Combined Cycle Power Plant: Introduction

Combined Cycle Power Plant

The process for converting the energy in a fuel into electric power involves the creation of mechanical work, which is then transformed into electric power by a generator. Depending on the fuel type and thermodynamic process, the overall efficiency of this conversion can be as low as 30 percent. This means that two-thirds of the latent energy of the fuel ends up wasted. For example, steam electric power plants which utilize boilers to combust a fossil fuel average 33 percent efficiency. Simple cycle gas turbine (GTs) plants average just under 30 percent efficiency on natural gas, and around 25 percent on fuel oil. Much of this wasted energy ends up as thermal energy in the hot exhaust gases from the combustion process.

To increase the overall efficiency of electric power plants, multiple processes can be combined to recover and utilize the residual heat energy in hot exhaust gases. In combined cycle Power plant, power plants can achieve electrical efficiencies up to 60 percent. The term “combined cycle” refers to the combining of multiple thermodynamic cycles to generate power. Combined cycle operation employs a heat recovery steam generator (HRSG) that captures heat from high temperature exhaust gases to produce steam, which is then supplied to a steam turbine to generate additional electric power. The process for creating steam to produce work using a steam turbine is based on the Rankine cycle.

The most common type of combined cycle power plant utilizes gas turbines and is called a combined cycle gas turbine (CCGT) plant. Because gas turbines have low efficiency in simple cycle operation, the output produced by the steam turbine accounts for about half of the CCGT plant output. There are many different configurations for CCGT power plants, but typically each GT has its own associated HRSG, and multiple HRSGs supply steam to one or more steam turbines. For example, at a plant in a 2×1 configuration, two GT/HRSG trains supply to one steam turbine; likewise there can be 1×1, 3×1 or 4×1 arrangements. The steam turbine is sized to the number and capacity of supplying GTs/HRSGs.

Combined Cycle Principles of Operation

The HRSG is basically a heat exchanger, or rather a series of heat exchangers. It is also called a boiler, as it creates steam for the steam turbine by passing the hot exhaust gas flow from a gas turbine or combustion engine through banks of heat exchanger tubes. The HRSG can rely on natural circulation or utilize forced circulation using pumps. As the hot exhaust gases flow past the heat exchanger tubes in which hot water circulates, heat is absorbed causing the creation of steam in the tubes. The tubes are arranged in sections, or modules, each serving a different function in the production of dry superheated steam. These modules are referred to as economizers, evaporators, superheaters/reheaters and preheaters.

The economizer is a heat exchanger that preheats the water to approach the saturation temperature (boiling point), which is supplied to a thick-walled steam drum. The drum is located adjacent to finned evaporator tubes that circulate heated water. As the hot exhaust gases flow past the evaporator tubes, heat is absorbed causing the creation of steam in the tubes. The steam-water mixture in the tubes enters the steam drum where steam is separated from the hot water using moisture separators and cyclones. The separated water is recirculated to the evaporator tubes. Steam drums also serve storage and water treatment functions.

An alternative design to steam drums is a once-through HRSG, which replaces the steam drum with thin-walled components that are better suited to handle changes in exhaust gas temperatures and steam pressures during frequent starts and stops. In some designs, duct burners are used to add heat to the exhaust gas stream and boost steam production; they can be used to produce steam even if there is insufficient exhaust gas flow.

Saturated steam from the steam drums or once-through system is sent to the superheater to produce dry steam which is required for the steam turbine. Preheaters are located at the coolest end of the HRSG gas path and absorb energy to preheat heat exchanger liquids, such as water/glycol mixtures, thus extracting the most economically viable amount of heat from exhaust gases.

The superheated steam produced by the HRSG is supply to the steam turbine where it expands through the turbine blades, imparting rotation to the turbine shaft. The energy delivered to the generator drive shaft is converted into electricity. After exiting the steam turbine, the steam is sent to a condenser which routes the condensed water back to the HRSG.


