Desulfurization Air Electric Heater

1. Overview

 Desulfurization air electric heaters and gasification units for boiler and furnace dust removal systems. In recent years, there has been an urgent demand and rapid development in flue gas desulfurization systems at power plants. As auxiliary equipment for desulfurization systems, electric air heaters have been widely used. Flue gas desulfurization is a large and complex system, composed of numerous components. The operation of each component affects the entire system. Manufacturers of desulfurization air electric heaters must design them reasonably, manufacture them meticulously, and conduct rigorous inspections. Users need to understand, master, and follow the key points of adjustment, operation, and energy-saving to correctly adjust and operate the equipment, aiming to conserve energy as much as possible. Only then can the desulfurization system operate normally and economically, achieving its intended purpose.

 2. The function of desulfurization air electric heater

 Air at normal temperature exiting the fan enters the desulfurization air electric heater, where it is heated and then discharged as air at a certain temperature, which is then delivered to the required equipment. In the flue gas desulfurization system, there are mainly two aspects:

 A.Used in desulfurization projects with circulating fluidized bed method for heating ash bin fluidized air and slant trough fluidized air.

 B.Limestone/Lime-gypsum desulfurization project, used for heating the sealing air of the flue gas damper door.

 3. Desulfurization Air Electric Heater Structure and Principle

 3.1 The desulfurization air electric heater consists of two parts: the heater body and the control cabinet.

 3.1.1The electric heater consists of multiple tubular electric heating elements, a housing, a protective cover, and a base. The heater elements are made of high-temperature resistance alloy wires, encased in stainless steel tubes, filled with crystalline magnesium oxide, and formed through compression technology. They feature good mechanical strength, high thermal efficiency, wear resistance, and corrosion resistance. The housing is equipped with a flow guide baffle, ensuring even heating when air circulates.3.1.2The working principle of the control cabinet is to use an intelligent digital temperature controller, a high-power可控硅(thyristor), and a thermal resistor to form a measuring, regulating, and controlling circuit. The thermal resistor converts the outlet temperature of the heater into a milliamperage signal, which is then sent to the intelligent digital temperature controller for amplification and comparison to display the corresponding temperature value. When the displayed value exceeds the set value, the可控硅 does not conduct. When the displayed value is below the set value, the intelligent digital temperature controller triggers the可控硅 to conduct. When the displayed value is close to the set value (i.e., near the set value), the intelligent digital temperature controller...P、I、DRegulated changes ensure that the control cabinet maintains excellent control accuracy and adjustment performance. The intelligent digital temperature controller receives a milliammeter signal from the resistance thermometer.,Automatically adjust the number of triggering pulses for the thyristor, controlling the conduction angle of the thyristor within a unit of time, regulating voltage, and controlling the heating element's power, ensuring energy saving and constant temperature, avoiding current surges, and extending service life. In the event of an abrupt shutdown, the control cabinet can automatically and smoothly adjust upon restart.

 3.1.3When heating elements are arranged in groups, the control cabinet can also be set for group control. The control section consists of digital circuits, trigger circuits, and other components, which automatically engage at low temperatures, sound an alarm at high temperatures, and automatically shut off power.,Achieve uniform temperature control.

 4. Tuning

 Calibration work is crucial for achieving168A key project in trial operation.

 4.1Tuning content

 4.1.1Inspect installation status

 4.1.2The display of gauges and indicator lights is accurate.

 4.1.3Temperature regulation is sensitive, with accurate control.

 4.1.4Automatically heats at low temperatures and shuts off power with an alarm at high temperatures.

 4.2Diagnostics Steps

 4.2.1 Are the air desulfurization electric heater housing and control cabinet housing reliably grounded?

 4.2.2Are the power cables, output wires, and thermoresistor connections correct, with good insulation? Are there any loose components or fasteners in the control cabinet? Any anomalies should be addressed promptly.

 4.2.3Turn off the power switch, close the air switch inside the control cabinet, the indicator lights should illuminate, and the digital temperature controller light should turn on.

 4.2.4 Set the highest and lowest temperature values on the intelligent digital temperature controller.

 4.2.5 Power on the electric heater; the heater will begin operating and automatically control the temperature as set.

 4.2.6 When the temperature falls below the lowest value, the electric heater will automatically turn on; when the temperature exceeds the highest value, the control cabinet will alarm and shut off power, the electric heater will not operate, but it can maintain a certain temperature for a short period of time.

 4.2.7 Toggle the conversion switch and check if the three-phase voltage is balanced. If it's unbalanced, try swapping the phases and check again for balance. If it remains unbalanced, further inspection and treatment are required.

 4.2.8 Ensure the three current meter pointers are roughly consistent. If one phase's current is significantly lower, it indicates that one or more heating elements in that phase are damaged. Immediate shutdown and inspection are required; measure the resistance of the heating elements with a multimeter. If the heating elements are damaged, replace them with a spare one. To do this, use a special disassembly tool to loosen and remove the bolts securing the heating element, then replace it.

