Process Optimization And Major Equipment Experime Nts Of The Boiler Flue Gas Heat Utilization System

Reported by the <2013world energy statistical yearbook>, China occupies50.22%of the coal consumption all over the world in2012, this is the first time that China consumes more than half of the coal resources. Being the most important power resource in China, about61%of the coal is cosumed by power generation industry. With the steady development of china’s economy, the contradiction between power supply and consumption becomes increasingly serious, increasing fossil’fuel utilization rate can serve as one of the most significant approach to solving this problem.While providing most of the electricity power for the country, China’s coal-fired power plants consumes large amount of coal and water resources, and lots of flue gas is exhausted without recycling measures, which accouts for70%-80%of the toal heat loss for the boiler. In order to avoid low-temperature corrosion at tail heating surfaces, exhaust gas temperature is usually20-30℃higher than the design temperature, in turn increasing the coal consumption of power units. Detailed calculation implies that when exhaust gas temperature increases by15-20℃, boiler efficiency reduces by1%, power supply standard coal consumption increases by3-4g/kW-h, which means extra3000t standard coal is needed. Hence, decreasing exhaust gas temperature can significantly reduce coal consumption, and it is of great importance to improve the economic performance of power plants.At present, many methods for reducing exhaust gas temperature are available, they could be concluded in three aspects as follow:(1) Structure design optimization of tail heating surfaces;(2) Improving the heat-transfer performances of existing heat exchanger;(3) Adding new heating surfaces.For existing power plant, changing the structure of tail heating surfaces not only requires huge investment, also it has great effect on its operation, thus it is not commendable to apply the first kind of method. In this paper, the third aspect is applied. It is found that using tail flue gas to heat the condensate is the simplest recycling method, by arranging low temperature economizer at the rear of heating surfaces, both exhaust gas temperature and coal consumption rate reduce, while economic performance of the power unit greatly improves. Subsequently, based on energy cascade utilization theory, in-depth analysis of regular low temperature economizer is proposed, finding out the reasons for its limited energy-saving efficiency, optimization of flue gas waste heat recovery system for regular low temperature economizer on both water side and gas side are proposed. Excellent performance is anticipated due to proper arrangement and utilization of waste heat.As far as flue gas waste heat recovery is concerned, overcoming low temperature corrosion at tail heating surfaces becomes the key point to improve the efficiency and safety of flue gas waste heat recovery system. High polymer material such as PVC not only has great acid-corrosion resistance, also it do not absorb containment due to smooth surface, thus lots of researchers have devoted to exploring new PVC to replace metal as tail heating surfaces material. Besides advantages mentioned above, plastic heat exchanger requires low investment, it will be a revolutionary movement in power generation industry if replacing metal heat exchanger by plastic ones. In this paper, we focus on analyzing major equipments arranged at rear flue gas channel, desiging and building new experiment table based on plastic heat exchanger, in-depth performance analysis is put forward in order to promote the utilization of plastic heat exchanger in waste heat recovery system.Research of this paper can serve as a new approach to realizing flue gas waste heat recovery.