First step is the same as the simple cycle gas turbine plant. Burning of gas, the thrust rotating a gas turbine and the coupled generator produces Electricity. In the second step the hot gases leaving the gas turbine passes into boiler to produce steam. This boiler is called the ‘Heat Recovery Steam Generator (HRSG). The steam then rotates the steam turbine and coupled generator to produce Electricity. The hot gases leave the HRSG at around 140 degrees centigrade and are discharged into the atmosphere. The steam condensing, and water recycling system is the same as in the steam power plant.
The attached scheme shows the working of the CCPP.

Combined Cycle Power Plant
Roughly the steam turbine cycle produces one third of the power and gas turbine cycle produces two thirds of the power output of the CCPP. Normally there will be two generators, one driven by the gas turbine and one driven by the steam turbine. There are also systems with one generator connected through a single shaft to both the gas turbine and steam turbine.
Even though this system is having the best efficiency, it has limitations. The gas turbine can only use Natural gas or high grade oils like aviation or diesel fuel. Because of this the combined cycle can be operated only in locations where these fuels are available and cost effective.
Developments for gasification of coal and use in the gas turbine are in advanced stages. Once this is proven, Coal as the main fuel can also be used in the combined cycle power plant.

Rotax Engine

Rotax Engine

Rotax is the brand name for a range of internal combustion engines developed and manufactured by the Austrian company BRP-Rotax GmbH & Co KG[1] (until 2016 BRP-Powertrain GmbH & Co. KG), in turn owned by the Canadian Bombardier Recreational Products.

Rotax four-stroke and advanced two-stroke engines are used in a wide variety of small land, sea and airborne vehicles. Bombardier Recreational Products (BRP) use them in their own range of such vehicles.[2] In the light aircraft class, in 1998 Rotax outsold all other engine manufacturers combined.[3]


The company was founded in 1920 in Dresden, Germany, as ROTAX-WERK AG. In 1930, it was taken over by Fichtel & Sachs and transferred its operations to Schweinfurt, Germany. Operations were moved to Wels, Austria, in 1943 and finally to Gunskirchen, Austria, in 1947. In 1959, the majority of Rotax shares were taken over[4] by the Vienna-based Lohner-Werke, a manufacturer of car and railway wagon bodies.

In 1970, Lohner-Rotax was bought by the Canadian Bombardier Inc. The former Bombardier branch, Bombardier Recreational Products, now an independent company, uses Rotax engines in its ground vehicles, personal water craft, and snowmobiles.[2]


Aircraft engines

 Rotax supplies aircraft engines for ultralight aircraft, light aircraft and unmanned aerial vehicles. Rotax engines designed specifically for light aircraft include both four-stroke and two-stroke models.

Current models are:

Historical models no longer in production include:

Karting engines

The company developed the Rotax MAX engine for Karting. This 2-stroke engine series was launched 1997.[6]


The company also produces unbranded engines, parts and complete power trains for Original Equipment Manufacturers (OEM).[7] Uses include motor bikes and scooters, with complete engines including the Rotax 122 and Rotax 804.[8] Motorcycle manufacturers using Rotax engines include Aprilia, BMW (F and G series), Buell and KTM.

Rotax 914

The Rotax 914 is a turbo-charged, four-stroke, four-cylinder, horizontally opposed aircraft engine with air-cooled cylinders and water-cooled cylinder heads. It is designed and built by the Austrian company BRP-Powertrain, owned by BRP, as part of its Rotax brand.

The engine commonly powers certified light aircraft, homebuilt aircraft, autogyros and military UAVs such as the MQ-1 Predator.

