Tail flue gas waste heat utilizing system of utility boiler based on hot blast recycling

Abstract

The invention relates to a tail flue gas waste heat utilizing system of an utility boiler based on hot blast recycling. The tail flue gas waste heat utilizing system comprises a boiler water supply regenerative heating device and a boiler tail flue gas waste heat utilizing device, wherein the boiler water supply regenerative heating device is provided with a low-pressure heating unit, a high-pressure heating unit, a deoxygenizing unit and a water supply pump, which sequentially communicate; low-pressure extraction steam generated after work application of steam generated by the boiler is used by the low-pressure heating unit as a heat exchanging heat source; and high-pressure extraction steam generated after work application of steam is used by the high-pressure heating unit as a heat exchanging heat source. According to the tail flue gas waste heat utilizing system disclosed by the invention, a circulating hot wind is utilized as a heat-transfer medium, so that the temperature level and the heat-into-power conversion efficiency of the flue gas waste heat recycled by the water supply regenerative system are improved, the purpose that the electricity supply efficiency of an electricity generating system is substantially improved is realized, the investment and the operation control difficulty of a waste heat recovery system are reduced, the problems of the corrosion, the ash deposition and the abrasion of the waste heat recovery system are solved, the cold end low temperature corrosion of an air preheater is avoided, besides, newly building a bypass flue is not needed, the system is compact in technological process, and the construction of the engineering is facilitated.

Description

technical field [0001] The invention belongs to the technical field of waste heat recovery and high-efficiency power generation of flue gas at the tail of a power station boiler, and in particular relates to a high-efficiency power generation system for recovery of waste heat from exhaust smoke of a power plant boiler and used in a steam turbine unit heat recovery system. Background technique [0002] There are abundant waste heat resources in the exhaust gas of boilers in thermal power plants. The exhaust gas temperature of the bituminous coal-fired boiler is about 125°C, and that of the lignite-fired boiler is about 150°C. Correspondingly, the heat loss of boiler exhaust smoke is about 5-8%, which is the largest heat loss of power plant boilers. In order to further improve the thermal efficiency of thermal power units and meet the increasingly stringent energy-saving and emission-reduction requirements of the power industry, the utilization of waste heat from flue gas at ...

AI Technical Summary

Problems solved by technology

The disadvantage of this system is: since the flue gas cooling range of the low-temperature economizer is from the boiler exhaust gas temperature to 90°C, the flue gas side flue gas temperature level is low, and the recovered flue gas waste heat can only squeeze out the working capacity Low steam turbine low-pressure extraction, so the energy-saving benefit of the generating set obtained by the waste heat recovery of the flue gas is low, and the coal-saving benefit of the bituminous coal-fired generating set is about 0.5%; moreover, due to the heat exchange between the low-temperature flue gas and the condensed water The low temperature difference makes the cost and volume of the low-temperature economizer larger, which reduces the economical efficiency of the waste heat utilization system engineering application

For the already huge thermal power generation system, the addition of bypass flue makes the system more complicated, and the difficulty of safe and reliable operation and automatic control increases

Moreover, the addition of a bypass flue requires a redesign of the flue at the tail of the boiler, which increases the investment in the transformation of the flue

[0007] (2) The use of flue gas to exchange heat directly with unit feed water or condensed water makes the risk of corrosion, wear and dust accumulation on the heating surface greater, and the reliability of the system operation is reduced. The investment in high-pressure economizers and low-pressure economizers in the bypass flue also larger

In order to reduce low-temperature corrosion, some low-pressure economizer cold-end heating surfaces need to use expensive corrosion-resistant materials, which increases the investment on the heating surface

In addition, because the economizer in the bypass flue is arranged in the flue gas with high ash concentration, in order to prevent the heating surface from wearing too fast, only a low flue gas flow rate can be used, and the ash particle pollution will affect the heat transfer of the heating surface. The weakening of the process makes the total heat transfer coefficient of the heating surface low. Moreover, in order to prevent serious ash accumulation on the heating surface, only heat exchange tubes with good anti-fouling effect but small finning can be used. Low heat transfer coefficient and low finning The investment of the economizer in the bypass flue will be further increased, and the operating cost of the system will also increase accordingly.

[0008] (3) The use of water-medium air preheater will significantly increase the system investment and operating costs, the system process will be more complicated, and the engineering feasibility and investment economy of the system will be reduced.

Due to the indirect heat transfer between low-temperature flue gas and air through the intermediate medium, the heat transfer temperature difference between the air side and the flue gas side of the water-medium air preheater is very small, resulting in the investment and operating costs of the water-medium air preheater Very large, causing a significant adverse effect on the technical economy of the system

Moreover, the risk of serious low-temperature corrosion and ash plugging on the heating surface of the flue gas side of the water-medium air preheater is also high, which increases the risk points that affect the safe and reliable operation of the system

In addition, the safe and reliable operation of the main air preheater of the boiler is directly related to the water medium air preheater, and the water medium air preheater is a system composed of the flue gas side, the air side heating surface and the closed water circulation loop. The heat exchange system makes the overall waste heat utilization system too complicated, and the operating parameters are not easy to adjust and control

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