Abstract: Some of China’s mega-cities have introduced policies aimed at encouraging the use of electric boilers in order to reduce air pollution levels. For regions with pronounced peak-and-valley electricity consumption patterns, electric heating boilers can store heat during off-peak periods and release it during peak demand hours—thus achieving the goal of “peak-shaving and valley-filling.” This article primarily introduces the operating principles and current application status of electric heating boilers, with a particular focus on the application of Powtran Technology’s online soft starters in electric heating boilers. Through fully automated and intelligent control technology, this approach achieves the objectives of low energy loss, zero pollution, and easy maintenance.

Keywords: online soft start; electric heating boiler; PLC; touch screen

I. Overview

An electric heating boiler consists primarily of the boiler body itself, an electrical control box, and a control system. Unlike conventional boilers that rely on combustion to convert chemical energy into thermal energy, electric heating boilers do not require the supply of air or fuel for combustion. As a result, they produce no harmful gases or ash residues, fully meeting environmental protection standards. With the dwindling availability and sharp price increases of finite energy resources (such as coal), electric heating boilers—as an emerging type of boiler equipment—are gaining increasing recognition. Their key features include being environmentally friendly, clean, pollution-free, noiseless, and equipped with fully automatic control.

II. Working Principle

There are many types of electrically heated boilers, and they are generally classified according to the form of their electric heating elements—namely, resistance-type, electrode-type, and film-type. The following explanation will focus primarily on the resistance-type boiler.

The resistance-type heater employs high-impedance tubular electric heating elements. Once the power is switched on, these tubular elements generate intense heat, turning water into hot water or steam. Each tubular heating element consists of a metal casing, a heating wire, and an oxide layer. The advantage of this type of element is that it does not carry an electrical charge in the water, making it relatively safe to use and causing no contamination of the water quality. However, increasing the boiler capacity relies on adding more tubular heating elements and adjusting the boiler load according to the number of elements put into operation. Consequently, the capacity of this type of boiler is limited by the structural arrangement of the heating elements. The heating elements used at the customer’s site are precisely of this resistance-type design. A 2-ton boiler uses 48 electric heating tubes, each rated at 30 kW (3~380V), while a 5-ton boiler also uses 48 electric heating tubes, each rated at 75 kW.

    电加热炉根据加热方式不同，又分为：电蒸汽加热炉和电热水加热炉，其采用的加热管材质也不同

Foldable electric steam boiler: It features a high-quality electric heating element housed in a thickened stainless steel tube, with the tube interior filled with high-purity magnesium oxide powder, ensuring a long service life for the electric heating tube. Each set of electric heating elements is connected via flanges, offering advantages such as simple structure, high mechanical strength, safety and reliability, and easy replacement.

Electric water boiler: It features advanced ceramic electric heating elements encased in high-quality seamless steel tubes, effectively preventing scale buildup and ensuring a long service life. The heat-absorbing structure has been optimized through computer-aided design, fully maximizing the heat transfer coefficient of the heated surface and achieving an exceptionally high thermal efficiency of over 98%. This significantly reduces electricity consumption.

III. Control Features of the Powtran Technology Online Soft Starter (Taking a 5-ton Electric Heating Furnace as an Example)

The electric heating furnace at the customer’s site is an electric water heating furnace, and its general structure is shown in the figure below:

1. Based on the site conditions, the boiler was changed from a vacuum electric heating boiler, as originally designed, to a atmospheric-pressure electric heating boiler.

1) Vacuum boilers have high requirements for vacuum levels, and also place stringent demands on the boiler’s airtightness, vacuum pumps, and solenoid valves. Moreover, the safety of sealed containers is of paramount importance. In contrast, atmospheric-pressure boilers are directly connected to the atmosphere and are as simple as boiling water; thus, their safety is significantly higher than that of vacuum boilers.

2) Under the condition that the vacuum equipment is well-maintained, the thermal efficiency of a vacuum boiler is comparable to that of a atmospheric-pressure boiler. However, the subsequent maintenance costs for a vacuum boiler are higher than those for an atmospheric-pressure boiler. Atmospheric-pressure boilers are easier to maintain and offer more stable operation in the long run. Therefore, taking into account factors such as the on-site usage environment—particularly its application in schools—and future maintenance requirements, the customer decided to switch to operating the boiler as an atmospheric-pressure boiler.

