How to select electric heating thermal oil furnace and analysis of heat carrier selection

How to Select an Electric Heating Thermal Oil Boiler and Analysis of Heat Carrier Selection

Electric heating thermal oil boilers are organic heat carrier heaters that are energy-efficient, environmentally friendly, and highly reliable, making them widely used. How to Select an Electric Heating Thermal Oil Boiler and Analysis of Heat Carrier Selection

1. Calculating the Thermal Efficiency of an Electric Heating Thermal Oil Boiler

Thermal efficiency is not only a key design parameter for a thermal oil boiler, but also serves as a metric for evaluating economic performance when selecting a thermal oil boiler. Electric heating thermal oil has the highest thermal efficiency, reaching 95%.

2. Confirming the Capacity of the Thermal Oil Boiler

When determining the maximum heat load, the following two factors should be considered:

① The fastest heating rate and the slowest heating time. The heating time and heating rate not only affect process performance but also product quality. If there are no special requirements for these two factors, a lower-power furnace can be selected.

② Heat loss from the oil pipeline. Depending on the insulation requirements, when selecting high-quality insulation materials, heat loss should be considered based on a 3% heating capacity. However, if using standard insulation materials, heat loss should be considered based on a 5% heating capacity. Furthermore, heat loss from outdoor facilities and their piping systems should be considered based on an 8% heating capacity.

3. Thermal Oil Pump Selection and Energy Saving

Based on previous design experience, when selecting a thermal oil circulation pump, two operating conditions should be considered. For example, Operating Condition 1 represents normal operation, with an operating temperature of 280°C, a density of 790 kg/m³, a viscosity of 0.27 mPas, a flow rate of 373 m³/h, and a head of 54 m. Operating Condition 2 represents winter operation, with an operating temperature of -34°C, a density of 1000 kg/m³, a viscosity of 420 mPas, a flow rate of 223 m³/h, and a head of 54 m.

By comparing the two operating conditions, the hot oil circulation flow rate is controlled using a regulating valve on the process pipeline during operation, ensuring that the pump motor power is maintained within normal shaft power. Based on this, the pump motor can be selected under normal operating conditions. This not only achieves energy conservation but also reduces investment costs.

4. Heat Transfer Oil Selection

4.1 Heat Transfer Oil Selection

Because the heat transfer oil undergoes long periods of continuous circulation heating in the furnace, it is prone to polymerization, coking, and deterioration. Therefore, the following points should be considered when selecting a heat transfer oil:

① Good high-temperature heat transfer performance

② Good stability and a long service life, ensuring a service life of more than ten years

③ The operating temperature should be below the boiling point, the freezing point should not be too high, and toxicity and corrosiveness should not be too high.

④ High initial boiling point and flash point, and good safety performance. Most heat transfer oils operating between 250 and 300°C are synthetic oils. Users can choose a different heat transfer oil based on their specific needs.

4.2 Heating, Dehydration, and Venting of the Heat Carrier

The heating, dehydration, and venting process of an electrically heated thermal oil boiler is a particularly dangerous phase of operation, so extreme caution is required. Specifically, heating should be stopped when the temperature reaches either 95°C to 110°C or 210°C to 230°C, and maintained at this temperature for a period of time.

Generally, this process takes approximately 48 hours. Once the thermal oil temperature exceeds 95°C, residual moisture in the piping system and less volatile components within the thermal oil begin to vaporize. Gases will escape from the vent port on the expansion tank. Therefore, the heating rate during dehydration and venting should not exceed 5°C/hour. Generally, the venting volume is greatest when the thermal oil is heated between 105°C and 130°C. During this period, close attention should be paid to the venting condition of the expansion tank, as well as the operation of the circulating oil pump and pressure gauge.

Once the thermal oil temperature reaches approximately 200°C, the equipment and the entire system should be inspected, and all bolted joints should be tightened simultaneously to prevent leaks caused by uneven thermal expansion. When the thermal oil boiler is ignited and heated, some of the water evaporates as vapor, entering the expansion tank through the expansion tube. Another portion is converted into gas and discharged through the vent pipe. Still another portion condenses into liquid water and settles to the bottom of the tank. During heating, the drain pipe below the expansion tank should be kept open to drain the condensed water.

After dehydration and venting are complete, continue heating at a rate of 20°C/hour. When the temperature reaches approximately 210°C, stop heating. The primary process at this point is to remove the light components from the thermal oil. The time required for light component removal should be determined based on the brand and quality of the thermal oil. If no gas is emitted from the vent pipe and the circulating thermal oil pump pressure is stable, continue heating at a rate of less than 10°C/hour to 230°C. After degassing is complete, the temperature is raised from 230°C to the desired temperature of the thermal oil boiler at a rate of 40°C/h. At this point, the thermal oil boiler, circulating heating system, and various supporting facilities and ancillary equipment should be inspected to ensure proper operation.

In summary, since electric thermal oil boilers are widely used, when designing an organic heat transfer medium heating system, it is important to select a heat transfer medium with high thermal efficiency based on the characteristics of the heated medium and arrange the equipment appropriately. This will achieve both energy conservation and environmental protection while also reducing operating costs.