Assignment No 4

Power Plant

Submitted To:
Sir Behzad Rustam

Submitted By:

Usama sagheer
BSME01163103
Section B

DEPARTMENT OF MECHANICAL ENGINEERING

THE UNIVERSITY OF LAHORE
Cogeneration:
Cogeneration is a technology which is used to generate heat and electricity which
is highly efficient. It is also known as combined heat and power system (CHP). It
is used to produce both electricity and heat from a single fuel. Exhaust energy is
utilized from gas turbine, in the heat exchanger we can generate useful heat which
can be used in many applications, with no consumption of additional fuel.
Conventional system produces either electrical or thermal energy but by
cogeneration system we can produce both energies.
When we compared with the normal power station, these systems are inexpensive.
This is used to reduce the emission of pollutants from particular products such as
mercury, sulfur dioxide, carbon dioxide, otherwise the greenhouse effect would
occur.

Cogeneration Plant Efficiency:

By comparing the separate supply of power from the national grid as well as a gas
boiler intended for on-site heating, the cogeneration system helps to achieve 40
percent additional energy savings. A cogeneration system's total energy efficiency
is the percentage of the fuel is converted to both electricity and useful thermal
energy. The total efficiencies of typical cogeneration systems vary from 65 to 90
per cent.

Typical cogeneration performance table:

Prime mover Nominal Electrical Efficiencies %
in range Generation
cogeneration (Electrical) Heat rate
Electrical Thermal Overall
(kcal/kWh) Conversion Conversion Cogeneration
 Steam 10-100 MW 2520-5040 17-34 50 84-92
Turbine
Smaller 800-10000 2770-3525 24-31 50 74-81
gas turbine kW
Larger gas 10-20 MW 2770-3275 26-31 50 78-81
turbine
Diesel 10-3000 kW 2770-3775 23-38 50 73-88
Engine
Reciprocating 500-3000 kW 2400-3275 26-36 50 76-86
Engine

Types of Cogeneration power plant:

Cogeneration power plants are classified on the basis of operating process and
energy utilization series. Cogeneration system are classified into two types:
1. Topping cycle
2. Bottoming cycle
1) Topping Cycle:
In this type of power plant, fuel is burnt in the boiler to produce high temperature
steam. This steam is expanded in a turbine which is coupled to a generator to give
electric power. The reject heat from turbine is used for manufacturing process. The
supplied fuel is first used to generate power then ultimately generate thermal
energy in the procedure. As steam required for the manufacturing process need low
temperature therefore topping is mostly used. Topping cycle is further classified
into four types:

i) Steam turbine Cogeneration System:

Steam turbines are one of the most versatile technology in general production. It
uses the system similar to thermal plant. Fuel may be oil, coal or wood. The high
pressure steam produced by the boiler drives turbine and generate electricity. The
low pressure exhaust form steam turbine is used for industrial process application.
Back pressure steam turbine is used as they exhaust low pressure steam. Therefore,
steam turbines are often used in those cases where demand reaches 1MW up to
hundreds of MW. Therefore, steam turbines are not ideal for areas of irregular
demand due to the inertia in the network.
This is used to reduce the emission of pollutants from particular products such as
mercury, sulfur dioxide, carbon dioxide, otherwise the greenhouse effect would
occur. When we compared with the normal power station, it is inexpensive. ii)
Gas turbine Cogeneration System:
Gas turbine operates on a thermodynamics cycle known as Brayton cycle.
Atmospheric air is compressed, heated and then expanded in a Brayton cycle, with
the turbine producing the excess power. The exhaust from combustion chamber is
used as process heat. In the waste heat recovery boiler where the heat of gases is
transferred to water the hot gases are actually used to raise steam.
The cost of electricity generated is high because of less supply and high prices of
petroleum products. Gas turbine need more maintenance than steam turbine.
Owing to greater availability of natural gas, substantial reduction in installation
costs and good environmental efficiency, the gas turbine system has probably
experienced most growth in recent years. iii) Combined cycle
Cogeneration System:
Combined cycle system is basically the combination of steam turbine and gas
turbine system. The gas turbine exhaust is used to collect steam in waste heat
boilers The boiler steam is used in back pressure turbine that drives another
alternator to generate electricity. The steam turbine low pressure exhaust is used as
process vapor. This system has greater versatility for topping process steam. Global
demand for a combined cycle power plant is rising significantly, with some
analysts predicting exponential growth over the next decade. It has a high overall
efficiency over the plant. iv) Internal combustion engine
Cogeneration system:
This machine uses a diesel engine driving the electrical generator. The engine
exhaust a jacket cooling are used as heat sources for the waste heat boiler which
converts water into process steam. This system has higher electricity to thermal
ratio than that required by the most industries.
This type of system is most widely used in areas and facilities which consume a
small amount of energy because heat recovery is efficient for smaller systems.
Therefore, it is widely used in facilities where need for electricity is greater than
thermal energy and also where we don’t require high quality heat.
2) Bottoming cycle:
In a bottoming cycle the main fuel is utilized for generating thermal energy at high
temperature. The heat discarded in this method is then utilized for generating
power using a recovery boiler a turbine generator. These days this type of plants is
extensively used in the process of manufacturing that needs heat at high
temperatures in the boiler, as well as refuse heat at very high temperature. Though
used in industries such as cement, steel, ceramics, petrochemicals, coal, etc.

Economics of Cogeneration:
The economics of power generation by cogeneration is proving to be more
attractive, due to low capital cost, and high reliability and flexibility in operation.
The cogeneration technology is more energy efficient than the separate heat and
power generation. However, this does not necessarily indicate that an individual
company has the profit maximizing option.
We can see cogeneration economics by two ways. One as a consumer of heat and
electricity, The other as a utility company exploiting cogeneration as a means of
supplying both heat and electricity to its customers. In the case of a consumer
cogeneration system this value will correspond to the utility tariff, with some
deduction being made for any services that are still desired from the utility
company.
The purchasing price of energy is usually higher than the avoided costs, and in the
case of consumer-exploited cogeneration schemes, economics will actually look
better.