2. Fully automatic and intelligent control technology, requiring no dedicated personnel for monitoring. The operating mode is flexible and can be set to either manual or automatic. In manual mode, individual electric heating tubes, circulation pumps, and make-up water pumps can be started and stopped independently, facilitating initial equipment commissioning. In automatic mode, the system collects external temperature and water level signals, compares them with the set temperature, and controls the number of electric heating tubes to be switched on or off accordingly, thereby achieving the desired heating temperature by precisely regulating the number of active heating tubes.

3. This electric heating boiler is equipped with a total of 48 electric heating tubes (AC 380V, 75 kW), divided into 12 groups of 4 tubes each. Each group is controlled by a soft starter. During startup, the initial number of groups to be activated is determined according to the parameter settings, and these groups are started first. Subsequently, the electric heating tubes are activated stepwise based on the parameter-set startup time intervals and temperature thresholds.

4. The system features automatic control of the water supply temperature and can automatically start and stop the electric heating elements, make-up water pumps, and circulating pumps in response to changes in load temperature.

5. Equipped with a full range of protection features, including leakage protection, low-water protection, grounding protection, overcurrent protection, and power supply protection—ensuring automatic boiler protection for ultimate safety.

6. Each set of electric heating elements features a flange connection, offering advantages such as simple structure, high mechanical strength, safety and reliability, and easy replacement.

IV. Selection of Control Systems for Electric Heating Boilers

1. Each electric heating tube has specifications of AC 380V and 75kW, with a total of 48 tubes. We are using 12 units of Powtran Technology’s online soft starters PS5300 320G3, each unit equipped with 4 electric heating tubes.

2. The circulating pump has a power rating of 18 kW and is equipped with variable-frequency control, using the PI500 018G3 model. The pump’s rotational speed is adjusted according to the temperature conditions in the pipeline network, thereby regulating the flow rate through the network. The output frequency of the frequency converter is adjusted via a keyboard potentiometer. At the site, there is one main motor and one standby motor.

3. Two water supply pumps, each with a power of 4 kW, are controlled by line frequency and are used to supply water to the boiler and pipelines, respectively.

4. The water tank uses a float switch for automatic water replenishment.

5. To ensure convenient operation for customers and more flexible temperature control during operation, the main control system adopts a partial touch-screen + Siemens PLC control approach. To acquire signals such as temperature and pressure, A/D conversion modules and PT100 expansion modules are used. All parameter settings and real-time monitoring parameters of the boiler are operated and displayed on the touch screen.

V. Advantages of Using Soft-Start Control for Electric Heating Boilers

1. Starting with a soft starter for electric heating tubes can reduce the impact of current on the power grid when multiple electric heating tubes are started simultaneously, ensuring a stable current flow. With online start-stop functionality, the use of AC contactors has been eliminated, making maintenance even more convenient.

2. As an energy source, electricity used to heat boilers produces no emissions of pollutants and boasts high thermal efficiency—exceeding 98%. Several ultra-large cities in China have already introduced policies encouraging the use of electric boilers in order to reduce air pollution levels. For regions with peak-and-valley electricity consumption patterns, electric heating boilers can store heat during off-peak periods and release it during daytime peak hours, effectively “smoothing out peaks and filling valleys.”

3. Environmentally friendly operation—no noise, no pollution, high thermal efficiency (thermal efficiency greater than 95%), and minimal heat loss.

4. Fully automatic and intelligent control technology—no need for personnel on duty.

5. The boiler occupies a small footprint, saving space.

6. Fully automatic electric heating boilers are widely suitable for use in hospitals, schools, textile mills, garment factories, clothing supermarkets, clothing manufacturers, dry cleaners, restaurants, hotels, steamed bun shops, guesthouses, cafeterias, dining halls, food processing plants, beverage plants, soybean product factories, meat processing plants, canning factories, wineries, pharmaceutical factories, packaging plants, building materials factories, paint factories, beauty salons, bathhouses, saunas, steam rooms, and other similar venues.