Presentation on theme: "Pharos University جامعه فاروس Faculty of Engineering كلية الهندسة Petrochemical Department قسم البتروكيماويات PE 330 ENERGY CONSERVATION LECTURE (4) Different."— Presentation transcript:
Pharos University جامعه فاروس Faculty of Engineering كلية الهندسة Petrochemical Department قسم البتروكيماويات PE 330 ENERGY CONSERVATION LECTURE (4) Different methods of energy conservation A- Energy Performance Assessment of Boilers 1- Boilers: A boiler is a device ( enclosed vessel) that converts the chemical energy of a fuel into a useful heat output, such as steam or hot water.
The hot water or steam under pressure is then usable for transferring the heat to a process. When water is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be extremely dangerous equipment that must be treated with utmost care. The fuel used could be gas, but some older coal and oil-fuelled boilers are still in operation. The main reasons for choosing oil firing are unavailability or unreliability of gas supplies. There are also a small number of biomass fired boilers in operation, where there is a good availability of fuel.
Basic Boiler Operation Inside a boiler, the fuel is combusted by burners. These produce flames, and the hot combustion gases created transfer the heat to water, which has been fed into the boiler from an external source. The feed water may enter the boiler directly, or via a buffer tank. The temperature that this water is heated to will depend on whether the boiler output is steam or hot water. High temperature hot water boilers produce hot water at temperatures of over 90ºC. Hot water boilers producing water at temperatures of 90ºC and below are classed as low temperature hot water boilers.
Steam and Water Mass Balances in boilers
Combustion Process Mass Balances in boilers
Boiler Types and Classifications There are virtually infinite numbers of boiler designs but generally they fit into one of two categories: A- Fire tube or "fire in tube" boilers; contain long steel tubes through which the hot gasses from a furnace pass down a tube and into bundles of tubes immersed below water level and around which the water to be converted to steam circulates. Fire tube boilers, typically have a lower initial cost, are more fuel efficient and easier to operate, but they are limited generally to capacities of 25 tons/hr and pressures of 17.5 kg/cm 2.
B-Water tube or "water in tube" boilers in which the conditions are reversed with the water passing through the tubes and the hot gasses passing outside the tubes. These boilers can be of single- or multiple-drum type. These boilers can be built to any steam capacities and pressures, and have higher efficiencies than fire tube boilers. In either case, the heat must transfer across the combustion gases. Therefore, these tubes are made of materials with good heat-transfer properties. After use, the combustion gases exit the boiler via a chimney known as a flue. The output steam or hot water will be fed out of the boiler into a distribution system. This is a network of insulated pipes that transfer the steam/hot water to the point(s) at which it is used.
Types of fuel used in boilers There are a wide range of fuels used. Boilers commonly burn standard hydrocarbon fuels, such as natural gas, oil and coal, but some burn tallow or waste materials. Some boilers, known as dual-fuel boilers, can burn gas or oil. This is useful in the rare cases where an interruptible gas supply contract is held. Coal burners can be a variety of designs mainly centring on how the coal is fed to the boiler and burnt. Currently, gas boilers are the most popular type of steam raising or hot-water-producing equipment.
Biomass boilers are becoming more popular. Biomass is any solid non-fossil-based organic fuel and includes wood (either grown specifically as a fuel or as waste material), straw, types of grass and many other organic by-products. The mechanisms for handling and burning fuel differ markedly for solid, liquid and gaseous fuels, and the design of a boiler depends on the intended fuel type(s). However, many of the general principles for saving energy are the same.
Boiler losses and measures of efficiency The operational efficiency of a boiler is measured by the percentage of the fuel input energy that is eventually delivered as useful heat output. Not all of the heat released when the fuel is combusted can be used and some potential heat is never released due to incomplete combustion. Major sources of heat loss from steam boilers are through the flue gas, blowdown and radiation to the boilers surrounding s.
When operated correctly, all modern boilers are capable of achieving an efficiency of around 80% (based on the gross calorific value of the fuel). If they do not, action should be taken to achieve at least this level of performance. Higher efficiencies(of up to 85%) are possible for condensing gas boilers and for plant fitted with economisers. However, note that the efficiencies that can be achieved by steam boilers are different from those available to hot water boilers. The type of economiser will have significant impact on the efficiency improvement achieved.
Steam losses As well as the energy losses associated with boilers, there will also be losses associated with the distribution of the steam and hot water. These losses will be due to heat loss from pipework, malfunctioning steam traps, and leaks and unnecessary use of the steam and hot water at the point of use