Rotax Engine 914


Specifications (914)

General characteristics

  • Type: four-cylinder, four-stroke liquid- / air-cooled engine with opposed cylinders
  • Bore: 79.5 mm (3.13 in)
  • Stroke: 61 mm (2.4 in)
  • Displacement: 1,211.2 cc (73.91 cu in)
  • Length: 561 mm (22.1 in)
  • Width: 576 mm (22.7 in)
  • Dry weight: 78 kg (172 lb) with electric starter, carburetors, fuel pump, air filters and oil system


  • Valvetrain: OHV, hydraulic lifters, pushrods, rocker arms
  • Fuel system: Dual CD carburetors, mechanical diaphragm pump
  • Fuel type: Unleaded: 91 octane AKI (Canada/USA) / 95 octane RON (European) or higher[1]
  • Oil system: Dry sump with trochoid pump, camshaft driven
  • Cooling system: Liquid-cooled cylinder heads, air-cooled cylinders
  • Reduction gear: Integrated reduction gear 1:2.273; 1:2.43 optional
  • Electronic dual ignition


  • Power output: Maximum 84 kW (115 hp) at 5,800 rpm, with 5 minute time limit; 73 kW (100 hp) continuous


  1. OM-914 Operator’s Manual 914 Series

Engineering Materials – Classification

Engineering Materials and their Examples


Elements with a valence of 1, 2 or 3. They are crystalline solids composed of atoms held together by a matrix of electrons. The “Electron Gas” that surrounds the “Lattice of atomic nuclei” is responsible for most of the properties.

Engineering Materials

1. General properties:

High electrical conductivity, high thermal conductivity, ductile and relatively high stiffness, toughness and strength. They are ready to machining, casting, forming, stamping and welding. Nevertheless, they are susceptible to corrosion.

2. Further description:

Engineering metals are generally Alloys. Alloys are metallic materials formed by mixing two or more elements, e.g.
a. Mild steel Fe + C
b. Stainless steel Fe + C + Cr + Mn …etc.
C improves strength
Cr improves the corrosion resistance…

3. Classification of metals and alloys:

Ferrous: Plain carbon steel, Alloy steel, Cast iron,
Nonferrous: Light Alloys (Al, Mg, Ti, Zn), Heavy Alloys (Cu, Pb, Ni), Refractory Metals (Mo, Ta, W), Precious metals (Au, Ag, Pt)

4. Applications:

  • Electrical wiring
  • Structures: buildings, bridges, etc.
  • Automobiles: body, chassis, springs, engine block, etc.
  • Airplanes: engine components, fuselage, landing gear assembly, etc.
  • Trains: rails, engine components, body, wheels
  • Machine tools: drill bits, hammers, screwdrivers, saw blades, etc.
  • Magnets
  • Catalysts

5. Examples:

  • Pure metal elements (Cu, Fe, Zn, Ag, etc.)
  • Alloys (Cu-Sn=bronze, Cu-Zn=brass, Fe-C=steel, Pb-Sn=solder)
  • Intermetallic compound (e.g. Ni3Al)


Inorganic, non-metallic crystalline compounds, usually oxides (SiO2, Al2O3, MgO, TiO2, BaO), Carbides (SiC), Nitrides (Si3N4), Borides (TiB2), Silicides (WSi2, MoSi2). Some literature includes glasses in the same category, however; glasses are amorphous (non-crystalline) compounds i.e. they possess “short range” order of atoms.

  1. General properties: Light weight, Hard, High strength,stronger in compression than tension, tend to be brittle, low electrical conductivity, High temperature resistance and corrosion resistance.
  2. Further description:Ceramics also includes ferrites (ZnFe2O4), semiconductors (ZnO, TiO2, CuO, SiC, AlN, BN, C, Si, Ge, SiGe), piezoelectric and ferroelectric ceramic (BaTiO3, PZT=PbZrTiO3) and superconducting ceramics (YBa2Cu3O7).
  3. Classification: of ceramics:

Traditional Ceramics: Includes pottery, china, porcelain products…etc, these products utilizes natural ceramic ores.

