Determine Thermal Efficiency, Work ratio, Pressure ratio of Gas Turbine Power Plant

I will solve Some problems of simple gas turbine power plant with the students during this power plant engineering lecture. This lecture on Gas Turbine Power Plant includes:
1) Calculation of thermal efficiency in gas turbine power plant
2) Calculation of work ratio of gas turbine power plant
3) Calculation of pressure ratio in gas turbine power plant

Condition of Maximum Work done in Brayton Cycle, Maximum Efficiency, work Ratio and Air Rate for simple gas Turbine

 

In this lecture on Power Plant engineering you will Learn: (1) Condition of maximum work (2) Joule cycle Maximum Thermal Efficiency derivation (3) Work Ratio of Gas Turbine: It is the ratio of net work produced by the plant to the turbine work. The work ratio represents the amount of net work generated by the gas turbine plant per unit turbine work output. The work ratio increases with an increase in turbine inlet temperature, a decrease in compressor inlet temperature, and a decrease in the pressure ratio of the cycle. the compressor inlet temperature is always atmospheric temperature particularly in the open cycle and turbine inlet temperature is limited by metallurgical consideration. The highest temperature ever used for a gas turbine power plant is about 1000 k. (4) Air rate: The size of the gas turbine plant is dependent upon the rate of air flow in relation to net output work. Compact gas turbine plant has a lower value of air rate. Air rate is expressed as kg of air per kWhr.
(1) Condition of maximum work
(2) Joule cycle Maximum Thermal Efficiency derivation
(3) Work Ratio of Gas Turbine: It is the ratio of net work produced by the plant to the turbine work. The work ratio represents the amount of net work generated by the gas turbine plant per unit turbine work output. The work ratio increases with an increase in turbine inlet temperature, a decrease in compressor inlet temperature, and a decrease in the pressure ratio of the cycle. the compressor inlet temperature is always atmospheric temperature particularly in the open cycle and turbine inlet temperature is limited by metallurgical consideration. The highest temperature ever used for a gas turbine power plant is about 1000 k. (4) Air rate: The size of the gas turbine plant is dependent upon the rate of air flow in relation to net output work. Compact gas turbine plant has a lower value of air rate. Air rate is expressed as kg of air per kWhr.

Ideal Brayton cycle efficiency for gas turbine with P V and T S diagram

The ideal cycle for gas turbine is Brayton or jule cycle. The Brayton cycle has two constant pressure and two isentropic processes. In this video, i have explained PV and TS diagram of Brayton cycle. This video will show you the Analysis of Brayton cycle, and at the end of the video, you will get the equation to find the thermal efficiency of a simple gas turbine power plant. The analysis of Brayton is carried out with the following assumptions: 1) Compression and expansion are isentropic. 2) Pressure losses in the system are neglected. 3) Heat losses in the system are neglected. 4) specific heat of working fluid is taken constant throughout the cycle. Considering the 1kg of working fluid.

Gas Turbine Engine Fuel

The gas turbine engine can be operated with gas, liquid and solid fuels. However, this statement is not true for all gas turbine engine. The selection of fuel for gas turbine is dependent on type of cycle, size and length of engine and application of gas turbine engine. The most important requirement of a gas turbine fuel are 
(1) composition should provide proper combustion and rapid burning,
(2) the product of combustion should contain a minimum of mater which might get deposited on the turbine blades or the heat exchanger,
(3) highest heating value per kg or m^3 volume specially for aircraft engine.


The modern gas turbine are normally operated on the following fuels:
a) Gaseous fuels: Natural gas, Blast furnace gas, Producer gas, Sewage gas, etc.…
b) Liquid fuels: Kerosene, Gasoline, Residual oils, etc.…
c) Solid Fuels: Coal


The solid fuel (Coal) is normally used in closed cycle gas turbine. The main problem with using solid fuel in the case of open cycle plans is of reducing the level of flyash in the gases leaving the combustion chamber so that the blades of the turbines are not eroded. For this, it is necessary to ensure proper cleaning of the combustion gases from fine ash and dust. Before the gas enters the turbine, it is purified with help of the various flyash collectors. The use of coal as a fuel of open cycle gas turbine is under the development. Coal is burnt in two methods. In the first method, the coal is completely or partially gasified and fuel gas produced is supplied to gas turbine combustor. In other method, pressurized bubbling or circulating fluidized bed, where fuel gas, after it is adequately filtered, expands in the gas turbine. Coal is usually considered as a gas turbine fuel in combined cycle power plant.

Liquid oil like kerosene, gasoline, etc. are easily used in a gas turbine combustor. Residual oils can be used as fuel in gas turbine. If the viscosity of the oil is high, some heating arrangement required.

What are the pros and cons of using closed cycle gas turbines?

As we know that in open cycle gas turbine power plant, the fuel is mixed with air in the combustion chamber and the combustion gases are expanded in the gas turbine which causes erosion and corrosion of turbine blades and therefore it is necessary to use fuel superior quality in the combustion chamber in order to minimize erosion and corrosion. This negative effect overcome in case closed gas turbine power plant. In the closed gas turbine power plant, the same air or working fluid is circulated over and over again. The working medium is not mixed with fuel, but it is heated by the burning of fuel in a separate supply of air in the combustion chamber and the transferring this heat to the working fluid which passes through tubes fitted in the combustion chamber. The working fluid does not come in to direct contact with products of combustion. The other disadvantage of open cycle gas turbine gas turbine plant is that the turbine exhaust is discharged into the atmosphere resulting in rejection of heat of exhaust gases to the atmosphere. In case of closed cycle these heat are recovered in a heat exchanger or recooler.

