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Furnace oil
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Thermal power plants in most cases burn furnace oil. following report deal with the information required for operation on furnace engine Internal combustion engines can deal with any hydro carbon fuel or fossil fuels. But different engine models are designed to run certain specifications of fuel and altering these specifications can seriously damage the engine components. Smaller engines for example automobile engines use refined petrol. Larger automobile engines for trucks and buses used diesel oil. And larger 2 stroke and 4 stroke engine can burn furnace oil up to 700 CST@ 50 degree C. The quality of fuel is stated in its analysis report and decides the suitability for different engine applications. For diesel engines impurity contents and handling properties are most important. The fuels customary traded or classed on viscosity. A wrong conception is that lower viscosity fuels are good fuels and higher viscosity fuels are bad fuels. In practice however this is possible that higher viscosity fuels may be better in quality than lower viscosity fuels. Since end users are normally not aware of the origin of the fuel or the technology used for refining therefore the only parameters available for him is the test report which must be supplied with the supply and further verified by independent laboratories.
A typical fuel specification is given below Density <991 kg/m cube Kin emetic Viscosity <700 CST @ 50 C Flash point <60 C Pour Point <30 C Carbon Residue <22 % (m/m) Total Sediment <0.10 % m/m Water <1.0 % (v/v) Sulphur <5.0 % (m/m) Vanadium <600 mg/kg Aluminum+Silicon <80 mg/kg
CARBON RESIDUES Carbon residue property is the coke forming property. Carbon residues can not be improved by centrifuging and purification. This property attributes to fouling in the combustion chamber and exhaust gas systems and turbochargers. If a severe problem of the fouling is experienced the carbon residue tests on fuel should immediately be carried out. ASHFALTNESS Asphaltness is aromatic, slow turning, semi solid hydro carbon compounds dispersed in the fuel oil. They also have the similar effects as carbon residues. Fouling of the exhaust system is mainly the results. Fuel oil with high Asphaltness will have a tendency to form sludge. In certain cases the fuel pump sticking is reported to be caused by high Asphaltness content fuel oil. The phenomenon can be accelerated with water and oil contamination. The damage can be controlled by pre treatment of the fuel by severe centrifuging. In case such problems experienced then the cycle of purification should be increased and the purifiers to be adjusted with low feed rate. DIESEL INDEX Diesel index determines the ignition quality of the fuel. This is related to hydro carbon composition of the fuel. Paraffin being the high quality, n-heptane medium and aromatics low quality. Fuel oil with low index numbers may cause problems in starting and running on low load Fuel oil with low diesel index cause retarded combustion resulting unburned fuel passing through the exhaust and hence causing fouling . SULPHER Sulphur is one the most severe hazard in fuel oil. During combustion Sulphur produce Sulphur di oxide and Sulphur tri oxide. Sulphur oxides when join water which is present in exhaust gases form Sulphuric acid which cause corrosion in running components. Cylinder liner wear and exhaust valve burning is attributed to Sulphur corrosion. Maintaining the temperatures above the dew point of sulphuric acid during combustion can prevent low temperature attack. Alkaline lubricating oils with high TBN provides maximum protection for Sulphur attack. VANADIUM AND SODIUM Vanadium is soluble in oil and hence impossible to be removed. Vanadium acts as catalysis for corrosion. Sodium is soluble in water and can be removed by centrifuging. Sodium Vanadium ash if formed in ratio of 1:3 cause high temperature corrosion and burning of valves. The combination works at a catalytic during combustion process and cause valve burning. The damage can be minimized by extensive centrifuging and removing sodium contents from the fuel WATER Water contents itself is not harmful for the fuel. But it reduces the quantity of fuel. For example if two fuel samples are available with 1 and 2 % of fuel. Then for the fuel which is containing 2% water in fact 1 % expensive than 1st sample. Water is removed during the centrifuging and heating of fuel. If water contents remained in water it absorbs latent heat from the combustion and hence increases fuel consumption. Water in fuel also may cause stopping of the engine and gives low exhaust temperatures. Water if emulsified with fuel may cause fuel pump sticking. ASH Ash contents are non combustible material s such as sand, rust, metal particles metal oxides etc are found. Ash contents can be removed by centrifuging. If passes through the engine they cause abrasive wear in fuel injection system. The early wearing of fuel injection pumps are normally caused by ash contents. Extensive centrifuging and fine filtration can prevent the damage due to ash contents VISCOSITY Viscosity is defined as the measure of the internal friction or resistance to flow. Older systems of viscosity measurements are obsolete and now kinemetic viscosity is measured Fuel oil is graded by the viscosity for example IF 180 or IF 380 saying the fuel of 380 CST at 50 degree centigrade. Viscosity is related to temperature. And therefore oil is heated up to bring the required viscosity for combustion. Viscosity is an important parameter for Operating engineers for pumping, pretreatment, and injection of fuel oil. The viscosity is monitored. DENSITY Density is defined as the mass of a unit volume. The density for operating engineers is required to calculate the weight of the fuel. For operating engineers the density is required to adjust the water interface in purifiers. POUR POINT The pour point is the lowest temperature at which the oil will flow or can be poured. For handling purpose the temperature of fuel to be maintained above pour point level. Certain additives in fuel can improve the pour point of fuel FLASH POINT. The flash point is defined as the lowest temperature at which the fuel start giving the vapor which can ignite when a open flame is provided. The flash point is maintained for safety reasons while handling fuel. DERING FURNACE OIL Before ordering fuel the suppliers should be asked to provide their fuel specs. The price of fuel can vary according to specifications. For example the fuel of 180 CST will be on higher price than 380 CST and higher Sulphur fuels are cheaper than low Sulphur fuels. Viscosity of the fuel is one of the most important parameter to be checked .This should accordance to fuel heating system available. Then pour point should be checked. Pour point determines that up to what temperature the fuel can flow or be pump able. While ordering the stock international market trends and the capacity of the fuel tank should be taken in account. This is also important that transportation charges also taken in account RECEIVING FURNACE The correct measurement of the delivery tank and the calculations according to temperature corrections should be carried out before the seals are broken and pumping started. After a joint checking of the tank the pumping can be started. If the pumping system is fitted with continuous sampling system then the bottles should be fitted and continuous sampling started. On those plants where such facility is not available then before pumping three samples should be obtained. One sample to be handed over to delivery person, one to be retained at power plant and 3rd to be sent to laboratory for analysis. Once the pumping is complete then again the tank measurements at source and receiving end to be carried out and the quantity to be verified before the delivery receipts are signed. TANK STORAGE The oil to be kept in storage tanks until it is transferred to settling tank. The tanks should be having the provision for heating. The temperature to be maintained should be enough to be above pour point level for trouble free transfer. The ranks if provided with water drain should be drained regularly to remove water contents SETTLING TANKS From the storage tank the furnace oil is transferred to settling tank. This is 1st place where pre treatment of the furnace is started. Here the oil kept to settle for at least 24 hours. And heated to 60 degree centigrade or higher. A good amount of water is separate and drained off. PURIFICATION From the settling tank the oil is passed through the purifiers where water and sludge is removed. The oil is heated to high temperatures and passes through centrifuges which work as purifiers and clarifiers. The oil from the purifier is stored in service thanks where it is ready to fed to engines SERVICE TANKS The oil in service tanks kept at high temperatures and its measurements are regularly recorded. For safety reasons the oil is kept below flash point level. FUEL SUPPLY UNITS Fuel supply unit consist of booster pumps, oil filters, heaters and viscosity controllers. Here the fuel is heated to the required viscosity. The heaters are thermostatically controlled and automatically maintain the viscosity
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