Advanced Ceramics: Alumina, magnesia, Carbides, Nitrides, Borides, Silicides …etc, they are synthetic materials, usually of better mechanical properties. Electronic ceramics falls in the same category.

Glass, Glass Ceramic and Vitro Ceramic: Glasses are essentially vitreous (amorphous, non crystalline), Glass ceramics are mostly re-crystallized from glassy medium and, Vitro Ceramics have crystalline microstructure which are partially vitreous at the grain boundaries.

Engineering Materials

  1. Applications:

  •   Electrical insulators
  •   Abrasives
  •  Thermal insulation and coatings
  •  Windows, television screens, optical fibers (glass)
  •  Corrosion resistant applications
  •   Electrical devices: capacitors, varistors, transducers, etc.
  •   Highways and roads (concrete)
  •   Bio-compatible coatings (fusion to bone)
  •   Self-lubricating bearings
  •   Magnetic materials (audio/video tapes, hard disks, etc.)
  •   Optical wave guides
  •   Night-vision
  1. Examples of technical ceramics

  • Barium titanate (often mixed with strontium titanate) displays ferroelectricity, meaning that its mechanical, electrical, and thermal responses are coupled to one another and also history-dependent. It is widely used in electromechanical transducers, ceramic capacitors, and data storage elements.
  •  Bismuth strontium calcium copper oxide, a high-temperature superconductor
  •   Boron carbide (B4C), which is used in ceramic plates in some personnel, helicopter and tank armor.
  • Boron nitride is structurally isoelectronic to carbon and takes on similar physical forms: a graphite-like one used as a lubricant, and a diamond-like one used as an abrasive
  •  Ferrite (Fe3O4), which is ferrimagnetic and is used in the magnetic cores of electrical transformers and magnetic core memory.
  •  Lead zirconate titanate is another ferroelectric material.
  •  Magnesium diboride (MgB2), which is an unconventional superconductor.
  •   Sialons / Silicon Aluminium Oxynitrides, high strength, high thermal shock / chemical / wear resistance, low density ceramics used in non-ferrous molten metal handling, weld pins and the chemical industry.
  •  Silicon carbide (SiC), which is used as a susceptor in microwave furnaces, a commonly used abrasive, and as a refractory material.
  • Silicon nitride (Si3N4), which is used as an abrasive powder.
  •   Steatite (MgSiO3), used as an electrical insulator.
  •   Uranium oxide (UO2), used as fuel in nuclear reactors.
  •  Yttrium barium copper oxide (YBa2Cu3O7-x), another high temperature superconductor.
  • Zinc oxide (ZnO), which is a semiconductor, and used in the construction of varistors
  •   Zirconium dioxide (zirconia), its high oxygen ion conductivity recommends it for use in fuel cells. In another variant, metastable structures can impart transformation toughening for mechanical applications; most ceramic knife blades are made of this material.
  1. Semiconductors Applications and Examples

  • Computer CPUs
  •  Electrical components (transistors, diodes, etc.)
  •  Solid-state lasers
  •  Light-emitting diodes (LEDs)
  •  Flat panel displays
  •  Solar cells
  •  Radiation detectors
  •   Microelectromechanical devices (MEMS)
  •  Examples: Si, Ge, GaAs, and InSb

Engineering Materials



High molecular weight organic substance made up of a large number of repeat (monomer) units. Their properties are linked directly to their structure, which is dictated mostly by intermolecular bonds.

Engineering Materials

1. General properties:

compared with metals, polymers have lower density, lower stiffness and tend to creep. They have higher thermal expansion and corrosion resistance. Furthermore, polymers have low electrical conductivity and low thermal conductivity. The prime weakness is that polymers do not withstand high temperatures

2. Further description:

Polymers generally formed via a “Polymerization Process”, in which the polymer chain builds up from monomers with the aid of heat and/or chemical agents. The C-C bonds form the backbone of the polymer chain; when the chains grow very long, they get tangled (twisted) and loose their lattice order, thus, changing increasingly to the amorphous state. Consequently, polymers are semi-crystalline to some “degree of crystallinity” that can be measured by X-ray Diffraction.

