Diesel power plant – Diagram , Parts , Working , Advantages and Disadvantages

Diesel power plant

Introduction
This is a fossil fuel plant since diesel is a fossil fuel. Diesel engine power plants are installed where supply of coal and water is not available in sufficient quantity.
(i) These plants produce the power in the range of 2 to 50 MW.
(ii) They are used as standby sets for continuity of supply such as hospitals, telephone exchanges, radio stations, cinema theatres and industries.
(iii) They are suitable for mobile power generation and widely used in railways and ships.
(iv) They are reliable compared to other plants.
(v) Diesel power plants are becoming more popular because of difficulties experienced in construction of new hydel plants and thermal plants

Layout of Diesel Power plant

The essential components of diesel power plant are

• Diesel engine
• Air filter and super charger
• Engine starting system
• Fuel system
• Lubrication system
• Cooling system
• Governing system
• Exhaust system

Diesel engine:
This is the main component of a diesel power plant. The engines are classified as two stroke engine and four stroke engines. Engines are generally directly coupled to the generator for developing power. In diesel engines, air admitted into the cylinder is compressed. At the end of compression stroke, fuel is injected. The fuel is burned and the burning gases expand and do work on the piston. The shaft of the engine is directly coupled to the generator. After the combustion, the burned gases are exhausted to the atmosphere.

Air filter and supercharger
The air filter is used to remove the dust from the air which is taken by the engine. Air filters may be of dry type, which is made up of felt, wool or cloth. In oil bath type of filters, the air is swept over a bath of oil so that dust particles get coated. The function of the supercharger is to increase the pressure of the air supplied to the engine and thereby the power of the engine is increased.

Engine starting system
Diesel engine used in diesel power plants is not self starting. Engine starting system includes air compressor and starting air tank. This is used to start the engine in cold conditions by supplying the air.

Fuel system
It includes the storage tank, fuel pump, fuel transfer pump, strainers and heaters. Pump draws diesel from the storage tank and supplies it to the small day tank through the filter. Day tank supplies the daily fuel need for the engine. The day tank is usually placed high so that diesel flows to engine under gravity.
Diesel is again filtered before being injected into the engine by the fuel injection pump.

The fuel injection system performs the following functions.

• Filter the fuel
• Meter the correct quantity of the fuel to be injected
• Time the injection process
• Regulate the fuel supply
• Secure fine atomization of fuel oil
• Distribute the atomized fuel properly in the combustion; chamber.

The fuel is supplied to the engine according to the load on the plant.

Lubrication system
It includes oil pumps, oil tanks, coolers and pipes. It is used to reduce the friction of moving parts and reduce wear and tear of the engine parts such as cylinder walls and piston. Lubrication oil which gets heated due to the friction of the moving parts is cooled before re-circulation.

In the lubrication system the oil is pumped from the lubricating oil tank through the oil cooler where the oil is cooled by the cold water entering the engine. The hot oil after cooling the moving parts return to the lubricating oil tank.

Cooling system
The temperature of the burning fuel inside the engine cylinder is in the order of 1500 0 C to 2000 0 C. In order to lower this temperature, water is circulated around the engine. The water envelopes (water jacket) the engine, the heat from the cylinder, piston, combustion chamber etc, is carried by the circulating water. The hot water leaving the jacket is passed through the heat exchanger. The heat from the heat exchanger is carried away by the raw water circulated through the heat exchanger and is cooled in the cooling tower.

Governing system
It is used to regulate the speed of the engine. This is done by varying the fuel supply according to the engine load.

Exhaust system
The exhaust gases coming out of the engine is very noisy. In order to reduce the noise a silencer (muffler) is used.

Working of Diesel Power Plant
The air and fuel mixture act as a working medium in diesel engine power plant. The atmosphere air enters inside the combustion chamber during the suction stroke and the fuel is injected through the injection pump. The air and fuel is mixed inside the engine and the charge is ignited due to high compression inside the engine cylinder. The basic principle in diesel engine is that, the thermal energy is converted into mechanical energy and this mechanical energy is converted into electrical energy to produce the power by using generator or alternator.

Applications of Diesel Engines in Power Field

The diesel electric power plants are ch briefly used in the following field.
(a) Peak load plant:

Diesel plants can be used in combination with thermal or hydro-plants as peak load units. They can be easily started or stopped at a short notice to meet the peak demand.
(b) Mobile plant:

Diesel plants mounted on trailers can be used for temporary or emergency purposes such as for supplying power to large civil engineering works.
(c) Standby unit:

If the main unit fails or cannot cope up with the demand, a diesel plant can supply the necessary power. For example, if water available in a hydro-plant is not adequately available due to less rainfall, the diesel station can operate in parallel to generate the short fall in power.
(d) Emergency plant:

During power interruption in a vital unit like a key industrial plant or a hospital, a diesel electric plant can be used to generate the needed power.
(e) Nursery station:

In the absence of main grid, a diesel plant can be installed to supply power in a small town. In course of time, when electricity from the main grid becomes available in the town, the diesel unit can be shifted to some other area which needs power on a small scale. Such a diesel plant is called a “nursery station”.
(f) Starting stations:

Diesel units can be used to run the auxiliaries (like FD and ID fans, BFP, etc.) for starting a large steam power plant.

(g) Central stations :

Diesel electric plants can be used as central station where the capacity required is small

Advantages and disadvantages of diesel power plant

Following are the advantages of diesel power plant

1. It is easy to design and install these electric stations.
2. They are easily avail able in standard capacities .
3. They can respond to lo ad change s without much difficulty.
4. There are less standby losses.
5. They occupy less space .
6. They can be started and stopped quickly.
7. They require less cooling water .
8. Capital cost is less.
9. Less operating and supervising g staff f required.
10. High efficiency of energy conversion from fuel to electricity.
11. Efficiency at part loads is also higher .
12. Less of civil engineering work is required.
13. They can be located near the load cent re.
14. There i s no a sh handling problem.
15. Easier lubrication system.

Disadvantages in in stalling diesel units for power generation .
1. High operating cost.
2. High maintenance and lubrication cost .
3. Capacity is restricted. Cannot be of very big size.
4. Noise problem.
5. Cannot supply overload .
6. Unhygienic emissions.
7. The life of the diesel power plant is less (7 to 10 years) as compared to that of a steam power plant which has a life span of 25 to 45 years. The efficiency of the diesel plant decreases to less than 10% after its life period.