Waste Heat Recovery Heat Exchanger for High Temperature Flue Gas

Waste Heat Recovery Heat Exchanger for High Temperature Flue Gas

High-temperature flue gas waste heat recovery heat exchanger is a kind of equipment used to recover the waste heat in high-temperature flue gas. Its basic principle is based on heat transfer, through the high temperature flue gas and low temperature medium (such as air, water, etc.) for heat exchange, so that the low temperature medium to absorb the heat of high temperature flue gas, so as to achieve the purpose of waste heat recovery.

For example, in the high temperature flue gas produced by industrial furnaces and kilns (the temperature can reach several hundred degrees or even thousands of degrees) contains a large amount of heat energy. When these flue gases pass through the heat exchanger, the heat can be transferred to the cold air on the other side, and the cold air can be used to preheat the air needed for combustion after the temperature of the cold air rises, which improves the efficiency of energy use.

Finned tube heat exchangers are mainly composed of finned tubes. The fins are usually attached to the surface of the base tube by welding, expansion or machining. The base tube is usually a round tube, and the material can be carbon steel, stainless steel, copper, etc. Its function is to transport the fluid being heated or cooled.

There are various shapes of fins, the common ones are rectangular fins, round fins, spiral fins and so on. For example, spiral fins are made by wrapping a steel strip around the base tube in the shape of a helix and welding it, which can increase the degree of fluid disturbance and strengthen the heat transfer effect. There are also various choices of fin materials, such as aluminium fins (for occasions where the requirements for corrosion resistance are not particularly high, and aluminium has better thermal conductivity), stainless steel fins (for environments with a certain degree of corrosiveness).

When the high temperature flue gas flows outside the finned tube, the heat is transferred to the low temperature fluid inside the tube through the fins and the wall of the base tube. The main function of fins is to increase the heat transfer area, because the convection heat transfer coefficient on the flue gas side is relatively low, and increasing fins can effectively make up for this deficiency.

Advantages

Highly efficient heat transfer: The fins greatly increase the heat transfer area, which can effectively recover the heat from the high temperature flue gas and improve the heat recovery efficiency. Under the same space and conditions, the heat transfer efficiency of finned tube heat exchanger can be increased several times than that of light tube heat exchanger.

Compact structure: Due to the presence of fins, the heat exchanger can be made more compact while ensuring higher heat transfer efficiency. This is very favourable for industrial sites where space is limited or where equipment installation locations are restricted.

Adaptation to a variety of fluids: It can be used for heat exchange between a variety of fluids, such as high-temperature flue gas and air, high-temperature flue gas and water. And for fluids with low thermal conductivity (e.g. air), the fins are more effective and can enhance the heat transfer process very well.

Application Scenarios

Air preheating: Widely used in industrial furnaces and kilns, such as heating furnace, annealing furnace and so on. The finned tube heat exchanger recovers the heat from the high temperature flue gas to preheat the air required for combustion, thus improving combustion efficiency and reducing fuel consumption. For example, in roller kilns in the ceramic firing industry, the use of finned tube heat exchangers to preheat combustion air can increase the thermal efficiency of the kiln by 10% - 20%.

Process Fluid Heating: In the chemical and petroleum industries, it is used to heat some process fluids. For example, in the petroleum refining process, the use of high-temperature reaction after the flue gas through the finned tube heat exchanger to heat the crude oil and other fluids, both to achieve waste heat recovery, but also to reduce energy costs.

Waste heat power generation: In some factories with high-temperature flue gas waste heat resources, such as cement factories, glass factories, etc., finned tube heat exchanger is used to recover the flue gas waste heat and transfer the heat to the organic workmass (e.g., the workmass in the Rankine Cycle) to evaporate and drive the turbine to generate electricity, so as to achieve the efficient use of waste heat.