In the previous column, Energy Sources for Generating Electricity (part 1), I mentioned several types of energy sources for generating electricity. In this column, I will tackle the diesel power plant as one of the energy sources. Here, the diesel internal combustion engine is used to drive the electric generator. It is dubbed in vernacular language as, “makina de krudo.” An example of this is the 70-megawatt diesel power plant in Ermita, Carbon, Cebu City. However, it is fed with bunker oil to run the engine. This column would tackle the basics of a diesel power plant that uses diesel fossil fuel to run the engine.
This type of power plant can be divided into two main parts: the generator, the driven part and the diesel engine, the prime mover or driving part. The generator is an electrical machine that converts mechanical energy into electrical energy. It works according to Faraday’s law of electromagnetic induction. The generator in itself has a rotor, the moving part and a stator winding, the stationary part. If the rotor is the one that provides electromagnetism — the magnetism produced by electricity, such as in magnetic lifter — the stator is the one that produces the electric current for the load, such as air-con, washing machine and many more. If the stator is the one that provides electromagnetism, the rotor is the one that produces the electric current.
The diesel engine is an internal combustion engine. It burns diesel fossil fuel inside the cylinder. The fuel is injected into the cylinder in atomized form for easy and complete burning as much as possible under high temperature. The burnt fuel creates a high pressure which pushes the piston down to the bottom of the cylinder. The piston is connected to a connecting rod which is connected to the crankshaft of the engine. The reciprocal movement of the piston inside the cylinder is converted into a rotary motion of the engine crankshaft. Thus, the engine rotates or runs. The engine of a 10-wheeler truck is an example.
However, in the case of large diesel power plant, the setup is somewhat different. The diesel engine is connected to the electric generator. When the engine rotates, the generator rotates and produces electricity. On the engine side, there are several systems involve: the fuel system, the lubricating system, the cooling system and the air system.
The fuel system is the one responsible for feeding fuel into the engine. There is a large fuel tank and fuel filter. A fuel pump draws the diesel fuel from this tank passing through the filter. The fuel is then stored in what is called “day tank,” a smaller tank serving as intermediary between the engine and the large fuel tank. From the day tank, the overflow fuel is routed back to the large tank. Another fuel pump draws the fuel from the day tank, passing once again through another fuel filter. This fuel is then fed into the fuel rail of the engine. The fuel injector then injects the fuel into the engine cylinder in atomized form for burning. Thus, in normal condition, the engine runs and the electric generator rotates and electricity is produced.
The lubricating system is responsible for the lubrication of the moving parts of the engine. The oil pump pumps the oil, passing through the oil filter, passing through the oil cooler, into the holes of the crankshaft and the camshaft to lubricate the bearings and into the other moving parts of the engine. It is to keep the engine smoothly running and to keep the moving parts from burning.
The cooling system is responsible for maintaining the engine at operating temperature. It is to avoid overheating which can damage the engine. It is responsible for circulating the cold water into the oil cooler, thus keeping the engine oil at normal operating temperature. The water then goes into the engine block, thus drawing the heat due to the burning of diesel fuel inside the engine cylinders. The hot water from the engine then moves to the “surge tank” which manages the coolant expansion. Then the water goes back to the water pump, which pumps the water to the “heat exchanger.” In the heat exchanger, the hot water from the engine is cooled by the cold water pumped from and to the cooling tower. Thus, the engine is kept at normal operating temperature.
The air system is responsible for providing the necessary air required for the burning of fossil diesel fuel inside the engine cylinders. We know from chemistry that the hydrocarbons in the fuel would burn with the oxygen in the air. Air enters the engine either of two ways. First, in normally aspirated engine, air is drawn using atmospheric pressure. Second, in a turbo-charged engine, air is compressed and pushed into the engine cylinder. In the cylinder, with both intake and exhaust valves closed, the air is compressed by the piston during compression stroke. This raises the air temperature high enough to burn the injected atomized diesel fuel. The fuel burns, expands and pushes the piston down the cylinder, causing the crankshaft to rotate. The exhaust gas is then removed through the exhaust valve, then to the exhaust manifold, then to the exhaust pipe, passing through catalytic converter, then to the atmosphere.
These are the fundamentals of the diesel engine used to drive electric generators to produce electricity. However, this type of energy source is used in small scale electric power plants. For example, the one in Barangay Ermita, Carbon, Cebu City, produces merely 70 megawatts of power. It cannot certainly supply the energy needs of a city as big as Cebu City. It is good only as back up source in case of shortage of electricity.