Finned Tube Radiator in Thermal Oil Heating System

Finned Tube Heat Exchanger in Thermal Oil Heating System

The thermal oil heating system uses thermal oil as the heat transfer medium, utilizing its characteristic of low vapor pressure at high temperature (can reach 200-350℃ at atmospheric pressure or low pressure) to provide a stable heat source for industrial processes. The role of finned tube heat exchanger in this system includes:

Main Heater: Heat the thermal oil by heat source (such as coal-fired, gas-fired, electric heating), and then transfer the heat to the process fluid (such as air, materials, chemical media) through the finned tube.

Waste heat recovery: use the waste heat of high temperature heat transfer oil to heat other low temperature fluids to improve the energy utilization of the system.

Heat transfer oil cooling: When the system needs to control the temperature of heat transfer oil, heat exchange with cooling water or air through finned tube heat exchanger prevents overheating and decomposition of heat transfer oil.

Core structural features

Fin design: welded or wound metal fins on the outer surface of the heat exchanger tube (mostly made of carbon steel, stainless steel, aluminum, etc.), greatly increasing the heat transfer area (3-10 times higher than the heat transfer area of the light tube), and strengthening the convection heat transfer.

Fin type:

Horizontal fins (ring fins): suitable for scenarios where the fluid outside the tube (e.g. air) has a low flow rate and a small heat transfer coefficient, e.g. thermal oil heating air.

Longitudinal fins: Suitable for scenarios where the fluid outside the tube flows in the axial direction, reducing pressure drop.

High-frequency welded fins: Firmly welded fins and tube body, high temperature resistant, anti-vibration, suitable for high temperature working condition of thermal oil.

Tube bundle arrangement: more fork row or down row arrangement, optimize the fluid flow field, enhance the perturbation, reduce the accumulation of ash or scaling.

Heat conduction oil flows in the tube (or shell program), carries heat through the tube wall to the fins, and then the fins dissipate heat to the fluid outside the tube (such as process media, air, cooling water).

The presence of fins reduces the “thermal resistance”: of the convective thermal resistance of the heat transfer oil and the tube wall, the thermal resistance of the tube wall to heat conduction, and the convective thermal resistance of the fins and the fluid outside the tube, the thermal resistance of the fluid outside the tube (especially gas) is often the greatest, and the fins effectively reduce this part of the thermal resistance by increasing the area, improving the overall heat transfer coefficient (K value).

Application Scenarios in Heat Transfer Oil System

Industrial Heating Scenarios

Chemical Reactor Heating: Heat transfer from heat transfer oil to materials in the reactor through finned tube heat exchanger to meet the demand of high temperature reaction (e.g. polymerization reaction, esterification reaction).

Food drying: in the baking and dehydration process, finned tube heat exchanger heats the air and dries the food (e.g. potato chips, nuts) through hot air circulation to avoid the effect of high temperature steam on the material.

Plastic extrusion molding: heating the extruder barrel or die to ensure that the plastic raw materials melt evenly at high temperatures, finned tube heat exchanger can accurately control the temperature of the heat transfer oil to avoid overheating and decomposition of the plastic.

Heat Recovery Scenario

Waste Heat Boiler System: High temperature thermal oil flows through the finned tube heat exchanger and heats water to generate steam, which can be used for power generation or other processes to reduce energy waste.

Utilization of flue gas waste heat: finned tube heat exchanger is installed at the end of thermal oil heating furnace to utilize the flue gas waste heat to preheat thermal oil or heat other media to improve the thermal efficiency of the system.

Design Points

Optimization of heat transfer efficiency

Fin parameter design:

Fin height and spacing should be adjusted according to the nature of the fluid outside the tube: for example, if the air side of the heat transfer coefficient is low, high fins and small spacing can be used; the liquid side of the pressure drop needs to be taken into account and low fins and large spacing are used.

Thickness of fins: under high temperature working condition (such as heat transfer oil >300℃), the thickness of fins should be increased to prevent high temperature deformation, commonly used 1-2mm stainless steel fins.

Flow path design: heat transfer oil in the tube flow rate is recommended to be controlled at 1.5-3m/s, to avoid too low a flow rate leading to coking, or too high to increase the pump power consumption; outside the tube fluid flow rate is adjusted according to the resistance requirements (such as air-side flow rate of 5-15m/s).

Material selection

Tube: 20# carbon steel for thermal oil temperature ≤300℃; 304/316 stainless steel for >300℃ or corrosion resistance to avoid corrosion of the tube by long-term high temperature oxidation of thermal oil.

Fin material: air side commonly used aluminum fins (low cost, good thermal conductivity), but at high temperatures (>250 ℃) need to change to stainless steel fins, to prevent annealing failure of aluminum fins.

Anti-coking and maintenance

Thermal oil is easy to decompose and coking at high temperature, need to control the wall temperature ≤ the maximum allowable film temperature of thermal oil (such as mineral heat transfer oil film temperature ≤ 300 ℃), the fin surface temperature uniformity design is particularly important.

Regular cleaning of the fin surface: If the fluid outside the tube for the dusty air, the need to set up a blowing device or self-cleaning fins (such as serrated fins to reduce the accumulation of ash); if the tube thermal oil coking, can be used for chemical cleaning or mechanical dredging.

Temperature difference and pressure control

The temperature difference between the import and export of thermal oil is recommended to be controlled at 20-40℃ to avoid uneven flow rate or localized overheating caused by too large a temperature difference; the pressure drop of the heat exchanger needs to be ≤0.1MPa, so as to avoid affecting the efficiency of the thermal oil circulating pump.