f What is meant by bottoming cycle and topping cycle in comb

f. What is meant by bottoming cycle and topping cycle in combined power plant?

g. Why is the combined gas steam cycle more efficient than either of the cycles operated alone?

h. What is the difference between cogeneration and regeneration?

i. What is the tri-generation? Give an example.

j. How is the utilization factor (the cogeneration thermal efficiency) for a cogeneration plant defined? Could this factor be unity for a cogeneration plant that does not produce any power? Explain

k. How can a combined cycle plant be used for cogeneration? Draw a schematic diagram showing the main components of such a system. Define its thermal efficiency?

l. A solar/fuel power system is composed by:

a solar collector and a storage tank connected to the Rankine cycle

Gas turbine unit with one intercooling.

Rankine cycle with three feed water heaters (1 open and 2 closed)

A steam is extracted at a pressure higher but very close to the condenser pressure.

This steam is used to drive a thermal desalination plant.

Draw schematically a diagram of such a plant.

m. Show that the thermal efficiency of a combined gas–steam power plant h_cc can be expressed as: (eta not h)

h_{cc =} h_{g +} h_s - h_gh_s

where h_g = W_g/Q_in and h_s = W_s/Q_g,out are the thermal efficiencies of the gas and steam cycles, respectively. Using this relation, determine the thermal efficiency of a combined power cycle that consists of a topping gas-turbine cycle with an efficiency of 40 percent and a bottoming steam-turbine cycle with an efficiency of 30 percent.

Show that h_cc is higher than h_g and h_s

Solution

f)

Both topping- and bottoming-cycle systems are types of cogeneration

Topping Cycle CHP

Topping-cycle systems produce electricity first, then recover the excess thermal energy for heating or cooling applications

Bottoming Cycle CHP

By contrast, bottoming-cycle systems, also known as “waste heat to power,” are a process whereby waste heat from an existing process is used to produce electricity

g)

The combined gas system cycle takes advantage of the desirable characteristics of the gas cycle at high temperature, and those of steam cycle at low temperature, and combines them. The high temperature exhaust gases from the turbine of gas cycle are used to heat the steam of power cycle thus using the heat energy of exhaust gases. The result is a cycle that is more efficient than either cycle executed operated alone

h)

Cogeneration is the production of more than one useful form of energy(such as process heat and electric power) from the same energy source .

Regeneration is the transfer of heat from the working fluid at some stage to the working fluid at some other stage in the cycle.

i)

Trigeneration or combined cooling, heat and power (CCHP) refers to the simultaneous generation of electricity and useful heating and cooling from the combustion of a fuel or a solar heat collector