 5. Operation

 5.1 Prior to use, the cold-state insulation resistance between the power connection terminals and the metal housing should not be less than 20MΩ.

 5.2 The input voltage for the heating element assembly of the electric heater is 380V. For a star connection, the voltage of a single heating element is 220V; for a delta connection, the voltage of a single heating element is 380V. The outgoing cable of the control cabinet should be connected to the heating element assembly on the heater body in accordance with the specified requirements, and must not be connected randomly. If in doubt, contact the manufacturer.

 5.3 Start the fan and blow through the desulfurization air electric heater body and pipes for five minutes, check for blockages.

 5.4 After the control cabinet is powered on, check if the indicator lights are indicating correctly, and ensure the smart digital temperature controller's temperature display, adjustment, and alarm are responsive and accurate. Any anomalies should be addressed promptly.

 During the 5.5 inspection, pay attention to whether there are significant deviations in the readings of the three current meters' pointers.

 5.6 In case the fan stops working for any reason during operation, the desulfurization air electric heater should be promptly disconnected from power. It is strictly prohibited to keep the desulfurization air electric heater powered on for an extended period when there is no positive airflow within the housing, to prevent premature damage to the heating elements.

 5.7 At startup, the fan must be turned on first before the power to the electric heating elements is connected. At shutdown, the power to the electric heating elements must be disconnected first before the fan is turned off.

 5.8 The exhaust pipe of the 5.8 electric heater must not be blocked or partially blocked under any circumstances; otherwise, it will cause the internal pressure of the electric heater to continuously increase, leading to accidents.

 5.9 Troubleshooting

 5.9.1 The power indicator light is not illuminated, and the voltage meter shows no reading. Check if the circuit breaker is engaged and if the control circuit fuse is intact.

 5.9.2 The temperature of the electric heater is not rising. Check if the fuse is intact, if the thermistor (thermocouple) is properly connected, and if the heating element is damaged.

 5.9.3 Ash Backflow

 5.9.3.1 During normal operation of the desulfurization air electric heater, due to the positive airflow within the housing, fly ash will not flow back into the housing.

 5.9.3.2 A fan malfunction occurred, causing a temporary shutdown with no air flow. There may be a small amount of soot flowing back into the heater housing through the pipes. The heating elements of the electric heater are encased in a stainless steel sheath, so a small amount of soot will not affect the electric heating elements. Furthermore, once the fan resumes operation, the soot will be blown back into the pipes.

 5.9.3.3 A long-term shutdown of the fan, combined with unobstructed or disconnected pipeline at one end, leads to a significant backflow of ash into the heater housing. This is an operational accident and should be handled accordingly; however, the electrical heating elements will not be damaged. This is because there is no moving air within the cylinder, causing the heater temperature to rise. Thanks to the automatic control and regulation of the intelligent digital temperature controller, the heater will automatically stop heating, preventing damage to the heating elements. If there is a large amount of ash, especially damp ash, within the housing, and poor air flow, the pressure gauge (part of the fan) will rise when the fan starts. In this case, inspect and clean the ash inside the cylinder. Inspection and cleaning method: Use the special disassembly tool (provided with the equipment) to remove the electrical heating element (electric heating tube), unscrew the bolts around the fixed plate of the electric heating tube with a wrench, remove the fixed plate, and then the ash inside the housing can be cleared.

 6. Energy-efficient

 In recent years, with the increasing demand for desulfurization projects in large power plant units, the power of desulfurization air electric heaters has also risen, with some reaching over 400KW. High electricity consumption and operating costs necessitate consideration from the following aspects to minimize energy usage as much as possible.

 6.1 Design air volume and temperature rise reasonably. The power of the desulfurization air electric heater is determined based on the air volume and temperature rise. Under the premise that the air volume and temperature rise meet the requirements, it is not advisable to use an excessive air volume or temperature rise, as this will directly lead to an overly high power of the heater, increasing energy consumption. Excessive air volume and temperature rise are unnecessary. Consideration should be given to a comprehensive design, determining appropriate parameters.

 6.2 The surface of the desulfurization air electric heater should be insulated. Most power plants (owners) only insulate the pipes at the outlet of the electric heater when using the desulfurization air electric heater, without any insulation treatment on the heater's surface. Comparative data shows that adding an insulating layer to the surface of the electric heater can reduce energy consumption by 5% to 10%. Over the long term, the energy saved is very significant. Power plants (owners) should insulate the desulfurization air electric heater in addition to installing insulation on the pipes.

 6.3 Reduce the pressure loss of the desulfurization air electric heater itself. As the air to be heated flows through the interior of the desulfurization air electric heater, pressure loss is generated. The greater the pressure loss, the higher the energy consumption of the fan. It is necessary to make improvements and innovations to the structure of the desulfurization air electric heater itself to minimize the pressure loss.