Energy conservation in Boilers | Energy is an indispensable resource that is required to run the economy and sustain the well being of people. Every day new discoveries are made to improve efficiency of the methods of power generation and transmission. After all, energy conservation must be our social responsibility.
Social responsibilities for exploring, harnessing, adopting the given energy sources to obtain effective means to consume those are no less important. The rapidly developing economies of Third World countries like India, China need to generate increasing amounts of energy as they grow. Energy shortages with rising cost confront every nation, especially those aspiring for industrial development. A time has come when no resource of this planet, including energy, should be used wastefully. To achieve this ideal, the society as a whole would require collective efforts of all groups, especially between the organizations harnessing energy and the consumers of energy. And both must understand the underlying principles of energy generation and energy consumption.
Every day new discoveries are made to improve efficiency of the methods of power generation and transmission. Some of the discoveries would fail to attract the users while some may be rejected or replaced by new claims. Such a circumstance would demand repeated explorations of energy opportunities and the way social responses can facilitate the use of new discoveries.
Energy Conservation Opportunities | The various energy efficiency opportunities in boiler system can be related to combustion, heat transfer, avoidable losses, high auxiliary power consumption, water quality and blowdown. Flue gases are the single most important cause of energy loss. As much as 18 to 22 percent of available energy goes up the chimney. Heat radiation and convection from boiler walls raise heat loss another 1 to 4 percent. Examining the following factors can indicate if a boiler is being run to maximize its efficiency:
1. Stack Temperature >> The stack temperature should be as low as possible. However, it should not be so low that water vapor in the exhaust condenses on the stack walls. This is important in fuels containing signficant sulphur as low temperature can lead to sulphur dew point corrosion. Stack o temperatures greater than 200 C indicates potential for recovery of waste heat. It also indicate the scaling of heat transfer/recovery equipment and hence the urgency of taking an early shut down for water / flue side cleaning.
2. Feed Water Preheating using Economiser >> Typically, the flue gases leaving a modern 3-pass shell o boiler are at temperatures of 200 to 300 C. Thus, there is a potential to recover heat from these gases. The flue gas exit temperature from a boiler is usually maintained at a o minimum of 200 C, so that the sulphur oxides in the flue gas do not condense and cause corrosion in heat transfer surfaces. When a clean fuel such as natural gas, LPG or gas oil is used, the economy of heat recovery must be worked out, as the flue gas temperature may be well o below 200 C.
3. Combustion Air Preheat >> Combustion air preheating is an alternative to feed water heating. In order to improve thermal efficiency by 1%, o the combustion air temperature must be raised by 20 C. Most gas and oil burners used in a boiler plant are not designed for high air preheat temperatures. Modern burners can withstand much higher combustion air preheat, so it is possible to consider such units as heat exchangers in the exit flue as an alternative to an economizer, when either space or a high feed water return temperature make it viable.
4. Incomplete Combustion >> Incomplete combustion can arise from a shortage of air or surplus of fuel or poor distribution of fuel. It is usually obvious from the colour or smoke, and must be corrected immediately. In the case of oil and gas fired systems, CO or smoke (for oil fired systems only) with normal or high excess air indicates burner system problems. A more frequent cause of incomplete combustion is the poor mixing of fuel and air at the burner. Poor oil fires can result from improper viscosity, worn tips, carbonization on tips and deterioration of diffusers or spinner plates.
5. Excess Air Control >> Excess air is required in all practical cases to ensure complete combustion, to allow for the normal variations in combustion and to ensure satisfactory stack conditions for some fuels. The optimum excess air level for maximum boiler efficiency occurs when the sum of the losses due to incomplete combustion and loss due to heat in flue gases is minimum. This level varies with furnace design, type of burner, fuel and process variables. It can be determined by conducting tests with different air fuel ratios….see complete article