26-07-2012, 04:09 PM
DIESEL POWER PLANT
INTRODUCTION:
A diesel engine (also known as a compression-ignition engine) is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber. This is in contrast to spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which uses a spark plug to ignite an air-fuel mixture. The engine was developed by Rudolf Diesel in 1893.
The diesel engine has the highest thermal efficiency of any regular internal or external combustion engine due to its very high compression ratio. Low-speed Diesel engines (as used in ships and other applications where overall engine weight is relatively unimportant) the largest of which can have a thermal efficiency that exceeds 50 percent.
ADVANTAGES OF DIESEL PLANTS OVER THERMAL PLANTS
1. The diesel power plants are more efficient than steam power plants in the range of 150 MW of capacity.
They maintain high operating efficiency in the load range of 50% to 100% of full load. DIESEL POWER PLANT
2. Diesel plants are cheaper in first cost than steam plants; plant units upto about 7 kW. Above this capacity, the diesel cost rises rapidly while that of steam plants continues to fall.
3. It has no standby losses.
4. It can burn fairly wide range of fuels.
5. It can be quickly started up and brought into service (within one minute).
6. Manufacturing periods are short and therefore, a diesel station may be rapidly extended to keep pace with load growth by just adding the generating units of suitable sizes.
7. Where skilled labor is scarce, the full automation of diesel station can be provided for starting, synchronizing and shutting down diesel sets with reasonably low capital costs.
8. Maintenance can be simplified by the provision of easily replaceable assemblies of parts, thus enabling Re-conditioning to be undertaken away from generating plants.
9. It is possible to install compact, light weight, high speed diesel sets of smaller capacity for sites that are remote, cramped or difficult for access, This was the main reason in adopting many small diesel plants in the “Namrup” area of Assam.
10. The cooling water required for the same capacity is considerably less than the thermal plant. The site of the thermal plant is dictated by the availability of cooling water in many cases whereas diesel plant can be located without giving much importance to the availability of cooling water. The water ratio for thermal to diesel is approximately 50 : 1.
11. The diesel plants can be located very near to the load centres, many times in the heart of the town.
The diesel plants are admirably suited to load centre location. The combination of fuel economy, remote operational control, flexibility as to installed capacity and high degree of freedom from hazard allow placement of diesel generation sets almost anywhere that it would be useful and economical.
12. The space required for diesel plant is considerably less than thermal plant and, therefore, cost of foundation and buildings is less.
13. The storage required for the fuel is considerably less than the thermal and it can be handled more easily.
14. There is no problem of ash handling as there is practically no refuse.
15. The plant layout is very simple compared with thermal plant. They are easy to operate and control.
16. The lubrication system is not only more economical but permits the use of specially compounded cylinder lubricants that provide dramatic improvement in wear rates. The cylinder liner life of 50,000 to 100,000 hours is common even burning the poorest grade of residual oils. The lubrication cost of diesel plant is 0.5 mills per kW-hr, even burning residual fuel oil which is 2 to 5 times compared with steam plant.
17. They can be employed in all climatic zones.
18. They are very adaptable and can be easily extended to the given power requirements.
19. Machine sets are readily available as standard sets in the range of 500 kW to 40 MW.
20. Operational reliability with high availability is ensured.
DISADVANTAGES OF DIESEL PLANTS OVER THERMAL PLANTS
1. The unit capacity of diesel engine is considerably low than the thermal unit. The cost of unit increases with an increase in unit capacity for diesel plant whereas the cost of the unit goes on decreasing in case of thermal plant with an increase in unit capacity.
2. The repair and maintenance costs are generally much higher than for steam plants. These costs are more or less fixed in case of steam plants and more or less are proportional to output in the case of diesel plants.
3. Life of 25 to 30 years is normal for thermal plant whereas the life of diesel plant is hardly 2 to 5 years or less.
4. The diesel plants are not economical where fuel has to be imported.
5. The noise is a serious problem in diesel plant.
6. Selected types of fuels are required in diesel engines whereas there is more mobility in case of thermal plant.
7. The lubrication cost is high.
8. The diesel plants are not guaranteed for continuous operation under overloads whereas steam plant can work at 25% overload continuously.