3. Classification:

according to their properties:
i. Plastics: (Hard), they can be semi-crystalline or amorphous (glassy).

1. Thermoplastics:

Such as Polyethylene (PE) and Polymethylmethacrylate (Acrylic and PMMA) are composed of “linear” polymer chains. They flow under shear when heated. They can be compression- or injection- molded.

2. Thermosets:

Such as Polystyrene (PS) and Polyvinylchloride (PVC) are composed of “branched” polymer chains. They not flow when heated. The monomers are ‘cured’ in a mold (‘RIM’).

ii. Elastomers:

(Soft) Rubbery cross-linked solids that will deform elastically under stress, e.g. natural rubber

iii. Solutions:

Viscosity modifiers, polymeric surfactants, lubricants.

4. Applications and Examples

  • Adhesives and glues
  • Containers
  • Moldable products (computer casings, telephone handsets, disposable razors)
  • Clothing and upholstery material (vinyls, polyesters, nylon)
  • Water-resistant coatings (latex)
  • Biodegradable products (corn-starch packing “peanuts”)
  • Biomaterials (organic/inorganic interfaces)
  • Liquid crystals
  • Low-friction materials (Teflon)
  • Synthetic oils and greases
  • Gaskets and O-rings (rubber)
  • Soaps and surfactants


A combination of two or more materials to achieve better properties than that of the original materials. These materials are usually composed of a “Matrix” and one or more of “Filler” material. Wood is a natural composite of cellulose fibers in a matrix of polymer called lignin. The primary objective of engineering composites is to increase strength to weight ratio. Composite material properties are not necessarily isotropic, i.e., directional properties can be synthesized according to the type of filler materials and the method of fabrication.

Engineering Materials
1. General properties:

Low weight, high stiffness, brittle, low thermal conductivity and high fatigue resistance. Their properties can be tailored according to the component materials.

2. Further description:

Engineering Materials

3. Classification:

i. Particulate composites (small particles embedded in a different material): e.g. Cermets (Ceramic particle embedded in metal matrix) and Filled polymers.
ii. Laminate composites (golf club shafts, tennis rackets, Shield Glass)
iii. Fiber reinforced composites: e.g. Fiber glass (GFRP) and Carbon-fiber reinforced polymers (CFRP)

4. Applications:

  • Sports equipment (golf club shafts, tennis rackets, bicycle frames)
  • Aerospace materials
  • Concrete
  • “Smart” materials (sensing and responding)
  •  Brake materials

5. Examples:

  • Fiberglass (glass fibers in a polymer)
  • Space shuttle heat shields (interwoven ceramic fibers)
  • Paints (ceramic particles in latex)
  • Tank armor (ceramic particles in metal)

Analysis and Design of Dynamic Systems

This article briefly explains what is involved in the analysis and design of dynamic systems.


System analysis means the investigation under specified conditions of the performance of a system whose mathematical model is known.

The first step in analyzing a dynamic system is to derive its mathematical model. Since any system is made up of components, analysis must start by developing a mathematical model for each component and combining all the models in order to build a model for the whole system. Once the latter model is obtained, the analysis may be formulated in such a way that the system parameters in the model are varied to produce a number of solutions. The engineer then compares these solutions and interprets and applies the results of his analysis to the basic task.

Always remember that deriving a reasonable model for the complete system is the most important part of the entire analysis.Once such a model is available, various analytical and computer techniques are used to analyze it. The manner in which analysis is carried out is independent of the type of physical system involved- mechanical, electrical, hydraulic and so on.


System design refers to the process of finding a system that accomplishes a given task. In general, the design procedure is not straightforward and will require trial and error.