The working fluid (air or any other suitable gas such as helium, argon, hydrogen, and neon) coming out from compressor is heated in the heat exchanger (heater) by an external source at constant pressure. The high temperature and high pressure air coming out from the external heater is passed through the gas turbine. The working fluid coming out from the turbine is cooled to its original temperature in the heat exchanger (cooler) using external heating source before passing in the compressor. In the closed cycle, the working fluid is continuously circulated through compressor, cooler, heater and turbine without its change of phase, the required heat addition and rejection taken place in the heater and cooler respectively.

The performance characteristics, component elements and analysis for open cycle apply equally as well as to the closed cycle gas turbine.

Advantages of closed cycle over open cycle:
1) In the closed cycle gas turbine, the working medium is heated externally and the fuel does not mix with it, hence any inexpensive solid fuel such as coal can be used to heat the working fluid. Also need for filtration of the incoming air is completely eliminated.
2) They are kept free from product of combustion. Hence absence of corrosion and abrasion of the interiors of turbines and compressors extends the life of the plant and maintains the efficiency of the plant constant throughout its life.
3) The working medium is at relatively high internal pressure. So, specific volume is less and the dimensions of the compressors and turbines can be reduced and the maximum unit capacity can be increased. 
4) A working medium such as helium, argon, hydrogen, neon may be used which has very good physical properties compared to those of air. For example thermal conductivity of hydrogen is about 6.8 times that of air and therefore require smaller heat exchanger.
5) The closed cycle can be operated with highest efficiencies in comparison to open cycle plants at an equal initial temperature of working fluid.
6) The power output at constant speed can be varied by adding or substracting the working fluid and thus altering the weight of the charge. This gives improved part load efficiency as compared to open cycle gas turbine.
7) High heat transfer can be possible

Disadvantages of closed cycle:
1) In closed cycle gas turbine considerable quantity of cooling water is required.
2) Heat addition to the working medium takes place through heat exchanger, hence full heat of fuel fired is not utilized.
3) Additional equipments such as externally fired heater, cooler are required, the plant and its operation makes additional complexity.

Essential hydraulics fluid power basic

FLUID POWER SYSTEM

Fluid power system is power transmission system in which, the transmission of power takes place by means of “oil under pressure” or “compressed air”.

If “oil under pressure” is used in the system for power transmission, then the system is called “hydraulic system”.

If “compressed air” is used in the system for the power transmission then the system is called “pneumatic system”.

If large force and low speed is needed, then hydraulic system should be selected.

Because, oil is incompressible. Its volume will not change with increase in pressure. Pressure can be increased to any amount, nothing happens to volume of oil.

More the pressure of oil, more will be the force developed.

Hydraulic systems are slower in operation because, oil has more viscosity. Oil can not flow fast as compressed air.

If less force and higher speed is required, then pneumatic system should be selected.

As air is compressible in nature, it can not be pressurized to large amount of pressure. Since the pressure of compressed air is less (about 10 bar), force developed is also less.

Pneumatic systems are faster in operation because, air has very less viscosity. It can flow very quickly. Air rushes in to the cylinder once the valve is opened and within no time, the cylinder extends.

If compressed air is readily available in the industry, then pneumatic system is preferred.

In many industries, air compressed plant is already installed, as compressed air is needed for different processes. In such case, we can use the compressed air for operating pneumatic system.

Advantage of fluid power system:

1.       Fluid power system avoids mechanical linkage (such as belts pulley, chains, sprockets, gears etc.) to a greater extent.

2.       Hence, breakdowns are reduced and production will increase.

3.       “design and construction” of fluid power system is easy, simple and compact, as pipes are flexible, can be bent and accommodated in the available space.

4.       Automatic and safety circuits are possible, which is very important to increase rate of production and safety to avoid accidents.

5.       Fluid power system are more flexible to cope-up with the design changes. Any modification in design can easily in the existing and the fluid power system.

6.       Vibration and noise, wear ad ear etc. are reduced, as the mechanical linkages are replaced by the pipes.

7.       If overloaded, the system stalls, the system starts working once the load is reduced.

8.       Maintenance, servicing, lubrication etc. are simple and easy.

What can a jobless mechanical engineering fresher in India do to get hired if he has a good knowledge of AutoCAD, catia and ansys?

well, before i give answer of question, i want to say that Mechanical engineer are awesome. being Mechanical engineer is not a joke. only smart and hard working person can become an engineer. and you have good knowledge of AutoCAD, catia and ansys which is your plus point. but you want job. and before you get job all you have to take care is “Apply to company only if they really require your expertise”. other wise you have some other option such as:

• go to foreign and use your skill to help those companies which really require your skills.
• prepare for government exams and you are engineer so you have habit of studying hard so it will be very easy as compare to other graduates to crack exam.
• open classes for engineering students and start teaching AutoCAD, catia & ansys and also start taking orders from other industries for designing.
• analyze your situation and situation of market by using your operation research skills which you already studied during your engineering and take decision. you should proud of having knowledge of everything and being scientist of Mechanism.