbine applications are found to be the best solution to the problem. The application is known to be highly efficient, have favorable energy conversion rates, comparatively lower start up time compared to conventional steam cycles and able to squeeze more power from the same amount of fuel.
As time goes by, the demand for energy rises while finite resources gradually diminish. The concept of going ‘green’ or using infinite resources has become more and more common in the marketplace. With this in mind, the abundance and reliability of solar energy makes for an attractive alternative. This is because solar power is different. This statement, of course, begs the question of HOW solar power differs.
Common traditional power plants still utilizes finite fuel. Steam power plants, for example, use the fuel as an energy source to boil water which, in turn, allows the the steam to turn the turbine and drive the generator to produce electricity. Concentrated solar power systems, however, use heat energy from the sun as a heat source – which is renewable. This system works by using utilizing mirrors or mirror-like materials to concentrate energy from the sun and then takes that energy to produce steam. The system can also store the energy that is absorbed during the day, to be used at night when the sun is not present. There are a few different types of concentrated solar power systems which one can choose from.
Heat recovery steam generators (HRSGs) are used in power generation to recover heat from hot flue gases (500-600 °C), usually originating from a gas turbine or diesel engine. The HRSG consists of the same heat transfer surfaces as other boilers, except for the furnace. Since no fuel is combusted in a HRSG, the HRSG have convention based evaporator surfaces, where water evaporates into steam. A HRSG can have a horizontal or vertical layout, depending on the available space. When designing a HRSG, the following issues should be considered:
The pinch-point of the evaporator and the approach temperature of the economizer
The pressure drop of the flue gas side of the boiler
Optimization of the heating surfaces
The pinch-point (the smallest temperature difference between the two streams in a system of heat exchangers) is found in the evaporator, and is usually 6-10 °C, which can be seen in Figure 2. To maximize the steam power of the boiler, the pinch-point must be chosen as small as possible. The approach temperature is the temperature difference of the input temperature in the evaporator and the output of the economizer. This is often 0-5 °C.
Global warming is a very popular topic at the present time. With the upwards trend of clean technology and the realization that strict climate policy should be implemented, demand of renewable energy has sky-rocketed while conservative plant popularity continues to fall. Additionally, the number of coal power plants have significantly dropped since its peak era, as they are now known as the largest pollutant contribution, producing nitrogen, sulfur oxide and carbon dioxides.
Renewable energy comes from many sources: hydropower, wind power, geothermal energy, bioenergy and many more. The ability to replenish and have no limit on usage and application makes renewable energy implementation attractive. To make this even better, it also produces low emission. Theoretically, with the usage of renewable energy, human-kind should be able to meet their energy needs with minimal environmental damage. With growth rates ranging from 10% to 60% annually, renewable energy is getting cheaper through the technological improvements as well as market competition. In the end, the main goal is to maximize profit while minimizing our carbon footprint. Since the technology is relatively new, capital costs are still considerably higher compared to more traditional (–and naturally harmful) implementations. This begs the question of exactly how we maximize the economic potential of a renewable energy power generation plant.
Though fossil fueled power plants aren’t as commonly used anymore, coal fired power generation is still a major source of global electricity, making up about 25% of the market in total. Compared to other options in fossil fuel power generation, coal is found to be the most economical choice as well as a reliable option. Making demands that are heavily reliant on other fuels, such as oil-fired for example, slowly levers to coal power generation. The global reserve of coal can be found in abundance when compared to other energy sources (such as oil for example) as there is about 3 times more of it. Also, IGCC comes with an economic benefit as the price of coal has remained relatively constant, which results in a higher degree of confidence when relying on coal as an energy source in the future.
How Does an IGCC Work?
The system uses a high pressure gasifier to turn coal and other carbon based fuels such as high-sulfur coal, heavy petroleum residues and biomass into pressurized clean coal synthesis gas (also known as syngas). The solid coal is gas-fired to produce syngas by gasifying coal in a closed pressurized reactor with a shortage of oxygen to ensure that coal is broken down by the heat and pressure. Before going out of the system, the syngas runs through a pre-combustion separation process to remove impurities, starting with water-gas-shift reaction to increase concentration of hydrogen and efficiency during combustion process, to a physical separation process (through variable methods). After that, a fairly pure syngas is used as a fuel in a combustion turbine that produces electricity. Waste heat contained in a gas turbine’s exhaust is used to produce steam from feed water that further turns a steam turbine to generate additional electricity.
In the ever-expanding market for waste-heat recovery methods, different approaches have been established in order to combat the latest environmental restrictions while achieving more attractive power plant efficiencies. As gas turbine cycles continue to expand within the energy market, one particular technology has seen a significant upsurge due to a number of its beneficial contributions. Supercritical CO2 (S-CO2) bottoming cycles have allowed low power units to utilize waste heat recovery economically. For many years, the standard for increasing the efficiency level of a GTU (Gas Turbine Unit) was to set up a steam turbine Rankine cycle to recycle the gas turbine exhaust heat. However, the scalability constraints of the steam system restrict its application to only units above 120MW.
The term, “mixed flow compressor”, refers to a type of compressor that combines axial and radial flow paths. This phenomenon produces a fluid outflow angle somewhere between 0 and 90 degrees with respect to the inlet path. Referred to as the meridional exit angle, the angled outflow of this mixed flow configuration possesses the advantages of both axial and centrifugal compressors. Axial compressors can produce higher order efficiencies for gas engines, but they have relatively low-pressure ratios unless compounded into several stages. Centrifugal compressors can produce high-pressure ratios in a single stage, but they suffer from a drop in efficiency. The geometrical distinction of mixed flow compressors allows for higher efficiencies while maintaining a limited cross-sectional area. The trade-off for a mixed flow compressor when introduced to aero gas turbines is that there is an associated weight increase due to the longer impellers needed to cover this diagonal surface. However, when related to smaller gas turbines, the weight increase becomes less significant to the overall performance of the engine.