(SEM VII) THEORY EXAMINATION 2019-20 POWER PLANT ENGINEERING

POWER PLANT ENGINEERING (RME-071)

B.Tech – Semester VII

SECTION A

(Attempt all questions)

(a) Why thermal power plants are not suitable for supplying fluctuating loads

Thermal power plants are not suitable for supplying fluctuating loads because they require a long time to start, shut down, or change operating conditions. The boiler, turbine, and condenser systems have high thermal inertia, which means sudden load changes can cause mechanical and thermal stresses. Frequent load variations reduce efficiency, increase fuel consumption, and may lead to operational instability. Hence, thermal power plants are best suited for base load operation rather than rapidly changing load demands.

(b) Pulverized coal and its use

Pulverized coal is coal that has been ground into a fine powder so that it burns more efficiently. When coal is pulverized, its surface area increases, leading to rapid and more complete combustion. Pulverized coal firing is used in modern thermal power plants because it improves combustion efficiency, reduces fuel wastage, increases boiler capacity, and allows better control over steam generation.

(c) Use of superheaters in steam power plants

Superheaters are used in steam power plants to increase the temperature of steam above its saturation point. Superheated steam improves the thermal efficiency of the plant by reducing moisture content in the turbine exhaust. It also prevents blade erosion in turbines and increases the overall power output of the plant. Therefore, superheaters play a crucial role in improving performance and reliability of steam power plants.

(d) Drawbacks of stationary gas turbine power plants

Stationary gas turbine power plants suffer from lower thermal efficiency compared to steam power plants, especially at part load conditions. They also require high-quality fuels, which increases operating cost. Additionally, the life of turbine components is affected by high operating temperatures, and performance decreases significantly in hot climatic conditions.

(e) Need for shielding in a nuclear reactor

Shielding in a nuclear reactor is necessary to protect operating personnel and the environment from harmful nuclear radiations such as gamma rays and neutrons. Without proper shielding, radiation exposure can cause severe biological damage. Materials like lead, concrete, and water are commonly used as shields to absorb radiation and ensure safe operation of the nuclear power plant.

(f) Advantages and limitations of geothermal power plants

Geothermal power plants utilize heat energy from the earth’s interior to generate electricity. Their main advantage is that they are renewable and environmentally friendly, with very low emissions. They provide reliable base load power and have low operating costs. However, their application is limited to specific geographical locations where geothermal resources are available. High initial cost and corrosion problems are also major limitations.

(g) Significance of two-part tariff and three-part tariff

Two-part tariff divides the electricity cost into fixed charges and energy charges, ensuring recovery of fixed costs irrespective of power consumption. Three-part tariff further includes demand charges, energy charges, and fixed charges, which provides a more accurate and fair billing system. These tariff systems encourage efficient electricity usage and help power utilities recover operational and maintenance costs effectively.

SECTION B

(Attempt any three)

(a) Thermal efficiency of Rankine cycle

The Rankine cycle is the basic operating cycle of a steam power plant. Thermal efficiency of the Rankine cycle is defined as the ratio of net work output to the heat supplied in the boiler. It depends on boiler pressure, condenser pressure, and steam temperature. Increasing boiler pressure and superheating steam improves cycle efficiency, while lower condenser pressure increases turbine work output. Rankine cycle analysis helps engineers evaluate plant performance and optimize operating conditions.

(b) Economics of power plant selection

The selection of a power plant is primarily based on economic considerations. Factors such as initial capital cost, fuel cost, operation and maintenance expenses, load factor, plant efficiency, and availability of fuel are taken into account. Fixed costs include interest, depreciation, and insurance, while running costs include fuel, labor, and maintenance. A proper economic analysis ensures minimum cost of power generation with maximum reliability and efficiency.

(c) Factors affecting choice of site for power plant

The location of a power plant is influenced by availability of fuel, water supply, transportation facilities, proximity to load center, and environmental considerations. Adequate land, disposal of waste, climatic conditions, and future expansion possibilities are also important. Proper site selection reduces transmission losses, operating cost, and environmental impact.

SECTION C

(Attempt any one)

4(a) Ash handling system in a thermal power plant

An ash handling system is used to remove and dispose of ash produced during coal combustion in thermal power plants. The system consists of ash collection, transportation, and disposal units. Bottom ash is collected from the boiler furnace, while fly ash is collected using electrostatic precipitators. Ash is transported using hydraulic, pneumatic, or mechanical systems. Handling ash efficiently is challenging due to dust pollution, equipment wear, and disposal issues. Proper ash handling ensures safe plant operation and environmental protection.

5(a) Combined Cycle Power Plant (CCPP)

A combined cycle power plant combines a gas turbine cycle with a steam turbine cycle to improve overall efficiency. In this system, exhaust gases from the gas turbine are used to produce steam in a heat recovery steam generator, which then drives a steam turbine. This arrangement utilizes waste heat effectively and achieves higher efficiency compared to conventional power plants. Combined cycle plants offer fast startup, lower emissions, and high fuel efficiency.