By synthesis, we mean the use of an explicit procedure to find a system that will perform in a specified way. Here the desired system characteristics are postulated at the outset, and then various mathematical techniques are used to synthesize a system having those characteristics. Generally, such a procedure is completely mathematical from the start to the end of design process.

Dynamic Systems

Basic approach to system design

The basic approach to the design of any dynamic system necessarily involves trial and error procedures. Theoretically, a synthesis of linear systems is possible and the engineer can systematically determine the components necessary to realize the system’s objective. In practice, however, the system may be subject to many constraints or may be nonlinear; in such cases, no synthesis methods are currently applicable. Moreover, the features of the components may not be precisely known. Thus, trial and error methods are almost always needed.



Design procedure

Frequently,the design of a system proceeds as follow:the engineer begins the design procedure knowing the specifications to be met and the dynamics of the components,the latter of which involve design parameters.The specification may be given in terms of both precise numerical values and vague qualitative descriptions.(Engineering specifications normally include statements on such factors as cost,reliability,space,weight,and ease of maintenance.) It is important to note that the specifications may be changed as the design progresses,for detailed analysis may reveal that certain requirements are impossible to meet.Next,the engineer will apply any applicable synthesis techniques, as well as other methods,to build a mathematical model of system.

Once the design problem is formulated in terms of a model,the engineer caries out a mathematical design that yields a solution to the mathematical version of the design problem.with mathematical design completed, the engineer simulates the model on a computer to test the effects of various inputs and disturbances on the behavior of the resulting system.If if the initial system configuration is not satisfactory,the system must be redesigned and the corresponding analysis completed.This process of design and analysis is repeated until a satisfactory system is found.then a prototype physical system can be constructed.

Note that the process of constructing a prototype is the reverse of mathematical modeling. The prototype is a physical system that represents the mathematical model with reasonable accuracy. Once the prototype has been built, the engineer tests it to see whether it is satisfactory. If it is, the design of the prototype is complete. If not, the prototype must be modified and retested. The process continues until a satisfactory prototype is obtained.

Basics of Tensile test


A tensile test, also known as a tension test, tests a material’s strength. It’s a mechanical test where a pulling force is applied to a material from both sides until the sample changes its shape or breaks. It’s is a common and important test that provides a variety of information about the material being tested, including the elongation, yield point, tensile strength, and ultimate strength of the material. Tensile tests are commonly performed on substances such as metals, plastics, wood, and ceramics.

Tensile test machine

Tensile testing systems use a number of different units of measurement. The International System of Units, or SI, recommends the use of either Pascals (Pa) or Newtons per square meter (N/m²) for describing tensile strength. In the United States, many engineers measure tensile strength in kilo-pound per square inch (KSI).

tensile test specimen

Tensile test with electronic extensometer

tensile test with electronic extensometer

This instrument is to be used on Tensile or Universal testing machines to find out Proof stress & Young’s modulus values. In case of many brittle materials such as high carbon steels, alloy steels, light aluminium & magnesium alloys, it is difficult to get yield values. For such materials stress corresponding to a certain allowable amount of plastic deformation is termed as proof stress say 0.1% or 0.2% proof stress. The measuring range is up to 5mm & resolution is 0.001mm.


tensile test machine

Tensile testing at elevated temperature.

tensile test at elevated temperature

High temperature tensile testing is a procedure to test the properties of a material at above room temperature. It will determine the following parameters:

  • Tensile strength (breaking strength)
  • Yield strength
  • Elongation
  • Reduction of area

Specialist testing, measurement and control equipment is required to perform this test.
The results of such a test will provide a good indication of the static load bearing capacity of the material and therefore establishes the suitability of a material for its intended purpose.

Tensile test on TOR steel Bars

TOR steel is one of the best grade of steel used in concrete reinforced. It’s a kind of high adherence steel. Other types of steel are used for less resistance concrete. Thermo-mechanically Treated (TMT) bars are a type of corrosion resistant steel reinforcing bar used in concrete construction.

tensile test on TOR steel bars

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